Patent Number: 
Section: description

FIG. 1 is a sectional view showing an embodiment of the radiation image storage panel in accordance with the present invention. As illustrated in FIG. 1, a radiation image storage panel 1 comprises a substrate 4, a stimulable phosphor layer 3, and a light reflecting layer 2, which is formed between the substrate 4 and the stimulable phosphor layer 3. The light reflecting layer may be formed on one surface of the stimulable phosphor layer. Alternatively, the substrate may be filled with a light reflecting substance such that the substrate may also act as the light reflecting layer. The radiation image storage panel in accordance with the present invention will be described hereinbelow by taking a radiation image storage panel, which has a typical constitution comprising the substrate, the light reflecting layer, and the stimulable phosphor layer, as an example. The substrate may be constituted of a material selected from various kinds of substrate materials, which are employed in known radiation image storage panels. Examples of the substrate materials include films of plastic substances, such as cellulose acetate, a polyester, a polyethylene terephthalate, a polyamide, a polyimide, a triacetate, and a polycarbonate; metal sheets, such as an aluminum foil and an aluminum alloy foil; and paper, such as ordinary paper, baryta paper, resin-coated paper, pigment paper containing a pigment, such as titanium dioxide, and paper sized with a polyvinyl alcohol, or the like. In cases where the constitution of the radiation image storage panel, characteristics of the radiation image storage panel required for an information recording material, and processing of the radiation image storage panel are taken into consideration, the substrate of the radiation image storage panel in accordance with the present invention should preferably be constituted of a plastic film. Such that the binding of the substrate of the radiation image storage panel with the light reflecting layer formed on the substrate to be enhanced, an adhesive property imparting layer constituted of a high-molecular weight substance, such as gelatin, may be formed on the substrate surface, on which the light reflecting layer is to be overlaid. The light reflecting layer may be formed by preparing a coating composition containing the light reflecting substance described above, a binder, and a solvent, and uniformly applying the coating composition onto the substrate surface to form a coating film of the coating composition thereon. The binder and the solvent for the formation of the light reflecting layer may be selected from binders and solvents, which are employed for the formation of the stimulable phosphor layer. ordinarily, the mixing ratio of the binder to a white pigment in the coating composition for the formation of the light reflecting layer may be selected from the range between 1:1 and 1:50 (weight ratio). From the view point of the reflection characteristics of the light reflecting layer, the proportion of the binder should preferably be as low as possible. When the easiness of the formation of the light reflecting layer and the mechanical and physical strength of the radiation image storage panel are taken into consideration, the mixing ratio of the binder to the white pigment in the coating composition for the formation of the light reflecting layer should preferably be selected from the range between 1:2 and 1:20 (weight ratio). The thickness of the light reflecting layer should preferably fall within the range of 5 xcexcm to 100 xcexcm. The coating composition for the formation of the light reflecting layer may be applied with ordinary coating means, such as a doctor blade, a roll coater, or a knife coater. After the coating film of the coating composition is formed on the substrate surface, the coating film is heated little by little and dried. In this manner, the light reflecting layer is formed on the substrate. The stimulable phosphor layer is formed on the light reflecting layer. A typical example of the stimulable phosphor layer comprises a binder and particles of a stimulable phosphor dispersed in the binder. As an example of the stimulable phosphor in the stimulable phosphor layer of the radiation image storage panel in accordance with the present invention, a bivalent europium activated barium fluorohalide stimulable phosphor may be employed. Examples of the bivalent europium activated barium fluorohalide stimulable phosphors include the following: a phosphor represented by the formula (Ba1xe2x88x92xxe2x88x92y, Mgx,Cay)FX:aEu2+ wherein X is at least one of Cl and Br, x and y are numbers satisfying 0 less than x+yxe2x89xa60.6 and xyxe2x89xa00, and a is a number satisfying 10xe2x88x926xe2x89xa6axe2x89xa65xc3x9710xe2x88x922, as disclosed in DE-OS No. 2,928,245, a phosphor represented by the formula (Ba1xe2x88x92x.M2+x)FX:yA wherein M2+ is at least one of Mg, Ca, Sr, Zn, and Cd, X is at least one of Cl, Br, and I, A is at least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, and Er, x is a number satisfying 0xe2x89xa6xxe2x89xa60.6, and y is a number satisfying 0 xe2x89xa6yxe2x89xa60.2, as disclosed in U.S. Pat. No. 4,239,968, a phosphor represented by the formula BaFX.xA:yLn wherein A is at least one of BeO, MgO, CaO, SrO, BaO, ZnO, Al2O3, Y2O3, La2O3, In2O3, SiO2, TiO2, ZrO2, GeO2, SnO2, Nb2O5, Ta2O5, and ThO2, 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, x is a number satisfying 5xc3x9710xe2x88x925xe2x89xa6xxe2x89xa60.5, and y is a number satisfying 0 less than yxe2x89xa60.2, as described in Japanese Unexamined Patent Publication No. 55(1980)-160078, a phosphor represented by the formula (Ba1xe2x88x92x, MIIx)F2.aBaX2:yEu,zA wherein MII is at least one of beryllium, magnesium, calcium, strontium, zinc, and cadmium, X is at least one of chlorine, bromine, and iodine, A is at least one of zirconium and scandium, a is a number satisfying 0.5xe2x89xa6axe2x89xa61.25, x is a number satisfying 0xe2x89xa6xxe2x89xa61, y is a number satisfying 10xe2x88x926xe2x89xa6yxe2x89xa62xc3x9710xe2x88x921, and z is a number satisfying 0 less than zxe2x89xa610xe2x88x922, as described in Japanese Unexamined Patent Publication No. 56(1981)-116777, a phosphor represented by the formula (Ba1xe2x88x92x,MIIx)F2.aBaX2:yEu,zB wherein MII is at least one of beryllium, magnesium, calcium, strontium, zinc, and cadmium, X is at least one of chlorine, bromine, and iodine, a is a number satisfying 0.5xe2x89xa6axe2x89xa61.25, x is a number satisfying 0 xe2x89xa6xxe2x89xa61, y is a number satisfying 10xe2x88x926xe2x89xa6yxe2x89xa62xc3x9710xe2x88x921, and z is a number satisfying 0 less than zxe2x89xa62xc3x9710xe2x88x921, as described in Japanese Unexamined Patent Publication No. 57(1982)-23673, a phosphor represented by the formula (Ba1xe2x88x92x,MIIx)F2.aBaX2:yEu,zA wherein M11 is at least one of beryllium, magnesium, calcium, strontium, zinc, and cadmium, X is at least one of chlorine, bromine, and iodine, A is at least one of arsenic and silicon, a is a number satisfying 0.5xe2x89xa6axe2x89xa61.25, x is a number satisfying 0xe2x89xa6xxe2x89xa61, y is a number satisfying 10xe2x88x926xe2x89xa6yxe2x89xa62xc3x9710xe2x88x921, and z is a number satisfying 0 less than zxe2x89xa65xc3x9710xe2x88x921, as described in Japanese Unexamined Patent Publication No. 57(1982)-23675, a phosphor represented by the formula Ba1xe2x88x92xMx/2Lx/2FX:yEu2+ wherein M is at least one alkaline metal selected from the group consisting of Li, Na, K, Rb, and Cs, L is at least one trivalent metal selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga, In, and Tl, X is at least one halogen selected from the group consisting of Cl, Br, and I, x is a number satisfying 102xe2x89xa6xxe2x89xa60.5, and y is a number satisfying 0 less than yxe2x89xa60.1, as described in Japanese Unexamined Patent Publication No. 58(1983)-206678, a phosphor represented by the formula BaFX.xA:yEu2+ wherein X is at least one halogen selected from the group consisting of Cl, Br, and I, A is a calcination product of a tetrafluoroboric acid compound, x is a number satisfying 10xe2x88x926xe2x89xa6xxe2x89xa60.1, and y is a number satisfying 0 less than yxe2x89xa60.1, as described in Japanese Unexamined Patent Publication No. 59(1984)-27980, a phosphor represented by the formula BaFX.xA:yEu2+ wherein X is at least one halogen selected from the group consisting of Cl, Br, and I, A is a calcination product of at least one compound selected from the hexafluoro compound group consisting of salts of hexafluorosilicic acid, hexafluorotitanic acid, and hexafluorozirconic acid with monovalent or bivalent metals, x is a number satisfying 10xe2x88x926xe2x89xa6xxe2x89xa60.1, and y is a number satisfying 0 less than yxe2x89xa60.1, as described in Japanese Unexamined Patent Publication No. 59(1984)-47289, a phosphor represented by the formula BaFX.xNaXxe2x80x2:aEu2+ wherein each of X and Xxe2x80x2 is at least one of Cl, Br, and I, x is a number satisfying 0 less than xxe2x89xa62, and a is a number satisfying 0 less than axe2x89xa60.2, as described in Japanese Unexamined Patent Publication No. 59(1984)-56479, a phosphor represented by the formula BaFX.xNaXxe2x80x2:yEu2+:zA wherein each of X and Xxe2x80x2 is at least one halogen selected from the group consisting of Cl, Br, and I, A is at least one transition metal selected from the group consisting of V, Cr, Mn, Fe, Co, and Ni, x is a number satisfying 0 less than xxe2x89xa62, y is a number satisfying 0 less than yxe2x89xa60.2, and z is a number satisfying 0 less than zxe2x89xa610xe2x88x922, as described in Japanese Unexamined Patent Publication No. 59(1984)-56480, a phosphor represented by the formula BAFX.aMIXxe2x80x2.bMIIXxe2x80x32.cMIIIXxe2x80x3xe2x80x23. xA:yEu2+ wherein MI is at least one alkali metal selected from the group consisting of Li, Na, K, Rb, and Cs, MII is at least one bivalent metal selected from the group consisting of Be and Mg, MIII is at least one trivalent metal selected from the group consisting of Al, Ga, In, and Tl, A is a metal oxide, X is at least one halogen selected from the group consisting of Cl, Br, and I, each of Xxe2x80x2, XIxe2x80x3, and Xxe2x80x3xe2x80x2 is at least one halogen selected from the group consisting of F, Cl, Br, and I, a is a number satisfying 0xe2x89xa6axe2x89xa62, b is a number satisfying 0xe2x89xa6bxe2x89xa610xe2x88x922, c is a number satisfying 0xe2x89xa6cxe2x89xa610xe2x88x922, and a+b+cxe2x89xa710xe2x88x926, x is a number satisfying 0 less than xxe2x89xa60.5, and y is a number satisfying 0 less than yxe2x89xa60.2, as described in Japanese Unexamined Patent Publication No. 59(1984)-75200, a stimulable phosphor represented by the formula BaX2.aBaXxe2x80x22:xEu2+ wherein each of X and Xxe2x80x2 is at least one halogen selected from the group consisting of Cl, Br, and I, and Xxe2x89xa0Xxe2x80x2, a is a number satisfying 0.1xe2x89xa6axe2x89xa610.0, and x is a number satisfying 0 less than xxe2x89xa60.2, as described in Japanese Unexamined Patent Publication No. 60(1985)-84381, a stimulable phosphor represented by the formula BaFX.aMIXxe2x80x2:xEu2+ wherein MI is at least one alkali metal selected from the group consisting of Rb and Cs, X is at least one halogen selected from the group consisting of Cl, Br, and I, Xxe2x80x2 is at least one halogen selected from the group consisting of F, Cl, Br, and I, a is a number satisfying 0xe2x89xa6axe2x89xa64.0, and x is a number satisfying 0 less than xxe2x89xa60.2, as described in Japanese Unexamined Patent Publication No. 60(1985)-101173, and a stimulable phosphor represented by the formula (Ba1xe2x88x92a,MIIa)F(Br1xe2x88x92b,Ib).cNaX.dCsXxe2x80x2.eA:xEu2+ wherein MII is Sr or Ca, each of X and Xxe2x80x2 is Cl, Br, or I, A is Al2O3, SiO2, or ZrO2, a is a number satisfying 0 less than axe2x89xa60.5, b is a number satisfying 0 less than b less than 1, c is a number satisfying 0 less than cxe2x89xa62, d is a number satisfying 5xc3x9710xe2x88x925xe2x89xa6dxe2x89xa65xc3x9710xe2x88x922, e is a number satisfying 5xc3x9710xe2x88x925xe2x89xa6exe2x89xa60.5, and x is a number satisfying 0 less than xxe2x89xa60.2, as described in Japanese Unexamined Patent Publication No. 63(1988)-101478. The stimulable phosphor layer may be formed by preparing a coating composition containing the stimulable phosphor described above, a binder, and a solvent, and uniformly applying the coating composition onto the surface of the light reflecting layer to form a coating film of the coating composition thereon. The coating composition for the formation of the stimulable phosphor layer may be applied with ordinary coating means, such as a doctor blade, a roll coater, or a knife coater. After the coating film of the coating composition is formed on the surface of the light reflecting layer, the coating film is heated little by little and dried. In this manner, the stimulable phosphor layer is formed on the light reflecting layer. The thickness of the stimulable phosphor layer may vary in accordance with the characteristics required of the radiation image storage panel, the kind of the stimulable phosphor, the mixing ratio of the binder to the stimulable phosphor, and the like. The thickness of the stimulable phosphor layer ordinarily falls within the range of 20 xcexcm to 1 mm, and should preferably fall within the range of 50 xcexcm to 500 xcexcm. The formation of the stimulable phosphor layer need not necessarily be performed in the manner described above by directly applying the coating composition on the light reflecting layer. For example, a stimulable phosphor layer may be formed previously by applying the coating composition onto a plate, such as a glass plate, a metal plate, or a plastic sheet, and drying the coating film of the coating composition. After the thus formed stimulable phosphor layer is separated from the plate, the stimulable phosphor layer may be pushed against and overlaid on the light reflecting layer. Alternatively, the stimulable phosphor layer may be adhered to the light reflecting layer by use of an adhesive agent. The white pigment may be filled in the stimulable phosphor layer together with the stimulable phosphor. In such cases, the ratio (weight ratio) of the stimulable phosphor to the white pigment should preferably fall within the range between 100:1 and 100:20. In cases where the white pigment is introduced into the stimulable phosphor layer, a light reflecting layer for reflecting the stimulating rays may be formed on one surface of the stimulable phosphor layer. Ordinarily, a transparent protective film constituted of a plastic material for physically and chemically protecting the stimulable phosphor layer is formed on the surface of the stimulable phosphor layer, which surface is opposite to the substrate side surface. The radiation image storage panel in accordance with the present invention should preferably be provided with such a transparent protective film. The protective film may be formed on the stimulable phosphor layer with, for example, a technique, wherein a plastic film is prepared previously and is then adhered to the surface of the stimulable phosphor layer with an adhesive agent. Alternatively, the protective film may be formed on the stimulable phosphor layer with a technique, wherein a coating composition containing a protective film material is applied onto the surface of the stimulable phosphor layer and is then dried. A fine particle filler may be contained in the protective layer in order to reduce interference nonuniformity and enhance the image quality of the radiation image. Examples of resins appropriate for the production of the light-permeable plastic film include polyester resins, such as a polyethylene terephthalate and a polyethylene naphthalate; and cellulose ester derivatives, such as cellulose triacetate. For the production of the light-permeable plastic film, various resin materials, such as a polyolefin and a polyamide, may also be employed. The thickness of the protective film should preferably fall within the range of approximately 3 xcexcm to approximately 20 xcexcm. The present invention will further be illustrated by the following non-limitative examples. A coating composition for the formation of a light reflecting layer was prepared by adding 100 g of yttrium oxide particles (particle diameters of 90 wt. % particles among all particles: 0.1 xcexcm to 1 xcexcm, mean particle size of all particles: 0.6 xcexcm, refractive index: 1.8), 8 g of a binder (a soft acrylic resin), and 2 g of a phthalic ester into methyl ethyl ketone, and subjecting the resulting mixture to a dispersing process, which was performed with a propeller mixer. The thus prepared coating composition for the formation of a light reflecting layer was then uniformly applied onto a transparent polyethylene terephthalate film (acting as a substrate, thickness: 250 xcexcm) with a doctor blade, and the thus formed coating film was dried. In this manner, a light reflecting layer having a thickness of 50 xcexcm was formed on the substrate. A coating composition for the formation of a stimulable phosphor layer was prepared by adding 200 g of a stimulable phosphor (BaFBr0.85I0.15:Eu2+, mean particle size: 5 xcexcm), a binder (a polyurethane: Desmolac 4125, supplied by Sumitomo Bayer Urethane K.K., solid content: 22.5 g), and 1.4 g of an anti-yellowing agent (an epoxy resin: Epikote 1004, supplied by Yuka Shell Epoxy K.K.) into methyl ethyl ketone, and subjecting the resulting mixture to a dispersing process. The thus prepared coating composition for the Information of a stimulable phosphor layer was then uniformly applied onto a polyethylene terephthalate sheet (acting as a temporary substrate, thickness: 180 xcexcm), which had been coated with a silicon type of releasing agent, with a doctor blade, and the thus formed coating film was dried. In this manner, a stimulable phosphor layer having a thickness of 350 xcexcm was formed. The thus formed stimulable phosphor layer was then separated from the temporary substrate and overlaid on the light reflecting layer, which had been formed on the substrate in the manner described above, to form a laminate. The thus obtained laminate was then passed between two heated rolls (roll temperature: 70xc2x0 C.) under the conditions of a roll pressure of 500 kgw/cm and a feed rate of 1 m/minute. In this manner, the stimulable phosphor layer was adhered to the light reflecting layer having been formed on the substrate. At this time, the thickness of the stimulable phosphor layer became equal to 270 xcexcm. Thereafter, a polyethylene terephthalate film (acting as a transparent protective layer, thickness: 10 xcexcm) was adhered to the stimulable phosphor layer. In this manner, a radiation image storage panel comprising the substrate, the light reflecting layer, the stimulable phosphor layer, and the transparent protective layer was obtained. A radiation image storage panel was formed in the same manner as that in Example 1, except that the thickness of the stimulable phosphor layer was set at 300 xcexcm. A radiation image storage panel was formed in the same manner as that in Example 1, except that the thickness of the stimulable phosphor layer was set at 240 xcexcm. A radiation image storage panel was formed in the same manner as that in Example 1, except that a light reflecting layer was formed in the manner described below. Specifically, in Example 4, a coating composition for the formation of a light reflecting layer was prepared by adding 100 g of non-spheric alumina particles (mean particle size: 0.4 xcexcm, bulk density: 0.5 g/cm2, BET specific surface area: 2 m2/g), 4 g of a binder (a soft acrylic resin), and 1 g of a phthalic ester into methyl ethyl ketone, and subjecting the resulting mixture to a dispersing process, which was performed with a propeller mixer. The thus prepared coating composition for the formation of a light reflecting layer was then uniformly applied onto a transparent polyethylene terephthalate film (acting as a substrate, thickness: 250 xcexcm) with a doctor blade, and the thus formed coating film was dried. In this manner, a light reflecting layer having a thickness of 50 xcexcm was formed on the substrate. A radiation image storage panel was formed in the same manner as that in Example 4, except that the thickness of the stimulable phosphor layer was set at 300 xcexcm. A radiation image storage panel was formed in the same manner as that in Example 4, except that the thickness of the stimulable phosphor layer was set at 240 xcexcm. A radiation image storage panel was formed in the same manner as that in Example 1, except that, in lieu of the yttrium oxide particles, particles of gadolinium oxide Gd2O3 (particle diameters of 90 wt. % particles among all particles: 1 xcexcm to 5 xcexcm, mean particle size of all particles: 2.2 xcexcm) were employed as the pigment in the light reflecting layer. A radiation image storage panel was formed in the same manner as that in Comparative Example 1, except that the thickness of the stimulable phosphor layer was set at 300 xcexcm. A radiation image storage panel was formed in the same manner as that in Comparative Example 1, except that the thickness of the stimulable phosphor layer was set at 240 xcexcm. A radiation image storage panel was formed in the same manner as that in Example 4, except that a light reflecting layer was formed by use of alumina particles (mean particle size: 0.4 xcexcm, bulk density: 1.1 g/cm2, BET specific surface area: 1 m2/g) having a shape closer to a spheric shape than the shape of the alumina particles employed in Example 4 was. A radiation image storage panel was formed in the same manner as that in Comparative Example 4, except that the thickness of the stimulable phosphor layer was set at 300 xcexcm. A radiation image storage panel was formed in the same manner as that in Comparative Example 4, except that the thickness of the stimulable phosphor layer was set at 240 xcexcm. A radiation image storage panel was formed in the same manner as that in Comparative Example 4, except that 10 mg of ultramarine was added when the coating composition for the formation of a light reflecting layer was prepared. A radiation image storage panel was formed in the same manner as that in Comparative Example 7, except that the thickness of the stimulable phosphor layer was set at 300 xcexcm. A radiation image storage panel was formed in the same manner as that in Comparative Example 7, except that the thickness of the stimulable phosphor layer was set at 240 xcexcm. The mean particle sizes, the bulk densities, and the BET specific surface areas of the light reflecting substances employed in Examples 1 to 6 and Comparative Examples 1 to 9 are listed in Table 1 below. Calculation of Scattering Length of Light Reflecting Layer: At least three light reflecting layer samples, which had the same composition as the composition of the light reflecting layer of the radiation image storage panel to be subjected to the measurement and which had different thicknesses, were prepared. Thereafter, the thickness (in MAm) and the diffuse transmittance (in %) of each sample were measured. The diffuse transmittance was measured with an apparatus comprising an automatic recording spectrophotometer (U-3210, supplied by Hitachi, Ltd.) and a 150-diameter integrating sphere (150-0901). The measured values of the thickness (in xcexcm) and the diffuse transmittance (in %) of the light reflecting layer sample, which had been obtained with the measurement described above, were substituted into the formula, which was derived from the Kubelka-Munk, s theory, and the scattering length of the light reflecting layer was thereby calculated. At this time, the measurement wavelength was set so as to coincide with the wavelength corresponding to the principal peak of the stimulation spectrum for the stimulable phosphor contained in the stimulable phosphor layer of the radiation image storage panel to be subjected to the measurement (600 nm was employed as a representative value of the wavelength corresponding to the principal peak), or the wavelength corresponding to the maximum peak (principal emission peak) of the emission spectrum of the stimulable phosphor (400 nm was employed as a representative value of the wavelength corresponding to the maximum peak). The scattering lengths of the light reflecting layers having been calculated in the manner described above are listed in Table 2 below. Evaluation of Radiation Image Storage Panel: As for each of the radiation image storage panels obtained in Examples 1 to 6 and Comparative Examples 1 to 9, the relationship between sharpness (the modulation transfer function (MTF) value at a frequency of 2 cycles/mm) and the intensity of light emitted by the stimulable phosphor (relative value) was investigated under the conditions of a tube voltage of 80 kVp and by utilizing a He-Ne laser beam as the stimulating rays. The results shown in FIG. 2 were obtained. FIG. 3 shows how the stimulating rays are scattered in each of the light reflecting layers of the radiation image storage panels obtained in Examples 1 to 6. As clear from Table 1, Table 2, and FIG. 2, in cases where the scattering length of the light reflecting layer is at most 5 xcexcm (in Examples 1 to 6), a radiation image having a high sharpness can be obtained. Specifically, in cases where the scattering length of the light reflecting layer is at most 5 xcexcm, as illustrated in FIG. 3, after the stimulating rays having passed through a stimulable phosphor layer 22 impinges upon a light reflecting layer 21, the stimulating rays emanate from the light reflecting layer 21 and again enter into the stimulable phosphor layer 22 at a position close to the position at which the stimulating rays having passed through the stimulable phosphor layer 22 impinged upon the light reflecting layer 21. Therefore, little decrease in sharpness occurs. In order for the scattering length of the light reflecting layer to be set at a value of at most 5 xcexcm, as in Examples 1 to 6, the mean particle size of the light reflecting substance may be set so as to fall within the range of 1/4 of the stimulation wavelengths to two times as large as the stimulation wavelengths. In cases where the mean particle diameter of the light reflecting substance is kept the same, if the bulk density of the light reflecting substance is at most 1 mg/cm3 or the BET specific surface area of the light reflecting substance is at least 1.5 m2/g as in Examples 4, 5, and 6, it is possible to obtain a radiation image having a higher sharpness than in cases where the bulk density of the light reflecting substance is higher than 1 mg/cm3 or the BET specific surface area of the light reflecting substance is smaller than 1.5 m2/g as in Comparative Examples 4, 5, and 6. In Comparative Examples 7, 8, and 9, the light reflecting layers in the radiation image storage panels of Comparative Examples 4, 5, and 6 are colored with ultramarine. It can be found that, in such cases, since absorption of the light emitted by the stimulable phosphor occurs due to ultramarine, the intensity of the light emitted by the stimulable phosphor decreases slightly. In addition, all of the contents of Japanese Patent Application No. 11(1999)-303914 are incorporated into this specification by reference.