Patent Number: 061880736
Section: description

EXAMPLE 1 (I) Production of Radiographic Intensifying Screen 1) Preparation of a support having light-reflecting layer containing titanium dioxide A rutile type titanium dioxide powder (500 g) having the mean grain size of 0.28 .mu.m (CR 95 [trade name], available from Ishihara Industries, Co., Ltd.) and 100 g of acrylic binder resin (Cryscoat P1018GS [trade name], available from Dainippon Ink & Chemicals, Inc.) were added into methyl ethyl ketone, and mixed to prepare a coating liquid having a viscosity of 10 PS. The coating liquid was then evenly applied by means of a doctor blade onto a polyethylene terephthalate film (thickness: 250 .mu.m) containing a titanium dioxide powder, and then dried to give a light-reflecting layer. The thickness of the dried light-reflecting layer was 40 .mu.m. The volume filling (packing) content of titanium dioxide in the support having the light-reflecting layer was 48 %, and the diffuse reflectance at a wavelength of 545 nm (which corresponds to the main peak of the luminescence emitted from terbium activated gadolinium oxysulfide Gd.sub.2 O.sub.2 S:Tb phosphor) was 95.5%. 2) Preparation of a phosphor sheet Terbium activated gadolinium oxysulfide (Gd.sub.2 O.sub.2 S:Tb, mean grain size: 3.5.mu.m, 250 g), 8 g of polyurethane binder resin (Pandex T5265M [trade name], available from Dainippon Ink & Chemicals, Inc.), 2 g of epoxy binder resin (Epikote 1001 [trade name], available from Yuka Shell Epoxy Kabushiki Kaisha) and 0.5 g of isocyanate compound (Colonate HX [trade name], available from Nippon Polyurethane Kogyo Kabushiki Kaisha) were added into methyl ethyl ketone, and mixed using a propeller mixer to prepare a coating liquid having a viscosity of 25 PS (at 25.degree. C). The coating liquid was then applied onto a temporary support (polyethylene terephthalate sheet having a surface beforehand coated with a silicon releasing agent), and dried to give a phosphor layer. The phosphor layer was then peeled off from the temporary support to prepare a phosphor sheet. 3) Fixing the phosphor sheet onto the support The above-prepared phosphor sheet was placed on the support prepared in the above 1), and then pressed by means of a calender roll at a pressure of 400 kgw/cm.sup.2 at 80.degree. C. The thickness of the resultant phosphor layer was 105 .mu.m. The volume filling content of the phosphor and the weight ratio of binder/phosphor in the phosphor layer were 68 % and 1/24, respectively. 4) Preparation of a surface protective layer Fluorocarbon resin (Lumiflon LF100 [trade name], available from Asahi Glass Co., Ltd., 10 g), 0.5 g of an alcohol modified-siloxane oligomer (X-22-2809 [trade name], available from The Shin-Etsu Chemical Co., Ltd.), 3.2 g of isocyanate (Orestar NP38-70s [trade name], available from Mitsui Toatsu Chemicals, Inc.), 0.4 g of anatase type titanium dioxide (A220 [trade name], available from Ishihara Industries Co., Ltd.; mean grain size: 0.15 .mu.m; refractive index: about 2.6) and 0.001 g of a catalyst (KS1269 [trade name], available from Kyodo Chemical Co., Ltd.) are added into a mixed solvent of methyl ethyl ketone and cyclohexanone (weight ratio: 1/1), and mixed to prepare a coating liquid. The coating liquid was then applied onto the phosphor layer by means of a doctor blade, and slowly dried. The coated layer was then heated at 120.degree. C. for 30 minutes to form a surface protective layer (thickness: 7 .mu.m). The content of titanium dioxide in the surface protective layer was 3 wt. %. (II) Calculation of the scattering length and the absorption length of the surface protective layer The coating solution of the above 4) was applied onto a transparent support (thickness: 180 .mu.m) so that the formed layer would have a thickness of 5 to 50 .mu.m. The diffuse transmittance (or diffused transmittance: %) of the formed layer was measured at a wavelength of 545 nm (corresponding to the main peak of the luminescence emitted from terbium activated gadolinium oxysulfide Gd.sub.2 O.sub.2 S:Tb phosphor), by means of an automatic recording spectrophotometer (U-3210, manufactured by HITACHI, Ltd.) equipped with an integrating sphere of 150 .phi. (150-0910). The results are set forth in Table 1. TABLE 1 thickness (.mu.m) 7 11 24 40 diffuse 70.3 62.6 48.4 40.2 transmittance (%) In accordance with the above-described formulas, the values of K and S were calculated from the data shown in Table 1. From the calculated values of K and S, the scattering length and the absorption length were determined to be 23 .mu.m (scattering length=1/S) and 10,000 .mu.m (absorption length=1/K), respectively. COMPARISON EXAMPLE 1 The procedure of Example 1 was repeated except that titanium dioxide was not added to the surface protective layer, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was then determined in the same manner as described above, and found to be more than 200 .mu.m. COMPARISON EXAMPLE 2 The procedure of Example 1 was repeated except that the content of titanium dioxide powder in the surface protective layer was set to be 0.1 wt. %, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was determined in the same manner as described above, and found to be 140 .mu.m. EXAMPLE 2 The procedure of Example 1 was repeated except that the content of titanium dioxide powder in the protective layer was set to be 1 wt. %, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was determined, and found to be 50 .mu.m. EXAMPLE 3 The procedure of Example 1 was repeated except that the content of titanium dioxide powder in the protective layer was set to be 10 wt. %, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was determined, and found to be 9 .mu.m. [Measurement of Sharpness and Sensitivity] (1) Measurement of sharpness On the surface protective layer of the sample intensifying screen, a "single emulsion layer type" radio-graphic film (X-ray film MINP 30 [trade name], available from Fuji Photo film Co., Ltd.) was overlaid so that the film might be directly contact with the protective layer. (A "single emulsion layer type" radiographic film comprises a silver halide emulsion layer provided on only one surface of its support.) The combination of the screen and the X-ray film was then exposed to X-rays through an CTF chart (made of molybdenum, thickness: 80 Am, space frequency: 0 to 10 lines/mm) in the following manner. The CTF chart was placed at a distance of 2 m from an X-ray source, and the X-ray film and the screen were placed behind the CTF chart in order. The X-ray source was composed of an X-ray generating apparatus and filters. The X-ray generating apparatus (DRX-3724HD [trade name], available from Toshiba Corporation; focal spot size: 0.6 mm.times.0.6 mm) equipped with a tungsten target and an aluminum filter (thickness: 3 mm) was activated with a three-phase pulse generator under 80 kvp, to generate X-rays. The generated X-rays were made to pass a water filter (thickness: 7 cm), which absorbed X-rays in the same amount as a human body, and then emitted from the X-ray source. After the exposure was made, the exposed film was developed in an automatic developing machine (FPM-5000 [trade name], available from Fuji Photo film Co., Ltd.) using a developer and a fixer (RD-3 and Fuji-F [trade name], respectively; available from Fuji Photo film Co., Ltd.) to obtain a sample for the measurement of sharpness. In the above exposure, the exposing conditions were adjusted so that the thick part of the resultant image would have a density of 1.8. In accordance with the method described in Japanese Patent Provisional Publication No. H9-21899, the sharpness was determined with the value at 2 lines/mm based on the obtained sample. The results are shown in Table 2. (2) Measurement of sensitivity Using the same X-ray source and the same X-ray film as described above, the combination of the screen and the X-ray film was exposed to X-rays. The distance between the X-ray source and the X-ray film was varied so that the amount of exposed X-ray might be stepwise changed (step width: logE=0.15). The exposed film was then developed in the same manner as described above to prepare a sample for the measurement of sensitivity. The density of the sample was measured with visible light to determine a characteristic curve. The sensitivity was determined with a reciprocal of the amount of exposed X-ray giving a fog density of 1.0. The sensitivity thus obtained was relatively shown so that the value of Comparison Example 1 would be 100. The results are set forth in Table 2. TABLE 2 scattering sharpness screen length (.mu.m) sensitivity (2 lines/mm) C. Ex. 1 above 200 100 0.590 C. Ex. 2 140 100 0.590 Ex. 1 23 99 0.630 Ex. 2 50 100 0.625 Ex. 3 9 97 0.615 The results shown in Table 2 indicate that each of the radiographic intensifying screens of the invention (Examples 1 to 3) gives a radiographic image having improved sharpness without lowering the sensitivity, as compared with those given by the screens of Comparison Examples 1 and 2. EXAMPLE 4 The procedure of Example 1 was repeated except that melamine resin particles (refractive index: 1.57, mean grain size: 0.6 .mu.m, content: 20 wt. %) were used in place of the titanium dioxide powder in the surface protective layer, to prepare a radiographic intensifying screen. The scattering length of the screen was determined and found to be 26 .mu.m. EXAMPLE 5 The procedure of Example 1 was repeated except that melamine resin particles (refractive index: 1.57, mean grain size: 0.6 .mu.m, content: 10 wt. %) were used in place of the titanium dioxide powder in the surface protective layer, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was measured, and found to be 60 .mu.m. COMPARISON EXAMPLE 3 The procedure of Example 1 was repeated except that melamine resin particles (refractive index: 1.57, mean grain size: 3 .mu.m, content: 10 wt. %) were used in place of the titanium dioxide powder in the surface protective layer, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was measured, and found to be 90 .mu.m. COMPARISON EXAMPLE 4 The procedure of Example 1 was repeated except that silicon dioxide particles (refractive index: about 1.46, mean grain size: 3 .mu.m, content: 10 wt. %) were used in place of the titanium dioxide powder n the surface protective layer, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was determined, and found to be 120 .mu.m. COMPARISON EXAMPLE 5 The procedure of Example 1 was repeated except that alumina particles (refractive index: about 1.56, mean grain size: 0.8 .mu.m, content: 5 wt. %) were used in place of the titanium dioxide powder in the surface protective layer, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was measured, and found to be 100 .mu.m. Measurement of Sharpness and Sensitivity (1) Measurement of sharpness The sharpness was measured in the same manner as described above. (2) Measurement of sensitivity The sensitivity was measured in the same manner as described above. The results are set forth in Table 3. TABLE 3 scattering sharpness screen length (.mu.m) sensitivity (2 lines/mm) C. Ex. 1 above 200 100 0.590 C. Ex. 3 90 100 0.600 C. Ex. 4 120 100 0.590 C. Ex. 5 100 100 0.595 Ex. 4 26 100 0.630 Ex. 5 60 100 0.620 The results shown in Table 3 indicate that each of the radiographic intensifying screens of the invention (Examples 4 and 5) gives a radiographic image having improved sharpness without lowering the sensitivity, as compared with those given by the screens of Comparison Examples 1 and 3 to 5. EXAMPLE 6 The procedure of Example 1 was repeated except that only polyethylene terephthalate was used as the binder resin to form a surface protective layer having a thickness of 6 .mu.m, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was measured, and found to be 30 .mu.m. COMPARISON EXAMPLE 6 The procedure of Example 1 was repeated except that only polyethylene terephthalate was used as the binder polymer and the titanium dioxide powder was not used to form a surface protective layer having a thickness of 6 .mu.m, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was measured, and found to be more than 200 .mu.m. Measurement of Sharpness, Sensitivity and Durability (1) Measurement of sharpness The sharpness was measured in the same manner as described above. (2) Measurement of sensitivity The sensitivity was measured in the same manner as described above. (3) Measurement of durability The durability of the surface protective layer was measured in the following manner. A great number of beads (diameter: 300 .mu.m) were sprinkled on a plate, and the sample intensifying screen was placed and fixed on the plate so that the support would be in contact with the beads and the surface protective layer would be pressed with the beads via the support to form a great number of convexes on the protective layer. On the surface protective layer having the convexes thus formed, a stainless steel plate (size: 4 cm.times.5 cm) and a weight of 100 g were placed and repeatedly moved so that the protective layer would be rubbed with the stainless steel plate. The rubbing had been continued until the protective layer produced crack and the phosphor layer was bared, and the times of the rubbing was counted. According to the counted rubbing times, the durability of the surface protective layer was determined. Needless to say, a large number indicates better durability. The results are set forth in Table 4. Table 4 TABLE 4 scattering sensi- sharpness dura- screen length (.mu.m) tivity (2 lines/mm) bility C. Ex. 6 above 200 98 0.595 above 10000 Ex. 6 30 97 0.635 above 10000 The results shown in Table 4 indicate that the radiographic intensifying screen of the invention gives a radiographic image having improved sharpness without lowering the sensitivity, as compared with those given by the screens of Comparison Example. Further, the results also indicate that polyethylene terephthalate binder resin gives extremely high durability to the surface protective layer. EXAMPLE 7 The procedure of Example 1 was repeated except that the thickness of the surface protective layer was set at 3 .mu.m, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was measured, and found to be 23 .mu.m. EXAMPLE 8 The procedure of Example 1 was repeated except that the thickness of the surface protective layer was set at 5 .mu.m, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was measured, and found to be 23 .mu.m. EXAMPLE 9 The procedure of Example 1 was repeated except that the thickness of the surface protective layer was set at 10 .mu.m, to prepare a radiographic intensifying screen. The scattering length of the prepared screen was measured, and found to be 23 .mu.m. Measurement of Sharpness and Sensitivity (1) Measurement of sharpness The sharpness was measured in the same manner as described above. (2) Measurement of sensitivity The sensitivity was measured in the same manner as described above. The results are set forth in Table 5. TABLE 5 thick- scattering sensi- sharpness screen ness (.mu.m) length (.mu.m) tivity (2 lines/mm) Ex. 7 3 23 100 0.640 Ex. 8 5 23 100 0.635 Ex. 1 7 23 99 0.630 Ex. 9 10 23 97 0.610 The results shown in Table 5 indicate that the radiographic intensifying screen of the invention gives a radiographic image having high sharpness and excellent sensitivity even if the thickness of the surface protective layer is varied. EXAMPLE 10 (1) Production of Radiographic Intensifying Screens Having Different Phosphor Layers 1) The procedure of Example 1 was repeated except that the thickness of the phosphor layer after calender treatment was set at 80 .mu.m, to prepare a radiographic intensifying screen (screen A, scattering length: 23 .mu.m). 2) The procedure of Example 1 was repeated except that 50 g of the phosphor particles having the mean grain size of 2.0 .mu.m and 200 g of those having the mean grain size of 6.2 .mu.m were used (the chemical contents of the phosphor were not changed) and that the thickness of the phosphor layer after calender treatment was set at 120 .mu.m, to prepare a radiographic intensifying screen (screen B, scattering length: 23 .mu.m). The volume filling content of the phosphor in the phosphor layer was 72%. 3) The procedure of the above 2) was repeated except that the thickness of the phosphor layer after calender treatment was set at 95 .mu.m, to prepare a radiographic intensifying screen (screen C, scattering length: 23 .mu.m). 4) The procedure of Example 1 was repeated except that a double phosphor layer consisting of a lower layer (thickness after calender treatment: 80 .mu.m) containing the phosphor particles having a mean grain size of 3.0 .mu.m and an upper layer (thickness after calender treatment: 100 .mu.m) containing those having a mean grain size of 6.2 .mu.m was formed (the chemical contents of the phosphor were not changed), to prepare a radiographic intensifying screen (screen D, scattering length: 23 .mu.m). The volume filling content of the phosphor in the phosphor layer was 70%. 5) The procedure of Example 1 was repeated except that a double phosphor layer consisting of a lower layer (thickness after calender treatment: 80 .mu.m) containing the phosphor particles having a mean grain size of 3.0 .mu.m and an upper layer (thickness after calender treatment: 240 .mu.m) containing those having a mean grain size of 6.2 Am was formed (the chemical contents of the phosphor were not changed), to prepare a radiographic intensifying screen (screen E, scattering length: 23 .mu.m). (2) Production of Silver Halide X-ray Film (Film-1) A "both-sided emulsion type" X-ray film was prepared in the same manner as described in Japanese Patent Provisional publication No. H7-219162 (sample 3 of Example 1). The subbing dye-I (described in the above publication) was applied in an amount of 45 mg per one surface. The light cross-over of the prepared film was measured by the method described in Example 1 of the above-mentioned publication, and found to be 6%. The chemical sensitization of the silver halide emulsion was adjusted so that the sensitivity and the tone might be the same as commercially available X-ray film (UR-2 [trade name], available from Fuji Photo film Co., Ltd.). (3) Evaluation of Combination of Radiographic Intensifying Screen and X-ray Film The combinations of the radiographic intensifying screens A to E and the above X-ray film (Film-1) were evaluated in the manner described in Japanese Patent Provisional publication No. H7-219162 (Example 1). In addition to that, the combinations of the screens A to E and the above commercially available X-ray film (UR-2), and those of commercially available radiographic intensifying screens (HGM2 and HGH2 [trade name], available from Kasei Optonics Co., Ltd.) and the X-ray film (UR-2) were also determined. The results are set forth in Table 6. TABLE 6 front back sensi- sharpness composition screen screen film tivity (2 lines/mm) No. 1 A B Film-1 100 0.630 No. 2 A B UR-2 100 0.580 No. 3 C D Film-1 132 0.510 No. 4 C D UR-2 132 0.470 No. 5 HGM2 HGM2 UR-2 100 0.500 No. 6 HGH2 HGH2 UR-2 130 0.410 No. 7 C E Film-1 190 0.365 No. 8 C E UR-2 190 0.315 The results shown in Table 6 indicate that the composition consisting of the screens of the invention and an X-ray film of low cross-over gives an image of improved sharpness. The results also indicate that the combination of the screens of the invention and a commercially available X-ray film gives an image having excellent balance of sensitivity and sharpness. EXAMPLE 11 1) Formation of a phosphor layer on the support having the light-reflecting layer The procedure of Example 1 was repeated except that 11 g of polyurethane binder resin was used to form a coating liquid for phosphor layer, to prepare a phosphor layer (thickness: 100 .mu.m) on the support. The volume filling content of the phosphor and the weight ratio of binder/phosphor in the phosphor layer were 66% and 1/18.5, respectively. 2) Preparation of a surface protective layer Anatase type titanium dioxide (P220 [trade name], available from Ishihara Industries Co., Ltd.) was added into melted polyethylene terephthalate (PET) resin in the amount of 3.5 wt. % (per PET resin). From thus prepared PET resin containing titanium dioxide, PET sheet (thickness: 70 .mu.m) was formed by a known extrusion method. The formed PET sheet was biaxially oriented (by 3.4 times.times.3.4 times), and then heated to prepare a thin PET film (thickness: 6.0 .mu.m) containing titanium dioxide. The diffuse transmittance of the prepared film at the wavelength of 545 nm was measured to be found 78%. Thin PET films having various thickness were also prepared in the manner described above, and then the scattering length of the PET film was measured in the same manner as described in Example 1, and found to be 25 .mu.m. The film thus prepared was overlaid and fixed on the above phosphor layer with adhesive, to provide a surface protective layer (thickness: 6.0 .mu.m). Thus, a radio-graphic intensifying screen of the invention was produced. COMPARISON EXAMPLE 7 The procedure of Example 11 was repeated except that commercially available polyethylene terephthalate film (thickness: 6 .mu.m, available from Toray Industries, Inc.) was used as the surface protective layer, to prepare a radiographic intensifying screen for comparison. The scattering length of the prepared screen was estimated to be more than 200 .mu.m. EXAMPLE 12 The procedure of Example 11 was repeated except that 15 g of polyurethane binder resin was used, to prepare a radiographic intensifying screen of the invention. The thickness of the phosphor layer, the volume filling content of the phosphor, and the binder/phosphor weight ratio in the phosphor layer were 110 .mu.m, 60%, and 1/14, respectively. COMPARISON EXAMPLE 8 The procedure of Example 12 was repeated except that commercially available polyethylene terephthalate film (thickness: 6 .mu.m, available from Toray Industries, Inc.) was used as a surface protective layer, to prepare a radiographic intensifying screen for comparison. EXAMPLE 13 The procedure of Example 11 was repeated except that 5.6 g of polyurethane binder resin and 1 g of epoxy binder resin were used, to prepare a radiographic intensifying screen of the invention. The thickness of the phosphor layer, the volume filling content of the phosphor and the weight ratio of binder/phosphor in the phosphor layer were 100 .mu.m, 70% and 1/35, respectively. COMPARISON EXAMPLE 9 The procedure of Example 13 was repeated except that commercially available polyethylene terephthalate film (thickness: 6 .mu.m, available from Toray Industries, Inc.) was used as a surface protective layer, to prepare a radiographic intensifying screen for comparison. EXAMPLE 14 The procedure of Example 11 was repeated except that 8 g of polyurethane binder resin was used, to prepare a radiographic intensifying screen of the invention. The thickness of the phosphor layer, the volume filling content of the phosphor and the binder/phosphor weight ratio in the phosphor layer were 105 .mu.m, 68% and 1/24, respectively. COMPARISON EXAMPLE 10 The procedure of Example 14 was repeated except that commercially available polyethylene terephthalate film (thickness: 6 .mu.m, available from Toray Industries, Inc.) was used as a surface protective layer, to prepare a radiographic intensifying screen for comparison. Measurement of Sharpness and Sensitivity (1) Measurement of sharpness The sharpness was measured in the same manner as described above. (2) Measurement of sensitivity The sensitivity was measured in the same manner as described above, and relatively shown so that the value of Example 14 might be 100. The results are set forth in Table 7. TABLE 7 scattering binder/phos- sensi- sharpness screen length (.mu.m) phor (wt.) tivity (2 lines/mm) Ex. 11 25 1/18.5 98 0.605 Ex. 12 25 1/14 95 0.580 Ex. 13 25 1/35 100 0.635 Ex. 14 25 1/24 100 0.635 C. Ex. 7 above 200 1/18.5 100 0.580 C. Ex. 8 above 200 1/14 99 0.570 C. Ex. 9 above 200 1/35 100 0.590 C. Ex. 10 above 200 1/24 100 0.590 The results shown in Table 7 indicate the following facts. Even if the ratio of binder/phosphor in the phosphor layer varies within the range of less than 1/12, each radiographic intensifying screen of the invention gives a radiographic image having improved sharpness without lowering the sensitivity, as compared with that given by each conventional screen having a transparent surface protective layer. Further, the screen of low binder/phosphor ratio gives good sharpness and sensitivity, and hence the ratio of binder/phosphor is preferred to be small (in other wards, the binder is preferred to be used in a small amount) in the invention. EXAMPLE 15 The procedure of Example 1 was repeated except that the thickness of the surface protective layer was set at 2 .mu.m, to prepare a radiographic intensifying screen of the invention. COMPARISON EXAMPLE 11 The procedure of Example 1 was repeated except that titanium dioxide was not used to form a surface protective layer having the thickness of 2 .mu.m, to prepare a radiographic intensifying screen for comparison. COMPARISON EXAMPLE 12 The procedure of Example 1 was repeated except that titanium dioxide was not used to form a surface protective layer having the thickness of 5 .mu.m, to prepare a radiographic intensifying screen for comparison. Measurement of Sharpness, Sensitivity, Stain Resistance and Abrasion Resistance (1) Measurement of sharpness The sharpness was measured in the same manner as described above. (2) Measurement of sensitivity The sensitivity was measured in the same manner as described above, and relatively shown so that the value of Comparison Example 1 might be 100. (3) Measurement of stain resistance 1 cc of screen cleaner (available from Fuji Photo film Co., Ltd.) was evenly applied and dried on the sample screen (size: 16 cm.times.16 cm). The thus treated sample screen and a silver halide X-ray film (UR-1 [trade name], available from Fuji Photo film Co., Ltd.) were stored at 25.degree. C., 84 %RH for 3 hours. After that, the sample screen was placed on the X-ray film so that the surface protective layer would be in contact with the film, and then pressed for fixation. The laminated screen and film were stored at 40.degree. C. for 24 hours. The screen was then peeled off from the film, and the stains caused with dyes transferred onto the protective layer from the X-ray film were observed by sight. According to the observation, the surface protective layer of each sample was classified into the following three grades: AA: not stained, PA1 BB: slightly stained, but usable, PA1 CC: stained too much to use. PA1 AA: not abraded, PA1 BB: hardly abraded and presumed to be usable even after rubbed 40,000 times, PA1 CC: slightly abraded and presumed to be usable even after rubbed 20,000 times, PA1 DD: abraded, but usable until rubbed 10000 times, PA1 EE: abraded so much that the protective layer was completely worn out and that the bared phosphor layer was stained. (4) Measurement of abrasion resistance The sample screen was rubbed 10,000 times with a UR-1 X-ray film (the rubbing film was renewed at regular intervals), and then the surface protective layer thus treated was observed by sight. According to the observation, the surface protective layer of each sample was classified into the following five grades: The results are set forth in Table 8. TABLE 8 scattering thickness sensi- sharpness length (.mu.m) binder (.mu.m) tivity (2 lines/mm) (Example 15) 23 fluoro* 2 100 0.645 stain resistance: BB abrasion resistance: DD (Example 7) 23 fluoro* 3 100 0.640 strain resistance: AA abrasion resistance: CC (Example 8) 23 fluoro* 5 100 0.635 stain resistance: AA abrasion resistance: BB (Example 1) 23 fluoro* 7 99 0.630 stain resistance: AA abrasion resistance: AA (Example 9) 23 fluoro* 10 97 0.610 stain resistance: AA abrasion resistance: AA (Comparison Example 11) above 200 fluoro* 2 100 0.635 stain resistance: BB abrasion resistance: DD (Comparison Example 12) above 200 fluoro 5 100 0.600 stain resistance: AA abrasion resistance: CC (Comparison Example 1) above 200 fluoro* 7 100 0.590 stain resistance: AA abrasion resistance: BB The results shown in Table 8 indicate that the present invention is very effective in the screen having a thick protective layer. The conventional screen having a thick protective layer gives a radiographic image of poor sharpness, while the screen of the invention having that of the same thickness gives relatively high sharpness. The results further suggests that the thick surface protective layer gives high stain resistance and high abrasion resistance. Therefore, the screen of the invention having the protective layer of enough thickness to keep sufficient resistance against stain and abrasion can give a radiographic image of high sharpness without lowering sensitivity. The results shown in Table 8 also reveal that the light-scattering particles do not lower the stain resistance but improve the abrasion resistance of the surface protective layer containing fluorocarbon resin. EXAMPLE 16 10 g of cellulose acetate (acetylation degree: about 56%) and 0.3 g of anatase type titanium dioxide (A220 [trade name], available from Ishihara Industries Co., Ltd.) were added into methyl ethyl ketone, and mixed to prepare a coating liquid for protective layer. After that, the procedure of Example 1 was repeated except that the prepared coating solution was used to prepare a surface protective layer of the thickness of 6.5 .mu.m, to prepare a radiographic intensifying screen. The content of titanium dioxide in the surface protective layer was 3 wt. %, and the scattering length of the prepared screen was 28 .mu.m. COMPARISON EXAMPLE 13 The procedure of Example 16 was repeated except that titanium dioxide was not used to form a surface protective layer, to prepare a radiographic intensifying screen for comparison. EXAMPLE 17 The procedure of Example 14 was repeated except that the thickness of the surface protective layer was set at 4 .mu.m, to prepare a radiographic intensifying screen of the invention. Measurement of Sharpness, Sensitivity, Stain Resistance and Abrasion Resistance (1) Measurement of sharpness The sharpness was measured in the same manner as described above. (2) Measurement of sensitivity The sensitivity was measured in the same manner as described above, and relatively shown so that the value of Comparison Example 10 might be 100. (3) Measurement of stain resistance The stain resistance was measured in the same manner as described above. (3) Measurement of abrasion resistance The abrasion resistance was measured in the same manner as described above. The results are set forth in Table 9. TABLE 9 scattering thickness sensi- sharpness length (.mu.m) binder (.mu.m) tivity (2 lines/mm) (Example 16) 28 cel.ac.* 6.5 100 0.630 stain resistance: BB abrasion resistance: BB (Example 17) 25 PET* 4 100 0.640 stain resistance: AA abrasion resistance: AA (Example 14) 25 PET* 6 100 0.635 stain resistance: AA abrasion resistance: AA (Comparison Example 13) above 200 cel.ac.* 6.5 100 0.585 stain resistance: BB abrasion resistance: BB (Comparison Example 10) above 200 PET* 6 100 0.590 stain resistance: AA abrasion resistance: AA (Comparison Example 1) above 200 fluoro* 7 100 0.590 stain resistance: AA abrasion resistance: BB Remark*) "cel.ac." and "PET" mean cellulose acetate and polyethylene terephthalate, respectively. The results shown in Table 9 indicate that the radiographic intensifying screen of the invention gives a radiographic image of excellent sharpness without lowering the sensitivity and the resistance against stain and abrasion even if cellulose acetate or polyethylene terephthalate is used as a binder of the surface protective layer.