JPS6118480Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a radiation intensifying screen (hereinafter abbreviated as "intensifying screen"). More specifically, the present invention relates to an intensifying screen with good graininess using a colored film, which is obtained by dyeing one side of a transparent film with a dye, as a protective film. Intensifying screens are used to improve the sensitivity of imaging systems in various fields such as medical radiography such as X-ray photography for medical diagnosis, and industrial radiography for non-destructive testing of materials. It is used in close contact with the film. This intensifying screen basically consists of a support such as paper or plastic and a phosphor layer provided on one side of the support. The phosphor layer is made by dispersing a phosphor that emits high-intensity light upon radiation excitation in a binder resin, and the surface of this phosphor layer (the surface opposite to the support) is
Generally, it is protected by a thin transparent protective film such as a polyethylene terephthalate film, cellulose acetate film, polymethacrylate film, or nitrocellulose film. In addition, some intensifying screens have a light-reflecting layer or a light-absorbing layer between the support and the phosphor layer, and are further used in industrial radiography for the purpose of non-destructive testing of materials. The intensifying screen used has a metal foil interposed between the support and the phosphor layer. In recent years, there has been an increasing demand for reducing the radiation exposure of examinees, and it is necessary to improve the sensitivity of the intensifying screen-X-ray film system. A highly sensitive system using a phosphor with high X-ray absorption and high light conversion exchange rate has been developed. The important factors for intensifying screens are high sensitivity to radiation (that is, high light conversion efficiency) and good photographic image quality such as graininess and sharpness. Although the sensitivity system improves sensitivity, it has the disadvantage that graininess increases (deteriorates).
This increase in graininess is due to statistical fluctuations in X-ray quanta accompanying a decrease in the amount of incident X-rays during imaging, and an improvement has been desired. The object of the present invention is to provide an intensifying screen with good photographic image quality, especially graininess. The present inventors have conducted various studies to achieve the above objective. As a result, they discovered that if a colored film is used as a protective film for the phosphor layer to absorb a portion of the amount of light emitted from the phosphor layer, the granularity can be significantly improved, leading to the completion of the present invention. The intensifying screen of the present invention has a basic structure in which a phosphor layer and a protective film are laminated in this order on a support. , terbium-activated rare earth phosphate phosphor, terbium-activated rare earth oxyhalide phosphor, thulium-activated rare earth oxyhalide phosphor, divalent europium-activated alkaline earth metal fluoride It consists of one or more types of fluorescers contained in halide-based phosphors, silver-activated sulfide-based phosphors, and hafnium phosphate-based phosphors, and the above-mentioned protective film coats one side of the transparent film with a dye. It is characterized by being a colored film dyed with. The intensifying screen of the present invention has better granularity than a conventional intensifying screen of equivalent sensitivity using the same phosphor. Further, the intensifying screen of the present invention has a sharpness equivalent to or better than that of a conventional intensifying screen using the same phosphor and having the same sensitivity. The present invention will be explained in detail below. The intensifying screen of the present invention is manufactured in the same manner as conventional intensifying screens except that a colored film is provided as a protective film instead of a transparent film. That is, first, an appropriate amount of the phosphor and a binder resin such as nitrified cotton are mixed, and then an appropriate amount of a solvent is added to this to create a phosphor coating liquid with an optimum viscosity.
Apply this phosphor coating liquid to a roll coater or knife coater.
The phosphor layer is coated onto a support using a tar or the like and dried to form a phosphor layer. In the case of an intensifying screen having a structure having a light reflection layer, a light absorption layer or a metal foil between the support and the phosphor layer, the light reflection layer, light absorption layer or metal foil is provided on the support in advance, A phosphor coating solution is applied thereon and dried to form a phosphor layer. Next, a colored protective film is formed on the phosphor layer to form an intensifying screen. The method for forming a colored protective film is to add an appropriate amount of solvent to a resin such as polyvinyl chloride, polyethylene, or cellulose acetate to achieve the optimum viscosity, and then coat the resin with a roll coater, knife coater, etc. A method in which the surface of a transparent film obtained by coating and drying on a phosphor layer is dyed with a dye, or a thin transparent film such as polyethylene terephthalate that is colored by dyeing one side with a dye. A method is used in which the phosphor layer is laminated onto the phosphor layer. When the protective film is colored to have the same light transmittance, from the viewpoint of graininess improvement, it is possible to color the entire transparent protective film uniformly or to color only one side of the transparent protective film. However, it is necessary to prevent the reduction in sharpness due to the scattering of the emitted light from the opposite intensifying screen on the surface of the protective film (so-called crossover effect), which occurs when two intensifying screens are actually used as a set. In order to prevent this, it is preferable to color only one side of the surface side of the protective film (the side from which the emitted light is taken out).In addition, the emitted light from the phosphor layer is totally reflected at the interface with the protective film, and is further scattered to the surroundings. In order to prevent deterioration in sharpness due to color change, it is preferable to color only one side of the protective film on the phosphor layer side. Note that with repeated use of intensifying screens that use a colored protective film, the surface of the protective film is worn away due to friction with the film or scratches caused by dust that has gotten between the film and the intensifying screen, resulting in reduced light transmission in that area. Because the ratio changes, graininess worsens, and density unevenness tends to occur in X-ray photographs, it is recommended to use a colored protective film that is dyed on one side so that the colored side is in contact with the phosphor layer surface. It is preferable to laminate the film (with one side of the phosphor layer side colored to form a colored protective film). As mentioned above, the purpose of the present invention is mainly to improve the deterioration of graininess in a high-sensitivity intensifying screen. From this point of view, the intensifying screen of the present invention mainly uses terbium-activated rare earth oxysulfide. Physical phosphors [Y ₂ O ₂ S: Tb, Gd ₂ O ₂ S: Tb, La ₂ O ₂ S: Tb,
(Y, Gd) ₂ O ₂ S: Tb, (Y, Gd) ₂ O ₂ S: Tb, Tm
], terbium-activated rare earth phosphate phosphors (YPO ₄ :Tb, GdPO ₄ :Tb, LaPO ₄ :Tb, etc.), terbium-activated rare earth oxyhalide phosphors (LaOBr:Tb, LaOBr: Tb, Tm, LaOC:
Tb, LaOC: Tb, Tm, GdOBr: Tb, GdOC
:Tb, etc.), thulium-activated rare earth oxyhalide phosphors (LaOBr:Tm, LaOC:Tm
), divalent europium-activated alkaline earth metal fluorohalide phosphor [BaFC: Eu ²⁺ ,
BaFBr: Eu ²⁺ , BaFC: Eu ²⁺ , Tb, BaFBr:
Eu ²⁺ , Tb, BaF ₂・BaC ₂・KC: Eu ²⁺ ,
BaF ₂・BaC ₂・xBaSO ₄・KC: Eu ²⁺ , (Ba,
Mg) F ₂・BaC ₂・KC: Eu ²⁺ etc.], silver-activated sulfide phosphor [ZnS:Ag, (Zn, Cd)S:Ag
], hafnium phosphate phosphor (HfP ₂ O ₇ :Cu
etc.) are used for high-sensitivity intensifying screens, which have high X-ray absorption and high light conversion efficiency. The dyes used in the colored film of the intensifying screen of the present invention include methylene blue, Victoria Blue B, insulin, etc. as blue dyes, and dispersion green 3B, malachite green, etc. as green dyes.
First Light Yellow G, Au
Ramin Gconc., Chrome Yellow-M, etc., and examples of red colors include Chrome Red G, Disperthread R, Oil Red, etc. The drawings show cross-sectional views of the intensifying screen of the present invention. FIG. 1 shows an intensifying screen in which the phosphor layer 2 side of the protective film 1 is colored with dye, and FIG. The surface side (the side opposite to the phosphor layer 12 side) is a colored intensifying screen with dye, 1 and 11 are colored protective films,
2 and 12 are phosphor layers, 3 and 13 are supports,
4 and 14 are colored layers. Table 1 shows the effects of the intensifying screen of the present invention, which uses Y ₂ O ₂ S:Tb for the phosphor layer and a colored film colored on one side with Chrome Yellow-M as a protective film. This figure shows a comparison with a conventional intensifying screen that uses a transparent film as a protective film. In Table 1, No. 1 is the conventional intensifying screen, No. 2, No. 3 and No.
4 is the intensifying screen of the present invention, and the intensifying screens No. 1, No. 2, and No. 3 have a light absorption layer, and the intensifying screen No. 4 has a light reflection layer. . The graininess of each intensifying screen is the RMS value at a photographic density of 0.8 and a spatial frequency of 0 to 5 lines/mm, and the sharpness is the spatial frequency of 2 lines/mm.
Each is expressed by the MTF value at .

[Table] As is clear from Table 1, when the protective film is colored, at the same phosphor coating weight, the intensifying screen of the present invention (No. 2) is different from that of the conventional intensifying screen without coloring (No. No. 1), both graininess and sharpness are improved, or, as a matter of course, the colored protective film absorbs a portion of the emitted light from the phosphor layer, resulting in a decrease in sensitivity. When the phosphor coating weight is increased to make the sensitivity the same (No. 3), the graininess becomes worse than No. 2, but the degree of this deterioration is relatively small and the graininess is still as good as No. 2. .1. On the other hand, the sharpness decreases as the weight of the phosphor coating increases, but the sharpness of No. 3 is slightly better than No. 1. In addition, when a light reflective layer is provided to make the sensitivity the same (No. 4), the graininess is the same as in No. 3.
Although it is worse than 2, its graininess is still No.
It is significantly better than No. 1, and the sharpness is equivalent to No. 1. As is clear from the explanation of Table 1 above,
Furthermore, as is clear from the description of the examples below, the intensifying screen of the present invention has better graininess than a conventional intensifying screen using the same phosphor and having equivalent sensitivity. Further, the intensifying screen of the present invention has a sharpness equivalent to or better than that of a conventional intensifying screen using the same phosphor and having the same sensitivity. When the phosphor layer is colored instead of the protective film as in the present invention, the sharpness is greatly improved, but the graininess is hardly improved. This is because when the protective film is colored, the light emitted from any position on the phosphor layer is attenuated at the same rate by the colored protective film.
This is thought to be because when the phosphor layer is uniformly colored, the rate of attenuation of light emitted from the phosphor on the support side is large, and the rate of attenuation of light emitted from the phosphor on the protective film side is small. It will be done. In other words, when the phosphor layer is colored, the sharpness is good, but the granularity is improved relatively little because the contribution of light emission from the phosphor on the side of the protective film, which is poor in graininess, is relatively small; In this case, the granularity is thought to be further improved because the light emitted from each phosphor in the phosphor layer is utilized more evenly. Regarding the degree of coloration of the protective film used in the intensifying screen of the present invention, if the degree of coloration is low, the sensitivity of the intensifying screen will not decrease much, but the graininess and sharpness will not improve much.
On the other hand, if the degree of coloring is too high, the graininess and sharpness will be further improved, but the sensitivity will be greatly reduced, which is not preferable. Therefore, when comparing the degree of coloring of the protective film with an intensifying screen having a phosphor layer with the same phosphor and coating weight, the photographic sensitivity when using a colored protective film is the same as when using a transparent protective film. of that time
It is desirable that it be in the range of 90 to 30%. The decrease in sensitivity caused by the coloring of the protective film can be reduced by increasing the coating weight of the phosphor in the phosphor layer, or by adding a light-reflecting layer between the phosphor layer and the support. This can be prevented by providing As explained above, the present invention significantly improves the graininess of intensifying screens, particularly high-sensitivity intensifying screens, and has great industrial utility value. Next, the present invention will be explained with reference to examples. Example 1 Y ₂ O ₂ S with an average particle size of 7 μm: 8 parts by weight of Tb and 1 part by weight of nitrified cotton were used in a solvent (a mixture of acetone, ethyl acetate and butyl acetate in a weight ratio of 1:1:8). and mixed to obtain a phosphor coating solution with a viscosity of 50 centistokes. This phosphor coating solution was knife-coated onto a polyethylene terephthalate support having a carbon black light absorbing layer approximately 250 μ thick so that the phosphor coating weight was approximately 60 mg/cm ² .
It was applied uniformly using a tar and dried at 50°C to form a phosphor layer. Next, nitrified cotton was uniformly applied on this phosphor layer and dried at 50°C to create a transparent protective film with a thickness of approximately 10μ, and then Chrome Yellow-M was uniformly applied on the surface. teY ₂ O ₂ S: Tb
The transmittance at 420nm, which is the main emission peak of
% of the colored protective film was formed. When the thus obtained intensifying screen having the structure shown in FIG. 2 is used in combination with an orthotype The graininess was better than that of the intensifying screen (obtained in the same manner as above) except that the coating weight of the photon was 40 mg/cm ² and a transparent protective film was formed instead of the colored protective film, and the sharpness was the same. It was hot. Example 2 A phosphor coating solution was prepared in the same manner as in Example 1 using LaOBr:Tb with an average particle size of 6μ, and this was coated on a polyethylene terephthalate support having a carbon black light absorption layer approximately 250μ thick. The phosphor was uniformly coated onto the body using a knife coater so that the weight of the phosphor was approximately 50 mg/cm ² and dried at 50° C. to form a phosphor layer. Next, one side of this phosphor layer was dyed with Disperse Green B.
LaOBr: A polyethylene terephthalate film with a thickness of about 10μ, which has a transmittance of about 80% at 420nm, which is the emission peak of Tb, is glued so that the dyed surface is in contact with the phosphor layer surface. This was used as a colored protective film. When the thus obtained intensifying screen having the structure shown in FIG. 1 is used in combination with a regular type X-ray film, the conventional intensifying screen ( Fluorescent coating weight: 40mg/
cm ² and had better graininess and sharpness than the intensifying screen (obtained in the same manner as above) except that a transparent protective film was formed instead of a colored protective film. Example 3 A phosphor coating solution was prepared in the same manner as in Example 1 using Gd ₂ O ₂ S:Tb with an average particle size of 6 μm, and this was applied to a polyethylene terephthalate film having a titanium oxide light-reflecting layer approximately 250 μ thick. - Apply a knife coater so that the coating weight of the phosphor is approximately 40 mg/cm ² on the substrate.
The phosphor layer was formed by applying it uniformly using a fluorophore and drying at 50°C. Next, one side of this phosphor layer was dyed with Kayasetsu Yellow 2G (manufactured by Nippon Kayaku) to obtain a transmittance of approximately 65% at 545 nm, which is the main emission peak of Gd ₂ O ₂ S:Td. A polyethylene terephthalate film having a thickness of approximately 10 μm was adhered so that the dyed surface was in contact with the surface of the phosphor layer to obtain a colored protective film. When the thus obtained intensifying screen having the structure shown in FIG. 1 is used in combination with an orthotype Same as above, except that instead of the 250μ thick titanium oxide light reflecting layer, the same support is used with a carbon black light absorbing layer approximately 250μ thick, and a transparent undyed polyethylene terephthalate film is used on one side. intensifying screen obtained by
The graininess and sharpness were both better than that of the original.

【table】

【table】 [Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views showing embodiments of the intensifying screen of the present invention, respectively. 1, 11... Colored protective film, 2, 12... Fluorescent layer, 3, 13... Support, 4, 14... Colored layer.

Claims (1)

[Claims for Utility Model Registration] (1) A radiation intensifying screen having a basic structure in which a phosphor layer and a protective film are laminated in this order on a support, wherein the phosphor layer is made of terbium-activated rare earth acid sulfide. Terbium-activated rare earth phosphate phosphor, terbium-activated rare earth oxyhalide phosphor, thulium-activated rare earth oxyhalide phosphor, divalent europium-activated alkaline earth phosphor Similar metal fluorohalide phosphors,
The protective film is a colored film in which one side of the transparent film is dyed with a dye, and the protective film is composed of one or more of the phosphors included in the silver-activated fluidized phosphor and the hafnium phosphate phosphor. A radiation intensifying screen characterized by: (2) The radiation intensifying screen according to claim 1, wherein the protective film is a colored film obtained by dyeing one side of the transparent film on the phosphor layer side with a dye. (3) Utility model registration claims 1 to 2, characterized in that the photographic sensitivity is 90 to 30% of the photographic sensitivity of a radiation intensifying screen using a transparent film instead of the colored film. Radiosensitizing screen as described.