JP2000162393A - Radiation intensifying screen set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation intensifying screen set obtaining radiation photograph with high definition and good quality. SOLUTION: An intensifying screen set is constituted of a front intensifying screen and a back intensifying screen provided each with a plurality of fluorescent layers where fluorescent body is scattered in bond agent resin on support bodies. The support body of the front intensifying screen consists of a light- reflecting support body and that of the back intensifying screen consists of a light-absorbing support body. In the fluorescent bodies of each fluorescent layer of the front intensifying screen and the back intensifying screen, particles are distributed so that the average particle diameters are smaller in the support body side than in the surface side (the side of taking out the luminescence).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-intensity radiation intensifying screen set for radiographic photography, which is a pair of a front intensifying screen and a back intensifying screen (hereinafter referred to as "intensifying screen set").
About.

[0002]

2. Description of the Related Art Radiation intensifying screens (hereinafter referred to as "intensifying screens") have been variously improved with respect to the structure of intensifying screens in order to further improve the image quality of radiographs. In response to requests, there is a demand for the development of intensifying screens with further improved image quality, such as improved sensitivity and sharpness.

[0003] By the way, regarding the improvement of the characteristics of intensifying screens,
Although there are many proposals centering on the structure of the intensifying screen alone, there is an example that proposes a means for improving characteristics as an intensifying screen set comprising a pair of a front intensifying screen and a back intensifying screen. Not much more than before.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an intensifying screen set which is particularly excellent in sharpness and can obtain radiographs of good image quality.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on intensifying screen sets having various configurations, and as a result of studying the correlation between the configurations and the photographic image quality obtained by using the same,
In addition to making the phosphor layer of each intensifying screen a multilayer instead of a single layer,
It has been found that the above object can be achieved by specifying the light reflection characteristics of the support of each intensifying screen constituting the intensifying screen set.

That is, the present invention is as follows. (1) In a radiation intensifying screen set, which is a pair of a front intensifying screen and a back intensifying screen each having a plurality of phosphor layers each formed by dispersing a phosphor in a binder resin and provided on a support, The radiographic intensifying screen set, wherein the support of the front intensifying screen comprises a support having high light reflectivity, and the support of the back intensifying screen comprises a support having high light absorbency. (2) A particle arrangement in which the phosphor in each of the phosphor layers of the front intensifying screen and the back intensifying screen has a smaller average particle diameter on the support side than on the surface side (side on which light is emitted). The radiographic intensifying screen set according to the above (1), wherein:

[0007]

Next, the present invention will be described in more detail. In order to manufacture the intensifying screen set of the present invention, the phosphor layers of each intensifying screen constituting the intensifying screen set are each composed of two or more phosphor layers having different phosphor particle diameter distributions, and As a support for each intensifying screen constituting the intensifying screen set, a conventional intensifying screen support is a light reflective support, while a back intensifying screen is a light absorbing support. Manufactured in the same manner as the paper.

That is, in both the front and back intensifying screens constituting the intensifying screen set, the phosphor layer is formed by one kind of phosphor coating solution in which a phosphor having a single particle size distribution is suspended. Instead, a suitable amount of a phosphor for forming a first phosphor layer on a support is mixed together with a binder such as nitrified cotton, and an organic solvent is further added thereto. In addition, a phosphor coating solution having an appropriate viscosity is prepared, and this coating solution is coated on a support with a knife coater, a roll coater, or the like, and dried to form a first phosphor layer. A second phosphor layer is formed in the same manner as the phosphor coating solution for forming the first phosphor layer, except that a phosphor having a different particle size distribution from the phosphor for forming the first phosphor layer is used. A phosphor coating solution for the first phosphor layer is prepared, and this is coated with the first phosphor layer formed earlier. It was coated on to form a second phosphor layer by drying. At this time, when forming the second phosphor layer, the phosphor coating solution for forming the first phosphor layer is applied on the support, and the applied phosphor coating solution is still in an undried state. At one time, a phosphor coating solution for forming a second phosphor layer is applied thereon, and then dried to form a two-layer phosphor composed of a first phosphor layer and a second phosphor layer. A body layer may be formed. It should be noted that the number of phosphor layers of each intensifying screen constituting the intensifying screen set of the present invention is not necessarily limited to two, and three or more phosphor layers may be sequentially formed on a support in the same manner. To form a multilayer structure. After forming a plurality of phosphor layers on the support as described above, if necessary, a protective layer is further formed on the phosphor layer to obtain a front intensifying screen and a back intensifying screen.

At this time, two particles having different particle size distributions are used.
More than one kind of phosphor coating solution is prepared, and the phosphor coating solution composed of a phosphor having a small average particle diameter is sequentially coated on the support, and then after drying or in an undried state one after another. By laminating a phosphor layer thereon, the phosphor layer having a smaller particle diameter on the support side than on the surface side (the side from which light is extracted) is obtained in the phosphor layer of each intensifying screen obtained. If the phosphor particles in the phosphor layer are arranged so as to be lined up, the phosphor layer having a smaller particle diameter than the surface side, which is arranged on the support side, functions as a light proximity reflection layer, In order to suppress the scattering of the light emitted from the phosphor, compared to the case where the phosphor having a uniform particle size distribution is uniformly arranged on the entire phosphor layer, the light reflecting property is higher when the light reflecting support is provided. The effect of sharpness improvement in addition to the sensitivity improvement effect by the support On the other hand, in the case of having a light-absorbing support, an effect of improving sensitivity in addition to the effect of improving sharpness is also obtained, so that the effect of further improving sensitivity and sharpness is obtained using any support. Is more preferable.

After preparing a phosphor coating solution for forming each phosphor layer and before applying the same, each of the phosphor coating solutions is subjected to a dispersion treatment such as a ball mill to disperse the phosphor in the coating solution. It is preferable to perform a treatment for improving the property, since the filling rate of the phosphor in the phosphor layer after application is increased and the uniformity of the coating film is improved.

The phosphor used in the phosphor layer of each intensifying screen in the intensifying screen set of the present invention is not particularly limited in terms of composition. For example, CaWO ₄ , YTaO ₄ , YTaO
_{4: Tm, YTaO 4: Nb} , BaSO 4: Pb, Hf
O ₂ : Ti, HfP ₂ O ₇ : Cu, CdWO ₄ , Gd ₂
O ₂ S: Tb, GdTaO ₄ : Tb, Gd ₂ O ₃ .Ta
₂ O ₅ .B ₂ O ₃ : Tb, (Gd, Y) ₂ O ₂ S: T
b, (Gd, Y) ₂ O ₂ S: At least one kind of phosphor that emits light with high luminance when irradiated with X-rays, such as Tb and Tm, can be used. The phosphor used for the first phosphor layer and the phosphor used for the second phosphor layer located on the surface side may have the same composition, or may have different compositions. The same effect can be obtained even if the film is used.Therefore, this is not particularly limited, and it can be freely selected according to the purpose of use, for example, by considering matching between the spectral sensitivity of the film and the emission spectrum from the phosphor layer. I can do it.

The binder resin used in the phosphor coating solution for producing the screen of the present invention includes nitrified cotton, cellulose acetate, ethyl cellulose, polyvinyl butyral, linear polyester, polyvinyl acetate, and vinylidene chloride. Vinyl chloride copolymer, vinyl chloride-vinyl acetate copolymer, polyalkyl- (meth) acrylate, polycarbonate, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, gelatin,
There is no particular limitation as long as the binder is conventionally known as a screen binder, such as polysaccharides such as dextrin, gum arabic, etc., and the amount of each binder resin used is not limited to the first phosphor layer, In both phosphor layers 2, it is particularly preferable that the content be 2 to 10% by weight with respect to the phosphor in the phosphor layer in that the sharpness and durability of the obtained screen are not reduced.

As the organic solvent used for preparing the phosphor coating solution, for example, ethanol, methyl ethyl ether, butyl acetate, ethyl acetate, ethyl ether, xylene and the like are used. In addition, a dispersant such as phthalic acid and stearic acid and a plasticizer such as triphenyl phosphate and diethyl phthalate are added to the phosphor coating solution as needed. Some screens have a structure in which a metal foil layer is provided between a phosphor layer and a support. In this case, a light reflecting layer, a light absorbing layer, or a metal foil layer is provided on the support in advance. The phosphor layer is formed by applying the above-mentioned phosphor coating solution and drying it.

As the support used in the intensifying screen set of the present invention, a light reflecting support is used for the support of the front intensifying screen, and a light absorbing support is used for the support of the back intensifying screen. Is used. In the intensifying screen set of the present invention, the light-reflective support has a reflectance of 450 nm to 7 on its surface.
It refers to a light having a reflectance of approximately 75% or more with respect to light in a wavelength range of 00 nm, and more preferably a light having a reflectance of 85% or more. Further, the light-absorbing support refers to a support whose surface shows a reflectance of about 5% or less.

Specifically, the base material of the support for both the front intensifying screen and the back intensifying screen includes polyester such as cellulose acetate, cellulose propionate, cellulose acetate butyrate, polyethylene terephthalate, polystyrene, and polymethyl. Methacrylate, polyamide,
Polyimide, vinyl chloride-vinyl acetate copolymer, resin such as polycarbonate molded into a film,
A material based on the same material as the support used for conventional intensifying screens, such as baryta paper, resin-coated paper, ordinary paper, and aluminum alloy foil, is used. A material in which a light-reflecting substance such as titanium dioxide or calcium carbonate is kneaded in a base of the above-described material, or a material containing air bubbles is used, but a support made of a base of the above-described material is used. MgO, Al ₂ O ₃ , SiO ₂ , ZnO, Ti
O ₂ , ZnS, etc., a light-reflective layer made of a reflective material having fine particles with a particle diameter of 0.5 μm or less and having a high refractive index, and having a surface with a reflectivity equal to or higher than that of the light-reflective support. It may be formed in advance, and a plurality of phosphor layers may be formed thereon. On the other hand, as the support of the back intensifying screen, a material obtained by kneading a light absorbing substance such as carbon black into the base of the above-described material is used, but the surface of the support made of the base of the above-described material is used. In advance, a light absorbing layer made of a light absorbing substance such as carbon black and having the same or lower reflectance as the light absorbing support is formed in advance, and a plurality of phosphor layers are formed thereon. You may. In the front intensifying screen, even when the above-mentioned light reflecting layer is provided between the phosphor layer and the support, a light reflective support may be used as the support, and in the back intensifying screen, When the above-described light absorbing layer is formed between the phosphor layer and the support, it goes without saying that a light absorbing support may be used as the support.

As described above, the support of the front intensifying screen is a light-reflective support, or the light reflecting layer is provided between the phosphor layer and the support, while the support of the back intensifying screen is provided. Conventionally, the backing is increased by using a light-absorbing support for the body, or by providing a light-absorbing layer between the phosphor layer and the support and providing a plurality of phosphor layers on top of each other to form a multilayer. A light-absorptive support can be used in the sensitivity region that could not be obtained unless a light-reflective support was used for the paper, and the front was increased to make effective use of the light emitted from the back intensifying screen. By using a light-reflective support for the sensitive paper and reducing the weight of the front side phosphor coating, an intensifying screen set with higher sensitivity and sharpness than the conventional intensifying screen set can be obtained. it can. In addition, by making the back intensifying screen support light absorbing, compared to the case where the back intensifying screen support is made to be light reflective, the phosphor coating weight at the same sensitivity is increased, so the graininess is also improved. Is done.

On the phosphor layer formed as described above, a protective film is further formed as necessary. Cellulose acetate, nitrocellulose, cellulose derivatives such as cellulose acetate butyrate,
A resin such as polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polycarbonate, polyvinyl butyral, polymethyl methacrylate, polyvinyl formal, and polyurethane is dissolved in a solvent to prepare a protective film coating solution having an appropriate viscosity. Is applied onto the phosphor layer on the surface side (the side from which light emission is taken out) previously formed and dried, or a protective film formed in advance, for example, polyethylene terephthalate, polyethylene naphthalate, polyethylene, polyvinylidene chloride, polyamide, etc. Is laminated on the phosphor layer to form a protective film.

The screen of the present invention can be manufactured by a method other than the above-described manufacturing method. For example, a protective film is formed on a smooth substrate in advance, and the second phosphor layer and the first phosphor layer are formed thereon. After the phosphor layers are laminated in this order, this is peeled off from the substrate together with the protective film, and the support is again bonded to the first phosphor layer (the surface opposite to the protective film). You can do it.

[0019]

The present invention will be described below with reference to examples. [Example] A bond obtained by dissolving a mixture of 20 parts by weight of a polyvinyl butyral resin, a urethane resin and dibutyl phthalate (plasticizer) in 80 parts by weight of an organic solvent composed of a mixture of toluene, 2-butanol and xylene. 13 parts by weight of Gd ₂ O ₂ S: Tb having an average particle size of 3 μm
87 parts by weight of the phosphor were mixed and sufficiently stirred, and the mixture was dispersed with a ball mill to prepare a “phosphor coating solution I”.

Apart from this, Gd ₂ O having an average particle diameter of 3 μm
Gd ₂ having an average particle diameter of 7 μm instead of ₂ S: Tb phosphor
“Phosphor coating solution I” except that O ₂ S: Tb phosphor was used.
"Phosphor coating liquid II" was prepared in the same manner as described above. Also,
A phosphor coating solution I was prepared in the same manner as in “Phosphor coating liquid I” except that a Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 5 μm was used instead of the Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 3 μm. A phosphor coating solution III "was prepared.

Next, a white polyethylene terephthalate film (manufactured by Toray; Lumirror E-2) as a light-reflective support into which titanium white having a thickness of 250 μm has been kneaded.
On the side of the adhesive layer 0), the phosphor coating weight after drying the phosphor coating solution I was 20 m using a blade coater.
g / cm ^2, and then apply the “phosphor coating liquid II” thereon in an undried state so that the phosphor coating weight after drying is 25 mg / cm ^2, and then dry. Then, a plurality of phosphor layers each having a two-layer structure are formed on the support, and a protective film made of a polyethylene terephthalate film having a thickness of 6 μm is adhered thereon via a polyester-based heat-sensitive adhesive. The surface of the protective film is subjected to satin finish using a roll, and the center line average roughness (R
a) A front intensifying screen "F-1" was manufactured with a 1.0 .mu.m uneven pattern.

Further, instead of the support (Lumirror E-20 manufactured by Toray Industries, Inc.) used for the front intensifying screen "F-1", black polyethylene kneaded with carbon black, which is a light-absorbing support, is used. Using a terephthalate film (manufactured by Toray Industries; Lumirror X-30), the fluorescent material was dried on this light-absorbing support so that the phosphor coating weight after drying was 30 mg / cm ² instead of 20 mg / cm ^2. body coating solution I "is applied, further thereon, a phosphor coating weight after drying the" phosphor solution III "instead of" phosphor solution II "is coated to a 40 mg / cm ² Except for the above, a back intensifying screen "B-1" was produced in the same manner as in the front intensifying screen "F-1". Thus, the intensifying screen “F-
Example 1 and an intensifying screen set consisting of intensifying screen "B-1" were obtained.

[Comparative Example 1] The phosphor had an average particle diameter of 3
μd Gd ₂ O ₂ S: Tb phosphor instead of average particle size 3
μm of _Gd 2 _O 2 S: Tb phosphor 17 parts by weight and the average particle size of 5μm _Gd 2 _O 2 S: except for using a mixed phosphor of Tb phosphor 70 parts by weight "phosphor coating of Example 1 Liquid I "
"Phosphor coating liquid R" of the comparative example was produced in the same manner as in the above.

Next, instead of forming a plurality of phosphor layers by sequentially applying the “phosphor coating solution I” and the “phosphor coating solution II” on the support, the “phosphor coating solution I” is formed on the support. increasing R "only, phosphor coating weight after drying in the same manner as the front intensifying screen" F-1 "in the example except for forming a phosphor layer of a single layer by applying a 50 mg / cm ² Two sheets of paper "R-1" were produced. An intensifying screen set of Comparative Example 1 was obtained in which the intensifying screen "R-1" was used as a front and back intensifying screen pair.

[Comparative Example 2] In the manufacture of the front intensifying screen "F-1" of the above embodiment, the phosphor coating weight after drying was applied on the "phosphor coating solution I" applied on the support. Is 25
mg / cm ² , instead of applying “phosphor coating liquid II”, the phosphor coating weight after drying is 30 mg / c.
m ² , except that the “phosphor coating liquid III” was applied in the same manner as in the front intensifying screen “F-1” of the above-mentioned embodiment, except that a plurality of phosphor layers each having a two-layer structure were supported by the light-reflecting support. Two intensifying screens "R-2" formed on the body were produced. An intensifying screen set of Comparative Example 2 was obtained in which the intensifying screen "R-2" was used as a pair of intensifying screens common to the front and the back.

Comparative Example 3 The intensifying screen "R-
1 ", a light-reflective support (manufactured by Toray; E-
20) was replaced with the light-absorbing support (X-30, manufactured by Toray Industries, Inc.) used for the back intensifying screen "B-1" in the above example.
On this, the coating weight of the “phosphor coating liquid R” after drying is 50
A single phosphor layer was formed on the light-absorbing support in the same manner as intensifying screen "R-1" of Comparative Example 1 except that the coating was performed so as to be 70 mg / cm ² instead of mg / cm ^2. Intensifying screen "R-3" was manufactured.

The intensifying screen "R-1" obtained in Comparative Example 1 was used as a front intensifying screen, and the intensifying screen "R-3" obtained as described above was used as a back intensifying screen. The intensifying screen set of Comparative Example 3 was obtained. Regarding the intensifying screen sets of the intensifying screen set of the example and the intensifying screen sets of Comparative Examples 1 to 3 obtained as described above, a film (manufactured by Fuji Photo Film Co., Ltd.) was placed between the front and back intensifying screens. , UR-2) are shown in Table 1 for the results of evaluation of sensitivity and sharpness.

The sensitivity and the sharpness are 10 cm thick.
The photographic sensitivity and the MTF value at a spatial frequency of 2 lines / mm when photographed with X-rays having a tube voltage of 80 kV through a water phantom were compared with the sensitivity and the MTF value of the intensifying screen set of Comparative Example 1, respectively. Were determined by relative values in the case of, and these were evaluated by comparison.

[0029]

[Table 1]

As can be seen from Table 1, the phosphor layer is composed of a plurality of layers, and at this time, the surface side (the side of the protective film from which light emission is taken out) than the average particle diameter of the phosphor particles in the phosphor layer located on the support side. In addition to having a particle arrangement such that the average particle diameter of the phosphor particles in the phosphor layer is large, the support of the front intensifying screen is a light reflective support, and the support of the back intensifying screen is light absorbing. The intensifying screen set of the embodiment having the photographic support, even if it is an intensifying screen set having the same photographic sensitivity as the intensifying screen set, has a single phosphor layer, a front intensifying screen, and a back intensifying screen. Compared with the conventional intensifying screen set in which the intensifying screen is the same as the conventional intensifying screen set, the sharpness is remarkably improved. Sharpness is even better than the paper set (Comparative Example 2) To.

[0031]

Since the intensifying screen set of the present invention has the above-described configuration, when it is used for radiographic photography together with a photographic film using the intensifying screen set, sharpness is higher than when a conventional intensifying screen set is used. Degree radiographs are obtained.

Claims (2)

[Claims] 1. A radiographic intensifying screen set which is a pair of a front intensifying screen and a back intensifying screen each having a plurality of phosphor layers each formed by dispersing a phosphor in a binder resin on a support. 3. The radiation intensifying screen set according to claim 1, wherein the support of the front intensifying screen comprises a light reflective support, and the support of the back intensifying screen comprises a light absorbing support. 2. The phosphor in each of the phosphor layers of the front intensifying screen and the back intensifying screen has an average particle diameter smaller on the support side than on the surface side (side on which light is emitted). The radiographic intensifying screen set according to claim 1, wherein the particles are arranged.