JP2000155198A - Radiation image conversion screen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screen that has a high sensitivity and sharpness and is excellent in durability. SOLUTION: In this screen, a first phosphor layer and a second phosphor layer are located in order of mention. The first phosphor layer is formed by dispersing, on a support, in a bonding material resin mixed phosphor of two kinds whose ratio of the average particle sizes is 1.4 to 3.0. The second phosphor layer is formed by dispersing in a bonding material resin phosphor whose standard deviation (σ) of particle size distribution is 2.5 or less and that has a single particle size distribution where the average particle size is larger than that of the mixed phosphor mentioned above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation image conversion screen (hereinafter simply referred to as "screen"). More particularly, it relates to a screen having high sensitivity, excellent sharpness and excellent durability.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for reducing exposure of a subject, and in X-ray diagnostics for performing a transmission inspection of a human body with X-rays, an increase in the use of a combination of intensifying screens and films has been used. There has been a demand for reduction in exposure to X-ray photography using a paper-film system or digital radiography using a fluorescent plate and an image sensor, which is a new radiation imaging method, by increasing the sensitivity of the radiation imaging system.

Various attempts have been made to increase the sensitivity of screens, such as intensifying screens and fluorescent screens, used to increase the sensitivity of such radiation imaging systems. However, the reciprocity between screen sensitivity and sharpness has been attempted. For this reason, there has been a problem that the sharpness of the screen is reduced as the sensitivity of the screen is increased. Attempts have been made to increase the sharpness by, for example, reducing the content of the binder resin in the phosphor layer or reducing the thickness of the protective film on the phosphor layer surface. Therefore, development of a screen having higher sensitivity, higher sharpness, and excellent durability has been desired.

Incidentally, conventionally, as one of means for suppressing a decrease in the sensitivity and sharpness of the screen, a method of controlling the particle size distribution of the phosphor constituting the phosphor layer has been proposed. The arrangement of the phosphor particles in the phosphor layer such that the diameter of the phosphor particles gradually decreases from the surface side (the side from which light is emitted) of the phosphor layer toward the support side is particularly effective in improving sharpness. Is known (see JP-A-55-33560).
The characteristics are not always satisfactory, and the development of a screen having higher sensitivity, higher sharpness, and excellent durability has been desired.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a screen having higher sensitivity, higher sharpness and excellent durability.

[0006]

In order to achieve the above-mentioned object, the present inventors have, in particular, described a method of arranging the particle diameter distribution and the particle arrangement of the phosphor constituting the phosphor layer of the screen and the characteristics of the screen. We have studied the correlation of.

As a result, it has been found that the above object can be achieved when a plurality of phosphor layers are used and phosphors having a specific particle size distribution are arranged in each of the phosphor layers. .

That is, the present invention is as follows. (1) A first phosphor layer in which a mixed phosphor of two kinds of phosphors having different particle size distributions is dispersed in a binder resin, and a phosphor having a single particle size distribution are combined. A second phosphor layer dispersed in an agent resin and a radiation image conversion screen provided on a support in this order, wherein each of the first phosphor layer and the second phosphor layer constitute the mixed phosphor. The ratio of the average particle diameter of the phosphor is in the range of 1.4 to 3.0, and the standard deviation (σ) of the particle diameter distribution of the phosphor in the second phosphor layer is 2.5 or less; A radiation image conversion screen, wherein an average particle diameter of the phosphor in the second phosphor layer is larger than an average particle diameter of the mixed phosphor in the first phosphor layer.

(2) The average particle diameter of the phosphor in the second phosphor layer is 4.5 μm or more, and the average particle diameter of the mixed phosphor in the first phosphor layer is 1.5 μm.
The radiation image conversion screen according to the above (1), wherein the thickness is from μm to 3.0 μm.

(3) The first phosphor layer has a mixed weight ratio of the phosphors constituting the mixed phosphor of 10:90.
(1) characterized in that it is in the range of 90:10.
Or the radiation image conversion screen according to (2).

(4) The content of the binder resin in the first phosphor layer and the second phosphor layer is 2 to 6% by weight based on the phosphor. The radiation image conversion screen according to any one of (1) to (3).

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The screen of the present invention is manufactured in the same manner as a conventional screen, except that a screen having a plurality of phosphor layers in which phosphors having a specific particle size distribution are arranged in a certain order. You.

That is, an appropriate amount of a phosphor for forming a first phosphor layer on a support is mixed with a binder such as nitrified cotton, and an organic solvent is added to the mixture to add a fluorescent material having an appropriate viscosity. A body coating solution is prepared, and this coating solution is coated on a support using a knife coater or a roll coater, and dried to form a first phosphor layer, which is located on the surface side (the side from which light is emitted). A second phosphor is formed on the first phosphor layer formed in the same manner as described above except that a phosphor coating solution is prepared using a phosphor for forming the second phosphor layer. Form a layer. When forming the second phosphor layer, the first phosphor layer
After coating the phosphor coating solution for forming a phosphor layer on the support, when the coating solution is still in an undried state, a phosphor coating solution for forming a second phosphor layer is coated thereon. It may be applied and then dried to form a two-layer phosphor layer composed of a first phosphor layer and a second phosphor layer.

After preparing a phosphor coating solution for forming each phosphor layer, and before applying the phosphor coating solution, each of the phosphor coating solutions is subjected to a dispersion treatment such as a ball mill so that the phosphor in the coating solution is dispersed. Is preferably applied to improve the dispersibility of the coating, because the uniformity of the coating film after application is improved.

The phosphor of the first phosphor layer provided on the support side is not a phosphor having a single particle diameter distribution, but a mixed phosphor of two kinds of phosphors having different average particle diameters. Then, compared to the case where a phosphor having a single particle size distribution is used, the phosphor filling rate of the obtained phosphor layer is increased, and when the amount of the binder resin is the same, the coating film strength is reduced. The strength of the phosphor layer can be increased, and the durability of the phosphor film can be increased. Also, when the same coating film strength is used, the amount of the binder can be reduced, and the reflectance of the phosphor layer can be increased. , The sharpness can be further improved.

That is, in the phosphor layer on the support side, which is the first phosphor layer, light emitted toward the support side emits light.
The phosphor is reflected at a position as short as possible from the light emitting point and can return to the surface side (that is, in order to shorten the optical path until light emission from each phosphor in the phosphor layer reaches the surface). It is preferable that the reflectance of the layer itself is high. To increase the reflectance of the phosphor layer, the particle diameter of the phosphor constituting the phosphor layer is reduced, and the amount of the binder resin in the phosphor layer is reduced. It is effective to reduce However, in terms of strength, if the phosphor particle diameter of the phosphor layer is reduced, the specific surface area is increased. Therefore, comparing the phosphor layer strength with the same binder resin amount to the phosphor amount, the small particle size The use of the phosphor tends to be inferior, and when the amount of the binder in the phosphor layer is reduced, the strength of the phosphor layer naturally decreases. Therefore, when trying to increase the reflectance of the phosphor layer, there is a problem in that the durability is reduced.

Therefore, in order to achieve both improvement in durability and increase in reflectance, it is necessary to use a mixed phosphor composed of two kinds of phosphors in which the ratio of the average particle diameters of both the mixed phosphors is within a certain range. Thereby, the phosphor filling rate in the phosphor layer is increased, and the coating strength is increased with the same amount of the binder as compared with the case where the phosphor having a single particle size distribution is used,
Durability can be increased. On the other hand, when the coating film strength is the same, the amount of the binder can be reduced, and the reflectance of the phosphor layer can be increased, so that the sharpness can be further increased.

If the ratio of the average particle diameters of the two kinds of phosphors to be mixed is too low, the improvement in the filling rate is small, and if the ratio is too high, the luminous efficiency of the small particle phosphor among the two kinds of phosphors decreases, and the sensitivity increases. In the mixed phosphor used in the first phosphor layer, the ratio of the average particle diameter of both phosphors constituting the mixed phosphor is in the range of 1.4 to 3.0. When a mixed phosphor having an average particle size of about 1.5 to 3.0 μm is used, a screen having particularly excellent image quality and durability can be obtained. When the mixture weight ratio of the two phosphors constituting the mixed phosphor of the first phosphor layer is in the range of 10:90 to 90:10, the sensitivity is higher than when the phosphor having a single particle size distribution is used. And sharpness.

On the other hand, the phosphor used for the second phosphor layer, which is located on the surface side, is capable of further improving sharpness.
It is preferable to use a phosphor having an average particle diameter larger than that of the phosphor used for the phosphor layer of (1) and further having an average particle diameter of 4.5 μm or more. When the second phosphor layer provided on the front side of the screen (on the side from which light is emitted) has such a configuration, phosphors having a large particle diameter are arranged on the front side, so that the surface is not scattered in all directions. , It is possible to obtain a screen with particularly high sharpness.

The phosphor used in the first phosphor layer and the second phosphor layer is not particularly limited in terms of composition. For example, CaWO ₄ , YTaO ₄ , and YTaO ₄ : T
m, YTaO ₄ : Nb, BaSO ₄ : Pb, HfO 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: Tb,
Gd ₂ O ₂ S: Tb, (Gd, Y) ₂ O ₂ S: Tb, T
At least one of phosphors that emit light of high luminance when irradiated with X-rays, such as m, can be used. The same applies to the case where both the phosphor used for the first phosphor layer and the phosphor used for the second phosphor layer have the same composition or the phosphors having different compositions. Is not particularly limited, and 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.

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 to set the content to 2 to 6% by weight based on the phosphor in the phosphor layer, from the viewpoint 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.

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 support used in the screen of the present invention includes polyesters such as cellulose acetate, cellulose propionate, cellulose acetate butyrate and polyethylene terephthalate, polystyrene, polymethyl methacrylate, polyamide, polyimide, vinyl chloride-vinyl acetate. A resin such as a copolymer or polycarbonate molded into a film, baryta paper, resin coated paper, ordinary paper, aluminum alloy foil, or the like is used. In addition,
As the plastic film or paper as described above as the support of the intensifying screen of the present invention, those into which a light-absorbing substance such as carbon black or a light-reflective substance such as titanium dioxide or calcium carbonate is kneaded, Can also be used.

Some screens have a structure in which a light reflecting layer, a light absorbing layer or a metal foil layer is provided between the phosphor layer and the support. In this case, the light is reflected on the support in advance. A layer, a light absorbing layer or a metal foil layer is provided, and the phosphor coating solution is applied thereon and dried to form a phosphor layer.

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.

The screen of the present invention is used in addition to an intensifying screen used for radiographic photography in close contact with an X-ray photographic film, a fluorescent plate for indirect photography, and a digital radiography used together with an image pickup device such as a CCD. Such as a fluorescent screen of X
It is useful as an image conversion medium for converting a line image into a visible image.

[0028]

The present invention will be described below with reference to examples. Example 1 A mixed resin of 16 parts by weight of a polyvinyl butyral resin and a urethane resin and 4 parts by weight of a plasticizer were mixed with 80 parts by weight of
The binder resin solution was prepared by dissolving and stirring in parts by weight of an organic solvent. Gd ₂ O ₂ S: T having an average particle diameter of 3 μm and a standard deviation (σ) of particle size distribution of 0.6 in 15 parts by weight of the binder.
A mixed phosphor of 60 parts by weight of b phosphor and 25 parts by weight of Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 2 μm and a standard deviation value (σ) of 0.3 in particle size distribution is mixed and stirred. A “phosphor coating solution I” was prepared, and the “phosphor coating solution I” was further subjected to a ball mill treatment.

Next, the above-mentioned "phosphor coating liquid I" was applied to a support of a white polyethylene terephthalate film (Lumilar E-20 manufactured by Toray Industries, Inc.) kneaded with titanium oxide having a thickness of 250 μm using a blade coater. Then, the phosphor was applied such that the applied weight of the phosphor after drying became 20 mg / cm ² , thereby forming a “phosphor layer 1” as a first phosphor layer in an undried state.

Next, 87 parts by weight of a Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 5 μm and a standard deviation (σ) of particle size distribution of 1.1 were added to 13 parts by weight of the binder resin liquid, The phosphor slurry is subjected to ball milling to prepare a “phosphor coating liquid II”, and the “phosphor coating liquid II” is formed on the previously formed “dry phosphor layer 1”. Is applied using a blade coater so that the phosphor coating weight after drying is 25 mg / cm ^2, and a second phosphor layer, “phosphor layer 2”, is formed, and then dried sufficiently. Thus, a phosphor layer having the first and second phosphor layer configurations was formed. Next, a polyethylene terephthalate film protective film having a thickness of 6 μm is laminated on the surface of the second phosphor layer previously formed via an adhesive, and the protective film is adhered using a hot roll at a temperature of 100 ° C. The surface is processed with a satin finish roll while heating, and the center line average roughness (R
a) The "screen A" of Example 1 was manufactured with a concavo-convex pattern of 1.0 μm.

Example 2 Gd ₂ having an average particle diameter of 3 μm and a standard deviation (σ) of particle size distribution of 0.6 as a mixed phosphor.
60 parts by weight of an O ₂ S: Tb phosphor, an average particle diameter of 2 μm,
Gd ₂ O ₂ S having a standard deviation (σ) of 0.3 in the particle size distribution:
Instead of using a phosphor mixed with 25 parts by weight of Tb phosphor, Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 3 μm and a standard deviation value (σ) of particle size distribution of 0.6, and an average particle diameter of 1. 5
μm, Gd ₂ having a standard deviation (σ) of 0.25 in the particle size distribution.
"Phosphor coating solution I" in the same manner as "Phosphor coating solution I" in Example 1 except that 85 parts by weight of a mixed phosphor mixed with O ₂ S: Tb phosphor at a weight ratio of 1: 1 was used. III), and the same procedure as in “Screen A” of Example 1 except that the same amount of the above “phosphor coating liquid III” is applied instead of the “phosphor coating liquid I” where the “phosphor coating liquid I” is to be applied. Thus, "Screen B" of Example 2 was manufactured.

Example 3 Instead of a Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 5 μm and a standard deviation value (σ) of 1.1 of the particle size distribution, an average particle diameter of 7 μm and a standard deviation of the particle size distribution A “phosphor coating solution IV” was prepared in the same manner as in “phosphor coating solution II” of Example 1, except that a Gd ₂ O ₂ S: Tb phosphor having a value (σ) of 1.7 was used. Body coating liquid II "
The "screen C" of Example 3 was manufactured in the same manner as the "screen A" of Example 1 except that the same amount of the above "phosphor coating solution IV" was applied instead of the "coating liquid". .

(Comparative Example 1) The "phosphor coating solution I" of Example 1 was used on the support without using the "phosphor coating solution I" of Example 1.
I "alone, the phosphor coating weight after drying was 45 mg / cm
It dried coating so as to be ^2, except for forming a phosphor layer of a single layer was prepared to "Screen R1" of the "screen A" Comparative Example In the same manner as the first embodiment 1.

Comparative Example 2 Gd ₂ O ₂ S having an average particle diameter of 3 μm and a standard deviation (σ) of particle size distribution of “Phosphor coating liquid I” used in Example 1 as a phosphor of 0.6: Instead of using a mixture of 60 parts by weight of Tb phosphor and 25 parts by weight of Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 2 μm and a standard deviation (σ) of 0.3 in particle size distribution, an average is used. Particle size 1.5
μm, Gd ₂ having a standard deviation (σ) of 0.25 in the particle size distribution.
Using 85 parts by weight of O ₂ S: Tb phosphor, “Phosphor coating solution V” was prepared in the same manner as “Phosphor coating solution I” used in Example 1, and “Phosphor coating solution I” was prepared. "Screen R2" of Comparative Example 2 was manufactured in the same manner as "Screen A" of Example 1 except that the same amount of the above-mentioned "phosphor coating solution V" was applied instead of the area to be coated.

Comparative Example 3 Gd ₂ O ₂ S: T having an average particle diameter of 1.5 μm and a standard deviation (σ) of the particle size distribution of 0.25.
"Phosphor coating" used in Comparative Example 2 except that a Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 2 μm and a standard deviation (σ) of particle size distribution of 0.3 was used instead of the phosphor b. "Phosphor coating liquid VI" is prepared in the same manner as "Liquid V", and the same amount of the above "phosphor coating liquid VI" is applied instead of the "Phosphor coating liquid V" where it should be applied. Except for the above, “Screen R2” of Comparative Example 3 was the same as “Screen R2” of Comparative Example 2.
3 "was produced.

Comparative Example 4 Gd ₂ O ₂ S: T having an average particle size of 1.5 μm and a standard deviation value (σ) of the particle size distribution of 0.25.
"Phosphor coating" used in Comparative Example 2 except that a Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 3 μm and a standard deviation (σ) of particle size distribution of 0.6 was used instead of the phosphor b. "Phosphor coating liquid VII" is prepared in the same manner as in "liquid V", and the same amount of the above "phosphor coating liquid VII" is applied instead of the "phosphor coating liquid V" where it should be applied. A "screen R4" of Comparative Example 4 was manufactured in the same manner as the "screen R2" of Comparative Example 2 except for the above.

(Comparative Example 5) Instead of a Gd ₂ O ₂ S: Tb phosphor having an average particle size of 5 μm and a standard deviation value (σ) of 1.1 for the particle size distribution, an average particle size of 4 μm and a standard deviation of the particle size distribution “Phosphor coating solution VIII” was prepared in the same manner as “Phosphor coating solution II” of Example 1 except that a Gd ₂ O ₂ S: Tb phosphor having a value (σ) of 1.0 was used. Body coating liquid II "
"Screen R5" of Comparative Example 5 in the same manner as "Screen A" of Example 1 except that the same amount of the above "phosphor coating solution VIII" is applied instead of the "Screen R5"
Was manufactured.

(Comparative Example 6) Instead of a Gd ₂ O ₂ S: Tb phosphor having an average particle diameter of 5 μm and a standard deviation value (σ) of 1.1 for the particle size distribution, an average particle diameter of 7 μm and a standard deviation of the particle size distribution A “phosphor coating solution IX” was prepared in the same manner as the “phosphor coating solution II” of Example 1, except that a Gd ₂ O ₂ S: Tb phosphor having a value (σ) of 2.0 was used. "Screen A" of Comparative Example 4 except that the same amount of the "Phosphor Coating Solution IX" was applied instead of the "Screen A" R6 ".

With respect to the screens A to C of Examples 1 to 3 and the screens R1 to R6 of Comparative Examples 1 to 6 obtained as described above, the same Using a photographic film (UR-2, manufactured by Fuji Photo Film Co., Ltd.), its sensitivity, sharpness and durability were evaluated. The results shown in Table 1 were obtained, and intensifying screens A to C of the present invention were obtained. Is the screen R1 of Comparative Example 1.
It has almost the same durability as that of, and has improved sensitivity and sharpness.

The intensifying screens A to C of the present invention were superior to the screens R2 and R3 of Comparative Examples 2 and 3 in sensitivity and durability. Furthermore, it showed the same durability as the screens R4 to R6 of Comparative Examples 4 to 6 and was excellent in sensitivity or sharpness.

The photographic performance of the screen was 10
It shows photographic sensitivity and sharpness when photographed with an X-ray having a tube voltage of 80 kV through a water phantom of cm, and the respective evaluation values are shown as the following values. Photosensitivity: Displayed as a relative value when the sensitivity of the screen R1 of Comparative Example 1 is 100. Sharpness: An MTF value at a spatial frequency of 2 lines / mm is obtained, and is displayed as a relative value when the MTF value of the screen R1 of Comparative Example 1 at the spatial frequency is 100. Durability: Each screen is cut into 2cm wide strips,
The phosphor layer was not peeled off at all from the support when the other end was strongly smashed three times on a hard flat plate with the once held (O), but peeling was partially observed. The evaluation was made in three grades: a sample (△) and a completely peeled sample (x).

[0042]

[Table 1]

[0043]

According to the present invention, a screen having high sensitivity, high sharpness, and excellent durability can be provided.

Claims (4)

[Claims] 1. A first phosphor layer in which a mixed phosphor of two kinds of phosphors having different particle diameter distributions is dispersed in a binder resin, and a phosphor having a single particle diameter distribution. And a second phosphor layer obtained by dispersing the mixed phosphor in a binder resin is a radiation image conversion screen provided on a support in this order, and constitutes the mixed phosphor in the first phosphor layer. The ratio of the average particle diameters of the respective phosphors to be formed is in the range of 1.4 to 3.0, and the standard deviation (σ) of the particle diameter distribution of the phosphors in the second phosphor layer is 2.5 or less. There and
A radiation image conversion screen, wherein an average particle diameter of the phosphor in the second phosphor layer is larger than an average particle diameter of the mixed phosphor in the first phosphor layer. 2. An average particle diameter of the phosphor in the second phosphor layer is 4.5 μm or more, and an average particle diameter of the mixed phosphor in the first phosphor layer is 1.5 μm.
2. The radiation image conversion screen according to claim 1, wherein the thickness is from 3.0 to 3.0 [mu] m. 3. A mixed weight ratio of the respective phosphors constituting the mixed phosphor in the first phosphor layer is from 10:90 to 9: 9.
3. The method according to claim 1, wherein the range is 0:10.
3. A radiation image conversion screen according to item 1. 4. The method according to claim 1, wherein the content of the binder resin in each of the first phosphor layer and the second phosphor layer is 2 to 6% by weight based on the phosphor. The radiation image conversion screen according to any one of claims 1 to 3.