JPH0321898A - Radiation sensitizing screen - Google Patents

Abstract

PURPOSE:To improve sharpness by using a thermoplastic elastomer which has >=67% packing ratio of phosphor in a phosphor layer and in which >=10wt.% and <=100wt.% of a binder has >=30 deg.C and <=150 deg.C softening temp. CONSTITUTION:For example, the phosphor of a tungstate system is used as the phosphor for radiation sensitization and the theremoplastic elastomer having 30 to 150 deg.C softening temp. or m. p. is used for the binder. The component ratio of the thermoplastic elastomer as the binder is preferably >=10wt.% and <=100wt.%. The mixing ratio of the binder and phosphor of the coating liquid is specified to, for example, a 1:8 to 1:40 (by weight ratio). The coating liquid for forming the phosphor is applied on a tentative base and is stripped from the tentative base after drying to form a phosphor sheet. This phosphor sheet is imposed on a base and is adhered onto the base while the sheet is compressed at the temp. above the softening temp. or m. p. of the binder. The pressure at the time of the compression is specified to about >=50kgW/cm<2>. The binder consists of the thermoplastic elastomer and, therefore, the degree of failure of the phosphor is deceased even if the binder consists of the thermoplastic elastomer.

Description

[Detailed description of the invention] [Field of invention] The present invention relates to radiation intensifying screens.

Specifically, the present invention relates to a radiation intensifying screen with improved sensitivity and image quality.

[Technical Background of the Invention and Prior Art] Radiation intensifying screens are used in various fields such as medical radiography such as X-ray photography for the purpose of medical diagnosis, and industrial radiography for the purpose of non-destructive testing of materials. In radiography, in order to improve the sensitivity of the imaging system, it is used by superimposing it on one or both sides of a radiographic film such as an X-ray film.

This radiation intensifying screen basically consists of a support and a phosphor layer formed on one side of the support. Note that a transparent protective film is generally provided on the surface of this phosphor layer opposite to the support (the surface not facing the support), which protects the phosphor layer from chemical alteration. Or protect it from physical impact.

The phosphor layer is composed of a binder containing and supporting phosphor particles in a dispersed state. The phosphor layer is generally attached onto the support using a coating method under normal pressure as described below. That is, a coating solution is prepared by mixing and dispersing phosphor particles and a binder in an appropriate solvent, and this coating solution is subjected to radiation sensitization under normal pressure using a coating means such as a doctor blade, roll coater, or knife coater. Either by directly coating the screen support and then removing the solvent from the coating film, or by applying the coating solution in advance on a temporary support such as a glass plate under normal pressure and then removing the solvent from the coating film. The phosphor layer is attached to the support by forming a phosphor-containing resin thin film, peeling it from the temporary support, and bonding it to the support of the radiation intensifying screen.

The phosphor in the phosphor layer has the property of emitting high-intensity light when excited by radiation such as X-rays.

Therefore, the phosphor emits high-intensity light depending on the amount of radiation that passes through the subject, and the radiographic film placed in contact with the surface of the phosphor layer of the radiation-sensitizing screen is exposed to this phosphor. Since exposure is also caused by the body's luminescence, sufficient exposure of photographic film can be achieved with a relatively small dose of radiation.

It is desired that a radiation intensifying screen having the basic structure as described above has high sensitivity and provides an image with good image quality (sharpness, granularity, etc.).

The sensitivity of a radiation intensifying screen basically depends on the total amount of light emitted by the phosphors contained in the panel. It also depends on the content of The high content of phosphor is also xII! This means that the absorption of radiation such as a is large, so higher sensitivity can be obtained, and at the same time, image quality (particularly graininess) is improved. On the other hand, when the content of phosphor in the phosphor layer is constant, the more densely packed the phosphor particles are, the thinner the layer thickness can be, which reduces the spread of emitted light due to scattering. It is possible to obtain relatively high sharpness.

The applicant has developed a radiation-sensitizing screen that has a phosphor layer densely packed with phosphors, in which the porosity of the phosphor layer is reduced by compressing the phosphor layer. and its manufacturing method have already been applied for (Japanese Patent Application No. 149069/1983;
No. 070).

The above-mentioned radiation-sensitizing screen had a phosphor layer that was subjected to compression treatment to increase the density of the phosphor in the phosphor layer compared to previous radiation-sensitizing screens. As a result, this radiation-sensitized screen has excellent sharpness, but on the other hand, the compression process destroys some of the phosphor, so it may actually deteriorate in terms of sensitivity and granularity. There was a problem that there was.

[Summary of the Invention] Another object of the present invention is to provide a radiation-sensitizing screen that has excellent sharpness and is also excellent in sensitivity and graininess.

The above object is to provide a radiation intensifying screen of the present invention substantially constituted by a support and a phosphor layer provided on the support and comprising a binder and a phosphor. The filling rate of the phosphor in the layer is 67% or more, and 10% by weight or more and 100% by weight of the binder is a thermoplastic elastomer having a softening temperature or melting point of 30°C or more and 180°C or less. This can be achieved by a characteristic radiation intensifying screen.

In the radiation-sensitizing screen of the present invention, even if the filling rate of the phosphor is 67% or more by compression treatment, since the binder of the phosphor layer is made of a thermoplastic elastomer, the softening temperature of the elastomer or By applying pressure at a temperature above the melting point, the degree of damage to the phosphor can be reduced. In addition, a phosphor sheet made of phosphor and a binder is made in advance, and this phosphor sheet is placed on a support and compressed at the same time as it is placed on the support at a temperature higher than the softening temperature or melting point of the binder. If this is done, damage to the phosphor can be further prevented.

In other words, during compression, phosphor crystals dispersed in a binder heated to a temperature above the softening or melting point are subjected to pressure with a certain degree of freedom, so the phosphor crystals are can be oriented. Furthermore, when the phosphor sheet is placed on the support while being compressed by applying pressure without being fixed to the support, the pressure applied to the phosphor sheet acts to orient the phosphor crystals, and at the same time, If the phosphor sheet is fixed, it will work to stretch and spread the sheet cleanly even under pressure that would destroy the crystals. Furthermore, in this case, compared to the case where the phosphor sheet is pressed while being fixed on the support, a higher phosphor filling rate can be obtained even if the phosphor sheet is compressed with the same pressure.

Preferred embodiments of the present invention are listed below.

<1> The thermoplastic elastomer consists of polystyrene, polyolefin, polyurethane, polyester, polyamide, polybutadiene, ethylene vinyl acetate, polyvinyl chloride, natural rubber, fluororubber, polyisoprene, chlorinated polyethylene, styrene-butadiene rubber, and silicone rubber. A radiation intensifying screen characterized in that it is at least one thermoplastic elastomer selected from the group.

(2) A radiation M intensifying screen characterized in that the binder is 100% by weight thermoplastic elastomer.

[Structure of the Invention] The radiation intensifying screen of the present invention can be manufactured, for example, by the method described below.

To produce the radiation-sensitizing screen of the present invention, a) forming a phosphor sheet consisting of a binder and a phosphor; b) placing the phosphor sheet on a support and adjusting the softening temperature of the binder; Alternatively, it is preferable to manufacture the phosphor sheet by two steps: adhering the phosphor sheet to the support while compressing it at a temperature higher than the melting point.

First, let's move on to step a).

The phosphor sheet, which becomes the phosphor layer of the radiation intensifying screen, is prepared by applying a coating solution in which the phosphor is uniformly dispersed in a binder solution to the temporary support-E for forming the phosphor sheet, and drying it. It can be manufactured by peeling it off from the support.

The phosphor used in the present invention will be described below.

Examples of radiation-sensitizing phosphors preferably used in the present invention include the following phosphors.

Tungstate-based phosphor (CaWO4.MgWO
4, C a WO 4 : P b etc.), terbium-activated rare earth oxysulfide-based phosphor [Y202 S:
Tb, Gd202S: Tb. La202S:
Tb, (YG d) 20 2 S: T b, (
Y, G d ) 2 02 S: Tb, Tm etc.1, terbium activated rare earth phosphate phosphor (YPO.: Tb,
GdPO4 :Tb, LaPO, :Tb, etc.), terbium-activated rare earth oxyhalide phosphor (LaOBr
:Tb, LaOBr :Tb, Tm% LadCn
:Tb, LaOCJ2 :Tb, Tm, GdOBr :
Tb, GdOCl:Tb, etc.), thulium-activated rare earth oxyhalide phosphors (LaOBr:Tm, La
OC1: Tm, etc.), barium sulfate-based phosphor [Ba
S04: Pb, BaS04: Eu” (Ba
S r) SO. : Eu'', etc.], divalent europium-activated alkaline earth metal phosphate phosphor [Ba3(PO4
)2:Eu”, (Ba, Sr)3 (P04)
2: Eu2+, etc.], 2{i1 eubium p
xi Alkaline earth metal fluoride halide phosphor [Ba
FCj2: Eu”, BaFBr:Eu”BaFCI
l: Eu”, Tb, BaFBr: Eu”Tb,
BaF2-BacIl2・KCJ2:Eu”BaF2・
BaCJ22 ・xBasO4 ・KCII:Eu”,
(Ba, Mg)F2 ・BaClt ・KCI! ．． :E
u2+, etc.], iodide-based phosphors (Csl: Na, Csl
:TIl, Nal, KI:Tn, etc.), sulfide-based phosphors [
ZnS:Ag, (Zn,Cd)S:Ag, (Zn,Cd
) S: Cu, (Zn, Cd) S: Cu, AIl
．． etc.], hafnium phosphate phosphor (H f P2 07
: Cu et al.). However, the phosphor used in the present invention is
The material is not limited to these materials, and any phosphor that emits light in the visible to near ultraviolet region when irradiated with radiation may be used.

The above-mentioned phosphor and binder are added to a suitable solvent and mixed thoroughly to prepare a coating solution in which the phosphor is uniformly dispersed in the binder solution.

As the binder, 10% by weight or more is a thermoplastic elastomer having a softening temperature or melting point of 30°C to 180°C.

Thermoplastic elastomer has elasticity at room temperature and becomes fluid when heated, so it can prevent damage to the phosphor due to pressure during compression. Examples of thermoplastic elastomers include polystyrene, polyolefins,
Polyurethane, polyester, polyamide, polybutadiene, ethylene vinyl acetate, polyvinyl chloride, natural rubber, fluororubber, polyisoprene, chlorinated polyethylene,
Examples include styrene-butadiene rubber and silicone rubber.

The effects of the present invention can be obtained if the component ratio of the thermoplastic elastomer in the binder is 10% by weight or more and 100% by weight or less, as described above, but the binder should contain as much thermoplastic elastomer as possible, especially 100% by weight. Preferably, the thermoplastic elastomer is made of a thermoplastic elastomer.

Examples of solvents for preparing coating solutions include lower alcohols such as methanol, ethanol, n-probanol, and n-butanol; chlorine-containing hydrocarbons such as methylene chlorite and ethylene chloride; and acetone, methyl ethyl ketone, and methyl isobutyl ketone. Examples include ketones; esters of lower fatty acids and lower alcohols such as methyl acetate, ethyl acetate, and butyl acetate; ethers such as dioxane, ethylene glycol monoethyl ether, and ethylene glycol monomethyl ether; and mixtures thereof.

The mixing ratio of the binder and phosphor in the coating solution varies depending on the characteristics of the intended radiation intensifying screen, the type of phosphor, etc., but in general, the mixing ratio of the binder and phosphor is as follows:
It is selected from the range of 1:1 to 1:100 (ffi ratio), and is particularly preferably selected from the range of 1:8 to 1:40 (weight ratio).

The coating liquid also contains a dispersant to improve the dispersibility of the phosphor in the coating liquid, and a dispersant to improve the bonding force between the binder and the phosphor in the phosphor layer after formation. Various additives such as plasticizers may be mixed. Examples of dispersants used for such purposes include phthalic acid, stearic acid, caproic acid, lipophilic surfactants, and the like. Examples of plasticizers include phosphate esters such as triphenyl phosphate, tricresyl phosphate, and diphenyl phosphate; phthalate esters such as diethyl phthalate and dimethoxyethyl phthalate; ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. and polyesters of polyethylene glycol and aliphatic dibasic acids, such as polyesters of triethylene glycol and adivic acid and polyesters of diethylene glycol and succinic acid.

The coating liquid containing the phosphor and binder prepared as described above is then uniformly applied to the surface of a temporary support for sheet formation to form a coating film of the coating liquid. This coating operation can be carried out using conventional coating means such as a doctor blade, roll coater, knife coater, etc.

The temporary support can be arbitrarily selected from, for example, glass, metal plates, or materials known as supports for radiation intensifying screens. Examples of such materials include cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate,
Films of plastic materials such as polycarbonate,
Metal sheets such as aluminum foil and aluminum alloy foil, regular paper, baryta paper, resin coated paper, pigment paper containing pigments such as titanium dioxide, paper sized with polyvinyl alcohol, etc., alumina, zirconia, magnesia, titania, etc. Examples include ceramic plates or sheets.

A coating solution for forming a phosphor layer is applied onto a temporary support, and after drying, it is peeled off from the temporary support to obtain a phosphor sheet that will become a phosphor layer of a radiation intensifying screen.

Therefore, it is preferable to apply a heel type agent to the surface of the temporary support in advance so that the formed phosphor sheet can be easily peeled off from the temporary support.

Next, step b) will be described.

First, a support for a radiation intensifying screen is prepared separately from the phosphor sheet formed as described above. This support can be arbitrarily selected from the same materials as the temporary support used when forming the phosphor sheet.

In known radiation-sensitizing screens, a phosphor layer is provided in order to strengthen the bond between the support and the phosphor layer, or to improve the sensitivity or image quality (sharpness, granularity) of the radiation-sensitized screen. A polymeric substance such as gelatin is coated on the surface of the side support to form an adhesion-imparting layer, or a light-reflecting layer made of a light-reflecting substance such as titanium dioxide, or a light-reflecting layer made of a light-absorbing substance such as carbon plaque. It is known to provide an absorbent layer or the like. The support used in the present invention can also be provided with these various layers, and their configurations can be arbitrarily selected depending on the purpose, use, etc. of the desired radiation intensifying screen.

The phosphor sheet obtained in step a) is placed on a support and adhered onto the support while being compressed at a temperature equal to or higher than the softening temperature or melting point of the binder.

In this way, by compressing the phosphor sheet without fixing it on a support in advance, it is possible to spread the sheet thinly, which not only prevents damage to the phosphor, but also improves the efficiency compared to when the sheet is fixed and pressurized. Thus, a high phosphor filling rate can be obtained even at the same pressure.

Examples of compression devices used for the compression treatment of the present invention include commonly known devices such as calender rolls and hot presses. For example, compression treatment using calender rolls is carried out by placing the phosphor sheet obtained by process a) on a support and passing it at a constant speed between rollers heated above the softening temperature or melting point of the binder. It will be done. However, the compression device used in the present invention is not limited to these devices, and any device may be used as long as it can compress the sheet as described above while heating it.

The pressure during compression is generally 50 kgw/cm2 or more.

The porosity of the phosphor layer formed on the support as described above can be theoretically determined by the following equation (1).

Below margin Vair/V = (a + b) ρg py V - A ( apr 10 b
ρx )V[(a+b)ρ. p-t-apy
pair - bρx ρair] (1) (where, V: total volume of the phosphor layer Vair: air volume in the phosphor layer A: total weight of the phosphor layer ρ8: density of the phosphor ρy: density of the binder ρair : Density of air a : Weight of phosphor b : Weight of binder) Furthermore, in equation (1), ρair is approximately 0, so equation (1) can be approximately expressed by equation (II) below. can.

Below margin Vair/V= (a+b)ρ8 ρy V A (aρy
+bp x )V [(a+b)ρ8 ρy] (II) (However, V, Vair %A, ρx.p,,
In the present invention, the porosity of the phosphor layer was calculated using equation (II).

Further, the filling rate of the phosphor can be determined by the following equation (1).

Aaρ, V [(a+b)ρ8 ρ,J --- (In) (However, V, Vair, A, ρx, ρy, a,
and b are the same as in formula (I)) In a normal radiation intensifying screen, a phosphor layer is physically placed on the surface of the phosphor layer on the side opposite to the side in contact with the support as described above. and a transparent protective film for chemical protection. It is preferable to provide such a transparent protective film also in the radiation intensifying screen of the present invention.

The transparent protective film may be made of, for example, a cellulose derivative such as cellulose acetate or nitrocellulose; or (polymethyl methacrylate, polyvinyl butyral,
A solution prepared by dissolving a transparent polymer material, such as a synthetic polymer material such as polyvinyl formal, polycarbonate, polyvinyl acetate, or vinyl chloride/vinyl acetate copolymer, in a suitable solvent is applied to the surface of the phosphor layer. It can be formed by a coating method. Alternatively, a protective film-forming sheet such as a plastic sheet made of polyethylene terephthalate, polyethylene naphthalate, polyethylene, polyvinylidene chloride, polyamide, etc. or a transparent glass plate is separately formed and properly adhered to the surface of the phosphor layer. It can also be formed by a method such as adhesion using an adhesive.

The thickness of the protective film is generally in the range of about 0.1 to 20 μm.

Next, examples of the present invention will be described. However, these examples do not limit the present invention.

[Example 1] For forming a phosphor sheet! ! As a commercial liquid, phosphor: Gd2
02 S: Tb- + + +-2oog Binder: Polyurethane (Desmolac TPKL-5 manufactured by Sumitomo Bayer Urethane ■
-2625 [Solid content 40%]>...20g: Nitrocellulose (nitrification degree l1.5%)...Add 2g to methyl ethyl ketone solvent and disperse with a propeller mixer,
A coating solution having a viscosity of 30 PS (25° C.) was prepared (binder/phosphor ratio =: 1/20). This was applied to a film thickness of 180 mm on polyethylene terephthalate (temporary support 5, thickness 180 μm) coated with a silicone mold release agent.
After drying, it was peeled off from the temporary support to form a phosphor sheet.

Separately, as an undercoat layer type coating liquid, soft acrylic resin solid content...90g nitrocellulose.
......50g was added to methyl ethyl ketone, dispersed, and mixed to prepare a dispersion having a viscosity of 3 to 6 PS (25°C).

Polyethylene terephthalate (support) with a thickness of 250 μm into which titanium monoxide has been kneaded is placed horizontally on a glass plate, and the coating solution for forming the undercoat layer is uniformly applied onto the support using a doctor blade. The coating film was dried by gradually raising the temperature from 25°C to 100°C to form an undercoat layer on the support (thickness of the coating film: 15 μm). The previously prepared phosphor sheet was placed on top of this and compressed.

Compression was done using calender rolls at 400K g w.
It was carried out continuously at a pressure of / cm 2 and a temperature of 80 °C. This compression completely fused the phosphor sheet and the support.

After this compression, a polyester adhesive is applied to one side. Transparent polyethylene terephthalate film (
J! ; [size: 10 μm)] was adhered with the adhesive side facing down to form a transparent protective film.

As described above, the radiation composed of the support, the undercoat layer, the phosphor layer, the transparent film, and the J film, 11! An intensifying screen was manufactured.

[Example 2] In Example 1, the pressure during compression was set to 600 κg w
A radiation intensifying screen consisting of a support, an undercoat layer, a phosphor layer, and a transparent protective film was produced in the same manner as in Example 1, except that the radiation intensifying screen was adjusted to 1.2 cm.

[Comparative Example 1] After forming an undercoat layer in the same manner as in Example 1, a coating liquid for forming a phosphor layer was subsequently applied thereon before the coating film dried. This was dried by gradually increasing the temperature from 25°C to 100°C to form a sheet consisting of a support, an undercoat layer, and a phosphor layer. Next, this sheet was heated to 400K using a calender roll in the same manner as in Example 1.
g/cm" pressure and a temperature of 80°C.Furthermore, a protective film was provided by the same method as in Example 1, and the material was composed of a support, an undercoat layer, a phosphor layer, and a transparent protective film. A radiation intensifying screen was manufactured.

[Comparative Example 2] In Comparative Example 1, the pressure during compression was set to 600K g w.
A radiation intensifying screen consisting of a support, an undercoat layer, a phosphor layer, and a transparent protective film was produced in the same manner as in Comparative Example 1, except that the radiation intensifying screen was set at 1/cm 2.

[Comparative Example 3] A radiation intensifying screen composed of a support, an undercoat layer, a phosphor layer, and a transparent protective film was manufactured in the same manner as in Comparative Example 1 except that no compression was performed. .

Holes in the phosphor layer of the radiation-sensitized screen The phosphor filling rate and porosity in the phosphor layer of each of the radiation-sensitized screens of Examples and Comparative Examples manufactured as described above are expressed by formula (n) and ( It was determined by the formula I[I]. However, the density of the phosphor was 7.5 g/cm', and the density of the binder was 1.14 g/cm3.

Results first! Shown in the table.

Table 1 with margin below Pressure Phosphor filling rate Porosity (kg/crn”) (%) (%) Example 1 400 68.0 2].
7 Comparative Example 1 400 B4.1
26.2 Example 2 600 70.1
19.2 Comparative Example 2 600 65.
6 29.4 Comparative Example 3 None 58.7
32.4 As is clear from Table 1, the radiation-sensitizing screen of the present invention has a higher phosphor filling rate than a radiation-sensitizing screen compressed with the same pressure.
It can be seen that the porosity has decreased.

In addition to the related screens, each radiation-sensitizing screen produced as described above was evaluated by the method described below.

(1) Sensitivity test A radiation intensifying screen was irradiated with X-rays at a tube voltage of 80 KVp, and the sensitivity was measured. The numerical values are shown as relative values with Comparative Example 3 set as 100.

(2) Image sharpness test A radiation intensifying screen and an X-ray photographic film (HR-S manufactured by Fuji Photo Film ■) were crimped together in a cassette, and X-rays were irradiated with a tube voltage of 80 KVp through a resolution cartridge. TeX
A radiograph was taken, and the contrast transfer function (CTF) of the completed radiograph was measured and evaluated as a spatial frequency of 2 cycles/mm.

(3) Image graininess test A radiation intensifying screen and an X&I photographic film (IR-S manufactured by Fuji Photo Film ■) were crimped together in a cassette, and a water phantom (thickness: 10 cm) and an aluminum plate (thickness = X-ray photography was performed by irradiating X-rays with a tube voltage of 80 KVp at a density of 1.0 through a tube (10 mm). This X-ray photographic film was processed for 90 seconds at a temperature of 35° C. using a developer (RDm, manufactured by Fuji Photo Film@) in an automatic processor (New 11N, manufactured by Fuji Photo Film). The obtained X-ray film was measured with a microphotometer (aperture: 300 μm×300 μm) to determine the RMS value. This RMS value was used as a measure of graininess.

The above test results are shown in Table 2.

Table 2 GTF (%) RMS (X 10-2) Example 1
103 2B. 7 1.37 Comparative Example 1 95 28.1 1.
40 Example 2 105 30.2
1. :12 Comparative Example 2 92 29.8
1.44 As is clear from Table 2 and FIG. 1, the radiation intensifying screen of the present invention has a sharpness that is lower than that of the comparative panel compressed at the same pressure.
It can be seen that the sensitivity and graininess are also in the direction of -E.

[Brief explanation of drawings]

FIG. 1 is a graph showing the image quality of radiation intensifying screens according to Examples and Comparative Examples. Comparative example 3 100 27.0 1
．． 44 We also summarized the results obtained regarding image quality and
It is shown in graphical form in the figure. In Figure 1, the vertical axis shows sharpness (spatial frequency 2 cycles/
CTF value at mm), and the higher the plot is, the higher the sharpness is. The horizontal axis indicates graininess, and the farther left the plot is, the better the graininess is.

Claims (1)

[Claims] 1. A radiation-sensitizing screen substantially composed of a support and a phosphor layer provided on the support and comprising a binder and a phosphor, the filling rate of the phosphor in the phosphor layer is 67% or more, and 10% by weight or more and 100% by weight or less of the binder is 30°C or more and 18% by weight or more.
A radiation intensifying screen characterized in that it is a thermoplastic elastomer having a softening temperature or melting point of 0° C. or lower.