JP3842206B2 - Binderless phosphor screen with colored interlayer - Google Patents

Description

[0001]
FIELD OF THE INVENTION This invention relates to a binderless storage phosphor screen having a deposited phosphor layer.
[0002]
BACKGROUND OF THE INVENTION A well-known use of storage phosphors is the generation of X-ray images. US-A 3859527 discloses a method for generating an X-ray image with a photostimulable phosphor contained in a panel. The panel is exposed to impinge an X-ray beam modulated according to the pattern, so that the phosphor temporarily stores the energy contained in the X-ray radiation pattern. At some interval after exposure, a beam of visible or infrared light scans the panel and stimulates the emission of stored energy as light. The light is detected and sequentially converted into an electrical signal that is processed to produce a visible image. For this purpose, the phosphor should store as much incident X-ray energy as possible and emit as little energy as possible until stimulated by the scanning beam. This is referred to as “digital radiography” or “computer radiography”.
[0003]
The image quality produced by any radiographic system that uses a phosphor screen, and therefore by a digital radiographic system, is highly dependent on the configuration of the phosphor screen. In general, the thinner the phosphor screen at a given amount of x-ray absorption, the better the image quality.
[0004]
This means that the lower the binder to phosphor ratio of the phosphor screen, the better the image quality that can be achieved with that screen. Thus, optimum sharpness can be obtained when a screen without any binder is used. Such a screen can be produced, for example, by physical vapor deposition of a phosphor material on a substrate, which may be thermal vapor deposition, sputtering, electron beam vapor deposition, and the like. However, this production method cannot be used to produce high quality screens with all available phosphors. The above manufacturing method leads to the best results when phosphor crystals with high crystal symmetry and simple chemical composition are used.
[0005]
The use of alkali metal halide phosphors in storage screens or panels is well known in the field of storage phosphor radiation, and the high crystal symmetry of these phosphors provides structured and binder-free screens. be able to.
[0006]
When binderless screens with alkali halide phosphors are produced, it is beneficial to deposit phosphor crystals such as some types of piles, needles, tiles and the like. US-A 4769549 discloses that the image quality of a binderless phosphor screen can be improved when the phosphor layer has a block structure formed of thin columns.
[0007]
US-A 5,055,681 discloses a storage phosphor screen with a pile-like structure and containing an alkali halide phosphor. The image quality of such screens still needs to be improved and JP-A 06/230198 discloses that the surface of the screen with columnar phosphors is rough and that leveling can improve sharpness. U.S. Pat. No. 5,874,744 focuses on the reflectivity of phosphors used to produce storage phosphor screens having needle-like or columnar phosphors.
[0008]
In EP-A 111 13458, in a binderless storage phosphor screen comprising an alkali metal storage phosphor, the screen has a (100) diffusion line with intensity I ₁₀₀ and a (110) diffusion line with intensity I ₁₁₀ and A storage phosphor screen is disclosed that exhibits an XRD spectrum such that I ₁₀₀ / I ₁₁₀ ≧ 1. Such phosphor screens show a good compromise between speed and sharpness.
[0009]
The use of anodized aluminum as a substrate for the deposited phosphor layer is known from US Pat. No. 4,769,549. The use of anodized aluminum is said to have the advantage that Al ₂ O ₃ on the anodized aluminum exists as a kind of tile. When depositing a storage phosphor layer on such a substrate, the phosphor is formed by thin columnar blocks separated from each other by a gap, and having such a storage phosphor layer realizes a very good speed / sharpness relationship. It is said that it will be done.
[0010]
However, the production of anodized aluminum presents the disadvantage that a large amount of electrical energy is typically required to roughen and oxidize the substrate surface. Furthermore, the roughening achieved by etching is generally only performed relatively slowly. A further disadvantage is that the reprocessing of waste formed during anodization and roughening of the substrate is expensive. All the elements taken together make anodized aluminum a very expensive substrate for phosphor screens, and therefore a need for an inexpensive substrate that retains the advantages of anodized aluminum is desirable.
[0011]
OBJECT AND SUMMARY OF THE INVENTION The object of the present invention is to stimulate phosphorescence useful for X-ray recording systems having a very good compromise between images with high sharpness and low noise and the speed of the recording system (ie the lowest patient dose possible). Is to provide a body screen.
[0012]
A further object of the present invention is a stimulus useful for X-ray recording systems having a very good compromise between an image having high sharpness and low noise on a very inexpensive substrate and the speed of the recording system (ie the lowest patient dose possible). It is to provide a phosphor screen.
[0013]
The above objective is accomplished by providing a stimulable phosphor screen having the features defined in claim 1. The features of preferred embodiments of the invention are disclosed in the dependent claims.
[0014]
Further advantages and embodiments of the present invention will become apparent from the following description.
[0015]
Detailed Description of the Invention Throughout this specification "deposited phosphor" is produced by any method selected from the group consisting of thermal evaporation, chemical vapor deposition, electron beam evaporation, radio frequency evaporation and pulsed laser evaporation. Means phosphor. This deposition is preferably carried out under conditions as described in EP-A 111 13458.
[0016]
It has now been shown that a binderless phosphor screen can be produced on a substrate coated with a ceramic layer. Such a ceramic layer contains at least one inorganic pigment selected from the group consisting of Al ₂ O ₃ , TiO ₂ , SiO ₂ and ZnO. Preferably, the ceramic layer for use in the storage phosphor screen of the present invention comprises Al ₂ O ₃ optionally mixed with other inorganic pigments.
[0017]
Apart from the advantages mentioned at the outset, the manufacture of the substrate for the binder-free storage phosphor screen by applying a ceramic layer on top is dependent on the size of the “tile” on which the deposited phosphor grows. There is also an advantage that it can be easily controlled by controlling the size of the pigment particles to be formed. Furthermore, the ceramic layer can also contain other pigment particles in addition to Al ₂ O ₃ . This gives the opportunity to obtain a support that can be colored, whose spectral reflectivity and absorbency is adjusted to have a support that absorbs stimulating light and reflects stimulated light Thus enhancing the sharpness of the storage phosphor screen. In contrast to anodized aluminum, which is essentially white and therefore reflects both stimulating light and stimulated light, absorption of stimulating light and reflection of stimulated light is provided as desired. . When it is desirable to have a colored ceramic layer on a substrate for the storage phosphor screen of the present invention, the ceramic layer is made to contain Al ₂ O ₃ and optionally TiO ₂ with a blue inorganic pigment.
[0018]
Commercially available very useful blue and blue-green inorganic pigments are SICOCER A, SICOCER B, SICOCER E, SICOCER F, SICOCER G, SICOCER I, SICOCER P, SICOCER R, SICOCER S, SICOCER U (all BASF, Ludwigshafen U Ceramic pigments such as blue or blue-green pigments selected from Germany.
[0019]
Several methods are known for depositing a ceramic layer on a substrate. One method involves selecting a particulate coating material and depositing the coating material on a substrate by a thermal spray technique. Such a method is disclosed, for example, in US-A 5881645. However, this is not a preferred example for producing a substrate for the storage phosphor screen of the present invention. This is because the energy consumption of thermal spray technology is extremely high.
[0020]
Another technique for providing a ceramic layer comprises applying a slurry of at least one monobasic phosphate and non-metallic inorganic particles to the surface of a substrate and forming the ceramic coating by burning the slurry at a temperature of at least 230 ° C. Including. Such techniques are disclosed in PCT application WO-A-83 00844. Because of the processing temperature of at least 230 ° C., this method is suitable for applying ceramic layers on metal substrates such as aluminum, steel, copper, brass and copper, but this method applies ceramic layers on polymer film substrates. Not very suitable to be applied to obtain.
[0021]
Another method for applying the ceramic layer on the substrate provides an aqueous dispersion comprising at least one inorganic pigment and a silicate compound, whereby the dispersion is applied to the substrate by known coating techniques, and 130-220 ° C. A step of drying at a temperature of Such a method is disclosed in U.S. Pat. No. 6,240,846 and corresponding EP-A 0993422, where one of the objects of the invention is very good and durable of the ceramic layer to the substrate without consuming a large amount of energy. It is to provide a method of manufacturing a material that leads to adhesion. According to the invention there is provided a material comprising a substrate and a ceramic layer applied to the surface of the substrate, wherein the ceramic layer is composed of at least one silicate compound and aluminum oxide (at least 99.6 wt% aluminum purity). The ceramic layer is then adhered to the substrate with a silicate compound that functions as a binder. This method is very suitable in the present invention for producing a substrate for use in a storage phosphor screen. This is because the considerably lower drying temperature in the process is very suitable for applying ceramic layers to both metal substrates and polymer film substrates. When a polymer substrate is used, it is preferred to use a polyester substrate such as polyethylene terephthalate, polyethylene naphthalate or polycarbonate substrate.
[0022]
The silicate compound, which is a preferred compound for use in the manufacture of screens or panels according to the present invention, contains sodium silicate in the form of sodium water glass as a binder, where the solid content of the aqueous solution of sodium water glass is 30% by weight. Advantageously, there are advantageously ₂ to 4 mol of SiO ₂ per mol of sodium oxide (Na ₂ O). Another suitable silicate compound is potassium silicate, which is less sensitive to air-carbon dioxide than sodium silicate.
[0023]
By adjusting the average particle size of the mixed inorganic pigment dispersed in the aqueous dispersion with respect to the thickness of the coated ceramic layer, the deposited phosphor has a substrate that grows in acicular crystals with a predetermined width. Thus, the texture of the ceramic layer can be designed. The pigment mixed in the dispersion preferably has a number average particle size of 0.5 to 100 μm, more preferably 3 to 60 μm, and even more preferably 4 to 40 μm. The thickness of the dried ceramic layer is preferably 0.5-20 μm and the average particle size of the pigment particles is adjusted to protrude from the ceramic layer in the average range of 0.5-80 μm. The aqueous dispersion containing the inorganic pigment is coated on the substrate in order to have inorganic pigment particles in an average amount of 10 ⁶ to 10 ¹¹ per m ² . More preferably, the dispersion is coated to have an average amount of inorganic pigment particles of 10 ⁷ to 10 ⁹ per m ² . The number of particles is optionally dependent on the average particle size of the particles, the diameter of the phosphor needles and the dimensions of the voids (gaps).
[0024]
The storage phosphor screen according to the invention is prepared by vacuum deposition of the phosphor crystals on the substrate as well as by mixing the components for the phosphor (phosphor precursor) and then evaporating the mixture to remove the phosphor in situ during the evaporation. It can be manufactured by forming.
[0025]
The phosphor in the binderless phosphor screen according to the invention can be any known stimulable metal phosphor. Preferably, the storage phosphor used in the binderless phosphor screen of the present invention is an alkali metal phosphor. Very suitable phosphors are, for example, phosphors according to formula I:
M ¹⁺ X. ^{_{aM 2+ X '2 bM 3+ X}} "3: cZ (I)
^Wherein M ¹⁺ is at least one element selected from the group consisting of Li, Na, K, Cs and Rb, and M ²⁺ is Be, Mg, Ca, Sr, Ba, Zn, Cd, Cu, Pb and At least one element selected from the group consisting of Ni, M ³⁺ is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, At least one element selected from the group consisting of Lu, Al, Bi, In and Ga, and Z is at least one element selected from the group consisting of Ga ¹⁺ , Ge ²⁺ , Sn ²⁺ , Sb ³⁺ and As ³⁺ X, X ′ and X ″ may be the same or different, each of which represents a halogen atom selected from the group consisting of F, Br, Cl, I, and 0 ≦ a ≦ 1, 0 ≦ b ≦ 1 and 0 < ≦ 0.2. Such phosphors have been disclosed in US-A 5736069, for example.
[0026]
A highly preferred phosphor for use in the binderless phosphor screen of the present invention is a CsX: Eu stimulated phosphor, where X represents a halide selected from the group consisting of Br and Cl, the phosphor Is produced by a method comprising the following steps:
- EuX _{'2, EuX' 3} and EuOX '(where, X' is F, Cl, an element of one selected from the group consisting of Br and I) ¹⁰ of europium compound selected from the group consisting of ^-3 Mix ~ 5 mol% and the CsX;
-Burning the mixture at a temperature of 450 ° C or higher;
-Cooling the mixture; and-recovering the CsX: Eu phosphor.
[0027]
Most preferably a CsBr: Eu stimulated phosphor produced by a method comprising the following steps is used:
- EuX _{'2, EuX' 3} and EuOX '(where, X' is F, Cl, an element of one selected from the group consisting of Br and I) ¹⁰ of europium compound selected from the group consisting of ^-3 Mix ~ 5 mol% and the CsX;
-Burning the mixture at a temperature of 450 ° C or higher;
-Cooling the mixture; and-recovering the CsX: Eu phosphor.
[0028]
The binderless screen is manufactured by providing a finished phosphor on the support by any method selected from the group consisting of thermal evaporation, chemical vapor deposition, electron beam evaporation, radio frequency evaporation and pulsed laser evaporation. Can. Alternatively, the alkali metal halide and the dopant can be brought together and they are deposited together on the support in such a way that the alkali metal phosphor is doped during the manufacture of the screen. The present invention is a method for producing a phosphor screen containing a CsX: Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br and Cl, and includes a method comprising the following steps: To:
A europium compound selected from the group consisting of EuX ′ ₂ , EuX ′ ₃ and EuOX ′ (where X ′ is a halide selected from the group consisting of F, Cl, Br and I) and a number of said CsX And-doped with 10 ^{−3 to 5} mol% of europium by a method selected from the group consisting of thermal evaporation, chemical vapor deposition, electron beam vapor deposition, radio frequency vapor deposition and pulsed laser vapor deposition Both the CsX and the europium compound are deposited on the substrate in such a ratio that a CsX phosphor is formed on the substrate.
[0029]
Vapor deposition can be carried out from a single container containing a mixture of starting compounds in the desired proportion. The method applied to the present invention is a method for producing a phosphor screen containing a CsX: Eu-stimulated phosphor (where X represents a halide selected from the group consisting of Br and Cl), and comprises the following steps: Further encompassing a method comprising:
- EuX _{'2, EuX' 3} and EuOX '(where, X' is F, Cl, a is selected halides from the group consisting of Br and I) ^{10 -3} ~ europium compound selected from the group consisting of Mix 5 mol% and the CsX;
Bringing the mixture into a state of vapor deposition; and- depositing the mixture on a substrate by a method selected from the group consisting of physical vapor deposition, thermal vapor deposition, chemical vapor deposition, electron beam vapor deposition, radio frequency vapor deposition and pulsed laser vapor deposition. .

Claims (3)

A binderless stimulable phosphor screen comprising an alkali metal halide phosphor layer deposited on a substrate, wherein the substrate is selected from the group consisting of aluminum, steel, brass and copper In a stimulable phosphor screen which is a film, a ceramic layer containing at least one inorganic pigment is present between the substrate and the phosphor layer, and the inorganic pigment has a number average particle size of 0.5 to 100 μm. Having a number average particle size adjusted to protrude from the ceramic layer in an average range of 0.5 to 80 μm, the thickness of the ceramic layer being 0.5 to 20 μm, and the screen being A binderless stimulable phosphor screen characterized in that it comprises inorganic pigment particles on the substrate in an average amount of 10 ⁶ to 10 ¹¹ per m ^2. N. ^{2. A} binderless stimulable phosphor screen according to claim 1, wherein the screen comprises inorganic pigment particles in an average amount of 10 < ⁷ > to 10 < ⁹ > per m < ² > on a substrate. Wherein the at least one inorganic pigment is _{Al 2 O 3, TiO 2,} SiO 2 and phosphor screen without binding agent according to claim 1 or 2 is a white pigment selected from the group consisting of ZnO.