JP2007155485A - Scintillator plate and method for manufacturing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a scintillator plate which delivers the light emission function sufficiently to equipment investment costs and is also highly efficient in the utilization of raw materials. <P>SOLUTION: The method for manufacturing the scintillator plate includes a process for preparing slurry by scattering a material for phosphors in water, a process (see Figure (a)) for freezing the slurry by painting it on a substrate 1 to cool the substrate 1, a lyophilization process (see Figure (b)) for lyophilizing the slurry in a vacuum after the freezing process and a process for sintering the slurry to form a phosphor layer on the substrate 1 after the lyophilization process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a scintillator plate manufacturing method and a scintillator plate manufactured by the manufacturing method.

  Conventionally, radiographic images such as X-ray images have been widely used for diagnosis of medical conditions in the medical field. In particular, radiographic images using intensifying screen-film systems have been developed as an imaging system that combines high reliability and excellent cost performance as a result of high sensitivity and high image quality in the long history. Used in the medical field. In recent years, digital radiation image detectors represented by flat panel radiation detectors (FPD (Flat Panel Detecter)) and the like have also appeared. Radiation images are acquired as digital information and image processing can be performed freely. It is possible to transmit image information instantly.

  By the way, the detector has a scintillator plate composed of a phosphor layer that receives radiation and emits visible light (fluorescence), and improving the luminous efficiency of the phosphor layer is radiography of the subject. Is very important for obtaining a radiographic image having excellent sharpness.

  The phosphor layer can be formed by a vapor deposition method such as a coating method, a vapor deposition method, or a sputtering method, and particularly when a raw material mainly composed of cesium iodide is formed by a vapor deposition method. It has a columnar crystal structure (a structure in which an infinite number of columnar crystals are gathered). For example, when the phosphor layer is formed by a vapor deposition method, a vapor deposition source composed of the phosphor raw material is heated by a resistance heater or electron beam irradiation to evaporate the vapor deposition source, and the surface of the substrate is evaporated. By depositing the evaporated material, a phosphor layer having a columnar crystal structure can be formed.

  A phosphor layer formed by a vapor deposition method is composed only of a phosphor and does not contain a binder, and a minute gap (space between one columnar crystal and another columnar crystal ( Microcracks) are present. Therefore, the light emitted inside each columnar crystal body is repeatedly reflected at the boundary between the columnar crystal body and the microcrack, and scattering of the light in the plane direction is suppressed. As a result, the efficiency of extracting emitted light is improved. The radiation image which is improved and excellent in sharpness can be obtained.

For example, Patent Document 1 is disclosed as an application example in which a phosphor layer is formed by a vapor deposition method. Specifically, in Patent Document 1, cesium iodide is vapor-deposited on the substrate, and simultaneously with the vapor deposition, another substance such as indium is sputtered to form a phosphor layer, thereby further improving the luminous efficiency. I am trying to do.
JP 2001-59899 A (see paragraph 0041)

However, when a columnar crystal is grown by vapor deposition to form voids in the phosphor layer, an expensive apparatus is required, and the phosphor material is also attached to the target substrate with high efficiency. However, most of them are dispersed toward portions other than the target substrate, so that the formation efficiency of the phosphor layer (use efficiency of raw materials) is as low as 5 to 20%. That is, in the method of forming the phosphor layer by the vapor deposition method, it is difficult to say that the scintillator plate corresponding to the capital investment cost is manufactured even though the capital investment cost is high.
An object of the present invention is to provide a method of manufacturing a scintillator plate that exhibits a sufficient light emitting function with respect to capital investment costs and has high use efficiency of raw materials.

In order to solve the above-mentioned problem, a method of manufacturing a scintillator plate according to claim 1 comprises:
A preparation step of preparing a slurry by dispersing phosphor materials in water;
After the preparation step, the slurry is applied to the substrate, the substrate is cooled, and the slurry is frozen.
After the freezing step, a freeze-drying step of vacuum lyophilizing the slurry;
After the freeze-drying step, firing the slurry to form a phosphor layer on the substrate; and
It is characterized by having.

The invention described in claim 2
In the manufacturing method of the scintillator plate of Claim 1,
The phosphor layer is characterized in that micropores extending from the surface to the substrate are formed.

The invention according to claim 3
In the manufacturing method of the scintillator plate of Claim 1 or 2,
The heating temperature in the baking step is 300 ° C. or higher, and the heat-resistant temperature of the substrate is 300 ° C. or higher.

The invention according to claim 4
In the manufacturing method of the scintillator plate as described in any one of Claims 1-3,
The phosphor material has cesium iodide and an activator.

The invention described in claim 5
In the manufacturing method of the scintillator plate of Claim 4,
The activator is a compound containing any one element or two or more elements of indium, thallium, lithium, potassium, rubidium, sodium, and europium.

The invention described in claim 6
It is manufactured according to the manufacturing method of the scintillator plate as described in any one of Claims 1-5, It is a scintillator plate characterized by the above-mentioned.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the scintillator plate which fully exhibits the light emission function with respect to capital investment cost, and also has high use efficiency of a raw material can be provided (refer the following Example).

  The best mode for carrying out the present invention will be described below with reference to the drawings. However, although various technically preferable limitations for carrying out the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.

  First, the configuration of the scintillator plate 10 according to the present invention will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the scintillator plate 10 has a configuration in which a phosphor layer 2 is formed on a substrate 1. When the phosphor layer 2 is irradiated with radiation, the phosphor layer 2 is incident. By absorbing the energy of the emitted radiation, an electromagnetic wave having a wavelength of 300 to 800 nm, that is, an electromagnetic wave (light) ranging from ultraviolet light to infrared light centering on visible light is emitted.

  The substrate 1 is a substrate capable of transmitting radiation, and specifically, a substrate having a heat-resistant temperature of 300 ° C. or higher, and is preferably made of metal such as aluminum or amorphous carbon.

  The phosphor layer 2 is a fired product of a phosphor material and may be any known phosphor, but is preferably a fired product of a phosphor material containing cesium iodide and an activator. As shown in FIG. 2A, the phosphor layer 2 is composed of a crystal wall 2a having a honeycomb shape (honeycomb shape), and innumerable micropores 2b are formed in the crystal wall 2a. Each micro hole 2b extends from the surface of the phosphor layer 2 to the surface of the substrate 1 as shown in FIG.

  The phosphor layer 2 is composed of a phosphor raw material as described above, but if it is mainly composed of cesium iodide, the activator is preferably thallium iodide. However, the activator may be any known compound, and can be arbitrarily selected according to required characteristics such as the emission wavelength and moisture resistance of the phosphor layer 2. As an example, thallium bromide may be applied instead of the above thallium iodide, and among indium, thallium, lithium, potassium, rubidium, sodium, europium, copper, cerium, zinc, titanium, gadolinium, terbium You may apply the compound containing any one element or two or more elements.

  Next, a method for manufacturing the scintillator plate 10 according to the present invention will be described with reference to FIG.

  First, a phosphor raw material (including cesium iodide and an activator) is added to water, and the phosphor raw material is dispersed in water while stirring and degassing the additive in vacuum to prepare a slurry. (Preparation process). In the preparation step, the phosphor raw material is preferably dispersed in water so that the ratio of water in the slurry is within the range of 5 to 50% by volume.

  If defoaming treatment is not performed in the preparation process, bubbles may remain in the slurry and defects resulting from the bubbles may be formed in the final product (scintillator plate 10). It is preferable to disperse the phosphor material in water while performing foam treatment.

  When the processing of the preparation process is finished, as shown in FIG. 3A, the slurry prepared in the preparation process is coated on the substrate 1 in a flush manner, and the substrate 1 is cooled on a predetermined temperature on a cooling plate 20 that has been cooled to a predetermined temperature. The substrate 1 is cooled by allowing to stand for a time, and the slurry on the substrate 1 is frozen (freezing step). In the freezing process, as shown in the enlarged view of FIG. 3A, the cooling heat of the cooling plate 20 is directly transmitted to the substrate 1, and as a result, an infinite number of frost columns are formed from the surface of the substrate 1 toward the surface of the slurry. The ice column grows in the slurry.

  In the freezing step, a refrigerant such as alcohol kept at a low temperature is put in a liquid tank, and only the substrate 1 is immersed and left in the refrigerant tank (the coated slurry portion is opened to the atmosphere). The upper slurry may be frozen. In this case, it is necessary to keep the temperature of the refrigerant put in the liquid tank below the freezing point of water.

  When the process of the freezing process is completed, as shown in FIG. 3B, the substrate 1 is placed in a freeze dryer 21 cooled to a predetermined temperature, and the slurry on the substrate 1 is freeze-dried in a vacuum (freeze-drying process). In the freeze-drying step, ice columns formed in the slurry are sublimated and disappear, and as shown in the enlarged view of FIG. 3B, micropores 2b are formed in the slurry as sublimation marks.

  After finishing the freeze-drying process, the slurry on the substrate 1 is baked for a predetermined time at a heating temperature of 300 ° C. or more (baking process). As a result, the slurry on the substrate 1 becomes the crystal wall 2 a and the phosphor layer 2 is formed on the substrate 1. In the firing step, the heating temperature is set to 300 ° C. or higher, but since the heat-resistant temperature of the substrate 1 is 300 ° C. or higher, the substrate 1 is not combusted and iodinated as an activator in the phosphor material. Since thallium is applied, the light emission characteristics of the phosphor layer 2 are improved. The scintillator plate 10 which concerns on this invention can be manufactured by performing the process of the above each process.

  Note that the size of the micropore 2b can be appropriately adjusted by the amount of water in the preparation step, the heating temperature in the baking step, the baking time, and the like.

  According to the manufacturing method of the scintillator plate 10 described above, the phosphor layer 2 having voids (micropores 2b) is formed by a simple technique such as preparation, freezing, freeze-drying, and firing of the slurry containing the phosphor raw material. The scintillator plate 10 having an excellent light emitting function can be manufactured without using an expensive device such as a device. In addition, since the slurry containing the phosphor material is coated on the substrate and frozen, freeze-dried, and fired as it is, the phosphor material is not wasted and the use efficiency of the raw materials can be dramatically improved. From the above, it is possible to provide the scintillator plate 10 that exhibits a light emitting function sufficiently with respect to the capital investment cost and has high use efficiency of raw materials (see the following example).

(1) Preparation of Sample (1.1) Preparation of Sample 1 A raw material powder obtained by adding 0.3 mol% of an activator material (TlI) to phosphor material (CsI) and water are mixed (water ratio is 25 vol%). The mixture was ball milled for 4 hours. The resulting slurry was stirred with a vacuum deaerator to remove bubbles in the slurry. Then, the slurry after foam removal was coated on a 0.5 mm thick aluminum substrate using a knife coater. The coated material was allowed to stand on a stainless steel cooling plate whose temperature was adjusted to −50 ° C. for 60 minutes to completely freeze the slurry in the coated material.

The slurry after freezing is put into a vacuum freeze dryer (TFD-550-8SP manufactured by Takara Seisakusho) and freeze-dried at a cold trap temperature of −80 ° C. for about one day. The slurry after freeze-drying is reduced to reducing gas (N ₂ (95% ) + H ₂ (5%)) at 400 ° C. for 4 hours to form a phosphor layer, and the final product after the firing was designated as “Sample 1”. In sample 1, the thickness of the phosphor layer was 500 μm, and in the sample 1, a large number of micropores having a diameter of about 5 to 10 μm penetrating from the surface of the phosphor layer to the aluminum substrate were observed (porosity of about 20%). ).

(1.2) Preparation of Sample 2 As a comparative sample of Sample 1, a raw material powder obtained by adding 0.3 mol% of an activator material (TlI) to a phosphor material (CsI) is deposited on one side of a 0.5 mm thick aluminum substrate. Thus, a phosphor layer was formed, and this was designated as “Sample 2”. Specifically, the raw material powder was filled in a resistance heating crucible of a vapor deposition apparatus as a vapor deposition material, and the aluminum substrate was installed in a substrate holder of the vapor deposition apparatus, and the distance between the resistance heating crucible and the aluminum substrate was adjusted to 400 mm.

  Subsequently, the inside of the vacuum vessel of the vapor deposition apparatus was once evacuated, and argon was introduced into the inside of the vacuum vessel to adjust the inside of the vacuum vessel to a degree of vacuum of 0.1 Pa. Thereafter, the substrate holder was rotated and heated, and the aluminum substrate was heated to 150 ° C. while rotating the aluminum substrate at a speed of 10 rpm. In this state, the resistance heating crucible was heated to evaporate the raw material powder to form a phosphor layer using the raw material powder as a deposition source on an aluminum substrate. Then, when the thickness of the phosphor layer reached 500 μm, the vapor deposition on the aluminum substrate was terminated, and the final product was designated as “Sample 2”. The porosity of the phosphor layer of Sample 2 was about 20%.

(2) Sample evaluation Each sample 1 and 2 is set on a 10 cm long x 10 cm wide CMOS flat panel (Rado Icon X-ray CMOS camera system Shadow-o-Box4KEV), and the luminance and MTF are calculated from 12-bit output data. Were measured and calculated for each of Samples 1 and 2.

(2.1) Measurement of Luminance Luminance X-ray with tube voltage of 80 kVp is irradiated from the back of each sample 1 and 2 (surface on which the phosphor layer is not formed), and the amount of light emitted from the phosphor layer is measured. It detected and measured with the COM flat panel, and the measured value was made into "light-emitting luminance (sensitivity)." The measurement results of Samples 1 and 2 are shown in Table 1 below. However, in Table 1, the value indicating the emission luminance of each sample 1 and 2 is a relative value when the emission luminance of sample 2 is 1.0.

(2.2) Calculation of MTF X-rays with a tube voltage of 80 kVp are irradiated from the back surface (surface on which the phosphor layer is not formed) of each sample 1 and 2 through a lead MTF chart, and image data is displayed on a CMOS flat panel. Detected and recorded on hard disk. Thereafter, the recording on the hard disk was analyzed by a computer, and the modulation transfer function (MTF (Modulation Transfer Function)) of the X-ray image recorded on the hard disk was calculated. The calculation results (MTF value (%) at a spatial frequency of 1 cycle / mm) are shown in Table 1 below. In the investigation results in Table 1, the higher the MTF value, the better the sharpness.

(3) Summary As shown in Table 1, from comparison between sample 1 and sample 2, sample 1 has higher emission brightness and MTF value than sample 2, and the phosphor raw material slurry was frozen, lyophilized and fired. It can be seen that the manufacturing method for forming the phosphor layer is more useful than the method for forming the phosphor layer by vapor deposition.

2 is a cross-sectional view showing a schematic configuration of a scintillator plate 10. FIG. It is (a) enlarged plan view (b) enlarged sectional view showing phosphor layer 2. It is drawing which shows the manufacturing method of the scintillator plate 10 typically, Comprising: It is explanatory drawing of each process of (a) freezing process (b) freeze-drying process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Phosphor layer 2a Crystal wall 2b Micro hole 10 Scintillator plate

Claims (6)

A preparation step of preparing a slurry by dispersing phosphor materials in water;
After the preparation step, the slurry is applied to the substrate, the substrate is cooled, and the slurry is frozen.
After the freezing step, a freeze-drying step of vacuum lyophilizing the slurry;
After the freeze-drying step, firing the slurry to form a phosphor layer on the substrate; and
A method for manufacturing a scintillator plate, comprising: In the manufacturing method of the scintillator plate of Claim 1,
A method of manufacturing a scintillator plate, wherein the phosphor layer is formed with micropores from the surface to the substrate. In the manufacturing method of the scintillator plate of Claim 1 or 2,
A method for manufacturing a scintillator plate, wherein a heating temperature in the baking step is 300 ° C. or higher and a heat-resistant temperature of the substrate is 300 ° C. or higher. In the manufacturing method of the scintillator plate as described in any one of Claims 1-3,
The method for producing a scintillator plate, wherein the phosphor material has cesium iodide and an activator. In the manufacturing method of the scintillator plate of Claim 4,
The activator is a compound containing any one element or two or more elements of indium, thallium, lithium, potassium, rubidium, sodium, and europium.   A scintillator plate manufactured according to the method for manufacturing a scintillator plate according to any one of claims 1 to 5.

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