Radiant energy – Invisible radiation responsive nonelectric signalling – Luminescent device
Reexamination Certificate
1998-10-06
2001-07-17
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiation responsive nonelectric signalling
Luminescent device
C250S581000, C250S484200, C430S139000
Reexamination Certificate
active
06262424
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a radiographic intensifying screen and radiation image converting panel, both having high image quality.
BACKGROUND OF THE INVENTION
Cited as a means for obtaining a radiographic image for medical diagnosis or non-destructive testing of various types of tissue and applying it to diagnosis and radiographic flaw detection are: radiography by a combination of a silver halide photographic light sensitive material and a radiographic intensifying screen, or a radiographic image conversion method by the use of a stimulable phosphor from which, after absorption of radiation energy, the accumulated radiation energy is emitted in the form of fluorescence by stimulation with electromagnetic waves such as visible light or infra-red rays (hereinafter referred to as stimulable phosphor).
Diagnosis or examination with radiography is such that radiation transmitted through or emitted from photographic object is converted, through absorption by phosphor contained in the radiographic intensifying screen and its excitation, into visible light, which produces a radiographic image on a silver halide photographic light sensitive material. The radiographic image is formed by exposing, to radiation through an object, the silver halide photographic light sensitive material having, on one side or both sides of a support, a silver halide emulsion layer, which is in contact with a radiographic intensifying screen to radiation through an object.
The phosphor has a high brightness and can form a radiographic image with a relatively small dose of radiation, so that exposure to radiation by the object is minimal. It is well known that sharpness and graininess of such images depend upon the particle size and dispersion and homogeneity of the phosphor, and in particular upon the filling ratio in the phosphor containing layer.
The radiographic image conversion method employing stimulable phosphor includes the employment of a radiation image converting panel containing the stimulable phosphor (hereinafter, referred to as a stimulable phosphor panel). In this case, the radiation transmitted through or emitted from the object is absorbed by a stimulable phosphor contained in the panel, followed by stimulating time-sequentially the phosphor with electromagnetic waves such as visible light or infra-red rays (also known as stimulating light), and emitting the radiation energy accumulated in the phosphor, in the form of light (photo-stimulated luminescence). The photo-stimulated luminescence is read as electric signals and based on the electric signals obtained, the object or its radiographic image is reproduced as a visible image. The panel which has already been read is treated to eliminate all residual images and made ready for the next photograph. Thus, the conversion panel can be employed repeatedly.
Similarly to the screen brightness, bending strength and abrasion resistance of the panel are also dependent upon dispersibility, homogeneity and filling ratio of the stimulable phosphor. Of these, the filling ratio of the stimulable phosphor is particularly influential.
Means for enhancing emission characteristics of the screen and panel is in general to enhance the filling ratio of the phosphor.
JP-A 3-21898 (herein, the term, JP-A means unexamined and published Japanese Patent Application) described, as a means for enhancing the filling ratio, the use of a resin having a glass transition temperature (hereinafter, denoted simply as Tg) of 30 to 150° C. and a radiation image converting panel with 70% or more filling ratio of a stimulable phosphor, which was achieved by compressing a phosphor containing layer (hereinafter, also denoted as a coating layer). Since the radiographic intensifying screen or the radiation image converting panel is employed with being rubbed with a photographic film or roll at room temperature, the Tg of a resin to be used is preferably not less than 30° C. However, when a resin with a high Tg is employed as a binder, the coating layer is not easily reduced in volume during drying, leading to a decreased filling ratio. Further, when the resulting coated layer is subjected to compression, due to deteriorated softening characteristics, the phosphor is under pressure liable to produce defects or destruction of the crystal structure, resulting in lowering of the sensitivity. Furthermore, the compression temperature needs to be raised to transform the resin, producing problems such as lowered manufacturing efficiency.
Accordingly, there is desired a radiographic intensifying screen or a radiation image converting panel with superior brightness and excellent image quality, and a manufacturing method thereof.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a radiographic intensifying screen or a radiation image conversion panel, whereby a radiation image with high image quality can be obtained, and a manufacturing method thereof.
It was found by the inventors of the present invention that when a resin, having a glass transition temperature (Tg) of −50 to 25° C., is contained as a binder resin in a phosphor layer, deformability of the phosphor layer during drying is improved, leading to an enhanced phosphor filling ratio, and further the use of a resin containing a polar group enhanced dispersion homogeneity and a filling ratio of the phosphor, leading to enhanced brightness. It was also found that when subjected to compression to enhance the phosphor filling ratio, the use of a resin with a low Tg enhanced the phosphor filling ratio even at low temperatures, and specifically in cases when a solvent remained in the phosphor layer in amounts of 1 to 30% by volume, the phosphor layer could be compressed under milder conditions. The above findings were applicable to the panel using a stimulable phosphor.
The object of the present invention can be achieved by the following constitution:
1. a method for preparing a radiographic intensifying screen comprising a support having thereon a phosphor layer, the method comprising the steps of:
(i) mixing a phosphor and a resin having a glass transition temperature of Tg1 to form a phosphor layer,
(ii) subjecting the phosphor layer to compression, and
(iii) making a glass transition temperature of the phosphor layer Tg2,
wherein the Tg1 and the Tg2 meet the following requirement:
Tg1<Tg2;
2. the preparation method of a radiographic intensifying screen described in 1, wherein the Tg1 is not less than −50° C. and not more than 25° C.;
3. the preparation method of a radiographic intensifying screen described in 2, wherein the Tg2 is not less than 30° C. and not more than 130° C.;
4. the preparation method of a radiographic intensifying screen described in 3, wherein the step of (i) comprises mixing the phosphor, resin having the glass transition temperature of Tg1 and a hardener;
5. the preparation method of a radiographic intensifying screen described in 4, wherein the hardener is a multifunctional isocyanate;
6. the preparation method of a radiographic intensifying screen described in 5, wherein the amount of the isocyanate is 5 to 30% by weight, based on the resin;
7. a method for preparing a radiographic intensifying screen comprising the steps of:
(i) coating a coating solution containing a phosphor and a resin having a glass transition temperature of −50° C. to 25° C., and
(ii) drying the coating solution coated on the support to form a phosphor layer;
8. the preparation method of a radiographic intensifying screen described in 7, wherein the coating solution further contains a hardener;
9. the preparation method of a radiographic intensifying screen described in 8, wherein the hardener is a multifunctional isocyanate;
10. the preparation method of a radiographic intensifying screen described in 9, wherein the isocyanate is contained in an amount of 5 to 30% by weight, based on the resin;
11. a method for preparing a radiographic intensifying screen comprising the steps of:
(i) mixing a phosphor with a resin having a glass transition temperature of −5
Amitani Kouji
Yanagita Takafumi
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Gagliardi Albert
Hannaher Constantine
Konica Corporation
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