Radiant energy – Invisible radiation responsive nonelectric signalling – Luminescent device
Reexamination Certificate
1999-11-29
2002-11-26
Mai, Huy (Department: 2873)
Radiant energy
Invisible radiation responsive nonelectric signalling
Luminescent device
C250S486100, C250S487100
Reexamination Certificate
active
06486477
ABSTRACT:
REARGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radiographic intensifying screen set (hereinafter referred to as intensifying screen set) comprising a pair of a front intensifying screen and a rear intensifying screen, for radiographing.
2. Discussion of Rearground
With respect to a radiographic intensifying screen (hereinafter referred to as intensifying screen), in order to improve sensitivity or sharpness, various improvements have heretofore been made, such as improving light-scattering characteristics of a support or a protective layer to be used for it, making phosphor layers have a multi-layer structure, or coloring the phosphor layers by e.g. a dye. However, it has been desired to develop an intensifying screen having more improved sensitivity and image quality, in the market. Further, with respect to the improvements in characteristics of an intensifying screen, although numbers of proposals have been made with respect to improvements in mainly characteristics of the intensifying screen alone, only a few proposals have been made with respect to constitution of the intensifying screen as an intensifying screen set.
It is an object of the present invention to provide an intensifying screen set which is excellent in both sensitivity and sharpness, and which presents a radiograph having an excellent image quality.
The present inventors have conducted extensive studies on correlation between an intensifying screen set comprising intensifying screens having various constitutions, and image quality of a radiograph which will be obtainable by using the intensifying screen set, and they have found that the above-mentioned objects can be achieved when each of phosphor layers for front and rear intensifying screens have a multi-layer structure, a fluorescent dye or a fluorescent pigment is contained in the phosphor layers, and particle size distribution of phosphors in the phosphor layers and light-reflection characteristics of the supports are specified.
SUMMARY OF THE INVENTION
The present invention provides:
(1) a radiographic intensifying screen set comprising a pair of a front intensifying screen and a rear intensifying screen, each comprising a support and a plurality of phosphor layers each having a binder resin and a phosphor dispersed therein, provided on he support, wherein at least some of the phosphor layers of the respective front intensifying screen and rear intensifying screen contain a fluorescent dye or a fluorescent pigment which absorbs some of emitted lights from the phosphors and emits lights having other wavelengths, the support for the front intensifying screen is a light-reflective support, and the support for the rear intensifying screen is a light-absorptive support,
(2) the radiographic intensifying screen set according to the above-mentioned (1), wherein the phosphors in the phosphor layers are aligned so that the average particle size decreases from the surface side (the side from which the emitted lights are taken out) toward the support side, and
(3) the radiographic intensifying screen set according to the above-mentioned (1) or (2), wherein a light-scattering protective layer having a transmission of at least 40% and a haze ratio of at least 20%, is provided on the surface of each of the front intensifying screen and the rear intensifying screen.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, the present invention will be explained in further detail.
The intensifying screen set of the present invention can be produced in the same manner as a conventional intensifying screen set, except that a fluorescent dye or a fluorescent pigment (hereinafter such fluorescent dye and pigment will generically be referred to simply as “fluorescent dye”) is added to at least some of the phosphor layers of the respective front intensifying screen and rear intensifying screen constituting the intensifying screen set, the phosphor particles in the phosphor layers are specifically aligned, and supports having specific light-reflection characteristics are employed.
Namely, both front intensifying screen and the rear intensifying screen constituting the intensifying screen set, are produced in such a manner that a predetermined amount of phosphor and fluorescent dye are mixed with a binder such as nitrocellulose, an organic solvent is further added thereto to prepare a phosphor coating solution having a suitable viscosity, the coating solution is coated on each of the supports by e.g. a knife coater or a roll coater, followed by drying to form a phosphor layer, and a protective layer is further formed on this phosphor layer, as the case requires, to obtain a front intensifying screen and a rear intensifying screen.
Here, the front and rear intensifying screens constituting the intensifying screen set of the present invention, do not have a phosphor layer of single-layer structure which is formed by one kind of phosphor coating solution having phosphors having a single particle size distribution suspended therein, but have a plurality of phosphor layers on the respective supports, which are formed by using at least two kinds of phosphor coating solutions having different particle size distributions, coating one phosphor coating solution on the respective supports, and after drying or in a non-dried state, successively coating another phosphor coating solution thereon. In such a case, when a plurality of phosphor layers are formed by successively coating phosphor coating solution from one containing a phosphor with a smaller average particle size on the support, and when the phosphor particles are aligned so that the particle size is smaller at the support side than at the surface side (the side from which the emitted lights are taken out), the layer of the phosphor having a smaller particle size than the surface side, aligned at the support side, functions as a close reflective layer of lights, and suppress scattering of emitted lights from the phosphors. Accordingly, as compared with a case where phosphors having a uniform particle size distribution are uniformly aligned on the entire phosphor layer, an effect to improve the sharpness, in addition to an effect to improve sensitivity by the light-reflective support, can be obtained in the case of the light-reflective support, and in the case of the light-absorptive support, an effect to improve sensitivity, in addition to an effect to improve sharpness, can be obtained. Accordingly, effects to improve sensitivity and sharpness can be obtained for both supports.
In order to improve dispersibility of phosphors in the respective coating solutions, it is preferred to carry out a dispersion treatment by e.g. a ball mill to the phosphor coating solutions, after the phosphor coating solutions to form the respective phosphor layers are prepared and before coated, as the packing density of the phosphors in the phosphor layers after coating will be high, and the uniformity of the coated phosphor layer will be excellent.
In the intensifying screen set of the present invention, the fluorescent dye to be contained in the phosphor layer, may be contained in the phosphor layer of at least one of front and rear intensifying screens. With respect to the content (percentage by weight of the added fluorescent dye to the weight of the phosphors in the phosphor layers) in the phosphor layers of both front and rear intensifying screens, if it is small, absorption of the emitted lights from the phosphors will be inadequate, and if it is high, the absorption amount of the emitted lights from the phosphors will be higher than the emission amount from the dye, whereby sensitivity will be decrease. Accordingly, the content of the fluorescent dye to be added to the phosphor layer is preferably at the level of from 0.001 to 0.05%, more preferably at the level of from 0.002 to 0.02%, to the phosphors, depending upon the type of the fluorescent dye to be added, as the absorption amount of the emitted lights from the phosphors and the emission from the fluorescent dye will be well balanced.
As mentione
Nakamura Masaaki
Suzuki Yujiro
Takahashi Kenji
Tanaka Michio
Yamane Katsutoshi
Kasei Optonix Ltd.
Mai Huy
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