This invention relates to a radiation image storage panel by use of a stimulable phosphor, more particularly to a radiation image storage panel which can stand uses for a long term.
Radiation image such as X-ray image has been frequently used for diagnosis of diseases, etc. For obtaining this X-ray image, the so-called radiation photography has been utilized, in which X-ray which has passed through a subject is irradiated on a phosphor layer (fluorescent screen), thereby forming visible light, and the visible light is irradiated on the film by use of a silver salt and developed similarly as in conventional photographing. However, in recent years, there has been contrived the method in which images are directly taken out from the phosphor layer without use of a film coated with a silver salt.
As this method, there is the method in which the radiation passed through a subject is absorbed in a phosphor, then the radiation energy stored by the above absorption in the phosphor is permitted to be radiated as fluorescence by excitation of the phosphor with, for example, light or heat energy, and the fluorescence is detected to form an image. Specifically, for example, U.S. Pat. No. 3,859,527 and Japanese Unexamined Patent Publication No. 12144/1980 disclose radiation image converting method with visible ray or IR-ray as the stimulating light by use of a stimulable phosphor. This method employs a radiation image storage panel having a stimulable phosphor layer formed on a support, and a latent image is formed by irradiating the radiation passed through a subject on the stimulable phosphor layer of the radiation image storage panel and accumulating the radiation energy corresponding to the transmission degree of the radiation at the respective portions of the subject, and thereafter the radiation energies stored at the respective portions are permitted to be radiated to be converted into light by scanning the stimulable phosphor layer with stimulating light, whereby images are obtained by the light signals according to intensity of the light. The final image may be reproduced as hard copy or reproduced on CRT.
The radiation image storage panel to be used in the radiation image converting method accumulates radiation image information and thereafter releases the stored energy by scanning of stimulating light, and therefore accumulation of radiation image can be again effected after scanning, thus enabling repeated uses.
Accordingly, the above radiation image storage panel should desirably have performances which can stand repeated uses for a long term or for a large number of times without deteriorating the image quality of the radiation image obtained. For this purpose, the stimulable phosphor layer in the above radiation image storage panel is required to be sufficiently protected from physical and chemical stimulations from outside.
Particularly, stimulable phosphors are strong in moisture absorption and when the above stimulable phosphor layer absorbs water, barium fluoride bromide type phosphor (e.g. BaFBr:Eu), etc. is decomposed to be lowered in sensitivity to radiation. Also, alkali halide type phosphors (e.g. RbBr:Tl), etc. are fluctuated in sensitivity to radiation by moisture absorption and dehumidication, and also increased or decreased in the fading speed of the radiation energy stored, whereby photographing conditions become unstable and also image quality of the radiation image obtained is deteriorated. For this reason, it has been desired to protect the above stimulable phosphor layer so that no water may be contained therein.
In the radiation image storage panel of the prior art, for solving the above problems, there has been employed a protective layer covering the stimulable phosphor layer, on the support of the radiation image storage panel.
This protective layer, as described in Japanese Unexamined Patent Publication No. 42500/1984, is formed by direct coating of a coating solution for protective layer on the stimulable phosphor layer, or alternatively by adhering a previously separately formed protective layer onto the stimulable phosphor layer.
Further, the present inventors have proposed in Japanese Unexamined Patent Publication No. 176900/1986 and Japanese Patent Application No. 156346/1985 a method for forming a protective layer by applying a coating solution for protective layer, containing a resin material which is cured by polycondensation or crosslinking reaction by irradiation of radiation and/or heating, on the stimulable phosphor layer and then curing the above resin material.
For increasing the life of the radiation image storage panel, further improvement, particularly in humidity resistance has been desired, but under the present situation, substantially no investigation has been made concerning moisture prevention except for the method for lowering moisture permeability of the above protective layer.