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(11) | EP 0 087 674 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Image tube |
| (57) An image tube having an output fluorescent screen structure for producing an output
image thereon, said output fluorescent screen structure comprising a transparent glass
substrate coated with a fluorescent screen, and an output window glass pane of a main
body of said image tube, said transparent glass substrate and said output window glass
pane being arranged to closely adhere to each other by a transparent bonding material
so as to form a laminated structure thereby, said laminated structure being set, in
its thickness, to such an extent as is sufficient to cause a total reflection of light
emitted at a peripheral portion of an effective visual field of said fluorescent screen
and incident into the laminated structure, to reach outside a concerned region within
said effective visual field of said output fluorescent screen. |
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an improvement of an output fluorescent screen structure for an image tube.
[0002] As shown in Fig. 1, conventionally, it has been a common practice that an output fluorescent structure (1) is attached to the inner face of an output glass pane (3) of an image tube main body through a vacuum layer (2). Therefore, there has been experienced such an inconvenience that part of a visible ray emitted at an output fluorescent screen (4) is subjected to a total reflection at an outer side face of a glass substrate or glass base plate (5) laminated with the output fluorescent screen (4), with the total reflection light (Ll) being again directed back to the output fluorescent screen (4), thus resulting in a deterioration in the contrast of the output image.
[0003] In order to overcome the disadvantage as described above, the present applicant has previously proposed, in Japanese utility model application 188578/80, a fresh means capable of preventing the deterioration in the contrast of the output image due to the total reflection light (L1) as described above, in which, the arrangement is so made that the total reflection light (Ll) produced at the outer side face of the glass substrate (5) is led out of an effective visual field region of the output fluorescent screen (4) by increasing the thickness of the glass substrate (5), thereby to improve the contrast of the output images.
[0004] However, in the above proposed arrangement, for the improvement of the contrast in the output image, the thickness of the glass base plate (5) which has been in the order of about 1 mm or thereabout up to the present must be increased to the range of at least ten and several mm or so, and in the case where the output fluorescent screen is to be formed on the glass substrate having the thickness to such an extent, various problems as follows are inevitably brought about.
[0005] More specifically, in the above arrangement, since the space occupied by the glass substrate and the weight of said glass substrate are markedly increased as compared with the conventional arrangements, there is such an inconvenience that a conventional output fluorescent screen manufacturing system can not cope with the situation owing to the construction of the machinery, while, even when the conventional output fluorescent screen manufacturing system is to be remodelled, the production efficiency will be extremely lowered, since spaces for the production required by the respective glass substrate are unavoidably increased.
[0006] Accordingly, an essential object of the present invention is to provide an improved image tube which will solve the problems related to the manufacture as described above, with simultaneous elimination of deterioration in the contrast of the output images.
[0007] More specifically, according to the present invention, an output fluorescent screen structure for the image tube is constituted by a transparent glass substrate coated with a fluorescent screen, and an output window glass pane of the image tube main body closely stuck onto the transparent glass substrate by a transparent bonding material to form a laminated structure thereby, while the thickness of the laminated structure is set to such an extent as is sufficient to cause a total reflection of light emitted at a peripheral portion of an effective visual field of said fluorescent screen and incident into the laminated structure, to reach outside a concerned or interested region within said effective visual field of said output fluorescent screen. In other words, the thickness of the output window glass pane is utilized as part of the thickness of the glass substrate required for improving the contrast of the output image, whereby it becomes possible to employ a plate with a thin thickness for the glass substrate to be coated with the output fluorescent screen, and thus, various problems related to the manufacture as described earlier may be advantageously solved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008]
Fig. 1 is a fragmentary side sectional view showing one example of an output fluorescent screen structure of a conventional image tube,
Fig. ? is a side sectional view showing an output - fluorescent screen strucure of an image tube according to one preferred embodiment of the present invention,
Fig. 3 is a side sectional view showing a modified embodiment according to the present invention in the case where another transparent glass plate (7) is further bonded onto the outer side face of the output window glass pane (3).
DETAILED DESCRIPTION OF THE INVENTION
[0009] Subsequently, specific constructions according to the present invention will be described hereinbelow with reference to the accompanying drawings.
[0010] Referring to Fig. 2, there is shown an output fluorescent screen structure of an image tube according to one preferred embodiment of the present invention.
[0011] In Fig. 2, the output fluorescent screen structure (1) is constituted by causing a glass substrate (5) coated with an output fluorescent screen (4), to closely adhere onto the inner face of an output glass pane (3) of the image tube main body through a transparent bonding material (6).
[0012] It should be noted here that, in the above case, the thickness (t) of the laminated structure thus constituted is set to such an extent as is sufficient to cause a total reflection light (L2) emitted at a peripheral portion (So) of an effective visual field of said fluorescent screen (4) and incident into the laminated structure, to reach the outer side of a concerned or interested region (S ) of the output fluorescent screen (4) which becomes an important portion, for example, in a medical diagnosis.
[0013] Normally, in the case where examination and photographing by X rays or fluorescopy are effected in the medical field, with respect to the portion which will become the concerned region in the output imape, the image at the region (S1) in the range of 10 to 12 mm in diameter at the central portion constitutes an important portion for the diagnosis, for example, when an effective visual field diameter (D) of the output image is 22 mm. Thus, 20 ~ 30 % of the central area of such a photographed area is of concern to the medical field. Accordingly, for improving the contrast of the output image at said concerned region (S1), it may be so arranged that the reflected light (L2) directed towards the output fluorescent screen (4) reaches the outer side beyond the concerned region (S1) in the range of 10 to 12 mm at the center of the output fluorescent screen (4). For the above purpose, the arrangement may be so made that the thickness (t) of the entire laminated structure in the above case is set to be larger than approximately 9 mm based on an equation t = X/(2·tan θ) representing the relation between the thickness (t) and(X) as shown in Fig. 2, where (X) represents a distance between a light emitting point (P ) on the output fluorescent screen (4) and a reaching point (PI) at which the visible ray in the light emitting point (P ) subjected to the total reflection at the outer side face of the output window glass pane (3) again returns back to the output fluorescent screen (4), and (θ) denotes a critical angle at a boundary face (3') between the output glass pane (3) and air when the refractive indexes of the respective layers are assumed the same.
[0014] Meanwhile, since the plate thickness of the output window glass pane (3) of the image tube main body is normally in the range of 4 to 5 mm, if the remaining plate thickness in the order of 4 to 5 mm is supplemented by the thickness of the transparent bonding material (6) and the glass substrate (5), it is possible to lead the total reflection light (L2) at the boundary face (3') between the output window pane (3) and air, towards the outer side of the concerned region (S1) of the output fluorescent screen (4) described earlier for the improvement of the contrast at said image portion (S1).
[0015] Referring to Fig. 3, there is shown a modification of the foregoing embodiment. In this modification, another transparent glass plate (7) is further arranged to closely adhere to the outer side face of the output window glass pane (3) by the transparent bonding material (6).
[0016] ln this case, the thickness of the laminated structure required for the improvement of the contrast of the output image may be shared by the thickness of the transparent glass plate (7), and therefore, the thickness of the glass substrate (5) can be reduced still further.
[0017] The reflection at the outer side face of the output window also degrades the contrast of output image. In this case, although application of a non-reflecting coating directly onto the outer side face of the output window glass pane (3) will become difficult owing to the large size of the image tube main body, such a purpose may be readily achieved in this case by causing the transparent glass plate (7) preliminarily applied with a non-reflecting coating, to closely adhere to the outer side face of the output window glass plate (3). In the drawings, the numeral (8) represents a metal hack layer.
[0018] It should be noted here that, for the transparent bonding material (6) to be employed in the foregoing embodiments, proper materials capable of maintaining durability even under a state of high vacuum and the same refractive index as the using glasses, for example, silicone rubber or the like, may be employed.
[0019] As is clear from the foregoing description, according to the present invention, since the output fluorescent screen structure is constituted by the laminated structure formed by close adhesion between the glass substrate and the output window glass pane, it is possible to arrange the plate thickness of the output fluorescent screen structure necessary for the improvement of the contrast in the output images, to be shared by the glass base plate and the output window glass pane. Therefore, it becomes unnecessary to employ a thick plate for the glass substrate to be coated with the output fluorescent screen, and thus, various problems in the aspect of manufacture involved in the case of production of the output fluorescent screen through employment of a thick glass substrated, can be advantageously avoided.
(1) An image tube having an output fluorescent screen structure for producing, an
output image thereon, said output fluorescent screen structure comprising a transparent
glass substrate coated with a fluorescent screen, and an output window glass pane
of a main body of said image tube, said transparent glass base plate and said output
window glass pane being arranged to closely adhere to each other by a transparent
bonding material so as to form a laminated structure thereby, said laminated structure
being set, in its thickness, to such an extent as is sufficient to cause a total reflection
of light emitted at a peripheral portion of an effective visual field of said fluorescent
screen and incident upon the laminated structure, to reach outside a concerned region
within said effective visual field of said output fluorescent screen.
(2) An image tube as set forth in claim 1, wherein the effective area includes a concerned
area in its central portion which comprise 20 ~ 30 % of the effective area.
(3) The main body of such image tube as set forth in claim 1, wherein a tranparent
glass substrate is bonded to the outer surface of the output glass pane by application
of a transparent bonding material.
(4) An image tube wherein the transparent glass substrate as set forth in claim 3
is provided with a non-reflective coating on its outer surface.