FLUORESCENT DISPLAY TUBE

Abstract: A fluorescent display tube adapted to a large screen display. It has an enlarged area on which electron beams impinge, and also eliminates the effect of electric field near the glass wall of the fluorescent display tube (1) upon the electron beams, enabling the phosphor segments R, G and B to be arranged at positions close to the peripheral side wall (13) of the tube. Therefore, the light-emitting area is increased to obtain bright display. Furthermore, the distances between neighboring phosphor segments of the RGB trio on the neighboring fluorescent display tubes (1) are shortened, and the distances between the trios are shortened in each of the fluorescent display tubes (1). Therefore, the pitch is shortened as a whole in the phosphor trio arrangement in the large-screen display system, thus contributing to improving resolution.

Description: The present invention relates to a fluorescent display tube and, particularly, to a fluorescent display tube for constituting a display device having a large size display screen formed of a plurality of the fluorescent display tubes by arranging display tubes in horizontal and vertical directions. In order to provide a large size display screen, for example a large size colour display screen, a display device has been proposed whose front and side views are shown in Figs. 1 and 2 respectively. As shown, the display device includes a plurality of fluorescent display tubes 1 arranged in rows and columns (i.e., in a vertical direction Y and a horizontal direction X). Each fluorescent display tube has a fluorescent surface on which 16 fluorescent segment trios, each including, for example, red, green and blue fluorescent segments R, G and B, are arranged. That is, 48 fluorescent segments R, G and B are arranged in two lines (rows) and 8 columns to form a large size display screen. A colour image display is provided on the large size display screen by selectively exciting the respective fluorescent segments thereon according to display information. In this case, an interval De between adjacent fluorescent segments, for example trios of adjacent fluorescent display tubes 1, tends to be large. This is partly due to a lower limit on the interval resulting from the thickness of the peripheral wall of the fluorescent tubes and/or the thickness of a portion in which lead wires 2 from, for example, side faces of the respective fluorescent display tubes 1 are arranged as shown in Fig. 2, and partly due to restriction of the range of the fluorescent segment to which electron beam bombardment is possible. Since, in order to achieve a uniform display in a large display screen, an interval Ds between the fluorescent trios in each fluorescent display tube is necessarily selected to be substantially the same as the interval De between the trios of adjacent fluorescent display tubes, it is desired to make the interval De between the trios in adjacent display tubes as small as possible to obtain higher resolution on the large display screen. Therefore, it is required to arrange the fluorescent segment trios in the respective fluorescent display tubes as close to the glass peripheral wall surface of the tube in the horizontal direction as possible. When the fluorescent segments are arranged in the vicinity of the glass tube surface, an electron beam path directed thereto is necessarily close to the glass wall surface and thus the electron beam tends to be influenced by an unstable electric field produced by electric charges accumulated on the glass wall surface, (i.e., insulating wall surface). Further, the possibility of collision of the electron beam with the wall surface is increased causing the instability of electric field therearound to be increased. This problem is enhanced for fluorescent segments located at the outermost ends in a horizontal direction when the respective fluorescent segments take the form of vertically extending stripes. In fluorescent display tubes used in such a display device, since respective fluorescent segments are fine, it is preferable, for simplicity of construction, to arrange a common line-shaped cathode over a plurality of fluorescent segments, for example each trio of fluorescent segments. In such a case, the line-shaped cathode is supported under tension by fixing both ends thereof to a mounting portion. Therefore, the temperature distribution in the cathode when it is heated exhibits a high temperature around a centre portion of the cathode and a low temperature around the end portions due to heat dissipation in the connections of the end portions to the mounting portion. This means that electron emission density in the centre portion is large while that in the opposite end portions is low. Consequently, even if a heating condition is set such that the temperature in the centre portion of the cathode during operation achieves a value at which electron emission is saturated, it does not become saturated in the opposite ends of the cathode, resulting in a difference in luminance of fluorescent segments opposing the centre portion and those opposing the end portions. Further, in the opposite end portions which are easily influenced by current supply to the cathode (heater), luminance of the segments corresponding to the opposite end portions of the cathode is varied, resulting in problems of difficulty of obtaining white balance and/or instability thereof. Even if one cathode is provided for each segment, uniformity and stability of luminance in the segment is degraded for the same reason. Further, in such fluorescent display tubes, since there is a difference in light emitting efficiency among fluorescent materials for red, green and blue fluorescent segments R, G and B, white balance is obtained by, for example, making the width of through-holes of respective grids G1 - G3 for transmission of electron beams different from one another. Therefore, it is very difficult to obtain white balance by compensating for electron emission efficiency due to non-uniformity of temperature of the cathode K while keeping the width difference as it is. Japanese Patent Application No. JP-A-60 158 779 discloses a luminescent display cell for a display tube of the general type described above. The cell includes a separator electrode disposed between a fluorescent trio and the cathodes and grids of an electron beam control mechanism. The separator has walls arranged between adjacent segments and on each side of the trio to shield the segments from electron beams directed to adjacent segments. The separator walls, all of which are of the same height, also serve as a diffusion lens to spread the electron beam from each cathode so that the electron beam is radiated throughout the corresponding segment. Patent Abstracts of Japan, Vol. 11, No. 384, (E-256) [2831], December 15, 1987 and JP-A-62 150 640 disclose a flat matrix type cathode ray tube in which an electroconductive layer of carbon or the like is applied to the inner surface of the glass side walls of a display tube adjacent the fluorescent plane. The electroconductive layer extends towards the cathodes beyond the height of the partitioning walls between the fluorescent elements. The layer supplements the function of the partitioning walls as acceleration electrodes to even out electron beam diffusion and prevent decreased luminosity adjacent the side walls. UK Patent Application No. GB-A-2 170 351 discloses a fluorescent display tube according to the pre-characterising portion of claim 1. According to the present invention there is provided a fluorescent display tube, comprising: a fluorescent plane within a flat type container having opposing first and second panels and a peripheral side wall, the fluorescent plane being formed by arranging fluorescent segments on an inner surface of said first panel; an electron beam control mechanism provided in opposed relation to said fluorescent plane for directing electron beams to respective fluorescent segments; and a separator electrode arranged between said fluorescent plane and said electron beam control mechanism and having partitioning walls between said fluorescent segments, a protruded side wall being provided on the separator electrode in a portion of the container in which the fluorescent segments are disposed in proximity to the peripheral side wall, said protruded side wall extending towards the electron beam control mechanism in opposed relation to the peripheral side wall; characterised in that the protruded side wall has a height higher than that of the partitioning walls of the separator electrode, and in that a further protruded side wall is provided on a low voltage electrode of the electron beam control mechanism in said portion of the container in which the fluorescent segments are disposed in proximity to the peripheral side wall, said further protruded side wall extending towards the separator electrode in opposed relation to the peripheral side wall. The electron beam control mechanism may comprise cathodes and grids for directing electron beams to the fluorescent segments, each of said cathodes comprising a linear cathode for each of the fluorescent segments or for a plurality of said fluorescent segments commonly, and side walls may be provided on a first grid of said grids opposing the linear cathodes, said side walls extending towards both end portions of the linear cathodes. The present invention makes it possible to improve resolution of a large screen display device by enlarging the electron impinging area for fluorescent segments in the vicinity of a peripheral wall of a tube to thereby increase the light emissive area of the segments and obtain a bright display, and, further, by making the inter-trio interval De of adjacent fluorescent segments of adjacent fluorescent display tubes, and hence the inter-trio interval Ds, small enough to thereby minimize the arranging pitch of fluorescent trios in the large screen display device as a whole. Further, the present invention makes it possible to arrange fluorescent segments as close to the peripheral wall of the container as possible by avoiding influence of the electric field around a glass peripheral wall surface on the electron beam. With such an arrangement, the inter-trio interval of the fluorescent segments is made small enough and thus resolution of the large screen display device is improved. Further, the present invention aims to improve uniformity of light emission in the segments and improve and stabilize white balance by obtaining substantially uniform current density throughout the length of the cathode. In the accompanying drawings: Fig. 1 is a front view of a large screen display device, and Fig. 2 is a side view thereof; Fig. 3 is a cross sectional view of a main portion of a fluorescent display tube, and Fig. 4 shows a cross section thereof in an orthogonal direction thereto: Fig. 5 shows a potential distribution: Fig. 6 is a cross sectional perspective view of a main portion of an electron beam control mechanism of Fig. 3; Fig. 7 is a disassembled perspective view of the electron beam control mechanism; Figs. 8 to 10 are perspective views of a main portion of a separator electrode of display tubes embodying the invention; Fig. 11 is a cross sectional side view of a main portion of a fluorescent display tube according to an embodiment of the present invention; Fig. 12 shows a potential distribution of the main portion of the fluorescent display tube, and Fig. 13 shows a potential distribution of a main portion of a comparative example; Fig. 14 is a cross sectional perspective view of a main portion of an electron beam control mechanism of a fluorescent display tube embodying the present invention, and Fig. 15 is a potential distribution in a direction along the cross section in Fig. 3. Before describing an embodiment of the present invention, the general construction of a display tube to which the invention may be applied will be described with reference to Figs. 3 to 10. Fig. 3 shows a cross section of a main portion of the display tube in a horizontal (X) direction and in the direction of thickness of the tube, and Fig. 4 shows a cross section thereof in a vertical (Y) direction and in the direction of thickness of the tube. A flat type container 15, i.e., a tube, is defined by a light transmissive first panel 11, a second panel 12 in opposed relation to the panel 11, and a peripheral wall 13. The interior of the container 15 is kept in high vacuum. The first and second panels 11 and 12 are formed from rectangular glass panels. The glass peripheral wall 13 consists of four side walls between the glass panels 11 and 12, all three being sealed with glass frit 14 to form the flat type container 15. A fluorescent plane 16 is provided on an inner surface of the first panel 11, and is formed by an arrangement of fluorescent segments, for example, red, green and blue fluorescent segments R, G and B. The fluorescent plane 16 is formed by arranging a plurality, for example 2 rows and 8 columns, of fluorescent trios, each trio being composed of red, green and blue fluorescent segments R, G and B, giving a total of 48 segments. Between the respective segments R, G and B, a light absorbing layer 20, such as a carbon coating layer, etc., is provided, and a metal back layer (not shown), such as a Aℓ, vapour-deposition membrane or the like, is formed to cover the whole fluorescent plane. An electron beam control mechanism 17 is provided in opposed relation to the fluorescent plane 16 for directing an electron beam to the respective fluorescent segments, R, G and B. Between the electron beam control mechanism 17 and the fluorescent plane 16, a separator electrode 19 is arranged. The separator electrode 19 includes partition walls 19A for partitioning spaces in front of the respective fluorescent segments R, G and B to avoid mutual interference of electron beams directed to the respective fluorescent segments R, G and B. The separator electrode 19 includes a protruded wall 19B which protrudes from a portion of the partition wall 19A at least in positions in which the fluorescent segments R, G and B are to be arranged in the vicinity of the peripheral wall 13, i.e., along the two sides of the peripheral wall which extend in the horizontal X direction. The protruded wall 19B has a height h2 which is higher than the height h1 of the other walls 19A. The separator electrode 19 has, as shown, for example, in Fig. 8, partition walls 19A having a height h1 and the protruded wall 19B having a height h2, higher than h1, formed by punching and bending up of a metal plate. The separator electrode 19 has, as shown in Fig. 3, a mounting piece 21 protruding from the peripheral wall which is fixed by, for example, glass frit 50 to the panel 11 and supported thereby. The electron beam control mechanism 17 provided in opposed relation to the fluorescent plane 16 has, as shown by the partially cut-away main portion in Fig. 6 and by the disassembled perspective view thereof in Fig. 7, a construction in which the cathode K, a first grid G1, a second grid G2 and a third grid G3 are arranged in a plane and in order toward the side of the fluorescent plane 16. The third grid G3 is composed of a lamination of a third grid frame F3, made of, for example, a metal plate, and a third grid main body M3 made of a thin metal plate. The frame F3 has through-holes H each being common to a trio of the red, green and blue fluorescent segments R, G and B of the fluorescent plane 16. Further, the third grid main body M3 is provided with mesh type through-holes H 3R , H 3G and H 3B , formed by photolithography, corresponding in position to the through-holes H F3 of the frame F3 in opposed relation to the respective fluorescent segments R, G and B. The third grid main body M3 i s mounted on the third grid frame F3 such that the through-holes H 3R , H 3G and H 3B thereof coincide with the through-holes H F3 of the frame F3 and, on the third grid main body, a first insulating spacer S1, made of ceramic or the like, which is common to, for example, four adjacent sets of trios arranged in 2 rows, is mounted. The first insulating spacer S1 has through-holes H s1 corresponding to the respective through-holes H F3 of the frame F3 and two protrusions 23₁ and 23₂ extend vertically in the Y direction between the through-holes H S1 (in the illustrated example, paired through-holes) in a common column, that is, in a vertical direction Y. On the third grid main body M3, the second grid G2 is arranged through the respective spacers S1. The second grid G2 has strip type parallel electrodes 24R, 24G and 24B common to a column of the respective mesh type through-holes H 3R , H 3G and H 3B of the third grid main body M3. The respective strip shaped electrodes 24R, 24G and 24B are formed by photolithography, for example, with paired mesh type through-holes H 2R , H 2G and H 2B corresponding to the paired through-holes H 3R , H 3G and H 3B in a common column in the Y direction of the frame M3. Opposite ends of the strip electrodes 24R, 24G and 24B become respective leads 24L, and they are connected at their outer ends by a frame portion 24F to form a lead frame before assembling. This lead frame is formed by photolithography, for example. The lead frame is mounted on the third grid G3 through the respective spacers S1 such that the protrusions 23₁ and 23₂ of the spacers S1 come in between the respective strip electrodes 24R, 24G and 24B, and the frame portion 24F is removed after assembling of the electron beam control mechanism 17 to electrically separate the respective electrodes 24R, 24G and 24B. On the lead frame of the second grid G2, the first grid G1 is mounted through a second insulating spacer S2 which is made of an insulating material such as ceramic or the like and serves also as a cathode support, in a similar manner. The second insulating spacer S2 is arranged, in a similar manner to the first insulating spacer S1, to be common to, for example, four adjacent fluorescent trios arranged in two rows and two columns, and has through-holes H s2 corresponding to the respective through-holes H F3 of the frame F3 of the third grid G3. On both sides of the respective through-holes H S2 , paired protrusions 25₁ and 25₂, which are integral with the spacer, are provided. The respective protrusions 25₁ and 25₂ are formed with a cathode support fitting portion 26 comprising a through-hole or groove open end at an end face of the cathode K. The first grid G1 is formed by laminating a first grid main body M1, a shield plate S H1 and a first grid frame F1 in order. The first grid main body M1 has, for example, mesh type through-holes H 1R , H 1G and H 1B , formed, for example, by photolithography, opposed to the respective mesh type through-holes H 3R , H 3G and H 3B and H 2R , H 2G and H 2B of the third grid G3 and the second grid G2. The shield plate SH₁ of the first grid G1 is common to four trios each including, for example, mesh type through-holes H 1R , H 1G and H 1B , that is, four adjacent trios arranged in two rows and two columns, and is formed by punching and bending, for example, a metal plate. The respective shield plates SH₁ are formed with side walls 27₁ and 27₂ at positions opposed to the mesh type through-holes H 1R , H 1G and H 1B of the first grid main body M1. The side walls 27₁, 27₂ extend in the vertical direction Y on both sides of the trio of through-holes H SH1R , H SH1G and H SH1B and are formed by bending up the metal plate. Side walls 27₃ are also formed similarly between the outer ends of the side walls 27₁, 27₂ by bending up the metal plate. The frame F1 of the first grid can be similarly formed by punching and bending a metal plate common to a plurality of shield plates S H1 . The first grid main body M1, the shield plate S H1 and the frame F1 constituting the first grid G1 are mounted sequentially on the second insulating spacer S2 such that the protrusions 25₁ and 25₂ of the spacer S2 protrude between the trios of the respective through-holes. Metal pieces 28 for mounting the cathode are inserted into the fitting portions 26 of the respective protrusions 25₁ and 25₂ of the spacer S2 such that they ride across the end faces of the protrusions 25₁ and 25₂ of adjacent through-holes H S2 . The cathode K takes the form of, for example, cathode material affixed by, for example, spraying it on a spiral heater extending, for example, linearly, and has opposite ends directly welded to the metal pieces 28. Alternatively, the cathode can be formed, as shown in Fig. 7, by initially extending the cathode heater tightly on, for example, a cathode support member 29 and, after spraying with cathode material, welding the metal pieces 28 to the opposite ends of the cathode heater and then cutting the cathode holder 29 at a position such as is shown by the chain line a between the opposite ends of the respective cathodes K to achieve electrical separation between the ends. The frame F3, the third grid main body M3 and the first insulating spacer S1 constituting the third grid G3, the lead frame F2 and the second insulating spacer S2 constituting the second grid G2, the first grid main body M1, and the shield plate S H1 and the frame F1 constituting the first grid G1 are stacked in order and caulked together with metal grommets (not shown) through the respective through-holes thereof. In this case, the insertion holes of the first grid G1 and the third grid G3 for the grommets for caulking are made larger in size alternately so that no electrical connection is provided by the metal grommets between the respective grids G1 - G3. The electron beam control mechanism 17 formed by integrating the cathode K and the first to third grids G1 - G3 as a unit is supported mechanically by leading out the leads 24L of the second grid G2 through the frit portion between the panel 12 and the peripheral wall 13, and the lead is derived externally of the container 15. Incidentally, in this case, as shown in Fig. 7, the frame portion 24F of the lead frame F2 constituting the second grid G2 is provided with a lead 31 which is connected to a terminal of the cathode K or the third and first grids G3 and G1 and welded to the electrodes G1, G3 corresponding thereto or the cathode holder 29 or the metal piece 28 in assembling the electron beam control mechanism 17. The lead 31 is derived, together with the leads 24L, through the frit portion of the container 15 as shown in Fig. 3. Further, on an inner surface of the second panel 12, a rear surface electrode 32 is formed, for example by a carbon coating layer etc., and is electrically connected to the first grid G1 by a resilient contact of a metal resilient piece 33 mounted on, for example, the first grid G1. On the other hand, for example, a high voltage lead 34 penetrates a centre portion, for example, of the flat type container 15. The inner end of the lead 34 is electrically connected to the separator electrode 19 to derive a terminal. With the construction described above, a high voltage, for example 5 KV, is applied through the high voltage lead 34 to the fluorescent plane 16 and the separator electrode 19. Further, a voltage, for example of 10 V, is applied through the lead 31 to the first grid G1 and the rear surface electrode 32, and a low potential, for example 0 V, is applied to the third grid G3. To the second grid G2, a voltage is selectively applied through the lead 24L which voltage is 15 V when it is in the ON state and -2 V when it is in the OFF state. By modulating respective electron beams toward the respective fluorescent segments R, G and B by means of this ON, OFF switching of voltage to the strip electrodes 24R, 24G and 24B of the second grid G2 and selection of voltage applied to the cathode K, the respective fluorescent segments emit light in, for example, line sequence. The fluorescent display tube described above can provide a colour display on a large screen by arranging a number of such tubes in a flat plane as mentioned with respect to Figs. 1 and 2. In the construction described above, a low potential, for example O V, is applied to the electrode on the fluorescent plane side of the electron beam control mechanism 17, for example the third grid G3. By applying an anode voltage, that is a fluorescent plane voltage, which is a high voltage of, for example, 5 KV to the separator electrode 19, equipotential lines in front of the separator electrode 19 are bent relatively substantially in the vicinity of the protruded side wall 19B of the separator electrode 19 as shown schematically by thin line a in Fig. 5. An electron beam b entering into this portion is deflected outwardly, that is toward the protruded side wall 19B, with respect to the vertical Y direction. That is, the range of possible electron beam impingement on the first panel 11 is enlarged. Thus, one purpose of the separator electrode 19 is to avoid mutual interference of electron beams directed toward the respective fluorescent segments R, G and B and the respective electron beams follow substantially straight lines in emitting directions from the electron beam control mechanism 17 toward the respective fluorescent segments R, G and B without being considerably deflected by the separator electrode 19. In the construction described above, however, in a peripheral portion of the fluorescent plane adjacent the peripheral wall 13 in which there is the protruded side wall 19B whose height h2 is higher than the height hl of other portions of the separator, the beam diverges towards the peripheral wall 13. Thus, in the electron beam path which the protruded side wall 19B faces, the electron beam is deflected towards the protruded side wall 19B to which the high voltage is applied to thereby diverge the electron beam. It is therefore possible to arrange the fluorescent segments in positions very close to the peripheral wall 13. Therefore, as described with reference to Fig. 1, where a large screen display device is constructed by arranging a plurality of adjacent fluorescent display tubes 1, the interval De between the adjacent fluorescent segments (trios), and hence the interval Ds, can be small enough, resulting in high resolution. The separator electrode 19 is not limited to the particular example shown in Fig. 8 referred to above. It is possible to use a construction in which the height is gradually changed from the protruded side wall 19B having height h2 to the partition wall 19A having height hl as shown in Fig. 9. Further, although, in the examples shown in Figs. 8 and 9, a set of separator electrodes 19 is common to the fluorescent segments on respective lines, it is possible to provide a set of separator electrodes 19 for each trio as shown in Fig. 10, or to provide a set of separator electrodes 19 for a plurality of trios. Further, although, in the above mentioned example, the reduction of the interval De is performed by enlarging the electron beam impinging range in only the vertical direction Y, it is possible to obtain a similar construction in the horizontal X direction by combining it with means for varying a segment pitch of the electrode portion. Further, although, the above described example relates to a colour display in which the respective fluorescent segments are formed by red, green and blue fluorescent segments R, G and B, the invention can be applied to monochromatic or various colour displays. Further, although, in the example mentioned above, the flat type container 15 is formed by the first and second panels 11 and 12 and the peripheral wall 13 all of which are welded by frit, it can be modified in various ways, for example, by constituting the peripheral wall 13 and, for example, the first panel 11 as a unit. An embodiment of the invention will be now described. As shown in Fig. 11 the main portion of the fluorescent display tube of this embodiment is similar to that described above. Duplication of explanation will therefore be avoided. In this embodiment, a protruded side wall 19B is provided on the separator 19 in a portion of the container 15 in which fluorescent segments R, G and B are arranged in the vicinity of a peripheral side wall 13, and in particular on both sides of the container in the horizontal direction X. The protruded side wall 19B is arranged in opposed relation to the peripheral side wall 13, and has a height h2 which is larger than that of the partition walls 19A in other portions of the separator. In addition, as shown in Fig. 14, which shows a partly cut-away perspective view, in the mentioned portion of the container 15, a protruded side wall 18A is provided on a low voltage electrode (in the example shown, a third grid G3) of an electron beam control mechanism 17. The protruded side wall 18A extends along the peripheral side wall 13 and towards the separator electrode 19. In this case, the provision of the separator electrode 19, to which an anode voltage (that is, a fluorescent plane voltage) which is a high voltage of, for example, 5 KV is applied, and the protruded side walls 19B and 18A on the separator 19 and the low voltage electrode G3 arranged in opposed relation to the peripheral side walls 13, enables the influence of electric field due to the peripheral side wall 13 on the electron beam path, and also distortion of electron beam path, to be avoided. That is, where the influence of the peripheral side wall 13 is reduced by providing only the protruded side wall 19B on the separator electrode 19 to which a high voltage is applied, the equipotential lines in the vicinity of the protruded side wall 19B may be sharply bent as shown in Fig. 13, so that the electron beam b is deflected outwardly, that is, towards the protruded side wall 19B, resulting in the disadvantage that the electron beam impinges on the protruded side wall 19B. According to the present embodiment, the protruded side wall 18A on the low voltage electrode, for example the third grid G3, to which a low voltage is applied subjects the electron beam b to an inward deflection as shown in Fig. 12, and it is possible to cancel the deflection due to the protruded side wall 19B to which a high voltage is applied. The electron beam b can therefore be substantially straight. As described, according to the present embodiment, it is possible to avoid the influence of unstable charge accumulation on a glass plane of the peripheral side wall 13 of the container 15 on the electron beam path, and to avoid an undesirable electron beam deflection by providing the protruded side walls 19B and 18A on the high voltage separator electrode 19 and the low voltage electrode G3 in the fluorescent tube. Therefore, it is possible to reduce the interval De mentioned with respect to Fig. 1 and to thereby reduce the interval Ds between adjacent segment trios of each fluorescent display tube. Thus, in a large screen display, resolution is improved and colour deviation etc. due to unstable deflection of the electron beam is avoided, resulting in an image projection with high image quality. Although, in the example described above, the protruded side walls 19B and 18A are provided on both sides of the container 15 in the horizontal direction X, that is, extending along the vertical direction Y, it is possible to use a similar construction for side surfaces in other directions. As shown in Figure 11, among a group of grids a first grid G1 which opposes the cathodes is formed with opposing side walls 27₁ and 27₂ extending towards the opposite end portions of respective cathodes K, such that the side walls 27₁, 27₂ protrude on either side of the cathode K in directions orthogonal to the extension of the cathode K. In this construction, a low voltage of, for example, 0 V is applied to electrodes on a fluorescent plane side of an electron beam control mechanism 17, for example to a third grid G3, an anode voltage, that is, a fluorescent plane voltage, which is a high voltage of, for example, 5 KV is applied to a separator electrode 19, and a voltage of, for example, 10 V is applied to the first grid G1. Due to the side walls 27₁ and 27₂ of the first grid G1 which are at the opposite ends of the cathode K, an electric field which acts to diverge the electron beam outwards is produced in front of the cathode K as shown by the thin line a in Fig. 15. Therefore, an electron beam emitted from the centre of the cathode K is deflected outwardly, so that the electron density in the centre is reduced while that in the opposite end portions is increased. Therefore, a low emission density due to low temperature at the opposite end portions of the cathode K is compensated by the current density distribution. That is, it is possible to obtain a substantially uniform current density throughout the length of the cathode K and, therefore, it is possible to improve the uniformity of light emission in the segments, improve white balance and stabilize the operation. Thus, in a large screen display, it is possible to project an image with high white balance.

Claims: A fluorescent display tube, comprising: a fluorescent plane (16) within a flat type container (15) having opposing first and second panels (11,12) and a peripheral side wall (13), the fluorescent plane (16) being formed by arranging fluorescent segments (R,G,B) on an inner surface of said first panel (11); an electron beam control mechanism (17) provided in opposed relation to said fluorescent plane (16) for directing electron beams to respective fluorescent segments (R,G,B); and a separator electrode (19) arranged between said fluorescent plane (16) and said electron beam control mechanism (17) and having partitioning walls (19A) between said fluorescent segments (R,G,B), a protruded side wall (19B) being provided on the separator electrode (19) in a portion of said container (15) in which the fluorescent segments (R,G,B) are disposed in proximity to the peripheral side wall (13), said protruded side wall (19B) extending towards the electron beam control mechanism (17) in opposed relation to the peripheral side wall (13); characterised in that the protruded side wall (19B) has a height (h2) higher than that of the partitioning walls (19A) of the separator electrode (19), and in that a further protruded side wall (18A) is provided on a low voltage electrode (G3) of the electron beam control mechanism (17) in said portion of the container (15) in which the fluorescent segments (R,G,B) are disposed in proximity to the peripheral side wall (13), said further protruded side wall (18A) extending towards the separator electrode (19) in opposed relation to the peripheral side wall (13). A fluorescent display tube as claimed in Claim 1, wherein the electron beam control mechanism (17) comprises cathodes (K) and grids (G1-G3) for directing electron beams to the fluorescent segments (R,G,B), each of said cathodes (K) comprising a linear cathode (K) for each of said fluorescent segments (R,G,B) or for a plurality of said fluorescent segments (R,G,B) commonly, and wherein side walls (27₁, 27 2) are provided on a first grid (G1) of said grids (G1-G3) opposing the linear cathodes (K), said side walls (27₁, 27₂) extending towards both end portions of the linear cathodes (K).

Inventors: HAYASHI MASATAKE, MAEDA MAKOTO, HAYASHI, MASATAKE, MAEDA, MAKOTO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1989
Main classification: H01J31
IPC codes: H01J31