Patent Grant
7902735
This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-118661, filed on Apr. 30, 2008, the entire contents of which are incorporated herein by reference.
The present invention relates generally to a gas discharge tube for a display device and, more particularly, to such a gas discharge tube in which reduction of light-emission at end portions thereof is improved.
In a known plasma display panel (PDP), plasma discharge is generated in closed discharge spaces of a large number of small cells arranged in length and width directions of the panel, and phosphor materials are excited by ultraviolet light of 147 nm emitted from the discharged plasma, to thereby emit light. The cell spaces are formed between two planar glass plates disposed one on the other. On the other hand, in a known plasma tube array (PTA), as disclosed in Japanese Patent Application Publication No. 2003-92085-A, a phosphor layer is formed within a thin, elongated glass tube in which a large number of cell spaces are formed. A large-sized display screen of 6 m×3 m, for example, can be provided by arranging a number of such plasma tubes side by side.
Japanese Patent Application Publication No. 2006-164635-A (which corresponds to US Patent Application Publication No. 2006/119247 A1) describes a method of manufacturing a gas discharge tube for a display device. In this method, an opening of a glass tube is closed by forming a glass layer with outer peripheral shape identical to the outer peripheral shape of the glass tube on an end face of the glass tube. An open end face of the glass tube is pressure-welded to a dry film containing a low-melting-point glass powder and a binder resin. The glass tube is then lifted up to transfer the dry film portion to the end face of the glass tube, to thereby close the opening of the glass tube. A phosphor support member is inserted into the glass tube through an opening on a side opposite to the end face and then an end of the phosphor support member is adhered to the dry film portion. The binder resin is burnt off, and the dry film is vitrified to produce a low-melting-point glass layer.
Japanese Patent Application Publication No. 2006-140075-A describes a method of manufacturing a gas discharge tube and a display device. The gas discharge tube includes a thin tube having a discharge space therein and an electron emissive coating formed within the thin tube. The thin tube has a display surface on which a pair of display electrodes is adapted to be disposed, and has a rear surface on which a signal electrode is adapted to be disposed. A surface portion facing toward the display surface is formed within the thin tube at a location nearer to the display surface from the midway between the display and rear surfaces. An electron emissive coating is formed on the surface portion. Thus the gas discharge tube can reduce its firing voltage.
In accordance with an aspect of an embodiment, a gas discharge tube includes: an elongated tube within which an electron-emissive film and a phosphor layer are formed, and which is filled with a discharge gas and sealed; a plurality of pairs of display electrodes disposed on a display side of the elongated tube; a signal electrode disposed on a rear side of the elongated tube; and an elongated support member inserted into the elongated tube and extending in the length direction of the elongated tube. The support member has a curved shape so that a curved inner surface thereof forms a discharge space, has longitudinally extending opposite edges, and has a phosphor layer formed on the inner surface of the support member. The support member further has an end wall at each of longitudinally opposite ends thereof. The end walls and the curved inner surface form an elongated depression in the support member.
In accordance with another aspect of the embodiment, a display device includes a plurality of such gas discharge tubes as above-described.
Additional objects and advantages of the embodiment will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The invention will be described in connection with non-limiting embodiments with reference to the accompanying drawings. Throughout the drawings, similar symbols and numerals indicate similar items and functions.
It is not practical to manufacture a large-sized plasma display device by the use of a single, large-sized array of plasma tubes arranged between front and rear support plates. A large-sized display device may be advantageously manufactured relatively easily by arranging, side by side, a plurality of separate or divided plasma tube array units or modules and by assembling the plasma tube array units.
The inventors have recognized that brightness or luminosity of a displayed image is lowered at end portions of plasma or gas discharge tubes near the seams or joints between adjacent arrays of plasma tubes.
An object of the present invention is to suppress the lowering of luminosity in the vicinity of end portions of gas discharge tubes.
According to the invention, the lowering of luminosity in the vicinity of end portions of gas discharge tubes can be suppressed.
A thin elongated tube 20 for the thin elongated plasma tubes 11R, 11G and 11B is formed of a transparent, insulating material, e.g. borosilicate glass, Pyrex®, soda-lime glass, silica glass, or Zerodur. Typically, the tube 20 has cross-section dimensions of a tube diameter of 2 mm or smaller, for example a 0.55 mm high and 1 mm wide cross section, and a tube length of 300 mm or larger, and a tube wall thickness of about 0.1 mm.
Phosphor support members having respective red, green and blue (R, G, B) phosphor layers 4 formed or deposited thereon are inserted into the interior rear spaces of the plasma tubes 11R, 11G and 11B, respectively. Discharge gas is introduced into the interior space of each plasma tube, and the plasma tube is sealed at its opposite ends. An electron emissive film 5 of MgO is formed on the inner surface of the plasma tube 11R, 11G, 11B. The phosphor layers R, G and B typically have a thickness within a range of from about 10 μm to about 30 μm.
The support member 6 has generally a shape of a trough or boat having a generally U-shaped or C-shaped transverse cross-section. Similarly to the plasma tubes 11R, 11G and 11B, the support member 6 is formed of a insulating material, e.g. borosilicate glass, Pyrex®, silica glass, soda-lime glass, or lead glass, and has the phosphor layer 4 formed thereon. The support member 6 can be disposed within the glass tube by applying a paste of phosphor over the support member 6 outside the glass tube and then baking the phosphor paste to form the phosphor layer 4 on the support member 6, and then inserting the support member 6 into the glass tube. As the phosphor paste, a desired one of various phosphor pastes known in this technical field may be employed.
The electron emissive film 5 emits charged particles, when it is bombarded with the discharge gas. When a voltage is applied between the pair of display electrodes 2, the discharge gas contained in the tube is excited. The phosphor layer 4 emits visible light by converting thereinto vacuum ultraviolet radiation generated in the de-excitation process of the excited rare gas atoms.
The signal electrodes 3 are formed on the front-side surface, or inner surface, of the rear support plate 32, and extend along the longitudinal direction of the plasma tubes 11R, 11G and 11B. The pitch, between adjacent ones of the signal electrodes 3, is equal to the width of each of the plasma tubes 11R, 11G and 11B, which may be, for example, 1 mm. The pairs of display electrodes 2 are formed on the rear-side surface, or inner surface, of the front support plate 31 in a well-known manner, and are disposed so as to extend perpendicularly to the signal electrodes 3. The width of the display electrode 2 may be, for example, 0.75 mm, and the distance between the edges of the display electrodes 2 in each pair may be, for example, 0.4 mm. A distance providing a non-discharging region, or non-discharging gap, is secured between one display electrode pair 2 and the adjacent display electrode pairs 2, and the distance may be, for example, 1.1 mm.
The signal electrodes 3 and the pairs of display electrodes 2 are brought into intimately contact respectively with the lower and upper peripheral surface portions of the plasma tubes 11R, 11G and 11B, when the display device 10 is assembled. In order to provide better contact, an electrically conductive adhesive may be placed between the display electrodes and the plasma tube surface portions.
In plan view of the display device 10 seen from the front side, the intersections of the signal electrodes 3 and the pairs of display electrodes 2 provide unit light-emitting regions. Display is provided by using either one electrode of each pair of display electrodes 2 as a scan electrode, generating a selection discharge at the intersection of the scan electrode with the signal electrode 3 to thereby select a light-emitting region, and generating a display discharge between the pair of display electrodes 2 using the wall charge formed by the selection discharge on the region of the inner tube surface at the selected region, which, in turn, causes the associated phosphor layer to emit light. The selection discharge is an opposed discharge generated within each plasma tube 11R, 11G, 11B between the vertically opposite scan electrode and signal electrode 3. The display discharge is a surface discharge generated within each plasma tube 11R, 11G and 11B between the two display electrodes of each pair of display electrodes disposed in parallel in a plane.
The pair of display electrodes 2 and the signal electrode 3 can generate discharges in the discharge gas within the tube by applying voltages between them. The electrode structure of the plasma tubes 11R, 11G and 11B illustrated in
In
Now, one exemplary method for driving an AC gas discharge display device of the plasma tube array type is described. One picture typically has one frame period. One frame consists of two fields in the interlaced scanning scheme, and one frame consists of one field in the progressive scanning scheme. For displaying a moving picture in a conventional television system, thirty or sixty frames per second must be displayed. In displaying on the display device 10 of this type of AC gas discharge display device, for reproducing colors by the binary control of light emission, one field F is typically divided into or replaced with a set of q subfields SF's. Often, the number of times of discharging for display for each subfield SF is set by weighting these subfields SF's with respective weighting factors of 20, 21, 22, . . . , 2q-1 in this order. N (=1+21+22+ . . . +2q-1) steps of brightness can be provided for each color of R, G and B in one field by associating light emission or non-emission with each of the subfields in combination. In accordance with such a field structure, a field period Tf, which represents a cycle of transferring field data, is divided into q subfield periods Tsf's, and the subfield periods Tsf's are associated with respective subfields SF's of data. Furthermore, a subfield period Tsf is divided into a reset period TR for initialization, an address period TA for addressing, and a display or sustain period TS for emitting light. Typically, the lengths of the reset period TR and the address period TA are constant independently of the weighting factors for the brightness, while the number of pulses in the display period TS becomes larger as the weighting factor becomes larger, and the length of the display period TS becomes longer as the weighting factor becomes larger. In this case, the length of the subfield period Tsf becomes longer, as the weighting factor of the corresponding subfield SF becomes larger.
The inventors have discovered that the brightness at the ends of the plasma tubes or gas discharge tubes 11, 110, 112 tends to be lower. The inventors have recognized that lowering of brightness or image artifacts in the vicinity of the seam or joint between the adjacent PTA units 300 and 302 can be suppressed by preventing the lowering of brightness at the ends of the plasma tubes.
The inventors have also discovered that, when plasma tubes or PTA units are being handled during manufacture and/or transportation thereof, part of phosphor layers formed on support members at the ends of the plasma tubes may be peeled off due to contacting with, rubbing against, or impacting on other members. The inventors have further recognized that little or almost no light can be emitted from discharge cells lacking phosphors in end portions of the plasma tubes even when discharge occurs in inner discharge spaces of the plasma tubes.
The inventors have further recognized that, in discharge cells lacking part of phosphors at end portions of plasma tubes, discharge conditions, such as charging characteristics and inter-line capacitance, may change, which causes a firing voltage to increase. The inventors have further recognized that discharge cells in end portions of plasma tubes having higher firing voltage than other discharge cells may fail to discharge or, otherwise, emit little light.
Generally semicircular or semi-elliptical end walls 602 with respective generally U-shaped or C-shaped edges are secured to longitudinally opposite ends of a support member 6 (6R, 6G or 6B) disposed within each plasma tube 11.
The support member 6 has a curved surface shape or contour generally conformable to the inner surface of the plasma tube 11 so as to provide a discharge space inside. The curved surface of the support member 6 forms, together with the end walls 602 on the opposite ends of the support member 6, a trough having an elongated recess, depression or discharge space therein.
The plasma tube 11 has outer walls 112 at its longitudinally opposite ends. The thickness of each outer walls 112 is generally the same as that of the thin tube 20 of the plasma tube 11 (
The upper edge 602te of each end wall 602 is generally leveled vertically with the upper edge 6te of the support member 6 extending in the length direction of the support member 6, as illustrated in
The presence of the end walls 602 can prevent the phosphor layer 4 from peeling off in the vicinity of the ends of the support member 6, even when the ends of the support member 6 or its end walls 602 contacts, rubs against or hits against other members, e.g. the interior surface or the outer walls 112 of the plasma tube 11. Furthermore, the presence of the end walls 602 can prevent or suppress increase of the firing voltage of the discharge cells near the end walls 602, which may be caused by peeling off of part of the phosphor layer 4. This can prevent decrease in brightness or luminosity in the vicinity of the ends of the plasma tube 11, which may be caused by peeling off of the phosphor layer 4 in the end portions of the support member 6.
Each end wall 602 is made of the same material as the support member 6 or of a glass material having a low melting point, and is secured to the support member 6 by fusing a separate glass chip in the shape of the end wall 602, directly or with a glass material having a low melting point interposed to the inner surface of the associated end of the support member 6.
An end wall 604 having a generally similar shape to that of the end walls 602 illustrated in
The presence of the end walls 604 can prevent the phosphor layer 4 from peeling off in the vicinity of the ends of the support member 64, even when the ends of the support member 64 or its end walls 604 contacts, rubs against or hits against other members, e.g. the interior surface or the outer walls 112 of the plasma tube 11. Furthermore, the presence of the end walls 604 can prevent or suppress increase of the firing voltage of the discharge cells near the end walls 604, which may be caused by peeling off of part of the phosphor layer 4. This can prevent decrease in brightness or luminosity in the vicinity of the ends of the plasma tube 11, which may be caused by peeling off of the phosphor layer 4 in the end portions of the support member 64.
An end wall 602 similar to the one illustrated in
The presence of the end walls 602 can prevent the phosphor layer 402 on the inner surface of each end wall 602 and the phosphor layer 4 in the vicinity of the ends of the support member 62 from peeling off, even when the ends of the support member 62 or its end walls 602 contacts, rubs against or hits against other members. Furthermore, the presence of the end walls 602 can prevent or suppress increase of the firing voltage of the discharge cells near the end walls 602, which may be caused by peeling off of part of the phosphor layer 4. This can prevent decrease in brightness or luminosity in the vicinity of the ends of the plasma tube 11, which may be caused by peeling off of the phosphor layer 4 in the end portions of the support member 62.
In the embodiment illustrated in
An end wall 604 having dimensions similar to the ones of the end wall 604 illustrated in
The presence of the end walls 604 can prevent the phosphor layers 404 on the inner surface of each end wall 604 and the phosphor layer 4 in the vicinity of the ends of the support member 64 from peeling off, even when the ends of the support member 64 or its end walls 604 contacts, rubs against or hits against other members. Furthermore, the presence of the end walls 604 can prevent or suppress increase of the firing voltage of the discharge cells near the end walls 604, which may be caused by peeling off of part of the phosphor layer 4. This can prevent decrease in brightness or luminosity in the vicinity of the ends of the plasma tube 11, which may be caused by peeling off of the phosphor layer 4 in the end portions of the support member 64.
In the embodiment illustrated in
An end wall 604 and a phosphor layer 404 having dimensions similar to the ones of the end wall 604 and the phosphor layer 404 illustrated in
Alternatively, the plasma tubes illustrated in
The sum of the thickness of the end wall 604 and the thickness of the outer wall 112 is, for example, between 0.2 mm and 0.6 mm. Accordingly, the sum thickness of the two end walls 604 and the two outer walls 112 at the joint of the two adjacent PTA units 300 and 302 of
A region BR (e.g., a distance of BR=0.5 mm) in the vicinity of the outer wall 112 of the plasma tube 11 and the end wall 604 of the support member 64 does not contribute to discharging for display.
In order to provide a sufficient discharge space inside the support member 64 to thereby produce a sufficient spatial charge, the outer edge of the display electrode 2 is preferably located inward, in the length direction of the plasma tube 11, by at least a small distance Dsw (e.g., between about 10 μm and about 50 μm) from the inner surface of the end wall 604 (602).
A width Des of an end non-discharge region, between the outer surface of the outer wall 112 of the plasma tube 11 and the outer edge of the display electrode 2 in the vicinity of the end of the plasma tube 11, is preferably smaller than a so-called reverse or spacing slit width or non-discharge region width Ds between adjacent pairs of display electrodes 2, and is, for example, between 0.4 mm and 6 mm. Generally, the width Des of the end non-discharge region is preferably half or slightly smaller than the width Ds (e.g., between 0.9 mm and 1.5 mm) of the non-discharge region. This prevents picture distortion at the joint between the arrays of plasma tubes 11 or between the PTAs 110 and 112 of the adjacent PTA units 300 and 302.
The distance Ds′ between the display electrodes 2 closest to the joint between the two arrays of plasma tubes 11 adjacent in the length direction preferably is substantially equal to the width Ds of the non-discharge region between the adjacent pairs of display electrodes 2 for each plasma tube 11. This prevents picture distortion at the joint between adjacent PTA units 300 and 302.
When a plurality of plasma tubes or gas discharge tubes 11 like the ones illustrated in
The distance Ds′ between the display electrode 2 closest to the first ends 110e of the first group of plasma tubes 110 and the display electrode 2 closest to the second ends 112e of the second group of plasma tubes 112 is substantially equal to the distance Ds between adjacent two pairs of display electrodes of each plasma tube 11 of the first or second group of plasma tubes 110 or 112.
The region BR (e.g., a distance of BR=0.5 mm) in the vicinity of the outer wall 11 of the plasma tube 11 and the end wall 604 of the support member 64 does not contribute to discharging for display. However, by virtue of the presence of the phosphor layer 404 on the inner surface of the end wall 604, a discharge cell Ce in the vicinity of the end wall 604 of the support member 64 can provide generally the same luminosity as other discharge cells Cc. The phosphor layers 402 on the end walls 602 of the support members 62 of
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
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