GB1577422A - Display tube with a glass cover - Google Patents

Description

(54) DISPLAY TUBE WITH A GLASS COVER (71) We, NIPPON ELECTRIC KAGOSHIMA, LIMITED, a Company duly organised and existing under the laws of Japan, of 12699, Takemoto, Izumi-shi, Kagoshima, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a display tube that is capable of selectively providing visual displays of numerals, letters or other symbols through a glass cover.

A display tube comprising a glass cover may be a fluorescent display panel or a gas discharge display panel and comprises an insulator substrate to which a plurality of display electrodes are fixed for providing a visual display. The glass cover has a viewing window and flange portions that surround the window and are hermetically sealed to the substrate with the display electrodes disposed in a space hermetically sealed by the substrate and the glass cover.

Such display tubes are widely used in electronic portable calculators, measuring instruments, and control panels. In the case of an electronic portable calculator, it is usually possible to observe the display with the display tube positioned so as to provide a readily readable display. As for control panels and some measuring instruments, the display has to be read with the display tube fixed in position, e.g. fixed to an upright wall. It is therefore desirable that the visual display is visible along various lines of vision. In other words, it is desirable that the display tube has a wide viewing angle over which the display is comfortably visible.

As will later be described with reference to figures of the accompanying drawings, the viewing angle is decided by the relative positions between the display electrodes and the viewing window.

A display tube generally has to display a plurality of aligned digits or other symbols.

It is therefore normal for the display electrodes to have a common centre line and for the glass cover to have a major centre axis. On the other hand, a display tube comprises lead-out conductors for leading the display electrodes outwardly of the hermetically sealed space. In a display tube wherein metal leads are used as the lead-out conductors, the centre line is usually offset relative to the major centre axis in order to provide room in the sealed space for connection of the metal leads to the display electrodes. This renders the viewing angle unduly narrow. It is possible to prevent the viewing angle from becoming narrow by enlarging the viewing window; this, however, results in an undesirably large display tube.

Alternatively, the space for connections is made as narrow as possible. Mere narrowing of the space requires considerable skill in reliably establishing the connections. In a sophisticated display tube, the lead-out conductors are provided by fired prints of silver or other conductive paste. This makes it possible to do without the space for connection and to solder or otherwise fix metal leads to the respective fired prints at the outside of the sealed space. It is, however, necessary to get rid of the known phenomenon of silver migration, e.g. by covering the fired prints with a film of synthetic resin, such as epoxy resin. This raises the cost. When the substrate is made of glass, the soldering often gives rise to cracks in the substrate.

In any event, the metal leads are liable to come away from the substrate.

It is therefore an object of the present invention to provide a display tube with a glass cover which enables a wide viewing angle to be provided with the display tube kept small in relation to the visible display provided thereby, but which makes it possible to manufacture a reliable display tube at low cost.

According to the present invention there is provided a display tube having electrodes on a substrate for providing a visual display through a glass cover of one or more sym bols, the glass cover comprising a window portion surrounded by a flange with a surface in a common plane sealed to the substrate and side wall portions connecting the window portion to the flange, the flange being formed by a pair of first mutually opposite flange portions connected by a pair of second mutually opposite flange portions, and the window portion comprising a central region which extends from one to the other of the second flange portions and which is canted relative to the common plane so as to be spaced from the common plane adjacent the said one and other flange portions by first and second distances respectively, of which the second distance is smaller than the first distance.

The invention will be described in more detail by way of example, with reference to the accompanying drawings, wherein: Fig. 1 is a schematic exploded perspective view of a display tube having a conventional glass cover; Fig. 2 is a schematic sectional view taken on the line 2-2 in Fig. 1; Fig. 3 is a schematic perspective view of a glass cover according to a first embodiment of the present invention; Fig. 4 is a schematic sectional view of a display tube comprising a glass cover shown in Fig. 3, the section being taken on the line 4-4 in Fig. 3; Fig. 5 is a schematic perspective view of a glass cover according to a second embodiment of this invention; Fig. 6 is a schematic sectional view of a display tube comprising a glass cover shown in Fig. 5, the section being taken on the line 6-6 in Fig. 5; and Fig. 7 is a sectional view similar to that illustrated in Fig. 6 except that the section is taken on the line 7-7 in Fig. 5.

Referring to Figs. 1 and 2, a display tube comprising a conventional glass cover 10 will be described at first for a better understanding of the present invention. The display tube is for displaying simultaneously a row of symbols, e.g. a plurality of digits and comprises a substrate assembly 11 comprising in turn, a substrate 12 of an insulating material, such as glass or a ceramic, and a plurality of display electrodes 13 arranged on a surface of the substrate 12. The electrodes 13 are arranged in a geometrical configuration suited to the symbols to be displayed, which usually have a common top and a common bottom, assumed to be respectively far from and near to the reader of Fig. 1.The glass cover 10 is rectangular or parallelogrammic in outline and comprises a window portion 15, a pair of shorter flange portions 16, a pair of longer flange portions 17 and side wall portions 18 between the window and flange portions 15-17. The flange portions 16-17 have a common surface to be hermetically sealed to the above-mentioned surface of the substrate 12. The side wall portions 18 space the window portion 15 from the said surface and merge into the window portion 15 at shoulders.

Referring more specifically to Fig. 1, the depicted display tube is a fluorescent display tube. The substrate assembly 11 therefore comprises fired prints of silver or other conductive paste on the substrate 12 in the form of segmented areas and internal leads therefor, an overlying layer of an insulating material, such as fused glass frit, with through holes formed at the positions of the respective segmented areas of the fired prints, and layers of a luminescent material in the through holes for the segmented areas to form the display electrodes 13 in cooperation with the underlying segmented areas.

The substrate assembly 11 further comprises a pair of cathode supports 21, at least one hot cathode 22 supported by the supports 21 over the display electrodes 13, a plurality of grids 23 between the cathode 22 and the display electrodes 13 for the respective digits, and a plurality of metal leads 25 on the substrate 12. The metal leads 25 are electrically connected to the internal leads by masses of fired silver or other conductive paste through additional through holes preliminarily formed through the overlying insulator layer of the substrate 12 and also to the cathode supports 21 and grids 23 and are mechanically fixed to the substrate 12 by masses of fused glass frit covering the fired silver masses. These masses are shown at 26.

It is possible to form a pair of seats 27 for each grid 23 by the fired prints of the paste and to attach the grids 23 thereto through further additional through holes also formed preliminarily through the overlying insulator layer. With a known transparent and electroconductive film formed on the inside surface of the glass cover 10 and with a layer of glass frit of, for example, a PbO-B2O3-ZnO system placed on the flange portion common surface, the flange portions 16-17 are hermetically sealed to a sealing area 28 of the substrate assembly 11. At the same time, an exhaust pipe 29 is sealed, in the illustrated example, to the glass cover 10.

Referring to Figs. 1 and 2 in more detail, the masses 26 for providing connection of the display electrodes 13 and the like to the metal leads 25 are placed downwardly in Fig. 1 of the display electrodes 13. A common centre line of the aligned display electrodes 13 is therefore offset rightwards in Fig. 2 relative to a major centre axis of the glass cover 10 or the window portion 15. An angle over which the visual display is comfortably visible is restricted by a pair of planes indicated by straight lines 31 and 32 passing through the top and bottom of the display electrodes 13 and the adjacent shoulders of the glass cover 10.From Figs. 1 and 2, it is readily understood that the displays have to be viewed nearly perpendicularly, or from below, when the metal leads 25 are extended leftwards in Fig. 2 with the centre line of the aligned display electrodes 13 offset rightwards relative to the major centre axis of the window portion 15. This results in various disadvantages and inconveniences already pointed out.

Referring now to Figs. 3 and 4, a glass cover 10 of a first embodiment of this invention comprises a window portion 15, a pair of first flange portions 16, a pair of second flange portions 17, a pair of first side wall portions 36 between the window portion 15 and the respective first flange portions 16, and a second side wall portion 37 between the window portion 15 and one of the second flange portions 17. The flange portions 1617 have the common surface mentioned hereinabove with reference to Figs. 1 and 2.

The window portion 15 has a first and a second area nearer to and farther from the second side wall portion 37, respectively.

The first area is spaced by the second side wall portion 37 from the common surface by a first distance. In the illustrated example, the glass cover 10 further comprises a perceptible side wall portion 38 between the second area and the other of the second flange portions 17 to space the second area from the common surface by a second distance that is shorter than the first distance.

The window portion 15 is thus inclined relative to the common surface.

From Fig. 4, it is readily understood that the glass cover provides a wider angle over which the visual display can be comfortably viewed without either enlarging the glass cover 10 or rendering the space for the connecting masses 26 objectionably narrow. It is also appreciated that it is possible to omit the perceptible side wall portion 38 to make the second distance substantially zero. The viewing angle is widened by about 20 , enabling comfortable viewing from above, as well as from below.

Turning to Figs. 5 to 7, a glass cover 10 of a second embodiment of this invention comprises similar parts designated by like reference numerals as in Figs. 3 and 4. The window portion 15 is subdivided into a transparent centre region 40 serving as a viewing window for the visible display and a pair of side regions 41 and 42 disposed between the centre region 40 and respective ones of the first side wall portions 16. The centre region 40 is over the display electrodes 13 and is arranged in the same way as the window portion of the first embodiment. However, the side regions 41--42 of the second area are uniformly spaced by the second distance from the common surface, a pair of third side wall portions 43 being provided between the respective side regions 41-42 and the said other of the second flange portions 17.

This glass cover is preferred for use in a fluorescent display tube because sufficient room is provided between the substrate 12 and each of the side regions 41--42 for the cathode supports 21 which protrude considerably from the substrate 12. The room provided by the side regions 41--42 furthermore serves as a getter room to prevent the getter used in a fluorescent display tube from being undesirably sputtered on to the inside surface of the viewing window 40 and therefore to render a shield for the getter unnecessary. In addition, the side regions 41-42 help to prevent the outside surface of the viewing window 40 from being inadvertently scratched. It has been confirmed that occurrence of scratches is reduced by about 60%.It is possible to provide only one of the side regions 41-42 with a view to, for example, merely providing a single getter space. A glass cover according to the first embodiment is preferred, because of its simple structure, for use in a gas discharge display tube wherein use is neither made of the cathode supports 21 nor of a getter.

It is possible to manufacture glass covers according to either embodiment on an industrial scale as readily as conventional glass covers. Use can be made of an upper, male moulding die conforming to the inner window surface with a frame portion corresponding to the window flanges spring biased to extend downwardly. A lower, female die conforms to the outer window surface and has a frame portion spring biased upwardly.

A preheated piece of sheet glass of a thickness between 1.3 and 1.8 mm and of an area of, for example, 80 mm by 20 mm is put between the dies which are preheated to a temperature between 5800 and 650"C.

The dies can be dimensioned to make second side wall portion 37 7.5 mm high and the perceptible side wall portion 38 1.5 mm high. The viewing window 40 then makes an angle of about 18 with the common surface. Each of the side regions 4142, if provided, is of a size 6 mm x 17 mm.

The dies are heated with the sheet glass piece therebetween to a temperature between 750" and 850"C. The upper die is pressed down at a speed between 1.5 and 3.5 cm/sec with a pressure between 2.0 and 3.5 kg/cm2. The flange portions of the window are initially clamped between the frame portions of the die which then retract as the main parts of the dies shape the window and side wall portions. The hotpressed glass cover is subsequently annealed at about 5500C. The die preheating serves to avoid loss of heat when the sheet glass piece is put between the mould pair.It is possible to manufacture the glass covers with the dies carried on a conveyor through an electric furnace having the desired temperature distribution and to achieve a uniform wall thickness of each glass cover by mainly controlling the temperature of hot press and the speed at which the male die is pressed relative to the female die.

It will be understood that other embodiments and modifications are possible. For example, a glass cover as employed in this invention is effective even in a display tube wherein the centre line of the aligned display electrodes and the major centre axis of the viewing window lie in a plane perpendicular to the substrate surface. The glass cover can have an outwardly convex viewing window and the flange portions 17 adjacent to the top and bottom of one or more display electrodes can be shorter than the other flange portions 16.

WHAT WE CLAIM IS:- 1. A display tube having electrodes on a substrate for providing a visual display through a glass cover of one or more symbols, the glass cover comprising a window portion surrounded by a flange with a surface in a common plane sealed to the substrate and side wall portions connecting the window portion to the flange, the flange being formed by a pair of first mutually opposite flange portions connected by a pair of second mutually opposite flange portions, and the window portion comprising a central region which extends from one to the other of the second flange portions and which is canted relative to the common plane so as to be spaced from the common plane adjacent the said one and other flange portions by first and second distance respectively, of which the second distance is smaller than the first distance.

2. A display tube according to claim 1, wherein the window portion also comprises two side regions flanking the central region and extending alongside the first flange portions respectively, the side regions being substantially parallel to the common plane.

3. A display tube according to claim 2, wherein the side regions are spaced from the common plane by the first distance adjacent both the second flange portions.

4. A display tube according to claim 1, 2 or 3, wherein the second distance is substantially zero.

5. A display tube according to claim 1, 2 or 3, comprising a perceptible side wall portion between the window portion and the said other second flange portion such as to render the second distance greater than zero.

6. A display tube according to claim 1 and substantially as hereinbefore described with reference to, and as illustrated in Figs.

3 and 4 of the accompanying drawings.

7. A display tube according to claim 1 and substantially as hereinbefore described with reference to, and as illustrated in Figs.

5 to 7 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. piece is put between the mould pair. It is possible to manufacture the glass covers with the dies carried on a conveyor through an electric furnace having the desired temperature distribution and to achieve a uniform wall thickness of each glass cover by mainly controlling the temperature of hot press and the speed at which the male die is pressed relative to the female die. It will be understood that other embodiments and modifications are possible. For example, a glass cover as employed in this invention is effective even in a display tube wherein the centre line of the aligned display electrodes and the major centre axis of the viewing window lie in a plane perpendicular to the substrate surface. The glass cover can have an outwardly convex viewing window and the flange portions 17 adjacent to the top and bottom of one or more display electrodes can be shorter than the other flange portions 16. WHAT WE CLAIM IS:-

1. A display tube having electrodes on a substrate for providing a visual display through a glass cover of one or more symbols, the glass cover comprising a window portion surrounded by a flange with a surface in a common plane sealed to the substrate and side wall portions connecting the window portion to the flange, the flange being formed by a pair of first mutually opposite flange portions connected by a pair of second mutually opposite flange portions, and the window portion comprising a central region which extends from one to the other of the second flange portions and which is canted relative to the common plane so as to be spaced from the common plane adjacent the said one and other flange portions by first and second distance respectively, of which the second distance is smaller than the first distance.

2. A display tube according to claim 1, wherein the window portion also comprises two side regions flanking the central region and extending alongside the first flange portions respectively, the side regions being substantially parallel to the common plane.

3. A display tube according to claim 2, wherein the side regions are spaced from the common plane by the first distance adjacent both the second flange portions.

4. A display tube according to claim 1, 2 or 3, wherein the second distance is substantially zero.

5. A display tube according to claim 1, 2 or 3, comprising a perceptible side wall portion between the window portion and the said other second flange portion such as to render the second distance greater than zero.

6. A display tube according to claim 1 and substantially as hereinbefore described with reference to, and as illustrated in Figs.

3 and 4 of the accompanying drawings.

7. A display tube according to claim 1 and substantially as hereinbefore described with reference to, and as illustrated in Figs.

5 to 7 of the accompanying drawings.