Abstract:
A discharge display device is disclosed which has upper and lower plates at least one of which is made transparent, a spacer disposed between said upper and lower plates, at least one cathode and at least one anode disposed between said spacer and said upper plate in opposed relation to said cathode, an adhesive agent sealing said upper and lower plates in an air-tight manner along their outer edges to form an envelope and an inert gas sealed within said envelope. In this case, at least said spacer is covered with an insulating porous layer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a discharge display device, and more particularly to a discharge display device employing a novel spacer. 
     2. Description of the Prior Art 
     In the prior art, discharge display device in which the response time interval is short and a discharge between a pair of the cathode and anode is rapidly transferred to another pair of the cathode and anode of the discharge display device are not known. 
     Accordingly, the prior art discharge display device can not be used in place of a Braun tube. 
     SUMMARY OF THE INVENTION 
     According to an aspect of this invention there is proposed a discharge display device which consists of upper and lower plates at least one of which is made transparent, a spacer disposed between said upper and lower plates, a plurality of cathodes disposed side by side between said spacer and said lower plate and selectively supplied with a voltage, a plurality of anodes disposed side by side between said spacer and said upper plate in opposed relation to said plurality of cathodes, an adhesive agent sealing said upper and lower plates in air-tight manner along their outer edges, and an inert gas sealed within said upper and lower plates, at least said spacer being covered with an insulating porous layer. 
     Accordingly, it is an object of this invention to provide a novel discharge display device. 
     It is another object of the invention to provide a discharge display device which has a short response time. 
     It is a further object of the invention to provide a discharge display device in which a discharge between a pair of the cathode and anode can be rapidly transferred to another pair of cathodes and anodes. 
     It is a yet further object of the invention to provide a discharge display device employing a novel spacer. 
     It is a still further object of the invention to provide a discharge display device which can be used in place of a Braun tube. 
     The other objects, features and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a fragmentary perspective view, partly in cross-section, showing one example of the discharge display device according to this invention; 
     FIG. 1B is an exploded perspective view, partly cut away, showing the principal part of the example depicted in FIG. 1A; 
     FIG. 2A is a fragmentary cross sectional view of a spacer employed in the example shown in FIG. 1A; 
     FIG. 2B is a schematic circuit diagram employed in experiments of spacer materials; 
     FIGS. 3A and 3B are graphs showing the discharging states in the cases of using various spacer materials, respectively; 
     FIG. 4 is a cross-sectional view of the principal part of a discharge display device, for explaining it; and 
     FIGS. 5 to 8 are schematic fragmentary diagrams, for explaining the discharging states in the cases of employing various spacers. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the drawings, an embodiment of this invention will hereinafter be described. 
     FIG. 1A is a fragmentary perspective view showing, partly in cross-section, a discharge display device in accordance with one embodiment of this invention. FIG. 1B is an exploded perspective view showing the principal part of the discharge display device exemplified in FIG. 1A. 
     In FIGS. 1A and 1B, reference numeral 1 indicates generally a discharge display device. The discharge display device 1 comprises upper and lower insulating plates 2 and 3 which are disposed in opposing relation to each other and at least one of which is formed of a transparent material such, for example, as glass, and an insulative spacer 5 which has bored therethrough a plurality of apertures 4 in a matrix manner (refer to FIG. 1B) and is disposed between the upper and lower insulating plates 2 and 3. Between the upper plate 2, which is transparent in this embodiment, and the spacer 5, there is disposed an anode 7 which is composed of a plurality of plate-shaped strip anode elements A 0 , A 1 , A 2 , - - - and A n . In this case, the anode elements A 0 , A 1 , A 2 , - - - and A n  are disposed side by side in opposing relation to the columns of the apertures 4 bored in the spacer 5 in a matrix form. Between the lower plate 3 and the spacer 5, there is disposed a cathode 8 which is composed of a plurality of plate-shaped strip cathode elements K 0 , K 1 , - - - and K n . The cathode elements K 0 , K 1 , - - - and K n  are disposed side by side in opposing relation to the rows of the apertures 4 bored in the spacer 5. Thus, the cathode elements K 0 , K 1 , - - - and K n  cross the anode elements A 0 , A 1 , - - - and A n  at right angles thereto, respectively. 
     After assembling of the above said parts into a structure such as shown in FIG. 1A, their peripheral edges are sealed by means of an adhesive 10, such as frit glass or the like to provide an envelope 1a. The envelope 1a is evacuated through an exhaust pipe 9b and then an inert gas such as neon, xenon, argon, mercury or the like is sealed in the envelope 1a through the exhaust pipe 9b,  thus providing the discharge display device 1. Of course, the exhaust pipe 9b is sealed up after sealing of the inert gas in the envelope 1a. 
     With such a construction, application of a voltage between selected ones of the cathode and anode elements K 0  and A 0  - - - produces a discharge through the aperture 4 of the spacer 5 corresponding to the intersecting point of the selected cathode and anode elements to emit glow light. Accordingly, the apertures 4 formed in the spacer 5 serve as discharge cells. 
     In this case, the cathode and anode elements have formed therein apertures 8a and 7a in alignment with those 4 of the spacer 5 so that the discharge can be seen from the outside of the envelope 1a. 
     In FIG. 1A, a gas reservoir 9 is mounted on the underside of the lower plate 3 in an airtight manner. The reservoir 9 communicates with the envelope 1a through an aperture 9a for exhaustion and gas diffusion. Between the reservoir 9 and the outside, the aforesaid exhaust pipe 9b is provided. In the envelope 1a and the reservoir 9, an inert gas, for example, a neon gas, is supplied and, when consumed, it can be replaced through the exhaust pipe 9b. 
     As illustrated in FIG. 2A, the spacer 5 is formed of a conductive metal plate 5a which is covered with an insulating layer 5b over the entire areas thereof including the peripheral surface of the aperture 4. The insulating layer 5b is formed porous to permit the passage therethrough of electrons and ions which are produced upon discharge and this layer should not be formed as a dense layer such as glass or mica. The porous insulating layer 5b can be obtained by spraying a chromium oxide or alumina powder material onto both sides of the conductive metal plate 5a together with water glass and then baking the plate 5a. In this case, the insulating layer 5b is required to have a heat resistance temperature higher than 400°C and, further, since a local magnetic field sometimes exhibits a particular high intensity during discharging of the discharge display device, the insulating layer 5b is required to have a uniform withstand voltage higher than 250 V ac . Therefore, it is preferred to check uniformity of the withstand voltage of the insulating layer 5b by measuring it, for example, with a measuring instrument employing a brush electrode. 
     In trial manufacture of the discharge display device of this invention in which the metal plate 5a and the spacer 5 were formed 0.25m/m and 0.4m/m thick, respectively, and the insulating layer 5b was formed about 0.07m/m in thickness, the results of measurement of the withstand voltage of the insulating layer 5b with the abovesaid brush measuring instrument and a bar electrode were 10 MΩ and higher than 100 MΩ, respectively. 
     The following will describe the operation of the discharge display device of this invention employing the abovementioned spacer 5, together with the results of my experiments conducted on the device. FIG. 2B is a schematic wiring diagram of the discharge display device used in my experiments in which a variety of spacers were employed. In FIG. 2B, reference character B indicates an external power source, that is, a battery; R designates a resistor. The anode 7 is supplied with the power source voltage (about 300V DC ) through the resistor R having a resistance value of about 480 KΩ. Reference characters S 1 , S 2 , - - - and S n  identify switches by means of which the cathode elements K 1 , K 2 , - - - and K n  are respectively connected thereto are grounded relative to the anode 7. In my experiments, the switches S 1 , S 2 , - - - and S n  are adapted to be closed one after another starting with the switch S 1 , for example, at regular time intervals of 100 μsec (micro seconds) in such a manner that turning-off of a preceding switch is immediately followed by turning-on of the next. As is apparent from FIG. 2B, no switch is connected to the cathode element K 0 . Consequently, switching from the switch S 5  to S 7  is achieved directly at the time interval of 100 μse. Further, selective discharge between the anode 7 and the cathode 8 is produced though the aperture 4 shown in FIG. 1B, as mentioned above. 
     FIGS. 3A and 3B are graphs showing the results of the experiments using various spacers in the discharge display device. FIGS. 3A and 3B respectively show the discharging conditions of a device employing, as the spacer 5, a spacer merely formed of a glass plate and a device employing a spacer having a porous insulating layer deposited on a metal plate, that is, the spacer according to this invention. 
     In FIGS. 3A and 3B, reference character P 1  indicates instants of turning on the switch P 2  indicates firing instants. The firing instants each correspond to the highest potential and, at this instant, the potential is lost due to discharging. 
     FIG. 3A indicates that, in the cathode element K 7 , there are some occasions when the firing instant P 2  is delayed as compared with the others and no discharge is produced. In FIG. 3B, however, the cathode elements are discharged at substantially equal time intervals and, at this time, the potential of the spacer 5 is 135 V DC  and no delay in discharging of the cathode element K 7  appears. 
     The reason for the difference in the firing potential between FIGS. 3A and 3B is that, in the experiments, the diameter of the aperture 4 of the spacer 5 and the thickness of the spacer 5 in the device of FIG. 3B were smaller and larger than those used in the device of FIG. 3A, respectively. Accordingly, as is evident from the FIGS., the time interval t 2  to the firing shown in FIG. 3B is long as compared with that shown in FIG. 3A. 
     As is seen from FIG. 3B, it may be considered that in the case of using the spacer of this invention, discharging of the cathode element K 7  is delayed because it is spaced away from the cathode element K 5 . In practice, however, even if the spacing of the cathode 8 is large, it is not so much related to the discharge response time and, in my experiment, the discharge response time was short and the discharge is started positively. 
     The above is the experimental results, which will be theorized with reference to FIGS. 4 to 8. Generally, the response speed is dependent upon surroundings which determine the speed of electrons in the direction of the arrow a which are generated during discharging, that is, the conditions in the envelope 1a. The effect of the spacer will hereinafter be further described. 
     FIG. 4 is a fragmentary cross-sectional view showing the relationship between the anode 7 and the cathode 8 of a discharge tube. FIG. 5 is a cross-sectional view of the spacer 5 in which the spacer 5 is formed of a glass material g. FIG. 6 is a cross-sectional view of the spacer 5 in which a dense insulating layer 5c is deposited on a conductor, that is, the metal plate 5a and the metal plate 5a is adapted to be supplied with a voltage from a battery B through a resistor R 1  and a switch S. FIG. 7 is a cross-sectional view of the spacer 5 in which the insulating layer 5c on the metal plate 5a in FIG. 6 is removed. FIG. 8 is a cross-sectional view of the spacer 5 of this invention in which the insulating layer 5c in FIG. 6 is replaced with the insulating porous layer 5b. These figures illustrate the acting conditions of electrons e and neon ions Ne +  during discharge. Reference numeral 11 identifies a plasma space in the discharge tube. 
     In the plasma space 11, during discharge, charged particles are diffused and recombined with one another to be extinguished. The charged particles do not so much have an affect on the other cathode elements spaced away from the cathode element being discharged. Since the ions are especially large in size as compared with the electrons, they exhibit a strong tendency of not affecting discharge of the other cathode elements. The electrons e exert a greater influence on the formation of a neighboring discharge as compared with the ions, as described previously. 
     Accordingly, in FIG. 4, the spacing between the anode 7 and the cathode 8 in the direction b is dependent upon a voltage e z  therebetween during discharge. In fact, the magnetude of the voltage e z  is related to the discharge of the next cathode element, but the speed of the electrons in the direction a perpendicular to the direction b has a strong relation to the discharge of the next cathode element and the start of discharge of the next cathode element is rapid. 
     By the way, in the case of FIG. 5, the electrons e produced by discharge readily adhere to the exposed glass surface as shown and attract ions to extinguish them, thus decreasing electrons promoting discharging of the next cathode element in the plasma space 11. 
     In the case of FIG. 6, neon ions are attracted to adhere to the surface of the insulating layer 5c and they are combined with electrons to provide the same results as shown in FIG. 5. Even if a voltage is applied to the metal plate 5a from the battery B, the same results are obtained. 
     Further, in the case of FIG. 7, when no voltage is applied, electrons decrease as in the case with FIG. 5. Upon application of a voltage, electrons e jump into a free electron layer on the conductor 5a more rapidly and ions are combined with free electrons, so that the same results are obtained. 
     In this case, by lowering the potential of the conductor 5a to the ground potential, electrons e are prevented from jumping into the conductor 5a, and consequently the amount of electrons e in the space 11 is increased, whereby the response time can be decreased. This results in a discharge between the anode 7 and the spacer 5, which implies that the spacer 5 serves as a cathode. 
     In FIG. 8 employing the spacer 5 of the present invention, the following assumption is probable. Namely, during discharging, electrons e generated in the plasma space 11 enter into the porous insulating layer 5b to lower its potential as compared with the conductor 5a. As a result of this, due to the intensity difference of the electric fields, the electrons go into the conductor 5a and propagate therein and, at the next discharging electrode position, they go out of the conductor 5a due to the electric field established between the anode 7 and the conductor 5a. However, these electrons of insufficient energy remain in the insulating layer 5b or on its surface and prevent movement of other electrons which are to enter into the conductor 5a from the plasma space 11 through the insulating layer 5b, or repel and direct them in the direction a, thus facilitating discharge of the next cathode element. 
     The following table shows the experimental values obtained with the spacers described above. 
     
                                           Table__________________________________________________________________________                     Measured Results                              Delay of discharge   Materials of           Distance between                              time intervalNo trial manufacture(spacer)                     K.sub.1 &amp; K.sub.2 (mm)                              (t.sub.2) of K.sub.2__________________________________________________________________________                              (μsec.)1  Insulating material    2.54     30-100   (the case of FIG. 5)   7.5      longer than 1002  Dense insulating material deposited                     2.54     30-100   on conductor   (the case of FIG. 6)   7.5      30-1003  Conductor              2.54     longer than 100   (the case of FIG. 7, +100V applied to                     2.54     80   conductor through resistor of 300KΩ)                     2.54     longer than 1004  Metal spacer of this invention                     100      20   (the case of FIG. 8, +160V applied                     100      40   to metal plate through resistor of 300KΩ)                     7.5      longer than 100__________________________________________________________________________ 
    
     As is apparent from the above table, too, when the spacer of the present invention is used, even if the spacing between adjacent ones of the cathode elements is large, the response time interval is short and the discharge is carried out positively. 
     The discharge conditions shown in FIG. 3B can be understood from the above and the response time interval can be shortened. Accordingly, the discharge display device of this invention can be employed as a plasma display in place of a Braun tube as mentioned previously and the spacer which is used for graphic display and TV picture display can be produced at lower cost and with more accuracy than those formed of glass. 
     Although the present invention has been described in connection with a spacer interposed between the anode and the cathode in discharge display, the invention is not limited specifically thereto. A part such, for example, as the inside of the envelope, which is exposed to the plasma space produced by discharge or which is exposed to positive and negative charges, is formed with the material according to this invention so that a conductor is deposited with a porous insulating layer. As a result, the inside surface of the envelope thus formed shifts discharges rapidly. 
     With the present invention described above, the priming electrodes and isotopes used in the prior art become unnecessary. 
     It will be apparent that many modifications and variations may be effected by one skilled in the art without departing from the scope of the novel concepts of this invention.