CATHODE RAY TUBE AND METHOD OF MAKING THE SAME

Abstract: A cathode ray tube subjected to an antistatic treatment and a method of making the same. A conductive surface of a panel (2) of a bulb body (7) is grounded through a metal reinforcement (4) serving as a reinforce­ ment for maintaining the bulb's inward bursting resisting properties to instantaneously leaking any electrified charge, thereby providing the antistatic cathode ray tube which is free from the effect of air-conditioned humidities. Thus, there is the effect of preventing the occurrence of erroneous operations of the cathode ray tube and peripheral units and adverse effects on the human body, e.g., electric shock due to the charged static electricity on the panel surface (2), and there is another effect that the implosion protective adhesive glass tape (5) or the member interposed between the conductive coating (1) and the metal reinforcement (4) is equivalent to lead wires thus eliminating the use of lead wires and thereby eliminating the provisions of complicated connections to the panel surface (2).

Description: The present invention relates to a cathode ray tube subjected to an antistatic treatment and a method of making the same, and more particularly the invention relates to a cathode ray tube so designed that the electrified charge on the surface of a panel is leaked to a set chassis by means of a metal reinforcement, thereby preventing erroneous operations of the cathode ray tube and peripheral units and ill effect on the human body due to static electricity. As a conventional antistatic treatment for cathode ray tubes, there has been proposed a method of making the surface of a panel of a cathode ray tube conductive as disclosed in JP-A-62-37850, and the desired antistatic effect has in fact been obtained by selecting the surface specific resistance of the panel less than 1 × 10¹¹ Ω when the operating environment of the cathode ray tube has a humidity of less than 40-60% RH (Relative Humidity). The technique disclosed in this prior art publication is such that in the cathode ray tube subjected to a non-glare treatment by forming a finely rugged and impressed surface layer on the outer surface of the face panel at the front of the glass bulb of the cathode ray tube, a thin silica film is additionally formed on the rugged and impressed surface layer thereby not only maintaining the desired non-glare effect but also enhancing the resolution and ensuring an excellent antistatic effect and electric shock preventing properties. On the other hand, a technique of applying lithium silicate and forming a rugged and impressed coating on the surface of a cathode ray tube to ensure the desired reflection reducing effect and antistatic effect has been disclosed in a literature entitled "Lithium Silicate Antiglare Faceplate System For RCA Color Data Display Tubes", RCA, June, 1986, U.S.A. However, both of these prior art techniques have not gone to refer in detail to the grounding of the panel surface. When an insulation is provided between the panel surface and the metal reinforcement, that is, when the panel surface is not grounded, the surface specific resistance must be reduced to less than 1 × 10¹⁰ Ω in cases where the air-conditioned humidity is less than 40% RH during the operation of the cathode ray tube. There is another disadvantage that where the humidity is less than 20% RH, no great antistatic effect can be obtained even if the surface specific resistance is selected less than 1 × 10⁷ Ω. Also, there has been disclosed in JP-A-62-43042 a technique by which a front panel is applied to the surface of a face panel of a cathode ray tube by means of a transparent conductive adhesive resin prepared by mixing finely powdered silver, copper, carbon or the like into polyester resin and lead wires are brought out from the adhesive resin, thereby maintaining the front panel as well as the fastening metal members and the external conductive coating at the ground potential to prevent the face panel surface from being charged with static electricity. In other words, the adhesive resin is made conductive and the lead wires are connected to the adhesive resin, thereby ensuring the desired grounding. In addition, JP-A-62-43043 has disclosed a technique by which a front panel composed of a conductive glass containing vanadium, etc., and having an electrical resistance of less than about 10³-10⁹ Ωcm is applied to the surface of a face panel of a cathode ray tube with an adhesive resin and lead wires are brought out from the front panel, thus maintaining the front panel as well as the fastening metal members and the external conductive coating at the grounding potential and thereby preventing the face panel surface from being charged with static electricity. In other words, the front panel is made conductive and the lead wires are connected to the front panel, thereby ensuring the desired grounding. With the methods disclosed in the above-mentioned JP-A-62-43042 and JP-A-62-43043, however, the lead wires are connected through the terminals so that the areas of the connection portions are small and conduction failure tends to occur, thus making it difficult to connect the lead wires to the conductive member. Moreover, there is a disadvantage that even if the lead wires are connected, conduction failure tends to occur at these portions. It is a primary object of the present invention to provide an antistatic cathode ray tube so designed that the surface of the front panel of the tube is conductive and is grounded through a metal reinforcement band or a reinforcing member for maintaining the inward bursting resistance of a bulb so as to instantaneously leak any electrified charge and to eliminate the effect of the air-conditioned humidity and a method of making such cathode ray tube. It is another object of the invention to provide such a cathode ray tube so designed that the air-conditioned humidity has practically no effect on the tube during its operation and also a satisfactory antistatic effect is ensured even in low humidity conditions. JP-A-6240138 discloses a cathode ray tube in accordance with the prior art portion of claim 1. A special conductive aluminium tape is required to conduct electrical charge from the surface of the cathode ray tube to the metal reinforcement. As compared therewith, the present invention, as specified in claim 1, not only has a conductive coating on the tube so as to facilitate discharge thereof, but also uses as the conductive connection, particles impregnated into the insulating material, preferably comprising reinforcement tape, about the periphery of the tube. This provides good leakage whilst at the same time not interfering with the efficiency of the reinforcement. Preferably, the coating itself also comprises electrically conductive particulate material to provide it with its electrical conductivity. JP-A-587751 discloses the idea of having a conductive connection between a conductive coating on a cathode ray tube and a metal reinforcement band about the tube. However, in this case, the conductive coating is provided on the rear of the tube, rather than the front panel and the tape is a conductive tape having a spike penetrating a layer of adhesive agent with there being no appreciation of the advantageous construction of the invention where the mounting insulating material is simply impregnated with conductive particulate material. Thus, the present invention provides a cathode ray tube in which conductivity is imparted to an insulating member (hereinafter referred to as an implosion protective adhesive glass tape, its preferred form) which insulates the conductive surface of a panel from a metal reinforcement, thereby grounding the conductive surface of the panel to a set chassis through the adhesive glass tape and the metal reinforcement. The conductivity of the adhesive glass tape is provided by for example impregnating it with 0.1 to 10 ml, per 290 mm diagonal (12 inches) cathode ray tube, of a solution prepared by dissolving or colloidally suspending 0.2 to 10% by weight of salts or oxides of such metal as tin (Sn), indium (In) or aluminium (Al) and non-metallic material such as silicon (Si) in water and alcohol or other organic solvents and drying the adhesive glass tape. By providing the implosion protective adhesive glass tape with the desired conductivity, it is possible to ground the conductive surface of the panel to the set chassis through the adhesive glass tape and the metal reinforcement. This has the effect of instantaneously leaking the electrified charge on the surface of the panel to the set chassis irrespective of the air-conditioned humidity, thereby preventing any erroneous operations of the cathode rate tube and the peripheral units and any ill effect on the human body, e.g. electric shock due to the electrification of the panel surface with static electricity. Further, in accordance with the invention, the implosion protective adhesive glass tape or insulating material interposed between the conductive coating and the metal reinforcement, because of the conductive particle impregnation, is equivalent to the lead wires, thus eliminating the lead wires which have heretofore been necessary. This has the effect of eliminating the complicated connections between the panel surface and the lead wires. The invention also provides a method of producing a cathode ray tube as defined in claim 4. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A is a side view of a first embodiment of a cathode ray tube according to the present invention. Fig. 1B is a schematic sectional view of Fig. 1A. Fig. 2 is a partial detailed view of Fig. 1B. Figs. 3A and 3B are graphs respectively showing the antistatic effects according to the invention. Fig. 4 is a side view of a second embodiment of the cathode ray tube according to the invention. Fig. 5 is a partial schematic sectional view of Fig. 4. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will now be described with reference to Figs. 1A and 1B and Fig. 2. Fig. 1A is a side view of the first embodiment of the invention and Fig. 1B is a schematic sectional view of Fig. 1A. Fig. 2 is a detailed view of the portion of Fig. 1B within a circle A. Note that a metal-backed coating, a shadow mask and etc., are not shown. In the Figures, numeral 1 designates a conductive coating, 2 a glass panel, 3 a fluorescent screen, 4 a metal reinforcement, 5 an implosion protective adhesive glass tape, and 6 a conductive material impregnated into the implosion protective adhesive glass tape 5. Numeral 7 designates a bulb body. A method of making the above-mentioned cathode ray tube according to the invention will now be described. First step: The method will be described by taking the case of a 290 mm diagonal (12-inch) color cathode ray tube. After a bulb body 7 has been produced, an implosion protective adhesive glass tape 5 and a metal reinforcement 4 are fastened around it and a solution containing tin dioxide, SnO₂, 1 wt%; ethyl silicate, Si(OC₂H₅)₄, 9 wt%; nitric acid, HNO₃, 1 wt%; water, H₂O, 10 wt%; and ethanol, C₂H₅OH, 79 wt% is applied to the outer surface of a glass panel 2 to a thickness of 300 nm (3000 Å) by a spray coating method. In this case, as will be seen from Fig. 1B, the area coverage of the applied solution extends from the front face of the glass panel 2 to the implosion protective adhesive glass tape 5. Second step: Then, to prevent the metal reinforcement 4 from rusting, a solution having the same composition as the previously mentioned solution except the elimination of nitric acid used as a catalyst is impregnated into the implosion protective adhesive glass tape 5 in an amount corresponding to about 0.5 mℓ per glass tape. This is effected after the implosion protective adhesive glass tape 5 has been fastened around the bulb body 7. Third step: Then, the whole surface of the cathode ray tube is dried by heating it at 100°C to 200°C for about 1 hour, thereby forming a conductive coating 1. The conductive coating 1 is formed to extend from the surface of the glass panel 2 to the implosion protective adhesive glass tape 5 and also a conductive material 6 is incorporated in the implosion protective adhesive glass tape 5, thereby imparting conductivity to the implosion protective adhesive glass tape 5. With the cathode ray tube constructed as mentioned above, the surface specific resistances of the conductive coating 1 and the implosion protective adhesive glass tape 5 are in the range from 1 × 10⁹ to 1 × 10¹¹ Ω. The following Table 1 shows the variations in antistatic effect due to the presence and absence of conductivity in the implosion protective adhesive glass tape 5 in terms of the attenuation rate of the charged voltage on the cathode ray tube panel surface (the time required for the charged voltage on the panel surface to decrease to less than 2 kV after the switch has been turned on and then off with the applied voltage of 23 kV). Figs. 3A and 3B are graphs respectively showing the antistatic effects due to the presence and absence of the conductivity in the implosion protective adhesive glass tapes in the cases where the air-conditioned humidities are 50% RH and 20% RH, respectively, as shown in Table 1. Thus, as will be seen from Table 1 and the graphs shown in Figs. 3A and 3B, the desired antistatic effect can be obtained even at low humidities by imparting conductivity to the implosion protective adhesive glass tape 5. While the above embodiment has been described as applied to a color cathode ray tube, it is needless to say that the invention is not limited thereto. Also, while the prestressed banded structure has been described as an example of the reinforcement as shown in Figs. 1A and 1B, any other reinforcement such as the P-O-P (Panoply) reinforcement may of course be employed. Fig. 4 shows a second embodiment of the invention, and Fig. 5 is a detailed view of the portion of Fig. 4 which is encircled by a circle B. In the Figure, a P-O-P (Panoply) reinforcement 8 is used in place of the metal reinforcement 4. In this case, the P-O-P reinforcement 8 is connected to a bulb body 7 through a resin 9 and then the P-O-P reinforcement 8 and a fitting lug 10 are fastened to the bulb body 7 by a tension band 11. Also, it is self-evident that various kinds of conductive coatings, conductive material compositions, coating thicknesses, impregnation quantities, etc., may be used and the insulating material for imparting conductivity is not limited to the implosion protective adhesive glass tape, that is, a fabric tape and resin may be applied. From the foregoing description, it will be seen that in accordance with the invention the surface of the panel of the cathode ray tube is conductive and is grounded to the set chassis through the implosion protective adhesive glass, or other, tape and the metal reinforcement, thus making it possible to instantaneously leak any stored charge on the panel surface. Moreover, the cathode ray tube is not practically subjected to the effect of the air-conditioned humidity during its operation and the desired antistatic effect can be ensured, even at low humidities. Further, in accordance with the invention, the implosion protective adhesive glass, or other, tape interposed between the conductive coating and the metal reinforcement is equivalent to lead wires and therefore there is no need to use any lead wires. This has the effect of eliminating the provision of any complicated connections to the panel surface.

Claims: 1. A cathode ray tube comprising a bulb body (7); a coating (1) formed on the surface of a panel (2) comprising the front of the bulb body; a metal reinforcement (4) arranged about the front side wall portion of the bulb body (7) comprising a skirt of the panel (2); a reinforcement tape of insulating material (5) provided between the bulb body (7) and the metal reinforcement (4); and conductive means (6) providing an electrical conductive connection between the coating (2) and the metal reinforcement (4) characterised in that the coating (2) is electrically conductive and in that the conductive means (6) comprise conductive particulate material impregnated into the insulating material comprising the reinforcement tape (5). 2. A cathode ray tube according to claim 1, characterised in that said metal reinforcement (4) is of a prestressed banded implosion protection structure. 3. A cathode ray tube according to claim 1, wherein the metal reinforcement (4) is of a P-O-P implosion protection structure. 4. A cathode ray tube according to claim 1, 2 or 3, wherein the coating (2) comprises electrically conductive particulate material. 5. A method of producing a cathode ray tube subjected to an antistatic treatment comprising the steps of: fastening an implosion protective adhesive glass tape (5) and a metal reinforcement (4) around a bulb body (7); coating an outer surface of a glass panel (2) with a solution containing 1 wt% tin dioxide, 9 wt% ethyl silicate, 1 wt% nitric acid, 10 wt% water and 79 wt% ethanol by a spray coating method; impregnating into said implosion protective adhesive glass tape (5) a solution having the same composition as said first-mentioned solution except the elimination of said nitric acid; and drying the whole surface of said bulb body (7) by heating the same at 100-200°C for 1 hour, whereby a conductive coating (1) is formed to extend from the surface of said glass panel (2) to said implosion protective adhesive glass tape (5), and a conductive material (6) is incorporated into said implosion adhesive glass tape (5), thereby imparting conductivity to said implosion protective adhesive glass tape (5).

Inventors: TOJO, TOSHIO
Applicants: HITACHI DEVICE ENGINEERING CO., LTD., HITACHI, LTD.
Application year: 1988
Main classification: H01J29
IPC codes: H01J29