Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/96—One or more circuit elements structurally associated with the tube
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/86—Vessels; Containers; Vacuum locks
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/86—Vessels; Containers; Vacuum locks
  • H01J29/88—Vessels; Containers; Vacuum locks provided with coatings on the walls thereof; Selection of materials for the coatings
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2229/00—Details of cathode ray tubes or electron beam tubes
  • H01J2229/88—Coatings
  • H01J2229/882—Coatings having particular electrical resistive or conductive properties

Definitions

• the present invention relates to a display device such as a cathode ray tube and more particularly a resistive coating arranged on the rear part of the tube.
• a luminescent screen is arranged on the internal surface of the front face, said screen comprising three phosphor networks corresponding to the three primary colors red, green and blue.
• An electron gun is placed at the rear of the tube to generate one or more beams intended to scan the screen under the influence of magnetic fields created by a deflection device placed on the tube at the exit of the electron gun.
• the front face and the rear part are sealed to each other thanks to a cord of sintered glass placed on the edges in coincidence, the whole being treated in an oven at high temperature so as to melt the sintered glass to seal the two parts.
• the sealing area is usually covered by a metal belt compressing the front area of the glass envelope, in order to avoid the risk of implosion of the tube during its operation by the end user.
• the rear part of the tube is coated with a first internal conductive layer, and partially with a second external conductive layer.
• the internal layer serves as an electrical connection between the last electrode of the electron gun and the screen on which the electrons of the electron beam (s) come to land.
• This conductive layer creates a space inside the tube which is thus shielded from electric fields, a space in which the electron beam (s) therefore do not undergo deflection.
• the external conductive layer is grounded, and forms with the internal layer a capacitor whose objective is to smooth the high voltage applied to the tube by capacitive effect.
• the ground connection is made by one or more conductive strips connecting the outer layer to the anti-implosion metal strip encircling the tube, which itself is connected to the ground potential.
• the capacity of the filtering capacitor produced by the internal and external conductive layers is typically in the range of 1000 to 3000 picofarads, and is variable depending on the size of the tube.
• the external conductive layer is generally produced from a mixture of graphite powder with vinyl compounds so as to form a solution; graphite provides electrical conduction and vinyl compounds cohesion of the mixture and adhesion to the surface of the tube.
• the solution obtained is then deposited using a brush on the surface of the flared rear part of the tube, leaving an uncoated window around the anode button intended to establish the high voltage electrical connection with the internal coating.
• the graphite layer is then dried by a stream of hot air for 10 to 15 minutes.
• the linear resistance of the layer is generally greater than
• the high voltage applied to the tube sees the capacitor represented by the internal and external conductive layers in series with the resistance formed by the graphite layer.
• the value of this resistance is taken into account in the time constant of the RC circuit represented by the graphite layers, which directly influences the capacity of the high voltage supply circuit to respond to sudden current peaks. If the resistance of the graphite layer is too great, the high voltage will drop with each significant demand for current, which results in distortions of the image reproduced on the screen of the tube.
• the production of the external graphite layer has numerous industrial drawbacks: - preparation, handling and maintenance of very dirty solution; the instruments necessary for the deposition of the graphite layer, the site on which this deposition takes place requires constant and complex cleaning.
• the thickness of the layer is difficult to control due to the application process using a brush; this results in variations in thickness which locally vary the resistance of said layer in large proportions.
• the invention proposes to provide a solution to improve the situation caused by the graphite layer deposited according to the state of the art, a solution which also makes it possible to obtain better behavior of the tube during the current peaks required at high voltage. .
• the cathode ray tube comprises a glass envelope composed of a substantially rectangular front face, a flared rear part and a substantially cylindrical neck, the flared part including an anode button for receive high voltage, the external surface of said flared part being partially covered with an electrically conductive layer, adhering to said external surface, characterized in that the electrically conductive layer is a metal layer whose electrical resistance is less than 1 Ohm per centimeter.
• FIG. 1 is a sectional view of a cathode ray tube according to the invention
• FIGS. 2a and 2b show in perspective the flared rear part mounting a conductive coating according to the invention.
• the cathode ray tube illustrated in Figure 1 is of the type to generate a color image; it includes a glass envelope 10 which is composed of a front face 12, a flared rear part 13, in the form of a funnel, and a substantially cylindrical neck 14.
• An electron gun 15 is placed in the neck 14 and generates one or more electron beams 19, 20, 21 generally co-planar, the axis of the gun coinciding with the longitudinal axis 22 of the tube.
• the front face 12 includes an internal surface forming a luminescent screen 23 and on which are deposited phosphor networks emitting respectively in the three primary colors red, green and blue in order to reproduce a colored image.
• a color selection mask 24 In front of the screen 23 a color selection mask 24 has been placed on which are made multiple openings 25, which may for example be of elongated shape and arranged in vertical lines, each electron beam (19,20,21) crossing the mask through these openings to illuminate the network of phosphors corresponding thereto.
• the electron beams scan the entire image screen 23 thanks to a magnetic deflection created by a deflection device 26, also called deflector.
• the deflector is arranged on the rear part of the tube, near the exit area of the electron beams from the gun.
• a conductive layer 42 is disposed inside the tube, on the internal surface of the flared rear part, which layer is brought to the high anode voltage from the outside by means of an anode button 16 passing through the thickness. of the flared rear part.
• the high voltage is brought to the electron gun by a spring 40 connected to an electrode of the gun, a spring coming into contact with the conductive layer 42.
• a conductive layer 28 is deposited on an area partially occupying the external surface of the flared rear part 13.
• this conductive layer is maintained at ground potential thanks, for example, to electrical connections with the metal anti-implosion belt disposed around the sealing area of the front face to the flared rear part, anti-implosion belt connected to the ground of the high voltage supply.
• the external conductive layer avoids the area around the anode button so as not to have two areas close to each other brought to different potentials of several tens of kilovolts.
• the external conductive layer is produced by bonding to the flared rear part a very conductive metal film.
• This structure was chosen because many metals are available today in the form of a very thin film, the cutting and use of which are easy for application to the surface of the tube. Furthermore, these films are of constant thickness which allows better control than in the past of the uniformity of the surface resistance of said film.
• the external surface of the rear part of the tube is glued, for example using an adhesive spray and the metal film 28, previously cut to the dimensions of the tube, is applied to the part coated with adhesive.
• a metallic film previously coated, on one of its faces with a layer of adhesive is used, which makes it possible to fix the metallic film simply by contact with the surface of the flared part. tube; this makes it possible not to have to handle glue in the tube manufacturing plant, the glue being a dirty material, necessitating significant maintenance of the tools necessary for its handling and for its deposition; moreover, the use of metallic film previously coated with adhesive reduces the time required to obtain a film adhering to the surface of the tube and therefore the total time for manufacturing said tube.
• the metal layer is produced by vacuum evaporation.
• the rear of the tube is placed in an enclosure so that the periphery of the enclosure matches the periphery of the tube.
• a specific quantity of metal is vaporized so conventional inside the enclosure previously evacuated, and is deposited on the rear part of the tube which is thus metallized.
• a mask may preferably have been placed on the rear part of the tube to avoid metallization of certain zones, such as that surrounding the anode button 16, mask which is removed after metallization.
• the quantity of vaporized material determines the thickness of the layer produced and therefore its resistive properties.
• aluminum has many advantages in the industry for manufacturing cathode ray tubes; in addition to the fact that its low resistivity, of the order of 2.5 10 "8 Ohm. m makes it possible to meet the essential characteristic of the invention, aluminum is a material which does not corrode, a requirement required to ensure performance of the tube over time.
• Aluminum can be used in all the embodiments of the invention; it is available industrially in the form of thin films, pre-glued or not, and it can be easily sublimed in empty chambers to aluminize a given surface.
• the metallic film 28 deposited on the external surface of the rear part of the tube is mainly composed of aluminum whose thickness is preferably less than 150 ⁇ m so as to obtain a metallized layer whose linear resistance is less than 0.5 Ohm per centimeter.
• the aluminum layer chosen is 60 ⁇ m thick, which allows a linear resistance of 0.1 Ohm per centimeter to be obtained.
• the metal chosen to produce the metallic layer may be any metal whose resistivity is sufficiently low to obtain the desired linear resistance in a thin layer, less than 1 ohm per centimeter. They can be aluminum alloys or metals whose resistivity is preferably less than 10 "7 Ohm. M.
• the other essential criterion is that the deposited layer does not corrode in order to ensure its electrical characteristics throughout the life of the tube; this characteristic can be obtained either by the intrinsic qualities of the metal chosen, or by means of a suitable treatment of the metal layer deposited on the tube.

Landscapes

• Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
• Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=32750477

Family Applications (1)

Country Status (8)

Family Cites Families (6)

• 2003
  • 2003-01-17 IT IT000068A patent/ITMI20030068A1/it unknown
  • 2003-12-23 EP EP03810018A patent/EP1584098A2/de not_active Withdrawn
  • 2003-12-23 CN CNA2003801084875A patent/CN1735955A/zh active Pending
  • 2003-12-23 WO PCT/FR2003/050210 patent/WO2004066343A2/fr not_active Ceased
  • 2003-12-23 KR KR1020057012839A patent/KR20050092399A/ko not_active Withdrawn
  • 2003-12-23 US US10/542,241 patent/US7256536B2/en not_active Expired - Fee Related
  • 2003-12-23 JP JP2004567030A patent/JP2006521663A/ja not_active Withdrawn
  • 2003-12-23 AU AU2003302202A patent/AU2003302202A1/en not_active Abandoned

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events