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
  • H01J29/86—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
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2229/00—Details of cathode ray tubes or electron beam tubes
  • H01J2229/92—Means providing or assisting electrical connection with or within the tube
  • H01J2229/925—Means providing or assisting electrical connection with or within the tube associated with the high tension [HT], e.g. anode potentials

Definitions

• This invention relates in general to color television picture tubes, and in particular to an improved stud coating composition and method for providing an electrical path between the color picture tube shadow mask and screened faceplate.
• the color television cathode ray picture tube comprises a glass bulb, consisting of a funnel and a faceplate with the faceplate sealed to the flared end of the funnel.
• An electron gun is mounted in the neck portion of the funnel to provide one or more electron beams.
• the faceplate has a nearly flat inner surface upon which is deposited groups of phosphors that are excited by the electron beams.
• the shadow mask provides color selection by masking groups of the phosphors so that they are excitable by only one of the electron beams.
• the shadow mask is attached in a precise relationship with the faceplate by means of a plurality of suspension springs which detachably engage metal studs that extend from the faceplate.
• An electrically conductive coating of colloidal graphite is applied to the internal surface of the funnel and has a high voltage applied thereto through an anode button in the funnel wall.
• the electrical path for accomplishing this comprises one or more springs that extend from.the shadow mask into engagement with the funnel coating.
• the anode potential on the shadow mask is conducted to the aluminum film through the shadow mask susponsion springs and the metal support studs.
• the metal support studs are painted with a conductive "moustache" that extends to the aluminum film.
• the material comprising the conductive moustache is commonly referred to as stud coating.
• a prior art conductive material that formerly was in extensive use as a stud coating comprises a water-soluble silicate in a form suitable for application by a brush.
• the water was driven off in a subsequent tube baking process, leaving a hard, electrically conductive film between the studs and the aluminum film.
• the water based solutions commonly-contained either potassium silicate or sodium silicate as a binder and did not always "wet" properly nor adhere to components. Consequently, fragments of the coating often flaked off the studs and glass area and blocked one or more apertures in the shadow mask which often resulted in an unacceptable tube. Such particles in the gun area could also result in interelectrode arcing and/or cathode poisoning.
• the water-soluble coatings required an extra baking cycle after aluminizing and before applying the stud Dag.
• the glass frit type of stud coating described in the above-discussed patents manifests a deficiency during a breakdown or interruption in the production process. Specifically, a problem arises when tubes are subjected to the high Lehr temperatures for an extended time period, such as occurs when the production line stops. The lead oxide in the glass frit reacts with the carbon in the graphite to form carbon dioxide and lead and destroys the conductivity of the stud coating. In many instances close attention to Lehr heat control during line shutdowns can obviate the problem, although during extensive shutdowns, the difficulty may still be present.
• the problem is often compounded by the fact that a sufficient amount of the stud coating may remain intact to enable the tube to pass final inspection and testing although it may be prone to recurrent arcing and ultimate failure in the field. While the problem is not severe in terms of numbers, it is catastrophic to the picture tube and an obvious expense and inconvenience to the consumer, since it may not show up during routine testing of the picture tube.
• a principal object of the invention is to provide an increase in the performance reliability of color cathode ray tubes.
• Another object of the invention is to provide a reduced manufacturing cost for color cathode ray tubes.
• a further object of the invention is to provide a cathode ray tube with minimal stud coating-related arcing.
• color cathode ray tubes have a phosphor bearing imaging faceplate overlaid successively with a lacquer film and an aluminum film.
• a shadow mask is secured next to the faceplate by a plurality of-metallic studs extending from the faceplate.
• An electrical bridge is provided between the shadow mask and the aluminum film via the studs and a stud coating to maintain the aluminum film at anode potential.
• the shadow mask is electrically connected to the anode voltage that exists on the coating inside the funnel by springs that bridge the nonconductive glass frit seal between the picture tube faceplate and the funnel.
• An improved bake-hard enable solution according to the invention for providing the stud coating electrical bridge or moustache as claimed comprises essentially a mixture of graphite particles in the micron-sized range.
• the particles are In suspension in an evaporable solvent for the lacquer film.
• the suspension includes a thickening agent in an amount sufficient to produce a paintable viscosity for application by a brush.
• the solution may have a viscosity in the range of 200.8 Pa ⁇ s (200800 centripoises) and preferably about 0.55 Pa ⁇ s (550 centripoises) After baking, the solution may have an electrical resistance in the range of 100 to 500 ohms per square.
• the electrically conductive stud coating of the invention may be compounded as follows (produces 3.75 l (one gallon). Equivalent materials supplied by other suppliers may be used.
• the coating preparation should be performed in an area of adequate ventilation with suitable precautionary procedures, such as wearing rubber gloves, respirator masks, lab coats, hair nets and shoe covers being followed by involved personnel. Care must also be taken because of the flammability of the N-butyl acetate and the resin binder solution.
• the stud coating prepared and used according to the invention eliminates the problem identified above in connection with the use of a glass frit based stud coating.
• a major leature of the new stud coating is its flexibility (after processing) which enhances its resistance to flaking. Additionally, the inventive stud coating is less costly and still enables the benefit of not requiring an extra bake cycle for the picture tube.
• the prior art frit-based stud coating was applied to the stud and aluminum film and subjected to a temperature of 450 degrees Centigrade for a period of two hours.
• the resistivity of the coating rose from 300 ohms to 73.000 ohms.
• the resistivity remained at 300 ohms.

Landscapes

• Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
• Paints Or Removers (AREA)
• Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
• Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=25432681

Family Applications (1)

Country Status (7)

Family Cites Families (3)

• 1998
  • 1998-08-13 ID IDP981129A patent/ID21510A/id unknown
  • 1998-08-14 DE DE69823284T patent/DE69823284T2/de not_active Expired - Fee Related
  • 1998-08-14 EP EP98402061A patent/EP0898295B1/en not_active Expired - Lifetime
  • 1998-08-14 KR KR1019980033022A patent/KR100266622B1/ko not_active IP Right Cessation
  • 1998-08-17 JP JP10230605A patent/JP3108406B2/ja not_active Expired - Fee Related
  • 1998-08-17 CN CN98117300A patent/CN1111572C/zh not_active Expired - Fee Related
  • 1998-09-04 TW TW087114680A patent/TW410359B/zh not_active IP Right Cessation

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