CRT developing apparatus

#The invention relates to an apparatus for developing a latent charge image formed on a photoreceptor which is disposed on an interior surface of an output window of a display device, such as a cathode-ray tube (CRT), and, more particularly, to a developer which provides a triboelectric charge of a desired polarity to the developing materials.

#U.S. Pat. No. 4,921,767, issued to Datta et al. on May 1, 1990, discloses a method for electrophotographically manufacturing a luminescent screen assembly on an interior surface of a CRT faceplate panel, using dry-powdered, triboelectrically-charged, screen structure materials deposited on a latent image formed on an electrostatically charged photoreceptor. The photoreceptor comprises a photoconductive layer overlying a conductive layer, both of which are deposited, serially, as solutions, on the interior surface of the CRT panel. In the aforementioned patent, the four developers utilized for depositing the screen structure materials are the so-called "powder cloud" developers of the type in which particles of screen structure materials are triboelectrically charged by contacting surface-treated carrier beads. The charged particles of screen structure materials are then expelled from the developers and onto the latent image. A drawback of this type of powder cloud developer is that it is unsuitable for manufacturing production quantities of luminescent screens, where the development time for depositing each of the different materials must be of the order of about 15 seconds for each material.

#In accordance with the present invention, an apparatus for developing a latent image formed on a photoreceptor, which is deposited on an interior surface of an output window of a display device, is disclosed. The developing apparatus includes a developing chamber, having a support surface for supporting the output window, a screen structure material reservoir for storing, deagglomerating and feeding the screen structure material, and a triboelectric gun assembly communicating with the reservoir. The gun assembly includes triboelectric charging means for imparting a desired charge polarity to the screen structure material and at least one material dispersing means spaced from the support surface for distributing the charged material for deposition onto the latent image.

#FIG. 1 is a plan view, partially in axial section, of a color CRT made according to the present invention.

#FIG. 2 is a section of a screen assembly of the tube shown in FIG. 1.

#FIG. 3 is a section of an alternative embodiment of a screen assembly of the tube shown in FIG. 1.

#FIG. 1 shows a color display device, such as a CRT, 10 having a glass envelope 11 comprising a rectangular faceplate panel 12 and a tubular neck 14 connected by a rectangular funnel 15. The funnel 15 has an internal conductive coating (not shown) that contacts an anode button 16 and extends into the neck 14. The panel 12 comprises a viewing faceplate or substrate 18 and a peripheral flange or sidewall 20, which is sealed to the funnel 15 by a glass frit 21. A three color luminescent screen 22 is carried on the interior surface of the faceplate 18. The screen 22, shown in FIG. 2, preferably is a line screen which includes a multiplicity of screen elements comprised of red-emitting, green-emitting and blue-emitting phosphor stripes, R, G and B, respectively, arranged in color groups or picture elements of three stripes, or triads, in a cyclic order and extending in a direction which is generally normal to the plane in which impinging electron beams are generated. In the normal viewing position for this embodiment, the phosphor stripes extend in the vertical direction. Preferably, the phosphor stripes are separated from each other by a light-absorptive matrix material 23, as is known in the art. Alternatively, the screen can be a dot screen. A thin conductive layer 24, preferably of aluminum, overlies the screen 22 and provides a means for applying a uniform potential to the screen as well as for reflecting light, emitted from the phosphor elements, through the faceplate 18. The screen 22 and the overlying aluminum layer 24 comprise a screen assembly.

#Again with respect to FIG. 1, a multi-apertured color selection electrode, or shadow mask, 25 is removably mounted, by conventional means, in predetermined spaced relation to the screen assembly. An electron gun 26, shown schematically by the dashed lines in FIG. 1, is centrally mounted within the neck 14, to generate and direct three electron beams 28 along convergent paths through the apertures in the mask 25, to the screen 22. The gun 26 may, for example, comprise a bi-potential electron gun of the type described in U.S. Pat. No. 4,620,133, issued to Morrell et al. on Oct. 28, 1986, or any other suitable gun.

#The tube 10 is designed to be used with an external magnetic deflection yoke, such as yoke 30, located in the region of the funnel-to-neck junction. When activated, the yoke 30 subjects the three beams 28 to magnetic fields which cause the beams to scan horizontally and vertically in a rectangular raster over the screen 22. The initial plane of deflection (at zero deflection) is shown by the line P--P in FIG. 1., at about the middle of the yoke 30. For simplicity, the actual curvatures of the deflection beam paths in the deflection zone are not shown.