MXPA00002341A - Method of developing a latent charge image - Google Patents

Abstract

A method for developing an electrostatic latent charge image formed on a photoreceptor (36) which is disposed on an interior surface of a faceplate panel (12) of a CRT (10) utilizes a developer (40) having a developingchamber (42) with a sidewall (50) closed by a bottom end (44) and a panel support (46) at the other end. An opening (48) is formed through the panel support (46) to provide access to and support for the faceplate panel (12). A panel grid (74) is disposed in proximity to said interior surface of said faceplate panel (12) and operated at a first potential to control the electric field from the latent charge image. A tank grid (56) is disposed within said developer (40) and spaced from the sidewall (50), the bottom (44) and the panel grid (74). A triboelectric gun (84) is disposed within the developer (40) for imparting a desired charge polarity to the screen structure material and for distributing the charged screen structure material onto the latent charge image. An electrometer (66) and a phosphor deposition monitor (90) monitor the deposition of the charged screen structure material onto the latent charge image;and a controller (68) terminates the deposition of the charged screen structure material when sufficient material is deposited. The tank grid (56) is operated at a potential different from the potential on the panel grid (74) so that the tank grid (56) controls the electrostatic forces within the developer (40).

Description

METHOD FOR DISCLOSING A LATENT LOAD IMAGE The invention relates to a method for revealing a latent charge image on a photoreceptor that is placed on an inner surface of a cathode ray tube (CRT) faceplate and, more particular, to a method of operating a tank grid to control the electrostatic forces in a developing apparatus. BACKGROUND OF THE INVENTION An apparatus for developing a latent charge image on a photoreceptor that is placed on an interior surface of a viewing face plate in a deployment device, such as a cathode ray tube (CRT) that utilizes triboelectrically charged particles. is disclosed in U.S. Patent Serial Number 5,477,285 issued December 19, 1995 to GHN Riddie and co-inventors. In a first embodiment of the developing apparatus, a developing chamber is described having insulating side walls and an insulating panel support. A triboelectric gun for directing loaded screen structure material in a photoreceptor provided on the inner surface of the front panel of the cathode ray tube is placed in the developing chamber. A disadvantage of the developing chamber is that the electrically charged screen structure material creates a charge buildup in the insulating side walls. The electrostatic forces of the side walls are not well controlled and the forces vary as the load varies. For example, when the developing chamber is cleaned, to remove excess material from the screen structure of the side walls, the electrostatic charge decreases. The electrostatic forces also vary when the humidity changes. Variations of 500 to 5000 volts have been recorded in the electrostatic fields measured from a developing developing chamber. In another embodiment of a developing chamber described in the aforementioned US Patent No. 5,477,285, an inner chamber of a conductive material, comprising a side wall and a lower part, is placed in the developing chamber. . The inner conductive chamber is floating electrically and attracts excess screen structure material out of the cloud of dust generated in the chamber by the triboelectric gun, thus preventing an accumulation of space charge in the chamber and a high electrical potential in the chamber. wall of the camera. However, it has been determined that the screen structure material accumulates in the conductive side wall of the inner chamber in the form of "snow banks" of agglomerated particles, which can cause large particles agglomerated on the screen if the particles they separate from the side wall. Thus, it is desirable that the disadvantages of the above development apparatus be addressed and eliminated. BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, there is disclosed a method for developing an electrostatic latent charge image that is formed in a photoreceptor that is placed on an inner surface of a front plate panel in a cathode ray tube. The method uses a developer tank having a side wall closed at one end by a lower portion and at the other end by a panel support having an opening therethrough to provide access to the panel. A panel grid is placed in proximity to the inner surface of the faceplate panel and a first potential is operated to control the electric field of the latent charge image. A tank grid is placed in the developer tank and separated from the side wall, the bottom and the panel grid. A triboelectric gun assembly is placed in the developer tank to impart a desired load polarity to the screen structure material and to distribute the material of screen structure loaded in the latent load image. Means are provided for monitoring the deposition of the loaded screen structure material in the latent load image and means for terminating the deposition of the loaded screen structure material. The novelty lies in operating the tank grid at a potential different from the potential in the panel grid so that the tank grid controls the electrostatic forces in the developer tank. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1, is a plan view, partially in axial section, of a color cathode ray tube made in accordance with the present method; Figure 2 is a section of a cathode ray tube front plate panel with a die on an interior surface thereof during a step of the manufacturing process; Figure 3 is a section of a completed screen assembly of the tube shown in Figure 1; Figure 4 is a section of a cathode ray tube front plate panel showing a photoreceptor superimposed on the die during another step of the manufacturing process; and Figure 5 is a front view of a developing apparatus used in the present method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 shows a color cathode ray tube 10 having a glass envelope 11 comprising a rectangular faceplate panel 12 and a tubular neck 14 connected by a rectangular funnel 15. Funnel 15 has an internal conductive coating (not shown) that contacts an anode button 16 and extends to the neck 14. The panel 12 comprises a front viewing plate 17 and a peripheral flange or side wall 18, which is sealed to the funnel 15 by a glass frit 19. As shown in Figure 2, a relatively thin light absorbing matrix 20, having a plurality of openings 21, is provided on an inner surface of the viewing face plate. A three color match display 22 is on the inner surface of the viewing faceplate 17 and is placed on the die 20. The display 22, shown in Figure 3, is a line display that includes a multiplicity of elements. of screen comprised of red emitting phosphor bands, green emitter and blue emitter R, G, and B, centered on different matrix openings 21 and arranged in groups of colors or three-band or three-dimensional picture elements, in a cyclical order. The bands extend in a direction that is generally normal to the plane in which the electron beams are generated. In the normal mode observation position, the match bands extend in the vertical direction. Preferably, portions of the phosphor bands overlap at least a portion of the light absorbing matrix 20 surrounding the openings 21. Alternatively, a dot screen may also be used. A thin conductive layer 24, preferably of aluminum, is placed on the screen 22 and provides means for applying a uniform potential to the screen, as well as for reflecting light, emitted from the phosphor elements, through the front plate 17. new with reference to Figure 1, a multi-aperture color selection electrode, such as a shadow mask or focus mask, is removably mounted, by conventional means, in predetermined spaced relation to the screen assembly. The color selection electrode 25 is removably attached to a plurality of bolts 26 embedded in the side wall 18 of the panel 12.

An electron gun 27, shown schematically by interrupted lines, is mounted centrally on the neck 14, to generate and direct three electron beams 28 along converging paths, through the openings in the color selection electrode. 25, to screen 22. The electron gun is conventional and can be any suitable gun known in the art. The tube 10 is designed to be used with an external magnetic deflection yoke, such as the 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 that cause the beams to scan horizontally and vertically, in a rectangular frame, on the screen 22. The initial plane of deviation (in zero deviation) is shown by the line PP in Figure 1, in about half of the yoke 30. For simplicity, the actual curvatures of the trajectories of the deflection beam, in the deviation zone, are not shown. The screen 22 is manufactured by an electrophotographic (EPS) screen formation process which is described in United States Patent Serial Number 4,921,767 issued to Datta and co-inventors of May 1, 1990. Initially, clean the panel 12 washing it with a caustic solution, it is rinsed with water, etched with stabilizing hydrofluoric acid and rinsed with water again, as is known in the art. Then, on the inner surface of the observation front plate 17 the light absorbing matrix 20 is preferably provided, using the conventional wet matrix process described in United States Patent Serial Number 3,558,310, granted to Mayaud on the 26th. January 1971. In the wet matrix process, a photoresist solution is applied to the interior surface, for example, by spin coating, and the solution is dried to form a photoresist layer. Then, the color selection electrode 25 is inserted into the panel 12 and the panel is placed in a three-in-one beacon (not shown) that exposes the photoresist layer to actinic radiation from a light source that projects light through the openings in the color selection electrode. The exposure is repeated twice more, with the light source placed to simulate the trajectories of the electron beams of the three electron guns. The light selectively alters the solubility of the exposed areas of the photoresist layer. After the third exposure, the panel is removed from the headlight and the color selection electrode is removed from the panel. The photoresist layer is developed, using water, to remove the most soluble areas of the same, thus exposing the underlying inner surface of the faceplate and leaving the exposed areas less soluble. Then, a suitable solution of light absorbing material is provided uniformly on the inner surface of the faceplate panel, to cover the exposed portion of the vision faceplate and the less soluble areas retained from the photoresist layer. The layer of the light absorbing material is dried and developed using a suitable solution which will dissolve and remove the retained portion of the photoresist layer and the superposed light absorbing material, forming the openings 21 in the matrix which adheres to the inner surface of the front view plate. For a faceplate panel 12 having a diagonal dimension of 51 cm, the openings 21 formed in the matrix 20 have a width of approximately 0.13 to 0.18 mm, and the opaque matrix lines have a width of approximately 0.1 to 0.15 mm. The inner surface of the vision front plate 17, which has the matrix 20 thereon, is then coated with a suitable layer of a volatilizable organic conductive (OC) material (not shown) that provides an electrode for an organic photoconductive layer ( OPC) volatilizable superimposed, also not shown. The organic conductive layer and the organic photoconductive layer, in combination, comprise a photoreceptor 36, shown in Figure 4. Suitable materials for the organic conductive layer include certain quaternary ammonium polyelectrolytes described in U.S. Pat. Series 5,370,952, granted to P. Datta and co-inventors on December 6, 1994. Preferably, the organic photoconductive layer is formed by coating the organic conductive layer with a solution containing polystyrene; an electron donor material, such as 1,4-di (2,4-methyl phenyl) -1,4 diphenybutatriene (2,4-DMPBT); electron accepting materials, such as 2,4,7-trinite-9-fluorenone (TNF) and 2-ethylanthroquinone (2-EAQ); and a suitable solvent, such as toluene, xylene, or a mixture of toluene and xylene. A surfactant, such as silicone U-7602 and a plasticizer, such as dioctyl phthalate (DOP), can also be added to the solution. Surfactant U-7602 is available from Union Carbide, Danbury, CT. The photoreceptor 36 is electrostatically charged in a uniform manner using a corona discharge device (not shown) but described in United States Patent Serial Number 5,519,217, issued May 21, 1996, to Wilbur and co-inventors, which charges the photoreceptor 36 to a voltage in the range of about +200 to +700 volts. The color selection electrode 25 is then inserted into the panel 12, which is placed in a headlight (not shown) and the positively charged organic photoconductive layer of the photoreceptor 36 is exposed, through the color selection electrode 25, to light of a xenon flash lamp, or other light source of sufficient intensity, such as a mercury arc, placed in the headlight. The light passing through the openings in the color selection electrode 25, at an angle identical to one of the electron beams of the tube electron gun, discharges the illuminated areas in the photoreceptor 36 and forms a charge image. latent (not shown). The color selection electrode 25 is removed from the panel 12 and the panel is placed in a first phosphor developer 40, as shown in Figure 5. The developer 40 comprises a developing chamber 42 having a lower end 44 and an upper end, or support of the panel 46. The support of the panel 46, preferably, is formed of insulating material and includes an opening 48 therethrough that is slightly smaller in dimensions than the front plate panel of cathode ray tube 12. The panel 12 is supported on the panel support 46. The development chamber 42 further includes an exterior wall 50 extending between the lower end 44 and the panel support 46. A conductive interior wall 52 is separated from the wall outer 50 and extends from an inner lower end 54 to a plane A-A adjacent to the panel support 46. The inner conductive wall 52 and the lower end 44 form a grid of the tank 56 that is connected to a high voltage source 55 and is polarized at a potential of at least 2 kV volts, but preferably in the range of 3 to 15 kV to repel the positively charged cloud of phosphor particles in chamber 42 and provide control of the cloud. A space 57, located in the upper periphery of the chamber 42, between the outer and inner side walls 50 and 52, provides a path for removing excess phosphor particles that do not deposit in the latent charge image formed in the photoreceptor 36. An exhaust port 58 is connected to a pump (not shown) to remove excess phosphor particles from the developer 40. An electrical contact, such as a pin contact spring 60, is positioned to contact the one of the bolts 26 embedded in the side wall 18 of the faceplate panel 12. The conductive coating of the photoreceptor 36 is electrically connected, via a contact patch (not shown) to the bolt 26. The contact patch is described in the patent of the United States of America Serial No. 5,156,770, issued to Wetzel and co-inventors on October 20, 1992. The electrical contact 60 is connected to, and grounded at A capacitor 64 develops a voltage proportional to the charge of the triboelectrically charged phosphor particles deposited in the latent charge image in the photoreceptor 36. The voltage developed in the capacitor 64 is monitored by an electrometer 66 and is connected to a controller 68 which is programmed to terminate the phosphor deposition when the voltage reaches a predetermined value corresponding to the required phosphor thickness. Prior to each development cycle, the voltage in the capacitor 64 is discharged to ground through a contact 70, by the action of the controller 68. A high voltage source 72 is connected to a grid of the panel 74 to control the electric field in the vicinity of the image. of latent charge formed in the photoreceptor 36. The structure and function of the panel grid 74 is described in United States Patent No. Serial No. 5,093,217, issued March 3, 1992, to Datta and co-inventors. The grid 74 is positively polarized at approximately 2 to 3 kV and has the same polarity as the triboelectrically charged phosphor particles that are being deposited in the latent charge image.

A developer 40 is required for each of the three color emitting phosphors, to avoid cross-contamination that would otherwise occur if a single developer were used and different color emitting phosphor materials were fed into a common chamber. External to the developing chamber 42 is a phosphorus reservoir 76 which contains a supply of dry powder phosphor particles. During the developing operation, the phosphor particles are transported from the reservoir 76 to a venturi chamber 78 where the phosphor particles are mixed with an adequate amount of air. The actuation of the air supply is achieved by opening a valve 80 which is controlled by the controller 68. The air pressure is fixed by a pressure regulator 82. The phosphor particles are carried to the chamber42 and through a triboelectric gun 84, wherein the phosphor particles are positively charged triboelectrically and directed towards the latent charge image in the photoreceptor 36. The positively charged phosphor particles of the first color are repelled by the positively charged areas in the pr36 and are deposited in the areas downloaded from it by the process known as "inverted" development. In inverted development, the triboelectrically charged particles of screen structure material are repelled by similarly charged areas of the photoreceptor 36 and deposited in the areas discharged therefrom. The phosphorus lines of the emitter phosphor of the first color are deposited in selected openings of the openings 21 in the matrix 20 and accumulate in width and height from the center of the openings 21 to the edges of the matrix surrounding them. When the deposition is completed, it is necessary that the phosphor lines be slightly larger in size than the size of the openings 21 in the light absorbing matrix 20, as shown in Figure 3, to completely fill each of the openings , and slightly overlap the absorbent matrix of light surrounding the openings. With reference to Figure 5, a phosphor deposition monitor (PDM) apparatus 90 includes a support assembly having a pair of side rails 92 and 93 that are mounted to the support surface 46 of the developer 40, adjacent the aperture. 48. The side rails 92 and 93 are sufficiently spaced to allow a faceplate panel 12 to be placed on the support surface 46 without interference from the side rails. A first pair of cross rails 94, only one of which is shown, is slidably attached to the side rails 92 and 93 and supports a first image forming device 96 that is slidably attached to the cross rails 94. second image-forming device 99 is also slidably connected to the cross-rails 94. The image-forming devices, 96 and 99, are mounted approximately 15 correction matrix on top of the viewing face plate 17. Each of the forming devices 96 and 99 can be moved in the x- and y-plane and can be tilted to be substantially parallel to the curvature of the viewing face plate 17. Imaging devices 96 and 99 can be placed anywhere above the 17 front view plate and provide a visual means of monitoring the deposition of match structure screen materials. The PDM apparatus 90 is disclosed in co-pending US Patent Application Serial No. 728,010, filed October 9, 1996 by Roberts, Jr. and co-inventors. In the present process, the potential exerted in the charged phosphorus cloud is dominated by the potentials in the grid of tank 56 and the grid of panel 74. The voltage of the tank grid can be adjusted in the range of 3 - 15 kV to control the electrostatic forces in the development chamber 42, thus optimizing the development process and the uniformity of the flow of phosphorus in the dust cloud. Another advantage of the tank grid 56 is that it can be used to remove the accumulated phosphor from the panel grid by "reverse" polarization of both grids, i.e., by polarizing grids 56 and 74 with negative voltages so that the particles of phosphorus can be carried from the panel grid 74 to the developer tank 40 where they can be removed through the exhaust port 58. Although described in the form of a phosphor developer, the present invention can also be used for applications of electrostatic sprays of aerosols such as fixative materials that are sprayed onto EPS deposited phosphor screens to improve the adherence of the phosphors to the underlying photoreceptor and give the films a flat shape, such as the layers comprising the photoconductor that are deposited in the matrix layer.

Claims (4)

1. CLAIMS 1. A method to reveal, with screen structure material, dry powder, triboelectrically charged • suitably, an electrostatic latent charge image formed in a photoreceptor 36 that is placed on an interior surface of a faceplate panel 12 of a cathode ray tube 10, using a developer apparatus 40 comprising: a development chamber 42 having a side wall 50 closed at one end by a lower portion 44 and at the other end by a panel support 46 having an opening 48 therethrough to provide access to said faceplate panel 12; a grid of the panel 74 in proximity to said inner surface of such a faceplate panel 12; a tank grid 56 positioned within said developing chamber 42 and spaced apart from such side wall 50, said lower portion 44 and such panel grid 74; a triboelectric barrel 84 for imparting a desired load polarity to such screen structure material and for distributing such a screen structure material loaded in such a latent load image; means 66, 90 for monitoring the deposition of such screen structure material loaded in said latent load image; and means 68 for completing the deposition of such loaded screen structure material, wherein said method includes the steps of operating such panel grid 74 at a first potential to control an electric field of said latent charge image and operate such a grid tank 56 to a second potential, different from said first potential to control the electrostatic forces in such a developer tank.
2. 2. The method according to claim 1, wherein said second potential is greater than said first potential.
3. 3. The method according to claim 2, wherein said first potential is approximately 2 kV.
4. 4. The method according to claim 2, wherein said second potential is in the range of about 3 to 15 kV.