MXPA97001453A - Method of manufacturing electrofotografica de unensamble de panta - Google Patents

Abstract

The present invention relates to a luminescent screen assembly assembly on an inner surface of a front plate panel of a CRT cathode ray tube, comprising the steps of: coating the inner surface of the panel with a conductive material organic, volatilizable to form a first organic conductive layer (OC), cover the first OC layer with a volatilizable photoconductive material to form a first organic photoconductive layer (OPC), establish a substantially uniform electrostatic voltage on the first OPC layer, expose the selected areas from the first OPC layer to visible light to affect the voltage thereon, without affecting the voltage over the unexposed area of the first OPC layer; depositing a light absorbing screen structure material, triboelectrically loading onto the unexposed area of the first layer OPC to form a substantially continuous matrix of mater The light absorber having open areas therein, wherein the improvement comprises: (a) forming a planarization layer, (b) overcoating the planarization layer with a second coating of the organic conductive material, volatilizable to form a second layer OC and (c) overcoating the second OC layer with a second coating of the organic photoconductive, volatilizable material to form a second layer O

Description

METHOD OF ELECTROPHOTOGRAPHIC MANUFACTURE OF A SCREEN ASSEMBLY The present invention relates to a method of manufacturing a luminescent screen assembly for a cathode ray tube (CRT) by the electrophotographic (EPS) projection process, using triboelectrically loaded screen structure materials and, more particularly, to a method for eliminating the mismatch of subsequently deposited phosphors caused by the loading properties of a previously deposited EPS matrix and, to form a "planarization" layer that provides a smooth surface for the screen assembly.

BACKGROUND OF THE INVENTION In the process of electrophotographic projection (EPS) described in U.S. Patent No. 4,921,767, issued to Datta et al., May 1, 1990 and in U.S. Patent No. 5,229,234, issued to Riddie et al., On July 20, 1993, color-emitting phosphors are deposited. triboelectrically charged, in dry powder, serially on an electrostatically charged photoreceptor having a triboelectrically charged light absorbing matrix, in dry powder thereon. The photoreceptor comprises an overlying organic photoconductor layer (OPC), preferably an organic conductive layer (OC), which are deposited, in bulk, on an internal surface of a CRT faceplate panel. Initially, the OPC layer of the photoreceptor is electrostatically charged to a positive potential, using an appropriate corona discharge apparatus of the type described in U.S. Patent No. 5,083,959, issued to Datta et al, on January 28, 1992. Afterwards, the selected areas of the photoreceptor are exposed to the visible light to discharge those areas, without affecting the load on the unexposed area. Next, the light-absorbing, negatively charged light material is deposited by direct development, over the unexposed area, charged from the photoreceptor to form a substantially continuous pattern of light-absorbing material, in the so-called matrix, which has open areas in it A fi In order to achieve sufficient optical density, it is necessary to accumulate a sufficient amount of light absorbing material. This, however, results in a matrix having a relatively rough surface. The photoreceptor and matrix are recharged by the corona discharge apparatus to impart An electrostatic charge to them It is desirable that the charge on the photoreceptor be of the same magnitude as that on the previously deposited matrix, however, it has been determined that the photoreceptor and the matrix are not necessarily charged to the same potential. Acceptance of charge of the matrix is different from acceptance of photoreceptor charge Consequently, when different selected areas of the photoreceptor are exposed to visible light to discharge those areas, to facilitate the inverse development with color-emitting phosphorus materials tpbo-electrically charged in the form positive, the matrix retains a positive charge of a different magnitude to that positive charge on the unexposed area of the photoreceptor. This difference in charge influences the deposition of positively charged color-emitting phosphor materials, causing the phosphors to be repelled more strongly by the charge on the matrix, than by the charge on the unexposed area of the photoreceptor. This stronger repellent effect of the matrix causes the color-emitting phosphors to shift slightly from their desired locations on the photoreceptor. Although, the repellent effect of the matrix is small, it is sufficient to narrow the width of the color emitting phosphor lines so that the lines do not They make contact and overlap the edges of the matrix. Therefore, there are slight spaces between the phosphorus lines and the surrounding matrix. These spaces are unacceptable since they reduce the brightness of the phosphorus in each image element., the spaces are visible when the screen assembly is aluminized to provide a reflector backing and anode contact to the screen assembly. A method of reducing the repellent effect of the EPS-deposited matrix is described in United States Patent Application no. of sene 250,231, filed on May 27, 1994 by Ritt et al., and entitled, METHOD OF DEPOSITION OF ELECTROPHOTOGRAPHIC PHOSPHORUS. In that application, instead of using an EPS-deposited matrix, a conventional wet pulp matrix is formed by the process described in U.S. Patent No. 3,558,310, issued to Mayaud et al., January 26, 1971. The conventional matrix is formed directly on the inner surface of the faceplate. The conventional matrix is thin and smooth and has the desired opacity so that the OC and OPC layers can be deposited directly on it. Additionally, superimposed OC and OPC layers eliminate the electrostatic interaction between the matrix and the EPS-deposited phosphors. However, to improve the efficiency of the projection operation and to have a completely dry projection process, it is also desirable to deposit the matrix by the EPS process, but without the damaging electrostatic interaction described above. Therefore there is a need to electrically isolate the previous EPS-deposited matrix so that the matrix is not charged electrostatically during the EPS deposition of the three color-emitting phosphors and, to form a planarization layer that provides a smooth surface for the process Subsequent screen assembly, so that the matches are in proper match with respect to the matrix.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, an electrophotographic manufacturing method of a luminescent screen assembly on an inner surface of a faceplate panel of a colored CRT comprises the steps of coating the inner surface of the panel with an organic, volatilizable conductive material. to form an organic conductive layer (OC) and, to cover the OC layer with a photoconductive, volatilizable material to form an organic photoconductive layer (OPC). Next, a substantially uniform voltage is established in the OPC layer and, the selected areas of the layer OPC are exposed to visible light to affect the voltage on it, without affecting the voltage on the exposed area of the OPC layer. Then, the triboelectrically charged light absorber screen structure material is deposited on the unexposed area of the the OPC layer, to form a substantially continuous matrix of light absorbing material having areas The present method is an improvement over the above methods since the present method includes the additional steps of forming a layer of planarization on the OPC layer overlaying the layering layer with a second coating of the organic conductive material, volatilizable for forming a second OC layer, and then, overcoating the OC layer with a second coating of volatizable, organic photoconductive material to form a second OPC layer. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail, with reference to the accompanying drawings, in which: Fig. 1 is a plan view, partially in axial section, of a color CRT made in accordance with the present invention, Fig. 2 is a section as a tube screen assembly shown in Fig. 1; Figs. 3-8 show a section of a faceplate panel during several conventional stages in the EPS process; Fig. 9 is a section of the faceplate panel in accordance with a novel process embodiment; and Fig. 10 is a section of the faceplate panel made in accordance with a second embodiment of the novel process.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Fig. 1 shows a color CRT 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) which makes contact with the anode button and extends inside the neck 14. The panel 12 comprises a front plate or substrate 18 and a peripheral flange or side wall 20, which is sealed to the funnel 15 by the glass frit 21 A screen Three-color match 22 is carried on the inner surface of the faceplate 18 The display 22, shown in Fig. 2 is a screen including a multiplicity of display elements comprised of phosphor bands emitting red, emitting green and station of blue R, G and B respectively, placed in groups of color or image elements of three bands or triads, in a cyclical order The bands extend in a direction in which it is generally normal to the plane in which the electron beams were generated In the normal view position of the mode, the phosphor bands extend in the vertical direction Preferably, at least portions of the phosphor bands overlap a light absorbing matrix , relatively thin 23 as known in the art A knitted screen can also be formed by the novel process A thin conductive layer 24, preferably of aluminum, is superimposed on the screen 22 and provides means to apply uniform potential to the screen, thus how to reflect the light, emitted from the phosphor elements, through the front plate 18 The screen 22 and the superimposed aluminum layer 24 comprise a screen assembly A multiple aperture color selection electrode or a shadow mask 25 removably mounted by conventional means, in predetermined separate relation to the screen assembly An electronic cannon 26, schematically mounted by the dotted lines in Fig. 1, is centrally mounted within the neck 14, to generate and direct three electronic beams 28 along converging paths, through from the openings in the mask 25, to the screen 22 The electronic cannon is conventional and can be any cannon known in the art. The tube 10 is designed to be used with an external magnetic deflecting yoke, such as the yoke 30, located in the funnel-to-neck junction region. When activated, the yoke subjects the three beams 28 to magnetic fields which cause the you scan horizontally and vertically, in a lighted frame, on the screen 22 The initial plane of deflection (in the zero deflection) is shown by the line PP in Fig 1, approximately in the middle of the yoke 30 For simplicity, the current curvatures of the deflection beam paths, in the deflection zone, are not shown. The screen is manufactured by the EPS process described in U.S. Patent No. 4,921,767. Portions of that process are shown in FIGS. 3 to 8. Initially, the panel 12 is prepared for the deposition of a light absorbing matrix 23 by washing the panel with a caustic solution, rinsing it in water, etching it with hydrofluoric acid in its pH and rinsing it again with water as is known in the art. Then the inner surface of the display area 18 of the faceplate panel 12 is coated with an organic, volatilizable conductive material to form an organic conductive (OC) layer 32 which provides an electrode for an organic, volatilizable, superimposed photoconductive layer (OPC) 34. The OC layer 32 and the OPC layer 34, in combination, form a photoreceptor 36. The front plate structure having the photoreceptor 36 comprising the OC layer. 32 with the OPC layer 34 therein is shown in Fig. 3. Materials suitable for the OC 32 layer include certain quaternary ammonium polyelectrolytes described in U.S. Patent No. 5,370,952, issued to Datta et al., on December 6, 1994. The OPC layer 34 is formed of a suitable resin, an electron donor material, an electron acceptor material, a surfactant and an organic solvent, which A solution is coated on the OC 32 layer. Examples of suitable materials used to form the OPC layer 34 are described in co-pending US Patent Application no. series 168,486, filed on December 22, 1993, by Datta et al. In order to form the matrix 23 by the EPS process, the OPC layer 34 is electrostatically charged to a suitable potential, within the range of about +200 to +700 volts, using a corona discharge device 38, of the type shown schematically in Fig. 4 and described in U.S. Patent No. 5,083,959. Then, the shading mask 25 is inserted into the faceplate panel 12 and the panel is placed over a point source of light, shown schematically in FIG. 5 as the device 40, which exposes the OPC layer 34 to visible light from a light source 42 that projects light through the openings in the shadow mask. The exposure is repeated two or more times with the light source located to stimulate the trajectories of the three electron beams from the electronic cannon 26 of the tube 10. The light discharges the exposed areas of the OPC layer 34 where the materials will subsequently be deposited. of phosphorus, but leaves a positive charge on the unexposed area of the OPC layer 34 After the third exposure, the panel is removed from the point source of light and the shadow mask is removed from the panel The positively charged area of the OPC layer 34 is developed directly by deposition thereon of triboelectrically charged particles positively of light absorbing material from a developer 44 of the type described in the United States Patent Application No. 132., 263, filed on October 6, 1993, by Riddie et al. The suitable light absorbing material generally contains a black pigment that is stable at a pipe process temperature of 450 ° C. The pigments suitable for use in the material manufacturing Light absorber include manganese iron oxide cobalt oxide iron, zinc sulfide iron, and black carbon insulator The light absorber material is prepared by blending-mixing the pigment, a polymer and an appropriate charge control agent that controls the magnitude of the charge transferred to the material, as described in the aforementioned U.S. Patent No. 4,921,767. A triboelectric barrel 46 within the developer 44 provides a negative charge to the light absorbing matrix particles. The negatively charged light absorbing particles of the matrix material are not attracted to the discharge areas of the OPC layer 34, but are attracted towards the positive charge area surrounding the discharged area, thereby forming the openings or windows in the otherwise substantially continuous matrix, to which the light-emitting phosphors will subsequently be superposed. As described in Patent Application No. 5,229,234, a second deposition of the matrix material can be done to increase the opacity of the matrix. The die 23, after development, is shown in Fig. 7. For the face plate having a diagonal dimension of 51 cm (20 inches), the window openings formed in the die have a width of about 0.13 to 0.18 mm. and, the matrix has a width of approximately 0.1 to 0.15 mm. As shown in Fig. 8 and described in the aforementioned U.S. Patent No. 4,921,767, the light absorbing material of the matrix 23 is fused to the overlaid OPC layer 34 to prevent movement of the material during the process Subsequent In the above EPS process, described in U.S. Patent No. 4,921,767, the coated matrix faceplate panel is uniformly recharged to a positive potential and exposed again by passing visible light through the openings in the mask. shadow to form a charge image and, development with color emitting matches However, as described above, matrix 23, in the previous process, acquires an electrostatic potential, during the recharge stage, which is different, and more positive that, the electrostatic potential acquired by the OPC layer 34 The higher positive voltage on the matrix 23 repels the phosphorus particles charged tpboelectpcamente in a positive way it goes so that the phosphor particles do not completely fill the openings in the matrix, but leave small spaces, which are objectionable. In order to eliminate those spaces, the matrix 23 must be electrostatically isolated from the subsequently deposited phosphors. This can be achieved by forming a layering layer 35 on the OPC layer 34 and, then, covering the layering layer 35 with a second layer OC 132 and a second layer OPC 134 In the first embodiment of the present method, shown in FIG. 9, the layering layer 35 it is not a separate layer, but is formed by the above-described fusion of the matrix 23 to the OPC layer 34 This is achieved by melting the polymer coating on the light absorbing matrix material or causing the matrix material to be absorbed into the matrix. of the OPC layer 34 by the melting operation Then the flat layer 35 is covered with a second coating of the same coating material Volatilizable organic conductor, used for the OC 32 layer, to form a second OC layer 132 The OC 132 layer is then overcoated with the same volatilizable organic photoconductive coating material, used to form the OPC 34 layer, to form a second layer OPC 134. This structure provides sufficient electrical isolation of the EPS-deposited matrix 23, so that the matrix will not influence the charge on the second OPC 134 layer, during the phosphor deposition described below. A second embodiment of the present method is shown in Fig. 10. The second embodiment is especially useful where the EPS-deposited matrix 23 has been accumulated to provide the required opacity and has a rough surface that prevents direct coating of a continuous OC layer. , a separate planarization layer 135 is provided on the matrix and OPC layer 134 by the application of a film forming emulsion of the type sold under the trademark RHOPLEX B-74, by ROHM and HAAS Co. Philadelphia, PA. The film-forming emulsion contains a volatilizable resin that can be removed by hardening the screen at a suitable temperature. After the planarization layer 135 was formed, the second layer OC 132 described above is overcoated thereon and then the OPC layer 134 is a dust jacket on the OC layer 132 The coating layer 135 provides a smooth and reasonably level surface on which the second OC 132 layer and the second OPC 134 layer of the screen assembly are formed and allows correlation or, coincidence between the matrix 23 and the subsequently deposited color-emitting phosphors A possible disadvantage of the second embodiment is that an additional amount of film-forming material is added to the screen structure and must be removed during the hardening stage of the screen Additional processing of the screen is similar to the previous EPS practice. The second OPC 134 layer is electrostatically charged in a uniform manner using the corona discharge device, described in U.S. Patent No. 5,083,959, which charges the second OPC 134 layer up to a voltage on the scale of about +200 to +700 volts. The shading mask 25 is then inserted into the panel 12 and the second positively charged OPC layer 134 is exposed, through the shading mask 25, to illuminate from a xenon flash lamp or other light source of sufficient intensity, such as a mercury arc, placed inside the point source of light (not shown). The light that passes through the openings in the shading mask 25 at an angle identical to that of one of the electron beams from the electronic tube of the tube, discharges the illuminated areas on the second layer OPC 134 on which the Shading mask is removed from panel 12 and the panel is placed over a first phosphor developer (not shown), although it is described in the co-pending US Patent Application No. 132,263 The first material of color-emitting phosphorus is triboelectrically charged positively within the developer and directed to the second layer OPC134. The first positively charged color emitting phosphor material is repelled by the positively charged areas on the second OPC 134 layer and is deposited on the areas discharged therefrom by the process known in the art as "inverse" development. In the inverse development, the triboelectrically charged particles of the screen structure material are repelled by similarly charged areas of the OPC layer 134 and deposited on the unloaded areas. The size of each of the lines of the first color emitting phosphor is slightly larger than the size of the openings in the matrix to provide full coverage of each aperture, and a slight overlap of the light absorbing matrix material surrounding the apertures . The panel 12 is then recharged using the corona discharge apparatus described above. A positive voltage is established on the second OPC layer 134 and on the first color emitting phosphor material deposited thereon. The light exposure and the phosphor development stages were repeated for each of the two remaining color emitting phosphors, with the position of the light within the point source of light, for each exposure being in accordance with the method described in co-pending United States Patent Application no. of series 250,231. The size of each of the lines of the other color emitting phosphor on the second OPC 134 layer is also larger than the size of the matrix openings, to ensure that no spaces are present and that a slight overlap of the matrix material is provided. light absorber that surrounds the openings. The three light-emitting phosphors are fixed on the second OPC layer 134 in the manner described in the co-pending US Patent Application no. of series 297,740, filed on August 30, 1994, filed by Ritt et al. The screen structure is then coated with aluminum and aluminized to form the luminescent screen assembly. Due to the high amount of organic materials used in the manufacture of the screen assembly, boric acid or ammonium oxalate is sprayed onto the film-coated screen structure prior to aluminization, as is known in the art, to provide small openings in the aluminum layer that allows the volatilized organics to leave without causing bubbles in the aluminum layer. The screen assembly is hardened at a temperature of about 425 ° C for about 30 minutes to remove the volatilizing constituents of the screen assembly

Claims (6)

1. CLAIMS In a method of electrophotographic fabrication of a luminescent screen assembly on an inner surface of a front plate panel (12) of a CRT cathode ray tube (10) comprising the steps of coating the inner surface of the panel with a matepal organic conductor, volatihzable to form a first organic conductive layer (OC) (32), cover the first OC layer with a volatile photoconductive material to form a first organic photoconductive layer (OPC) (34), establish a substantially uniform electrostatic voltage on the first OPC layer, exposing the selected areas of the first OPC layer to visible light to affect the voltage thereon, without affecting the voltage over the unexposed area of the first OPC layer depositing a light absorbing screen structure material, tpbolectly loaded onto the unexposed area of the first OPC layer to form a substantially continuous matrix (23) of light-absorbing material having open areas therein wherein the improvement comprises (a) forming a layer of plating (35,135), (b) overcoating the planarization layer with a second coating of the organic conductive material, volatilizable to form a second layer OC (132); and (c) overcoating the second layer OC with a second coating of the organic photoconductive material, volatilizable to form a second layer OPC (134)
2. 2. The method as described in the claim 1, wherein the planarization layer (35) is formed by fusing the light absorbing material to the first OPC layer (34)
3. 3. The method as described in claim 1, wherein the planarization layer (135) is formed applying a suitable film that is superimposed on the first layer (34) and the light absorbing matrix material (23)
4. 4. The method as described in claim 1. further including the steps of: (d) re- set an electrost voltage substantially uniform attic over the second OPC layer (134); (e) exposing selected areas of the second OPC layer to visible light to affect the voltage thereon; (f) depositing a first color-emitting phosphor tribographically charged on the selected, exposed areas of the second OPC layer so that the first color emitting phosphor overlaps the open areas in the matrix (23) corresponding to the location of the The first color and at least a portion of the light-absorbing material surrounding the open areas recharge the unexposed area of the second OPC layer and the first color-emitting phosphor to restore an electrostatic voltage thereon. ) exposing the selected areas of the second OPC layer to the visible light from a light source to affect the voltage on it, while not affecting the voltages on the unexposed area of the second OPC layer and the first emitter phosphor color, and (i) depositing a second color emitter phosphate tpboeléctpcamente loaded on the selected areas, exposed from the second layer OPC so that the second phosphor overlaps to the open areas in the matrix corresponding to the second color and at least a portion of the light absorbing material surrounding said open area. The method as described in claim 4, further including the steps of (j) recharging the exposed area of the second OPC layer (134) and the first and second color emitting matches to restore an electrostatic voltage thereon; (k) expose the selected areas of the second OPC layer to visible light from a light source to affect the voltage thereon, while not affecting the voltages on the unexposed area of the second OPC layer and the first and second color emitting phosphors, and (I) depositing a third triboelectrically charged color emitter phosphor on the selected, exposed areas of the second OPC layer so that the third phosphor overlaps the open areas in the matrix (23) and at least a portion of the light absorbing material that surrounds said open areas. The method as described in claim 5, including the additional steps of: (m) attaching the phosphors to the second OPC layer (134) of the luminescent screen; (n) cover the screen with film; (o) aluminize the film coated screen; and (p) hardening the aluminized screen to remove the volatilizable constituents thereof to form the luminescent screen assembly. SUMMARY In accordance with the present invention, a method for the electrophotographic fabrication of a luminescent screen assembly on an inner surface of a faceplate panel (12) of a color CRT (10) comprising the steps of coating the inner surface of the panel with an organic conductive material, volatilizable to form an organic conductive layer (OC) (32) and, overcoat the organic layer OC with a volatilizable photoconductive material to form an organic photoconductive layer (OPC) (34) After a voltage is substantially established uniform on the OPC layer, and the selected areas of the layer are exposed to visible light to affect the voltage on it, without affecting the voltage on the unexposed area of the OPC layer. Next, the structure material is deposited. light absorbing screen, tpboelectply loaded onto the unexposed area of the OPC layer to form a substantially continuous matrix (23) of abs material light orbitor having open areas therein The present method is an improvement over the above methods in that the present method includes the additional steps of forming a layer of layering (35,135) on the OPC layer overlaying the layering layer with a second coating of the volatilizable organic conductive material to form a second layer OC (132) and then overcoating the second layer OC with a second coating of the organic photoconductive material, volatilizable to form a second layer OPC (134). The phosphor materials are deposited on an exposed and properly charged second OPC layer so that the phosphors completely overlap the openings in the matrix and protrude at least a portion of the matrix adjacent the openings.