CATAPHORETIC PROCESS FOR SCREENING COLOR RAY TUBES

Abstract: An improved cataphoretic process is disclosed for use in the manufacture of a color cathode ray tube. The process provides for depositing in sequence on the tube screening surface at least two separate patterns of phosphor elements, with each pattern of elements capable of emitting light of a different color when excited. The process according to the invention comprises first depositing an electrically conductive coating over the screening surface for use as an electrode during each deposition operation. Second, an electrically insulative barrier is deposited over the conductive coating. Portions of the barrier are removed selectively and sequentially for controlling patterned, sequenced cataphoretic access to the electrically conductive coating.

Description: CATAPHORETIC PROCESS FOR SCREENING COLOR RAY TUBES This invention relates to color cathode ray picture tubes, and is addressed specifically to an im¬ proved cataphoretic process for manufacturing color cathode ray tubes . The process is applicable to the 5 manufacture of conventional color picture tubes; that is, tubes having a curved faceplate and a correlatively curved shadow mask, and in the manufacture of color tubes hav¬ ing shadow masks of the tension foil type mounted in as¬ sociation with, a flat or substantially flat faceplate. Color tubes * of various, types can be screened by the pro¬ cess, including thos-e used in home entertainment tele¬ vision receivers. The cataphoretic process according to the invention is particularly valuable in the manufacture of medium-resolution, high-resolution, and ultra-high 5 resolution tubes intended for color monitors. To meet the requirement for high resolution and high definition in such tubes, the phosphor elements must be extremely small and well defined. The problems inherent in screen¬ ing such, tubes is pointed up by the fact that there are D more than five million such, elements deposited on the screen of an ultra-high, resolution color tube. The de¬ positing of so many elements is at the limit of capability of conventional photoscreening processes. The cataphoretic process also offers an economical benefit in that it is 5 much less wasteful of the expensive phosphors used in color screening. The conventional process of depositing patterns of color phosphor elements on the screening surface of a color picture tube faceplate utilizes the well-known photoscreening process. A shadow mask, which in effect functions as. a perforated optical stencil, i used in conjunction with, a light source to expose in successive steps, three discrete light-sensitive photoresist pat- terns on the screening surface. The shadow mask is typically "mated" to each, faceplate; that is, the same mask is used in the production of a specific tube through¬ out the production process, and is permanently installed in the tube in final assembly. At least four engagements and four disengagements of the mask, as well as six exposures, are required in the standard screening process. In certain processes, a "master" may be used for exposing the photoresist patterns in lieu of the mated shadow mask. In a typical photoscreening process, the screening surface is first coated with a fluidized light- sensitive material to fabricate a grille, and which hardens upon drying. The. sladow mask, mounted on a rigid frame, is temporarily installed in precise relationship to the faceplate, and the light-sensitive material is exposed to light actinic to the coating projected through the apertures of the mask from a light source located at a position that corresponds to the beam-emission point of the associated electron gun of the end-product tube. The faceplate is than separated from the shadow mask and the coating is "developed, " resulting in a hardened pat¬ tern of openings in the grille. A slurry of dark surround material is coasted on the faceplate and the hardened resist is stripped, leaving a light-absorbing material surrounding the areas where the phosphors are to be de¬ posited. The red green and blue light emitting phosphor elements are then sequentially deposited in respective grille openings with, a separate slurry of phosphor in a light-sensitive material for each color. The final pro- duct is a faceplate having on its screening surface a pattern of groups of dots or lines capable of emitting, upon excitation by electron beams, red, green or blue light. In U.S. Patent No. 4,130,472, Kaplan discloses a process for making color television screens by electro- phoretic deposition. The process comprises the deposit¬ ing of groups of periodically repeating electrically conductive stripes of predetermined graduated length from relatively long to relatively short on the screening surface. Both ends of stripes of similar length are electrically excited with, a charge of first polarity during immersion in an electrolytic bath that includes color-image-related compounds charged to an opposite polarity. Both, ends of stripes of successively shorter length are serially excited in conjunction with a dif- ferent bath, and a, different image-related compound. By electrically contacting both ends of the stripes, the effect of a single discontinuity in the electrically conductivity of any stripes is nullified. A process for electrostatically screening a color cathode ray tube is disclosed by Lange et al in U. S. Patent No. 3, 475,169. In this process, the screening surface is provided with a photoconductive surface to establish thereon a uniform charge. A latent charge image is then created in the photoconductor by exposing selected portions to light actinic to the photoconductor. The exposure of the photoconductor takes place through a shadow mask so that areas which are to represent phosophor elements of a particular color are selectively dis¬ charged by the exposure. The latent image that results is developed by the application of a toner that includes a phosphor. The toner-phosphor responds to the electrical fields of the photoconductor and is deposited on the discharged areas.. This process is repeated three times to provide the three color phosphors necessary for the cathode ray tube color image. A similar process is set forth in British Patent Specification No. 1,242,999. U.S " . Patent No. 3,681,223 to Gupton discloses means whereby color phosphors are electrophoretically deposited on a cathode ray tube screening surface to pro¬ vide a dot screen. A plurality of conductive dot patterns are deposited on the faceplate, one pattern for each. color to be deposited. Each pattern includes land of material on which the dots are to be deposited, with conductive paths interconnecting the lands. The con¬ ductive patterns are deposited with a single masking operation using an interchangeable master. The different color phosphors are then successively deposited on the dot patterns by electrophoresis, one color being deposited on each discrete conductive pattern. The conductive paths are said to be one mil wide. While the blue- and green- receiving patterns are indicated as being relatively short, the conductive path, for the red phosphor is relatively long—estimated to b.e about 900. feet in a 25-inch color picture tube. The problem of laying down a conductive path of such, length, with an inter-dot width of only one mil is considered to be insurmountable. A gap in the path at any point would halt electrophoresis along the un¬ charged path; also, variations in voltage drop along the narrow conductive stripe could result in uneven deposits of phosphor. In Canadian Patent No. 964,713, Standaart discloses a process for the electrophoretic deposition of color phosphors in a. dot-screen pattern. A separate dot pattern with, an inter-connecting conductive path is pro¬ vided for each color. An electrical potential is applied to an end of each, path by means of a selective clamping device for the deposition of each color. The means for applying the potential are not disclosed. An interchangeable mask is used for the path deposition. In a journal article, Sadowsky describes the preparation of luminescent screens, including deposition by electrophoresis, in which "the phosphor in liquid suspension is attracted to an immersed electrode upon which it deposits." Sadowsky comments: "...there is not much advantage to this method. It is uneconomical merely c to apply screens in this manner, since screens -of as good a quality can more easily be deposited by other means. The controls neces. * sary on particle size, e.m.f., current, suspension, composition, temperature, etc., and the need for a conductive substrate militates against -. Q its ues . " (_"Th.e Preparation of Luminous Screens," Meier Sadowsky, Society for Information Display, March 1949. Pages 119-120.).. In general this invention aims to provide an improved process for the manufacture of color cathode ray ■•r tubes using the cataphoretic process. The present invention therefore provides for use in the manufacture of a color cathode ray tube, an improved cataphoretic process for depositing in sequence on the screening surface of the tube faceplate at least 20 two separate patterns of substantially round phosphor elements, with, each pattern of elements capable of emitting light of a different color when excited, the process comprising first depositing an electrically conductive coating over said screening surface for US e as an electrode 25 during each, deposition operation, and secondly, depositing an electrically insulative barrier over said conductive coating and selectively and sequentially removing por¬ tions of said barrier for controlling patterned, sequenced cataphoretic access to said electrically conductive coating , 30 The improved process of the invention is ap¬ plicable to most types of color cathode ray tubes, in¬ cluding the conventional curved screen-curved faceplate tube, as well as two tubes having a tensed foil shadow mask and a flat faceplate. 35 Among the advantages of the invention is that it provides a more feasible and economical process for deposit¬ ing screening materials on the screening surface of cathode ray tuh.es.. Further features and advantage of the pres¬ ent invention may best b.e understood by reference to the following description of preferred embodiments of the invention taken in conjunction with, the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which: Figure 1 is a side view in perspective of a color cathode ray tube having a flat faceplate and a tensed foil shadow mask, with, cut-away sections that in¬ dicate the location and relation of the screen to other major tube components; Figure 2 is a cut-away view in elevation of a color cathode ray tube having the conventional "curved faceplate and curved screen; Figure 3 is. a detail plan view of the screen of a color cathode ray tube having a "dot" screen; Figure 4 is a view similar to Figure 3 except that the screen is a "line" screen shown with associated shadow mask; Figure 5 is another view similar to Figures 3 and 4 except the screen shown is the type that may be used in a beam index tube; Figure 6 is a view in elevation of a section of a flat faceplate with, a dot screen, and indicating the screening area following preliminary steps in the cata¬ phoretic process according to the invention (.Note: the dot screen is. used as an example in the following descrip¬ tion of the invention).; Figure 7 is a sectional side-elevational dia¬ grammatical view of a "lighthouse" used for exposing the screening area in the screening process according to the invention; the photoscreening of a flat tension mask faceplate assembly is indicated by way of example; Figure 8 is a in elevation of a section of the faceplate shown by Figure 6, and indicating the imping¬ ing of light beamlets on selected areas o f the screening surface of a dot screen during exposure of the screen to light actinic to photosensitive areas as ac- complished in the lighthouse depicted in Figure 7; Figure 9 is a plan view of a section of a dot screen faceplate following the exposure step indicated by Figure 8; ' Figure 10 is a schematic view in elevation of a bath used in the cataphoretic screening process ac¬ cording to the invention, and containing a section of the faceplate shown by Figure 9 as immersed in the bath; Figure 11 is a view in elevation of the section of faceplate shown by Figure 9, with a wash-off spray operation indicated diagrammatically; Figure 12 is a plan view of the section of the faceplate shown by Figure 9, showing the results of pre¬ vious steps in the cataphoretic process according to th.e invention; Figure 13 is a view similar to Figure 8 showing the selective impinging of light beamlets on the screen¬ ing surface in another s * tep in the process according to the invention; Figure 14 is a view of a cataphoretic bath similar to the bath, of Figure 10, but showing a further step in the process according to the invention; Figure 15 depicts another step in the selective impinging of light beamlets on the screening surface; and Figures 16 and 17 are views of cataphoretic baths similar to the bath of Figure 10, and depicting further steps in the process according to the in¬ vention. The process according to the invention can be used for the manufacture of various types of color cathode ray tubes including tubes having a tension foil shadow mask in conjunction with a flat faceplate, and tubes having ttie conventional curved screen-curved mask tubes. The operating principles of the two types are essentially the same; that is, an electron gun projects three beams through a color selection electrode to excite groups of color phosphors emitting red, green or blue light when excited by the respective electron beam. A color cathode ray tube 20 having a tension foil shadow mask is shown by Figure 1. The front assembly 22 includes a faceplate 24, on the screening surface of which, is deposited a phosphor screen 28. A film of aluminum 30 is indicated as covering the screen 28. A funnel 32 is shown as mating with, the peripheral sealing area 34 αf faceplate 24. Front assembly 22 includes a shadow mask sup- port structure 48 for mounting a metal foil shadow mask 50 which, is secured to support structure 48 in tension. The round apertures shown in shadow mask 50 indicate that the tube is a dot-screen type. The anterior-posterior axis of tube 20 is indicated by reference number 56. A magnetic shield 58 is shown as being enclosed within funnel 32. High, voltage for tube operation is applied to a conductive coating 60 on the inner surface of fun¬ nel 32 by way of an anode button 62 connected in turn to a high-voltage conductor 64. The neck 66 of tube 20 is indicated as enclosing and in-line electron gun 68, indicated as providing three discrete in-line electron beams 70, 72 and 74 for exciting respective red-ligh±-emitting, green-light-emitting, and blue-light-emitting phosphor elements on screen 28. The electron gun may be one of the types disclosed in referent copending applications Serial No. 808,137 and Serial No. 828,568. Yoke 76 receives scanning signals and provides for the scanning of beams 70, 72 and 74 across screen 28. A contact spring 78 provides an elec- trical path between the funnel coating 60 and the mask support structure 48. With, reference now to Figure 2 there is shown schematically a conventional color picture tube 80. Tube 80 is similar in form and function to the tube 20 described in connection with Figure 1 in that it has an electron gun 82 that projects three beams 84 that converge on the phosphor-bearing screen 86 of th.e faceplate 88 after passing through a shadow mask 90 which, as has been noted, provides for color selection. This configuration differs however in that the faceplate 88 is curved, as indicated, and the shadow mask 90 is correlatively curved. Screen 86 may be of the dot screen or line screen type. Th.e improved cataphoretic process according to the invention may be used to deposit image-related compounds on the screen 86 of this type of color cathode ray tube, noted as having a curved faceplate. Types * of color picture cathode ray tube screens on which, can be applied image-related compounds according to the invention are depicted in Figures 3-5. It is noted that the process according to the invention is not limited to the examples shown as other applications will readily suggest themselves to those skilled in the art. The improved cataphoretic process according to the invention provides, for depositing in sequence on the screening surface of a color cathode ray tube at least two separate patterns of phosphor elements. Figure 3 represents a dot screen 92 shown as having three such patterns by way of example, and comprising R, a red pat¬ tern, G, a green pattern, and B, a blue pattern, with, each pattern capable of emitting light of the color designated. The three patterns —R, G, and B— are distributed through¬ out the screen. In a flat tension mask having a diagonal measure of 14.2 inches and a constant aperture pitch of 0.2 millimeters, there are about 1,700,000 apertures. Since each aperture passes three beamlets—one beamlet for each of the three patterns—there are about 5,100,000 phosphor elements which, can be deposited on the screen¬ ing surface by the cataphoretic process according to the invention. So each, pattern— , G, and B—consists of 1,700,000 phosphor elements. The patterns are grouped in triads of red, green and blue, as indicated by triad 94, delineated by the dash-line outline, and the adjacent triad 96. Dot-pattern screen 92 is depicted as including a ligh-t-absorptive, black surround material 98 also known as the "grille"; the black surround is indicated sym¬ bolically by the stippling. The associated shadow mask (.not shown in this, example), generally has apertures of the same round shape, with, one aperture for each triad of phosphor elements. Figure 4 is a depiction of a line-screen pattern 104, with the associated shadow mask 106 shown to in¬ dicate the vertically rectangular configuration of the apertures 108, The three electron beams 110, 112 and 114 are depicted as passing through, a typical aperture 116 to selectively impinge upon respective blue-, red- and green-light-emitting lines of phosphor 116, 118 and 120. An opaque, light-absorptive black-surround 122 is indicated as separating the lines of phosphor. Figure 5 is a view similar to Figures 3 and 4 except that a typical screen of a beam index tube is depicted. Stripes 122, 124 and 126 are indicated sym¬ bolically as emitting green, red and blue light when ex¬ cited by the horizontal traverse of a single electron beam (not shown) . The stripes are depicted as being separated by a black surround material 128, as indicated by the stippling. An "index" stripe 130 may comprise, for example, an emitter of ultraviolet radiation used to "index" the system; that is, to locate the beam in relation to the phosphor stripes 122, 124 and 126 across which it passes. These and other screen patterns not shown but which function according to the same general principles may be deposited by the cataphoretic process according to - li ¬ the invention. In essence, the improved cataphoretic process according to th.e invention provides for the deposition in sequence on the screening sτιrface of the tube faceplate 5 at least two separate patterns of phosphor elements, with each pattern of elements capable of emitting light of a different color when excited. In the following descrip¬ tion of the inventive process first, second and third separate patterns of phosphor elements are depicted which j _0 are capable of emitting such light when excited for exemplary purposes, the separate patterns are in¬ dicated symbolically as being red-light-emitting, green- light-emitting, and blue-light-emitting phosphor elements. Essentially, the process according to the in- j _5 vention comprises first depositing an electrically con¬ ductive coating over the screening surface to serve as an electrode during each deposition operation, and secondly, depositing an electrically insulative barrier over the conductive coating and selectively and sequen- 2o tially removing portions of the barrier for controlling patterned, sequenced cataphoretic access to the electrical¬ ly conductive coating. With reference to Figure 6 , there is shown a section of a cathode ray tube faceplate 132 having a 25 screening surface 134 on which there is indicated as being deposited an electrically conductive coating 136. Conductive coating 136 comprises metal or other electrical¬ ly conductive composition. It functions as an electrode during each deposition operation. The conductive coat- 30 ing 136 may comprise a film of aluminum evaporated on the screening surface. The thickness of the aluminum is preferably in the range of 100 to 200 Angstrom units. In application, the screening surface 134 is first washed to remove all trace of contaminants and dried, then the 35 aluminum is deposited by an evaporation process. The aluminum coating could as well be applied by a hot-stamping method. The aluminum coating is opaque even in the form of a very thin film, and hence must be removable so that the light emitted by the phosphors in the finished tube will 5 not be obstructed. The thickness of the metal must therefore by carefully controlled so that the metal can be removed either by oxidation during the sealing of the tube in final assembly, or by chemically leaching it out after the last application of phosphor elements. j _0 The conductive coating 136 could as well be transparent to visible light., and thus not require a specific removal step. An electrically conductive material with, suitable, transparency is indium tin oxide, which may also b.e applied by the evaporation process. 3_5 This compound however does not have to be removed as in the case, of aluminum, as it is transparent. Other types of materials which, are electrically conductive and trans¬ parent, and lend themselves to application in the form of very thin films, may as well be used. Gold is an ex- 20 ample. With, reference again to Figure 6, an electrically insulative barrier 138 deposited over electrically con¬ ductive coating 136. Barrier 138 preferably comprises an electrically resistive photoresist layer such as a photo- 25 sensitive dichromated PVA (.polyvinyl alcohol) which may be applied in liquid form; e.g., by spin-application or by curtain coating. Following the application, the coating is allowed to dry. The photoresist comprising barrier 138 is then 30 exposed through a mask to light actinic to the photo¬ resist layer to form a fixed latent image in the layer that represents a sum pattern corresponding to the sum of aforedescribed first, second and third patterns of phosphor elements. Exposure is accomplished by means of a "lighthouse," a schematic example of which is shown by Figure 7. Lighthouse 140 is shown as having a base 142 within which, is contained a source 144 of UV (ultraviolet) light actinic to the photoresist generated by col- limated light or a fine bare arc, typically an approximate point source when used for screening with shadow masks having round apertures, or a line source for masks having slit or slot apertures. The light source 144 is locat- able in three positions to simulate the deflection center of each of the electron beams used to excite the phos¬ phor elements deposited on the screening surface. This type of printing is known as "first order printing"; it requires the use of a special correction lens 145 for dot screens, to correct for a displacement of the de- flection centers. The method of photoscreening may as well by an interchangeable mask system, in which, by way of example, a separate "master" is used for printing each, of the three colors and the matrix. Each master has only the apertures for the respective color; for example, the "red" master would only have apertures for printing the red phosphor deposits on the screening surface. The master is placed in contact, or near-contact, with the screening surface, and the mask is irradiated with a flood light rather than a point source of light to print the areas that are to receive the red phosphor elements. Very exact registration of the masks is a requisite for suc¬ cessful implementation of this system. The benefit of the interchangeable mask manufacturing system is that there is no need to permanently "pair" a mask with a specific faceplate—the screened faceplates can be interchanged, each with all others, and the shadow masks can also be interchanged, each, with all the others, with consequent economies in manufacture and enhanced tube performance. Lighthouse 140. includes a table assembly 146 for receiving a cathode ray tube front assembly 148. Front assembly 148 will be noted as including the flat faceplate 132 described in connection with. Figure 6, with its deposits of an electrically conductive coating 136 and electrically insulative barrier 138 comprising the photoresist layer on its screening surface 134. A foil shadow mask 150. is depicted as being suspended a pre¬ determined distance from the screening surface 134 by a shadow mask support structure 152. Following the depositing of the electrically conductive coating and the electrically insulative bar¬ rier, the. inventive process will be seen as comprising the forming of a first pattern, a second pattern, and a third pattern of holes in the insulative barrier cor¬ responding to the sum of the first ( second and third pattexn of phosphor elements to be deposited on the screening surface, of the tube faceplate. The first and third patterns of holes, is in effect plugged with an insulative material, then a second pattern of phosphor elements is cataphoretically deposited in the second pat¬ tern of holes which, are, in effect, not plugged. The first pattern of holes is then, in effect, unplugged and the first pattern of phosphor elements are cataphoretically deposited in the holes. The third pattern of holes is then, in effect, unplugged, and the third pattern of phosphor elements are deposited in the holes. Front assembly 148 must be assembled and dis¬ assembled at least four times in the process of de- positing the screening materials. Precision registration and re-registration of the faceplate and the shadow mask in the screening process is indicated as being provided by the support blocks 154A and 154B in conjunction with, by way of example, ball-and-groove indexing means 156A and 156B. CTh.ere are actually three sets of such ball-and- groove indexing means, only two of which are shown in this example. Other means for precision registration known to those skilled in the art may as well be used. The light rays 158 from source 144 (sequentially located at the three deflection centers) , are depicted as irradiat- ing the screening surface 134 after passing through a neutral density filter 160 and the correction lens 145. The effect of irradiating the screening surface 134 from the green, blue, and red deflection centers is shown diagrammatically by Figure 8 (.faceplate 132 is shown as a fragment and in section in this and ensuing figures) . Light rays 158, indicated by the wavy lines, are depicted as passing through apertures 164A, 164B and 164C in shadow mask 150 to form beamlets 166 which, impinge upon the photosensitive electrically insulative barrier 138. The effect of the ligh t is to "fix" the areas 167A, 167B and 167C impinged upon, and form a fixed latent image in the photoresist representing a sum pat¬ tern corresponding to the sum of the first, second and third patterns of phosphor elements; that is, all areas on which the three colored-light-emitting phosphors are to be deposited are formed as latent images. The screening surface is then "developed"; that is, the unfixed photoresist layer that surrounds each of the patterns is removed by spraying with water, for example. The hardened, or "fixed," patterns are not af¬ fected by the water spray. The result is depicted in Figure 9 wherein there remains on the electrically con¬ ductive coating 136 of faceplate 132 a fixed-resist- covered sum pattern of discrete, electrically insulative photoresist elements 168 surrounded by bared areas 170 of the electrically conductive coating 136. The means for photoprinting the screen is de¬ scribed in the foregoing as being accomplished using a shadow mask as a stencil, and sequentially locating the actinic light source at the three deflection centers of the "red, green and blue" guns. τ_ n this system, it is necessary to pair the. masks and faceplates, and maintain the parity throughout the manufacturing and assembly processes. As noted heretofore, screening can as well be accomplished by an interchangeable mask system, as has been described. With, reference now to Figure 10, there is rep¬ resented schematically a cataphoretic bath 172 for the depositing of the screening materials according to the invention. The faceplate 132 is indicated diagrammatical- ly as being immersed in vertical orientation in cata¬ phoretic bath.172, Bath.172 contains an electrolytic fluid 174 which may include, by way of example, a light- absorptive, black-surround material which is preferably non-co ductive. This material may comprise manganese carbonate by way of example, which when deposited by cataphoresis is light: in color, but turns black and opaque as it oxidizes during the bake-out of the tube in final assembly. Other suitable black-surround materials in¬ clude cobalt oxide black, and iron oxides with cobalt oxides. An electrical potential is depicted as being applied between the electrically conductive coating 136 and an anode 179, with, the potential depicted schematical¬ ly as being applied by a battery 176. The negative electrode 178 of battery 176 is indicated as being electrically connected to the conductive coating 136. The positive electrode 177 is indicated as being electrically connected to the anode electrode 179 which may comprise, by way of example, a sheet of stainless steel preferably having approximately the same area as the in-process faceplate. The difference in potential may be for example about 100 volts, and the duration of the cataphoretic process about one minute. The difference in potential results in the cataphoretic deposition on the bared areas 170 of the electrically conductive coating 136, a coating of electrically insulative, interstitial material. This deposition is indicated by the build-up 180 of electrically insulative material in hitherto bared areas 170, depicted diagrammatically by the stippling. As noted, the electrically insulative photoresist elements prevent cataphoretic deposition on areas covered. With reference now to Figure 11, faceplate 132 is indicated as having been removed from the cata¬ phoretic bath 172 and subjected to a spray wash 182. The composition of the wash depends upon the type of photoresist; for example, the wash may be hydrogen per¬ oxide in a 10 percent concentration. The wash results in a removal of the fixed photoresist sum pattern of discrete photoresist elements to bare areas of the conductive coating corresponding to the sum pattern. These areas are surrounded by the interstitial, electri¬ cally insulative material 186 represented by the stippling, In brief, the photoresist elements 168 (see Figure 10) , noted as comprising PVA, are washed off the electrically conductive coating 136, leaving a bare metal conductor. To bare the areas, a water wash is applied; the washing operation is indicated diagrammatically by the spray ap¬ paratus 182; however, it is noted that a wash gentler than a spray is recommended in all washing operations, such as a very low-velocity curtain wash. The result is shown by Figure 12, wherein the screening surface 134 of faceplate 132 is depicted as having bare areas 184G (representing the first pattern) , 184B (.representing the second pattern) and 184R (re¬ presenting the third pattern) ; the suffixes G, B and R indicate the color emission of the phosphors that will subsequently be deposited thereon (NOTE: paterns 184G, 184B and 184R, although, not in the form of a triad, comprise, for purposes of example, a typical group of phosphors representing all groups that will eventually be deposited on the screening surface; that is, a first, second and third pattern of holes, or bare areas, corresponding to the separate patterns of phosphor elements to b.e applied. The bare areas will be observed as being surrounded by interstitial material 186, as indicated by the stippling. Following each cataphoretic bath, the cata¬ phoretic deposits are rinsed with a suitable wash such as isopropyl alcohol or methanol; this step is necessary to remove loose particles in the bath which may have adhered to the screening surface. The coatings are then dried before subsequent processing. If the coatings require additional hinder to withstand further processing steps, suitable binder may be applied in the form of an overcoat, or the binder may be incorporated in the respective baths, Another layer of insulative photoresist is applied to the screening surface to form an electrically insulative barrier. With reference to Figure 13, there is shown an electrically insulative barrier 188 depicted as overlaying the interstitial material 186, noted as being indicated by the stippling, and the previously bared areas 184R, 184B and 184G. This barrier may com¬ prise PVA-AD. The photoresist layer 188 is then exposed through mask 15Q to light actinic to the photoresist. The light beamlet 166A originates from the blue deflec¬ tion center, and secondly, light beamlet 166G originates at the green deflection center; it will be noted that no light is irradiating area 184R, so the red deflection center is inactive. As a result, the photoresist is fixed in areas 184G and 184B. Since no light originates from the red deflection center, the photoresist layer 188 over area 184R remains unfixed. The unfixed photoresist over area 184R is then removed to bare electrically conductive areas in a pat¬ tern corresponding to the first pattern represented by area 184R. As a result, a second and third pattern of fixed photoresist elements is formed, represented by 184G and 184B. To bare area 184R, a water wash is applied as noted heretofore, a very low-velocity curtain wash is recommended. While using the conductive coating 136 again as an electrode, a first phosphor, which is red-light- emitting by way of example, is cataphoretically deposited on the bared areas of the electrically conductive coating 136. This step is depicted in Figure 14 wherein there is represented schematically a cataphoretic bath 192 into which faceplate 132 is inserted, and which contains an electrolytic fluid 194 which, includes in suspension a red-light-emitting phosphor compound. An electrical potential is indicated as being applied between the electrically conductive coating 136 and electrolytic fluid 194, with the potential depicted schematically as being applied by a battery 196 in which the negative electrode 197 is shown as being connected to the electrical¬ ly conductive coating 136. The difference in potential may be for example about 200 volts, and the duration of the cataphoretic process about one minute, by way of example. The difference in potential results in the cataphoretic deposition on the bared area 184R of the electrically conductive coating 136, of a coating of phosphor 198, indicated diagrammatically as being a red- light-emitting phosphor. Phosphor 198 is deposited to a predetermined thickness which forms, after drying, a sub- stantial electrical barrier that prevents further cata¬ phoresis. The thickness of the phosphor is preferably in the range of 10-20 microns. During the deposition process, the phosphor builds up rapidly at first; the build-up then becomes progressively slower with increasing thickness. At the end of the deposition period, the phosphor is sufficiently thick and thus electrically resistive enough to prevent subsequent deposition of phosphor. The electrically insulating barrier in areas 184B and 184G, noted as comprising PVA-AD in a fixed state, is then removed to bare electrical conductive areas 184B and 184G by stripping with a 10 percent solution of hydro¬ gen peroxide. Another layer of electrically insulative photoresist is than applied to form an electrically in¬ sulative barrier comprising a photosensitive photoresist. This condition is shown by Figure 15, in which an elec¬ trically resistive barrier 200 is depicted as overlying the entire screening area, including phosphor element 198. The photoresist layer is then exposed to light actinic to the photoresist to form a fixed latent image in area 184B. The light rays emanate from the blue de- flection center to form, upon passing through shadow mask 150, light beamlet 202. It will be noted that area 184G is not being irradiated. The unfixed photoresist is then removed to bare the electrically conductive layer 136 in area 184G, which is to receive a deposition of green- light-emitting phosphor. It will be noted that the un¬ fixed photoresist is removed from all areas except area 184B, including the areas of the interstitial material 186 and including phosphor element 198. Removal of the unfixed photoresist is accomplished by a gentle flow of water. With reference to Figure 16, the cata¬ phoretic process is repeated, again using the conductive coating 136 as an electrode. It will be observed that, as a result of the previous step, only area 184B is covered with an electrically resistive barrier, barrier 185. A cataphoretic bath 204 is depicted into which faceplate 132 is immersed. At this time, a green-light- emitting phosphor is deposited as the electrolytic fluid 206 contained in ba.th 204 comprises a suspension of green- light-emitting phosphor particles. As before, and as indicated schematically by battery 208, an electrical potential is provided between the electrolytic fluid 206 and the conductive coating 136. As a result, a green- light-emitting phosphor element 210, indicated symbolica- iy, is indicated as being deposited in area 184G. The difference in potential may be for example about 200 volts, and the duration of the cataphoretic process about l.-g minutes, by way of example. The difference in po¬ tential results in the cataphoretic depositing on the bared area 184G of the electrically conductive coating 136, a coating of phosphor 210. As with the red-light- emitting phosphor 198 previously deposited, green- light emitting phosphor element 210 is deposited to a predetermined thickness which forms a substantial barrier to further cataphoresis. As has been noted, the thickness of the phosphor is preferably in the range of 10-20 microns. The final depositing of phosphor elements is the deposition of the blue-light-emitting elements. No further photoscreening is required as the electrically resistive barrier 185 overlying area 184B need only be removed to bare the underlying electrically conductive coating 136. As before, the means of removal is a gentle wash with a 10 percent solution of hydrogen peroxide. The final cataphoretic step is depicted in Figure 17, in which, a cataphoretic bath 212 contains an electrolytic fluid 214 that comprises a suspension of blue-light-emitting phosphor particles. The difference in electrical potential induced by the circuit of battery 216 cataphoretically causes deposition of a blue-light- emitting phosphor deposit 218 in areas 184B. As noted, the red-light-r-emitting phosphor element 198 and green- light-emitting phosphor element 210 form a substantial electrical barrier to further cataphoresis in the res¬ pective areas 184R and 184G. If the underlying conductive coating is a film of aluminum, noted as being not transparent, the coating may be removed by chemically stripping it away to pre¬ vent obstruction of the light emitted by the phosphors thereon deposited. Experiments have shown that the ad¬ herence of the phosphor elements to the glass of the face- plate is not affected by the removal of the underlying conductive coating. Following the cataphoretic deposition pro¬ cess according to the invention, the screening surface may be aluminized by any of the well-known processes. In the cataphoretic process according to the c invention, the use of standard, material-type phosphors is acceptable. The median diameter of the particles of the phosphors that emit red, green and blue light is about six microns. The phosphor concentration in the baths is about two grams per 100 milliliters. The bath medium -,0 recommended is 75 percent isopropyl alcohol (Reagent grade, 0.2% water), and 25% methyl carbitol. The electrolyte concentration is 0.04 grams lanthanum nitrate plus 0.02 grams aluminum nitrate plus 0.2 milliliters of deionized water per 100 milliliters of suspension. The density of 15 the phosphors when deposited is typically about 2.5 milligrams per square centimeter, With regard to the composition of the grille, manganese carbonate may be used, by way of example, with the particles having a median diameter of one to two 20 microns. Concentration of the grille bath is 1 gram per 100 milliliters by way of example, and the liquid medium is the same as for the phosphors. The electrolyte component is 0.03 grams lanthanum nitrate plus 0.015 grams of aluminum nitrate plus 0.15 milliliters of deion- 25 ized water per 100 milliliters of suspension. The voltage for cataphoresis is preferably in the range of 100 to 200. The current for grille coating at 100 volts is about 0.3 x 10 -3 amperes per square cen- -3 timeter, and for the phosphors, 2 or 3 x 10 amperes 30 per square c entimeter. The specific resistance of the baths is in the range of 1.7 x 10 ohms per centimeter 5 to 1.0 x 10 ohms per centimeter. The anode electrode may for example be stainless steel of about the same dimensions as the faceplate to be screened. The anode 35 electrode is suspended in the bath evenly spaced from the faceplate being processed by about 2.5 inch. It is to be noted that these and other values cited in this disclosure are not limiting, but are supplied for exemplary purposes only.

Claims: CLAIMS 1. For use in the anufa c ture of a color cathode ray tube, an improved cataphoretic process for depositing in sequence on the screening surface of the tube faceplate at least two separate patterns of sub¬ stantially round phosphor elements, with each pattern of elements capable of emitting light of a different color when excited, the process comprising first depositing an electrically conductive coating over said screening sur¬ face for use as an electrode during each deposition op¬ eration, and secondly, depositing an electrically in¬ sulative barrier over said conductive coating and sel¬ ectively and sequentially removing portions of said barrier for controlling patterned, sequenced cataphoretic access to said electrically conductive coating. 2. The process according to claim 1 wherein said common conductive coating is opaque but removable, or is transparent to visible ligh t. 3. The process according to claim 1 or 2 wherein said insulative layer includes a light- bsorptive, black-surround material t 4. The process of claim 1, 2 or 3 including the steps of forming a first pattern and a second pattern of holes in said insulative barrier corresponding to the sum of said first and second separate patterns of phos¬ phor elements; in effect, plugging the first pattern of holes with an insulative material, and then cataphoretical¬ ly depositing said second pattern of phosphor elements in said second pattern of holes, and in effect, un¬ plugging said first pattern of holes and cataphoretically depositing said first pattern of phosphor elements therein. 5. The process of claim 4, wherein first and second separate patterns of phosphor elements de¬ posited on said screening surface are interspaced by a light-absorptive, black surround material and the electrically conductive coating deposited over said screening surface, comprises an aluminum film removing said aluminum coating after completion of the cata¬ phoretic deposition process. 6. The process of claim 4 or 5 wherein the cataphoretic process includes the deposit on a screening surface of the tube faceplate of third separate pattern of phosphor elements capable of emitting light of a different color when excited from that of the first and second pattern of phosphor elements including the step of forming a third pattern of holes in said in¬ sulative barrier which together with the first and second patterns corresponds to the sum of said first, second and third separate patterns of phosphor elements in effect, plugging the first and third pattern of holes with an insulative material and then cataphoretically depositing said second pattern of phosphor elements in said second pattern of holes, in effect, unplugging said first pat¬ tern of holes and then cataphoretically depositing said first pattern of phosphor elements in said holes, and in effect, unplugging said third pattern of holes and cataphoretically depositing said third pattern of phosphor elements in said holes and, in effect, unplugging sai d third pattern of holes and cataphoretically depositing said third pattern of phosphor elements in said holes. 7. The process of claim 1, 2 or 3 wherein access to the conducting coating is accomplished by causing to be formed in said barrier in sequence and mutually exclusive in time at least two patterns of coating-baring openings corresponding to said patterns of phosphor elements, each pattern formation being fol¬ lowed b y a cataphoretic deposition of one of said pat¬ terns of phosphor elements on the bared areas of said con d uctive coating using said conductive coating as an electrode. 8. The process of claim 1 , wherein the cataphoretic process includes the deposit on the screening surface of the tube faceplate of a third separate pattern of substantially round phosphor elements capable of emitting light of a different color when excited from that of the first and second patterns of phosphor elements and wherein access to the conductive coating is accomplished by causing to be formed in said barrier in sequence and mutually exclusive in time first, second and third patterns of coating-baring openings corresponding to said first, second and third patterns of phosphor elements , each pattern formation being fol¬ lowed by a cataphoretic deposition of one of said pat¬ terns of phosphor elements on the bared areas of said conductive coating using said conductive coating as an electrode. 9. The process of claim 8, wherein the electrically conductive initially deposited coating over said screening s.urface comprises an aluminum film which the electrically insulative shielding barrier includes a light-absorptive, black surround material, said process including the step of removing &aid aluminum coating following completion of the cataphoretic depo¬ sition on the conductive coating. 10. For use in the manufacture of a color cathode ray tube, an improved cataphoretic process for depositing on the screening surface of the tube faceplate at least first and second separate patterns of phosphor elements emitting light of different colors, respectively, and an interstitial pattern occupying interstices between said first and second patterns, the process comprising: depositing on said screening surface an electrically conductive coating; applying a first layer of electrically insulative photoresist over said electrically conductive coating to form an electrically insulative barrier; exposing said photoresist layer through a mask to light actinic to said photoresist to form a fixed latent image in said photoresist layer representing a sum pattern corresponding to the sum of said first and second pat¬ terns; removing unfixed areas of said photoresist layer, leaving a fixed-resist-covered sum pattern of discrete, electrically insulative photoresist elements surrounded by bared areas of the electrically conductive coating; while using said conductive coating as an electrode, cataphoretically depositing on the bared areas of said electrically conductive coating a layer of electrically insulative, interstitial material; removing the fixed photoresist sum pattern of discrete photoresist elements to bare areas of the conductive coating corresponding to said sum pattern surrounded by said interstitial, electrically insulative material; applying another layer of electrically insulative photoresist to form an elec¬ trically insulative barrier; exposing said photoresist layer to light actinic to said photoresist through a mask having a pattern of openings corresponding to said first pattern, said mask blocking light corresponding to said second pattern to form a fixed latent image in said photoresist layer of said first pattern; removing un¬ fixed photoresist to bare electrically conductive areas in a pattern corresponding to said second pattern, thereby forming a first pattern of fixed photoresist elements; while using the conductive coating again as an electrode, cataphoretically depositing a firstphosphor on the bared areas of said electrically conductive coating to a pre¬ determined thickness at which is formed a substantial electrical barrier to further cataphoresis of the first phosphor; removing the first pattern of fixed photoresist elements; using the conductive coating again as an electrode, cataphoretically depositing a second phosphor on the bared areas of the conductive coating in a pattern corresponding to said first pattern. 11. The process of claim 10 wherein said conductive coating is a film of aluminum. 12. The process of claim 11 wherein said film of aluminum is removed following completion of said cataphoretic process.

Inventors: LIBMAN PHILOMENA C, PRAZAK CHARLES J III, LIBMAN, PHILOMENA, C., PRAZAK, CHARLES, J., III
Applicants: ZENITH ELECTRONICS CORP, ZENITH ELECTRONICS CORPORATION
Application year: 1988
Main classification: H01J9
IPC codes: C03C17, C23C14, C25D13, H01J9