US 3767395 A
In forming a light-absorbing grille or mat for a black-surround color tube, the screen area is covered with clear but sensitized polyvinyl alcohol (pva) and is thereafter exposed to develop a family of pva dots individually covering an elemental area of the screen that is subsequently to receive a deposit of one of three phosphors, green, blue and red. The exposure step is accomplished with seven light sources one of which is positioned to simulate one of the electron guns of the tube and this source accomplishes first order printing or exposure of the pva layer. The remaining six light sources are symmetrically and equidistantly spaced with respect to the first light source to accomplish second order printing or exposure of the same elemental areas exposed by the first mentioned light source. In this fashion each elemental screen area that is to receive a phosphor deposit is concurrently subjected to exposure from seven light sources.
Description (OCR text may contain errors)
I United States Patent [191 Rowe et al.
[451 Oct. 23, 1973 1 MULTIPLE EXPOSURE COLOR TUBE SCREENING  Assignee: Zenith Radio Corporation, Chicago,
 Filed: Sept. 13, 1971  Appl. No.: 179,920
Primary Examiner-Norman G. Torchin Assistant Examiner-Edward C. Kimlin Attorney-John J. Pederson and Cornelius J.
O'Connor  ABSTRACT In forming a light-absorbing grille or mat for a blacksurround color tube, the screen area is covered with clear but sensitized polyvinyl alcohol (pva) and is thereafter exposed to develop a family of pva dots individually covering an elemental area of the screen that is subsequently to receive a deposit of one of three phosphors, green, blue and red. The exposure step is accomplished with seven light sources one of which is positioned to simulate one of the electron guns of the tube and this source accomplishes first order printing or exposure of the pva layer. The remaining six light sources are symmetrically and equidistantly spaced with respect to the first light source to accomplish second order printing or exposure of the same elemental areas exposed by the first mentioned light source. In this fashion each elemental screen area that is to receive a phosphor deposit is concurrently subjected to exposure from seven light sources.
9 Claims, 10 Drawing Figures MULTIPLE EXPOSURE COLOR TUBE SCREENING CROSS REFERENCE TO RELATED APPLICATION This application is a further development of exposure techniques described and claimed in a concurrently filed application of Sam H. Kaplan, Ser. No. 179,921 filed Sept. 13, 1971.
BACKGROUND OF THE INVENTION The invention is directed to screening a color cathode-ray tube and, while of general application, it is especially attractive for screening a color tube of the black-surround variety in which the various phosphor deposits are separated from one another and in which a light-absorbing material is placed in the screen areas that separate such phosphor deposits. For convenience, the invention will be described with particularity in relation to such a black-surround tube.
The most preferred form of black-surround tube is one in which the screen comprises a mosaic of phosphor dot deposits arranged to define a multiplicity of dot triads individually having a component of green, a component of blue and a component of red phosphor dimensioned to be smaller in area than the individual electron beams utilized to excite the phosphors in synthesizing an image in simulated natural color. A screen of this character is described and claimed in U.S. Pat. No. 3,146,368, issued on Aug. 25, 1964 to Joseph P. Flore et al and assigned to the assignee of the present invention. As explained in that patent, such a screen has attractive improvements in respect of brightness and contrast of the color pictures.
The F iore et al patent makes clear an election in the screening process as to the order in which the phosphor and the light-absorbing materials are deposited. There is a preference to applying the light-absorbing material first and providing holes in the light-absorbing layer into which phosphor may subsequently be deposited. The benefit here is a relaxation of processing tolerances in applying the phosphor materials since essentially only the phosphor laid down in the holes of the light-absorbing material contributes materially to image reproduction; segments of the phosphor dots that overlap the light-absorbing material are inefiective by comparison in image reproduction.
One method of preparing a grille of light-absorbing material with openings to receive phosphor is described in U.S. Pat. No. 3,558,310, issued Jan. 26, 1971 to E. E. Mayaud. The process disclosed in that patent includes covering the screen area with a layer of sensitized polyvinyl alcohol which is exposed through the apertures of the shadow mask. This exposure is, in all material respects, the same as that heretofore utilized in forming dot shaped deposits on the screen by exposing elemental areas of a photosensitive phosphor slurry with ultraviolet light projected through the apertures of the shadow mask. Each such step insolubilizes the exposed portions of the photosensitive layer and the unexposed portions of the layer are removed by washing. Performing this same general process three times, with the light source appropriately positioned as well understood in the art, covers all elemental portions of the screen intended to receive phosphor with a deposit of clear pva. With the pva deposits in position, the screen is completely covered with a graphite slurry and dried. Following this, the screen is treated with a chemical stripper, such as hydrogen peroxide, which frees the pva dots removing them and the portions of the graphite slurry coated over them. This prepares the screen with a carefully designed pattern of apertures for receiving phosphor through generally the same photosensitive printing process.
It has been found that imperfections in the shadow mask employed in the described photosensitive printing of the grille produce a mottled appearance to the completed screen during operating intervals when the beams are cut off or, when the receiver including such a tube is de-energized. Commercial experience confirms that such imperfections may occur with sufficient frequency to undesirably reduce screening yields. The present invention improves the yields and acceptability of screens by novel exposure steps which tend to minimize undesirable mottling attributable to imperfections of the mask.
Another patent disclosure pertinent to the subject invention is U.S. Pat. No. 3,282,691, issued on Nov. 1, 1966 to A. M. Morrell et al. This patent describes what is referred to as second order printing of the screen of a color picture tube. Second order printing may be used to form phosphor dot triads which are equilateral in the central area of the screen but are distorted in the 3, 6, 9 and 12 oclock positions to achieve improved beam landings in the presence of degrouping of the beam triangle attributable to such things as astigmatism of the scanning yoke. The Morrell et al disclosure is pertinent for an understanding of first and higher order printing techniques.
It is an object of the present invention to provide a novel method of applying a pattern of phosphor dot triads on the screen of a shadow mask type of color picture tube.
It is a specific object of the invention to improve the yields and screen product obtained in photographically or photoelectrically screening a shadow mask type of color picture tube.
It is a further specific object of the invention to improve the grille making process utilized in screening a black-surround color picture tube.
SUMMARY OF THE INVENTION The invention is in a method of applying a pattern of phosphor dot triads on the screen of a color cathoderay tube in which color selection is achieved by means of an apertured shadow mask positioned between the screen and a gun cluster for developing three electron beams. The inventive method comprises covering the screen with a layer of material having a surface characteristic that is subject to change in response to impingement by actinic energy. The covered screen is exposed from a plurality of energy sources spaced about a reference position that is conventionally utilized in first order printing in which an energy source located to simulate the electron beam assigned to excite the phosphor in process projects energy through apertures of the mask to expose one set of elemental areas of the triads aligned with the mask apertures, respectively. The plural energy sources, in turn, are spaced from the aforesaid reference position by distances selected for second or higher order printing in which the aforesaid one elemental area of each of the triads is exposed by energy projected through a corresponding plurality of apertures of the mask spaced about the mask aperture employed in exposing those same elemental screen areas by first order printing. Thereafter the exposed layer is developed.
In a preferred embodiment of the invention the exposure is performed by a cluster of light sources in which a centrally located source exposes elemental areas of the screen in the manner of first order printing while the remaining light sources simultaneously expose the same elemental screen areas in the fashion of second order printing. This exposure technique is applicable to photosensitive printing of the screen featuring the use of photosensitive resists and also to electrostatic screening featuring photoconductive materials and charge patterns.
BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:
FIGS. 15 are fragmentary views of a color tube screen in various stages of screening;
FIG. 6 is an enlarged showing of one mask aperture having an out-of-round imperfection;
FIGS. 7 and 8 are sketches used in explaining different orders of printing or exposure; while FIGS. 9 and 10 represent exposure light sources.
DESCRIPTION OF THE PREFERRED EMBODIMENT The envelope of a shadow mask color tube has a faceplate section that is initially separated from a conically shaped envelope portion which is a convenience in screening. A fragmentary portion 10 of such a faceplate is represented in FIG. 1 and, after it has been made chemically clean, it is coated with a removable layer 11 of a first coating material having a surface characteristic that is subject to change in response to impingement by actinic energy. As stated, there is a choice in using photographic or electrostatic printing which, of course, usually will involve different classes of materials. For the purpose of the present specific disclosure it will be assumed that the material of layer 11 is a photosensitive slurry or resist that has the property that its adherence to the screen may be attacked and destroyed by an active agent or chemical stripper. It is desirable that this layer be ultimately confined to cover interleaved sets of elemental areas of the screen that are separated from one another and are designated to receive assigned ones of the various phosphor materials. This is readily accomplished by the utilization of an organic photosensitive material, such as polyvinyl alcohol (pva) sensitized with ammonium dichromate, which is convenient because this material is normally soluble in water but is rendered insoluble upon exposure to ultraviolet light. Accordingly, in the specific application of the inventive process, a layer 11 of pva is initially applied over the entire inner surface of screen 10. This layer contains no ingredient that is not readily removable through'volatilization which is here used in a broad sense to encompass removal by conversion to a vapor state or decomposition through heat or chemical treatment.
After pva layer 11 has been dried, selected portions thereof are exposed to actinic energy, more specifically ultraviolet light, to establish in the layer interleaved sets of images of those elemental areas of the screen that are to receive assigned ones of the phosphor materials from which the mosaic screen is formed. In general, this is accomplished in a step analogous to that conventionally employed in photoresist screening to define elemental areas of the screen which are toreceive phosphor and to distinguish them from the remainder of the screen that are not to receive that phosphor. Such discrimination is easily obtained by exposing layer 11 through the shadow mask 12 of the tube in process. For that purpose, such a mask having a plurality of electron permeable portions or apertures is installed in the usual way within the faceplate portion of the tube envelope and this subassembly is then supported in an exposure position in any known form of exposure chamber or lighthouse having an energy source which directs ultraviolet light to elemental areas of the screen through transparent portions of the shadow mask. The departure in the exposure techniques of the subject invention and that of the prior art will be most readily appreciated by first explaining the method of exposure heretofore practiced in screening black-surround color tubes.
If a single, small area or point light source of the lighthouse is positioned to simulate, for example, the electron gun of the tube in process which is to excite the green phosphor material, the ultraviolet light will be confined to expose only those portions 11g of layer 11 which overlie elemental areas of screen 10 assigned to receive deposits of green phosphor. After this exposure step, portions lllb are similarly exposed, these contituting the portions of the layer that overlie elemental screen areas that are to receive deposits of blue phosphor. To achieve their exposure, it is only necessary to change the position of the light source in the exposure chamber so that it now simulates the electron gun of the tube intended to energize the blue phosphor dots. In a third position of the light source, where it simulates the red electron gun of the tube, a third set of small portions llr of layer 11 are exposed and these portions overlie elemental areas of the screen intended to receive red phosphor. In short, as a consequence of these three separate exposure steps, there are estab lished in layer 11 interleaved sets of images of elemental areas of the screen that are separated from one another and are to receive assigned ones of the phosphor materials. This will be recognized as an exposure technique which, as stated above, is very similar to that of photoresist color screening but there is one significant distinction to be noted, namely, the exposed elemental areas of layer 1 l are smaller in size than the transparent portions or apertures of the shadow mask as used in the completed tube. The correct relative size of phosphor dot to beam cross section may be realized in a variety of ways. One that suggests itself directly involves coating the shadow mask initially to temporarily close down the size of its apertures so that the dimensions of the phosphor dots determined by exposure through the closed-down shadow mask are properly related to the final size of the mask apertures. After the mask has been used in screening, the coating is removed so that when the mask is positioned between the completed screen and the usual gun cluster that generates the three electron beams, the beams, in arriving at the screen through the apertures of the mask, will be larger in size than the phosphor dots as required by the teachings of the Fiore et al patent.
Other ways of achieving the same result are known and one practiced commercially is described in application Ser. No. 811,318, filed Mar. 28, 1969 in the name of Sam H. Kaplan and assigned to the assignee of the present invention. That application discloses a process in which the apertures of mask 12 are initially formed of the proper size for use in screening and, after screening has taken place, including the application of light-absorbing material as well as the three different phosphor materials, the shadow mask is re-etched to open up or enlarge its apertures to a desired final size. This has an advantage in precisely controlling the dimensions of the phosphor dots and also in attaining a higher degree of uniformity in the size and configuration of the dots.
By Whichever approach is selected portions 11g, 11b and llr of coating 11 are exposed to create latent images of pva dots. The resulting interleaved sets of latent images are next developed by removing all unexposed portions of photosensitive layer 11, producing the screen condition of FIG. 2. The photosensitive material of layer 11 is soluble in water as applied to screen but all exposed portions thereof are insoluble so that washing the screen after the three exposure steps removes all of the unexposed portions of layer 11. The screen of FIG. 2 may be described as having clear deposits or dots of pva separated from one another by screen areas which are bare and are to receive a pigment or a material having light-absorbing capabilities. The next step constitutes depositing at least in the spaces between the elemental areas of the screen that are covered by dots of clear pva a coatin of a second material comprising an inorganic pigment having lightabosrbing capabilities and whose adherence to the screen is substantially immune to attack by the active agent referred to above which is to be utilized to destroy the adherence of pva dots 11g, 11b and llr. While the second coating material may, at least in theory, be confined to only the areas surrounding the clear pva dots, it is more convenient to apply a second coating 13 over the entirety of the screen as indicated in FIG. 3 in which case portions of the second coating cover the clear pva dots in the nature of an overcoat. Preferably, layer 13 is applied as a slurry and also preferably it is a colloid having in suspension fine powdered inorganic material of light-absorbing capabilities. Suitable materials are fine powders of metals or oxides of metals, for example black iron oxide, powdered mica, molybdenum disulphide, manganous carbonate, ceramic black and graphite. Very-acceptable black surround patterns have been formed using colloidal graphite. The graphite coating 13 is fixed to the screen by drying.
It is next necessary to remove all of the coating materials from screen 10 except for'the graphite coating over those portions of the screen which intervene the dots of clear pva 11g, 11b and llr. To that end the screen is treated with a chemical stripper which reacts with the pva in the manner of a solvent or an oxidant to free or lift the pva dots off panel 10. An acceptable stripper is hydrogen peroxide which may be poured onto the center of the screen and slurried to form a coat of substantially uniform thickness. After a processing interval of approximately 30 seconds, the excess stripper solution is poured off and the screen is washed with a fluid spray of air or water, such as deionized water at a pressure of 25 psi, and in this washing the pva dots 11g, 1 1b and 1 1r are washed off giving the screen condition of FIG. 4 in which elemental areas of the screen 11 11b and llr that are to receive phosphor materials are exposed. Each of these elemental areas of the screen is totally surrounded by the residue 13a of colloidal graphite.
The screen is now in condition to be coated with the various phosphor materials to present the final structure of FIG. 5 in which reference characters 11g", 11b" and llr designate deposits of green, blue and red phosphors, respectively, individually surrounded by colloial graphite. Essentially the same kind of photographic printing is employed in positioning the various phosphor deposits. For example, a photosensitive resist including a suspension of the phosphor in process is applied over the entire screen and only those elemental areas intended to receive that particular phosphor are subjected to ultraviolet light directed to the screen through the shadow mask 12 simply by properly positioning the exposing light source. Thereafter, the screen is washed to develop the deposits of that particular phosphor by removing the slurry from all elemen: tal areas of the screen except those which have been exposed and are intended to accept the phosphor in process. Following this screening process for each of the three colors, green, blue and red, completes the screening process and all of the organic constituents of the materials deposited on the screen are readily removed during bakeout. To this point, the entire process represents the knowledge and practice of the prior art and attention will now be directed to the improvement introduced by the present invention.
A deficiency of the described process which is overcome or materially minimized by practicing the present invention will be understood from a consideration of a shadow mask with one or more imperfectly formed apertures having, by way of illustration, the configuration shown in the enlarged view of FIG. 6. This mask aperture is deformed by an inwardly extending projection and since it constitutes a pattern used in the formation of three sets of clear pva dots during grille making, the dot of each such set developed by exposure through that particular aperture has a similar out-of-round condition. The graphite coating 13 which covers the entir'ety of the screen projects within the intended outline that such pva dots would have had if the mask aperture in question had been truly round. In subsequent processing steps wherein the clear pva dots are replaced by phosphor deposits to form phosphor triads, the triad aligned with the imperfect aperture is likewise imperfect, suffering from the grille extending within the in: tended circular fields of its phosphor dots. Such imperfect phosphor dots have no particularly adverse effect on a color picture but their presence is undesirably manifest when the tube is turned off. In the deenergized state of the tube the screen has a darkened or black background which is the grille interspersed with dots of a comparatively white material representing the unexcited phosphor deposits. Where the grille is formed using a mask with imperfections of the type represented in FIG. 6, the regular appearance of the ideal screen is disturbed by the projection of the grille into the intended field of three or more phosphor deposits. Since the grille is a distinct black whereas the de-energized phosphor is comparatively white, or at least a light grey, the result is a mottled appearance to the screen and if too many such imperfections are present they cause the screen to be a reject. This problem is greatly minimized by using a distinctly different exposure step which will be explained with reference to the diagrams of FIGS. 7 through 9.
In FIG. 7 the triangle 20, 21 and 22 is equilateral and is centered with respect to the longitudinal axis 23 of the tube. Each apex of this triangle is the location of, ideally, a point light source for the exposure steps of the prior art. With reference to FIG. 8 a light ray 20a from a source 20 passes through a mask aperture 12a in illuminating one component T, of a dot triad. The dash-dot construction line 21a indicates that a light ray from another light-source position, namely that designated 21 in FIG. 7, passes through the same aperture of the mask in exposing another component T of the same dot triad. While difficult to show in this drawing, it can be established that for the type exposure under consideration a light ray from the third source 22 passes through the identical mask aperture 12in exposing the third component of the same dot triad. This is referred to in the art as first order printing or exposure and designates that the light beams from each of the three possible sources 20-22 project through the same aperture of the mask in exposing a single phosphor dot triad and that aperture is the one which is in substantial alignment with the dot triad in process. This is described more fully in the above-identified Morrell et al patent and the exposure phenomenon is the same all over the screen area. That is to say, first order printing or exposure takes place through every aperture of mask 12 producing the multiplicity of dot triads that constitute the screen. It will, of course, be appreciated that the exposures from the three possible light sources 20-22 occur sequentially and the phosphors are processed individually and in sequence.
With further reference to FIG. 8, the full construction line 20b represents a light ray from a point source 20' passing through mask aperture 12b and also exposing triad component T This simply indicates that instad of positioning the light source as represented at 20 in FIG. 8, it could alternatively or additionally be at position 20' to expose triad component T In like fashion dash-dot construction line 21b demonstrates that the other component T of the illustrative triad may as well be exposed from a light position 21 as from the firstdescribed light position 21. As explained in the Morrell et al patent exposure from the alternate light source positions 20 and 21 is referred to as second order printingor exposure. It is characterized by the fact that mask apertures 12b and 120 through which the exposure of the single illustrative triad takes place when utilizing the alternate positions 20 and 21' of the light sources are different from the aperture 12a utilized in first order exposure. Indeed, the apertures 12b and 12c are members of a ring of apertures symmetrically disposed about and at equal distances from aperture 12a of consequence for first order exposure.
With reference to FIG. 7 the circle 25 is the locus of apertures available for second order printing of the elemental areas of the screen which would be exposed from light source 20 in first order printing. The crosses at equispaced distances along circle 25 locate six possible positions any one of which could be utilized in second order printing. It may be shown that the radius of circle 25 is three times the spacing of light source position 20 from tube axis 23.
To accomplish second order printing as contemplated by the Morrell et al patent one of the six possible light source locations is utilized to expose the elemental areas of the screen that otherwise would be exposed from a light source position 20 in first order printing but the exposure technique in practicing the present invention is distinctly different. More particularly, the present invention utilizes a plurality of energy sources spaced about the reference position 20 utilized in first order printing and energized sequentially, but preferably simultaneously, to achieve multiple exposures of the second order. The diagram of FIG. 8, in showing the exposure of triad component T, from source locations 20-20' holds good for whatever one of the six possible light source positions available for second order printing may be utilized. These, of course, are the six positions designated by the crosses applied to locus 25 in FIG. 7. Accordingly, a light source may be placed at each such position and if they are simultaneously energized they would result in six registered exposures of the triad component T,. It is clear from the geometry represented in FIG. 7 that the exposing light beam from each of the six light sources reaches triad component T through a different one of six apertures of mask 12 which ring aperture 12a. If five of these six apertures have perfect conformation, whereas the sixth is de formed in the manner of FIG. 6, the imperfection resulting from the malformation of the aperture of FIG. 6 is greatly suppressed since it contribures only onesixth of the total exposure utilized in forming triad component T Still further improvement may be realized with an exposing light arrangement of the type represented in FIG. 9 wherein light source L is positioned at a point corresponding to apex 20 of FIG. 7 while light sources L L-, are located at each of the available positions shwon on locus 25. In short, seven exposure lights are utilized and are energized simultaneously. Exposure from source L is first order whereas exposure from sources -1 are of the second order. Each exposes the same component T for the illustrative triad discussed in connection with FIG. 8. In using the preferred exposure process resulting from the light arrangement of FIG. 9 there is not only a further attenuation of aperture defects but also a decrease in required exposure time. Exposure is basically an integration of light and time so that a given amount of exposure is accomplished with a reduction in exposure time as the number of light sources is increased. It of course is not necessary to use all seven exposing lights; much flexibility is available although the arrangement of FIG. 9 is preferred. One can, for example, totally omit light source L, or may omit desired ones of the family L L Still further flexibility is available when it is realized that higher printing orders may be used. By way of example, full construction line 20c represents a light ray from a source 20 passing through mask aperture 12d to illuminate the same triad component T This is referred to as third order printing and is also discussed in the Morrell et al patent. While higher orders can be used, it is convenient as a practical matter to use second order exposure with plural light sources, augmented by first order expoure in the manner of FIG. 9.
As explained in the Morrell et al patent a phenomenon known as degrouping is experienced in commercial forms of shadow mask color tubes having a mosaic type of screen. It is attributable to astigmatism of the scanning yoke and to the geometry of the structure, especially with respect to changes in the spacing of the shadow mask'to the screen with increasing distance from the center of the screen toward its edges. It tends to cause misregistration of the beam triads and the phosphor triads where the latter have been formed by first-order printing. The object of second-order printing disclosed by Morrell is to locate phosphor deposits on particular portions of the screen, especially those remote from the center, in a manner not conveniently obtained by first-order printing and determined to minimize misregistration in the presence of degrouping. This same consequence of second-order printing, namely exposing screen areas not reached in first-order printing, will tend to cause a lack of coincidence of the six second-order images resulting from the exposure technique described with the arrangement of FIG. 9 especially at portions of the screen remote from the center. This means that if the benefits of the multiple second-order imaging are to be obtained all over the screen some compensating or correcting arrangement is required to insure coincidence of the multiple images. Optical devices, including mechanical collimators and special lenses, may be employed for this purpose.
A suitable mechanical collimator is disclosed in patent 3,494,267 issued Feb. 10, 1970 to J. W. Schwartz. It consists of a light source and a control element which has a multiplicity of light conducting channels that determine the paths of light rays from the source to the apertures of the mask to the end that desired elemental areas of the screen are in fact exposed.
In U.S. Pat. No. 3,495,511 issued Feb. 17, 1970 to L. Javorik there is disclosed a lens assembly that may be used to achieve optical correction. The lens is interposed between the light source and shadow mask and is characterized by having a heterogeneous index of refraction which is an increasing function of the distance from the center of the lens.
As a further alternative, the multiple exposure may be confined to the central portions of the screen wherein degroupling is not a perceptible phenomenon. An arrangement to achieve the latter is indicated in FIG. 10 which shows mercury arc lamp 30 as the exposing light source, the usual reflector 31 and diffusion plate 32 which direct light to apertures 33 formed in a plate 34. If the light arrangement is to be similar to that shown in FIG. 9 there would be six such apertures 33 each of which simulates a separate light source. Plate 34 additionally has a centrally located aperture 35 in which a collimator tip 36 is positioned to simulate light source L, of FIG. 9. With this arrangement and sufficient depth of plate 34 the effectiveness of light from simulated sources 33 may be confined to the central region of the screen area in process whereas exposure light from the first order light source 35 remains effective over the entire screen area.
It has been convenient in discussing FIGS. 7-9 to make reference to. the exposures of components T and T of one triad of the screen in process. Viewed more broadly, T, and T may be though of as any of the various sets of elemental areas of the screen that are required to be exposed in one or more steps of the screening process. For the production of a blacksurround screen discussed in relation to FIGS. 1-5, designations T, and T simply illustrate two of the three sets of interleaved clear pva dots that are formed by exposure over elemental areas of the screen to be protected against the covering of graphite layer 13. After the grille has been made with the pva dots protecting this multiplicity of elemental areas of the screen, the more usual phosphor screening takes place. In laying down phosphor materials in the holes of the grille one may employ a negative photosensitive resist and first order printing or, alternatively, the same exposure techniques utilizing multiple light sources as described in connection with FIGS. 7-9 may be used. In phosphor screening, as distinguished from grille forming, T, represents one component or one color phosphor of a dot triad and T is another component or different phosphor of the same triad. The multiple-registered exposures described above may be used in any or all of these various screening steps.
While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. I
1. The method of applying a pattern of phosphor dot triads on the screen of a color cathode-ray tube in which color selection is achieved by means of an apertured shadow mask positioned between said screen and an electron gun arrangement for developing at least one electron beam, said method comprising:
covering said screen with a layer of material responsive to impingement by actinic energy; exposing said layer from a plurality of energy sources that are spaced about a reference position which is utilized in first-order screen printing to project energy through said mask to expose one elemental area of each of said triads;
said plurality of sources being spaced from said reference position by distances selected for second or higher order printing in which said one elemental area of each of said triads is exposed by energy projected through a corresponding plurality of apertures of said mask spaced about the mask aperture employed in exposing said one elemental area in said first-order printing;
and therafter developing said exposed layer.
2. The method in accordance with claim 1 in which said layer is exposed simultaneously from said plurality of sources.
3. The method in accordance with claim 2 in which said plurality of sources are symmetrically spaced about said reference position.
4. The method in accordance with claim 3 in which said plurality of sources are equally spaced from said reference position.
5. The method in accordance with claim 4 in which the spacing of said sources from said reference position is selected for second-order printing.
6. The method in accordance with claim 1 in which said layer is further exposed in said exposing step by an additional energy source located at said reference position to further expose said one elemental area of each of said triads for first-order printing.
7. In the manufacture of a shadow mask-type color cathode ray tube which has a phosphor screen on an inside surface of a faceplate for the tube including interleaved patterns of red, blue and green phosphor elements, a method comprising:
depositing a photosensitized coating on the faceplate; supporting adjacent the faceplate a mask having a pattern of apertures corresponding in geometry to the desired patterns of the phosphor elements; and
exposing said coating through said mask to a substantially registered plurality of radiation patterns corresponding to said aperture pattern in said mask by activating a predetermined plurality of sources of radiation actinic to said coating disposed at second order color center locations such that the total integrated radiation pattern exposing said coating represents a multiple exposure through a plurality of different apertures in said mask, thus averaging out any irregularities in the individual mask apertures.
8. In the manufacture of a shadow mask-type color cathode ray tube which has a phosphor screen on an inside surface of a faceplate for the tube including interleaved patterns of red, blue and green phosphor elements, a method for forming a black surround grille for filling and interstitial areas between the phosphor patterns, comprising:
depositing a photosensitized coating on the faceplate;
supporting adjacent the faceplate a mask having a pattern of apertures corresponding in geometry to the desired patterns of the phosphor elements; exposing said coating through said mask to a substantially registered plurality of red-associated radiation patterns, a substantially registered plurality of blue-associated radiation patterns and a substantially registered plurality of green-associated radiation patterns, each being interleaved with the others and each corresponding to said aperture pattern in said mask, said exposing being accomplished by activating a predetermined plurality of sources of radiation actinic to said coating disposed at second order red, blue and green color center locations such that the total integrated radiation pattern exposing said coating represents a multiple exposure through a plurality of different apertures in said mask member, thus averaging out any irregularities in the individual mask apertures;
developing said coating to remove unexposed portions of said coating; depositing over the remaining exposed portions of said coating a layer of black surround material; and
chemically stripping off said remaining exposed portions of the coating and the overlying black surround material.
9. The method defined by claim 8 including during said exposing step, activating also a source of actinic radiation disposed at first order red, blue and green color center locations to expose said coating to a radiation pattern for each color which is substantially registered with said other radiation patterns for that color to further contribute to said averaging out of any irregularities in said individual apertures in said mask.