US2992107A

US2992107A - Method of manufacturing luminescent screens

Info

Publication number: US2992107A
Application number: US463176A
Authority: US
Inventors: Sam H Kaplan; Theodore S Noskowicz
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1954-10-19
Filing date: 1954-10-19
Publication date: 1961-07-11
Anticipated expiration: 1978-07-11

Description

July 11, 1961 S. H. KAPLAN ET AL METHOD OF MANUFACTURING LUMINESCENT SCREENS Coot with photo-sensitive resist Dry resist layer Expose selected oreos of resist Settle luminescent powder through water column Remove excess settling liquid Dry Wash with water to remove unexposed reslst and excess powder Filed Oct. 19, 1954 FIG. 2

Coot with photo-sensitive resist FIG.3

Coot with photo-sens itive resist Dry resist layer Dry resist loyer Settle luminescent powder through water column Expose selected areas of resist Remove excess settling liquid Sproy with water to wash away unexposed resist Dry Settle luminescent powder through water column Expose selected areas of resist Remove excess settling liquid Wash with water to remove unexposed resist and excess powder Dry Wosh vi orously with we er to remove excess powder SAM H. KAPLAN THEODORE S. NOSKOWICZ INVENTORS.

THEIR ATTORNEY.

United States Patent 2,992,107 METHOD OF MANUFACTURING LUMINESCENT SCREENS Sam H. Kaplan, Chicago, and Theodore S. Noskowicz, Wooddale, Ill., assignors, by mesne assignments, to Zenith Radio Corporation, a corporation of Delaware Filed Oct. 19, 1954, Ser. No. 463,176 9 Claims. (Cl. 96-35) This invention pertains to a new and improved method of depositing luminescent material upon predetermined target areas on the surface of a cathode-ray tube viewing screen. Although the method is applicable to the fabrication of any cathode-ray tube requiring precise control of the location and configuration of minute target areas, it is particularly valuable in the manufacture of picture tubes for color television and will be described in that connection.

There are several different types of cathode-ray tubes presently known in the art which are capable of repro ducing images in simulated natural color; each of these different devices utilizes a luminescent screen comprising a multitude of interspersed target areas forming two, three or more distinct groups. The different target-area groups comprise phosphors which emit light having different color characteristics when subjected to electron bombardment. Typically, a luminescent screen of this type includes three different groups of color target areas which emit light corresponding to the red, green and blue portions of the spectrum. The individual target areas may comprise minute dots, usually circular in configuration, or may constitute extremely narrow strips or hands extending across the screen.

Color accuracy in images reproduced by devices employing screens of this type is almost completely dependent upon the accuracy and consistency of the configuration and dimensions of the individual target areas and their positions with respect to one another. The target areas are extremely small; for example, there may be as many as 600,000 individual target areas in the screen of a picture tube having a viewing surface nineteen inches in diameter. Consequently, the techniques and processes utilized to fabricate these screens must permit the maintenance of extremely precise dimensional tolerances; moreover, because three similar groups of target areas must be incorporated in each screen, it is necessary that the methods employed produce consistent results upon repeated application to the same viewing-screen surface.

Silk screening, printing, and similar techniques have been successfully adapted to the fabrication of color television viewing-screens where the supporting surface for the screen comprises a flat plate. However, these techniques are not readily adaptable to the formation of color targets upon the surfaces of spherical elements such as are normally employed for the faceplates of cathode-ray tubes. It has been suggested that photographic techniques may be utilized to deposit multi-color targets upon spherical surfaces and these methods have been used, with varying degrees of success. However, although the adaptation of photographic techniques to the manufacture of color screens on a limited basis is not particularly troublesome, it presents several difficult and complex problems relating to both the technical and economic aspects of screen manufacture when applied in mass production.

In one prior art process, the luminescent powder for one group of color target areas is mixed with a soluble photosensitive resist material and is spread upon the view ing screen surface by knife coating or by spraying. The coating thus formed is then selectively exposed by means of a suitable light source and a master target-area pattern, which for some tubes may comprise the color-selection electrode of the tube, to alter the solubility characteristics of the photo-sensitive resist in predetermined areas corresponding to the desired target areas. The remaining portions of the resist-phosphor mixture are then washed away and the process is repeated for the other target area groups. However, it has been difficult to obtain adequate accuracy in exposing the mixture of resist material and luminescent powder, since the phosphor tends to diffuse the light employed to expose the desired target areas in the resist. The presence of the phosphor in the resist also tends to increase the exposure time to a marked extent.

In another known photographic process for fabricating color television targets, a substantially uniform layer of color phosphor is first settled upon the viewingscreen surface by techniques conventionally employed in the manufacture of monochrome television picture tubes. This layer of luminescent material is then coated with a photo-sensitive resist which must penetrate through the phosphor layer into contact with the screen substrate, usually the internal surface of the picture tube envelope. The photo-sensitive resist is then exposed to make the desired target areas insoluble and the target pattern is developed by washing away the remaining portions of resist and phosphor. This procedure is, of course, repeated for each of the three color target area groups. This process also presents considerable difficulty in 0btaining the requisite accuracy in the target area pattern, since the presence of the luminescent material tends to interfere with exposure. In addition, the required exposure times are excessive and are subject to considerable variations depending upon the thickness of the layers of luminescent powder and resist and the light-diffusion characteristics of the phosphor.

In any photographic technique applied to the mass production of color image reproducers, it is desirable that the photo-sensitive materials employed be adapted to development by water in view of its tremendous economic advantage as compared to organic solvents. On the other hand, it i also extremely desirable to deposit the luminescent powder upon the screen surface through a settling liquid in which water is a principal ingredient in accordance with techniques well known in the cathoderay tube art, since these settling methods represent by far the most economical and efiicient means for uniformly depositing luminescent screens yet discovered. However, it has been thought that these two techniques are incompatible with each other where the photo-sensitive material is first deposited upon the viewing screen surface and the luminescent powder is subsequently settled on the resist, since the settling liquid also constitutes a developing medium for the resist.

It is a primary object of the invention, therefore, to provide a new and improved method of depositing a luminescent powder upon predetermined target areas of the surface of a cathode-ray tube viewing-screen which overcomes the difficulties and disadvantages inherent in previously employed processes.

It is another object of the invention to provide a new and improved photographic process for fabricating a luminescent screen comprising a multiplicity of minute target areas in which process a photo-sensitive material is first deposited upon a viewing screen surface and a luminescent powder is subsequently settled onto the resist through a column of liquid which constitutes a developer for that resist.

It is a specific object of the invention to provide a new and improved method of water-settling a luminescent powder upon predetermined target areas of a cathode-ray tube viewing-screen surface in which the con- 3 figuration and distribution of the target areas are determined by a photographic process employing water-soluble photo-sensitive materials.

It is a corollary object of the invention to provide a new and improved process for depositing a luminescent target upon predetermined areas of a viewing-screen surface economically and efiiciently without any sacrifice in accuracy of either the individual target area dimensions or the overall target pattern.

Accordingly, the invention is directed to the method of depositing a luminescent powder upon predetermined target areas on the surface of the viewing-screen of a cathode-ray tube in accordance with a preselected pattern which comprises the following steps: The viewing screen surface is coated with a photosensitive resist having a predetermined water-solubility characteristic, the watersolubility being subject to alteration upon exposure to radiation. Predetermined portions of this resist are exposed to alter their solubility characteristic and establish in the resist coating a solubility pattern in which the portions corresponding to the desired target areas are relatively insoluble in water as compared with the remaining portions of the resist coating. A luminescent powder is settled onto the resist coating through a column of settling liquid, in which water is a principal ingredient, in contact with the coated viewing screen surface. The excess settling liquid is, of course, removed from that surface. In addition, the coated surface must be washed with water to dissolve and remove therefrom the aforementioned remaining portions of the resist coating and any excess luminescent powder. Washing of the viewingscreen surface to remove excess phosphor material may be accomplished simultaneously with removal of the nontarget area portions of the resist or may constitute a separate step in the process; moreover, the sequence of steps employed may vary in accordance with different embodiments of the invention.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The organization and manner of operation of the invention, together With further objects and advantages thereof, may best be understood by reference to the following description of the method involved and the accompanying drawing, in which:

FIGURE 1 is a flow chart illustrating the sequence of process steps employed in one embodiment of the invennon;

FIGURE 2 illustrates the sequential procedure followed in another embodiment of the invention;

FIGURE 3 illustrates the major steps utilized in a preferred embodiment of the invention.

In the embodiment of the invention illustrated by the flow chart of FIGURE 1, the viewing-screen surface for a cathode-ray tube is first coated with a thin uniform layer of photo-sensitive resist material. The viewingscreen surface employed may be the surface of a suitable flat transparent element to be mounted internally of the cathode-ray tube envelope; ordinarily, however, it is desirable to utilize the internal surface of the transparent faceplate of the envelope as a support for the luminescent target in order to obtain a viewing screen of maximum size in an envelope of given dimensions. Of course, the surface should be clean and dry at the start of the screening process. The photo-sensitive resist employed must have a predetermined water-solubility characteristic subject to alteration by illuminating or otherwise exposing the resist to radiation. For example, the resist material may comprise properly sensitized gum arabic, albumen, photographic gelatin, or polyvinyl alcohol. All of these particular materials are normally water-soluble but may be reversed, i.e., made substantially insoluble in water by subjecting them to radiations of predetermined wave length; on the other hand, so-called inverse resist materials which are originally insoluble in water but may be exposed to become soluble, such as bichromated colloid containing a colloidal dispersion of water-insoluble acrylate resin, may also be employed.

After the viewing screen surface has been coated with the photo-sensitive resist, it may be necessary to dry the resist layer, particularly if the resist is applied in solution form. This drying procedure is indicated as the second step in the process of FIGURE 1. Subsequently, predetermined portions of the resist coating are exposed to radiation to alter the solubility characteristic of those portions and establish in the resist a solubility pattern in which the portions corresponding to the desired target areas are relatively insoluble as compared with the remaining portions. When using a resist which is originally water-soluble, such as polyvinyl alcohol, it is the desired target areas which are exposed to become insoluble; the other portions of the resist layer are not exposed. This exposure pattern is of course reversed in the case of an inverse-type resist. For a color picture tube of the familiar shadowmask variety, in which color selection is achieved through use of a mask having a multitude of minute apertures corresponding in configuration and distribution to a single group of color target areas, exposure of the resist layer may be conveniently accomplished by illuminating the resist through the mask itself from a point spaced from the mask to provide optical characteristics corresponding to the electron-optical characteristics of the cathode-ray tube. In other types of color television picture tubes, it may be necessary to provide a special master pattern for use in exposing the resist in accordance with techniques Well known in the art.

After exposure of the resist coating, the luminescent powder which is to form the light-emitting portion of the viewing screen is deposited upon the resist coating by settling the powder onto the resist through a column of settling liquid in contact with the coated viewing-screen surface. This settling liquid may consist entirely of water; in any event, water should constitute a principal ingredient of the settling liquid in order to obtain the full economic advantages of the invention. It is usually preferable to employ a dilute aqueous silicate solution as the settling liquid in order to obtain improved adherence between the luminescent powder and the resist; a suitable electrolyte may be added to the silicate solution in accordance with conventional screen-settling procedures. After the desired layer of luminescent material has been settled onto the resist, the excess settling liquid is removed from the coated surface in accordance with known techniques; for example, the settling medium may be slowly decanted or may be siphoned from the viewing-screen surface as indicated by the next step in the sequence of FIGURE 1.

The process outlined above may appear to be inoperative, due to the fact that the non-target portions of the resist coating are soluble in water, which is employed as a principal ingredient in the settling liquid. Thus, it might be expected that the unexposed portions of the resist coating would dissolve in the settling liquid and that at least a portion of the luminescent powder would be deposited directly upon the viewing-screen substrate surface, after which it would be impossible to remove the powder from the substrate, usually glass, without at the same time removing the desired target area portions of the resist. However, this apparent difficulty does not actually occur. Deposition of the settling liquid upon the resist coating does not immediately dissolve the unexposed resist areas to an extent sufficient to permit the powder to settle directly upon the viewing screen; normal settling and decantation procedures may be completed long before the unexposed resist is sufficiently dissolved to expose any portion of the substrate.

In the next step of the embodiment of FIGURE 1, the composite resist-phosphor coating upon the viewing screen surface is dried to insure adequate adherence between the luminescent powder and the exposed portions of the resist. At the same time, of course, the excess phosphor powder adheres to the unexposed portions of the resist. In the next step of the process, however, the coated viewingscreen surface is sprayed with water to dissolve and remove the unexposed portions of the resist. Because the undesired luminescent powder particles adhere to the unexposed resist areas, this excess powder is also washed away, leaving only the desired target areas coated with the exposed resist and the luminescent powder. The particles deposited on the exposed portions of the resist, on the other hand, adhere very strongly to those target-area portions and can withstand a relatively high-pressure water spray, so that the process is well suited to mass production operation.

For a three-color screen, the entire process outlined in FIGURE 1 is repeated two more times with displaced target-area patterns and different phosphors to form three separate interleaved groups of target areas coated with resist material and the three desired color phosphors. The composite color target is then coated with a heatdecomposable organic film, and a conductive metallic layer is deposited on that film in accordance with known techniques; usually, nitrocellulose is the principal component of the film and aluminum is employed for the metallic layer. Subsequently, the entire target is baked to decompose the film material and the residual photosensitive resist in order to volatilize both of these materials and remove them from the target. The filming, metallizing, and baking techniques employed are all well known in the manufacture of monochrome television picture tubes and need not be described in detail here.

The embodiment of the invention illustrated by the flow chart of FIGURE 1 provides excellent accuracy in the manufacture of multi-area luminescent screens, such as those employed in color television, at a minimum cost. Because the resist material is deposited directly upon the surface of the screen substrate, there is little or no danger that the target-area pattern will be marred or otherwise damaged due to poor adherence between the screen materials and the substrate. The use of conventional settling techniques to deposit the luminescent powder on the target areas provides maximum economy in the amount of phosphor required, whereas the use of water both as a settling medium and as a developer adds further to the economies realized by the process. Sharp, clear target areas are produced and contamination by deposition of phosphor powder in undesired areas is minimized.

FIGURE 2 illustrates the sequence of process steps for another embodiment of the invention, in which the resist is exposed after settling of the luminescent powder and subsequent decantation. In this process, as in that of FIGURE 1, the viewing-screen surface of the cathoderay tube is first coated with a thin uniform layer of a photo-sensitive resist, after which this layer is dried. The resist employed is preferably one which is readily soluble in warm water but relatively insoluble in cold water, such as grade 72-60 polyvinyl alcohol; cold water should be employed for settling. As before, the viewing-screen surface may be the surface of a separate transparent screen base to be mounted within a cathode-ray tube envelope or may comprise the internal surface of the faceplate of the tube. After the resist coating is dried, the luminescent powder is settled onto the unexposed resist coating through a liquid column in contact with the coating. As before, the settling liquid comprises water as a principal ingredient; in fact, water alone may be employed. The excess settling liquid is then decanted or otherwise removed from the coated viewing-screen surface, after which the composite resist-phosphor screen is suitably dried.

The resist is then illuminated or otherwise subjected to radiation to expose predetermined portions thereof and -alter the water-solubility characteristic of those portions. Preferably, an originally soluble resist is employed and the areas of the coating which are to form the target areas in the finished screen are exposed, leaving the remaining portions of the resist in their original soluble condition. The coated viewing-screen surface is then 6 washed with water to dissolve the unexposed portions of the resist coating and to remove those portions from the screen surface; this same washing step also removes the excess luminescent powder deposited upon the non-target areas of the screen. The entire process is repeated twice for a tricolor screen.

Screens produced by the sequence of steps shown in FIGURE 2 retain most of the advantages of those produced in accordance with the embodiment of FIGURE 1. The process is economical and efiicient in that water is employed for both settling and developing and a minimum amount of luminescent powder is required. Exposure problems are somewhat more pronounced in this embodiment, since the resist is exposed after the luminescent powder has been settled onto the screen. It is usually preferable to expose the resist through the transparent viewing-screen substrate, to provide more accurate control of the exposure of those portions of the resist in contact with the viewing screen surface and thus assure adequate adherence between the screen and the resist as well as improved definition in the outlines of the target areas. The resist coating is not adversely affected by the settling step as long as the settling period is not unduly lengthened.

FIGURE 3 illustrates, in flow-chart form, a preferred embodiment of the invention which provides somewhat more positive control of the removal of luminescent powder from non-target areas of the viewing-screen surface. In this embodiment, as in that of FIGURE 1, the viewing screen surface of the tube is first coated with a thin uniform layer of a photo-sensitive resist. This resist layer is then dried and exposed to alter its water-solubility characteristic in predetermined areas, thus establishing a solubility pattern in which the portions corresponding to the desired target areas are relatively insoluble as compared with the remaining portions of the coating. Preferably, an originally soluble resist is employed, in which case it is the desired tar-get areas which are exposed.

The resist coating is then sprayed with water to dissolve and wash away all of the unexposed portions of the resist, leaving only the target portions. Next, the luminescent powder is settled onto these exposed resist areas through a column of water or preferably a settling liquid including a binder and an electrolyte in addition to water. After settling, the excess liquid is removed from the viewing-screen surface by decanting, siphoning, or other similar techniques and the screen is dried. The screen surface is then washed vigorously with a highpressure water spray to remove the luminescent powder which has settled onto those portions of the viewingscreen surface not covered by the exposed resist.

Upon first examination, this preferred embodiment of the invention appears to be completely inoperative, since luminescent powder is settled equally upon the desired resist-covered target areas of the viewing-screen surface and upon the remaining uncovered areas of that surface. It has been discovered, however, that the powder deposited upon the exposed portions of the resist adheres much more strongly than the powder settled onto the screen base, so that vigorous washing effectively removes the undesired phosphor without disturbing the luminescent powder on the target areas, even when potassium silicate or some equivalent binder is employed in the settling liquid. In fact, a single layer of powder particles adheres very tightly to the resist and any excess phosphor present on the target areas is also washed away so that extremely precise control of the thickness of the luminescent powder deposit may be maintained. Moreover, when the process is repeated to form additional target-area groups in a color picture tube, the luminescent powder which settles onto previously formed target areas of a different color does not adhere sufliciently to withstand the final washing step, so that color contamination is not encountered.

The embodiment of FIGURE 3 provides consistent and accurate control of the configuration and dimensions of the target areas in a color television image screen. In order to present a more complete picture of a specific application of the preferred embodiment to a particular picture tube, the full details of each step employed in depositing a dot-type color screen upon the spherical internal faceplate surface of a 19 inch round cathode-ray tube envelope are set forth hereinafter. It should be understood that this data is presented merely by way of illustration and by no means as a limitation upon the invention.

The internal faceplate surface of the 19 inch envelope is first coated with a water-soluble photo-sensitive resist comprising an aqueous solution of polyvinyl alcohol. The basic resist solution is compounded from grade 52-22 medium-viscosity polyvinyl alcohol, 88% saponified, dissolved in deionized water to form a 4.5% solution. To each 100 cc. of this polyvinyl alcohol solution there is added 2 cc. of a saturated solution of ammonium dichromate; the ammonium dichromate functions as a sensitizing agent for the polyvinyl alcohol. The sensitized polyvinyl alcohol is an excellent resist material for a production process since it is not readily exposed by light from conventional illumination sources; it is primarily sensitive to light in the blue and ultra-violet ranges. Consequently, a relatively high level of illumination may be maintained throughout the process so long as ultra-violet light is avoided; yellow fluorescent lamps are very good for this purpose. The resist may be kept for several days after sensitization before it starts to change its solubility without exposure.

Approximately 100 cc. of the sensitized resist solution is applied to the internal faceplate surface; the faceplate is then rotated, coated side down, about a transverse axis, preferably corresponding to the envelope axis, for approximately two minutes at 75 rpm. to spin the coating so that a thin uniform resist layer is formed and excess resist solution is forced to the periphery of the faceplate where it may be caught and removed. The resist coating is then dried with warm air; if preferred, it may be permitted to dry at room temperature.

The dry resist coating is then exposed through the color-selection barrier or parallax mask to be used in the tube in order to render portions of the resist layer corresponding to the desired target areas relatively insoluble in water. The radiation source utilized for exposure comprises a pair of tungsten electrodes spaced approximately apart; an electrical discharge is established between these two electrodes and argon is blown through and around the arc gap to provide the desired spectral characteristics. A preferred light source is described and claimed in the copending application of Theodore S. Noskowicz, Serial No. 501,391, filed April 14, 1955, and assigned to Zenith Radio Corporation. In this specific process, best exposure results are obtained with an exposure time of approximately 2.25 minutes and an arc current of 45 amperes. A substantially shorter exposure time may give rise to inadequate adherence between the target-area portions of the resist and the screen substrate; on the other hand, overexposure may lead to poor adherence between the resist and the phosphor. Preferably, the exposure is timed to make the target areas somewhat tacky when wet with water but almost completely insoluble in water; the timing for a particular resist material of given thickness is readily determinable by one or two trial runs of the process.

After exposure, the resist layer is developed by means of a water spray which dissolves and removes the unexposed portions of the resist. The phosphor powder is then settled onto the coated screen surface through a liquid column comprising water and potassium silicate with barium nitrate as an electrolyte. In preparing the settling solution, 9 liters of deionized water are first mixed with 90 cc. of a barium nitrate solution which includes 1.6 grams of barium nitrate per 100 cc. of water. This first portion of the settling liquid is deposited on the coated viewing-screen surface; subsequently, a second portion of the settling liquid comprising 30 cc. of concentrated potassium silicate solution and 500 cc. of deionized water is added. The potassium silicate concentrate employed contains 21% silica by weight. The phosphor powder is preferably mixed with this second portion of the settling liquid before it is added to the first portion; for a 19 inch screen, only approximately 4.5 grams of the powder are required.

A ten minute settling period is employed, after which the faceplate is gradually tilted to decant and remove the excess settling liquid from the viewing-screen surface. The tilting period is about ten minutes. The screen is then dried with warm air to obtain maximum adherence between the phosphor powder and the target-area portions of the resist, after which the entire screen area is subjected to a high-pressure water spray to remove any phosphor deposited on the viewing screen surface in undesired areas and also to remove excess phosphor deposits from the target areas. The entire process is repeated twice more with laterally displaced target-area patterns and different phosphors for a complete threecolor screen, after which the usual filming, aluminizing, and baking steps may be carried out. All of the screening process steps may be effected at ordinary room temperatures.

Each of the various embodiments of the invention provides an efiicient, elfective, and economical method of depositing luminescent powders upon the minute target area patterns required for color television screens. Contamination by mixture of different phosphors is effectively eliminated and the size and configuration of the target areas are accurately controlled. Only a minimum amount of the relatively expensive phosphors is required, and no special organic solvents are needed in the process.

While particular embodiments of the present invention have been described, it is apparent that changes and modifications may be made without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. The method of depositing a phosphor powder upon predetermined target areas on the surface of a viewingscreen in accordance with a preselected pattern, said method comprising the following steps: coating said surface with a photo-sensitive resist of predetermined water-solubility with said resist capable of being changed by exposure to radiation between a condition in which it is soluble in water and a condition in which it is insoluble in water; exposing to said radiation predetermined portions of said resist to change said solubility of said portions and establish in said resist a solubility pattern in which the portions corresponding to said target areas are relatively insoluble in water as compared with the remaining portions; thereafter settling said powder onto the exposed resist coating through a column of settling liquid, comprised substantially entirely of water and including minor portions of potassium silicate and an electrolyte, in contact with said coated viewing-screen surface; removing excess settling liquid from said surface; and washing said coated surface with water to dissolve and remove therefrom said remaining portions of said resist coating and any excess powder.

2. The method of depositing a phosphor powder upon predetermined target areas on the surface of the viewingscreen of a cathode-ray tube in accordance with a preselected pattern, said method comprising the following steps: coating said surface with a thin uniform layer of photo-sensitive resist of predetermined water-solubility with said resist capable of being changed by exposure to radiation between a condition in which it is soluble in water and a condition in which it is insoluble in Water; drying said resist layer; exposing predetermined portions of saidresist to change said solubility of said portions and establish in said resist a solubility pattern in which the portions corresponding to said target areas are relatively insoluble in water as compared with the remaining portions; thereafter settling said powder onto the exposed resist coating through a column of settling liquid, comprised substantially entirely of water and including minor portions of an electrolyte and a water-soluble binder promoting adherence of said powder, in contact with said coated viewing-screen surface; removing excess settling liquid from and drying said surface; and washing said coated surface with water to dissolve and remove therefrom saidremaining portions of said resist coating and any excess powder.

3. The method of depositing a phosphor powder upon predetermined target areas on the surface of the viewingscreen of a cathode-ray tube in accordance with a preselected pattern, said method comprising the following steps: coating said surface with a thin uniform layer of a water-soluble photo-sensitive resist, said resist capable of being rendered water-insoluble by exposure to radiation; exposing to said radiation predetermined portions of said resist layer corresponding to said target areas to render said portions relatively insoluble in water; thereafter settling said powder onto the exposed resist coating through a column of settling liquid, comprised substantially entirely of water and including minor portions of an electrolyte and a water-soluble binder promoting adherence of said powder, in contact with said coated viewingscreen surface; removing excess settling liquid from said surface; and washing said coated surface with water to dissolve and remove therefrom the remaining soluble portions of said resist coating and any excess powder.

4. The method of depositing a phosphor powder upon predetermined target areas on the surface of the viewingscreen of a cathode-ray tube in accordance with a preselected pattern, said method comprising the following steps: coating said surface with a photo-sensitive resist of predetermined water-solubility with said resist capable of being changed by exposure to radiation between a condition in which it is soluble in water and a condition in which it is insoluble in water; exposing to said radiation predetermined portions of said resist to change said solu bility of said portions and establish in said resist a solubility pattern in which the portions corresponding to said target areas are relatively insoluble in water as compared with the remaining portions; thereafter settling said powder onto the exposed resist coating through a column of settling liquid in contact with said coated viewingscreen surface, said settling liquid comprising a dilute aqueous silicate solution and an electrolyte; and washing said coated surface with water to dissolve and remove therefrom said remaining portions of said resist coating and any excess powder.

5. The method of depositing a phosphor powder upon predetermined target areas on the internal surface of the faceplate of a cathode-ray tube envelope in accordance with a preselected pattern, said method comprising the following steps in the recited sequence: coating said surface with a photo-sensitive resist of predetermined watersolubility with said resist capable of being changed by exposure to radiation between a condition in which it is soluble in water and a condition in which it is insoluble in water; exposing to said radiation predetermined portions of said resist to change said solubility of said por tions and establish in said resist a solubility pattern in which the portions corresponding to said target areas are relatively insoluble in water as compared with the remaining portions; settling said powder onto said exposed resist coating through a column of settling liquid, comprised substantially entirely of water and including minor portions of an electrolyte and a water-soluble binder promoting adherence of said powder, in contact with said 7 l0 coated faceplate surface; from and drying said surface; and thereafter washing said coated surface with water to dissolve and remove therefrom both said remaining portions of said resist coating and any excess powder.

6. The method of depositing a phosphor powder upon predetermined target areas on the internal surface of the faceplate of a cathode-ray tube envelope in accordance with a preselected pattern, said method comprising the following steps in the recited sequence: coating said surface with a photo-sensitive resist of predetermined wa ter-solubility with said resist capable of being changed by exposure to radiation between a condition in which it is soluble in water and a condition in which it is insoluble in Water; exposing to said radiation predetermined portions of said resist to change said solubility of said portions and establish in said resist a solubility pattern in which the portions corresponding to said target areas are relatively insoluble in Water as compared with the remaining portions; washing said coated surface with water to dissolve and remove therefrom said remaining portions of said resist coating; settling said powder onto said insoluble portions of said exposed resist coating through a column of settling liquid, comprised substantially entirely of water and including minor portions of an electrolyte and a water-soluble binder promoting adherence of said powder, in contact with said coated faceplate surface; removing excess settling liquid from said surface; and washing said coated surface with water to remove any powder deposited on areas other than said target areas.

7. The method of depositing a phosphor powder upon predetermined target areas on the internal surface of the glass faceplate of a cathode-ray tube envelope in accordance with a preselected pattern, said method comprising the following steps in the recited sequence: coating said surface with a thin, uniform layer of a watersoluble photo-sensitive resist comprising an aqueous solution of polyvinyl alcohol and a sensitizing agent, said resist capable of being rendered water-insoluble by exposure to radiation; illuminating with said radiation predetermined portions of said resist layer corresponding to said target areas to expose and render said portions relatively insoluble in water; developing said pattern in said resist layer by spraying said layer with water to dissolve and wash away all of said resist layer except said exposed portions; thereafter settling said powder onto said exposed portions of said resist layer through a column of settling liquid comprising a dilute aqueous solution of a silicate and an electrolyte to form a layer of said powder on said resist; removing excess settling liquid from said coated faceplate surface; and spraying said faceplate with water to wash away any of said powder deposited on said glass faceplate without removing said powder from said exposed resist areas.

8. The method of depositing a phosphor powder upon predetermined target areas on the internal surface of the glass faceplate of a cathode-ray tube envelope in accordance with a preselected pattern, said method comprising the following steps in the recited sequence: coating said surface with a thin uniform layer of a watersoluble photo-sensitive resist comprising an aqueous solution of polyvinyl alcohol with ammonium dichromate added as a sensitizing agent, said resist capable of being rendered water-insoluble by exposure to radiation; drying said resist layer; illuminating with said radiation predetermined portions of said resist layer corresponding to said target areas to expose and render said portions relatively insoluble in water; developing said pattern in said resist layer by spraying said layer with water to dissolve and wash away all of said resist layer except said exposed portions; thereafter settling said powder onto said coated faceplate surface through a column of settling liquid comprising a dilute aqueous solution of potassium silicate and barium nitrate to form a layer removing excess settling liquid of said powder on said resist; removing excess settling liquid from said coated faceplate surface; drying said layer of powder; and spraying said faceplate with water 'to wash away any of said luminescent powder deposited on said glass faceplate Without removing said powder from said exposed resist areas.

9. The method of depositing a phosphor powder upon predetermined target areas on the surface of a viewingscreen in accordance with a preselected pattern, said method comprising the following steps: coating said surface With a photo-sensitive resist of predetermined water-solubility with said resist capable of being changed by exposure to radiation between a condition in which it is soluble in water and a condition in which it is insoluble in water; exposing to said radiation predetermined portions of said resist to change said solubility of said portions and establish in said resist a solubility pattern in which the portions corresponding to said target areas are relatively insoluble in Water as compared to the remaining portions; thereafter settling said powder onto the exposed resist coating through a column of settling liquid, comprised substantially entirely of water and including minor portions of an electrolyte and a water-soluble binder promoting adherence of said powder, in contact with said coated viewing-screen sur-.

References Cited in the file of this patent UNITED STATES PATENTS 679,501 Garchey 'Ju-1y 3.0, 1901. 2,221,474 Gardner Nov. 12, 1940 2,423,626 Szegho July 8, 1947 2,683,769 Banning July 13, 1954 2,769,733 Pool NOV. .6} 195 6 2,870,010 Sadowsky Jan. 20, 1959 2,950,193 Payne Aug. 23,. 196.0

FOREIGN PATENTS 713,908 Great Britain Aug. 18,1954

OTHER REFERENCES Sylvania Technologist, July 1953,.vo1. VI, No. 3, pp. 60-63.

Sadowsky et al.: Journal ,of Electrochemical Society, vol. 105, No.2 (1958).

Claims

1. THE METHOD OF DEPOSITING A PHOSPHOR POWDER UPON PREDETERMINED TARGET AREAS ON THE SURFACE OF A VIEWINGSCREEN IN ACCORDANCE WITH A PRESELECTED PATTERN, SAID METHOD COMPRISING THE FOLLOWING STEPS: COATING SAID SURFACE WITH A PHOTO-SENSITIVE RESIST OF PREDETERMINED WATER-SOLUBILITY WITH SAID RESIST CAPABLE OF BEING CHANGED BY EXPOSURE TO RADIATION BETWEEN A CONDITION IN WHICH IT IS SOLUBLE IN WATER AND A CONDITION IN WHICH IT IS INSOLUBLE IN WATER; EXPOSING TO SAID RADIATION PREDETERMINED PORTIONS OF SAID RESIST TO CHANGE SAID SOLUBILITY OF SAID PORTIONS AND ESTABLISH IN SAID RESIST A SOLUBILITY PATTERN IN WHICH THE PORTIONS CORRESPONDING TO SAID TARGET AREAS ARE