US2950193A - Method of manufacturing electrical apparatus - Google Patents

Description

Aug.- 23, 196 0 P. D.' PAYNE, JYR 0,

METHOD OF MANUFACTURING ELECTRICAL APPARATUS Filed Aug. 25; 13s:

INVENTOR. P190! 0. P1970! J/f.

WUJW

ilnited States Patent F METHGD OF MANUFACTURING ELECTRICAL APPARATUS Paul D. Payne, Jr., Lansdale, Pa., assiguor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Aug. 25, 1953, Ser. No. 376,345

'12 Claims. (Cl. 96-34) The present invention relates to improvements in methods of manufacturing cathode ray tube screen structures and, more particularly, to improvements in methods of manufacturing cathode ray tube screen structures of the kind which have different portions made of materials which are differently responsive to electron beam impingement.

While different specific forms of such screen structures are suitable for a wide variety of applications, the form which has been receiving the most careful attention in recent times is that which is particularly suitable for use as the image reproducing screen of a color television picture tube. in this form, the screen structure consists of solid translucent substrate, which may be either the glass face plate of the cathode ray tube itself or an additional glass plate separately supported within the cathode ray tube envelope, and having different portions of its beam confronting surface coated with phosphors emissive of light of different primary colors, such as red, green and blue, for example. In a preferred embodiment of such a screen structure, the different colored light emissive phosphors take the shape of narrow, parallel strips, adjacent strips being made of phosphors emissive of light of ditferent colors so that, proceeding in a direction transverse to the longitudinal dimensions of these strips, red, green and blue light emissive phosphor strips, for example, will be encountered in recurrent succession. Of course, other configurations of phosphor elements have also been found useful as, for example, one in which tiny phosphor dots are disposed in triangular groups of three, each member of each group of dots being made of a phosphor emissive of light of a particular primary color and different ones of these dots being emissive of light of different colors. The selection of the best phosphor element configuration depends upon a variety of factors including the nature of the signal which is used to control the intensity of the cathode ray beam with which the finished screen will eventually be scanned and the nature of the system which is provided for maintaining exact coincidence between the instants of time at which this cathode ray beam is representative of intelligence concerning a particular image color and instants at which the beam is impinging upon phosphor elements of the screen structure which are emissive of light of that particular color. In one such system the differently colored light emissive phophors are arranged in the aforetioned strip-like pattern and their cathode ra beam confronting surfaces are covered with an electron permeable film made of some conductor such as aluminum, for example. On top of this aluminum film there are then deposited so-called indexing strips, preferably one for each group of three differently colored light emissive phosphor strips, these indexing strips being made of a material whose secondary electron emission ratio is substantially different from that of the aluminum. As the electron beam, in scanning its raster on this screen structure, traverses successive groups of three differently colored light emissive phosphor strips, it also traverses suc- 2,950,193 Patented Aug. 23, 1950 ice cesive indexing trips and intervening regions of bare aluminum. The variations in secondary emission current which occur by reason of alternate beam traversals of indexing strips and bare aluminum are sensed by an external circuit and are utilized to control either the rate of scran of the electron beam across successive groups of three phosphor strips, or the rate of application of colored light intelligence representative signal portions to the beam intensity control electrode of the cathode ray tube, or both. The specific manner of utilizing the signals produced by these indexing strips has no bearing on the invention under consideration and need therefore not be discussed in detail.

While various methods are known for forming the different types of screen structures hereinbefore briefly described, the one which has been used with the greatest success involves the deposition of the various phosphor and/or indexing material particles by a photographic process. This process was initiated by depositing, on the glass substrate, a layer of photosensitive gel in which there had previously been distributed particles of one of the three colored light emissive phosphors. This gel was exposed to illumination through translucent portions in a mask, the translucent portions having the same configuration as that in which it was desired to dispose, in the final screen structure, the screen elements of the particular phosphor being processed. As a result of this exposure, the portions of the gel which had been illuminated became insoluble in water, while unilluminated portions remained water soluble, as before. The screen was then washed with water, thereby removing the unexposed portions of the gel and also the phosphor particles distributed therein. There remained in place those portions of the gel, and the phosphor particles distributed therein, which had been exposed and thereby rendered insoluble Next there was applied another layer of gel having distributed therein particles of a second one of the three different phosphor materials. This second layer of gel was again exposed to illumination through translucent portions in a mask having such configuration as to produce exposure of the gel in the particular configuration in which it was desired to dispose the elements of the second phosphor in question. In practice it was often possible to use the same mask for this second exposure as was used for the exposure of the first deposited gel, it being necessary, of course, to relocate this mask between exposures so that the translucent portions thereof were aligned with different regions of the transparent substrate during successive exposures. This second exposure was also followed by washing to remove the unexposed gel together with the phosphor particles distributed therein. A third layer of photosensitive gel was then applied, this one bearing particles of the third phosphor material to be deposited on the substrate. This third layer of gel was again exposed through a suitably positioned mask and the unexposed portions thereof washed away. The foregoing method of depositing phosphor strips in a predetermined pattern is described in more detail in the copending US. patent application of John W. Tiley, Serial No. 248,356, filed September 26, 1951, and assigned to the assignee of the present invention. The deposition of the phosphor strips having thus been completed, there was next applied the aforementioned electron permeable aluminum film by conventional techniques, and finally there was applied still another layer of photosensitive gel. This latter layer of gel was dried and was then covered with a layer of indexing material particles. This final layer of gel was then exposed, in a manner similar to that in which the phosphor bearing gel layers were exposed and preferably through the same mask as the latter, this mask having, if necessary, been repositioned again so as to expose portions of the indexing material bearing gel in the desired geometrical relationship to the st ips of phosphor materials beneath the aluminum film. Again unexposed portions of the gel weredissolved and removed, after which theentire screen structure was dried and baked, thereby vaporizing those portions of the photosensitive gels which had been rendered insoluble by exposure .and which had therefore remained in place in spite of the repeated washing operations.

Screen structures manufactured by the process hereinbefore briefly outlined, while satisfactory in some respects, were uniformly characterized by having phosphor elements with irregular, or fuzzy edges. This seemingly minor imperfection proved to be asource of serious diffieulties because, in a practicalscreen structure, the individual phosphor strips are extremely small and are closely crowded together. It is, for example, common to position. :a group of three phosphor strips emissive of light of different colors, side by side, within a regiononly 45 mils wide and with each individual phosphor strip only. approximately l mils wide. In this arrangement, spaces about mils wide were left between adjacent phosphor strips to enhance the purity of the colors reproduced on the screen structure. Alternatively, adjacent phosphor strips were sometimes located substantially contiguously, with no appreciable spaces between them. In the case of contiguous phosphor strips, irregularities in their adjoining edges caused overlapping of the difierent phosphorswith the result that no sharp line of demarcation could be maintained between beam impingement on phosphor strips of one color and on phosphor strips of a different color. With spaced phosphor strips, on the other hand, irregularity of the strip edges caused unpredictable reductions in the improvement in color purity which spaced-apart positioning of the phosphor strips would otherwise have produced.

It has also been found that phosphor strips deposited by the aforedescribed process were subject to appreciable variations in density from one phosphor strip to the next or even'from one portion of a single phosphor strip to another portion of that same strip. By density I mean the concentration of phosphor particles in a unit volume of exposed photosensitive gel. Since the intensity of the light which is emitted from a beam impinged phosphor region, all other factors being equal, depends upon the number of color centers which is, in turn, a function of the number of phosphor particles present within this beam impinged region, the aforementioned variations in density also lead to unpredictable variations in the light emissivities of different portions of the screen structure, thereby making it Very difficult to achieve a sufiiciently high degree of uniformity and reproducibility of color balance between the differently colored light emissive phosphor strips.

All of the foregoing remarks apply to the indexing strips as well as to the colored light emissive phosphor strips. Of course, it will be undersoood that, in the case of the indexing strips, the aforementioned irregularities in strip edges and variations in particle density afiected their secondary electron emissivity and, consequently, their utility for the production of uniform indexing indications.

While it has proved perfectly feasible to apply both the phosphor strips and the indexing strips by exposure from that side of the glass substrate which faces the exterior of the tube, there are reasons why it may be even more advantageous to form this screen structure by exposure from the interior of the tube. Chief among these reasons is the fact that exposure from the substrate side which faces the exterior of the tube requires illumination of the indexing material bearing gel through the previously deposited aluminum film. A very intense source of illumination is required to penetrate this aluminum film at all, and this illumination must be continued for a considerable length of time before a layer of gel of suflicient thickness has been exposed and rendered insoluble. If, on the other 4 hand, the several exposures are carried out entirely from the interior side of the screen structure, then the gel which contains the indexing material will be deposited on that side of the aluminum film which confronts the source of illumination so that the light from this source need not penetrate the aluminum film. When one proceeds in thislatter manner, the power requirements of the light source and the exposure time are substantially reduced and a considerable increase in the efliciency of the entire process is realized. On the other hand, if each successive exposure is made from the interior side of the screen structure then the light from the source of illumination must traverse the entire depth of each layer of phosphor and/ or indexing material bearing gel before exposing and rendering insoluble that portion of each of these gel layers which is most closely adjacent to its supporting material (this being the glass. substrate in the case of the phosphor bearing gel and the aluminum film in the case of the indexing material bearing gel). It has been found that so much light may be lost during traversal of the intervening materials that the portions of the gel which are closest to the supporting material are not exposed suificiently to render them completely insoluble. Where that occurs, the washing operation which follows each exposurewill remove not only that part of the gel whichwas deliberately left unexposed but will also dissolve that portion of the gel nearest its substrate which hasbeen, unintentionally underexposed and, with it, the

superposed, sufficiently exposed portions of the gel layers together with the useful materials distributed therein.

.Accordingly, it is a primary object of my invention to provide an improved method of manufacturing screen structures for cathode ray tubes;

It is another object of my invention to provide an improved photographic method of manufacturing the screen structures of color television cathode ray tubes.

It is. still another object of the invention to provide an improved method fo manufacturing cathode ray tube screen structures involving the exposure of selected portions of photosensitive gels in such a manner as to fix particles of different materials in different ones of said selected portions.

It is a still further object of the invention to provide an improved photographic method of manufacturing cathode ray tube screen structures whereby sharply delineated elements containing particles of certain materials with substantially uniform densities are formed.

To achieve the foregoing objects of the invention, as well as others which will appear, there are deposited successive layers of photosensitive gel, one for each of the different materials which are to be formed into screen elements of a desired configuration. However, unlike those of the prior art, these gel layers do not contain the various materials at the time of their deposition. Instead, each layer of gel is deposited and portions thereof are selectively exposed while this gel still contains no screen forming material. The particular material (phosphor or indexing) whose configuration in the completed screen structure is determined by the exposure pattern of a given gel layer is deposited on this gel layer only after the same has been selectively exposed, but before its unexposed portions have been removed by washing. After deposition of this material on a gel layer, the resulting structure is washed and the unexposed gel, together with the material deposited thereon, is removed. The material deposited on the exposed gel, on the other hand, will have penetrated the same to some extent and will therefore be trapped inside or will adhere to the outer surface of the gel owing to the tackiness of the latter. In any case, the material deposited on the exposed gel will resist removal by washing and most, if not all of it, will remain in place even after the unexposed gel and the material deposited thereon have been washed away. The same process, involving the successive steps of. depositing gel alone, selectively exposing this gel, depositing screen material thereon and washing off unexposed gel, are carried out in turn for each of the difierent screen materials which are to be deposited by this photo graphic process. By proceeding in this manner in accordance with the invention the edges of the exposed portions of each gel layer are caused to be extremely sharp and well defined. This, I believe, results from the absence of particles of screen constituent material from this gel layer during exposure, which would otherwise scatter the light traversing the gel layer in undesirable directions.

The density of the screen material which remains in place on the exposed portions of the photosensitive gel after washing is also much more uniform than in the case where the screen material was distributed throughout the photosensitive gel for, in my improved method, this density can be controlled by controlling the manner of deposition of the screen material on the exposed gel layer without concern for variations in the degree of insolubility of different exposed portions of the gel layer which cause variations in its retentivity for other material distributed therein.

Finally, there is now no danger that, if the exposure is made from the interior surface of the screen structure, the portions of the gel which are closest to its supporting member will not be properly exposed. This is because the gel is substantially translucent and permits light used for exposure to penetrate all the way down to the supporting member without undergoing appreciable attenuation.

Details concerning a particular manner of carrying out my improved method of screen manufacturing are presented hereinafter in the course of the description of the accompanying drawings in which Figure l is an enlarged fragmentary view of a typical cathode ray tube screen for color television reception;

Figure 2 is a simplified, diagrammatic illustration of certain of the equipment used in manufacturing screen structures by photographic methods; and

Figures 3A to 35. inclusive show an enlarged fragment of the screen structure illustrated in Figure 2 at various stages of its manufacture by the method which embodies my invention.

The structure of the cathode ray tube screen illustrated in Figure l of the drawings, to which more particular reference may now be had, is entirely conventional in all respects, consisting of a glass substrate which may be either the face plate of the cathode ray tube itself or a separate glass plate supported within the tube envelope. Upon this glass substrate there are disposed a plurality of parallel vertical phosphor strips, of which those designated 11 are made of a fluorescent material emissive of red light in response to impingement by the electron beam of the cathode ray tube. Those strips designated 12 are made of a fluorescent material responsive to electron beam impingement to emit green light, while those designated 13 are similarly responsive to emit blue light. As is also conventional, the entire surface area of these strips 11, 12 and 13 is covered by a film 14 of a highly reflective, conductive material, such as aluminum, and suficiently thin to be permeable to the electrons of the cathode ray beam. On the electron beam confronting side of this aluminum film 14 there are disposed a plurality of socalled indexing strips 15 which are arranged in a predetermined geometrical relationship with respect to the phosphor strips 11, 12 and 13 and which are characterized by having a secondary electron emission ratio which differs substantially from that of the aluminum film. In practice the indexing strips 15 will frequently be disposed in alignment with phosphor strips emissive of light of one particular color, say green. There will then be an indexing strip superimposed upon every third phosphor strip and separated therefrom by the aluminum film 14. However, it will be understood that this particular arrangement of indexing strips is not essential to my inventive concept, which is concerned only with the method of forming these indexing strips, as well as the phosphor strips beneath the aluminum film, and is entirely independent of the geometrical configuration thereof. Suitable materials of which these indexing strips may be made include principally those having high secondary electron emission ratios relative to that of the aluminum film. A variety of materials, such as magnesium oxide, silver, gold, tungsten and various other high atomic Weight materials have this property. It has been explained previously that differences in the intensity of the secondary electron emission current flowing from these indexing strips and from the bare aluminum film between them, when one or the other is impinged by the electron beam, are utilized to insure fidelity of color reproduction. It will be understood that, instead of relying on differences in secondary electron emissivity between indexing strips and bare aluminum film, differences in light emissivity between these portions of the screen structure can also be used to produce indexing indications. If this latter form of indexing indications is preferred then the indexing strips 15 may be made of a phosphor material rather than of a material having high secondary electron emission ratio.

For the manufacture of such a screen structure as is illustrated in Figure 1 of the drawings, there is required certain precision equipment which is illustrated in simplified form in Figure 2 of the drawings to which reference may now be had. The apparatus illustrated in Figure 1 includes a box-like supporting frame 16 which is preferably of very rigid construction, as it must support a number of other components in precise and unvarying alignment relative to each other. At the upper end of this supporting frame 16 there is provided an aperture which is adapted to receive the face plate of a cathode ray tube 18. This face plate 17 is preferably supported in this aperture by a separate insert frame 16a which is clamped securely around the rim of the face plate of the cathode ray tube before the screen forming operations are begun and which remains thus mounted on the tube during all of these operations, as hereinafter described. The outer dimensions of this insert frame are such that it fits snugly into the aperture in supporting frame 16. Its function is to insure exact repositioning of the tube face with respect to the aperture in, and with respect to other apparatus mounted on supporting frame 16 after each of the several removals of the bulb from this frame which are necessary during screen formation.

If the tolerances required in the manufacture of an insert frame which fits snugly into the aperture of the supporting frame are deemed too difiicult to maintain economically then the location of the insert frame may be conveniently determined by means of accurately adjustable stop members.

The face plate 17 is placed in this aperture with its exterior surface confronting the interior of the frame 16. While, at this stage of the manufacturing process of the cathode ray tube, the face plate 17 may be completely severed from the other portions of the cathode ray tube, it is preferred to form this face plate integrally with the flared portion 19 which, in the completed tube, connects the neck of the tube to the face plate. In practicing my invention, there is no objection to inserting this face plate into the aperture in supporting frame 16 with its flared portion 19 and its neck 19a attached. This flared portion and the neck will then extend upwardly above the supporting member 16. At the lower end of the supporting frame 16 there is disposed a light source 2% which is adapted to illuminate the exterior surface of the screen structure 17 at the upper end of the supporting member 16. Intermediate the light source 20 and the face plate 17, and as close as possible to the latter, there is disposed a mask 21 having alternate opaque and translucent portions formed in the same configuration as is desired for the phosphor and indexing elements of the screen structure. Means are provided,

I point source in every case.

, 7 such as, for example, a micrometer adjustment diagrammatically illustrated by crank 22 of Figure 2 for effecting lateral displacement of-this mask relative to the supporting frame 16 and also relative to the face plate 17 and to light source 20, both of which are stationary within this supporting frame.

When it is desired to forma screen structure like that of Figure 1, having phosphor and indexing elements in the form of parallelstrips, the translucent portions of the mask 21 will, naturally, also be in the form of parallel strips and the lateral displacement of the mask 21 will be carried out in a direction transverse to the longitudinal dimensions of the translucent strips so as to permit illumination, at different times, of difierent laterally disposed strip-like portions of the face plate 17 and of any materials deposited thereon. In this connection it is to be noted that the light source for the exposure. technique under consideration is preferably a However, known point sources provide light of comparatively low intensity so that their use requires relatively long periods of exposure. For screen elements having the form of narrow strip-like portions this exposure period can be shortened by the use of a more intense line source of light whose long dimension parallels the long dimension of the translucent portions of mask 21. If, on the other hand, the phosphor and/ or indexing elements of the screen structure are to take the form of dots whose dimensions measured in all directions are substantially the same, then the light source should be as nearly a point source as possible. I have found in practice that, While a wide variety of suitable light sources are available, good results can be obtained with a high-pressure mercury arc lamp such as, for example, that sold by the General Electric Company under the type number EH6.

The process of forming the individual strip-like elements, using the apparatus of Figure 2, is illustrated for one particular element in Figures 3A through 3E of the drawings to which more particular reference may now be had. In Figure 3A there is shown a small fragment of the face plate 17 of Figure 2. Superposed on this face plate is a layer 25 of a stock solution of photosensitive gel which may be used equally well for the deposition of all ofthe different screen constituting materials which necessitate photoelectric deposition. Such a stock solution may consist, for example, of 25 grams of polyvinyl alcohol in 600 cc. of distilled water. Various polyvinyl alcohols of different average viscosityvalues, and hence of different degrees of polymerization may be used. However I have found that satisfactory results are obtained with a polyvinyl alcohol of medium viscosity such as prepared by Dupont under the trade name Elvanol 52-22.

The polyvinyl alcohol is added to the distilled water and, with continuous stirring at approximately 120'degrees Fahrenheit, is completely dissolved in about two to three hours. After filtering the solution, 200 cc. of ethyl alcohol and 25 cc. of a solution of ammonium or potassium dichromate containing 22 grams of the salt for each 100 cc. of water are added. The resulting solution is photosensitive and should be kept under subdued light. The application of this photosensitive solution to the face plate 17 to form the layer 25 thereon may be carried out in any desired manner, as for example, by introducing the liquid into the tube so that it will flow down the wall of the flared portion 19 of Figure 2 or by spraying it from a nozzle positioned within this flared portion 19 near the neck 19a. I have found that a more uniform layer of this photosensitive material can be produced by spraying and this is how I prefer to apply the material.

After a sufficient thickness of this photosensitive solution, which may be of the order of .005 to .025 inch, is obtained it is dried thoroughly in the dark at a relatively cool temperature, i.e. by means of an air blast at a temperature somewhat less than 75 degrees Fahrenheit. The coating which is thus formed on the interior surface of the face plate 17 is then subjected to illumination from the light source 20 through the several translucent portions of the mask 21. The effect which this illumination has on each illuminated portion of the photosensitive layer 25 is illustrated in Figure 33 where the insolubility of the exposed portion is symbolized by the shading of region 26 of the photose nsitive layer 25. It will be understood that this shading is purely symbolic and does not necessarly correspond to any actual change in the light transmissive characteristics of the photosensitive layer, which usually remains translucent as before. Next, and as illustrated in Figure 3C, there is deposited over both the exposed and unexposed portions of the photosensitive layer 25 a substantially uniform layer 27 of phosphor particles of the particular phosphor material which it is desired to form into strips in the locations of the exposed portions 26 of the photosensitive material. This phosphor layer may be applied by any conventional technique such as, for example, spraying in a water suspension, dusting or otherwise. Sufiicient phosphor is preferably deposited so that the layer 27 contains approximately 0.5 to 6 milligrams of phosphor material per square centimeter. As has been indicated this phosphor forms a layer on or near the surface of the photosensitive layer and is retained in place by the tacky condition of the latter.

Next water is poured into the bulb, agitated and de canted. In this manner the unexposed portion of the photosensitive layer 27 is dissolved and removed by decanting, carrying away with it those parts of the phosphor layer 27 which were not deposited on top of an exposed portion 26. Neither the amount of water used in this process nor the degree of agitation thereof are critical. In fact, if it appears by inspection that a single washing operation is insufiicient to remove all traces of the phosphor particles deposited on unexposed portions of the photosensitive layer, then this washing action may conveniently be repeated until such complete removal has been obtained. In practice, however, I have found that a single washing operation will usually suffice in this process, as distinguished from prior practice where the phosphor was sometimes applied to the glass substrate without the intervening photosensitive layer. The reason for this is that the phosphor particles tend to adhere to the material on which they are deposited and, if this material happens'to be the glass substrate itself, then they will be difficult to flush away, whereas if, as in the present process, the actual supporting medium is the photosensitive layer, then dissolution of the latter during the washing operation will leave the phosphor particles unsupported and will facilitate their removal.

The structure which remains after this washing operation is illustrated in Figure 3D where there is shown the glass substrate 17, the exposed portion 26 of photosensitive material superposed thereon and the portion 27a of the phosphor layer 27 which was applied to the exposed portion of the photosensitive layer. It is apparent that this washing operation, as well as other succeeding washing operations, is preferably carried out away from supporting frame 16. At the end of the washing process, however, the bulb 18 is repositioned in the supporting frame 16 preferably in substantially the same position that it occupied during the initial exposure through mask 21. While considerable care must be exercised in repositioning this bulb so as to restore it to its'former position, it has proven practical, particularly by use of the aforedescribed separate insert frame, to carry out several such removals and replacements without introducing any appreciable error in bulb location. Either before or after, but prefgably after the bulb has been repositioned in the supporting frame 16, the mask 21 is displaced to a new position such that light emanating from source will be projected upon portions of the face plate corresponding to the desired locations of strips of phosphor of a difierent color. The steps illustrated in Figures 3A through 3D are then repeated for this second phosphor and again, after wash-out and replacement of the bulb and repositioning of the mask, for the third phosphor.

Thereafter, the aluminum film 14 of Figure l is applied to the previously formed portions of the screen structure in any conventional manner, as for example by evaporating a layer of aluminum of suitable thickness onto an organic protective film which has previously been deposited on the phosphor strips, and also onto the portions of the glass substrate which remain bare between adjacent phosphor strips. On top of this aluminum film there is then formed a second organic film in accordance with the teachings of copending application of Guy F. Barnett, Serial No. 367,181, filed July 10, 1953, and assigned to the assignee of the present invention which deals in detail with the technique of applying any particular material over an electron permeable aluminum film. After this second organic film has been applied to the aluminum layer the steps illustrated in Figures 3A through 3D are repeated once again, using indexing material instead of phosphor material. When the foregoing steps have been completed, the tube is baked until substantially all the organic materials used in the process of screen formation, and which include the remnants of the photosensitive layers as well as the organic films used in the process of forming the aluminum film, have been substantially completely vaporized. The remaining portions of the internal tube structure, such as its electron gun and various internal coatings may then be added.

At the conclusion of the foregoing process a phosphor strip which is formed in the manner illustrated in Figures 3A through 3D has the appearance illustrated in Figure 3E where it is shown to consist simply of the phosphor material which had been left deposited on the exposed portion of the photosensitive layer after washoif, and which had settled on the glass substrate when the exposed photosensitive material was vaporized during bake-out.

It will be noted that, in a manufacturing process which uses the rig of Figure 2, the indexing strips are formed by exposure of photosensitive material through the previously formed aluminum film. Since this aluminum film is substantially less light transmissive than the photosensitive materials used in the deposition of the phosphor strips, the exposure of the photosensitive material, to which the indexing material is to be applied, must be carried out under much more intensive illumination and/or for a much greater length of time than the exposure of the photosensitive materials which bear the colored light emissive phosphors. The first alternative increases the complexity of the equipment because provisions must be made for varying the intensity of illumination produced by the light source 20. The second alternative delays the completion of the process. While neither of these complications is prohibitive, yet, where speed and efiiciency of processing are of the essence, it may be preferred to use a difierent exposure rig wherein the light source is disposed above the narrow end of the flared tube portion and wherein an appropriately scaled down mask is disposed within this narrow end of the flared portion, between the light source and the screen. To avoid interference with the illumination of the screen through the mask it is preferred, in this alternative arrangement, to remove the tube neck before carrying out the various exposures and to replace it at the end of the process.

The foregoing discussion has been directed to the case where exposure of the photosensitive material renders the latter substantially less soluble than it was before exposure. In the event that the opposite effect should take place and the material be rendered more soluble by exposure then it will be apparent that the method of my invention can continue to be practiced provided only that the exposure mask is aligned with the cathode ray tube face plate during each exposure in such manner that those portions which are eventually to be covered with a substance of the particular kind being deposited are shielded from illumination.

it is apparent that various other alternatives to the method outlined in detail hereinbefore will occur to those skilled in the art without departing from my inventive concept. Accordingly, I desire the latter to be limited only by the appended claims.

I claim:

1. The method of forming a cathode ray tube screen structure on a glass substrate which is suitable for in corporation in a cathode ray tube as the screen supporting portion thereof, said method comprising the steps of: depositing on all areas of said substrate a substantially transparent layer of unexposed photosensitive material having substantially different solubility in a predetermined solvent before and after exposure, exposing throughout the entire depth of said layer those portions of said layer deposited on selected areas of said substrate thereby to modify the solubility in said solvent of all of the photosensitive material occupying said last-mentioned selected areas, depositing directly on exposed and unexposed portions of said layer solid particles of a substance which is substantially unafiected by temperatures at which said photosensitive material vaporizes and which is responsive to electron beam impingement to emit radiant energy, said layer being retentive of said substance at least in its condition of lesser solubility, and subsequently washing the resultant assembly with said solvent so as to remove selectively substantially all of said material constituting those portions of said layer having the greater solubility and said substance deposited thereon while leaving in place those portions of said layer having the lesser solubility and said substance deposited on said last-named portions.

2. The method of forming a cathode ray tube screen structure on a glass substrate which is suitable for incorporation in a cathode ray tube as the screen supporting portion thereof, said method comprising the steps of: depositing on all areas of said substrate a substantially transparent layer of unexposed photosensitive material which is soluble in a predetermined solvent before ex posure and insoluble in said solvent after exposure, exposing throughout the depth of said layer those portions of said layer deposited on selected areas of said substrate thereby to render insoluble all of the photosensitive material occupying said selected areas, depositing directly on exposed and unexposed portions of said layer solid particles of a substance which is substantially unaifected by temperatures at which said photosensitive material vaporizes and which is responsive to electron beam impingement to emit radiant energy, said layer being reteurive of said substance when insoluble, and subsequently washing the resultant assembly with said solvent so as to remove selectively substantially all of said material constituting of the soluble portions of said layer and said substance deposited thereon while leaving in place the insoluble portions of said layer and said substance deposited on said last-named portions.

3. The method of forming a cathode ray tube screen structure on a glass substrate which is suitable for incorporation in a cathode ray tube as the screen supporting portion thereof, said method comprising the steps of: depositing on all areas of said substrate a first substantially transparent layer of unexposed photosensitive material having substantially difierent solubility in a predetermined solvent before and after exposure, exposing throughout the entire depth of said layer those portions of said layer deposited on selected areas of said substrate thereby to modify the solubility in said solvent 7 w 11 a r of all of the photosensitive material occupying said selectedi'areas, depositing directly on exposed and unexposed portions of said layer solid particles of a first substance which is substantially unatfected by temperatures at which said photosensitive material vaporizes and which is responsive to electron beam impingement to emit radiant energy, said layer being retentive of said substance at least in its conditionof lesser solubility, subsequently washing the resultant assembly with said solvent so as to remove selectively substantially all of said material constituting those portions of said layer having the greater solubility and said substance deposited thereon while leaving in place those portions of said layer having the lesser solubility and said substance deposited on said last-named portions, depositing on all areas of the previously formed portions of said screen structure a second substantially transparent layer of unexposed photosensitive material, said last-named material having substantially difierent solubility in a predetermined solvent before and after exposure, exposing throughout the entire depth of said second layer those portions of said second layer deposited on selected areas of said previously formed portions of said screen structure thereby to modify the solubility in said solvent of all of the photosensitive material of said second layer occupying said last-mentioned'selected areas, depositing directly on exposed and unexposed portions of said second layer solid particles of a second substance which is substantially unafiected by temperatures at which said second photosensitive layer vaporizes and which is responsive to electron beam impingement to emit radiant energy which is distinctively different from that of which said first substance is emissive, said second layer being retentive of said second substance at least in its condition of lesser solubility, and subsequently washing the resultant assembly with said solvent so as to remove selectively substantially all of said material constituting those portions of said second layer having the greater solubility and said second substance deposited thereon While leaving in place those portions of said layer having the lesser solubility and said second substance deposited on said last-named portions.

4.-The method of claim 3 further characterized in that all areas of said previously formed portions of said screen structure are coated with a light reflective, electron transmissive metallic layer before depositing said second layer of unexposed photosensitive materiah 12 w r 5. The method of claim 1 further characterized in that the structure so formed is baked until said photosensitive material is substantially completely vaporized.

6. 'Ihemethod of claim lturther characterized in that a solvent forjsaid photosensitive, material is water.

- 7. The method of claim 1 further characterized in that said photosensitive material is a water solution of polyvinyl alcohol and a dichromate salt.

8. The method of claim- 1 further characterized in that said substrate is of substantially transparent material and in that said exposure is carried out by illumination through said substrate. 7

' 9. The method of claim 3 further characterized in that said firstand second substances are phosphors emissive of light of different colors in response to electron impingement.

10. Thern'ethod of claim 9 further characterized in that said selectively exposed portions of photosensitive material are inthe form of narrow parallel strips.

11. The method of claim 3 further characterized in that said first substance is a phosphor and in that said second substance is a material having a secondary electron emission ratio substantially in excess of unity.

12. The method of claim 11 further characterized in that said material of secondary electron ratio in excess of unity is magnesium oxide.

References Cited in the file of this patent UNITED STATES PATENTS Color Television Tubes, Sylvania Technologist, July 1953,

Claims (1)

1. THE METHOD OF FORMING A CATHODE RAY TUBE SCREEN STRUCTURE ON A GLASS SUBSTRATE WHICH IS SUITABLE FOR INCORPORATION IN A CATHODE RAY TUBE AS THE SCREEN SUPPORTING PORTION THEREOF, SAID METHOD COMPRISING THE STEPS OF: DEPOSITING ON ALL AREAS OF SAID SUBSTRATE A SUBSTANTIALLY TRANSPARENT LAYER OF UNEXPOSED PHOTOSENSITIVE MATERIAL HAVING SUBSTANTIALLY DIFFERENT SOLUBILITY IN A PREDETERMINED SOLVENT BEFORE AND AFTER EXPOSURE, EXPOSING THROUGHOUT THE ENTIRE DEPTH OF SAID LAYER THOSE PORTIONS OF SAID LAYER DEPOSITED ON SELECTED AREAS OF SAID SUBSTRATE THEREBY TO MODIFY THE SOLUBILITY IN SAID SOLVENT OF ALL OF THE PHOTOSENSITIVE MATERIAL OCCUPYING SAID LAST-MENTIONED SELECTED AREAS, DEPOSITING DIRECTLY ON EXPOSED AND UNEXPOSED PORTIONS OF SAID LAYER SOLID PARTICLES OF A SUBSTANCE WHICH IS SUBSTANTIALLY UNAFFECTED BY TEMPERATURES AT WHICH SAID PHOTOSENSITIVE MATERIAL VAPORIZES AND WHICH IS RESPONSIVE TO ELECTRON BEAM IMPINGEMENT TO EMIT RADIANT ENERGY, SAID LAYER BEING RETENTIVE OF SAID SUBSTANCE AT LEAST IN ITS CONDITION OF LESSER SOLUBILITY, AND SUBSEQUENTLY WASHING THE RESULTANT ASSEMBLY WITH SAID

Images