US2729583A - Method of fabricating electrical apparatus - Google Patents

Description

Jan. 3, 1956 M. SADOWSKY METHOD OF' FABRICATING ELECTRICAL APPARATUS Filed Sept. 14, 1951 com' @m55 .sussrmre a//rH smack F/Lm 00 #7000/76 .5779/25 can/w Guss, pms/wan .vnf pawn INVENTOR ATTOE EY METHUD OF FABRICATING ELECTRICAL APPARATUS Meier Sadowsky, Elkins Park, Pa., assigner to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application September 14, 1951, Serial No. 246,689

Claims. (Cl. 154-95) The present invention relates to improvements in the manufacture of cathode ray tubes and, more particularly, to improved methods of fabricating the screen structures of such tubes. p

In the past it has been the practice to form cathode ray tube screens by consecutively depositing, on a transparent substrate, the several different constituents of the screen. In the case of a cathode ray tube for black and White television reception, these constituents may be the phosphor and the conventional aluminum backing. In the case of a cathode ray tube adapted for color television reception, there may be a plurality of phosphors emissive of light of different colors, together with an aluminum backing and additional elements, such as strips of a material having a secondary electron emissivity substantially different from the secondary electron emissivities of the phosphors and/ or the aluminum, fo-r producing electrical indications of cathode ray beam impingement upon predetermined portions of the screen area. The latter form of screen structure is fully described in the copending U. S. patent application of Carlo V. Bocciarelli, Serial No. 198,709, filed December l, 1950, and assigned to the assignee of the present invention.

Although each step in these consecutive deposition processes was critical and required great care and skill for satisfactory performance, none was more delicate than that of aluminum filming. For, no matter how closely controlled were the conditions under which this step was carried out, there was still no way of guaranteeing a uniformly successful result. As is well known, the aluminum films of which I speak must be extremely thin; in fact so that that the electron beam of the cathode ray tube can penetrate the conductive material without substantial attenuation. Since this film serves as a light refleeting mirror for the fluorescent screen, it must also be substantially free of blemishes. Since bubbles, tears, variations in thickness and like deformations occur uncontrollably in the process of depositing such a thin film, the manufacture of aluminized cathode ray tube screens has heretofore been inefficient in the extreme, for it has been common to have to discard an otherwise completed screen structure because of the appearance of one of the aforementioned defects iu the aluminum film. The resulting waste is serious even in black-andwhite tubes, wherein the entire fluorescent screen area is usually made of a uniform layer of phosphor. But in color television tubes, wherein the formation of the multi-colored screen involves the deposition of many minute elements of different phosphors in accurateregistry by methods costly in both manpower and materials, the danger of wasting these efforts by reason of a defect in the superimposed aluminum film has actually been a serious deterrent to the use of such films in spite of their well known advantages.

it will be understood that similar dangers arise, with varying degrees of urgency, whenever it is necessary to form va sandwich-like structure such as a cathode ray tube screen by the successive deposition of different materials.

y United States PatentI O lCe It is, accordingly, a primary object of the invention to provide an improved method of depositing a layer of one material on the surface of another material with substantial reduction of the danger that failure of the deposited material will destroy the usefulness of the entire structure.

lt is another object of the invention to deposit a thin metallic film on an inorganic surface by a method which minimizes the likelihood of structural failure of the film.

it is still another object of the invention to provide an improved method of aluminizing cathode ray tube screens, which method substantially reduces the likelihood of producing a defective screen.

ln practicing my invention, the most conspicuous departure from the prior art resides in the formation of the aluminum film on a separate substrate, preferably of organic material, this formation being carried out externally of the cathode ray tube. The far reaching improvements which this modification produces 4will be better appreciated from a consideration of the following detailed discussion in conjunction with the accompanying drawings wherein:

Figure l is an enlarged fragmentary view of a typical cathode ray tube screen for color television reception;

Figure 2 is a ow diagram outlining a method of fabrieating the screen of Figure 1 in accordance with my invention; and Y Figure 3 is a fiow diagram outlining another method of fabricating the screen of Figure 1 in accordance with 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, as `it does, of a glass substrate i0 which may be either the face plate of the cathode ray tube itself or else 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 niaterial 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 liuorescent 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 f4 made of a highly light: reflective material such as aluminum and sufficiently thin so as to be electron permeable. Gn the electron beam` confronting side of this aluminum film 14 there are, in turn, disposed a plurality of so-called indexing strips 15, which are arranged in a predetermined geometrical relationship with respect to the phosphor strips 11, l2 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 1li. However, it will be understood that this particular arrangement of indexing strips is not essential to my inventive concept, having been disclosed in the aforementicned copending application. 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 niaterials, such as magnesium oxide, silver, gold, tungsten and various other high atomic weight materials have this property.

Again, as fully explained in the above-identified copending application, the cathode ray beam is conventionallyli'swepttiacros'srthe"screenirstructure illustrated in Figure i 1 so as to trace across the phosphor strips approximately at right angles, thus causing emission of red, green and blue light in rapid succession'. The beam intensity is then successively controlled in accordance-with received red, green and blue-color:informatiomtthe timingof this controllbeingsuch'thatimpingement ofi the electron beam uponaI strip emissive of light of one particular color, say green, Icoincides with: control ofi the electron beam intensity by green color information. It is in order to assure this-.coincidencerthat thelindexing strips are provided on-.topyof aluminum: t1'rfrr14;` For, as the electron beam;sweepstperpendicularly across consecutive phosphor strips, it will-.also traverse successiveY indexing strips, thereby producing periodic changes'in the'zse'condary emission current from;the'. screen. Conventional .means of .the type described in detail in the aforementioned. eopending application.A may-thenrbe. connectedto the screen for the purpose of-vv derivingtherefrom a .signal correspon din gk to thesevariationsinsecondaryemission current. This signal providesindications yofb'earn impingement upon particular. portions .ofthe screen `and' may therefore be utilizedsto controlttherateof beam intensitymodulation with..color information tov coincide with. beam impingementupon.particularlightemissive phosphor strips. Inasmuch as the means for so utilizing the indexing' signal arenotdirectly related-to my inventive concept, which resides'.intheimprovedfmethod-of fabrication of the screen-..itself,v and .inasmuch as.these1utilization means are fully describedin-.tle aforementioned copending application,l no showing thereof is made in the present instance.

One particular. manner of practicing the method which constitutesmyinvention.isfillustrated-in the flow diagram of Figure 2', to which more particular reference may now be had. Thesalient.characteristic ofthis method, as will betseen by. inspectionofFigure-Z, is the separate carryingvout onf-'certain steps. of the method followed by the combination of the sub-assemblies. produced by the separate processeswith. subsequent joint processing of the entire assembly. One of. the aforementioned separate processes starts with. the vdepositionfofl the. phosphor strips on the glass substrate 1U .ofFi'gure l. This operation issyrnbolized by rectangle 16j of Figurel. It may be carried out in a variety of wellknowrL-ways, as, for example, by settling, silk. screeningpor photographically depositing the various phosphorstrips. I n practice, l prefer to. use the latter method,1which consistsof first applying auniformj coatingVv of oneiof 'thefiuorescent materials to the entire glass substrate, together with a photosensitive emulsion, then exposing portions of this fluorescent material`througli slitslin-anfotherwise opaque mask, these slitsliaving been cutat. positions corresponding to the de siredl'ocation of Vstrips ofthatparticular phosphor. This exposurefixesl the phosphor ofthe. exposed portions and' the-remainder of the.-unexposedplosphor can besirnply Washed olf; ThisV process is repeated successively with eachof the'oth'er two phosphors, the mask being, of course, relocated each time so` as to permit exposure of the proper portions ofthe phosphor which it is desired to have remain onv the glass substrate. A variety of phosphors are known whichllendthemselves to this process of manufacture: Particular pho'sphors'which I.l have used with successlimformingj the fiuores'cent portions of .my screen are zinc-phosphate for the redli'ght emissive strips, zincorthosilicatef for'th'e green light emissive, strips and calcium magnesium silicate'for theblue light'ernissive strips. The

'next'step' in processing theassembly of glass substrate and phosphor stripsconsists' of wetting. the exposed surface ofxth'e phosphor strips'w'ith a material'which willact as afsolventfororganic substances.v A material suitable for thispurpjoseisacetone. Others are toluene and xylene. Thiss'tepis''symbolizedbyrectangle 17 of Figure 2'. and concldestthef-formation ofoneof the sub-assemblies. of which my 'screen' structure is'constituted; The formation of the other sub-assembly, begins .with the` formation. of a: sntiooth-surface'dl organic film, symbolized `by rectangle 4k 18"of Figure 2. This organic material is preferably characterized by beingadapted to be baked out completely at temperatures below 400 centigrade without leaving a residue. Numerous substances are known which fulfill this requirement. I have had good success with isobutyl methacrylate and nitrocellulose, each of which can readily be formed into a film ofas. littleas one mil thickness and still be capable of supporting a substantial. layer of other material such asaluminum;- On: one surface of this organic film there is then deposited the aluminum film required by the screen structurez'illustrated` in: Figure l of the drawings, thisstep'being. symbolized by rectangle 19 of Figure 2. Next, there is deposited, on the exposed surfaceofthe aluminum film, aplurality of strips made of an indexing material such as magnesium oxide, or gold, and correspondingto the indexing strips 15 of Figure l. In the deposition of these indexing strips the necessary precautions will, of course, have to be taken to maintain their .proper spacing relativeuto.the^phosphorr strips deposited on ythe glasszsubstratesothat they will bercapable of-.fuliilling their roleof providing indications ofbeam impingement upon these phosphor strips. FftheV next. step in the formation 'of this sub-assembly, which issymbolized by reetangle'Zlv of Figure-.2, and. which consists` of selectinga portion ofthe sandwichrconsi'sting ofrorganicfilm,

aluminum film-andindexing strips that isifree from blemish,- doesy not constitute anessential. step of the inventive process inasmuch as inspection ofthe vsub-assembly may take placeateach` step of itseformation. However, the fact that inspection` of zthe Vforrnedaluminum film prior to its.A applicationv to thev phosphorstrips is' possible when practicing mymethod, emphasizes one of the principal advantages thereof/over they priorart, wherein the aluminum filmfwasformed directly on the phosphor strips so that, by the' time blemishes occurring in the process ofV formation became visible, it was too'late to save the phosphor strip sub-assembly. The first sub-'assembly formed by steps 16 and 17 andthesecond sub-assembly formed by steps.18, k19, 20, the latter having been preferablyinspected for defects `rin'the aluminum film, are now combined, as symbolized by rectangle 22, by depositing the sandwich-like structure' of. organic: film, aluminum film and indexing strips jointly on thephosphor strips which have previously been Wet .with-solvent, this deposition being carriedout so that-'the organic film is in contact withu the solvent. Thefinaly step of my process, which is symbolized by rectangle'23. of Figure 2, consists. of baking the final a'ssembly,upreferably at a-temperature below 400 centigrade, until the organic. film-dissolved by the solvent has completelyvaporized, at which .point there is left only the structure of Figure 1. The use of temperatures below 400 centigrade is prompted by the fact` that`.the.phosphorshereinbefore listed and others which may he. suitable for the colored .lightemissive rstrips of .the structure Vtend .toloseefliciency athighertempera.- tures. If more heat resistant phosphore are used, the baking temperature. may, ofcourse, also beraised.

It will be understood that .my inventive process of forme ing thev screen. structure is complete even without baking out of the organic` film. If. this isl notdone at this point,

however, there is thedangen that heating due to impingement by theelectron-beam; during actual operationof a completely assembledtube incorporating thatscreen, will cause vaporizatioruof theorganic-film which. will then contaminate.otherelementsof thetube suchas the electron, emissive cathode, for. example. Alternatively, the organiolm may carbonize, leaving` a layer of carbon which. is lightI absorbent. and also has low secondary electron emissivity.

While. the .invention is. not. limited. to. any particular manner ofcarryingout. the aforementioned steps, certain of the Vinherent..advantageszof.my novel method over those of the. prior art..will..become.apparent.from a. detailed consideration ofthe. preferred mode; of. practicing steps 3.9, 20`and 21,.which,. respectively, relateto the. deposition ofthe aluminum film, the deposition ofthe indexingstrips annalisa 5 and the selection of a surface free from blemishes for combination with the phosphor strips. The organic film formed in step 18 may, for example, be supplied in the form of a roll of sufficient width to cover `the greatest vertical dimension of the phosphor strip lined glass substrate. This roll may be unwound through a continuously evacuated bell jar containing an aluminum evaporator from which the aluminum necessary for the formation of the aluminum film on the organic lm is continuously evaporated. The rate of evaporation of the aluminum and the rate of traversal of the organic layer may be so adjusted relatively to each other that aluminum of the desired thickness is continuously formed on the organic film. After the combined organic and aluminum films have left the evacuated bell jar, the exposed surface of the aluminum may be uniformly coated, for example by spraying, with the material of the indexing strips, together with a photosensitive emulsion. The assembly thus produced is then passed behind an opaque mask having a narrow slit through which a strip the width of an indexing strip is exposed to illumination at such intervals, relative to the rate of film displacement under the opaque mask, that portions spaced in accordance with the requirements of the indexing strip spacing disposition are exposed and fixed, after which the entire sub-assembly is passed through a bath in which unexposed portions of the index material are washed away, leaving deposits of indexing material in the appointed locations. The final inspection of this product can be carried out by passing it between a source of light and a photoelectric cell so that light transmission to the photoelectric cell occurs only at discontinuities in the aluminum film, thereby giving automatic warning of defects in this film. Portions of the proper size for application to the phosphor strip assembly are then cut and applied thereto in accordance with step 22.

Note the tremendous advantage of practicing my method in the manner outlined hereinabove and which resides not only in the formation of a screen having a awless aluminum film backing without danger of ruining the expensive phosphor sub-assembly, but which also permits the formation of the major portions of the assembly by a completely automatic process which is continuous and requires no human supervision. Evidently, the aforementioned steps can also be carried ont by hand.

Where it is desired to avail oneself still further of automatic machinery in the fabrication of a screen structure in accordance with my invention, the process diagrammed in Figure 2 may be somewhat modified, principally with respect to the order of occurrence of the various steps, in the manner diagrammatically represented in Figure 3, to which more detailed reference may now be had. Again it is an important characteristic of my process that two sub-assemblies are first separately formed, then appropriately combined and submitted to final joint processing. The formation of one sub-assembly, in accordance with my invention, involves the coating of the glass substrate upon which the remaining portions of the screen are to be supported with a material adapted to bind fluorescent phosphors to this glass substrate. Such a binder material may be potassium silicate, the step of coating the substrate therewith being symbolized by rectangle 24 of Figure 3. Other silicates may also be used. The formation of the other subassembly begins with the formation of a smooth-surfaced organic film, just as it did in the case of Figure 2. Accordingly, this step is symbolized by a rectangle similarly designated by reference numeral 18. Instead of depositing the aluminum film on this organic film, as was done in the process of Figure 2, the first deposit formed on the organic film consists of the appropriately disposed indexing strips, as symbolized by rectangle 25. On top of these indexing strips, the aluminum film is then deposited, as symbolized by rectangle 26. At this point in the process, the inspection of the previously formed `aluminum film is preferably carried out to insure its freedom from blemishes, and perfectly formed por tions are selected for subsequent utilization. This step which is, again, not essential to the practice of the invention, is symbolized by rectangle 27 of Figure 3. On the exposed surface of the aluminum :film there are next deposited the phosphor strips which constitute the light emissive portions of the cathode ray tube screen structure, this operation being symbolized by rectangle 28. The sub-assembly heretofore produced thus comprises a sandwich-like arrangement of an organic film, indexing strips, aluminum film and phosphor strips adjacently disposed in the order named. In the next step, symbolized by rectangle 29 of Figure 3, this sub-assembly is deposited on the binder-coated glass substrate formed in step 24, so that the phosphor strips will be in contact with the binder. Finally the entire structure so formed is baked until the organic film has been substantially completely vaporized, as indicated by rectangle 3l).

Note that in the process diagrammed in Figure 3 the deposition of indexing strips and aluminum film on top of the organic film may be carried out automatically in exactly the same way as in the process of Figure 2, except that the order in which these two operations are carried out is reversed. Similarly, the inspection and surface selection may be carried out automatically as explained in the discussion of Figure 2. The additional deposition of the phosphor strips on this sub-assembly, prior to its combination with the glass substrate to form the complete screen structure, permits the deposition of these phosphor strips by automatic processes similar to those by which the indexing strips are deposited. That is, the organic film, after having been coated with indexing strips and aluminum film may be continuously sprayed, first with a phosphor emissive of red light, for example, together with a photosensitive emulsion, then with a phosphor emissive of green light, again with a photosensitive emulsion and finally with a phosphor emissive of blue light and a photosensitive emulsion. Between applications of any two successive ones of these different phosphors, the film is passed beneath an opaque mask, slit so as to permit illumination of a region corresponding to one phosphor strip, successive illuminations being produced at such a rate, relative to the rate of passage of the film under the slit, that portions spaced in accordance with the requirements of phosphor strip configuration of that particular color become developed and fixed, after which the remainder of the undeveloped phosphor of that particular color is washed off.

It will be understood that still further modifications of the method will occur to those skilled in the art without departing from my inventive concept. Therefore, I desire the latter to be limited only by the appended claims.

I claim:

l. The method of forming a screen structure for cathode ray tubes, said method comprising the steps of: forming a first sandwich-like assembly of a solid transparent substrate and a layer of fluoroscent materials, forming a film of organic material having approximately the same surface area as said layer of fluorescent materials, depositing on said organic film a metal film of electron permeable thickness to form a second sandwichlike assembly of organic material and metal, depositing said second assembly on said layer of fluorescent materials, and baking the structure so :formed until said organic film has been substantially completely vaporized.

2. The method of forming a screen structure for cathode ray tubes on a glass substrate coated with a binder for phosphor materials and including a face-plate, said method comprising the steps of: forming externally of said substrate a film of organic material, depositing a layer of aluminum on said organic film and a layer of phosphor materials on said aluminum film to form a sandwich-like assembly of organic film, aluminum and phosphor materials, depositing said assembly on said binder coated, substrate Withrsaid4 phosphor materials ir contactwith` said'y binder* and baking the structure so formed'untillr said organic' iilmhas been, substantially completely vaporized.'

3; The method of forming a screen structure for cath'- ode' ray'tubesi on a' glass substrate coated with, a binder for'phosphor materials and including a face'-p1ate,rsaid method"comprising` the steps of: formingv externally of saidlsubstratea .film of' organic material, depositing spaced ,parallel strips oflindexing materials on said organic film, depositing a layer. of aluminum on said'strips of indexingv materialsand on saidy organic lilrn in the spaces' between said: strips, and depositing` a layer of phosphor materials on saidr aluminum film to form a sandwichflile assembly'of organic iilm, indexing mate ria'ls', aluminumand phosphor materials, depositing said assembly ion said Ybinder coated substrate with saidi phos phot"materialsV in contact with said binder and baking the structurey so` formeduntil said organic iilmY hasbeen substantially completely vaporized;

4.' The method of forming a screen structureA for cathoder raytubes'on` a" glass' substrate coated with a binder for phosphor materials andjincluding a face-plate, said methodmo'mprisingthe steps of: forming',externally of said ysubstrate a" film` oflorganic material, depositing` a layerofspacedparallelgstrips of indexing materials on said' organic film,` depositing a layer or"V aluminum on saidstrips"of indexing materials'andon saidorgauic iilm in the spaces between said strips, and depositing on said aluminum film spaced strips of phosphor materials in p redter'mined;l geometrical configuration relative to said strips' of! indexing materialto'. form a sandwichlile assembly oforganic' lm, indexingpmaterials, aluminum and phosphor materials,` dii'erent. ones'of said phosphor strips beingp made ofjmaterials,responsive to electron impingen ment to emit light of different primary colors, depositing said, assembly` on said binder coated substrate with said phosphor stripsY in contact with saidybinder andY baking the structure so-formediuntil said organic film has been substantially completely vaporized;y

5. inthev method'oi-'forminga screen structure forV References Cited'the me; of this patent.

UNITED- STATES'PATENTS- 2g40'4g90`4" Collins s July 30, 1946 2,566,735y Lepie' Sept. 4', 1951 25,606,822 Pakswer Aug. 12,1952

Claims (1)

1. THE METHOD OF FORMING A SCREEN STRUCTURE FOR CATHODE RAY TUBES, SAID METHOD COMPRISING THE STEPS OF: FORMING A FIRST SANDWICH-LIKE ASSEMBLY OF A SOLID TRANSPARENT SUBSTRATE AND A LAYER OF FLUOROSCENT MATERIALS, FORMING A FILM OF ORGANIC MATERIAL HAVING APPROXIMATELY THE SAME SURFACE AREA AS SAID LAYER OF FLUOROSCENT MATERIALS, DEPOSITING ON SAID ORGANIC FILM A METAL FILM OF ELECTION PERMEABLE THICKNESS TO FORM A SECOND SANDWICHLIKE ASSEMBLY OF ORGANIC MATERIAL AND METAL, DEPOSITING SAID SECOND ASSEMBLY ON SAID LAYER OF FLUORESCENT MATERIALS, AND BAKING THE STRUCTURE SO FORMED UNTIL SAID ORGANIC FILM HAS BEEN SUBSTANTIALLY COMPLETELY VAPORIZED.

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