US3738233A

US3738233A - Camera process for color tube screen printing

Info

Publication number: US3738233A
Application number: US00218144A
Authority: US
Inventors: J Schwartz
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1972-01-17
Filing date: 1972-01-17
Publication date: 1973-06-12
Anticipated expiration: 1990-06-12

Abstract

A photographic replica of a shadow mask of given transmission, i.e., ratio of aperture area to mask area, is made with the transmission of the photographic replica of the mask being less than that of the shadow mask. Thereafter, the photographic replica is used in place of the mask for screening the elemental phosphor deposits on the faceplate of a color television picture tube. In the case of a black surround type color tube, the replica is used to initially photoexpose the matrix pattern of phosphor receiving areas and subsequently used to deposit the phosphors. When the screen is fully fabricated, the shadow mask is assembled in position and the photographic replica is discarded.

Description

United States Patent 1 Schwartz CAMERA PROCESS FOR COLOR TUBE SCREEN PRINTING James W. Schwartz, Glenview, Ill.

Zenith Radio Corporation, Chicago, 111.

Filed: Jan. 17, 1972 Appl. No.: 218,144

Inventor:

Assignee:

US. Cl. 95/1 R, 96/36.1, 313/92 B Int. Cl G03 Field of Search ..29/25.1, 25.11, 25.13;

References Cited UNITED STATES PATENTS Flood Light 3,666,462 5/1972 Kaplan 313/92 B X Primary ExaminerSamuel S. Matthews Assistant E x qmirre r-Richard M. Sheer Attorney Nicholas A. Camasto and John J. Pederson [57] ABSTRACT A photographic replica of a shadow mask of given transmission, i.e., ratio of aperture area to mask area, is made with the transmission of the photographic replica of the mask being less than that of the shadow mask. Thereafter, the photographic replica is used in place of the mask for screening the elemental phosphor deposits on the faceplate of a color television picture tube. In the case of a black surround type color tube, the replica is used to initially photoexpose the matrix pattern of phosphor receiving areas and subsequently used to deposit the phosphors. When the screen is fully fabricated, the shadow mask is assembled in position and the photographic replica is discarded.

19 Claims, 9 Drawing Figures PATENIEDJUNIZIBH 3.738.233

SHEHZUFS Correct Panel Ehsmoced Surkme Pena Sufluce Electron Roy F 4 Projection Corrected IUII Lens

Correcfion Lens Vertucl RepHco PAIENIE JUN v 2 ma suwanra Flood Hlumincuon Correct' n Repllca Lens IO FIG, 7

Dot Image R pllccl Apertu re ht Sou rce J DHCG Camera K Lens CAMERA PROCESS FOR COLOR TUBE SCREEN PRINTING BACKGROUND OF THE INVENTION The present invention concerns processing screens for color television picture tubes of the type having elemental phosphor deposits which are smaller than the size of the shadow mask apertures. A commercial version of such a tube is the so-called black surround picture tube. The black surround tube differs from conventional shadow mask color tubes in that the elemental deposits of different colored light emitting phosphors are individually surrounded by a light absorptive material such as graphite.

A commercial version of such a tube includes a mosaic of dot triads arranged in a regular pattern over the faceplate area. Each triad includes a green phosphor dot, a blue phosphor dot and a red phosphor dot, each of which is smaller than normal such that the phosphor dots of a triad as well as adjacent triads are physically separated rather than being tangential to each other. The separation of the dots provides an area for reception of the black surround material which is generally applied prior to deposition of the phosphor dots. The

faceplate assembly is completed after aluminizing of the phosphor dot mosaic and black surround pattern by positioning a curved shadow mask (which was used in applying the black surround and phosphor dots) in registry with the phosphor dot screen. The shadow mask serves to accomplish color selection in the usual way, that is, the shadow mask is arranged such that elemental phosphor deposits of a given color only visible to the electron beams emanating from a predetermined point (gun) in the neck of the color picture tube. Preferably, the shadow mask apertures are larger than the phosphor dots of the screen and the spaces between the dots provide a tolerance or guard band for the improved purity of the white color field.

A black surround tube of this type is described in U.S. Pat. No. 3,146,368, issued Aug. 25, 1964 to Joseph Fiore et al. and assigned to the assignee of the present invention.

A number of different techniques have been put forward for processing the screens of black surround tubes. In particular, the problem faced is that of obtaining the proper size relationship between the shadow mask apertures and the individual phosphor deposits. It has been suggested that the form shadow mask with the desired final hole size be subjected to a procedure for closing the holes temporarily for photographic screening. Hole closure may be accomplished by means of a filler which is removed after screening so that the mask apertures in the completed tube have the desirable size relationship to the phosphor-deposits. Numerous problems have been encountered in trying to utilize this technique.

A commercially successful approach is one that is referred to as re-etch. In this process the shadow mask is initially formed with apertures of desired size for screening or laying down the phosphor dots. After screening, the shadow mask is subjected to another etching for enlarging the size of the original apertures. This process has achieved substantial success and many tubes are in commercial use which have been constructed in accordance therewith.

An inherent disadvantage exists in the re-etch process since, if the tube is damaged in processing after mask re-etch, the mask cannot be reused. If the black surround screen could be satisfactorily fabricated without requiring re-etch or other modification of the size of the mask apertures during tube manufacture, significant economies could be realized. With the process of the present invention, the desirable relationship between the aperture mask holes and phosphor deposits may be obtained without resort to mask modification.

Accordingly, it is an object of the invention to provide an improved process for the manufacture of cathode ray tube screens of the shadow mask variety which are characterized by mask apertures which are larger than the elemental phosphor deposits.

Another object of the invention is to improve the processing of a black surround screen for a shadow mask type picture tube.

SUMMARY OF THE INVENTION The process of the invention is directed to manufacturing the screen of a shadow mask type color picture tube wherein the mask apertures are larger than the elemental phosphor deposits and comprises the following steps.

A photographic replica of a curved (formed) shadow mask is made. During exposure of the photographic replica, relative motion is introduced between the shadow mask and the film plane of the camera, for example, to develop proportionally smaller apertures on the film than exist in the shadow mask being photographed. Stated differently, the transmission of the shadow mask is made greater than the transmission of the shadow mask photographic replica. (Transmission is defined as the ratio of aperture area to mask area and is a direct indicator of the porosity of the shadow mask.) The replica is then used as a shadow mask in further tube fabrication, such as in forming the black surround pattern and in depositing the phosphor ele ments. In the finished tube, the original shadow mask is used and has apertures which are larger than the phosphor elements.

A conventional shadow mask color tube consists of a front glass portion called a panel and a glass funnel scalable thereto by a glass-to-glass weld. The panel includes a clear faceplate for the viewing screen and a continuous upstanding wall having at least three, and sometimes four, shadow mask mounting studs embedded therein. A color tube of the patented black surround type mentioned above has three panel studs which are the basic geometrical points used to locate the other tube elements. The shadow mask is conventionally formed into a curved surface and mounted on a frame which includes means for releasably mounting the mask in fixed spatial relationship to the panel. These means generally comprise springs affixed to the mask frame and adaptable for engagement with the studs to facilitate removal of the mask and its accurate replacement in the panel during screening operations.

Normal screening involves coating the inner surface of the faceplate with a slurry of photosensitive material including a first of three colored light-emitting phosphors, assembling the shadow mask and exposing the photosensitve surface to a source of appropriate energy through the mask'apertures. This is accomplished in a lighthouse and the source of energy is positioned at an optical-point corresponding to the ultimate location of the source of electron beam energy associated with that particular color phosphor. After removal of the mask and screen washing, the process is repeated for the remaining color phosphors. In a black surround type tube, the faceplate may be initially coated with a photosensitive material such as a mixture of polyvinyl alcohol (PVA) and ammonium dichromate, and exposed to actinic energy through the shadow mask with the light source being moved to all three positions corresponding to the three electron gun centers in the finished picture tube. Generally, three exposures are made on three different lighthouses, thus forming on the faceplate exposed dots of hardened PVA corresponding to areas where the elemental phosphor deposits will ultimately be made. The shadow mask is removed and a black coating such as graphite is applied over both the exposed and unexposed surface area and dried. The panel is then washed with hydrogen perioxide under pressure resulting in removal of the dots of exposed PVA and black material from each of the elemental areas, leaving the panel with a black honeycomb pattern. After drying, the panel and its mating shadow mask are used to photodeposit the elemental phosphor dots of red, blue and green in the corresponding holes in the black honeycomb pattern. Conventional techniques are used to further process the screen and complete the assembly of the color picture tube.

An alternative technique is to initially screen the phosphor elements onto the faceplate and then form the black surround by photoexposure of a sensitized coating applied over the phosphor elements through the front of the faceplate. The first mentioned technique is, however, believed to be the most desirable one in practice.

In a black surround type picture tube of the type described in the above patent, a further etching (or reetch, as it is called) of the shadow mask is carried out to enlarge the apertures to a predetermined size.

' Thereafter, when the shadow mask is reassembled with its mating panel, the effect is that the electron beams passed through the mask apertures are larger than the phosphor deposits and overlap onto the black material surrounding the deposits. In a non-black surround tube, the spaces between phosphor dots are filled with aluminum. In any case, a tolerance band is provided for minimizing beam landing overlap onto the wrong color phosphors.

This commercially successful process has a number of inherent disadvantages. For example, the shadow mask must be inserted and removed to form the black honeycomb pattern and during photodeposition of each color phosphor. Further handling is required if rcetch or other mask hole enlargement techniques are used. The possibility of rejects due to dented masks, plugged aperture holes, striking the phosphor screen with the mask, etc. is greatly increased with each handling of the shadow mask. Defects incurred prior to reetch or mask enlargement are not as serious as those occurring after since in the latter instance, the mask holes are too large to be recycled in another tube making process.

In the process of the invention, the shadow mask is replaced by the photographic replica thereof which is accurately positioned with regard to the face panels and utilized for both forming the black honeycomb pattern and for photodepositions of the respective color phosphor elements. The advantages of this process are that no subsequent mask hole enlargement techniques are required, the mask need not follow the panel through the screening areas of the factory, a greater flexibility in phosphor dot size is obtainable and corrections for beam landing errors may be introduced directly on the replica. Additionally, the black surround pattern may be formed after photodeposition of small phosphor dots, through the replica, if desired.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention which are believed to be novel are set forth with particularity in the claims. The invention together with other objects and advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

FIG. 1 represents aschematic diagram of structure required in a camera system to make a photographic replica of a shadow mask.

FIGS. 2-6 are useful in connection with a mathematical analysis of the requirements of camera systems utilizing the process of the invention.

FIG. 7 shows one technique for photodepositing a color phosphor screen utilizing the shadow mask replica developed in the process of the invention.

FIG. 8 depicts the size relationships between the light source, the aperture in the photographic replica and the size of the phosphor dot image formed.

FIG. 9 represents an alternative approach for using the replica of a shadow mask for photodepositing the color phosphor pattern on a picture tube faceplate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The camera process of the invention lends itself to a number of systems. For convenience, the systems will be referred to as Systems I and II and alternates, IA and IIA thereof.

In FIG. 1, a rudimentary method of making the replica of the shadow mask is shown. A conventional formed shadow mask 10 is shown supported by means of a pair of supports 11 in front of a dark background surface 12. Mask 10 is illuminated on its concave side by a floodlight source. A photographic camera 15 is positioned a predetermined distance from the shadow mask-and through a lens 16 forms a replica of the shadow mask on camera film plane 17. The distance between the center of lens 16 and film plate 17 is indicated as p. A dashed line 19 situated a distance p between lens 16 and shadow mask 10 represents a virtual image of the shadow mask. The predetermined distance is selected such that camera lens 16 is situated at the approximate position occupied by the light source in a conventional lighthouse. In practice it may be desirable to coat the shadow mask temporarily with a reflective coating for proper illumination during the exposure interval. This temporary coating will, of course, be removed prior to assembly of the mask in the finished tube. As indicated by block 18, means are provided for introducing small circular movement of the film plane during exposure. This technique results in the apertures in the replica of the shadow mask being proportionally smaller than the apertures in the shadow mask. Defocusing of the camera lens may also be used to produce proportionally smaller apertures on the replica.

In an effort to more fully understand the process of the invention and the advantages afforded, the following mathematical analysis of the geometrical relationships of the camera process compared with the conventional lighthouse process is offered. It is well known in the three-gun shadow mask color tube sytem that the paths of light rays in a lighthouse differ from the actual electron beam paths in the finished tube. For example, the three electron beams do not emanate from a common point and hence experience differing magnetic yoke fields. The apparent electron source location also moves as a function of raster position. These and other effects, such as faceplate deformation during tube processing, have necessitated the use of correction lenses in connection with optical screening. FIG. 2 illustrates (in an exaggerated manner) the axial displacement k of the electron ray projection for a large deflection angle as well as the path of an optically corrected light ray. The correction lens is seen to compensate for the apparent displacement k of the electron ray projection with raster position. In this conventional exposure system, the distance between the shadow mask and faceplate is extremely small (on the order of one-half inch) and consequently, the placement of correction lenses between the mask and screen is virtually impossible. This is not true in the camera process where a replica of the mask is used and this distinction gives rise to the differences between System I and System II, namely, that in System I, a correction lens is placed between the replica and the screen whereas in System II the correction lens is placed between the source and the replica.

SYSTEM I Referring to FIG. 3, the geometrical relationships for System I will be derived. FIG. 3 shows the projection of an electron ray intersecting the axis through the light source at a distance k. For each point of the shadow mask, a prescribed apparent source deviation k exists. In conventional screening, the surface of the correction lens is made to deviate the apparent source position in accordance with the functional relationship Where r,, and 6 are the cylindrical co-ordinates of the point of intersection of the electron ray and mask surface. In the remaining analysis a dependence upon 0 will not be shown explicity since individual rays will be considered. I

A line passing from the light source through a specific opening at r of the secondary mask intersects the shadow mask at a specific opening location at r,,.. An electron ray (emanating a distance k from the light source origin) intersects the screen at r,. The corrective lens must deviate a light ray passing through the secondary mask opening at r, so that it too intersects the screen at r,. The ray impinges the corrective lens surface at r, where it is appropriately deviated to effect the correction. The backwardly projected deviated ray intersects the axis at a distance j from the light source. It will be noted that the vertical projection of the mask to screen separation d is a slowly varying function of r,,,.

The following expressions may be obtained from observation of FIG. 3.

From (2) and (3) Equating (4) and (5) (p+q+dj)l(p+q+ (p+qj)= which may be rearranged to j=(dk)/(d+[p+qu ]/u[p+q+dk]) The quantity d (typically one-half inch) in the denominator of (7) is generally small compared with the other term in the denominator. The remaining term is only a slowly varying function of r and a typically numerical value would be approximately 10 inch. Hence, a j correction lens is nearly proportional to a conventional k correction lens, but about one-twentieth as strong.

The following analysis will derive an expression for calculating the error due to mask-screen spacing deviations.

A j corrected ray does not follow a path identically coincident with a k corrected or an electron ray in the vicinity of the screen. Hence, variations in the maskscreen spacing projection g will result in a misregister e of the phosphor dot relative to the electron beam landing position.

Aymqtb9r Phy y p ac d a g. The electron beam will land at r and the jat r asshown in FIG. 4. By inspection it follows that e r,, r

Since] and k are small compared to p q d (ll) reduces closely to or using (7) or to good approximation At the center of the screen where r, 0, the misregister e is also zero. Since k is measured from the light source it can arbitrarily be made zero at any one value of r, by appropriate source location. If k is set to zero at the largest value of r, (in the corners of the screen) e will also be zero there. The maximum value of e can be even further diminished by adjusting the source so that k at a smaller value of r, than that of the screen extremity.

It can be shown that for a quadratic dependence of k on r,, the optimum choice of r, for which k o is onehalf of the maximum value of r,. This reduces the maximum value of e to one-fourth of the value that would otherwise occur with k set equal to zero at the center of the screen.

From expression (14) the possible magnitude of e may be found.

The quantity r,/(p q d) reaches unity at the tube corners (for a 90 tube). The range of k is generally less than tone-fourth inch leading to a maximum value of k/p q d of less than 0.025

The mask-screen tolerances set an upper limit on g of less than 0.040 inch. Hence the maximum value of e can be restricted to less than l X 0.025 X 0.040 0.001

Although this is a relatively small amount of misregister, it is not negligible.

At this point in the anaylsis it is useful to differentiate between the two types of misregister-radial and degrouping. The former refers to displacement of the center of the elemental phosphor dot triad from the center of the RGB beam landing triad. Degrouping refers to landing errors caused by improper triad shape, size, or orientation. The radial or symmetrical contribution to k is independent of azimuth while degrouping generally is not.

K may be set equal to o for an arbitrary ray intersecting the screen at r, by judicial choice of light source and camera lens location. A corrective lens in the camera optics can effectively make k nearly zero for all rays. Since degrouping requires different optical correction for each phosphor color, however, three different secondary masks would be required to incorporate the total correction.

About two-thirds of the total contribution to k is symmetrical radial misregister for which compensation can be incorporated within a single secondary mask.

FIG. 5 illustrates the use of a radial misregister optical field correction lens for producing a System I replica. Residual degrouping misregister using such a secondary mask will be less than 0.0003 inch.

When mask-screen spacing deviations induce electron beam triad degrouping, corresponding degrouping of the phosphor dots generally detrimental because of loss of tolerance with respect to adjacent dot triads. The residual degrouping misregister of System I is in a direction tending to reduce this effect and is a distinct advantage over conventional screening techniques.

SYSTEM 1i System II utilizes a configuration employing a correction lens between the light source and the secondary mask during screen exposure. By inspection of the arrangement shown in FIG. 6, it follows that al r =0 q d "j)/(P -j) and r /r, (p q)/p (17) Dividing (l6) by (15) yields Equating (l7) and (18) equation (19) can be solved for j yielding Expression (20) for System II is analogous to expression (7) for System l. They differ only by the second term in the denominator containing q/p for System II and (p q u)/u in System I. Both terms are of order unity and in specific systems either might be chosen to be larger. Hence, System II lenses are also quite weak compared to conventional k lenses and are quite similar to System I lenses.

A carful comparison of FIGS. (4) and (6) reveals that the former is valid for analysis of mask-panel spacing induced misregister in System II as well as System I. This results from the lack of explicit dependence upon the secondary mask or replica location. Hence expression (12) applied to System II. Expression (13), however, does not apply since it was derived using (7) whereas (20) must be used for System II. In this case Practical geometric parameters dictate that the quantity will only be modestly less than unity. Hence if optical field correction is not incorporated in the replica, System II is about equal to System I in susceptibility to mask-panel tolerance induced misregister. Since radial misregister can be compenstated for in an identical manner as in System I it is not an unavoidable factor of consequence in either system.

ALTERNATIVE OPTICAL SYSTEMS The successful use of either System depends upon obtaining an accurately projected image within the camera when the replica is produced. Optical field distortion must be either extremely small or must be subsequently corrected in the tube exposure optics.

FIG. 7 illustrates an alternative arrangement which is insensitive to field distortion due to the use of a wide angle camera lens. The same (or an identical) lens used to produce the replica is reciprocally used to project the replica on the tube faceplate. Hence field distortion of the lens is cancelled out.

Since a virtual image of the replica appears on the panel side of the projection lens, at a distance p from the lens, the correction lens analyses for both Systems I and II also apply to the Alternative Systems. If p u System I analysis applies. If p u System II analysis is applicable.

OPTICAL EFFICIENCY OF SYSTEMS I & II

The exposure time required for screen printing depends on several parameters. For the System I the parameters include source diameter h, source brightness l,, aperture size n, source position p, and source to screen distance p q D. FIG. 8 shows how these relate to image size H. The following expressions result from inspection of FIG. 8.

I-I/h (Da)/a Ma n/p-a Eliminating a yields For source and dot image sizes small compared to D, the following expression for the average illumination intensity I at the screen is valid I= 17/4 1, (n h )/(p H) Expression (25) is obtained in the following manner:

For each point of the source the cone of rays which can pass through aperture n lie within a solid angle (11 n')/(4 p). The totality of such points at the source is proportional to its area (11' h)/4. The energy at the image, however, is distributed (non-uniformly) over an area equal to (11 H)/4.

Substituting (24) in (25) =1 "')/(p H) {P(H h)]/D h} 2 Holding p, q, D and H constant, the maxima of (26) is found by partial differentiation relative to parameter h, the source size.

from (24), (25) and (30) then Ind-t a q )/(P 4 q ([1 0 1/1 1 DV which simplified to mar =77/64 s P )/(q D2) The parameters H and D have the same value in the camera systems as in a conventional exposure system. Parameters 1,, p and q, however, will in general, differ from those of the conventional system. Typically in a conventional system n 0.014 inch h 0.170 inch p 10 inch q 0.5 inch H 0.023 inch Derived from (24) The intensity from (25) then is This compares to the maximum obtainable value predicted by (32) for the optimum source and mask hole sizes for the conventional system of 1 1r164 [(0.023) X l00]/[0.25 X 1.04 X 10 llcom:

In the camera system, p is smaller and q larger than in the conventional case. Both of these factors are therefore relatively unfavorable for the camera system. For 0.023 dot extreme illumination, even for a p/q ratio of 4, the maximized brightness would be For equivalent exposure times, therefore, the apparent source brightness for the camera process must exceed the conventional tip apparent brightness by If a smaller secondary or replica is used so that p/q l, for example, the brightness requirement is further increased by 16 times to 350 times that of a conventional tip.

Mercury arc sources of either the capillary are or short are type have a brightness of approximately 300 candles/mm? Measurements of the brightness of the collimator tip of a conventional lighthouse indicate that the tip brightness is about one-fourth that of the are itself. Hence, it is unlikely that a suitable mercury arc source can be developed that would make System I as fast as the conventional system.

More exotic sources such as a scanned laser, or a laser with a divergent (or convergent) lens could be used even for small replicas. An ultraviolet output of the order of 1 watt would be required. Since very small sources of extreme apparent brightness are thus obtainable, the calculation for optimum replica aperture size is not applicable. This is because a fixed limit on apparent source brightness, rather than fixed emitted power was assumed. I

The replica aperture size obtained by substituting (30) into (24) for fixed brightness is This is, of course, exactly one-half the size (and onefourth the area) of the required replica aperture opening for a point" source. Hence the laser source output power impinging on the replica need by only onefourth that of a larger fixed brightness source. Additives to the photoresist can extend its sensitivity into the visible and could relieve the need for an ultraviolet emitting laser.

SYSTEMS IA & [IA

The factors governing the optical efficiency of alternative Systems IA and IIA are intrinsically different from those of Systems I and II. The exposure speed of the A system is essentially independent of replica mask transmission. It depends upon the efficiency of relaying the brightness of an enlarged source to the camera lens, the camera lens speed and the camera lens-to-panel distance.

FIG. 9 discloses a process for screening the faceplate, the replica of the shadow mask, an extended primary light source, an optional reflector and a condenser lens. Since the replica is not between the light source and the panel but on the opposite side thereof, this is an A type process. A great deal of flexibility is allowed since the use of a condenser lens between the primary light source and the replica allows a much greater concentration of light energy. The condenser lens focuses the light from the light source in the plane of the replica and the diverging light rays passing therethrough are again converged by the camera lens for exposure of the photosensitive material on the screen. The camera lens is situated at the position of the conventional light source at the lighthouse. This approach also permits use of relatively small replicas without the light scattering which would normally occur if a small replica were used in System I or in System Il.

If I, is the brightness of the primary source, E the brightness efficiency of the relay optics system illuminating the lens, C the camera lens effective diameter and p and D the distance, the illumination 1 at the screen is 1 1,, E Wm 4 D2) The allowable value of C is limited by depth of field and aberration considerations. For D 10 inch and a i 0.0005 inch dot size variation induced by a i 0.017 panel contour variation (present specified limit) the maximum value of C is C 10 inch X 0.0005 inch/0.017 0.30 inch This results in a maximum illumination of the panel of This compares very favorably with the value 8.3 X 10' I obtained previously for a conventional lighthouse. With proper relay optics I,,E may even exceed slconv.

The focal length F of the camera lens is, of course, given by Hence the maximum speed of the lens f/ must be less than In our example, for p 5 inch For a curved panel, the panel exposure lens must have a curved image surface which matches the panel contour. While the mask and panel contour differ slightly, a lens designed to project 'a planar object onto the panel contour will suffice since defocusing enhances aperture size reduction in the replica.

Precise orientationof the shadow mask relative to the panel is necessary in any optical screen printing process. Normally the mask-panel is determined by the relationship of the mask springs to the panel studs. Since the geometrical relationship between panels and studs is not precisely reproduced from unit to unit, care must be taken to assure proper registration of the replica relative to the shadow mask-panel assembly.

Proper registration may be assured by precisely indexing the replica during both the camera and screen exposure steps relative to reference locations on the panel, which may be the studs themselves. The replica may, of course, be properly oriented relative to the panel by any number of well-known techniques, including optical ones.

What has been described are novel processes for photodepositing screens in shadow mask type color picture tubes wherein the phosphor deposits are made smaller than the mask apertures without resort to mask hole enlargement techniques. It is recognized that numerous modifications may be made in the disclosed preferred embodiments of the invention without departing from the true scope thereof.

I claim:

I. The method of manufacturing a color picture tube of the type having a predetermined pattern of elemental color phosphors deposited on the inner surface of a faceplate and an aperture mask of given transmission spaced from said panel for shadowing said elemental phosphors to all but predetermined electron beams, comprising the steps of:

making a photographic replica of said aperture mask with apertures of reduced area such that the transmission of said replica is lower than that of the mask;

depositing a pattern of elemental phosphors on a faceplate by photoexposure through said replica such that said elemental phosphors are of smaller size than the projected size of the apertures of said mask; and

assembling said mask to said faceplate in registry with said pattern of elemental phosphors.

2. The method of claim 1 further comprising the steps of:

coating said mask with a temporary coating of reflective material prior to making said photographic replica, and

removing said coating from said mask prior to assembly of said mask to said faceplate.

3. The method of claim 1 further comprising the steps of:

providing a lens system for correcting anticipated radial misregister caused by differences in the trajectories between light rays used for exposure purposes and the electron beams in the picture tube; and

making said photographic replica of said mask through said lens system whereby said elemental phosphors are positioned at locations on said faceplate as though the radial correction of said lens system were incorporated.

4. The method of claim 1 further including the steps of:

providing a camera with its object lens positioned on the axis of said color tube and substantially at the apparent center of origin of said predetermined electron beams;

making said photographic replica of said aperture mask through said object lens;

providing a correction lens compensating for differences between the trajectories of light rays in a lighthouse and the electron rays in said picture tube; and

depositing said elemental phosphors photoexposure through said replica and said correction lens.

5. The method of claim 4 wherein a lighthouse is provided having a point source of light positioned near said origin and wherein said replica is interposed between said point source and said correction lens.

6. The method of claim 4 wherein a lighthouse is provided having a point source of light positioned near said origin and wherein said correction lens is interposed between said source and said replica.

7. The method of claim 4 further comprising the steps of: providing a lighthouse with an extended light 5 9. The method of claim 1 further comprising the steps of:

providing a camera with its object lens positioned on the axis of said color tube and at the center of origin of said predetermined electron beams; making said photographic replica of said aperature mask through said camera object lens; and providingan extended light source and a condenser lens for photodepositing said pattern of elemental color phosphors on said faceplate through said replica and a lens corresponding to said object lens. 10. The method of manufacturing a color picture tube of the type having a predetermined pattern of separated elemental color phosphors deposited on the 15 inner surface of a faceplate and an aperture mask of given transmission spaced from said panel for shadowing said elemental phosphors to all but predetermined electron beams, comprising the steps of:

forming a pattern of separated phosphor receiving areas on a faceplate by photoexposure through said replica such that said phosphor receiving areas are of smaller size than the projected size of the apertures of said mask;

depositing elemental color phosphors in said phosphor receiving areas; and

assembling said mask to said faceplate in registry with said pattern of elemental color phosphors.

11. The method of claim 10 further comprising the step of:

covering said pattern of phosphor receiving areas on said faceplate with an opaque material, leaving said separated phosphor receiving areas free of said opaque material. 12. The method of claim 10 wherein said elemental color phosphors are deposited in said receiving areas by photoexposure through said replica.

13. The method of claim 12 further comprising the steps of:

providing a lens system for correcting anticipated radial misregister caused by differences in the trajectories between light rays used for exposure purposes and the electron beams in the picture tube; and making said photographic replica of said mask through said lens system whereby said elemental phosphors are positioned at locations on said faceplate as though the radial correction of said lens system were incorporated. 14. The method of claim 12 further including the steps of:

providing a camera with its object lens positioned on the axis of said color tube and at the center of origin of said predetermined electron beams;

performing said forming and depositing steps through said replica and said correction lens.

15. The method of claim 14 wherein a lighthouse is provided having a point source of light positioned near 15 16 said origin and wherein said replica is interposed beand a supplemental lens corresponding to the obtween said point source and said connection lens. ject lens of said camera, the arrangement of ele- 16. The method of claim 14 wherein a lighthouse is ments in said lighthouse being as follows: provided having a point source of light positioned near said extended light source, said supplemental lens, said origin and wherein said correction lens is intersaid correction lens, said replica and said faceplate. posed between said source and said replica. 19. The method of claim 12 further comprising the 17. The method of claim 14 further comprising the steps of: steps of: providing a camera with its object lens positioned on providing a lighthouse with an extended light source the axis of said color tube and at the center of oriand a supplemental lens corresponding to the obgin of said predetermined electron beams; ject lens of said camera, the arrangement of elemaking said photographic replica through said object ments in said lighthouse being as follows: lens; and said extended light source, said supplemental lens, providing an extended light source and a condenser said replica, said correction lens and said faceplate. lens for performing said forming and depositing 18. The method of claim 14 further comprising the 15 steps through said replica and a lens corresponding steps of: to said object lens.

providing a lighthouse with an extended light source

Claims

1. The method of manufacturing a color picture tube of the type having a predetermined pattern of elemental color phosphors deposited on the inner surface of a faceplate and an aperture mask of given transmission spaced from said panel for shadowing said elemental phosphors to all but predetermined electron beams, comprising the steps of: making a photographic replica of said aperture mask with apertures of reduced area such that the transmission of said replica is lower than that of the mask; depositing a pattern of elemental phosphors on a faceplate by photoexposure through said replica such that said elemental phosphors are of smaller size than the projected size of the apertures of said mask; and assembling said mask to said faceplate in registry with said pattern of elemental phosphors.

2. The method of claim 1 further comprising the steps of: coating said mask with a temporary coating of reflective material prior to making said photographic replica, and removing said coating from said mask prior to assembly of said mask to said faceplate.

3. The method of claim 1 further comprising the steps of: providing a lens system for correcting anticipated radial misregister caused by differences in the trajectories between light rays used for exposure purposes and the electron beams in the picture tube; and making said photographic replica of said mask through said lens system whereby said elemental phosphors are positioned at locations on said faceplate as though the radial correction of said lens system were incorporated.

4. The method of claim 1 further including the steps of: providing a camera with its object lens positioned on the axis of said color tube and substantially at the apparent center of origin of said predetermined electron beams; making said photographic replica of said aperture mask through said object lens; providing a correction lens compensating for differences between the trajectories of light rays in a lighthouse and the electron rays in said picture tube; and depositing said elemental phosphors photoexposure through said replica and said correction lens.

7. The method of claim 4 further comprising the steps of: providing a lighthouse with an extended light source and a supplemental lens corresponding to the object lens of said camera, the arrangement of elements in said lighthouse being as follows: said extended light source, said supplemental lens, said replica, said correction lens and said faceplate.

8. The method of claim 4 further comprising the steps of: providing a lighthouse with an extended light source and a supplemental lens corresponding to the object lens of said camera, the arrangement of elements in said lighthouse being as follows: said extended light source, said supplemental lens, said correction lens, said replica and said faceplate.

9. The method of claim 1 further comprising the steps of: providing a camera with its object lens positioned on the axis of said color tube and at the center of origin of said predetermined electron beams; making said photographic replica of said aperature mask through said camera object lens; and providing an extended light source and a condenser lens for photodepositing said pattern of elemental color phosphors on said faceplate through said replica and a lens corresponding to said object lens.

10. The method of manufacturing a color picture tube of the type having a predetermined pattern of separated elemental color phosphors deposited on the inner surface of a faceplate and an aperture mask of given transmission spaced from said panel for shadowing said elemental phosphors to all but predetermined electron beams, comprising the steps of: making a photographic replica of said aperture mask with apertures of reduced area such that the transmission of said replica is lower than that of the mask; forming a pattern of separated phosphor receiving areas on a faceplate by photoexposure through said replica such that said phosphor receiving areas are of smaller size than the projected size of the apertures of said mask; depositing elemental color phosphors in said phosphor receiving areas; and assembling said mask to said faceplate in registry with said pattern of elemental color phosphors.

11. The method of claim 10 further comprising the step of: covering said pattern of phosphor receiving areas on said faceplate with an opaque material, leaving said separated phosphor receiving areas free of said opaque material.

12. The method of claim 10 wherein said elemental color phosphors are deposited in said receiving areas by photoexposure through said replica.

13. The method of clAim 12 further comprising the steps of: providing a lens system for correcting anticipated radial misregister caused by differences in the trajectories between light rays used for exposure purposes and the electron beams in the picture tube; and making said photographic replica of said mask through said lens system whereby said elemental phosphors are positioned at locations on said faceplate as though the radial correction of said lens system were incorporated.

14. The method of claim 12 further including the steps of: providing a camera with its object lens positioned on the axis of said color tube and at the center of origin of said predetermined electron beams; making said photographic replica of said aperture mask through said object lens; providing a correction lens compensating for differences between the trajectories of light rays in a lighthouse and the electron rays in said picture tube; and performing said forming and depositing steps through said replica and said correction lens.

15. The method of claim 14 wherein a lighthouse is provided having a point source of light positioned near said origin and wherein said replica is interposed between said point source and said connection lens.

16. The method of claim 14 wherein a lighthouse is provided having a point source of light positioned near said origin and wherein said correction lens is interposed between said source and said replica.

17. The method of claim 14 further comprising the steps of: providing a lighthouse with an extended light source and a supplemental lens corresponding to the object lens of said camera, the arrangement of elements in said lighthouse being as follows: said extended light source, said supplemental lens, said replica, said correction lens and said faceplate.

18. The method of claim 14 further comprising the steps of: providing a lighthouse with an extended light source and a supplemental lens corresponding to the object lens of said camera, the arrangement of elements in said lighthouse being as follows: said extended light source, said supplemental lens, said correction lens, said replica and said faceplate.

19. The method of claim 12 further comprising the steps of: providing a camera with its object lens positioned on the axis of said color tube and at the center of origin of said predetermined electron beams; making said photographic replica through said object lens; and providing an extended light source and a condenser lens for performing said forming and depositing steps through said replica and a lens corresponding to said object lens.