US 3787937 A
In one step of the screening process, the shadow mask of a color tube is mounted from studs provided in the faceplate section. The faceplate is then introduced into an exposure chamber where it is supported at three points spaced along the sealing land near the locations of the support studs. This establishes the faceplate in a reference mode, free of twisting moments and elastic deformation. When the screening process is completed, the faceplate is superposed over the enlarged end of the funnel section of the tube envelope and supported therefrom at three spaced points similarly disposed along the sealing land of the funnel to engage the faceplate at the same spaced points of support effective in the exposure step. This re-establishes the faceplate in its reference mode. Frit sealing material is disposed between the sealing lands of the envelope sections and the assembly is heated to seal the faceplate and funnel to one another along the entirety of the sealing lands.
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Description (OCR text may contain errors)
United States Patent 1 Palac 1 Jan. 29, 1974 METHOD OF PROCESSING A COLOR CATHODE-RAY TUBE  Inventor: Kazimir Palac, Carpentersville, Ill.
 Assignee: Zenith Radio Corporation, Chicago,
22 Filed: Feb. 7, 1973 21 Appl.No.:330,374
Related US. Application Data  Division of Ser No. 138,073, April 28, 1971, Pat.
Primary ExaminerRoy Lake Assistant ExaminerJ. W. Davie Attorney, Agent, or Firm-Cornelius J. OConnor; John J. Pederson [5 7] ABSTRACT In one step of the screening process, the shadow mask of a color tube is mounted from studs provided in the faceplate section The faceplate is then introduced into an exposure chamber where itis supported at three points spaced along the sealing land near the 10- cations of the support studs. This establishes the faceplate in a reference mode, free of twisting moments and elastic deformation. When the screening process is completed, the faceplate is superposed over the enlarged end of the funnel section of the tube envelope and supported therefrom at three spaced points similarly disposed along the sealing land of the funnel to engage the faceplate at the same spaced points of support effective in the exposure step. This re-establishes the faceplate in its reference mode. Frit sealing mate rial is disposed between the sealing lands of the envelope sections and the assembly is heated to seal the faceplate and funnel to one another along the entirety of the sealing lands.
4 Claims, 6 Drawing Figures PAIENTED JAN 2 9 I974 SHEET 1 8F 2 METHOD OF PROCESSING A COLOR CATHODE-RAY TUBE RELATED APPLICATION This application is a division of application Ser. No. 183,073, filed Apr. 28, 1971, now US. Pat. No. 3,737,065 by the present applicant for AN ENVE- LOPE FOR, AND METHOD OF PROCESSING, A COLOR CATHODE-RAY TUBE, which is assigned to the same assignee as the present application.
BACKGROUND OF THE INVENTION Color cathode-ray or picture tubes come in a variety of sizes and shapes and are formed of a multisection envelope of which the faceplate and funnel are major components. The faceplate has a screen area and a circumscribing flange the free end of which serves as a sealing land. The edge at the large end of the funnel likewise constitutes a sealing land which matches the faceplate with respect to size and configuration. While tubes may be round or rectangular, the rectangular shape is currently the more popular.
The envelope is sectioned, as described, to facilitate the application of various phosphor materials to constitute an image screen. Here again, there is a choice as to structure but usually the screen is an interlaced pattern of green, blue and red phosphors. They may be arrayed in a repeating sequence of stripes or, more usually, they may be phosphor dots collectively defining a multiplicity of color triads regularly disposed throughout the screen area. 4
The screen is photographically printed in a process that is very well known. Basically, a photoresist material which becomes insoluble in water upon exposure to actinic energy, such as ultraviolet light, is prepared as a slurry having one phosphor material suspended therein. The faceplate is given a coating of the slurry and the color-section electrode or shadow mask is then installed in position within it. Thereafter, this subassembly is put into a lighthouse or exposure chamber where the slurry layer is exposed to light through the shadow mask. This creates a latent image of the pattern of that phosphor which is subsequently developed by removing the shadow mask and washing the panel with water. Repeating this general process three times, utilizing different phosphor slurries on each occasion and appropriately positioning the exposure light source, accomplishes photographic printing of all three phosphors materials on the screen after which the faceplate and funnel sections are united to one another.
Integrating these envelope sections is a well known technique employing a frit type of glass-sealing material. The frit is usually applied to the sealing land of the funnel with the funnel supported in a generally vertical position and the faceplate is then superposed thereover with the two sealing lands in registration with one another. The envelope assembly is then heat treated in an oven having an appropriate heat profile and time cycle to permit the frit to establish a vacuum type seal all along the sealing lands of the faceplate and funnel.
This entire process is well understood and is successfully practiced in the production of shadow mask color tubes on a mass production basis. Great care is exercised in the fabrication of the component parts and in the various processing steps to assure proper and precise beam landings in the finished tube. For example, the sealing lands of the faceplate and funnel are frequently precision ground in an effort to attain an optimum mating of these sections in the sealing process. And yet, beam landing errors are encountered.
If the tube in process is of the shadow mask variety with phosphor dot triads to be excited by a cluster of three electron guns, the three beams ideally are concentric with the phosphor dots on which they impinge. Deviation from this condition of registration is the conditioned referred to as a beam landing error. It has been suspected heretofore that the sealing edge of the faceplate pane] experiences viscoelastic deformation in the sealing cycle resulting in a shift or displacement of the mask relative to the panel and consequently producing beam landing errors. This conclusion was reached because it was observed that there was very little, if any, shift of the mask relative to the screen as the faceplate panel was introduced into the various exposure chambers required in processing the three phosphors but a shift did result when the panel was placed on the funnel and sealed.
Applicant has discovered that viscoelastic deformation is not the cause of the mask to panel shift and has further determined that the panel exhibits the property of elasticity to a sufficient extent that, even at ambient temperatures, the sealing land of the panel accommodates or conforms to the specifics of the sealing land of the funnel and for this reason is a principal source of beam landing error. The present invention obviates or minimizes this aspect of beam-spot misregistration.
Accordingly, it is an object of this invention to provide a new fabricating technique, for color picture tubes which reduces beam landing errors.
It is another object of the invention to provide a novel color tube envelope in the processing of which superior results are attained in respect of beam landing errors.
Another specific object of-the invention is to improve the processing of color picture tubes to reduce beam landing errors.
SUMMARY OF THE INVENTION An envelope for a color cathode-ray tube in accordance with the invention comprises a faceplate section having an image area and a circumscribing flange the free end surface of which constitutes a first sealing land of a given size and configuration. The funnel section of the envelope likewise has a free end surface, usually its large end, which constitutes a second sealing land corresponding in size and configuration to that of the faceplate. At least one of these envelope sections has a plurality of spaced supports projecting from and disposed along the sealing land thereof for achieving support of the faceplate at spaced points as distinguished from the linear or planar support of prior envelope structures.
The processing aspect of the invention includes the steps of photographically printing the screen with different phosphor materials, essentially as described above, in which process the faceplate, with the colorselection electrode or mask supported within it, is exposed while being supported at three spaced points along its sealing land, establishing the faceplate in a reference mode in which the panel is free of deformation and twisting moments. After the printing step, and with the funnel substantially vertically disposed with its sealing land uppermost, the faceplate is placed on the funnel with the two sealing lands facing and in registration with one another, with a frit-sealing material disposed between the sealing lands, and with the faceplate supported from the funnel through a plurality of spaced contacts disposed along the sealing lands to reestablish the faceplate in its aforesaid reference mode. This assembly is then subject to heat treatment to seal the faceplate and funnel to one another along the entirety of the sealing lands.
DESCRIPTION OF THE DRAWINGS FIG. 1 shows a portion of an exposure chamber and the faceplate section of a picture tube in process;
FIG. 2 is a plan view, partially broken away, of the faceplate in the exposure position;
' FIG. 3 is a sectional view taken along line 3-3 of FIG. 2;
FIGS. 4 and 5 represent steps in the sealing of the faceplate and funnel sections;
while FIG. 6 shows a novel form of funnel section.
DESCRIPTION OF THE PREFERRED EMBODIMENT supporting the shadow mask to facilitate its insertion and removal as required in various stages of manufacture, especially during screening. The free end 10d of the faceplate constitutes a sealing land of a given size and configuration; for the case under consideration it is rectangular in shape and may be 23 inches in diagonal dimension.
The color-selection electrode or shadow mask 11 has a multiplicity of apertures 11a uniformly distributed over a rectangular field and a frame 11b to which the apertured component is attached. Mounting springs 110 are secured at one end to the frame and have an aperture at the free end for engaging mounting studs 100 to psoition the mask within faceplate 10 with a desired spacing relative to screen 10a. Both three and four point suspension systems are known but, for the case illustrated, only three mounting springs are employed. One is located in the central part of the uppermost periphery of the mask and the other two are located symmetrically on the two sides of the mask with the apertured ends disposed below the central axis. This is a conventional structure which is easily inserted into and removed from faceplate 10. As described below, phosphor dots are photographically printed on screen area 10a through a process that is very well known and need not be described here in any detail. One necessary step is the exposure of the inner surface of screen 10a with actinic energy after that surface has received a coating of a phosphor bearing photosensitive resist. That step, which is of interest to the present discussion, takes place in an exposure chamber or lighthouse 12 which is indicated in FIGS. 1 and 3. It is a conventional structure including a source (not shown) of ultraviolet light, such as a mercury arc lamp, positioned to simulate the electron beam of the tube which is assigned to excite the particular phosphor ingredient of the slurry coating. The coated faceplate, with its shadow mask 11 in position, is supported at a plurality of spaced points disposed along its sealing land 10d rather than having a line contact along the entirety of the sealing surface. This is achieved by means of three pads 120 secured to a shelf 12b which has an aperture or cutaway area 12c of essentially the same size and configuration as screen 10a. The pads are located so that the faceplate, when properly installed inits exposure position, is supported at three points through the engagement of these pads with sealing surface 10d at essentially the location of mounting studs 10c as illustrated in FIG. 2. The supports establish the faceplate in a reference mode, that is to say, in a rest condition in which the faceplate experiences neither deformation nor twisting moments because the pads are positioned as described to exert equalized supporting forces at the three points of support. It is common practice to have vertically extending positioning posts 12d on table 12b to permit rapid and precise positioning of faceplare 10 on the exposure chamber.
The validity of this three point support of the faceplate in the exposure position has been established in that examination shows that the reference conditions exists when the faceplate is installed in any of the three exposure chambers generally used in screening where the prevailing practice is to assign one such chamber to the processing of one of the three color phosphors. In other words, it is found that the space relation of shadow mask 11 relative to screen is essentially the same in all three'exposure chambers which is the condition to be maintained if beam landing errors are to be avoided or at least minimized.
After all three color phosphors have been applied to the screen by the photographic resist process featuring exposure of the faceplate for each such phosphor, the screen is filmed and aluminized in a well known manner and is then ready to be sealed to the funnel section 13 of the envelope which, as indicated in FIG. 4, is held in a generally vertical position by means ofa sealing fixture '14 described and claimed in US. Pat. No. 3,329,422, issued July 4, 1967 in the name of Hajduk and assigned to the assignee of the present invention. The large and free edge 13a of the funnel constitutes a second sealing land which has the same size and configuration as land 10d of the faceplate in order that they may properly register with one another. The first step of the sealing operation is placing faceplate 10 on funnel l l with sealing lands 10d and 13a facing and in registration with one another, with a frit material 15 deposited between the lands, and with faceplate l0 supported from funnel 13 through a plurality of spaced contacts disposed along the sealing lands to re-establish faceplate 10 in its aforesaid reference mode. The necessary condition to be attained is reestablishing the faceplate in its reference mode and this condition may be satisfied in a variety of different ways. For example, high spots may be provided in the sealing land of either faceplate 10 or funnel l3; alternatively, particularly when processing a tube having an envelope of conventional construction, shims or othersupport elements may be positioned at the proper locations on sealing land 13a before the faceplate is placed on that land. FIG. 4 illustrates this approach in which shims 16 of very small area are placed on sealing land 13a to engage land d of the faceplate preferably at the same spaced points at which the faceplate was supported during exposure. An important consideration is that the envelope sections 10 and 13 are supported at spaced points chosen to establish the faceplate in its reference mode as distinguished from past practices wherein the sealing lands are in line or continuous contact with one another. The shims 16 may be ballpoints, small glass rod segments or any material which affords the necessary mechanical support of the faceplate and is compatible with the envelope sections and the sealing material applied to these component parts to effect a vacuum type seal between them. Usually, a frit-seal composition is applied to sealing land 13a and also to all surfaces of shim 16 after which faceplate 10 is placed upon the shims. The envelope is now ready for sealing and this is accomplished by subjecting the assembly to heat treatment in a lehr having the appropriate temperature profile and time cycle to seal the faceplate and funnel to one another along the entirety of the sealing lands. Of course, the material of which shims 16 are formed must retain its mechanical and physical integrity during the heat treatment or sealing process. For a 23 inch rectangular tube the shims may be formed of glass or ceramic having the same thermal expansion coefficient as the funnel glass. The shims should be electrical insulators and present a support area of approximately 0.0625 square inch and a height of approximately 0.015 inch. Satisfactory results have been obtained through the use of glass rod segments having a diameter of 0.015 inch and a length of 0.5 inch. Flat shims, having a support area of 0.25 X 0.25 inch and a thickness of 0.015 inch, are also suitable.
FIG. 6 represents a novel form of funnel 13 which has raised elemental areas 16a on its sealing land at places corresponding to the locations of shims 16 in FIG. 4. This is an approach in which the spaced supports are formed integrally with. the funnel and this may be achieved by molding orby grinding in fabricating the funnel.
Measurements have been made of color picture tubes fabricated in accordance with the present invention which verify the efficacy of the described process in reducing beam landing errors attributable to deformation of the faceplate in sealing. By supporting the faceplate at spaced points relative to the funnel, rather than having them in line contact, one is able to establish the faceplate in its reference mode and the desired spaced relation to mask 11 relative to screen 10a is preserved to a much higher degree of accuracy than with prior practices in which sealing lands of the faceplate and funnel engage in line contact. Because of the property of elasticity exhibited by the face panel, the line contact of these envelope sections permits the panel flange to accommodate to the funnel and in a great many instances result in an undesirable change in the mask to screen space relation, leading to beam landing errors. Practicing the present invention not only reduces the change in mask to screen spacing but is further attractive in that it makes unnecessary the expense of prior procedures in grinding the landing surfaces of the envelope sections.
While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.
I claim: 1. In the processing of a color cathoderay tube which has a color-selection electrode and a multisection envelope comprised of a faceplate and a funnel, said faceplate including a screen and a circumscribing flange having provisions for mechanically supporting said electrode and further having an edge portion constituting a first sealing land of a given size and configuration and said funnel having an edge portion constituting a second sealing land of said size and configuration, the steps which include:
photographically printing on said screen a pattern of different phosphor materials in the application of which said faceplate with said electrode positioned within it is exposed to actinic energy while supported at three spaced points disposed along said first sealing land to establish a reference mode in which said faceplate is free of twisting moments;
positioning said funnel substantially vertically with said second sealing land uppermost; placing said faceplate on said funnel with said sealing lands facing and in registration with one another, with a frit sealing material deposited between said lands, and with said faceplate supported from said funnel through a plurality of spaced contacts disposed along the surface of said sealing lands to reestablish said faceplate in said reference mode;
and subjecting the assembly to a heat treatment to seal said faceplate and said funnel to one another along the entirety of said sealing lands.
2. The processing of a color cathode-ray tube in accordance with claim 1 in which said faceplate is supported from saidfunnel at three spaced points disposed along said sealing lands and corresponding to said three spaced points supporting said faceplate during exposure in said printing step.
3. The process of a color cathode-ray tube in accordance with claim 2 in which three support elements are inserted between said facing sealing lands to support said faceplate from said funnel.
4. In the processing of a color cathode-ray tube which has a color-selection electrode and a multisection envelope comprised of a faceplate and a funnel, said faceplate including ascreen and an edge portion constituting a first sealing land of a given size and configuration and said funnel having an edge portion constituting a second sealing land of said size and configuration, the steps which include:
photographically printing on said screen a pattern of different phosphor materials in the application of which said faceplate with said electrode positioned adjacent it is exposed to actinic energy while supported at three spaced points disposed along said I first sealing land to establish a reference mode in which said faceplate is free of twisting moments; positioning said funnel substantially vertically with said second sealing land uppermost;
placing said faceplate on said funnel with said sealing lands facing and in registration with one another, with a frit sealing material deposited between said lands, and with said faceplate supported from said funnel through a plurality of spaced contacts disposed along the surface of said sealing lands to reestablish said faceplate in said reference mode; and subjecting the assembly to a heat treatment to seal said faceplate and said funnel to one another along the entirety of said sealing lands.