US3387975A - Method of making color screen of a cathode ray tube - Google Patents

Description

June 11, 1968 MICHIO TAMURA METHOD OF MAKING COLOR SCREEN OF A CATHODE RAY TUBE 2 Sheets-Sheet 1 Filed March 10, 1965 meTalback layer ImzsnT'ur M/chz'o 721772117'0.

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METHOD OF MAKING COLOR SCREEN OF A CATHODE RAY TUBE Filed March 10, 1965 June 11, 1968 MICHIO TAMURA 2 Sheets-Sheet :3

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United States Patent 3,387,975 METHGD OF MAKING COLOR SCREEN OF A CATHODE RAY TUBE Michio Tamara, Fujisawa-shi, Japan, assignor to Sony Corporation, Tokyo, Japan, a corporation of Japan Filed Mar. 10, 1965, Ser. No. 438,558 11 Claims. (Cl. 96-461) ABSTRACT OF THE DISCLOSURE Method of forming color phosphor patterns on the inner face of a cathode ray tube screen wherein preselected areas of the screen are coated with a phosphor slurry containing a radiation hardenable composition and an initially light transparent inhibitor, exposing the thus coated areas to radiation through the outer face of the screen to thereby harden said composilion and render said inhibitor opaque, and removing the excess unhardened slurry from the inner face of the tube.

The present invention relates to methods for producing color screens for cathode ray tubes used in color television reception, and is particularly applicable to the manufacture of striped screen surfaces of the type used in postdeflection-focusing type cathode ray tubes.

It is well known that cathode ray tubes used for color television reception must provide a series of phosphors on the inner face of the tube which are precisely registerd so that no distortion or color blurring will be produced as the result of electron bombardment. Many techniques have been suggested for the application of such color phosphor patterns on the inner faces of cathode ray tubes, but for the most part, these methods are very expensive, and are incapable of producing phosphor deposits of reasonable thickness on the inner face of the tube.

One of the objects of the present invention is to provide a method for coating the inner face of a cathode ray tube, particularly of the post-deflection-focusing type such as that known as a Chromatron type tube.

Another object of the invention is to provide a method for making improved cathode ray tubes which is simple, accurate, and economical in use, requires less fabrication, and enhances the registry between the color screen phosphor elements and the color control electrode structure.

Another object of the invention is to provide a method for making a registered color screen which avoids the distortion or color contamination produced as a result of electron bombardment on the phosphor elements.

Basically, the present invention involves a sequence of steps for forming color phosphor patterns in predetermined positions on the inner face of the cathode ray tube screen and involves coating the inner face with a layer of an electron or light sensitive material, exposing selected areas of the layer to electron beams of different scan factors or light beams of different intensities, the selected areas corresponding to the predetermined positions to be ultimately occupied by the phosphor patterns. Then, the areas which have been exposed to the highest intensity of bombardment or irradiation are removed from the face of the tube, after which the face is coated with a composition including a phosphor and a light transparent inhibitor capable of becoming opaque upon exposure to light of a predetermined frequency. The resulting coated screen is then exposed to the aforementioned light, and the excess phosphor coating from the areas of the face other than the coating appearing in the areas previously void is then removed. This sequence of operations is continued for each of the three colors involved in the screen, with the exception that the light inhibitor may be omitted in the final phosphor coating.

Other objects, features and advantages of this invention will become apparent from the following description of the attached drawings, in which:

FIGURE 1 is a cross-sectional view of a Chromatron type picture tube embodying the principles of the present invention;

FIGURE 2 is an enlarged cross-sectional View of the face of the tube showing the arrangement of color phosphors; and

FIGURES 3A to 3L are diagrammatic showings of the steps involved in the complete process of coating the inner face of the tube.

As shown in the drawings:

In FIGURE 1, there is shown a Chromatron type cathode ray picture tube 1 having an electron gun 2 positioned in a neck portion 1a of the cathode ray tube 1. Electron deflection means such as a coil 3 are also provided on the outer side of the conical or throat portion 1b of the cathode ray tube 1. Adjacent the face 1c of the cathode ray tube, there is provided a grid device 4 to which a color switching signal superimposed on a constant direct current voltage is supplied. An electron beam 5 emitted from the electron gun 2 and directed at the screen 10 is post-deflected and focused in accordance with the color switching signal applied to the grid 4. The electron beam impinges upon phosphor strips constituting a color screen 6 on the inner face of the screen. The individual strips, of course, give off a characteristic color when bombarded by electron beams of a sufficient intensity. In the normal type of color screen, the screen 6 is provided with a plurality of phosphor strips 'R which emit a red colored light, phosphor strips G which emit a green colored light, and phosphor strips B emitting a blue colored light. The phosphor strips are sequentially arranged in the order of red-green-blue-green-red-greenblue, etc., as best seen in FIGURE 2 of the drawings.

Referring now to FIGURE 3, in the first step of the process as seen in FIGURE 3A, the inner face of the screen 10 is first coated with an electron sensitive material coating layer 7 which becomes hard and opaque by exposure to electron beams. The photographic resist material known as Kodak Photographic Resist is particularly suitable for this use. This material is a photosensitive lacquer used in the photo-engraving arts. Then, as indicated in FIGURE 3B, the grid 4 is positioned adjacent the inner face of the screen 1c in the position which it will occupy in the finished tube. The screen 10 is then attached to the conical portion 1!), and the tube 1 is evacuated to the pressure which will be employed in actual operation of the television receiver. The switching grid device 4 has applied thereto a fixed DC. potential of the given magnitude and polarity sufficient to set up an electric field in the area of the grid wires which causes the beam of electrons to impinge the face panel at a location which is to be occupied ultimately by strips of one of the three colors, in the illustrated instance, the red phosphor strips. After this original orientation, an electron beam 5 is emitted from the electron gun 2 and a color switching signal corresponding to the red color is applied to the grid 4 to post-deflect the electron beam creating latent image areas 8R along the electron sensitive material coating 7. A second electron beam printing operation is then carried out by supplying a color switching signal corresponding to the blue color to the grid device 4 to post-deflect the electron beam, causing the production of latent image areas identified at 8B in FIGURE 3C. In providing these areas, the scan factor is considerably reduced from the value used in forming the initial latent image areas 8R. Scan factor is the product of the electron beam density and time of scan, and determines the degree of exposure and therefore is a direct function of the time necessary for developing the electron image.

For obtaining a difference in exposure between the two printings, the scan factor employed during the first electron beam printing is chosen to be about times that of the second printing.

After the initial printing to form the latent image areas 8R and 3B, the screen as well as the grid device 4 are disassembled from the conical portion 1b, and the grid device 4- is removed from proximity to the screen 1c. Then, the inner face of the screen 1c is subjected to a developing process which consists in applying a solvent such as trichloroethylene by spraying under pressure or the like, over the entire inner face of the screen 10 to wash away selectively those areas which have been exposed to the highest scan factor. In the example shown in the drawings, this results in a removal of the areas previously designated at 8R, leaving void areas 8R which are to form the red bands in the finished cathode ray tube. As illustrated in FIGURE 3D, this selective removal of the bands 8R leaves the latent image areas 8B which were exposed to a. smaller scan factor, and areas 8G which were substantially unexposed to the electron beam during either of the printings.

After this initial developing process, a phosphor slurry which is to form the red stripe R shown in FIGURE 2 is deposited over the entire inner face of the screen 10, as illustrated in FIGURE 3E at reference numeral 9R. This deposition may take place by means of conventional methods, such as rotary painting processes. The applied phosphor is a slurry consisting of a phosphor, a light transmitting inhibitor which is capable of becoming opaque upon exposure to light of a predetermined frequency, such as ultraviolet light, and a photo-sensitive lacquer. The lacquer used is one which is polymerized and hardened by ultraviolet radiation, and usually consists of a solution of polyvinyl alcohol in water, sensitized with a dichromate. Such compositions have a maximum sensitivity at a wave length of about 365 millimicrons.

The use of the light transparent inhibitor forms an important feature of the present invention, as it has been found that through the use of such compositions, better registry is achieved, and coating stripes of increased thickness can be built up on the inner face of the tube. Specific examples of light transparent inhibitors which can be used in the practice of the present invention are listed below:

Zinc chloride double salt of paradiazo diphenylamine Diphenylamine p,p' tetrazonium chloride Sodium 4,4 diazide stilbene 2,2 sulfonate SOaNa NaSO;

Bis-naphthoquinone 1,2 diazide-S-sulfonic ester of 2,2 diphenyl propane A typical example of a red phosphor slurry is given in the following table:

4 Table I Zinc chloride double salt of paradiazo diphenylamine g 2 Red phosphor (Zn (PO :'M g Polyvinyl alcohol (7% aqueous solu.) cc Water c 3O Ammonium dichromate (10% aq. solu.) cc 12 The next step consists in exposing the thus coated face to irradiation by ultraviolet light, the rays of which are designated at reference letter u" in FIGURE 3E. An exposure of several minutes is usually sufficient to convert the phosphor composition into an opaque coating. During this exposure to ultraviolet light, the portion of the phosphor slurry identified at reference numeral 9R in the void areas identified at 8R are the only portions to be exposed to the light, since the remaining portions of the inner face of the screen are masked by the strips 88 and 8G. Accordingly, only the red phosphor layer which has become deposited in the previously void areas, and identified at reference numeral SR", is photochemically hardened and rendered opaque.

At the conclusion of this portion of the process, the excess red phosphor layer which has not been exposed to ultraviolet radiation is washed off by rinsing with water, leaving the red phosphor stripes R in spaced relation along the face of the tube, as best seen in FIGURE 3F.

The next step consists of a second developing treatment by means of which the blue forming latent image areas 83 are removed. In this developing treatment, the areas 8B are selectively removed by treatment with a suitable solvent such as trichloroethylene, as for example, by means of spraying. In this case, the pressure of spraying the solvent solution is selected so as to be larger than that employed in the original development wherein the areas 8R were removed, but less than the presssure which would remove the non-exposed areas 8G remaining. The result of this development treatment is shown in FIG- URE 3G, wherein the void areas are designated at 8B.

Next, as illustrated in FIGURE 3H, the entire inner face of the screen 10 is given a coating with a blue containing phosphor. This phosphor coating identified at 9B could be composed of substantially the same material as the first named phosphor composition with the exception that the red phosphor is replaced by a blue phosphor such as a zinc-silver sulfide. As in the preceding sequence, the coated face is then subjected to the action of ultraviolet light, so that the portions of the blue phosphor appearing in the void areas 8B are photochemically hardened, while the excess blue phosphor coating 9B is masked. from the effects of the irradiation by the strips 86' and R. Then, the portions of the phosphor layer 9B which have not been exposed are washed away to leave the blue strips B separated from the previously applied red phosphor strips R by the strips 8G, as illustrated at FIGURE 31.

The next stages of the process involve removal of the remaining unexposed layers 86', and the application of the green phosphor coating on the inner face of the tube. First, the layer 86' is removed by spraying a solvent such as a trichloroethylene solution onto the face of the tube at a spraying pressure in excess of that used previously to remove the electron sensitive layer, but less than that which would tend to remove the fixed and registered color stripes R and B. Then, a phosphor slurry lacquer is coated on the inner face of the screen as illustrated at reference numeral 9G in FIGURE 3K. The screen is again subjected to irradiation by ultraviolet light from the front of the screen 10. Accordingly, the green phosphor layer G is photochemically hardened and fixed to the inner face of the screen 1C between the stripes R and B in alternating relation. The excess green phosphor layer 96 is then washed away with water, leaving the finished color screen 6 on the inner face of the tube as illustrated in FIGURE 3L.

In theapplication of the green phosphor slurry, it is 3 not necessary to provide a light transmitting inhibitor, as the green phosphors, such as a manganese-zinc silicate, may be incorporated alone with the polyvinyl alcohol-dichromate lacquer solution.

As a final step, the color screen thus obtained may be metallized with aluminum and the like, followed by baking to remove or disperse the opaque material which is photochemically formed by the irradiation of the light transparent inhibitor with ultraviolet irradiation.

In a modified form of the present invention, the inhibitor can be rendered opaque by chemical treatment rather than by irradiation with ultraviolet light. For example, the face of the tube can be coated with a slurry composi tion having the following ingredients:

Table II Diphenylamine p,p' tetrazonium chloride g 2 Phosphor g 90 Polyvinyl alcohol (7% aq. solu.) cc 100 Ammonium dichromate (10% aq. solu.) cc 12 Phenol g 2 Tributyl borate g 1 This coating can be hardened by treatment with an aqueous solution of ammonium hydroxide.

The process of the present invention provides for the sequential deposition of the three color phosphor strips in a regular arrangement, utilizing the previously coated phosphor strips as optical masks. This substantially facilitates the application of the phosphor strips. Furthermore, there is no overlapping of the coating between the different colored phosphor strips so that there is no color distortion or color contamination resulting.

One of the advantages of using the type of compositions employed by the present invention resides in the fact that it is possible to produce substantially thicker coatings than previously. In the past, the limit of thickness of the phosphor strips has been on the order of 20 microns, whereas with the process of this invention, it is possible to secure coating thicknesses up to 30 microns without difficulty.

While the invention has been specifically described in conjunction with a method for applying stripes of the phosphors on the face of the screen, it should be apparent that the method is equally applicable to make screens having other types of phosphor orientation, such as those employing dot patterns.

It should also be realized that the electron beam printing method disclosed herein can, in certain instances, be replaced by a light beam printing process.

It should also be evident that various modifications and variations may be effected without departing from the scope of the present invention.

I claim as my invention:

1. The method of forming color phosphor patterns in predetermined positions on the inner face of a cathode ray tube screen which comprises coating said inner face with a layer of an electron sensitive material, exposing selected areas of said layer to electron beams of different scan factors, said selected areas corresponding to the predetermined positions to be occupied by said phosphor patterns, removing the areas which have been exposed to the highest intensity of electron bombardment from said face, coating the inner face with a composition including a phosphor, a lacquer hardenable by light of a predetermined frequency and a light transparent inhibitor capable of becoming opaque upon exposure to said light, exposing said face through the glass face of said screen to said light to harden and render opaque, and removing the excess phosphor coating from the areas of said face other than the coatings appearing in the areas previously void.

2. The method of claim 1 in which said light of a predetermined frequency is ultraviolet light.

3. The method of claim 1 in which said inhibitor is the zinc chloride double salt of paradiazo diphenylamine.

4. The method of claim 1. in which said inhibitor is diphenylamine p,p tetrazonium chloride.

5. The method of claim 1 in which said inhibitor is sodium 4,4 diazide stilbene 2,2 sulfonate.

6. The method of claim 1 in which said inhibitor is th bis-naphthoquinone 1,2 diazide-S-sulfonic ester of 2,2 diphenyl propane.

7. The method of forming color phosphor bands of three colors in sequential relation on the inner face of a cathode ray tube screen which comprises coating said inner face with a layer of an electron sensitive material, exposing selected areas of said layer to electron beams of different scan factors, said selected areas corresponding to the predetermined positions on said face to be occupied by the three colored phosphor bands, the areas in which the first of said colors is to appear being subjected to scanning at a relatively high scan factor, the areas in which the second of said colors is to appear being subjected to scanning at a significantly smaller, intermediate scan factor, and the areas in which the third of said colors is to appear being substantially unscanned, removing the areas on said face which have been subjected to the highest scan factor, coating said inner face with a composition including a phosphor of said first color, an ultraviolet radiation hardenable lacquer, and a light transparent inhibitor capable of becoming opaque upon exposure to said ultraviolet radiation, irradiating the outer face of said screen with ultraviolet radiation to harden and render opaque, removing excess phosphor from said inner face while leaving said phosphor deposited in the void areas created by such removal, removing the areas on said face which have been subjected to said intermediate scan factor, coating said inner face with a composition including a phosphor of said second color, an ultraviolet radiation hardenable lacquer, and a light transparent inhibitor capable of becoming opaque upon exposure to said ultraviolet radiation, irradiating the outer face of said screen with ultraviolet radiation to harden and render opaque, removing excess phosphor from said inner face while leaving said second color phosphor deposited in the void areas previously created for deposition of said second color phosphor, removing the areas of coating on said face which were substantially unscanned, coating said inner face with a composition including a phosphor of the third color and a ultraviolet radiation hardenable lacquer, irradiating the outer face of said tube with said ultraviolet radiation to harden, and thereafter washing off excess third color phosphor from said face while leaving said third phosphor deposited in the void areas previously created for deposition of said third color phosphor.

8. The method of claim 7 in which said inhibitor is zinc chloride double salt of paradiazo diphenylamine.

9. The method of claim 7 in which said inhibitor is diphenylamine p,p tetrazonium chloride.

10. The method of claim 7 in which said inhibitor is sodium 4,4 diazide stilbene 2,2 sulfonate.

11. The method of claim 7 in which said inhibitor is the bis-naphthoquinone 1,2 diazides-S-sulfonic ester of 2,2 diphenyl propane.

References Cited UNITED STATES PATENTS 1,983,005 12/1934 Sakurai 9691 2,618,555 11/1952 Reichel 9691 X 2,848,328 8/1958 Hepher 9691 2,893,866 7/1959 Haefeli 96-91 X 3,046,118 7/1962 Schmidt 9691 X 3,067,349 12/1962 Kasperowicz et a1. 11733.5 X 3,114,065 12/1963 Kaplan 117-335 X RALPH S. KENDALL, Primary Examiner.

A. L. LEAVITT, Examiner.

R. L. BROWDY, Assistant Examiner.

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