US3658530A - Process for forming an opaque interstitial web in a color crt screen structure - Google Patents

Abstract

An improved process for forming an opaque interstitial web pattern for a color cathode ray tube screen structure on the interior of the viewing panel. A pattern of substantially clear polymerized PVA dots is formed on the subsequently occupied phosphor areas, and an opaque graphite coating applied thereover. A chemical agent is employed to degrade the dots and loosen the contiguous opaque coating thereon. Removal of these loosened materials provides an opaque interstitial web defining multitudinous bare glass window areas wherein the phosphor pattern elements are subsequently disposed. The improvement comprises using a hydrazo-reducing agent as the chemical agent.

Description

United States Patent Hedler et al. [451 Apr. 25, 1972 [54] PROCESS FOR FORMING AN OPAQUE INTERSTITIAL WEB IN A COLOR CRT Primary Examiner-Norman Tofchin Assistant Examiner.l. Winkelman SCREEN STRUCTURE Att0rneyNorman J. OMalley, Donald R. Castle and [72] Inventors: Robert A. Hedler; Jerry F. Janssen, both Frederick H- R m of Seneca Falls, NY. [57] ABSTRACT [73] Assigneez Sylvama Electric Products, Inc.

. An improved process for forming an opaque interstitial web [22] Filed: May 1970 pattern for a color cathode ray tube screen structure on the interior of the viewin anel. A pattern of substantially clear [2]] Appl' No" 41,536 polymerized PVA air? is formed on the subsequently occupied phosphor areas, and an opaque graphite coating applied [52] U.S. Cl. ..96/36.l, 117/335 CM the eo e A chem ca agent is employed to degrade the dots [51] Int. Cl ..G03c 5/00 and loosen the Contiguous p q Coating thereon Removal [58] Field of Search ..96/36.1,36.3; 117 335 CM of these loosened materials Provides an Opaque interstitial web defining multitudinous bare glass window areas wherein [56] References Cited the phosphor pattern elements are subsequently disposed. The Y improvement comprises using a hydrazo-reducing agent as the UNITED STATES PATENTS chemical agent- 3,558,310 l/l97l Mayaud ..96/36.l 5 Claims, N0 Drawings PROCESS FOR FORMING AN OPAQUE INTERSTITIAL WEB IN A COLOR CRT SCREEN STRUCTURE CROSS-REFERENCES TO RELATED APPLICATIONS This application contains matter disclosed but not claimed in two related US. Pat. applications filed concurrently herewith and assigned to the assignee of the present invention. These related applications are Ser. No. 41,530, and Ser. No. 41,5 35.

, BACKGROUND OF THE INVENTION This invention'relates to the manufacturing of cathode ray tubes and more particularly to a process for forming a portion of a color screen structure.

Cathode ray tubes capable of presenting multi-color display imagery, such as those employed in color television applications, conventionally utilize patterned screens comprised of repetitive groups of related phosphor materials. These groupings are normally disposed as bars, stripes or dots depending upon the type of color tube structure considered; For example, in the well-known shadow mask tube construction, the screen pattern is conventionally composed of a vast multitude of dots formed of selected cathodoluminescent phosphors, which, upon predetermined excitation, produce additive primary hues to provide the desired color imagery. The individual dots comprising the screen pattern are often in substantially tangential contact with one another, while in other instances they are separated by relatively small interstitial spacings provided to enhance color purity by reducing the possibility of electron excitation of adjacent dots. Associated with the screen and spaced therefrom is a foraminous structure or shadow mask. Each of the apertures therein is related to a specific grouping of dots of the screen pattern in a spaced manner to enable the selected electron beams traversing the apertures to impinge the proper dots therebeneath.

Toimprove brightness and contrast of the color screen image, a screen structure has been developed wherein a dotdefining interstitial spacing is effected between the dots in the form of an opaque lightabsorbing material. In essence, each phosphor dot is encircled or defined by a substantially dark encompassment which collectively comprise a foraminous pattern in the form of a windowed webbing having an array of substantially opaque connected interstices.- Such web-like structures have been fabricated, either before or after screening, by several processes wherein photo-deposition techniques play a prominent role. Some of the methods achieve a weblike opaque interstitial pattern by including convertible pigments in a photosensitized liquid applied to the viewing or face panel of the tube. By a subsequent heating step, these pigment materials are converted or darkened to produce the desired opaque quality. From a production consideration, the multiplicity of required steps are normally time consuming in view of various degrees of complexity. Additionally, in certain instances the cost of the materials and the necessary steps involved make the processes expensive in consideration of the results obtained. Furthermore, another deterrent is sometimes evidenced in those procedures wherein the opaque webbing is disposed subsequent to screen pattern formation, wherein there is the possibility of extraneous opaque material contaminating the respective phosphor dots of the screen.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to reduce the aforementioned disadvantages and to provide an improved process for expeditiously forming an opaque interstitial webbing for a color cathode ray tube screen structure. Another object is to produce an interstitial web-forming process comprising a minimal number of steps and one that is easily adaptable to production techniques. A further object is to provide a webforming process wherein there is minimum opportunity for contamination of the phosphor screen.

The foregoing objects are achieved in one aspect of the invention by a process wherein the interior surface of the panel is coated with a thin uniform layer of a polyvinyl alcohol solution photosensitized with a dichromate material. The coated panel is then exposed by beaming light through the multiple openings of the pattern mask to polymerize the pattern therein. Next, the exposed panel is developed to remove the unpolymerized areas thereby providing polymerized screen format pattern surrounded by a web pattern of substantially bare glass. Following this, the panel is overcoated with an opaque colloidal suspension of graphite, and then treated chemically to effect an effervescence to degrade the screen format pattern. An improvement in the process has been the employment of a hydrazoreducing agent as a degrading material. The resultant degrading effervescent reaction also loosens the associated graphite contiguous thereover. The loosened materials are then removed by pressurized water development to produce an opaque interstitial web having multitudinous windows therein defining bare glass areas wherein the phosphor pattern is subsequently formed.

The terms degrade" and degradation as used in this specification are intended to denote substantially physical decomposition of the polymerized material.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following specification and appended claims.

In preparation of the web-forming process, the viewing or face panel portion of the cathode ray tube is cleaned in a normal manner by washing particularly the interior of the panel with a 5-l0 percent aqueous solution of hydrofluoric acid, whereupon it is water rinsed. The panel is then precoated, for example, with a 0.3 percent aqueous solution of polyvinyl al coho] and dried in a conventional manner thereby providing a surface consistency to promote uniformity of wetting when the process forforming the web is initiated.

In one embodiment of the process for forming the windowed web on the color tube viewing panel, the interior surface of the panel is coated with a thin uniform layer of a substantially clear polyvinyl alcohol (PUA) solution photosensitized with a chromate material, such as potassium or ammonium bi or dichromate. The dissolved PVA solids are carried in a water-primary alcohol dilutent, such as ethyl and/or methyl alcohol; and the amount of photosensitizing material contained therein is preferably greater than the amount normally utilized in screen formation. Such increase has been found to be beneficial for the subsequent removal of polymerized PVA as will be described. Normally the amount of chromate material employed in phosphor screen formation is in the order of 0.15 weight percent. In the instance of this invention, the chromate solids therein are within the range of substantially 0.2 to 0.4 weight percent. The sensitized coating material is formulated to provide a thin covering function and exhibits an area density less than that of the conventional application of such material for promoting phosphor adherence. The PVA solution comprises PVA solids ranging from substantially 1.2 to 2.4 weight percent, the water ranges from substantially 43.0 to 64.0 weight percent, and the primary alcohol ranges from substantially 33.0 to 54.0 weight percent. The coating solution as applied, has a viscosity ranging from substantially 3.0 to 5.0 centipoises. The PVA solids are, for example, a blend of low and medium viscosity partially hydrolized (-90 percent) materials such as Vinol 205-K and 523 as available from Airco Chemicals and Plastics Div., Air Reduction Co., Inc., New York, NY.

After deposition of the uniform coating, a multiple-opening pattern mask, such as a foraminous shadow mask, is positioned within the panel. The coated panel is then exposed by beaming light through the multiple openings of the mask to light-polymerize discrete portions of the photosensitive panel coating in the areas subsequently occupied by the screen pattern phosphor elements.

The mask is removed from the panel and the exposed coating is developed by rinsing with water to remove the unexposed PVA, thereby providing a web pattern of substantially bare glass defining the interstitial spacings between the substantially clear polymerized pattern elements.

The patterned panel is then overcoated with a uniform layer of a substantially opaque colloidal suspension of graphite. An exemplary suspension is comprised of substantially 15 weight percent of a 22 percent homogeneous graphite dispersion in water, such as Aquadag formulated by Acheson Colloids Company, Port Huron, Mich.; to which is added substantially 40 weight percent of water; and substantially 45 weight percent of a water miscible alcohol, such as methyl alcohol.

After drying, the overcoated panel is treated at substantially room temperature, i.e., about 72-78 degrees Fahrenheit with a compatible water-soluble reducing agent to effect an effervescence to degrade the screen pattern element areas of lightpolymerized material and loosen the associated graphite contiguous thereon. The degraded materials and loosened graphite film are removed by pressurized water thereby providing an opaque interstitial web having multitudinous windows now defining bare glass areas wherein cathodoluminescent phosphors are subsequently disposed to form the screen pattern elements.

In greater detail, in one embodiment of the process for forming the windowed web on the clean interior surface of the open panel, the panel is oriented in an inverted position with the opening facing downward.

The interior of the inverted panel is coated with a uniform layer of a substantially clear PVA aqueous-alcohol solution photosensitized with a dichromate material. This PVA solution is upwardly applied in a streamlike manner free of aeration to provide a uniform bubble-free application. For example, the PVA comprises about 1.5 weight percent of PVA solids, approximately 45.0 weight percent of water, about 53.0 weight percent of methyl alcohol, and about 0.3 weight percent of ammonium dichromate solids. The coated panel is drained and dried to provide a consistent layer of substantially clear sensitized PVA on the screen area thereof.

A pattern or foraminous shadow mask is positioned within the panel in spaced adjacency to the sensitized coating. The mask-panel assembly is thence positioned in a lighthouse and optically exposed by discretely beaming light, having actinic characteristics, through the mask openings to light-polymerize specific portions of the photosensitive coating in those areas subsequently to be covered by screen pattern phosphor elements. Normally, the panel is sequentially exposed three times, the light source for each exposure being oriented to substantially correspond to a subsequent electron gun location utilized to excite the respective color pattern in the finished tube.

After exposure, the shadow mask is removed and the exposed panel coating is developed with water to remove the unexposed and unpolymerized areas of PVA to provide a plurality of repetitive pattern elements formed of substantially clear polymerized polyvinyl alcohol separated by an interstitial webbing of substantially clear glass.

The developed panel is again oriented in an inverted position with the opening thereof facing in a downward direction; whereupon the interior is overcoated with a substantially opaque suspension of colloidal graphite of the type previously mentioned. This opaque overcoating is applied in an upwardly directed stream-like manner free of aeration to provide a uniform bubble-free application. The temperature application is substantially within the range of 72 to 78 degrees Fahrenheit.

Excess overcoating is allowed to drain from 2 to 5 minutes to provide a uniform opaque coating. The overcoating is removed from the skirt and seal areas, as by wiping, and the overcoated panel is then dried. To hasten the process and form the opaque film, infrared heaters are usually employed, whereupon a drying temperature in the range of substantially 100-120 degrees Fahrenheit is utilized.

After drying, the panel is re-oriented in an inverted position. The interior of the panel is treated in a manner free of aeration with an upwardly directed flow of degrading material in the form ofa reducing agent, as for example, an 8.0 to 12.0 weight percent aqueous solution of at least one composition selected from the group consisting of hydrazine hydrate, hydrazine hydrochloride, hydrazine dihydrochloride, phenyl hydrazine, methyl hydrazine, potassium hydrazodicarboxylate. and potassium azobiscarboxylate. This panel treatment is consummated in a normal ambient temperature substantially within the range of 72 to 78 degrees Fahrenheit. A first upcoating of the reducing agent is uniformly applied over the screen area to initiate the degradation and after a period of l to 3 minutes a second application is applied. The resulting reaction degrades the plurality of light-polymerized PVA pattern elements and loosens the associated graphite film contiguous thereon. It has been found that the aforementioned reducing agents perform as efficient degraders of the light-polymerized material.

While the mechanics of the degradation reaction are not fully understood, it appears to be directly related to the excess dichromate in the PVA wherein the physical properties of the polymerized material are apparently substantially altered by one or more of the selected reducers to effect the release of a noticeable gaseous effervescence. It is thought that this effervescence or rapid bubbling reaction tends to physically disrupt the chelate cross-linkages existent between the molecules in the polymerized PVA. This degrading reaction of the polymerization also loosens or destroys the bonding of the PVA with the surface of the glass panel. It has been found that the effervescent disgregation of the polymerized material beneficially fractures the contiguously associated overlying coating. Consequently, when the panel is subsequently treated or developed with a vigorous water rinse, the many discrete pattern areas of loosened degraded materials and the directly associated loosened graphite material thereover are simultaneously removed to produce a multitude of window areas. To fully utilize the effect of the effervescence of the reaction, it is important that the treated panel not be allowed to dry prior to water developing. Since the degradation does not affect the adjacent graphite material that is adheringly disposed directly on the glass of the panel, the many windows are welldefined by an opaque interstitial web of graphite.

After developing, the window patterned panel is dried, and a multiple phosphor cathodoluminescent screen is subsequently formed in the respective window areas by conventional screening techniques.

Thus, an expeditious and improved method is provided for forming a windowed web foundation pattern for a cathode ray tube screen structure, wherein the phosphor elements of the screen pattern are subsequently disposed. Since the opaque interstitial webbing, discretely defining the utilized areas of the respective phosphor elements, is formed prior to screening, there is little opportunity for phosphor contamination. The improved process involves a minimal number of steps and is readily adaptable to production techniques.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An improvement in the process for forming a windowed web having opaque forming on the clean interior surface of a cathode ray tube viewing panel prior to fabrication of the phosphor screen thereon, whereon said panel is coated with a layer of substantially clear polyvinyl alcohol sensitized with at least 0.2 weight percent of a dichromate material, discretely exposed to substantially actinic light beamed through the multiple openings of a pattern mask positioned adjacent thereto to selectively light-polymerize a substantially clear dot patterned array in said coating, developed to remove the unpolymerized coating surrounding said array, and overcoated with a layer of colloidal graphite, said process improvement comprising:

treating said overcoated panel with a hydrazo-reducing agent to degrade said polymerized pattern and loosen the associated graphite thereon; and rinsing said panel in a manner to remove materials resultant from said degrading treatment and said associated graphite to provide an opaque interstitial web on said panel having multitudinous windows thereon defining bare glass areas wherein cathodoluminescent phosphors are subsequently disposed to form said phosphor screen. v2. A process improvement for forming a windowed web according to claim 1 wherein said reducing agent is at least one composition selected from the group consisting of hydrazine hydrate, hydrazine hydrochloride, hydrazine dihydrochloride, phenyl hydrazine, methyl hydrazine, potassium hydrazodicarboxylate, and potassium azobiscarboxylate.

3. A process improvement according to claim 2 wherein said overcoated panel is treated with a 3 to 5 minute rinse of an 8 to 12 weight percent solution of at least one of said reducing agents to produce a degradation in the form of a gaseous effervescence in said polymerized dot patterned array.

4. A process improvement according to claim 2 wherein said coated panel is oriented in an inverted position and treated in a manner free of aeration with an upwardly directed flow of at least one of said reducing agents to provide a uniform application of said reducing material on said panel.

5. A process improvement according to claim 4 wherein said upward flow of said reducing agent is accomplished by a first upcoating uniformly applied over the screen area to initiate degradation whereupon after a period of from 1 to 3 minutes a second upcoating application is applied.

32 3 I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atentm 3,658,530 Dated April 25, 1972 lnventofls) Robert A. Hedler and Jerry F. I Janssen It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2, line 42 (PUA) should read (PVA) Col. 4, line 65 (Claim 1, line 2) delete "forming" and insert "interstices" Signed and sealed this 25th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims (4)

1. 2. A process improvement for forming a windowed web according to claim 1 wherein said reducing agent is at least one composition selected from the group consisting of hydrazine hydrate, hydrazine hydrochloride, hydrazine dihydrochloride, phenyl hydrazine, methyl hydrazine, potassium hydrazodicarboxylate, and potassium azobiscarboxylate.
2. 3. A process improvement according to claim 2 wherein said overcoated panel is treated with a 3 to 5 minute rinse of an 8 to 12 weight percent solution of at least one of said reducing agents to produce a degradation in the form of a gaseous effervescence in said polymerized dot patterned array.
3. 4. A process improvement according to claim 2 wherein said coated panel is oriented in an inverted position and treated in a manner free of aeration with an upwardly directed flow of at least one of said reducing agents to provide a uniform application of said reducing material on said panel.
4. 5. A process improvement according to claim 4 wherein said upward flow of said reducing agent is accomplished by a first upcoating uniformly applied over the screen area to initiate degradation whereupon after a period of from 1 to 3 minutes a second upcoating application is applied.