US3589791A

US3589791A - Processing of cathode-ray tubes

Info

Publication number: US3589791A
Application number: US856248A
Authority: US
Inventors: John A Kanellopoulos
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1969-09-02
Filing date: 1969-09-02
Publication date: 1971-06-29
Anticipated expiration: 1988-06-29
Also published as: CA919895A

Abstract

The envelope of a color picture tube has a faceplate section and a funnel section. While they are separated from one another, the faceplate is screened, aluminized and then baked at a high temperature. A frit material is coated on the meeting surfaces of the faceplate and funnel sections after which the envelope is subjected to another high temperature heat treatment to unite these envelope sections. The envelope is then transported, neck facing downwardly, to a gun sealing station, where it is to receive a gun assembly and a sponge, that has been saturated with water, is inserted into the mouth of the neck as the envelope leaves the frit sealing station. In its traverse to the gun sealing station, the envelope draws air in through the sponge, injecting water vapor into the envelope.

Description

3,221,197 11/1965ce pe1a;

United States Patent John A. K anellopoulos [72] inventor Chicago, Ill. [2]] Appl. No. 856,248 [22] Filed Sept. 2, 1 969 [45] Patented .June 29, 1971 [73] Assignee Zenith Radio Corporation Chicago, Ill.

13 Claims, 1 Drawing Fig.

[52] U.S.Cl. 3l6/24, I 29/251 1 [51] Int. Cl. 01] 9/38 [50] Field ofSearch 316/24, 17; 29/251 l, 25.19

[56] References Cited UNITED STATES PATENTS 2,868,533 1/1959 Pratt 16/24 316/24 3,311,439 3/1967 Pace 316/24 3,322,522 5/1967 Meiresonne 29 2511 3,485,931 12/1969 Williams 3l6/24 Primary Examiner-John F. Campbell ABSTRACT: The envelope of a color picture tube has a faceplate section and a funnel section. While they are separated from one another, the faceplate is screened, aluminized and then baked at a high temperature. A frit material is coated on the meeting surfaces of the faceplate and funnel sections after which the envelope is subjected to another high temperature heat treatment to unite these envelope sections. The envelope is then transported, neck facing downwardly, to a gun sealing station, where it is to receive a'gun assembly and a sponge, that has been saturated with water, is inserted into the mouth of the neck as the envelope leaves the frit sealing station, In its traverse to the gun sealing station, the envelope 7 draws air in through the sponge, injecting water vapor into the envelope.

PATENTEUJUNZQISH 3589.791

Inventor John A. Konellopoulos By At orney PROCESSINGOF CATHODE-RAY TUBES BACKGROUND OF THE INVENTION The present invention is addressed generally to the processing of cathode-ray tubes and concerns more particularly a modification in processing which leads to materially improved emission properties. While the invention has application to both monochrome and color cathode-ray tubes, for convenience, it will be described with respect to the latter.

The currently popular form of color cathode-ray tube is the so-called shadow mask variety featuring a multiplicity of phosphor dot triads disposed about the screen area of the faceplate section of the tube envelope. Each such triad comprises a dot of green, a dot of blue and a dot of red phosphor and a cluster of three electron guns is sealed in the neck se'ction of the envelope to issue electron beams for exciting the phosphor deposits. Color selection is achieved by a colorselection electrode, usually a mask formed of a sheet of suitable metal, such as steel, and having a pattern of apertures corresponding to the pattern of dot triads on the screen and juxtaposed in relation thereto with one aperture of the mask in alignment with an assigned phosphor triad. The geometry of the structure, augmented by a dynamic convergence system, permits the electron beam issuing from each of the tree guns to impact only an assigned one of the color phosphor deposits which leads to assigning a designation of green, blue and red to the guns of the cluster.

The envelope of such a tube has two principal parts, namely, the faceplate section which serves as the screen and the body or conically shaped funnel section. These parts are initially separate which is a convenience in screening the faceplate section. After the phosphor has been applied and a film layer has been deposited thereover as a suitable substrate, the screen is aluminized. This completes the screening process after which the faceplate is baked at a high temperature to remove the volatilizable ingredients, for example, the filming layer which served as a substrate for the aluminized layer established in the aluminizing step.

At this juncture, the faceplate section is ready to be united with the funnel which has previously been coated internally with conductive material such as a commercial form of graphite referred to as Aquadag. The uniting of these envelope sections is accomplished by depositing a layer of frit sealing material to the sealing land of the funnel after which the faceplate section is placed thereover. The envelope is now introduced into a frit sealing oven for further treatment at a high temperature in which the frit material bonds the envelope sections to one another. The completed envelope is now ready to receive the gun assembly which is usually inserted through the open end of the neck termination of the funnel and sealed thereto. These several processing steps are thoroughly well understood in the art and are representative of the conventional process through which a color picture tube is fabricated.

Sometimes this is referred to as a double-bake process for the reason that at least portions of the tube envelope are subjected to two heat treatments at a high temperature of the order of 400450 C. Experience with this process has met with both success and failure in that the emission characteristics of the tube do not always have the stability desired. Periods of acceptable emission properties are interrupted by other periods of unacceptable emission without any clear understanding of why either result is attained on a particular occasion. Obviously, emission problems are most serious and the present invention is directed to improving the aforedescribed fabricating process to achieve uniformly good or acceptable emission of cathode-ray tubes in general and color picture tubes in particular.

Accordingly, it is an object of the present invention to improve the processing of cathode-ray tubes.

It is a specific object of the invention to improve the fabricating process of cathode-ray tubes in general, and of SUMMARY OF THE INVENTION Generally, a cathode-ray tube has a phosphor screen and a gun assembly enclosed within an evacuated envelope. The processing of such a tube usually includes the steps of: (l applying phosphor, a filming layer and a superposed conductive backing layer to the screen of the tube; (2) heating the tube to a temperature greatly in excess of the vaporization temperature of water for a predetermined period of time to effect bakeout of the screen; (3) sealing the gun assembly in position within the envelope; and (4) evacuating the envelope. The present invention improves that process by injecting a predetermined amount of water into the envelope prior to the evacuating step. Preferably, the water is injected while the envelope is at a temperature sufficiently above the vaporization temperature of water to convert the injected water into water vapor.

In the fabrication of color cathode-ray tubes, there is an additional processing step of frit sealing the faceplate section to the funnel section after screening. This is a double bake process in which an appropriate temperature desired to practice the invention exists when the envelope comes out of the sealing lehr wherein the faceplate and funnel sections are bonded to one another. Water may be easily added to the envelope atmosphere by saturating a sponge with water and inserting it into the neck of the envelope so that air drawn into the envelope as it travels from the exit end of the sealing lehr to the gun sealing station draws water vapor along with it.

BRIEF DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing the single figure of which is a representation in cross section of a shadow mask type of color cathode-ray tube undergoing improved processing in accordance with the subject invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The color cathode-ray tube represented in the drawing will be assumed to be of the tricolor shadow mask variety. It has an envelope composed of two principal parts, a faceplate section 10 and a funnel or body section 11 of conical configuration. The specific configuration of the envelope, whether it be round or rectangular, is of no particular consequence to the invention although there is a distinct trend to rectangularshaped tubes. Whatever shape is adopted, it is apparent that the portions of envelope sections 10 and 11 that are to be sealed together must match, that is to say, they must be the same as to dimension and configuration.

The faceplate section may be likened to a flanged dish with a flange surrounding an image or screen area 10a. In processing the faceplate section, it is first made chemically clean and then receives a deposit 10b of phosphor material. For the type of tube under consideration the phosphor is applied in a series of three similar processes in each of which dot deposits of a particular color phosphor are applied to screen area 10a. This is usually accomplished by covering the area of the screen with a photosensitive resist which includes one of the three phosphors as an ingredient. The layer is exposed by actinic energy, such as ultraviolet light, through the colorselection electrode or shadow mask 13 with the light source positioned to simulate the electron gun of the tube that is assigned to energize the phosphor in process. The exposure forms latent images of the dots of the phosphor in process and washing of the resist layer with its solvent develops those images, leaving on the faceplate only islands or dots of the particular color phosphor. As stated, the three phosphors are aplied in this fashion, it being only necessary to adjust the position of the exposing light source on each occasion so that the three series of phosphor dots are interlaced on the screen area. They define, in this fashion, the well-known mosaic or dot triad-type of tricolor screen.

After the application of the phosphor, the screen receives a layer of a filming composition which provides a suitable substrate or base desired for aluminizing. When the filming has been completed, and it is easily applied through a spray or flotation process, the faceplate is deposited in an aluminizer where through the process of evaporation an electron permeable layer lic of aluminum is formed over the film layer and as a backing for the phosphor deposits. The purpose of the aluminum layer, of course, is to serve as a reflector for light emitted as the phosphor areas are excited and also, since it is conductive, to permit establishing the screen at a desired operating potential. The faceplate after it has been screened, filmed and aluminized, is introduced into a lehr or oven where it is baked for approximately 2% hours at a temperature which is very high compared to the vaporization temperature of water. The faceplate experiences-a temperature cycle as it traverses the layer, achieving a maximum temperature in the range of from 400450 C. and this bakes out volatilizablc ingredients of this portion of the tube including, in particular, the organic components of the screen and the film layer. The processing of the faceplate is now complete and it is ready for uniting with funnel section 1 l.

The funnel section is provided with an internal wall coating 11a of conductive material such as graphite in the commercially available form known as Aquadag. The conductive coating extends throughout the cone-shaped portion of funnel section 11 and even extends into the adjacent portion of a terminating neck section 12 of the envelope. A principal purpose of the conductive coating is to extend the high voltage from a terminal (not shown) provided in funnel section 11 to the final anode of the electron guns and the gun cluster to be installed in the tube. Each such gun will have conductive contacts extending from the anode electrodes into physical contact with conductive coating Ila, thereby completing a circuit connection from a high-voltage system to the anode electrodes of the guns. It is common practice to seal faceplate and funnel 11 through a frit-sealing process which involves introducing a layer of frit, having appropriate thermal characteristics, between the meeting lands of envelope sections 10 and 11 and then subjecting the envelope to a further or second heat treatment. lt is convenient to arrange the parts in the manner indicated in the drawing with the funnel section disposed vertically with its enlarged section uppermost. A layer of frit is applied to the uppermost surface of funnel 11 after which faceplate section 10 is superposed in precise alignment with the funnel so that these parts are temporarily united simply through their juxtaposition and the effect of gravity. This assembly is then introduced into a lehr or oven where there is a similar heat treatment at much the same high temperature and for about the same time period as previously described for the faceplate-screen bake, through which a frit bonds envelope sections 10 and 11 and effects a vacuumtight bond therebetween.

As the envelope emerges from the sealing oven, it is transported to a further work station where a gun assembly is inserted through the open end of neck 12 and sealed in position. The specifics of the gun assembly are, of course, determined by the nature of the tube in process. For the case under consideration, it is a cluster of three electron guns since the screen 100 is a tricolor triad arrangement. After the gun assembly has been sealed in position, the envelope is evacuated, the cathodes of the several guns are activated and other similar steps are taken in finishing the tube. As thus far described, the entire process is the conventional double-bake affair widely used heretofore in fabricating color tubes. Particular attention will now be directed to the improvement in that process contributed by the present invention. 7

In accordance with the invention, there is an added process step of injecting a predetermined quantity of water into the envelope of the tube prior to the evacuating step which has been found to greatly increase processing latitude in respect of cathode emission and to attain cathode emission characteristics that are at least equal, if not superior, to that of a single bake process. The water may be injected while the envelope is at a temperature above the vaporization temperature of water to convert the injected water into water vapor or immediately prior to a processing step wherein such temperature conditions are encountered. Preferably, for the double bake process that has been described water is injected after the second bake, or after frit sealing and prior to scaling of the gun assembly within neck 12. In practicing the invention, it is convenient to soak a sponge in de-ionized water and insert the sponge into the open end of neck 12. In the FIGURE, the sponge is designated 14 and it is chosen dimensionally to be self-retaining when it is inserted into neck 12 with the neck facing downwardly. At the same time, the sponge is selected of such porosity that ambient air is readily admitted into the envelope through the sponge, drawing water vapor along with it. More particularly, the tube is at a high temperature, perhaps l200 C., as it leaves the sealing oven and it tends to cool as it is transported from the frit sealing station to the gun-sealing work station simply because it travels through an ambient that may be 25 C. As it cools, it will, of course, take in air in a process similar to inhaling. With sponge 14 in place, the air is drawn through the sponge and water is taken in along with it as water vapor, otherwise it is vaporized because of the high temperature of the envelope.

The amount of water injected is subject to fairly wide latitude. in processing a 23 inch color tube, for example, acceptable results have been achieved by the addition of as little as 0.6 cc. and as much as 10 cc. of water. It appears that optimum results are obtained when the amount of water injected establishes a controlled atmosphere within the envelope having a dew point prior to gun seal within the range of-4 to +l0 F. Another manner of specifying theamount of water to be injected is to establish a controlled atmosphere having a water vapor content of at least about 900 parts per million (ppm) by volume within the envelope. A range of 900 to 2,000 ppm. by volume has been used successfully. This controlled atmosphere preferably is attained, at least for the processing of 23 inch rectangular tubes, with an inside centerface temperature of 45 C. maximum just prior to gun sealing. Experience indicates that if these conditions are satisfied the envelope will have inhaled approximately 16 liters of air through which the volume of injected water vapor will have reached an optimum value.

As indicated in the drawing, it is desirable that sponge 14 is inserted within neck 12 to such a depth that there is a distinct separation between the leading edge of the sponge and the adjacent edge of conductive coating 1 la. it is desirable that they be separated from one another by at least 1 inch measure along the axis of the tube.

The mechanism by which the injection of water improves the emission properties of the tube is not known. Usually, the presence of water vapor within the envelope during the processing of the tube is thought to be disadvantageous and it has heretofore, so far as applicant is aware, always been avoided. Injecting water in the above-described manner is found to give latitude with respect to processing the cathode and to improve its emission properties. It may be speculated that the double bake process removes some oxygen and/or hydrogen or hydroxide radicals and water the removal of which has been responsible for uncertain emission characteristics and perhaps the injected water vapor by replenishing desired constituents that have otherwise been eliminated is the reason for more stable emission properties. It may also be speculated that the water vapor reacts with graphite coating 11a, itis known that Aquadag is hygroscopic, and is converted to methane gas producing a more reducing bulb atmosphere. Spectrographic observation of a double bake tube processed in accordance with the invention shows no material difference in relation to a single bake tube that does not have water injection but does exhibit desirable emission properties. in other words the double bake tube with water injected as described, ends up after evacuation with presumably essentially the same water content as a single bake tube without the added step of water injection. Q

Of course, other methods of injecting water will suggest themselves but the one described is especially attractive since it is simple and most compatible with gun sealing. The sponge temperature cycle from an initial value of --30 C. to a peak of 420 C. where maximum outgassing occurs and then a lower value of 300 C. At this point the tube enters a radiofrequency field, generated by an external induction heater, for some 12.5 minutes which causes grids one and two of each electron gun in the gun cluster to react an elevated temperature of about 750 C. for outgassing these electrodes. At the same time cathode break down occurs. Thereafter, exhaust pumping continuesfor another 5 minutes and the temperature is reduced to' 240 C. A voltage isapplied to the heaters of the electron guns of the tube to convert'the cathode emitting material after which pumping is continued'for another l0l5 minutes and the .tube is then tipped off. This is a'conventional exhaust cycle and, per se, constitutes no part of the subject invention.

As the tube leaves the exhaust station it is checked for bulb pressure and cathode activity. Useof the present invention has been found to yield a markedly improved emission record. In plant yields have been increased materially and field returns have been reduced significantly. I

While a particular embodiment'of the invention has been shown and described, it will be obvious to-those. skilled in the art that changes and modifications may be made .therein without departing from the invention and 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.

1 claim:

1. In the processing of a cathode-ray tube, having a phosphor screen and a gun assembly enclosed within an evacuated envelope, which processing includes the steps of: (l) applying phosphor, a filming layer and a superposed conductive backing layer to said screen of said tube; (2) heating said'tube to a temperature exceeding the vaporization tem perature of water for a predetermined period of time to effect bakeout of said screen; (3) sealing said gun assembly in position within said envelope; and (4) evacuating said envelope, the improvement which comprises injecting a predetermined amount of waterinto said envelope subsequent to said step of applying phosphor butprior to said evacuating step.

2. The process improvement in accordance with claim I in which the water is injected while said envelope is at a temperature above the vaporization temperature of water to convert the injected water into water vapor or immediately prior to the heating of said envelope to such a temperature.

3. The process improvement in accordance with claim 2 in which the water is injected after said heating step and prior to said evacuating step. Y

- 4. The process improvement in accordance with claim 3 in which water is injected into said envelope prior to said gun assembly sealing step. Y

5. The process in accordance with claim 4, for processing a 'tube having a faceplate section including said screen and another section for accommodating said gun assembly and. to besealed to said faceplate section to form said envelope, in ,which water is injected at the completion of the step of sealing said envelope"sections together and asthe envelope is transported to the work station for gun assembly sealing.

6. The improvement in accordance with claim 5, for processing a tube having a reduced neck section into which said gun assembly is to be inserted, in which water is injected into said envelope by soaking a sponge in water and thereafter inserting said sponge into said neck section. I

7. The process improvement in accordance with claim 6 in which said sponge is dimensioned to be self-retaining within said neck and has sufficient porosity to admit ambient air into said envelope as said envelope is transported to said work station for gun assembly sealing.

8. The process improvement in accordance with'claim 7 in which said envelope is transported to said work station with its neck facing downwardly and with said, sponge in position within said neck. I

'9. The process improvement in accordance with claim 1 in which the amount of water injected 'into said envelope establishesa controlled atmosphere therein having a water vapor content of at least about 900 parts per million by volume. I

10.The process improvement inaccordance with claim 1 in which the amount of water injected into said envelope establishes a controlled atmosphere thereinhaving a dew point within the range of minus 4 and plus 10 F. g

11. In the processing of a cathode-ray tube, having a phosphor screen" and a gun-assembly enclosed within an evacuated envelope comprising a faceplate section sealed to a conically shaped body section, which processing includes the steps of: l) applying-phosphor, a filming layer and a superposed conductive backing layer to-said faceplate section to constitute the screen of said tube; (2) heating said tube to a temperature exceeding the vaporization temperature of water 1 for a predetermined period of time to effect bakeout of said screen; 3) applying a sealing frit between meeting surfaces of said faceplate and body sections and further heating said envelope at a temperature exceeding the vaporization temperature of water to unite said envelope sections to one another; (4) sealing said gun assembly in position within said envelope;

and (5) evacuating said envelope, the improvement which comprises injecting water into said envelope after said frit sealing step but prior to said gun assembly step and while said envelope is at a temperature above the vaporization temperature of water to convert the injected water into water vapor.

12. The improvement, in accordance with claim 11, for processing a cathode-ray tube in which said body section of said envelope tenninates in a reduced-diameter neck for accepting said gun assembly, in which said body section has an internal coating of conductive material extending partially into said neck and in which said water is injected by soaking a sponge in water and inserting said sponge into said neck to a depth that leaves a portion of said neck separating the leading edge of said sponge and the adjacent edge of said conductive coating. v

13. The process improvement in accordance with claim 9 in which the amount of water injected establishes 'a controlled atmosphere having a water vapor content within the range 900 to 2,000 parts per million by volume.

Claims

1. In the processing of a cathode-ray tube, having a phosphor screen and a gun assembly enclosed within an evacuated envelope, which processing includes the steps of: (1) applying phosphor, a filming layer and a superposed conductive backing layer to said screen of said tube; (2) heating said tube to a temperature exceeding the vaporization temperature of water for a predetermined period of time to effect bakeout of said screen; (3) sealing said gun assembly in position within said envelope; and (4) evacuating said envelope, the improvement which comprises injecting a predetermined amount of water into said envelope subsequent to said step of applying phosphor but prior to said evacuating step.

2. The process improvement in accordance with claim 1 in which the water is injected while said envelope is at a temperature above the vaporization temperature of water to convert the injected water into water vapor or immediately prior to the heating of said envelope to such a temperature.

3. The process improvement in accordance with claim 2 in which the water is injected after said heating step and prior to said evacuating step.

4. The process improvement in accordance with claim 3 in which water is injected into said envelope prior to said gun assembly sealing step.

5. The process in accordance with claim 4, for processing a tube having a faceplate section including said screen and another section for accommodating said gun assembly and to be sealed to said faceplate section to form said envelope, in which water is injected at the completion of the step of sealing said envelope sections together and as the envelope is transported to the work station for gun assembly sealing.

6. The improvement in accordance with claim 5, for processing a tube having a reduced neck section into which said gun assembly is to be inserted, in which water is injected into said envelope by soaking a sponge in water and thereafter inserting said sponge into said neck section.

8. The process improvement in accordance with claim 7 in which said envelope is transported to said work station with its neck facing downwardly and with said sponge in position within said neck.

9. The process improvement in accordance with claim 1 in which the amount of water injected into said envelope establishes a controlled atmosphere therein having a water vapor content of at least about 900 parts per million by volume.

10. The process improvement in accordance with claim 1 in which the amount of water injected into said envelope establishes a controlled atmosphere therein having a dew point within the range of minus 4* and plus 10* F.

11. In the proceSsing of a cathode-ray tube, having a phosphor screen and a gun assembly enclosed within an evacuated envelope comprising a faceplate section sealed to a conically shaped body section, which processing includes the steps of: (1) applying phosphor, a filming layer and a superposed conductive backing layer to said faceplate section to constitute the screen of said tube; (2) heating said tube to a temperature exceeding the vaporization temperature of water for a predetermined period of time to effect bakeout of said screen; (3) applying a sealing frit between meeting surfaces of said faceplate and body sections and further heating said envelope at a temperature exceeding the vaporization temperature of water to unite said envelope sections to one another; (4) sealing said gun assembly in position within said envelope; and (5) evacuating said envelope, the improvement which comprises injecting water into said envelope after said frit sealing step but prior to said gun assembly step and while said envelope is at a temperature above the vaporization temperature of water to convert the injected water into water vapor.

12. The improvement, in accordance with claim 11, for processing a cathode-ray tube in which said body section of said envelope terminates in a reduced-diameter neck for accepting said gun assembly, in which said body section has an internal coating of conductive material extending partially into said neck and in which said water is injected by soaking a sponge in water and inserting said sponge into said neck to a depth that leaves a portion of said neck separating the leading edge of said sponge and the adjacent edge of said conductive coating.

13. The process improvement in accordance with claim 9 in which the amount of water injected establishes a controlled atmosphere having a water vapor content within the range 900 to 2,000 parts per million by volume.