D. BENDA Jan. 5, 1971 METHOD FOR PROCESSING A CATHODE RAY TUBE HAVING IMPROVED LIFE Original Filed Nov. 1'7, 1966 0 F- MD R6 was SUM. M& P
M IM 1 T S H HS 3 5 w HM E U mm Vs E INVENTOR. DAV D BENDA ATTORNEY United States Patent 3,552,818 METHOD FOR PROCESSING A CATHODE RAY TUBE HAVING IMPROVED LIFE David Benda, Geneva, N.Y., assignor to Sylvania Electric Products Inc., a corporation of Delaware Original application Nov. 17, 1966, Ser. No. 595,104, now
Patent No. 3,432,712, dated Mar. 11, 1969. Divided and this application July 18, 1968, Ser. No. 745,812
Int. Cl. HOlj 9/38 US. Cl. 316-11 Claims ABSTRACT OF THE DISCLOSURE A method for processing an improved cathode ray tube employing an open metallic structure positioned relative to the screen, for example, a shadow mask color tube wherein the mask is a continuous selected gaseous giving mechanism during tube operation. During tube processing the mask sorbs a selected introduced gas such as hydrogen. Electron beam impingement of the mask during subsequent tube operation effects gradual release of the occluded selected gas from the mask to provide a replenishable partial pressure of hydrogen which in relation to the total tube pressure is consistent for the promotion of enhanced emission and extended tube life.
CROSS REFERENCE TO RELATED APPLICATION This application is a divisional application of SN. 595,104, filed Nov. 17, 1966 which issued as US. Pat. 3,432,712 on Mar. 11, 1969, and is assigned to the assignee of the present invention.
BACKGROUND OF THE INVENTION This invention relates to cathode ray tubes and more particularly to a cathode ray tube employing a substantially open metallic member spaced relative to the screen whereof the tube has improved life performance and a method for processing the tube to achieve the desired performance.
The useful operational life of electron tubes, of which cathode ray tubes are an example, is dependent largely upon the level of electron emission available for utilization in the device. In color cathode ray tubes, for example, one or more cathodic sources are incorporated in the electron gun structures oriented within the conventionally evacuated envelope to provide a continuous supply of electrons to effect tube operation. These electrons substantially released by heat from the barium compounds of the cathodes are formed or shaped into beams, focused, accelerated, and directed from the terminal end of the gun structure toward an electron responsive screen by appropriately associated gun elements. Means external of the tube are utilized to deflect the beams in a predetermined sweeping manner to provide discrete impingement of the beams on the screen thereby producing desired luminescent displays. Thus, the sustained generation of electrons of a predetermined level of supply is necessary to maintain prolonged tube operation of a desired degree.
In shadow mask cathode ray tubes of the type described, it is customary to position a getter structure adjacent the terminal end of the gun. This getter is formed to eifuse a gas-adsorbing material, such as barium, during a specific sequence in tube processing to dispose a thin film of gettering material substantially on the walls of the envelope and on the surface of the shadow mask facing thereto. While a thin film of gas-adsorbing barium material, having a substantially uniform thickness, is desired for optimum gas clean-up, the directional dispersion of the gettering material in the reduced atmosphere tends to 3,552,818 Patented Jan. 5, 1971 dispose a thicker and somewhat less efficient film on predominantly the central surface area of the mask.
While degassing of the tube components is practical before and during tube processing, additional occluded gases are released during tube operation from the various elemental tube structure and envelope into the substantially evacuated interior. These gases, as for example, N 0 H C0, C0 and H 0 are for the most part effectively adsorbed by the getter film, but as tube life progresses getter clean-up etficiency decreases, and some of the heavier gaseous hydrocarbons, such as acetylene (C H are sometimes evidenced. These hydrocarbon ions, being attracted by the cathode, deleteriously bombard and impair the emissive surface thereof. As the supply level of electron generation decreases as a result of cathode deterioration, a change is evidenced in the tube operating characteristics. When these characteristics drop below a certain prescribed parameter, tube life is said to be affected.
It is known that the electron emission of electron tubes may be benefited by the introduction thereinto of specific pressure of selected gases such as, for example, nitrogen or hydrogen, but there has been no readily feasible means for maintaining an optimum emission-promoting partial pressure of the desired gas within the operating tube.
OBJECTS AND SUMMARY OF THE INVENTION It is an object of this invention to reduce the aforementioned disadvantages and to produce an improved cathode ray tube that, when processed, has a continuous selected gaseous giving mechanism during tube operation to enhance electron emission and promote extended tube performance.
A further object is to produce a color cathode ray tube that has improved gas adsorbing capabilities.
An additional object is to provide a method for processing a color cathode ray tube to effect means for maintaining therein an electron emission-promoting-partial pressure of a selected gas during tube operation to extend the life thereof.
The foregoing objects are achieved in one aspect of the invention by the provision of a method for processing a cathode ray tube for example a color tube employing an open metallic member, such as a shadow mask, wherein the tube is heated and substantially evacuated of occluded gases, the cathode materials converted to the electron emission state, the tube evacuation terminated, and a volume of a selected gas introduced into the substantially evacuated tube while the mask temperature is of a level to effect selected gas sorption therein. The selected gas, being chemically compatible with the screen and electron emission materials, is appreciably sorbed by the conditioned mask and released in a gradual manner therefrom by electron bombardment of the mask in said subsequent 1y operating tube. Thus, there is provided therein a replenishable partial pressure of the selected gas in relation to a total tube pressure to promote enhanced electron emission and extended tube life. Subsequent to the initial introduction of the selected gas, a layer of gas sorbing getter material is diffused over the mask surface proximal to the electron gun; this getter material having a low sorption sensitivity for the selected gas.
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 connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS 3 FIG. 2 is a perspective view of one type of material effusing structure; and
FIG. 3 is a plan view showing one embodiment for introducting the selected atmosphere in the evacuated tube.
DESCRIPTION OF THE PREFERRED EMBODIMENT For simplicity and ease of understanding, while in no way limiting, the invention will be described with reference to a inch rectangular shadow mask color cathode ray tube having substantially 90 degree electron beam deflection as indicated by Lot in FIG. 1. The shadow mask is but one type of open metallic member. Other structures intended to be within the scope of the invention include grids, perimetric frames and other structures that are oriented relative to the screen and can be impinged by the scanning electron beam.
With further reference to the figures there is shown a shadow mask color cathode ray tube 11 of the type above noted having an envelope 13 integrally comprising a neck portion 15, a funnel portion 17, and a panel portion 19. A patterned cathodoluminescent screen 21 of selected electron responsive phosphors is formed on the inner surface of the panel portion 19. Adjacent to the screen and spaced therefrom is the foraminous shadow mask structure 23 which comprises the supporting frame 25 and the peripherally attached apertured mask 27. The mask frame is spacedly oriented within the panel by suitable support means 29.
In greater detail, the formed apertured mask portion 27 is of low carbon steel material, such as SAE 1010 formulation or a similar material, of a thickness in the order of .006 inch. The supporting frame portion 25 is of similar low carbon steel material having a nominal thickness of .093 inch. The holes 26 in the apertured portion which are associated with the screen pattern therebeneath are substantially circular in shape and range in diametrical size from about .0110 inch at the center to about .0098 inch at the edge. While the apertured mask portion compirses a multitudinous number of these holes, the transmission of the mask is in the order of about 16 percent at the center diminishing to about 11 percent at the edge. Thus, the solid web of mask material 28 comprises about 84 to 89 percent of the mask area.
Extending from the mask frame is electrical connective means 31 which makes contact with the Aquadag coating 33 disposed on the interior surface of the funnel 17 and extending partially into the neck portion 15.
Disposed within the neck of the tube is the electron gun mount structure 35- which for clarity is only partially detailed and illustrates only one electron source or cathode 37. The beam covergence means 39 terminally oriented on the mount has reilient support and connective means 41 making pressured electrical contact with the Aquadag coating extending into the neck portion. Spaced from and supported relative thereto by a positioner 42 extending from the covergence means is one type of a material effusing structure 43 which will be detailed later in this specification. The mount structure 35 is further positionally supported on electrically conductive pins (of which only four are shown) 45, 46, 47, and 48 which are hermetically sealed in the stem wafer closure portion 51 to extend interiorly and exteriorly therefrom.
An exhaust tubulation 53 is connected through appropriate valving 55 to a conventional vacuum or gas evacuation system. In the tubulation there is noted, by dotted lines, the region of hermetic tubulation seal 57 which is consummated by heat prior to removal of the tube from the valve.
In processing, the tube 11 is oriented in a manner to expedite connection of the exhaust tubulation 53 with the evacuation system. External heat is applied to the tube, by means not shown, to substantially degas the envelope 13, the screen 21, the shadow mask structure 23, the Aquadag coating 33, and the gun mount structure 35 of gases occluded therein. During this outgassing heating step the mask reaches a temperature in the order of 380 to 400 degrees centigrade. The internal ambient and released occluded gases within the tube are evacuated through the externally connceted vacuum system by extended pumping during the heating sequences. It is conventional to supply extra heat to the electron gun mount structure 35, especially to the lower portion thereof, by induction heating means substantially localized relative to the neck portion of the tube.
Additional heat is applied to the cathode 37 during at least part of the latter sequences of the evacuation period and during at least a portion of the latter part of the tube heating period to chemically convert the emission materials 38 to an electron emitting state. For example, the major constituent of the emission materials combination, barium carbonate (BaCO is converted during tube processing to barium which is the functional electron emitter during subsequent tube operation, the emissive action of which may be augmented by including strontium and calcium in the emissive coating. The aforementioned additional cathode heat is supplied thereto by electrically activating the cathode heater 40 which is insulatively positioned within the nickel alloy cathode sleeve 37. This heater activation is accomplished by connecting heater pins 46 and 47 to an appropriate electrical supply source, not shown.
When degassing and evacuation have reached predetermined levels, the externally connceted evacuation period is teminated in accordance with the way the selected gas is to be introduced into the tube. If the selected gas 56 is supplied by a subsequently activated giver oriented within the tube, the evacuation termination is consummated by etfecting a tip off heat seal 57 in the exhaust tubulation. Alternatively, if the selected gas is to be supplied from an external pressurized supply as shown in FIG. 3, the valve is replaced by a twoway valving device 55 which terminates the evacuation, and when desired, can be adjusted to allow a predtermined pressure of the selected gas to enter the substantially evacuated tube envelope, after which the valve is closed and the tubulation seal 57 effected.
At the termination of externally connected evacuation period, the temperature of the shadow mask is approximately 200 degrees centigrade. It has been found desirable to introduce the selected gas while the mask temperature is at least degrees centigrade and preferably while it is in the range between 100 and degrees centigrade. While the mask is cooling through the aforementioned temperature range, the expansive surface of the foraminous mask structure of degassed porous low carbon steel sorbs or getters a large amount of the selected gas. Naturally other internal components of the tube sorb a certain amount of the selected gas, but the amount is far less than that sorbed by the mask.
The term selected gas is herein used with reference to a gaseous composition, of one or more gases, that is chemically compatible with the phosphors of the screen and the converted electron emission materials of the cathode, and one that is not appreciably sorbed by the subsequently applied getter material, such gases for example may be hydrogen or nitrogen or an inclusive mixture. By way of example in this instance, hydrogen (H will be described as the selected gas of the desired type. It has been discovered that maintenance of a predetermined partial pressure range of H in the subsequently operating cathode ray tube enhances electron emission and improves overall tube life performance.
As previously mentioned, the selected gas can be introduced in several ways. By way of example, one type of material eifusing structure 43 will be described. This ringlike structure is of a metallic material such as nonmagnetic stainless-steel formed as an open trough or channel facing the mask and containing at least two types of efiusing materials 44. One of these is a hydrogen giver as for example a hydride of a metal such as zirconium or titanium, of an amount which when heated will release the desired volume of hydrogen; the other material is a gettering substance such as -BaAl from which barium is released upon heating. Although not shown, it is in keeping with the invention to utilize a separate H eifusing structure and a separate getter structure, if so desired.
When the mask is in the desired temperature range, the material etfusing structure 43 is heated by localized induction means, not shown. As the ring reaches the 500 to 600 degree centigrade temperature range, dissociation of the hydride materializes and H is released into the substantially evacuated interior of the tube. As previously mentioned, a large quantity of the released H is sorbed by the conditioned mask while the remainder constitutes a partial pressure within the tube. Another gas evidenced as a partial pressure at this stage of processing is argon (Ar). This inert gas, which is conventionally utilized as an ambient medium during the storage of etfusing structures and sorbed to a limited degree thereby, is released by heat to contribute to theinitial total tube pressure. During early tube life, this inert gas appears to be largely sorbed in a seemingly harmless manner by the tube components other than the Ba getter material. Increasing the ring temperature to approximately 1100 degrees centigrade volatilizes the Ba gettering material which is directively etfused into the partial pressures of hydrogen and argon by the open channel shaping of the ring. The barium molecules in contacting and colliding with the predominantly hydrogen molecules, sorb a limited amount of the hydrogen and are beneficially deflected and diffused to form a layer of gas sorbing getter material of an efficient thickness over the surface of the mask proximal to the electron beam source. Some of the getter material is also diffused toward and deposited on the surface of the Aquadaged funnel portion. The presence of the additional partial pressure of H provides a more uniform distribution of gettering material than is possible in a tube having a low total pressure. After flashing of the getter, the tube is high voltage conditioned and further electrically processed in substantially the conventional manner.
If it is desired to introduce the H from a pressurized external source as aforementioned and shown in FIG. 3, the material effusing structure would be a conventional channelized getter, formed similar to the structure already described but containing only getter material. After the H is introduced and the tube seal 57 accomplished, the conventional getter ring is inductively heated whereupon the Ba material is advantageously flashed or diffused as previously described.
As an aid to further description, the cathode ray tube shown in FIG. 1 will be considered as a sealed and finished tube having a hydrogen atmosphere 56 therein and operating in a typical situation, the conditions of which are not shown. The electron beam 59 emanating from the electron gun is appropriately deflected through the Lot to sweep the screen, and in so doing, usually overscans the mask. Thus, the beam impinges substantially the whole of the gettered surface of the shadow mask structure 23. In a color cathode ray tube the electron guns operate at much higher cathode currents and anode voltages than do monochrome guns; the color gun conditions being in the order of 1 ma. cathode current and 25 kv. anode potential. The beam impingement on the aforedescribed expansive surface of the mask structure converts a large portion of the electrokinetic energy of the beam into heat. The impact of the beam appears to be at least two-fold, namely the high velocity electron impingement of the moving beam frees some of the loosely held sorbed H from the Ba getter layer, and the heat resultant from the sequential impacts promotes continued release of occluded H from the mask material proper. The mask temperature due to beam bombardment in a normally operating color tube will be substantially in the range of 55 to 60 degrees centigrade.
This is substantially an equalized temperature resulting from the conduction and dissipation of the electron-mask impact heat within the material web of the mask effected by the rapidly scanning electron beam; whereof the momentary temperature rise at the point of impact is appreciably above 60 degrees centigrade. Thus, it has been found that the mask, which is processed to be literally impregnated with H becomes a continuing H giver under operational electron bombardment and the heat resultant therefrom to provide a replenishable partial pressure of hydrogen at a rate to promote enhanced electron emission and extended tube life.
The efficient and substantially uniform thickness of the getter layer not only provides improved gettering but also promotes uniform heating of the mask by the beam which augments constancy of H release.
Since the low carbon steel mask and frame material exhibits a great affinity for hydrogen, a greater partial pressure of this selected gas is introduced into the tube during processing than is evidenced in the subsequently finished tube. The desired amount of hydrogen content has been determined by extensive experimentation and observation of total tube pressures and related partial pressures during tube life. Thus, by analytical observations of the desired results, desired initial gaseous content can be calculated.
Immediately following gettering, the total tube pressure is relatively high, and may be, for example, in the order of 10'- torr. At this stage, the major partial pressures contributing to the total include H Ar, C0, C0 and N During tube aging, stabilization, and testing a semblance of gaseous equilibrium becomes evidence within the tube. For example, at a very early period in life, such as during the one to two hour period, the total gas pressure may drop to the vicinity of 10- torr, the major portion of which is a partial pressure of H not lower than substantially one magnitude (9X10- below the total tube pressure. In other words, the partial pressure of hydrogen comprises substantially ninety percent of the total tube pressure. This relationship is substantially maintained during ensuing tube life; for example, at 1000 hour life the total tube pressure may be 1X10 torr whereof the H partial pressure would not be less than substantially 9 l0- torr. Likewise, at the 5000 hour level, the range between total tube pressure and the H partial pressure would not exceed substantially one magnitude. Too great a H pressure is not desired; for optimum benefits, it should be substantially less than the total tube pressure but not more than substantially one magnitude therebelow.
During tube operation, there are minor partial pressures of gases evolved, most of which are of insignificant pressure gradients or of a type successfully gettered in accordance with the capabilities of the respective gettering materials utilized.
The reasons for the beneficial effects of the major partial H pressure in the operating tube are not fully understood. In most conventional color cathode ray tubes, a minor partial H pressure, evidenced during early life, disappears or drops to an insignificant level as life progresses. The enhanced electron emission and extended tube life are results evidenced from the continued presence of a major partial H pressure as furnished by the replenisher within the tube. Hydrogen content of the pres sure values indicated appear to deter the formation of certain heavy hydrocarbons, such as ethane (C H and acetylene (C H which seem to be associated with slumping emission in conventional tubes. It is thought that the positive ions of these undesirable hydrocarbons deleteriously bombard the negatively charged emissive cathode coating. It is further thought that the presence of a major partial H pressure may effect a carbon combination in other than a gaseous form. Whatever the chemical and electrical mechanisms involved, marked life improvement is noted when a cathode ray tube is processed in a manner that the open metallic structure becomes a continuous selected gaseous giving mechanism during tube operation.
While there have 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 inven tion as defined by the appended claims.
I claim:
1. In the manufacture of a cathode ray tube employing within an envelope the elemental structure of a cathodoluminescent screen, a fora-minous metallic member spaced adjacent thereto and being of a porous material particularly conducive for gas sorption, and at least one source of electron beams employing a cathode having emission materials thereon, a processing procedure to effect, in the subsequently operating tube, a replenishing partial pressure of a selected gas by electron bombardment of said foraminous member, said process comprising the steps of:
heating said tube to substantially degas said envelope and said elemental structures of gases occluded therein;
substantially evacuating said tube of internal ambient and said released occluded gases through an eX- ternally connected system;
heating said cathode to chemically convert said emission materials to an electron emitting state, said cathode heating being effected during at least part of said evacuation period and at least during part of said tube heating period;
terminating said externally connected evacuation period of said tube;
introducing a predetermined volume of a selected gas into said substantially evacuated tube while the temperature of said foraminous metallic member adjacent said screen is decreasing but still at a level to effect appreciable gas sorption, said selected gas being chemically compatible with said screen and said con verted emission materials, said volume being suflicient to provide in said subsequently operating tube a replenishable high partial pressure of said selected gas in relation to a total tube pressure to promote enhanced electron emission and extended tube life; and
disposing a layer of active gas sorbing getter material of an eflicient thickness over the surface of said forarninous metallic member proximal to said electron beam source, said getter material having a low sorption sensitivity for said selected gas.
2. The cathode ray tube processing procedure according to claim 1 wherein said introduced selected gas is substantially hydrogen, and wherein said temperature of said foraminous metallic member is at least degrees centigrade when said gas is introduced.
3. The cathode ray tube processing procedure according to claim 1 wherein said selected gas is introduced in a volume to provide in said operating tube a high partial pressure not lower than substantially one magnitude below said total tube pressure.
4. The cathode ray tube processing procedure according to claim 1 wherein at the termination of said evacuation period said tube is sealed and said selected gas is subsequently introduced by the subsequent activation of a selective gas given priorly positioned within said envelope.
5. The cathode ray tube processing procedure according to claim 1 wherein said selected gas is introduced from an external pressurized supply after which the tube is sealed prior to deposition of said getter material.
References Cited UNITED STATES PATENTS 2,497,911 2/1950 Reilley et al 316-1 1X 2,884,777 7/1958 Szegho 313-178X 3,108,706 10/ 1963 Matsch et al. 2060.4X 3,167,678 1/1965 Griessel 2060.4X
H. A. KILBY, JR., Primary Examiner Patent 'No. 3 ,552 ,818
Inventor 5) Dated January 5, 1971 DAVID BENDA It is certified that error appears in the above-identified patent and that saidletters Patent are hereby corrected as shown below:
Column 3, line 53, of the specification, "covergence" should read--convergence--.
Column 3, line 54 "reilient" should read--resilient--.
Column 8, Claim 4, Line 25 "given" should read--giver--.
Signed and sealed this 6th day of April 1971 (SEAL) Attest:
WILLIAM E. SCHUYLER, JR.
EDWARD M.FLET0HER,JR
Commissioner of Patents Attesting Officer