CA1304774C - Aging process for cathode ray tubes - Google Patents
Aging process for cathode ray tubesInfo
- Publication number
- CA1304774C CA1304774C CA000540074A CA540074A CA1304774C CA 1304774 C CA1304774 C CA 1304774C CA 000540074 A CA000540074 A CA 000540074A CA 540074 A CA540074 A CA 540074A CA 1304774 C CA1304774 C CA 1304774C
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- Prior art keywords
- grid
- volts
- cathode
- aging
- tube
- Prior art date
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/44—Factory adjustment of completed discharge tubes or lamps to comply with desired tolerances
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/44—Factory adjustment of completed discharge tubes or lamps to comply with desired tolerances
- H01J9/445—Aging of tubes or lamps, e.g. by "spot knocking"
Abstract
ABSTRACT:
Improved aging process for cathode ray tubes.
An improved aging process for a cathode ray tube in which the main focusing grid (G3) is aged at a potential below that of the G2 grid, resulting in significantly reduced incidence of dark center cathode.
In a typical example of the process the G3 grid is at a voltage of at least 100 volts, which voltage is at least 50 volts less than the G2 grid voltage.
Improved aging process for cathode ray tubes.
An improved aging process for a cathode ray tube in which the main focusing grid (G3) is aged at a potential below that of the G2 grid, resulting in significantly reduced incidence of dark center cathode.
In a typical example of the process the G3 grid is at a voltage of at least 100 volts, which voltage is at least 50 volts less than the G2 grid voltage.
Description
~3~4n4 PHA.60062 1 27-2-1987 Improved aging process for cathode ray tubes.
This invention relates to the aging of cathode ray tubes, and more particularly relates to an improved aging process in which dark center cathodes caused by the aging of the focusing electrode are substantially reduced.
S In the manufacture of cathode ray tubes for television and other display applications, various tube processing steps are carried out to ensure an acceptable life of reliable operation in the field. This processing begins after assembly of the tube components, and includes:
exhausting and baking the tube to evacuate the envelope and outgas the tube components; flashing a getter onto the internal surfaces of the tube and components to provide continuous gettering of residual contaminants which are outgassed during tube operation; activating the cathodes of the electron gun by heating to promote the formation of low work function species in the emission layer; aging the cathode and lower grid elements of the gun to maintain cathode activation; and finally high voltage conditioning of the electron gun to remove particles and projections 20 which could lead to interelectrode arcing.
The rate of outgassing is time and temperature dependent, and the throughput demands of the manufacturing process as well as the limited thermal stability of certain tube components make complete outgassing during exhausting and baking impractical. Thus, some residual gas and gas-producing contaminants, such as hydrocarbons, remain in the tube after sealing of the exhaust tubulation.
Getter flashing usually introduces additional hydrocarbon contaminants into the tube. These hydrocarbons 30 cannot be effectively adsorbed by the non-bakable barium getters commonly employed in many types of colour television picture tubes. However, during subsequent aging, these hydrocarbons are dissociated into getterable components, 1304'Y74 PHA.60062 2 27-2-1987 resulting in the reduction of residual gas in the tube to acceptable levels.
Unfortunately, the aging process has also been found to result in a condition known as "dark center cathode", which by analysis has been found to be due to a carbon deposit in the center of the emissive layer of the cathode.
Surprisingly, this deposit does not materially reduce cathode emission. However, it does restrict emisSion to the area of the perimeter of the emissive layer, resulting in a hollow beam which interferes with proper focusing and image resolution at the screen.
In U.S. Patent Specification 4,457,731, the dark center cathode problem is addressed for reprocessed cathode ray tubes. Tubes rejected for gun-related defects can be lS salvaged by "regunning", that is replacing the defective gun with a new one. Since this regunning operation necessa-rily reopens the envelope to the ambient, the tube must be reprocessed. This patent specification teaches that dark center cathodes can be substantially reduced by flashing the getter after aging, so-called "post-flashing". However, when post-flash~g is practiced on virgin tubes, unaccepata-bly high gas levels result.
An object of this invention is to reduce the incidence of dark center cathodes in a manner which does not result in unacceptably high gas levels.
Another object of this invention is to age a cathode ray tube after sealing and getter flashing without producing dark center cathodes, and simultaneously reduce residual gas to an acceptable level.
According to the present invention there is pro-vided a process for aging a cathode ray tube after the tube has been evacuated, sealed and getter flashed, and the cathode has been activated; the process comprising applying predetermined voltages to the cathode heaters and G1 grid of the tube's electron gun, so as to result in the emission of electrons from the cathodes, and then sequentially adding predetermined voltages to the G2 and G3 grid electrodes of the gun, respectively, the G2 and G3 grid voltages being PHA.60062 3 27-2-1987 larger than the cathode and G1 grid voltages characteri-zed in that the G3 grid voltage is smaller than the G2 grid voltage.
In accordance with the invention, it has been discovered that the successively higher voltages impressed on the G1, G2 and G3 grids during aging results in the focusing of the electrons emitted from the cathodes into an electron beam which dissociates residual hydrocarbons present in the tube after exhausting, baking and getter flashing, and that such dissociation results in the forma-tion of a beam of positive carbon ions which travel in the reverse direction from the electron beam and are deposited on the cathode.
It has further been discovered that reducing the lS potential of the G3 grid during aging to a critical level above a threshold needed for effective aging of this grid, but sufficiently below the potential of the G2 grid to create a potential barrier to prevent the positive beam from reaching the cathode, significantly reduces the inci-dence of dark center cathodes while substantially retainingthe benefits of G3 aging.
In an embodiment of the process in accordance with the present invention, the G3 grid electrode is at least 100 volts, and at least 50 volts less than the G2 grid electrode.
In another embodiment of the process in accordance with the present invention, the G2 and G3 grids are connect-ed to the same potential source, and the lower G3 grid potential is achieved by inserting a resistor between these two electrodes.
The present invention will now be explained and described, by way of example, with reference to the accompa-nying drawings, wherein:
Fig. 1 is a partial cross-section view of a sealed and getter flashed cathode ray tube to be aged in accordance with the process of the invention;
Fig. 2 is a partial cross-section of the neck portions of the cathode ray tube of Fig. 1, showing the 1304~74 PHA.60062 4 27-2-1987 cathode and grid elements of a bipotential electron gun to be aged in accordance with the process of the invention;
Fig. 3 is a view similar to that of Fig. 2, showing the elements of a quadripotential electron gwn to S be aged in accordance with the process of the invention;
Fig. 4 is a graph of time in minutes versus potential in volts for a typical cathode activating and tube aging schedule of the prior art;
Fig. 5 i9 an enlarged plan view of a dark center lG cathode resulting from the prior art aging schedule of Fig. 4;
Fig. 6 is a graph of time in minutes versus potential in volts for a typical cathode activating and tube aging schedule of the invention;
Fig. 7 is a schematic diagram of a prior art arrangement for achieving the schedule of Fig. 4; and Fig. 8 is a schematic diagram of an arrangement of the invention for achieving the schedule of Fig. 6.
With reference to the drawings, Fig. 1 is a sectiol~ed view showing the essential elements of a plural beam in-line colour cathode ray tube 11 aged in accordance with the process of the present invention. Cathode ray tube 11 is oriented to have a central longitudinal axis 14 and X and Y axes normal to axis 14. The encompassing tube envelope is a glass structure comprised of a hermetically sealed integration of neck 13, funnel 15 and viewing panel 17 portions. Dispo~ed on the interior surface of the viewing panel is a patterned cathodoluminescent screen 19 of stripes or dots of colour-emitting phosphor materials.
30 A multi-opening structure 21, in this instance an apertured mask, is positioned within the viewing panel in spaced relationship to the patterned screen 19. Encompassed within the neck portion 13 of the envelope is a unitized plural-beam in-line electron gun assembly 23, from which emanate three electron beams, a center beam 25 and two side beams 27 and 29 in a common in-line plane. These beams are directed and focused to traverse the apertured mask 21 and converge at screen 19 to excite the colour-emitting phosphors.
"` ~.304"~'74 PHA.60062 5 27-2-1987 The exterior surface of the tube has an electri-cally conductive coating 31, applied to the forward region of the funnel 15, and maintained at ground potential during tube usage.
The plural gun assembl~ 23 is positioned within the neck portion 13 in a manner whereby the three in-line beams 27, 25 and 29 are in a common horizontal "in-line"
plane substantially coincident with the X axis of the tube. The gun assembly is a longitudinal construction of a plurality of spatially-related unitized in-line apertured electrode members. The electrodes are positioned in a spaced, sequential arrangement forward of individual electron emitting cathode elements to form, focus and accelerate each of the individual electron beams. The a~sembly is forwardly terminated by a convergence cup 39, and the whole structure is integrated by at least two oppositely disposed insulative multiform members, only one of which, 41, is shown. A getter container 35 is supported by a wand 37 attached to a convergence cup 39. A thin layer of getter 20 material, not shown, was flashed from container 35 by induction heating, and covers portions of the inner surface of the envelope, mask and other tube components.
In Fig. 2, a unitized bi-potential electron gun assembly comprises a plurality of unitized in-line apertured electrode members sequentially positioned forward of individual cathode elements, K1, K2, K3- The bi-potential electrode arrangement includes an initial beam forming grid G1, and initial beam accelerating grid G2, a main focusing grid G3 having a longitudinal dimension defined 30 by rearward and forward apertured ends and a final accele-rating grid G4.
In Fig. 3, a unitized quadri-potential in-line gun assembly has a plurality of electrodes positioned forward of individual cathode elements K1, K2, K3, including an initial beam forming grid G1, an initial beam accele-rating grid G2, a first high focusing grid G3, a low focusing grid G4 electrically connected to the G2 grid, a second high focusing grid G5 electrically connected to ;, "'~ .. :, ' ' , 130~74 PHA.60062 6 27-2-1987 the G3 grid, and a final accelerating grid G6. Each of the G3, G4 and G5 grids has a longitudinal dimension defined by forward and rearward apertured ends.
It is a standard practice in the manufacture of cathode ray tubes to subject the cathodes and lower grid elements of the electron gun to an aging treatment subsequent to exhausting, baking, sealing and getter flashing the tube. Such aging takes place immediately after the cathodes are activated, and prior to high voltage conditioning. Aging has at least two objectives in addition to preparing the emission layer itself, both of which are directed to maintaining cathode activation and thereby insuring adequate electron emission from the cathodes.
The first object of aging is to "condition" the surfaces of the adjacent grid elements, that is, heat the grids to remove particles, adsorbed gases and other residue which are potential sources of cathode contamination.
The second object of aging is to convert residual gases, mainly hydro-carbons, into getterable species.
20 This is donc by selecting the voltages on the cathode and various grid elements so as to result in an electron beam of sufficient energy to dissociate these residual gas molecules into smaller components.
A typical prior art schedule for activating the cathodes and aging the tube for a 19V mini-neck colour picture tube having a quadripotential focus electron gun is illustrated graphically in Fig. 4. Heater filament and G1, G2 and G3 grid potentials, expressed in volts and designated EF, EG1, EG2 and EG3, respectively, are plotted 30 versus time in minutes. As can be seen from the graph, the heater filaments are initially subjected to a relatively low potential (EF) of about 6.5 volts for about 1 minute to preheat the cathodes, and then the heater voltage is raised to about 9.5 volts for about 1 minute to activate the cathodes. Aging begins immediately after activation.
A voltage of about 8.5 volts is maintained on the cathode heater filaments throughout the 33 minute aging cycle.
4~74 PHA.60062 7 27-2-1987 At the start of aging, the G1 grid is subjected to a slightly lower potential of about 8 volts. After about 4 minutes, the G1 grid potential is increased to about 15 volts, and the G2 grid is subjected to a substantially higher potential of about 300 volts. After another 4.5 minutes the G2 potential is increased to 350 volts, and 11 minutes after that EG1 is reduced to 10 volts. At this time, about 19 minutes after the start of aging, the G3 grid is subjected to a potential of about 350 volts for about 13 minutes.
EF is maintained for about 1 minute after EG1, EG2 and EG3 have been turned off, and is subsequently reapplied for an additional two minutes to insure against the formation of detrimental deposits on the cathodes from the grids, and to further reduce any contaminants on the cathode surface.
An arrangement for achieving the above activating and aging schedule is shown schematically in Fig. 7, wherein potential source EF supplies the cathode heater filaments, source EG1 supplies the grid G1 and source EG2 supplies both the G2 and G3 grids. The actual potential values for each gun element being aged are controlled by the values of the resistors. Typical values for resistors RK1-3, for example, are 150 ohms each, for RG1, 100 ohms, and for RG2, 5000 ohms. Since there is no resistor between G2 and G3, these grids are subjected to the same potential.
As has already been explained, when the G3 grid is subjected to a potential similar to that of G2, the positively charged carbon particles resulting from the 30 dissociation of residual hydrocarbons are formed into a beam and directed back onto the cathodes, forming dark center cathodes similar to that illustrated in Fig. 5s wherein cathode 90 includes carbon deposit 92 in the center of emissive layer 94. In order to avoid such detrimental deposits, the potential of the grid G3 must be lowered to create a barrier to the positively charged particle beam.
"~ 1304~74 PHA.60062 8 27-2-1987 However, lowering the potential of the grid G3 too far can have at least two adverse effects. First, it reduces the effectiveness of gas dissociation, by reducing the energy of electron beam. Second, it reduces the effec-tiveness of G3 grid conditioning, by reducing the temperatureproduced by energy dissipation in the grid. Both residual gas and contaminants on the G3 grid can find their way to the cathodes during later tube operation, reducing emission and consequently shortening tube life.
lG In order to avoid these disadvantages, it is necessary to maintain the G3 potential within a critical range during aging, high enough to provide effective gas dissociation and conditioning, but low enough to provide a barrier to the deposition of carbon on the cathodes.
In this regard, it has been determined that the G3 potential should be at least 100 volts, and at least 50 volts below the G2 potential, and preferably at least 150 volts and at least 100 volts below the G2 potential.
In order to demonstrate the advantages of the 20 invention, an illustrative example is presented. Three sets of samples of 26V CFF colour picture tubes were divided into two groups. The first group was aged according to a prior art schedule similar to that described above for mini-neck tubes, and the second group was aged according to a schedule of the invention, depicted in Fig. 6.
The samples were then compared for emission, dark center cathodes and emission slump.
Arrangements similar to those shown in Figs. 7 and 8 were used. In the prior art aging, (Fig. 7) the 30 values of EG2 and RG2 were 600 volts and 5000 ohms, res-pectively, resulting in potentials of 515 volts at both the G2 and G3 grids. The currents flowing to the G2 and G3 grids were 0.8 and 17 milliamps, respectively.
In the aging schedule of the process in accordance 35 with the invention, EG2 was reduced to 400 volts, and a 5000 ohm resistor (RG3 in Fig. 8) was inserted into the circuit between the grids G2 and G3, resulting in poten-tials of 325 and 255 volts at the grids G2 and G3, ~ 1~104~74 PHA,60062 9 27-2-1987 respectively. The currents flowing to the grids G2 and G3 were 0.5 and 15 milliamps, respectively.
Results are shown in the Table below.
TABLE
Cathode Emission Emission Slump Elec_tron Volts _ Appearance of (Percent) Red Gun Green Gun Blue Gun Cathode Centers Red Green Blue X s X s X s Set ~1 Group 1 3438 44 3482 29 3498 39 20 light deposits --~
out of 30 15 Group II
3468 40 3453 36 3485 43 1 light deposit ----------out of 36 Set ~2 Group 1 3391 _ 3484 40 3490 35 7 light deposits 8 6 9 Group II
3436 40 3483 21 3471 34 0 out of 33 3 0 7 Set ~
Group 1 3433 77 3443 73 3412 92 6 heavy deposits,4 8 8 2 moderate deposits, 12 light deposits out of 33 Group II
3461 32 3462 28 3452 31 2 light deposits 4 2 2 out of 33 Emission and emission slump are reported for each of the red, green and blue guns. Emission is reported in micro-amperes as an average ( X ) of 10 to 12 samples, withstandard deviations ( s ). Emission slump is reported as percent decrease in emission after 5 seconds at a filament potential of 5 volts and zero bias. Appearance of the ~1~0~774 PHA.60062 10 27-2-1987 cathodes after aging was visually rated as zero, light, moderate and heavy deposits, and reported without distinc-tion between individual guns.
As can be seen from the results, the aging schedule of the process in accordance with the invention (Group II) resulted in good emission levels, significantly better stability as indicated by lower slump, and substan-tially reduced incidence of dark center cathodes.
This invention relates to the aging of cathode ray tubes, and more particularly relates to an improved aging process in which dark center cathodes caused by the aging of the focusing electrode are substantially reduced.
S In the manufacture of cathode ray tubes for television and other display applications, various tube processing steps are carried out to ensure an acceptable life of reliable operation in the field. This processing begins after assembly of the tube components, and includes:
exhausting and baking the tube to evacuate the envelope and outgas the tube components; flashing a getter onto the internal surfaces of the tube and components to provide continuous gettering of residual contaminants which are outgassed during tube operation; activating the cathodes of the electron gun by heating to promote the formation of low work function species in the emission layer; aging the cathode and lower grid elements of the gun to maintain cathode activation; and finally high voltage conditioning of the electron gun to remove particles and projections 20 which could lead to interelectrode arcing.
The rate of outgassing is time and temperature dependent, and the throughput demands of the manufacturing process as well as the limited thermal stability of certain tube components make complete outgassing during exhausting and baking impractical. Thus, some residual gas and gas-producing contaminants, such as hydrocarbons, remain in the tube after sealing of the exhaust tubulation.
Getter flashing usually introduces additional hydrocarbon contaminants into the tube. These hydrocarbons 30 cannot be effectively adsorbed by the non-bakable barium getters commonly employed in many types of colour television picture tubes. However, during subsequent aging, these hydrocarbons are dissociated into getterable components, 1304'Y74 PHA.60062 2 27-2-1987 resulting in the reduction of residual gas in the tube to acceptable levels.
Unfortunately, the aging process has also been found to result in a condition known as "dark center cathode", which by analysis has been found to be due to a carbon deposit in the center of the emissive layer of the cathode.
Surprisingly, this deposit does not materially reduce cathode emission. However, it does restrict emisSion to the area of the perimeter of the emissive layer, resulting in a hollow beam which interferes with proper focusing and image resolution at the screen.
In U.S. Patent Specification 4,457,731, the dark center cathode problem is addressed for reprocessed cathode ray tubes. Tubes rejected for gun-related defects can be lS salvaged by "regunning", that is replacing the defective gun with a new one. Since this regunning operation necessa-rily reopens the envelope to the ambient, the tube must be reprocessed. This patent specification teaches that dark center cathodes can be substantially reduced by flashing the getter after aging, so-called "post-flashing". However, when post-flash~g is practiced on virgin tubes, unaccepata-bly high gas levels result.
An object of this invention is to reduce the incidence of dark center cathodes in a manner which does not result in unacceptably high gas levels.
Another object of this invention is to age a cathode ray tube after sealing and getter flashing without producing dark center cathodes, and simultaneously reduce residual gas to an acceptable level.
According to the present invention there is pro-vided a process for aging a cathode ray tube after the tube has been evacuated, sealed and getter flashed, and the cathode has been activated; the process comprising applying predetermined voltages to the cathode heaters and G1 grid of the tube's electron gun, so as to result in the emission of electrons from the cathodes, and then sequentially adding predetermined voltages to the G2 and G3 grid electrodes of the gun, respectively, the G2 and G3 grid voltages being PHA.60062 3 27-2-1987 larger than the cathode and G1 grid voltages characteri-zed in that the G3 grid voltage is smaller than the G2 grid voltage.
In accordance with the invention, it has been discovered that the successively higher voltages impressed on the G1, G2 and G3 grids during aging results in the focusing of the electrons emitted from the cathodes into an electron beam which dissociates residual hydrocarbons present in the tube after exhausting, baking and getter flashing, and that such dissociation results in the forma-tion of a beam of positive carbon ions which travel in the reverse direction from the electron beam and are deposited on the cathode.
It has further been discovered that reducing the lS potential of the G3 grid during aging to a critical level above a threshold needed for effective aging of this grid, but sufficiently below the potential of the G2 grid to create a potential barrier to prevent the positive beam from reaching the cathode, significantly reduces the inci-dence of dark center cathodes while substantially retainingthe benefits of G3 aging.
In an embodiment of the process in accordance with the present invention, the G3 grid electrode is at least 100 volts, and at least 50 volts less than the G2 grid electrode.
In another embodiment of the process in accordance with the present invention, the G2 and G3 grids are connect-ed to the same potential source, and the lower G3 grid potential is achieved by inserting a resistor between these two electrodes.
The present invention will now be explained and described, by way of example, with reference to the accompa-nying drawings, wherein:
Fig. 1 is a partial cross-section view of a sealed and getter flashed cathode ray tube to be aged in accordance with the process of the invention;
Fig. 2 is a partial cross-section of the neck portions of the cathode ray tube of Fig. 1, showing the 1304~74 PHA.60062 4 27-2-1987 cathode and grid elements of a bipotential electron gun to be aged in accordance with the process of the invention;
Fig. 3 is a view similar to that of Fig. 2, showing the elements of a quadripotential electron gwn to S be aged in accordance with the process of the invention;
Fig. 4 is a graph of time in minutes versus potential in volts for a typical cathode activating and tube aging schedule of the prior art;
Fig. 5 i9 an enlarged plan view of a dark center lG cathode resulting from the prior art aging schedule of Fig. 4;
Fig. 6 is a graph of time in minutes versus potential in volts for a typical cathode activating and tube aging schedule of the invention;
Fig. 7 is a schematic diagram of a prior art arrangement for achieving the schedule of Fig. 4; and Fig. 8 is a schematic diagram of an arrangement of the invention for achieving the schedule of Fig. 6.
With reference to the drawings, Fig. 1 is a sectiol~ed view showing the essential elements of a plural beam in-line colour cathode ray tube 11 aged in accordance with the process of the present invention. Cathode ray tube 11 is oriented to have a central longitudinal axis 14 and X and Y axes normal to axis 14. The encompassing tube envelope is a glass structure comprised of a hermetically sealed integration of neck 13, funnel 15 and viewing panel 17 portions. Dispo~ed on the interior surface of the viewing panel is a patterned cathodoluminescent screen 19 of stripes or dots of colour-emitting phosphor materials.
30 A multi-opening structure 21, in this instance an apertured mask, is positioned within the viewing panel in spaced relationship to the patterned screen 19. Encompassed within the neck portion 13 of the envelope is a unitized plural-beam in-line electron gun assembly 23, from which emanate three electron beams, a center beam 25 and two side beams 27 and 29 in a common in-line plane. These beams are directed and focused to traverse the apertured mask 21 and converge at screen 19 to excite the colour-emitting phosphors.
"` ~.304"~'74 PHA.60062 5 27-2-1987 The exterior surface of the tube has an electri-cally conductive coating 31, applied to the forward region of the funnel 15, and maintained at ground potential during tube usage.
The plural gun assembl~ 23 is positioned within the neck portion 13 in a manner whereby the three in-line beams 27, 25 and 29 are in a common horizontal "in-line"
plane substantially coincident with the X axis of the tube. The gun assembly is a longitudinal construction of a plurality of spatially-related unitized in-line apertured electrode members. The electrodes are positioned in a spaced, sequential arrangement forward of individual electron emitting cathode elements to form, focus and accelerate each of the individual electron beams. The a~sembly is forwardly terminated by a convergence cup 39, and the whole structure is integrated by at least two oppositely disposed insulative multiform members, only one of which, 41, is shown. A getter container 35 is supported by a wand 37 attached to a convergence cup 39. A thin layer of getter 20 material, not shown, was flashed from container 35 by induction heating, and covers portions of the inner surface of the envelope, mask and other tube components.
In Fig. 2, a unitized bi-potential electron gun assembly comprises a plurality of unitized in-line apertured electrode members sequentially positioned forward of individual cathode elements, K1, K2, K3- The bi-potential electrode arrangement includes an initial beam forming grid G1, and initial beam accelerating grid G2, a main focusing grid G3 having a longitudinal dimension defined 30 by rearward and forward apertured ends and a final accele-rating grid G4.
In Fig. 3, a unitized quadri-potential in-line gun assembly has a plurality of electrodes positioned forward of individual cathode elements K1, K2, K3, including an initial beam forming grid G1, an initial beam accele-rating grid G2, a first high focusing grid G3, a low focusing grid G4 electrically connected to the G2 grid, a second high focusing grid G5 electrically connected to ;, "'~ .. :, ' ' , 130~74 PHA.60062 6 27-2-1987 the G3 grid, and a final accelerating grid G6. Each of the G3, G4 and G5 grids has a longitudinal dimension defined by forward and rearward apertured ends.
It is a standard practice in the manufacture of cathode ray tubes to subject the cathodes and lower grid elements of the electron gun to an aging treatment subsequent to exhausting, baking, sealing and getter flashing the tube. Such aging takes place immediately after the cathodes are activated, and prior to high voltage conditioning. Aging has at least two objectives in addition to preparing the emission layer itself, both of which are directed to maintaining cathode activation and thereby insuring adequate electron emission from the cathodes.
The first object of aging is to "condition" the surfaces of the adjacent grid elements, that is, heat the grids to remove particles, adsorbed gases and other residue which are potential sources of cathode contamination.
The second object of aging is to convert residual gases, mainly hydro-carbons, into getterable species.
20 This is donc by selecting the voltages on the cathode and various grid elements so as to result in an electron beam of sufficient energy to dissociate these residual gas molecules into smaller components.
A typical prior art schedule for activating the cathodes and aging the tube for a 19V mini-neck colour picture tube having a quadripotential focus electron gun is illustrated graphically in Fig. 4. Heater filament and G1, G2 and G3 grid potentials, expressed in volts and designated EF, EG1, EG2 and EG3, respectively, are plotted 30 versus time in minutes. As can be seen from the graph, the heater filaments are initially subjected to a relatively low potential (EF) of about 6.5 volts for about 1 minute to preheat the cathodes, and then the heater voltage is raised to about 9.5 volts for about 1 minute to activate the cathodes. Aging begins immediately after activation.
A voltage of about 8.5 volts is maintained on the cathode heater filaments throughout the 33 minute aging cycle.
4~74 PHA.60062 7 27-2-1987 At the start of aging, the G1 grid is subjected to a slightly lower potential of about 8 volts. After about 4 minutes, the G1 grid potential is increased to about 15 volts, and the G2 grid is subjected to a substantially higher potential of about 300 volts. After another 4.5 minutes the G2 potential is increased to 350 volts, and 11 minutes after that EG1 is reduced to 10 volts. At this time, about 19 minutes after the start of aging, the G3 grid is subjected to a potential of about 350 volts for about 13 minutes.
EF is maintained for about 1 minute after EG1, EG2 and EG3 have been turned off, and is subsequently reapplied for an additional two minutes to insure against the formation of detrimental deposits on the cathodes from the grids, and to further reduce any contaminants on the cathode surface.
An arrangement for achieving the above activating and aging schedule is shown schematically in Fig. 7, wherein potential source EF supplies the cathode heater filaments, source EG1 supplies the grid G1 and source EG2 supplies both the G2 and G3 grids. The actual potential values for each gun element being aged are controlled by the values of the resistors. Typical values for resistors RK1-3, for example, are 150 ohms each, for RG1, 100 ohms, and for RG2, 5000 ohms. Since there is no resistor between G2 and G3, these grids are subjected to the same potential.
As has already been explained, when the G3 grid is subjected to a potential similar to that of G2, the positively charged carbon particles resulting from the 30 dissociation of residual hydrocarbons are formed into a beam and directed back onto the cathodes, forming dark center cathodes similar to that illustrated in Fig. 5s wherein cathode 90 includes carbon deposit 92 in the center of emissive layer 94. In order to avoid such detrimental deposits, the potential of the grid G3 must be lowered to create a barrier to the positively charged particle beam.
"~ 1304~74 PHA.60062 8 27-2-1987 However, lowering the potential of the grid G3 too far can have at least two adverse effects. First, it reduces the effectiveness of gas dissociation, by reducing the energy of electron beam. Second, it reduces the effec-tiveness of G3 grid conditioning, by reducing the temperatureproduced by energy dissipation in the grid. Both residual gas and contaminants on the G3 grid can find their way to the cathodes during later tube operation, reducing emission and consequently shortening tube life.
lG In order to avoid these disadvantages, it is necessary to maintain the G3 potential within a critical range during aging, high enough to provide effective gas dissociation and conditioning, but low enough to provide a barrier to the deposition of carbon on the cathodes.
In this regard, it has been determined that the G3 potential should be at least 100 volts, and at least 50 volts below the G2 potential, and preferably at least 150 volts and at least 100 volts below the G2 potential.
In order to demonstrate the advantages of the 20 invention, an illustrative example is presented. Three sets of samples of 26V CFF colour picture tubes were divided into two groups. The first group was aged according to a prior art schedule similar to that described above for mini-neck tubes, and the second group was aged according to a schedule of the invention, depicted in Fig. 6.
The samples were then compared for emission, dark center cathodes and emission slump.
Arrangements similar to those shown in Figs. 7 and 8 were used. In the prior art aging, (Fig. 7) the 30 values of EG2 and RG2 were 600 volts and 5000 ohms, res-pectively, resulting in potentials of 515 volts at both the G2 and G3 grids. The currents flowing to the G2 and G3 grids were 0.8 and 17 milliamps, respectively.
In the aging schedule of the process in accordance 35 with the invention, EG2 was reduced to 400 volts, and a 5000 ohm resistor (RG3 in Fig. 8) was inserted into the circuit between the grids G2 and G3, resulting in poten-tials of 325 and 255 volts at the grids G2 and G3, ~ 1~104~74 PHA,60062 9 27-2-1987 respectively. The currents flowing to the grids G2 and G3 were 0.5 and 15 milliamps, respectively.
Results are shown in the Table below.
TABLE
Cathode Emission Emission Slump Elec_tron Volts _ Appearance of (Percent) Red Gun Green Gun Blue Gun Cathode Centers Red Green Blue X s X s X s Set ~1 Group 1 3438 44 3482 29 3498 39 20 light deposits --~
out of 30 15 Group II
3468 40 3453 36 3485 43 1 light deposit ----------out of 36 Set ~2 Group 1 3391 _ 3484 40 3490 35 7 light deposits 8 6 9 Group II
3436 40 3483 21 3471 34 0 out of 33 3 0 7 Set ~
Group 1 3433 77 3443 73 3412 92 6 heavy deposits,4 8 8 2 moderate deposits, 12 light deposits out of 33 Group II
3461 32 3462 28 3452 31 2 light deposits 4 2 2 out of 33 Emission and emission slump are reported for each of the red, green and blue guns. Emission is reported in micro-amperes as an average ( X ) of 10 to 12 samples, withstandard deviations ( s ). Emission slump is reported as percent decrease in emission after 5 seconds at a filament potential of 5 volts and zero bias. Appearance of the ~1~0~774 PHA.60062 10 27-2-1987 cathodes after aging was visually rated as zero, light, moderate and heavy deposits, and reported without distinc-tion between individual guns.
As can be seen from the results, the aging schedule of the process in accordance with the invention (Group II) resulted in good emission levels, significantly better stability as indicated by lower slump, and substan-tially reduced incidence of dark center cathodes.
Claims (9)
1. A process for aging a cathode ray tube after the tube has been evacuated, sealed and getter flashed, and the cathode has been activated; the process comprising applying predetermined voltages to the cathode heaters and G1 grid of the tube's electron gun, so as to result in the emission of electrons from the cathodes, and then sequentially adding predetermined voltages to the G2 and G3 grid electrodes of the gun, respectively, the G2 and G3 grid voltages being larger than the cathode and G1 grid voltages;
characterized in that the G3 grid voltage is smaller than the G2 grid voltage.
characterized in that the G3 grid voltage is smaller than the G2 grid voltage.
2. A process as claimed in Claim 1, characterized in that the G3 grid voltage is at least 100 volts.
3. A process as claimed in Claim 1, characterized in that the G3 grid voltage is at least 50 volts less than the G2 grid voltage.
4. A process as claimed in claim 2, characterized in that the G3 grid voltage is at least 50 volts less than the G2 grid voltage.
5. A process as claimed in Claim 1, characterized in that the G3 grid voltage is at least 150 volts.
6. A process as claimed in Claim 1, characterized in that the G3 grid voltage is at least 100 volts less than the G2 grid voltage.
7. A process as claimed in Claim 1, characterized in that the heater voltage is within the range of from about 5 to 10 volts.
8. A process as claimed in Claim 1, characterized in that the G1 grid voltage is within the range of from about 5 to 20 volts.
9. A process as claimed in Claim 1, characterized in that the G2 grid voltage is within the range of from about 250 to 400 volts.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US87615086A | 1986-06-19 | 1986-06-19 | |
| US876,150 | 1986-06-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1304774C true CA1304774C (en) | 1992-07-07 |
Family
ID=25367087
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000540074A Expired - Lifetime CA1304774C (en) | 1986-06-19 | 1987-06-18 | Aging process for cathode ray tubes |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0250053A3 (en) |
| JP (1) | JPS6324530A (en) |
| KR (1) | KR880001015A (en) |
| CA (1) | CA1304774C (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3966287A (en) * | 1975-06-27 | 1976-06-29 | Rca Corporation | Low-voltage aging of cathode-ray tubes |
| JPS61110935A (en) * | 1984-11-05 | 1986-05-29 | Toshiba Corp | Manufacture of cathode-ray tube |
-
1987
- 1987-06-16 EP EP87201145A patent/EP0250053A3/en not_active Ceased
- 1987-06-16 KR KR1019870006077A patent/KR880001015A/en not_active Application Discontinuation
- 1987-06-18 CA CA000540074A patent/CA1304774C/en not_active Expired - Lifetime
- 1987-06-19 JP JP62151524A patent/JPS6324530A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0250053A3 (en) | 1990-03-28 |
| KR880001015A (en) | 1988-03-30 |
| EP0250053A2 (en) | 1987-12-23 |
| JPS6324530A (en) | 1988-02-01 |
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