Note: Descriptions are shown in the official language in which they were submitted.
~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
1304774
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.
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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.
