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Патент USA US2409515

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EXAMINER"
CROSS REFERENCE
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XX
Patented Oct. 15, 1946
2,409,514
(a
‘UNITED STATES PATENT OFFICE
' act
vXJOVJISLQS
0’
2,409,514
CATHODE-RAY TUBE
George W. Pratt, Lancaster, Pa., a'ssignor to
Radio Corporation of America, a corporation of .
Delaware
Application January 30, 1945, Serial No. 575,273
I
1
10 Claims.
.
.
(Cl. 250x155“
,
is e 8 “V2
ing. The preferred form of striping material is
My invention relates to vacuum tubes in which
adjacent regions of a glass or other vitreous Wall
much like a oi t
along the wall of the tube, and more particularly
to cathode ray tubes with electrodes comprising
conducting matings on the inner wall of the tube.
‘ng a pigment of ferric ox
ide, FezOs, in a vehicle of alkali metal silicate.
are electrically charged at widely different poten
tials, for example by conductive coatings spaced
en a - yer of this striping ma eria 1s
5
epo-s1 e
on the bulb surface from a, suspension of ?nely
powdered F8203 in an aqueous solution of sodium
silicate and baked out, for example, at abou '
,
o ~~ 00°, _.
1‘ about an hour, it produces'on
Some types of cathode ray tu es 1n w ‘ch an
‘Tl’iWélf‘Efthe bulb an adherent, hard, smooth,
electron beam from an electron gun is directed
lengthwise of the tube to a ?uorescent screen on 10 substantially gas-free coating which appears to
the opposite end of the tube have as part of the
second anode of the, conventional electron gun
a conductive coating on the tube wall, and an
auxiliary or post accelerator electrode, usually an
annular coating of conducting material on the
inner wall of the tube, between the second anode
and the screen. The second anode and the ac
be almost electrically nonconductive and is dark
red in color when the ?ne powder is ferric oxide,
F6203. When this striping material is so used the
breakdown potential across the gap between con
ductive regions on the bulb walls, such as the con
ductive coatings, is greatly increased. In conven
tional tubes having conductive coatings with the
usual gap of about one inch between their adja
cent edges, breakdown of the gap and arcing
uncoated glass to permit a difference of potential 20 are apt to occur when the potential difference
between the coatings is about/3000 to 4000 volts,
of several thousand volts to be maintained be
celerator electrode are separated by a gap or zone,
which may be as much as an inch wide, of clean
tween the second anode andthe accelerator elec
which is frequently too low for best results in
trode. Di?iculty has been encountered due to
spark discharges through this gap or zone along
tubes of this kind. I have found that if the strip
In accordance with my invention I apply to the
wall of the bulb between the regions of different
some extent.
ing material of my invention is used, the potential
the surface of the glass between the adjacent 25 difference may be increased to as much as 75,000
volts, and that the gap between thecoatings may
edges of the second anode and the accelerator
be as small as about three-eighths of an inch
electrode particularly where the electrode coat_
without the occurrence of arcing or breakdown
ings contain enough graphite or similar carbona
between the edges of the coatings.
ceous material to produce the black and non
My invention will better be understood in con-~
reflecting coatings generally used in tubes of this
nectlon with the accompanying drawing in which
type.
merely for purposes of illustration I have shown
Attempts have been made to increase the break
a, cathode ray tube of a commercial type having
down potential of the gap between the two elec
the second anode and ‘the accelerator electrode
trodes or coatings by applying at the adjacent
edges of the electrodes highly conductive smooth 35 in the form of annular conductive coatings on the
interior of the bulb and in which Fig. 1 is a view
coatings of striping material on the glass and in
in longitudinal section partly broken away of a
contact with the electrodes in the form of stripes
cathode ray tube embodying my invention and
of silver paste, which is a, suspension of powdered
having the striping material of my invention ap
silver in an organic binder.
'
i
The principal object of my'invention is to pro 40 plied as an overlapping stripe along and coex
tensive with each of the edges of the conductive
vide means by which in a tube of this type the
coatings, and Fig. 2 is a' fragmentary view of the
breakdown potential between wall regions of
widely different potentials, such as the adjacent
middle portion of a similar tube with the striping
material applied as a'coating which covers all of
edges of electrodes comprising conductive coat
ings, is greatly increased and arcing and spark 45 the interior surface of the bulb in the zone be
tween the adiacent edges of the conductive coat
discharges across the gap between such regions
ings and overlaps the edges of the coatings to
is minimized.
'
potential, such as the adiacent edges of the con
ductive coatings, a gas-free adherent ,,
_-
.e -. of
striping material comprising a fine powder, pref
erablyn'fglic oxide, Pesos, intimately mixed with
an alkali metal silicate sughwaasmsondigm silicate,
The drawing illustrates a commercial cathode
50 ray tube having a conventional glass or similar
vitreous elongated envelope l with a ?attenedv
end on which there is a conventional ?uorescent
screen 2, ‘and a neck in which there is schemati
cally shown some electron discharge or beam-pro
either as a coating which covers the surface of 55 ducing means, such as an electron gun of the
type shown in U. S. patent to Holshouser, 2,348,
the glass wall or zone between the adjacent edges
216, May 9, 1944, an indirectly heated thermionic
of the conductive coatings, or as a stripe along
cathode, a ?rst anode 3, and a second electrode 4.
each of those edges. The striping material,
The beam deflection means, not shown, may be of
whether applied as stripes or continuous coating,
should overlap or otherwise be in electrical con 60 the conventional electrostatic or electromagnetic
type. The second electrode 4 of the electron gun
tact with all of the edge of the conductive coat—
2,409,514
4
3
is electrically connected to a conductive coating
of the conductive coatings or electrodes, with a
zone of clean glass between the stripes.
5 of graphite on the inner surface of the neck
I have obtained good results with striping ma
of the envelope adjacent the electrode 4 and pref
terial prepared by dissolving 100 to 125 grams of
erably extending a short distance into the flared
portion of the envelope. The electrode 4 and the 5 sodium silicate in 260 to 500 cubic centimeters of
distilled water, which may be heated if desired,
coating 5 constitute the second anode of the tube.
The post accelerator electrode 6 is an annular
electrode coaxial with the other electrodes and
an a
ng s owly and with constant stirring 500
grams of finely powdered ferric oxide, FezOs, stir
surrounding the path of the electron beam, and
is preferably a black conductive coating of graph
ring until all of the oxidedd?fa?dla'uhiform
mixture free from lumps is obtained. The result
ite on the wall of the envelope between the second
anode and the ?uorescent screen. A black con
is a kind of paint, with sodium silicate as the
vehicle and ferric oxide as the pigment in which
the pigment is the major constituent by weight.
ductive coating of graphite on the inner wall of
The weight of the FezOs is preferably from about
cathode ray tube is well known in the art, and
is disclosed in U. S. patent to Zworykin, 1,988,469, 15 two to five times the weight of the sodium sili
cate, but the proportions of the constituents can
Jan. 22, 1935. Operating potentials are applied to
be varied considerably Without impairing the ef
the tube electrodes in the conventional way by a
fectiveness of the coating. Other oxides of about
voltage source 1 shown diagrammatically. The
the same electrical conductivity as ferric oxide,
electrodes cooperate to produce an electronic dis
?nely powdered metallic or ?nely powdered elec
charge lengthwise of the envelope in the form of
trically nonconductive material‘ may be substi
an electron beam from the electron gun to the
> tuted in whole or in part for the ferric oxide pig
?uorescent screen.
ment.
The breakdown voltage over the clean uncoated
conductors, such as the adjacent edges 8 of the ’
coating 5 of the second anode and 9 of the accel
erator electrode, may be increased by placing
along the edge of each of the electrodes a stripe In
of striping material coextensive with those edges
as shown in Fig. 1 in which there is a zone ll
This paint may be applied to the glass
envelope with a brush, or in any other conven
ient way, in as thin a coat as will produce the de
glass surface forming the gap between two spaced
sired results.
The application of the striping
material to the glass surface to form a continu
ous coating between the edges of the electrodes
in Fig. 2 by covering all the glass surface of the
may be somewhat facilitated by adding to the so
lution above described some binder, such as 5
grams U. S. P. gelatin, and a small amount, such
as 1 cc., of ammonium-hydroxide.
zone between the electrodes with a continuous
coating 12 of striping material in electrical con
first and the conductive coating which forms
tlon of‘ an allghibitweamhsuchas gddgumfor
e or ?g resistance surface films, such as
films of oxide. Such a coating is much more con
of uncoated glass between the stripes or as shown
\
The silica e coa mg
ay
e app ied to the bulb
the electrode may be applied to overlap the edge
tact with the edges of both electrodes through
of the silicate coating, or the silicate coating may
out the entire length of those edges. The strip
be applied after the conductive coating and over
ing material may to advantage be in contact with
lap it at the edge. Either method is satisfac
and electrically connected to the electrodes, for
tory, but the latter is somewhat more convenient.
example, by overlapping the edges of the two elec
I have also found that the breakdown or spark
trodes preferably about 116 to 1/4 of an inch. All of 40
ing potential between the edges of the electrodes
the edge of the electrode should be covered by
may be greatly increased by making the narrow
thestriping material, else sparking may occur
stripes at the edges of the electrodes of coating
from an uncovered part of the edge.
material consisting of a mixture‘ of_s_q_di_ufnws;ili;
In accordance with my invention the striping
material is deposited on the glass wall from a 45 cate and ?ne particles of metal, such as silver,
“gem” or platinum which do not have noncon
suspension of a?ne/powqder in an aqueous solu
‘potassium sil cate, and the deposit baked until the
ductive then a coating containing ferric oxide.
and the deposit' converted into
a hard adherent substantially gas-free coating 50 For example, the ohmic resistance of striping ma
terial consisting of sodiumasilicateaogtaining ,
of striping material composed of the ?ne powder
wa er s riven o
dispersed through the dehydrated silicate. This
coating is nonconductive or very slightly conduc
tive. While I have obtained the best results with
?nely powdered sill'er and
%” wide and
k =$141,510at,g1a,.§$,...=.1j.i1e
long is t?‘filt 0.1 ohm. Ap
parently_high ohmic resistance is not necessary
a mixture of sodium silicate and ?nely powdered 55 in these narrow stripes of coating material, but is
important and necessary where the coating mate
ferric oxide iezyOa, wH1ch gives good results and
rial completely covers the glass surface between
is mined; other fine powders of insulating
the electrodes.
or semi-insulating material may be used. I have
I have found that conductive striping materials
found that green chromic oxid can be substi—,
tuted in who e or
'
ic oxide,
u't
it ism’e'expensive and is not usually available in
fine enough particle size to produce as smooth a
coating as can be obtained with ferric oxide.
Finely powdered metals which have surface lay
60 used as narrow stripes along the edges of the
electrodes must be entirely free from carbon in
any form, either as a constituent or as a residue
from an organic binder, in order to be effective
in increasing the potential difference at which
ers of insulating or semi-insulating oxide, for ex 65 breakdown or sparking occurs between the edges
of the electrodes. The fact that the presence of
ample, iron, nickel and copper, may be substituted
carbon in any form in these stripes tends to pre
for the ferric oxide,’si?c_e_é'ach particle is in
vent the increase in breakdown potential obtain
sulated by a layer of surface nonconductive oxide
able with stripes free from carbon is well estab
and the metal powders are essentially noncon
ductive materials. The nonconductive or very 70 lished, although no acceptable explanation of
that fact is at present available.
slightly conductive coatings made in accordance
The way in which the striping material in
Wl
y
ven 1011 may e used as a continuous
creases the breakdown voltage and prevents
coating covering the entire area between the con
arcing across the gap between the edges of the
ductive coatings of electrodes, or may be used as
narrow stripes on the glass overlapping the edges 75 electrodes is not fully understood.
Heretofore
' 2,409,514
6
5
the glass envelopes of cathode ray tubes of the
kind in which my invention may be used to ad
vantage were very carefully cleaned on the in
side, particularly in the zone between the edges
of the electrode coatings and, in addition, the
tubes were treated or aged by maintaining for
about two minutes a spark discharge between the
silicate and ?nely divided ferric oxide uniformly
dispersed throughout said layer, the weight of
ferric oxide in said layer being from two to ?ve
times the weight of sodium silicate.
6. A vacuum device comprising an envelope of
vitreous material enclosing electrodes for produc
ing an electron discharge, means for producing
on the inner walls of said envelope spaced ad
edges of the electrodes, but nevertheless the
jacent regions at different potentials and an ad
breakdown potential could not in all cases be
raised to the desired value and in no case to the 10 herent coating on said wall between said regions
consisting of a dried paint composed of a vehicle
value obtainable by using the ferric oxide mixture
of an alkali metal silicate and a uniformly dis
of my invention. It may be that the ?nely pow
persed ?nely powdered substantially nonconduc
dered material in the coating of striping material
tive metallic pigment constituting the major part
tends to distribute the electrostatic stress and
make the potential gradient between the edges 15 by weight of the dried paint.
7. An electron discharge device comprising a
of the electrodes more uniform than it would
glass envelope enclosing means for producing an
otherwise be.
electron discharge in said envelope, two cooperat;
My invention is not limited to the particular
ing electrodes surrounding the path of said dis
type of tube shown by way of illustration, but is
applicable to any electron discharge tube in which 20 charge and comprising conductive coatings on
and spaced along the inner wall of said envelope
di?erences of potential between adjacent regions
to provide between their adjacent edges a zone
of the tube walls are such that sparking or are
discharges are liable to occur along the walls be
tween such regions.
I claim:
1. A cathode ray tube comprising a highly evac
uated elongated vitreous envelope enclosing elec
trodes for producing an electron discharge
of clean uncoated glass wall, and a narrow stripe
of ?nely powdered carbon-free electrically con
25 ductive material dispersed in a layer of dehy
drated alkali metal silicate on said inner wall
and extending along and. in contact with the edge
of each of said electrodes and projecting into
said zone less than half the width of said zone,
lengthwise of said envelope, two conductive coat
ings on the inner wall of said envelope and spaced 30 said stripes being separated throughout their
length by a clean uncoated zone on said inner wall.
along the length of said envelope, and an ad
8. An electron discharge device comprising a
herent substantially gas-free coating of ?nely
vitreous envelope enclosing means for producing
powdered FezOa and sodium silicate on and cov
an electron discharge in said envelope, two coop
ering said inner wall between the adjacent edges
of said coatings and adjoining said edges.
35 erating electrodes surrounding the path of said
discharge and each comprising a conductive coat
2. A cathode ray tube comprising a highly evac
ing on the inner wall of said envelope and a nar
uated vitreous envelope enclosing means for pro
row stripe of ?ne metal particles having an elec
ducing an electron discharge in said envelope, 2.
trically conductive surface dispersed in a layer oi
second anode and an accelerating electrode con
sisting of annular conductive coatings on the tube 40 dehydrated alkali metal silicate on said inner
wall and extending along and in contact with
wall and spaced along the tube coaxial with the
the edge of “said conductive coating, said electrodes _
path of said discharge and a coating consisting
being spaced along said inner wall with the ad
of ?nely powdered insulating or semi-insulating
jacent edges of the stripes of said electrodes sep
material dispersed through an alkali metal silicate
on the tube wall between and electrically con
nected with both said anode and said accelerat
45 arated by a clean uncoated zone on said inner
wall.
9. An electron discharge device comprising a
vitreous envelope enclosing means for producing
an electron discharge in said envelope, two coop
uated elongated vitreous envelope enclosing means
for producing an electron discharge lengthwise 60 erating annular electrodes comprising conductive
coatings on and spaced along the inner wall of
of said envelope, an electrode on the inner sur
said envelope and surrounding the path of said
face of said envelope comprising conductive ma
discharge, two narrow stripes of ?ne metal par
terial, and a baked gas-free stable coating on the
ticles having high surface conductivity dispersed
inner surface of said envelope and adjoining said
in a layer of dehydrated sodium silicate on said
electrode and consisting of the dehydrated residue
inner wall, said stripes being separated through
of a suspension of ?nely powdered ferric oxide in
out their length by a clean uncoated zone on said
a water solution of sodium silicate.
inner wall and extending along and in contact
4. An electron discharge device comprising a
with the edges of the respective electrodes.
highly evacuated vitreous envelope enclosing
10. An electron discharge device comprising a
means for producing an electron discharge in 60
vitreous envelope enclosing means for producing
said envelope, two cooperating electrodes com
an electron discharge in said envelope, two coop
prising conductive coatings on and spaced along
erating annular electrodes surrounding the path
the inner wall of said envelope and surround
of said discharge and each comprising a conduc
ing the path of said discharge, and a coating of
iron oxide and sodium silicate on said inner wall 65 tive coating on the inner wall of said envelope
and a narrow stripe of ?nely powdered silver
between the adjacent edges of said electrodes
dispersed in a layer of dehydated sodium silicate
and in electrically conductive contact with all of
on said wall and extending along and in contact
said edges.
with one edge of said electrodes, said electrodes
5. A vacuum device comprising an envelope of
vitreous material enclosing means for producing 70 being spaced along said wall and separated by a
clean uncoated zone on said inner wall coextensive
an electron discharge in said envelope and hav
with and between the adjacent edges of said
ing on its inner wall two spaced electrodes, and
stripes.
an adherent coating between and overlapping the
GEORGE W. PRATT.
adjacent edges of said electrodes and consisting
essentially of a layer of baked dehydrated sodium 75
ing electrode.
“'
3. A cathode ray tube comprising a highly evac
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