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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electron gun for a cathode ray tube used in a
projector tube, a color TV tube and an index tube and the like, for
example.
2. Description of Related Art
As the related art electron gun for a cathode ray tube, the gun shown in
FIG. 33, for example, is well known in the art.
This electron gun is of a uni-potential type, wherein the first to fifth
grids acting as accelerator electrodes and focusing electrodes are
coaxially (a Z-axis) arranged against a cathode K for discharging
electrons. Then, electron beams discharged from the cathode K are focused
on a fluorescent surface under an action of pre-focusing lens formed by
the second and third grids G.sub.2, G.sub.3 and an action of a main lens
formed by the third to fifth grids G.sub.3 to G.sub.5. These cathode K and
the first to fifth grids G.sub.1 to G.sub.5 are fixed to a beading glass
through melting and integrally assembled. In addition, the first to fifth
grids G.sub.1 to G.sub.5 are made of metal such as stainless steel, for
example.
However, such electron gun had some problems as described below.
That is, in the aforesaid configuration, a certain displacement may easily
occur in a degree of concentricity of electrodes, the third to the fifth
grids G.sub.3 to G.sub.5, resulting in that the electron beams may be
moved away from an axis to cause a blooming of the electron beams to be
easily generated.
In addition, since there was a high potential gradient between the
electrodes, an electrical discharging was apt to occur among the third to
the fifth grids G.sub.3 to G.sub.5, a spherical aberration of a lens
diameter was increased to cause a beam spot diameter to be increased.
In addition, when a gap between the third grid G.sub.3 and the fourth grid
G.sub.4 and another gap between the fourth grid G.sub.4 and the fifth grid
G.sub.5 are widened by more than a certain space, this operation shows a
problem that the electron beams are leaked out and a charge-up occurs at
the neck part or the beading glass. These gaps are related to a
performance of an electron gun (in particular, a coefficient of spherical
aberration) and so it is desired to make the most suitable gap.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention has been invented and it is
an object of the present invention to provide an electron gun for a
cathode ray tube in which a gap between the grids can be designed to the
most suitable value in which a performance of the electron gun is improved
without generating any charging-up at the neck part or the beading glass
and the like.
In order to attain the aforesaid object, the electron gun for a cathode ray
tube of the present invention is fabricated such that an electron lens
composing part is composed of a resistive cylindrical member, at least a
ring-shaped first electrode, a ring-shaped third electrode and a
ring-shaped second electrode are arranged in this order from a cathode
side along an axis within the resistive cylindrical member, and a ratio of
a gap between the third electrode and the second electrode against another
ratio to a gap between the third electrode and the second electrode is 1
or more, preferably 1 to 3 and more preferably 1 to 2.
The aforesaid resistive cylinder is made of ceramic, for example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view for illustrating an entire configuration of an
electron gun for a cathode ray tube of the first preferred embodiment of
the present invention.
FIG. 2A is a front elevational view for showing a cylindrical holder of the
first preferred embodiment.
FIG. 2B is a sectional view taken along a line a-0-a- of FIG. 2A.
FIG. 2C is a sectional view taken along a line b-b' of FIG. 2A.
FIG. 2D is a sectional view taken along a line c-c' of FIG. 2C.
FIG. 3 is a top plan view for showing an HV shield of the preferred
embodiment.
FIG. 4 is a conceptional view for showing a gap between the electrodes.
FIG. 5 is a graph for showing a relation between a gap ratio of b/a and a
coefficient of spherical aberration.
FIG. 6 is a graph for showing a relation between a gap ratio of b/a and a
coefficient of spherical aberration x an amplification rate.
FIG. 7 is a flow chart for showing manufacturing steps for an electron gun
of the preferred embodiment.
FIGS. 8A to 8G are illustrative views for showing manufacturing steps of
the preferred embodiment.
FIG. 9 is a sectional view for showing a fixing part of a G.sub.4 pin of
the preferred embodiment.
FIG. 10 is an illustrative view for showing an example of a method for
coating resistive paste in the preferred embodiment.
FIG. 11 is an illustrative view for showing an example of a method for
trimming a resistive layer in the preferred embodiment.
FIG. 12 is an illustrative view for showing an example of forming a helical
state resistive layer in the preferred embodiment.
FIG. 13 is a sectional view for showing another example of a method for
fixing a cylindrical holder in the preferred embodiment.
FIG. 14 is a sectional view for showing an entire configuration of an
electron gun for a cathode ray tube in the preferred embodiment of the
present invention.
FIG. 15 is a sectional view for showing an entire configuration of an
electron gun of the second preferred embodiment of the present invention.
FIGS. 16A to 16D are graphs applied for describing an action of a
conductive layer.
FIG. 17 is an illustrative view for showing a principle of an effect of the
second preferred embodiment.
FIG. 18A is a sectional view for showing a substantial part of an electron
gun of one preferred embodiment of the present invention.
FIG. 18B is a graph for indicating a potential gradient.
FIG. 19A a sectional view for showing a substantial part of an electron gun
of another preferred embodiment of the present invention.
FIG. 19B is a graph for indicating a potential gradient.
FIG. 19C is a sectional view for showing a substantial part of an electron
gun of a still another preferred embodiment of the present invention.
FIG. 19D is a graph for indicating a potential gradient.
FIGS. 20A to 20D are illustrative views for indicating manufacturing steps
in the preferred embodiment.
FIGS. 21A to 21C are illustrative views for showing the first example of a
method for forming an electrode and a conductive layer.
FIGS. 22A to 22D are illustrative views for showing the second example of a
method for forming an electrode and a conductive layer.
FIGS. 23A to 23C are illustrative views for showing the electrode and the
conductive layer formed in accordance with the second example.
FIG. 24 is an illustrative view for showing the third example of a method
for forming an electrode and a conductive layer.
FIGS. 25A to 25E are illustrative views for showing the fourth example of a
method for forming electrodes and conductive layers.
FIGS. 26A and 26B are illustrative views for showing the fifth example of a
method for forming an electrode and a conductive layer.
FIGS. 27A to 27C are sectional views for showing the sixth example of a
method for forming electrodes and conductive layers.
FIGS. 28A and 28B are illustrative views for showing another example of a
method for fixing a resistive cylindrical device.
FIGS. 29A and 29B are a sectional view and a top plan view for showing a
substantial part of the third preferred embodiment of the present
invention, respectively.
FIGS. 30A and 30B are sectional views for showing a substantial part of the
fourth preferred embodiment of the present invention.
FIG. 31 is a view for showing an entire configuration of the fourth
preferred embodiment.
FIG. 32 is a view for showing an entire configuration of the fifth
preferred embodiment of the present invention.
FIG. 33 is an illustrative view for showing a schematic configuration of
the related art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the experiments performed by the present inventors, as shown
in FIG. 5, a coefficient of spherical aberration Cs of a lens of an
electron gun is substantially changed in the case that a gap ratio between
a gap (a) between the first electrode and the third electrode and another
gap (b) between the third electrode and the second electrode (b/a) is
changed. In this case, an X-axis in FIG. 5 is b/a and a Y-axis is a
coefficient of spherical aberration. The coefficient of spherical
aberration Cs may substantially influence against a spot diameter of the
cathode ray tube. A spot diameter D can be expressed by the following
equation.
D=dc.times.M+1/2.times.Cs.times.M.times..theta..sup.3 :
where, dc is a spot diameter, M is an amplification rate and .theta. is a
dispersion angle.
From the above-equation, it becomes apparent to be satisfactory that the
coefficient of spherical aberration Cs is decreased in order to reduce the
spot diameter D. Accordingly, in the present invention, the value of b/a
is set to be more than 1 in view of the result shown in FIG. 5. Mere
consideration of the coefficient of spherical aberration Cs shows that it
is satisfactory if the value of b/a is more than 1 and a further
consideration of the amplification rate M also shows that a value of
Cs.times.M has a minimum value against the value of b/a as shown in FIG.
6, so that the value of b/a is practically 1 to 3, preferably 1 to 2 in
order to reduce the spot diameter D.
In the present invention, it is possible to set a minimum value of
spherical aberration by setting the aforesaid gap ratio b/a to have a
predetermined range and thereby it is possible to improve a resolution of
a cathode ray tube.
In addition, since the electrodes are formed on the inner surface of
resistive cylindrical device, there is no possibility that the electron
beams are leaked out of a space between the electrodes and no charged-up
state occurs at the beading glass. Further, since the electron lens
configuration part is formed by the resistive cylindrical device, a
displacement in concentricity of the electron lens system is almost fixed.
An HV spring 5 is made of Inconel, for example. As shown in FIG. 1, the HV
spring 5 is fabricated such that it is fixed to both ends of the HV shield
4 by welding and its extremity end presses the inner surface of the neck
tube 1. Then, this HV spring 5 is electrically connected to an anode not
shown through an electrical conductive layer made of carbon and the like.
As shown in FIG. 41 the preferred embodiment of the present invention is
designed such that a gap ratio of a gap (a) between the third grip G.sub.3
(the first electrode) 8 and the fourth grid G.sub.4 (the third electrode)
9 against a gap (b) between the fifth grid G.sub.5 (the second electrode)
10 and the fourth grid G.sub.4 is set to be 1 or more, preferably 1 to 3
and more preferably 1 to 2.
Reasons why the aforesaid gap ratio (b/a) is set to the aforesaid range
will be described as follows.
As shown in FIG. 5, in the case that the aforesaid gap ratio (b/a) is
varied, the coefficient of spherical aberration Cs of a lens of an
electron gun is widely changed. In this case, the X-axis in FIG. 5
indicates the ratio of b/a and the Y-axis in FIG. 5 indicates the
coefficient of spherical aberration Cs. The coefficient of spherical
aberration Cs may substantially influence on the spot diameter of the
cathode ray tube. The spot diameter D can be expressed by the following
equation.
D=dc.times.M+1/2.times.Cs.times.M.times..theta..sup.3
where, dc is a spot diameter, M is an amplification rate and .theta. is a
dispersion angle.
It is apparent from the above equation that the coefficient of spherical
aberration Cs is reduced in order to decrease the spot diameter D.
Accordingly, the value of b/a in the preferred embodiment is set to be 1
or more in view of the result shown in FIG. 5. Although a mere
consideration of the coefficient of spherical aberration Cs shows that it
is satisfactory if the value b/a is 1 or more and also a consideration of
even the amplification rate M shows that Cs.times.M has a minimum value
against the value b/a, so that more practically the value b/a is 1 to 3
and preferably 1 to 2 in order to reduce the spot diameter D.
In addition, the practical size of the gap (a) between the third grid
G.sub.3 and the fourth grid G.sub.4 is varied in reference to a size of
the cathode ray tube.
In the preferred embodiment, it is possible to set the minimum value of the
spherical aberration by setting the aforesaid gap ratio to the
predetermined range and thereby to improve a resolution of the cathode ray
tube. In addition, since the outer circumferences of the grids G.sub.3,
G.sub.4 and G.sub.5 are formed on the inner surface of resistive
cylindrical device 3, there is no possibility that the electron beams are
leaked out of a space between the grids and charged up at the beading
glass.
Then, referring now to FIGS. 7 and 8, the method for manufacturing the
electron gun of the preferred embodiment will be described.
At first, a hole 16 for use in fixing the G.sub.4 pin 15 is formed at the
resistive cylindrical device 3 (the step (1) in FIG. 7 and FIG. 8A) and
then this resistive cylindrical device 3 is cleaned (the step (2) in FIG.
7). Then, as shown in FIG. 9, the G.sub.4 pin 15 and the flit glass (g)
are set within this hole 16 (the step (3) in FIG. 7).
In addition, the G.sub.4 pin 15 is fixed by a jig and then a flit baking is
carried out under its state (the step (4) in FIG. 7 and FIG. 8B).
Then, electrodes 8 to 10 are coated and formed at both ends and the central
part of the inner surface of the resistive cylindrical device 3 (the step
(5) of FIG. 7 and FIG. 8C). In this case, as the electrical conductive
paste, RuO.sub.2 -glass paste (a product name of #9516 manufactured by
Dupont), for example, is used so as to cause a film thickness to be made
uniform.
In addition, as shown in FIG. 8D, the aforesaid conductive paste is coated
in a longitudinal direction at the outer circumference where the G.sub.4
pin 15 of the resistive cylindrical device 3 is not arranged in order to
perform an electrical connection between the electrode 8 acting as the
third grid G.sub.3 and the the electrode 10 acting as the fifth grid
G.sub.5 and then a conductive layer 17 is formed. Then, a leveling drying
is carried out for making the electrodes 8 to 10 and the conductive layer
17 flat from each other (the step (6) in FIG. 7).
Then, as shown in FIG. 8E, a resistive layer 11 is coated and formed over a
substantial entire inner surface of the resistive cylindrical device 3,
i.e. with the portions having electrodes 8 and 10 at both ends of the
resistive cylindrical device 3 being slightly left (the step (7) in FIG.
8). In this case, as theresistive paste, RuO.sub.2 -glass paste (a product
name #9518 manufactured by Dupont), for example, is used and then the
coating is carried out in such a way that the film thickness may become
uniform.
FIG. 10 shows an example of a method for coating the resistive paste. As
shown in this figure, the resistive cylindrical device 3 is rotated around
a Z-axis, i.e. an axis direction of the tube so as to supply a specified
amount of resistive paste 18 at the inner surface of the resistive
cylindrical device 3 from a nozzle 20 connected to a tank 19 for the
resistive paste 18.
Then, after the leveling drying for the resistive layer 11 is carried out
(the step (8) in FIG. 7), both trimming and cleaning are performed for the
resistive layer by the method shown in FIG. 11 (the step (9) in FIG. 7).
FIG. 11 shows one example of the trimming method. That is, the resistive
cylindrical device 3 is moved in a direction of the X-axis while the
resistive cylindrical device 3 is being rotated around the Z-axis, the
extremity end of a marking-off needle 21 is contacted with the surface of
the resistive layer 11, thereby the resistive layer 11 is marked off in a
helical shape. In this case, only the portion not overlapped with the
electrodes 8 to 10 is marked off. Through this step, the resistive layer
11 is formed in a helical shape between the electrodes 8, 9 and between
the electrodes 9, 10, respectively (FIG. 8F). Cut dusts generated by the
trimming operation are completely removed from the resistive cylindrical
device by air blowing operation and the like (cleaning). Alternatively,
the marking-off needle 21 may be moved.
In turn, the resistive layer 11 may be formed in a helical shape not by
such a method as described above, but by the following method. That is,
after performing the leveling drying at the step (6) in FIG. 7, the
resistive cylindrical device 3 is moved in a direction of X-axis while
being rotated around the Z-axis as shown in FIG. 12, and the resistive
paste 18 can be supplied from a dispenser 22 (a hypodermic needle)
connected to the tank 19 for the resistive paste 18.
In this case, it is preferable that a distance between the dispenser 22 and
the resistive cylindrical device 3 is kept constant. In addition,
alternatively, the dispenser 22 may be moved.
After the helical resistive layer 11 is formed by the aforesaid step, the
resistive cylindrical device 3 is baked for ten minutes at a temperature
of 850.degree. C., for example (the step (10) in FIG. 7). With such an
arrangement as above, the electrodes 8 to 10 and the resistive layer 11
are melted, fixed to the resistive cylindrical device 3 and stabilized.
Then, after the resistive cylindrical device 3 is cleaned and dried (at the
step (11) in FIG. 7), the resistive cylindrical device 3 is centered by a
position setting jig and vertically set, the cylindrical holder 12 is set
at the resistive cylindrical device 3 (the step (12) in FIG. 7), a flit 23
is arranged at a connected part between the cylindrical holder 12 and the
resistive cylindrical device 3 as shown in FIG. 8G so as to perform a
baking operation (the step (13) in FIG. 7).
After this operation, both the HV shield 4 and the HV spring 5 are
assembled by applying the position setting jig and welded in respect to
one cylindrical holder 12a. In addition, the triodes (cathode K, the first
grid G.sub.1, the second grid G.sub.2 and the cup member G3.sub.A)
assembled in advance by a well-known beading method are assembled by the
position setting jig and welded against the other cylindrical holder 12b
(the step (14) in FIG. 7).
In addition, the lead lines 24, 25 of the first and second grids G.sub.1,
G.sub.2 and the lead line 26 of the G.sub.4 pin 15 are connected to the
stem pin 6 buried in the stem 2, thereby an electron gun shown in FIG. 1
is completed.
In the preferred embodiment having such a configuration as described above,
since the electrodes 8 to 10 corresponding to the third to fifth grids
G.sub.3 to G.sub.5 forming the main lens are formed into a high precision
and integral-formed resistive cylindrical device 3, an axial displacement
of these electrodes 8 to 10 in respect to the Z-axis is reduced.
Accordingly, in accordance with the preferred embodiment of the present
invention, it is possible to restrict some electron beams moved away from
the axis.
In addition, in the preferred embodiment of the present invention, since
the helical resistive layer 11 is formed among the electrodes 8 to 10, a
potential gradient among the electrodes 8 to 10 (an electric field
intensity variation rate) is reduced as compared with that of the related
art, resulting in that an electrical discharging is hardly generated among
the electrodes 8 to 11. In addition, since the spherical aberration is
reduced, it is possible to reduce the beam spot diameter and further to
improve a resolution.
In the aforesaid preferred embodiment, although the electrodes 8 and 10 are
connected through the conductive layer 17 and the cylindrical holders 12a,
12b, the present invention is not limited to this arrangement and it may
also be applicable that the cylindrical holders 12a, 12b are connected by
lead lines.
In addition, in the preferred embodiment described above, although the
cylindrical holders 12a, 12b are fixed to the resistive cylindrical device
3 through the flit glass 23 as shown in FIG. 8G, for example, the present
invention is not limited to this arrangement, and the present invention
can be configured such that a concave part 3a is formed at the outer
surface of the resistive cylindrical device 3 as shown in FIG. 13, for
example, and the concave part 3a and the projection 14 of the cylindrical
holder 12 are fitted to each other. In this case, it is satisfactory that
the HV shield 4 and the cylindrical holder 12 are welded in advance. In
addition, the HV shield 4 and the HV spring 5 may not be welded but fitted
to each other to fix from each other. In addition, in the present
invention, the number of projections 14 formed at the cylindrical holder
12 is not limited to that described in the aforesaid preferred embodiment,
but any optional number of a plurality of projections can be selected.
In addition, in the preferred embodiment described above, although only the
first grid G.sub.1, the second grid G.sub.2 and the third grid G3.sub.A
are fixed by the beading glass 7, the present invention is not limited to
this arrangement and it is possible to extend the beading glass 7, for
example, and to fix the HV shield 4 together with it. With such an
arrangement as above, it is possible to assemble the electron gun more
rigidly. In this case, the fixing with the beading glass is carried out at
the last stage of the assembling operation of the electron gun.
In addition, the present invention is not limited to the aforesaid
preferred embodiment, but it may be changed into various modifications.
For example, in the present invention, the aforesaid resistive layer 11 is
not necessarily required. In addition, the first electrode, the third
electrode and the second electrode arranged within the resistive
cylindrical device 3 acting as the resistive member are not limited to the
third grid G.sub.3, the fourth grid G.sub.4 and the fifth grid G.sub.5,
but they may be of other grids.
Then, the electron gun of the cathode ray tube of the present invention
will be described in detail in reference to the preferred embodiments
shown in the drawings as follows. The gap ratio between the electrodes is
similar to that described in the aforesaid preferred embodiment.
In FIG. 14 is illustrated an entire configuration of the first preferred
embodiment. The electron gun of the preferred embodiment of the present
invention is of a uni-potential type. As shown in this figure, in the
preferred embodiment, a cathode K for radiating electrons is arranged near
a stem 2 of a neck tube 1, and then the first grid G.sub.1, the second
grid G.sub.2 and a cup member G3.sub.A forming the third grid G.sub.3 are
arranged coaxially near the cathode K. Then, a resistive cylindrical
device 3A to be described later for use in forming a main lens is arranged
at a position adjacent to the cup member G3.sub.A. In addition, the HV
shield 4 and the HV spring 5 are fixed at the upper end of this resistive
cylindrical device 3A. A plurality of stem pins 6 are buried in the stem
2.
The resistive cylindrical device 3A is made of conductive substance formed
by mixing oxidized materials such as Ti, W, Cu in alumina (Al.sub.2
O.sub.3), for example, and baking them or made of ferrite, titania
ceramics and the like and its major substance is insulating material
having a high anti-voltage characteristics.
This resistive cylindrical device 3A is formed into a cylindrical shape
having a high degree of true circle (for example, 20 .mu.m or less) and
ring-like electrodes 8, 9 and 10 made of RuO.sub.2 -glass paste, for
example, are coated on and formed at its both ends and the inner surface
of the central part. In this case, the electrode 8 forms the third grid
G.sub.3 together with the cup member G3.sub.A, and each of the electrodes
9, 10 may act as the fourth grid G.sub.4 and the fifth grid G.sub.5. A
high voltage of about 30K to 32 KV is applied to the third grid G.sub.3
(the first electrode) and the fifth grid G.sub.5 (second electrode) and a
middle voltage of about 7K to 10 KV is applied to the fourth grid G.sub.4
(the third electrode).
Conductive layers 11A made of the same material as that of the electrodes 8
to 10 are formed among the electrodes 8, 9 and 10. In this case, the
electrodes 8 to 10 and the conductive layer 11A are formed in a
longitudinal direction of the resistive cylindrical device 3, i.e. a
direction perpendicular to a Z-axis.
It is preferable that a resistance value of the resistive cylindrical
device 3A is set to be 100 M.OMEGA. to 10 T.OMEGA. between each of the
electrodes 8, 9 and each of the electrodes 9, 10 and more preferably it is
about 1 G.OMEGA. under an assumption that the diameter of the resistive
cylindrical device 3A and a space between the electrodes 8, 9 and between
the electrodes 9, 10 are set to be about 12 mm, respectively. If the
resistance is smaller than this value, it may easily generate heat and in
turn if the resistance is larger than this value, it may easily produce a
charged state. In the case that such a resistance value is set to be 1
G.OMEGA., a volumetric resistivity of the resistive cylindrical device 3A
becomes 10.sup.8 .OMEGA..multidot.cm.
In addition, a conductive layer 17 extending in a longitudinal direction is
formed at one outer surface of the resistive cylindrical device 3A.
Cylindrical holders 12 (12a, 12b) for use in electrically connecting the
electrodes 8, 10 are fixed to both ends of the resistive cylindrical
device 3A. The cylindrical holders 12 are made of metal such as stainless
steel, for example, and as shown in FIGS. 2A to 2D, the holder has a
ring-shaped flange part 13 fitted to the resistive cylindrical device 3.
Opposing pairs of projections 14 are arranged at three locations at the
inner circumference of this flange 13, and the inside projections of these
projections 14 are contacted with the electrodes 10, 12 formed at the
inner surface of the resistive cylindrical device 3. The cylindrical
holder 12a and the cylindrical holder 12b are electrically connected
through the conductive layer 17 formed at the outer surface of the
resistive cylindrical device 3.
As shown in FIG. 14, a G.sub.4 pin 15 is arranged at a substantial central
part of the resistive cylindrical device 3. It is preferable that this
G.sub.4 pin 15 is made of cobalt (Co) iron or Ti alloy having a
coefficient of expansion which is approximately equal to a coefficient of
expansion of the resistive cylindrical device 3. Then, this G.sub.4 pin 15
is fixed to be contacted with the electrode 9 through the hole 16 formed
in the resistive cylindrical device 3. A lead line 26 is connected to the
G.sub.4 pin 15. This lead line 26, although not shown, is connected with
and fixed to the stem pin 6.
As shown in FIG. 3, the HV shield 4 is a flat plate-like member made of
SUS304, for example, and there is provided a hole 8 at its central part
for use in transmitting electron beams therethrough. As shown in FIG. 1,
this HV shield 4 is fixed to the cylindrical holder 12a by welding.
The HV spring 5 is made of Inconell, for example. As shown in FIG. 1, the
HV spring 5 is fixed to both ends of the HV shield 4 by welding and its
extremity end presses the inner surface of the neck tube 1. This KV spring
S is electrically connected to an anode button (not shown) through a
conductive layer made of carbon and the like.
In this preferred embodiment, as shown in FIG. 18A, a conductive layer 11A
is arranged between the third grid G.sub.3 (the first electrode) and the
fourth grid G.sub.4 (the third electrode) formed by the electrode 9 and a
potential gradient between the grids becomes one as shown in FIG. 18B. A
gap X between the electrode 8 and the electrode 9 is about 10 to 20 mm in
the preferred embodiment. Although the gap between the electrode 9 and the
electrode 10 shown in FIG. 14 is not specifically restricted, but in the
case that the gap X is defined as 1, it is 1 or more, preferably 1 to 3
and more preferably 1 to 2. Under such a setting as above, it is confirmed
that a coefficient of spherical aberration can be made further small.
In the preferred embodiment, the conductive layer 11A is arranged near the
electrode 9 constituting the third electrode, a ratio of a:b:c indicating
a positional relation of the arrangement of the conductive layer 11A is
preferably 1 to 2:2 to 4:8 to 10.
The arranging position of the conductive layer 11A is not limited to the
preferred embodiment shown in FIG. 4, but the conductive layer 11A can be
arranged near the electrode 8 which is applied a high voltage as shown in
FIG. 19A and further a plurality of conductive layers 11B can be arranged
as shown in FIG. 19C. It is also possible to make an optional changing of
a potential gradient as shown in FIGS. 19B and 19(D) by changing the
arranging position and the number of arrangement of the conductive layers
11A, 11B, respectively.
In the preferred embodiment shown in FIG. 14, although the conductive layer
11A is also arranged between the electrode 9 acting as the third electrode
and the electrode 10 acting as the high voltage electrode, the arranging
position and the number of arrangement of the conductive layer 11A are not
restricted in particular. In addition, in the present invention, one of
the conductive layers 11A of the conductive layer 11A between the
electrode 8 and the electrode 9 and the conductive layer 11A between the
electrode 9 and the electrode 10 may not be necessarily arranged.
In the electron gun of the cathode ray tube in the preferred embodiment of
the present invention, since the outer circumferences of the electrodes 8,
9 and 10 are arranged on the resistive cylindrical device 3A, there is no
possibility that the electron beams are leaked out of a space between the
electrodes and charged up at the beading glass. In addition, since the
electron lens configuration part is formed by the resistive cylindrical
device 3A, a displacement of a degree of concentricity in the electron
lens system is scarcely produced.
In addition, in the present invention, the ring-shaped electrode films 8, 9
and 10 formed at the a inner circumference of the resistive cylindrical
device 3A can make an optional setting of these gaps. Further, the
conductive layer 11A is arranged among the ring-shaped electrodes 8, 9 and
10 to enable potential gradient between these electrodes to be optionally
changed and then only the coefficient of spherical aberration Cs can be
reduced without changing an amplification rate M.
The coefficient of spherical aberration Cs may substantially influence over
the spot diameter of the cathode ray tube. Accordingly, in the preferred
embodiment of the present invention, the conductive layer 11A is arranged
among the ring-shaped electrodes 8, 9 and 10 to cause a potential gradient
among these electrodes to be optionally changed and further it becomes
apparent from FIG. 17 that the coefficient of spherical aberration Cs can
be reduced. As a result, the spot diameter is reduced and a resolution can
be improved.
FIG. 15 shows an example in which a plurality of conductive layers 11A are
arranged among the electrodes 8 to 10.
For example, as shown in FIG. 16B, in the case that the electrode 8 is
arranged at the location of Z=0 mm and the conductive layer 11A is
arranged at Z=100 mm, a value of disturbance in the aforesaid resistance
among the electrodes 8 to 10 and the conductive layer 11A becomes low in
the case that the conductive layer 11A is arranged (R.sub.1 >R.sub.2,
R.sub.4 >R.sub.5). In the case that the conductive layer 11A is also
arranged at the location of Z=50 mm, as shown in FIG. 16C, the value of
disturbance in the aforesaid resistance becomes low (R.sub.2 >R.sub.3,
R.sub.5 >R.sub.6 =0).
Referring now to FIGS. 7 and 2D, the method for manufacturing the electron
gun of the preferred embodiment shown in FIG. 14 will be described.
At first, the hole 16 for fixing the G.sub.4 pin 15 is formed at the
resistive cylindrical device 3A (the step (1) in FIG. 7 and FIG. 20A), the
resistive cylindrical device 3A is cleaned and dried (the step (2) in FIG.
7).
Then, the electrodes 8 to 10 and the conductive layer 11A are coated and
formed at the inner surface of the resistive cylindrical device 3A (the
step (3) in FIG. 7 and FIG. 20B). In this case, as the conductive paste,
RuO.sub.2 -glass paste (a product name #9516 manufactured by Dupont and
the like), for example, is applied and coated to have a uniform film
thickness.
FIG. 21 shows the first example of the method for forming the electrodes 8
to 10 and the conductive layer 11A.
FIG. 21A shows a method for coating the conductive paste, wherein a
rotatable rubber roller 68 having an approximate same height as that of
the resistive cylindrical device 3A is installed within the resistive
cylindrical device 3A, and the rubber roller 68 is pushed against the
inner surface of the resistive cylindrical device 3A by a pair of springs
69. In this case, after a specified amount of conductive paste 70 is
placed in a longitudinal direction of the rubber roller 68 as shown in
FIG. 21B, it is set as shown in FIG. 21A and the resistive cylindrical
device 3A is rotated around a rotating axis O.sub.1. With such an
arrangement as above, the rubber roller 68 is also rotated around the
rotating axis O.sub.2 and the conductive paste 70 is widely coated over
the front inner surface of the resistive cylindrical device 3A. After this
operation, the rubber roller 68 is pulled out of the resistive cylindrical
device 3A and it is heated with hot air, for example, while the resistive
cylindrical device 3A is being rotated and then dried. This operation is
carried out for preventing the conductive paste 70 from being dripped.
FIG. 21C shows a trimming method for the conductive paste 70. As shown in
this figure, a marking-off disk 72 made of ultra-hard alloy is
eccentrically attached to the extremity end of the supporting rod 71 and
in turn this supporting rod 71 is pulled by the spring 73 in a direction
crossing at a right angle with a longitudinal direction. Then, during the
trimming step, the resistive cylindrical device 3A is rotated in a
direction of an arrow (a) and the supporting rod 71 is arranged within the
resistive cylindrical device 3A. When the supporting rod 71 is caused to
be moved in either a direction (b) or a direction (c) and come to a
position where the conductive paste 70 is not required, the spring 73 is
operated to push the marking-off disk 72 against the conductive paste 70
so as to perform the trimming operation. In turn, as for the location
where the conductive paste 70 is required, the spring 73 is released to
cause the conductive paste 70 to be left. In addition, it may also be
applicable that the conductive paste 70 is evaporated with heat generated
after absorbing a laser beam so as to remove the paste.
FIG. 22 shows the second example of the method for forming the conductive
layers 8 to 10 and the conductive layer 11A. This method is carried out
with an exposing method using a negative type resist material (for
example, PVA-ADC and the like).
In the case that this method is carried out, at first, as shown in FIG.
22A, the resist material 80 is coated at the inner surface of the
resistive cylindrical device 3A while the tube is being rotated. Then, as
shown in FIG. 22B, a mask 81 is inserted into the resistive cylindrical
device 3A and its position is aligned with that of the tube. This mask 81
is fabricated such that patterns 82 having the same patterns as those of
the electrodes 8 to 10 and the conductive layer 11A are formed at an outer
circumference of ultraviolet ray transmittance glass (for example, quartz)
having an outer diameter equal to the inner diameter of the resistive
cylindrical device 3A.
Then, as shown in FIG. 22C, the ultraviolet ray radiating lamp 83 is
installed inside the mask 81 and an exposing operation is performed. Then,
the mask 81 is removed from the resistive cylindrical device 3A, water is
blown against it to perform a developing operation, resulting in that the
electrode pattern of the resist 84 as shown in FIG. 23A is formed.
Then, as shown in FIG. 22D, the resistive cylindrical device 3A is arranged
within a vacuum pump 85, a wire 86 made of metals such as Al, Au or the
like is heated by a heater 87 and a metallic film 88 is vapor deposited at
the inner surface of the resistive cylindrical device 3A (FIG. 23B). In
addition, a reversing development with H.sub.2 O.sub.2 and a baking
(430.degree. C., 30 minutes) are carried out and the electrodes 8 to 10
and the conductive layer 11A are formed as shown in FIG. 23C.
FIG. 24 shows the third example of the method (a metal mask vapor
depositing method) for forming the electrodes 8 to 10 and the conductive
layer 11A. In this method, a metallic ring-like mask 110 is inserted in
such a way that the mask is closely contacted with the inner surface of
the resistive cylindrical device 3A, and this resistive cylindrical device
3A is arranged within a container 89 connected to a vacuum pump. Then, an
inner area of the container 89 is changed into a vacuum state and at the
same time the aforesaid vapor depositing metal 90 is heated by a heater
89a so as to vapor deposit the metal against the inner surface of the
resistive cylindrical device 3A.
FIG. 25 shows the fourth example of the method for forming the electrodes 8
to 10 and the conductive layer 11A (a heat transfer method).
In this method, at first, a heat transfer base film 91 made of polyester is
formed into a cylindrical shape (FIG. 25A). Each of a peeling-off layer
(not shown), a conductive layer 92 and an adhering layer (not shown) is
coated and formed in sequence on the base film 91 so as to complete the
heat transfer sheet 93 (FIG. 25B). Then, as shown in FIG. 25C, a position
of the heat transfer sheet 93 is set and the sheet is inserted into the
resistive cylindrical device 3A. Then, the heat transfer sheet 93 is
closely contacted with the inner surface of the resistive cylindrical
device 3A, and both heating and pressurizing are carried out by a silicon
roller 94 having a heater stored therein (FIG. 25D). With such an
arrangement as above, the conductive layer 92 on the heat transfer sheet
93 is transferred to the inner surface of the resistive cylindrical device
3A so as to form the electrode layers 8 to 10 and the conductive layer
11A. After this operation, the base film 91 is peeled off and removed as
shown in FIG. 13E.
In addition, as shown in FIGS. 26A and 26B, concave portions 3a and 3b are
formed in advance at the inner surface of the resistive cylindrical device
3A, and the conductive paste 70 is fully coated by applying a rubber
roller 68 shown in FIG. 9 as described above, thereby it is also possible
to form the electrodes 8 to 10 having a predetermined pattern and to form
the conductive layer 11A.
FIG. 27 shows the sixth example of the method for forming the electrodes 8
to 10 and the conductive layer 11A. At first, as shown in FIG. 15A, this
example is operated such that the conductive paste 102 is placed at the
end part of the base 100 having a predetermined pattern 101, the roller
103 is rolled in a direction crossing at a right angle with the pattern
101, for example, thereby the conductive paste 102 is filled in the
concave part between the patterns 101.
Then, as shown in FIG. 27B, the same roller 104 as that used in the first
example (refer to FIG. 21A) is rolled in a direction crossing at a right
angle with the roller 103, thereby the conductive paste 102 is adhered to
the roller 104 as shown in FIG. 15C.
In addition, as shown in FIG. 21A, the roller 104 is pressed against the
inner surface of the resistive cylindrical device 3A in the same manner as
that of the first example and the resistive cylindrical device 3A is
rotated. With such an arrangement as above, the conductive paste 102 is
adhered to the inner surface of the resistive cylindrical device 3A and
the electrodes 8 to 10 and the conductive layer 11A are formed.
Additionally, it is also possible to | | |
