Cathode-ray tube having alternating electric field reduction device

In a cathode-ray tube, in order to readily and inexpensively reduce an alternating electric field irradiated by a deflection yoke to a front of the cathode-ray tube through a funnel part and a face panel, a conductive film for forming an electric field shield is formed from a neck part to a cone part of a glass bulb and is electrically connected to another conductive film formed on a funnel body part. The deflection yoke is mounted on the conductive film via an insulation sheet interposed therebetween. The conductive film is grounded to form an equipotential surface of 0 V in front of the deflection yoke. A transparent conductive film can be also formed on the external surface of the face panel to raise the reduction of the alternating electric field.

BACKGROUND OF THE INVENTION 
i) Field of the Invention 
The present invention relates to a cathode-ray tube having a reduction 
device of an alternating electric field emitted by a deflection yoke. 
ii) Description of the Related Arts 
In FIG. 1, there is shown a conventional cathode-ray tube. In this 
cathode-ray tube, a funnel part 1 is composed of a neck part 1a, a cone 
part 1b and a funnel body part 1c having a high voltage anode button 1d 
and is secured to a panel part 2 by using a frit seal. A neck seal line 1e 
is a coupling part for connecting the neck part 1a and the cone part 1b 
and is formed of glass somewhat thin in thickness, and thus is a weak part 
compared with other parts. As described above, the funnel part 1 and the 
panel part 2 constitute a glass bulb 20. An electron gun 3 is mounted and 
sealed within the neck part 1a. An implosion-protection band 4 for 
ensuring an implosion-proof property is wound around the side surfaces of 
the panel part 2, and four latch members 4a, for suspending the glass bulb 
20 within a box frame (not shown), are integrally formed at the four 
corner portions of the band 4. A silicon resin film 5 for insulation is 
formed around the high voltage anode button 1d provided on the funnel body 
part 1c, and a conductive film 6 for adding a capacitance to the 
cathode-ray tube is formed on an external surface of the funnel body part 
1c. This conductive film 6 is usually formed by applying graphite. A 
numeral 28 denotes a tube axial of a straight line parallel with the neck 
part 1a. 
As shown in FIG. 2, a deflection yoke 7 for deflecting the electron beam is 
mounted on the above-described cathode-ray tube between the cone part 1b 
and the neck part 1a. As shown in FIG. 3, the deflection yoke 7 is 
composed of a horizontal deflection coil 7a, a vertical deflection coil 7b 
and a deflection yoke body part 7c. 
The operation of the above-described cathode-ray tube will be described. 
That is, when the electron beam is irradiated by the electron gun 3 sealed 
within the neck part 1a, and the irradiated electron beam is deflected a 
predetermined amount in the horizontal and vertical directions by the 
horizontal deflection coil 7a and the vertical deflection coil 7b of the 
deflection yoke 7 to scan on a fluorescent film formed on the internal 
surface of the panel part 2. As a result, a desired image is projected on 
the panel part 2. At this time, the deflection width is in inverse 
proportion to a square root of a voltage applied to the high voltage anode 
button 1d. 
In the conventional cathode-ray tube described above, no measures for 
shielding an alternating electric field radially generated around the 
deflection yoke during the deflection of the electron beam by the 
deflection yoke are provided. Thus the alternating electric field harmful 
to the human body permeates the funnel part 1 and the panel part 2 of the 
cathode-ray tube to irradiate forwards from the cathode-ray tube. 
For reducing an influence on a radiation line of the electron beam due to a 
leakage magnetic field from a flyback transformer and the like, for 
example, as disclosed in Japanese Patent Laid-Open No. Sho 61-138433, a 
covering member for annularly covering a focusing electrode system 
constituting an electron gun by using a non-magnetic conductive magnetic 
shield body has been proposed. However, this covering member does not pay 
any consideration to the alternating electric field and can not reduce the 
alternating electric field as before. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a cathode-ray 
tube in view of the problems of the prior art, which is capable of 
reducing an alternating electric field irradiated from a deflection yoke 
to the front of the cathode-ray tube. 
According to the present invention, the object is achieved by providing 
alternating electric field reduction means for reducing an alternating 
electric field irradiated from a deflection yoke to a front surface of a 
face panel through a funnel part in a predetermined area extending from a 
cone part where the deflection yoke is set to a neck part of the funnel 
part in the cathode-ray tube. 
More specifically, a grounded conductive film is formed on the 
predetermined area of a surface of the funnel part, and an insulator is 
formed on a surface of the conductive film for electrically isolating the 
deflection yoke from the conductive film. 
In the construction described above, an equipotential surface of 0 V, i.e., 
an electric field shielding surface of plane is formed on an internal 
surface of an opening part of the deflection yoke, and thus the 
alternating electric field irradiated to the front surface of the face 
panel through the funnel part and the face panel can be reduced. 
Further, a grounded transparent conductive film is formed on the external 
surface of the face panel to form an electric field shielding plane on the 
surface of the face panel, and thus the alternating electric field 
irradiated from the deflection yoke to the front surface of the face panel 
through the funnel part and the face panel can be further reduced. 
Furthermore, a grounded conductive film is formed on an external surface of 
the cone part from a first area having a larger diameter than an open 
diameter of a horizontal deflection coil of the deflection yoke to a 
second area apart frontwards from a connection between the neck part and 
the cone part. Hence, a shield plane for sufficiently shielding the 
alternating electric field irradiated from the front part of the 
deflection yoke can be formed, and the neck seal line part having a thin 
glass thickness and thus a weak strength is kept to be a large electric 
resistance. Thus, it can be prevented to concentrate the electric field to 
the local low resistance position to maintain the reliability of the 
cathode-ray tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described in connection with its 
preferred embodiments with reference to the attached drawings, wherein 
like reference characters designate like or corresponding parts throughout 
the views and thus the repeated description thereof can be omitted for 
brevity. 
In FIGS. 4 to 6, there is shown the first embodiment of a cathode-ray tube 
according to the present invention, wherein the same numerals as those of 
the conventional cathode-ray tube shown in FIGS. 1 to 3 designate the same 
or corresponding parts. In this embodiment, a conductive film 8 for 
shielding an electric field is formed by applying graphite from the end of 
cone part 1b to the end of neck part 1a of a funnel part 1 so as to 
electrically contact with a conductive film 6. A conical insulation sheet 
9 is provided on the neck part 1a and extends to the cone part 1b of the 
funnel part 1 in order to electrically isolate the conductive film 8 and a 
coil part of a deflection yoke 7. The conical insulation sheet 9 as shown 
in FIG. 5 is attached to the cone part 1b and the neck part 1a of the 
funnel part 1. On a glass bulb 20 constructed as described above, as shown 
in FIG. 6, the deflection yoke 7 is mounted on the insulation sheet 9. 
Next, the operation of the cathode-ray tube described above will now be 
described in detail. By electrically grounding the conductive film 8, the 
conductive film 8 becomes an equipotential surface of 0 V. Since the 
conductive film 6 electrically conducts to the conductive film 8, a 
surface or plane having an electric field shielding effect is formed in 
the open front area of the deflection yoke 7 so as to reduce the 
alternating electric field irradiated from the deflection yoke 7 to the 
front surface of a face panel through the funnel part 1. Further, since 
the insulation sheet 9 is interposed between the coil part of the 
deflection yoke 7 and the conductive film 8, the coil part of the 
deflection yoke 7 is electrically isolated from the conductive film 8 and 
a problem such as a discharge or the like can not happen. 
In this embodiment, as described above, the conductive film 8 for shielding 
the electric field is formed from the neck part 1a to the end of the cone 
part 1b of the funnel part 1 of the glass bulb 20 so as to electrically 
connect with the conductive film 6, and the deflection yoke 7 is arranged 
on the conductive film 8 through the insulation sheet 9. The conductive 
film 8 is grounded in order to form the equipotential surface of 0 V in 
front of the deflection yoke 7. Hence, due to this equipotential surface, 
the alternating electric field irradiated by the deflection yoke 7 and 
permeating the funnel part can be reduced by approximately 40% as compared 
with the conventional cathode-ray tube. 
In FIG. 7, there is shown the second embodiment of a cathode-ray tube 
according to the present invention, having the same construction as the 
first embodiment shown in FIGS. 4 to 6, except that a conductive material 
is formed inside the funnel part 1. That is, a conductive material 8a such 
as aluminum foil for shielding the electric field is embedded within the 
funnel part 1 so as to cover the open front surface of the deflection yoke 
7. A metallic conducting button 10 is provided on the external surface of 
the funnel part 1 so as to contact with the conductive film 8a but so as 
not to contact with the coil of the deflection yoke 7. 
Next, the operation of the above-described cathode-ray tube will now be 
described in detail. By electrically grounding the conducting button 10, 
the conductive film 8a becomes an equipotential surface of 0 V, and a 
shield plane having an electric field shielding effect is formed in front 
of the opening part of the deflection yoke 7. Hence, the alternating 
electric field irradiated by the deflection yoke 7 and permeating the 
funnel part can be reduced by approximately 40% as compared with the 
conventional cathode-ray tube. Further, since the conductive film 8a is 
embedded in the glass constituting the funnel part 1 in a sandwich-like 
form the conductive film 8a is electrically isolated from the external 
part, and no problem such as a discharge between the conductive film 8a 
and the deflection yoke 7 or the like can occur. Thus, in this embodiment, 
an insulation member for insulating the conductive film 8a from the 
deflection yoke 7 is not required. 
In FIGS. 8 to 10, there is shown the third embodiment of a cathode-ray tube 
according to the present invention, having the same construction as the 
first embodiment shown in FIGS. 4 to 6, except that a conical insulation 
member 11 having a conductive film 11a formed on its internal surface is 
interposed between the funnel part 1 and the deflection yoke 7 from the 
cone part 1b to the neck part 1a of the funnel part 1 so as to cover the 
internal open part of the deflection yoke 7. As example of the conductive 
film, the graphite is applied on the internal surface of the conical 
insulation member 11. 
Next, the operation of the above-described cathode-ray tube will now be 
described in detail. By electrically grounding the conductive film 11a 
formed on the internal surface of the conical insulation member 11, the 
conductive film 11a becomes an equipotential surface of 0 V, and a shield 
plane having an electric field shielding effect is formed in front of the 
opening part of the deflection yoke 7. Thus, the alternating electric 
field irradiated by the deflection yoke 7 and permeating the funnel part 
can be reduced by approximately 40% as compared with the conventional 
cathode-ray tube. Further, since the conductive film 11a is electrically 
isolated from the coil part of the deflection yoke 7, and thus the problem 
such as a discharge between the conductive film 11a and the deflection 
yoke 7 or the like can not be caused. In this embodiment, although the 
graphite as the conductive material is applied on the internal surface of 
the conical insulation member 11, a conductive metal such as aluminum or 
the like can be also applied onto the internal surface of the conical 
insulation member 11 by vapor deposition or the like with the same results 
and effects. In this case, as described above, by mounting the insulation 
member having the internal conductive film or the like, the alternating 
electric field can be effectively reduced without applying a particular 
processing to the glass bulb 20 and the deflection yoke 7. 
In FIG. 11, there is shown a deflection yoke 7 of the fourth embodiment of 
a cathode-ray tube according to the present invention. In this embodiment, 
as shown in FIG. 11, a conductive film 13 is formed in front of the 
opening part of the deflection yoke 7 via an insulation film 12. That is, 
the deflection yoke 7 includes the insulation film 12 for covering the 
horizontal deflection coil 7a from the inside and the conductive film 13 
of graphite or the like is applied on the internal surface of the 
insulation film 12. Further, a conducting tape 14 is attached to the 
conductive film 13 and is extended outside the deflection yoke 7. In FIG. 
11, although the part of the horizontal deflection coil 7a is exposed for 
readily understanding the structure, actually, the insulation film 12 
covers the entire inner surface of the horizontal deflection coil 7a, and 
the conductive film 13 is applied onto the whole internal surface of the 
insulation film 12. 
Next, the operation of the above-described cathode-ray tube will now be 
described in detail. By electrically grounding the conductive film 13 
formed on the internal surface of the conical insulation film 12 by the 
conducting tape 14, the conductive film 13 becomes an equipotential 
surface of 0 V, and a shield plane having an electric field shielding 
effect is formed in front of the opening part of the deflection yoke 7. 
Hence, the alternating electric field irradiated by the deflection yoke 7 
and permeating the funnel part can be reduced by approximately 40% as 
compared with the conventional cathode-ray tube. Further, since the 
insulation film 12 is interposed between the horizontal deflection coil 7a 
and the conductive film 13, both can be electrically isolated from each 
other, and thus the problem such as a discharge between the conductive 
film 13 and the deflection yoke 7 or the like can not occur. 
In FIGS. 12 and 13, there is shown a deflection yoke 7 of the fifth 
embodiment of a cathode-ray tube according to the present invention. In 
this embodiment, a conical insulation member 15 having a conductive film 
16 of graphite or the like applied onto the internal surface thereof, as 
shown in FIG. 13 is mounted in front of the opening part of the deflection 
yoke 7, as shown in FIG. 12. Further, a conducting tape 14 is attached to 
the conductive film 16 and is extended outside the deflection yoke 7. 
Next, the operation of the above-described cathode-ray tube will now be 
described in detail. By electrically grounding the conductive film 16 
formed on the internal surface of the conical insulation member 15 by the 
conducting tape 14, the conductive film 16 becomes an equipotential 
surface of 0 V, and a shield plane having an electric field shielding 
effect is formed in front of the opening part of the deflection yoke 7. 
Hence, the alternating electric field irradiated by the deflection yoke 7 
and permeating the funnel part can be reduced by approximately 40% as 
compared with the conventional cathode-ray tube. In this instance, the 
deflection yoke 7 and the insulation member 15 can be separately produced, 
and the latter can be readily mounted to the former. Further, since the 
insulation member 15 is interposed between the horizontal deflection coil 
7a and the conductive film 16, both the members can be electrically 
isolated from each other, and thus the problem such as a discharge between 
the conductive film 13 and the deflection yoke 7 or the like can not 
occur. 
In FIGS. 14 to 16, there is shown the sixth embodiment of a cathode-ray 
tube according to the present invention, having the same construction as 
the first embodiment shown in FIGS. 4 to 6, except that a conductive film 
17 for shielding the electric field is formed in a predetermined portion 
of the cone part 1b of the funnel part 1 by applying the graphite separate 
from the neck part 1a and the neck seal line le. More specifically, in the 
cone part 1b, the conductive film 17 is formed in the area surrounded by a 
first circular circumference having a diameter at least larger than the 
maximum diameter 7d of the horizontal deflection coil 7a of the deflection 
yoke 7 and a second circular circumference at a position shifted at least 
10 mm from the neck seal line 1e toward the panel part 2 in the direction 
of the tube axial 28 on the external surface of the funnel part 1. Also, 
the conductive film 17 is connected to the conductive film 6 by a 
conducting tape 18 to ground it. A conical insulation member 19 to be 
mounted on the conductive film 17 is designed so as to entirely cover the 
conductive film 17, as shown in FIG. 15. Further, as shown in FIG. 16, the 
conical insulation member 19 is interposed between the conductive film 17 
and the coil of the deflection yoke 7 fixed on the funnel part 1. The 
maximum diameter 7d of the horizontal deflection coil 7a of the deflection 
yoke 7 in FIG. 14 indicates the maximum diameter of the horizontal 
deflection coil 7a cut in section taken along the X-Y plane in FIG. 3, and 
hence, when the X-Y section is an ellipse, the maximum diameter 7d 
indicates the long diameter of the ellipse. 
Next, the operation of the above-described cathode-ray tube will now be 
described in detail. By electrically grounding the conductive film 17 by 
the conducting tape 18 conducting to the conductive film 6, the conductive 
film 17 becomes an equipotential surface of 0 V, and a shield plane having 
an electric field shielding effect is formed in front of the opening part 
of the deflection yoke 7. Hence, the alternating electric field irradiated 
by the deflection yoke and permeating the funnel part can be reduced by 
approximately 40% as compared with the conventional cathode-ray tube. 
Further, since the front end of the conductive film 17, i.e., the panel 
side end of the same is the larger circular circumference than the maximum 
diameter 7d of the horizontal deflection coil of the deflection yoke 7, 
the shield plane for sufficiently shielding the alternating electric field 
irradiated from the front side of the deflection yoke 7 can be formed. 
Also, since the conductive film 17 is formed to the position shifted at 
least 10 mm from the neck seal line 1e in the panel side direction, the 
neck seal line part having a thin glass thickness and thus a weak strength 
is kept to be a large electric resistance. Thus, it is prevented to 
concentrate the electric field to the local low resistance position to 
maintain the reliability of the cathode-ray tube. Further, since the 
insulation member 19 is interposed between the coil part of the deflection 
coil 7 and the conductive film 17, both the members can be electrically 
isolated from each other, and thus the problem such as a discharge between 
the conductive film 18 and the deflection yoke 7 or the like can not 
occur. 
In FIG. 17, there is shown the seventh embodiment of a cathode-ray tube 
according to the present invention, having the same construction as the 
sixth embodiment shown in FIGS. 14 to 18, except that a transparent 
conductive film 21 is further formed on the external surface of the panel 
part 2 and is coupled to the conductive film 6 by a conducting tape 19 to 
ground it so that the alternating electric field permeating the panel part 
2 is effectively reduced. 
Next, the operation of the above-described cathode-ray tube will now be 
described in detail. In addition to the operation of the sixth embodiment 
described above, by electrically grounding the transparent conductive film 
21 formed on the external surface of the panel part 2 by the conducting 
tape 19 conducting to the conductive film 6, the transparent conductive 
film 21 becomes an equipotential surface of 0 V, and a shield plane having 
an electric field shielding effect is formed on the front surface of the 
panel part 2 to raise the reduction effect of the alternating electric 
field. Hence, the alternating electric field irradiated by the deflection 
yoke 7 can be more effectively reduced by approximately 70 to 80% as 
compared with the conventional cathode-ray tube. 
In FIG. 18, there is shown the eighth embodiment of a cathode-ray tube 
according to the present invention, having the same construction as the 
first embodiment shown in FIGS. 4 to 6, except that an insulation sheet 22 
having a heat contraction property is used. In this embodiment, as shown 
in FIG. 18, the insulation sheet 22 having a heat contraction property is 
mounted on the funnel part 1 so as to extend over the cone part 1b and the 
neck part 1a, and then a heat treatment of the insulation sheet 22 is 
carried out by using, for example, a dryer or the like to readily and 
exactly perform a close contact with the funnel part 1. As a result, the 
reliability of the electric insulation property can be raised. In this 
case, the same effects and advantages as those of the first embodiment can 
be obtained. 
According to the present invention, it is apparent that a transparent 
conductive film 21 can be further formed on the external surface of the 
panel part 2 and be grounded to expect the same effect resulted in the 
seventh embodiment in the first to sixth and eighth embodiments. 
As described above, in the cathode-ray tube according to the present 
invention, an alternating electric field reduction means for reducing the 
alternating electric field irradiated from the deflection yoke to the 
front surface of the face panel through the funnel part is provided in a 
predetermined area extending from the cone part to the neck part where the 
deflection yoke is mounted, and the equipotential surface or the electric 
field shielding plane is formed in the internal circular circumference of 
the opening part of the deflection yoke. As a result, the alternating 
electric field irradiated from the deflection yoke to the front surface of 
the face panel through the funnel part and the face panel can be reduced 
to provide a cathode-ray tube having high safety. 
According to the present invention, the transparent conductive film to be 
grounded can be further provided on the external surface of the face 
panel, and thus the electric field shielding plane is also formed on the 
front surface of the face panel. As a result, the alternating electric 
field permeating the face panel can be further reduced. 
Furthermore, since the alternating electric field reduction means is 
separated at least a certain distance from the neck seal line of the 
funnel part in the panel side direction, the neck seal line part having a 
thin glass thickness and thus a weak strength is kept to be a large 
electric resistance, and thus it is prevented to concentrate the electric 
field to the local low resistance position to maintain the reliability of 
the cathode-ray tube. 
Although the present invention has been described in its preferred 
embodiments with reference to the accompanying drawings, it it readily 
understood that the present invention is not restricted to the preferred 
embodiments and that various changes and modifications can be made by 
those skilled in the art without departing from the spirit and scope of 
the present invention.