JPH05217522A - Cathode-ray tube - Google Patents

Abstract

PURPOSE:To suppress unwanted radiation with VLF electric field from the front surface of a CRT display, with the simple structure. CONSTITUTION:An electric conductive coated part 10 is formed so as to surround the neck part 6 of a cathode ray tube and is grounded. Further, insulating coating 11 is applied on the electric conductive coated part 10. Since the unwanted radiation 9 with VLF electric field irradiated from the horizontal deflecting coil 8 of a deflecting yoke 12 installed along the outer periphery of the neck part 6 is effectively absorbed by the electric ally conductive coated part 10, the radiation quantity from the front surface part 2 of a display is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode ray tube or CRT for displaying an image. More specifically, it relates to a structure for preventing unwanted radiation in the VLF range from the CRT surface.

[0002]

2. Description of the Related Art In order to facilitate understanding of the present invention, a general structure of a CRT will first be briefly described with reference to FIG.
The CRT is composed of a glass tube 1 whose interior is held in vacuum. A resistance material film 3 is applied to the inside of the front portion 2 that constitutes the image surface. An electron gun 4 is housed in the rear end portion of the glass tube 1 and emits an electron beam 5 toward the resistance material film 3. Further, a vertical deflection coil 7 is housed inside the neck portion 6 of the glass tube 1.
The electron beam 5 is scanned along the direction perpendicular to the image plane.
A horizontal deflection coil 8 is arranged along the outer circumference of the neck portion 6 and scans the electron beam 5 along the horizontal direction of the image plane. A magnetic field is generated by driving the vertical deflection coil 7 and the horizontal deflection coil 8, and the electron beam 5 is deflected in the vertical direction and the horizontal direction by electromagnetic action. A two-dimensional image can be displayed by performing a so-called raster scan.

Generally, one screen of a television is composed of 525 scanning lines. 525 scanning lines are sequentially formed horizontally from top to bottom to form one frame. To prevent flickering of images on the TV and to display fast moving images, 1
The number of frames included in a second is 30, for example. In this way, in order to repeatedly scan the electron beam 5 in the horizontal direction,
A drive voltage as shown in FIG. 3 is applied to the horizontal deflection coil 8. This drive voltage contains a high voltage pulse or flyback pulse synchronized with the repeated horizontal scanning frequency f. The peak value is about 800 to 1200 Vpp, and the frequency is 30 to 100 kHz.

[0004]

2 and 3 will be continued.
The problem to be solved by the present invention will be described with reference to FIG.
When a high voltage flyback pulse is periodically applied to the horizontal deflection coil 8 arranged around the neck portion 6, unnecessary electric field radiation 9 is radiated toward the front portion 2 as indicated by an arrow. The frequency of the unnecessary electric field radiation 9 is synchronized with the horizontal scanning frequency and is included in the VLF frequency band.

Since this VLF electric field unnecessary radiation is radiated from the front of the CRT, it is difficult to shield it, which is a problem in terms of safety measures. Some countries have safety standards in place to regulate VLF unwanted electric field radiation. For example,
According to the Swedish safety standard MPRII, VLF electric field radiation must be less than 2.5 V / m within 50 cm of the circumference of the CRT display body. As mentioned above, satisfying this standard is a CRT.
It was difficult because the VLF radiation from the surface was large. Conventionally,
The most effective measure against radiation was to apply conductive coating to the entire face plate of the CRT. However, if this measure is taken, the manufacturing cost will rise and most practical CRTs will
Not suitable for display.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems and problems of the conventional technique, the present invention has a simple structure and is suitable for VLFs.
An object of the present invention is to provide a CRT display capable of effectively suppressing unnecessary electric field radiation. In order to achieve this object, a means of providing an electrically conductive coating portion so as to surround the neck portion of the cathode ray tube or the CRT and applying an insulating coating thereon is taken. Also, preferably, the conductive coating portion is grounded.

[0007]

In the present invention, the conductive coating portion is provided along the outer circumference of the CRT neck portion. A deflection yoke is placed on top of it with an insulating coating. The VLF electric field unnecessary radiation emitted from the horizontal deflection coil of the deflection yoke is effectively absorbed by the conductive coating portion, so that the amount of radiation from the CRT surface can be suppressed. Since the conductive coating part is grounded, a reliable shield effect can be obtained. Further, since the insulating coating is interposed between the deflection yoke and the conductive coating portion, there is no possibility of arc discharge.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic view showing the structure of a cathode ray tube for a display according to the present invention. Since the internal structure is the same as the general structure shown in FIG. 2, it is partially omitted for clarity. A conductive coating portion 10 is provided along the outer circumference of the neck portion 6 of the glass tube 1. The conductive coating portion 10 can be formed by applying, for example, high resistance carbon (SIC) or low resistance carbon (GA37). The coating range of the conductive coating portion 10 covers the entire neck portion 6 and extends up to the rear inclined surface facing the front portion 2 of the glass tube 1. The conductive coating portion 10 is grounded.

An insulating coating 11 is applied on the conductive coating portion 10. This can be formed, for example, by adhering silicone rubber or the like.

A ring-shaped deflection yoke 12 is mounted along the outer circumference of the neck portion 6. The deflection yoke 12 includes the horizontal deflection coil 8. The deflection yoke 12 is electrically insulated from the conductive coating portion 10 through the insulating coating 11, and the horizontal deflection coil 8 is effectively shielded from the display front portion 2 by the conductive coating portion 10.

The operation of the illustrated cathode ray tube will be described with reference to FIG. In order to perform so-called raster scanning, a high voltage flyback pulse as shown in FIG. 3 is applied to the horizontal deflection coil 8. Unwanted electric field radiation 9 is emitted toward the display front part 2 by the induction action of the coil. Since this radiation 9 is synchronized with the horizontal scanning frequency, it belongs to the VLF band. In the present invention, the path of the unwanted radiation 9 toward the display front portion 2 is effectively blocked by the conductive coating portion 10 provided on the rear shoulder portion of the glass tube 1. In other words, the unwanted radiation 9 is absorbed by the conductive coating portion 10 and radiated via the ground. An insulating coating 11 is interposed between the conductive coating portion 10 and the deflection yoke 12.
Therefore, the horizontal deflection coil 8 of the deflection yoke 12 is
Even if a flyback pulse of about 1200 Vpp is applied, there is no fear of arc discharge.

In order to confirm the effect of the present invention, a CRT sample having a conductive coating on the neck and a CR having no conductive coating
V emitted from the front of the display for the T sample
The amount of LF electric field unwanted radiation was measured. The results are shown in Table 1.

[Table 1]

In measuring the VLF electric field unnecessary radiation, two types of 16-inch models were used as samples in order to eliminate factors other than conductive coating. Further, in order to determine whether or not the above-mentioned Swedish safety standard MPRII was satisfied, the VLF electric field radiation intensity was measured at a distance of 50 cm from the front of the display in accordance with the measurement conditions. As shown in the results of Table 1, in the 16-inch model 1, the radiant intensity was 2.20 V / m when the conductive coating was applied, and was 3.20 V / m when the conductive coating was not applied. Further, in the 16-inch model 2, the voltage was 1.33 V / m when the conductive coating was applied, while it was 3.61 V / m when the conductive coating was not applied. Clearly, the effect of conductive coating is showing. In addition, Swedish safety standard MPRII for ELF / VLF electric field radiation
It is sufficiently satisfied with 2.5 V / m.

[0014]

As described above, according to the present invention, C
A conductive coating is applied to the periphery of the RT neck portion, and further an insulating coating is applied to insulate the deflection yoke and the CRT body. Accordingly, there is an effect that VLF electric field radiation that occurs when a high voltage flyback pulse is applied to the horizontal deflection coil of the deflection yoke can be suppressed very effectively. In addition, compared to the conventional method of applying conductive coating on the front of the display, a simple structure in which conductive coating is simply applied around the neck has been adopted, so the cost required for measures can be kept low. effective.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a cathode ray tube according to the present invention.

FIG. 2 is a schematic sectional view showing a conventional cathode ray tube structure.

FIG. 3 is a waveform diagram of a flyback pulse applied to a horizontal deflection coil of a cathode ray tube.

[Explanation of symbols]

 1 Glass Tube 2 Display Front 6 Neck 8 Horizontal Deflection Coil 9 Unwanted Electric Field Radiation 10 Conductive Coating 11 Insulation Coating 12 Deflection Yoke

Claims (2)

[Claims] 1. A cathode ray tube characterized in that a conductor coating portion is provided so as to surround a neck portion of the cathode ray tube, and an insulating coating is applied thereon. 2. The cathode ray tube according to claim 1, wherein the conductive coating portion is grounded.