JPS6241375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing glass cracks in the neck portion of a cathode ray tube that occur during operation of a cathode ray tube apparatus.

FIG. 1 is a diagram showing the arrangement of accessory parts around a cathode ray tube of a conventional projection type cathode ray tube device using an electromagnetic focusing method. An electron gun 3 is sealed in a network tube 2 of a cathode ray tube 1. An internal conductive film 4 is coated on the inner wall of the neck tube 2, and a high voltage is applied from an anode button 6 embedded in a part of the funnel portion 5 and a high voltage lead wire 7. Further, an alignment magnet 8, a focusing coil 10 held by a holder 9, and a deflection coil 11 are attached to the outside of the neck tube 2. Inside the cathode ray tube 1, there is a phosphor 1 on the surface.
A concave mirror 14 having a hole in the center is arranged opposite to the target 13 coated with 2. In operation, a high voltage of 25 to 30 KV is applied to the anode, and the electrons emitted from the electron gun 3 are electromagnetically focused by the focusing coil 10, bent by the deflection coil 11, and applied to the target 13. The light that collides with the phosphor 12 and is converted into optical energy is reflected by the concave mirror 14 and radiated to the outside of the cathode ray tube. By the way, the conventional cathode ray tube device had a drawback in that glass cracks were generated in the network tube during use.The inventor of the present application analyzed the cause of this problem and discovered the following facts. In other words, the internal conductive film 4 has an anode voltage of 25
A high voltage of ~30KV is applied to the network tube 2.
The outer wall of the network tube 2 is positively charged due to the capacitance of the outer wall. The focusing coil 10 is generally housed in a metal case 15 and fixed to a holder 9, as shown in FIG. Holder 9 is grounded for safety reasons, so metal case 1
5 is at ground potential. Therefore, the network tube 2
The positive charges on the outer wall of the metal case 15 will be discharged along the surface toward the metal case 15 as indicated by the arrow in FIG. Also, the alignment magnet 8 has a tightening metal fitting 16, and the electric charge charged thereon is also transferred to the metal case 1 as shown by the arrow.
5, creeping discharge occurs. After the creeping discharge, negative charges remain on the outer wall of the neck tube 2 and the clamp 16, so when the power switch is turned off, the potential of the internal conductive film 4 decreases, and the potential of the outer wall of the neck tube 2 and the clamp 16 decreases. It becomes negative, and conversely, creeping discharge occurs from the metal case 15 to the outer wall of the neck tube 2 and the fastening fitting 16. In other words, creeping discharge occurs twice when the power switch is turned on and off.
Similarly, the creeping discharge described above also occurs due to the intraluminal discharge generated between the electrodes of the electron gun 3. The above steps involve putting a conventional cathode ray tube device in a dark room, turning on the power switch,
This can be confirmed for the first time by observing when it is OFF.
When the creeping discharge is viewed from the surface of the network tube 2, it appears as shown in FIG. 3, and the streamer 17 flowing into the metal case 15 can be visually observed. If you enlarge the A-A' cross section of the network tube 2 where the streamer 17 is generated, it will become as shown in Figure 4, and the streamer 17
Since the potential at the point where this occurs is lower than that of the surrounding surface, a new electric field Ex is generated in the circumferential direction of the tube in addition to the electric field Ey in the tube center direction, so that the streamer 17 is The potential between the generated point and the internal conductive film 4 is distorted, and therefore a locally large electric field E is generated there, which is a combination of the electric field Ey in the tube center direction and the electric field Ex in the circumferential direction. In addition, for the electric field Ey′ in the direction of the tube center at a positively charged point,
The relationship is E>Ey>Ey′. As a result, dielectric breakdown occurs in the network tube 2, resulting in fatal damage to the cathode ray tube.

This invention discovered through experiments the creeping discharge that causes the dielectric breakdown of the network tube as described above, and attempts to cover the metal case that is close to the network tube with an insulating film in order to prevent this. .

FIG. 5 shows an embodiment of the present invention, in which a portion of the metal case 15 of the focusing coil 10 close to the neck tube 2 is coated with an insulating coating 18. There is no place for the charges on the surface of the network tube 2 to be discharged, and therefore the streamer 17 does not occur. The fact that the charge on the surface of the network tube 2 is not discharged means that it does not become negative when the power switch is turned off, so the streamer 17 does not emit light even when the power switch is turned off, and therefore the network tube 2 does not crack. The potential on the surface of network tube 2 is the number of anode voltages.
The thickness of the insulating film must be at least a certain level, as it can reach up to 10%. For example, when the thickness of the polyester insulation coating is 0.2 mm and the anode voltage is 30 KV,
The number of defects that occurred when there was no insulation coating was reduced to almost zero. Although the tightening fitting 16 of the alignment magnet 8 is floating from the ground potential, it is a large lump of metal, and the electrostatic capacitance with the ground increases, causing a gap between it and the electric charge on the surface of the nearby network tube 2. Since this may cause creeping discharge, it is better to cover it with an insulating material. Further, the focusing coil 10 may use an insulating case instead of the metal case 15. In particular, creeping discharge occurs when the conductive exposed part of the attached part is within 10 cm from the outer wall of the neck, so in this case the effect of the coating is particularly pronounced. Note that although the above description has been made using a projection type cathode ray tube as an example, the present invention is not limited to this and can of course be applied to other cathode ray tubes.

As explained above, the present invention includes a network tube made of glass to which an anode voltage is applied to the inner surface;
In a cathode ray tube device equipped with a conductive accessory part close to and spaced apart from the outer surface of the neck tube, at least the outer surface of the conductive accessory part on the side facing the neck tube is coated with an insulating material. This has the excellent effect of eliminating creeping discharge and preventing damage to the glass at the neck portion.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a projection cathode ray tube with accessories attached, Figure 2 is an enlarged view of a portion of Figure 1, and Figures 3 and 4 explain the causes of glass cracks. FIG. 5 is a sectional view showing an embodiment of the present invention. In the figure, 2...connect pipe, 15...metal case,
18...Insulating coating. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A cathode ray tube device comprising a network tube made of glass to which an anode voltage is applied to the inner surface, and conductive accessories close to and spaced apart from the outer surface of the network tube, wherein the conductive accessories are A cathode ray tube device characterized in that at least the outer surface of the component on the side facing the neck tube is coated with an insulating material. 2. The cathode ray tube device according to claim 1, wherein the cathode ray tube device is a conductive accessory disposed within 10 cm circumferentially outward from the outer wall of the network tube.