JP2001266762A - Cathode ray tube - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In a CRT having a flat face plate,
Mislanding due to geomagnetism tended to worsen significantly. In particular, it was difficult to achieve both tube axis characteristics and transverse magnetic field characteristics. A short side of an electron shield is made non-magnetic, and a part of a long side skirt portion of a magnetic shield is connected to a frame.

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, and more particularly, to a combination of a frame and an internal magnetic shield for improving geomagnetic characteristics, and more particularly to an electron shield.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional cathode ray tube of a television or a personal computer monitor, in which a deflection yoke deflects an electron beam emitted from an electron gun in a vertical and horizontal direction and scans the entire screen to form an image. Reproduce. At this time, when an external magnetic field such as terrestrial magnetism acts on the cathode ray tube, the electron beam is distorted,
Mislanding that does not reach a predetermined position with respect to the phosphor on the panel occurs. As a countermeasure, an internal magnetic shield is provided in the cathode ray tube.

Since it is impossible to completely shield an external magnetic field, the role of an internal magnetic shield is to provide a certain degree of magnetic field shielding and to change the direction of the magnetic field lines so that the electron beam is not subjected to a force, or to a certain part. It is to correct the received force.

[0004] Except in special cases, the main cause of the external magnetic field is terrestrial magnetism. Geomagnetism is divided into a horizontal component and a vertical component. As is well known, the vertical component changes the landing almost uniformly over the entire screen, and does not pose a problem because the correction is performed by a correction lens or the like when the fluorescent screen is formed. As shown in FIG. 5, the horizontal magnetic field 100 varies in size and direction depending on the relative position of the magnetic field with respect to the CRT, and is generally divided into a tube axis direction 101 and a lateral direction 102 of the CRT. After all, when considering the shield by the geomagnetism, it is necessary to satisfy the characteristics by the transverse magnetic field which is the component of the horizontal component of the geomagnetism and the tube axial magnetic field. When the characteristics are evaluated by the CRT, a magnetic field equivalent to the geomagnetism or more is applied from the outside, and the amount of change in beam landing at that time is measured. The measurement points are four corners as shown in FIG. 6 and the upper and lower central portions on the short side (hereinafter referred to as NS portions).

Particularly important characteristics here are (1) the characteristics of the corner portion when a transverse magnetic field is applied (hereinafter referred to as "lateral corners"), and (2) the characteristics when a tube axial magnetic field is applied.
NS characteristics (hereinafter referred to as “tube axis NS”).

The shape of the internal magnetic shield is generally formed by opposing long side walls and opposing short side walls as shown in FIG. 7, and has an opening in the center. In addition, as shown in JP-A-5-335520, the V-shaped notch shown in FIG. 8 was formed on the short side wall of the internal magnetic shield.

In a recent system in which a tension is applied to a mask, a method disclosed in JP-A-6-333507 or a method shown in FIG. 9 is generally used for joining an internal magnetic shield and a frame. there were.

As shown in FIG. 10, between the internal magnetic shield and the frame, an electron beam reflector called an electron shield is formed at an outer edge along the bottom of the frame.

[0009]

In recent years, CRTs having a large screen and a flat face plate have become mainstream. In this type of CRT, mislanding due to terrestrial magnetism tends to be significantly deteriorated in the magnetic shield of the related art.

For example, in a conventional 25 ″ CRT, both the horizontal corner and the tube axis NS are about 10 μm, but the horizontal corner is 15 μm and the tube axis NS is 30 μm.

In order to improve the characteristics of the structure shown in FIG. 9, optimization is performed by changing the depth and width of the notch, so that the amount of change in beam landing with respect to an external magnetic field equivalent to geomagnetism is expressed by (transverse magnetic field). , Tube axis NS) = (21 μm, 23 μm). However, the transverse magnetic field and the characteristics of the tube axis NS have almost the same rate of change, are opposite in sign, and are in a trade-off relationship. It was impossible to improve.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has an internal structure that reduces mislanding due to distortion of an electron beam due to an external magnetic field such as terrestrial magnetism, and reduces color shift and color unevenness over the entire screen. It is intended to provide a magnetic shield.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention contemplates a method of joining an extension (hereinafter referred to as a skirt) of an end of a magnetic shield to a shadow mask and a mask frame. I do.

More specifically, by reducing the magnetic permeability of the electron shield on the short side relatively to the long side, it is possible to suppress the blowing of undesired magnetic flux into the electron beam passage area. Becomes

Further, the vicinity of the center of the frame-side extension (hereinafter referred to as a skirt) of the internal magnetic shield is connected to the frame, and the other portion is provided with a gap with the frame.

With such a configuration, the magnetic resistance between the frame and the internal magnetic shield body with respect to the magnetic flux from the tube axis direction is relatively increased on the short side and the amount of magnetic flux is reduced.

[0017] Thus, it is possible to relatively increase the flow of the magnetic flux to the NS section, thereby eliminating undesired magnetic flux near the corner section and reducing the change in the beam landing amount.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows Embodiment 1 of the present invention.
5 is a perspective view and a side view of an internal magnetic shield, a mask, and a frame in a 25 ″ stretch mask type CRT. The internal magnetic shield is composed of opposing long side walls and opposing short side walls. The inner magnetic shield body has an opening at a center portion thereof, and a cutout portion is formed on a short side wall of the opening at the center of the deflection. Has a skirt 1 of 3 to 6 cm in length and 40 cm in width.

An electron shield is formed of a thin plate between the inner magnetic shield and the frame, substantially along the connection with the inner magnetic shield of the frame.

At this time, by making the electron shield non-magnetic, the magnetic resistance between the internal magnetic shield and the frame increases.

In this configuration, when a magnetic field is applied from the tube axis direction, the magnetic flux that has conventionally flowed on the short side flows to the long side.

As a result, the landing change amount could be reduced by about 5%.

As a configuration for further improving the effect, the outer shape of the magnetic shield is almost the same, but the skirt portion 1 is in contact with the frame only near the center of the long side portion 2 of the frame as shown in FIG. The other skirt has a distance of 4 mm from the side of the frame. At this time, the variation of the beam landing with respect to the external magnetic field equivalent to the geomagnetism is (transverse magnetic field, tube axis NS) = (18 μm, 21 μm).

Further, while improving the transverse magnetic field characteristics,
As shown in FIG. 2, a slit is provided in a part of the skirt portion to improve the ease and reliability of manufacture. At this time, the variation amount of the beam landing with respect to the external magnetic field equivalent to the earth magnetism is (transverse magnetic field, tube axis NS) = (15 μm, 20 μm), and the magnetic characteristics and the characteristics are relatively simple without increasing the number of manufacturing steps. In particular, the transverse magnetic field characteristics were improved.

(Embodiment 2) Fig. 2 is a perspective view and a side view of an internal magnetic shield and a mask frame in a 25 "stretched mask type CRT according to Embodiment 2 of the present invention. In the embodiment, the geomagnetic characteristics were improved by changing the length of the skirt in the lateral direction.

FIG. 3 shows a change in the amount of beam landing when the length of the skirt portion in the long side direction (hereinafter referred to as L) is changed. Here, the original length L0 is about 40 cm
It is. When L is shortened from 40 cm, the center part on the side of the rope is symmetrical, and both ends are cut by equal lengths.

As shown in FIG. 3, as L is shortened, the transverse magnetic field characteristics are greatly improved. Further, the tube axis NS does not change much compared to the case where the cutout shape of the short side wall portion is changed. However, when the length is shorter than 4 to 5 cm, the characteristics of the tube axis NS deteriorate significantly.

It is considered that the magnetic characteristics are improved in the first and second embodiments for the following reasons.

The magnetic field applied from the lateral direction easily flows to the mask frame when the skirt portion is L = 40 cm. This is particularly remarkable when the skirt portion is in contact with the frame, and when the distance between the mask frame and the skirt portion is large, magnetic coupling is small and magnetic flux does not easily flow through the mask frame. When a magnetic field of a certain level or more is applied, the magnetic capacity exceeds the magnetic capacity of the mask frame, and the magnetic flux flowing into the frame from the magnetic shield or the elect shield overflows into the space.

As a result, it is considered that an undesired electric field is applied to the electron beam to greatly change the beam landing. At the same time, the tube axis NS gradually deteriorates, though gradually.

This is because when a magnetic field is applied in the tube axis direction, the magnetic resistance is relatively small due to the anisotropy of the shadow mask. For this reason, even if L becomes small, the magnetic flux easily flows from the magnetic shield to the frame and the shadow mask, so that the deterioration becomes smaller as compared with the horizontal corner. When L is less than 4 or 5, the sudden deterioration is because the magnetic flux from the magnetic shield is less likely to flow and an undesired magnetic field blows out into the space.
In this embodiment, L = 12 cm. At this time, the variation of the beam landing with respect to the external magnetic field equivalent to the geomagnetism was (transverse magnetic field, tube axis NS) = (10 μm, 19 μm).

In this embodiment, a 25 "CRT has been described as an example, but the optimal deflection yoke and the like also change as the inch size changes. As a result, the trajectory of the electron beam also changes. In addition to the change, the effect is improved by making the magnetism of the frame different between the short side and the long side, and in particular, by making the short side non-magnetic, the characteristics of the tube shaft corner are improved.

[0034]

As described above, according to the first embodiment of the present invention,
In the second embodiment as well, the short side of the electron shield is made non-magnetic, and in order to make it more effective, the vicinity of the center of the frame and the skirt portion of the magnetic shield are connected to form an external magnetic field equivalent to terrestrial magnetism. The variation is greatly improved simultaneously with the transverse magnetic field and the tube axis NS.

By using the internal magnetic shield as described above, it is possible to reduce or cancel the force of the electron beam received from an external magnetic field such as terrestrial magnetism on the orbit to the fluorescent screen.

As a result, the force applied to the electron beam was reduced, the mislanding due to the distortion of the electron beam was reduced, and color shift and color unevenness were prevented over the entire screen.

[Brief description of the drawings]

FIG. 1 is a diagram showing a magnetic shield, an electron shield, and a mask frame according to an embodiment of the present invention.

FIG. 2 is a diagram showing a magnetic shield and a mask frame according to another embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a lateral length of a skirt portion and magnetic characteristics.

FIG. 4 shows a conventional cathode ray tube.

FIG. 5 is a diagram illustrating a relative position between a horizontal magnetic field and a CRT.

FIG. 6 is a diagram showing landing measurement points on a CRT screen.

FIG. 7 is a view showing a conventional general magnetic shield body.

FIG. 8 is a diagram showing a conventional magnetic shield having a V-shaped notch.

FIG. 9 is a diagram showing a magnetic shield used for a conventional tension mask.

FIG. 10 is a diagram showing a magnetic shield used for a conventional tension mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Skirt part 100 Horizontal magnetic field 101 Tube axis direction 102 Lateral direction

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Iwamoto 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Hiromi Wakazono 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F term (reference) 5C031 CC02 CC03 CC05 CC06

Claims (6)

[Claims] 1. A cathode ray tube provided with at least a mask, a frame, an electron shield and an internal magnetic shield, wherein a permeability of a short side of the electron shield is smaller than that of an electron shield on a relatively long side. A cathode ray tube characterized by the above-mentioned. 2. The cathode ray tube according to claim 2, wherein the magnetic permeability of the frame is relatively smaller on the short side than on the long side. 3. The cathode ray tube according to claim 1, wherein the electron shield on the short side is non-magnetic. 4. A mask-side extension of the internal magnetic shield,
4. The cathode ray tube according to claim 1, wherein there is a gap between the cathode ray tube and the frame. 5. The cathode ray tube according to claim 1, wherein the extension of the mask-side end of the magnetic shield exists only in the center of the long side of the frame. 6. The length of the contact portion is ２ of the length of the long side.
The cathode ray tube according to claim 4 or 5, wherein: