JP2002117782A - 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. Further, the transverse magnetic field and the characteristics of the tube axis NS have almost the same rate of change, have opposite signs, and have a trade-off relationship, and it is impossible to improve both characteristics simultaneously. SOLUTION: In a skirt portion of a magnetic shield, a skirt portion near a center portion of a long side portion and a vicinity of a frame top portion are joined. The other skirt portion is provided with a certain distance from the mask frame so as not to make contact with the mask 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 coupling shape and form of a frame and an internal magnetic shield for improving geomagnetic characteristics.

[0002]

2. Description of the Related Art FIG. 8 shows a conventional cathode ray tube for 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 the external magnetic field, the role of the 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 geomagnetism. Geomagnetism is divided into horizontal and vertical components. As is well known, since the vertical component changes the landing almost uniformly over the entire screen, there is no problem in correcting the vertical component with a correction lens or the like when forming the fluorescent screen. As shown in FIG. 9, 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 geomagnetism,
It is necessary to satisfy the characteristics by the transverse magnetic field, which is the component of the horizontal component of terrestrial magnetism, and the tube axial magnetic field. When the characteristics are evaluated by a CRT, a magnetic field equivalent to geomagnetism or more is externally applied, and the amount of change in beam landing at that time is measured. As shown in FIG. 10, the measurement points are four corners and the upper and lower central portions on the short side (hereinafter referred to as NS portions).
The characteristics that are particularly important here are (1) the characteristics of the corner portion when a lateral magnetic field is applied (hereinafter referred to as “lateral corner”).

(2) When a magnetic field in the direction of the tube axis is applied, N
Characteristics of S part (hereinafter referred to as “tube axis NS”). It is.

The shape of the internal magnetic shield is generally formed by opposing long side walls and opposing short side walls as shown in FIG. 11, and has an opening in the center. In addition, the internal magnetic shield has a V-shaped notch in FIG. 12 formed on the short side wall.

Further, in the recent system in which a tension is applied to a mask, the bonding between the internal magnetic shield and the frame is performed by a method disclosed in Japanese Patent Application Laid-Open No. Hei 6-333507,
The method shown in FIG. 13 was common.

[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 with the structure shown in FIG. 13, optimization is performed by changing the depth and width of the cutout portion.
The variation of the beam landing with respect to the external magnetic field equivalent to the geomagnetism was improved to (transverse magnetic field, tube axis NS) = (21 μm, 23 μm). However, as shown in FIG. Have the same rate of change and the opposite sign in a trade-off relationship, and it is impossible to improve both characteristics simultaneously.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned 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.

[0012]

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

There are the following three variations.

(1) Of the skirt portion of the magnetic shield, the skirt portion near the center of the long side and the vicinity of the top of the frame are joined. The other skirts are kept away from the mask frame at a certain distance.

(2) The skirt portion of the magnetic shield is present only near the center of the long side.

(2) In the structure of (2), the skirt portion is in contact with or joined to the frame.

(3) The skirt portion of the magnetic shield is present only near the center of the long side.

The other part of the long side of the magnetic shield has a certain distance from the top of the frame.

According to the present invention, mislanding of an electron beam due to an external magnetic field such as terrestrial magnetism is reduced.

In particular, it is possible to provide a magnetic shield that simultaneously improves the horizontal corner and the tube axis NS.

[0021]

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.
5A and 5B are a perspective view and a side view of an internal magnetic shield and a mask frame in a 25 "stretched mask type CRT. The internal magnetic shield is formed by opposing long side walls and opposing short side walls. An opening is provided at the center, and a notch is formed on a short side wall of the opening on the deflection center side.

A skirt portion 1 having a length of 3 to 6 cm is provided at an end of the long side of the internal magnetic shield on the mask frame side.

The skirt has a width of about 40 cm.

At this time, the outer shape of the magnetic shield is shown in FIG.
However, as shown in FIG. 1, the skirt 1 is in contact with the frame only near the center of the long side 2 of the frame, and the other skirts have a distance of 4 mm from the side of the frame. is there.

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) = (19 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, with respect to an external magnetic field equivalent to geomagnetism,
The amount of change in beam landing was (transverse magnetic field, tube axis NS) = (16 μm, 20 μm), and the magnetic properties, particularly the horizontal magnetic field properties, were improved without a relatively simple shape and without increasing the number of manufacturing steps.

(Embodiment 2) Fig. 3 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 properties were improved by changing the length of the skirt in the horizontal direction.

FIG. 4 shows a change in the beam landing amount 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. 4, as L is reduced, 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.

The reason why the magnetic characteristics are improved in the first and second embodiments is considered as follows.

The magnetic field applied from the lateral direction easily flows through 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. When the distance between the mask frame and the skirt portion is large, the magnetic coupling is small and the magnetic flux does not easily flow through the mask frame.

When a magnetic field exceeding a certain level is applied,
The magnetic flux that has exceeded the magnetic capacity of the mask frame and has flowed into the mask frame from the magnetic shield will overflow 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 this time, at the same time, the tube axis NS gradually deteriorates.

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 is smaller than that of the horizontal corner. When L becomes less than 4 or 5, the sudden deterioration is caused by the difficulty in flowing the magnetic flux from the magnetic shield body and the undesired magnetic field blowing into the space.

In this embodiment, L = 12 cm.

At this time, with respect to an external magnetic field equivalent to geomagnetism,
The variation of the beam landing was (transverse magnetic field, tube axis NS) = (11 μm, 21 μm), and the magnetic characteristics were greatly improved.

(Embodiment 3) FIG. 5 shows an internal magnetic shield according to Embodiment 2 of the present invention. This internal magnetic shield is for further improving the characteristics of the second embodiment. L = 12 cm, and the end of the skirt is brought into contact with the frame. As a result, when a magnetic field is applied in the tube axis direction, the magnetic flux flowing from the magnetic seal body easily flows in the frame mask direction. Because of this, the characteristics of the horizontal corners hardly deteriorate because L = 12, which is short.

At this time, with respect to an external magnetic field equivalent to geomagnetism,
The amount of change in beam landing was (transverse magnetic field, tube axis NS) = (12 μm, 18 μm).

As a method of contact at this time, it has been experimentally confirmed that the magnetic shield body is bent deeply in advance in anticipation of contact with the frame at the time of pressing, or that the contact by welding is preferable.

Further, it was experimentally confirmed that the effect of the joint portion near the top of the frame as shown in FIG. 6 was even more effective.

At this time, with respect to an external magnetic field equivalent to the earth magnetism,
The change amount of the beam landing is (transverse magnetic field, tube axis NS) = (12 μm, 16 μm).

In Embodiments 1 and 2, the same effect can be obtained even if the ratio between the gap and the contact portion is appropriately changed. Further, as shown in FIG. 7, it is more effective to provide a gap in the long side portion of the magnetic shield without a skirt portion to reduce the flow of magnetic flux with the frame.

In FIGS. 1 to 6, the distance between the magnetic shield and the mask frame is drawn slightly apart for easy understanding.

By using the internal magnetic shield as described above, it is possible to reduce or cancel the force that the electron beam receives from the external magnetic field such as terrestrial magnetism on the orbit to the fluorescent screen. As a result, the force received by the electron beam was reduced, mislanding due to distortion of the electron beam was reduced, and color shift and color unevenness were prevented over the entire screen. In this embodiment, a 25 "CRT is assumed.
The size of the skirt at that time is CRT
It depends on. Further, notches or the like may be formed in the shape of the skirt portion to further control two characteristics.

[0050]

As described above, the first embodiment of the present invention,
In the second embodiment as well, by connecting the skirt portion of the magnetic shield with the vicinity of the center of the frame, the amount of change in beam landing with respect to the external magnetic field equivalent to the geomagnetism is significantly improved both in the transverse magnetic field and the tube axis NS at the same time.

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

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

[Brief description of the drawings]

FIG. 1 is a view showing a magnetic shield and a mask frame according to an embodiment of the present invention;

FIG. 2 is a view showing a case where the shape of a skirt portion is changed in FIG. 1;

FIG. 3 is a view showing a magnetic shield and a mask frame according to a second embodiment of the present invention;

FIG. 4 is a view showing experimental results of a lateral length of a skirt portion and magnetic characteristics.

FIG. 5 is a diagram in a case where the skirt portion and the side surface of the frame portion in FIG. 3 are connected;

FIG. 6 is a diagram in a case where the skirt portion and the top portion of the frame portion in FIG. 3 are connected.

FIG. 7 is a diagram showing a state where the vicinity of a long side end of the magnetic shield is cut in the second embodiment.

FIG. 8 shows a conventional cathode ray tube.

FIG. 9 is a diagram illustrating a relative position between a horizontal magnetic field and a CRT.

FIG. 10 is a diagram showing landing measurement points on a CRT screen.

FIG. 11 is a diagram showing a conventional general magnetic shield body.

FIG. 12 is a diagram showing a conventional magnetic shield having a V-shaped notch.

FIG. 13 is a view showing a magnetic shield used for a conventional tension mask.

FIG. 14 is a diagram showing a relationship between a notch width and a landing change amount.

[Explanation of symbols]

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

Continued on the front page (72) Inventor Hiroshi Iwamoto 1006 Kadoma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. Inventor Takayuki Yonezawa 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F term (reference) 5C031 CC01 EE15

Claims (7)

[Claims] 1. A cathode ray tube comprising a mask, a frame, and an internal magnetic shield having an extension at an end on the mask side, wherein the extension is located near a center of a long side of the frame. The extension of is in contact with the frame,
A cathode ray tube, wherein an extension of the extension except a portion near a center of a long side of the frame is not in contact with the frame. 2. The cathode ray tube according to claim 1, wherein the contact portion with the frame is a top portion of the frame. 3. The cathode ray tube according to claim 1, wherein there is a gap between the mask-side extension of the internal magnetic shield not in contact with the frame and the frame. 4. The length of the contact portion is / of the length of the long side.
The cathode ray tube according to claim 1, wherein: 5. The cathode ray tube according to claim 1, wherein the extension and the frame are joined by welding. 6. The frame according to claim 1, wherein a portion of the long side of the internal magnetic shield that does not have an extension of the mask-side end of the internal magnetic shield is not in contact with the frame. A cathode ray tube according to claim 1. 7. The cathode ray tube according to claim 1, wherein a notch is provided in an extension of the mask-side end of the internal magnetic shield.