JP2001332182A - Cathode ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode ray tube generating a less amount of mislanding due to the distortion of an electron beam with an external magnetic field such as an earth magnetism and less color drift or irregularity on a whole screen. SOLUTION: An internal magnetic shield 30 has an extension portion 34 at a central portion of a long side wall 31 along the edge on the incident side of an electron beam. A height H1 of the extension portion 34 (the height of a cut portion from a bottom side) is greater than a height H2 of a short side wall 32 (the height of the cut portion from the bottom side) neighboring the long side wall at the edge on the incident side of the electron beam.

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 shape of an internal magnetic shield for improving external magnetic characteristics such as terrestrial magnetism.

[0002]

2. Description of the Related Art FIG. 11 shows a conventional cathode ray tube (hereinafter referred to as "CRT") for a television or a personal computer monitor.
Is shown. As shown in the figure, in a CRT, an electron beam 111 emitted from an electron gun is deflected in a vertical and horizontal direction by a deflection coil 112, and is scanned over the entire screen to reproduce an image. At this time, when an external magnetic field such as terrestrial magnetism acts on the CRT in a direction orthogonal to the traveling direction of the beam, the electron beam 1
Numeral 11 is distorted as shown by a broken line in the figure (illustrated in a slightly exaggerated manner), and so-called mislanding that the phosphor 114 on the panel 113 does not reach a predetermined position occurs. As a countermeasure, an internal magnetic shield 115 is generally provided inside the CRT (here, inside the funnel) so as to surround the passage of the electron beam. In addition, CRT
In (2), the electron beam is horizontally scanned in the horizontal direction of the screen (from the near side to the far side of the drawing or from the far side to the near side of the drawing) by controlling the deflection amount by the deflection coil, and in the vertical direction (arrow Y in the drawing). The raster scan method is generally used in which a raster is formed by performing vertical scanning in the direction (1).

Since it is impossible to completely shield the external magnetic field, the internal magnetic shield 115 has a substantial role of shielding a certain magnetic field, changing the direction of the magnetic field lines, and preventing the electron beam from receiving a force. Or to correct the force received at a certain point. Now,
Except in special cases, the main source of external magnetic fields is geomagnetism.
The geomagnetism is divided into a horizontal component (a vector component in a direction horizontal to the screen) and a vertical component (a vector component in a direction perpendicular to the screen). Of these, as is well known, the vertical component uniformly changes the landing over substantially the entire screen, and does not pose a problem because the position of the phosphor screen is corrected by a correction lens or the like when the phosphor screen is formed. On the other hand, FIG.
As shown in FIG. 2, the horizontal magnetic field 120 changes its direction depending on the relative position of the magnetic field and the CRT, and is generally decomposed into a tube axis direction 121 and a lateral direction 122 of the CRT. Note that, here, the space region through which the electron beam passes has a substantially conical shape diverging toward the traveling direction of the electron beam, and the central axis of the conical electron beam passage region is called a tube axis. Therefore, when considering the geomagnetic shield, it is necessary to consider the horizontal magnetic field, which is a component of the horizontal component of the geomagnetic field, and the magnetic characteristics of the tube axial magnetic field. Then, by applying a magnetic field equivalent to geomagnetism or more from the outside and measuring the amount of change in beam landing on the phosphor screen at that time, this characteristic of the CRT can be evaluated. The measurement points can be, for example, four screen corners as shown in FIG. 13 and upper and lower central portions (hereinafter, referred to as NS portions) of a long side of the screen. 1) Characteristics of a corner portion when a lateral magnetic field is applied (hereinafter referred to as “lateral corner”).

(2) When a magnetic field in the tube axis direction is applied, N
Characteristics of S part (hereinafter referred to as “tube axis NS”). It is. Now, the shape of the internal magnetic shield 115 is as shown in FIG.
2 is generally a polygonal pyramidal cylinder formed with an opening 143 at the top of the weight. On the other hand, in recent years, CRTs having a large screen and a flat face plate have become mainstream. In particular, in a CRT having a flat face plate, a method in which tension is applied to the shadow mask as described above is generally adopted. This imparts tension by stretching a linear material on a frame.

In this type of CRT, mislanding due to terrestrial magnetism tends to be significantly deteriorated in the conventional internal magnetic shield. This is thought to be due to the fact that the application of tension to the shadow mask increases the magnetic resistance of the shadow mask and generates an undesirable magnetic field near the shadow mask (Murai et al., SID2000DIG
EST, P582-585). For example, in the conventional 25 ″ CRT, both the horizontal corner and the tube axis NS are about 10 μm, but when tension is applied to the shadow mask, the horizontal corner: 30 μm,
Tube axis NS: deteriorates to 25 μm.

[0006]

In order to improve the characteristics of the internal magnetic shield having the structure shown in FIG.
The cut portion 144 having a character shape is provided, and the depth of the cut,
Attempts have been made to optimize by changing the width. In particular, changing the depth of the V-shaped cutout changes the characteristics more greatly than changing the width or the like. This is shown in FIG. As shown in FIG. 15, as the cutting depth is increased, the characteristics of the horizontal corner are significantly improved. However, the characteristics of the tube axis NS hardly change. When the V-shaped depth is changed from 0 mm to 150 mm, the horizontal corner changes by about 10 μm, but the tube axis NS hardly changes.

After all, in the optimization of the V-shape, the amount of change in beam landing with respect to an external magnetic field equivalent to the earth's magnetism was improved to (lateral corner, tube axis NS) = (20 μm, 23 μm). It was not possible to improve the properties at the same time. And the horizontal corner and the tube axis NS
Are in a trade-off relationship with almost the same rate of change and opposite signs, and it was impossible to improve both properties simultaneously.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and reduces the amount of 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 cathode ray tube.

[0009]

In order to achieve the object, the present invention devises a magnetic field distribution near the end of the internal magnetic shield near the deflection coil and a magnetic field distribution near the shadow mask. . When displaying the periphery of the CRT screen, the magnetic field distribution on the orbit through which the electron beam passes is important. This corresponds to about 20% of the plane of the inner magnetic shield at the entrance plane, along the edge.

In order to improve the tube axis NS described above, when a magnetic field is applied from the tube axis direction, a vertical magnetic field (By, the vertical direction is a direction along the vertical scanning direction). It is known that it is necessary to devise the distribution of. Specifically, as shown in FIG. 16, it is extremely effective to set the By component near the deflection coil and the By component near the shadow mask in the plus / minus reverse direction. Note that in this figure, the magnetic field By is a relative value. As a result, the electron beam trajectory can be displaced in advance in the electron beam entrance side entrance of the internal magnetic shield in the direction opposite to the shift occurring near the mask on the electron beam trajectory.
The force that the electron beam receives in the vertical direction is canceled, and the amount of movement of the electron beam by the magnetic field can be reduced.

In order for the By component on the deflection coil side to be in the minus direction, the present inventors devised (1) the shape of the internal magnetic shield so that the vertical scanning direction on the electron beam entrance side on the deflection coil side. The amount of magnetic flux absorbed by the upper and lower ends (long side walls in the embodiment) along the direction of the horizontal axis is determined by the magnetic flux at the left and right ends (short side walls in the embodiment) along the horizontal scanning direction. More than the absorption. (2) By changing the effective magnetic permeability, the amount of magnetic flux absorbed at both ends on the upper and lower sides in the vertical scanning direction on the electron beam entrance side on the deflection coil side is increased along the horizontal scanning direction. More than the amount of magnetic flux absorbed at the portions located at the left and right ends in the direction.

As a method of changing the magnetic permeability, the inner magnetic shield is made of a material having substantially large magnetic permeability at both ends on the upper and lower sides in the vertical scanning direction on the electron beam entrance side on the deflection coil side. And that the portions located at the left and right ends in the direction along the horizontal scanning direction are made of a material having a substantially low magnetic permeability. As described above, the present invention makes it possible to reduce the amount of mislanding of the electron beam by devising the magnetic field distribution near the deflection coil side end of the internal magnetic shield and the magnetic field distribution near the shadow mask.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiments]
The CRT will be specifically described. <Schematic Configuration of CRT and Structure of Internal Magnetic Shield> FIG. 1 is a sectional view of an embodiment of the present invention.

This CRT is a flat type (front surface of a face plate is flat) which is becoming mainstream in recent years, and a 25 ″ CRT in which a shadow mask is stretched. Specifically, the CRT includes a face plate 10 having a flat front surface, a funnel portion 15 having an internal magnetic shield 30, a neck portion 20, and an electron gun 25 inserted into the neck portion 20. Main components.

On the inner surface of the front portion of the face plate 10, phosphor portions 11 of each color are formed. Funnel part 1
A deflection coil 16 is attached to the outer peripheral surface of the end opposite to the face plate 10 so as to cover the entire circumference.
FIG. 2 is a diagram showing a main internal structure of a portion related to the invention of the CRT, and is an exploded perspective view of the state where the internal magnetic shield 30 and the mask frame 40 are attached.

In FIG. 2, the internal magnetic shield 30 is
It has a polygonal pyramid shape formed by opposing long side walls 31 and opposing short side walls 32, and has an opening 33 at the top of the weight. At both upper end portions (deflection coil side) of the long side wall 31, rectangular extension portions 34 are formed, the center portions of which are extended to the deflection coil side except for the vicinity of both left and right ends thereof.

As a result, notches 35 are formed on both sides of the extension 34. A cutout portion 36 connected to the cutout portion 35 is also formed in a portion near the long side wall 31 at the upper end of the short side wall 32. Further, the height H1 of the upper edge 34A of the extension 34 from the bottom of the notch 35 is equal to the upper edge 3 of the short side wall 32.
The height is defined to be higher than the height of the uppermost end of 2A, that is, the height H2 from the bottom of the notch 36. Note that the bottom sides of both cutouts 35 and 36 have the same height.

Next, the mask frame 40 includes a pair of stretching members 41 and a pair of holding members 42 having a U-shaped appearance. The tension members 41 are arranged to face each other so as to extend in the same direction, and the U-shaped holding member 42 is fixed to both ends by welding. A tension is applied to the stretching member 41 by a shadow mask Ma formed by assembling a plurality of linear members, and the upper and lower ends are held. The holding member 42 is
In order to maintain the tension of the shadow mask Ma and increase the strength of the frame, the tension member is provided to position the tension member along the tension direction.

The lower end of the internal magnetic shield is fixed to the mask frame 40 on the side opposite to the surface on which the shadow mask Ma is stretched by welding or the like. <Function and effect of internal magnetic shield> As described above, an extension is provided at the upper end of the long side wall, and the height of this edge is higher than the height of the upper end of the short side wall. The amount of magnetic flux absorption (Φ) in the upper and lower portions in the direction along the vertical scanning direction on the electron beam entrance side on the deflection coil side
1) is set to be larger than the amount of absorbed magnetic flux (Φ2) in the portions located on the left and right sides in the horizontal scanning direction (Φ1> Φ)
2) Yes. In other words, the magnetic flux density (B1) in the upper and lower portions in the direction along the vertical scanning direction on the electron beam entrance side on the deflection coil side is changed to the magnetic flux density (B1) in the right and left portions in the direction along the horizontal scanning direction. B2) (B1> B2).

When attention is paid to the vicinity of the same long side wall, the amount of magnetic flux absorbed by the extension 34 is larger than that of the notch 35, and therefore, the magnetic flux density of the magnetic flux absorbed by the extension 34 is reduced by the notch 35. Higher than near. That is, the magnetic field concentrates on the extension 34. By forming a difference between the absorption amount and the magnetic flux density of the magnetic flux by the internal magnetic shield in the horizontal direction and the vertical direction, the By on the deflection coil side is formed.
The component and the By component near the shadow mask are in the plus / minus opposite directions. As a result, the trajectory of the electron beam is displaced in advance in the electron beam entrance side entrance portion of the internal magnetic shield in the direction opposite to the shift occurring near the mask on the trajectory of the electron beam, so that the electron beam is received in the vertical direction. Power is offset. As a result, the NS characteristics of the tube axis are effectively improved, and mislanding of the electron beam is reduced particularly in the tube axis N.
S can be effectively improved.

In this way, by providing the extension at the upper end of the long side wall and making the height of this edge higher than the height of the upper end of the short side wall, the amount of magnetic flux absorption can be improved. Therefore, the absorption curvature (R1) of the magnetic flux at the portion where the amount of magnetic flux absorption is large on the upper and lower sides in the vertical scanning direction on the electron beam entrance side on the deflection coil side is higher than that on the horizontal scanning direction. The magnetic flux absorption curvature (R2) is made larger than the magnetic flux absorption curvature (R2) at the portion where the magnetic flux absorption amount located on the left and right sides of the direction is small.
> R1) state is realized.

When attention is paid to the vicinity of the same long side wall, the curvature at the time when the magnetic flux is absorbed by the extension portion 34 is reduced by the notch portion 35.
Greater than. That is, the magnetic field concentrates on the extension 34. This is because the external magnetic field traveling straight along the tube axis is absorbed by the electron beam entrance of the internal magnetic shield, but the amount of magnetic flux absorbed in the upper and lower directions along the vertical scanning direction is larger than in the horizontal direction. Since the absorption efficiency is higher in the vertical direction, it is considered that such a difference appears in the curvature of the magnetic flux.

Normally, an external magnetic field coming from the outside world is
It is absorbed by all parts surrounding the electron beam passage area at the electron beam entrance part of the internal magnetic shield. On the other hand, by providing the extended portion at the upper end portion of the long side wall as described above, the external magnetic field is uniformly absorbed in all portions surrounding the electron beam passage area at the electron beam entrance portion of the internal magnetic shield. Instead, the absorption in the extension will take precedence.

The effect of causing a difference in the amount of absorbing the external magnetic field (absorbing amount of magnetic flux) as described above is caused by H1 and H2.
There is an optimum range depending on the difference between It is desirable that the dimension of H1 be defined within a range that does not prevent the edge of the internal magnetic shield from entering the space surrounded by the deflection coil and hindering the deflection control by the deflection coil. Here, when the difference between H1 and H2 is changed (H2 is set to 2c
When H1 is changed when a fixed value of m or 4 cm is set. FIG. 3 shows the result of measuring the variation in the amount of mislanding of the electron beam when W1 = W2 = 3 cm).

As shown in this figure, H2 = 2 cm and H2
In the case of = 4 cm, the amount of change in the amount of beam mislanding has a similar tendency, although the absolute value is different. It can be seen that the effect is particularly high when H2 = 2 cm. In this case, there is an optimum value in the range of H1 = 2 cm to 4 cm, and it is understood that the effect is worse in other ranges.

The effect of causing a difference in the amount of absorbing the external magnetic field (absorbing amount of magnetic flux) is caused by the notch 3 in the upper end portion near the boundary with the short side wall as described above.
Providing 5, 36 makes it even more remarkable. This is because, by providing the notches 35 and 36, the magnetic flux absorbed from the portions can be reduced,
It is considered that the magnetic flux from the extension is more effectively absorbed. There is an optimum range for the size of the notch.

Here, the notches 35 and 36 have a depth of 2
FIG. 4 shows a change in the amount of beam landing when the widths W1 and W2 of the notches in cm are changed. In addition,
Here, the measurement was performed by defining the notch width W1 = W2. As can be seen from FIG. 4, the change in the lateral corners is more pronounced by providing a notch around the corner than when changing the parameters of the V-shaped notch on the short side wall of the magnetic shield (see FIG. 15). Is small, but the change of the tube axis NS can be slightly increased, and both characteristics can be compatible. In addition,
From this result, although not shown in the experimental data, it has been found that the length of the notch 35 is desirably less than half the width of the upper end of the long side wall.

Therefore, in the case of a pipe type in which the characteristics of the horizontal corner are not so problematic, this is a very effective method for improving the pipe axis NS characteristics. If further adjustment is required,
1 and W2 are different from each other on the long side (W
1) and by changing it on the short side (W2). What has been described so far has been the case where the cut depth is fixed at 2 cm. However, a similar effect can be obtained by changing the cut depth.

FIG. 5 shows the notch width 3c on the short side.
m shows the change in beam landing amount when the notch depth is changed when the notch width on the long side is 5 cm.
By using the internal magnetic shield as described above, a demagnetizing field is formed that cancels out the force that the electron beam receives from an external magnetic field such as terrestrial magnetism on the trajectory to the phosphor screen. As a result, the force that the electron beam receives is reduced. In addition, mislanding due to electron beam distortion can be reduced, and color shift and color unevenness can be prevented over the entire screen. In addition, it is possible to improve the tube axis NS characteristic by canceling out the influence of an external magnetic field represented by geomagnetism while reducing the mislanding in the entire screen.

<Modification> The short side wall 32 in the opening 33 on the deflection center side has V
Characteristic cuts can be formed to further improve the characteristics. Specifically, it can be shaped as shown in FIGS. 6A and 6B. 6, the internal magnetic shield 60 has a polygonal pyramid shape formed by opposing long side walls 61 and opposing short side walls 62. The inner magnetic shield 60 has an opening 63 at the apex of the weight and is located on the deflection center side. The cut portion 64 is formed on the short side wall of the opening.

In FIG. 6A, the cut portion 64 is a simple one in which the cut is simply made at a fixed cut angle (Θ1). On the other hand, in FIG. 6B, the cut portion 64 is not simply cut at a fixed cut angle but at least two cut angles of a deep cut angle (Θ2) and a shallower cut angle (Θ3). It has a notch, so to speak, a home base shape. Next, as shown in FIG. 7A, the shape of the bottom portion 64A of the cut portion 64 is not an acute angle, but may be flat and have a constant width, or may be an arc shape as shown in FIG. 7B.

Here, as the actually measured value, the notch 6
FIG. 8 shows a change in the beam landing amount when the width of the maximum opening of No. 4 (the dimension indicated by L in FIG. 6A) is changed. At this time, the change between the tube axis NS and the horizontal corner is substantially equal. As a result, if L = 30 mm, it was possible to realize the characteristics of tube axis NS = 15 μm and horizontal corner = 10 μm.

The extension may be a plurality of projections 91 as shown in FIGS. 9A and 9B. And
The shape of the projection may be a rectangular shape as shown in FIG. 9A or a semicircular shape as shown in FIG. 9B. Further, as shown in FIG. 10, the central portion of the extension may be formed into an acute angle. Thereby, the magnetic flux can be more effectively absorbed in this portion.

In FIGS. 1 to 10, the distance between the magnetic shield and the mask frame is drawn slightly apart for easy understanding. Finally, in this embodiment,
A 25 ”CRT was assumed, but it can be applied to CRTs of other sizes as well as this size. At that time, the dimensions of each part such as the height of the extension and the width of the notch are the size of the CRT and the size of the CRT used In addition, even if the CRT has the same size, the fact that the electron beam causes mislanding as a factor causing mislanding does not negate the effect of the magnetic field generated by the deflection coil in addition to the external magnetic field. Therefore, if the characteristics of the deflection coil are different, the trajectory of the electron beam will be different even if the shape of the internal magnetic shield is devised, so the optimal fine dimensions of each element of the internal magnetic shield will also depend on the characteristics of the deflection coil. It depends.

[0035]

As described above, according to the cathode ray tube of the present invention, the internal magnetic distribution is adjusted, the amount of mislanding caused by the distortion of the electron beam due to an external magnetic field such as terrestrial magnetism is reduced, and the entire screen is displayed. In addition, it is possible to reduce color shift and color unevenness.

[Brief description of the drawings]

FIG. 1 is a sectional view of a CRT according to an embodiment of the present invention.

FIG. 2 is a diagram showing a main part of an internal structure of the CRT, and is an exploded perspective view of the internal magnetic shield 30 and a mask frame 40 in a mounted state.

FIG. 3 is a diagram showing a change in an amount of mislanding of an electron beam when a difference between H1 and H2 is changed.

FIG. 4 is a diagram showing a relationship between a width W1 of a notch 35 and a mislanding amount of an electron beam.

FIG. 5 is a diagram showing the relationship between the depth of a notch 35 and the amount of mislanding of an electron beam.

6A and 6B are perspective views each showing a configuration of an internal magnetic shield according to a modification of the embodiment.

7A and 7B are both plan views showing only a short side wall portion showing a configuration of an internal magnetic shield according to a modification of the embodiment;

FIG. 8 is a diagram showing a relationship between a length L of a cut portion 64 and an amount of mislanding of an electron beam.

9A and 9B are perspective views each showing a configuration of an internal magnetic shield according to a modification of the embodiment.

FIG. 10 is a perspective view showing a configuration of an internal magnetic shield according to a modification of the embodiment.

FIG. 11 is a sectional view of a conventional CRT.

FIG. 12 is a diagram showing a vector component of a horizontal magnetic field generated in a CRT.

FIG. 13 is a diagram showing measurement points of a mislanding amount on a screen of a CRT.

FIG. 14 is a perspective view showing a configuration of an internal magnetic shield used in a conventional CRT.

FIG. 15 is a diagram showing a relationship between a cut depth of a cut portion and a mislanding amount of an electron beam in an internal magnetic shield in a conventional CRT.

FIG. 16 is a diagram illustrating a distribution state of a magnetic field generated in a vertical direction in a CRT according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Face plate 11 Phosphor 15 Funnel part 16 Deflection coil 20 Neck part 25 Electron gun 30 Internal magnetic shield 31 Long side wall 32 Short side wall 33 Opening 34 Extension 35 Notch 36 Notch 40 Mask frame 41 Stretch Member 42 Holding member Ma Shadow mask H1 Height of long side wall (from bottom of cutout) H2 Height of short side wall (from bottom of cutout)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Iwamoto 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Tetsuro Ozawa 1006 Odaka Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 72) Inventor Shigeo Nakadera 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 5C031 CC01

Claims (15)

[Claims] 1. A cathode ray tube comprising an internal magnetic shield, a mask, and a frame, wherein an internal magnetic shield is provided on a side opposite to a direction in which an electron beam is shifted near the mask due to a magnetic field generated inside the cathode ray tube. A means for previously displacing the trajectory of the electron beam on the electron beam incident side. 2. A cathode ray tube comprising an internal magnetic shield, a mask, and a frame, wherein the cathode ray tube acts on an electron beam passing through 20% of upper and lower ends in a direction along a vertical scanning direction of an electron beam passage area. In magnetic flux, when the central axis of the electron beam passage area is the tube axis,
The direction of the magnetic flux from the electron beam incident side to the vicinity of the incident direction center is the direction from the tube axis to the region, and the direction of the magnetic flux from the vicinity of the center to the mask side is the direction from the region to the tube axis and A cathode ray tube, wherein directions are opposite to each other. 3. A cathode ray tube comprising an internal magnetic shield, a mask, and a frame, the magnetic flux acting on an electron beam passing through 20% of upper and lower ends of a direction along a vertical scanning direction of an electron beam passage area. In the case where the central axis of the electron beam passage area is defined as the tube axis, the magnetic flux density of the magnetic flux generated from the tube axis at the entrance of the electron beam incident side of the internal magnetic shield in the direction of the relevant region is in the horizontal scanning direction from the tube axis. A cathode ray tube characterized in that the magnetic flux density is higher than the magnetic flux density of the magnetic flux generated at both ends in the direction. 4. A cathode ray tube comprising an internal magnetic shield, a mask, and a frame, wherein the electron beam passes through 20% of the upper and lower ends of the electron beam passage area in the direction along the vertical scanning direction. When the center axis of the electron beam passage area is the tube axis, the magnetic flux from the tube axis is absorbed by the portions located at both ends in the direction along the vertical scanning direction of the electron beam incident side of the internal magnetic shield. A cathode ray tube, wherein the curvature of the magnetic flux is larger than the curvature of the magnetic flux when the magnetic flux is absorbed by the portions located at both ends in the horizontal scanning direction. 5. A magnetic flux acting on an electron beam passing through 20% of upper and lower ends of a cathode ray tube comprising an internal magnetic shield, a mask, and a frame in a direction along a vertical scanning direction of an electron beam passage area. In the case where the central axis of the electron beam passage area is defined as the tube axis, the magnetic flux density of the magnetic flux generated from the tube axis at the entrance of the electron beam incident side of the internal magnetic shield in the direction of the relevant region is in the horizontal scanning direction from the tube axis. Regarding the magnetic flux density which is larger than the magnetic flux density of the magnetic flux generated at both ends in the direction, and which is generated at the entrance side of the electron beam incident side from the direction end along the vertical scanning direction from the tube axis, the edge of the entrance A cathode ray tube having a central portion larger than that of a peripheral portion. 6. A cathode ray tube comprising an internal magnetic shield, a mask, and a frame, wherein the cathode ray tube acts on an electron beam passing through 20% of upper and lower ends of an electron beam passage area in a direction along a vertical scanning direction. % Of the electron beam passing through the central axis of the electron beam passage area with respect to the tube axis, and both ends of the internal magnetic shield in the vertical scanning direction on the electron beam incident side of the internal magnetic shield with respect to the magnetic flux from the tube axis. The curvature of the magnetic flux when absorbed in the portion located in the horizontal scanning direction is larger than the curvature of the magnetic flux when absorbed in the portions located at both ends in the direction along the horizontal scanning direction, and the magnetic flux from the tube axis On the other hand, regarding the curvature of magnetic flux when absorbed by the portions located at both ends in the direction along the vertical scanning direction of the electron beam incident side of the internal magnetic shield, the portion along the direction of the edge of the electron beam entrance entrance portion You A cathode ray tube wherein the central portion is larger than the peripheral portion. 7. A cathode ray tube comprising an internal magnetic shield, a mask, and a frame, wherein the height of the electron beam incident side edge located at both ends in the vertical scanning direction in the internal magnetic shield is ,
A cathode ray tube, wherein the height of the cathode ray tube is higher than the height of an electron beam incident side edge located at both ends in a direction along a horizontal scanning direction. 8. The cathode ray tube according to claim 7, wherein said internal magnetic shield has cutouts at both ends in a direction along an edge of said electron beam incident side edge which is relatively high along said edge. A cathode ray tube characterized by comprising a part. 9. The cathode ray tube according to claim 8, wherein the notch is formed in a direction along each edge of the electron beam incident side edges located at both ends in the vertical scanning direction. A cathode ray tube having a width of less than half the width. 10. A cathode ray tube having a pyramidal cylindrical shape having an opening at the top of a cone, comprising an internal magnetic shield comprising opposing long side walls and opposing short side walls, a mask, and a frame. A tube, wherein the internal magnetic shield includes an extension at a central portion in a direction along the edge at an electron beam incident side edge of the long side wall, and a height of the extension is set to the long side wall. A height of which is higher than a height of an electron beam incident side edge of a short side wall adjacent to the cathode ray tube. 11. The cathode ray tube according to claim 10, wherein the extension is a plurality of protrusions. 12. The cathode ray tube according to claim 11, wherein the plurality of projections have a rectangular shape or a semicircular shape. 13. The cathode ray tube according to claim 1, wherein the width of the internal magnetic shield gradually decreases from the electron beam incident side edge to the mask side on the short side wall. A cathode ray tube, comprising: 14. The cathode ray tube according to claim 13, wherein the cut portion is formed with at least two cut angles. 15. The cathode ray tube according to claim 1, wherein a tension is applied to the mask.