JPH04315737A - Color picture tube - Google Patents

Abstract

PURPOSE:To provide a color picture tube whose color purity is less deteriorated by the vertical component of an external magnetic field. CONSTITUTION:In a color cathode-ray tube which has a cathode and an electrode gun 30 for applying voltages of different degrees to a plurality of electrodes arranged on the cathode and which deflects using a deflecting yoke 11 an electron beam emitted from the electron gun to make the beam incident on a fluorescent screen 6, those of the electrodes constituting the electron gun to which relatively low voltages are applied are each made from a material of high magnetic permeability or the outer peripheries of the electrodes to which relatively low voltages are applied are surrounded by the material of high magnetic permeability so that a magnetic field acting on the electrode beam between the cathode and the center of deflection of the deflecting yoke is shut off.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color picture tube, and more particularly to a color picture tube that improves color purity by reducing deviations in beam landing caused by vertical components of an external magnetic field.

0003

2. Description of the Related Art Generally, a color picture tube has an envelope consisting of a panel 1 and a funnel-shaped funnel 2 integrally joined to the panel 1, as shown in FIG. An electron gun 5 that emits three electron beams 4B, 4G, and 4R is disposed therein. Further, a phosphor screen 6 consisting of a dot-shaped or striped three-color phosphor layer that emits blue, green, and red light is formed on the inner surface of the panel 1.
A shadow mask 7 is mounted inside the phosphor screen 6, facing the phosphor screen 6. This shadow mask 7 consists of a mask main body 8 in which a large number of electron beam passage holes are formed, and a mask frame 9 attached to the periphery of the mask main body 8. An internal magnetic shield 10 located on the inside is attached. The electron beams 4B, 4G, and 4R emitted from the electron gun 5 are deflected by horizontal and vertical deflection magnetic fields generated by a deflection yoke 11 mounted outside the boundary between the large-diameter portion of the funnel 2 and the neck 3. By scanning the phosphor screen 6 horizontally and vertically,
It is formed in a structure to display a color image on this phosphor screen 6.

In order to improve the color purity of the color image drawn on the phosphor screen 6, it is necessary to properly land the three electron beams 4B, 4G, and 4R on the three-color phosphor layer. However, when an external magnetic field acts on the three electron beams 4B, 4G, and 4R emitted from the electron gun 5, the trajectory of the electron beams changes due to the Lorentz force, causing a deviation in beam landing. The internal magnetic shield 10 is for shielding an external magnetic field and preventing deviation of beam landing due to the external magnetic field.
Even if the internal magnetic shield 10 is provided as described above, there are color picture tubes in which the trajectory of the electron beam still changes.

[0005] By the way, the Lorentz force F (vector) acting on an electron beam in an external magnetic field is defined by the electron charge as e, the electron speed as v (vector), and the magnetic flux density as B (vector).
Then,

[0006]

[Math 1]

[0007]F=-ev×B……
...... It is expressed as (1).

To simplify the explanation, let us consider a color picture tube in which the three-color phosphor layer is made up of striped phosphor layers elongated in the vertical (y-axis) direction. In a tube, even if the landing is deviated in the vertical direction, no color shift occurs. However, landing deviation in the horizontal (x-axis) direction deteriorates color purity.

That is, the vertical component and the component in the tube axis (z-axis) direction of the electron velocity v are respectively vy, vz,
If the vertical component and tube axis component of the magnetic flux density B are By and Bz, respectively, then the horizontal component of the Lorentz force F acting on the electron beam is Fx,

0010

[Math 2]

Fx = −e(vy Bz −vz
By ) ......... (2) This indicates that the vertical component By and the tube axis direction component Bz of the magnetic flux density B interact with the tube axis direction component vz and the vertical component vy of the electron velocity v to cause landing deviation. In addition, when there is a magnetic field that crosses in the horizontal direction, the horizontal component Bx of the magnetic flux density B also changes to the internal magnetic shield 10 and the mask body 8 of the shadow mask 7.
Due to the influence of the magnetic flux density B and the mask frame 9, a vertical component By of the magnetic flux density B is generated, which affects the electron beam.

In FIGS. 8(a) to 8(c), arrows 13 indicate the direction of beam landing deviation with respect to the tube axis component Bz, vertical component By, and horizontal component Bx of the magnetic flux density B, respectively. Note that the broken line 14 shown in FIG. 8(c) is a magnetic field that crosses in the horizontal direction. Regarding geomagnetism, the direction of deviation of the beam landing with respect to the tube axis direction component Bz of the magnetic flux density B shown in Fig. 8(a) corresponds to the case where the color picture tube is changed from facing south to north, and The direction of deviation of the beam landing with respect to the horizontal component Bx shown in (c) corresponds to the case where the direction is changed from westward to eastward. Furthermore, the direction of deviation of the beam landing with respect to the vertical component By shown in FIG. 8(b) corresponds to the case where the color picture tube is moved from the southern hemisphere to the northern hemisphere. (However, as will be explained later, the direction of the force applied to the electron beam and the direction of the landing deviation may differ.) The amount of beam landing deviation (NS movement amount) when the color picture tube is changed from facing south to north. ) and the amount of beam landing deviation when changing from westward to eastward (E
When the amount of W movement is large, the beam landing of the color picture tube changes greatly depending on the direction in which it is arranged, and the color purity deteriorates. In addition, the vertical component By of the earth's magnetism changes depending on the region (mainly latitude), so if the beam landing shift (BV shift) when moving from the southern hemisphere to the northern hemisphere is large, the location where the color picture tube is used may change. Deterioration of color purity sometimes occurs. Therefore, it is necessary to make these NS movement amount, EW movement amount, and BV movement amount as small as possible.

Here, in particular, the vertical component B of the magnetic flux density B
To further explain the beam landing shift due to y, the deflection of the deflection yoke with respect to the electron beam emitted from the electron gun is handled as approximately bending at a virtual center of deflection. To simplify the explanation, let us consider an electron beam directed toward the center of the screen. As shown in FIG. The electron beam passes straight through the electron beam passage hole 17 at the center of the shadow mask 7 and reaches a point 18 at the center of the phosphor screen 6. However, when a downward vertical magnetic field is applied as shown by arrow 19, the electron beam is bent by ΔxC until it reaches the deflection center plane 16, as shown at 4a, and passes through point 20. Of this electron beam 4a, the electron beam 4b passing through the electron beam passage hole 17 at the center of the shadow mask 7 reaches a point 21 shifted by ΔxS from a point 18 on the center of the phosphor screen 6. In other words, when the vertical component By of the magnetic flux density B acts on the electron beam emitted from the electron gun, the electron beam is
It is bent during the time it reaches , and a landing error occurs on the phosphor screen 6 in the direction opposite to the bending direction.

By the way, the above ΔxC is the electron charge e, the electron density m, and the vertical component of the magnetic flux density B by By.
(z), and the voltage as a function of z is expressed as V(z).

[
0015

[Math 3]

It is expressed as follows. However, zC is the deflection center plane 16 when the cathode K is the origin of the coordinates (z=0)
is the z-coordinate of The trajectory of this electron beam actually requires consideration of the lens action of the electron gun, but this is not an essential issue and will therefore be omitted here.

Here, the electron beam passes through the shadow mask 7.
and the phosphor screen 6, and the movement from the deflection center plane 16 to the shadow mask 7 is expressed as ΔxC.
Shadow mask 7 when M and cathode K are set to z=0
and the z coordinate of the phosphor screen 6 as zM,
zS and L=zM −zC q=zS −zM,

[0018]

[Math 4]

[0019]

[0020]

[Math 5]

ΔxS is expressed as ΔxCM and ΔxCM.
The sign changes depending on the size of xC.

Regarding this ΔxS, in the conventional color picture tube, ΔxCM and ΔxC happened to cancel each other out, so the amount of BV movement was not a very large value, and there was no need to take any special measures. . However, in color picture tubes used for high-definition broadcasting and the like, in order to obtain the required high resolution, an electron gun with a longer overall length than that of conventional color picture tubes is used. When an electron gun with a long overall length is used, the distance from the cathode K to the deflection center plane becomes long, so ΔxC increases, and Δx
S has a large value in the direction opposite to the direction in which the electron beam is bent before reaching the center plane of deflection.

In order to reduce this ΔxS, it can be corrected by lowering the height (length in the z-axis direction) of the internal magnetic shield, but on the other hand, reducing the height of the internal magnetic shield reduces the NS
This is not preferable because the amount of movement and the amount of EW movement become large. Furthermore, even if the height of the internal magnetic shield is reduced, ΔxS may not be made sufficiently small. Rather, in conventional color picture tubes, the direction in which the electron beam is bent while reaching the center plane of deflection is the same direction as the direction in which ΔxS occurs, so in order to reduce ΔxS, the height of the internal magnetic shield must be adjusted. It needs to be as high as possible. In other words, Δ
This is the opposite of the case where xC is large, and there is no effective method.

[0024]

As described above, for color picture tubes, it is necessary to reduce deviations in beam landing due to external magnetic fields such as earth's magnetism. Of this beam landing deviation, the amount of Bv movement depends on the magnitude of the amount of bending ΔxC from the cathode of the electron gun to the deflection center and the amount of movement ΔxCM from the deflection center to the shadow mask. , the magnitude and sign are determined. Therefore, when an electron gun with a longer overall length than a conventional electron gun is used to achieve high resolution, ΔxC becomes large, and the amount of BV movement, ΔxS, is the direction in which the electron beam is bent before reaching the center plane of deflection. increases in the opposite direction. In this case, with conventional technical means, NS
BV without increasing the amount of movement or EW movement.
It was not possible to reduce the amount of movement.

The present invention has been made to solve the above-mentioned problems, and is capable of suppressing landing deviations due to vertical components of external magnetic fields without being affected by landing deviations due to horizontal components of external magnetic fields such as geomagnetism. An object of the present invention is to configure a color picture tube in which color purity is less degraded.

[Configuration of the invention]

[0027]

[Means for solving the problem] An electron gun is provided which forms an electron beam by applying voltages of different heights to a cathode and a plurality of electrodes arranged on the cathode, accelerates and focuses the electron beam, and emits the electron beam. In a color picture tube in which the electron beam emitted from the electron gun is deflected horizontally and vertically by a magnetic field generated by a deflection yoke and incident on a phosphor screen, a relatively Either the electrode to which a low voltage is applied is formed of a high-magnetic material, or the outer periphery of the electrode to which a relatively low voltage is applied is surrounded by a high-magnetic material between the cathode and the deflection center of the deflection yoke. The structure is such that the external magnetic field acting on the electron beam is shielded.

[0028]

[Operation] As mentioned above, among the electrodes that make up the electron gun,
Either the electrode to which a relatively low voltage is applied is made of a high-magnetic material, or the outer periphery of the electrode to which a relatively low voltage is applied is surrounded by a high-magnetic material, thereby creating a connection between the cathode and the deflection center of the deflection yoke. If a structure is adopted in which an external magnetic field acting on the electron beam is shielded between the two electrodes, the bending of the electron beam from the cathode to the center of deflection can be reduced. On the other hand, (3
) As can be seen from the equation, the shielding effect on the electron beam is
The smaller the distance z is, or the lower the voltage V is, the larger it becomes. In reality, the behavior of electrons in an electron gun is simply (3)
Although it cannot be expressed in a formula, the above-mentioned tendency of the shielding effect holds true. Therefore, B
V The amount of movement can be reduced.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments with reference to the drawings.

FIG. 1 shows a color picture tube which is one embodiment of the present invention. This color picture tube has an envelope consisting of a panel 1 and a funnel-shaped funnel 2 integrally joined to the panel 1, and a three-color phosphor layer that emits blue, green, and red on the inner surface of the panel 1. A phosphor screen 6 consisting of
A shadow mask 7 is mounted inside the phosphor screen 6, facing the phosphor screen 6. This shadow mask 7 consists of a mask main body 8 in which a large number of electron beam passage holes are formed, and a mask frame 9 attached to the periphery of the mask main body 8. A magnetic shield 10 is attached. In addition, 3 electron beams 4B, 4G,
An electron gun 30 which will be described later and emits 4R is provided. Further, an anode terminal 31 is formed on the large diameter portion of the funnel 2, and an internal conductive film 32 is further formed from the large diameter portion of the funnel 2 to the inner surface of the adjacent portion of the neck 3.

Note that 11 is a deflection yoke mounted on the outside of the boundary between the large diameter portion of the funnel 2 and the neck 3.

In order to improve its performance, the electron gun 30 has more electrodes and a longer overall length than a conventional ordinary electron gun. That is, as shown in FIG.
0 has three cathodes K (only one is shown in the drawing),
Three heaters H heat these three cathodes K separately.
, a control grid G1 and a screen grid G2 constituting an electron beam forming section arranged adjacent to each other in order on the cathode K, and an electron lens section for extracting and accelerating and focusing the electron beam from the electron beam forming section. It comprises first to eighth grids GD1 to GD8, and these heaters H, cathodes K and each grid G1,
G2, GD1 to GD8 are integrally fixed by a pair of insulating supports 31.

[0033] The above grids G1, G2, GD1 to G
Of D8, the control grid G1 and screen grid G2 of the electron beam forming section are made of plate-shaped electrodes. Also, the first to seventh grids GD1 of the electronic lens section
~ GD7 is composed of a cylindrical electrode that is a combination of a plurality of cup electrodes, and in particular, the second grid GD2 is formed in a structure in which the cylindrical electrode is combined with a plate electrode. Three electron beam passage holes are formed in these grids G1, G2, GD1 to GD7, corresponding to the three cathodes K. Further, the eighth grid GD8 is composed of a large-diameter cylindrical electrode that surrounds the tip end side of the seventh grid GD7. Particularly in a color picture tube, the first to fifth grids GD1 to GD of the electronic lens section
5 is made of a high magnetic permeability material with an initial magnetic permeability μ of about 3000.

The voltage is applied to each electrode of the electron gun 30 except for the eighth grid GD8 to which a high voltage is applied to the anode.
It is supplied via a stem pin 35 that hermetically passes through. In addition, the eighth grid GD8 includes an anode terminal 31 provided in the large diameter portion of the funnel 2, an internal conductive film 32, and an eighth grid GD8.
It is supplied via a valve spacer 36 attached to the grid GD8 and in pressure contact with this internal conductive film 32 (Fig.
reference). The voltage is, for example, approximately 150V on the cathode K.
A voltage obtained by adding the video signal to the cutoff voltage of is applied,
Control grid G1 is grounded, screen grid G2 is 500~1kV, first, third, fifth, seventh grids GD1, GD3, GD5, GD7 are 5~1kV.
10KV, 0 to 1kV to the second grid GD2, 0 to 3kV to the fourth grid GD4, 15 to 20kV to the sixth grid GD6, 25 to 35kV to the eighth grid GD8
A high anode voltage of V is applied.

In a color picture tube equipped with such an electron gun 30, for example, a 32-inch color picture tube, the distance LC from the cathode to the deflection center plane is 170 mm, and the distance LC from the deflection center plane to the phosphor screen 6 is 170 mm. LCS is 3
The distance LC from the cathode to the deflection center plane of a conventional color picture tube of the same type is approximately 140 mm, but as the overall length of the electron gun 30 becomes longer,
The 3rd part of the neck is longer.

By the way, when the neck 3 becomes longer as described above, when an external magnetic field is applied to the color picture tube, the amount ΔxC of the electron beam being bent by the vertical component from the cathode K to the center of deflection increases. growing. In other words, in a color picture tube such as the electron gun 30 in this example in which part of the electrode is not made of a material with high magnetic permeability, as the electron gun becomes longer, the amount of bending between the cathode and the center of deflection decreases. ΔxC is large and is then bent significantly in the opposite direction, resulting in a large beam landing deviation on the phosphor screen (see FIG. 9). The curve 38 shown in FIG. 3 represents the vertical component By of the magnetic flux density B for a color picture tube in which the electrodes are not made of a high magnetic permeability material as described above.
This is the relationship between the distance LC from the cathode to the deflection center plane and the deviation amount ΔxS of the beam landing on the phosphor screen, which was actually measured while changing the angle by ±35 μT. As can be seen from this curve 38, ΔxS changes in the negative direction as LC increases. Also, this cathode K
By weakening the vertical component By of the magnetic flux density B applied from 1 to 2 to the center of deflection, ΔxS changes in the positive direction.

Therefore, in contrast to the ΔxS that occurs in the case of a conventional color picture tube in which the distance LC from the cathode to the center plane of deflection is approximately 140 mm, the color picture tube in this example has a longer LC of 170 mm. , a part of the electrodes, that is, the first to fifth grids GD1 to GD5, are formed of a high magnetic permeability material to shield external magnetic fields that act on the electron beam between the cathode and the deflection center plane, so that the electron beam is substantially separated from the cathode. The distance LC to the deflection center plane becomes shorter, and Δ
xS can be made smaller.

FIG. 4(a) shows the first to fifth grids GD.
1 to GD5 for a 32-inch color picture tube made of high magnetic permeability material, at the center of the screen, at the horizontal axis end, at the vertical axis end, and at the diagonal axis end when the vertical component By of the magnetic flux density B is changed by ±35 μT. The beam landing deviation amount ΔxS is shown. The - sign indicates that the direction is opposite to the direction in which the electron beam is bent between the cathode and the center plane of deflection. FIG. 6(b) is a comparative example of the same type of color picture tube in which the first to fifth grids are not made of a high magnetic permeability material. As can be seen from the comparison of (a) and (b), when the first to fifth grids GD1 to GD5 are made of a high magnetic permeability material, the beam landing occurs over the entire screen compared to when they are not made of a high magnetic permeability material. The amount of deviation ΔxS can be significantly reduced.

Note that in the electron gun 30 of this example, FIG.
), if the electrodes are not made of high magnetic permeability material,
Because the beam landing deviation is quite large, the 5th grid in front of the 1st grid GD1 to 6th grid GD6
Although grids up to GD5 are made of high magnetic permeability material, in general, electrodes made of high magnetic permeability material should be selected depending on the deviation amount ΔxS of beam landing when the electrodes are not made of high magnetic permeability material. However, it is not limited to the first to fifth grids GD1 to GD5.

In addition, as can be seen from equation (3), the selection of the electrode formed of the high magnetic permeability material is based on the electrode close to the cathode (z
The smaller the applied voltage, the better, and the lower the applied voltage, the more effectively the amount of bending of the electron beam between the cathode and the deflection center plane can be reduced. It is preferable to use a material with high magnetic permeability. Note that the sixth grid GD6, which is a focusing electrode,
Regarding forming the subsequent electrodes with high magnetic permeability material,
A ring-shaped permanent magnet for static convergence and color purity adjustment is attached to the outside of the neck of the sixth grid GD6, so if the electrodes after the sixth grid GD6 are formed of a high magnetic permeability material, the magnetic field of the permanent magnet This is undesirable because it makes it difficult to adjust static convergence and color purity, and it also disturbs the rear leakage magnetic field of the deflection yoke. On the other hand, even if the electrodes on and after the sixth grid GD6 are formed of a high magnetic permeability material, it is difficult to obtain the expected effect because a high voltage is usually applied to these electrodes.

Next, another embodiment will be explained.

In the above embodiment, a part of the electrode of the electron gun was made of a material with high magnetic permeability to reduce the amount of bending of the electron beam between the cathode and the center plane of deflection.
An electron gun 30 having the same electrode configuration as in the above embodiment is disposed inside the neck 3, and a cylindrical tube made of a high magnetic permeability material is provided on the outside of the neck 3 facing the first to fifth grids of the electron lens section of the electron gun 30. A body 40 is arranged. For example, in the case of a 32-inch color picture tube, such a cylindrical body 40 is formed to have a thickness of about 0.25 mm and a length of about 30 mm.

FIG. 6 shows the vertical component B of the magnetic flux density B for the color picture tube with the cylindrical body 40 attached in this manner.
The beam landing deviations at the screen center, horizontal axis end, vertical axis end, and diagonal axis end are shown when y is changed by ±35 μT. In this case as well, the amount of deviation ΔxS can be significantly reduced compared to the beam landing deviation of the color picture tube that does not use a high magnetic permeability material as shown in FIG. 4(b).

Note that Japanese Patent Laid-Open No. 61-138433 discloses a color picture tube in which a non-magnetic magnetic shield for shielding external magnetic fields is arranged from the deflection yoke to the neck. The magnetic shield is used to prevent the magnetic field generated by the permanent magnet for static convergence and color purity adjustment attached to the outside of the neck from changing due to an external magnetic field after adjustment. , which covers at least the focusing electrode portion of the electron gun, and is different from the color picture tube of this example described above in terms of structure and operation and effect.

[0045]

[Effects of the Invention] Among the electrodes constituting the electron gun, the electrodes to which a relatively low voltage is applied are made of a high magnetic coefficient material, or the outer periphery of the electrodes to which a relatively low voltage is applied is made of a high magnetic coefficient material. If the structure is such that the external magnetic field acting on the electron beam is shielded between the cathode and the deflection center of the deflection yoke, the vertical component of the external magnetic field will cause the electron beam to bend between the cathode and the deflection center. Because of its large size, the deviation of the beam landing on the phosphor screen is in the opposite direction to the bending of the electron beam between the cathode and the center of deflection. The bending of the electron beam can be reduced, and a color picture tube with less deterioration in color purity can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a color picture tube that is an embodiment of the present invention.

FIG. 2 is a diagram showing the configuration of an electron gun in which a part of the electrode is formed of a high magnetic permeability material.

FIG. 3 is a diagram showing the relationship between the distance from the cathode of the electron gun to the center of deflection and the deviation of beam landing on the phosphor screen.

[Fig. 4] Fig. 4(a) is a diagram showing the amount of beam landing deviation of a color picture tube equipped with an electron gun whose electrodes are partially formed of high magnetic permeability material, and Fig. 4(b) is a diagram showing a comparison. FIG. 4 is a diagram showing the amount of deviation in beam landing of a color picture tube provided with an electron gun in which the electrodes shown in FIG.

FIG. 5 is a diagram showing the main part configuration of another embodiment of the present invention.

FIG. 6 is a diagram showing the amount of beam landing deviation in the other embodiment.

FIG. 7 is a diagram showing the configuration of a conventional color picture tube.

8(a) is a diagram showing the beam landing deviation with respect to the tube axis direction component of the magnetic flux density, FIG. 8(b) is a diagram showing the beam landing deviation with respect to the vertical direction component of the magnetic flux density, FIG. c) is a diagram showing the deviation of beam landing with respect to the horizontal component of magnetic flux density.

FIG. 9 is a diagram for explaining a beam landing shift due to a vertical component of an external magnetic field.

[Explanation of symbols]

3...Neck 4B, 4G, 4R…3 electron beams 6...phosphor screen 7...Shadow mask 10...Internal magnetic shield 11...Deflection yoke 30...electron gun 31...Insulating support G1...Control grid G2…Screen grid GD1...1st grid GD2...Second grid GD3...Third grid GD4...4th grid GD5...5th grid GD6...6th grid GD7...7th grid GD8...8th grid 40...Cylindrical body made of high permeability material

Claims (1)

[Claims] 1. An electron gun that forms an electron beam by applying voltages of different heights to a cathode and a plurality of electrodes arranged on the cathode, accelerates and focuses the electron beam, and emits the electron beam. In a color picture tube in which the electron beam emitted from the gun is deflected horizontally and vertically by a magnetic field generated by a deflection yoke and incident on a phosphor screen, a relatively low voltage is applied among the electrodes that make up the electron gun. The electron beam is formed between the cathode and the deflection center of the deflection yoke by forming the electrode to be applied with a high magnetic coefficient material, or by surrounding the outer periphery of the electrode to which a relatively low voltage is applied with a high magnetic coefficient material. A color picture tube characterized in that it is formed in a structure that shields an external magnetic field acting on the color picture tube.