JP2746962B2 - Color picture tube - Google Patents

Description

The present invention relates to a color picture tube, and more particularly to a color picture tube having an improved magnetic shielding effect by an inner shield.

(Prior Art) Generally, a color picture tube has an envelope composed of a panel (1) and a funnel-shaped funnel (2) integrally joined to the panel (1) as shown in FIG. A phosphor screen (3) composed of a three-color phosphor layer is formed on the inner surface of the panel (1), and a large number of electron beam passage holes are formed inside the panel so as to approach and face the phosphor screen (3). A shadow mask (4) is provided. An electron gun (6) for emitting three electron beams is disposed in a neck (5) of the funnel (2).
The three electron beams emitted from the screen are deflected in the horizontal and vertical directions by a deflection yoke (7) mounted outside the funnel (2), and a color image is displayed by scanning the phosphor screen (3). It has a structure to do.

In order to correctly display a color image on the phosphor screen (3), the three-color phosphor layer of the phosphor screen (3) and the electron beam passage holes of the shadow mask (4) have a matching relationship. However, even if the three-color phosphor layer is correctly aligned with the electron beam passage hole, the electron beam actually emitted from the electron gun (6) receives an external magnetic field such as terrestrial magnetism, and thus the electron beam (3).
Does not land correctly on the color phosphor layer. Therefore,
In order to prevent the influence of the external magnetic field, conventionally, one end is fixed to the inside of the cone portion (8) of the funnel (2) or the shadow mask (4) or the vicinity thereof and extends in the direction of the electron gun (6). An inner shield (9) made of a magnetic metal is provided.

FIG. 6 shows a basic inner shield arranged inside the cone portion of a funnel funnel having a substantially rectangular cross section. This inner shield (9a) has a thickness of 0.1-0.3mm
It is made of mild steel and has a substantially rectangular hollow trapezoidal shape.

However, in this inner shield (9a), there is a limit in magnetic shielding, and an intended beam landing may not be obtained in some cases. In order to solve this, it is necessary to make the direction of the magnetic field match the trajectory of the electron beam as much as possible, or to convert the magnetic field into a component of the direction that does not affect the beam landing.

In order to explain the magnetic shielding effect of the inner shield, a magnetic field component affecting beam landing will be described as follows. For simplicity,
The most common three-color phosphor screen today is a phosphor screen in which the three-color phosphor layer is a striped phosphor layer parallel to the vertical axis (short axis) of the screen. In this case, the longitudinal direction of the phosphor layer, that is, the screen vertical Even if a landing displacement occurs in the axial direction, no color displacement occurs in principle. However, a landing shift occurs in the horizontal axis (long axis) direction of the screen as described below, which affects color shift.

Assuming that the vertical axis of the screen is y and the tube axis is z, the magnetic field component affecting beam landing is the magnetic flux density , And a tube axis direction component Bz. By the way, the Lorentz force generally applied to charged particles Is given by g charge and v It is represented by Therefore, for an electron beam, if the electron charge is e, Becomes Therefore, the horizontal component of the Lorentz force that affects the landing in the horizontal direction of the screen is Fx, and the vertical component and the vertical component of the electron are v
Assuming that y and vz, Fx = −e (vyBz−vzBy), and the vertical axis component By and the tube axis component Bz of the magnetic flux density interact with the tube axis component vz of the velocity and the vertical axis component vy of the velocity, respectively. As a result, a landing deviation occurs.

FIG. 7A shows the direction of movement of the beam spot by the tube axial component Bz of the magnetic flux density by an arrow (11). This is actually a beam shift caused by the horizontal component Bx of the geomagnetism and the vertical component vy of the electron beam due to vertical deflection when the color picture tube is installed to the north. Also, the arrow (12) shows the moving direction of the beam spot due to the vertical axis component By of the magnetic flux density in FIG. This is a beam shift caused by the vertical axis component By of the magnetic flux density in the northern hemisphere and the velocity component of electrons traveling toward the phosphor screen, that is, the velocity component vz of electrons in the tube axis direction.

From the relationship between this magnetic flux and the electron beam, see JP-A-53-15061.
FIG. 8 shows an inner shield (9b) in which a V-shaped cut (14) is formed on the short side of a substantially rectangular hollow trapezoidal inner shield as shown in FIG. Further, Japanese Utility Model Publication No. 55-36928 discloses an example in which inner shields are unevenly distributed on the upper and lower sides of the screen.

In these inner shields, the magnetic flux component Bz in the tube axis direction absorbed by the short side wall (15) of the inner shield (9a) shown in FIG. 6 is forced in the long side direction (vertical axis direction),
Accordingly, the component By in the vertical axis direction is larger than that of the inner shield (9a) in FIG. As a result, as shown by a broken line (16) in FIG.
It moves to the right at the top of the screen and to the left at the bottom of the screen,
A clockwise rotation effect occurs. This offsets the beam shift in the left rotation direction shown in FIG. 7 (a), and improves the color purity when the color picture tube is installed facing north or south. On the other hand, when the color picture tube is installed facing east or south, the horizontal axis component Bx is more likely to pass through the electron beam passage area inside the inner shield. As a result, the magnetic flux density in the electron beam passage area inside the inner shield increases, and the magnetic field (17) is shaped into a barrel as shown in FIG. 9, and the lower the corner of the screen, the higher the vertical axis component By increases. As a result, a trapezoidal landing shift is generated, and the beam shift in the left rotation direction shown in FIG. 7A is canceled to improve the color purity.

There are various improvements of this kind of inner shield,
For example, Japanese Patent Application Laid-Open No. 54-13253 discloses an inner shield (9c) in which the inner shield is divided into two parts along a vertical axis as shown in FIG. As shown in FIG. 11, an inner shield (9d) having an opening (18) in the side wall is further provided in Japanese Patent Application Laid-Open No. 58-178945.
In the official gazette, as shown in FIG. 12, a V-shaped cut (1
An inner shield (9e) in which 4) is combined with an opening (18) in the long side wall is shown.

However, none of these inner shields corrects the landing deviation on the entire screen to the extent that the landing deviation can be satisfied. Therefore, the arrangement pitch of the electron beam passage holes of the shadow mask is smaller than that of the ordinary color picture tube, and the arrangement pitch of the three-color phosphor layers is correspondingly small, and the shadow mask and the fluorescent mask In a color picture tube having a large distance from the body screen, a landing deviation due to terrestrial magnetism cannot be ignored and a remarkable color deviation occurs on the screen. That is, none of the conventional inner shields can sufficiently reduce the landing deviation due to terrestrial magnetism over the entire screen, and may cause color deviation on the screen.

(Problems to be Solved by the Invention) As described above, in the conventional color picture tube, a trapezoidal hollow inner shield is arranged inside the cone portion of the funnel-shaped funnel in order to prevent landing displacement due to an external magnetic field such as terrestrial magnetism. doing. However, this hollow trapezoidal inner shield may not have a sufficient magnetic shielding effect, and may not be able to obtain a desired beam landing. Therefore, there is a structure in which the shape of the inner shield is improved so that the direction of the magnetic field matches the trajectory of the beam, or the direction is changed to a direction that does not affect the beam landing. However, none of these inner shields corrects the landing deviation over the entire screen to a satisfactory degree. Especially in the case of a high-definition color picture tube, the landing deviation due to terrestrial magnetism cannot be ignored in practical use.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a color picture tube capable of enhancing a magnetic shielding effect of an inner shield and suppressing a landing deviation due to terrestrial magnetism to a practically acceptable level. And

[Constitution of the Invention] (Means for Solving the Problems) An inner shield made of a ferromagnetic metal is disposed between a shadow mask and an electron gun so as to surround a passage area of an electron beam emitted from the electron gun. In this color picture tube, a mesh or a thin wire array made of ferromagnetic metal thin wires was arranged at the opening of the inner shield on the electron gun side.

(Operation) As described above, when a mesh or a thin wire array made of a ferromagnetic metal thin wire is arranged in the electron gun side end opening of the inner shield disposed between the shadow mask and the electron gun, the inner shield and the mesh or The thin wire array shields the inner space in the inner shield against an external magnetic field so as not to affect the landing, and it is possible to reduce landing deviation due to terrestrial magnetism until practically no problem occurs.

Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

FIG. 1 shows the structure of a color picture tube according to an embodiment of the present invention. This color picture tube has a substantially rectangular panel (1) and an outer container composed of a funnel-like funnel (2) integrally joined to the panel (1). , A phosphor screen (3) comprising a three-color phosphor layer that emits green and red light is formed, and a number of electron beam passage holes are formed inside the phosphor screen (3) so as to approach and face the phosphor screen (3). Shadow mask (4)
Are arranged. An electron gun (6) for emitting three electron beams is provided in a neck (5) of the funnel (2). The electron beam emitted from the electron gun (6) is horizontally and thrust driven by a deflection yoke (7) mounted outside the boundary between the cone (8) and the neck (5) of the funnel (2). It is deflected and scans the phosphor screen (3) through the electron beam passage holes of the shadow mask (4).

The inner conductive film (20) extends from the inside of the cone (8) of the funnel (2) to the inner surface of the adjacent part of the neck (5).
One end is fixed to a shadow mask (4) so as to surround a passage area of the electron beam emitted from the electron gun (6) inside the cone portion (8), and the electron gun (6) is formed. An inner shield (21) having a hollow trapezoidal integrated structure made of a ferromagnetic metal extending in the direction is disposed. As shown in FIG. 2, a coarse mesh (22) made of a ferromagnetic metal fine wire is attached to an end opening of the inner shield (21) on the electron gun (6) side. This mesh (22) is obtained, for example, by stretching a mild steel wire having a diameter of about 0.1 mm so as to intersect at a pitch of about 10 mm. That is, when the wire diameter of the metal wire is large and the pitch is small, the number of electrons colliding with the electron beam and reaching the phosphor screen is reduced. The number of scattered electrons and secondary electrons increases, and the image trust decreases.
On the other hand, if the wire diameter is too small, the shielding of terrestrial magnetism is weakened, and if the pitch is too large, the shielding of terrestrial magnetism is weakened. Therefore, it is preferable to use a ferromagnetic metal wire having a wire diameter of about 0.1 mm and to form the wire to have a mesh of 1 to 2 mesh or less, preferably about 0.2 mesh.

The inner shield (21) is connected to the inner conductive film (20) and the shadow mask (4) via the PF connector (24) and the shadow mask (4) which are pressed against the inner conductive film (20). Then, an anode voltage supplied to an anode terminal (not shown) provided on the side wall of the cone portion (8) is applied, and the mesh (22) attached to the inner shield (21) also has the same potential.

Therefore, in this color picture tube, the electron beam emitted from the electron gun (6) goes straight in the equipotential space surrounded by the inner shield (21) and the mesh (22),
The phosphor screen (3) is irradiated through the electron beam passage holes of the shadow mask (4).

By the way, as described above, an inner shield (21) made of a ferromagnetic metal is provided inside the cone portion (8) so as to surround the passage area of the electron beam.
If a mesh (22) made of a ferromagnetic metal thin wire is provided in the opening at the side of the electron gun (6) in 1), the geomagnetism is substantially reduced in the space surrounded by the inner shield (21) and the mesh (22). Completely shielded, the electron beam is hardly affected by geomagnetism in this space. Therefore,
The difference in the movement of the electron beam when the color picture tube is installed in the north or south direction and the difference in the movement when the color picture tube is installed in the east or west direction can be suppressed to be small.

That is, the influence of the terrestrial magnetism on the color picture tube is as follows in the mounting portion of the deflection yoke (7) shown by the area A in FIG.
The electron beam is shielded by the annular core made of ferromagnetic metal of the deflection yoke (7), so that the electron beam is not affected by geomagnetism. Between the region A and a region C which is a space surrounded by the inner shield (21) and the mesh (22), the deflection sensitivity is reduced, the deflection magnetic field distribution is disturbed, or an eddy current generated by the deflection magnetic field is generated. A space indicated by a region B is provided to prevent the inner shield (21) from generating heat,
In this region B, the electron beam is affected by geomagnetism. However, since the region B can be made narrower than the regions A and C, the moment can be reduced even if it is affected by geomagnetism. That is, in a normal color picture tube, the area A is about 100 mm, the area C is 150 to 200 mm, and the area B is about 30 mm based on the above deflection sensitivity and deflection magnetic field distribution, which is smaller than the areas A and C. The space between the shadow mask (4) and the phosphor screen (3), which is indicated by the area D, is usually about 10 to 15 mm, and there is almost no problem with the influence of terrestrial magnetism.

By the way, when the color picture tube is configured as described above,
The inner shield (21) and the mesh (22) shield a large part of the passage area of the electron beam emitted from the electron gun (6) from terrestrial magnetism, and match the direction of the magnetic field with the trajectory of the electron beam as in the past. Unlike the method in which the electron beam is moved in a direction that does not affect the beam landing, the amount of movement of the electron beam itself is reduced by the shielding, so that the influence on the beam landing can be greatly reduced.

In the above embodiment, the mesh is attached to the inner shield having a hollow trapezoidal integral structure, but as shown in FIG. 3, for example, a substantially rectangular hollow base having a V-shaped cut (14) formed on the short side. A ferromagnetic metal wire is stretched over the electron gun-side end opening of the inner shield (9b) in the shape of a mesh (2
2) can also be formed. With such a structure, landing displacement can be almost completely eliminated by the interaction between the action of changing the direction of the magnetic field based on the shape of the inner shield (9b) and the shielding action by the mesh (22).

In the above embodiment, the mesh of the opening at the end of the electron gun side of the inner shield is arranged, but instead of this mesh, as shown in FIG. 4, the trapezoidal hollow inner shield (9a) has the mesh at the electron gun side. A ferromagnetic metal thin wire may be stretched in the same direction in the end opening to form a thin wire row (25).

Note that it is not necessary to apply tension to the thin metal wire that extends to the opening at the electron gun side end of the inner shield.

[Effect of the Invention] An inner shield made of a ferromagnetic metal is provided so as to surround an electron beam passage area between the shadow mask and the electron gun, and a ferromagnetic metal thin wire is provided at an opening of the inner shield on the electron gun side. By arranging a mesh or a thin wire row consisting of, the inner shield and the mesh or the thin wire row can shield the space inside the inner shield against an external magnetic field so as not to affect the landing of the electron beam,
Landing deviation due to terrestrial magnetism can be reduced to a level that does not cause any practical problem, and deterioration in color purity can be eliminated. Therefore, even in a high-definition color picture tube in which a color shift occurs in the conventional inner shield, the influence of the terrestrial magnetism can be reduced to a state where there is no problem. In addition, the present invention can be applied to a color picture tube for an in-vehicle or an airplane required to keep the absolute amount of a landing deviation due to terrestrial magnetism small.

[Brief description of the drawings]

FIGS. 1 to 4 are explanatory views of an embodiment of the present invention. FIG. 1 is a view showing the structure of a color picture tube according to an embodiment of the present invention.
FIG. 3 is a perspective view showing the structure of the inner shield, FIGS. 3 and 4 are perspective views showing the structure of the inner shield of another embodiment different from each other, and FIG. 5 is a view showing the structure of a conventional color picture tube. , FIG. 6 is a perspective view showing the structure of the inner shield, and FIGS. 7 (a) and 7 (b) show the movement of the beam sbot by the tube axial component of the magnetic flux density and the movement of the beam sbot by the vertical component, respectively. FIG. 8 is a perspective view of a substantially rectangular hollow trapezoidal inner shield in which a V-shaped cut is formed on a short side, and FIG.
FIGS. 10 to 12 are a plan view, a front view, and a perspective view showing different conventional inner shields, respectively, for explaining the operation of the inner shield having the V-shaped cuts formed therein. DESCRIPTION OF SYMBOLS 1 ... Panel 2 ... Funnel 3 ... Phosphor screen 4 ... Shadow mask, 6 ... Electron gun 7 ... Deflection yoke, 8 ... Cone section 14 ... V-shaped cut, 21 ... Inner shield 22 ... mesh, 25 ... fine line

Claims (1)

(57) [Claims] 1. A phosphor screen, comprising: a shadow mask positioned close to and opposed to the phosphor screen; and an electron gun for emitting an electron beam for scanning the phosphor screen. In a color picture tube provided with an inner shield made of a ferromagnetic metal so as to surround an electron beam passage area between the mesh, a mesh made of a ferromagnetic metal thin wire or A color picture tube characterized by having a thin line array.