Optimal inner shield assembly for shielding an external magnetism in a color cathode ray tube

ABSTRACT

An inner shield assembly capable of maximizing an external magnetism shield effect. The inner shield assembly is provided at the rear side of a frame assembly for shielding external magnetism and includes a main body for shielding the inside of a funnel, a rectangular beam shield combined to the front of the main body and a front portion extending from the edge of the front of the beam shield around the outside of the shadow mask and the frame assembly. The material of the front portion has a maximum permeability of at least 3,000 and a coercivity of at most 1.25 Oe.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of an inner shield assembly according to the present invention will be described in detail with respect to the accompanied drawings in which the same reference numerals are used throughout the different drawings to designate the same or similar components.

FIGS. 6and are a deployed view and an assembled view, respectively, for illustrating an inner shield assembly which is an external magnetism shield structure of a color cathode ray tube according to the present invention.

As shown in FIGS. 6and , an inner shield assembly covers the inside of the funnel ( in FIG. ), the frame assembly and the shadow mask in the rear of the frame assembly comprising the main frame and the sub-frame

In addition, the inner shield assembly generally comprises a rough pyramid-shaped main body for shielding the inside of the funnel, a rectangular beam shield combined to the front of the main body , and a front portion formed extending from the edge to the front of the beam shield around the outside of the shadow mask and the frame assembly .

In addition, the beam shield and front portion of the inner shield assembly are integrally formed and the main body is attached to the beam shield by means of a fixture pin in a state that a combining hole formed on a flange of the main body and a combining hole of the beam shield are aligned with registration.

On the other hand, an external magnetism shield effect is affected by thickness and magnetic characteristic of material, as well as the structure of the inner shield assembly . The present invention optimizes the magnetic characteristic of component material of the inner shield assembly in order to improve the magnetism shield function.

Accordingly, particularly, there is a need to limit permeability and coercivity of material of the front portion and main body of the inner shield assembly according to the present invention within a predetermined range.

FIG. 7 is a graph showing a magnetic hysteresis loop for explaining permeability and coercivity of material employed in the present invention.

For the purpose of easy understanding, permeability and coercivity of the inner shield assembly of the cathode ray tube are briefly described with reference to FIG. 7 below.

When a magnetizing force H of ferromagnetic substance is increased to some degree, and after that, is decreased, a path that magnetic flux density B is increased when the magnetizing force is increased is not equal to a path that the magnetic flux density is decreased when the magnetizing force is decreased. And, when coercivity is decreased, the magnetic flux density is delayed. This phenomenon is referred to as “magnetic hysteresis” and a curve formed by the paths is referred to as “magnetic hysteresis loop”.

In addition, in the magnetic hysteresis loop in FIG. 7, a curve (oab) is referred to as “normal induction curve”, a magnetic flux density when H=0 is referred to as “residual magnetic flux density (Br)”, and an absolute value of negative magnetizing force when B=0 is referred to as “coercivity(Hc)”.

In addition, point (b) is referred to as “maximum magnetic flux density (Bm)”, a magnetizing force corresponding to the point (b) is referred to as “maximum magnetizing force (Hm)”, a curve (cd) is referred to as “demagnetizing curve”, and product of a magnetic flux density by a magnetizing force at any point on the curve (cd) is referred to as “energy product”.

In addition, a ratio of a magnetic flux density to a magnetizing force at any point on the normal induction curve is referred to as “normal permeability” and a maximum value of the normal permeability is referred to as “maximum permeability”.

FIG. 8 is a graph showing the relationship between the beam movement and permeability of the front portion material of the inner shield assembly according to the present invention, and FIG. 9 is a graph showing the relationship between the beam movement and coercivity of the front portion material of the inner shield assembly according to the present invention.

The meaning of the magnetism shield is not that magnetism is interrupted, but that an incoming magnetic field is decreased by concentrating magnetism on a material having a good magnetization. Particularly, the material having a good magnetization has a high permeability and a weak coercivity.

In order to prevent the electron beams from hitting on other colors at the time of rotation of direction of the color cathode ray tube so that color purity of a screen is maintained, an amount of movement of beams at the time of such a rotation due to an external magnetism, particularly, an earth magnetism, should be at most 60 μm.

Accordingly, as shown in the graphs of FIGS. 8 and 9, it is preferable that material of the front portion has the maximum permeability of at least 3000 and coercivity of at most 1.25 Oe so that the front portion shields the earth magnetism effectively.

FIG. 10 is a graph showing a relationship between the beam movement and a ratio of permeability of the front portion to that of main body material of the inner shield assembly according to the present invention, and FIG. 11 is a graph showing a relationship between the beam movement and a ratio of coercivity of the main body to that of front portion material of the inner shield assembly according to the present invention.

Similar to the front portion , when material having a high maximum permeability and a low coercivity is used as the material of the main body , excellent shield effect can be obtained. However, since magnetism is concentrated on the shield material having a high permeability, it is not preferable that magnetic characteristic of material of the front portion is greatly different from that of the main body .

Accordingly, as shown in FIGS. 10 and 11, it is required to limit the magnetic characteristic between the front portion and the main body within a predetermined range.

In other words, the magnetic characteristic of each of material is adjusted to have an interrelation of 0.5≦μ2/μ1≦1.5, where, maximum permeability of material of the main body is μ1 and maximum permeability of material of the front portion is μ2. In addition, the magnetic characteristic of each of material is adjusted to have an interrelation of 0.5≦H/H≦3.0, where, coercivity of material of the main body is H and coercivity of material of the front portion is H. As a result, an optimal magnetism shield effect can be obtained.

As described above, according to the present invention, since the inner shield assembly extends around the outside of the shadow mask and the frame assembly, the magnetism shield function can be improved. In addition, since magnetic characteristic of material of each portion of the inner shield assembly is optimized, the magnetism shield effect may be enhanced.

Accordingly, a margin of directional rotation of the cathode ray tube can be increased and the color purity also can be maintained.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a partial sectional view for illustrating a structure of a conventional color cathode ray tube;

FIG. 2 is a state diagram showing movement of electron beams by an effect of earth magnetism in a conventional color cathode ray tube;

FIG. 3 is a view showing a variation of electron beam landing position of A portion of FIG. 2;

FIGS. 4and are a deployed view and an assembled view, respectively, for illustrating an example of an inner shield assembly structure of a conventional color cathode ray tube;

FIGS. 5and are a deployed view and an assembled view, respectively, for illustrating another example of an inner shield assembly structure of a conventional color cathode ray tube;

FIGS. 6and are a deployed view and an assembled view, respectively, for illustrating an inner shield assembly structure of a color cathode ray tube according to the present invention;

FIG. 7 is a graph showing a magnetic hysteresis loop for explaining permeability and coercivity of material employed in the present invention;

FIG. 8 is a graph showing a relation between beam movement and permeability of the front portion material of the inner shield assembly according to the present invention;

FIG. 9 is a graph showing a relation between beam movement and coercivity of the front portion material of the inner shield assembly according to the present invention;

FIG. 10 is a graph showing a relation between beam movement and a ratio of permeability of the front portion to that of main body material of the inner shield assembly according to the present invention;

FIG. 11 is a graph showing a relation between the beam movement and a ratio of coercivity of the main body to that of front portion material of the inner shield assembly according to the present invention.

CLAIMS

1. An inner shield assembly provided at the rear side of a frame assembly having a main frame and a sub-frame for shielding an external magnetism, comprising: a main body for shielding the inside of a funnel; a rectangular beam shield attached to the front of the main body; and a front portion formed extending from the edge to the front of the beam shield around the outside of a shadow mask and the frame assembly, wherein material of the front portion is different from the material of the main body and has a maximum permeability of at least 3000 in order to concentrate said external magnetism on a material having good magnetization.

2. The inner shield assembly according to claim 1, wherein material of the front portion has coercivity of at most 1.25 Oe.

3. The inner shield assembly according to claim 2, wherein a magnetic characteristic of each of material of said main body and said front portion has an interrelation of 0.5≦μ2/μ1≦1.5, where, the maximum permeability of material of the main body is μ1 and the maximum permeability of material of the front portion is μ2.

4. The inner shield assembly according to claim 2, wherein the magnetic characteristic of each of material of said main body and said front portion has an interrelation of 0.5≦H1/H2≦3.0, where, coercivity of material of the main body is H1 and coercivity of the material of the front portion is H2.

5. The inner shield assembly according to claim 1, wherein the magnetic characteristic of each of material of said main body and said front portion has an interrelation of 0.5≦μ2/μ1≦1.5, where, maximum permeability of material of the main body is μ1 and maximum permeability of material of the front portion is μ2.

6. The inner shield assembly according to claim 1, wherein the magnetic characteristic of each material of said main body and said front portion has an interrelation of 0.5≦H1/H2≦3.0, where, coercivity of material of the main body is H1 and coercivity of material of the front portion is H2.

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