JP2000331594A - Cathode for electron tube - Google Patents

Abstract

(57) Abstract: Provided is a cathode for an electron tube, which can easily form a thermal stress strain relaxation structure in which a change in a distance between an electron emission surface and an electrode due to deformation of a base is suppressed. A support tube (2) having a heater (3) inside, a plate-shaped substrate (1) whose peripheral surface is in contact with the inner wall of the support tube (2) and closes one end of the support tube (2), and a substrate (1) A cathode for an electron tube, comprising a metal layer 4 provided on the upper surface of the substrate and an electron-emitting substance (not shown) adhered to the upper surface of the metal layer 4, wherein the substrate 1 is in contact with the inner wall of the support tube 2. Of the support tube 2 includes a portion in contact with the inner wall and a portion not in contact with the inner wall. At this time, the portion not in contact with the inner wall of the support tube 2 is cut into at least one concave portion 21 formed on the upper or lower surface of the peripheral portion of the base 1 or at least one cut formed on the peripheral portion of the base 1. It can be constituted by a notch (not shown). The width of the notch can be gradually reduced toward the center of the base.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode for an electron tube used for a cathode ray tube for a display monitor or an image pickup tube, and more particularly to a technique for suppressing a change in a cutoff voltage of the electron tube.

[0002]

2. Description of the Related Art FIG. 10 is a cross-sectional view showing a structure of a conventional cathode for an electron tube, and shows a cathode for an electron tube disclosed in Japanese Patent Publication No. Sho. ing. The cathode for an electron tube shown in FIG.
The structure includes a base 51, a support tube 52 supporting the base 51, a heater 53 housed in the support tube 52, and an electron emitting material layer 54 provided on the upper surface of the base 51. The electron-emitting material layer 54 contains a rare-earth metal oxide 56 with an alkaline-earth metal oxide 55 as a main component. Then, the substrate 51 is heated by the heater 53, and thermoelectrons are emitted from the electron emitting material layer 54. In the cathode for an electron tube shown in FIG. 10, the cathode temperature 60 is increased by adding a rare earth metal oxide 56 to the electron emitting material layer 54 in order to increase the current density operation level.
At an operating temperature of 0 ° C. or higher, 1.32 to 2.64 [A]
/ Cm ² ].

[0003] However, in the invention disclosed in Publication 1,
The life characteristics in a high current density operation of 2.0 [A / cm ² ] or more are significantly reduced. In order to solve this, Japanese Patent Laid-Open No. Hei 3-25
In the invention of the cathode for an electron tube disclosed in JP 7735 (hereinafter referred to as JP 2), a uniformly formed metal layer is provided between a substrate and an electron emitting material layer, and this is diffused into the substrate. As a result, the life characteristics in a high current density operation of 2.0 [A / cm ² ] or more can be improved.

[0004] However, in the invention disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2 (1994), when the base is heated by a heater to emit thermoelectrons from the electron emitting material layer, the linear expansion coefficient of the metal layer and the linear expansion coefficient of the base material are determined. , Resulting in thermal deformation. In order to avoid this, Japanese Patent Laid-Open No. 9-19076
In the invention of the cathode for an electron tube disclosed in Japanese Patent Publication No. 1 (hereinafter referred to as Patent Publication 3), a metal layer such as tungsten is not formed uniformly on the surface of the base, but is patterned using a mask or the like to form a discontinuous layer. Is formed.

FIG. 11 is a diagram showing a metal layer provided on the upper surface of the base of the cathode for an electron tube disclosed in Japanese Patent Publication No.
FIGS. 11A to 11C are top views showing the shape of a tungsten layer 57 which is a metal layer provided on the upper surface of the base body 51.
FIG. 11D is a cross-sectional view showing a contact state between the base 51 and the support tube 52. As shown in FIG.
By not uniformly forming the substrate 7 on the substrate 51, the restraint of the expansion of the substrate 51 by the tungsten layer 57 is relaxed, and the strain stress of the substrate 51 near the tungsten layer 57 is reduced. By doing so, it is possible to form a cathode for an electron tube in which distortion is reduced as compared with the invention disclosed in Japanese Unexamined Patent Publication (Kokai) Publication.

[0006]

However, even if the metal layer is discontinuously formed as described in the above-mentioned publication 3, the strain stress is most strongly concentrated on the substrate at the contact portion with the support tube. Therefore, the effect of relaxing the stress in the direction of the peripheral edge of the base is hardly obtained, and the base remains strained and the thermoplastic deformation is accumulated. For this reason, there is a problem that the distance between the electron emission surface and the electrode disposed at a predetermined distance from the electron emission surface varies. When the distance between the electron emission surface and the electrode changes, the cutoff voltage representing the control characteristics of the electron emission current from the electron emission surface gradually changes during the operation of the cathode ray tube, during the life of the cathode ray tube, causing color shift and contrast. Cause problems such as a decrease in

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a thermal stress distortion relieving structure in which a change in a distance between an electron emitting surface and an electrode due to deformation of a base is suppressed is easily formed. It is an object of the present invention to provide a cathode for an electron tube that can be used.

[0008]

A cathode for an electron tube according to the present invention is arranged such that a support tube provided with a heater therein and a peripheral surface thereof abut on an inner wall of the support tube to close one end of the support tube. A cathode for an electron tube, comprising: a plate-shaped base that has been formed; and an electron-emitting substance that is adhered to an upper surface of the base, wherein a peripheral surface of the base that comes into contact with an inner wall of the support tube has a peripheral surface of the support tube. It includes a portion that is in contact with the inner wall and a portion that is not in contact.

In the electron tube cathode according to the present invention, the non-contact portion may be constituted by at least one concave portion formed on an upper surface or a lower surface of a peripheral portion of the base.

Further, the cathode for an electron tube according to the present invention,
The non-contact portion may be constituted by at least one notch formed in a peripheral portion of the base.

In this case, the width of the notch can be gradually reduced toward the center of the base.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals denote the same or corresponding components. In Embodiments 1 and 2, a cathode for an electron tube having an alloy layer on the upper surface of a substrate will be described. However, a structure without an alloy layer may be employed.

Embodiment 1 FIG. FIG. 1 is a perspective view showing a configuration of an electron tube cathode according to Embodiment 1 of the present invention.
FIG. 2 is a perspective view showing a receiver provided with a cathode for an electron tube.

The cathode for an electron tube shown in FIG. 1 has a substantially disk-shaped base 1, a substantially cylindrical support tube 2, a heater 3, and a base 1
Having an alloy layer 4 formed on the upper surface (the surface opposite to the heater 3, that is, the upper surface shown in FIG. 1) and at least one concave portion 21 formed on the upper surface of the peripheral portion of the base 1. 1, in FIG.
At positions, there are provided recesses 21 having a substantially rectangular shape as viewed from above in the drawing at substantially equal intervals. The point at which the central axis 15 intersects with the alloy layer 4 is the center 16 of the electron emission surface. The support tube 2 supports the base 1 so that the peripheral surface of the base 1 contacts one end (the upper end in FIG. 1) of the inner wall, and houses the heater 3 therein. The alloy layer 4 is provided on the upper surface of the base 1 and includes at least one or more metals selected from tungsten, molybdenum, tantalum, and the like, and nickel. FIG.
Although not shown, the upper surface of the alloy layer 4 is coated with an electron-emitting substance containing an alkaline earth metal oxide containing barium and strontium or calcium as a main component and a rare earth metal oxide such as scandium oxide. ing.

The receiver shown in FIG. 2 corresponds to FIG.
And a deflection yoke 41 as shown in FIG.
, A tension band 42, a panel glass 43, a phosphor screen 44, a shadow mask 45, and an internal conductive film 46. The electron tube cathode 20 is disposed at the neck of the receiver and is used as an emission source of the electron beam 47.

FIG. 3 is a sectional view of the cathode for an electron tube shown in FIG. 1, FIG. 3 (a) is a side sectional view taken along the central axis 15 of FIG. 1, and FIG. A-
It is A 'sectional drawing.

FIG. 4 is an enlarged view showing a part of the contact portion between the base and the support tube for performing an elasto-plastic simulation of the stress distribution of the cathode for an electron tube according to the first embodiment of the present invention. In the simulation, the heater operating temperature was 1000 [° C]
Under the conditions described above, an elasto-plastic simulation of the stress distribution was performed on the base 1 having the thermal stress / strain relaxation structure as shown in FIG. 4, and the nodes a to g and The Mises equivalent stresses generated at the nodes a ′ to g ′ of the support tube 2 were compared. Here, the base 1 is mainly composed of nickel, the material of the support tube 2 is nichrome, the alloy layer 4 is an alloy of tungsten and nickel, and the thickness thereof is 1.0 [μm]. Table 1 shows the coefficient of linear expansion, the coefficient of longitudinal elasticity, the Poisson's ratio, the coefficient of longitudinal elasticity at the yield point, and the coefficient of longitudinal elasticity after the yield point.

[0018]

[Table 1]

FIG. 5 is a diagram showing a state of stress distribution obtained by the simulation of FIG. As shown in FIG.
The nodes 1 to g of the base 1 and the nodes a 'to g' of the support tube 2 receive Mises equivalent stress under the condition of a heater operating temperature of 1000 ° C. when the base 1 and the support tube 2 come into complete contact. The stress values generated at the nodes g and g ′ are normalized to one. As is clear from FIG. 5, nodes a to c where the concave portion 21 of the base 1 exists.
Since the outer circumference of the base 1 is not in contact with the support tube 2, the stress generated in the base 1 is about 1/2 of the stress generated at the node g, and the base 1 comes into contact with the support tube 2. It can be seen that expansion is possible at the portion where the stress is not present, and that stress strain is reduced.

FIG. 6 is a diagram showing a cut-off voltage of a cathode ray tube using a cathode for an electron tube according to the first embodiment of the present invention and a conventional example. In FIG. 6, the cathode for an electron tube of the present invention and the cathode for a conventional electron tube shown in FIG. 11B are mounted on an actual display monitor cathode ray tube as shown in FIG. The cut-off voltage when the cathode ray tube completed through the exhaust process is operated at a current density of 2.0 [A / cm ² ] is compared. As is apparent from FIG. 6, the cut-off voltage of the cathode-ray tube equipped with the cathode for an electron tube in the first embodiment has an operation time of 300
The initial value is maintained until 0 hour elapses, and it increases by about 1% at 4000 hours. On the other hand, the cut-off voltage of the conventional cathode ray tube equipped with an electron tube cathode is increased by about 2% from the initial value when the operation time has passed 2000 hours, and 4% at the time of 4000 hours.
It is rising above. As described above, in the cathode ray tube using the cathode for an electron tube in the first embodiment, the fluctuation of the cutoff voltage during operation is suppressed as compared with the conventional example, and stable operation can be performed for a long time. Understand.

Hereinafter, the principle of thermal stress relaxation will be described with reference to FIG. FIG. 7 is a diagram showing the relationship between the thermal expansion and the stress of the base of the electron tube cathode shown in FIG. FIG. 7 (a)
7B is a cross-sectional view of the base, FIG. 7B is a cross-sectional view showing a state in which an alloy layer is formed on the upper surface of the base, and FIG. 7C is a view in which the base on which the alloy layer is formed is supported. It is sectional drawing which shows the state attached to the pipe.

FIG. 7A shows a state of expansion when the substrate 1 is uniformly heated when there is no restriction due to contact of the support tube or the like. At this time, the substrate 1 is moved in all directions. The substrate 1 can be expanded without receiving any stress, and the stress distortion of the substrate 1 is 0, resulting in elastic deformation. Therefore, if it is possible to use the substrate 1 in a state in which no stress is applied in this way, the substrate 1 may be deformed even if a repeated test corresponding to turning on and off the power of the CRT such as heating and cooling is performed. Absent. For this reason, the surface of the substrate 1 from which electrons are emitted and the electrode located on the downstream side of the electron beam can be kept at a constant distance, and if the electron-emitting substance of the substrate 1 does not evaporate, the cutoff voltage varies. Will not occur.

As shown in FIG. 7B, when the alloy layer 4 is formed on the substrate 1, the substrate 1 has a lower linear expansion coefficient than the alloy layer 4 as shown in Table 1. Because it ’s big
In particular, the portion near the alloy layer 4 of the base 1 cannot be expanded sufficiently, and receives a strain stress. Therefore, when a repeated test is performed, plastic deformation is accumulated in the base 1,
Since the periphery of the surface of the base 1 is deformed toward the electrode,
The surface of the base 1 and the electrode cannot be kept at a fixed distance, and electrons are not uniformly emitted.

As shown in FIG. 7C, when the base 1 on which the alloy layer 4 is attached is attached to the support tube 2,
As shown in Table 1, since the base 1 has a larger linear expansion coefficient than the support tube 2, the expansion of the base 1 is restrained not only by the alloy layer 4 but also by the support tube 2, resulting in a stronger strain. As a result, the shape of the surface of the base 1 is complicatedly deformed.

In such a case, the publication 3 shown in FIG.
In the cathode for an electron tube disclosed in Japanese Patent Application Laid-Open No. H11-207, almost no effect of relaxing the stress in the direction of the peripheral edge of the base is obtained. On the other hand, in the present invention, the concave portion 2 is provided on the upper surface side where the alloy layer 4 is formed on the peripheral portion where the base 1 is in contact with the support tube 2.
Since the base 1 is released from a completely restrained state of radial expansion of the base 1, even if a stress as shown in FIG. As described above, the stress is reduced, and the distortion in the direction of the peripheral portion is greatly reduced.

That is, by providing the concave portion 21 in a part of the base 1, it is possible to reduce the Mises equivalent stress applied to the outer peripheral surface of the base 1, and to reduce the amount of plastic strain. As a result, it is possible to realize a cathode for an electron tube, which is capable of operating at a high current density of 2.0 [A / cm ² ] or more and has a small amount of deformation even in a repetitive test corresponding to ON / OFF of a cathode ray tube and has a long term stability. it can.

Next, the arrangement and shape of the recess 21 will be described. By arranging a plurality of the recesses 21 on the peripheral edge of the base 1, it is possible to release more strain stress in the direction of the peripheral edge generated when the base 1 expands, as compared with the case where only one is provided. Even in a state where a high thermal activation energy required for electron emission is received, the amount of plastic strain can be reduced. When a plurality of the recesses 21 are arranged, by disposing them at equal intervals on the peripheral edge of the base 1, it is possible to release strain stress evenly and to prevent the center axis of the base 1 and the support tube 2 from shifting. The electron beam intensity can be kept stable.

FIG. 8 is a diagram showing another shape of the concave portion provided on the base of the cathode for an electron tube according to the first embodiment of the present invention. In the simulation in FIG. 5, since the concave portion 21 is rectangular, the node d where the support tube 2 and the base 1 come into contact with each other is set.
In, the stress is increased by 10% or more as compared with the node g. For this reason, as shown in FIG. 8, the corner formed by the side wall of the concave portion 21 near the nodes c and d and the upper surface of the base 1 shown in FIG. The stress in the vicinity of the node d can be reduced by making the shape gradually approach the inner wall.

In the first embodiment, the shape of the recess 21 is described as the rectangle shown in FIG. 3 or the rectangle having a smooth corner as shown in FIG. 8, but the shape of the recess 21 is not limited to this. Other shapes such as a wedge shape and a slit-shaped linear shape may be used, or a plurality of shapes may be used in combination. Further, the number and size of the recesses 21 can be freely selected.
It can also be. Further, the concave portion 21 may be provided on the lower surface of the base 1 (the surface on the heater 3 side). Further, the thickness of the peripheral portion may be uniformly reduced over the entire circumference of the base 1.

Embodiment 2 FIG. FIG. 9 is a perspective view showing a configuration of an electron tube cathode according to Embodiment 2 of the present invention.
The cathode for an electron tube shown in FIG. 9 includes a substantially disk-shaped base 1, a substantially cylindrical support tube 2, and a heater 3 housed in the support tube 2.
And an alloy layer 4 provided on the upper surface of the base 1, and at least one notch 22 formed in a peripheral portion of the base 1 so as to penetrate from the upper surface to the lower surface.
In FIG. 9, substantially wedge-shaped cutouts 22 as viewed from above are provided at two substantially opposing peripheral edges of the base 1. The cathode for an electron tube shown in FIG. 9 has substantially the same configuration as that of the cathode for an electron tube in the first embodiment shown in FIG. 1, and has a notch 22 instead of the recess 21 shown in FIG.
Are formed.

As shown in FIG. 9, by providing the notch 22 at the end of the base 1 which comes into contact with the support tube 2, the thermal expansion distortion of the base 1 can be released as in the first embodiment. Further, since the notch 22 is penetrated from the upper surface to the lower surface of the base 1, thermal stress distortion can be further reduced as compared with the first embodiment.

At this time, the notch 22 is formed so as to be gradually narrowed toward the central axis 15 of the base 1, so that the heater 3 provided in the center of the support tube 2 is provided.
Of the heat from the notch 22 to the outside can be suppressed, and the processing is easy.

Further, when the notches 22 are arranged at a plurality of locations, by disposing them at equal intervals on the periphery of the base 1, strain stress can be released evenly. Accordingly, since no bias occurs in the strain deformation of the base 1 and the displacement of the central axis 15 between the base 1 and the support tube 2 can be prevented, the voltage is applied so as to be maximum at the center 16 of the electron emission surface. The electron beam intensity can be kept stable without changing the positional relationship with respect to the voltage distribution.

In the second embodiment, the shape of the notch 22 has been described with reference to the wedge type shown in FIG. 9. , But not limited to rectangles, rectangles,
Other shapes such as a slit-shaped linear shape may be used,
A plurality of shapes may be used in combination. Notch 22
The number, position, size, etc. of the can be freely selected.

[0035]

As described above, according to the first aspect of the present invention, the peripheral surface of the base that comes into contact with the inner wall of the support tube includes a portion that is in contact with the inner wall of the support tube and a portion that is not in contact with the inner wall of the support tube. Therefore, when a substrate having a high coefficient of linear expansion is heated by a heater together with a support tube having a low coefficient of linear expansion, deformation of the outer periphery of the substrate is not completely suppressed by the support tube, and stress is generated in a portion not in contact with the support tube. Since the release is released, the stress strain applied to the base from the support tube is reduced, and the accumulation of plastic deformation due to the plastic strain of the base can be reduced. Therefore, 2.0
A high-current-density operation of [A / cm ² ] or more is possible, and a thermal stress-strain relieving structure in which a change in the distance between the electron emission surface and the electrode due to deformation of the base is suppressed can be obtained.

According to a second aspect of the present invention, at least one concave portion formed on the upper surface or the lower surface of the peripheral portion of the base forms a portion which is not in contact with the inner wall of the support tube, so that the heat of the heater is transferred to the outside. Therefore, it is possible to easily form a portion that is not in contact with the substrate without releasing the same to the outside.

According to a third aspect of the present invention, a portion not in contact with the inner wall of the support tube is formed by at least one notch formed in the peripheral portion of the base, thereby making a comparison with the second aspect of the invention. Therefore, the thermal stress distortion can be further reduced.

According to a fourth aspect of the present invention, the width of the notch is gradually narrowed toward the center of the base, so that the heat of the heater provided inside the support tube is different from that of the third aspect. There is an effect that release to the outside from the notch can be suppressed and processing of the notch can be facilitated.

In this way, by easily forming the thermal stress strain relief structure in which the change in the distance between the electron emission surface and the electrode due to the deformation of the base is suppressed, the change in the cut-off voltage during the operation of the cathode ray tube is achieved. And a long-term stable and highly reliable cathode for an electron tube can be formed. Further, since the variation in the distance between the electron emitting surface and the electrode slightly occurs even when the metal layer is not provided on the upper surface of the base, the present invention relates to an electron tube for which the metal layer is not provided. This is also effective in reducing the distortion generated in the cathode base.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an electron tube cathode according to Embodiment 1 of the present invention.

FIG. 2 is a perspective view showing a receiver provided with a cathode for an electron tube.

FIG. 3 is a cross-sectional view of the electron tube cathode shown in FIG.

FIG. 4 is an enlarged view showing a part of a base and a support tube for performing an elasto-plastic simulation of a stress distribution of a cathode for an electron tube according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a stress distribution state obtained by the simulation of FIG. 4;

FIG. 6 is a diagram showing a cut-off voltage of a cathode ray tube using an electron tube cathode according to the first embodiment of the present invention and a conventional example.

FIG. 7 is a view showing a relationship between thermal expansion and stress of a base of the cathode for an electron tube shown in FIG.

FIG. 8 is a view showing another shape of the concave portion provided in the base of the cathode for an electron tube according to the first embodiment of the present invention.

FIG. 9 is a perspective view illustrating a configuration of an electron tube cathode according to Embodiment 2 of the present invention.

FIG. 10 is a cross-sectional view showing a configuration of a conventional electron tube cathode.

FIG. 11 is a view showing a metal layer provided on an upper surface of a base of an electron tube cathode in a conventional example.

[Explanation of symbols]

1,51 base, 2,52 support tube, 3,53 heater, 4 alloy layer, 15 center axis, 16 center of electron emission surface, 20 cathode for electron tube, 21 concave portion, 22
Notch, 41 deflection yoke, 42 tension band, 43 panel glass, 44 phosphor screen, 4
5 shadow mask, 46 internal conductive film, 47 electron beam, 54 electron emitting material, 55 alkaline earth metal oxide, 56 rare earth metal oxide, 57 tungsten layer.

Claims (4)

[Claims] 1. A support tube provided with a heater inside, a plate-shaped base member whose peripheral surface is in contact with an inner wall of the support tube and closes one end of the support tube, and an upper surface of the base plate A cathode that is in contact with the inner wall of the support tube, and a portion where the peripheral surface of the base is in contact with the inner wall of the support tube and a portion that is not in contact with the inner wall of the support tube. A cathode for an electron tube, comprising: 2. The cathode for an electron tube according to claim 1, wherein the non-contact portion is constituted by at least one concave portion formed on an upper surface or a lower surface of a peripheral portion of the base. 3. The cathode for an electron tube according to claim 1, wherein the non-contact portion is constituted by at least one notch formed in a peripheral portion of the base. 4. The cathode for an electron tube according to claim 3, wherein the width of the notch gradually decreases toward the center of the base.