JP2000208024A - Cathode for electron tube and method for manufacturing electron gun - Google Patents

Abstract

(57) [Problem] To provide a cathode used for a cathode ray tube, to specify an upper limit of a thickness of an electron emitting material layer, and to reduce a variation in a cutoff voltage. SOLUTION: 1 is a substrate mainly containing nickel, which contains a trace amount of a reducing agent such as silicon and magnesium;
Is an electron-emitting material layer formed on the substrate 1 and containing at least barium and an alkaline earth metal oxide containing strontium and / or calcium. 3
Reference numeral denotes a cathode sleeve for fixing the base 1, which uses nichrome which is a heat-resistant metal. Reference numeral 4 denotes a heater for heating the substrate 1 and the electron emitting material layer 2. Here, in the cathode 10, the upper limit of the thickness T of the electron emitting material layer 2 is set to 9
It was limited to 0 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cathode for an electron tube used for an electron tube such as a color cathode ray tube and a cathode ray tube for a display, and a method for manufacturing an electron gun.

[0002]

2. Description of the Related Art An electron gun of a cathode ray tube (CRT) used for a television, a cathode ray tube for a display, etc., comprises a control electrode, an acceleration electrode, a focusing electrode, a high voltage electrode, a cathode, and the like. And a desired image is displayed on the phosphor screen.

FIG. 6 shows, for example, a patent registration number 166763.
FIG. 1 is a cross-sectional view showing a cathode ray tube disclosed in No. 1; In the figure, reference numeral 1 denotes a base, for example, a main component is made of nickel, silicon (Si), magnesium (M
g) and a small amount of a reducing element (reducing agent). Reference numeral 2 denotes an electron-emitting material layer which contains at least barium (Ba) and also contains strontium (Sr) and / or an alkaline earth metal oxide containing calcium (Ca) as a main component. Reference numeral 3 denotes a cathode sleeve made of nichrome or the like. The structure in which the substrate 1, the electron-emitting material layer 2, and the cathode sleeve 3 are combined is hereinafter referred to as a cathode 10. Reference numeral 4 denotes a heater disposed in the cathode sleeve 2, and thermionic electrons are emitted from the electron emitting material layer 2 by heating the heater 4.

[0004] A method of manufacturing the cathode 10 having the above-described structure and its operation characteristics will be described. First, a predetermined amount of a ternary carbonate of barium, strontium, and calcium is mixed with a binder and an organic solvent to form a suspension. Next, the suspension is applied onto the cathode substrate 1 which has been previously heat-treated in a reducing atmosphere. At this time, the suspension is applied to a uniform thickness by a spray method, a screen printing method, an electrodeposition method or the like. In order to form the electron emitting material layer 2, the applied thickness of the suspension must be 50 or less.
μm or more is required. Then, the electron emission material layer 2 of the cathode
Is heated by the heater 4 in a step of evacuating the inside of the cathode ray tube, and the alkaline earth metal carbonate is thermally decomposed to be changed to an alkaline earth metal oxide. In the subsequent activation step, a part of the alkaline earth metal oxide is reduced by a trace amount of the reducing agent contained in the base 1,
Free barium, which is a source of electron radiation, is formed.

[0005] One of the characteristics of cathode ray tubes is a cutoff voltage. Here, the cutoff voltage is a cathode voltage at a boundary where electron emission from the cathode is started in a state where voltages other than the cathode, such as the control electrode, the acceleration electrode, the focusing electrode, and the high-voltage electrode, are fixed. This value is generally determined by the shape of three elements called a triode, a cathode, a control electrode, and an acceleration electrode. That is, the cut-off voltage depends on the interval between the electrodes of the triode, the thickness of the electrodes, and the shape of the electron passage hole, and is set in a predetermined voltage range according to the type of the electron gun. . The reason why the cut-off voltage is set within the predetermined voltage range is to suppress the display definition of the cathode ray tube, that is, the variation in the focus characteristic. If the variable range of the cathode voltage in the television set can be reduced, an inexpensive power supply can be used. Can be used, thereby enabling cost reduction and the like.

FIG. 7 is a diagram showing a measurement result obtained by measuring a cutoff voltage after the completion of the manufacture of a cathode ray tube. here,
The horizontal axis indicates the thickness (μm) immediately after the application of the electron-emitting material layer 2, and the vertical axis indicates the cutoff voltage Vco.

[0007] From FIG. 7, it can be seen that firstly, the variation in the thickness of the electron-emitting material layer 2 has a considerable effect on the cut-off voltage, and secondly, the thickness of the electron-emitting material layer 2 is reduced. It can be seen that the cutoff voltage varies in a large range as the value increases.

[0008]

As described above, after the electron-emitting material layer 2 is attached to the base 1 and formed as a cathode, the cut-off voltage is measured in a state where the electron-emitting material layer 2 is incorporated in the electron tube. In the cathode in which the layer 2 is formed to have a thickness of more than about 90 μm, the variation from the straight line indicating the average value of the cutoff voltage becomes remarkable.

Accordingly, in a color cathode ray tube, for example, electrons emitted from three electron guns reach the phosphor screen to form a color image, and the difference between the cut-off voltages corresponding to each electron gun is different. If it increases, there is a problem in that the focus characteristics also vary, and the quality of the color image deteriorates.

If the cutoff voltage deviates from the designed value, the voltage adjustment function set for the television set may become invalid. For this reason, the voltage variable range is large depending on the degree of variation in the cutoff voltage of the cathode, and therefore, it is necessary to use an expensive power supply device, and there has been a problem in terms of cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to improve the focus quality of a display image and reduce the cost of a television set. It is to provide a manufacturing method.

[0012]

A cathode for an electron tube according to the present invention includes a metal substrate containing a trace amount of a reducing agent, and an electron emitting material layer containing at least one metal carbonate among alkaline earth metals. In the electron tube cathode which is heat-treated after being incorporated in the electron tube, the electron emitting material layer
It is applied on a metal substrate with a thickness in the range of 0 to 90 μm.

Further, in the method for manufacturing an electron gun according to the present invention, an electron emitting material layer containing at least one kind of alkaline earth metal carbonate is coated on a metal substrate containing a trace amount of a reducing agent. In the method for manufacturing an electron gun having a cathode, a step of measuring the thickness of the electron-emitting material layer attached to the cathode, and a step of selecting those whose thickness is equal to or less than a reference value,
Incorporating the selected cathode into an electron gun.

Further, it is preferable that the reference value of the thickness of the applied electron emitting material layer is set to 90 μm.

Further, when the electron emitting material layer is applied,
The target value of the thickness is set to 80 μm.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

FIG. 1 is a sectional view of a cathode for an electron tube according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a substrate mainly composed of nickel containing a trace amount of a reducing agent such as silicon or magnesium, and 2 denotes a substrate formed on the substrate 1 and containing at least barium, and strontium and / or An electron emitting material layer made of an alkaline earth metal oxide containing calcium. Reference numeral 3 denotes a cathode sleeve for fixing the base 1, which uses nichrome which is a heat-resistant metal. Also,
Reference numeral 4 denotes a heater for heating the base 1 and the electron emitting material layer 2.

The above configuration is the same as that of the conventional cathode 10, but the cathode for an electron tube of the present invention is configured so that the coating thickness T of the electron emitting material layer 2 falls within a set upper limit value or less. . That is, when an electron gun is manufactured by applying the electron emitting material layer 2 to the substrate 1, the thickness of the applied electron emitting material layer is measured, and for the cathode exceeding the upper limit value,
They are excluded before they are incorporated into the electron gun. As a result, only the cathode whose electron-emitting material layer has a predetermined thickness or less is used for the electron tube electron gun.

Next, a method of manufacturing the electron gun configured as described above will be described.

First, a cathode sleeve 3 is welded and fixed to a nickel base 1 containing a small amount of silicon and magnesium, and then heat-treated to clean the base 1 in a reducing atmosphere or vacuum. Thereafter, a ternary carbonate composed of barium, strontium, and calcium, and a binder composed of nitrocellulose and butyl acetate are mixed, and the suspension is applied on a substrate 1 by a spray method to form an electron emitting material layer 2 of about Apply to a thickness of 80 μm. In this case, 80 μm is a central value which is a target in the process control, and is actually applied to a thickness dispersed before and after this central value. Therefore, the thickness T of the electron emitting material layer 2 is measured, and at that time, for a cathode having a thickness exceeding 90 μm,
It is excluded so as not to be incorporated in the electron gun and is not used in a later assembling process. In the measurement of the thickness of the electron emitting material layer 2, the electron emitting material layer 2 was removed from the surface of the substrate 1 using a projector.
Was measured in a non-contact manner.

Next, an electron gun which is a component of a general cathode ray tube will be described.

FIG. 2 is a sectional view showing a schematic structure of an electron gun for a color cathode ray tube. In FIG. 2, the electron gun is
In addition to the cathodes 10R, 10G, and 10B corresponding to red, blue, and green, a control electrode 21, an acceleration electrode 22, a focusing electrode 23, and a high-voltage electrode 24 are provided. FIG. 3 is a sectional view showing a schematic configuration of the entire CRT. In FIG. 3, the electron gun 3
Numeral 0 is sealed to a cathode ray tube 41 integrally with a display panel 40 coated with a phosphor that emits red, blue and green.

As shown in FIG. 2, each electrode 2 of the electron gun 30
In 1 to 24, electron passing holes are provided corresponding to the three cathodes 10R, 10G, and 10B. In a normal television set or display set, these electrodes 2
A voltage fixed to 1 to 24 is applied, and the cathode 10
The amount of electrons emitted from R, 10G, 10B, ie, the cathode current, is controlled by modulating the voltage applied to the cathodes 10R, 10G, 10B themselves.

When the voltage of the control electrode 21 is used as a reference, a voltage ranging from 0 to a cutoff voltage is applied to each of the cathodes 10R, 10G, and 10B, and a few hundred volts are applied to the accelerating electrode 22. Control the cathode voltage to electrode 2
By approaching the voltage of 1, the electric field from the acceleration electrode 22 penetrates through the electron passage hole of the control electrode 21, and electrons are emitted toward the display panel 40. The focusing electrode 23 and the high voltage electrode 24 are connected to the cathodes 10R, 10G, 10G.
It is provided to focus and accelerate electrons emitted from B.

The cathode produced by such a method is incorporated into an electron gun as shown in FIG. 2, and further incorporated into a cathode ray tube 41 shown in FIG. Cut-off measurements were performed.

FIG. 4 is a diagram showing cut-off voltage values actually measured. FIG. 4 also shows, for comparison, cut-off voltage measurement values of a cathode ray tube assembled in the same manner as described above using a cathode having a coating thickness exceeding 90 μm to be removed. The measured values are as follows: the thickness T of the electron emitting material layer is 90 μm or less,
110 μm and 111 to 130 μm are shown by rank. According to such a comparison, it can be seen that the variation in the cutoff voltage increases as the coating thickness increases.

Next, the variation of the cut-off voltage in the initial operation of the CRT will be described.

As described above, the cut-off voltage is determined by the structure of the triode portion and the voltage applied to the electrodes. Variations in the cut-off voltage are caused by changes in the component accuracy and assembly accuracy of the electron gun and changes in the thermal structure thereof. Involved. That is,
When the mass production of the CRT is completed, the CRT must be manufactured so as to have a predetermined cutoff voltage. However, in practice, some variation in the cutoff voltage is inevitable. The main cause of the variation is considered to be variation in the interval between the control electrode 21 and the cathodes 10R, 10G, and 10B. Therefore, C before product shipment
In order to keep the cut-off voltage in the initial operation of the RT within a predetermined range, it is necessary to measure the thickness of the electron-emitting material layer deposited on the cathode, and select and incorporate those having a reference value or less. Yes, and it is preferable to set the reference value of this thickness to 90 μm.

The control electrode 21 and the cathodes 10R, 10G,
The interval from 10B varies mainly due to two factors. The first factor is a variation in the assembly accuracy in the electron gun manufacturing process, and the second factor is considered to be a thermal change in the electron gun structure in the cathode ray tube manufacturing process. And
Variations in the assembly dimensions in the electron gun manufacturing process greatly contribute to the former, and thermal changes in the latter are caused by shrinkage of the electron emitting material layer 2 caused by heating in the cathode ray tube manufacturing process, particularly in the exhaust process and the activation process. , And also due to thermal deformation of the control electrode and the acceleration electrode due to heating in the exhaust step and the activation step.

Next, a description will be given of the cause of the increase in the variation of the cutoff voltage according to the thickness T of the electron emitting material layer 2. The carbonate composed of barium or the like used as the electron-emitting substance is a crystal generated by coprecipitation, and the crystal has a maximum temperature of about 1000 ° C. in the evacuation step and the activation step. It gradually evaporates by heating, or causes shrinkage of the crystal itself. In this manner, the shrinkage of individual crystals causes the entire electron emitting material to shrink, and the thickness T during coating decreases. As a result, the distance between the surface of the electron emitting material layer 2 and the control electrode 21 increases, and the cutoff voltage increases.

FIG. 5 is an enlarged view showing a cross section of the electron emitting material layer. Here, 12 is a crystal of an alkaline earth metal carbonate containing barium or the like. The arrangement of the crystals is random, and voids occupy most of the occupied volume. By the way, during the production of cathode ray tubes, carbon dioxide is released due to decomposition of carbonate in the exhaust gas, or during activation, the evaporate from the alkaline earth metal oxide crystal is diffused into the voids at high temperatures and regenerated on the crystal surface. Crystallization occurs. Therefore, this decomposition into carbon dioxide, evaporation of crystal components,
As the recrystallization is repeated, the amount of shrinkage of each crystal increases, causing a decrease in the thickness of the entire electron emitting material layer. And
It can be considered that this phenomenon increases as the thickness T of the electron-emitting material layer increases, and that the variation increases due to the randomness of the arrangement of the crystals. Further, from the correlation between the thickness T of the electron emitting material layer and the cut-off voltage Vco shown by the solid line in FIG.
It can be estimated that for a contraction of m, the cut-off voltage applied to the cathode will drop on average by about 1V.

In the above embodiment, the case where the electron emitting material layer is applied by the spray method has been described.
Similar results were obtained with electrodeposition, screen printing, and other forming methods.

[0034]

Since the present invention is configured as described above, it has the following effects.

In the cathode for an electron tube according to the present invention, since the cathode having a predetermined coating thickness or more is excluded, the shrinkage of the electron emitting material layer generated in the cathode ray tube manufacturing process is suppressed.
Variations in cut-off voltage can be suppressed, and quality in which variations in focus characteristics are suppressed can be improved. Further, an inexpensive power supply device can be used as a power supply for applying the cathode voltage, which is advantageous in terms of the cost of the entire television set.

Further, in the method for manufacturing an electron gun according to claim 2,
Since the thickness of the electron emitting material layer is measured and the thickness of the electron emitting material layer is smaller than the reference value, variations in thickness due to shrinkage of the crystal of the electron emitting material layer can be suppressed, and the cutoff voltage can be reduced. Can be reduced.

According to the third aspect of the present invention, as a result of setting the reference value to 90 μm, variations in focus characteristics indicating screen quality can be effectively suppressed, which contributes to stabilization of image quality and reduces the cathode voltage. There is an effect that the variable range is reduced and an inexpensive power supply can be used.

Further, according to the present invention, the target value of the thickness of the electron-emitting material layer is set at 80 μm when the electron-emitting material layer is applied, so that the thickness of the electron-emitting material layer is reliably reduced to the reference value of 90 μm or less. There is an effect that can be formed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a cathode for an electron tube according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic configuration of an electron gun for a color cathode ray tube.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of the entire CRT.

FIG. 4 is a diagram showing cut-off voltage values actually measured.

FIG. 5 is an enlarged view showing a cross section of an electron emitting material layer.

FIG. 6 is a cross-sectional view showing a conventional cathode for cathode ray tubes.

FIG. 7 is an explanatory diagram showing a variation in cutoff voltage in a conventional cathode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate, 2 Electron emission material layer, 3 Cathode sleeve, 4 Heater, 10 Cathode, 11 Alkaline earth metal oxide, 12 Alkaline earth metal carbonate, 2
1 control electrode, 22 accelerating electrode, 23 focusing electrode,
24 high voltage electrode, 30 electron gun, 40 display panel, 41 cathode ray tube.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Riichi Kondo 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Electric Corporation (72) Inventor Naohisa Yoshida 2- 2-3 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation F-term (reference) 5C012 AA02 BE01 5C027 CC01 CC02 CC03 CC04 5C031 DD09

Claims (4)

[Claims] 1. An electron tube comprising: a metal substrate containing a trace amount of a reducing agent; and an electron emitting material layer containing at least one metal carbonate of alkaline earth metals. In the tube cathode, the electron emission material layer has a thickness in a range of 50 to 90 μm,
A cathode for an electron tube, which is attached on the metal substrate. 2. On a metal substrate containing a trace amount of a reducing agent,
In a method for manufacturing an electron gun having a cathode coated with an electron emitting material layer containing at least one metal carbonate among alkaline earth metals, a step of measuring a thickness of the electron emitting material layer applied to the cathode A method for selecting an electrode having a thickness equal to or less than a reference value, and a step of incorporating the selected cathode into an electron gun. 3. The method according to claim 2, wherein the reference value is set to 90 μm. 4. The method for manufacturing an electron gun according to claim 2, wherein a target value of the thickness of the electron emitting material layer is set to 80 μm when the electron emitting material layer is applied.