JPH06325687A - Negative electrode structure and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the mechanical strength of a negative electrode sleeve, and to improve the reliability by forming the black coating film of the inner surface of a negative electrode sleeve from a sintered layer, which is obtained by mixing tungsten and alumina respectively having a specified mean grain diameter at a specific weight ratio. CONSTITUTION:Butyl acetate and nitrocellulose are mixed in the mixture powder, which is obtained by mixing tungsten having a mean diameter at 0.5-2mum and alumina having a mean grain diameter at 0.1-1mum at a weight ratio in a range of 90:10-65:35 to form the slurry. Next, the inner surface of a negative electrode sleeve 15 is coated with this slurry, and dried. Thereafter, the inner surface of the negative electrode sleeve 15 is heated at a predetermined temperature in the vacuum atmosphere to form a blackened layer 23. A negative electrode structure, in which the mechanical strength of the sleeve 15 is higher than that of the element material and which has the excellent reproducibility and a high reliability, is thereby obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode assembly used in an electron tube such as a color picture tube and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a color picture tube having an increased number of scanning lines to improve the resolution and a display tube compatible with a super high frequency have been developed. Further, also in a projection tube or the like, improvement in brightness is desired. In these applications, the electron density emitted from the cathode needs to be significantly increased. By the way, an emitter-impregnated cathode can obtain a larger current density than an oxide cathode. Therefore, this impregnated cathode has been used in electron tubes such as traveling wave tubes and klystrons. However, recently, the above-described color picture tube and the like have been developed for the purpose of effectively utilizing the high current density characteristics of the impregnated cathode.

As is well known, the impregnated type cathode assembly has an operating temperature higher than that of an oxide cathode by about 200 ° C., and accordingly the heater temperature is also high, and it is 1250 ° C. at the rated operation.
Reach even more. As a result, the heat deformation of the heater and the heater
The withstand voltage performance between the cathodes is likely to deteriorate. Therefore,
By increasing the heat transfer efficiency from the heater to the cathode disk,
Some attempts have been made to reduce the heater temperature.
For example, Japanese Patent Application Laid-Open No. 61-288339 proposes an impregnated-type cathode assembly in which a blackening layer containing a refractory metal or its powder and an inorganic binder is formed on the inner surface of the cathode sleeve. That is, for example, a slurry in which a mixture of tungsten powder and aluminum oxide, that is, alumina powder is put into an alumina sol liquid is applied to the inner surface of a tantalum (Ta) sleeve, dried, and then baked at a temperature of about 1600 ° C. for 5 minutes. To form a blackened layer.

[0004]

By the way, the cathode sleeve which supports the electron emitting portion has a wall thickness of, for example, 15 so as to suppress heat conduction to the portions other than the electron emitting portion and improve thermal efficiency.
It is formed to be very thin such as μm to 20 μm. When the blackening layer is attached to the inner surface of such a thin cathode sleeve by the above-described method, the strength is remarkably deteriorated, and cracks and cracks are likely to occur during manufacturing, and deformation is likely to occur due to thermal fatigue during operation. . In particular, Ta or Ta as the cathode sleeve
It has been confirmed that when an alloy is used, the reaction between the alumina and the Ta sleeve causes the formation of a compound in the entire sleeve, resulting in significant strength deterioration. If this sleeve is deformed during the operation of the cathode, the characteristic of the color picture tube is deteriorated, and the deterioration of the luminance due to the deterioration of the cut-off characteristic or the color misregistration occurs. In addition, when acicular alumina sol is used, the electric field is concentrated on the acicular tip, so that insulation failure between the heater and the sleeve is likely to occur.

The present invention solves the above problems and improves the mechanical strength of the cathode sleeve beyond the strength of the material, and provides a highly reproducible and highly reliable cathode assembly and a method for manufacturing the same. The purpose is to provide.

[0006]

According to the present invention, an inner surface blackening layer of a cathode sleeve has a mean particle size of tungsten in the range of 0.5 μm or more and 2 μm or less and alumina having a mean particle size of 0.1 μm to 1 μm. Is a cathode assembly which is a sintered layer mixed in a weight ratio (tungsten: alumina) in the range of (90:10) to (65:35).

In the invention of the manufacturing method, tungsten having an average particle diameter of 0.5 μm or more and 2 μm or less and alumina having an average particle diameter of 0.1 μm or more and less than 1 μm are weighted on the inner surface of the cathode sleeve. Slurry mixed with a ratio (tungsten: alumina) in the range of (90:10) to (65:35) is applied and sintered at a temperature in the range of 1250 ° C to 1580 ° C in a non-oxidizing atmosphere. And a blackened layer is formed.

[0008]

According to the present invention, the cathode sleeve has a mechanical strength higher than that of the material, is highly reproducible, and has a high reliability.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the present invention is applied to an impregnated type cathode assembly which constitutes a part of an electron gun assembly of a color picture tube will be described with reference to the drawings. In FIG. 1, reference numeral 11 is an electrode supporting glass bead, 12 is a first control grid, 13 is an emitter impregnated cathode disk which is an electron emitting portion, 14 is a disk holding cap, and 15 is a disk and a cap fixed to an end portion. A cathode sleeve, 16 three straps for supporting the cathode sleeve, 17 a cylinder for heat reflection, 18 a support ring thereof, 19 a cylinder for holding a cathode, 20 a support arm for supporting the cathode structure on a glass bead, 21 Is a coiled coil heater for heating, and 22 is a heater terminal.

The impregnated cathode disk 13 has a porosity of about 2
A 0% porous tungsten (W) substrate was impregnated with an electron emitting material. In addition, this cathode disk 1
An iridium (Ir) -tungsten (W) alloy layer is formed on the surface of No. 3. Further, the heater 21 is
It is composed of a 3% Re-W alloy wire, and its surface is coated with alumina, which is an insulator. Further, the surface of the alumina is coated with a mixture of tungsten and alumina in order to improve heat radiation characteristics. And
The cathode sleeve 15, the disk holding cap 14, and the three straps 16 are all made of tantalum (Ta) or an alloy containing tantalum as a main component. Blackening layers 23, 24, 25 are attached to the inner surface of the cathode sleeve, the back surface of the cathode cap, and the entire surface of the strap, as shown in an enlarged view in FIG.

Next, regarding the blackened layers 23, 24 and 25,
A description will be given including a preferable manufacturing method. The following mainly describes a case where a blackening layer is mainly formed on the inner surface of the cathode sleeve.

Example 1 Tungsten powder having an average particle size of 0.9 μm and alumina (A) having an average particle size of 0.7 μm
and l ₂ O ₃₎ powder, a mixed powder was 80:20 by weight, by mixing butyl acetate and nitrocellulose to prepare a slurry.

Next, this slurry was treated to have an outer diameter of 1.3 m.
m, the wall thickness was 20 μm, and the length was 4.2 mm. The inner surface of the cathode sleeve 15 made of tantalum was applied by an injection method and dried.
The coating film in this state had an average thickness of about 10 μm.

Thereafter, this is heat-treated at a temperature in the range of 1250 ° C. to 1580 ° C., for example, 1450 ° C. for 10 minutes in a vacuum atmosphere of 10 ⁻⁶ torr or less, to mix and sinter tungsten powder and alumina powder. Blackened layer 2 consisting of layers
Formed 3.

The conditions for setting the heat treatment temperature were determined as follows. That is, the width is 0.32 mm,
After coating the above slurry on the entire surface of a tantalum ribbon having a thickness of 30 μm and a length of 150 mm and drying it, 1
In a vacuum of 0 ^-6 torr or less, change the temperature from 1000 ℃ to 170
Firing at various temperatures in the range of 0 ° C. for 10 minutes each,
A ribbon having a blackened layer was produced. The average thickness of the blackening layer is about 10 to 15 μm. For comparison, a tantalum ribbon without the slurry was also treated at the same time. Then, the breaking strength of the ribbon treated under each condition was examined by a tensile test. As shown in FIG. 3, the fracture load increases from around the treatment temperature of over 1200 ° C., becomes maximum at the treatment at 1500 ° C., and becomes about twice as high as that of the Ta ribbon not coated with the slurry. When the temperature drops sharply and exceeds 1580 ° C, it is equivalent to or less than the tantalum ribbon that does not apply slurry,
An unexpected fact was confirmed that the fracture load was reduced.

As a result, the heat treatment temperature is 1250 ° C.
It was confirmed that the range of ˜1580 ° C. is preferable because the mechanical strength of the cathode sleeve is higher than that of the material.
Then, by heat-treating in the range of 1400 ° C. to 1550 ° C. and sintering, particularly good strength results were obtained. The reason why the mechanical strength of the cathode sleeve is higher than that of the material at the heat treatment temperature in the specific range is that oxygen, aluminum, or tungsten in the blackening layer forming material is contained in the tantalum grain boundary part in the tantalum base material. It is presumed that a small amount of precipitation hinders abnormal coarsening of the base crystal and equiaxed crystallization.

Next, in order to examine whether the above-mentioned heat treatment temperature range is appropriate for other performance evaluations, the surface hardness of the ribbon having the blackened layer and the broken portion are observed with a scanning electron microscope. Assembling property when actually manufacturing a cathode sleeve and assembling it into an impregnated cathode structure was evaluated. Further, the completed impregnated-type cathode assembly was incorporated into a color picture tube, and the thermal fatigue characteristics during the life test were investigated.

The results are summarized in Table 1. The results shown in Table 1 will be described in more detail. That is, the hardness was measured by mechanically peeling the blackened material from the blackened sample and then measuring the Vickers hardness of the surface. As a result, the heat treatment temperature gradually increases from 1200 ° C. to 1580
It was found that the temperature rises sharply when the temperature exceeds ℃, and becomes brittle at the processing temperature of 1600 ℃ or higher.

According to the scanning electron microscope observation of the fractured portion, in the case of the blackened sample, the one having a heat treatment temperature of 1580 ° C. or lower has a ductile fracture form accompanied by crystal elongation. I understood. On the other hand, when the heat treatment temperature exceeded 1600 ° C., it was confirmed that fracture occurred at the grain boundary, leading to brittle fracture. The particle diameters of tungsten and alumina remained almost unchanged before and after sintering.

[0020]

[Table 1]

Further, the assembling property is evaluated by checking whether or not peeling of the blackening layer occurs when the jig of the assembling apparatus is inserted inside the cathode sleeve, and by pressing the cathode disk inside the opening end of the cathode sleeve. At this time, the cathode sleeve was evaluated for cracks. As for the thermal fatigue characteristics, changes in the cutoff voltage during the life test of the color picture tube were investigated. Generally, in a picture tube, when the distance between the first grid and the cathode surface changes for some reason, the cutoff voltage changes and the anode current changes. When the cathode is used in a color picture tube, the cutoff voltages of the red, green and blue electron guns are adjusted to be equal. However, when the color image receiver is used for a long time, the cathode constituent material is deformed due to thermal fatigue, and the distance dimension between the first grid and the cathode surface is changed. Since this dimensional change is usually not constant in each of red, green, and blue electron guns, the electron beam current incident on the phosphor screen changes, causing color shift.
In addition, brightness deterioration also occurs. Therefore, a dimensional change due to thermal fatigue of the cathode sleeve when various heat treatment temperatures were changed was confirmed by a cathode heating and cooling test of a color picture tube. Under these test conditions, the applied voltage was set so that the temperature reached by the cathode was about 1150 ° C., and the test was repeated for 5 minutes on and 10 minutes off. Since the dimensional changes of the cathode surface and the first grid are approximately proportional to the change amount of the cutoff voltage, the deformation of the sleeve due to thermal fatigue can be measured relatively accurately by measuring the change amount of the cutoff voltage. The change in the cutoff voltage was judged based on the result after repeating ON and OFF 4000 times.

As is clear from Table 1, the heat treatment temperature for forming the blackening layer is 1 because of the degree of variation in the cutoff voltage.
It was confirmed that the range of 250 ° C to 1580 ° C showed good characteristics.

(Example 2) Samples were prepared by combining tungsten powder and alumina powder used for blackening with different particle sizes, and evaluated. The average particle diameter of the used tungsten powder is 0.1 μm, 0.5 μm, 0.9 μm,
Seven types of 2 μm, 3 μm, 5 μm and 10 μm were prepared. Alumina powder is fine alumina powder (average diameter is about 0.01 μm, length is about 0.1 μm), average particle size is 0.1 μm, 0.3 μm, 0.5 μm, 0.6 μm,
A total of nine types of 0.8 μm, 1.0 μm, 2 μm, and 5 μm were prepared. The heat treatment temperature of the coating after drying the slurry was 1450 ° C., and the treatment atmosphere was a vacuum of the same vacuum degree. The results of the tests with various combinations of each powder are shown in Table 2.

[0024]

[Table 2]

In this evaluation, the degree of adhesion strength of the blackened layer after the heat treatment and the withstand voltage between the heater and the cathode were measured. Regarding the adhesion strength of the blackened layer, the degree of the adhesion strength was judged by scratching the coating film with a needle having a sharp tip and peeling at that time. The withstand voltage was evaluated by assembling five samples of each sample as an impregnated type cathode assembly, further using each of them as a picture tube, applying a DC voltage between the heater and the cathode, and measuring the discharging voltage. In this test, the heater heating voltage was evaluated as 1.1 times the rated value.

As is clear from Table 2, the average particle size of the tungsten powder is 0.5 μm in terms of adhesion strength and withstand voltage.
It was proved that the above range of 2 μm or less is suitable. On the other hand, alumina powder has an average particle size of 0.1 μm.
It was confirmed that the above range of less than 1 μm is suitable. The reason why the sample using the alumina fine powder is significantly inferior in the withstand voltage performance is considered to be that the electric field is concentrated on the tips of the fine particles due to the use of the alumina having the sharp tips, and thus the discharge is likely to occur. To be

(Embodiment 3) This is an impregnated type cathode assembly in which the inner surface of the cathode sleeve and the entire surface of the strap are blackened. As the method of forming the blackening layer on the inner surface of the cathode sleeve, the method described in the above embodiment was adopted. And
The strap has a width of 0.2 mm and a thickness of 0.02 m.
It is made of m. A blackened layer having an average thickness of 3 μm was formed on the entire surface of this strap material. The tungsten powder used had an average particle size of 0.9 μm, and the alumina powder had an average particle size of 0.6 μm. The sintering temperature in vacuum after the slurry was applied and dried was 1450 ° C.

The impregnated-type cathode assembly thus manufactured was incorporated into a picture tube, and changes in the cutoff voltage during the life test were investigated. The evaluation conditions are the same as those described above (Example 1). The results are shown in Table 3.

[0029]

[Table 3]

As is clear from Table 3, by forming the blackening layer also on the strap, the mechanical strength of the strap is improved as compared with that of the material, so that the change in the cutoff voltage can be reduced. It was

(Embodiment 4) This embodiment is also a case of an impregnated cathode assembly in which a blackening layer is formed on the inner surface of the cathode sleeve by using tungsten powder and alumina powder. Then, samples having various weight ratios of tungsten powder and alumina powder used for blackening were prepared and evaluated. That is, the average particle diameter of the used tungsten powder is 0.9 μm, and that of the alumina powder is 0.8 μm. The temperature of heat treatment after the slurry was applied and dried was 1500 ° C., and heat treatment was performed for 10 minutes in a vacuum atmosphere.

In the evaluation in this example, the appearance color of the blackened layer after heat treatment, the adhesion strength, and the heater temperature at which the cathode temperature reached 1100 ° C. were measured. Regarding the adhesion strength of the blackened layer, the degree of the adhesion strength was evaluated by scratching the film with a needle having a sharp tip and peeling at that time. Further, the cathode temperature was measured by assembling each sample into the impregnated cathode structure and then producing a dummy tube into which a heater was inserted. The results are shown in Table 4.

[0033]

[Table 4]

As is clear from Table 4, the weight ratio of tungsten powder and alumina powder (tungsten: alumina) is as follows in terms of adhesion strength of the blackening layer and cathode temperature characteristics.
It was confirmed that the range of (90:10) to (65:35) is preferable. And especially, the weight ratio of these tungsten and alumina (tungsten: alumina)
It was confirmed that even better performance was obtained in the range of (70:30) to (85:15).

(Other Embodiments) In the above embodiments, the case where the tantalum (Ta) material is used as the cathode sleeve and the strap material has been described. However, the present invention is not limited to this. For example, a Ta alloy containing Ta as a main component containing 10% by weight of W or a Ta alloy containing Ta as a main component containing 2.5% by weight of W had the same effect. . Further, it may be a Ta alloy containing 40% by weight of Nb. Furthermore, this cathode sleeve may be Nb, or it is mainly composed of Nb as known from USP4820954, and Ti, Zr, Hf,
At least 1 selected from V, Ta, Mo, or W
One of them may be an alloy containing 15% by weight or less in total.

In the above embodiment, the case where the blackening layer is formed on the cathode sleeve and the strap material has been described, but the blackening layer 25 may be formed on the back surface of the disk holding cap. Not only the strength of the structure is improved, but also the effect of reducing the temperature of the heater by the increase of the heat transfer effect through the cap is further enhanced.

The present invention is not limited to the impregnated cathode structure, but can be applied to other indirectly heated cathodes, directly heated cathodes and the like. Further, in addition to the tungsten powder and the alumina powder, other heat resistant powder may be contained by several wt% or less.

[0038]

As described above, according to the present invention,
The mechanical strength of the cathode sleeve is higher than the strength of the material,
A highly reliable cathode assembly with high reproducibility can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a characteristic diagram showing the relationship between heat treatment temperature and fracture load.

[Explanation of symbols]

 13 ... Impregnated cathode disk 14 ... Disk holding cap 15 ... Cathode sleeve 21 ... Heater 23, 24, 25 ... Blackening layer

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Toru Yabei 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Stock Company Toshiba Horikawa-cho Factory

Claims (6)

[Claims] 1. A cathode sleeve having a blackened inner surface, an electron emitting portion provided at an end portion of the cathode sleeve directly or through a holding body, and a heater inserted inside the cathode sleeve. In the provided cathode assembly, the black coating on the inner surface of the cathode sleeve has an average particle size of 0.5.
Tungsten in the range of μm or more and 2 μm or less and alumina in the range of average particle size of 0.1 μm or more and less than 1 μm are mixed in a weight ratio (tungsten: alumina) of (90:10) to (65:35). A cathode assembly, which is a sintered layer. 2. The cathode assembly according to claim 1, wherein the cathode sleeve is made of tantalum, an alloy containing tantalum as a main component, or niobium or an alloy containing niobium as a main component. 3. The weight ratio of tungsten to alumina (tungsten: alumina) is (70:30) to (8).
The cathode assembly according to claim 1, which is in the range of 5:15). 4. A method of manufacturing a cathode assembly, wherein an electron emitting portion is provided directly or via a holding body with a black coating formed on the inner surface of the cathode sleeve.
A weight ratio (tungsten: alumina) of tungsten having an average particle size of 0.5 μm or more and 2 μm or less and alumina having an average particle size of 0.1 μm or more and less than 1 μm is (90:10) to (65: 35) A suspension mixed with the dispersion solution is applied in the range of 35), and this is sintered in a non-oxidizing atmosphere at a temperature in the range of 1250 ° C to 1580 ° C to form a black coating film. Method of manufacturing cathode assembly. 5. The method of manufacturing a cathode structure according to claim 4, wherein the cathode sleeve is made of tantalum, an alloy containing tantalum as a main component, or niobium or an alloy containing niobium as a main component. 6. The sintering temperature is 1400 ° C. to 155 ° C.
The method for manufacturing a cathode assembly according to claim 4, wherein the temperature is in the range of 0 ° C.