JPH1021819A - Manufacture of cathode for electron tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for cathode for electron tube by which cathode with extremely small emission slump even after the use at electric current density as high as 2-4A/cm<2> can be manufactured. SOLUTION: A cathode 8 for electron tube is constituted of a heater coil 1, a cylindrical sleeve 2 in which the heater coil 1 is built, a substrate 3 installed in the open part in one end of the sleeve 2, and an emitter 7 consisting of a barium-containing alkali earth metal oxide 5 and a terbium oxide 6. The emitter 7 is produced by coating the substrate 3 with a mixture of alkali earth metal carbonate which satisfies a/b <=2.3 (wherein a stands for the average particle size in the longer axis direction of unit particle of the alkali earth metal carbonate and b for the average particle size in the shorter axis direction) and terbium oxide and thermally decomposing the mixture in vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a cathode for an electron tube (CRT) used for a television, a display and the like.

[0002]

2. Description of the Related Art As shown in FIG. 10, a conventional oxide cathode for an electron tube has a heater coil 1, a cylindrical sleeve 2 containing the heater coil 1, and an opening at one end of the sleeve 2. The substrate 3 includes a base 3 containing a trace amount of a reducing element such as magnesium, and an emitter 4 mainly composed of an alkaline earth metal oxide containing barium and deposited on the base 3. In such a conventional oxide cathode, it takes several seconds to several minutes from the start of electron emission until the current stabilizes, during which the current gradually decreases slightly (hereinafter, this phenomenon). Is called an emission slump), and as shown in the equation (1), the initial current value I
The ratio (%) of the difference between the current values I (m) and I (0) after m minutes with respect to (0) is expressed as the emission slump rate ΔI (m).

ΔI (m) = (I (m) −I (0)) / I (0) × 100 (1) The value of the emission slump rate after 5 minutes is ± The allowable range is within 5%. The emission slump becomes larger as the current density at the time of operating the cathode is increased, and has become an obstacle in responding to the recent trend of CRT technology to increase the current density.

In order to solve this problem, Japanese Patent Laid-Open No.
As disclosed in JP-A-59725, oxides such as yttrium and europium are contained in an emitter in addition to an alkaline earth metal oxide to suppress emission slump. As an example, as a result of examining an emission slump with respect to a current density at the time of operation in an oxide cathode using an emitter composed of an alkaline earth metal oxide and yttrium oxide, the results are as shown in FIG. The line A1 in the figure indicates the current density during operation of 1 A /
In the case of cm ² , the line A2 is 2 A / cm ² , the line A3 is 3 A / cm ² , and the line A4 is 4 A / cm ² . As described above, in the conventional oxide cathode in which the emitter contains yttrium oxide, the emission slump rate is within an allowable range in a range of ^{2 A} / cm ² or less.

[0005]

However, in recent years, the current density required for CRTs has been increasing to exceed 2 A / cm ² , and the emission slump rate is within an allowable range even when operated at about 3 A / cm ^2. There is a demand for an inner cathode. However, the conventional oxide cathode has a 2A
If it exceeds / cm ² , the magnitude of the emission slump rate starts to increase rapidly, and exceeds the allowable range.

An object of the present invention is to provide a method of manufacturing a cathode for an electron tube, which can obtain stable electron emission even when used in a current density exceeding 2 A / cm ² and has a very small change in emission slump rate. And

[0007]

According to a first aspect of the present invention, there is provided a method of manufacturing a cathode for an electron tube, comprising: mixing a mixture of barium-containing alkaline earth metal carbonate and terbium or terbium oxide on a substrate of the cathode for an electron tube. When the mixture is applied and the mixture is thermally decomposed in a vacuum to form an emitter, the average particle size in the major axis direction of the single particle of the alkaline earth metal carbonate is defined as a (μm), Has a relationship of a / b ≦ 2.3, where b (μm) is the average particle size of Thereby, electron emission is stabilized, and a cathode for an electron tube with extremely small emission slump can be realized.

According to a second aspect of the present invention, there is provided a method of manufacturing a cathode for an electron tube according to the first aspect.
The amount of the terbium or terbium oxide added to the alkaline earth metal carbonate is 0.001 wt% by weight of terbium atoms with respect to the total weight of the emitter.
Not less than 5 wt%. Thereby, electron emission is stabilized, and a cathode for an electron tube with extremely small emission slump can be realized.

According to a third aspect of the present invention, there is provided a method of manufacturing a cathode for an electron tube according to the first or second aspect, wherein the average particle diameter a is 1 μm or more and 3.5 μm or less. Thereby, the emission slump can be improved and the cathode can have a longer life.

A method for manufacturing a cathode for an electron tube according to a fourth aspect is the method for manufacturing a cathode for an electron tube according to the third aspect,
The average particle diameter a is set to 1 μm or more and 3.5 μm or less by crushing particles of the alkaline earth metal carbonate having an average particle diameter a of more than 3.5 μm. According to this method, the individual alkaline earth metal carbonate particles are uniformly pulverized, and particles having a small variation in particle diameter can be produced. As a result, a cathode for an electron tube having a small emission slump can be realized.

According to a fifth aspect of the present invention, there is provided a method for producing a cathode for an electron tube, comprising: depositing a coprecipitated carbonate of an alkaline earth metal containing barium and terbium on a substrate of the cathode for an electron tube; In generating the emitter by pyrolysis in a vacuum, the average particle size in the major axis direction of a single particle of the coprecipitated carbonate is defined as a (μm), and the average particle size in the minor axis direction is defined as b.
(Μm), a / b ≦ 2.3. According to this method, the adhesion strength between the emitter and the base is increased, and peeling of the emitter can be prevented.

A method of manufacturing a cathode for an electron tube according to claim 6, wherein a mixture of an alkali earth metal carbonate containing barium and a composite oxide of an alkaline earth metal and terbium is added to the substrate of the cathode for an electron tube. When the mixture is thermally decomposed in vacuum to form an emitter, the average particle diameter in the major axis direction of a single particle of the alkaline earth metal carbonate is defined as a (μm); Average particle size in the direction
(Μm), a / b ≦ 2.3. According to this method, terbium is uniformly dispersed in the inside of the emitter, so that a cathode with less variation in emission slump can be realized.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic structure of an embodiment of an electron tube cathode obtained by the method for producing an electron tube cathode according to the present invention. In FIG. 1, a cathode 8 for an electron tube is
A heater coil 1, a cylindrical sleeve 2 containing the heater coil 1, a cap-shaped base 3 made of nickel containing a small amount of magnesium provided at one end opening of the sleeve 2, and a cover 3 on the base 3. It is composed of a deposited alkaline earth metal oxide 5 containing barium and an emitter 7 made of terbium oxide 6.

(Embodiment 1) A first embodiment of the present invention will be described.

The alkaline earth metal carbonate used in the first embodiment is a ternary carbonate containing barium, strontium, and calcium in a molar ratio of 45:45:10. Terbium oxide in a weight ratio of 0.2 wt.
% (0.23 wt% of terbium atoms with respect to the total weight of the oxide emitter) to form a mixture.
These are mixed with a mixed medium of diethyl oxalate and diethyl acetate (diethyl oxalate: diethyl acetate volume ratio = 1: 1)
Was dispersed in a solution containing a small amount of nitrocellulose (5 to 30 g per liter of the mixed medium) to prepare a dispersion. This dispersion is applied to a thickness of about 50 μm on a cathode substrate by a spray gun and pyrolyzed at 930 ° C. in vacuum to obtain an emitter 7 comprising terbium oxide and barium / strontium / calcium oxide. A cathode having the structure shown in FIG.

The cathode thus obtained is used for display C
When used for RT, the current density during the operation of this CRT is 3.0 A
/ Cm ² and the emission slump rate was measured up to 5 minutes after the start of electron emission, and the result shown in FIG. 2 was obtained. Here, the average particle diameter a in the major axis direction of the single particle of the ternary carbonate is 1.5 μm, and the average particle diameter b in the minor axis direction is 1.0 μm. Line B in FIG.
Shows the case where terbium atoms are contained in the emitter in an amount of 0.23 wt%, and line A shows that the emitter contains 0.23 wt% of yttrium atoms.
In the case where 23% by weight is contained, the line C shows the emission slump rate when the emitter contains 0.23% by weight of europium atoms. As is clear from FIG. 2, when terbium oxide is contained in the emitter, the emission slump rate at a current density of 3.0 A / cm ² is reduced by the conventional oxide cathode (line A).
And about 1/4 of the line C), and it can be seen that it can be suppressed within the allowable range. In addition, even when terbium is contained in the emitter in the form of metal atoms instead of terbium oxide, the effect of improving the emission slump is also seen. Regarding the addition amount of terbium and terbium oxide, the emission slump rate after 5 minutes from the start of electron emission should be kept within ± 5% in the range of 0.001 to 5% by weight of terbium atoms with respect to the total weight of the emitter. Was completed. In particular, as shown in this embodiment, terbium atoms are added in an amount of 0.1 to the total weight of the emitter.
When the content was around 23 wt%, the effect of improving emission slump was the highest.

The emission slump rate is also increased by the ratio of the average particle diameter a in the major axis direction to the average particle diameter b in the minor axis direction of a single particle of the alkaline earth metal carbonate deposited on the substrate. different. FIG. 3 shows that the ternary carbonate contains 0.2 wt% of terbium oxide (0.23 wt% of terbium atoms based on the total weight of the emitter), and the ratio of a to b of a single particle of the ternary carbonate. 3 shows the emission slump rate from the start of electron emission to 5 minutes after the start of electron emission. A line B in FIG. 3 represents a case where a / b = 1.5, a line D represents a case where a / b = 2, and a line E represents a / b = 2.3.
, Line F corresponds to a / b = 3, and line G corresponds to a / b =
6 is shown. Here, the line B is the line B in FIG.
And the results under the same conditions are denoted by the same reference numerals in the following figures. As is apparent from FIG.
When / b is 2.3 or less, the emission slump rate falls within the allowable range. Therefore, when terbium or terbium oxide is contained in the emitter and the particles of the alkaline earth metal carbonate satisfy the relationship of a / b ≦ 2.3, the high-current density exceeding 2 A / cm ² can be obtained. Emission slump can be improved.

Next, FIG. 4 shows the emission slump rate 5 minutes after the start of electron emission when a / b is set to about 1.5 and a of the single particle of the ternary carbonate is changed. FIG. 5 shows the emission residual ratios after the accelerated life test of FIG. Here, the emission residual ratio means a ratio (%) of Imax after 2000 hours of the accelerated life test to the maximum current Imax that can be taken out before the start of the accelerated life test. From the results of FIG. 4, a must be set to 3.5 μm or less in order to keep the emission slump rate within the allowable range. However, as shown in FIG. 5, when a falls below 1 μm, the emission residual rate decreases. Increases rapidly. Therefore, in order to suppress a decrease in Imax due to long-term operation and to improve emission slump, a is set to 1 μm
It is preferable to set the range to 3.5 μm.

Next, a terbium atom is added to the emitter in an amount of 0.1.
23% by weight, and a single particle of ternary carbonate has a = 2 μm,
FIG. 6 shows the emission slump rate 5 minutes after the start of electron emission at various current densities of the cathode obtained when a / b = 1.5. From the result of FIG.
/ Cm ² or less is within the allowable range. Therefore, the cathode prepared by the manufacturing method of the present invention has a current density of 4 A
/ Cm ² or less, stable electron emission can be obtained, and it can be used at a current density about twice that of a conventional oxide cathode.

In this embodiment, the case where the emitter is made of a ternary oxide of barium / strontium / calcium has been described. However, the emission slump can be similarly improved by using a binary oxide of barium / strontium.

(Embodiment 2) Next, a second embodiment of the present invention will be described.

In the cathode having the structure shown in FIG. 1, terbium is contained in a weight ratio of 0.005 wt% to the entire carbonate.
(0.0068 wt% based on the total weight of the oxide emitter)
A quaternary coprecipitated carbonate of barium, strontium, calcium, terbium, containing a barium, strontium, calcium, molar ratio of 45:45:10, is deposited on the substrate, and the carbonate is heated at 930 ° C. To produce a cathode having an emitter composed of barium / strontium / calcium / terbium oxide.
Here, the average particle diameter a in the major axis direction of the single particle of the quaternary coprecipitated carbonate is 1.5 μm, and the average particle diameter b in the minor axis direction is 1 μm.

This cathode was used for a display CRT and operated at various current densities to perform an accelerated life test of 2,000 hours. As a result, as shown in FIG. 7, the one using the quaternary coprecipitated carbonate (line H) was 4 A higher than the one using barium / strontium / calcium carbonate mixed with terbium oxide particles (line B). Even under a high current density of / cm ² or more, no peeling of the emitter was observed.

In this embodiment, the coprecipitated carbonate is barium
The case of quaternary coprecipitated carbonate of strontium calcium terbium is described, but the same effect as described above was obtained also in the case of ternary coprecipitated carbonate of barium strontium terbium. Therefore, by using a coprecipitated carbonate of an alkaline earth metal and terbium for the emitter, peeling of the emitter can be prevented. The emission slump rate of the cathode using the coprecipitated carbonate of alkaline earth metal and terbium as the emitter is almost equivalent to the case of using the mixture of alkaline earth metal carbonate and terbium oxide particles. . In this embodiment,
Terbium was contained in the entire carbonate in an amount of 0.005 wt%. However, if the terbium was contained in the range of 0.001 wt% to 0.1 wt%, the emission slump rate was within an allowable range, and no emitter peeling was observed. Was.

(Embodiment 3) Next, a third embodiment of the present invention will be described.

The alkaline earth metal carbonate used in the third embodiment is a ternary carbonate having a molar ratio of barium, strontium and calcium of 45:45:10,
The average particle diameter a in the major axis direction of the single particle of the ternary carbonate is 1.5
μm, and the average particle size b in the minor axis direction is 1 μm. The ternary carbonate is mixed with a barium / terbium composite oxide Ba ₃ Tb ₄ O
_The mixture to which ₉ was added was deposited on a substrate, and the mixture was thermally decomposed in vacuum at 930 ° C. to produce a cathode having an emitter composed of Ba ₃ Tb ₄ O ₉ and barium strontium calcium oxide. At this time, Ba ₃ Tb ₄ O
The amount of ₉ added is 0.3 wt% based on the weight of the ternary carbonate.
(Terbium atoms are 0.22% of the total weight of the emitter.
wt%). When the emission slump rate of the cathode thus obtained was measured 5 minutes after the start of electron emission by the same method as in the first embodiment, the result as shown in FIG. 8 was obtained. In FIG. 8, I represents the case where the emitter is made of Ba ₃ Tb ₄ O ₉ and barium strontium calcium oxide, and B represents the embodiment 1
In this case, the emitter is made of terbium oxide and barium / strontium / calcium oxide. As shown in FIG. 8, when Ba ₃ Tb ₄ O ₉ is contained in the emitter, the variation in the emission slump rate of each cathode is smaller than in the case where terbium oxide is contained. Therefore, by including Ba ₃ Tb ₄ O ₉ in the emitter, it is possible to prevent a color shift or the like caused by a variation in emission slump rate in a color CRT, and to improve display quality. As for the added amount of Ba ₃ Tb ₄ O _9, 0.1~5wt respect to the emitter total weight
% (0.53 to 2.7 wt% in terms of terbium atoms), an improvement effect is seen in the variation of the emission slump rate. In particular, as shown in this embodiment,
The improvement effect was highest when the addition amount was around 0.3 wt%.

(Embodiment 4) Next, a fourth embodiment of the present invention will be described.

The alkaline earth metal carbonate used in the fourth embodiment is a ternary carbonate in which barium, strontium and calcium have a molar ratio of 45:45:10.
The average particle diameter a in the major axis direction of a single particle of ternary carbonate is 6 μm
m, average particle diameter b in the minor axis direction is 4 μm (a / b = 1.5)
It is. Terbium oxide is added to this ternary carbonate to a weight ratio of 0.2 wt% to form a mixture, and these are mixed with a mixed medium of diethyl oxalate and diethyl acetate (diethyl oxalate: diethyl acetate volume ratio = 1: 1). In 1), add a small amount of nitrocellulose (5 liters per liter of the mixed medium).
To 30 g) to prepare a dispersion. This dispersion was placed in a ball mill containing 30 porcelain balls having a capacity of 4 liters and a diameter of 2.5 cm.
Milling for 250 hours at the speed of rotation. As a result, a = 2μ
A ternary carbonate having a particle shape of m, a / b = 1.5 was obtained. The dispersion obtained by pulverizing the ternary carbonate particles in this manner is applied to the cathode substrate with a spray gun in the same manner as in Embodiment 1, to produce the cathode shown in FIG.
At A / cm ² , the emission slump rate was measured. FIG. 9 shows the result. The line J in FIG. 9 represents the case where the ternary carbonate was pulverized with a ball mill, and the line B represents a = 1.5 μm.
When ternary carbonate particles having m, a / b = 1.5 are used,
Line G was not pulverized with a ball mill, a = 6 μm, a / b =
The case where 1.5 ternary carbonate particles are used is shown. As is clear from FIG. 9, the one crushed by a ball mill (line J)
Has significantly improved emission slump as compared with the non-crushed one (line G), and is substantially equivalent to the one originally with a = 1.5 μm (line B). Therefore, by crushing the particles of alkaline earth metal carbonate with a ball mill,
Particles having a large a can be pulverized to the preferable value of the present invention, whereby the emission slump can be improved. In the present embodiment, the pulverization is performed in a state where the alkaline earth metal carbonate is mixed with the dispersion liquid. However, the same effect can be obtained by directly pulverizing the alkaline earth metal carbonate in a powder state. Moreover, you may grind with a mortar etc.

[0030]

As described above, according to the method of the present invention, the emitter contains terbium or terbium oxide and has a single particle shape of alkaline earth metal carbonate deposited on the substrate. , And a / b of 2.3 or less, a cathode for an electron tube having an extremely small emission slump can be realized even when used under a high current density of ^{2 to} 4 A / cm ² .

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic structure of a cathode for an electron tube obtained by a method of the present invention.

FIG. 2 is a diagram showing a change over time of an emission slump rate in a cathode for an electron tube obtained by a conventional method and the method of the present invention.

FIG. 3 is a diagram showing a change with time of an emission slump rate in a cathode for an electron tube obtained by a method of the present invention.

FIG. 4 is a diagram showing the relationship between a of alkaline earth metal carbonate and emission slump rate in a cathode for an electron tube obtained by the method of the present invention.

FIG. 5 is a diagram showing the relationship between a of alkaline earth metal carbonate and the residual emission ratio in the cathode for an electron tube obtained by the method of the present invention.

FIG. 6 is a diagram showing the relationship between current density and emission slump rate in a cathode for an electron tube obtained by the method of the present invention.

FIG. 7 is a diagram showing a relationship between current density and peeling frequency in a cathode for an electron tube obtained by the method of the present invention.

FIG. 8 is a diagram showing a variation in emission slump rate in a cathode for an electron tube obtained by the method of the present invention.

FIG. 9 is a diagram showing a change with time of the emission slump rate in the cathode for an electron tube obtained by the method of the present invention.

FIG. 10 is a diagram showing a schematic structure of a conventional cathode for an electron tube.

FIG. 11 is a diagram showing a change with time of an emission slump rate in a conventional cathode for an electron tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater coil 2 Sleeve 3 Base 5 Alkaline earth metal oxide 6 Terbium oxide 7 Emitter 8 Cathode for electron tube

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01J 9/04 H01J 9/04 D

Claims (6)

[Claims] 1. A mixture obtained by adding terbium or terbium oxide to an alkaline earth metal carbonate containing barium is deposited on a substrate of a cathode for an electron tube, and the mixture is thermally decomposed in a vacuum to produce an emitter. In this case, the average particle size in the major axis direction of the single particle of the alkaline earth metal carbonate is defined as a (μm), and the average particle size in the minor axis direction is defined as b (μ
m), wherein a / b ≦ 2.3. 2. The amount of terbium or terbium oxide added to the alkaline earth metal carbonate is 0.001 wt% or more and 5 wt% or less in terms of terbium atom weight ratio with respect to the total weight of the emitter. The method for manufacturing a cathode for an electron tube according to claim 1, wherein 3. The average particle diameter a is 1 μm or more and 3.5 μm.
The method for producing a cathode for an electron tube according to claim 1 or 2, wherein: 4. The method for producing a cathode for an electron tube according to claim 3, wherein the particles of the alkaline earth metal carbonate having an average particle diameter a of more than 3.5 μm are pulverized to reduce the average particle diameter a to 1 μm. A method for producing a cathode for an electron tube, wherein the thickness is not more than 3.5 μm. 5. A method for depositing a coprecipitated carbonate of an alkaline earth metal containing barium and terbium on a substrate of a cathode for an electron tube and thermally decomposing the coprecipitated carbonate in a vacuum to form an emitter. When the average particle size of the single particles of the coprecipitated carbonate in the major axis direction is a (μm) and the average particle size in the minor axis direction is b (μm), a / b ≦ 2.3. A method for manufacturing a cathode for an electron tube, characterized by having a relationship. 6. A mixture obtained by adding a composite oxide of an alkaline earth metal and terbium to an alkaline earth metal carbonate containing barium is deposited on a substrate of a cathode for an electron tube, and the mixture is heated in a vacuum. In generating the emitter by decomposition, the average particle diameter in the major axis direction of the single particle of the alkaline earth metal carbonate was defined as a (μm), and the average particle diameter in the same minor axis direction was defined as b (μm). A method for producing a cathode for an electron tube, wherein a / b ≦ 2.3.