JP2003197099A - Method for manufacturing cold cathode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold cathode of a cold cathode discharge tube usable for a long period, providing a high brightness, and stably performing light emitting operation. <P>SOLUTION: This method of manufacturing the cold cathode of the cold cathode discharge tube having the cold cathode at the tip part of an inlet wire sealingly fitted to the end part of a glass tube having rare gas or mercury sealed therein comprises a step for heating by energization a sintered body containing a metal with high melting point in vacuum and a step for impregnating electron emission substance in the sintered body heated by energization. A heating temperature in the step for heating by energization comes desirably within the range of 1200 to 1500°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold cathode in a cold cathode discharge tube having a cold cathode.
The present invention relates to a method for manufacturing a cold cathode in a cold cathode discharge tube having a stable light emitting operation.

[0002]

2. Description of the Related Art In recent years, a cold cathode discharge tube having a cold cathode has been used in a backlight light source of a liquid crystal display, a film with a lens, a strobe of a digital camera and the like. This type of cold cathode discharge tube generates less heat,
There are demands for low power consumption, high brightness, high efficiency, long life, and miniaturization. In particular, as a recent strobe for digital cameras, a thin tube type with an outer diameter of 2 mm or less and a length of 30 mm or less has been developed. With the spread of mobile phones equipped with digital cameras in the future,
It is considered that the cold cathode discharge tube will be further miniaturized. Along with this, it is necessary to reduce the size of the cold cathode sealed at the end of the cold cathode discharge tube, and the development of a cold cathode having an outer diameter of 1 mm or less and a length of 1 mm or less is progressing.

Usually, in a cold cathode discharge tube, when a predetermined voltage is applied to the cold cathode, secondary electrons are emitted from the cold cathode by the ions of the initial plasma generated, and a glass tube in which mercury or a rare gas is previously sealed. Discharging starts at. Then, mercury atoms or rare gas atoms excited by the electron energy accompanying this discharge radiate ultraviolet rays, and the ultraviolet rays are converted into visible light by the phosphor layer coated on the inner surface of the glass tube. Occurs and emits light.

As the cold cathode, a porous sintered body made of a refractory metal such as nickel or tungsten having a cylindrical shape has been studied and used at present. However, recently, from the viewpoint of improving the luminous efficiency, it is higher than titanium. Attention has been focused on a cold cathode made of a porous sintered body made of a melting point metal such as niobium.

The above cold cathode is inserted into a lead wire such as a tungsten wire, a Kovar wire or a Dumet wire,
It is joined to the lead-in wire by caulking. After that, the cold cathode is impregnated with an electron emitting material, then sealed at the end of the glass tube, and a rare gas such as mercury or xenon gas is sealed in the glass tube to manufacture a cold cathode discharge tube. The electron emitting materials are mainly cesium compounds, barium compounds, yttrium compounds, lanthanum compounds and the like.

For example, in order to produce a cold cathode made of a porous sintered body of titanium and a refractory metal, titanium powder and powder of a refractory metal are mixed, filled in a mold and pressure-molded. However, the method of sintering after that in vacuum is common.

[0007]

However, a small-sized porous sintered body made of titanium and a refractory metal having an outer diameter of 1 mm or less and a length of 1 mm or less is produced, and a cold cathode discharge tube is formed by the method described above. When manufactured and actually made to emit light, the following problems occurred. That is, in the porous sintered body composed of titanium and the refractory metal, the refractory metal is mainly oxidized by oxygen slightly present in the vacuum during the sintering process in the vacuum to generate an oxide. After that, when a discharge tube is manufactured using a cold cathode made of this porous sintered body and continuous light emission is performed, a vigorous sputtering phenomenon occurs because the melting point of the generated oxide is low. Therefore, the refractory metal oxide mainly adheres to the inside of the glass tube near the cold cathode, and the light emission amount is reduced. Furthermore, along with this phenomenon, the consumption of electron-emissive materials such as impregnated cesium compounds, barium compounds, yttrium compounds, and lanthanum compounds becomes severe, and as a result, the starting voltage, which is a parameter that affects the light emission operation, increases. There is a problem that the time for maintaining low power consumption is shortened and finally the light emission life is also shortened. This phenomenon was more remarkable as the size became smaller.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a cold cathode in a discharge tube which has a long life and a stable emission operation with high brightness.

[0009]

In order to achieve the above object, the cold cathode manufacturing method of the present invention employs the following constitution. That is, the method for producing a cold cathode of the present invention is a method for producing a cold cathode in a cold cathode discharge tube having a cold cathode at the tip of an introduction line sealed at the end of a glass tube filled with a rare gas or mercury. It is characterized by including a step of electrically heating a sintered body having a high melting point metal in a vacuum and a step of impregnating the electrically heated sintered body with an electron emitting substance.

Further, in the method for manufacturing a cold cathode of the present invention,
The step of electrically heating is a method of heating a sintered body having a high melting point metal while applying an electric current, and the heating temperature is 1200 ° C.
It is preferably 1500 ° C. or lower.

Further, in the method for manufacturing a cold cathode of the present invention,
The sintered body having a high melting point metal is preferably a sintered body made of titanium and a high melting point metal.

Further, in the method for manufacturing a cold cathode of the present invention,
The refractory metal is preferably niobium, tungsten, molybdenum or tantalum.

(Function) As a result of earnest studies and studies on the cold cathode, the present inventor has produced a cold cathode made of titanium and a refractory metal and, after impregnating it with an electron-emitting substance, conducts electric heating in vacuum. It was found that the oxide of refractory metal generated during the sintering process in vacuum was removed. Therefore, the phenomenon of sputtering of refractory metal oxides and the consequent consumption of electron emitting material do not occur from the obtained cold cathode, and as a result, the starting voltage of the discharge tube equipped with this cold cathode is stable and the emission life is long. Was found to be long enough for practical use. Here, the high melting point metal means a metal having a melting point of 2000 ° C. or higher, and in the present invention, niobium,
It is preferably tungsten, molybdenum or tantalum.

The above-mentioned effect is that when a cold cathode made of titanium and a refractory metal is manufactured, the oxide of the refractory metal produced during the sintering process in a vacuum has a low melting point, so that in a vacuum. It utilizes the phenomenon that it easily evaporates when heated by electric current. That is, the melting point of the refractory metal forming the cold cathode is 2470 ° C. for niobium and 3380 for tungsten.
℃, 2610 ℃ for molybdenum, 3000 ℃ for tantalum
Is. On the other hand, the melting point of the oxide produced by oxidizing the refractory metal is 1500 for niobium oxide (Nb ₂ O ₅ ).
C., tungsten oxide (WO ₃ ) is 1470 ° C., molybdenum oxide (MoO ₃ ) is 795 ° C., tantalum oxide (T
It is 1470 ° C. for a ₂ O ₅ ). The melting point of titanium is 1670 ° C. From the above-mentioned comparative examination of melting points, it is understood that the oxide easily precedes and vaporizes when electrically heated in a vacuum.

The electric heating of the present invention is a method of heating a sintered body while passing an electric current through it, and it is about 1200 to 1 instantaneously.
This is a heating method in which the temperature is raised to 500 ° C. The reason for instantaneously raising the temperature is to prevent shrinkage and deformation of the sintered body due to evaporation and melting of titanium. The volume ratio of the oxide generated during the sintering process in vacuum to the whole sintered body is small, and the existing locations are unevenly distributed on the surface, so that the oxide is easily removed by this operation. Moreover, the reason why the electric heating is used is that the oxides are again generated on the surface of the sintered body by the oxygen slightly existing in the vacuum in the heating by the normal radiant heat. On the other hand, in the electric heating, since the sintered body is heated while being always supplied with electrons, the sintered body is subjected to a reducing action and an oxide is not generated. For the above reason, the cold cathode manufacturing method of the present invention is provided with a cold cathode in which oxide of a refractory metal, which is a cause of unstable light emitting operation, is removed, and which has a long life, high brightness, and stable light emitting operation. It becomes possible to provide a cold cathode discharge tube.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing the structure of a cold cathode discharge tube having a cold cathode. The cold cathode 1 is caulked and joined to the tip of the lead-in wire of the tungsten wire 2 sealed at the end of the thin glass tube 3. The glass tube has a length of 40 mm and a diameter of 2 mm, for example, and the inside of the glass tube 3 is filled with xenon gas. Reference numeral 4 in FIG. 1 is a glass for sealing, and the material thereof is the same as that of the glass tube 3. Figure 2
Is a schematic sectional view showing the structure of the cold cathode 1.
It is made of a cylindrical porous sintered body having a through hole made of titanium and a refractory metal. The tungsten wire 2 is passed through the penetrating hole and caulked to join the tungsten wire 2. Further, FIG. 3 is a flowchart showing a method of manufacturing a cold cathode, and FIG. 4 shows a processing temperature profile in a sintering process. FIG. 5 and FIG. 6 are schematic diagrams showing an example of a method for electrically heating in vacuum. FIG. 7 is a schematic diagram showing a heating method in vacuum as a comparative example of the present invention.

In the cold cathode of the present invention, first, for example, a powder of titanium or titanium hydride and a powder of refractory metal are mixed to prepare a mixed powder.

Thereafter, this mixed powder is mixed with a binder made of an organic polymer compound and an organic solvent by using a stirrer,
Then, for example, by spray compounding into a compound (granule), the fluidity is improved and the mold is smoothly filled. Then, after filling the mold, a constant pressure is applied to form a molded body, which is then sintered in a vacuum furnace. At this time, as shown in FIG. 4, the sintering step consists of two steps of a binder removal step and a step of melting the powders and bonding the powders together, but titanium hydride was used as the raw material powder. In this case, it is preferable to introduce a heat treatment step at a temperature of 400 ° C. to 600 ° C. for about 1 to 2 hours as a dehydrogenation step between the debinding step and the step of binding the powder to the powder. Thus, a cold cathode, which is a porous sintered body containing titanium and a refractory metal, is produced.

After that, as shown in FIG. 5 or 6, the cold cathode was installed in a heating device provided in the vacuum vessel, and the cold cathode was instantly heated by passing an electric current. The present inventor has confirmed that the vacuum degree at this time is preferably 5 × 10 ⁻⁵ or less. In addition, the temperature and time during heating are approximately 120
It is preferable to hold the temperature at 0 to 1500 ° C. for about 5 to 20 seconds, and it is desirable that the temperature rising rate up to the heating temperature is as fast as possible, and preferably the heating temperature is reached within 1 minute.
Regarding cooling, it is desirable to lower the temperature to room temperature within a few minutes. In fact, since the heat capacity of the cold cathode itself is small, it is possible to naturally cool after stopping the electric heating. If the temperature is higher than 1500 ° C., the titanium and refractory metal that compose the cold cathode will be heavily consumed.
If the temperature is lower than ℃, the effect becomes small. The holding time is the same as the temperature. Titanium and the non-oxidized refractory metal constituting the cold cathode are consumed more than 20 seconds, and oxide removal by evaporation is not sufficient at less than 5 seconds. It has been confirmed that the effect of is reduced. The reason for increasing the rate of temperature increase and the rate of cooling is that as the temperature increases, titanium and the unmelted refractory metal that constitute the cold cathode also evaporate to a small extent and are consumed during the period.

The cold cathode obtained as described above is inserted into an introduction wire such as a tungsten wire 2, a Kovar wire or a Dumet wire and joined by caulking, and then the cold cathode is impregnated with an electron emitting substance. The cold cathode discharge tube is completed by sealing the end of the glass tube and filling a rare gas such as mercury or xenon gas in the glass tube.

[0022]

EXAMPLES Specific examples of the present invention will be described below with reference to FIGS. (Example 1) First, as shown in the flow chart of the manufacturing method of FIG. 3, raw material powders of titanium and niobium were weighed so that the weight ratio was titanium: niobium = 80: 20,
Mixed. The average particle size of titanium and niobium is 20μ each
It was m. This raw material powder was put into 1000 g of acetone in which 20 g of a binder BL-S (manufactured by Sekisui Chemical Co., Ltd.) made of an organic polymer compound was dissolved, and mixed using a stirrer to prepare a slurry. Then, using this slurry, a compound (granule) having a particle size of about 50 μm was prepared by a spray dryer method. Subsequently, this compound was filled in a mold, press-worked by applying a pressure of 5 ton / cm ² , and a cylindrical outer diameter of 1.05 m having a through hole.
m, an inner diameter of 0.504 mm, and a length of 1.07 mm were produced.

Then, the above-mentioned compact was placed in a vacuum furnace and sintered in a temperature rising pattern as shown in FIG. At this time,
11 is a step for debinding, and 12 is a sintering step for melting particles of titanium and niobium to produce a porous sintered body. The degree of vacuum was 2 × 10 ⁻⁵ Torr in all the steps, the temperature of the step 11 was 500 ° C., the holding time was 2 hours, and the temperature of the step 12 was 120.
The temperature was 0 ° C. and the holding time was 2 hours. In this way, as shown in FIG. 2, the cold cathode 1 which is a cylindrical porous body having a through hole made of titanium and niobium having an outer diameter of 1 mm, an inner diameter of 0.5 mm and a length of 1 mm was produced. .

Here, the porosity of the cold cathode 1 is controlled by the pressure during pressing, the temperature during sintering, and the time.
The porosity is preferably 20 to 30%. The reason is that when the porosity exceeds 30%, the mechanical strength decreases, and further, the electron emitting substance impregnated in the cold cathode 1 evaporates excessively and disappears quickly, so that the life as a cold cathode is short. On the contrary, when the porosity is less than 20%, the electron emitting substance cannot be impregnated from the outside, and the supply of the electron emitting substance to the surface of the cold cathode during operation is hindered, so that the electron emission characteristic is deteriorated. Because it does. The porosity of the cold cathode of this example is 24%.
Met. Further, in the present embodiment, the cold cathode 1 has a cylindrical shape, but the shape is not limited to this, and the size is not limited to this.

Next, as shown in FIG. 5, the cold cathode 1, which is a sintered body made of titanium and niobium, is placed on a heating tray 23 which also serves as a heater provided in a vacuum container, and an electric current is passed through the tray. Then, the cold cathode 1 was instantly heated. Specifically, the cold cathode 1 is placed on the heating tray 23 made of tungsten.
Were arranged and heated by passing an electric current through the heating tray 23. Therefore, since both the heating tray 23 and the cold cathode 1 have conductivity, a current also flows through the cold cathode 1. Although not shown in the figure, the temperature control was adjusted while monitoring the temperature with a thermocouple. The heating temperature was 1500 ° C., the temperature rising time up to 1500 ° C. was 40 seconds, the holding time was 10 seconds, then the current was cut off, and the temperature was naturally cooled within 5 minutes to room temperature.

(Example 2) As in Example 1, the weight ratio of the raw material powders of titanium and niobium was titanium: niobium =.
The weight was adjusted to 80:20, and a compound (granule) having a particle size of about 50 μm was prepared by a spray dryer method. Subsequently, this compound was filled in a mold, press-worked, then placed in a vacuum furnace and sintered to obtain titanium having an outer diameter of 1 mm, an inner diameter of 0.5 mm and a length of 1 mm as shown in FIG. A cold cathode 1 made of niobium, which is a cylindrical porous body having a through hole, was produced.

Thereafter, as shown in FIG. 6, a heating wire 24 made of tungsten and also having a diameter of 3 mm and having a diameter of 3 mm penetrates the cylindrical cold cathode 1 which is a sintered body made of titanium and niobium. The heating wire 24 was placed on a heating electrode provided in a vacuum container, and an electric current was passed through the heating wire 24 to instantaneously heat the cold cathode 1. Therefore, since the heating wire 24 and the cold cathode 1 both have conductivity, a current also flows through the cold cathode 1. Although not shown in the figure, the temperature control was adjusted while monitoring the temperature with a thermocouple. The heating temperature is 1500 ° C, and the heating time up to 1500 ° C is 40
Second, holding time was 10 seconds, and then the current was cut off, and the mixture was naturally cooled to room temperature within 5 minutes.

(Comparative Example 1) As in Example 1, the weight ratio of the raw material powders of titanium and niobium was titanium: niobium =.
The weight was adjusted to 80:20, and a compound (granule) having a particle size of about 50 μm was prepared by a spray dryer method. Subsequently, this compound was filled in a mold, press-worked, then placed in a vacuum furnace and sintered to obtain titanium having an outer diameter of 1 mm, an inner diameter of 0.5 mm and a length of 1 mm as shown in FIG. A cold cathode 1 made of niobium, which is a cylindrical porous body having a through hole, was produced.

(Comparative Example 2) As in Example 1, the weight ratio of the raw material powders of titanium and niobium was titanium: niobium =.
The weight was adjusted to 80:20, and a compound (granule) having a particle size of about 50 μm was prepared by a spray dryer method. Subsequently, this compound was filled in a mold, press-worked, then placed in a vacuum furnace and sintered to obtain titanium having an outer diameter of 1 mm, an inner diameter of 0.5 mm and a length of 1 mm as shown in FIG. A cold cathode 1 made of niobium, which is a cylindrical porous body having a through hole, was produced.

Next, as shown in FIG. 7, the cold cathode 1 is installed on a heating tray 33 provided in a vacuum container, and an electric current is supplied to a tungsten heater 34 placed below the heating tray, not by electric heating. By flowing, the cold cathode 1 was indirectly heated by the radiant heat of the tungsten heater 34. Although not shown in the figure, the temperature control was adjusted while monitoring the temperature with a thermocouple. The heating temperature was 1500 ° C., the temperature rising time to 1500 ° C. was 40 seconds, the holding time was 10 seconds, and then the current was cut off, and the temperature was naturally cooled within 5 minutes to room temperature.

The cold cathodes 1 of Examples 1 and 2 and Comparative Examples 1 and 2 obtained as described above have a diameter of 0.
A 45 mm tungsten wire was inserted and joined by caulking. After that, the cold cathode 1 is impregnated with an electron emitting material, then sealed at the end of a glass tube, and a xenon gas is sealed in the glass tube to produce a cold cathode discharge tube. A life test was carried out in which the starting voltage was measured after each light was emitted for 3000 times. The results are summarized in Table 1.

[0032]

[Table 1]

As can be seen from Table 1, in the cold cathode discharge tubes equipped with the cold cathode 1 obtained in the examples, the starting voltage is stable even after the life test, as is clear from comparison with the comparative example. Although not shown here, it was confirmed that excellent characteristics were exhibited in other evaluation items such as color temperature and brightness which are light emission characteristics. On the other hand, in the cold cathode discharge tube equipped with the cold cathode 1 of the comparative example, the starting voltage after the life test was significantly increased. Further, after the life test, a large amount of blackish brown powder, which is considered to be formed by sputtering of the oxide of the refractory metal, was attached around the cold cathode portion of the cold cathode discharge tube of the comparative example. No such phenomenon was observed in the cold cathode discharge tubes of the examples. Further, in this example, titanium was used as the raw material powder, but similar results were obtained even if titanium hydride powder was used. In addition, in this embodiment, niobium was used as the refractory metal, but similar effects were obtained with other refractory metals such as tungsten, molybdenum, and tantalum.

[0034]

As described above, according to the method for producing a cold cathode of the present invention, after the cold cathode made of titanium and the refractory metal is produced, it is electrically heated in vacuum before being impregnated with the electron emitting substance. As a result, the refractory metal oxide generated during the sintering process in vacuum is removed, and as a result, the sputtering phenomenon of the refractory metal oxide and the consequent consumption of the electron emitting material are suppressed. I understood. As a result, it has become possible to provide a cold cathode having a stable starting voltage and a long emission life and stable emission behavior, and thus a cold cathode discharge tube having such a cold cathode.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a structure of a cold cathode discharge tube having a cold cathode.

FIG. 2 is a schematic sectional view showing the structure of a cold cathode.

FIG. 3 is a flowchart showing a method of manufacturing a cold cathode.

FIG. 4 is a processing temperature profile in a sintering step in the cold cathode manufacturing method.

FIG. 5 is a schematic diagram showing a method of electrically heating in vacuum in the method of manufacturing a cold cathode of the present invention.

FIG. 6 is a schematic diagram showing a method of electrically heating in vacuum in the method for manufacturing a cold cathode of the present invention.

FIG. 7 is a schematic diagram showing a method of heating in vacuum as a comparative example in the method of manufacturing a cold cathode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cold cathode 2 Tungsten wire 3 Glass tube 4 Glass for sealing 11 Debinding process 12 Process which melt | dissolves between powders and couple | bonds powder with powder 21 Vacuum container 22 Exhaust port 23 33 Heating tray 24 Heating wire 34 Tungsten heater

Claims (4)

[Claims] 1. A method of manufacturing a cold cathode in a cold cathode discharge tube comprising a cold cathode at the tip of a lead-in wire sealed at the end of a glass tube filled with gas. A method for producing a cold cathode, comprising: a step of heating a contained sintered body while applying electricity directly; and a step of impregnating the heated sintered body with an electron emitting substance. 2. The heating temperature in the heating step is 120.
The method for producing a cold cathode according to claim 1, wherein the temperature is in the range of 0 ° C to 1500 ° C. 3. The method of manufacturing a cold cathode according to claim 1, wherein the sintered body contains titanium. 4. The method of manufacturing a cold cathode according to claim 1, wherein the refractory metal is niobium, tungsten, molybdenum or tantalum.