JP2003197146A - Cold-cathode discharge tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold-cathode discharge tube having a long service life and a stable light emitting operation even if discharge is repeated in a short period like an electric flash or the discharge tube is lit over a long time like a backlight source for a liquid-crystal display. <P>SOLUTION: This cold-cathode discharge tube is equipped with a cold cathode at a tip part of an introduction wire sealed at an end of a glass tube filled with a rare gas or mercury. The discharge tube is characterized by having an adsorbent for adsorbing oxygen and hydrogen in the glass tube and preferably in the vicinity of the cold cathode. In the cold-cathode discharge tube, the adsorbent for adsorbing oxygen and hydrogen preferably has titanium and a high-melting point metal. <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 discharge tube having a cold cathode, and more particularly to a structure of a cold cathode discharge tube having a long life and 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 is required to have performance such as low heat generation, low power consumption, high brightness, high efficiency, long life, and miniaturization. Especially for backlights of recent liquid crystal displays, the outer diameter is 2 mm.
Hereafter, a thin tube type tube having a length of 50 mm or less has been developed, and it is considered that the downsizing of the cold cathode discharge tube will be further advanced in the future as the size and weight of information devices such as mobile phones and PDAs are reduced. Along with this, the cold cathode sealed at the end portion of the cold cathode discharge tube is also required to be small in size and have high performance, 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.

Normally, 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 generated initial plasma, and the secondary electrons are sealed in advance in the glass tube. The discharge is started by colliding with excited rare gas such as mercury or argon and exciting it. Then, the excited mercury atoms or rare gas atoms emit ultraviolet rays, and the ultraviolet rays are converted into visible light by the phosphor layer coated on the inner surface of the glass tube to generate visible light and emit light.

As the cold cathode, a porous body made of a refractory metal such as nickel or tungsten having a cylindrical shape has been studied and used at present, but from the viewpoint of improving luminous efficiency,
Recently, attention has been focused on a porous cold cathode made of titanium and a refractory 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,
The leading end of the lead-in wire is joined to the lead-in wire by caulking with the tip exposed. 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 argon gas is sealed in the glass tube to form a cold cathode discharge tube. The electron emitting substance is mainly a cesium compound, a barium compound, a yttrium compound, a lanthanum compound, or the like.

For example, in order to produce a cold cathode of a porous body composed of titanium and a refractory metal, titanium powder and powder of a refractory metal are mixed, filled in a mold and pressure-molded. Then, a means of sintering in vacuum is common.

[0007]

However, for example, a small-sized conductive porous 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 cold cathode discharge is performed by the method described above. When a tube was produced and light was actually emitted, the following problems occurred. That is,
A porous body made of titanium and a refractory metal has a high temperature in the entire cold cathode when a discharge is repeatedly performed in a short time like a strobe or when it is turned on for a long time like a backlight source of a liquid crystal display. As a result, a slight amount of hydrogen or oxygen gas is generated from the cold cathode or the glass tube. This cannot be solved by the current technology, and when such gas is generated, the starting voltage, which is a parameter that affects the light emission operation, rises, and the time for maintaining low power consumption is shortened, and finally the light emission occurs. There is a problem that the life is shortened. The reason is that oxygen oxidizes the surface of the cold cathode and raises its work function, and hydrogen is ionized in the discharge space and traps electrons in the space. This phenomenon was more remarkable as the size became smaller. Therefore, it is difficult to provide a cold cathode discharge tube having a long life and a stable light emitting operation.

On the other hand, the cold cathode made of titanium and a refractory metal has a getter (adsorption) effect of adsorbing the hydrogen or oxygen gas generated as described above due to the nature of the material. However, the main role of the cold cathode is to store an electron emitting substance and emit an electron when a voltage is applied, and the surface of the pores in the porous body forming the cold cathode is almost occupied by the electron emitting substance. Therefore, it was difficult to sufficiently exert the getter effect. In addition, in order to expose the surface of the pores in the porous body in order to obtain the getter effect, the impregnated amount of the electron emitting substance must be reduced, and as a result, the life of the cold cathode discharge tube is reduced. There was a problem that it became extremely short.

The present invention has been made in view of the above problems, and an object thereof is to provide a cold cathode discharge tube having a long life and a stable light emitting operation.

[0010]

In order to achieve the above object, the cold cathode discharge tube of the present invention adopts the structure described below. That is, the cold cathode discharge tube of the present invention is a cold cathode discharge tube having a cold cathode at the tip of the introduction line sealed at the end of a glass tube in which a rare gas or mercury is sealed, and oxygen and hydrogen The adsorbent to be adsorbed is inside the glass tube, and more preferably in the vicinity of the cold cathode.

Further, in the cold cathode discharge tube of the present invention, the adsorbent for adsorbing oxygen and hydrogen preferably has titanium and a refractory metal.

(Operation) As a result of earnest studies on the cold cathode discharge tube, the present inventor installed an adsorbent for adsorbing oxygen and hydrogen in the glass tube to obtain the electron emission function of the cold cathode and the cold cathode. While maintaining the practical life as a discharge tube, it has become possible to fully exhibit the getter effect of adsorbing hydrogen and oxygen gas generated during discharge. At this time, the adsorbent installed in the glass tube is preferably installed in the vicinity of the cold cathode, and the size of the adsorbent is the same length as the cold cathode so as not to reduce the luminous efficiency of the cold cathode discharge tube. Is preferred.

Further, the adsorbent that adsorbs oxygen and hydrogen preferably contains titanium and a refractory metal. This is because titanium has an effect of mainly adsorbing oxygen gas generated from the cold cathode and the glass tube, and refractory metal has an effect of adsorbing hydrogen gas in addition to oxygen gas. The high melting point metal generally means a metal having a melting point of 2000 ° C. or higher, and specifically niobium, tungsten, molybdenum, zirconium or tantalum. By adopting such a configuration, it is possible to provide a cold cathode discharge tube that suppresses an increase in starting voltage, has a long life, and has a stable light emitting operation.

[0014]

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 the cold cathode discharge tube of the present invention. The cold cathode 1 is installed at the tip of a tungsten wire 3 that is an introduction wire sealed at the end of a thin tubular glass tube 4, and an adsorbent 2 that adsorbs oxygen and hydrogen is installed near the cold cathode 1. Has been done. The length of the glass tube is, for example, 40 mm, the outer diameter is 2 mm, and the inner diameter is 1.6 mm. The glass tube 4 is filled with a rare gas such as mercury or argon gas. Reference numeral 5 in FIG. 1 is a glass for sealing, and the material thereof is the same as that of the glass tube 4. 2 to 4 are schematic sectional views showing an example of the structure in the vicinity of the cold cathode 1 bonded to the tungsten wire 3 of the present invention.

The cold cathode 1 and the adsorbent 2 are both porous bodies made of titanium and a refractory metal, and the cold cathode 1 has a through hole for joining to the tungsten wire 3. Insert the tungsten wire 3 into this hole,
It is joined to the tungsten wire 3 by caulking. The adsorbent 2 is installed in the vicinity of the cold cathode 1 as shown in FIGS.

FIG. 5 is a flow chart showing a method of manufacturing a cold cathode discharge tube, showing the steps from the manufacturing process of the cold cathode 1 and the adsorbent 2 to the subsequent manufacturing of the cold cathode discharge tube. FIG. 6 is a temperature rising pattern in the process of sintering the molded body of the cold cathode 1 and the adsorbent 2. FIG. 7 is a schematic sectional view showing an example of a structure in the vicinity of the cold cathode which does not include the adsorbent 2 used in the comparative example.

In the cold cathode 1 of the present invention, for example, powder of titanium or titanium hydride and powder of refractory metal are mixed to prepare a mixed powder, and the mixed powder is used as a binder made of an organic polymer compound. The organic solvent is mixed using a stirrer, and then compounded (granulate) by, for example, a spray dryer method. As a result, the fluidity is improved and the mold is smoothly filled.

After the compound is filled in a 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. 6, the sintering step includes two steps of a binder removal step 11 and a sintering step 12 of melting the powders and bonding the powders to each other. When using as raw material powder, debinding process 1
As a dehydrogenation step, it is preferable to introduce a heat treatment step at a temperature of 400 ° C. to 600 ° C. for about 1 to 2 hours between 1 and the step 12 of binding the powder to the powder. In this way, the organic polymer compound is removed and sintered to form a porous body composed of titanium and a refractory metal.

The porosity of the cold cathode 1 is preferably smaller than that of the adsorbent 2. Specifically, it is desirable that the porosity of the cold cathode 1 is in the range of 15 to 30% and the porosity of the adsorbent 2 is 28% or more. This is because the cold cathode 1 has a reduced mechanical strength when the porosity exceeds 30%,
Further, it is because the electron emitting substance impregnated in the cold cathode is excessively evaporated and disappears quickly, and the life as a cold cathode is shortened. This is because impregnation becomes impossible, and further, 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. Further, the lower limit value of 28% of the porosity of the adsorbent 2 is the volume of the discharge space of the cold cathode discharge tube which is the object of the present invention, the volume of the cold cathode, and the expected amount of released gas, It is a value obtained by inferring it from the surface area of the cold cathode required for gettering (adsorbing) it. If the porosity is not 28% or more, the surface area required for gettering oxygen or hydrogen can be secured. It will be difficult.

The position of the adsorbent 2 is not particularly limited, but it is preferable that the adsorbent 2 be installed adjacent to or around the cold cathode 1. Specifically, the cold cathode may be superposed along the introduction line, or the adsorbent 2 may be installed so as to surround the cold cathode. Alternatively, the adsorbent 2 and the cold cathode 1 may be separated, and the adsorbent 2 may be installed near the glass tube.

The adsorbent 2 is also manufactured by the same method as the cold cathode 1. However, in order to control the porosity to be 28% or more, the temperature of the step 12 of melting the powders in the sintering step in a vacuum and binding the powders together causes the cold cathode 1 to be sintered. Usually lower than process temperature. afterwards,
According to the flowchart showing the manufacturing process of FIG. 5, the cold cathode 1 obtained as described above is impregnated with an electron emitting substance, and then the cold cathode 1 and the adsorbent 2 are placed at predetermined positions, respectively, and thereafter, in a glass tube. The cold cathode discharge tube of the present invention is completed by filling in with a rare gas such as mercury or argon gas.

[0023]

EXAMPLES Specific examples of the present invention will be described below with reference to FIGS. (Example 1) First, the raw material powders of titanium and niobium were mixed at a weight ratio of titanium: niobium = 80: 20 and a total weight of 200.
Weighed to 0 g and mixed. At this time, the average particle diameters of titanium and niobium were each 20 μm. This raw material powder is used as a binder BL-S made of an organic polymer compound.
20 g (manufactured by Sekisui Chemical Co., Ltd.) was put into 1000 g of dissolved acetone, 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 and subjected to a press work by applying a pressure of 5 ton / cm ² to produce a cylindrical molded body. Its dimensions were an outer diameter of 1.05 mm, an inner diameter of 0.504 mm, and a length of 1.07 mm.

Then, the above-mentioned compact was put into 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, the outer diameter 1
A cold cathode 1, which is a cylindrical porous body having a through hole, made of titanium and niobium, having a diameter of 0.5 mm, an inner diameter of 0.5 mm, and a length of 1 mm was produced. The porosity of the cold cathode 1 obtained through the above steps was 18%.

The adsorbent 2 was also manufactured by the same method as the cold cathode 1. That is, after producing a compound (granule) having the same composition as that of the cold cathode 1, the compound was filled in a mold and subjected to a press work by applying a pressure of 5 ton / cm ² to produce a cylindrical molded body. Its dimensions were an outer diameter of 1.05 mm, an inner diameter of 0.504 mm, and a length of 0.58 mm. afterwards,
The above molded body was placed in a vacuum furnace and sintered in a temperature rising pattern as shown in FIG. The vacuum degree at this time is 2 × 10 ⁻⁵ To
rr, the temperature of the step 11 was 500 ° C. and the holding time was 2 hours, and the temperature of the step 12 was 1000 ° C. and the holding time was 2 hours. In this way, an adsorbent 2 made of titanium and niobium having an outer diameter of 1 mm, an inner diameter of 0.5 mm and a length of 0.5 mm having a through hole as shown in FIG. 2 was produced. The porosity of the adsorbent 2 obtained through the above steps was 32%. After that, the cold cathode 1 obtained as described above was impregnated with an electron emitting substance according to the method for producing a cold cathode discharge tube shown in FIG. After that, as shown in FIG. 2, the cold cathode 1 and the adsorbent 2 have an outer diameter of 0.45 in each of the through holes.
mm tungsten wire 3 is inserted and joined by caulking, then sealed at the end of the glass tube, and a rare gas such as mercury or argon gas is sealed in the glass tube to obtain the cold cathode discharge of the present invention. A tube was made.

(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, and titanium and niobium having an outer diameter of 0.8 mm, an inner diameter of 0.5 mm, and a length of 1.0 mm were used. Then, the cold cathode 1 which is a cylindrical porous body having a through hole was prepared. The porosity of the cold cathode 1 obtained through the above steps was 18%.

The adsorbent 2 was also manufactured in the same manner as the cold cathode 1. That is, after producing a compound (granule) having the same composition as that of the cold cathode 1, the compound was filled in a mold and subjected to a press work by applying a pressure of 5 ton / cm ² to produce a cylindrical molded body. Then, the above-mentioned molded body was put into a vacuum furnace and sintered in a temperature rising pattern as shown in FIG. At this time, the degree of vacuum is 2 × 10 ⁻⁵ Torr, the temperature is 500 ° C. for the step 11 and the holding time is 2 hours, and the temperature is 10 for the step 12
The temperature was 00 ° C. and the holding time was 2 hours. In this way, FIG.
An adsorbent 2 made of titanium and niobium having an outer diameter of 1.2 mm, an inner diameter of 0.8 mm, and a length of 1.0 mm having a through hole as shown in FIG. The porosity of the adsorbent 2 obtained through the above steps was 32%. Then, the cold cathode 1 obtained as described above was impregnated with an electron emitting substance according to the method for producing a cold cathode discharge tube shown in FIG. The cold cathode 1 was press-fitted and integrated. After that, the outside diameter is 0.45 mm in the through hole of the cold cathode 1.
After the tungsten wire 3 is inserted and joined by caulking from the outer peripheral portion of the adsorbent 2, the adsorbent 2 is sealed at the end portion of the glass tube, and a rare gas such as mercury or argon gas is sealed in the glass tube, thereby The cold cathode discharge tube of the invention was produced.

(Embodiment 3) As in Embodiment 1, the weight ratio of the raw material powders of titanium and niobium is 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, and titanium and niobium having an outer diameter of 0.8 mm, an inner diameter of 0.5 mm, and a length of 1.0 mm were used. Then, the cold cathode 1 which is a cylindrical porous body having a through hole was prepared. The porosity of the cold cathode 1 obtained through the above steps was 18%.

The adsorbent 2 was also manufactured in the same manner as the cold cathode 1. That is, after producing a compound (granule) having the same composition as that of the cold cathode 1, the compound was filled in a mold and subjected to a press work by applying a pressure of 5 ton / cm ² to produce a cylindrical molded body. Then, the above-mentioned molded body was put into a vacuum furnace and sintered in a temperature rising pattern as shown in FIG. At this time, the degree of vacuum is 2 × 10 ⁻⁵ Torr, the temperature is 500 ° C. for the step 11 and the holding time is 2 hours, and the temperature is 10 for the step 12
The temperature was 00 ° C. and the holding time was 2 hours. In this way, the second conductive adsorbent 2 having an outer diameter of 1.6 mm, an inner diameter of 1.2 mm, and a length of 1.0 mm and made of titanium and niobium having through holes was produced. The porosity of the adsorbent 2 obtained through the above steps was 32%. Then, according to the method for manufacturing the cold cathode discharge tube shown in FIG. 5, the adsorbent 2 was inserted into the inner diameter portion of the glass tube 4 and fixed as shown in FIG. After that, the cold cathode 1 is impregnated with an electron emitting substance, and then a tungsten wire 3 having an outer diameter of 0.45 mm is inserted into a hole through which the cold cathode 1 penetrates, caulked and joined, and then sealed at an end of a glass tube. A cold cathode discharge tube of the present invention was manufactured by filling a rare gas such as mercury or argon gas in a glass tube.

(Comparative Example) As in Example 1, the weight ratio of the raw material powders of titanium and niobium was titanium: niobium = 8.
It was weighed to be 0:20, 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, pressed, then placed in a vacuum furnace and sintered, and the porosity was 18%, the outer diameter was 1.0 mm, the inner diameter was 0.5 mm, and the length was 1. 0
A cold cathode 1 which is a cylindrical porous body having a through hole and made of titanium and niobium having a size of mm was produced. After that, the tungsten wire 3 was inserted into the through hole of the cold cathode 1 and caulked and joined, and then the cold cathode 1 was impregnated with an electron emitting substance. Then, the end of the glass tube was sealed, and a rare gas such as mercury or argon gas was sealed in the glass tube to manufacture a cold cathode discharge tube of Comparative Example 1 as shown in FIG.

With respect to the cold cathode discharge tubes of Examples 1 to 3 obtained as described above and the comparative example which is the configuration of the conventional cold cathode discharge tube, the starting voltage and the light amount (GNo.
(Represented by (G number), pass 8.0 or more), and then perform a life test in which the lamp is lit continuously for 6000 hours, and measure the starting voltage and light quantity that are the standard of stability of discharge characteristics before and after the test. went. The results are summarized in Table 1. In addition, the test was conducted for each 10 pieces.

[0032]

[Table 1]

As can be seen from Table 1, in the cold cathode discharge tubes obtained in this example, as is clear from comparison with the comparative example, the starting voltage and the light amount showing the stability of the discharge characteristics are almost at the initial stage. It has been confirmed that it has not changed. This is because the adsorbent 2 that adsorbs oxygen and hydrogen gas is installed in the vicinity of the cold cathode, so that hydrogen and oxygen generated during discharge can be obtained while ensuring the electron emission function and the practical life of the cold cathode discharge tube. It is considered that the getter effect of adsorbing the gas worked effectively. On the other hand, in the cold cathode discharge tube of the comparative example, the starting voltage after the test is remarkably increased, the light amount is also decreased,
It has reached a level where it cannot be used in practice. As described above, according to the present invention, it is possible to provide a cold cathode discharge tube that suppresses an increase in starting voltage, has a long life, and has a stable light emitting operation.

In this embodiment, the arrangement of the cold cathode 1 and the adsorbent 2 is
Although three examples of the configuration are shown, the present invention is not limited to this, and other arrangements and configurations may be adopted. 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 this embodiment, titanium and niobium are described as examples of the cold cathode 1 and the adsorbent 2, but the cold cathode 1 and the adsorbent 2 do not have to have the same material and composition ratio, and the refractory metal is niobium. The same effect was obtained not only with tungsten, molybdenum, zirconium or tantalum. Further, the adsorbent 2 of this example was a porous body composed of a mixed powder of titanium and a refractory metal, but the adsorbent 2 was a combination of a titanium porous body and a refractory metal porous body. May be

[0035]

As described above, in the cold cathode discharge tube of the present invention, oxygen and hydrogen gas are provided in the vicinity of the cold cathode made of titanium and refractory metal, that is, the cold cathode body impregnated with the electron emitting material. A getter that captures hydrogen and oxygen gas generated during discharge while maintaining the practical life as a cold cathode discharge tube by installing an adsorbent that absorbs and separating the getter function from the electron emission function As a result, it is possible to provide the effect of the cold cathode discharge tube, which suppresses the rise of the starting voltage, has a long life, and has a stable light emitting operation.

[Brief description of drawings]

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

FIG. 2 is a schematic sectional view showing the arrangement and configuration of a cold cathode and an adsorbent in the cold cathode discharge tube of the present invention.

FIG. 3 is a schematic cross-sectional view showing the arrangement and configuration of a cold cathode and an adsorbent in the cold cathode discharge tube of the present invention.

FIG. 4 is a schematic sectional view showing the arrangement and configuration of a cold cathode and an adsorbent in the cold cathode discharge tube of the present invention.

FIG. 5 is a flowchart showing a method of manufacturing a cold cathode discharge tube.

FIG. 6 is a processing temperature profile in a sintering step in the cold cathode manufacturing method.

FIG. 7 is a schematic sectional view showing a configuration of a cold cathode of a comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cold cathode 2 Adsorbent 3 Tungsten wire 4 Glass tube 5 Glass for sealing 11 Debinding process 12 Process of melting powders and binding powders

Claims (3)

[Claims] 1. A cold cathode discharge tube having a cold cathode at the tip of an introduction line sealed at the end of a glass tube enclosing gas, the adsorption having an action of adsorbing oxygen and hydrogen in the glass tube. Cold cathode discharge tube with a body. 2. The cold cathode discharge tube according to claim 1, wherein the adsorbent is adjacent to the cold cathode. 3. The cold cathode discharge tube according to claim 1, wherein the adsorbent contains titanium and a refractory metal.