JP2002175776A - Electrode for cold cathode discharge tube and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sputtering resistivity of an electrode for a cold cathode discharge tube. SOLUTION: By forming a discharging part 19 of the electrode for a cold cathode discharge tube with a metal selected from tungsten, niobium, titanium, tungsten alloy, niobium alloy, and titanium alloy, wherein little sputtering is caused, it is possible to obtain a long-life electrode enabling reduction of wear of the discharging part 19 caused while the cold cathode discharge tube is lighted and to form the discharging part 19 with a length shorter than conventional ones.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode, particularly an electrode for a cold-cathode discharge tube having sputtering resistance and a method for producing the same.

[0002]

2. Description of the Related Art A cold-cathode discharge tube in which a pair of electrodes are opposed to each other inside a glass tube filled with a rare gas and mercury vapor and a fluorescent film is coated on the inner wall of the glass tube has been conventionally used in a liquid crystal display. Widely used as a light source for backlights. One end of an introduction wire is connected to a pair of electrodes of the cold cathode discharge tube, and the other end of the introduction wire is led out from both ends of the glass tube. When a voltage is applied between the pair of electrodes, electrons are emitted from one of the electrodes, and the electrons collide with mercury atoms in the glass tube to generate ultraviolet rays. This ultraviolet light is wavelength-converted to visible light by a fluorescent film formed on the inner wall of the glass tube.

Japanese Unexamined Patent Publication No. Sho 60-100354 discloses a method of processing a tungsten electrode in which a tungsten rod is used as an electrode in an inert atmosphere containing nitrogen to make a discharge-side tip of the electrode spherical. . In this machining method, even when a current of 7.5 A per mm ^{2 of} tungsten electrode is applied to perform electric discharge machining, an electrode having a spherical tip on the discharge side can be easily obtained.

Japanese Patent Application Laid-Open No. 4-48546 discloses that a rod-shaped body made of tungsten or a tungsten alloy is simultaneously irradiated with laser beams from a plurality of directions having different irradiation angles, and a spherical discharge portion having a larger diameter than the main portion is provided at the tip. 1 shows an electrode for a discharge lamp in which is formed. The tip portion of the tungsten or tungsten alloy rod is instantaneously melted at a high temperature upon irradiation with the laser and is formed into a spherical shape by surface tension. Since the energy from the laser is dispersed in the laser-irradiated portion of the rod-shaped body by laser irradiation from a plurality of directions having different irradiation angles from each other, the thickness of the amorphous layer formed on the surface of the spherical portion is reduced. This has the effect of making the whole uniform and increasing the roundness of the spherical portion.

A conventional cold cathode discharge tube (40) shown in FIG. 6 comprises a glass tube (7) having a discharge gas filled therein, and a glass tube (7).
It is fixed to both ends of (7) and is covered with the electrode assembly (20) and the inner surface (7a) of the glass tube (7). A fluorescent film (9) for emitting light. As shown in FIG. 7 (c), the electrode assembly (20) includes an introduction line (11) and a cup-shaped electrode (3) fixed to the introduction line (11). Is formed by fusing a first introduction line component (14) and a second introduction line component (15). The lead-in wire (11) of the electrode assembly (20) has a lead-out part (28), a buried part (29) formed in the glass tube (7),
A connecting part (16) for connecting the lead-out part (28) and the buried part (29) is provided, and the lead-out part (28) of the lead wire (11) is connected to the external lead (8) outside the glass tube (7). Connected.

When manufacturing a cold cathode discharge tube (40), first, as shown in FIG. 7 (a), an introduction wire (11), a glass bead (2) formed into a cylindrical shape, and a press A nickel electrode (3) that is easy to process is prepared. The lead-in wire (11) is a first lead-wire component (14) made of nickel having excellent solderability.
And a second lead wire component (15) made of tungsten excellent in glass fusing property, and the first and second lead wire components (14, 15) having substantially the same diameter are fused with each other. Be worn.
Next, as shown in FIG. 7 (b), the second guide line component (15) of the guide line (11) is inserted into the hole (2a) of the glass bead (2), and the protrusion (11a) is inserted into the glass bead (2). While projecting from the beads (2), the glass beads (2) are fused to the second introduction line component (15). The hole (2a) of the glass bead (2) has a smaller diameter than the joint (16) and a larger diameter than the second introduction line component (15), and the glass bead (2) is formed by the joint (16). Is set. Then, as shown in FIG.
An electrode assembly (20) is formed by welding the tip (11b) of the projection (11a) to the outer bottom surface (3a) of the electrode (3), and the electrode assembly is provided at both ends of the cylindrical glass tube (7). Place (20). After filling the glass tube (7) with a discharge gas containing a rare gas and mercury vapor, the glass beads (2) were fused to the glass tube (7), and as shown in FIG. 3) and the buried portion (29) are sealed in the glass tube (7), and the connecting portion (16) and the lead-out portion (28) are led out of the glass tube (7). Derivation unit (28)
After being cut to an appropriate length, the external leads (8) are soldered to form a cold cathode discharge tube (40) shown in FIG.

[0007] A conventional cold cathode discharge tube (40) has a cup-shaped electrode (cup electrode) (3) fixed to the end of an introduction wire (11) formed of a round bar. There is known a round bar-shaped electrode (round bar electrode). The round bar electrode has the advantage of being inexpensive to manufacture, but does not have the hollow effect unlike the cup electrode, thus reducing power consumption.
There is a problem in low heat generation and long life. On the other hand, in the cup electrode, low power consumption, low heat generation,
Although the service life can be extended relatively well, the manufacturing process is complicated and the production cost is high. The conventional cup electrode is formed by stretching a nickel round bar piece into a disk shape, forming the same into a cup shape by pressing, and welding the tip of a round shaft to the bottom of the cup portion. For this reason, the manufacturing process is complicated and the production cost is higher than the round bar electrode. Further, the cup portion formed relatively wider than the round bar portion hinders the narrowing of the discharge tube. Further, the cup electrode which does not become a light emitting region has a drawback that it becomes an obstacle to effectively extend the light emitting region in the longitudinal direction of the discharge tube.

[0008]

In the cold-cathode discharge tube (40), when the first and second lead wire constituting members (14, 15) are fused by resistance welding in a state where they are pressed against each other, FIG. As shown in a), a first and a second having substantially equal diameters
A bump of molten metal larger than the diameter is formed at the joint (16) between the introduction wire components (14, 15). The diameter is about 0.8m
In the case of the first and second introduction line components (14, 15) of m, the length (L) of the connecting portion (16) shown in FIG. 7A is about 0.6 mm. For this reason, when connecting the external lead (8) to the lead-out part (28), as shown in FIG. 7D, the external lead (8) is separated from the glass tube (7) and the connection part (16) instead of the connection part (16). External lead
(8) must be soldered, and the size of the cold cathode discharge tube (40) cannot be reduced. If the coupling portion (16) is large, the non-light-emitting region increases, and the luminous efficiency decreases.
(16) The non-light-emitting area can be reduced by soldering the external leads (8) to the bumps, but it is a fusion part of nickel and tungsten and has a curved and irregularly shaped joint.
(16) has poor solderability, and the external lead (8) is connected to the joint (16).
When an external force is applied even when the external lead (8) is adhered, the external lead (8) tends to come off. Therefore, sufficient connection strength between the external lead (8) and the lead-out section (28) cannot be obtained, which causes a connection failure.

In the cold-cathode discharge tube (40), ions of mercury or a discharge gas (inert gas) are turned on during discharge.
The sputtering action colliding with (3) occurs, and the electrode (3) and the mercury in the glass tube (7) are gradually worn. If the current density between the pair of electrodes (3) is small, the amount of sputtering of the electrodes (3) decreases.In this case, the desired life time can be maintained by setting the internal pressure of the discharge tube to be relatively low. , The required brightness cannot be secured. When the current density is increased to increase the brightness, the amount of sputtering of the electrode (3) increases, and the sputtered electrode metal reacts with mercury that emits ultraviolet rays to deteriorate the mercury. ) Has the drawback of shortening the service life. Therefore, it is necessary to increase the internal pressure of the glass tube (7) to suppress the amount of sputtering and maintain a desired life.

When p is the internal pressure, i is the current density, and A and B are constants, the current density generated between a pair of nickel electrodes and the glass tube when a minimum life of 10,000 hours is given to the discharge tube. Satisfies a certain functional relationship represented by the following equation: p = Ai + B. Therefore, at least 1
In order to secure a life of 000 hours, it is necessary to operate at a current density and pressure corresponding to the upper region of the straight line represented by the above function: p ≧ Ai + B. In other words, when a conventional discharge tube having a nickel electrode is operated at a current density and pressure corresponding to a region below a solid line represented by the above function: p <Ai + B, a life of 10,000 hours is obtained. Can not secure.

Although it is necessary to reduce the dimensions of the electrodes as much as possible to reduce the non-light-emitting region of the discharge tube, the smaller the electrodes, the higher the current density. The pressure in the tube must be increased. When the pressure in the discharge tube is increased, the following problems occur. Various problems such as [1] an increase in the tube voltage, [2] an increase in the voltage at the start of lighting of the discharge tube, and [3] a decrease in luminance occur. Therefore, it has been desired to realize a discharge tube capable of downsizing electrodes without increasing the pressure in the discharge tube. Further, a desired life time must be obtained by maintaining a constant relationship between the internal pressure of the glass tube (7) and the current density between the electrodes (3).

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrode for a cold cathode discharge tube having a sputtering resistance and a method for producing the same. Another object of the present invention is to provide an electrode for a cold cathode discharge tube capable of increasing the effective light emitting area by making the discharge tube thinner, and a method for producing the same. Another object of the present invention is to provide an electrode for a cold cathode discharge tube having a good hollow effect, a reduced length and a reduced diameter, and a method for producing the same.

[0013]

According to the present invention, there is provided an electrode for a cold cathode discharge tube, comprising:
Since the discharge part (19) is formed of a metal selected from niobium, titanium, a tungsten alloy, a niobium alloy and a titanium alloy, the amount of wear of the discharge part (19) during lighting of the cold cathode discharge tube is small. Further, when the concave portion (10) is formed at the tip of the discharge portion (19), the area of the tip portion of the discharge portion (19) for emitting electrons can be increased to increase the light emission luminance, and the length is shorter than in the conventional case. Thus, the discharge part (19) can be formed. In the electrode for a cold cathode discharge tube according to the embodiment of the present invention, the concave portion (10)
Is formed with an inclined surface (10a) tapering inward toward the inside. The discharge part (19) is connected to the lead-out part (18) and has a uniform diameter over the entire length up to the joint part (16) with the lead-out part (18). If the lead-out part (18) is connected to the discharge part (19), the external lead (8) can be satisfactorily connected to the lead-out part (18).

According to the method of manufacturing an electrode for a cold cathode discharge tube according to the present invention, a shaft (60) formed of a metal selected from tungsten, niobium, titanium, a tungsten alloy, a niobium alloy or a titanium alloy is applied to a laser emitting portion. Coaxially arranging the assist gas and the assist gas at one end (6
While emitting toward (1), a laser beam is irradiated on one end (61) of the shaft body (60), and a recess (10) is formed on one end (61).
And forming a. In the present invention, a concave portion (10) having a tapered inclined surface (10a) inclined at the same angle (θ) as the converging angle of a converging lens for condensing a laser beam is provided on one side of a shaft body (60). Forming the end (61), irradiating the laser beam in parallel with the tapered inclined surface (10a) forming the recess (10), forming the other end (62) of the shaft body (60) Step of controlling the irradiation direction of the laser beam in the direction in which the central axis (50) of the laser beam passes through the plane (A) to be drawn, and the laser beam guides to the other end (62) of the shaft body (60) at the other end (62). 18) or the step of forming a recess (10) at one end (61) opposite to the other end (62) connected to the lead-out portion (18). It may be included in combination.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an electrode for a cold cathode discharge tube according to an embodiment of the present invention and a method for manufacturing the same will be described with reference to FIGS. In FIG. 1, the same portions as those shown in FIGS. 6 and 7 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1 shows a cold cathode discharge tube (3
The electrode (6) used in (0) is a conventional electrode assembly (10) in that a discharge portion (19) is formed by a sputtering resistant metal selected from tungsten, niobium, titanium, a tungsten alloy, a niobium alloy, and a titanium alloy. 20) is different.
For example, as shown in FIG.
Has a uniform diameter L ₁ = 0.8 mm, so that a cup-shaped electrode (3) provided in a conventional discharge tube having a width of about 10 mm
The width of the electrode (6) can be reduced as compared with the case of FIG. The discharge part (19) formed of a sputtering-resistant metal,
Since the amount of sputtering by the discharge gas (inert gas) such as mercury or argon or nitrogen generated during the operation of the cold-cathode discharge tube is small, the discharge part (19) has a small amount of wear and an electrode with a long life can be obtained. Can be Incidentally, the stampering ratio S is 0.37 for titanium, 0.35 for niobium, and 0.51 for tantalum, and is 0.71 for nickel. The sputtering rate S mentioned here is an amount defined by S≡N ₁ / N _S when atoms constituting the target of N _S are ejected from the target material where N ₁ high-speed particles collide. In the present invention, the concave portion (10) formed in a tapered shape whose diameter decreases inward at the tip of the discharge portion (19) increases the area of the tip portion of the discharge portion (19) that emits electrons to emit light. The brightness can be increased, and the concave portion (10) formed at the tip of the discharge portion (19) also serves as a conventional cup electrode. Therefore, the discharge portion (10) has a shorter length than the conventional electrode assembly (20). 19) can be formed.

In manufacturing the electrode for a cold cathode discharge tube according to the present invention, a shaft body (60) formed of a sputter-resistant metal selected from tungsten, niobium, titanium, a tungsten alloy, a niobium alloy or a titanium alloy is prepared. The shaft body (60) is arranged coaxially with respect to the laser emitting portion, and the center axis (50) of the laser beam is aligned with the center axis (51) of the shaft body (60) as shown in FIG. . In this state, while discharging the assist gas toward one end (61) of the shaft body (60), Q
A laser beam of a switch YAG laser or a CO ₂ laser is applied to one end (61) of the shaft body (60) to form a recess (10) at one end. In this case, the mechanical action of removing the melt by the flow of the assist gas such as oxygen, and the heating that generates heat when the tungsten is heated to 300 ° C. when oxidized to promote the melting or evaporation of the tungsten. The laser drilling speed can be improved by the synergistic action with the action. An inert gas such as argon or nitrogen may be supplied as an assist gas to cool the irradiated part of the laser beam, thereby avoiding excessive burning of the shaft body (60) during processing.

In the present invention, laser drilling can be performed by various methods. For example, a tapered concave portion (10) having the same angle (θ) as the converging angle of the converging lens that condenses the laser beam may be formed at one end (61) of the shaft body (60). it can. Alternatively, a laser beam may be irradiated in parallel with the inclined surface (10a) forming the tapered recess (10). The laser beam may be irradiated by moving the central axis (50) of the laser beam so as to draw a concentric circle with respect to the central axis (51) of the shaft body (60). In any case, the irradiation direction of the laser beam is set such that the center axis (50) of the laser beam passes through a plane (A) formed by the projection surface of the other end (62) of the shaft body (60). It is important to control. In the present embodiment, since the discharge portion (19) is made of tungsten having an excellent fusion property with glass, cylindrical glass beads can be fused well.

FIG. 4 shows an annular shaft body (60a) having a through hole (60c) formed by laser drilling and a solid cylindrical shaft body (60b).
And a structure in which are joined at a joint (63). Annular shaft (60
The connection between a) and the solid cylindrical shaft body (60b) can be performed by various methods such as resistance welding or laser welding.

As shown in FIG. 1, the electrode (6) leads the discharge part (19) from the inside to the outside of the glass tube (7) and connects the external lead (8) directly to the discharge part (6). Figure 5
As shown in FIG. 2, a lead-out portion (18) made of nickel is connected to the other end (62) of the discharge portion (19) having the recess (10) opposite to the one end (61). If the external lead (8) leads out (18)
The discharge part (19) is connected to the lead-out part (1).
8) have a uniform diameter over the entire length up to the joint (16), and the diameter L ₁ of the discharge section (19) made of tungsten and the diameter L ₂ of the lead-out section (18) made of nickel are substantially the same. Formed approximately the same 0.8 mm, forming a continuous outer surface of substantially uniform diameter. The depth L _{4 of the} recess (10) (the distance between the bottom surface of the recess (10) and the other end face of the introduction line) is about 1 mm, and the diameter L ₃ of the other end face is L ₃ = L ₁ = L ₂ It is. When connecting the lead-out section (18), the recess (10) can be formed in the discharge section (19) before or after connecting the lead-out section (18) to the discharge section (19). The discharge part (19) and the lead-out part (1
8), the lead-out section (18) may be connected to the other end (62) of the shaft body (60) by a laser beam (laser joining). After connecting the discharge section (18) to the discharge section (19), the discharge section (1)
A recess (10) can be formed at the end opposite to the end connected to (8). Since the lead-out portion (18) is made of nickel having good solderability, the external lead (8) can be soldered with high reliability. Further, by changing the irradiation condition of the laser beam, it is possible to easily manufacture the concave portion with a different shape in the discharge portion (19).

[0021]

As described above, in the present invention, since the amount of wear of the discharge portion is small during the operation of the cold cathode discharge tube, an electrode having a long life can be obtained. Further, it is possible to manufacture a cold-cathode discharge tube which can be made thinner than a conventional discharge tube and can increase the effective light emitting area. Further, since the discharge portion having the concave portion can be integrally formed, the electrode can be manufactured in a manufacturing process with a small number of components and a small number of steps. Furthermore, since laser processing is possible, electrodes can be formed with high accuracy in a short time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cold cathode discharge tube manufactured using an electrode according to the present invention.

FIG. 2 is a side view of an electrode according to the present invention.

FIG. 3 is a cross-sectional view showing a state in which a recess is formed in a shaft body by laser processing.

FIG. 4 is a cross-sectional view showing another embodiment of the electrode according to the present invention.

FIG. 5 is a sectional view showing still another embodiment of the electrode according to the present invention.

FIG. 6 is a sectional view of a conventional cold cathode discharge tube.

FIG. 7 is a processing state diagram showing a manufacturing process of a conventional electrode and a cold cathode discharge tube.

[Explanation of symbols]

(6) ・ ・ Electrode, (10) ・ ・ Recess, (10a) ・ ・ Slope,
(16) ・ ・ Coupling part, (18) ・ ・ Derivation part, (19) ・ ・ Discharge part, (50) ・ ・ Center shaft, (60) ・ ・ Shaft body, (61) ・ ・ One end, (62) ・ ・ Other end, (A) ・ ・ Plane,

Claims (9)

[Claims] 1. A discharge portion formed of a metal selected from tungsten, niobium, titanium, a tungsten alloy, a niobium alloy, and a titanium alloy, and a concave portion is formed at a tip of the discharge portion. Electrodes for cold cathode discharge tubes. 2. The cold-cathode discharge tube electrode according to claim 1, wherein the concave portion has an inclined surface tapering inward in a tapered shape. 3. An output unit connected to the discharge unit,
2. The electrode for a cold cathode discharge tube according to claim 1, wherein the discharge unit has a uniform diameter over the entire length up to a joint with the lead-out unit. 3. 4. A step of arranging a shaft formed of a metal selected from tungsten, niobium, titanium, a tungsten alloy, a niobium alloy or a titanium alloy coaxially with respect to a laser emitting portion, and supplying an assist gas to said shaft. Irradiating a laser beam to one end of the shaft body while emitting toward one end of the shaft body to form a concave portion at the one end. Manufacturing method for tube electrode. 5. A step of forming a concave portion having a tapered inclined surface inclined at the same angle as the converging angle of the converging lens for condensing the laser beam at one end of the shaft body. Item 5. A method for producing an electrode for a cold cathode discharge tube according to Item 4. 6. The method for producing an electrode for a cold cathode discharge tube according to claim 4, further comprising a step of irradiating the laser beam in parallel with a tapered inclined surface forming a concave portion. 7. The cold cathode according to claim 4, further comprising a step of controlling an irradiation direction of the laser beam in a direction in which a center axis of the laser beam passes through a plane forming the other end of the shaft body. Manufacturing method for electrodes for discharge tubes. 8. The method for producing an electrode for a cold cathode discharge tube according to claim 4, further comprising a step of connecting a lead-out portion to the other end of the shaft by a laser beam. 9. A step of connecting a lead-out section to the other end of the shaft body by a laser beam, and a step of forming the recess at one end opposite to the end to which the lead-out section is connected. The method for producing an electrode for a cold-cathode discharge tube according to claim 4.