JPH0613024A - Low voltage discharge lamp - Google Patents

Abstract

PURPOSE:To provide a low voltage discharge lamp for preventing the rise of lamp voltage by diffusely emitting electrons through an inner emitter even when an emitter on the surface of a sintered electrode is spattered. CONSTITUTION:An electrode 4 is sealed in the end part of a bulb 1, and the electrode 4 is provided on an electrode shaft 41 with an electrode head 142 made of porous sintered compact of metal of high melting point, and a lowvoltage discharge lamp is provided by impregnating the electrode head made of the sintered compact with an emitter. The electrode head 142 made of the sintered compact is formed into flat shape. Since the electrode head is formed into flat shape, the thickness is reduced and the heat capacity is reduced, raising temperature throughout the inside. Electrons are thus emitted by the emitter on the inside, which is diffused to the surface, even when the emitter on the surface is spattered. Reduction in the brilliance and the rise of the lamp voltage are thus prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low pressure discharge lamp using electrodes made of sintered metal.

[0002]

2. Description of the Related Art Recently, small fluorescent lamps have been used as backlights for liquid crystal display devices, light sources for office automation equipment such as copying machines and facsimiles, and illumination light sources for meters. In this type of fluorescent lamp, the bulb has a small outer diameter of, for example, 3 to 4.5 mm and a bulb length of 50 to 20 mm.
It is necessary to make it about 0 mm, and in order to obtain high brightness, it is necessary to flow the lamp current to several tens mA or more. However, if a conventional coil filament is used for such a small lamp, the filament must be small because the lamp is small.
Such a small size has a problem that the surface area becomes small and the electrode temperature becomes high, and the electrode material is violently scattered to blacken the valve early.

Usually, the filament electrode is coated on its surface with an emitter (thermoelectron emitting substance) made of a carbonate such as barium Ba, calcium Ca and strontium Sr. However, there is a problem that the emitter is consumed and exhausted as the lighting time elapses, the thermoelectrons are not smoothly emitted, and the lighting becomes impossible early.

For these reasons, recently, as shown in FIGS. 4 and 5, the use of a sintered electrode made of a refractory metal as the electrode 4 has been studied. That is, in FIG. 4, 1 is a bulb made of a glass thin tube, 2 is its discharge space, 3 is a phosphor coating formed on the inner surface of the bulb 1, 4
Is an electrode, and the electrode 4 is bonded to an electrode shaft 41 made of a Dumet wire or the like, and an electrode head 42 made of a sintered metal made of a refractory metal such as tungsten W, titanium Ti, nickel Ni, or niobium Nb. Is configured. It should be noted that no more than 10 rare gases such as argon are contained in the valve 1.
About 150 Torr is enclosed, and the electrodes 4 and 4 of this lamp are connected to the high frequency lighting circuit 10 so that the lamp current is lit at 3 to 30 mA.

The electrode head 42 made of a sintered metal as described above has a large heat capacity as compared with a coil filament and can suppress an increase in electrode temperature and prevent scattering of an electrode substance, and thus a valve. It is possible to prevent the early blackening. Moreover, this type of high melting point metal sintered body has a large number of pores formed throughout,
Such a large number of pores, that is, pores, can be impregnated with a large amount of the emitter, and there are advantages that a large amount of the emitter is retained and the electron emission characteristics are excellent.

[0006]

When such a sintered electrode is used, a cold cathode mode is set immediately after the lamp is started, and thermoelectrons are emitted from the emitter as the temperature of the electrode rises. And it becomes the hot cathode mode.

However, the sintered electrode, which has been considered to be adopted in the past, has a nodular shape like a column, as shown in FIGS. Is relatively large, and the heat capacity tends to be too large. In such a case, the temperature of the electrode is unlikely to rise, and thus there is a problem that it is difficult to shift from the cold cathode mode to the hot cathode mode.

Further, an arc spot is usually formed at the tip of the electrode head 42, and the temperature of this spot rises to stabilize the arc spot generation point. However, a sintered electrode having a nodular shape such as a cylindrical shape is formed. In the case of the head 42, the temperature of the center of the inside is unlikely to rise, so the heat of the arc spot escapes to the inside and the temperature of the arc spot does not rise, so that the arc spot generation point fluctuates each time the polarity is reversed. ,
An unstable state such as an arc fluctuating may occur.

Further, the sintered electrode head 42 of this type is
During normal lighting, it is used in the hot cathode mode, so the emitter held on the surface scatters. When the emitter scatters, the emission of electrons decreases, and in order to compensate for this decrease, the emitter held inside the electrode head 42 may diffuse to the surface and emit thermoelectrons. It is necessary to raise the temperature of s sufficiently. However, the internal temperature of the sintered electrode head 42 having a cylindrical shape is unlikely to rise,
Therefore, when the emitter on the surface scatters and disappears, the internal emitter does not diffuse sufficiently to the surface, the emission of thermoelectrons is reduced, and the electrode becomes in the cold cathode mode. When the cold cathode mode is reached, the brightness is lowered, the lamp voltage is increased, and the lamp cannot be lit.

The present invention has been made in view of the above circumstances. An object of the present invention is to make the internal emitter diffuse and emit electrons even if the surface emitter is scattered, thereby stabilizing the arc spot. In addition, it is an object of the present invention to provide a low-pressure discharge lamp using a sintered electrode that can prevent an increase in lamp voltage.

[0011]

According to the first aspect of the present invention, an electrode is sealed at the end of a valve, and the electrode has an electrode head made of a porous sintered body of a refractory metal. ,
In a low-pressure discharge lamp in which an electrode head made of this sintered body is impregnated with an emitter, the electrode head made of the sintered body is formed in a flat plate shape. A second aspect of the present invention is characterized in that the electrode head made of a sintered body is formed in a cylindrical shape.

[0012]

According to the present invention, since the electrode head made of the porous sintered body is formed in a flat plate shape or a cylindrical shape, the wall thickness is relatively small and the heat capacity becomes small as compared with the case of the cylindrical shape. Therefore, the temperature rises rapidly at the time of start-up to promote the emission of thermoelectrons, and the mode shifts to the hot cathode mode within a short time. Also, since the temperature rises to a predetermined value, the arc spot stabilizes, and when the surface emitters scatter, the internal temperature is relatively high, so the internal emitter diffuses to the surface and emits electrons. Therefore, it is possible to maintain the hot cathode mode for a long period of time and prevent a decrease in brightness and an increase in lamp voltage.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the first embodiment shown in FIG. In this embodiment, the entire structure of the lamp may be the same as the conventional case shown in FIG.
Therefore, 1 is a bulb, 2 is a discharge space, 3 is a phosphor coating, and 4 is an electrode. As shown in FIG. 1, the electrode 4 of this embodiment is composed of an electrode shaft 41 made of a Dumet wire or the like and an electrode head 142 joined to the tip of the electrode shaft 41. The electrode head 142 is made of a sintered body of a refractory metal, such as tungsten W and titanium T.
A powder of a refractory metal composed of at least one of i, nickel Ni, and niobium Nb is molded into a shape described later and sintered at a high temperature to form a high-melting-point porous sintered body. That is, in this sintered body, voids are formed between the powders, and the porosity can be set to 60 to 80%, for example.

In the case of the present embodiment, the electrode head 142 made of the above sintered body is formed in a flat plate shape, one end of which is joined to the electrode shaft 41 and the other end of which faces the discharge space 2. Facing. An example of the dimensions of the flat plate electrode head 142 is that the length is 3 to 4 mm, the width is 1.5 mm, and the wall thickness is about 0.3 to 0.7 mm.

The electrode head 1 made of this sintered body
The pores of 42 are impregnated with an emitter (electron emitting substance) not shown in the voids. The emitter is at least 1 selected from Ba, Ca, Sr, etc.
Specific carbonates, Ba ₂ CaWO _6, etc. are used.

In such a lamp, as in the case of FIG. 4, the electrodes 4 and 4 at both ends are connected to the high frequency lighting circuit 10 so that the lamp current is lit at 3 to 30 mA.

The operation of the fluorescent lamp having such a structure will be described. At the time of starting the lamp, a starting voltage is applied between the electrodes 4 and 4 at both ends. In this case, since the electrodes 4 and 4 have not been preheated, a negative glow discharge is generated in the cold cathode mode. In this case, the negative glow discharge heats the electrode, and in this case, the electrode head 142 has a flat plate shape, so that the heat capacity is smaller than that of the solid type,
Therefore, the temperature rises quickly, and the emitter is heated to a predetermined operating temperature to promptly emit electrons. Therefore, the transition from the negative glow to the main arc discharge is performed in a short time.

When the main arc discharge is reached, the electrode head 142 made of a sintered body reaches a predetermined temperature, and the impregnated emitter is heated to emit thermoelectrons to enter the hot cathode mode. In this case, since the plate-shaped electrode head 142 has a larger surface area than the coil filament, the emitter exposed on the surface emits a large amount of thermoelectrons. As a result, the cathode drop voltage is lowered, the lamp voltage is lowered, lamp extinction and scattering of electrode substances, emitters, etc. are reduced, and a relatively large lamp current flows to enable high-luminance light emission.

On the other hand, in the case of the plate-shaped electrode head 142, the wall thickness is smaller than that of the cylindrical solid-structured electrode head 142 shown in FIG. 5, and the heat is easily transferred to the central portion. For this reason, the temperature of the entire electrode head 142 becomes relatively high, the heat of the arc spot formed at the tip portion becomes difficult to escape, and the generation point of the arc spot becomes stable. Therefore, it is possible to prevent unstable discharge such as sway of the arc.

Further, even if the emitter on the surface of the electrode head 142 is scattered and consumed with the lapse of use time, since the electrode head 142 has a thin shape, heat is transmitted to the inside and the temperature of the central portion becomes high. Since the emitter impregnated in the central part is heated and diffuses to the surface, the electrons are emitted. Therefore, it is possible to compensate for the decrease in electron emission due to the scattering of the emitter on the surface, and it is possible to maintain the electrode in the hot cathode mode. As a result, it is possible to maintain high brightness, prevent the lamp voltage from rising, and prolong the service life for a long period of time.

The present invention is not limited to the first embodiment shown in FIG. That is, FIG. 2 shows a second embodiment of the present invention. In this case, in the electrode head, two flat plate-shaped sintered bodies 242 and 242 are arranged side by side with a space 243 therebetween. The flat plate-shaped sintered bodies 242 and 242 are two sheets,
For example, they face each other with the electrode shaft 41 in between, and are each impregnated with an emitter.

In the case of such a structure, the capacity is larger than that of the first embodiment, so that the amount of the emitters held is large and the life is extended accordingly. Further, in the case of such a structure, a negative glow is generated in the space 243 formed between the flat plate-shaped sintered bodies 242 and 242 at the time of starting, and the space 243 is formed.
Ultraviolet rays are emitted by the negative glow generated therein, and the ultraviolet rays stimulate the emitters on the inner surfaces of the flat plate-shaped sintered bodies 242 and 242 facing the interval 243 to accelerate the emission of electrons. That is, the electrode of the present embodiment has the function of the hollow cathode, and the interval 243.
Since a large amount of electrons are emitted from the battery, the transition to arc discharge is promoted. Also, although the emitter is emitted in the interval 243,
The emitted emitters are flat plate-shaped sintered bodies 242, 2 facing each other.
42 prevents the particles from scattering to the outside, and reduces the rate of adhesion to the valve wall, which prevents the valve from blackening.

Further, the present invention may be the third embodiment shown in FIG. In the case of the third embodiment, the electrode head 3
The reference numeral 42 is formed into a shape obtained by bending a flat plate into a circle, that is, a cylindrical shape. The cylindrical electrode head 342 is impregnated with the emitter and has a hollow portion 343 inside.

Also in the case of such a structure, since the capacitance is larger than that of the first embodiment, the amount of the retained emitters is large and the life is long. In addition, in the case of such a structure,
At the time of starting, negative glow is generated in the hollow portion 323, and ultraviolet rays are emitted by the negative glow generated in the hollow portion 323.
This ultraviolet ray exposes the hollow portion 343 to the cylindrical electrode head 34.
2 stimulates the emitter on the inner surface to promote the emission of electrons. That is, also in the case of the electrode of the present embodiment, the function of the hollow cathode is exhibited and a large amount of electrons are emitted from the hollow portion 343, so that the transition to arc discharge is promoted. Further, although the emitter is emitted to the hollow portion 343, the emitted emitter is the hollow portion 343.
The wall of the cylindrical electrode head 342 that surrounds the outer wall prevents scattering to the outside and reduces the rate of adhesion to the valve wall, thus preventing blackening of the valve. Also, the electron emitting material is Ba, Ca, Sr or Ba ₂ CaWO ₆
Outside, Ba ₃ WO ₆ or oxide of an alkaline earth metal oxide of an alkaline earth, Ba-M-O (where M is, W,
Ta, Ti, Zr, V, Nb, Hf, etc.), Al ₂ O ₃ , Th ₂ O, Y ₂ O ₃ , Sc
₂ O _{3 and the} like may be mixed. Further, the enclosed gas is not limited to argon, and may be a gas in which Xe, Ne, He and the like are appropriately combined and mixed. Further, the present invention is not limited to the fluorescent lamp, but can be implemented in the case of a rare gas discharge lamp in which mercury is not enclosed.

[0025]

As described above, according to the present invention, since the electrode head made of the porous sintered body is formed in the flat plate shape or the cylindrical shape, the wall thickness is made smaller than that of the solid cylinder shape. The temperature variation can be reduced and the temperature can be made relatively high. For this reason, the temperature rises rapidly at the time of starting, the electrons can be quickly emitted from the emitter, the mode can be switched to the hot cathode mode within a short time, and the temperature of the arc spot is stabilized, so that the arc is Stabilize. Further, even if the emitter is scattered and disappears from the surface, the emitter impregnated inside is sufficiently heated and diffuses to the surface to maintain the emission of electrons.
For this reason, it is possible to prevent a decrease in luminance, prevent a rise in lamp voltage, and maintain a long life.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention, in which (A) is a cross-sectional view of one end of a fluorescent lamp using a sintered electrode, and (B) is a line BB in (A). Sectional view of.

FIG. 2 shows a second embodiment of the present invention, in which (A) is a sectional view of one end of a fluorescent lamp using a sintered electrode, and (B) is a line BB in (A). Sectional view of.

FIG. 3 shows a third embodiment of the present invention, where (A) is a cross-sectional view of one end of a fluorescent lamp using a sintered electrode, and (B) is a line BB in (A). Sectional view of.

FIG. 4 is a cross-sectional view showing an entire fluorescent lamp using a conventional sintered electrode.

FIG. 5 shows a conventional main part, (A) is a cross-sectional view of one end, (B) is a cross-sectional view taken along line BB in (A).

[Explanation of symbols]

1 ... Valve, 4 ... Electrode, 41 ... Electrode shaft, 142, 24
2, 342 ... Electrode head.

Claims (3)

[Claims] 1. An electrode is sealed at an end of a bulb, and the electrode has an electrode head provided with an electrode head made of a porous sintered body of a refractory metal, and the electrode head made of this sintered body has an emitter. A low pressure discharge lamp in which the electrode head made of the sintered body is formed in a flat plate shape. 2. The low pressure discharge lamp according to claim 1, wherein the electrode head made of the sintered body is formed by arranging a plurality of flat plates. 3. An electrode is sealed at the end of the bulb, and the electrode has an electrode shaft provided with an electrode head made of a porous sintered body of a refractory metal, and the electrode head made of this sintered body has an emitter. A low pressure discharge lamp in which the electrode head made of the above-mentioned sintered body is formed in a cylindrical shape.