JPH0689700A - Low pressure electric discharge lamp - Google Patents

Abstract

PURPOSE:To provide a low pressure electric discharge lamp of such structure that may prevent attaching part of an emitter and other materials, all scattered from each electrode, to a seal end-portion and accordingly may prevent causing abnormal electric discharge in the lamp. CONSTITUTION:In a low pressure electric discharge lamp comprising electrodes 4 each retaining an emitter 6 sealingly joined to either seal end-portion 5 of a bulb 1 having electric-discharge gas filled thereinto, a shielding body 7 of diameter larger than that of each electrode 4 and for preventing scattering part of the emitter 6 retained by the electrode 4 to the seal end-portion 5 is installed between the electrode 4 and either seal end-portion 5 of the bulb 1. The shielding body 7 thus impedes the attachment of part of the emitter 6 and electrode materials, all scattered from the electrode 4, to the seal end- portion 5 and accordingly prevents the breakdown of the lamp due to abnormal electric discharge.

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 such as a small fluorescent lamp or a rare gas discharge lamp, in which its electrodes are lit in a hot cathode mode to improve efficiency and to improve life characteristics. Regarding technology to improve.

[0002]

2. Description of the Related Art Recently, a backlight of a liquid crystal display device,
2. Description of the Related Art Small fluorescent lamps are used as light sources for office automation equipment such as copiers and facsimiles or illumination sources for meters. Despite being small, this type of fluorescent lamp has conditions such as high brightness required and a predetermined light emission length. To realize these conditions, for example, outside the bulb, It is necessary to make the diameter as small as about 2 to 3 mm and the bulb length to be about 50 to 300 mm, and it is necessary to flow a lamp current of 2 to 20 mA or more to obtain high brightness. However, since such a lamp has a small bulb diameter, when a conventional coil filament is used, the efficiency of the lamp is high, but the amount of thermionic emission material (emitter) retained in the filament is relatively small, which results in an early stage. It is easy to run out. Further, in the case of a plate-shaped or tubular metal cold cathode used for a cold cathode lamp, the cathode drop voltage becomes large, and the lamp efficiency is significantly lowered.

Under these circumstances, recently, studies have been conducted on the use of sintered electrodes as electrodes in this type of low pressure discharge lamp. That is, since a sintered metal made of a refractory metal such as tungsten W, titanium Ti, nickel Ni, or niobium Nb can form a nodule shape such as a columnar shape, the volume of the electrode is increased, and the heat capacity is increased. Since it also becomes larger, it is possible to suppress an increase in the electrode temperature and prevent the scattering of the electrode material, and thus prevent the blackening of the valve early.

Moreover, since a large number of pores are formed throughout the sintered electrode of this kind of refractory metal, it is necessary to impregnate the emitter with such a large number of pores. , The amount of emitters that can be held on the electrodes increases, and even if the emitters disappear on the surface, the emitters held on the internal holes supply electrons to the surface to replenish it,
A good emitter effect can be maintained for a long period of time.

[0005]

However, when a sintered electrode impregnated with an emitter is used in a small discharge lamp of this kind, the emitter held by the electrode scatters, and the scattered emitter is at the end of the bulb. May adhere to the seal. In other words, since this type of discharge lamp is small, the electrode height is low, so the distance between the electrode assembly made of a sintered body provided at the tip of the electrode shaft and the sealing portion at the bulb end is relatively close. is doing. For this reason, the emitters scattered from the electrodes adhere to the sealing part and do not discharge from the electrode structure when the lamp is started. The discharge may start from some parts.

When such an abnormal discharge occurs, the sealing portion cracks due to the heat of the discharge, the airtightness of the lamp is impaired, the bulb is damaged, and the electrode shaft is melted and thinned. Easily breaks.

The present invention has been made in view of the above circumstances, and an object thereof is to prevent emitters and other substances scattered from electrodes from adhering to the sealing portion and to cause abnormal discharge. It is intended to provide a low-pressure discharge lamp that prevents the above.

[0008]

DISCLOSURE OF THE INVENTION The present invention is a low-pressure discharge lamp in which an electrode holding an emitter is sealed in a sealing portion of a bulb in which a discharge gas is sealed, and between the electrode and the sealing portion of the bulb. In addition, a shield having a diameter larger than that of the electrode and preventing the emitter held by the electrode from scattering to the sealing portion is provided.

[0009]

According to the present invention, the shield provided between the electrode and the sealing portion of the bulb prevents the emitters and electrode substances scattered from the electrode from adhering to the sealing portion, and the lamp due to abnormal discharge. It is possible to prevent damage to the electrode and breakage of the electrode.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

In FIG. 1, reference numeral 1 is a valve having an inner diameter of 3 m.
m, outer diameter is about 4 mm, and the distance between electrodes is 60 to 1
It is formed by a straight tube type glass tube having a length of about 50 mm. Both ends of the bulb 1 are sealed to form a discharge space 2 inside the bulb 1.
A phosphor coating 3 is formed on the inner surface of the.

Electrodes 4 and 4 are sealed at both ends of the bulb 1. These electrodes 4 are sintered electrodes, the details of which are shown in FIG. That is, 41 is an electrode shaft that also serves as a lead wire, and is composed of a high melting point metal wire such as nickel or tungsten. An electrode assembly 42 is attached to the tip of the electrode shaft 41. This electrode structure 4
2 is composed of a sintered body of a refractory metal having an outer diameter of about 1 mm. For example, a refractory metal powder made of at least one of W, Ti, Ni and Nb is molded into a predetermined shape. ,
This is sintered at high temperature to form a high melting point porous sintered body. That is, in this sintered body, voids having a porosity of, for example, 60 to 80% are formed between the respective powders. The electrode structure 42 made of this sintered body has its pores impregnated with an emitter (thermoelectron emitting substance) 6 by utilizing its porosity. As the emitter 6, at least one selected from oxides of Ba, Ca and Sr is used. The electrode structure itself may be a mixture of these emitters before sintering and subsequent sintering.

The electrode shaft 41 is joined to a sealing wire 45, and the sealing wire 45 is made of, for example, a Dumet wire having a diameter larger than that of the electrode shaft 41. This sealing line 45 is the valve 1
It is hermetically sealed by penetrating the sealing portion 5 at the end of the above, and an external lead wire 46 is connected to the outer surface thereof.

A shield 7 is provided on the electrode shaft 41 at the rear end side of the electrode assembly 42, that is, between the electrode assembly 42 and the sealing portion 5 at the end of the valve 1. There is. The shield 7 has an annular shape, and the central portion is fixed to the electrode shaft 41 via the support wire 8 or directly. The shield 7 has an inner diameter equal to or less than the outer diameter of the electrode assembly 42,
For example, it is set to 0.5 to 1.0 mm, and the outer diameter is formed to be larger than the outer diameter of the electrode assembly 42 but smaller than the inner diameter of the valve 1, for example, about 2.5 mm.

In this embodiment, the shield 7 is fitted with a mercury-releasing structure. That is, the shield 7 has a ring shape made of nickel plated with iron, and
A groove is formed on the opposite side to the entire circumference, and a mercury-releasing structure 9, for example, a compound of Ti-Hg (for example, GEME) is formed in this groove.
DIS = brand name) is filled. Such a mercury-releasing structure 9 is capable of discharging mercury by heating it from the outside of the valve 1 by high-frequency induction heating after sealing the valve 1, whereby mercury can be enclosed in the valve 1.

A getter such as Zr-Al is attached to the shield 7. Further, the valve 1 is filled with a rare gas such as argon at about 10 to 100 Torr. The electrodes 4 and 4 are connected to the high frequency lighting circuit 10 so that the lamp current is lit at 5 to 30 mA.

The operation of the fluorescent lamp having such a structure will be described. When the lamp is turned on, since the electrodes 4 and 4 have not been preheated immediately after the start, the cold cathode mode is set and a negative glow discharge is generated. In this case, the electrode structure 42 is heated by the negative glow discharge, the emitter 6 is heated to a predetermined operating temperature and emits electrons. Therefore, the negative glow shifts to the main arc discharge. When the main arc discharge occurs between the electrodes 4 and 4, the electrode assembly 42 reaches a predetermined temperature,
The impregnated emitter 6 is heated to emit thermoelectrons, and the hot cathode mode is set. Therefore, the emitter 6 emits a large amount of thermoelectrons, lowers the lamp voltage, and reduces excessive scattering of the electrode material, the emitter, etc. due to the extinction of the lamp and overheating of the electrode structure.

By the way, in such a lamp,
The emitter 6 is scattered from the electrode 4 with the lapse of use time. Since the electrode 4 is formed of a porous sintered body, a large amount of the emitter 6 can be impregnated in the void portion, and even if the electrode 4 is small, the holding amount of the emitter 6 can be increased. it can. Then, even if the emitter 6 disappears on the surface of the electrode 1, electrons are replenished from the emitter held in the internal cavity, so that the emitter action can be maintained for a long period of time. Therefore, the life of the lamp due to exhaustion of the emitter can be extended, and good startability can be maintained for a long period of time.

On the other hand, the emitter 6 scattered from the electrode 4 is
It adheres to the inner surface of the valve 1. Since this type of lamp is small, the distance between the electrode structure 42 and the sealing portion 5 is short, and the scattered emitters 6 and the electrode material are scattered in the sealing portion 5, especially the sealing wire 4 having a large diameter.
May adhere to 5. In such a case, an arc spot does not occur at the tip of the electrode assembly 42 when the lamp is turned on, and an abnormal discharge occurs between the sealing portion or the sealing wire 45 and the electrode on the other end side opposite to this. , It may damage the lamp.

On the other hand, in the case of the present embodiment, since the shield 7 is provided between the electrode structure 42 and the sealing part 5, the emitter 6 and the electrode substance scattered from the electrode structure 42 are sealed. Before it reaches the sealing wire 45, it is shielded by the shield 7 and thus is prevented from adhering to the sealing portion 5 or the sealing wire 45. For this reason, abnormal discharge at the time of starting the lamp also occurs between the shield 7 and the electrode on the other end side facing the shield 7, so that early damage of the lamp and fusing of the sealing wire 45 and the electrode shaft 51 are prevented.

Further, in the above embodiment, since the mercury releasing structure 8 is attached to the shield 7, the amount of mercury enclosed can be regulated with high accuracy. That is, when mercury is sealed in a liquid state, it is difficult to weigh a small amount with high accuracy because the surface tension is large, but when sealed in the form of an alloy, the second amount is easy, and the sealed amount is small. Even if there is, it can be managed with high accuracy. Moreover, since such a mercury-releasing structure 8 is attached to the shield 7, a special support structure for the mercury-releasing structure is unnecessary.

From the above, since the fluorescent lamp of the above-mentioned embodiment uses the sintered electrode 4 which has a large amount of the emitter 6 in spite of its small size, it excels in electron emission and is a small electrode, but it can be heated. It becomes possible to light in the cathode mode, resulting in a highly efficient lamp. Further, even if the held emitter 6 is scattered, the shield 7 does not adhere to the sealing portion 5 or the sealing wire 45, and the lamp can be prevented from being damaged due to abnormal discharge. In addition, since the shield 7 holds the mercury-releasing structure 8, a supporting structure for the mercury-releasing structure 8 is not necessary.
In addition, the amount of mercury required until the end of the life of the valve can be sufficiently sealed with high accuracy. Further, since the getter is applied to the shield 7, impurities in the tube can be adsorbed, blackening of the bulb can be prevented, and the life can be extended. The present invention is not limited to fluorescent lamps, but can be implemented in rare gas discharge lamps that do not contain mercury.

[0023]

As described above, according to the present invention, the shield provided between the electrode and the sealing portion at the end of the valve prevents the emitter or electrode material scattered from the electrode from sealing the portion or the electrode. Prevents adhesion to the base of the shaft or the base of the wells, so that arc spots do not occur at the base of these sealing parts, the electrode shaft, or the base of the wells, preventing the lamp from being damaged due to abnormal discharge. be able to. Therefore, the lamp life can be extended in a highly efficient hot cathode mode lamp.

[Brief description of drawings]

FIG. 1 is a sectional view of a fluorescent lamp showing a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of an electrode portion of the embodiment.

[Explanation of symbols]

1 ... Bulb, 4 ... Electrode, 5 ... Sealing part, 6 ... Emitter, 7
... Shield, 8 ... Mercury emitting structure, 41 ... Electrode shaft, 42 ... Electrode structure, 45 sealing wire.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masami Takagi 1-28-3, Mita, Minato-ku, Tokyo Toshiba Lighting & Technology Corporation

Claims (4)

[Claims] 1. A low-pressure discharge lamp in which an electrode holding an emitter is sealed in a sealed portion of a bulb filled with a discharge gas, and a diameter larger than that of the electrode is provided between the electrode and the sealed portion of the bulb. And a shield for preventing the emitter held by the electrode from scattering to the sealing portion. 2. The electrode according to claim 1, wherein the electrode is a sintered electrode made of a porous sintered body of a refractory metal, and an emitter is impregnated and held in the porous hollow portion. The low-pressure discharge lamp described. 3. The low-pressure discharge lamp according to claim 1, wherein the conductor sealed at the end of the bulb has a diameter larger than that of the electrode shaft connected to the electrode. 4. The low-pressure discharge lamp according to claim 1, wherein the shield has a mercury alloy.