JPS62165847A - Discharge lamp - Google Patents

Abstract

PURPOSE:To suppress the evaporation and scattering of an electron emitting substance and realize a discharge lamp of a long service life, by including an alkaline earth metal oxide and iridium Ir in the electron emitting substance spread on an electrode, and making the amount of Ir 0.1%-10% in the electron emitting substance. CONSTITUTION:A coil 7 formed by winding tungsten wires on an electrode shaft 6 of tungsten is prepared, over which an electron emitting substance 8 is spread. The electron emitting substance 8 consists of barium oxide BaO and calcium oxide CaO, which are alkaline earth metal oxides, yttrium oxide Y2O3, and iridium Ir, the ratio of iridium being 2wt% of the electron emitting substance 8. Since a metallic layer of an alkaline earth metal such as Ba and Ir is formed on the surface of the electrode 3B in such a composition of lamp, the work function at the portion is reduced, the starting is made easier, and evaporation and scattering of the electron emitting substance is restricted. Therefore, a remarkable drop of the luminous flux is prevented and a long service life is realized.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to discharge lamps, and in particular to improvements in electrodes thereof.

(Technical background of the invention and its problems) Conventionally, the electrodes of discharge lamps, such as mercury lamps and high-pressure sodium lamps, are wound around a coil made of tungsten wire with an electrode shaft made of tungsten, and this coil carries an electron radioactive substance. Therefore, the electron radioactive substances are generally alkaline earth metal oxides, or these oxides and high melting point oxides such as thoria Th○2, alumina Al2O3
, scandium oxide 5C203, ittria Y2O3,
A mixture with barium tungstate, BaWOa, etc., is used.

For example, in a 40W mercury lamp equipped with an electrode that uses an alkaline earth metal oxide as the electron radioactive material, the temperature at the tip of the electrode during operation is 14 + O.
The temperature exceeds O℃b (brightness temperature).

A coil coated with an electron radioactive material also has a concentration of 1200'Cb or more in a portion near the tip of the electrode. Therefore.

The rate of evaporation of electron radioactive materials increases, and furthermore, they are scattered and consumed by the impact of ions and electrons, which determines their lifespan. Moreover, the evaporated and scattered electron radioactive substances and the metallic barium produced by their reduction adhere to the inner surface of the arc tube near the electrodes, causing a blackening phenomenon, increasing the loss of light and reducing the luminous flux. This results in a shortened lifespan from the surface.

To deal with these inconveniences, methods have been developed to suppress the evaporation of barium by mixing high-melting-point oxides with alkaline earth metal oxides as mentioned above, but they are still insufficient. At present, satisfactory results have not been achieved.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances.

The purpose is to provide a long-life discharge lamp by suppressing evaporation and scattering of electron radioactive materials.

[Summary of the invention]

In the present invention, the electron radioactive substance deposited on the electrode for a discharge lamp contains at least an alkaline earth metal oxide and iridium Ir, and the Ir content is 0.1% to 10% in the electron radioactive substance.
% (weight ratio).

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the arc tube of a 40W mercury lamp, in which (1) is quartz glass pulp for the arc tube, and sealants (2A) and (2B) are formed on both ends of the pulp by heating and crushing.

(3A) and (3B) are a pair of electrodes, (3C) is a starting auxiliary electrode, and each is made of metal foil for sealing (4A),
(4B), External lead wire (5A) via (4C)
, (5B), and (5C), and an appropriate amount of starting rare gas such as argon gas and mercury is sealed in the tube. Such an arc tube is housed in an outer tube (not shown) whose interior is evacuated to form a lamp. As shown in an enlarged view in FIG. 2, the electrodes (3A) and (3B) are equipped with a coil (7) made of a tungsten wire wound around an electrode shaft (6) made of tungsten. is coated with an electron radioactive substance (8) (indicated by dots).The electron radioactive substance (8) consists of alkaline earth metal oxides such as barium oxide BaO and calcium oxide Ca.
Consists of O, yttrium oxide Y2O3, and iridium Ir.

Ir is present in the electron radioactive substance (8) at a ratio of 2% (weight ratio).

Formation of such an electron radioactive substance (8) is carried out, for example, as follows. Namely.

Y2O3 with an average particle size of 2μ...
・Mix 33 mol% BaCO3 (barium carbonate) with an average particle size of 2 μm and 29 mol% CaC03 (calcium carbonate) with an average particle size of 5 μm with a solvent such as butyl acetate to make a suspension, and add to this suspension. All of the above materials are oxides (Y2O3.

(Bad, CaO), the content ratio is 2%.
(weight ratio) of Ir metal powder is added and further mixed, this suspension is applied to the coil (7) part of the electrode, and after drying, the temperature is 1.500℃ in a vacuum or reducing atmosphere. ~
If heated to 2,000°CK, the above electron radioactive substance (8)
Electrodes (3A) and (3B) are obtained.

A lamp with such a configuration has electrodes (3A), (313)
Since a metal layer of alkaline earth metals such as Ba and Ir is formed on the surface, the number of work curves in that part is lowered.

Starting is easier, there is less evaporation and scattering of radioactive materials, and a significant drop in luminous flux is therefore prevented, resulting in a long life.

Next, FIGS. 3 to 5 show the results of a test on the influence of various changes in the content (weight ratio) of Ir contained in the electron radioactive substance on the lamp characteristics for the 40W mercury lamp. Figure 3 is related to the starting voltage, Figure 4 is the luminous flux maintenance factor, and Figure 5 is related to the electrode tip temperature.First, as shown in Figure 3, those containing Ir.

The starting voltage is lower and the starting characteristics are improved compared to the one that does not contain it (conventional example), and this tendency is 1. It can be seen that the higher the r content, the more remarkable this becomes. Furthermore, as shown in Figure 4, the luminous flux maintenance factor is improved by incorporating Ir, and this effect is particularly noticeable in the Ir content range of 1 to 3%, but when the Ir content exceeds 10% 15%
When this happens, the evaporation of Ir becomes noticeable, and on the contrary, it becomes lower than in the conventional case. Note that when the Ir content reaches 0.05%, which is less than 0.1%, the improvement effect of the above characteristics becomes insufficient, and in particular, there is almost no difference from the conventional one in terms of luminous flux maintenance.

Therefore, the range of Ir content that can significantly improve both lamp characteristics, starting characteristics and lumen maintenance factor, is 0.1 to 0%.
It can be seen that the reason why such an improvement effect is obtained is thought to be due to the first-order point. That is, as shown in Fig. 5, when Ir is included, the operating temperature of the pole can be lowered, and the starting characteristics are improved, and the evaporation and scattering of electron radioactive substances are also reduced, which reduces the blackening of the tube wall. This also reduces the luminous flux maintenance factor and improves the luminous flux maintenance factor. Moreover, it has been found that such a lamp also has the additional effect of reducing high-frequency noise and almost no longer generating it.

Note that the present invention is not limited to the above embodiments (similar effects can be obtained in those containing at least an alkaline earth metal oxide, which is generally used as an electron radioactive substance for electrodes for discharge lamps). In addition to mercury lamps, other discharge lamp pressures such as high pressure sodium lamps, xenon lamps, and neo lamps can also be applied.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a mercury lamp arc tube according to an embodiment of the present invention, FIG. 2 is an enlarged vertical cross-sectional view of the electrode of the same lamp, and FIG.
Figures 5 to 5 are curve diagrams showing the relationship between the Ir content in the electron radioactive material and the lamp characteristics. FIG. 3 shows the starting voltage, FIG. 4 shows the luminous flux maintenance factor, and FIG. 5 shows the electrode tip temperature. (1)... Arc tube bulb, (3A), (3
B)... Electrode. (8)...Electron radioactive material.

Claims (1)

[Claims] The electron radioactive material deposited on the electrode contains at least an alkaline earth metal oxide and iridium Ir, and the Ir
is present in an electron radioactive substance in an amount of 0.1% to 10% (by weight).