JPS64692Y2 - - Google Patents

Description

[Detailed explanation of the idea]

This invention relates to high-pressure metal vapor discharge lamps, such as high-pressure sodium lamps in which metallic sodium is sealed together with rare gases and mercury, and metal halide lamps in which metal halides are sealed together with rare gases and mercury, and particularly relates to the electrodes thereof. The explanation will be given below using a high pressure sodium lamp as an example. The arc tube of a high-pressure sodium lamp has a structure as shown in FIG. 1, and the arc tube 1 is made of polycrystalline alumina or single crystal alumina. Electrodes 2a and 2b are installed facing each other at both ends of the arc tube 1.
They are connected to introducers 3a and 3b each made of a niobium tube. Inside the arc tube 1, excess sodium, mercury, and xenon as a starting rare gas are sealed. The high-pressure sodium lamp is a saturated vapor pressure discharge lamp, and the vapor pressure of sodium within the arc tube during lighting depends on the temperature of the coldest part of the arc tube 1. The biggest problem with high-pressure sodium lamps is that the lamp voltage increases while the lamp is on, which can cause the lamp to turn off and turn off.
The increase in the lamp voltage is also related to the increase in the temperature of the coldest part of the arc tube 1. This increase in the temperature of the coldest part is mainly caused by the scattering and evaporation of electron emitting material from the electrodes during startup. A conventional high-pressure sodium lamp, for example a 400W high-pressure sodium lamp, uses an electrode structure as shown in Figure 2. That is, an inner coil 5 and an outer coil 6 with a diameter of 0.6 mm made of a heat-resistant metal such as tungsten are wound around an electrode core wire 7 made of a tungsten rod with a diameter of 1.2 mm, and then an electron emitting material is applied. The structure is such that the electron emitting material on the surface of the outer coil 6 is removed by brushing or the like so that the electron emitting material 8 is not directly exposed to discharge. Note that the number of windings is usually 10 turns for the inner coil 5 and 9 turns for the outer coil 6. However, in high-pressure sodium lamps using electrodes with this structure, the glow discharge time when starting the lamp is as long as 4 to 5 seconds. When applied to a high color rendering type high pressure sodium lamp in which the sodium vapor pressure is higher than that of conventional lamps, it has the drawback of causing early blackening of the inner wall of the arc tube and causing a significant increase in lamp voltage. A technology to eliminate this type of defect was developed in JP-A-53-
No. 45072 and Japanese Patent Application Laid-Open No. 53-4383.
That is, in the former case, the heat capacity of the electrode is reduced by configuring the discharge electrode with a mandrel, an inner multiple coil body wound around the concentric rod, and an outer coil body surrounding the mandrel and the inner multiple coil body. In addition, thorium tungsten is used as the material for the inner coil body and electrode mandrel, and the electron radioactive substance that is the main cause of blackening of the arc tube near the electrodes is not made of anything other than thorium tungsten. This suppresses the rise in lamp voltage. Furthermore, in the latter case, the electrode is composed of an inner coil consisting of three or more coils surrounding an electrode mandrel and to which an electron radioactive substance is attached, and an outer coil surrounding the inner coil, and the electrode mandrel is formed by an outer coil. Since the lamp protrudes from the tip of the lamp, it is possible to form an electrode with a small heat capacity to which a large amount of electron radioactive material can be attached, which reduces the scattering of electron radioactive material during startup and suppresses the increase in lamp voltage. However, since the former does not use an electron emitting material, sufficient electron emission cannot be obtained.
In particular, there was a problem in that it took a long time to start the discharge. Furthermore, in the latter case that uses an electron emitting material, the heat capacity is reduced by making the inner coil a multilayered coil of three or more layers. There was a need to cover it. Therefore, it is difficult to bend the tip of the outer coil, and it is difficult to manufacture multiple coils for the inner coil.
Productivity was poor. In addition, since the heat capacity of the electrode itself is small, the electrode temperature is high, the electron emitting material undergoes a lot of heat evaporation, and the luminous flux maintenance rate is poor. In order to improve the conventional problems as described above, this invention consists of an electrode core wire and an inner coil that is wound around the electrode core wire, holds an electron emitting material, and whose tip is substantially open to the arc side. , and an outer coil wound around the inner coil, the tip of the electrode core wire protruding from the tip of the outer coil, the electron emitting material is an electron emitting material containing a rare earth oxide, and the An electrode consisting of a double coil in which the inner coil is composed of a primary coil and a secondary coil wound around this primary coil and having a diameter smaller than the diameter of the primary coil is connected to the electrode core wire for the diameter of the secondary coil. By setting the ratio (R/r) to the diameter of 8≦R/r≦22,
Without reducing the heat capacity of the entire electrode, the synergistic effect of the inner double coil layer and the rare earth oxide in the electron emitting material allows the electrode spot to be stabilized for a short period of time immediately after the lamp is started, thereby reducing the length of the lamp. This makes it possible to extend the lifespan and improve the luminous flux maintenance rate. Therefore, as in JP-A No. 53-45072, it takes a long time to start the discharge, and as in JP-A-53-4383, it is difficult to manufacture the inner and outer coils, and the luminous flux deteriorates significantly during the service life. This also improves the problems. The details of this invention will be explained below based on the drawings. FIG. 3 shows an example of the electrode structure of a high-pressure sodium lamp based on this invention. Electrode core wire 7 made of tungsten with a diameter of 1.2 mm
As the inner coil 5, a double coil consisting of a primary coil made of a 0.3φ tungsten wire and a secondary coil made of a 0.1φ tungsten wire is wound in advance for 10 turns, and then barium, strontium, and calcium are wound. The outer coil is coated with an electron-emitting material 8 consisting of a mixture of tungstate (Ba1.8 Sr0.2 CaWO ₆ ), yttrium oxide (Y ₂ O ₃ ) and beryllium oxide (BeO), and has a diameter of 0.6 mm. 6 is wound around the inner coil 5 for 11 turns, and the tip and end portions of the outer coil are caulked to hold the outer coil to complete the electrode. The tip of the electrode core wire 7 protrudes beyond the tip of the outer coil 6. After that, the above electrode is subjected to high temperature heat treatment in an inert gas atmosphere,
The electron emitting substance 8 is fixedly held on the electrode. Next, the conventional electrodes described above and the electrodes created using this invention were attached to an arc tube made of polycrystalline alumina with an inner diameter of 8 mm and an arc length of 89 mm to complete a 400 W high color rendering type high pressure sodium lamp. When these two types of lamps were lit at their rated values in a test cycle of 5 hours on and 1 hour off, the lamp voltage increase after 20,000 hours of lighting was 23V for the conventional lamp (conventional example 1), and 23V for the lamp of this invention. In the lamp obtained by carrying out Example 1, the voltage was 5V. Next, the primary coil and secondary coil of the inner coil are made of tungsten containing thorium (thorium tungsten), and the electrodes are created without using an electron emitting substance, and the rest is the same as in Example 1 above.
We have manufactured a 400W high color rendering type high pressure sodium lamp. (Experiment Example 1) Furthermore, a 400W high color rendering type high pressure sodium lamp was fabricated using a mixture of barium, ursium, and thorium oxides as the electron emitting material, but having the same electrode dimensions and structure as in Example 1 above. did. (Experiment Example 2) Next, around the 90μ diameter tungsten wire,
A coil wound with 25.5μ tungsten wire has a diameter of
Wrap it around a 300μ tungsten wire, then wrap this coil around a core wire made of a 1.2mm diameter tungsten rod to complete the inner coil. Then, an electron emitting material made of barium oxide, calcium oxide, and thorium oxide is deposited on the cavity and surface of this inner coil, and this inner coil is formed of an electrode core wire and an outer coil (0.6φ11 turns of tungsten wire). After that, the outer coil was bent to cover the electrode core wire and the opening of the outer coil so as not to expose the inner coil to the discharge, completing the electrode with a triple coil structure. A high pressure sodium lamp was created. (Experimental Example 3) The starting characteristics and luminous flux maintenance rates of these experimental lamps and the lamps of Conventional Example 1 and Example 1 described above were investigated after 6000 blinking tests (15 minutes on-15 minutes off). The results are shown in Table 1.

[Table] The discharge start characteristics in the table are the percentage of lamps that start discharging within 15 seconds after the power is turned on at a power supply voltage of 170V (pulse voltage approximately 25KV) using a commercially available ballast for high-pressure sodium lamps of 400W. It shows.
As can be seen from the table, even if the inner coil has a double coil structure, when no electron emitting material is used (Experimental Example 1), the emission is insufficient, and the discharge start characteristics after blinking lighting become extremely poor. In addition, even if the inner coil structure is a double structure, the electron-emitting substance is BaO−
In the case of CaO-ThO ₂ (Experimental Example 2), the discharge start characteristics and spot stability are somewhat good, but the luminous flux maintenance rate is greatly reduced. This is because, in the case of a double coil structure in which the tip of the inner coil is substantially open to the arc side, electrode spots are likely to be formed at the double coil part during starting, resulting in excellent electron emission and heat resistance at high temperatures. This is thought to be because, in the case of the electron emitting material mentioned above that does not contain a rare earth oxide, the electron emitting material scatters from the open part between the electrode core wire and the outer coil. Furthermore, even in Experimental Example 3 in which the inner coil has a triple coil structure, the luminous flux maintenance factor decreases significantly.
Since the discharge initiation characteristics and spot stability characteristics are relatively good, the cause of the large decrease in the luminous flux maintenance factor is the thermal evaporation of the electron emitting material after startup, rather than the scattering of the electron emitting material during startup. Conceivable. Incidentally, the electrode of Experimental Example 3 and the outer coil 2 of Example 1
When the electrode temperature of the turn was measured, it was found that Experimental Example 3
In Example 1, it was 1480° CBr, and in Example 1 it was 1400° CBr. As described above, in the lamp according to the present invention, due to the synergistic effect of the double coil structure of the inner coil and the rare earth oxide in the electron emitting material, there is no need to cover the tip of the inner coil with the outer coil. This makes it possible to have an open structure. Therefore,
The ratio of the diameter of the core wire (Rmm) to the diameter of the secondary coil of the double coil has a great influence on the starting characteristics and deterioration characteristics of the lamp. Figure 4 shows the lamp voltage rise and electrode spot stabilization time after 6000 flashings of lamps with various R/r changes, and Figure 5 shows the R/r.
6000 blinking lights using electrodes with different
It shows the luminous flux maintenance rate after recovery. As can be seen from these results, all properties are stable and extremely good in the range of 8≦R/r≦22. The reason why extremely good characteristics can be obtained when the R/r ratio is within the optimum range is considered to be based on the following reason. Normally, when the lamp is started, the surface conditions of the tip end of the electrode core wire 7 and the surface of the electrode coil are unstable, and it is observed that the electrode spot moves on the tip end of the core wire or the tip of the coil. However, in the electrode made by implementing this invention, the inner coil is a double coil consisting of a primary coil and a secondary coil wound around the primary coil, which has a smaller wire diameter than the primary coil. An electrode spot at the time of starting is likely to be formed near the double coil. Furthermore, since R/r is within the optimum range, the temperature rise of the electrode at the time of startup is maintained at an appropriate level, and a stable electrode spot that quickly diffuses is formed over the entire tip of the coil. If the R/r ratio is less than the optimum range, it may not be easy to form the electrode spot on the secondary coil, or the temperature at the tip of the core wire will rise quickly, causing the electrode spot to fail during startup. Since the ions move between parts of the coil tip or between the coil tip and the core wire tip, it takes a long time for the above-mentioned diffused stable spot to form over the entire coil tip, resulting in ion bombardment. This causes scattering and evaporation of the electrode constituent members and the electron emitting material, resulting in an increase in lamp voltage after 6000 blinks and a decrease in luminous flux maintenance factor. On the other hand, if R/r is larger than the optimum range, the electrode spot at startup tends to concentrate on the secondary coil, but since the temperature rise rate at the tip of the electrode is fast, the electrode spot will concentrate on the secondary coil or secondary coil. It becomes easier to move between different parts in the vicinity, the time required to form a stable electrode spot diffused over the entire tip of the coil increases, and the lamp voltage increases and the luminous flux maintenance factor decreases significantly after 6000 blinks. As described above, in the discharge lamp manufactured by implementing the present invention, the tip of the inner coil can be improved by the synergistic effect of the double coil structure of the inner coil and the electron emitting substance, and by strictly regulating the R/r ratio. It becomes possible to have a structure that is essentially open to the discharge side,
As a result, it is possible to realize a discharge lamp that has a quick spot stability during starting and less consumption of electron emitting material during starting and stabilization. It has many advantages, such as making it possible to provide a discharge lamp with little color change and excellent luminous flux maintenance, and furthermore, the electrodes are easy to manufacture and have high reliability. In addition, metal halide lamps, like high-pressure sodium lamps, have difficulty transitioning from glow discharge to arc discharge and improving luminous flux maintenance.
By implementing this idea, it has been confirmed that the lamp voltage increase and deterioration after long-term lighting have been improved, and it is also effective when used in high-pressure metal vapor discharge lamps other than those mentioned above. As mentioned above, this idea is used in high-pressure metal vapor discharge lamps such as high-pressure sodium lamps and metal halide lamps, and uses an electrode core wire that is wound around the electrode core wire and holds an electron-emitting substance so that the tip end is substantially on the arc side. It consists of an open inner coil and an outer coil wound around the inner coil, the tip of the electrode core wire protrudes beyond the tip of the outer coil, and the electron emitting material contains a rare earth oxide. The inner coil consists of a double coil consisting of a primary coil and a secondary coil wound around the primary coil and having a smaller diameter than the primary coil, and the diameter R of the electrode core wire and the diameter of the secondary coil are By providing an electrode with a ratio of 8:1 to 22:1, the stability of the electrode spot at the time of starting the lamp is improved, and the sputtering and thermal evaporation of the electron emitting material are prevented at the time of starting and stable lighting. This has the effect of making it possible to extend the life of the lamp.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the structure of a high-pressure sodium lamp, Fig. 2 is an enlarged sectional view showing a conventional electrode structure, Fig. 3 is an enlarged sectional view of an electrode structure showing an embodiment of this invention, and Fig. 4. and FIG. 5 are characteristic diagrams showing the effects of this invention.

Claims (1)

[Scope of utility model registration request] Consisting of an electrode core wire, an inner coil wound around the electrode core wire, holding an electron emitting substance, and having a tip end substantially open to the arc side, and an outer coil wound around the inner coil, The tip of the electrode core wire protrudes beyond the tip of the outer coil, and the electron emitting material includes a rare earth oxide,
The inner coil consists of a double coil consisting of a primary coil and a secondary coil wound around the primary coil and having a smaller diameter than the primary coil. A high-pressure metal vapor discharge lamp comprising an electrode whose ratio R/r to a diameter r satisfies 8≦R/r≦22.