JPS58189953A - Electrode for high-pressure discharge lamp - Google Patents

Abstract

PURPOSE:To enable the starting voltage of a high-pressure discharge lamp to be lowered, by mixing barium calcium tungstate with the adequate amount of barium aluminate, calcium oxide and aluminum oxide in order to obtain an electron emission substance. CONSTITUTION:First, an electron emission substance is obtained by mixing 50-90wt% of barium calcium tungstate powder with 10-50wt% of barium aluminate powder, 2-17wt% of calcium oxide powder and 2-25wt% of aluminum oxide powder. Next, ethylene glycol is added as a binder into said electron emission substance and stirred well to obtain a mixture, which is thereafter spread on the part of an electrode coil 2 wound around an electrode mandrel 1. After said coil wound mandrel 1 is dried at an ordinary temperature, it is burnt at the temperature of 1,350-1,600 deg.C in order to complete the electrode. By doing this, the starting voltage of the high-pressure discharge lamp can be lowered, as well as the light velocity maintenance rate improved and the life time prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrodes used in high-pressure metal vapor discharge lamps such as high-pressure mercury lamps and high-pressure sodium lamps, and particularly relates to improvements in electron-emitting materials applied to or filled in electrodes.

Conventionally, as an example of an electron-emitting material used in the electrodes of high-pressure discharge lamps as described above, barium calcium tungstate (BazCa'WOs) is the main component, and barium oxide (Bad), thorium oxide (ThOx), and thorium are added to this as a main component. A mixture of at least one type of barium acid (BaTh0m) is used. Since such an electron emitting material uses barium calcium tungstate, it has the great feature that it is difficult to scatter even at high temperatures, and therefore the arc tube is less likely to darken, thereby greatly extending the life of the lamp. However, on the other hand, barium calcium tungstate has the property of absorbing moisture and decomposing naturally when left in the air, so it has the disadvantage that it tends to absorb moisture and carbon dioxide during handling. In addition, when an electron emitting material containing barium calcium tungstate as its main component and mixed with barium oxide, thorium oxide, barium thorate, etc. is applied to an electrode and fired, the surface of the electron emitting material becomes relatively porous. This makes it easier to adsorb moisture and carbon dioxide. When moisture or carbon dioxide enters the arc tube, the purity of the starting rare gas is reduced, causing undesirable phenomena such as an increase in starting voltage and poor starting. Further, although barium calcium tungstate itself is difficult to scatter at high temperatures, if the surface of the electron emitting material is porous, it will scatter more easily than if the surface is dense.

The present invention has been made in view of the above points, and its purpose is to provide a device that is easy to handle and can adsorb impurities, and therefore is less likely to cause an increase in the starting voltage of the discharge lamp or cause poor starting. In addition, it is an object of the present invention to provide an electrode for a high-pressure discharge lamp, which is equipped with an electron-emitting material that has the characteristics that when the electrode is coated, the surface becomes dense and does not easily scatter even when used at high temperatures.

As a result of various experimental studies to achieve the above object, the inventors mixed barium calcium tungstate with appropriate amounts of barium aluminate (BaA204), calcium oxide (Cab), and aluminum oxide (Altos). It was confirmed that the intended purpose could be achieved by using it as an electron emitting material.

The electrode for a high pressure discharge lamp according to the present invention is molded as follows. First, to barium calcium tungstate powder with a direct weight ratio of 50 to 90 liters, add 10 to 5 liters of barium aluminate, 2 to 17% of calcium oxide, and 2 to 25 percent of aluminum oxide powder. Mix to make an electron emitting substance.Next, add ethylene glycol as a binder and stir well, then apply the mixture to the part of the electrode coil Z wound around the electrode core 1 as shown in Figure 1. Then, after drying at room temperature, it will be about 1350~1600
The electrode is completed by firing at a temperature of C. In this case, if the barium calcium tungstate that constitutes the electron emitting material is less than 50% by weight, it will not be possible to take advantage of the advantage of barium calcium tungstate that it is difficult to scatter even when used at high temperatures; If it exceeds %, the sinterability during firing will deteriorate. In addition, when barium aluminate exceeds 50 hiss, electron radioactivity decreases,
If it is less than 0%, the sinterability will deteriorate due to the balance with other components. On the other hand, if a large amount of calcium oxide is added, the sinterability will improve or the starting voltage of the discharge lamp will increase. This is thought to be because excess calcium oxide decomposes into carbonate, reducing the purity of the starting gas sealed in the arc tube of the discharge lamp. As a result of experiments, it was found that the optimum amount of calcium oxide to be added is between 2 and 17 inches. Further, the amount of aluminum oxide needs to be selected within the range of 2 to 25 ts. This is because if it is less than 2 inches, the evaporation and scattering of the electron emitting material will become noticeable, and if it exceeds 25 degrees, the starting pressure of the discharge lamp will increase.

The second picture shows an arc tube for a high-pressure mercury lamp incorporating the electrodes completed as described above. 3 is an arc tube body made of quartz glass; 4 and 5 are main electrodes hermetically sealed to both ends of the arc tube body 3; 6 is an auxiliary electrode sealed close to at least one of the main electrodes, for example 5; 7. 8' is molybdenum foil, 3
．． 10' is an external lead wire. In the arc tube having such a structure, the inner diameter is Igmm, the distance between the main electrodes is 70 mm, and 60 mg of mercury and 20 mmH are placed inside the arc tube body 3.
When the arc tube was filled with argon gas of 1.5 g and then housed in an outer bulb (not shown) and started at a rated power of 400 W, the initial starting voltage was 127 cm on average, and the total luminous flux was 2.
32,001 m, and 1 m after 12,000 hours. In contrast to this η, a high-voltage device with the same structure and equipped with an electrode using a conventional electron-emitting material containing barium calcium tungstate as its main component, to which an appropriate amount of barium oxide, thorium oxide, and barium thorate was added. For mercury lamps, the initial starting voltage is 133V on average, and the total luminous flux is 2250V.
01m, the average starting voltage after 12,000 hours is 14
6V, and the total luminous flux was 199004 m.

As described above, according to the present invention, not only can the starting voltage of the high-pressure discharge lamp be lowered, but also the luminous flux maintenance rate can be improved and the life span can be extended. The reason why such an effect is not obtained is that, first, by replacing a portion of barium calcium tungstate with relatively stable barium aluminate, stability is increased without reducing electron radioactivity. . The second is that the main ingredients are barium calcium tungstate and barium aluminate, and when appropriate amounts of calcium oxide and aluminum oxide are added to these, these additives improve the sinterability of the electron emitting material. It is presumed that this is not only because the surface of the electron-emitting substance becomes denser.

It is believed that this resulted in less scattering of the electron emitting material and less deterioration in the purity of the starting gas due to the release of impurities, resulting in good characteristics.

As described above, according to the present invention, it is possible to improve the starting voltage, luminous flux maintenance rate, lifespan, etc. of high-pressure discharge lamps such as high-pressure mercury lamps, and to make the manufacturing work of discharge lamps easier and more reliable. It has the effect of being able to do a lot of things, so it has great utility value as a bramble.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway side view of an electrode for a high pressure discharge lamp according to the present invention, and FIG. 2 is a side view of an arc tube for a high pressure discharge lamp using the same electrode. Patent applicant Iwasaki Electric Co., Ltd. Figure 1?

Claims (1)

[Claims] Barium calcium tungstate (Ba*CaW)s) of 50-90'j), barium aluminate (BaAJ, Oa) of 10-50'j, and 2-17
1. An electrode for a high-pressure discharge lamp, characterized in that a mixture of calcium oxide (Cab) of 30% and aluminum oxide (1zOs) of 2 to 25% is used as an electron emitting material.