JPS6366024B2 - - Google Patents

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 filled with mercury and rare gases, and high-pressure sodium lamps filled with sodium metal in addition to mercury and rare gases, and particularly relates to electrodes for use in high-pressure metal vapor discharge lamps such as high-pressure mercury lamps filled with mercury and rare gases, and high-pressure sodium lamps filled with sodium metal in addition to mercury and rare gases. This is related to the improvement of. The structure of the arc tube of a high-pressure metal vapor discharge lamp, such as a high-pressure mercury lamp, is generally constructed as shown in FIG. That is, a suitable amount of mercury and argon gas is sealed inside a transparent arc tube 1 made of quartz glass or the like, and main electrodes 2a and 2b are installed facing each other at both ends of the arc tube 1. Conductive wires 6 are connected through sealed molybdenum foils 4a and 4b, respectively.
a, 6b. Further, an auxiliary electrode 3 is provided at at least one end of the arc tube 1 to facilitate starting, and is connected to a conducting wire 7 via a molybdenum foil 5. And main electrodes 2a, 2
b has a structure as shown in FIG. 2, and has an electrode core wire 8 made of a heat-resistant metal such as tungsten.
An inner coil 9 and an outer coil 10 made of a heat-resistant metal such as tungsten are wound around the inner coil 9 and an outer coil 10, and an electron emitting substance 11 is fixed to the surfaces of the inner coil 9 and the outer coil 10. As the electron emitting material 11, for example, as disclosed in Japanese Patent Publication No. 55-9777, a mixture of an alkaline earth metal oxide and yttrium oxide containing at least barium oxide (BaO), or at least barium oxide (BaO) is conventionally used. Alkaline earth metal oxides including beryllium oxide (BeO)
and yttrium oxide (Y ₂ O ₃ ) were used. However, the former has difficulty adhering to the electrode components, and increases the starting voltage during long-term use.
This method also has the disadvantage of causing phenomena such as a rapid decrease in luminous flux maintenance factor. On the other hand, the latter
Due to the effect of forming a solid solution with Y ₂ O ₃ , it has the advantage of extremely excellent and stable luminous flux deterioration characteristics and starting characteristics after long-time lighting, and the above-mentioned drawbacks of the conventional example are greatly improved. be done. However, since BeO contained in the electron emitting material 11 is harmful to the human body, sufficient care must be taken in its handling, which has the drawback of hindering productivity improvement. In addition, in the high-pressure metal vapor discharge lamp using the electron-emitting material 11, a phenomenon was observed in which black deposits were often formed on the inner wall of the arc tube at the initial stage of lighting. This black deposit gradually turns white as the lighting time elapses, so it does not affect the life characteristics of the lamp in any way, but it has the disadvantage that the luminous flux value at the initial stage of lighting becomes slightly low. The present invention was made in view of such conventional drawbacks, and by using an electron emitting material containing at least an alkaline earth metal oxide containing barium oxide, lanthanum oxide, and yttrium oxide, In addition to improving the luminous flux drop during the initial stage of lamp operation, it does not contain BeO, which is harmful to the human body, so there is no need for special consideration when handling it.
The object of the present invention is to provide an electrode for a discharge lamp that can be handled in a general manner and thus enables improved productivity. Embodiments of the present invention and conventional examples will be explained below. First, as a conventional example, the electrode core wire 8 has a diameter of
Electrode components were constructed using a 1.2 mm tungsten rod, inner and outer coils 9 and 10, and 0.6 mm diameter tungsten wire. On the other hand, electron-emitting material 11, which is a mixture of BaO...42.3 (mol%), CaO...16.5 (mol%), BeO...37.1 (mol%), and Y ₂ O ₃ ...4.1 (mol%), is mixed with acetic acid with a nitrocellulose lacquer. After putting it in butyl and performing a ball mill for 24 hours to create a suspension, immersing the electrode component in this suspension, applying the electron emitting substance 11 to the electrode component and drying it,
The electron emitting material 11 was fixed to the electrode component by heating at 1700° C. for 2 minutes in an argon gas atmosphere. Using the electrodes 2a and 2b having the electron emitting material 11 manufactured in this way, the inner diameter was 18 (mm), with an appropriate amount of mercury and starting argon gas sealed inside.
A 400W high-pressure mercury lamp equipped with an arc tube 1 with an arc length of 70 (mm) was created, and as an accelerated test, flashing was performed (15 minutes on, 15 minutes off), and the luminous flux maintenance rate after 50 and 6000 times. was measured. As a result, the luminous flux maintenance rate after 50 blinks was 85%, and a lamp with black deposits on the inner wall of the arc tube was observed. When this black deposit was analyzed, beryllium and barium were detected. Furthermore, the luminous flux maintenance rate after 6000 flashes was 62%. Next, to explain an embodiment of the present invention, lanthanum oxide (LaBO ₃ ) is added to alkaline earth metal oxides such as barium oxide (BaO) and calcium oxide (CaO).
Electrodes 2a and 2b are manufactured by fixing the electron emitting material 11, which is a mixture of yttrium oxide and yttrium oxide (Y ₂ O ₃ ) in various proportions, to the electrode constituent members in the same manner as in the conventional example described above, and these are placed in a 400W high-pressure mercury lamp. The test was conducted using The results are shown in Table 1.

[Table] As is clear from Table 1, when using an electron emitting material containing La ₂ O ₃ and Y ₂ O ₃ , the conventional
The luminous flux maintenance rate after 50 blinks is improved compared to the case of using electron emitting material 11 containing BeO and Y ₂ O ₃ , and in particular, the La ₂ O ₃ :Y ₂ O ₃ (molar ratio) is 19:1. It can be seen that in the range of 1:9 to 1:9, the luminous flux maintenance rate after 6000 blinks is also improved compared to the conventional one. The cause of such a difference in characteristics is thought to be as follows. That is, in the conventional electron emitting material 11 described above, BeO and Y ₂ O ₃ form a solid solution to improve adhesion to electrode constituent members, and also have the function of maintaining an appropriate level of active barium generation during lighting. do. However, when the electron emitting material 11 is applied to the electrode component and dried, and then subjected to high temperature heat treatment to fix it to the electrode component, BeO in the solid solution is mixed with the electron emitting material 11. Partially reacts with BaO to form a composite compound with a relatively low melting point such as BeO/3BaO, and when the arc spot moves to the electrode component near where this composite compound was formed when the lamp is lit, the above composite compound The lamp rapidly becomes hot, and beryllium and barium selectively evaporate and adhere to the inner wall of the arc tube, causing a decrease in luminous flux at the initial stage of lighting. On the other hand, in the electron emitting material 11 containing La ₂ O ₃ and Y ₂ O ₃ according to the present invention, in addition to forming a solid solution or a stable composite compound, La ₂ O ₃ and Y ₂ O ₃ moreover
Since La ₂ O ₃ and Y ₂ O ₃ do not react with BaO,
Since the production of active barium from the electron emitting material is maintained in a stable state at an appropriate level both at the initial stage of lighting and even during the life of the lamp, the luminous flux maintenance factor is stable and good throughout the life. As described above, if the molar ratio of La ₂ O ₃ to Y ₂ O ₃ in the electron emitting material 11 is in the range of 19:1 to 1:9, the above-mentioned improvement effect is remarkable. When the molar ratio of La ₂ O ₃ is greater than 19:1,
The melting point of the solid solution increases significantly, and the electron emitting substance 11
The adhesion to the electrode component has decreased and the flashing is 6000.
As shown in Table 1, the luminous flux maintenance rate after the lapse of time is somewhat lower than that of the conventional example. Similarly, when the molar ratio of Y ₂ O ₃ becomes larger than the molar ratio of 1:9, the melting point of the solid solution rises significantly, and the adhesion of the electron emitting material 11 to the electrode constituent members decreases, causing a blinking of 6,000 yen. The luminous flux maintenance rate decreases after the lapse of time. Here, the experimental results shown in Table 1 above will be discussed based on FIG. In FIG. 4, the vertical axis shows the luminous flux maintenance factor (%), and the horizontal axis shows the molar ratio of La ₂ O ₃ and Y ₂ O _3. For convenience, La ₂ O ₃ :Y ₂ O ₃ and La ₂ O ₃ /La ₂ O ₃ +Y ₂ O ₃ are written together in the lower and upper rows, respectively. In Fig. 4, each point P ₁ to P ₆ indicates the result after 50 blinks, and each point Q ₁ to Q ₆ indicates the result after 6000 blinks; P ₁ to P ₆ , Q ₁ to Each subscript 1 to Q ₆
6 corresponds to each of Examples 1 to 6 in Table 1. As is clear from the figure, P ₂ , Q _{2 ,} that is, La ₂ O ₃ :
When Y ₂ O ₃ becomes smaller than the value of 1:9, the luminous flux maintenance factor decreases rapidly, and P ₅ , Q _{5 ,} that is, La ₂ O ₃ :
It can be seen that when Y ₂ O ₃ becomes larger than the value of 19:1, the luminous flux maintenance factor decreases rapidly. Here, in order to confirm the influence of the molar ratio of La ₂ O ₃ and Y ₂ O ₃ on the adhesion of the electron emitting material 11 to the electrode component, the conditions described above (heating at 1700°C for 2 minutes in an argon gas atmosphere) were performed. ) After fixing the electron emitting material 11, the electrode was loaded into a ball mill together with tungsten powder, and after rotating for 2 hours, the peeling of the electron emitting material 11 was measured. The results are shown in Figure 5, and R ₁ to R ₆ are shown in Table 1 and 4.
Examples 1 (P ₁ , Q ₁ ) to Example 6 (P ₆ ,
Corresponding to Q ₆ ), BaO is added as a new experimental example:
CaO: Y ₂ O ₃ = 42.3: 16.5: 41.2 (R ₀ ) and BaO:
Added CaO: La ₂ O ₃ = 42.3: 16.5: 41.2 (R ₇ ). The sample for each electron emitting material composition was 20 electrodes, and the value (% value) obtained by dividing the average weight change after the experiment by the average weight of the electron emitting material before the experiment is plotted in FIG. As is clear from this figure, La ₂ O ₃ :Y ₂ O ₃ =
When the La ₂ O ₃ ratio is smaller than 1:9, or
When La ₂ O ₃ :Y ₂ O ₃ =19:1 or more, the amount of detached electron emitting material 11 increases rapidly. This is because in the range of La ₂ O ₃ :Y ₂ O ₃ = 1:9 to 19:1, an almost uniform solid solution is formed when La ₂ O ₃ - _{Y 2} O ₃ is fixed, and the melting point of the electron emitting material 11 is lowered. 1700℃
However, outside the above range, La ₂ O ₃ or
It is considered that since Y ₂ O ₃ becomes excessive and La ₂ O ₃ alone or Y ₂ O ₃ alone remains as a high-melting point substance, the amount of exfoliation of the electron emitting material 11 increases rapidly. By the way, in general, the aging of the electron emitting material basically depends on the melting state of the electron emitting material during the electrode heat treatment, but as in the measurement test above, applying a mechanical shock to the electrode after the heat treatment, Regarding the rationality of evaluating age-related peeling based on the amount of electron emitting material peeled off, the reason will be described below. One of the main causes of peeling over time during use is mechanical shock during use, and regarding this point, for example, Japanese Patent Publication No. 52-312, page 1, column 1, line 31 to column 2 of the same page, In the first line, the problem with electron-emitting materials made only of alkaline earth metal oxides is that they have weak binding strength with the base metal, so they are susceptible to mechanical shocks and impacts from ions and electrons during use, and are susceptible to peeling and disintegration. It is stated that the product is prone to wear and tear and has a short lifespan. From this, one of the main causes of the aging of electron-emitting materials that causes a short lifespan is the mechanical impact during use and the impact caused by ions and electrons, and the binding force of the electron-emitting material controls the aging properties. It is understood that there are Furthermore, what governs peeling over time during use is the binding force or adhesion of the electron emitting material to the electrode constituent members, and this binding force is basically determined by the molten state of the electron emitting material during electrode heating treatment. determined by Regarding this binding force, for example,
Publication No. 24692, page 2, column 1, line 1 to 11
In the row, BaO―SrO―BeO system electron emitting material
BeO and BaO or SrO form a solid solution,
It is stated that the melting point is lowered and the adhesive force between the base metal and the electron emitting material is improved. In other words, considering the statements from JP-B-43-24692, page 1, line 40 to page 2, line 4 of the same publication, the melting point of the electron emissive material can be determined based on the degree of electrode heat treatment after application of the electron emissive material. By lowering the temperature, the electron emitting material is melted during this heat treatment, so the adhesive strength of the electron emitting material is improved. Therefore, it is understood that a strong adhesive force can be obtained by lowering the melting point of the electron emitting material below the electrode heat treatment temperature. For example, "Ceramics, 15 (1980) No.
5, page 356, lines 10 to 11, taking the case of a mercury lamp as an example, the operating temperature of 1100 to 1500°C is higher than the electrode heat treatment temperature of 1700°C in the example. It should be noted that the adhesive strength of the electron emitting material, such as a sufficiently low temperature, is determined by the adhesive properties of the electron emitting material after the electrode heat treatment. As mentioned above, one of the main causes of the aging of electron emitting materials is mechanical shock during use, and this aging depends on the cohesion or adhesion of the electron emitting materials after electrode heating treatment. The above measurement test, in which the adhesive strength of the electron emitting material after the electrode heat treatment was evaluated by the amount of peeling of the electron emitting material due to mechanical impact, is one of the reasonable evaluation tests as a peeling test of the electron emitting material. think. In addition, in the above examples, the mol% of BaO and CaO
Although the effect of the present invention was shown in the case where % is the same as that of the conventional example, the same effect can be obtained even when the mol % is different from the above. Furthermore, although the case where BaO and CaO are used as the alkaline earth metal oxide has been described, the alkaline earth metal oxide containing BaO and CaO may be a combination of BaO, CaO, and SrO; SrO has chemical properties similar to BaO, and has better heat resistance than BaO.
In the electrode for a discharge lamp having the above-mentioned structure of the present invention, in addition to the effects of the solid solution composed of La ₂ O ₃ and Y ₂ O ₃ , effects contributed by the excellent performance of CaO and SrO can be obtained. Although the embodiment of the present invention has been described based on the electrode structure shown in FIG. 2, it is also possible to apply an electrode structure as shown in FIG. Even in an electrode structure in which a coil 9 having a gap around the coil 8 and an outer coil 10 wound around the outside of the coil 9 and an electron emitting substance 11 filled in the gap and fixed by baking,
The effects of this invention can be obtained. Furthermore, although we have described the case where an oxide is used as a component of the electron emitting material 11, it is mixed in the form of carbonate, oxalate, etc. and applied to the electrode component, and then heated to a high temperature to form the electron emitting material. The effects of this invention can also be obtained when the compositional components are changed to oxides. As described above, according to the present invention, an alkaline earth metal oxide containing barium oxide and calcium oxide, lanthanum oxide, and yttrium oxide is contained, and the molar ratio of lanthanum oxide and yttrium oxide is specified. By using an electron-emitting material, it is possible to improve the decrease in luminous flux during the initial stage of lamp operation, and because it does not use substances harmful to the human body, such as conventional beryllium oxide, it also makes it possible to improve productivity. have an effect.

[Brief explanation of drawings]

Figure 1 is a front view showing the configuration of the arc tube section of a high-pressure mercury lamp, Figure 2 is an enlarged cross-sectional view of the electrode in Figure 1, Figure 3 is a cross-sectional view showing another electrode configuration, and Figure 4 is a cross-sectional view showing another electrode configuration.
The figure and FIG. 5 are tables showing experimental results in an example of the present invention. In the figures, the same reference numerals indicate the same or corresponding parts. 2a, 2b...electrode, 11...electron emitting material.

Claims (1)

[Scope of Claims] 1. An electrode for a discharge lamp comprising an alkaline earth metal oxide containing barium oxide and calcium oxide; lanthanum oxide; and yttrium oxide. The molar ratio of the yttrium oxide is 1:9 to 1:9.
An electrode for a discharge lamp characterized by a ratio of 19:1. 2. The electrode for a discharge lamp according to claim 1, wherein the alkaline earth metal oxide comprises barium oxide, calcium oxide, and strontium oxide.