JPS644304B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to electrodes used in discharge lamps such as high-pressure mercury lamps and low-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 discharge lamps such as high-pressure mercury lamps and low-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. It concerns the improvement of substances. The details of this invention will be explained below with reference to a high pressure metal vapor discharge lamp. The arc tube section 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 6a and 6 are connected through sealed molybdenum foils 4a and 4b, respectively.
connected to b. Further, at least one end of the arc tube 1 is provided with an auxiliary electrode 3 for facilitating starting, and is connected to a conducting wire 7 via a molybdenum foil 5. The main electrodes 2a and 2b are
It has a configuration as shown in FIG. 2, in which an inner coil 9 and an outer coil 10 made of a heat-resistant metal such as tungsten are wound around an electrode core wire 8 made of a heat-resistant metal such as tungsten. Electron emitting material 11 is fixed to the surfaces of inner coil 9 and outer coil 10. The electron emitting substance 11 is tungstate of barium, strontium, and calcium (Ba ₂ -
xSrxCaWO ₆ However, the value of x is 0 to 0.5. A mixture _{of tungstate and beryllium oxide (BeO) and yttrium oxide (Y 2 O 3 ) was used} . In the case of the former electron-emitting material, the melting point of Y ₂ O ₃ is high and it is difficult to adhere to the electrode base, and part of the electron-emitting material peels off during lamp lighting, resulting in an increase in starting voltage during the lamp's life. This causes phenomena such as defective development of the lamp and a rapid decrease in luminous flux maintenance rate due to consumption of the electron radioactive material, resulting in a short lamp life. Such drawbacks are based on the high melting point of Y ₂ O ₃ , therefore mixtures of oxides of barium, strontium and calcium (BaO, SrO, CaO)
Even when using an electron emitting material consisting of and Y ₂ O ₃ ,
The above-mentioned drawbacks were not improved. On the other hand, in the case of the latter electron-emitting material consisting of tungstate, BeO, and Y ₂ O ₃ , the luminous flux deterioration characteristics and starting characteristics after long-term lighting are lower than those of the former due to the effect that BeO and Y ₂ O ₃ form a solid solution. It has the advantage of being extremely stable compared to other electron emitting materials. This is described, for example, in Japanese Patent Publication No. 55-9777. 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 in which black deposits were often generated in the initial stage of lighting was observed. This black deposit gradually turns white as the lighting time passes, so it does not affect the lamp's life characteristics in any way, but it may cause the luminous flux value at the initial stage of lighting to be slightly lower, or the large current at the time of startup or ion bombardment. It has the disadvantage that the luminous flux maintenance rate is low in blinking and lighting conditions, where the electron emitting material is often consumed due to intense energy. This invention was made in view of these conventional drawbacks, and is based on tungstates of barium, strontium, and calcium (Ba ₂ -
By using an electron-emitting material containing xSrxCaWO ₆ (where the value of In addition, it provides a long-life electrode with excellent luminous flux maintenance even in flashing lighting that consumes a large amount of electron emitting material, and 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
The electrode components were constructed using a 1.2 mm tungsten rod and 0.6 mm diameter tungsten wires as the inner and outer coils 9 and 10. On the other hand, tungstate of barium, strontium, and calcium (Ba _1.8 Sr _0.2 CaWO ₆ )...15.2
(mol%), beryllium oxide (BeO)...76.3 (mol%), and yttrium oxide (Y ₂ O ₃ )...8.5 (mol%) were placed in butyl acetate together with a nitrocellulose lacquer, and the mixture was placed in a ball mill. was carried out for 24 hours to create a suspension, the electrode component was immersed in this suspension, the electron emitting material 11 was applied to the electrode component, and after drying, the electrode component was immersed in the suspension in an argon gas atmosphere. The electron emitting material 11 was fixed to the electrode component by heating at 1700° C. for 2 minutes. 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 86%, 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 blinks was 70%. Next, an example of the present invention will be described. Lanthanum oxide (La ₂ O ₃ ) and yttrium oxide (Y _{2 O 3 ) are added to tungstate of barium, strontium, and calcium (Ba 1.8 Sr 0.2 CaWO 6 ) in} various proportions. The electron emitting material 11 mixed in step 1 is fixed to the electrode component in the same manner as in the conventional example described above to form the electrode 2.
Various types of a and 2b were manufactured and tested using them in a 400W high-pressure mercury lamp. The results are shown in Table 1.

[Table] As is clear from Table 1, when the electron emitting material 11 containing La ₂ O ₃ and Y ₂ O ₃ is used, the conventional
The luminous flux maintenance rate after 50 blinks is improved compared to the case of using the 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. It is known that the blinking frequency of blinking lighting is related to the scattering wear and tear of the electrode, and it can be seen that the electrode formed by implementing the present invention has excellent life characteristics even under such severe conditions. By the way, 6000 flashes are continuous lights.
This corresponds to 12,000 to 18,000 hours, and the electrode made by implementing the present invention has excellent long-life characteristics. Regarding this point, for example, see the Mitsubishi Electric Technical Report.
Vol.40, No.9 P1398-P1399 (1966) or Institute of Electrical Engineers of Japan Light Source and Related Devices Study Group Material LS-74-10 P6
(1974). By the way, the cause of the above-mentioned characteristic difference 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 the electrode constituent members, and also have the function of maintaining an appropriate level of active barium production 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 in order to fix it to the electrode component, BeO in the solid solution is mixed with the electron emitting material 11. Partial reaction with tungstate
A relatively low melting point composite compound such as BeO and 3BaO is formed, and when the arc spot moves to the electrode component near where this composite compound is formed when the lamp is turned on, the composite compound suddenly becomes hot and Be , Ba selectively evaporates and adheres to the inner wall of the arc tube, causing a decrease in luminous flux at the initial stage of lighting. Furthermore, when a large current flows during blinking lighting, BeO and BaO are selectively scattered due to ion bombardment.
It becomes difficult to supply free Ba from electron-emitting materials,
If the flashing is repeated, the luminous flux maintenance rate will decrease significantly. 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, La ₂ O ₃ and Y ₂ O ₃ form a solid solution or a stable composite compound to emit electrons. In addition to lowering the melting point of the substance, improving its adhesion to electrode components, and maintaining an appropriate level of active barium production during lighting, La ₂ O ₃ and Y ₂ O ₃ are also tungstic acid. Since it does not react with salt, even at the initial stage of lighting,
Furthermore, even during the lifetime, the generation of Ba from the electron emitting material 11 is maintained at an appropriate level in a stable state, so that the luminous flux maintenance factor is stable and good throughout the lifetime. As described above, the molar ratio of La ₂ O ₃ and Y ₂ O ₃ in the electron emitting material 11 is 19:1 to 1;9.
Within this range, the above-mentioned improvement effect is significant;
When the molar ratio of La ₂ O ₃ is larger than 19:1, the melting point of the solid solution increases significantly, and the adhesion of the electron emitting material 11 to the electrode component decreases, resulting in a decrease in the luminous flux maintenance rate after 6000 blinks. As shown in Table 1, this is somewhat lower than in the conventional example. Similarly, when the molar ratio of Y ₂ O ₃ is greater than 1:9, the melting point of the solid solution increases significantly, and the adhesion of the electron emitting material 11 to the electrode component decreases, making it difficult to maintain the luminous flux after 6000 blinks. rate decreases. Here, the tendency of the experimental results in Table 1 above will be explained based on FIG. 4. In Figure 4, the vertical axis represents the luminous flux maintenance factor, and the horizontal axis represents the luminous flux maintenance factor.
La ₂ O ₃ /La ₂ O ₃ +Y ₂ O ₃ and La ₂ O ₂ :Y ₂ O ₃ are shown, respectively. In the figure, P ₁ to _{P 6} indicate the measured values after 50 blinks, Q ₁ to Q ₆ indicate the measured values after 100 blinks, and each subscript of P ₁ to P ₆ and Q ₁ to _{Q 6} is 1.
-6 correspond to Examples 1-6 in Table 1. As is clear from the figure, La ₂ O ₃ : Y ₂ O ₃ is 1:
In the case of less than 9 and in the case of greater than 19:1,
It is understood that in each experiment after 50 and 100 blinks, the luminous flux maintenance rate 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 amount of the electron emitting material 11 peeled off was measured. The results are shown in FIG. 5, and R ₁ to R ₆ correspond to Example 1 (P ₁ , Q 1 ) to Experimental Example ₆ (P 6 , Q ₁ ) in Table 1 and FIG.
Q ₆ ), and as a new experimental example Ba _1.8 Sr _0.2
CaWO ₆ :Y ₂ O ₃ = 15.2 = 84.8 (R ₀ ) and Ba _1.8 Sr _0.2
CaWO ₆ :La ₂ O ₃ = 15.2 = 84.8 (R ₇ ) was added. 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 peeled off 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 above measurement test, mechanical shock is applied to the electrode after the heat treatment, and the resulting electron Regarding the rationality of evaluating the aging of radioactive materials based on the amount of detachment, the reasons are 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 basic metals, so they are susceptible to mechanical shock and impact from ion electrons during use, and are susceptible to peeling and disintegration. It is stated that it is easy to wear out 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 is shown.
BeO and BaO or SrO form a solid solution,
It is stated that the melting point is lowered and the adhesive strength 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. It is understood that by lowering the temperature, the electron emitting material is melted during this heat treatment, so that 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 since the temperature is sufficiently low, the adhesive strength of the electron emitting material 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 the above examples, the effects of the present invention were shown when the mol% of barium, strontium, and calcium tungstates was the same as in the conventional example, but the same effect can be obtained even when the mol% is different. Furthermore, the effects of the present invention can be obtained even when a small amount of Al ₂ O ₃ , SiO ₃ and tungsten are further added to the composition of the electron emitting material 11 according to the present invention. Further, although the embodiment of the present invention has been described based on the electrode structure shown in FIG. 2, for example, an electrode structure as shown in FIG. Even in an electrode structure in which an inner coil 9 having a gap around it and an outer coil 10 wound around the outer side of the inner coil 9, an electron emitting substance 11 is filled in the gap and fixed by baking.
The effects of this invention can be obtained. Although the above description is for a high-pressure mercury lamp, the same effect can be obtained with a metal vapor discharge lamp other than a high-pressure mercury lamp such as a high-pressure sodium lamp, or a low-pressure discharge lamp such as a fluorescent lamp. As stated above, this invention is based on barium, strontium, and calcium tungstates (Ba ₂ -xSrxCaWO ₆ , where X is 0 or 0).
By using an electron-emitting material containing lanthanum oxide and yttrium oxide with a molar ratio of 0.5) to 1:9 to 19:1, a decrease in luminous flux at the initial stage of lamp operation and a decrease in luminous flux during operation with repeated blinking can be reduced. In addition to providing an electrode with a long lifespan, it also has excellent effects such as improving productivity because it does not use substances harmful to the human body, such as conventional beryllium oxide.

[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 sectional view of the electrode in Figure 1, Figure 3 is a sectional view showing another electrode configuration, and Figures 4 and 5. The figure is a diagram showing experimental results of an example of this invention. In the figure, 2a and 2b are electrodes, and 11 is an electron emitting material. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1 Barium, strontium, calcium tungstate (Ba ₂ -xSrxCaWO ₆ , where the value of X is 0 to 0.5) and a molar ratio of 1:9 to
An electrode for a discharge lamp, comprising an electron emitting substance containing lanthanum oxide and yttrium oxide in a ratio of 19:1.