Discharge lamp and method for manufacturing electrode for discharge lamp

Abstract

To suppress peeling of a coating layer during lamp lighting in a discharge lamp.SOLUTION: The discharge lamp 10 is provided with a pair of electrodes 20, 30, and the body part 34 of the electrode 30 as the anode is provided with the heat radiation structure 40 formed on the side surface thereof. In the heat dissipation structure 40, the groove 42 is formed along the circumferential direction, and the coating layer 44 is formed on the groove 42. In the coating layer 44, tungsten particles having a relatively small particle diameter are contained with respect to zirconium nitride as a base material.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to discharge lamps, such as short arc discharge lamps, and more particularly to coatings for electrode surfaces. [Background technology]

[0002] When a discharge lamp is turned on, the electrode tips become very hot, causing the electrode material, such as tungsten, to melt and evaporate, resulting in blackening of the discharge tube. Since blackening of the discharge tube reduces the lamp's illuminance, it is necessary to prevent this blackening.

[0003] For example, a coating method is known in which tungsten particles are attached to a portion of the outer surface of the coating (see Patent Document 1). In this method, tungsten evaporated from the electrode adheres to the tungsten particles attached to the surface of the coating layer, thereby suppressing blackening of the discharge tube.

[0004] Another known coating method is to form a coating layer on the electrode surface using ceramics made of zirconium nitride, in which the atomic concentration (%) of Zr (zirconium) is higher than the atomic concentration (%) of N (nitrogen) (see Patent Document 2). In this method, by creating a zirconium-rich state, nitrogen separated from the coating layer is recombined, allowing the coating layer to function for a long period of time. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7121932 [Patent Document 2] Japanese Patent Publication No. 2023-174123 Summary of the Invention [Problem to be solved by the invention]

[0006] In the case of short arc discharge lamps, the area near the tip of the electrode is prone to overheating due to arc discharge. In addition, while the lamp is lit, gas convection occurs within the discharge tube, occurring along the surface of the electrode. This makes the coating layer more likely to peel off. When the coating layer peels off from the electrode surface, it loses its functionality, and not only do the electrode materials, such as tungsten, evaporate and adhere to the discharge tube, but the components of the peeled coating layer also adhere to the discharge tube, resulting in a decrease in illuminance.

[0007] Therefore, it is necessary to suppress peeling of the coating layer while the lamp is operating. [Means for solving the problem]

[0008] A discharge lamp according to one aspect of the present invention comprises a discharge tube and a pair of electrodes arranged opposite each other within the discharge tube, and a coating layer is formed on the surface of at least one of the electrodes. In a discharge lamp in which a groove is formed on the side surface of at least the body of the electrode along the circumferential direction or the electrode axis direction, the coating layer can be formed on the groove.

[0009] In the present invention, the coating layer contains dispersed particles whose particle diameter is different from that of the base material of the coating layer and whose components are different from those of the base material. The base material here is the main component of the coating layer and can also be said to be configured as a matrix. Furthermore, the dispersed particles refer to particles scattered throughout the base material.

[0010] The base material can be made of various substances as long as it exhibits a coating function, and can be made of at least one of nitrides, oxides, borides, carbides, and silicides. For example, the base material can be made of ceramics.

[0011] The dispersed particles can also be made of various materials, and can be made of metal particles, for example, tungsten, molybdenum, tantalum, and / or titanium.

[0012] The particle size of the dispersed particles can be smaller than that of the base material, provided that the proportion of dispersed particles with relatively smaller particle sizes than the base material is greater in the entire coating layer.

[0013] For example, when the depth of the groove is D and the distance from the bottom of the groove to the surface of the coating layer is d, the groove can be configured to satisfy the following formula: 0.02 ≦ d / D < 1

[0014] Another aspect of the present invention is a method for manufacturing an electrode for a discharge lamp, which involves forming an electrode having a columnar body portion and a tapered portion at the tip, placing a powder of base material particles consisting of at least one of nitride, oxide, boride, carbide, and silicide, and a powder of dispersed particles having a particle size different from that of the base material and of a different component from that of the base material, in a solvent, applying the solvent to at least the side of the body portion, and heat-treating the electrode to form a coating layer on the side of the body portion. [Effects of the Invention]

[0015] As described above, according to the present invention, in a discharge lamp, peeling of the coating layer can be suppressed while the lamp is lit. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic plan view of a discharge lamp according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic plan view of an electrode (anode). [Figure 3] 10 is a graph showing the change in illuminance over time of the discharge lamp of the example and the discharge lamp of the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0017] The discharge lamp according to this embodiment will be described below with reference to the drawings.

[0018] FIG. 1 is a schematic plan view of a discharge lamp according to this embodiment.

[0019] The short arc type discharge lamp 10 is a large discharge lamp capable of outputting high-intensity light, and includes a substantially spherical discharge tube (arc tube) 12 made of transparent quartz glass, within which a pair of tungsten electrodes 20, 30 are arranged facing each other (coaxially). On both sides of the discharge tube 12, sealed tubes 13A, 13B made of quartz glass are connected to and integrally formed with the discharge tube 12. A discharge space DS within the discharge tube 12 is filled with mercury and a rare gas such as argon gas, or a mixed gas.

[0020] Electrode 20, which serves as the cathode, is supported by electrode support rod 17A. Sealed in sealed tube 13A are a glass tube (not shown) through which electrode support rod 17A is inserted, lead rod 15A that connects to an external power supply, and metal foil 16A that connects electrode support rod 17A to lead rod 15A. Similarly, for electrode 30, which serves as the anode, are sealed with mounting parts such as a glass tube (not shown) through which electrode support rod 17B is inserted, metal foil 16B, and lead rod 15B. Furthermore, bases 19A and 19B are attached to the ends of sealed tubes 13A and 13B, respectively.

[0021] When a voltage is applied to the pair of electrodes 20, 30, an arc discharge occurs between the electrodes 20, 30, and light is emitted toward the outside of the discharge tube 12. Here, a power of 1 kW or more is input. The light emitted from the discharge tube 12 is guided in a predetermined direction by a reflector (not shown).

[0022] 2 is a schematic plan view of the electrode (anode) 30. The electrode (cathode) 20 can also have a similar structure.

[0023] The electrode 30 has an electrode tip surface 32T and is composed of a tapered portion (hereinafter referred to as the tip tapered portion) 32 and a columnar portion (hereinafter referred to as the body portion) 34 connected to the electrode support rod 17B. Here, the electrode 30 is composed of an integral body, but it is also possible to form the electrode 30 by joining a member having the tip tapered portion 32 and a member having the body portion 34 by solid-state bonding such as diffusion bonding. It is also possible to join them via an intermediate member. The electrode 30 can be composed of tungsten, molybdenum, or an alloy thereof.

[0024] A coating layer 44 (solid area in FIG. 2) is formed on the side surface 34S of the body portion 34, and grooves 42 are formed in the circumferential direction (around the electrode axis) at a predetermined pitch relative to the electrode axis C (see the enlarged portion (symbol B) of the side surface 34S in FIG. 2). The side surface 34S of the body portion 34 on which the coating layer 44 and grooves 42 are formed has a higher emissivity than the bare surface of the electrode 30, i.e., a surface not equipped with any special heat dissipation function, and thus functions to enhance heat dissipation. The grooves 42 may be grooves along the electrode axis direction.

[0025] Here, the portion where the coating layer 44 and grooves 42 are formed (hereinafter referred to as the heat dissipation structure 40) is configured over the entire side surface 34S of the body portion 34. However, the heat dissipation structure 40 may be configured to be provided on only a portion of the side surface of the body portion 34. The heat dissipation structure 40 may also be provided on the tip-side tapered portion 32. Alternatively, the heat dissipation structure 40 may be configured to have only the coating layer 44 without the grooves 42, or to have only the grooves 42.

[0026] In the coating layer 44, a ceramic with thermal properties (including heat resistance and heat dissipation) serves as the base material (matrix). The ceramic may be composed of nitrides such as zirconium nitride, silicon nitride, and aluminum nitride, oxides such as aluminum oxide and zirconium oxide, carbides such as zirconium carbide and silicon carbide, silicides such as tantalum silicide, or borides such as zirconium boride, or a combination of at least two or more of these. In this example, the base material is ceramics made of zirconium nitride (ZrN).

[0027] Furthermore, particles of a component (substance) different from the base material (ZrN) are dispersed in the coating layer 44 (hereinafter referred to as dispersed particles). The dispersed particles can be composed of metal particles, and can be made of at least one of tungsten, molybdenum, tantalum, and titanium, for example. In this example, individual tungsten (W) particles are dispersed in the ceramic base material of the coating layer 44.

[0028] The tungsten particles (W) that are dispersed particles have a smaller particle size (grain size) than the zirconium nitride (ZrN) particles that serve as the matrix. However, it is not necessary for all tungsten particles (W) to be smaller in particle size than the zirconium nitride (ZrN) particles; some tungsten particles may be smaller. It is sufficient that the proportion of tungsten particles (W) that are relatively smaller in particle size than zirconium nitride (ZrN) is greater throughout the coating layer 44. Here, the particle size of zirconium nitride (ZrN) is set to a range of 1 μm to 10 μm, and the particle size of tungsten (W) is set to a range of 0.1 μm to 1 μm.

[0029] In the coating layer 44, small tungsten (W) particles are interspersed between the zirconium nitride (ZrN), forming a dense structure between the particles. This improves the strength of the coating layer 44 and prevents peeling of the coating layer 44 due to gas convection. The tungsten particles that have penetrated into the coating layer 44 are less likely to fall out, so they do not cause blackening.

[0030] Furthermore, the dense structure of the coating layer 44 firmly holds the zirconium nitride (ZrN) particles together due to the anchor effect that occurs when the particles intersect with each other. Furthermore, the dense structure of the coating layer 44 increases its strength, allowing it to be made thicker. The dense structure prevents the coating layer 44 from peeling, allowing the thermal performance (heat dissipation and heat resistance) of the coating layer 44 to be maintained for a long period of time.

[0031] If the amount of tungsten (W) particles is too large, the tungsten particles will adhere to each other and form large clumps that will not penetrate between the zirconium nitride (ZrN) particles and will be scattered by gas convection. To prevent this, the weight percentage of the tungsten (W) particles contained in the coating layer 44 is determined. Here, the weight percentage (%) of the tungsten (W) particles relative to the total weight of the coating layer 40 is determined to be 20 wt% or less. Preferably, the weight percentage (%) of the tungsten (W) particles is determined to be 2 wt% or less. This prevents the dispersed particles from adhering to each other and makes it easier for each particle to be dispersed in the base material.

[0032] The grooves 42 of the heat dissipation structure 40 can be formed by laser, cutting, or the like. The grooves 42 can be formed at a very small pitch or at a wide pitch like a screw groove. For example, the grooves 42 can be formed at a pitch of 200 μm to 800 μm and at a depth of 100 μm to 500 μm. By forming a coating layer 44 over such grooves 42, the amount of zirconium nitride (ZrN) that serves as the base material increases, which helps to suppress the electrode temperature.

[0033] Furthermore, since the particle size of zirconium nitride (ZrN) and tungsten (W) is minute, the particles can easily penetrate into the minute cracks that occur when the grooves 42 are formed, and the anchor effect can prevent the coating layer 44 from peeling off from the electrode 30.

[0034] Here, to prevent the coating layer 44 from being too thin to exhibit thermal performance and to prevent the grooves 42 from being filled with the coating layer 44, the following equation (1) is satisfied, where D is the depth of the groove and d is the distance from the bottom of the groove to the surface of the coating layer. 0.02 ≦ d / D < 1 (1)

[0035] The coating layer 44 may be made of a metal base material containing ceramic particles as dispersed particles. The particle size of some of the dispersed particles may be larger than or the same as that of the base material. The base material and dispersed particles may be made of any material that does not melt while the lamp is lit. For example, the coating layer 44 may be made of a base material and dispersed particles made of a material with a melting point of 1500°C or higher. In this case, it is preferable to combine dispersed particles with a melting point higher than that of the base material to achieve the above-mentioned effects.

[0036] The discharge lamp described above can be manufactured, for example, by the following manufacturing method.

[0037] First, an electrode is formed with a cylindrical body and a tapered tip. To form a groove, a circumferential groove is formed on the side of the body using a laser, cutting, or other processing. Next, a coating layer is applied over the groove. Powders of the materials that make up the ceramic described above and tungsten powder with a particle size relatively smaller than that of the ceramic powder are dispersed in a solvent. The amount of tungsten powder added is less than that of the ceramic powder. Preferably, the amount of tungsten powder added is 20% or less by weight of the total weight. The coating can be applied using known methods such as spraying, vapor deposition, sputtering, or CVD. The resulting product is then heat-treated in a heating device such as a vacuum furnace. [Example]

[0038] The discharge lamp of this embodiment will be described below with reference to FIG.

[0039] The discharge lamp of the example has a configuration corresponding to the discharge lamp of the embodiment, and is configured as a short arc type discharge lamp. By the manufacturing method described above, a coating layer containing tungsten (W) particles in a zirconium nitride (ZrN) base material was formed on the side of the body part of the electrode. In addition, a groove was formed on the side of the electrode.

[0040] Then, the coating layer 44 was formed so that the weight percentage (%) of tungsten (W) particles was 1 weight percent. When the coating layer was observed using a scanning electron microscope (SEM), it was confirmed that the tungsten (W) particles had entered between the zirconium nitride (ZrN), forming a dense structure.

[0041] 3 is a graph showing the change in illuminance over time for the discharge lamp of the example and the discharge lamp of the comparative example. The discharge lamp of the comparative example has a coating layer that does not contain tungsten, but otherwise has the same configuration as the discharge lamp of the example.

[0042] In the graph of Figure 3, the change in illuminance of the discharge lamp of the comparative example is indicated by the symbol L1, and the change in illuminance of the discharge lamp of the example is indicated by the symbol L2. As shown in Figure 3, it was confirmed that the discharge lamp of the example maintains its illuminance over time, that is, blackening is suppressed. Note that, since it was confirmed that the illuminance is maintained even when the weight percentage (%) of tungsten (W) particles is 1 weight percent, it is considered that the illuminance is similarly maintained even at a weight percentage higher than that (e.g., 2 weight percent). [Explanation of symbols]

[0043] 10. Discharge lamp 30 electrode (anode) 40 Heat dissipation structure 42 Groove 44 coating layer

Claims

1. A discharge tube; a pair of electrodes disposed opposite each other within the discharge tube; A coating layer is formed on the surface of at least one of the electrodes; A discharge lamp characterized in that the coating layer contains dispersed particles whose particle diameter is different from that of the base material of the coating layer and whose component is different from that of the base material.

2. the base material is ceramic, 2. The discharge lamp according to claim 1, wherein the dispersed particles are metal particles.

3. 3. The discharge lamp according to claim 1, wherein the particle diameter of the dispersed particles is smaller than the particle diameter of the base material.

4. The particle size of the base material of the coating layer is set in the range of 1 to 10 (μm), 3. The discharge lamp according to claim 1, wherein the particle size of the dispersed particles is set in the range of 0.1 to 1 (μm).

5. 3. The discharge lamp according to claim 1, wherein the base material is made of at least one of nitride, oxide, boride, carbide, and silicide.

6. 3. The discharge lamp according to claim 1, wherein the dispersed particles are made of at least one of tungsten, molybdenum, tantalum, and titanium.

7. A groove is formed in at least the side surface of the body portion of the electrode along the circumferential direction or the electrode axis direction, 3. The discharge lamp according to claim 1, wherein the coating layer is formed on the groove.

8. 8. The discharge lamp according to claim 7, wherein the following formula is satisfied, where D is the depth of the groove and d is the distance from the bottom of the groove to the surface of the coating layer. 0.02≦d / D<1

9. An electrode having a cylindrical body and a tapered tip is formed. A powder of particles of a base material made of at least one of nitride, oxide, boride, carbide, and silicide and a powder of dispersed particles having a particle size different from that of the base material and a component different from that of the base material are placed in a solvent; Applying the solvent to at least the side surface of the body portion; A method of manufacturing an electrode for a discharge lamp, comprising the steps of: forming a coating layer on the side surface of the body portion by heat treatment;

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