Short-arc type discharge lamp with a scale-like structure and a coating film on the outer surface of at least one electrode

Abstract

Short-arc discharge lamp, comprising a pair of electrodes opposite each other in a light-emitting tube, a scale-like structure formed on an outer surface of at least one of the electrodes of the pair of electrodes, and a coating film that covers the outer surface along with the scale-like structure formed on the outer surface, wherein the scale-like structure has a plurality of plate-like projections that project beyond the outer surface in a direction inclined with respect to a direction perpendicular to the outer surface, wherein each plate-like projection has an outer surface facing away from the rest of the electrode, the angle of which formed with the outer surface being an obtuse angle, and a back surface, the angle of which formed with the outer surface being an acute angle, wherein the coating film comprises at least one compound selected from the group consisting of metal oxides, metal carbides, metal borides, metal silicides and metal nitrides and mixtures thereof, and Part of the coating film lies in a space between the back surface and the outer surface.

Description

CROSS-REFERENCE TO SIMILAR REGISTRATIONS

[0001] The present invention contains content relating to the Japanese patent application JP 2022 - 10 699 A, filed with the Japanese Patent Office on June 29, 2020, to which reference is made herein. TECHNICAL AREA

[0002] The present invention relates to a short-arc type discharge lamp and in particular to a short-arc type discharge lamp in which a heat-radiating layer is formed on an outer surface of an electrode in order to lower the electrode temperature, especially when the lamp is switched on. STATE OF THE ART

[0003] For example, a short-arc discharge lamp (hereinafter also referred to simply as a "lamp") is used as a light source in an irradiation apparatus used in a process for manufacturing a semiconductor element, a liquid crystal display element, or similar, or in various types of projectors. The short-arc discharge lamp is designed such that an anode and a cathode are arranged opposite each other in a light-emitting tube, and a light-emitting compound such as mercury or xenon gas is sealed inside the light-emitting tube.

[0004] In such a short-arc discharge lamp, it is known that due to the high temperature stress on the anode when the lamp is switched on, electrode material evaporates due to overheating of the anode or similar factors, and the resulting evaporated material adheres to an inner wall of the light-emitting tube, thus reducing its light transmission. This is known as blackening.

[0005] To solve this problem, a technique for suppressing the temperature rise of an electrode by forming a heat-radiating layer on an electrode surface is known, and subsequent patent document 1 publishes a lamp in which a heat-radiating layer containing at least one metal oxide is formed on the outer surface of the electrode except for the neighborhood of the electrode tip.

[0006] Such a heat-emitting layer has the problem that it adheres poorly to the electrode surface during manufacturing and is easily detached. In particular, ceramics like metal oxides are stable even at high temperatures, and therefore this problem is noticeable.

[0007] While the coefficient of thermal expansion of the tungsten forming the electrode is, for example, 4.5 · 10 -6 The coefficient of thermal expansion of the zirconium oxide (ZrO2) forming the heat-radiating layer is 10.5 · 10 / K. -6 / K. There is therefore a large difference between these coefficients of thermal expansion, and consequently the problem arises that the heat-radiating layer is peeled off due to expansion and contraction of the electrode caused by switching the lamp on and off.

[0008] To solve this problem, attempts were made to increase the unevenness of the electrode surface by sandblasting or similar methods and to increase the adhesion strength through an anchoring effect.

[0009] DE 10 2005 007 767 A1 and JP 2019 - 194 982 A describe short-arc discharge lamps with electrodes whose surface is structured. DOCUMENTS OF THE STATE OF THE TECHNOLOGY PATENT DOCUMENT

[0010] Patent document 1: JP 2004 - 259 639 A SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0011] The irregularities formed by creating grooves through incisions in the electrode surface, sandblasting, or similar processes, only result in depressions on the electrode surface. Although there is some anchoring effect against a horizontal force with respect to the electrode surface, the anchoring effect against peeling in a perpendicular direction to the electrode surface cannot be described as strong, and peeling can occur.

[0012] In view of the above problems, it is an object of the present invention to provide a short-arc type discharge lamp in which a pair of electrodes is arranged opposite each other within a light-emitting tube and in which a heat-radiating layer is formed on an outer surface of at least one electrode of the pair of electrodes, wherein the short-arc type discharge lamp has a long life and excellent heat-radiating capability and is free from peeling of the layer. MEANS TO SOLVENT THE PROBLEM

[0013] A short-arc discharge lamp according to the invention comprises a pair of electrodes arranged opposite each other in a light-emitting tube, wherein a scale-like structure is formed on an outer surface of at least one electrode of the pair of electrodes, and a coating film covers the outer surface together with the scale-like structure formed on the outer surface. The scale-like structure comprises a plurality of plate-shaped projections that project from the outer surface in a direction inclined relative to a direction perpendicular to the outer surface, each plate-shaped projection having an outer surface facing away from the rest of the electrode, the angle of which with the outer surface is an obtuse angle, and a back surface, the angle of which with the outer surface is an acute angle.The coating film contains at least one of the following: metal oxides, metal carbides, metal borides, metal silicides, and metal nitrides. Part of the coating film extends into a space enclosed between the back surface and the outer surface.

[0014] Because the outer surface of the electrode, according to this configuration, is covered with a coating film (heat-radiating layer) with high emissivity and contains at least one of metal oxides, metal carbides, metal borides, metal silicides, and metal nitrides, the electrode exhibits excellent heat emission. Since a portion of the coating film extends into the space enclosed between the back surface of the plate-shaped projection and the outer surface of the electrode, an anchoring effect can be effectively achieved to counteract a peeling force of the coating film in a direction perpendicular to the outer surface, thus ensuring a long service life for the short-arc discharge lamp according to the invention without causing the film to peel.

[0015] In the short-arc discharge lamp according to the invention, the outer surface on which the scale-like structure is formed can be an outer peripheral surface of the electrode with a cylindrical body. The projection can protrude in a direction inclined in the circumferential direction of the electrode with respect to the perpendicular direction of the outer peripheral surface. The coating film can have a film thickness of 5 µm or more and 200 µm or less. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation illustrating a configuration of a short-arc discharge lamp according to the invention; Fig. 2 is an enlarged view of an area P located in Fig. 1 short-arc discharge lamp shown; Fig. 3A is an enlarged photograph of the outer surface of an anode before the formation of a coating film (surface image); Fig. 3B is an enlarged photograph of an outer surface of the anode before the application of the coating film (cross-sectional image); Fig. Figure 4 is a view illustrating the shape direction of the plate-shaped projections; Fig. 5A, Fig. 5B and Fig. 5C are enlarged views of a scale-like structure; Fig. 6 is an enlarged view of an area Q of which in Fig. 3B shown anode; Fig. Figure 7 is an enlarged view of a circumferential cross-section of a conventional structure; Fig. 8 is a diagram that schematically shows the state of a turning operation; Fig. 9 is the evaluation result of examples and similar things and Fig. Figure 10 is a schematic representation showing a state of a milling operation. FORM OF EXECUTION OF THE INVENTION

[0016] An embodiment of a short-arc discharge lamp according to the invention is described below with reference to the drawings. The following drawings are schematic; the dimensional relationships in the drawings do not necessarily correspond to the actual dimensional relationships, and the dimensional relationships within the drawings do not necessarily correspond.

[0017] The following description may refer to an XYZ coordinate system. In this description, when a direction is specified and positive and negative directions are distinguished, the directions are described with a positive or negative sign, such as "+X direction" and "-X direction." If a direction is specified without distinguishing between a positive and a negative direction, the direction is simply referred to, for example, as "X direction." Thus, in this description, a simple designation of "X direction" refers to both the "+X direction" and the "-X direction." The same applies to the Y direction and the Z direction.

[0018] Fig. Figure 1 is an illustrative representation of an embodiment of a short-arc discharge lamp according to the invention. A short-arc discharge lamp 100 (hereinafter referred to as "lamp 100") comprises a light-emitting tube 1, an anode 2 and a cathode 3, which are arranged opposite each other inside the light-emitting tube 1, and connecting rods 4, which support the anode 2 and the cathode 3, respectively.

[0019] The lamp 100 of this embodiment is a large lamp used in an irradiation apparatus or similar, which is used in a process for the manufacture of semiconductor elements, liquid crystal display elements or similar, and has, for example, a rated power of 2 kW to 35 kW.

[0020] The light-emitting tube 1 is formed by inflating the center of a glass tube. The light-emitting tube 1 is a section of a glass tube whose inner diameter increases in the X-direction from both ends towards the center. The outer shape of the light-emitting tube is spherical or elliptical.

[0021] The light-emitting tube 1 has a pair of sealed tube sections 11 that extend continuously in opposite directions from both ends of the light-emitting tube 1 in the X-direction. The light-emitting tube 1 is formed integrally with the sealed tube sections 11, for example, from quartz glass. The central axes of the pair of sealed tube sections 11 overlap each other and are connected by an axis X1. Fig. 1 illustrates.

[0022] A light emission chamber S1 is formed inside the light-emitting tube 1. In addition to a light-emitting substance such as mercury, a starting buffer gas such as argon gas or xenon gas is expediently enclosed in the light emission chamber S1.

[0023] Anode 2 and cathode 3 are arranged opposite each other in the X-direction inside the light-emitting tube 1. In the present embodiment, the short-arc discharge lamp is a discharge lamp in which anode 2 and cathode 3 are arranged opposite each other with a distance of 40 mm or less (value at room temperature without thermal expansion). In the present embodiment, anode 2 is made of tungsten and cathode 3 is made of thorium oxide-tungsten.

[0024] The anode 2 and the cathode 3 are each connected to the connecting rods 4, which extend in the X direction within the sealed tube section 11. The anode 2 and the cathode 3 are each attached to the tips of the connecting rods 4. A central axis of the connecting rods 4 can overlap with the axis X1. The connecting rods 4 are made of a material containing a high-melting-point metal such as tungsten.

[0025] Each socket 7 covers one side of the sealed tube section 11, with the side facing away from the anode 2 and the cathode 3. Each socket 7 is electrically connected to the connecting rod 4.

[0026] Fig. 2 is an enlarged representation of an area P that is in Fig. In the lamp 100 shown in Figure 1, a coating film 5 is provided as a heat-radiating layer on an outer surface of the anode 2. The outer surface of the anode 2 is, in this case, an outer surface with the exception of a pointed surface 2a facing the cathode 3. Because the temperature of the pointed surface 2a of the anode 2 can rise to a temperature equal to or higher than the melting point of the coating film 5 when the lamp is switched on, the coating film 5 is not present on the pointed surface 2a of the anode 2 in the present embodiment. Although the coating film 5 is provided in the present embodiment on an outer peripheral surface 2b of a cylindrical body centered about the axis X1 on the outer surface of the anode 2, the coating film 5 can also be provided on an inclined surface 2c located between the outer peripheral surface 2b and the pointed surface 2a.Additionally, the coating film 5 can also be provided on a backward inclined surface 2d located on a +X side of the outer peripheral surface 2b of the anode 2.

[0027] For the material of the coating film 5, melting point, vapor pressure, emissivity, coefficient of thermal expansion, and similar properties are important. To lower the temperature of the anode 2, the coating film 5 is preferably made of a material with high emissivity to increase the amount of heat radiation. The coating film 5 can therefore be a high-emissivity film to improve heat dissipation.

[0028] The material of the coating film 5 contains at least one of metal oxides, metal carbides, metal borides, metal silicides, and metal nitrides. Advantageously, a material with a melting point of 2000 °C or higher can be used as the material of the coating film 5, and examples include aluminum oxide (Al₂O₃), zirconium oxide (ZrO₂), zirconium carbide (ZrC), zirconium boride (ZrB₂), tantalum silicide (TaSi₂), and zirconium nitride (ZrN).

[0029] Fig. 3A and Fig. 3B are enlarged photographs (SEM images) of the outer surface of the anode 2 before the coating film 5 is formed, wherein Fig. 3A an image of the surface and Fig. Figure 3B shows a cross-sectional view. A fine, scale-like structure is formed on the outer surface of the anode 2. The scale-like structure is characterized by a scaly surface condition and a multitude of plate-like projections 6. The plate-like projections 6 extend from the outer surface of the anode 2 in a direction inclined relative to a direction perpendicular to the outer surface of the anode 2.

[0030] Fig. Figure 4 is a view showing one shape direction of the plate-like projections 6. Fig. 5A, Fig. 5B and Fig. 5C are enlarged views of the scale-like structure. Fig. 5A is an enlarged view of an axial cross-section of anode 2, Fig. 5B an enlarged view of one plane of anode 2 and Fig. 5C an enlarged view of a circumferential cross-section of anode 2. In Fig. 5A, Fig. 5B and Fig. 5C the axial direction of the anode 2 is defined as the X direction, the circumferential direction (tangential direction in the circumferential direction) as the Y direction and the perpendicular direction is defined as the Z direction.

[0031] The plate-like projection 6 is formed by peeling away an electrode surface at an acute angle, for example by turning. More precisely, the plate-like projection 6 is produced by pressing a cutting tool against the outer peripheral surface 2b while the anode 2 is rotated circumferentially. As in Fig. As shown in Figure 4, the plurality of plate-like projections 6 are shaped such that they all project in the same direction. The plate-like projection 6 of the present embodiment projects in a direction that is inclined in the circumferential direction (Y-direction) of the anode 2 with respect to the perpendicular direction (radial direction of the outer peripheral surface 2b) of the outer peripheral surface 2b.

[0032] The plate-shaped projection 6 has an outer surface 61, the angle formed with the outer peripheral surface 2b of which is an obtuse angle, and a back surface 62, the angle formed with the outer peripheral surface 2b of which is an acute angle (see Fig. 5C). The angle formed with the outer peripheral surface 2b is an angle formed with the tangential direction of the outer peripheral surface 2b in a region in which the plate-shaped projection 6 is arranged when the outer peripheral surface 2b has a curved surface shape.

[0033] Fig. 6 is an enlarged view of region Q of the in Fig. 3B shown anode 2. An angle θ formed by the back surface 62 of the plate-shaped projection 6 and the outer peripheral surface 2b is between 5 and 30°.

[0034] The height H from the outer peripheral surface 2b to a projecting end 62a of the back surface 62 of the plate-shaped projection 6 is 3 to 15 µm.

[0035] The projection length L of the back surface 62 of the plate-shaped projection 6, viewed in the perpendicular direction (Z-direction) to the outer peripheral surface 2b, is 10 to 50 µm. The projection length L is a length in the Y-direction from a foot end 62b to the projecting end 62a of the back surface 62.

[0036] The width of the plate-shaped projection 6 in the X direction is approximately 10 µm at the minimum and approximately 0.4 mm at the maximum.

[0037] The coating film 5 is produced by dispersing particles (for example, zirconium oxide (ZrO2) with a particle size of 10 µm or less) of the material forming the coating film 5 in a solvent (for example, a solvent composed of nitrocellulose and butyl acetate), applying the mixture to the outer peripheral surface 2b of the anode 2 with a brush, drying the coating at 150 °C for 30 minutes, and then performing a heat treatment at 1900 °C for 120 minutes in a vacuum atmosphere. During this application, particles forming the coating film 5 enter a gap between the back surface 62 of the plate-shaped projection 6 and the outer peripheral surface 2b (in Fig. 5A, Fig. 5B and Fig. 5C are the particles of the coating film 5 (schematically represented as circles). As in Fig. As shown in Figure 5C, the coating film 5 is formed in a state in which a portion of it enters a gap enclosed between the back surface 62 and the outer peripheral surface 2b. If the plate-shaped projections 6 partially overlap in the Z-direction, a portion of the coating film 5 can enter a gap between the back surface 62 of one of the plate-shaped projections 6 and the outer surface 61 of another plate-shaped projection 6. The thickness of the coating film 5 is preferably 5 µm or more and 200 µm or less. If the thickness of the coating film 5 is too thin, sufficient emissivity cannot be obtained, and if the thickness is too thick, the coating film is likely to detach. The thickness of the coating film 5 according to the present embodiment is approximately 10 to 50 µm.

[0038] The average particle size of the particles of the material forming the coating film 5 is preferably between 1 and 10 µm. For example, a plurality of materials with different average particle sizes can be used, such as a combination of particles with an average particle size of 2 µm and particles with an average particle size of 5 µm.

[0039] The anchoring effect caused by the scale-like structure with the multitude of plate-like projections 6 is described with reference to Fig. 5A, Fig. 5B and Fig. 5C described. Fig. Figure 7 is an explanatory illustration of the anchoring effect in a conventional structure (structure shaped by sandblasting) and corresponds to the enlarged view of the circumferential cross-section of the Fig. 5 C. The cross-section of the depression 9 of the conventional structure is similar in the Y-direction.

[0040] As in Fig. As shown in Figure 5A, the height at which the plate-like projections 6 are detached upwards is not uniform and varies in the scale-like structure. Similar to the one in Fig. In the conventional structure shown in Figure 7, the particles are thus held in the X-direction.

[0041] As in Fig. As shown in Figure 5B, the plate-shaped projections 6 are provided continuously in the Y-direction, and there are variations in the height at which the plate-shaped projections 6 stand upwards. Similar to the one shown in Fig. In the conventional structure shown in Figure 7, the particles are held in the Y direction.

[0042] As in Fig. As shown in Figure 5C, particles additionally enter the gap between the back surface 62 of the plate-shaped projection 6 and the outer peripheral surface 2b, and the particles are connected to each other, so that the particles are held in the Z-direction. Although in the Fig. In the conventional structure shown in Figure 7, the anchoring effect can be obtained in the X-direction and the Y-direction (the axial direction and the circumferential direction of the anode 2), but on the other hand, the holding force in the Z-direction (vertical direction) is weak, and a strong anchoring effect cannot be obtained.

[0043] As described above, a stronger anchoring effect can be obtained in the scale-like structure of the present invention than in the conventional structure, and the peeling force of the coating film 5, which is provided on the outer surface of the anode 2 (the outer peripheral surface 2b in the present embodiment), is increased. EXAMPLE

[0044] The following examples describe a specific design and the effect of the invention. The evaluations in the examples were carried out using the following tests. (1) Adhesive tape removal test

[0045] To evaluate the adhesion of the coating film 5 after sintering, a peel-off adhesion test was performed according to Japanese Industrial Standard (JIS) K 6854. Specifically, a cellophane adhesive strip (CT 405 AP, manufactured by Nichiban Co., Ltd., adhesive strength: 3.93 N / 10 mm) with a width of 15 mm was first applied circumferentially to the outer peripheral surface 2b of the anode 2 with a diameter φ of 29 mm after the coating film 5 had been applied and sintered. The strip was then quickly peeled off, and it was visually confirmed whether the coating film 5 adhered to the adhesive surface of the strip. (2) Repeated temperature rise / fall test

[0046] To evaluate the adhesion of the coating film 5 to the expansion and contraction of the electrode due to heat, a periodic on / off illumination test was performed. In this test, a lamp 100, equipped with an anode 2 in which the coating film was applied and sintered, was switched on for 1 hour at a rated power of 6000 W and then switched off for 30 minutes. The peeling of the coating film 5 was visually confirmed. During this time, an area of ​​the coating film 5 on the outer peripheral surface 2b of the anode 2, closest to the tip surface 2a, reached a temperature of approximately 2000 °C. Example 1

[0047] An anode 2 with the following features was fabricated and designated as Example 1. The scale-like structure of the outer peripheral surface 2b of the anode 2 was produced by turning. The turning operation was performed using a carbide alloy cutting tool (bit) under the following conditions. Fig. Figure 8 shows a schematic representation of a turning operation. During turning, cutting is achieved by moving the bit in the axial direction while the anode 2 is rotated in the circumferential direction. The material of the coating film 5 was ZrO2 (zirconium dioxide). The film thickness of the formed coating film 5 is approximately 50 µm. - Bit (cutting tip): made of hard metal alloy, rounded distal end of the tip with a radius of curvature R = 0.4 mm (see enlarged detail) - Rotational speed: 346 RPM - Cutting tool feed: 50 µm - Rake angle: 20° to 30° Comparative example 1

[0048] An anode 2 without fine irregularities formed on the outer peripheral surface 2b was designated as comparison example 1. The material and film thickness of the coating film 5 were the same as those in example 1. Comparative example 2

[0049] An anode 2, onto which an aluminum powder was sprayed on the outer peripheral surface 2b to form fine irregularities (sandblasting was performed), was designated as comparison example 2. This simulates the one described above with reference to Fig. The structure described in 7. The material and film thickness of the coating film 5 were the same as those in Example 1.

[0050] The evaluation results of the above test are in Fig. Figure 9 illustrates this. A case in which the coating film adhered to the adhesive surface of the adhesive strip in the adhesive strip peel test was designated 'A', and a case in which the coating film did not adhere was rated 'B'. A case in which the coating film 5 peeled off in the repeated temperature rise / fall test was rated 'C', and a case in which the coating film did not peel off was rated 'D'.

[0051] As in Fig. As shown in Figure 9, in comparative example 1, adhesion of the coating film 5 to the adhesive surface of the adhesive strip was observed in the adhesive strip removal test. Because the result of the adhesive strip removal test was rated as "A", the repeated temperature rise / fall test was not performed.

[0052] Although the result of the adhesive tape peel test in comparison example 2 was rated as "B", peeling of the coating film was visually observed in the repeated temperature rise / fall test. Furthermore, in comparison example 2, foreign material was confirmed due to the peeling of the coating film 5 inside the light-emitting tube 1 in a state where the lamp 100 was switched on horizontally.

[0053] In example 1, no detachment of the coating film occurred, neither in the adhesive strip detachment test nor in the repeated temperature rise / fall test.

[0054] Specific designs according to the present invention are not limited to the embodiments described above with reference to the drawings. The scope of the present invention is not limited by the above descriptions of the embodiments, but is particularly clarified by the claims, and equivalents of the claim wording and modifications within the scope of the claims fall within the scope of the present invention.

[0055] The structures specified in the respective embodiments can be adopted in any other embodiment. Specific designs of parts are not limited to those in the embodiments described above; numerous modifications are possible within the scope of the core statement of the invention. In addition, the components, methods, and similar elements from various modified examples described below can be selected at will and used as components, methods, and similar elements in the embodiments described above.

[0056] (1) In the above embodiments, a coating film can also be used on the outer surface of the cathode 3, although the coating film is only provided on the outer surface of the anode 2, or a coating film can be provided only on the outer surface of the cathode 3.

[0057] (2) In the embodiment above, the scale-like structure is formed by turning, but the invention is not limited thereto. For example, the scale-like structure can be formed by milling. As in Fig. As shown in Figure 10, during milling, cutting is achieved by moving the tool in the axial direction while the electrode is rotated circumferentially in predetermined increments. The plate-like projection formed by the milling cutter extends in a direction that is inclined in the axial direction of the electrode with respect to the perpendicular direction of the outer peripheral surface.

Claims

[1] Short-arc discharge lamp comprising a pair of electrodes opposite each other in a light-emitting tube, a scale-like structure formed on an outer surface of at least one of the electrodes of the pair of electrodes, and a coating film that covers the outer surface along with the scale-like structure formed on the outer surface, wherein the scale-like structure has a plurality of plate-like projections that project beyond the outer surface in a direction inclined with respect to a direction perpendicular to the outer surface, wherein each plate-like projection has an outer surface facing away from the rest of the electrode, the angle of which formed with the outer surface being an obtuse angle, and a back surface, the angle of which formed with the outer surface being an acute angle, wherein the coating film comprises at least one compound selected from the group consisting of metal oxides, metal carbides, metal borides, metal silicides and metal nitrides and mixtures thereof, and Part of the coating film lies in a space between the back surface and the outer surface. [2] Short-arc discharge lamp according to claim 1, wherein the outer surface on which the scale-like structure is formed is an outer peripheral surface of the electrode with a cylindrical body. [3] Short-arc discharge lamp according to claim 2, wherein the projections extend in a direction which is inclined in a circumferential direction of the electrode with respect to a direction perpendicular to the outer peripheral surface. [4] Short-arc discharge lamp according to any one of claims 1 to 3, wherein the coating film has a film thickness of 5 µm or more and 200 µm or less.

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