JP7491646B2 - Discharge lamp and method of manufacturing electrode for discharge lamp - Google Patents

Description

The present invention relates to a discharge lamp with electrodes, and in particular to the internal structure of the electrodes.

When a discharge lamp is turned on, the electrode tip becomes very hot, causing the electrode material, such as tungsten, to melt and evaporate, blackening the discharge tube and reducing the lamp's illuminance. To prevent the electrode tip from overheating, an electrode structure is known in which the electrode tip, made of a durable metal, and the body, made of a metal with higher thermal conductivity, are molded separately and joined by solid-state welding or the like (see, for example, Patent Document 1).

An electrode configuration in which a heat dissipation space is formed inside the electrode is also known (see Patent Document 2). In this case, a columnar portion is coaxially arranged in a cylindrical recess formed inside the electrode, and gaps are formed along the electrode axis direction and in a direction perpendicular to the electrode axis.

Japanese Patent No. 5472915 JP 2018-142482 A

In a structure in which the columnar portion is joined to the recess inside the electrode, there is a risk that the columnar portion will peel off from the bottom of the recess when the lamp is turned on. In particular, if the columnar portion is made of a material with a higher thermal expansion coefficient than the electrode material, the difference in the amount of thermal expansion may cause the bottom surface to peel off, resulting in a decrease in thermal conductivity. Even in an electrode structure in which the columnar portion contacts the bottom of the recess, there is a risk that gaps will form at the contact surface due to electrode deformation while the lamp is turned on, resulting in a decrease in thermal conductivity along the electrode axis direction.

In addition, there is a greater demand than ever for higher lamp output (higher power) to accommodate larger objects to be exposed and to improve throughput. This leads to higher electrode temperatures while the lamp is on, and an electrode structure is required that can more effectively suppress the rise in electrode temperature than ever before.

Therefore, in discharge lamps in which an internal space is formed in the electrode, there is a demand for an electrode structure that can more effectively suppress the temperature rise of the electrode.

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, with at least one of the electrodes having a recess along the electrode axis direction and a columnar portion arranged in the recess. For example, the columnar portion can be configured so that the end face on the tip side of the electrode is joined or in contact with the bottom surface of the recess. When the lamp is turned on, at least a portion of the internal space formed between the recess and the columnar portion is occupied by a non-convective liquid heat transfer material.

Here, the "internal space formed between the recess and the columnar portion when the lamp is turned on" can be configured in various spatial shapes, sizes, and formation locations, and includes, for example, the space formed between the recess and the columnar portion along the electrode axis direction. In addition, if a gap occurs at the joint or contact portion between the columnar portion and the recess during lamp manufacture and/or lamp turning on, this also includes that gap.

Meanwhile, a "non-convection liquid heat transfer material" is defined here as a heat transfer material that is suppressed in the internal space to such an extent that it does not function as a heat transfer material by convection, unlike a heat transfer material that transfers heat in the electrode axial direction by convection of molten liquid when the lamp is turned on. The liquid heat transfer material can be configured so that a substance contained in the columnar portion beforehand dissolves, or it can be configured so that a heat transfer material that melts when the lamp is turned on is contained in the internal space beforehand.

The "non-convection" state of the liquid heat transfer material is based on the viscosity characteristics of the liquid heat transfer material, the size and shape of the internal space formed between the recess and the columnar portion, i.e., the pressure loss of the flow path formed between the recess and the columnar portion, etc. For example, it is possible to reduce the internal space formed between the recess and the columnar portion along the electrode axis, i.e., to shorten the distance between the recess and the columnar portion along the direction perpendicular to the electrode axis. It is also possible to provide flow path resistance by providing a groove on the columnar portion or the side of the recess. If a gap occurs at the joint or contact part between the electrode tip side end face of the columnar portion and the bottom surface of the recess during lamp manufacturing and/or lamp lighting, for example, the gap part is a small space, so it can be said to be in a "non-convection" state.

Meanwhile, another aspect of the present invention, a discharge lamp, comprises a discharge tube and a pair of electrodes arranged opposite each other within the discharge tube, at least one of the electrodes having a recess along the electrode axis direction and a columnar portion arranged in the recess, and the columnar portion is configured so that a liquid heat transfer material can dissolve into the internal space formed between the recess and the columnar portion when the lamp is turned on. The columnar portion may be configured from a porous heat conductive material and may contain a substance with a melting point that causes the columnar portion to become liquid when the lamp is turned on. For example, it may be configured from silver tungsten.

In order to make the liquid heat transfer material non-convective, for example, the width of the columnar part along the direction perpendicular to the electrode axis and the side of the recess in the internal space may be configured to be smaller than the radius of the columnar part. In addition, in order to make the liquid heat transfer material non-convective, the columnar part may be configured to have a groove or film formed on the side at least near the tip of the electrode.

The electrode can be configured, for example, so that the columnar portion is joined to a rear end member having a protrusion that connects to the electrode support rod, and the recess is formed in the front end member including the electrode tip surface. In this case, the position along the electrode axis of the joint surface between the columnar portion and the protrusion should be located closer to the electrode tip surface side than the position along the electrode axis of the joint surface between the front end member and the rear end member.

In another aspect of the present invention, a method for manufacturing an electrode for a discharge lamp is to form a cylindrical recess around the central axis of a columnar tip-side solid member, form a convex portion around the central axis of a cylindrical solid member that is smaller than the inner diameter of the cylindrical recess, form a thermally conductive member containing a substance with a melting point that becomes liquid when the lamp is lit, form the thermally conductive member into a columnar shape that matches the height from the bottom of the recess, and join the tip-side solid member, thermally conductive member, and rear-side solid member together so that the thermally conductive member is coaxially arranged in the cylindrical recess, thereby forming an electrode.

According to the present invention, in a discharge lamp in which an internal space is formed in the electrode, the temperature rise of the electrode can be more effectively suppressed.

1 is a plan view of a discharge lamp according to a first embodiment; FIG. 2 is a schematic cross-sectional view of an electrode according to the first embodiment. 4 is a cross-sectional view showing the internal state of an electrode during lamp lighting. FIG. FIG. 5 is a schematic cross-sectional view of an electrode of a discharge lamp according to a second embodiment.

The short arc type discharge lamp 10 is a large discharge lamp capable of outputting high-intensity light, and includes a transparent quartz glass, approximately spherical discharge tube (light emitting tube) 12, in which a pair of tungsten electrodes 20, 30 are arranged facing each other (coaxially). On both sides of the discharge tube 12, quartz glass sealing tubes 13A, 13B are connected to the discharge tube 12 and formed integrally with it. Mercury and rare gases such as halogen and argon gas are sealed in the discharge space DS within the discharge tube 12.

The cathode electrode 20 is supported by an electrode support rod 17A. Sealed in the sealed tube 13A are a glass tube (not shown) through which the electrode support rod 17A is inserted, a lead rod 15A that connects to an external power source, and metal foil 16A that connects the electrode support rod 17A and the lead rod 15A. Similarly, the anode electrode 30 is sealed with mounting parts such as a glass tube (not shown) through which the electrode support rod 17B is inserted, metal foil 16B, and lead rod 15B. In addition, caps 19A and 19B are attached to the ends of the sealed tubes 13A and 13B, respectively.

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). For example, when the discharge lamp 10 is incorporated in an exposure device, the emitted light becomes a pattern light and is irradiated onto a substrate, etc.

Figure 2 is a schematic cross-sectional view of the electrode (anode) 30. Note that the electrode (cathode) 20 can also have a similar structure.

The electrode 30 is composed of a tip side member 32 having an electrode tip surface 32D and a rear end side member 34 connected to the electrode support rod 17B, and the electrode 30 is formed by joining the tip side member 32 and the rear end side member 34. Here, they are joined by solid-state joining such as SPS.

The rear end member 34 includes a cylindrical member 35 having a protrusion 35A with the electrode axis X (hereinafter also referred to as the axial direction X) as the central axis, and a columnar portion 50 (here, cylindrical) is formed from the protrusion 35A toward the electrode tip surface 32D. The tip member 32 has a cylindrical recess 40 formed coaxially along the axial direction X surrounding the columnar portion 50, facing (recessed) in the opposite direction to the electrode tip surface 32D.

The tip-side member 32 and the rear-side member 34 are solid-state welded at their ends 32E, 34E. The end face 50B of the columnar portion 50 on the electrode support rod side is solid-state welded to the end face 35D of the convex portion 35A of the cylindrical member 35, and the end face 50A on the electrode tip side is solid-state welded to the bottom face 40B of the recess 40. The position along the electrode axis X of the end face 50B of the columnar portion 50, i.e., the position of the joint surface between the columnar portion 50 and the cylindrical member 35, is located closer to the electrode tip surface than the position along the electrode axis X of the end 34E of the rear-side member 34 (position of the joint surface).

The tip member 32 and the cylindrical member 35 of the rear member 34 are formed from a thermally conductive metal such as tungsten or molybdenum, and are maintained as solids while the lamp is lit. The columnar portion 50 is also a thermally conductive member that is maintained as a solid while the lamp is lit, but is configured to dissolve into a liquid heat transfer material when the lamp is lit or the electrode is heated to a high temperature.

Here, the columnar portion 50 is made of a porous tungsten alloy (silver-tungsten) impregnated with silver, which has a higher thermal conductivity than tungsten. When the electrode is heat-treated or the lamp is turned on, the high temperature (approximately 1500°C or higher) causes the silver to dissolve from the surface of the columnar portion 50, such as the side surface 50S.

Between the columnar portion 50 and the recess 40, a tubular internal space 60 is formed along the axial direction X, all around the columnar portion 50. The central axes of both the columnar portion 50 and the recess 40 coincide with the electrode axis X, and are symmetrical with respect to the electrode axis X. The bottom surface 40B of the recess 40 is also symmetrical with respect to the electrode axis X, and the internal space 60 has a symmetrical spatial shape with respect to the electrode axis X. The angle formed by the bottom surface 40B and the side surface 40S (the corner of the recess 40) may be configured to have a curved surface.

The volume of the internal space 60 is smaller than the volume of the columnar portion 50. If the radius of the columnar portion 50 is r and the distance from the electrode axis X to the side surface 40S of the recess 40 is R, the internal space 60 is formed to satisfy R-r<r. In other words, the columnar portion 50 is configured with a thickness such that it occupies most of the internal space formed by the recess 40, so that the width in the direction perpendicular to the electrode axis between the side surface 40S of the recess 40 and the side surface 50S of the columnar portion 50 in the internal space 60 is shorter than the radius r of the columnar portion 50.

Figure 3 is a cross-sectional view showing the internal state of the electrode while the lamp is lit.

The columnar portion 50 has a different thermal expansion coefficient from the cylindrical member 35 of the rear end member 34 and the tip end member 32. Therefore, the end face 50A of the columnar portion 50 is easily peeled off from the bottom face 40B of the recess 40 (or the end face 50B of the columnar portion 50 is easily peeled off from the end face 35D of the cylindrical member 35) due to the electrode heat treatment process during lamp manufacturing or the rise in electrode temperature caused by the lamp being turned on. Figure 3 (A) shows a gap 60D (part of the internal space 60 formed during lamp manufacturing and/or while the lamp is turned on) formed by the peeling of the joint surface between the end face 50A of the columnar portion 50 and the bottom face 40B of the recess 40.

On the other hand, when the columnar portion 50 is heated by heat from the tip side member 32 while the lamp is on and exceeds the melting point of the silver 70, the impregnated silver 70 dissolves from the columnar portion 50 into the internal space 60. The liquid silver 70 then enters the gap 60D formed between the columnar portion 50 and the recess 40 (see FIG. 3B). This allows heat from the bottom surface 40B side of the recess 40 to be transported to the columnar portion 50 via the silver occupying the gap 60D. The silver 70 entering the gap 60D maintains thermal conductivity, and the presence of silver 70 with high thermal conductivity results in improved thermal conductivity performance.

As described above, the volume of the internal space 60 is smaller than the volume of the columnar portion 50, or is formed so that it is much smaller than the inner space formed by the recess 40. This means that the side surface 40S of the recess 40 and the opposing side surface 50S of the columnar portion 50 provide a flow path resistance that allows the liquid silver 70 to convect in at least the electrode axis direction in the internal space 60, i.e., prevents the heated fluid in the electrode axis direction from rising upward and the surrounding low-temperature fluid from flowing in.

The liquid silver 70 that enters the gap 60D between the columnar portion 50 and the recess 40 is also restricted from moving along the electrode axis X. This restricted movement of the liquid silver 70 occupies part of the internal space 60 (including the gap 60D) in a non-convective manner, allowing heat to be transported from the tip member 32 to the columnar portion 50 without reducing thermal conductivity. The columnar portion 50, made of silver tungsten with high thermal conductivity, efficiently transports heat to the electrode support rod 17B, and can more effectively suppress temperature rise in the electrode.

Thus, according to this embodiment, the electrode 30 is composed of a tip side member 32 including the electrode tip surface 32D and a rear end side member 34 that connects to the electrode support rod 17B, a recess 40 is formed in the tip side member 32, and a columnar portion 50 is formed within the recess 40 so as to be coaxial with the recess 40. The columnar portion 50 is made of silver tungsten, and when the lamp is turned on, liquid silver dissolves into the internal spaces 60, 60D formed between the columnar portion 50 and the recess 40.

By disposing a columnar portion 50 made of silver-tungsten inside the electrode 30, it is possible to provide a configuration in which, while the lamp is lit, there are two heat transfer bodies, namely, the columnar portion 50 that functions as a heat conducting member, and the liquid silver 70 that has high thermal conductivity.

The electrode 30 can be manufactured as follows. That is, a cylindrical recess is formed around the central axis of a columnar, thermally conductive, tip-side solid member that will have the electrode tip surface. A protrusion that is smaller than the inner diameter of the recess is formed around the central axis of the thermally conductive, cylindrical solid member. Then, a columnar member made of porous silver-tungsten is formed in a columnar shape that matches the diameter of the protrusion and the height from the bottom of the recess.

Then, the components including the tip side solid component, the columnar component, and the rear side solid component are combined so that the columnar component is coaxially arranged in the recess, and solid-phase bonding such as SPS is performed to form an electrode including the tip side solid component and the rear side solid component.

By using this manufacturing method, it is possible to manufacture an electrode 30 in which liquid silver 70 dissolves from the columnar portion 50 during heat treatment of the electrode or when the lamp is turned on, without the need for a separate process of sealing in a liquid heat transfer material. The discharge lamp manufacturing processes other than the electrode 30 (such as placement of the electrode 30 in the discharge tube 12 and the sealing process) can be carried out using conventional manufacturing methods.

The diameter of the columnar portion 50 and the diameter of the protrusion 35A do not have to be the same. The rear end side member 34 may be configured so that the columnar member 35 does not have to be provided with the protrusion 35A. The columnar portion 50 may be configured so that its both end faces 50A and 50B are not solid-phase bonded to the end face 35D of the protrusion 35A of the columnar member 35 and the bottom face 40B of the recess 40, respectively, and may simply be in contact with either one of the end faces or both end faces. In the above embodiment, the gap 60D is formed, but it goes without saying that the gap 60D does not have to be formed, and on the other hand, the axial length of the columnar portion 50 may be designed to be slightly shorter, and a gap (gap 60D) along the electrode axis perpendicular direction may be formed at the stage of electrode manufacturing.

The preferred joining method is solid-phase joining (SPS, HP, etc.), but other joining methods (e.g., fusion joining) can also be used. During joining, an intermediate member may be sandwiched between the leading end member and the trailing end member to ensure close contact between the joining surfaces. An intermediate member may also be sandwiched between both end faces 50A, 50B of the columnar portion 50 and the end face 35D of the cylindrical member 35 and the bottom face 40B of the recess 40. Examples of intermediate members that can be used include rhenium, tantalum, molybdenum, tungsten, or alloys of these.

The shape and size of the columnar portion and the recess are arbitrary. For example, it is possible to form a columnar portion 50 whose diameter changes (expands or contracts) along the axial direction X, and form a recess of a corresponding (complementary) shape. In addition, the bottom surface 40B of the recess 40 may be provided with a convex portion, a concave portion, or a curved surface, and the shape of the end portion of the electrode tip side of the columnar portion 50 may be made to match (complement) the above. It is also possible for the cross-sectional shapes of the recess 40 and the columnar portion 50 to be shapes other than circular.

In this embodiment, the columnar portion 50 extends toward the tip of the electrode, but the opposite configuration, that is, the columnar portion is formed in the tip member and the recess is formed in the rear member, may also be used. Furthermore, the columnar portion may be configured to fit into the recess so that there is no internal space along the electrode axis X and no gap is generated.

Conversely, the internal space is not limited to a tubular internal space along the electrode axis X, but may be a U-shaped internal space with a gap between the columnar portion and the recess along the direction perpendicular to the electrode axis. Furthermore, it is also possible to reduce the diameter of the columnar portion and configure the majority (more than half) of the inner space of the recess as an internal space.

The columnar portion 50 may be made of a material other than porous silver-tungsten impregnated with silver, as long as the liquid heat transfer material dissolves from the columnar portion during lamp manufacture and/or lamp operation. For example, copper-tungsten, copper-molybdenum, silver-diamond, etc. may be used.

Next, a discharge lamp according to a second embodiment will be described with reference to FIG. 4. In the second embodiment, a heat transfer material that becomes liquid when the lamp is lit is provided in advance in the internal space.

Figure 4 is a schematic cross-sectional view of an electrode of a discharge lamp according to the second embodiment.

The electrode (anode) 30' is composed of a tip side member 32' and a rear end side member 34', as in the first embodiment, and a columnar portion 50' is disposed in the recess 40'. The columnar portion 50' is joined to the recess 40' and the cylindrical member 35' of the rear end side member 34'.

The columnar section 50' does not contain any substances that dissolve at the lamp lighting temperature, and is made of the same material as the leading end member 32' and the trailing end member 34'. For example, it can be made of a metal such as tungsten or molybdenum or an alloy thereof. Alternatively, a material with high thermal conductivity, such as a boride such as zirconium boride or ceramic, may be used.

Granular heat transfer material 70' is sealed in advance in the internal space 60' formed between the recess 40' formed in the tip side member 32' and the columnar portion 50'. The heat transfer material 70' is solid before the lamp is turned on (at room temperature), and a liquid that melts when the lamp is turned on can be used. For example, fluorides such as magnesium fluoride and calcium fluoride, and oxides such as tungsten oxide and bismuth oxide can be used. Copper is used here. A fine groove M is formed along the circumferential direction on the side surface 50'S of the columnar portion 50' over the entire length of the columnar portion 50'. The fine groove M can be formed, for example, by laser processing.

When the lamp is turned on, the molten heat transfer material 70' enters the gap (not shown in FIG. 4) that is created when the columnar portion 50' peels off from the bottom surface 40'B of the recess 40', and even if peeling occurs, the thermal conductivity along the electrode axis X is maintained. Furthermore, the heat transfer material 70' present in the internal space 60' is in a non-convection state in which convection, which causes a fluid to flow upward at least along the electrode axis direction, is suppressed, so it remains in the internal space 60' (including the gap), resulting in better thermal conductivity along the electrode axis X.

On the other hand, as in the first embodiment, the position along the electrode axis X of the end face 50'B of the columnar portion 50', i.e., the position of the joint surface, is located closer to the electrode tip surface than the position along the electrode axis X of the end 34E' of the rear end member 34', so that the liquid heat transfer material 70' can be prevented from leaking out from the joint surface between the tip side member 32' and the rear end side member 34'.

By forming the fine grooves M on the side surface 50'S of the columnar portion 50', the side surface 50'S of the columnar portion 50' has an uneven shape, which contributes to increasing the flow resistance. As a result, the movement of the liquid heat transfer body 70' can be suppressed to create a non-convection current. In addition, heat can be easily absorbed inward in the direction perpendicular to the electrode axis, and heat can be easily transported from the columnar portion 50' to the electrode support rod side. Instead of forming the grooves M on the side surface 50'S of the columnar portion 50', a radioactive film may be formed. In addition, it is possible to form the fine grooves M in the first embodiment as well, and it is sufficient to form them at least near the tip side of the electrode (the bottom surface 40B of the recess 40).

REFERENCE SIGNS LIST 10 Discharge lamp 30 Electrode 32 Front end member 34 Rear end member 40 Recess 50 Columnar portion 60 Internal space 70 Silver (heat conductor)

Claims (9)

A discharge tube;
A pair of electrodes disposed opposite each other within the discharge tube,
At least one of the electrodes has a recess along an electrode axial direction and a columnar portion disposed in the recess,
A discharge lamp, characterized in that, when the lamp is lit, at least a part of an internal space formed between said recess and said columnar portion is occupied by a non-convective liquid heat transfer material. A discharge tube;
A pair of electrodes disposed opposite each other within the discharge tube,
At least one of the electrodes has a recess along an electrode axial direction and a columnar portion disposed in the recess,
A discharge lamp characterized in that the columnar portion is constructed so that a liquid heat transfer material can dissolve into an internal space formed between the recess and the columnar portion when the lamp is turned on. The discharge lamp according to claim 1 or 2, characterized in that the width of the side surface of the recess in the internal space and the columnar portion along the direction perpendicular to the electrode axis is smaller than the radius of the columnar portion. A discharge lamp according to any one of claims 1 to 3, characterized in that the columnar portion has a groove or film formed on the side surface at least near the tip of the electrode. A discharge lamp according to any one of claims 1 to 4, characterized in that the columnar portion is joined or in contact with the end face of the electrode tip side and the bottom surface of the recess. the columnar portion is joined to a rear end member having a protrusion for connection to an electrode support rod;
The recess is formed in a tip member including an electrode tip surface,
6. The discharge lamp according to claim 1, wherein a position along an electrode axis of a joint surface between the columnar portion and the protruding portion is located closer to the electrode tip surface side than a position along an electrode axis of a joint surface between the front end side member and the rear end side member. A discharge lamp according to any one of claims 1 to 6, characterized in that the columnar portion is a porous heat-conductive material containing a substance with a melting point that becomes liquid when the lamp is lit. A discharge lamp according to any one of claims 1 to 7, characterized in that the columnar portion comprises silver tungsten. A cylindrical recess is formed around a central axis in a columnar tip side solid member,
a protrusion having a diameter smaller than an inner diameter of the cylindrical recess is formed around a central axis of the cylindrical rear end side solid member;
a heat conductive member containing a substance having a melting point that becomes liquid when the lamp is lit, the heat conductive member being formed in a columnar shape in accordance with the height from the bottom surface of the cylindrical recess;
a manufacturing method for an electrode for a discharge lamp, comprising: joining the front end solid member, the thermally conductive member, and the rear end solid member together so that the thermally conductive member is coaxially arranged in the cylindrical recess, thereby forming an electrode.

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