Discharge lamp, and electrode used for the discharge lamp

Abstract

To achieve higher output and longer life of a discharge lamp.SOLUTION: At least one electrode of the discharge lamp includes a body that has a sealed space inside the electrode, a heat transfer body filled within the sealed space and having a lower melting point than a material that constitutes the body, and a regulating body that is arranged in the sealed space, regulates the convection of the heat transfer body, and has a higher melting point of the surface than the melting point of the heat transfer body. The regulating body includes a first regulating body, the density of which is higher than that of the heat transfer body and a second regulating body, the density of which is lower than that of the heat transfer body.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a discharge lamp and an electrode used for the discharge lamp.

Background Art

[0002] Conventionally, a discharge lamp has been used as a light source in an exposure apparatus used in a manufacturing process of a semiconductor element, a liquid crystal display element, or a printed circuit board. In this discharge lamp, an anode and a cathode are disposed to face each other in the axial direction in a light-emitting tube, and a light-emitting substance such as mercury is enclosed in the light-emitting tube.

[0003] In such a discharge lamp, since the thermal load applied to the electrodes during lighting is high, evaporation of the electrode material may occur due to overheating of the electrodes or the like. When this evaporated material adheres to the inner wall of the light-emitting tube, the discharge lamp causes so-called "blackening", and a problem occurs in that the light transmittance of the light-emitting tube decreases.

[0004] To solve this problem, a discharge lamp having a structure in which a sealed space is provided inside an electrode, particularly an anode, and a heat transfer body is enclosed in the sealed space has been proposed. The heat transfer body is melted during the lamp lighting state and convects in the sealed space due to the temperature distribution of the entire anode. The convection of this heat transfer body transfers the heat at the tip (the end closest to the cathode) of the anode to the rear end (the end farthest from the cathode), thereby lowering the temperature at the tip of the anode and suppressing the evaporation amount of the electrode material.

[0005] Patent Document 1 and Patent Document 2 describe that a restricting body for restricting the circumferential convection of the heat transfer body is provided in the sealed space. By providing the restricting body in the sealed space, the formation of holes at the tip of the electrode due to the circumferential convection of the heat transfer body is prevented.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] Recently, further higher output and longer life of discharge lamps have been demanded in the market. When the output of a discharge lamp is increased, the thermal load on the electrodes increases, so electrodes that can withstand the increasing thermal load for a long time are required. An object of the present invention is to provide a discharge lamp that achieves higher output and longer life, and an electrode used in the discharge lamp. MEANS FOR SOLVING THE PROBLEMS

[0008] In order to investigate the thermal load on the electrodes when the discharge lamp is used at high power, the present inventor measured the temperature distribution on the electrode surface during lighting using a radiation thermometer. As a result of the measurement, the present inventor noticed that there are discharge lamps with a high temperature at the electrode tip and discharge lamps with a large temperature fluctuation range on the electrode surface. Temperature fluctuation refers to the temperature fluctuating within a short period of time (for example, 1 minute). If the state of a high temperature at the electrode tip or a large temperature fluctuation range on the electrode surface continues for a long time, a hole will open at the electrode tip due to high-temperature creep deformation, leading to leakage of the heat transfer medium. Then, the heat dissipation property of the electrode is lost, and the discharge lamp has a short life.

[0009] Although details will be described later, as a result of the earnest research by the present inventor, it has been found that the expansion of the temperature fluctuation range at the electrode tip is caused by the convection of the heat transfer medium becoming turbulent. To suppress the turbulent flow of the heat transfer medium, it is advisable to review the design of the restricting body provided in the sealed space. In particular, increasing the size of the restricting body can effectively suppress the turbulent flow. However, increasing the size of the restricting body increases the volume of the restricting body occupying the sealed space and decreases the capacity of the heat transfer medium. When the capacity of the heat transfer medium decreases, the heat transfer efficiency decreases, and the function of reducing the temperature at the electrode tip by the heat transfer medium is impaired. Therefore, while suppressing an increase in the volume of the restricting body, a suitable design of the restricting body that suppresses the turbulent flow of the heat transfer medium was studied, and the following discharge lamp was devised.

[0010] The discharge lamp of the present invention is a discharge lamp having a pair of axially opposed electrodes inside, and at least one of the pair of electrodes is a main body having a sealed space inside, a heat transfer body located in the sealed space and having a melting point lower than that of the material constituting the main body, a regulating body located in the sealed space, having a surface with a melting point higher than that of the heat transfer body, and regulating the convection of the heat transfer body, and is provided with the regulating body is a first regulating body having a density greater than that of the heat transfer body, a second regulating body having a density smaller than that of the heat transfer body, and includes

[0011] The convection of the heat transfer body is regulated by the first regulating body located near the bottom of the heat transfer body and the second regulating body located near the interface of the heat transfer body. By controlling the convection of these regulating bodies, the turbulent flow of the heat transfer body can be suppressed. When the turbulent flow of the heat transfer body is suppressed, the temperature fluctuation range on the inner surface of the electrode becomes smaller. Furthermore, since the total volume of the regulating body divided into the first regulating body and the second regulating body is smaller than the volume occupied by the non-divided regulating body, the capacity of the heat transfer body can be ensured. Therefore, the heat transfer efficiency is less likely to decrease, and the temperature at the electrode tip can be maintained at a low level. As a result, the formation of holes at the electrode tip due to high-temperature creep deformation and the blackening of the arc tube due to the evaporation of the electrode material are suppressed, and the high output and long life of the discharge lamp can be achieved.

[0012] The shape of the first regulating body may be different from the shape of the second regulating body.

[0013] The second regulating body may be in the form of a rod extending in one direction.

[0014] The shape of the second regulating body in a cross-section perpendicular to the one direction may be circular, triangular, or trapezoidal.

[0015] The first restricting body and the second restricting body each include a plurality of blades extending radially outward from a central axis along the axial direction, and the number of blades of the first restricting body may be larger than the number of blades of the second restricting body.

[0016] The second restricting body may mainly contain titanium or ceramics.

[0017] Let the axial length of the first restricting body be L1 (mm), Let the axial length of the second restricting body in contact with the heat transfer body be D2 (mm), When the interval in the axial direction between the first restricting body and the second restricting body is H2 (mm), the following formula (1) may be satisfied. 0 < H2 / (L1 + D2) ≦ 2 …(1)

[0018] When the axial length of the second restricting body in contact with the heat transfer body is D2 (mm), the following formula (2) may be satisfied. D2 ≧ 1.5 …(2)

[0019] The electrode used in the discharge lamp of the present invention has a main body having a sealed space inside, a heat transfer body filled in the sealed space and having a melting point lower than that of the material constituting the main body, and a restricting body disposed in the sealed space, restricting the convection of the heat transfer body and having a surface melting point higher than the melting point of the heat transfer body. The restricting body includes a first restricting body having a density greater than that of the heat transfer body, and a second restricting body having a density smaller than that of the heat transfer body.

Advantages of the Invention

[0020] It is possible to provide a discharge lamp with increased output and extended lifespan, and an electrode used in the discharge lamp.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5A

Figure 5B

Figure 6

Figure 7A

Figure 7B

Figure 8A

Figure 8B

Figure 9

Figure 10

Figure 11A

Figure 11B

Figure 12A

Figure 12B

Figure 13A

Figure 13B

Figure 14

Figure 15

Figure 16

Embodiments for Carrying Out the Invention

[0022] Embodiments of the discharge lamp will be described with reference to the drawings. Note that each of the following drawings, excluding the graphs, is schematically illustrated, and the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios, nor do the dimensional ratios necessarily match between the drawings.

[0023] In the following, each of the drawings, excluding the graphs, will be described with reference to the XYZ coordinate system. In this specification, when expressing a direction, when distinguishing between positive and negative directions, it is described with positive and negative signs, such as “+X direction” and “-X direction”. When expressing a direction without distinguishing between positive and negative directions, it is simply described as “X direction”. That is, in this specification, when simply described as “X direction”, both “+X direction” and “-X direction” are included. The same applies to the Y direction and the Z direction. In the embodiments described below, the -Z direction represents the direction of gravity.

[0024] [Overview of Discharge Lamp] With reference to FIG. 1, the overview of an embodiment of the discharge lamp will be described. The discharge lamp 100 is a short arc type discharge lamp including a discharge tube 1, an anode 2 and a cathode 3 disposed to face each other in the extending direction of the central axis Z1 inside the discharge tube 1, and lead rods 4 supporting the anode 2 and the cathode 3 respectively. In this embodiment, the discharge lamp 100 is arranged such that the anode 2 is located above the cathode 3 (+Z direction), and the discharge lamp 100 is lit.

[0025] A short arc type discharge lamp refers to one in which the tip of the anode 2 and the tip of the cathode 3 are arranged with a gap of 40 mm or less (the value at normal temperature without thermal expansion). As an example of such a discharge lamp, there is a discharge lamp with a rated power of 2 kW to 35 kW, which is used in an exposure apparatus used in the manufacturing process of semiconductor elements, liquid crystal display elements, printed circuit boards, etc. Note that in the discharge lamp 100 of the present embodiment, the tip of the anode 2 and the tip of the cathode 3 are arranged with a gap of 6 mm.

[0026] The arc tube 1, the anode 2, the cathode 3, and the lead rod 4 are all arranged around the central axis Z1. The anode 2 is arranged above the cathode 3 in the +Z direction. Sealing tubes 11 are provided at both ends of the arc tube 1 in the extending direction of the central axis Z1. A base 12 electrically connected to the lead rod 4 is attached to the sealing tube 11.

[0027] The arc tube 1 is formed of a glass tube. The arc tube 1 has a region where the inner diameter of the glass tube increases as it goes from both ends of the central axis Z1 toward the center. This region where the inner diameter increases may have a spherical or ellipsoidal shape. For example, quartz glass can be used for the glass tube. The region where the inner diameter increases functions as a light-emitting space. A light-emitting substance such as mercury is enclosed in the light-emitting space.

[0028] [Overview of the Anode] While referring to FIG. 2, the overview of the anode 2 will be described. FIG. 2 is an enlarged cross-sectional view of the anode 2 in the discharge lamp of FIG. 1. The anode 2 has a rotating body shape around the central axis Z1. In FIG. 2, the cross-section of the anode 2 in the plane passing through the central axis Z1 is shown. In FIG. 2, the tip 13 of the anode 2 close to the opposing cathode 3 is shown on the lower side (-Z side), and the rear end 14 to which the lead rod 4 (not shown in FIG. 2) is connected is shown on the upper side (+Z side). Note that the restricting bodies (10, 20) shown in FIG. 2 are shown by their side shapes, not their cross-sectional shapes.

[0029] The anode 2 includes a main body 5 of the anode 2, a heat transfer body 9, and regulators (10, 20) for restricting the convection of the heat transfer body 9. The main body 5 includes a container 5a and a lid 5b. The lid 5b is attached so that it cannot be removed from the container 5a. When the lid 5b is attached to the container 5a, a sealed space 6 is formed inside the main body 5. The main body 5 is made of a high melting point material so that the main body 5 is difficult to melt when the discharge lamp 100 is lit. In the present embodiment, the main body 5 (the container 5a and the lid 5b) is mainly made of a material containing tungsten.

[0030] In the case of the present embodiment, in addition to the heat transfer body 9 and the regulators (10, 20), a gas space 8 is provided in the sealed space 6. The gas space 8 is filled with, for example, air or an inert gas (for example, argon). The central axis of the sealed space 6 of the present embodiment is the same as the central axis Z1 of the anode 2. The shape of the inner wall 15 of the sealed space 6 in the anode 2 of the present embodiment is a shape composed of a truncated cone arranged such that the bottom surface is small and the upper surface is large, and a cylinder arranged in contact with the truncated cone.

[0031] The heat transfer body 9 exists as a liquid at a high temperature when the discharge lamp 100 is lit. The heat transfer body 9 exists as a solid when the discharge lamp 100 is turned off. Therefore, the melting point of the heat transfer body 9 is lower than the melting point of the material constituting the main body 5. When the heat transfer body 9 melts due to the lighting of the discharge lamp 100, the heat transfer body 9 convects in the sealed space 6, and the heat near the tip 13 of the anode 2 is transferred to the rear end 14 of the anode 2. The heat transferred to the rear end 14 is transferred to the lead bar 4 (not shown in FIG. 2) and is released from the electrode surface to the outside of the electrode by radiation. As a result, the temperature of the tip 13 of the anode 2 decreases.

[0032] The material constituting the heat transfer body 9 is made of a heat conductive material. The material constituting the heat transfer body 9 is preferably a material having a higher thermal conductivity than the material constituting the main body 5. In the present embodiment, a material mainly containing silver is used as the material constituting the heat transfer body 9. A material mainly containing gold may be used as the material constituting the heat transfer body 9.

[0033] [Overview of the Regulator] In addition to FIG. 2, the outline of the restricting bodies (10, 20) will be described with reference to FIGS. 3, 4A and 4B. FIG. 3 is a perspective view showing the inside of the sealed space 6. In FIG. 3, only the restricting bodies (10, 20) are drawn in solid lines. FIG. 4A is a cross-sectional view taken along the line segment A-A in FIG. 2 as viewed in the direction of the arrow. FIG. 4B is a cross-sectional view taken along the line segment B-B in FIG. 2 as viewed in the direction of the arrow. In FIGS. 4A and 4B, only the main body 5 is shown hatched with oblique lines.

[0034] As shown in FIGS. 2 and 3, in this embodiment, the restricting bodies (10, 20) are composed of a first restricting body 10 and a second restricting body 20. The first restricting body 10 and the second restricting body 20 are arranged side by side along the Z direction.

[0035] The density of the first restricting body 10 is greater than the density of the heat transfer body 9. The density of the second restricting body 20 is smaller than the density of the heat transfer body 9. Therefore, when the heat transfer body 9 melts due to the lighting of the discharge lamp 100, the first restricting body 10 sinks into the heat transfer body 9, and the second restricting body 20 floats on the heat transfer body 9. Thus, the second restricting body 20 is located in the +Z direction of the first restricting body 10.

[0036] As shown in FIG. 4A, the central axis of the first restricting body 10 is shown as Z2. The central axis Z2 extends in a direction along the Z direction (axial direction). It is preferable that the central axis Z2 overlaps with the central axis of the sealed space 6. However, when the first restricting body 10 is pushed by the convection of the heat transfer body 9 and tilts, the central axis Z2 may not overlap with the central axis of the sealed space 6.

[0037] In this embodiment, the first restricting body 10 includes four blades 10b. Each blade 10b extends radially outward from the central axis Z2 along the Z direction. In FIGS. 2, 3, and 4A, among the four blades 10b, the states in which two of the blades 10b extend from the central axis Z2 in the ±X directions are shown. Among the four blades 10b, the states in which the remaining two blades 10b extend from the central axis Z2 in the ±Y directions are shown. When the first restricting body 10 is viewed from the +Z direction, the first restricting body 10 is in a cross shape. There is usually a gap G1 between most of the outer surface of the first restricting body 10 and the inner wall 15 that constitutes the sealed space 6 (see FIG. 4A).

[0038] In this embodiment, the second restricting body 20 is in a rod shape that is long in one direction (the Y direction in FIG. 4B). When the heat transfer body 9 is melted, the longitudinal direction of the second restricting body 20 is along the interface 9s between the gas space 8 and the heat transfer body 9. The portion of the second restricting body 20 above the interface 9s is in contact with the gas space 8. The portion of the second restricting body 20 below the interface 9s is in contact with the heat transfer body 9. There is usually a gap G2 between the end portions (E1, E2) facing each other in the longitudinal direction of the second restricting body 20 and the inner wall 15 that constitutes the sealed space 6 (see FIG. 4B).

[0039] [Actions by the Two Restricting Bodies] With reference to FIGS. 5A and 5B, the actions by the two restricting bodies (10, 20) will be described. FIGS. 5A and 5B are perspective views showing the inside of the sealed space 6, respectively, and simply showing the results of the convection simulation of the heat transfer body 9. FIG. 5A includes the two restricting bodies (10, 20) having the above-described shapes respectively. FIG. 5B includes only the restricting body 30 having the shape of the first restricting body 10 described above. When the discharge lamp 100 is lit, the heat transfer body 9 melts and starts to convect. The arrows shown in the sealed space 6 in FIGS. 5A and 5B indicate the directions in which the heat transfer body 9 convects.

[0040] A description will be given of FIG. 5B. The regulating body 30 is submerged in the molten heat transfer body 9. It is separated from the upper surface of the regulating body 30 to the interface 9s between the heat transfer body 9 and the gas space 8, and a large amount of the heat transfer body 9 exists above the regulating body 30. In FIG. 5B, two flows of the heat transfer body 9 regulated by the regulating body 30 are indicated by arrows labeled "fb". The heat transfer body 9 regulated by the regulating body 30 forms a flow that rises toward the interface 9s. When the flow of the heat transfer body 9 reaches the vicinity of the interface 9s, it spreads radially outward along the interface 9s. At this time, a region cf where the two flows fb of the heat transfer body 9 collide with each other is generated. In the region cf, a turbulent flow is generated due to the collision of the two flows fb. When the turbulent flow is generated, the heat transfer by the heat transfer body 9 becomes unstable, and the temperature fluctuation range of the anode 2 increases.

[0041] A description will be given of FIG. 5A. In FIG. 5A, two flows of the heat transfer body 9 regulated by the first regulating body 10 are indicated by arrows labeled "fa". The heat transfer body 9 regulated by the first regulating body 10 forms a flow that rises toward the interface 9s. When the flow of the heat transfer body 9 reaches the vicinity of the interface 9s, it spreads radially outward along the interface 9s. However, since the second regulating body 20 exists between the two flows fb of the heat transfer body 9, it is difficult for the two flows fb to collide with each other. Therefore, the generation of turbulent flow in the region cf as shown in FIG. 5B is suppressed.

[0042] The conditions used in the above convection simulation are as follows. <Discharge lamp 100> It has the shape shown in FIG. 1. Material of the arc tube 1: Quartz glass Distance between the anode 2 and the cathode 3: 6 mm Filling in the arc tube 1: Mercury 2.0 mg / cc, Argon 100 kPa Rated current: 200 A Rated power: 12 kW <Outline of the electrode> The anode 2 has a sealed space 6 inside. It has the shape shown in FIG. 2. Volume of the sealed space 6: 17 cm 3 Material of the heat transfer body 9: Silver Enclosed gas in the gas space 8: Argon 100 kPa Material of the main body 5: Material mainly containing tungsten <First regulator 10 and regulator 30> Material of the regulator: Material mainly containing tungsten <Second regulator 20> Material of the regulator: Material mainly containing titanium

[0043] Figure 6 is a graph showing the relationship between the heat transfer body occupancy rate for the regulators (10, 20) and the maximum value TX of the temperature fluctuation range. This graph was obtained by performing a convection simulation of the heat transfer body 9. The conditions of the convection simulation are the same as those described above.

[0044] The heat transfer body occupancy rate will be described. First, as shown in FIG. 3, the following parameters are set. Length in the Z direction of the first regulator 10: L1 (mm) Distance from the bottom surface of the second regulator 20 to the interface 9s: D2 (mm) Distance from the upper surface of the first regulator 10 to the lower surface of the second regulator 20: H2 (mm)

[0045] The sum of the length L1 and the distance D2 means the total length of the first regulator 10 and the second regulator 20 in the Z direction in the heat transfer body. The distance H2 means the length in the Z direction in the heat transfer body where the regulators (10, 20) do not exist. The ratio of these lengths, that is, H2 / (L1 + D2), can be regarded as the ratio of the existence region of the regulator in the Z direction to the existence region of the heat transfer body. And the ratio of the existence region of the regulator in the Z direction to the existence region of the heat transfer body can be simply approximated as the heat transfer body occupancy rate for the regulators (10, 20). Therefore, in this specification, the value obtained from H2 / (L1 + D2) is defined as the heat transfer body occupancy rate for the regulators (10, 20).

[0046] The maximum value TX of the temperature fluctuation range will be described. The temperature fluctuation range is represented by the difference between the maximum temperature and the minimum temperature at an arbitrary location on the inner surface of the electrode (the inner wall 15 of the sealed space 6) during the lighting of the discharge lamp for a predetermined time (for example, one minute). If a state with a large temperature fluctuation range continues for a long time, deformation such as denting occurs on the inner surface of the electrode near the electrode tip due to high-temperature creep deformation, a hole opens at the electrode tip, and the heat transfer body 9 leaks out. Then, since the heat dissipation property of the electrode is lost, the electrode becomes overheated, and the deterioration of the discharge lamp rapidly progresses. The temperature fluctuation range shows different values depending on the location on the inner surface of the electrode. When actually measuring the temperature fluctuation range, since it is difficult to directly measure the temperature of the inner surface of the electrode, it is preferable to estimate the temperature of the inner surface of the electrode by measuring the outer surface of the electrode with a radiation thermometer or the like as an alternative.

[0047] The maximum value TX of the temperature fluctuation range (the unit is °C, hereinafter sometimes referred to as the "maximum value TX") indicates the maximum value of the temperature fluctuation range that varies depending on the location on the inner surface of the electrode. Suppressing the maximum value TX can reduce the thermal load applied to the anode 2 and suppress damage such as hole opening at the electrode tip due to high-temperature creep deformation. The smaller the maximum value TX, the better. As a guideline, it is preferable that the maximum value TX is 13 °C or less.

[0048] Figure 6 shows the relationship between the heat transfer body occupancy ratio approximated by H2 / (L1 + D2) and the maximum value TX. The points plotted with triangular marks are based on the reference form (see Figure 5B) with the regulating body 30 corresponding to the first regulating body 10 and no second regulating body 20. The curve C1 is the approximation curve of the points plotted with triangular marks. The points plotted with circular marks are based on the present embodiment (see Figure 5A) having two regulating bodies (10, 20). The curve C2 is the approximation curve of the points plotted with circular marks. In the case of the reference form without the second regulating body 20, since the distance D2 is 0 (mm), the value approximating the heat transfer body occupancy ratio is substantially H2 / (L1 + 0), that is, H2 / L1.

[0049] As can be seen from FIG. 6, even when the heat transfer body occupancy rate is the same, the maximum value TX of the embodiment (curve C2) is smaller than the maximum value TX of the reference embodiment (curve C1). This indicates that even without a change in the capacity of the heat transfer body 9, the maximum value TX can be reduced by changing one regulating body into two regulating bodies.

[0050] As described above, it is preferable that the maximum value TX is 13° C. or less. From FIG. 6, when the maximum value TX of the C2 curve is 13° C. or less, H2 / (L1 + D2) satisfies the formula (1). 0 < H2 / (L1 + D2) ≦ 2 …(1)

[0051] Conversely, when the formula (1) is satisfied, the maximum value TX of the temperature fluctuation range becomes 13° C. or less. Although the formula (1) is based on the above simulation conditions and the shapes of the regulating bodies (10, 20), the formula (1) still holds even if other simulation conditions and different shapes of the regulating bodies (10, 20) are considered.

[0052] Incidentally, the distance D2 from the bottom surface of the second regulating body 20 to the interface 9s can be rephrased as the sedimentation depth of the second regulating body 20. The inventor considered that when the distance D2 decreases (that is, when the sedimentation depth of the second regulating body 20 becomes shallower), the convection regulating effect by the second regulating body 20 is affected. Therefore, through convection simulation, the value of the distance D2 was changed to obtain the maximum value TX of the temperature fluctuation range in each case.

[0053] Table 1 below shows the results of the convection simulation. Note that H2 / (L1 + D2) = 2.0 was set as an index of the heat transfer body occupancy rate.

Table 1

[0054] From Table 1, it was found that in order to make the maximum value TX of the temperature fluctuation range 13°C or less, the distance D2 from the bottom surface of the second regulator 20 to the interface 9s, that is, the sedimentation depth, may be set to 1.5 mm or more. The distance D2 can be adjusted by designing the shape, size (volume), or density (material, etc.) of the second regulator 20.

[0055] Incidentally, pay attention to the amount of the heat transfer body 9. In Fig. 5A, compared with Fig. 5B, the amount of the heat transfer body 9 decreases by the volume in which the second regulator 20 is immersed in the heat transfer body 9. When the amount of the heat transfer body 9 decreases, the heat transfer efficiency by the heat transfer body 9 decreases. However, as a result of the above simulation, the average temperature of the anode tip in the case of Fig. 5B was 3060°C, whereas the average temperature of the anode tip in the case of Fig. 5A was 3063°C. That is, the temperature drop width of the anode tip due to the arrangement of the second regulator 20 is only slightly 3°C, and it was found that the decrease in the heat transfer efficiency due to the decrease in the amount of the heat transfer body 9 is limited. From this, it was found that the merit of lowering the maximum value TX is greater than the demerit of the decrease in the heat transfer efficiency due to the decrease in the amount of the heat transfer body 9 by arranging the second regulator 20 shown in Fig. 6.

[0056] [Details of the regulator] With reference to Figs. 7A, 7B, 8A, and 8B, the details of the dimensions and shapes of the regulators (10, 20) will be described. Fig. 7A is a top view of the first regulator 10, looking at the first regulator 10 in the -Z direction. Fig. 7B is a side view of the first regulator 10, looking at the first regulator 10 in the +X direction. Fig. 8A is a top view of the second regulator 20, looking at the second regulator 20 in the -Z direction. Fig. 8B is a side view of the second regulator 20, looking at the second regulator 20 in the +Y direction.

[0057] The four blades 10b constituting the first restricting body 10 are designed to withstand the collision of the heat transfer body 9 in convection or the stress due to the thermal expansion of the heat transfer body 9. For example, the thickness T1 of the blade 10b (see FIG. 7A) is preferably 2 mm or more, and more preferably 3 mm or more. The height (length in the Z direction) L1 of the blade 10b (see FIG. 7B) is preferably 3 mm or more, and more preferably 6 mm or more. The radial length B1 of the blade 10b is preferably 40% or more, and more preferably 45% or more of the inner diameter D6 of the sealed space 6 (see FIG. 3). The length B2 in the X or Y direction of the restricting body (see FIG. 7B) is preferably 80% or more, and more preferably 90% or more of the inner diameter D6 of the sealed space 6 (see FIG. 3). The lengths B1 and B2 are preferably smaller than the inner diameter D6 of the sealed space 6 (see FIG. 3) to the extent that the gap G1 can be provided.

[0058] In the present embodiment, the second restricting body 20 is a rod shape that is long in the Y direction (see FIG. 8A). The length B3 in the Y direction of the second restricting body 20 is preferably 80% or more, and more preferably 90% or more of the inner diameter D6 of the sealed space 6 (see FIG. 3). The central axis in the Z direction of the second restricting body 20 is at the position of Z3. The width of the second restricting body 20 is not uniform, and the width W1 at the end E1 in the +Y direction is larger than the width W2 at the end E2 in the -Y direction. The width gradually decreases from the end E1 to the end E2. Since the second restricting body is in a rod shape in which the width gradually decreases from one end E1 to the other end E2, the convection of the heat transfer body 9 is stabilized. The width W1 is preferably 3 mm or more and 6 mm or less.

[0059] The second regulating body 20 has a risk of rotating and falling about the Y direction which is the longitudinal direction. When the second regulating body 20 falls, it generates a turbulent flow in the heat transfer body 9. Reducing the risk of the second regulating body 20 falling leads to suppressing the generation of the turbulent flow. The second regulating body 20 has a shape of an isosceles trapezoid in a cross section parallel to the XZ plane orthogonal to the longitudinal direction (Y direction) (see FIG. 8B). In this cross section, the width of the upper base V1 of the second regulating body 20 in the X direction is smaller than the width of the lower base V2 in the X direction. Thereby, the center of gravity of the second regulating body 20 is biased toward the lower base V2 side, and the risk of the second regulating body 20 falling in the melted heat transfer body 9 can be reduced. The angle θ1 is preferably 30 degrees or more and 60 degrees or less. The length (height) L2 of the second regulating body 20 in the Z direction is preferably 3 mm or more, and more preferably 6 mm or more. Note that the second regulating body 20 may have a triangular shape in a cross section parallel to the XZ plane.

[0060] In the above simulation, the first regulating body 10 is made of a material mainly containing tungsten, and the second regulating body 20 is made of a material mainly containing titanium, but it is not limited to this combination of materials. As the material of the second regulating body 20, ceramics such as aluminum oxide and magnesium oxide may be used.

[0061] When the discharge lamp 100 is lit, it is preferable that the melting point of the material constituting the restrictor (10, 20) is higher than the melting point of the material constituting the heat transfer body 9 so that the restrictor (10, 20) does not melt. Further, so that the restrictor (10, 20) does not react with the material constituting the main body 5 or the material constituting the heat transfer body 9 and deteriorate, the material constituting the restrictor (10, 20) has sufficiently low reactivity with the material constituting the main body 5 and the material constituting the heat transfer body 9. However, the base material of the second restrictor 20 may be made of a material that can react with the material constituting the main body 5 or the material constituting the heat transfer body 9 (for example, when the heat transfer body 9 is silver, chromium, zirconium, etc.), and a material having sufficiently low reactivity with the material constituting the main body 5 and the material constituting the heat transfer body 9 around the base material (for example, titanium) may be formed so as to surround it. As a method of forming so as to surround titanium or the like around the base material, for example, formation by vapor deposition or formation by various plating methods can be considered.

[0062] Regarding the manufacturing method of the first restrictor 10, four blades 10b may be arranged at 90-degree intervals around the Z2 axis and joined. The first restrictor 10 may be formed by intersecting a flat plate extending in the X direction and a flat plate extending in the Y direction with the Z1 axis and joining them. The first restrictor 10 may be manufactured by integral molding. Even when two blades 10b extending in a straight line are formed of a single flat plate, the single flat plate is counted as being composed of two different blades extending radially outward from the center. The same applies to other examples of the restrictor.

[0063] [Method for obtaining dimensions of each member from the manufactured anode] A method for obtaining the dimensions of each member or each part from the manufactured anode 2 will be described. The method described below is particularly suitable for obtaining the design value of the dimensions of the anode 2 in the discharge lamp lit for use or testing after the manufacture of the discharge lamp. This is because in the anode 2 used for lighting, the interface 9s is not formed flat and the position of the interface 9s in the Z direction is difficult to determine. The position of the interface 9s in the Z direction is used to calculate the distance D2 from the bottom surface of the second restrictor 20 to the interface 9s.

[0064] Explain the main reason why the interface 9s of the anode 2 that has been used for lighting once is not formed flat. FIG. 9 is a cross-sectional view of the anode 2 cooled after the heat transfer body 9 is heated and melted. In FIG. 9, the second restricting body 20 is shown by a dashed line in order to make it easier to read the shape of the interface 9s. Regarding the anode 2 of the discharge lamp 100 that has been lit for use or testing after the manufacture of the discharge lamp 100, the heat transfer body 9 has been heated and melted at least once. When the anode 2 is cooled as the lamp is turned off, the temperature decreases from the surface of the anode 2 toward the inside of the anode 2. As a result, since the timing of thermal contraction due to solidification is different between the surface and the inside of the anode 2, as shown in FIG. 9, the interface 9s between the heat transfer body 9 and the gas space 8 may be recessed near the central axis Z1.

[0065] To obtain the dimensional design value from the manufactured anode 2, follow the following procedure. (Step 1) Remove the anode 2 from the discharge lamp 100 and measure the outer diameter D1 of the anode 2. At a position (line segment P-P in FIG. 10) crossing the gas space 8 (portion not including the heat transfer body 9) relatively above in the sealed space 6, cut the container 5a along the XY plane. By the cutting, the anode 2 is divided into a first electrode portion p1 including the heat transfer body 9 and the restricting bodies (10, 20), and a second electrode portion p2 including the lid 5b (see FIG. 10).

[0066] (Step 2) Measure the weight a of the first electrode portion p1. Also, collect a minute amount of the heat transfer body 9 from the cut surface and estimate the component analysis and the density ρ. For the component analysis, for example, a fluorescent X-ray device or the like may be used.

[0067] (Step 3) Immerse the first electrode portion p1 in a liquid in which the anode 2 does not dissolve and the heat transfer body 9 dissolves, and dissolve the heat transfer body 9 from the first electrode portion p1 and remove the restricting bodies (10, 20). As such a liquid, for example, nitric acid is used. Nitric acid dissolves the silver used as the heat transfer body 9 and hardly dissolves the main body 5 of the anode 2 and the restricting bodies (10, 20). Then, measure the weight b including the restricting bodies (10, 20) excluding the heat transfer body 9 from the first electrode portion p1. Thereby, the volume VM of the heat transfer body 9 is obtained by the formula (3). VM = (a - b) / ρ …(3)

[0068] (Step 4) Measure the length L2 of the second restricting body in the Z direction. Also, float the second restricting body 20 on the melt of a metal having a density close to that of the heat transfer body 9, and measure the distance D2 from the bottom surface of the second restricting body 20 to the interface 9s, which is the sedimentation depth.

[0069] (Step 5) Put a liquid (for example, water) having the same volume as the volume VM of the heat transfer body 9 obtained in Step 3 into the sealed space 6 of the anode 2, and immerse the restricting bodies (10, 20) in the liquid. Then, measure the distance H3 from the upper part of the first restricting body 10 to the liquid surface. The interval H2 in the Z direction between the first restricting body 10 and the second restricting body 20 is obtained using Equation (4). H2 = H3 - L2 …(4)

[0070] [Modified Example of the Second Restricting Body] FIGS. 11A and 11B show a first modified example of the second restricting body. FIG. 11A is a top view of the second restricting body 25, looking at the second restricting body 25 in the -Z direction. FIG. 11B is a side view of the second restricting body 25, looking at the second restricting body 25 in the +Y direction. The second restricting body 25 is long and rod-shaped in the Y direction and has a shape in which the bottom surfaces of two frustums of a cone are in contact with each other. The position C5 in the longitudinal direction (Y direction) passes through the central axis Z3 extending in the Z direction. The diameter W3 at the position C5 is larger than the diameter W4 at the positions (E1, E2) of the longitudinal ends. And the diameter gradually decreases from the position C5 toward the position E1 (or E2). Such a second restricting body 25 can align the direction of the second restricting body 25 with the direction of the convection of the heat transfer body 9 by a slight rotation of the second restricting body 25 around the central axis Z3 when the direction of the second restricting body 25 does not coincide with the direction of the convection of the heat transfer body 9. Also, since the diameter gradually decreases toward the outer side in the radial direction, the convection of the heat transfer body 9 is stabilized. Further, when the side surface or cross section presents a circle like the second restricting body 25, the second restricting body 25 does not fall over, so that the turbulent flow caused by the fall of the second restricting body 25 is not generated. Also, it is easy to process into the shape of this modified example, and the processing cost is low.

[0071] Figures 12A and 12B show a second modification example of the second restricting body. Figure 12A is a top view of the second restricting body 26, looking at the second restricting body 26 in the -Z direction. Figure 12B is a side view of the second restricting body 26, looking at the second restricting body 26 in the +Y direction. The second restricting body 26 is in the shape of a frustum of a cone that is long in the Y direction and has circular end portions E1 and E2. The diameter of the second restricting body 20 is not uniform, and the diameter W1 at the end portion E1 in the +Y direction is larger than the diameter W2 at the end portion E2 in the -Y direction. The diameter gradually decreases from the end portion E1 toward the end portion E2. Since the second restricting body is rod-shaped with a gradually decreasing width from one end portion E1 to the other end portion E2, the convection of the heat transfer body 9 is stabilized. Also, it is easy to process into the shape of this modification example, and the processing cost is low.

[0072] Figures 13A and 13B show a third modification example of the second restricting body. Figure 13A is a top view of the second restricting body 27, looking at the second restricting body 27 in the -Z direction. Figure 13B is a cross-sectional view of the second restricting body 27 along the line segment F-F, looking at the second restricting body 27 in the -Y direction. As shown in Figure 13A, the second restricting body 27 is in a Y shape. As shown in Figure 13B, the cross-section of the second restricting body 27 along the line segment F-F is a rectangle with the Z direction as the longitudinal direction. The three blades (27a, 27b) of the second restricting body 27 all contact a tangent line C6 extending in the Z direction. The tangent line C6 is at a position shifted from the central axis Z3 in the Y direction length and the X direction length. Therefore, among the three blades (27a, 27b), one blade 27b is longer than the other two blades 27a. Since convection of the heat transfer body 9 is likely to be formed along one long blade 27b, it is easy to be stabilized. Also, since the second restricting body 27 has a Y shape, after the second restricting body 27 once coincides with the direction of convection of the heat transfer body 9, the elements of turbulent flow due to the overturning etc. of the second restricting body 27 are small, so the posture of the second restricting body 27 is difficult to change, and thereby, the convection is easy to be stabilized.

[0073] Although not shown and described, as a fourth modification example, the second restricting body 20 may have a cross shape like the first restricting body 10. The number of blades of the second restricting body 20 being less than the number of blades of the first restricting body 10 makes it easier for the convection of the heat transfer body 9 to be stable.

[0074] FIG. 14 shows a first modification example of the first restricting body. FIG. 14 is a top view of the first restricting body 17, looking at the first restricting body 17 in the -Z direction. As shown in FIG. 14, the first restricting body 17 has a T shape. Each of the three blades (17a, 17b) of the first restricting body 17 is in contact with a tangent line C6 extending in the Z direction. The tangent line C6 may be at a position offset from the central axis Z3 or may overlap with the central axis Z3. Since the T-shaped first restricting body 17 has fewer blades than the cross-shaped first restricting body 10, the volume of the restricting body is small, and the amount of the heat transfer body 9 can be increased. Note that, since the two blades 17a of the first restricting body 17 are arranged in a straight line, the two blades 17a may be formed of a single plate.

[0075] FIG. 15 shows a second modification example of the first restricting body. FIG. 15 is a top view of the first restricting body 18, looking at the first restricting body 18 in the -Z direction. The first restricting body 18 has three blades 18b. Each of the three blades is in contact with a tangent line C6 extending in the Z direction. The tangent line C6 overlaps with the central axis Z3. Since the first restricting body 18 has fewer blades than the cross-shaped first restricting body 10, the volume of the restricting body is small, and the amount of the heat transfer body 9 can be increased. Also, since each blade 18b forms an equal angle (120°) with each other, the first restricting body 18 is less likely to tilt and is likely to maintain a stable posture. The stability of the first restricting body 18 leads to the stabilization of convection.

[0076] FIG. 16 shows a third modification example of the first restricting body. FIG. 16 is a side view of the first restricting body 19, looking at the first restricting body 19 in the +X direction. The first restricting body 19 has four blades 19a. The outer surface 19t of each blade 19a has a tapered shape. Therefore, the radial length of the upper surface (+Z side surface) of the blade 19a is smaller than the radial length of the lower surface (-Z side surface).

[0077] The embodiments and their modifications have been described above. The present invention is not limited to the above-described embodiments and their modifications, and various improvements or changes can be made to the above-described embodiments and modifications, or the various modifications can be combined, without departing from the spirit of the present invention.

[0078] In the above, the restricting body was composed of the first restricting body 10 and the second restricting body 20, but it may be composed of three or more restricting bodies.

[0079] In the above, an example has been described in which the anode 2 has a main body 5 having a sealed space 6, a restricting body (10, 20) in the sealed space 6, and a heat transfer body 9 in the sealed space 6. The cathode 3 may have a main body having a sealed space, a plurality of restricting bodies in the sealed space, and a heat transfer body. The discharge lamp 100 may be arranged such that the cathode 3 is located above the anode 2.

Explanation of Signs

[0080] 1: Light-emitting tube 2: Anode 3: Cathode 4: Lead rod 5: Main body 5a: Container 5b: Lid 6: Sealed space 8: Gas space 9: Heat transfer body 9s: Interface (between the heat transfer body and the gas space) 10, 17, 18, 19: First restricting body 10b, 17a, 17b, 18b, 19a: Blade (of the first restricting body) 11: Sealing tube 12: Base 13: Tip (of the electrode) 14: Rear end (of the electrode) 15: Inner wall (of the main body) 19t: Outer surface (of the blade) 20, 25, 26, 27: Second restricting body 27a, 27b: Blade (of the second restricting body) 30: First regulator (when there is no second regulator) 100: Discharge lamp

Claims

1. In a discharge lamp having a pair of electrodes arranged to face each other in the axial direction, at least one of the pair of electrodes includes a main body having a sealed space inside, a heat transfer body located in the sealed space and having a melting point lower than that of the material constituting the main body, a restricting body located in the sealed space, having a surface showing a melting point higher than that of the heat transfer body, and restricting the convection of the heat transfer body, wherein the restricting body includes a first restricting body having a density greater than that of the heat transfer body, and a second restricting body having a density smaller than that of the heat transfer body. A discharge lamp characterized by the above.

2. The discharge lamp according to claim 1, characterized in that the shape of the first restricting body is different from the shape of the second restricting body.

3. The discharge lamp according to claim 2, characterized in that the second restricting body is in the form of a rod extending in one direction.

4. The discharge lamp according to claim 3, characterized in that the shape of the second restricting body in a cross-section perpendicular to the one direction is circular, triangular or trapezoidal.

5. The discharge lamp according to claim 2, characterized in that the first restricting body and the second restricting body each include a plurality of blades extending radially outward from a central axis along the axial direction, and the number of blades of the first restricting body is larger than the number of blades of the second restricting body.

6. The discharge lamp according to any one of claims 1 to 5, characterized in that the second restricting body mainly contains titanium or ceramics.

7. Let the axial length of the first restricting body be L1 (mm), let the axial length of the second restricting body in contact with the heat transfer body be D2 (mm), and when the axial interval between the first restricting body and the second restricting body is H2 (mm), the following formula (1) is satisfied 0 < H2 / (L1 + D2) ≦ 2 … (1) The discharge lamp according to any one of claims 1 to 5, characterized by the above.

8. When the axial length of the second restricting body in contact with the heat transfer body is D2 (mm), the following formula (2) is satisfied D2 ≧ 1.5 … (2) The discharge lamp according to any one of claims 1 to 5, characterized by the above.

9. An electrode used in a discharge lamp, the electrode including a main body having a sealed space inside, and a heat transfer body inside the sealed space and having a melting point lower than that of the material constituting the main body. A restricting body that is within the sealed space, has a surface with a melting point higher than that of the heat transfer body, and restricts convection of the heat transfer body; The restricting body is a first restricting body having a density greater than that of the heat transfer body; and a second restricting body having a density smaller than that of the heat transfer body. The electrode is characterized by the above.

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