JP5346428B2 - Super high pressure mercury lamp - Google Patents

Description

The present invention relates to an ultra-high pressure mercury lamp used in a projector device such as a liquid crystal display device or a DLP (digital light processor) using a DMD (digital mirror device). In particular, the present invention relates to an ultrahigh pressure mercury lamp in which 0.15 mg / mm ³ or more of mercury is sealed in an arc tube, and the mercury vapor pressure during lighting is 150 atmospheres or more.

  Currently, for example, in a liquid crystal projector device and a projection type projector device represented by DLP using DMD, it is required to illuminate an image with a sufficient color rendering property on a screen. In order to meet such demands, it is necessary to use a light source that is reduced in size and made into a point light source. For example, an ultra-high pressure mercury lamp in which mercury is sealed is used as the light source.

  In ultra-high pressure mercury lamps, the mercury vapor pressure when the lamp is steadily lit is over 150 atm. Thus, the mercury vapor pressure when lit is extremely high. Can be improved. Such an ultra-high pressure mercury lamp is disclosed in Patent Documents 1 and 2, for example.

FIG. 1 is a cross-sectional view of an ultrahigh pressure mercury lamp cut along a plane including a tube axis.
The ultra-high pressure mercury lamp 100 includes a bulb 10 having a substantially spherical light emitting part 11 in which an internal space S is formed, and columnar sealing parts 12 that are continuous at both ends of the light emitting part 11. In the internal space S, a pair of electrodes 13 and 14 are arranged to face each other, and 0.15 mg / mm ³ or more of mercury as a luminescent material and a halogen gas for performing a halogen cycle are enclosed. The electrodes 13 and 14 are partially embedded in the sealing portion 12, and the base end portion is connected to one end of the power supply metal foil 15. An external lead 16 that protrudes outward from the sealing portion 12 is connected to the other end of the metal foil 14.

  By the way, such an ultra-high pressure mercury lamp has an extremely high pressure in the light emitting unit 11 when it is turned on. Therefore, the sealing unit 12 shown in FIG. 14 and the metal foil 15 for power supply need to be adhered sufficiently and firmly. This is because, if the adhesion is poor, the halogen gas enclosed in the internal space S in the light emitting section 11 is lost, and cracks are also caused. Therefore, in the sealing step of sealing the electrode and the metal foil to form the sealing portion, for example, a quartz tube serving as a bulb is heated and melted at a high temperature of 2000 ° C., and in that state, a thick quartz glass Is gradually contracted to improve the adhesion between the quartz glass, the electrode and the metal foil.

However, when the diameters of the electrodes 13 and 14 embedded in the quartz glass constituting the sealing portion 12 are large, if the quartz glass is baked at an excessively high temperature when the sealing portion 12 is formed, the quartz glass and the quartz glass In contrast, the adhesion to the thin metal foil 15 is improved, but there is a problem that the sealing portion 12 is easily damaged when the lamp is turned on or when the lamp is turned off.
As a cause of this, when the temperature of the sealing portion 12 rises all at once when the quartz glass is baked at a high temperature, the difference in expansion coefficient between the tungsten constituting the electrodes 13 and 14 and the quartz glass constituting the sealing portion 12. This is because the relative expansion amount differs between the electrodes 13 and 14 and the sealing portion 12, so that cracks are generated at portions of the sealing portion 12 that are in contact with the electrodes 13 and 14. Although this crack is extremely small, it grows as the internal space S becomes an ultra-high pressure state of 150 atm or more when the lamp is turned on, and eventually causes the sealing portion 12 to be damaged.
For this reason, the diameters of the electrodes 13 and 14 at the portion in contact with the sealing portion 12 cannot be 1.5 mm or more, for example.

  Further, in the manufacturing process of the ultra high pressure mercury lamp, the impurities contained in the electrodes 13 and 14 are released before the electrodes 13 and 14 are inserted into the bulb 10, so that the electrodes 13 and 14 are, for example, in an electric furnace. Is heat treated. However, when the temperature of the heat treatment is too high, the electrode constituent material (for example, tungsten) is crystallized to promote the growth of crystal grain boundaries of the electrode constituent material.

As described above, in the ultra high pressure mercury lamp as described above, the diameters of the electrodes 13 and 14 cannot be increased to 1.5 mm or more. Further, conventionally, in the above heat treatment, no consideration was given to the growth of crystal grain boundaries, so that the growth of the crystal grain boundaries of the electrode constituent materials present in the electrodes 13 and 14 was excessively promoted, and the electrode In some cases, the grain boundary of the electrode constituent material is larger than the diameter. In such a case, since the strength at the crystal grain interface of the electrode constituent material is reduced, for example, when the electrodes 13 and 14 are inserted into the bulb 10 in the process of manufacturing the ultra high pressure mercury lamp, or when the ultra high pressure mercury lamp is used. For example, when vibration is applied to the electrodes 13 and 14, there is a problem that electrode breakage occurs from the crystal grain interface of the electrode constituent material.
JP-A-2-148561 JP-A-6-52830

  In view of the above, an object of the present invention is to provide a highly reliable ultra-high pressure mercury lamp while suppressing the occurrence of electrode breakage starting from the crystal grain interface of the electrode constituent material.

The invention of claim 1 of the present application is
An arc tube having a light-emitting part having an internal space and a sealing part continuous at both ends of the light-emitting part, a pair of electrodes are arranged oppositely in the internal space, and 0.15 mg / mm ³ or more of mercury is contained. In the enclosed ultra-high pressure mercury lamp,
In the electrode, the diameter of the minimum diameter portion is d, and the number of crystal grain boundaries of the electrode constituent material crossed by a straight line orthogonal to the electrode central axis in a cross section obtained by cutting the minimum diameter portion along a plane including the electrode central axis is n. Then, the above problem is solved by satisfying the relationship of d ³ × n ² ≧ 1.73.

Easiness of electrode breakage occurs in the diameter of the minimum diameter portion (hereinafter also simply referred to as the minimum diameter portion) in the portion embedded in the sealing portion of the electrode and the cross section obtained by cutting the minimum diameter portion in the longitudinal direction of the electrode. It is determined by the number of crystal grain boundaries (hereinafter also simply referred to as crystal grain boundaries) that intersect a straight line perpendicular to the central axis.
That is, when the minimum diameter portion, which is the most prone to electrode breakage, is thick, electrode breakage is suppressed even if the number of crystal grain boundaries is small. As a matter of course, when the minimum diameter portion is thick, if the number of crystal grain boundaries is large, it is possible to more reliably suppress electrode breakage. However, as described above, since the electrode diameter cannot be larger than, for example, 1.5 mm, there is a limit to increasing the minimum diameter portion.
On the other hand, even if the minimum diameter portion has to be reduced due to the design of the ultrahigh pressure mercury lamp, if the number of crystal grain boundaries is large, electrode breakage can be suppressed.
Therefore, the occurrence of electrode breakage can be reliably suppressed by optimally defining the relationship between the size of the minimum diameter portion and the number of crystal grain boundaries according to the specifications of the ultra-high pressure mercury lamp, particularly the electrode. . The reason why the relationship between the diameter d of the minimum diameter portion and the number n of crystal grain boundaries is defined as d ³ × n ² ≧ 1.73 is that when the inventors verified the experimental results described later, This is because all of the electrode samples that did not satisfy the relationship d ³ × n ² ≧ 1.73.

  Furthermore, the invention according to claim 2 of the present application is characterized in that the electrode front portion protruding from the internal space is made of a tungsten material having a purity of 99.99% or more.

  According to this, in addition to preventing the above-described electrode breakage, the amount of impurities contained in the front portion of the electrode, which is the portion of the electrode protruding into the internal space, is extremely reduced. Therefore, it is possible to reliably prevent the occurrence of a problem that blackening occurs in the light emitting part due to the adhesion of impurities to the inner wall of the light emitting part. Furthermore, since there is little content of potassium etc. which is a typical impurity contained in a tungsten material, it has the advantage that the load with respect to an environment is also small.

  Further, the invention of claim 3 of the present application is characterized in that the electrode is formed by joining the electrode front portion and the electrode rear portion.

The technical significance of the invention of claim 3 of the present application will be described below.
As described above, it is desirable that the electrode front portion protruding into the internal space of the electrode is made of a material having high tungsten purity. However, if the entire electrode is made of a tungsten material having a purity as high as 99.99% or more, it is not preferable in the following points.
The heat treatment of the tungsten material is performed for the purpose of removing impurities contained in the tungsten material in advance. Usually, since the tungsten material is disposed in a heating furnace, the entire tungsten material is heated. . Further, a tungsten material having a high purity of 99.99% or more is more likely to grow crystal grain boundaries during heat treatment than a tungsten material having a low purity (high impurity content). Therefore, when the entire electrode is made of a tungsten material having a high purity, crystal grain boundaries grow over the entire electrode, and the number of crystal grain boundaries decreases. Therefore, it is good in that the amount of impurities contained in the front part of the electrode is reduced, but the crystal grain boundary in the minimum diameter part of the electrode grows and the number of crystal grain boundaries existing in the minimum diameter part is small. Thus, the above-described problem of electrode breakage cannot be solved.
For this reason, by joining the electrode front part and the electrode rear part prepared separately, the number of crystal grain boundaries existing in the minimum diameter part of the electrode is large, but it is contained in the protruding part. The amount of impurities can be reduced.

  Furthermore, the invention according to claim 4 of the present application is characterized in that the electrode front portion and the electrode rear portion are joined by a laser.

  By using a laser, the electrode front part and the electrode rear part can be easily joined.

Further, the invention of claim 5 of the present application is an electrode for an ultrahigh pressure mercury lamp, wherein the diameter of the minimum diameter portion of the electrode is d, and the minimum diameter portion is cut by a plane including the electrode central axis. The relationship d ³ × n ² ≧ 1.73 is satisfied, where n is the number of crystal grain boundaries of the electrode constituent material crossed by a straight line orthogonal to the electrode central axis.

  Thereby, since the number of crystal grain boundaries existing in the minimum diameter portion of the electrode is large, the mechanical strength of the electrode itself becomes high, and the problem of electrode breakage can be suppressed.

  Furthermore, the invention of claim 6 of the present application is characterized in that the electrode is formed by joining an electrode front portion having a purity of 99.99% or more and an electrode rear portion.

  Thereby, in addition to being able to suppress the malfunction of electrode breakage, the impurity content in the front part of the electrode can be reduced.

  Furthermore, according to the invention of claim 7 of the present application, the electrode is characterized in that an electrode front portion and an electrode rear portion are joined by a laser.

  By using a laser, the electrode front part and the electrode rear part can be easily joined.

  Furthermore, according to invention of Claim 8 of this application, it is a manufacturing method of the electrode for an ultrahigh pressure mercury lamp, Comprising: The process of heat-treating the said electrode front part, The process of heat-treating the said electrode rear part, Electrode front part And a step of melting the portion to be joined between the electrode front portion and the electrode rear portion with a laser in a state where the electrode rear portion and the electrode rear portion are in contact with each other, and joining the electrode front portion and the electrode rear portion. Features.

The technical significance of the invention of claim 8 of the present application will be described below.
For the front part of the electrode having a high purity of 99.99% or more, heat treatment is performed to grow a grain boundary, whereby impurities contained in the front part of the electrode are released in advance, and the impurity content is reduced. To do.
On the other hand, the rear portion of the electrode is heat-treated using a tungsten material having a low purity so that the crystal grain boundary does not easily grow, or under the condition that the crystal grain boundary is difficult to grow even if a high-purity tungsten material is used.
In this way, in the state where the front part of the electrode and the rear part of the electrode that have been separately heat-treated are brought into contact with each other, the portion to be joined between the front part of the electrode and the rear part of the electrode is melted by the laser, The electrode and the back portion of the electrode are joined, so that an electrode with a small amount of impurities contained in the front portion of the electrode can be easily manufactured while the number of crystal grain boundaries existing in the back portion of the electrode is large. .

  According to the present invention, since the mechanical strength of the electrode is high, it is possible to reliably solve the problem of electrode breakage during the production of an ultra high pressure mercury lamp or the use of an ultra high pressure mercury lamp.

FIG. 1 is a longitudinal sectional view showing a schematic configuration of an extra-high pressure mercury lamp according to the present invention.
The ultra-high pressure mercury lamp 1 is made of quartz glass, and includes a bulb 10 including a substantially spherical light emitting portion 11 and a cylindrical sealing portion 12 continuous to both ends of the light emitting portion 11. In the internal space S of the light emitting unit 11, for example, 2 × 10 ⁻⁴ μmol / mm ^{3 to} 7 × 10 ⁻³ μmol / for mainly performing a halogen cycle with 0.15 mg / mm ³ or more of mercury as a light emitting substance. A halogen gas such as bromine of mm ³ and a rare gas such as argon of 5 kPa or more are enclosed for improving startability. Further, a pair of electrodes 13 and 14 made of tungsten are disposed in the internal space S of the light emitting unit 11 with their tips facing each other. The base end portions of the electrodes 13 and 14 are connected to one end of a power supply metal foil 15 embedded in the sealing portion 12 and made of molybdenum. The other end of the metal foil 15 is connected to one end of an external lead 16 made of molybdenum and partly protruding outward from the sealing portion 12.
In such an ultra-high pressure mercury lamp 1, a power supply device (not shown) is connected to the external leads 16 at both ends, and power is supplied to the electrodes 13 and 14, thereby causing dielectric breakdown between the electrodes 13 and 14 and discharging between the electrodes. An arc is formed, and light rays including visible light are emitted from the light emitting unit 11 to the outside of the light emitting unit 11.

FIG. 2 shows an enlarged cross-sectional view in the vicinity of the electrode. One electrode 13 has an electrode front portion 131 and an electrode rear portion 132 joined by, for example, a laser.
The large-diameter electrode front portion 131 is a portion that receives electron collision from the other electrode 14, and is disposed in the internal space S of the light emitting portion 11 so as to face the other electrode 14. The cylindrical electrode rear portion 132 joined to the electrode front portion 131 is embedded in the sealing portion 12 so as to substantially coincide with the central axis of the bulb, and the base end portion of the metal foil 15 embedded in the sealing portion 12 Are connected by spot welding, for example.
Hereinafter, “embedding” means a state in which the electrode rear portion 132 is in contact with the inner peripheral surface of the sealing portion 12, and a minute gap between the electrode rear portion 132 and the inner peripheral surface of the sealing portion 12. It means both of the states that are intervening.

  The other electrode 14 is configured by attaching a coil-shaped start assisting portion 141 in the vicinity of the tip of a shaft portion 142 having a pointed tip. In the electrode 14, a part of the coiled auxiliary start portion 141 and the shaft portion 142 are arranged in the internal space S of the light emitting portion 11 so that the electrode 14 substantially coincides with the central axis of the bulb, and most of the shaft portion 142 is sealed. It is embedded in the part 12. By providing the coil-shaped start assisting portion 141, the start assisting portion 141 easily rises in temperature at the time of lighting start, so that it can be started easily.

  As shown in FIG. 2, the “minimum diameter portion” of the electrode is an arbitrary portion when the shaft portion 131 and the electrode rear portion 132 have a cylindrical shape and the outer diameter is uniform in the longitudinal direction. Say. When one electrode 13 has a shape as shown in FIG. 3, d shown in FIG. 3A and d shown in FIG. 3B are the diameters of the minimum diameter portion.

An example of the specifications of the ultrahigh pressure mercury lamp according to the present invention as described above is as follows.
The bulb 10 has a total length of 10.8 mm, a maximum outer diameter of the light emitting portion 11 of 12.0 mm, and a maximum outer diameter of the sealing portion 12 of 7.6 mm. One electrode 13 has a total length of 13.5 mm, a maximum outer diameter of the electrode front portion 131 of 3.0 mm, a maximum outer diameter of the electrode rear portion 132 of 0.8 mm, and the electrode rear portion 132 embedded in the sealing portion 12. The length is 6.0 mm. The other electrode 14 has an overall length of 11.0 mm, a maximum outer diameter of the shaft portion 142 of 1.3 mm, and an embedded length of the shaft portion 142 in the sealing portion 12 of 5.0 mm. The metal foil 15 has a total length of 14.0 mm and a thickness of 20 μm. The lamp operating power is 270W to 300W.

Below, the manufacturing method of the electrode of this invention is demonstrated. FIG. 4 is a view for explaining the electrode manufacturing method of the present invention.
(I)
A tungsten material 131 ′ having a purity of 99.99% or more, which becomes the electrode front portion, is prepared. This tungsten material is placed in a heating furnace, and heat treatment is performed under predetermined processing conditions. As a result, the crystal grain boundaries existing in the tungsten material grow and the number of crystal grain boundaries becomes small, so that the impurities originally contained in the tungsten material become small.
As an example of the heat treatment conditions, the temperature was increased to 2200 ° C. at a temperature increase rate of 40 ° C./min, and this state was maintained for 2 hours.
(B)
A tungsten material 132 ′ having a purity of about 99.0%, which becomes the electrode rear portion, is prepared. By placing this tungsten material in a heating furnace and performing heat treatment under predetermined processing conditions, impurities contained in the tungsten material are released to some extent from the tungsten material, while the grain boundaries existing in the rear part of the electrode are removed. Control the number optimally.
As an example of the heat treatment conditions, the temperature was increased to 2200 ° C. at a temperature increase rate of 40 ° C./min, and this state was maintained for 2 hours.
(C)
In a state where the end surfaces of the tungsten material 131 ′ that is the front portion of the electrode and the tungsten material 132 ′ that is the rear portion of the electrode that have undergone the heat treatment are in contact with each other, the tungsten material that becomes the front portion of the electrode and the tungsten that becomes the rear portion of the electrode A laser is irradiated to the part to be joined with the material. Thereby, both tungsten materials 131 ′ and 132 ′ are melted to form the joint portion 133, and the electrode 13 is formed.
As an example of laser irradiation conditions, when a YAG laser is used, the irradiation intensity of laser light is 72 J and the irradiation time is 90 msec.

  According to the electrode manufacturing method as described above, since the tungsten material having a purity of 99.99% or more is used, the growth of the crystal grain boundary of the electrode front portion 131 is promoted and contained in the electrode front portion 131. In addition, the number of crystal grain boundaries existing in the electrode rear portion 132 does not grow excessively and the number of crystal grain boundaries existing in the electrode rear portion is increased. The electrode 13 can be manufactured. Therefore, since the mechanical strength of the minimum diameter portion of the electrode, which is a portion where electrode breakage is likely to occur, becomes high, it is possible to suppress problems that cause electrode breakage.

Therefore, in the ultra high pressure mercury lamp incorporating the electrode obtained by the above manufacturing method, the mechanical strength of the minimum diameter portion of the electrode 13 is sufficiently high. For example, in the process of manufacturing the ultra high pressure mercury lamp, the electrode 13 Is reliably prevented from breaking when the electrode is inserted into the bulb 10 or when the ultra high pressure mercury lamp is turned on.
In addition, since the impurity contained in the electrode front portion 131 protruding into the internal space S of the light emitting portion 11 is extremely small, impurities are released into the internal space S and the halogen cycle in the internal space S is hindered. Thus, it is possible to reliably prevent the occurrence of the problem that blackening occurs on the inner wall of the light emitting unit 11.

According to the ultra-high pressure mercury lamp of the present invention, the diameter d of the minimum diameter portion of the electrode (electrode rear portion 132 in the example shown in FIG. 2) and the cross section obtained by cutting the minimum diameter portion along a plane including the electrode central axis Since d ³ × n ² expressed by the relationship between the number n of the straight lines orthogonal to the central axis crossing the grain boundaries is defined as 1.73 or more, the mechanical strength at the minimum diameter portion of the electrode is reduced. Since it becomes sufficient, the problem of electrode bending can be solved reliably. This effect has been confirmed by experiments described below.

  Below, the experiment conducted in order to confirm the effect of this invention is demonstrated. In order to use for the experiment, 300 sample electrodes for the experiment were produced based on the configuration of the electrode 13 shown in FIG. The sample electrode is made of tungsten, unified with a total length of 13.5 mm and a maximum outer diameter of 3.0 mm, and a minimum d diameter d of 0.3 mm, 0.4 mm, 0.6 mm, 0.8 mm, and 1.0 mm. The number of crystal grain boundaries n crossed by a straight line perpendicular to the electrode central axis in the longitudinal section of the smallest diameter portion is changed to 1, 3, 5 by changing the heat treatment method for each of the six types of 1.2 mm. , 7, and 9 types. That is, the breakdown of the 300 sample electrodes includes 30 types of combinations of the diameter d of the minimum diameter portion and the number n of crystal grain boundaries, and 10 combinations of each.

Here, a method of counting the number n of crystal grain boundaries will be described with reference to FIG. FIG. 5 shows an enlarged view of a cross section obtained by cutting the minimum diameter portion of the electrode along a plane including the electrode central axis with a microscope.
A region X surrounded by a solid line portion shown in FIG. 5 represents one crystal grain boundary. The number of crystal grain boundaries is determined by polishing the cross section at the smallest diameter portion of the electrode to expose the crystal plane, taking a photograph, and drawing a straight line M orthogonal to the electrode central axis L in the cross section on the photograph. The number n of crystal grain boundaries indicated by a solid line X that intersects with. In addition, as shown in FIG. 5, the area | region Y enclosed by the ridgeline R and the continuous line X of the electrode was also counted as one crystal grain boundary.
In FIG. 5, the numbers on the straight line M indicate the number of crystal grain boundaries X crossed by the straight line M. In the example shown in FIG. 5, the number of crystal grain boundaries is counted as nine.

  FIG. 6 is a schematic diagram for explaining an experimental method performed on all of the sample electrodes. The fixing jig 51 is formed with a bottomed hole 52 having a size substantially the same as the diameter of the minimum diameter portion of the sample electrode. The load applying means 53 is used from the side of the sample electrode 13 ′ while the sample electrode 13 ′ is fixed in the direction perpendicular to the ground by fitting the minimum diameter portion 132 ′ of the sample electrode 13 ′ into the bottomed hole. A load of 5 kgf was applied, and the presence or absence of breakage of the sample electrode 13 ′ was visually confirmed. The reason why the load of 5 kgf is applied is that, based on the experience of the present inventors, if the electrode used in the ultrahigh pressure mercury lamp according to the present invention can withstand the load of 5 kgf, the electrode will not break. Because it is expected.

  In Table 1, “◯” indicates that none of the electrode breaks occurred in the 10 sample electrodes, and “Δ” indicates that 1 or 2 electrode breaks occurred in the 10 sample electrodes. “×” indicates that 3 or more electrode breaks occurred in 10 sample electrodes.

According to Table 1, when the diameter d of the minimum diameter portion 132 ′ of the sample electrode 13 ′ is 1.2 mm, the cross section of the minimum diameter portion 132 ′ cut along a plane including the electrode axis is orthogonal to the electrode axis. It was confirmed that even if the number n of crystal grain boundaries crossed by the straight line was 1, no electrode breakage occurred. Thereby, when the diameter d of the minimum diameter portion 132 ′ is 1.2 mm or more, it is expected that no electrode break occurs even if the number n of crystal grain boundaries is one. In the case where the diameter d of the minimum diameter portion 132 ′ is 0.6 mm or more, it was confirmed that electrode breakage does not occur if the number n of crystal grain boundaries is 3 or more. When the diameter d of the smallest diameter portion 132 ′ is 0.4 mm, the number n of crystal grain boundaries is 7 or more, and when the diameter d of the smallest diameter portion 132 ′ is 0.3 mm, the number of crystal grain boundaries. It was confirmed that n was 9 or more and no electrode breakage occurred.
Then, it was confirmed that when d ³ × n ² expressed by the relationship between the diameter d of the minimum diameter portion 132 ′ and the number n of crystal grain boundaries is 1.73 or more, no electrode breakage occurs. . On the other hand, when d ³ × n ² is less than 1.73, it was confirmed that electrode breakage occurred in at least one of the ten sample electrodes.
Therefore, by using an electrode with d ³ × n ² of 1.73 or more, it is possible to reliably prevent electrode breakage during the production of an ultrahigh pressure mercury lamp or when the ultrahigh pressure mercury lamp is used. can do.

  As mentioned above, although embodiment of the ultra-high pressure mercury lamp of this invention was described, this invention is not limited to said embodiment, It can also be set as the following embodiments.

  The present invention can be applied to both one electrode and the other electrode, or can be applied to only one of the electrodes.

  In the present invention, it is not always necessary to increase the number of crystal grain boundaries present in the minimum diameter portion of the electrode and to configure the front portion of the electrode with a tungsten material having a purity of 99.99% or more. That is, when only the problem of electrode breakage is to be intensively solved, the front portion of the electrode can be made of a tungsten material having a purity of less than 99.99%.

  The present invention does not necessarily exclude that the entire electrode is made of a tungsten material having a purity of 99.99% or more. That is, high-purity tungsten material is easy to grow crystal grain boundaries, but by devising a heat treatment method, the number of crystal grain boundaries existing in the minimum diameter part of the electrode is controlled to be a predetermined number. It is possible. For example, for a single tungsten material, using a heating furnace capable of providing a local temperature distribution in the furnace chamber, the minimum diameter part of the electrode is subjected to heat treatment under conditions that do not cause excessive growth of crystal grain boundaries, About the electrode front part, heat processing can also be performed on the conditions which grow a crystal grain boundary.

  The present invention is not limited to a method of forming two electrodes by joining two tungsten materials with a laser. For example, the two tungsten materials can be joined by press-fitting the other tungsten material that is the rear portion of the electrode into the bottomed hole formed in one of the tungsten materials that is the front portion of the electrode.

  In the present invention, the electrode forming method is not necessarily limited to joining two separate members. That is, an electrode can also be formed by joining three or more electrode constituent members.

  The present invention can be applied to either a DC lighting ultra-high pressure mercury lamp or an AC lighting ultra-high pressure mercury lamp.

It is sectional drawing of the longitudinal direction of the ultra-high pressure mercury lamp of this invention. It is an enlarged view of the electrode vicinity of FIG. It is sectional drawing of the longitudinal direction which shows the other structure of the electrode which concerns on this invention. It is a figure for demonstrating the manufacturing method of the electrode of this invention. The figure which expanded the cross section which cut | disconnected the minimum diameter part of the electrode with the plane containing an electrode central axis with the microscope is shown. It is the schematic for demonstrating the experiment which confirms the effect of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Super high pressure mercury lamp 10 Bulb 11 Light emission part 12 Sealing part 13 One electrode 131 Electrode front part 132 Electrode rear part 14 The other electrode 141 Start auxiliary part 142 Shaft part 15 Metal foil 16 External lead S Internal space

Claims (4)

A bulb having a light emitting part having an internal space and a sealing part continuous at both ends of the light emitting part is provided, and a pair of electrodes are arranged oppositely in the internal space and 0.15 mg / mm ³ or more of mercury is enclosed. In the ultra-high pressure mercury lamp
The electrode is composed of an electrode front part and an electrode rear part having a smaller diameter than the electrode front part and extending into the sealing part,
The diameter of the minimum diameter portion of the electrode rear portion is d (mm), and the crystal grain boundary of the electrode constituent material crossed by a straight line perpendicular to the electrode central axis in a cross section obtained by cutting the minimum diameter portion along a plane including the electrode central axis. An ultrahigh pressure mercury lamp characterized by satisfying a relationship of d ³ × n ² ≧ 1.94 , where n is the number of.   2. The ultra high pressure mercury lamp according to claim 1, wherein the electrode is made of a tungsten material having a purity of 99.99% or more at an electrode front portion protruding into the internal space.   The ultra high pressure mercury lamp according to claim 2, wherein the electrode is formed by joining the electrode front portion and the electrode rear portion.   The ultra-high pressure mercury lamp according to claim 3, wherein the electrode front part and the electrode rear part are joined by a laser.

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