JP2001118538A - High-pressure discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-pressure discharge lamp which can suppress a blackening phenomenon. SOLUTION: A high-pressure discharge lamp comprises a discharge tube, having discharge space with filled luminous material and a pair of electrodes in which base end is supported by the discharge tube and heat parts are faced each other in a given distance in the discharge space. Each of the electrodes has a mass portion based on tungsten mounted on the heat parts of an electrodes axis based on tungsten, and the scam total of content of impurities other than tungsten contained in the electrode is 40 ppm or lower, of which potassium content is 12 ppm or lower and iron content is 20 ppm or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-pressure discharge lamp used for general lighting and optical equipment.

[0002]

2. Description of the Related Art Hitherto, as an illumination optical device incorporated in an image display device such as a liquid crystal projector, a device in which a light source and a concave reflecting mirror are integrated has been often used. As the light source, a high-pressure mercury lamp with a short arc close to a point light source is preferred because of its high luminous efficiency, high brightness, good balance of red, blue, and green in emitted light and long life. Used. Hereinafter, a conventional high-pressure mercury lamp will be described as an example of a high-pressure discharge lamp.

In general, a high-pressure mercury lamp includes an arc tube having a light-emitting portion and a sealing portion. The light emitting portion has a pair of electrodes inside, and is filled with mercury as a light emitting metal, a rare gas such as argon as a starting gas, and free halogen for promoting a halogen cycle during operation. FIG. 15 shows an example of an electrode used in a conventional high-pressure mercury lamp. As shown in the figure, a conventional electrode 901 includes an electrode shaft 90 made of tungsten.
At the tip of 2, a coil 9 also made of tungsten
03 was used. This coil 90
3 has a two-layer closely wound structure, and the first layer 903a has 15 layers.
The second layer 903b has eight turns.

When the high-pressure mercury lamp as described above is turned on, the temperature at the electrode tip becomes extremely high. As a result, in the conventional device, even if free halogen is sealed, the tungsten used for the electrode is vaporized and scattered, and this is condensed and adhered on the inner surface of the arc tube glass, so that the arc tube is formed. There is a problem that the lamp life is shortened due to blackening.

Techniques for preventing the blackening of the arc tube include those disclosed in US Pat. No. 5,357,167 and those disclosed in Japanese Patent Application Laid-Open No. Hei 10-92377. FIG. 16 shows US Pat.
7 shows an electrode disclosed in US Pat. As shown in the figure, the electrode 911 is such that a sleeve 913 made of a high-melting-point hardly-soluble metal is arranged on an electrode shaft 912 made of a high-melting-point hardly-soluble metal, such as tungsten or molybdenum.
By heating and melting the metal derived from the electrode shaft 912 and the sleeve 913, the electrode shaft 912 and the sleeve 9 are melted.
13 is provided with a hemispherical electrode end 914 which is integrally connected. With such a structure, the heat capacity of the electrode end portion is kept large, excessive heating of the electrode end portion is suppressed to prevent a blackening phenomenon due to scattering of a high melting point metal such as tungsten, and the electrode shaft 912 is made thin. By this, the electrode shaft 912
That the temperature of the electrode end can be prevented from lowering below the temperature required for electric discharge.

Japanese Patent Application Laid-Open No. Hei 10-92377 discloses an electrode 921 as shown in FIG. 17 and a method for manufacturing the same. Specifically, the tungsten electrode shaft 9
22 is covered with a covering member 923 in a state where the electrode shaft 922 protrudes toward the discharge side, and an inert gas atmosphere is provided between the tip of the electrode shaft 922 and a discharge electrode (not shown). Keep and discharge. The discharge causes the electrode shaft 9
Since the protruding portion of the electrode 22 is melted, the shape of the electrode tip portion 924 is shaped by polishing or grinding a molten portion solidified into, for example, a substantially spherical shape or a water droplet shape.
The electrode 921 of FIG. 17 is manufactured.

[0007]

However, as a result of intensive studies, the present inventor has found that when an electrode is actually manufactured by the electrode manufacturing method disclosed in each of the above publications,
The inventor has found that various problems may occur, and further studies have led to the present invention as a means for solving the problems. Hereinafter, the knowledge obtained by the above study, the history of the present inventor reaching the present invention, and the like will be described in detail.

First, as described in each of the above publications, the present inventor has proposed a method in which an electrode shaft is covered with a sleeve or a coil and the tip is melted. In addition to the fact that the shape of the portion is not stable and mechanical processing such as polishing and grinding is often required, it has been found that the blackening phenomenon cannot be sufficiently prevented in actual use.

That is, when the electrode shaft is melted in a state where the electrode shaft protrudes more than the discharge side end of the sleeve or coil as the covering member, the shape of the electrode tip portion after solidification becomes
It does not have a shape that can be used for actual use as it is, and mechanical processing such as polishing or grinding after solidification of a molten portion is performed as described in, for example, JP-A-10-92377. In many cases, it is necessary to shape into an appropriate shape.

On the other hand, on the other hand, the case where the tip of the electrode is melted while the coil covering the electrode shaft is projected from the tip of the electrode shaft has been examined. It was found that the phenomenon could not be sufficiently prevented. In this case, the inventor of the present application investigates the manufactured electrode, and in this case, the coil (mainly melts).
It was found that a cavity was formed between the electrode and the electrode axis (most of the electrode remained without melting). When the cavity is formed at the electrode tip portion, the heat capacity of the electrode tip portion becomes small, so that the temperature of the electrode tip excessively increases during actual use, and the occurrence of blackening due to the scattering of tungsten cannot be prevented. Will be.

The present invention has been made to solve the above-described problems based on the above findings, and has as its object to provide a high-pressure discharge lamp capable of suppressing the blackening phenomenon.

[0012]

In order to achieve the above object, a high pressure discharge lamp according to the present invention has a discharge tube having a discharge space in which a luminescent substance is sealed, and a base end supported by the discharge tube, A high-pressure discharge lamp comprising a pair of electrodes whose tips are opposed to each other with a predetermined distance in the discharge space, wherein each of the electrodes is mainly made of tungsten at the tip of an electrode shaft mainly made of tungsten. Wherein the total content of impurities other than tungsten contained in the electrode is 40 ppm or less, of which potassium content is 12 ppm or less and iron content is 20 ppm or less. It is characterized by being.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a front view showing an example of the configuration of a high-pressure mercury lamp 10 as an example of a high-pressure discharge lamp according to the present embodiment. As shown in the figure, the high-pressure mercury lamp 10 of the present embodiment includes a substantially spheroidal arc tube 11 made of quartz glass. The arc tube 11 is
The light emitting unit 12 includes a light emitting unit 12 and sealing portions 13 formed at both ends of the light emitting unit 12, and the light emitting unit 12 according to the present embodiment has a central maximum inner diameter of 7.0 mm and an inner volume of 0.1 mm. 24c
m ³ and the wall thickness are 2.5 mm. A pair of opposed electrodes 14 are provided in the light emitting section 12, and the length between the discharge-side tips of the pair of electrodes 14 (hereinafter, referred to as “arc length”) is 1.55 mm. In the light emitting section 12, 36 mg (about 0.16 mg / mm ³ ) of mercury as a luminescent metal and 9.0 of bromine as a halogen are provided.
× 10 ⁻⁵ μmol / mm ³ , and argon gas as a starting gas are sealed at a sealing pressure of 100 mbar.
The end of the electrode 14 on the side opposite to the discharge side is connected to an external lead wire 16 via a metal foil conductor 15 such as molybdenum sealed in the sealing portion 13.

The electrode 14 has a diameter (R) as shown in FIG.
2) 0.4 mm rod-shaped electrode shaft 141 and this electrode shaft 1
41 is provided with a coil 142 having a wire diameter (R1) of 0.25 mm provided at the distal end. The coil 142 is the first layer 14
2a has a two-layer close winding structure in which the second layer 142b has 15 turns and the second layer 142b has eight turns. In this embodiment, the tip of the electrode 14 is the tip of the electrode shaft 141 on the discharge side. So that it protrudes (ΔL) by 0.10 mm from the tip,
The coil 142 is wound around the tip of the electrode shaft 141 by a normal method, and in this state, the coil 142 is fixed to the electrode shaft 141 by resistance welding.

The first discharge generated at the start of use of the high-pressure mercury lamp 10 causes the electrode 14 to be heated and melted at the distal end of the electrode shaft 141 and the coil 142, and as shown in FIG. A block-like portion 143 is formed in the portion. The formation of the mass portion 143 allows the electrode 14
The heat capacity of the discharge-side tip of the electrode increases to an appropriate value, and the rise in the heat capacity suppresses the temperature rise of the electrode tip even during discharge, and further stops the melting of the electrode tip. Electrode 14 having a shape as shown in FIG.
Will function as

As described above, when the lump portion 143 is formed by melting the tip of the electrode by heating at the time of discharge, a change in the arc length due to deformation of the tip of the electrode becomes a problem. In particular, when the arc length is shortened due to the melting of the coil at the tip of the electrode, the voltage between the electrodes drops, and a large amount of current must be flown, thus promoting the occurrence of the blackening phenomenon. This is because However, according to the study of the present inventor, as shown in FIG.
It has been clarified that a change in the arc length between the pair of electrodes 14 can be prevented by protruding the discharge-side tip of the coil 142 slightly from the discharge-side tip of the coil 142.

The results of an examination of the relationship between the length of the protruding portion of the electrode shaft 141 with respect to the coil 142 (ΔL in FIG. 2) and the change in the arc length will be described below. FIG. 4 and FIG. 5 are diagrams showing the change (ΔA) in the arc length when the length of ΔL is variously changed, and the evaluation for the change.
In the figure, the top column shows the value (mm) of the above ΔL, and the second row shows ΔL as the maximum outer diameter of the tip of the coil 142 on the discharge side (R3 in FIG. Divided by the maximum outer diameter.) In the example of FIG.
The electrode shaft 141 used had an outer diameter (R2) of 0.4 mm, and the coil 142 used had a wire diameter (R1) of 0.2 mm (therefore, the maximum outer diameter R3 of the tip of the coil 142).
Is 0.4 + 0.2 * 4 = 1.2 mm. ). The column in the third row is the change ΔA (mm) in the arc length when the initial arc length is 1.5 mm. The “evaluation” at the bottom is the initial arc length (1.5 mm). ) Is evaluated as “○” when the change is within ± 10%, and “X” otherwise. The example of FIG. 5 is the same as FIG. 4 except that the coil 142 has a wire diameter (R1) of 0.25 mm.

As shown in both figures, in each case,
When the ratio of the value of the protrusion length ΔL to the maximum outer diameter R3 of the tip of the coil 142 is 1/50 to 1/5, it indicates that the value of the change ΔA in the arc length is within the allowable range. That is,
When the value of the length ΔL of the protruding portion satisfies the relationship shown in the following formula (1), the change in the arc length is within an allowable range even when the electrode tip is melted and integrated by heating during discharge. It was recognized that.

1/50 * R3 ≦ ΔL ≦ １ ／ * R3 (1) As described above, the reason why the change in the arc length is suppressed when the relationship of the above equation (1) is satisfied will be considered below. .
First, when the length of ΔL is less than 1/50 of the maximum outer diameter (R3) of the distal end portion of the coil 142 (when ΔL <0, that is, the discharge end of the coil 142 is discharged from the electrode shaft 141). In this case, the coil 142 melts before the electrode shaft 141. In this case, it is considered that the coil 142 is melted so as to cover from the outside of the electrode shaft 141. Therefore, a cavity is formed between the electrode shaft 141 and the coil 142 after the melting, so that the coil rises from the electrode shaft 141. As a result, the arc length is reduced. On the other hand, when the length of ΔL exceeds ５ of the maximum outer diameter (R3) of the tip of the coil 142, the coil 142 hardly melts, and the electrode shaft 141 melts, and the electrode shaft 141 melts. It is considered that as a result, the arc length becomes longer as a result.

From the above considerations, when the relationship of the above equation (1) is satisfied, it is expected that not only the change in the arc length can be suppressed but also the above-mentioned problem of the prior art will be solved. First problem of the prior art (the occurrence of blackening phenomenon)
The second problem (instability of the shape of the electrode tip) is that a cavity is formed between the electrode shaft 141 and the coil 142.
Is caused by melting.

In fact, the present inventor investigated the shape of the electrode after fusion and integration, and found that even if the change in the arc length was within the allowable range, most of the fusion was on the coil 142 side. It has been confirmed that the electrode shaft 141 remains almost unchanged in shape. That is, by defining the value of the length ΔL of the protruding portion, even if the coil 142 is to be melted, it is possible to control so that the coil 142 is appropriately brought into close contact with the electrode shaft 141 to be melted and integrated. It is thought that the formation of cavities can be prevented.

From the above findings, the use of the high-pressure mercury lamp 10 according to the present embodiment reduces the heat capacity of the electrode tip due to the formation of a cavity between the electrode shaft 141 and the coil 142, and the resulting blackening. In addition to preventing the occurrence of the phenomenon, it is not necessary to mechanically process the shape of the electrode tip. Next, the general relationship between the outer diameter (R2) of the electrode shaft 141 and the wire diameter (R1) of the coil 142 for the electrode 14 of the present embodiment will be described.
It is preferable that both satisfy the relationship of the following expression (2).

1/4 ≦ R1 / R2 ≦ 3/4 (2) The reason will be described below. 1/4> R1 / R
2, the outer diameter of the electrode shaft 141 (R2)
If the wire diameter (R1) of the coil 142 is too small,
In some cases, the outer diameter (R2) of the electrode 14 is too large, but in the former case, the heat capacity of the discharge-side tip of the electrode 14 does not become sufficiently large, and the temperature of the electrode tip during use rises excessively. On the other hand, the blackening phenomenon is caused. In the latter case, the heat conduction of the electrode shaft 141 becomes too large, so that the temperature at the tip of the electrode 14 is lowered more than necessary, and thermions cannot be emitted, and the discharge is maintained. This is because there is a problem that it becomes impossible.

When the relationship of 3/4 <R1 / R2 is satisfied, the outer diameter (R2) of the electrode shaft 141 is
The wire diameter (R1) of the coil 42 is too large, and the outer diameter (R2) of the electrode shaft 141 is too small with respect to the wire diameter (R1) of the coil 142. 141
On the other hand, in the latter case, the heat conduction of the electrode shaft 141 becomes too small, and the temperature of the electrode tip during use becomes excessively high, resulting in blackening. This is because a phenomenon occurs.

It should be noted that, for example, from a rated power of 100 W to 200 W
When a high-pressure discharge lamp of W is manufactured, the optimum range of the wire diameter (R1) of the coil 142 is generally 0.1 mm.
15 mm to 0.30 mm, the outer diameter of the electrode shaft 141 (R
The optimal range of 2) is from 0.3 mm to 0.5 mm,
It is preferable to select the members used as the electrode shaft 141 and the coil 142 so as to satisfy the relationship of the above expression (2) within this range.

Although the electrode shaft 141 and the coil 142 are mainly composed of tungsten, it is difficult to completely remove impurities in tungsten. That is, in the present embodiment, the total content of potassium, iron, aluminum, calcium, chromium, molybdenum, nickel and silicon as impurities is 20 ppm, and the content of potassium is 5 ppm and the content of iron is Although those containing 5 ppm are used, it can be generally said that the smaller the content, the better. The impurity content in the electrodes of the high-pressure discharge lamp of the present invention will be described later in detail.

As described above, by using the high-pressure discharge lamp of the present embodiment, the occurrence of the blackening phenomenon can be suppressed, and the shape of the electrode tip does not need to be shaped by mechanical processing or the like. (Embodiment 2) In the first embodiment, first, an electrode around which a coil is wound is sealed in an arc tube, and the tip of the electrode is melted and integrated by the first discharge generated when a high-pressure mercury lamp is used. did. However, as described in detail in the first embodiment, the fact that the arc length can be prevented from changing by controlling the length ΔL of the protruding portion of the electrode shaft from the coil means that the arc length can be prevented. Even in the case of manufacturing an electrode for a high-pressure discharge lamp without encapsulating the electrode, the similar problem of the prior art can be solved by defining the protruding length in the same manner.

In this embodiment, as in the first embodiment, the electrodes are first sealed in the arc tube, and the electrodes are not melted and integrated at the first discharge in the arc tube. A case of manufacturing an electrode will now be described. FIG. 6 is a front view showing the configuration of the high-pressure mercury lamp 20 in the present embodiment. High-pressure mercury lamp 2 of the present embodiment
0 is the same as that of the first embodiment shown in FIG. 1 except for the shape of the electrode 24, and therefore, the description of each part other than the electrode 24 is omitted.

FIG. 7 shows the structure of the electrode 24 of the present embodiment. As shown in FIG.
Is substantially the same as that shown in FIG. 3 in the first embodiment, that is, the state where the tip portion of the electrode 14 of the first embodiment is heated and melted by electric discharge, and has a diameter of 0.4 mm.
A coil 2 having a wire diameter of 0.25 mm is
After winding 42, the tip of the electrode 24 is melted to provide a lump portion 243. As in the first embodiment, the coil 242 has a two-layer tightly wound structure in which the first layer 242a has 15 turns and the second layer 242b has 8 turns. However, in the present embodiment, the electrode shaft 241 is formed by a normal method such that the discharge end of the electrode shaft 241 protrudes from the discharge end of the coil 242 by a length that satisfies the relationship of the above equation (1). After winding the coil 242 around the tip and fixing the coil 242 to the electrode shaft 241 by resistance welding, about 0.73 mm from the discharge side tip of the electrode shaft 241
And about 0.6 from the tip of the coil 242 on the discharge side.
By simultaneously heating and melting a portion up to 3 mm (2.5 turns), the discharge-side tips of the electrode shaft 241 and the coil 242 are fused and integrated before the encapsulation of the electrode 24 in the arc tube 21. Is being converted.

The first embodiment, such as the relationship between the length of the projecting portion ΔL of the electrode shaft 241 and the maximum outer diameter of the tip of the coil 242, the relationship between the diameter of the electrode shaft 241 and the wire diameter of the coil 242, etc. However, in this embodiment, since the tip of the electrode 24 is heated and melted prior to encapsulation in the arc tube, the tip is heated and melted here. The length of the portion will be described.

FIG. 8 is a diagram for explaining a preferable range of the length. The length L1 (mm) of the portion to be melted from the discharge-side tip of the coil 242 is
2 is R1 (mm), and the length of the uppermost coil portion (the second layer in the present embodiment) of the coil 242 is N1 (mm).
In this case, it is preferable to satisfy the following expression (3).

R1 ≦ L1 ≦ 0.5 * N1 (3) The reason why it is preferable to satisfy this relationship will be described below. If the length L1 of the portion to be melted satisfies the relationship of R1> L1, that is, if the length L1 of the portion to be melted is shorter than the wire diameter R1 of the coil 242, melting only the portion of the length L1 is a manufacturing problem. In addition to being difficult, the heat capacity of the discharge-side tip of the electrode 24 cannot be increased so much that the temperature of the tip of the electrode 24 excessively increases,
Therefore, there are cases where the blackening phenomenon cannot be prevented. If the length L1 satisfies L1> 0.5 * N1, that is, if the length exceeds the half of the length of the second layer 242b of the coil 242, the heat capacity of the tip of the electrode 24 increases. Too much, the tip temperature of the electrode 24 drops unnecessarily,
A problem arises in that thermal electrons cannot be emitted and discharge cannot be maintained.

As a method of melting the tip of the electrode, for example, laser or plasma can be used.
By controlling the discharge interval and the number of discharges of the argon plasma, the length of the portion to be melted from the electrode tip can be controlled. That is, when the length L1 is increased, the number of discharges may be increased and the discharge interval may be shortened.

As described above, by using the high-pressure discharge lamp electrode 24 of the present embodiment, there is no need to perform mechanical processing or the like at the electrode tip, and if the high-pressure discharge lamp is manufactured using the electrode, It is possible to suppress the occurrence of a blackening phenomenon caused by the generation of a cavity at the electrode tip. (Embodiment 3) Next, a third embodiment of the present invention will be described. In this embodiment mode, results obtained by examining the content of impurities contained in an electrode containing tungsten as a main component will be described.

In general, in an electrode containing tungsten as a main component, the content of impurities such as potassium, iron, aluminum, calcium, chromium, molybdenum, nickel, and silicon is preferably as small as possible. Complete removal of impurities is difficult with current purification methods. Therefore, the inventor of the present application proposes that the second
Regarding the high-pressure discharge lamp electrode 24 described in the first embodiment, when the content of impurities in the electrode is,
We examined whether the occurrence of the blackening phenomenon could be suppressed more efficiently.

The following briefly describes how the presence of impurities relates to the occurrence of the blackening phenomenon. That is, the tungsten of the material of the electrode 24 is
It is easy to form an alloy with each of potassium, iron, aluminum, calcium, chromium, molybdenum, nickel and silicon, which are impurities contained in the electrode 24. As a result, the melting point of this alloy, that is, the melting point of the electrode 24 is lowered, the electrode 24 is scattered, and the arc tube 21 is liable to be blackened.

First, when the degree of blackening with respect to the total content of the above impurities was examined, the result shown in FIG. 9 was obtained. The figure shows that the high-pressure mercury lamp is manufactured by the method described in the second embodiment while changing the impurity content in the electrode 24, and after 3 hours of continuous lighting, the black It shows the result of visually confirming the state of formation. As the “degree of blackening”, “◎” indicates no blackening, “○” indicates almost no blackening, “▲” indicates slight blackening,
“X” indicates increased blackening, and the impurity content was measured by the atomic absorption method (the same applies to the following figures).

As shown in FIG. 9, it was found that if the total content of the above impurities is 40 ppm or less, there is no practical problem, and if it is 25 ppm or less, it is more preferable.
Next, the content of iron (Fe) was also examined. This is because iron is particularly easy to form an alloy with tungsten. When the degree of blackening was examined by variously changing the iron content in the electrode 24, the result as shown in FIG. 10 was obtained.

As shown in the figure, the iron content was 20%.
It was found that if it is less than ppm, it can be used practically without any problem, and if it is less than 10 ppm, it is more preferable. Further, the content of potassium (K) was examined. This is because potassium is known to inhibit the halogen cycle. When the degree of blackening was examined by variously changing the content of potassium in the electrode 24, the result as shown in FIG. 11 was obtained.

As shown in the figure, when the content of potassium is 12 ppm or less, it can be used without any practical problem, and it is found that the content is particularly preferably 10 ppm or less. As described above, the sum of the contents of the respective impurities is 40 ppm or less, the potassium content is 12 ppm or less, and the iron content is 2 ppm or less.
It became clear that it is preferable to define the content to be 0 ppm or less. As described above, the smaller the amount of the above impurities, the better.

(Embodiment 4) Next, an illumination optical device and an image display device using the high-pressure discharge lamp according to the present invention will be described. FIG. 12 is a partially cutaway perspective view showing an example of the configuration of an illumination optical device 40 using the high-pressure discharge lamp of the present embodiment. As shown in the figure, a cap 3 is connected to one external lead wire (not shown) of the high-pressure mercury lamp 30.
7 is connected, and the power supply line 38 is connected to the other external lead wire 36. As the high-pressure mercury lamp 30 in the present embodiment, the high-pressure mercury lamp 10 described in the first embodiment may be used, or the high-pressure discharge lamp electrode 24 described in the second embodiment may be used. It goes without saying that the high-pressure mercury lamp 20 constituted by using this may be used.

Then, the high-pressure mercury lamp 30 is connected to the reflecting mirror 39.
The arc axis of the high-pressure mercury lamp 30 is
The illumination optical device 40 is integrated so as to be located on the optical axis of
Is configured. The reflecting mirror 39 of the present embodiment is made of ceramic and has a funnel shape, and has a reflecting surface 39a made of a titanium oxide-silicon oxide deposited film on the inner surface thereof. The portion 39b has a diameter of about 70 mm. The reflecting mirror 39 has a support cylinder portion 39c on the half opening side thereof, and a base 37 is fixed to the support cylinder portion 39c with insulating cement 41. Further, the power supply line 38 connected to the external lead wire 36 penetrates the reflecting mirror 39 and extends to the opposite side from the reflecting surface 39a.

Next, an image display device using the high-pressure discharge lamp of the present invention will be described. FIG. 13 shows the illumination optical device 4 using the high-pressure mercury lamp 30 as described above.
FIG. 3 is a diagram for describing a schematic configuration of an image display device 50 using 0 as a light source. The image display device 50 includes a light source unit 51 including the illumination optical device 40, a mirror 52, dichroic mirrors 53 and 54 for separating white light from the light source unit 51 into three primary colors of blue, green and red. Mirrors 55, 56, 57, respectively, liquid crystal light valves 58, 59, 60, and a field lens 6 for forming a monochromatic light image for each of the separated three primary colors.
1, 62, 63; relay lenses 64, 65; dichroic prism 66, which recombines light transmitted through liquid crystal light valves 58, 59, 60;
7 so that an image from the image display device 50 is projected on a screen 68. The image display device 50 as shown in FIG. 1 is well known as a so-called three-plate type image display device except that the light source unit 51 uses the high-pressure discharge lamp according to the present invention. Therefore, a detailed description of the configuration is omitted. In the figure, illustration of some other optical elements such as a UV filter is omitted.

Next, the projection length of the electrode shaft of the image display device (hereinafter referred to as "the present invention") 50 of the present invention having the above-described configuration and the lamp used for the light source 51 is expressed by the formula (1). The product of the present invention 50 except that the relationship is not satisfied.
The result of comparison with a conventional image display device having the same configuration (hereinafter referred to as “conventional product”) will be described. In each of the product 50 of the present invention and the conventional product, an AC power supply is connected between the base of the lamp and the power supply line, the lamp voltage is about 75 V, the lamp current is about 2.3 A, and the lamp power is 175 W.
Then, a high-pressure mercury lamp was turned on to perform a life test. As a result, the results shown in FIG. 14 were obtained.

As shown in the figure, the product of the present invention (indicated by the line a) had a screen illuminance maintenance ratio of 94% even after 3000 hours from the start of lighting, while the conventional product ( (Indicated by the line b)) after 3000 hours, the screen illuminance maintenance ratio was only about 60%, which resulted in a practical problem. Such a result was obtained because the blackening phenomenon did not occur on the inner surface of the arc tube in the product 50 of the present invention, whereas a large amount of blackening occurred on the inner surface of the arc tube in the conventional product. . That is, as described in detail in each of the above embodiments, by using the high-pressure discharge lamp according to the present invention, it is possible to prevent blackening from occurring on the inner surface of the arc tube, and thus reduce the illuminance maintenance ratio. It has been clarified that it is possible to provide a high-pressure discharge lamp, an illumination optical device, and an image display device having improved service life.

<Modifications> Although the present invention has been described based on various embodiments, it goes without saying that the contents of the present invention are not limited to the specific examples described in detail in the above embodiments. For example, the following modified example can be considered. That is, in the above-described embodiment, the description has been given of the high-pressure mercury lamp of 175 W, but the same effect can be obtained even with 200 W or the like.

The high-pressure discharge lamp of the present invention is not limited to a high-pressure mercury lamp, but may be replaced by mercury as a luminous substance, argon gas, bromine for accelerating a halogen cycle, or other various types. Can also be used. Specifically, various metal halides generally used for metal halide lamps can be used instead of mercury, and various rare gases such as xenon gas and neon gas can be used instead of argon gas. Further, instead of bromine, free halogen such as chlorine or iodine may be sealed. Further, the material of the electrode shaft and the coil is not limited to tungsten, and a material mainly composed of another hardly soluble metal such as molybdenum can be used.

[0048]

As described in detail above, the high-pressure discharge lamp according to the present invention has an effect that the blackening phenomenon can be suppressed.

[Brief description of the drawings]

FIG. 1 is a front view of a high-pressure mercury lamp 10 according to a first embodiment of the present invention.

FIG. 2 is a high-pressure mercury lamp 10 according to the first embodiment.
FIG. 2 is an enlarged front view of an electrode 14 used in the embodiment.

FIG. 3 is a diagram showing an example of the shape of an electrode 14 after the electrode tip is melted in the high-pressure mercury lamp 10 according to the first embodiment.

FIG. 4 is a diagram showing a result of studying a relationship between a length ΔL of a protruding portion and a change ΔA of an arc length in the high-pressure mercury lamp 10 of the first embodiment.

FIG. 5 is a diagram showing a result of studying a relationship between a length ΔL of a protrusion and a change ΔA of an arc length in the high-pressure mercury lamp 10 according to the first embodiment.

FIG. 6 is a front view of a high-pressure mercury lamp 20 according to a second embodiment of the present invention.

FIG. 7 is a high-pressure mercury lamp 20 according to a second embodiment.
FIG. 3 is an enlarged front view of an electrode 24 used for the first embodiment.

FIG. 8 shows a high-pressure mercury lamp 20 according to the second embodiment.
FIG. 4 is a diagram for explaining a process of melting a tip portion of an electrode 24 used for (1).

FIG. 9 is a diagram showing a result of examining a relationship between a total amount (ppm) of an impurity content and a degree of occurrence of a blackening phenomenon in the third embodiment.

FIG. 10 is a graph showing the Fe content (p
FIG. 6 is a diagram showing a result of an examination on a relationship between pm) and a degree of occurrence of a blackening phenomenon.

FIG. 11 is a graph showing the K content (pp) in the third embodiment;
FIG. 9 is a diagram showing the result of studying the relationship between m) and the degree of occurrence of the blackening phenomenon.

FIG. 12 is a schematic diagram showing an example of the configuration of an illumination optical device using the high-pressure mercury lamp of the present invention.

FIG. 13 is a schematic diagram showing an example of the configuration of an image display device using the high-pressure mercury lamp of the present invention.

FIG. 14 is a diagram illustrating a relationship between a lighting time and a screen illuminance maintenance ratio in an image display device according to a fourth embodiment.

FIG. 15 is a diagram showing an example of an electrode used in a conventional high-pressure mercury lamp.

FIG. 16 is a diagram showing a structure of an electrode disclosed in US Pat. No. 5,537,167.

FIG. 17 is a diagram showing a structure of an electrode disclosed in Japanese Patent Application Laid-Open No. 10-92377.

[Explanation of symbols]

 10, 20 High-pressure mercury lamp 11, 21 Arc tube 12, 22 Light emitting unit 13, 23 Sealing unit 14, 24 Electrode 15, 25 Metal foil conductor 16, 26 External lead wire 141, 241 Electrode shaft 142, 242 Coil 143, 243 Lump part 39 Reflecting mirror 40 Illumination optical device 50 Image display device 58, 59, 60 Liquid crystal light valve 66 Dichroic prism 67 Projection lens 68 Screen

Claims (1)

[Claims] A discharge tube having a discharge space in which a luminescent substance is sealed; and a pair of electrodes whose base ends are supported by the discharge tube and whose distal ends face each other at a predetermined distance in the discharge space. Wherein each of the electrodes is provided with a lump-shaped portion mainly made of tungsten at a tip end of an electrode shaft mainly made of tungsten, and other than tungsten contained in the electrodes. The high-pressure discharge lamp according to claim 1, wherein the total content of impurities is 40 ppm or less, of which potassium content is 12 ppm or less and iron content is 20 ppm or less.