JP5580136B2 - Discharge lamp - Google Patents

Description

  The present invention relates to a discharge lamp in which an electrode is arranged in an arc tube, and more particularly to a surface structure of an electrode used for a high-intensity discharge lamp (HID lamp) such as a short arc type discharge lamp.

  In a short arc type discharge lamp, a cathode and an anode are disposed opposite to a quartz glass discharge tube, and arc discharge is generated by emission of electrons from the cathode to the anode, and discharge light is emitted. As an electrode material, tungsten (W) having a high melting point is generally used to prevent electrode melting during lighting.

In addition, in the case of a cathode used in a high-intensity discharge lamp, doping with thorium oxide (ThO ₂ ), which is an electron-emitting material (electron-emitting material) having a relatively low operating temperature, is performed in order to increase electron emission capability and emit high-intensity light. A tungsten cathode (commonly known as a tritan cathode) is used (see, for example, Patent Documents 1 and 2).

  During arc discharge, the temperature of the cathode tip and anode tip rises due to electron emission. When the temperature rises to near the melting point of the electrode material, the cathode tip and anode tip are melted and evaporated, and the electrode is consumed. The evaporated metal adheres to the inner wall of the discharge tube, thereby blackening the inner wall of the arc tube. That is, the adhesion of metal causes a decrease in transmittance, and the light output of the lamp decreases. Further, when the inner wall of the arc tube is blackened, the blackened portion is locally heated to accumulate heat distortion in the arc tube, and the lamp may burst.

  In the case of a tritan cathode, thorium forms a monoatomic layer on the electrode surface by the reduction action, but oxygen separated from thorium from the surface binds to tungsten at the tip of the anode, which lowers the melting point of the anode tip, Exhaust. In order to prevent such electrode consumption, for example, after a tritan cathode is formed, a layer not containing thorium oxide (a thorium oxide layer) is formed near the cathode surface by vacuum heat treatment (see Patent Document 3).

Alternatively, it is possible to prevent blackening of the arc tube by coating the inner surface of the arc tube with transparent polycrystalline alumina (Al ₂ O ₃ ) (see Patent Documents 4 and 5). Alumina is chemically and physically more stable than quartz glass, a discharge tube material, and does not react with charged particles such as metals and ions emitted from electrodes during lighting, compounds, etc. prevent.

JP-A-57-9044 Japanese Patent Laid-Open No. 2003-22780 JP 2003-257365 A JP-A 61-294752 JP 2002-157974 A

  The process of forming a special metal layer such as a thorium-free layer in the vicinity of the cathode surface is a complicated work process and reduces lamp production efficiency. Further, if an appropriate thorium layer is not formed on the cathode surface during arc discharge, the discharge tube will be blackened or the luminance will be reduced. For example, if too much thorium is recrystallized on the cathode surface in order to emit electrons, thorium evaporates as the electrode temperature rises and adheres to the discharge tube. Conversely, if the amount of thorium is too small, the electron emission capability of the cathode will not increase.

  On the other hand, the process of coating the inner surface of the discharge tube with alumina or the like is also a complicated work process, which deteriorates the production efficiency. Even when coating is performed, the heat-formed discharge tube itself has heat, so that sufficient coating performance is not satisfied due to the influence of heat, and the transmittance is reduced.

  The discharge lamp of the present invention is a discharge lamp that can prevent blackening of the discharge vessel without requiring a complicated work process, and includes a discharge vessel, and an anode and a cathode that are arranged to face each other in the discharge vessel. For example, a discharge lamp such as a short arc type discharge lamp that outputs high-intensity light when the electrode is at a high temperature is configured. However, you may apply to the electrode of discharge lamps other than a short arc type discharge lamp. The discharge vessel may be made of quartz glass that transmits light, and the electrode may be made of a metal material such as tungsten. Further, potassium may be contained in the anode.

  In the present invention, fine irregularities are formed at least on the anode surface. For example, minute unevenness can be formed by performing a surface treatment. Here, the fine unevenness refers to, for example, a rough and glossy state (texture state), and refers to unevenness on the order of several tens of μm. As the surface treatment, surface finishing can be performed by blasting such as shot blasting, wet blasting, and sand blasting. Alternatively, fine unevenness (unevenness of the order of several hundreds μm) can be formed by a method other than surface treatment such as mechanical finishing, laser processing, or electrical discharge machining, that is, the surface can be roughened. When the blackening suppressor enters these minute irregularities, it easily adheres to the anode surface.

  And in this invention, what prevents blackening of a discharge vessel (henceforth a blackening suppression body) is scattered and adhering to the anode surface in which micro unevenness | corrugation was formed. Here, the “blackening inhibitor” means that the light transmittance does not react with the composition material (for example, quartz glass) of the discharge vessel (it does not cause the blackening phenomenon) and adheres to the inner surface of the discharge vessel. It shows that it is a granular material and composition that are not lowered as much as possible. “Dispersed” indicates that the surface is scattered sparsely (in a uniformly dispersed state), and is different from, for example, a state in which the blackening suppression body covers the anode surface without any defects. The blackening suppressor is composed of an aggregate of minute lumps such as granules and powder, and the size is not limited. The degree (size) of minute irregularities on the anode surface can also be determined according to the size of the blackening inhibitor.

  When the anode temperature rises due to the arc discharge, the blackening inhibitor adhering to the anode surface melts and evaporates. Since the anode surface is roughened, the blackening suppressor tends to evaporate. Due to the thermal convection generated in the discharge vessel, the evaporated blackening suppression body comes into contact with the inner surface of the discharge vessel and adheres as a solid. Since the blackening inhibitor is scattered on the anode surface, it is evaporated randomly from the anode surface and adheres to the discharge vessel by thermal convection. As described above, in the present invention, the protection process such as coating is performed on the inner surface of the discharge vessel with the lighting time by the lighting operation after the lamp is manufactured.

  Metals such as tungsten and thorium, which are electrode materials, melt and evaporate when the electrode is heated, and cause blackening on the inner surface of the discharge vessel when attached to the discharge vessel. In particular, in the case of a short arc type discharge lamp, the cathode and anode tips are heated up to about 2000 ° C., and the electrode metal is likely to evaporate.

  However, in the present invention, when the lighting is started after the lamp is manufactured, the blackening suppression body previously adhered to the anode surface evaporates and adheres to the discharge vessel. The blackening suppression body attached to the inner surface of the discharge vessel does not react with the discharge vessel and does not lower the light transmittance, so that the discharge vessel is not blackened.

  On the other hand, when the blackening suppressor adheres to the inner surface of the discharge vessel, the metal of the electrode material evaporating from the electrode such as tungsten or the metal enclosed in the discharge tube for light emission such as mercury does not react with the glass. That is, the metal that causes blackening is prevented from adhering to the discharge vessel. As a result, even if the lamp is used for a long time, the blackening phenomenon does not proceed and the lamp continues to be lit with a stable illuminance.

  From the lamp manufacturing process to the start of lighting, it is desirable to perform surface treatment as a method of securely fixing the blackening suppressing body to the anode surface without peeling off. Since the surface of the anode becomes rough due to the surface treatment, the blackening inhibitor strongly adheres to the anode surface, and the blackening inhibitor does not peel off from the anode surface during the lamp manufacturing process such as electrode heating, and the lamp is turned on for the first time after production. The blackening inhibitor is firmly fixed to the anode surface.

  In particular, in order to reliably attach the blackening suppressing body by a simple method, it is preferable to perform a blasting process so that the blackening suppressing body collides with the anode surface. By spraying the blackening suppressor onto the anode surface with high compression, an uneven state (satin finish) is formed on the anode surface, while some of the collided blackening suppressors are fixed by collision while the anode surface is depressed. ing. Since it is a blast process, the blackening suppression body adheres to the anode surface in a scattered state.

  In addition, by attaching the blackening suppressor to the concave portion of the anode surface, the blackening suppressor is prevented from protruding from the anode surface, and the flow into the arc tube during the vacuum exhausting process of the lamp manufacturing process such as the vacuum exhausting process. Even if it occurs, the blackening inhibitor does not peel off.

  When electrode metal such as tungsten evaporates, the evaporated metal floats in the discharge vessel. In order to evaporate the blackening suppression body as soon as possible from the start of lighting and adhere it to the inner surface of the discharge vessel, it is preferable to use a blackening suppression body that evaporates before the metal that is the electrode material of the anode.

  Further, when mercury is sealed in the discharge vessel, the discharge vessel such as quartz reacts with mercury or mercury oxide. When mercury enters the discharge vessel, the amount of mercury that contributes to light emission decreases and the illuminance decreases. In order to prevent this, it is desirable that the blackening suppressor is a blackening suppressor that does not cause a chemical reaction with a metal or a metal compound as compared with a composition material (such as quartz glass) of the discharge vessel.

  As the blackening suppressor, a metal blackening suppressor or a metal compound blackening suppressor such as a metal oxide may be used. For example, it is desirable to use alumina (aluminum oxide) that does not react with quartz glass. Alumina is a physically and chemically stable polycrystal, and for example, transparent alumina is used.

  For the purpose of melting and evaporating the blackening suppression body as soon as possible after starting the lamp, the region where the blackening suppression body melts and evaporates can be determined most efficiently for the anode surface region to which the blackening suppression body adheres.

  On the other hand, when the discharge lamp is installed in such a manner that the electrode is arranged in the vertical direction with the anode facing upward, the temperature distribution on the anode surface becomes unique. That is, due to electron emission from the cathode, the anode tip becomes extremely hot, and the temperature at the anode end surface on the electrode support bar side is lower than that on the electrode tip near the cathode side. Further, convection is generated in the discharge tube along the outer peripheral surface (side surface) of the anode.

  Therefore, by attaching the blackening suppression body along the outer peripheral surface (side surface) of the anode, the blackening suppression body can be quickly melted and attached to the inner surface of the discharge tube. It is also possible to adhere partially along the circumferential direction, and the blackening suppression body may be adhered over the front surface in the circumferential direction. For example, when the anode is composed of a tapered tip portion and a columnar body portion, a blackening suppression body may be attached to the outer peripheral surface of the body portion. In particular, it is possible to analyze the anode temperature distribution during lighting, determine a region where the blackening suppressor is most likely to evaporate along the electrode axis direction, and attach the blackening suppressor intensively.

  In order to ensure that the alumina adheres to the anode surface, it is desirable to form (for example, along the circumferential direction) a fine groove (for example, a μm order groove) into which the blackening suppressor fits. By fitting the blackening suppressing body into such a fine groove, it becomes easy to adhere to the anode surface. Further, when the blackening suppression body evaporates, the fine groove functions as a heat dissipation structure. For example, it is preferable to form a fine groove in an optimum region from the temperature distribution of the anode.

  In order to increase the adhesion amount of the blackening suppressor, it is desirable to form a cross-sectional corrugated groove along the circumferential direction on the outer peripheral surface of the anode. This groove is a groove (for example, mm order) much larger than the fine groove, and an inclined surface is formed on the anode surface. As a result, more blackening suppressors can be attached by surface treatment or the like. For example, the cross-sectional corrugated groove may be formed in the most suitable region in consideration of the temperature distribution.

  If fine irregularities are formed on the anode surface, the projections are easily peeled off in the lamp manufacturing process, and foreign substances such as dust are likely to adhere to the anode surface. In order to prevent this, it is preferable that the anode is provided with a reduced diameter portion having an outer diameter smaller than the outer diameter of the anode, and the blackening suppressing body is adhered to the surface of the reduced diameter portion. This is also effective when fine grooves and corrugated grooves are formed on the anode surface, particularly on the outer peripheral surface.

  On the other hand, in order to place the evaporated blackening suppression body on the convection in the discharge tube and quickly attach it to the region where the blackening of the inner surface of the discharge tube is likely to occur, a recess is formed on the rear end surface of the anode on the electrode support rod side. Good. Since the airflow descending along the electrode support rod from the vertical upward to the downward (cathode side) collides with the concave portion and becomes an upward airflow, the upward airflow along the outer peripheral surface (side surface) of the anode discharges the blackening inhibitor. It can be intensively transported to a region where the blackening phenomenon on the inner surface of the tube is likely to occur. Therefore, the distortion of the discharge vessel due to blackening can be suppressed. For example, a relatively large groove is formed along the circumferential direction.

  The method for producing a discharge lamp according to the present invention projects a blackening inhibitor on the anode surface by blasting, and disperses and adheres the blackening inhibitor on the anode surface, depending on the temperature below the melting point of the blackening inhibitor. The heat treatment for removing impurities is performed on the anode.

  According to the present invention, blackening of the discharge vessel can be prevented without complicated work steps. In addition, accumulation of thermal strain in the discharge vessel due to blackening can be suppressed, and damage to the discharge vessel can be prevented.

It is a schematic sectional drawing of the short arc type discharge lamp which is 1st Embodiment. It is the enlarged plan view seen from the side surface side of an anode. It is an expanded sectional view of the anode surface in a 2nd embodiment. It is an anode top view in a 3rd embodiment. It is an anode top view in a 4th embodiment. It is an anode sectional view in a 5th embodiment. It is an electron microscope enlarged photograph of the anode side surface before blasting and after blasting. It is the electron microscope enlarged photograph which looked at the anode surface of the discharge lamp which is a present Example from the top. It is the electron microscope enlarged photograph which looked at the anode surface from the diagonal direction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of a short arc type discharge lamp according to a first embodiment.

  The short arc type discharge lamp 10 includes an arc tube 12 made of transparent quartz glass, and a cathode 20 and an anode 30 are disposed in the arc tube 12 so as to face each other with a predetermined interval. On both sides of the arc tube 12, quartz glass sealing tubes 13 </ b> A and 13 </ b> B are connected to the arc tube 12 and are integrally formed. The discharge space S in the arc tube 12 is filled with rare gas such as mercury and argon gas.

  Conductive electrode support rods 17A and 17B that support the cathode 20 and the anode 30 are disposed inside the sealing tubes 13A and 13B. The electrode support rods 17A and 17B are connected to conductive lead rods 15A and 15B through metal foils 16A and 16B, respectively. Both ends of the sealing tubes 13A and 13B are blocked by the caps 19A and 19B, and are welded to the glass tube 21 and the glass rod (not shown) provided inside, thereby the arc tube 12 is sealed. The

  The lead bars 15A and 15B are connected to an external power source (not shown), and power is supplied to the cathode 20 and the anode 30 via the lead bars 15A and 15B. When a voltage is applied between the cathode 20 and the anode 30, an arc discharge is generated between the electrodes of the cathode 20 and the anode 30, and light is emitted toward the outside of the arc tube 12. Here, the discharge lamp 10 is arranged so that the anodes 20 and 30 are arranged along the vertical direction.

  FIG. 2 is an enlarged plan view of the anode viewed from the side surface side.

  The anode 30 is an electrode containing 0.002 percent potassium in a tungsten electrode, and a cylindrical body part 30B connected to the electrode support rod 17B, and a tip formed in a tapered shape from the body part 30B toward the cathode 20 30A. During lamp operation, electrons are emitted from the tip of the cathode, and arc discharge occurs between the cathode 20 and the anode 30.

Alumina 26 (Al ₂ O ₃ ), which is a transparent polycrystalline body, is scattered and adhered in the adhesion region R on the outer peripheral surface (side surface) 30C of the body portion 30B having a constant outer diameter. The adhesion region R is defined as a region having a predetermined width along the electrode axis X direction and extending over the entire circumferential direction. The width of the adhesion region R can be determined in consideration of the anode surface temperature distribution along the electrode axis X during lighting, but it may be determined so as to include at least the tip end side anode surface that becomes high in temperature.

  The alumina 26 is a physically and chemically stable crystal and does not react with the arc tube 12 made of quartz glass. The alumina 26 is attached to the anode 30 by a surface treatment. In the present embodiment, blasting is performed as the surface treatment, specifically, shot blasting in which alumina is injected onto the anode 30 at a high pressure. When shot blasting, alumina powder having a predetermined range of particle size (105 μm to 125 μm) is injected at a high pressure toward the adhesion region 30R of the outer peripheral surface 30C.

  The adhesion region R of the outer peripheral surface 30C of the anode 30 is formed in a satin shape or an uneven shape as a result of being struck by alumina. That is, it becomes a rough surface with minute irregularities. A part of the alumina colliding with the outer peripheral surface 30C is stabbed into the outer peripheral surface 30C (bite), and is collided and fixed to the outer peripheral surface 30C while the outer peripheral surface 30C is recessed by its own collision.

  Further, during shot blasting, the alumina powder is uniformly sprayed toward the outer peripheral surface 30C. For this reason, the adhering alumina is dispersed throughout the outer peripheral surface 30C and scattered. In an injection device (not shown) that performs surface treatment, the injection pressure is set so that alumina adheres as it is after colliding with the outer peripheral surface 30C.

  When the blast process is performed, the anode 20 is heated in a vacuum atmosphere. The heat treatment is performed at a temperature lower than the melting point of alumina to prevent evaporation of alumina. For example, the anode 30 is heated at about 1600 ° C. for several minutes to several tens of minutes. Thereby, the alumina adhering to the anode 30 is familiar and fixed to the outer peripheral surface 30C, and impurities contained in the electrode are removed in the process of assembling the electrode.

  When the lamp is turned on after the lamp is manufactured, the temperature of the anode 30 reaches the vicinity of the melting point of alumina (about 2000 ° C.). As a result, the alumina 26 melts and evaporates. As the lighting time elapses, the alumina 26 evaporates one after another, and most of the alumina adhering to the anode 30 finally leaves the anode 30. The evaporated alumina adheres to a predetermined region on the inner surface of the arc tube 12 by thermal convection in the arc tube 12. This region is a region where metal or the like is relatively easily attached by thermal convection.

  Alumina deposited over the entire inner surface of the arc tube 12 performs the same function as the coating film. That is, tungsten, thorium evaporated in the arc tube 12, thorium, mercury oxide generated by discharge light emission, and other impurities do not adhere to the area on the inner surface of the arc tube 12 to which alumina has adhered, and alumina. It will stick to areas that are not attached to it, or will continue to float.

  Thus, according to the present embodiment, alumina is sprayed onto the outer peripheral surface 30C of the anode 30 by shot blasting, and the alumina 26 is adhered to the side surface 30C in a scattered state. Then, the anode 30 is subjected to vacuum heat treatment at a temperature equal to or lower than the melting point of the alumina 26 to remove impure gas. When the lamp is turned on, the alumina 26 melts and evaporates as the temperature of the anode 30 rises. The evaporated alumina adheres to the inner surface of the arc tube 12.

  Although the melting point of tungsten is very high, tungsten is evaporated when the cathode tip surface and anode tip surface are heated very much. The mercury sealed in the arc tube reacts with oxygen to produce mercury oxide, which adheres to the inner surface of the arc tube. Such adhesion of mercury oxide and tungsten promotes blackening of the arc tube.

  Alumina, on the other hand, is a transparent polycrystal and does not react with tungsten, mercury, impure gas generated during discharge light emission, charged particles, or the like, stably compared to quartz glass, which is the material of the arc tube 12. Yes.

  In this embodiment, after a lamp is started after the lamp is manufactured, alumina is evaporated and adheres to the arc tube 12 after a while. The deposition of alumina is earlier than the evaporation of tungsten, and almost at the same time as the thorium evaporation evaporating from the cathode tip. As a result, the alumina 26 adhering to the anode side surface 030 </ b> C first moves onto the inner surface of the arc tube 12 so as to prevent blackening.

  Therefore, even if tungsten and mercury oxide float in the arc tube 12, they do not adhere to the arc tube 12, but tungsten and mercury oxide adhere to the inner surface of the arc tube and the arc tube becomes black (the transmittance decreases). Can be prevented as a whole. In addition, since heat convection is generated in the arc tube 12, the evaporated alumina is mainly attached to a region where the blackening phenomenon of the inner surface of the arc tube 12 is likely to occur, thereby preventing the arc tube 12 from being blackened.

  Since such a protective function by coating is realized without performing a coating operation in the lamp manufacturing process, it is not necessary to provide a complicated operation in the lamp manufacturing process. Furthermore, it is possible to perform blasting as the surface finish of the electrode surface and deposit alumina in accordance therewith, and there is no need to provide a special process for depositing alumina.

  Alumina 26 adheres to the anode surface with certainty because the surface of the anode is rough and provided with irregularities so that alumina sticks, bites, or is depressed. Therefore, it is possible to prevent peeling during the manufacturing process before starting the lamp lighting. Further, alumina is adhered and fixed to the anode surface after the anode is integrally formed. That is, alumina does not form a strong bonded body with respect to the anode surface as compared with the case where it mixes inside the anode, so when the electrode temperature rises to near the melting point of alumina, alumina easily evaporates from the anode surface. .

  While the discharge lamp is on, the anode is disposed above the cathode, and an upward flow is generated along the side surface of the anode due to thermal convection in the discharge space. In the present embodiment, since alumina is attached to the side surface of the anode, the alumina evaporates early, and quickly moves in the discharge space by the convection directed above the electrode axis, and adheres to the arc tube. Furthermore, since the alumina adhesion region R is determined based on the anode temperature distribution during lighting, the alumina can be reliably evaporated.

  In the present embodiment, alumina is attached to the anode side surface that is easy to move by convection in the discharge space. However, alumina may be attached to other anode surface portions. Moreover, you may spray the powder and granule other than an alumina with respect to an anode. The particles to be sprayed are transparent crystals that do not lower the transmittance of the arc tube, such as quartz glass and other materials that convect inside the arc tube, such as tungsten, mercury, discharge gas, Any particles (metal particles, metal oxides, etc.) that do not cause a chemical reaction with the compound and are physically and chemically stable may be used.

  As the blasting treatment, any of sand blasting, wet blasting (liquid honing), and shot blasting may be used. Further, the anode may be subjected to a surface processing treatment other than blasting, and alumina may be adhered. Furthermore, the particles may be scattered and adhered to the anode surface by a method other than the surface processing (for example, by strongly pressing the particles to enter the inside from the anode surface).

  Next, the discharge lamp which is 2nd Embodiment is demonstrated using FIG. In the second embodiment, fine grooves are formed along the circumferential direction of the anode surface. Other configurations are substantially the same as those in the first embodiment.

  FIG. 3 is an enlarged cross-sectional view of the anode surface in the second embodiment.

  On the surface 130C of the anode 130, a minute pitch groove 130N (herein referred to as a fine groove) is formed along the circumferential direction by laser machining, blade machining, electric discharge machining, or the like, and a series of grooves have a predetermined width in the axial direction. It is formed with.

  The recesses 130G of the fine grooves 130N are formed in a wedge shape (acute angle), and grooves are formed at a pitch 130J on the order of micrometers (μm) so that alumina fits into the recesses 130G during blasting. The anode surface region in which the fine groove 130N is formed is a part or the entire region of the adhesion region R shown in the first embodiment, and is particularly determined as a region where alumina is easily evaporated during lighting.

  The pitch J of the fine grooves 130N is set to be relatively large in order to prevent the surface convex portions 130T appearing alternately with the fine grooves 130N from being peeled (not chipped) and fitted into the concave portions 130G. That is, the width of the convex portion 130T is sufficiently larger than the width of the concave portion 130G.

  By forming such fine grooves, the surface of the alumina is more reliably adhered by the sandblasting process and adheres even during lamp manufacturing. Further, since the fine groove 130 is formed in a region where the alumina evaporation is most effectively realized based on the temperature distribution along the electrode axis direction, the alumina evaporation is ensured. Furthermore, after the alumina has evaporated, the fine groove 130 functions as a heat radiating fin and can prevent the electrode from overheating.

  Note that alumina may be attached to the fine groove by a process other than the blast process. For example, it is possible to deposit alumina by pressing it against the anode surface. Moreover, you may concentrate an alumina adhesion area | region to a more specific area | region.

  Next, the discharge lamp which is 3rd Embodiment is demonstrated using FIG. In the third embodiment, corrugated (cross-sectional wave shape) grooves are formed on the anode surface. About another structure, it is the same as 1st Embodiment.

  FIG. 4 is an anode plan view according to the third embodiment.

  On the outer peripheral surface 230C of the anode 230, a corrugated groove 230W is formed in a region W that is a part of the alumina adhesion region R. The corrugated groove 230W is a groove that forms a series of sawtooth cross-sectional waveforms along the electrode axis direction, and has a recess that is sufficiently larger (visible) than the alumina particles. Here, the grooves 230 </ b> W are formed along the circumferential direction of the outer peripheral surface 230 </ b> C in the order of millimeters (mm) by cutting or the like.

  By forming the corrugated groove 230W along the circumferential direction, the area of the anode surface is enlarged. For this reason, the amount of alumina adhered increases, and it becomes easier to adhere alumina by sandblasting from an oblique direction.

  As in the second embodiment, alumina may be attached to the fine groove by a process other than the blast process. Further, the fine groove described in the second embodiment may be further formed on the corrugated groove.

  Next, the discharge lamp which is 4th Embodiment is demonstrated using FIG. In the fourth embodiment, a small diameter portion having a small outer diameter is formed on the anode surface. About another structure, it is substantially the same as 3rd Embodiment.

  FIG. 5 is a plan view of an anode according to the fourth embodiment. The anode 330 is formed with a small-diameter portion 330B having a relatively small outer diameter over the width Z as compared with the outer diameter of the end portion 330A near the electrode support rod. Alumina is adhered to the partial region R of the anode surface 330C by sandblasting. Further, a corrugated groove 330 </ b> W is formed in the circumferential direction over the region W.

  By forming such a small diameter portion on the anode, it is possible to prevent the alumina adhered at the time of lamp manufacture from peeling off. In addition, it prevents alumina from adhering to the anode surface together with foreign matter such as fine dust. Further, the fine convex portions formed on the surface by the sandblasting process or the convex portions of the fine grooves are prevented from peeling off, or foreign matters are prevented from adhering together.

  Note that alumina may be attached by a method other than surface treatment such as sandblasting. Further, the corrugated groove may not be formed, and the fine groove may not be formed.

  Next, the discharge lamp which is 5th Embodiment is demonstrated using FIG. In the fifth embodiment, a recess is formed on the back side of the electrode. About another structure, it is substantially the same as 3rd Embodiment.

  FIG. 6 is a cross-sectional view of the anode according to the fifth embodiment. A groove 430M is formed on the end surface of the anode 430 on the electrode support rod side so as to draw a circle along the circumferential direction. Alumina adheres over the region R, and corrugated grooves 430W are formed in the circumferential direction over the region W.

  By providing such a recess as a depression on the anode end face side, the downdraft generated during lamp lighting collides with the electrode and flows upward together with the updraft. The alumina riding on this quickly moves to the portion where it tends to drift in the discharge tube, and it is possible to enhance the coating effect by concentrating the area to which the alumina adheres in advance.

  Hereinafter, embodiments of the discharge lamp will be described.

  The discharge lamp of this example corresponds to the discharge lamp described in the first embodiment.

  FIG. 7 is an electron microscope enlarged photograph of the anode side surface before blasting, after blasting, and after processing. As shown in FIG. 7A, the anode side surface is almost smooth before the blasting treatment. On the other hand, the side surface of the anode after the blasting treatment is in a lustrous state (matte state) with no gloss, and has a fine uneven shape. In the enlarged photograph of FIG. 7 (B), a portion where alumina is sharply pierced, a portion where electrode fragments are attached, and a portion where alumina collides with the side surface of the anode and bites in are shown. .

  This example corresponds to the discharge lamp in the second embodiment.

  FIG. 8 is an electron microscope enlarged photograph of the anode surface of the discharge lamp according to the present embodiment as viewed from above. FIG. 9 is an electron microscope magnified photograph of the anode surface viewed from an oblique direction.

  As is apparent from FIGS. 8 and 9, fine grooves having a groove pitch larger than the groove width are formed on the anode surface along the circumferential direction. It can be seen that a large amount of alumina is firmly fitted and adhered to the fine groove portion.

  The discharge lamp of this example corresponds to the discharge lamp described in the fifth embodiment.

  An experiment was conducted to confirm the effect of suppressing the blackening of the arc tube when alumina was adhered to the anode surface. The short arc type discharge lamp of the embodiment has an outer diameter of 121 mm, a volume of 885 cc, and an arc tube made of quartz glass. About 30 mg / cc of mercury was enclosed in the arc tube. Moreover, argon gas was enclosed so that it might become about 190 kPa at normal temperature.

The anode is a tungsten electrode containing about 0.002% potassium by weight. The cathode is a tungsten electrode doped with thorium oxide (ThO ₂ ) at a weight ratio of about 2%, and the distance between the electrodes is set to about 12 mm. The anode and cathode shapes are almost the same as those shown in the above embodiment. The cathode has a tapered tip.

A blasting process of spraying alumina (Al ₂ O ₃ ) was performed on the side surface on which the corrugated groove of the anode was formed, and the anode side surface was surface processed. Alumina powder having a particle size of about 115 μm was used, and the alumina powder was made to collide with a predetermined region on the side surface of the anode with the injection pressure of the pressurized gas to finish the surface and adhere alumina.

  On the other hand, as a comparative example, a short arc type discharge lamp having the same configuration as that of this example except for the adhesion of alumina was prepared.

  And confirmation experiment of alumina evaporation was conducted. Here, the anode was heat-treated in a vacuum environment to actually create an electrode temperature environment (1500 ° C. or higher) when the lamp was turned on, and the residual amount of alumina was examined at an electrode temperature lower than the alumina melting point and higher electrode temperature.

  When the electrode was heated to 1500 ° C., alumina remained, but when heated to 2200 ° C., alumina did not remain.

  Next, a confirmation experiment was conducted to prevent blackening by attaching alumina to the anode surface. Here, the short arc type discharge lamp of the above example was turned on with a power of 12 kW, and the blackened state on the inner surface of the arc tube after lighting for 1000 hours was inspected.

  The illuminance maintenance rate was measured with an illuminometer having sensitivity around 350 nm. While the corrugated groove is not formed and the illuminance maintenance ratio of the conventional lamp without the alumina adhesion by the sandblasting process is 67%, the illuminance maintenance ratio of the present embodiment lamp is 75%, and the black color of the arc tube It was confirmed that the conversion was suppressed.

10 Short arc type discharge lamp 12 Arc tube (discharge vessel)
20 Cathode 26 Alumina 30 Anode

Claims (16)

A discharge vessel;
An anode and a cathode disposed opposite to each other in the discharge vessel,
At least minute irregularities are formed on the anode surface,
A discharge lamp characterized in that metal oxide is scattered and adhered to the surface of the anode, and evaporates during lighting. The discharge lamp according to claim 1, wherein the metal oxide evaporates before a metal that is an electrode material of the anode. 3. The metal oxide according to claim 1, wherein the metal oxide does not cause a chemical reaction with a metal or a metal compound floating in the discharge vessel during lighting, as compared with a composition material of the discharge vessel. Discharge lamp. The discharge lamp according to any one of claims 1 to 3 , wherein the metal oxide contains alumina. The discharge lamp according to any one of claims 1 to 4, wherein the metal oxide is attached to a concave portion on the surface of the anode. The anode is surface-treated by a blasting treatment in which the metal oxide collides with the anode surface,
The discharge lamp according to any one of claims 1 to 5 , wherein the metal oxide is collision-fixed while the anode surface is depressed. The discharge lamp according to any one of claims 1 to 6 , wherein the metal oxide is attached to an outer peripheral surface of the anode. The anode has a tapered tip and a columnar body,
The discharge lamp according to any one of claims 1 to 7 , wherein the metal oxide is attached to an outer peripheral surface of the body portion. The discharge lamp according to any one of claims 1 to 8 , wherein a fine groove is formed on the outer peripheral surface of the anode so as to fit the metal oxide . The discharge lamp according to claim 9 , wherein a gap between the fine grooves is equal to or larger than a size of the metal oxide . The discharge lamp according to any one of claims 1 to 10 , wherein a cross-sectional wave-shaped groove is formed on an outer peripheral surface of the anode. The anode has a reduced diameter portion having an outer diameter smaller than the outer diameter of the anode;
Wherein the metal oxide is a discharge lamp according to any one of claims 1 to 11, characterized in that attached to the reduced diameter portion surface. The discharge lamp according to any one of claims 1 to 12 , wherein the anode contains potassium. The discharge lamp according to any one of claims 1 to 13 , wherein a concave portion is formed on a rear end surface of the anode on the electrode support rod side. The metal oxide is projected on the anode surface by blasting, interspersed said metal oxide to said anode surface, is deposited,
A method for manufacturing a discharge lamp, wherein a heat treatment for removing impurities is performed on the anode at a temperature lower than the melting point of the metal oxide . A discharge vessel;
An anode and a cathode disposed opposite to each other in the discharge vessel,
At least minute irregularities are formed on the anode surface,
Metal oxide is scattered and adhered to the anode surface, and evaporates during lighting.
A discharge lamp characterized in that a cross-sectional groove is formed on the surface of the anode.