Discharge lamp cathode containing electron-emitting material and method for manufacturing the same

Abstract

To provide a cathode that is free from a problem with bonding strength and can supply an electron emitting material from a tip of an electrode.SOLUTION: A cathode 1 has a main body 2 and a tip 4. Both the main body 2 and the tip 4 are made of tungsten (W) containing 2 wt.% of thorium oxide (ThO2) 11 which is an electron radioactive material. A thoria removal layer 7 is formed on a side face of the main body 2. The thoria removal layer 7 is irradiated with a laser under a condition that forms irregularities with an average roughness Ra of 10 μm or less, and as a result, thoria near a surface is removed. This makes it possible to more reliably prevent abnormal discharge from the side face of the main body 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cathode for a discharge lamp to which an electron-emitting material is added, and more particularly to the prevention of abnormal discharge from portions other than the tip. [Background technology]

[0002] Patent Document 1 discloses a cathode containing thorium oxide as an emitter material. Specifically, it discloses a bonded cathode structure in which the cathode body is made of tungsten and thoriated tungsten (hereinafter referred to as thoriated tungsten) containing 2 wt% thorium oxide (hereinafter referred to as thoria) is solid-phase bonded to the tungsten. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-015007 A Summary of the Invention [Problem to be solved by the invention]

[0004] The cathode described in Patent Document 1 has a problem in that the bonding strength at the bonding interface is weak, and mechanical fracture occurs starting from this bonding interface.

[0005] In order to avoid such problems with the bonding strength, the inventors considered constructing the entire cathode from thoriated titanium, but when the entire cathode is made of thoriated titanium, there is a problem in that abnormal discharge occurs from parts other than the tip.

[0006] This problem also arises when a metal containing an electron emitting substance is used at the tip of the cathode in order to improve the electron emission characteristics.

[0007] An object of the present invention is to provide a cathode which does not cause problems with bonding strength and which is capable of supplying an electron emitting material from the tip of the electrode. [Means for solving the problem]

[0008] (1) The discharge lamp cathode according to the present invention is composed of a tip portion and a main body portion, both of which are doped with an electron-radioactive material, and the main body portion has fine irregularities on its surface and a layer lacking the electron-radioactive material on its side surface, in which the electron-radioactive material is depleted. Therefore, even if both the tip portion and the main body portion are doped with an electron-radioactive material, abnormal discharge from the side surface of the main body portion can be more reliably prevented.

[0009] (2) In the discharge lamp cathode of the present invention, the tip portion has a fine irregularity formed on the surface and has an electron-radiating material presence region where the electron-radiating material is present in the vicinity of the surface, so that a cathode in which discharge from the electron-radiating material presence region is likely to occur at the start of discharge can be provided.

[0010] (3) In the discharge lamp cathode according to the present invention, the electron-emissive material-depleted layer is covered with an insulating film, so that discharge from the electron-emissive material-depleted layer can be more reliably prevented.

[0011] (4) In the discharge lamp cathode according to the present invention, the insulating film is made of a material having a higher emissivity than the main body, so that an electrode having a heat dissipation effect can be provided.

[0012] (5) In the cathode for a discharge lamp according to the present invention, the above-mentioned electron-emitting material is The presence region is provided at a position spaced a predetermined distance from the tip, so that the possibility of discharge occurring in the region up to the predetermined distance from the tip at the start of discharge can be reduced.

[0013] (6) The method for manufacturing a cathode for a discharge lamp according to the present invention includes a cutting step of cutting a cathode material for a discharge lamp containing an electron-emitting substance throughout to a shape of a main body while leaving the shape of the tip in a roughly processed state, a first laser processing step of irradiating a laser to melt and solidify the side surface of the main body under conditions that irregularities with an average roughness Ra of 10 μm or less are formed in an area of ​​the main body that will become an electron-emitting substance depleted layer, an electron-emitting substance removal step of removing the electron-emitting substance located from the side surface of the main body to a predetermined depth by heating the electrode in a vacuum state, a step of cutting the tip into a desired shape, and a second laser processing step of irradiating a laser to melt and solidify the electrode surface under conditions that irregularities with an average roughness Ra of 10 μm or less are formed on the surface of the tip. Therefore, even if both the tip and the main body are doped with an electron-emitting substance, it is possible to provide a cathode that can more reliably prevent abnormal discharge from the side surface of the main body.

[0014] (7) The method for producing a discharge lamp cathode according to the present invention includes a step of covering the surface from which the radioactive material has been removed with an insulating film in the step of removing the radioactive material, thereby making it possible to produce a cathode that can more reliably prevent discharge from the radioactive material depleted layer.

[0015] The terms used in the claims are explained below. In the embodiment, the "electron-emitting material-deficient layer" corresponds to the thoria-removed layer 7. The "electron-emitting material-deficient state" includes not only the case where all the electron-emitting material has been removed, but also the state where some electron-emitting material remains but is deficient to the extent that abnormal discharge does not substantially occur.

[0016] In this specification, the average roughness Ra refers to the arithmetic mean roughness that represents the average of the absolute value of Z(x) over a reference length in JIS B 0601. Furthermore, the maximum roughness Rz refers to a measurement parameter according to JIS B 0601-2001 that is calculated by extracting a portion of a roughness curve measured with a roughness meter over a reference length and summing the highest part (maximum peak height: Rp) and the deepest part (maximum valley depth: Rv). [Brief description of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view of a main part of a cathode 1 according to the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a thoria removal layer 7. [Diagram 3] 2A to 2C are diagrams illustrating a manufacturing process of the cathode 1. [Figure 4] 1 is a SEM photograph of a thoria removal layer 7 after laser processing. [Diagram 5] 1 is a SEM photograph of a thoria removal layer 7 after vacuum heating. [Figure 6] 2A to 2C are diagrams illustrating a manufacturing process of the cathode 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] 1. Structure of cathode 1 The structure of the cathode according to the present invention will be described with reference to the drawings. As shown in Fig. 1, the cathode 1 has a main body 2 and a tip 4. Both the main body 2 and the tip 4 are made of tungsten (W) containing 2 wt% of thorium oxide (ThO2) 11, which is an electron radioactive material.

[0019] A thoria-removal layer 7 is formed on the side surface of the main body 2. The thoria-removal layer 7 has irregular projections and recesses having an average roughness Ra of 10 μm or less in the horizontal and vertical directions formed by laser processing, which will be described later, and the thoria in the vicinity of the surface has been removed.

[0020] Fig. 2 shows an enlarged cross-sectional view near the surface of the thoria removal layer 7. As is clear from Fig. 2, no thoria is present in the surface vicinity layer 7a, but thoria 11 is present in the internal layer 7b. The white parts are the thoria 11. In addition, voids 31 are formed in the surface vicinity layer 7a when tungsten melts and solidifies due to the heat of laser processing, which will be described later.

[0021] In addition, in Fig. 2, lines are drawn between the surface vicinity layer 7a and the internal layer 7b, and between the surface vicinity layer 7a and the surface, but these are added to make the explanation easier to understand and do not actually exist. The same applies to the dashed dotted line in Fig. 1.

[0022] 1, the thoria removal layer 7 is covered with a heat-dissipating insulating film 15. In this embodiment, the heat-dissipating insulating film 15 is made of zirconium oxide and has a thickness of 100 μm, but is not limited to this.

[0023] The tip portion 4 has a normal layer 4a and a discharge starting layer 4b located closer to the main body than the normal layer 4a. The discharge starting layer 4b has irregular projections and recesses with an average roughness Ra of 10 μm or less in the horizontal and vertical directions formed by laser processing, which will be described later, and the near-surface tria 21 is located near the surface. This allows discharge to occur from this discharge starting layer 4b.

[0024] 2. Manufacturing method of cathode 1 A method for manufacturing the cathode 1 will be described with reference to FIGS.

[0025] 1) Machining step A tungsten (W) rod containing 2% by weight of thorium dioxide (ThO2) 11 with a diameter of 25 mm is prepared, and the main body 2 is cut into the shape of an electrode, leaving a region that will become the tip 4, as shown in FIG. 3A.

[0026] 2) First laser processing step The surface of the main body 2 is irradiated with laser light under the following conditions.

[0027] Equipment used: Fiber laser marker TF450 (Gravotec Co., Ltd.) Laser power: 80% of the maximum output of the device (50 W) (40 W), Repetition rate: 80 kHz, Pulse width: 100 nm, Wavelength: 1064 nm, Laser diameter: approx. 60μm, Scan speed: 150 mm / s, Distance between two adjacent lines: about 0.01 mm, Ambient temperature: room temperature, Surrounding gas: Nitrogen, Pressure: Atmospheric pressure, Irradiation conditions: 3 times In this case, energy per pulse [J] = laser output [W] / laser repetition frequency [Hz], so in this embodiment, the energy per pulse is 40 W / 80 kHz = 0.5 mJ. The tungsten and thoria 11 around the laser irradiation melt and then solidify. During solidification, irregular unevenness with an average roughness Ra of 10 μm or less is formed on the surface of the tungsten in the horizontal and vertical directions, and irregular cracks are generated inside (see FIG. 4B). In addition, some of the thoria 11 evaporates due to the laser processing, and some of the thoria melts and then solidifies together with the tungsten. FIG. 4A shows an SEM photograph of the surface of the main body 2 after laser processing. The white granular material in the figure is the surface-nearby thoria 21 that has solidified after being melted. FIG. 4B shows the cracks formed by laser irradiation. In FIG. 4B, the laser irradiated portion 41 is hollow. Further, the near-surface thoria 21 is observed not only on the surface but also at a position about several tens of μm from the surface.

[0028] Such a state is shown in Fig. 3B, in which near-surface thoria 21 are present on the surface of the side surface of main body 3 and in the vicinity of the surface.

[0029] 3) Thoria removal step In this state, it is heated in a vacuum furnace at 2200°C for 3 hours. As a result, the near-surface thoria 21 evaporates from the surface and from the gaps in the cracks (see FIG. 4B), and a thoria-free layer 7 is formed from the surface of the main body 2 to a predetermined depth (see FIG. 3C).

[0030] The depth of the thoria removal layer 7 is set to about 100 μm from the surface, but is not limited to this. The depth can be changed by changing the irradiation conditions of the laser processing.

[0031] FIG. 5A shows a surface SEM photograph of the thoria removal layer 7. As is clear from the figure, there is no near-surface thoria 21 near the surface. FIG. 5B shows a cross-sectional SEM photograph of the thoria removal layer 7. As is clear from the figure, the cracks in the tungsten have been slightly repaired by the vacuum heat treatment. Also, the near-surface thoria 21 located at the depth where the cracks exist has evaporated as described above.

[0032] In addition, in Fig. 5B, thoria does not evaporate even in the region of the thoria removal layer 7, but remains. This is because, depending on the irradiation conditions of the laser processing, the cracks may not reach the thoria that exists at a position away from the irradiated periphery. Thus, the thoria removal layer includes not only the case where thoria is completely removed, but also the state where thoria is deficient to the extent that abnormal discharge does not substantially occur.

[0033] 4) Tip cutting process step Next, the tip portion 4 is cut to have a desired cathode shape, resulting in the shape shown in FIG. 6A.

[0034] 5) Second Thoria Exposure Step Except for the first tip portion 4a at a predetermined distance from the tip of the tip portion 4, the discharge starting layer 4b on the side closer to the main body is laser processed under the same conditions as in the first laser processing step. As a result, as shown in Fig. 6B, the surface of the discharge starting layer 4b has a tip uneven surface 23 formed thereon, and the near-surface tria 21 is located near the surface.

[0035] 6) Heat dissipation insulating film formation step On the surface of the main body 2, a heat dissipating insulating film made of zirconia (ZrO2) is formed.

[0036] For example, a solution is prepared by mixing 1.0 g of nitrocellulose and 6.6 g of zirconium oxide powder in 11 mL (9.7 g) of butyl acetate. This is stirred for about a day using a stirrer. By stirring, a zirconium oxide paste with sufficiently small particle size is obtained. This zirconium oxide paste is applied to the surface of the main body 2 with, for example, a brush. Next, sintering is performed. In this embodiment, the sintering conditions are as follows: in a vacuum, from room temperature to 1300°C at 50°C / min, from 1300 to 1800°C at 500°C / min, and kept at 1800°C for 2 minutes, to sinter the zirconium oxide on the electrode surface.

[0037] The zirconium oxide paste was applied and dried several times to form a heat dissipation insulating film having a thickness of about 100 μm, thereby producing the cathode 1 shown in FIG.

[0038] In the present embodiment, the insulating layer 15 is made of zirconium oxide, but it may be made of other heat-dissipating insulating films such as oxides or nitrides having high electrical resistance. For example, aluminum oxide may be used.

[0039] 3. Efficacy of Cathode 1 In the cathode 1, the thoria present within a predetermined distance from the surface is once melted by the heat of the laser processing, and then heated in a vacuum in this state to remove the thoria from the cracks in the tungsten. Therefore, the thoria removal layer 7 can be made depleted of thoria from the surface to a predetermined depth. This makes it possible to more reliably prevent abnormal discharge from this portion.

[0040] Furthermore, if such an abnormal discharge occurs, the heat dissipating insulating film 15 formed on the body portion of the cathode may peel off due to the difference in thermal expansion with the cathode body. In this embodiment, such an abnormal discharge can be suppressed, and therefore peeling of the heat dissipating insulating film 15 can be prevented.

[0041] In addition, the surface of the discharge starting layer 4b has small irregularities due to laser processing, and thoria is present near the surface. Therefore, when the discharge starts, the discharge can be surely discharged from that part. This improves starting performance. Even if the discharge starts from a part other than the tip of the cathode in this way, the starting point of the arc moves to the tip as the temperature of the cathode rises, so no particular problem occurs.

[0042] An insulating layer 15 is formed on the surface of the main body 2. This provides high insulation and prevents discharge from this area. In addition, the insulating layer 15 is made of zirconium oxide, which has a higher emissivity than tungsten, and therefore provides high heat dissipation and can lower the temperature of the entire cathode.

[0043] In addition, because the entire cathode is made of thoriated tungsten, the heat of the cathode during steady-state operation can be transported to the rear of the cathode more reliably than with cathodes that are made of tungsten and thoriated tungsten joined together. This prevents the cathode temperature from becoming excessively high, and suppresses wear on the cathode.

[0044] In this embodiment, thoriated tungsten containing an electron emitting substance is used as the material of the cathode 1, but other materials such as lanthanum-doped tungsten and ceria-doped tungsten may also be used.

[0045] The present invention has been described in terms of preferred embodiments, but these are used for purposes of illustration and not limitation, and modifications may be made within the scope of the appended claims without departing from the scope and spirit of the invention.

[0046] For example, the heat dissipation insulating film 15 on the surface of the thoria removal layer 7 is not essential.

[0047] Moreover, in order to more reliably initiate discharge from the tip portion 4 at the time of starting, laser processing of the discharge initiation layer 4b is not essential.

[0048] In this embodiment, the heat dissipating insulating film 15 is formed after cutting and laser processing of the tip portion 4, but this order may be arbitrary.

[0049] In this embodiment, the surface of the thoria removal layer 7 has minute irregularities with an average roughness Ra of 10 μm or less, but the size of the irregularities is not limited.

[0050] For example, the average roughness Ra may be 1 to 10 μm, or 1 to 20 μm.

[0051] If the average roughness Ra is less than 1 μm, the degree of adhesion between the heat dissipating insulating film 15 and the thoria removal layer 7 (hereinafter referred to as adhesion degree) is large, but the adhesion strength between them is weak, and if the average roughness Ra exceeds 10 μm, the adhesion strength between the heat dissipating insulating film 15 and the thoria removal layer 7 is strong, but the adhesion degree is low. Therefore, in either case, the heat dissipating insulating film 15 is likely to peel off. On the other hand, if the average roughness Ra is in the range of 1 to 10 μm, the conflicting conditions of adhesion strength and adhesion degree can be satisfied.

[0052] Incidentally, a smaller average roughness Ra can improve the processing efficiency.

[0053] If the heat dissipation insulating film 15 is not provided, there is no such problem, so the thickness may be about 20 μm.

[0054] 4. About the Invention The cathode 1 can be understood as the following invention.

[0055] 1) First, as already explained, even if the entire cathode is made of an emitter-containing metal, by removing the emitter material from near the surface of the side of the main body 2, abnormal discharge from that part can be prevented.

[0056] 2) Furthermore, by configuring the discharge starting layer 4b of the tip 4 so that the emitter material is located on the surface side, it is possible to actively discharge from the tip 4 at the time of starting. This invention can be applied not only to cases in which the electrode body is configured from an emitter-containing metal, but also to cathodes in which an emitter-containing metal is embedded or joined to the tip of the electrode.

[0057] It should be noted that methods other than laser processing may be used to position such emitter material on the surface.

[0058] 3) In addition, in this embodiment, the electrode body is made of an emitter-containing metal, and a thoria-removal layer 7 is formed on the surface of the main body 2, and the surface is then covered with an insulating film. However, this is not limiting, and it is also possible to prevent emission of the emitter substance from the side surface by forming an insulating film on the surface of the main body 2 without forming the thoria-removal layer 7. [Explanation of symbols]

[0059] 1...Cathode 2. Main body 4...Tip 4a...Normal layer 4b...Discharge starting layer 5...Uneven surface 7. Thoria removal layer 10. Tungsten 11. Tria 15...Heat dissipation insulating film 21. Near-surface thoria 23 Uneven tip surface

Claims

1. A discharge lamp cathode comprising a tip portion and a body portion, both of which are doped with an electron-emitting material, the main body has a surface having minute irregularities, and an electron radioactive material depleted layer in which the electron radioactive material is depleted is formed on a side surface of the main body; A cathode for a discharge lamp comprising:

2. 2. The discharge lamp cathode according to claim 1, the tip portion has a surface having minute irregularities and has an electron radioactive material presence region in which the electron radioactive material is present in the vicinity of the surface; A cathode for a discharge lamp comprising:

3. 3. The discharge lamp cathode according to claim 1, the electron emissive material depleted layer is covered with an insulating film; A cathode for a discharge lamp comprising:

4. 4. The discharge lamp cathode according to claim 3, the insulating film is made of a material having a higher emissivity than the main body; A cathode for a discharge lamp comprising:

5. 3. The discharge lamp cathode according to claim 2, the electron radioactive material presence region is provided at a position spaced a predetermined distance from the tip; A cathode for a discharge lamp comprising:

6. 1. A method for manufacturing a cathode for a discharge lamp, comprising: a body having an electron-emissive material-deficient layer on a side surface; and a tip portion located at a tip of the body and having an electron-emissive material-exposed layer formed on a side surface thereof, the method comprising the steps of: a cutting step of cutting the discharge lamp cathode material containing an electron radioactive substance throughout to form a shape of a main body while leaving the shape of the tip portion in a roughly machined state; a first laser processing step of irradiating a laser beam to melt and solidify a side surface of the main body under conditions in which irregularities having an average roughness Ra of 10 μm or less are formed in a region of the main body that will become an electron radioactive material depleted layer; an electron radioactive material removing step of removing the electron radioactive material located from the side surface of the main body to a predetermined depth by heat-treating the electrode in a vacuum state; cutting the tip into a desired shape; a second laser processing step of irradiating the electrode with a laser under conditions in which irregularities having an average roughness Ra of 10 μm or less are formed on the surface of the tip portion, thereby melting and solidifying the electrode surface; A method for manufacturing a cathode for a discharge lamp comprising the steps of:

7. A method for producing a cathode for a discharge lamp according to claim 6, comprising the steps of: a step of covering the surface from which the electron radioactive material has been removed in the electron radioactive material removing step with an insulating film; A method for manufacturing a cathode for a discharge lamp comprising the steps of:

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