JP2005166382A - Gas discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve stability of a light output, in an extra-high pressure discharge lamp of a type made to light after transferring from glow discharge to arc discharge. <P>SOLUTION: A cathode is constituted by coupling a cathode main body made of porous high-melting point metal material made to contain an easily electron emitting matter with a base body made of a high-melting point metal material so as its tip to protrude further than the base body. A tip part of the cathode is formed into a cusp shape with a solid angle of 50° or more, and a glow discharge coil is fitted to a body of the cathode from outside. Pressure of rare gas for glow discharge start-up in discharge gas is preferred to be 101×10<SP>3</SP>Pa(760 torr) or less and a solid angle of the tip of the cathode is preferred to be 50° or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gas discharge lamp, and more particularly to a gas discharge lamp that improves the stability of light output.

  For example, gas discharge lamps are often used as light sources for various inspection devices, projection devices, photochemical reaction devices, and the like. In this gas discharge lamp, a cathode and an anode are opposed to each other and sealed in a discharge gas, and an arc discharge is performed between the cathode and the anode so that the lamp is turned on.

As this type of gas discharge lamp, there is an ultra-high pressure discharge lamp, for example, an ultra-high pressure mercury lamp that is switched on from a glow discharge to an arc discharge (see Patent Document 1, Patent Document 2, etc.). The cathode of this type of ultra-high pressure discharge lamp is made of a refractory metal material doped with about 2% thorium, such as tungsten or molybdenum, and has a pointed shape with a sharp tip and a glow discharge made of tungsten, for example. It has a structure in which a coil is externally fitted.
Japanese Patent Laid-Open No. 02-61957 Japanese Patent Laid-Open No. 11-354077

  Since the above thorium-doped cathode has a high melting point, it has an advantage that the electrode consumption is small even when the tip of the cathode is exposed to a high temperature by glow discharge at the time of starting the lamp, and has been often used as a cathode for industrial lamps.

  However, since the conventional ultra-high pressure discharge lamp uses a thorium-doped cathode, there is a problem that the cathode has a low electron emission capability, the light output fluctuates, and its stability is not so good.

  In view of such problems, the present invention has an object to provide a gas discharge lamp capable of improving the stability of light output, which is a drawback of a thorium-doped cathode.

  Therefore, the gas discharge lamp according to the present invention is a gas discharge lamp in which the cathode and the anode are opposed to each other in a discharge atmosphere in which mercury and a rare gas are sealed, and the lamp is turned on by moving from glow discharge to arc discharge. Is composed of a base made of a refractory metal material and a cathode body made of a porous refractory metal material containing an electron-emitting substance so that its tip protrudes from the base. The tip portion is formed in a pointed shape, and a glow discharge coil is fitted on the cathode.

  One of the features of the present invention is that a porous cathode containing an electron-emitting material is used, and a glow discharge starting coil is fitted on the porous cathode. Thereby, since the electron emission capability of the cathode is improved, the light output of the gas discharge lamp can be stabilized.

By the way, the pressure of the rare gas and the solid angle of the cathode in the discharge atmosphere are closely related to the smooth start of the glow discharge and the smooth transition from the glow discharge to the arc discharge in this type of gas discharge lamp. In a conventional thorium-doped cathode, the tip of the cathode has a sharp pointed shape (for example, a solid angle of about 30 ° in the case of a 100 W gas discharge lamp), and therefore an unstable arc during glow discharge. Discharge sometimes started. Even if the solid angle of the tip of the cathode is large, if the pressure of the rare gas is higher than 101 × 10 ³ Pa (760 torr), an unstable arc discharge is similarly started during the glow discharge. There was a case.

In the present invention, a porous cathode containing an electron-emitting substance is used, so that the cathode has a high electron emission capability, and stable arc discharge can be performed even when the solid angle of the cathode tip is large. . In addition, since the pressure of the rare gas in the discharge atmosphere is set to 101 × 10 ³ Pa (760 torr) or less, even if the solid angle of the tip of the cathode is a large solid angle of 50 ° or more, the glow discharge is changed to the arc discharge. Smooth transition can be achieved.

That is, the pressure of the rare gas is desirably 101 × 10 ³ Pa (760 torr) or less, and the tip portion of the cathode is preferably formed in a pointed shape having a solid angle of 50 ° or more.

The pressure of the rare gas can be freely selected as long as it is 101 × 10 ³ Pa (760 torr) or less. The solid angle at the tip of the cathode is also related to the pressure of the rare gas, but it is preferably 50 ° or more, preferably 65 ° or more, more preferably 75 ° or more.

  The glow discharge coil is externally fitted to the body of the cathode (the part following the peak), but it suppresses and reduces exposure to high temperatures caused by glow discharge at the tip of the porous cathode, which is relatively heat-sensitive. Thus, it is preferable to project at least one turn on the tip side of the glow discharge coil on the pointed taper portion of the cathode.

  The cathode body may be bonded to the substrate. For example, the cathode body may have a structure in which the flat rear end surface of the cathode body is bonded to the substrate using a suitable bonding material. It is possible to have a structure in which a recessed portion is formed, the cathode body is inserted into the recessed portion, and if necessary, joined with a bonding material, and the concave rear end surface of the cathode body is inserted into the convex front end surface of the substrate. Further, if necessary, a structure may be formed by bonding with an appropriate bonding material, or a through hole may be formed in the center of the substrate, and a rod-shaped cathode body may be inserted therethrough.

  The three-dimensional shape of the tip of the cathode may be a pyramid, but it is preferably a cone so that arc discharge can be performed smoothly. In the case of a pyramid shape, the solid angle of the cathode tip is obtained from the angle between the center line and the surface of the pyramid.

  As the refractory metal material constituting the cathode body and the substrate, a refractory metal material used in this type of gas discharge lamp, such as tungsten or molybdenum, can be used.

  In addition, as an easy electron emission material to be included in the cathode body, a material used in this type of gas discharge lamp, for example, an oxide of an alkaline earth metal such as barium, calcium, strontium, or a mixture of two or more thereof, What added aluminum oxide to these can be used.

  Further, the manufacturing method of the cathode body is not particularly limited as long as the cathode body is made of a porous refractory metal material containing an electron-emitting substance and the tip portion is formed in a pointed shape. For example, the cathode body may be mixed and sintered with a powder of a refractory metal material and a powder of an electron-emitting material. You may make it impregnate an electron emission substance. In the claims, “made of a porous refractory metal material containing an electron-emitting substance” means this.

Hereinafter, the present invention will be described in detail based on specific examples shown in the drawings. 1 to 3 show a preferred embodiment of a gas discharge lamp according to the present invention, which is an example applied to a 100 W high pressure mercury lamp. In the gas discharge lamp, for example, a cathode cap 11 and an anode cap 12 are provided at both ends of a bulb 10 made of transparent quartz glass, and a gas filling portion 17 is formed in the middle of the bulb 10. 20 mg and argon gas 266 × 10 ² Pa (200 torr) which is a rare gas for starting glow discharge are enclosed.

  A cathode 14 and an anode 13 are disposed opposite to each other in the gas sealing part 17 of the bulb 10 and are supported by the bulb 10. The cathode 14 and the anode 13 are connected to the base 11 by connecting metal conductors such as molybdenum foils 16 and 15. , 12 is connected to the external terminal, and by applying a voltage between the external terminals, a glow discharge occurs between the cathode 14 and the anode 13, and when mercury evaporates, the glow discharge is changed to an arc discharge, Discharge is maintained.

  The anode is made of a rod having a substantially circular cross section using, for example, tungsten. The cathode 14 is composed of a cathode main body 140 and a base body 141, and the base body 141 is manufactured using a refractory metal material such as molybdenum. The base 141 has a rod shape with a substantially circular cross section having a diameter of, for example, 1.8 mm, the tip is tapered into a truncated cone shape, and a fitting recess 141A is formed in the tip surface.

  The cathode body 140 is manufactured in a substantially columnar shape using, for example, a porous material having a high melting point, for example, a barium-containing porous refractory metal material such as porous tungsten, and the tip portion is tapered in a conical shape. The cathode main body 140 is fitted and fixed in the fitting recess 141A of the base body 141, and thus the tip portion of the cathode 14 is formed in a conical point shape.

  Further, a glow discharge coil 142 is externally fitted and fixed to the distal end portion of the body portion (columnar portion) of the base body 141. The heat radiating coil 142 is manufactured to have a diameter of approximately 1.8 mm using tungsten. One turn on the tip side of 142 protrudes from the pointed portion of the cathode 14.

  An example of the cathode manufacturing method of this example will be described. When manufacturing the cathode of this example, for example, a tungsten powder having an average particle diameter of 3 μm and a mixed powder of barium oxide and aluminum oxide as an emitter are mixed at a volume ratio of 4: 1, and a press mold is manufactured on molybdenum. Embed the mixed powder and press.

  Thereafter, the mixed powder and molybdenum are cut into a predetermined cathode shape, and the heat radiating coil 142 is attached to the tip portion of the cathode base material. When this is heated to 1750 ° C. in an electric furnace in a hydrogen atmosphere and barium oxide and aluminum oxide are reduced and activated, the cathode of this example is obtained. Thereafter, a gas discharge lamp is manufactured in the same manner as in a normal manufacturing method.

  The stability of the light output of the gas discharge lamp using the cathode of this example (FIG. 4A) and the thorium-doped cathode (FIG. 4B) was measured. Since the cathode of this example can be operated at 1050 ° C., as shown in FIG. 4A, the solid angle of the conical pointed portion of the cathode is 80 ° C. On the other hand, since the thorium-doped cathode is operated at 1700 ° C., as shown in FIG. 4B, the solid angle of the conical pointed portion of the cathode is 30 °. The measurement was performed using an instantaneous multi-photometry system (MCPD-3000) manufactured by Otsuka Electronics. As a result, the variation in light output is about 2.0% in the thorium-doped cathode, whereas the variation in light output is less than 1.0% in the cathode of this example, and the stability of the light output is improved. It was confirmed that

It is a figure which shows preferable embodiment of the gas discharge lamp which concerns on this invention. It is a general view which shows the cathode in the said embodiment. It is a cross-sectional enlarged view which shows the cathode in the said embodiment. It is a figure which shows the cathode of the said embodiment used for the measurement of optical output stability, and the conventional cathode.

Explanation of symbols

13 Anode 14 Cathode 140 Cathode body 141 Base 142 Glow discharge coil

Claims (4)

In a gas discharge lamp in which a cathode and an anode are opposed to each other in a discharge atmosphere in which mercury and a rare gas are sealed, and is switched on from a glow discharge to an arc discharge.
The cathode is composed of a base made of a refractory metal material and a cathode body made of a porous refractory metal material containing an electron-emitting substance so that the tip protrudes from the base. A gas discharge lamp characterized in that a tip portion of a cathode is formed in a pointed shape, and a glow discharge coil is fitted on the cathode.   2. The gas discharge lamp according to claim 1, wherein at least one turn of the glow discharge coil is projected on a pointed portion of the cathode. The gas discharge lamp according to claim 1, wherein the pressure of the rare gas is 101 × 10 ³ Pa (760 torr) or less. The gas discharge lamp according to claim 1, wherein the tip of the cathode is formed in a pointed shape with a solid angle of 50 ° or more.

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