JP4338466B2 - Discharge tube - Google Patents

Description

  The present invention relates to a discharge tube, and in particular, as a switching spark gap for supplying a constant voltage for lighting or ignition to a high pressure discharge lamp such as a projector or a metal halide lamp of an automobile, or an ignition plug of a gas cooker, or The present invention relates to a discharge tube that can be suitably used as a gas arrester for absorbing surge voltage.

  As this type of discharge tube, the present applicant has previously proposed Japanese Patent Application Laid-Open No. 2003-7420. As shown in FIG. 3, the discharge tube 60 hermetically seals the openings at both ends of a cylindrical case member 62 made of an insulating material opened at both ends with a pair of lid members 64 and 64 that also serve as discharge electrodes. Thus, an airtight envelope 66 is formed, and a predetermined discharge gas is sealed in the airtight envelope 66.

The lid member 64 includes a flat discharge electrode portion 68 that protrudes greatly toward the center of the hermetic envelope 66, and a joint portion 70 that contacts the end surface of the case member 62. A predetermined discharge gap 72 is formed between the discharge electrode portions 68 and 68.
A plurality of pairs of trigger discharge films 78, 78 are formed on the inner wall surface 74 of the case member 62 so as to face each other with a minute discharge gap 76 therebetween. Of the pair of trigger discharge films 78, 78, one trigger discharge film 78 is electrically connected to one discharge electrode portion 68, and the other trigger discharge film 78 is electrically connected to the other discharge electrode portion 68. It is connected.
On the surface of the discharge electrode portion 68, an insulating film 80 containing an alkali iodide effective for stabilizing the discharge starting voltage is formed.
As the discharge gas sealed in the hermetic envelope 66, for example, a rare gas such as argon, neon, helium, xenon, or an inert gas such as nitrogen gas or a mixed gas is applicable. In addition, a single gas or a mixed gas of a rare gas or an inert gas and a mixed gas of a negative gas such as H ₂ are applicable.

  When a voltage equal to or higher than the discharge start voltage of the discharge tube 60 is applied between the discharge electrode portions 68, 68 of the discharge tube 60 having the above-described configuration, an electric field is generated in the minute discharge gap 76 between the trigger discharge films 78, 78. As a result, electrons are emitted into the minute discharge gap 76, and creeping corona discharge as a trigger discharge is generated. Next, this creeping corona discharge shifts to glow discharge due to an electron priming effect. Then, this glow discharge is transferred to the discharge gap 72 between the discharge electrode portions 68 and 68, and is transferred to arc discharge as the main discharge.

In the conventional discharge tube 60, as the constituent material of the trigger discharge film 78, a carbon-based material using fine graphite as a main raw material is widely used. The trigger discharge film 78 is formed, for example, by rubbing a core material made of a carbon-based material mainly made of graphite against the inner wall surface 74 of the case member 62.
JP 2003-7420 A

By the way, when the discharge tube 60 is left for a long time, a small amount of impure gas contained in the discharge gas or impure gas mixed in the sealing process of the hermetic envelope 66 is caused by the discharge electrode portion 68 or the coating 80. The work function of the discharge electrode portion 68 and the coating film 80 is changed by being adsorbed on the surface of the film, and as a result, the initial discharge start voltage increases and an initial discharge delay may occur.
The trigger discharge film 78 is formed to supply a function of preventing the initial discharge delay by supplying initial electrons. The trigger discharge film 78 is a conventional trigger composed of a carbon-based material mainly composed of graphite. The discharge film 78 could not sufficiently prevent the initial discharge delay. In addition, the conventional trigger discharge film 78 composed of a carbon-based material whose main raw material is fine-grained graphite has a small adhesive force with the inner wall surface 74 of the case member 62 and can be easily peeled off by an impact during energization. Therefore, the function of preventing the initial discharge delay may not be achieved.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to realize a long-life discharge tube that can prevent an increase in the initial discharge start voltage and does not cause an initial discharge delay. There is.

In order to achieve the above object, the discharge tube according to the present invention is hermetically sealed by hermetically sealing both end openings of a case member made of an insulating material having both ends open with a pair of lid members that also serve as discharge electrodes. Forming an envelope, enclosing a discharge gas in the hermetic envelope, and forming a discharge gap between the discharge electrode portions of the lid member disposed in the hermetic envelope; and A discharge tube in which a trigger discharge film is formed on the inner wall surface of the member with both ends thereof spaced apart from the lid member by a minute discharge gap. The trigger discharge film is made of a mixture of carbon nanotubes and amorphous carbon. It is characterized by comprising a carbon-based material obtained by impregnating a sintered body with silicon oil .

In the discharge tube according to the present invention, the trigger discharge films, since an excellent carbon nanotube electron emission characteristic is constituted by the carbon-based material comprising a raw material, it is possible to supply the initial electrons in large quantities, its As a result, an increase in the initial discharge start voltage can be prevented, and a long-life discharge tube that does not cause an initial discharge delay can be realized.
In addition, the trigger discharge film of the present invention composed of a carbon-based material containing carbon nanotubes as a raw material has long and narrow carbon nanotubes entangled with minute irregularities on the inner wall surface of the case member, and has a high adhesive force with the inner wall surface of the case member. Peeling hardly occurs and the function of preventing the initial discharge delay is sufficiently exhibited.

Amorphous carbon functions as a binder, and carbon nanotubes can be firmly bonded to each other through the amorphous carbon.

  As shown in FIG. 1, a discharge tube 10 according to the present invention includes a pair of lid members 14 that serve as discharge electrodes at both ends of a cylindrical case member 12 made of ceramic as an insulating material with both ends open. The hermetic envelope 16 is formed by hermetically sealing with 14.

The lid member 14 includes a planar discharge electrode portion 18 projecting greatly toward the center of the hermetic envelope 16, and a joint portion 20 in contact with the end surface of the case member 12. A predetermined discharge gap 22 is formed between the discharge electrode portions 18 and 18. The discharge gap 22 is, for example, about 1.5 mm.
The lid member 14 provided with the discharge electrode portion 18 and the joint portion 20 is made of oxygen-free copper or zirconium copper containing oxygen-free copper containing zirconium (Zr). Note that the end face of the case member 12 and the joint portion 20 of the lid member 14 are hermetically sealed through a sealing material (not shown) such as silver solder.

A predetermined discharge gas is sealed in the hermetic envelope 16. As this discharge gas, for example, a rare gas such as argon, neon, helium, or xenon, or an inert gas such as nitrogen gas or a mixed gas is applicable. In addition, a single gas or a mixed gas of a rare gas or an inert gas and a mixed gas of a negative gas such as H ₂ are applicable.

In addition, a plurality of linear trigger discharge films 28 are formed on the inner wall surface 24 of the case member 12 so that both ends of the case member 12 are spaced apart from the lid members 14 and 14 that also serve as discharge electrodes and a minute discharge gap 26. ing.
The trigger discharge film 28 is made of a carbon-based material whose main material is carbon nanotubes. Specifically, it is composed of a carbon-based material obtained by impregnating silicon oil into a sintered body of a mixture in which 80% carbon nanotubes as main raw materials and 20% amorphous carbon are mixed. The amorphous carbon functions as a binder, and carbon nanotubes can be firmly bonded to each other through the amorphous carbon.

  The carbon nanotube is a conductor having a low work function in which a graphite structure composed of a continuous six-membered ring of carbon atoms is formed into a cylindrical shape, and its tip is conical and extremely sharp. Carbon nanotubes are long and thin with a diameter of about 2 nm to several tens of nm and a length of about 0.5 to 1 μm, and have a large aspect ratio, which is the ratio of the height to the diameter. Thus, the carbon nanotube has a sharp tip and a large aspect ratio. Therefore, a strong electric field concentration occurs at the tip and has excellent electron emission characteristics. The carbon nanotubes may be not only single-walled carbon nanotubes but also multi-walled carbon nanotubes formed by overlapping a plurality of cylindrical graphite structures concentrically.

The trigger discharge film 28 is obtained by rubbing a core material made of a carbon-based material obtained by impregnating silicon oil into a sintered body of a mixture of carbon nanotubes and amorphous carbon, against the inner wall surface 24 of the case member 12 to obtain a carbon-based material. It can be formed by attaching.
In this case, by impregnating a sintered body of a mixture of carbon nanotubes and amorphous carbon with silicon oil, the adhesion of the carbon-based material when the core material is rubbed against the inner wall surface 24 of the case member 12 is improved. .
The silicon oil generates impure gas, but in the process of forming the hermetic envelope 16, the silicon oil evaporates and exhausts, so that the discharge gas composition in the hermetic envelope 16 is adversely affected. Never give. That is, the hermetic envelope 16 evacuates the case member 12 in a heated atmosphere of about 800 degrees, introduces a predetermined discharge gas, and then connects the case member 12 and the lid member 14 together. Since it is hermetically sealed through a sealing material, the silicon oil evaporates in a heated atmosphere of about 800 degrees and is exhausted in the vacuum exhaust process.

On the surface of the discharge electrode portion 18, an insulating film 30 containing an alkali iodide effective for stabilizing the discharge starting voltage is formed. This coating 30 is made of a simple substance or a mixture of alkali iodides such as potassium iodide (KI), sodium iodide (NaI), cesium iodide (CsI), rubidium iodide (RbI), etc., from a sodium silicate solution and pure water. It can be formed by applying to the surface of the discharge electrode portion 18 what is added to the binder.
In this case, the alkali iodide alone or a mixture is mixed at a blending ratio of 0.01 to 70% by weight, and the binder is 99.99 to 30% by weight. Moreover, the compounding ratio of the sodium silicate solution and the pure water in the binder is 0.01 to 70% by weight for the sodium silicate solution and 99.99 to 30% by weight for the pure water.

In the coating 30, cesium bromide (CsBr), rubidium bromide (RbBr), nickel bromide (NiBr ₂ ), indium bromide (InBr ₃ ), cobalt bromide (CoBr ₂ ), iron bromide (FeBr ₂ ). , FeBr ₃ ) and other bromides can be added to further stabilize the discharge start voltage of the surge absorber 10.
Incidentally, barium chloride (BaCl), barium fluoride (BaF), yttrium oxide (Y ₂ O ₃ ), yttrium chloride (YCl ₂ ), yttrium fluoride (YF ₃ ), potassium molybdate (K ₂ MoO ₄ ), tungsten One or more of potassium acid (K ₂ WO ₄ ), cesium chromate (Cs ₂ CrO ₄ ), praseodymium oxide (Pr ₆ O ₁₁ ), potassium titanate (K ₂ Ti ₄ O ₉ ) together with the bromide, or In addition to the bromide, addition to the coating 30 also contributes to stabilization of the discharge start voltage of the surge absorber 10.
These substances are added at a blending ratio of 0.01 to 10% by weight in the alkali iodide alone or a mixture of the mixture and the binder.

The insulating film 30 containing alkali iodide has a function of lowering the discharge start voltage because of its small work function and excellent electron emission characteristics, and in particular, potassium iodide (KI). Is added to a binder composed of a sodium silicate solution and pure water to form the coating 30, the effect of reducing the discharge start voltage is remarkable.
In this case, when the compounding ratio of potassium iodide added to the binder (the mixing ratio of sodium silicate solution and pure water is 1: 1) exceeds 40% by weight, the solubility of potassium iodide in the binder becomes saturated and is not dissolved any more. Therefore, the blending ratio of potassium iodide is preferably in the range of 0.1 wt% to 40 wt%. When the blending ratio of potassium iodide is 40 wt%, the action of decreasing the discharge start voltage is the largest. Become.

  In the discharge tube 10 of the present invention, when a voltage equal to or higher than the discharge start voltage of the discharge tube 10 is applied between the pair of lid members 14 and 14 also serving as discharge electrodes, the trigger discharge film 28 The electric field concentrates in the minute discharge gap 26 between the both ends and the lid members 14 and 14, whereby electrons are emitted into the minute discharge gap 26 to generate creeping corona discharge as a trigger discharge. Next, this creeping corona discharge shifts to glow discharge due to an electron priming effect. Then, the glow discharge is transferred to the discharge gap 22 between the discharge electrode portions 18 and 18, and the arc discharge as the main discharge is transferred.

Thus, in the discharge tube 10 of the present invention, the trigger discharge film 28 is made of a carbon-based material mainly made of carbon nanotubes having excellent electron emission characteristics, so a large amount of initial electrons are supplied. As a result, an increase in the initial discharge start voltage can be prevented, and a long-life discharge tube that does not cause an initial discharge delay can be realized.
In addition, the trigger discharge film 28 of the present invention composed of a carbon-based material using carbon nanotubes as a main raw material, the elongated carbon nanotubes are entangled with minute irregularities on the inner wall surface 24 of the case member 12, and the case member inner wall surface 24 Since the adhesive force is large, peeling hardly occurs and the function of preventing the initial discharge delay is sufficiently exhibited.

  FIG. 2 shows that the trigger discharge film 28 is formed of a carbon-based material obtained by impregnating silicon oil into a sintered body of a mixture of carbon nanotubes and amorphous carbon, and the trigger discharge film 28 includes: It is a graph which shows the relationship between the frequency | count of discharge and the initial stage discharge start voltage in the discharge tube comprised with the carbon-type material which used graphite as the main raw material. As shown in this graph, in the case of a discharge tube in which the trigger discharge film 28 is composed of a carbon-based material using graphite as a main material (graph B in FIG. 2), the number of discharges is about 600,000 to the initial discharge. While the starting voltage rises and an initial discharge delay occurs, in the case of the discharge tube 10 of the present invention (graph A in FIG. 2), the initial discharge starting voltage is large even if the number of discharges exceeds 1 million. There is no change, and therefore a long life is realized without causing an initial discharge delay.

It should be noted that both ends of each trigger discharge film 28 of the discharge tube 10 of the present invention are arranged with the micro discharge gap 26 spaced from the lid members 14 and 14 that also serve as discharge electrodes. As long as the electrode material that is spattered and scattered by the discharge electrode portion 18 does not adhere to both of the provided small discharge gaps 26, insulation deterioration does not occur. For this reason, the discharge tube 10 of the present invention can suppress the occurrence of insulation deterioration as compared with the conventional discharge tube 60 in which the pair of trigger discharge films 78 and 78 are opposed to each other with a minute discharge gap 76 therebetween. it can.
In this case, since the trigger discharge film 28 is not electrically connected to the lid members 14 and 14 that also serve as the discharge electrodes, the degree of electric field concentration in the minute discharge gap 26 is suppressed, but as described above, the trigger discharge film 28 However, it is composed of a carbon-based material mainly composed of carbon nanotubes with excellent electron emission characteristics, and the surface of the discharge electrode portion 18 also contains alkali iodide with a small work function and excellent electron emission characteristics. Since the coated film 30 is formed, high responsiveness is not impaired.

It is sectional drawing which shows the discharge tube which concerns on this invention. A discharge tube according to the present invention in which the trigger discharge film is made of a carbon-based material obtained by impregnating silicon oil into a sintered body of a mixture of carbon nanotubes and amorphous carbon, and the trigger discharge film is made of carbon mainly composed of graphite. It is a graph which shows the relationship between the frequency | count of discharge and the initial stage discharge start voltage in the discharge tube comprised with the system material. It is sectional drawing which shows the conventional discharge tube.

10 discharge tube
12 Case material
14 Lid member
16 Airtight envelope
18 Discharge electrode
22 Discharge gap
26 Micro discharge gap
28 Trigger discharge membrane
30 coating

Claims (1)

An airtight envelope is formed by hermetically sealing the opening at both ends of the case member made of an insulating material with both ends open with a pair of lid members that also serve as discharge electrodes, and a discharge is generated in the airtight envelope. Gas is sealed, and a discharge gap is formed between the discharge electrode portions of the lid member disposed in the hermetic envelope, and both ends of the case member are disposed on the inner wall surface of the case member. A discharge tube formed by forming a trigger discharge film arranged at a distance from each other, wherein the trigger discharge film is made of a carbon-based material formed by impregnating a silicon oil into a sintered body of a mixture of carbon nanotubes and amorphous carbon. A discharge tube characterized by that.

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