JP4133797B2 - 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. 4, the discharge tube 60 is hermetically sealed with a pair of lid members 64, 64 that also serve as discharge electrodes, at both ends of a cylindrical case member 62 made of an insulating material that opens at both ends. 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 and 78 are formed in the circumferential direction of 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 this alkali iodide, the simple substance or mixture of alkali iodides, such as potassium iodide (KI), sodium iodide (NaI), cesium iodide (CsI), and rubidium iodide (RbI), corresponds.
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.
JP 2003-7420 A

By the way, the above-mentioned film 80 containing alkali iodide has a function of lowering the discharge start voltage because of its small work function and excellent electron emission characteristics. In particular, potassium iodide (KI) is used as sodium silicate. When the coating film 80 is formed by depositing a binder made of a solution and pure water on the surface of the discharge electrode portion 68, the action of lowering the discharge starting voltage is remarkable, which is preferable.
However, when the coating film 80 is formed using a potassium iodide added to a binder composed of a sodium silicate solution and pure water, the discharge start voltage varies greatly when the discharge tube 60 is used in a high temperature environment. It turns out that there is.

  The present invention has been made in view of the above problems, and the object of the present invention is to adhere a surface of a discharge electrode to which potassium iodide is added to a binder composed of a sodium silicate solution and pure water. An object of the present invention is to realize a discharge tube capable of suppressing a variation rate of a discharge start voltage when used in a high temperature environment in a discharge tube having a coating formed thereon.

In order to achieve the above object, a discharge tube according to the present invention has a plurality of discharge electrodes arranged with a discharge gap therebetween, which is enclosed in a hermetic envelope together with a discharge gas, and further, In a discharge tube in which a film formed by adding potassium iodide to a binder made of sodium silicate solution and pure water is deposited on the surface to form a film containing potassium iodide, the potassium iodide is added to the binder. The addition amount is 5 to 15% by weight .

In the discharge tube according to the present invention, the amount of potassium iodide added to the binder consisting of a sodium silicate solution and pure water is 5 to 15% by weight. The variation rate of the starting voltage can be suppressed within ± 5% .

  As shown in FIGS. 1 and 2, a discharge tube 10 according to the present invention has a pair of lids that serve as discharge electrodes at both ends of a cylindrical case member 12 made of ceramic as an insulating material having both ends open. The hermetic envelope 16 is formed by hermetically sealing with the members 14 and 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 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 surface 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.

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. 1 and 2 exemplify a case where eight trigger discharge films 28 are formed at intervals of 45 degrees in the circumferential direction of the inner wall surface 24 of the case member 12.
The trigger discharge film 28 is made of a conductive material such as a carbon-based material. The trigger discharge film 28 can be formed, for example, by rubbing a core material made of a carbon-based material.

An insulating film 30 containing potassium iodide (KI) is formed on the surface of the discharge electrode portion 18. The coating 30 is effective for stabilizing the discharge start voltage, has a small work function, is excellent in electron emission characteristics, and has an action of reducing the discharge start voltage.
The coating 30 can be formed by applying (depositing) potassium iodide to a surface of the discharge electrode portion 18 with a potassium silicate solution and pure water added to a binder.
In this case, the amount of potassium iodide added to the binder comprising the sodium silicate solution and pure water is 0.01 to 23% by weight, preferably 5 to 15% by weight.
The blending ratio of the sodium silicate solution and the pure water in the binder is 50 to 67% by weight for the sodium silicate solution, preferably 60% by weight, and 50 to 33% by weight for pure water, preferably 40% by weight. Is done.

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 ). The addition of one or more bromides such as FeBr ₃ ) can further stabilize the discharge start voltage of the discharge tube 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 discharge tube 10.
These substances are added in a mixture ratio of 0.01 to 10% by weight in the mixture of potassium iodide and binder.

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 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 is performed as the main discharge.

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 discharge electrode portion 18 Since the film 30 having a small work function and excellent electron emission characteristics is formed on the surface, high responsiveness is not impaired.

Thus, in the discharge tube 10 of the present invention, the amount of potassium iodide added to the binder composed of the sodium silicate solution and pure water is 0.01 to 23% by weight. Even when used in the above, the fluctuation rate of the discharge start voltage can be reduced.
FIG. 3 shows the relationship between the amount of potassium iodide (KI) added to the binder and the variation rate of the DC discharge starting voltage when the discharge tube 10 according to the present invention is heated at 150 ° C. and left for 50 hours. It is a graph to show. In addition, the used discharge tube 10 comprises the discharge electrode portion 18 with oxygen-free copper and the discharge gas with Ar, and the blending ratio of the sodium silicate solution and pure water in the binder is 60% by weight: 40% by weight. It is made.
If the variation rate of the DC discharge start voltage is within ± 10%, there is no practical problem. As shown in the graph of FIG. 3, if the amount of potassium iodide added to the binder is 0.01 to 23% by weight, In addition, the variation rate of the discharge start voltage can be suppressed within ± 10%. Further, when the amount of potassium iodide added to the binder is 5 to 15% by weight, it can be said that the variation rate of the discharge start voltage can be suppressed to within ± 5%, which is even more preferable.

If the amount of the sodium silicate solution in the binder is large, the viscosity of the binder increases, and therefore the film thickness of the coating 30 formed by applying (attaching) the binder to the surface of the discharge electrode portion 18 is likely to be uneven. As a result, the discharge start voltage varies.
On the other hand, if the amount of the sodium silicate solution in the binder is small, the viscosity of the binder is low, so the adhesive force between the surface of the discharge electrode portion 18 and the coating 30 is small, and as a result, the coating 30 is easily sputtered, and the life characteristics It becomes a factor which causes deterioration.
From the above, the blending ratio of the sodium silicate solution and the pure water in the binder is 50 to 67% by weight, preferably 60% by weight, preferably 50 to 33% by weight, and preferably 50 to 33% by weight, as described above. Is suitably 40% by weight.

It is sectional drawing which shows the discharge tube which concerns on this invention. It is AA sectional drawing of FIG. It is a graph which shows the relationship between the addition amount of potassium iodide (KI) to a binder, and the fluctuation rate of DC discharge start voltage. It is sectional drawing which shows the conventional discharge tube.

Explanation of symbols

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)

A plurality of discharge electrodes are arranged with a discharge gap therebetween, and this is enclosed in a hermetic envelope together with a discharge gas, and further, potassium iodide is bonded to the surface of the discharge electrode with a sodium silicate solution and pure water. In the discharge tube in which a film containing potassium iodide is formed by depositing what is added to the above, the amount of potassium iodide added to the binder is 5 to 15% by weight. Discharge tube.

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