JPH09265941A - Metal vapor discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce corrosion caused by a rare earth metal halide and enhance the stability of its vaporizing amount by forming a neck part whose diameter is smaller than the central portion at both ends of a ceramic tube. SOLUTION: Alumina slender tubes 2a, 2b having the outer diameter almost the same as the inner diameter of the end part are integrally sintered to the both ends of a translucent alumina tube 1 in which the outer diameter of the central part is larger than that of the edge part. Alumina tubes 3a, 3b are integrally sintered to the alumina slender tubes 2a, 2b on the opposite side to the translucent alumina tube 1. Closing caps 4a, 4b made of conductive cermet for closing the opening parts of the alumina tubes 3a, 3b are fixed. Reliability against the corrosion of the closing cap caused by excess halide is enhanced and life is lengthened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal vapor discharge lamp, and more particularly to improving the color rendering property by using a ceramic arc tube and improving the end sealing structure of the arc tube.

[0002]

2. Description of the Related Art In high color rendering metal halide lamps, halides of rare earth metals such as dysprosium iodide, thallium iodide and sodium iodide are used as metal halides to be enclosed in the arc tube. In addition, the operating temperature of the arc tube is higher than that of quartz by using a tube of alumina, which has higher heat resistance and is chemically stable, instead of the arc tube made of quartz. And lamps with improved color rendering have been developed.

The use of a conductive cermet as an end sealing member of this type of arc tube is disclosed in, for example, Japanese Patent Laid-Open No. 52-716.
No. 95 discloses this. Also, JP-A-55-765
No. 63 discloses a shape that suppresses heat loss of the arc tube, and it is also mentioned that the conductive cermet itself has high heat radiation characteristics. In this way, squeeze the end of the arc tube,
By reducing the volume of the conductive cermet cap that is sealed to the end, heat loss from the arc tube is reduced, the temperature of the coldest part in the arc tube is raised, and the vapor pressure of the enclosed metal halide is increased. It has been shown to raise.

Generally, in order to improve the color rendering properties, the temperature of the end portion of the arc tube is raised. For this reason, the frit glass that seals the conductive cermet cap to the ceramic tube is exposed to the liquid phase of the excess halide, and the frit glass is easily corroded, and the amount of halide that can be evaporated decreases and the arc tube This may cause a change in the balance of the spectrum radiated from the. To prevent this, Japanese Examined Patent Publication No. 5-21298 discloses a method of simultaneously firing a conductive cermet cap at one end when firing the main body of the arc tube to sinter both members. The characteristics are being improved.

An arc tube using a conventional conductive cermet cap will be described with reference to FIG. Translucent ceramic tube 1
The opening portions at both ends of 1 are closed by closing caps 12 and 14, and are provided with an electrode mandrel 16 implanted inside the caps 12 and 14, and a lead rod 18 implanted outside the caps. There is. Here, the closing cap 14 is made of a conductive cermet, and is formed by integrally sintering the electrode cap 16 inside the closing cap 14 and the lead rod 18 outside. In addition, since tungsten is used as the material of the electrode mandrel 16 and alumina-tungsten cermet is used as the material of the closing caps 12 and 14, each material has excellent halogen resistance even at high temperatures, so that the inside of the arc tube is not affected. Encapsulating a metal halide in the lamp enables lighting. Further, one end of the closing cap 14 and the translucent ceramic tube 11 is airtightly sintered at the time of firing, and corrosion of the sealing portion between the closing cap and the translucent ceramic tube due to the excess portion of the enclosed metal halide. Since it does not occur, the arc tube has a longer life.

On the other hand, a ceramic metal halide lamp in which a pin-shaped power supply member such as niobium or tantalum having low halogen resistance is sealed with a glass frit is a glass frit or a pin-shaped power supply device which reduces end heat loss. It is necessary to remove or mitigate the corrosion due to the enclosed halides in JP-A-3-1777 and JP-A-6-
It is disclosed in Japanese Patent Publication No. 196131. This is because the outer shape of the end of the arc tube is smaller than the maximum outer shape of the discharge vessel in the center of the arc tube, and only a part of the portion surrounded by the power supply body leaving a small gap at the end of the discharge vessel is a metal halide component. The glass frit seals the temperature range that is not affected by the corrosive action. In addition, the gap between the power supply and the end of the discharge vessel is 100μ.
The reason for the small gap of about m is that even if the halide liquid phase infiltrates there, the liquid surface reaches a high temperature range where evaporation is sufficiently possible, and the halide liquid phase reaches the end of the temperature range where evaporation is impossible. There is a point that it is possible to prevent all of the water from entering.

[0007]

An arc tube in which an electrode and a cap that seals the electrode are arranged in a straight line has a coldest portion on the sealing portion side of the coil portion at the tip of the electrode. In the arc tube in which the metal halide is sealed, the temperature of the coldest part influences the amount of evaporation of the metal halide, which affects the balance of the emission spectrum. In addition, in the arc tube in which the neck portion having a diameter smaller than the central portion is formed in the ceramic tube and the surface position inside the arc tube of the conductive cermet cap is located in the neck portion to form the concave space, the concave space is formed. Is the coldest part, and the temperature of this part affects the spectral balance of the arc tube. That is, the conductive cermet cap has a higher temperature as it is closer to the arc, and a good spectrum balance is obtained.

However, the above-mentioned improvement of the light emitting characteristics and the corrosiveness of the halide acting by the conduction heat and the radiant heat received by the cap conflict with each other. In particular, when the excess liquid phase of the halide penetrates into the electrode embedding part of the conductive cermet, the contact between the electrode and the conductive cermet is interrupted, the contact resistance increases, and the cermet cap is heated by Joule heat. There are cases where cracks occur in the tube and the arc tube leaks. If such a defect occurs, it is estimated to be 80 from the temperature measurement of the outer surface of the arc tube.
It is considered that the inner surface of the cap has risen to a temperature of 0 ° C or higher.

A metal halide lamp using a halide of a rare earth metal as a filling additive does not have a well-balanced spectrum unless the inner surface temperature of the cap, which is the coldest part, reaches this temperature. At this temperature, there is a contradictory phenomenon that the halide of rare earth metal is highly corrosive to alumina ceramics. Therefore, as a means to mitigate the corrosiveness of the embedded portion of the electrode core of the conductive cermet cap, the inner surface of the cap is moved away from the center of the arc tube to lower its temperature, and the temperature of the portion where the liquid phase of the halide stays is kept constant. In order to do so, it is conceivable to embed the concave space with a ceramic molded body through which the electrode penetrates. However, in this arc tube, the end length is extended without changing the outer diameter of the end of the discharge vessel, and the loss due to radiant heat increases. Further, when the electrode mandrel and the ceramic molded body are in close contact with each other, the halide liquid phase gradually infiltrates between the ceramic molded body and the electrode mandrel, and the contact time with the ceramic molded body becomes longer, and the ceramic molded body becomes longer. And corrodes a cavity to cause the halide liquid phase to accumulate there and not evaporate. This phenomenon is particularly noticeable in the case of a rare earth metal halide.

The present invention has been made in view of the above,
This is a metal vapor that has a long life span of the arc tube, which aims to reduce the corrosion caused by the rare earth metal halide and to improve the stability of its evaporation amount, which is received by the embedded part of the electrode core of the conductive cermet cap of the translucent ceramic tube. An object is to provide a discharge lamp.

[0011]

To achieve the above object, in a metal vapor discharge lamp according to the present invention, conductive cermet caps are sealed at both ends of a translucent ceramic tube, and electrodes are sealed in the caps. And in a discharge lamp comprising an arc tube in which at least a halide of a rare earth metal is sealed, a neck portion having a diameter smaller than that of a central portion is formed at both ends of the ceramic tube, It is fixed to the neck portion by penetrating a small-diameter ceramic cylindrical molded body so as to form a concave space inside the tube, the electrode is penetrated with a slight gap in the molded body, and the outer side of the arc tube of the molded body The second ceramic tube is fixed in the direction, and the conductive cermet cap is integrally sintered and fitted to one end of the second ceramic tube.

[0012]

With the above construction, the liquid phase of the excess halide is dispersed and present in the small axial gap formed between the ceramic tube at the end of the arc tube and the current conductor of the electrode. With this structure, since the closing cap of the conductive cermet must be located outside the arc tube, the inner surface temperature of the closing cap is lowered. Further, in this structure, the total volume of the end portion of the arc tube increases, and the thermal loss also increases. Therefore, in the arc tube of the present invention, it is necessary to connect the tube surrounding the arc and the tube to which the closing cap is sealed with a tube having an outer diameter smaller than both of them, and the reliability of the closing cap against corrosion due to excess halide. The property is improved, and the change in the optical characteristics of the arc tube during the life can be reduced.

[0013]

Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing an arc tube according to the present invention. At both ends of a translucent alumina tube 1 having a central outer diameter larger than the end outer diameter, an alumina thin tube 2a having substantially the same outer diameter as the end inner diameter is provided. , 2b are integrally sintered. Also,
Alumina tubes 3a and 3b are integrally sintered on the opposite sides of the alumina thin tubes 2a and 2b from the translucent alumina tube 1, respectively. And, a closing cap 4a made of a conductive cermet for closing the openings of the alumina tubes 3a, 3b,
4b is fixed. Electrodes 5 and 6 have electrode portions 5a and 6a provided with coils, conductors 5b and 6b are welded to the electrode mandrel, and buried conductors 5c and 6c are welded to the intermediate conductors 5b and 6b, so that the closing cap 4a, Conductors 5c and 6c are embedded inside 4b. Furthermore, the closure cap 4
External lead rods 7a and 7b are embedded outside a and 4b.

Here, the material of the conductive cermet forming the closing caps 4a, 4b is preferably a tungsten-alumina cermet obtained by adding a small amount of tungsten to alumina ceramics. Also, the electrode portions 5a and 6a
Is tungsten, the intermediate conductors 5b and 6b are molybdenum, and the buried conductors 5c and 6c are tungsten.
The alumina tube 3a, which is one end of the discharge vessel, is sealed to the cap 4a with a glass frit, and the alumina tube 3b, which is the other end, and the cap 4b that closes are sintered integrally. .

Next, an experimental example will be described. The distance at which the alumina tube 1 and the alumina thin tubes 2a and 2b are integrally sintered (the sealing distance), the sealing distance between the alumina thin tubes 22 and 2b and the alumina tubes 3a and 3b, and the seal between the alumina tube 3b and the closing cap 4b. All distances are 3 mm. Also, the maximum inner diameter of the alumina tube 1 is 10 mm,
The distance between the necks on both sides is 14 mm. The alumina thin tubes 2a, 2b have a total length of 7.0 mm and an outer diameter of 3.1 mm, and the wall thickness of the alumina tubes 1, 3a, 3b over the sealing distance is 1 mm. Furthermore, the alumina thin tube 2a,
The inner diameter of 2b is 1.0 mm, and the intermediate conductors 5b and 6b having an outer diameter of 0.9 mm pass through with a gap of about 50 μm. The buried conductors 5c and 6c having an outer diameter of 0.5 mm are 1.
It is embedded in the closure cap at a depth of 5 mm. Further, the electrode portions 5a and 6a have a coil having a diameter of 0.25 mm wound around the tip of a tungsten rod having an outer diameter of 0.4 mm and a length of 4 mm.

The arc tube has an inner volume of 0.7 cc, an arc length of 9 mm, and an input of 150 W, the wall load is 52 W / c.
m ² . Dy by weight ratio of metal halide in the tube
3.4 mg of I ₃ : TlI: LiI in a ratio of 10: 4: 3.
It is enclosed. In addition, mercury 10 mg and argon gas 8
× 10 ³ Pascal is enclosed. The optical characteristics in this case are that the total luminous flux is 12,300 lm and the color temperature is 4,300 lm.
K, the average color rendering index Ra is 91, and the special color rendering index R ₉ is 89.

In the arc tube having the above-mentioned specifications, the inner surface temperature of the end caps 4a and 4b is changed by changing the lengths of the alumina thin tubes 2a and 2b and the intermediate conductors 5b and 6b. The temperature is lowered, and corrosion of the buried portions of the buried conductors 5c and 6c due to the halide liquid phase is eliminated. However, the volume of the gap between the intermediate conductors 5b and 6b and the alumina thin tubes 2a and 2b is increased, the amount of halide that can penetrate into this portion is also increased, and the ratio of the amount of halide that can be evaporated to the enclosed amount is decreased. This change corresponds to the increase in color temperature with respect to the lighting time of the arc tube. Therefore, in order to determine the optimum length of the alumina tubes 2a and 2b, an arc tube having the above-mentioned specifications was prototyped and a lamp blinking test was conducted. The length of the alumina tubes 2a, 2b and the closing cap 4a for the distance from the neck portion to the inner surface of the end cap,
FIG. 3 shows the crack occurrence rate of 4b up to 2000 hours and the increase in color temperature with respect to the initial color temperature. In the figure, 1 is the distance (mm) from the neck portion to the inner surface of the end cap.

As is apparent from FIG. 3, when the distance (l) from the neck portion is 9 mm to 13 mm, it is possible to prevent the occurrence of cracks and suppress the increase in color temperature.
Further, in order to improve the above characteristics, the intermediate conductors 5b, 6b
By winding a thin wire made of the same material as the intermediate conductor over the entire surface thereof, the surface area is increased, and the heat flowing from the electrode portions 5a, 6a is dissipated more and the embedded conductors 5c, 6c.
The temperature of the closing caps 4a, 4
It is possible to reduce the occurrence rate of corrosion due to the halide of c. Furthermore, it has the effect of keeping the halides that have entered the gaps between the alumina thin tubes 2a, 2b and the intermediate conductors 5b, 6b between the thin wires, so that the entry of the halides into the low temperature portion can be suppressed and the color temperature of the arc tube can be controlled. Change can be reduced.

As described above, in the arc tube having the conventional structure, the excess halide in the liquid state is present on the inner surface of one of the closing caps, so to speak, in the lateral direction. And if you do not raise the temperature in the vicinity of
The embedded portion of the electrode mandrel on the inner surface of the blocking cap made of a conductive cermet is corroded. On the other hand, in the arc tube according to the present invention, the liquid phase of the excess halide is dispersed and present in the small gap between the ceramic tube at the end of the arc tube and the current conductor to the electrode in the axial direction of the tube. According to this structure, since the closing cap is located outside the arc tube, the inner surface temperature of the closing cap is lowered. Further, in this structure, the total volume of the end portion of the arc tube increases, and the thermal loss also increases. Therefore, in the arc tube, the tube surrounding the arc and the tube to which the closing cap is sealed must be connected by a tube having a small outer diameter. With such a structure, the reliability of the closure cap against corrosion due to excess halide is improved, and changes in the optical characteristics of the arc tube during the life can be reduced.

[0020]

As described above, in the metal vapor discharge lamp according to the present invention, the corrosion caused by the rare earth metal halide received by the buried portion of the electrode core of the conductive cermet cap of the translucent ceramic tube is reduced and its evaporation amount is reduced. Can be improved in stability, and not only the life characteristics are excellent, but also the optical characteristics such as color temperature are excellent.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an arc tube according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a main part of the same.

FIG. 3 is a diagram showing a relationship between a distance from a neck portion to an inner surface of an end cap, a crack generation rate of a closing cap up to 2000 hours, and an increase in color temperature with respect to an initial color temperature.

[Explanation of symbols]

 1 translucent alumina tube 2a, 2b alumina thin tube 3a, 3b alumina tube 4a, 4b end cap 5a, 6a electrode part 5b, 6b intermediate conductor 5c, 6c embedded conductor 7a, 7b external lead rod

Claims (1)

[Claims] 1. A discharge tube comprising an electrically conductive cermet cap which is sealed at both ends of a translucent ceramic tube, electrodes are sealed in the cap, and at least a halide of a rare earth metal is sealed inside. In an electric lamp, a neck portion having a diameter smaller than that of a central portion is formed at both end portions of the ceramic tube, and a narrow space is formed inside the tube by penetrating a thin ceramic cylindrical molded body in the neck portion. A second ceramic tube is fixed to the molded body in a direction outside the arc tube of the molded body, and the electrode is penetrated through the molded body with a slight gap. A metal vapor discharge lamp in which a conductive cermet cap is integrally sintered and fitted.