JPH01236573A - Light emitting tube for high voltage metallic vapor discharge lamp - Google Patents

Abstract

PURPOSE:To prevent initiation of cracks at the time of baking and frit sealing, by inserting and embedding the end of an electrode shaft in a hole of a conductive cermet end cap together with an element wire thinner than the electrode shaft, and by forming an electric insulative layer from a cermet material with electric insulativeness. CONSTITUTION:Together with a thinner element wire 30, one end of an electrode shaft 18 is embedded upright in a hole 32 at the inner side face of a conductive disc 22. i.e. the surface exposed in a ceramic tube 16. On the surface (inner side face) 36 on the electrode side at which the electrode shaft 18 is installed upright, an electric insulation layer 38 for prevention of back arc is fitted in specified thickness in single piece construction, and the whole inner face of the conductive cermet constituting the conductive disc 22 is covered with this electric insulation layer 38 with its exposure well avoided. This prevents initiation of cracks at the time of baking and frit sealing.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an arc tube for a high-pressure metal vapor discharge lamp (hereinafter referred to as an HID lamp), and particularly relates to an arc tube for a high-pressure metal vapor discharge lamp (hereinafter referred to as an HID lamp). The present invention relates to a structure for closing the end of an arc tube, in which the end is closed using a conductive closing body and frit-sealed.

(Background Art) Conventionally, in HID lamps using translucent ceramic tubes as arc tubes, end closures of the arc tubes have been disclosed, for example, in Japanese Patent Application Laid-Open No. 71695/1983. A conductive cermet disk (endocamp) is used, which is made of a conductive cermet material obtained by mixing and sintering ceramics such as aluminum oxide powder and heat-resistant metals such as metallic tungsten powder. There is.

In such a cermet disk, a tungsten discharge electrode shaft is normally installed on the surface located inside the arc tube, while a power supply electrode shaft is provided on the surface located outside the arc tube. A lead member is provided such that power from the power source is applied from the lead member through the cermet disc to the tungsten electrode.

In addition, in an HID lamp equipped with an arc tube closed with such a cermet disk, at the time of starting,
Due to the so-called back-arc phenomenon, in which the arc does not occur between the opposing electrodes, but between the electrode axis and the cermet disk, such disks are cranked, resulting in
There are problems such as leakage of the arc tube, and heat-resistant metal components of the cermet material that evaporate and scatter from the disk, which adhere to the inner wall of the arc tube and turn black, resulting in a decrease in luminous flux. Therefore, in order to prevent such problems, it has been proposed to provide at least the inner surface of the cermet disk with an electrically insulating layer made of an insulating ceramic such as alumina to cover the surface.

By the way, when installing the discharge electrode shaft upright on this conductive cermet disk, it is necessary to use a frit material to prevent the electrode shaft from being corroded by the metal vapor sealed in the arc tube, especially the metal halide in a metal halide lamp. It is desirable to avoid fixing with adhesive materials such as cermet discs, and for this purpose, a hole is usually provided in the molded body (green body) of the cermet disk, and a specified electrode shaft is buried in the hole. By sintering and integrating the molded body under such conditions, a shrink-fitting method is employed in which the electrode shaft is mechanically fixed within the buried hole.

Furthermore, when attaching the cermet disk obtained as described above to the arc tube, it is conceivable that the cermet disk may be shrink-fitted during sintering of the arc tube, but a predetermined luminescent substance or the like may be placed inside the arc tube. Because it is necessary to enclose
Normally, at least one open end side is attached by fitting a cermet disk with an electrode shaft erected on the inner surface, and then sealing the gap between the disk and the inner surface of the open end with a predetermined frit sealing material. It is said to be a structure.

The opening end of such an arc tube is sealed with a frit sealant, in order to prevent the luminescent substances injected into the arc tube from evaporating and scattering, usually by rapid heating and cooling operations up to about 1500 degrees Celsius. It will be done by.

However, the cermet disk having the above-mentioned structure has a problem in that the disk tends to crack due to shrinkage during sintering when the electrode shaft is shrink-fitted during sintering. be.

In particular, the ceramic material forming the electrically insulating layer on the inner surface of the cermet disk has poor toughness and has a significant difference in thermal expansion from the metal material forming the electrode shaft. When mounting using a lamp, cranks are likely to occur in the electrical insulating layer during heating operations, and these can grow due to the thermal cycle caused by repeated turning on and off of the arc tube, resulting in leaks and a decrease in luminous flux. There were also inherent problems such as:

(Problem to be solved) The present invention has been made in view of the above circumstances, and the problem to be solved is to prevent the occurrence of cracks as much as possible during firing and frit sealing. The object of the present invention is to clarify the cermet disk structure and provide an arc tube for an HID lamp that does not cause problems such as leakage of the arc tube due to the rack or reduction in luminous flux.

(Solution Means) In order to solve the above-mentioned problems, the present invention has the following features:
A conductive cermet end cap having an electrode shaft erected on the inner surface is fitted into one end of the translucent ceramic tube, and the conductive cermet end cap is sealed with a predetermined frit sealing material. In the arc tube for a high-pressure metal vapor discharge lamp, the electrode shaft is provided at least on the inner surface thereof with an electrically insulating layer, and the surface thereof is coated with an electrically insulating layer. While inserting and burying the electric cotton 8i layer together with at least one strand thinner than the electrode axis,
Its feature is that it is constructed from an electrically insulating cermet material.

(Examples) Hereinafter, in order to clarify the present invention more specifically, examples of the present invention will be described in detail with reference to the drawings.

First, FIG. 1 shows a vertical lighting type H to which the present invention is applied.
This diagram schematically shows the entire ID lamp, in which IO is a light-transmitting bulb (outer bulb) made of glass or the like, the opening of which is sealed with a base 12; The inside is filled with an inert gas such as nitrogen or maintained in a vacuum state, and the H
Depending on the type of ID lamp, a luminous tube 14 filled with various metals, metal oxides, or their vapors is housed.゛Such a luminous tube 14 is constructed such that the openings at both ends of a tubular translucent ceramic tube 16 made of alumina porcelain or the like are provided with conductive disks 20 and 22 serving as end caps each having an electrode shaft 18 erected on its inner surface. conductive disks 20.22
Lead members 24 each integrally provided on the outer surface of the
On the other hand, the electric power supplied from the base 12 is guided through conductive members 26 and 26 that support the arc tube I4. Note that the arc tube 1 in this example
4, the coldest point is set at the lower end,
The conductive disk 20 that closes the lower end opening is fixed by shrink fitting using shrinkage during sintering of the arc tube 14, while the conductive disk 22 that closes the upper end opening is fitted with a sealing material 28. (See Figure 2).

By the way, in this embodiment, such an arc tube 14
The major feature lies in the structure of the conductive disk 22 whose one end is closed together with the sealing material 28, and detailed views thereof are shown in FIGS. 2 and 3.

Specifically, the conductive disk 22 is made of various known conductive cermet materials, particularly those having a coefficient of thermal expansion intermediate between the constituent material of the ceramic tube 16 and the heat-resistant metal used as the electrode shaft 18, for example. It is made of a composite material of tungsten metal or molybdenum metal and aluminum oxide, tungsten carbide, tungsten polymer, etc., and is formed in the shape of a thick disk as a whole.

The conductive disk 22 has an inner surface thereof,
In other words, on the surface exposed inside the ceramic tube 16, the electrode shaft 18 has a thin wire 30 at one end thereof.
At the same time, it is buried in the buried hole 32 and stands vertically. A known coil portion 34 is provided at the tip of the electrode shaft 18 with a predetermined length thereof exposed.

Further, on the electrode side surface (inner surface) 36 of the conductive disk 22 on which the electrode shaft 18 is erected, an electrical insulating layer 38 for preventing back arcing is integrally provided with a predetermined thickness. The layer 38 covers the entire inner surface of the conductive groove forming the conductive disk 22,
Its direct exposure is avoided.

Here, the electrode shaft 18 has a conductive disk 22
For the green body before firing to form
By sintering the embedding hole 3 in the embedding state, the embedding hole 3
It is shrink-fitted and fixed within 2.

In this way, the electrode shaft 18 is inserted into the buried hole provided in the green body before firing to form the conductive disk 22.
When it is embedded together with the wire 30 and sintered at high temperature and sinter-fitted, as shown in FIG. ,
By deforming the cross-sectional shape of the strands 30, good shrink-fitting strength can be exhibited while alleviating the stress generated during shrink-fitting.
Further, good electrical contact with the electrode shaft 18 can be obtained. In FIG. 4, the state of the conductive disk 22 before firing is shown by a solid line, and the state after firing is shown by a broken line.

That is, if an electrode shaft that completely fills the hole in the conductive disk is used as in the past, the shrinkage stress during firing of the tetraconductor disk cannot be effectively alleviated, and therefore, the BgB electric However, in this embodiment, a space exists between the electrode shaft 18 and the strands 30 and the embedding hole 32, so that the above-mentioned embedding hole 32 and electrode shaft 18
, the wire 30 can be deformed, and the conductive disk 22
This means that the shrinkage stress of is effectively alleviated.

Note that the wire 30 is generally made of the same material as the electrode shaft 18, for example, a metal material such as tungsten, from the viewpoint of heat resistance and the like.

Further, as the electrode shaft 18, one having a thickness of about 0.4**φ to 1.5fiφ is used for −1'IQ, and as for the strand 30, the electrode shaft 18
It is preferable to use one having a diameter smaller than that, generally about 1/10 to 8/10 of the thickness.

However, if the diameter of the wire 30 becomes too thin,
This is because the effect of preventing cracks is lost, and if the diameter exceeds 8/10 of the thickness of the electrode shaft 18, the gap between it and the buried hole 32 becomes large, reducing the reliability of the electrical contact area. This is because the heat capacity of the electrodes may decrease or the heat capacity of the electrodes may increase, resulting in poor lighting startability.

Further, the height of the wire 30 is desirably set to be lower than at least the coil portion 34 of the electrode shaft 18 in order to prevent discharge from the element 'fa 30 during lighting. It is set flush with the inner surface of the conductive disk 22 or so as to slightly protrude.

In addition, in the conductive disk 22 in this embodiment, the lead member 24 erected on the outer surface thereof is also provided with a wire 40 in the same manner as the electrode shaft 18.
This prevents the outer surface of the conductive disk 22 from being cranked during firing. Of course, the height of the wire 40 attached to this lead member 24 will be selected as appropriate without being subjected to any special pressure, but the height of the wire 40 attached to this lead member 24 will be selected as appropriate. When inserting and shrink-fitting the lead member 24 and the wire 40, the element L? is easy to set in the jig. It is desirable that the length of i40 be approximately the same as that of the lead member 24.

On the other hand, the electrically insulating layer 38 covering the electrode-side surface 36 of the conductive disk 22 is made of a cermet material that is substantially electrically insulating, and usually forms the conductive disk 22. It is formed by being laminated on the surface of the green body and integrally fired.

Specifically, the cermet material forming the electrical insulating layer 38 is a known cermet material having a coefficient of thermal expansion comparable to that of the conductive disk 22, such as Alz.
Ch-W series and A7! Any cermet material such as □03-Mo can be suitably used, but by adjusting the content of metal powder, it is possible to use lXlO12Ω so that it exhibits substantially electrical insulation properties. - It is formed with a resistivity of about cIm or more, and thereby the back arc phenomenon at the time of starting can be advantageously prevented. Further, the thickness of the electrical insulating layer 38 is appropriately determined within a range that can effectively suppress the back arc phenomenon, but is generally 0.05 to 0.05.
It will be set to about 8yx■.

By using such a cermet material as the material for forming the electrical insulating layer 38, the toughness can be advantageously improved compared to that using a conventional insulating ceramic material, thereby preventing cracks. The occurrence can be effectively prevented.

That is, the conductive disk 22 having the structure as described above
As is well known, the end of the ceramic tube 16 is fitted into the end and hermetically sealed with a suitable sealing material 28. For example, the ring-shaped sealing material 28 is made of ceramic.

interposed between the box tube 16 and the conductive disk 22,
This sealing operation is performed by heating and melting the gas to about 1500° C. in an argon atmosphere. In order to prevent the evaporation and scattering of the luminescent substances, etc., this is done by rapid heating and rapid cooling operations. However, in this embodiment, since the electrical insulating layer 38 is made of an insulating cermet material, the heat By improving the expansion difference and toughness, it is possible to extremely advantageously prevent the occurrence of cracks during sealing, and furthermore, the growth of cracks due to thermal cycles caused by repeated turning on and off.

Note that as the sealing material 28, a known metal halide resistant composition is suitably used, such as Yz 03,
l, az o:l, Dyz 03, AJz 03,
A composition selected from SiO□ or the like with an appropriate mixing ratio and pressure-molded into a ring shape can be used satisfactorily.

In particular, the translucent ceramic tube 1 in this embodiment
6 has a stepped portion 42 extending in the shape of an inner flange on the inner circumferential surface of the end portion, and the conductive disk 22 fitted into the stepped portion 42 extends along the inner circumferential edge of the stepped portion 42. The sealing material 28 is not substantially exposed to the inner surface of the arc tube by being attached in such a manner that the sealing material 28 is in contact with the metal or metal halide vapor inside the arc tube. This makes it possible to prevent deterioration and the occurrence of leaks and the like associated with it.

Therefore, as described above, in the conductive disk 22 in which the electrically insulating layer 38 is formed of an insulating cermet material, this effect is combined with the effect of the wire 30 being attached to the electrode shaft 18 as described above. Therefore, the generation of cranks on the disc 22 body and the electrical insulating layer 38 during firing of the mTL disc 22 and when attaching it to the end of the translucent ceramic tube 16 can be extremely effectively avoided.
As a result, problems such as occurrence of leakage and reduction in luminous flux in the arc tube 14 obtained can be completely eliminated, and its durability and reliability can be greatly improved.

Note that there is a concern that the electrical insulating layer 38 formed of such a cermet material may react with metal vapor, especially metal halide vapor, sealed in the arc tube 14. Since such a reaction hardly occurs except at the coldest point where the excess metal halide liquid phase etc. condense in the process, as shown in this embodiment (the conductive disk 22 attached to the upper end of the vertical lighting type arc tube I4) In this case, there are no problems such as scattering of metal particles (tungsten particles) due to such a reaction and blackening caused by the metal particles adhering to the inner surface of the arc tube.

Incidentally, it has several different tungsten (W) contents. l! In the conductive disk 22 having the above-described structure and having the electrically insulating layer 38 made of a 203-W cermet material, crack occurrence and sealing during firing (when the electrode shaft 18 is shrink-fitted) Table 1 below shows the results of an experiment to investigate the occurrence of cranking during heat treatment (rapid temperature increase of 15°O°C/2 minutes) to the same extent as in the previous example.

Table 1*1: W content = W/(W+-Al2O2) From Table 1, it is easy to understand the excellent crank prevention effect of the present invention. Note that, as is clear from the experimental results, the electrical insulating layer 38 is made of A7! z
In the case of forming an Off-W type cermet material, the original purpose of the electrical insulating layer, which is to prevent back arcing, can be achieved while advantageously preventing the occurrence of cranking. It is desirable to set the content to 10% by weight, preferably 4 to 8% by weight.

Although the typical embodiments of the present invention shown in the drawings have been described above, the present invention should not be construed in any limited manner depending on the illustrated structure, the specific explanation accompanying it, or the experiments thereof. Without departing from the spirit of the present invention, various changes, modifications, improvements, etc. can be made to the present invention based on the knowledge of those skilled in the art, and the present invention It goes without saying that the present invention also includes embodiments of the present invention.

For example, it goes without saying that the present invention can be advantageously applied not only to vertically lit arc tubes for HID lamps, but also to horizontally lit arc tubes for HID lamps. In addition, in such an arc tube, in order to avoid the reaction of the electrically insulating layer with the metal vapor sealed inside the arc tube, the coldest part of the arc tube is placed in a region other than the open end sealed with a frit sealant. It is desirable to set a point.

Furthermore, it is also possible to set two or more wires 30 to be attached to the electrode shaft 18.

Further, the specific shape of the conductive disk 22 may be various shapes, such as a stepped disk shape, in addition to the thick disk shape as illustrated, and the electrically insulating layer 38 may be formed on its side surface. It is also possible to form it around the periphery or even on the outer surface.

(Effects of the Invention) As is clear from the above description, according to the present invention, a wire is attached to an electrode shaft whose end is embedded in and stands up in a conductive cermet end cap, and the conductive end cap is By forming the electrically insulating layer covering the inner surface with electrically insulating cermet material, the end cap can be fired and attached to the translucent ceramic 7X tube in a timely manner (
Therefore, the occurrence of cracks in the end cap body and the electrically insulating layer during frit sealing can be extremely advantageously prevented. In the arc tube for an HID lamp according to the present invention, which is sealed with This makes it possible to extremely advantageously improve durability.

[Brief explanation of the drawing]

FIG. 1 shows an H equipped with an arc tube constructed according to the present invention.
FIG. 2 is a partially cutaway explanatory diagram showing an example of an ID lamp;
The figure is an enlarged cross-sectional view of the main part showing the upper end of the light emitting tube constituting such an HID lamp. FIG. 3 is a cross-sectional view taken along the line ■-■ in FIG. FIG. 2 is an enlarged cross-sectional view of a main part for explaining a state in which an electrode shaft is shrink-fitted in a conductive disk that constitutes a tube. 14: Arc tube 16: Translucent ceramic tube 18:
Electrode shaft 20, 22: Conductive disk 28: Sealing material 30: Wire 32: Buried hole 36: Electrode side surface (inner surface) 38: Electrical insulation layer

Claims (1)

[Claims] A conductive cermet end cap having an electrode shaft erected on the inner surface is fitted into one end of a translucent ceramic tube, and the end cap is sealed with a predetermined frit sealing material. In the arc tube for a high-pressure metal vapor discharge lamp, the electrically insulating layer is provided on at least the inner surface of the conductive cermet end cap to cover the surface thereof, and the electrode shaft is connected to the conductive cermet end cap at its end. while inserting and burying it together with at least one strand thinner than the electrode axis into the embedding hole,
An arc tube for a high-pressure metal vapor discharge lamp, wherein the electrically insulating layer is made of an electrically insulating cermet material.