JP2009123509A - Metal halide lamp for automobile head lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal halide lamp for an automobile head lamp, which contains much halide formed of a rare earth element with a low vapor pressure (a high melting point), and which exhibits an excellent light emission color maintaining property and excellent luminous efficiency. <P>SOLUTION: The metal halide lamp comprises a quartz glass arc tube having electrode sealing parts at both ends, a pair of electrodes arranged inside the arc tube through the electrode sealing parts, coils formed of high melting point metal and covering the electrodes at parts where the electrodes are sealed, and a shroud tube arranged on an outer circumference of the arc tube. The rare earth element halide is contained 40-95% based on a total amount of the halide as metal halide inside the arc tube. A distance L between an inner surface of the shroud tube and the arc tube satisfies 2<L≤9.5 mm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a metal halide lamp used for an automobile headlamp, and more particularly to an improvement of a metal halide lamp containing a rare earth element halide.

In recent years, metal halide lamps are being adopted for automobile headlamps for reasons such as high efficiency. In the metal halide lamp, mercury or a rare gas and a metal halide (metal halide) having light emission of each wavelength are enclosed in an arc tube. In general, sodium, scandium, thallium, indium, sodium, or the like is enclosed in the metal halide as an iodide. The emission color (color temperature) of the metal halide lamp is determined by the type of metal halide and the mixing ratio thereof. In recent years, however, the types and mixing ratios of metal halides are dysprosium, neodymium, thulium, and other halides that are widely used in conventional general-purpose metal halide lamps, etc., in line with the diversification of customer needs, especially emission colors Some rare earth halides tend to be used.

FIG. 1 shows a structure of a metal halide lamp conventionally used for an automobile headlamp. That is, an arc tube 2 made of quartz glass having electrode seal portions 1 at both ends, a pair of electrodes 3 disposed inside the arc tube 2 through the electrode seal portion 1, and the electrodes 3 are sealed. In this portion, a coil 4 made of a refractory metal covered with the electrode 3 and a shroud tube 5 disposed on the outer periphery of the arc tube 2 are provided. A metal foil 6 made of molybdenum is welded to the end of the electrode 3 in the electrode seal portion 1, and the metal foil 6 is welded to quartz glass so that the arc tube 2 is kept airtight. When the electrode 3 and the quartz glass are completely welded in the electrode seal portion 1, a crack is generated in the quartz glass (hereinafter referred to as an electrode crack) in the quartz glass due to a difference in thermal expansion between the electrode and quartz during lighting, and a leak occurs. It will be. In order to prevent this, as shown in FIG. 1, it is a well-known technique to prevent electrode cracking by covering the electrode 3 and quartz glass by covering the electrode with a coil 4 made of high melting point metal such as a tungsten coil. It is.

However, when the electrode is covered with a coil, a slight gap is generated from the inside of the arc tube to the metal foil through the welded portion of the quartz and the electrode, and the emission color changes when the encapsulated material enters here. An improvement technique has also been proposed for this (for example, JP-A-10-269941).

However, when a rare earth element halide with a high melting point, such as dysprosium halide, is mainly enclosed in the arc tube, it has been used from the slight gap between the electrode and the coil in the electrode and metal foil welded part as it is repeatedly turned on and off. More halides intrude than conventional halides such as sodium and scandium, and as a result, the emission color of the lamp changes greatly due to the decrease in halides that contribute to light emission as in the past. Occurred. Many rare earth element halides have a higher melting point than conventional halides such as sodium, thallium, and indium. Even in the bonded state, the radius of atoms or molecules is large and the mean free path is shortened, so that it is estimated that it is difficult to return to the arc tube.

Also, if a rare earth element halide such as dysprosium halide is mainly encapsulated, the desired luminous flux cannot be obtained because the luminous efficiency is poor in comparison with the case where conventionally used halides such as sodium and scandium are used. The problem also occurred. In this regard, JP-A-6-20645 describes that the temperature and luminous efficiency of the light emitting part can be optimized by setting the gap between the luminous tube and the shroud tube to 2 mm or less. As the metal halide, general sodium iodide and scandium iodide are used.

Furthermore, Japanese Patent Laid-Open No. 2001-110358 describes the relationship between the luminous flux between the arc tube and the shroud tube and the luminous flux. Here, the luminous flux is impaired by setting the gap between the luminous tube and the shroud tube to about 0.3 mm. Although there is a description that the luminous flux is reduced when it is more than this, this applies to the use of a halide of sodium iodide or scandium iodide as a metal halide. It does not correspond to those mainly composed of rare earth metal halides mentioned in.
Japanese Patent Laid-Open No. 10-269941 JP-A-6-20645 Japanese Patent Laid-Open No. 2001-110358

The problem to be solved by the present invention is that the electrode seal portion has a structure in which a coil made of a refractory metal is attached to the electrode, and even if the rare earth element halide is mainly sealed, it has entered the gap on the metal foil side. It is an object of the present invention to provide a metal halide lamp in which the rare earth element halide can be easily returned to the inside of the arc tube so that the emission color change due to the reduction of the inclusion is reduced and the luminous efficiency can be improved.

In order to solve the above problems, the present invention has a metal halide lamp for automobile headlamps having the following configuration. That is, an arc tube made of quartz glass having electrode seal portions at both ends, a pair of electrodes arranged inside the arc tube through the electrode seal portion, and the electrodes are covered at portions where the electrodes are sealed. A refractory metal coil and a shroud tube disposed on the outer periphery of the arc tube, and a rare earth element halide as a metal halide in the arc tube is 40% or more based on the total amount of halide. 95% or less, and the distance L between the inner surface of the shroud tube and the arc tube satisfies 2 mm <L ≦ 9.5 mm.

Moreover, the said structure is applicable also to the lamp | ramp which is not coat | covered with the coil made from a refractory metal to an electrode.

Furthermore, the above configuration can also be applied to a metal halide lamp that does not contain mercury in the arc tube.

Since the present invention is configured as described above, even a metal halide lamp in which a coil made of a refractory metal is attached to an electrode in an electrode seal portion and a rare earth element halide is mainly enclosed enters the gap on the metal foil side. Since the rare earth element halide easily returns to the inside of the arc tube, it is possible to provide a metal halide lamp in which the emission color change due to the reduction of the inclusion is small and the luminous efficiency can be improved.

Next, the best embodiment of the present invention will be described in detail with reference to the drawings and tables. The metal halide lamp according to the present invention has the structure shown in FIG. 1 except for the features regarding the amount of rare earth element halide sealed in the arc tube and the distance between the arc tube and the shroud tube disposed on the outer periphery thereof. . That is, a quartz glass arc tube 2 having electrode seal portions 1 at both ends, a pair of electrodes 3 disposed inside the arc tube through the electrode seal portion 1, and a portion where the electrodes 3 are sealed A coil 4 made of a refractory metal covered with the electrode 3 and a shroud tube 5 disposed on the outer periphery of the arc tube 2 are provided. A metal foil 6 made of molybdenum is welded to the end of the electrode 3 in the electrode seal portion 1, and the metal foil 6 is welded to quartz glass so that the arc tube 2 is kept airtight. In addition, the metal halide lamp according to the present invention has an electrode 3 with a tube power of 35 W (tube voltage 85 V, tube current 0.41 A), a diameter Φ0.25 made of tungsten containing 1% wt of thorium oxide, and a total length of 7 mm. The one end is connected to a metal foil 6 made of molybdenum, and the other electrode protrudes into the arc tube 2 made of quartz glass. The electrode 3 is covered with a coil 4 having a wire diameter of Φ0.05 mm. In the arc tube 2, mercury, buffer gas and iodide, dysprosium and neodymium are combined and sealed in a weight ratio of 75%, and in addition, sodium is sealed as iodide. Further, a shroud tube 5 made of quartz glass is provided on the outer periphery of the arc tube 2.

In addition, the life test used the test method described in Japan Light Bulb Industry Association Standard JEL215, and evaluated up to 1500 hours, and confirmed the color temperature change. Considering the headlight white range, the color temperature change was good up to the initial 110%. Lamps with different intervals between the inner surface of the shroud tube 5 and the arc tube 2 were created and evaluated, and changes in color temperature after lighting for 1500 hours were confirmed. The results are shown in Table 1.

According to Table 1, those having a color temperature of 110% or less with respect to the initial value were Examples 3 to 18, and the other examples were 110% or more. The distance between the inner surface of the shroud tube and the arc tube in Examples 3 to 18 is that the region where the rare earth metal halide can move due to the heat energy emitted from the arc tube is appropriately kept, and enters the gap on the metal foil side where the temperature is low. It is presumed that the rare earth metal halide was easily returned to the arc tube and contributed to the maintenance of the emission color without any loss of emission.

Furthermore, the initial luminous flux of the lamp in which the interval between the arc tube side inner surface of the shroud tube and the arc tube was changed was confirmed. Further, a metal halide using sodium iodide or scandium iodide was also compared and confirmed as a conventional example. The results are shown in Table 2.

According to Table 2, the luminous flux rise was seen in Examples 3-18 of this invention with respect to the prior art example. The reason for this is also presumed to be that the excitation of rare earth metal increased due to appropriate heat retention as described above.

In this experiment, the halide of rare earth elements was set to 75% of the total amount by weight ratio, but other than this (40% or more and 95% or less), the light emission color change suppressing effect and the light emission efficiency increasing effect are good. However, if it is 95% or more, the arc tube is eroded, and the luminous flux maintenance factor is lowered and the emission color is changed. Further, if it is 40% or less, the effect of improving the color rendering properties by the rare earth elements becomes thin, so 40% or more is preferable.

Further, in the lamp of the present example where the coil was not attached to the electrode, the emission color maintenance and the luminous flux increase were similarly observed, but the coil is preferably attached from the viewpoint of preventing electrode cracks.

In addition, similar results were obtained in a so-called mercury-free metal halide lamp for automobile headlamps that does not contain mercury in the arc tube, which has been attracting attention in recent years from the viewpoint of environmental conservation.

INDUSTRIAL APPLICABILITY The present invention can be used industrially as a structure of a metal halide lamp for automobile headlamps that has a particularly small emission color change and improved luminous efficiency.

Reference diagram showing the structure of a metal halide lamp for automotive headlamps

Explanation of symbols

1: Electrode seal part 2: Arc tube 3: Electrode 4: Coil made of high melting point metal 5: Shroud tube 6: Metal foil

Claims (3)

A quartz glass arc tube having electrode seal portions at both ends, a pair of electrodes disposed inside the arc tube through the electrode seal portion, and a high portion covered with the electrodes at the portion where the electrodes are sealed It comprises a coil made of a melting point metal and a shroud tube disposed on the outer periphery of the arc tube. Inside the arc tube, a rare earth element halide as a metal halide is 40% or more and 95% with respect to the total amount of halide. A metal halide lamp for an automotive headlamp, comprising: a distance L between an inner surface of the shroud tube and the arc tube satisfying 2 mm <L ≦ 9.5 mm. 2. The metal halide lamp for an automotive headlamp according to claim 1, wherein the electrode is not coated with a coil made of a refractory metal. The metal halide lamp for automobile headlamps according to claim 1 or 2, wherein the arc tube does not contain mercury.

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