JP3268190B2 - Arc tube for discharge lamp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc tube for a discharge lamp, and more particularly to a technique for an arc tube for a discharge lamp used as a light source of a headlamp for an automobile.

[0002]

2. Description of the Related Art In recent years, as a bulb for an automobile headlamp, it has advantages that it has good luminous efficiency and color rendering properties and has a longer life than a filament bulb.
The use of a discharge lamp is being studied, and in this type of discharge lamp, a metal halide arc tube is used as a light source. In the structure of this type of discharge lamp, as shown in FIG. 5, an arc tube 4 is supported by a pair of metal lead supports 2 and 3 projecting from an insulating base (base) 1.

The arc tube 4 has a pinch seal at both open ends of a quartz glass tube to form a sealed glass bulb 4a serving as a discharge portion at the center in the longitudinal direction. Pinch seal part 4
b, tungsten electrode rod 5a and molybdenum foil 5
An electrode assembly 5 in which b and a molybdenum lead wire 5c are integrated is sealed, and the tip of an electrode rod 5a protrudes into a closed glass bulb 4a to form a pair of opposed electrodes.

The lead wire 5c is led out from the pinch seal portion 4b and is welded to the lead supports 2 and 3. The lead supports 2 and 3 support the arc tube 4 and also serve as a current path to the lead wire 5c. The sealed glass bulb 4 of the arc tube 4 which is the discharge part
Mercury and metal iodide, which are luminescent substances, are enclosed in a together with an inert gas (Xe). However, in the conventional discharge lamp having such a structure, the luminous flux maintenance factor is not always satisfactory as a headlamp for an automobile.

Accordingly, the present inventors conducted various experiments,
As a result of the analysis, the cause of the decrease in the luminous flux maintenance rate was
It is known that the emission of metal iodide, especially scandium iodide (ScI ₃ ), enclosed in the closed glass bulb 4a is caused by a decrease in light emission. I also learned. That is, the decrease in the emission of scandium iodide described above is caused by the occurrence of a chemical reaction between scandium iodide and quartz glass (SiO ₂ ), and the disappearance of scandium iodide. The disappearance of scandium iodide causes the scandium iodide and quartz glass to undergo a reaction represented by the following chemical formula. As a result, scandium iodide changes to an oxide, which causes a decrease in Sc vapor pressure, and a luminous flux. Decrease.

4ScI ₃ + 3SiO ₂ → 2Sc ₂ O ₃ + 3SiI ₄ (1) On the other hand, when the reaction shown in this equation occurs, not only scandium iodide is lost but also erosion (devitrification) of the quartz glass ) Will also occur. Further, SiI ₄ generated by this reaction shows the following reaction with tungsten of the electrode rod 5a, and free iodine (4
I ⁻ ) is generated and the melting point of the electrode is lowered,
The electrodes are deformed and lighting becomes unstable, or in the worst case lighting becomes impossible.

SiI ₄ + nW → SiW _n + 4I ⁻ (2) Further, the reaction between scandium iodide and quartz glass is, in the presence of water (H ₂ O), 2ScI ₃ + 2SiO ₂ + 3H ₂ O + 3Hg → Sc ₂ Si ₂ O ₇ + 3HgI ₂ + 3H ₂ (discharged as a gas to the outside) (3), and scandium iodide is changed into a silicon oxide, which causes problems such as a decrease in Sc vapor pressure in the same manner as described above. .

The reaction between scandium iodide and quartz glass is as follows: 4ScI ₃ + 4SiO ₂ + 3O ₂ + 6Hg → 2Sc ₂ Si ₂ O ₇ + 6HgI ₂ (4) in the presence of oxygen (O ₂ ). As described above, scandium oxide is converted into silicon oxide, which causes problems such as a decrease in Sc vapor pressure and erosion of quartz glass.

Further, an electrode rod 5a made of tungsten is used.
In order to improve the discharge performance, a material doped with ThO ₂ (Thria) as an auxiliary substance for increasing the electron emission is used for the discharge lamp. The electrode rod 5a having such a structure is employed. In this case, free iodine (4I ⁻ ) represented by the formula (2) reacts with this ThO ₂ as shown in the following formula, ThO ₂ disappears from the electrode rod 5a, and the temperature of the electrode rises. Then, there was a problem that blackening progressed. ThO ₂ + 4I ⁻ → ThI ₄ +20 ^2- (5) By the way, it seems that the above problem can be solved by, for example, increasing the amount of scandium iodide enclosed. Even if the amount of scandium iodide is increased, the amount of the above-mentioned reaction with quartz glass only increases, and scandium once converted to oxide or silicon oxide is chemically stable. Does not contribute to the improvement of the luminous flux maintenance rate.

Therefore, the inventor focused on a metal Sc having a high reactivity with halogen and a high chemical affinity with H ₂ O and O _2, and sealed a predetermined amount of the metal Sc in a closed glass bulb of an arc tube. By doing so, the replenishing action of scandium iodide, the effect of preventing the disappearance thereof, and the effect of preventing the disappearance of ThO ₂ are obtained, and the generation of Sc oxides and sulfates, the decrease in Sc spectrum intensity, and the disappearance of ThO _{2 at} the electrode are prevented. A proposal has been made (Japanese Unexamined Patent Publication No. Hei 6-162994) that the problems such as a reduction in luminous flux, a change in chromaticity, and unstable lighting can be eliminated.

[0011]

However, Japanese Patent Application Laid-Open No.
In the arc tube according to 162994, metal Sc
Compared to an arc tube without sealing, problems such as a decrease in luminous flux maintenance rate, a change in chromaticity, and instability of lighting are resolved, but after 1000 hours of blinking lighting (SAE standard) six times per hour. A devitrification phenomenon occurs in which the inner wall of the quartz glass tube of the arc tube becomes cloudy white, and this leads to a decrease in the luminous flux, so that there is still room for improvement.

Therefore, erosion of the inner wall of the quartz glass tube due to the reaction represented by the above formulas (1), (3) and (4) is the main cause of devitrification. Is
The inventors paid attention to bromine (Br), which has a stronger binding energy with Sc than iodine (I), because the reaction amount of quartz glass with ScI ₃ should be small. That is, a part of ScI _3, be replaced with a larger (dissociation hard) ScBr ₃ binding energy than ScI _3, the amount of reaction between ScI ₃ and the quartz glass (SiO ₂₎ Few would, namely,
As a result of repeating the experiment from the viewpoint that the progress of the reactions (1), (3) and (4) will be eased, the amount of ScI ₃ encapsulated is reduced, and when ScBr ₃ is encapsulated accordingly, metal Sc is reduced. It has been confirmed that devitrification is suppressed in both cases of encapsulation and non-encapsulation, and the present invention has been proposed.

The present invention has been made under the above-mentioned problems of the prior art and the above-mentioned considerations of the inventor, and an object of the present invention is to suppress the devitrification of a sealed quartz glass sphere on the tube wall. An object of the present invention is to provide an arc tube for a discharge lamp having an improved luminous flux maintenance factor.

[0014]

According to a first aspect of the present invention, there is provided an arc tube for a discharge lamp, comprising electrodes disposed opposite to each other in a sealed glass bulb. in a Xe gas, and mercury, in the arc tube for a discharge lamp which is NaI and ScI ₃ is a metal iodide sealed and so as to encapsulate ScBr ₃ of a predetermined amount with respect to the ScI _3. Claim 2
The arc tube for a discharge lamp according to the present invention has electrodes opposed to each other in a hermetically sealed glass bulb, and contains Xe gas, mercury, and a metal iodide, NaI, in the glass.
And ScI ₃ and the arc tube for encapsulated discharge lamp is a metal S of a predetermined amount with respect to the metal iodides
A predetermined amount of ScBr ₃ was sealed with respect to c and ScI ₃ . It is desirable that the amount of ScBr ₃ enclosed in claims 1 and 2 is set in the range of 20 to 80% by weight of the total weight of ScI ₃ and ScBr ₃ . Here, in the amount of encapsulation 20 wt% or less ScBr _3, without encapsulation effect of ScBr ₃ (reaction suppressing effect of ScI ₃ and glass) is sufficiently exhibited, and if equal to or more than 80 wt%, strong Excessive Br exhibiting chemical activity is present, causing problems such as erosion and scattering of the electrodes. Therefore, the amount of ScBr ₃ encapsulated is ScI ₃ and S
cBr is preferably in the range of 20 to 80% by weight of the total weight of _3. Further, it is desirable that the amount of the metal Sc in claim 2 is set in a range of 1 to 5% by weight based on the weight of the ScI _{3 to be} sealed. That is, when the amount of the metal Sc is 1% by weight or less based on the weight of the metal iodide,
This is because the effect of enclosing the metal Sc is not sufficiently exhibited, and when the content is 5% by weight or more, problems such as deformation of the electrode are increased. Next, the operation of the present invention will be described. According to the arc tube for a discharge lamp of claim 1 and claim 2, a predetermined amount of ScBr ₃ is sealed with respect to ScI ₃ , and ScBr ₃ has a larger binding energy than ScI ₃ . S near the cold pipe wall
cBr ₃ is difficult to dissociate, and (1), (3),
The progress of the reaction (4) is moderated. That is, a part of ScI ₃ is, because it is replaced with a hard ScBr ₃ reacts with quartz glass, the reaction between the quartz glass is relaxed, the tube wall of devitrification is prevented. According to the discharge lamp arc tube of claim 2, the metal iodide, and a predetermined amount of metal Sc is sealed, the metal Sc are rich in reactivity, strong reactivity with halogen, In addition, H ₂ O, O ₂
Has a strong chemical affinity with, as described in detail below,
Replenishment and prevention of scandium iodide
The effect of preventing hO ₂ from disappearing is obtained. The replenishment of scandium iodide is such that when free iodine is generated according to the above formulas (1) and (2), the free iodine and metal Sc react as shown in the following formula. Scandium halide is generated, and a decrease in Sc emission can be suppressed. Metal Sc + 3I ⁻ + 3e ⁻ → ScI ₃ (6) However, when scandium iodide is replenished in this way, the reactions of equations (1) and (2) continue to move rightward,
Therefore, the deformation (nW → SiWn) of the glass erosion (SiO ₂ → SiI ₄ ) electrode becomes larger than usual. For this reason, if the metal Sc is excessively encapsulated, such a problem becomes remarkable. Therefore, it is desirable that the upper limit of the amount of encapsulated metal is suppressed to 5% by weight or less based on the weight of the metal iodide. Also,
When a predetermined amount of metal Sc is sealed, the above equation (3),
In (4), before these reactions occur, H ₂ O,
O ₂ is adsorbed on the metal Sc, and the amounts of H ₂ O and O ₂ decrease. For this reason, the rightward reactions in Formulas (3) and (4) are suppressed, the disappearance of scandium iodide can be minimized, and the decrease in Sc spectrum intensity can be suppressed. Further, the free iodine itself represented by the formula (5) is reduced by the recycling of the free iodine which leads to the above formulas (1), (2) and (6), so that the tungsten electrode is doped with ThO _2. However, it is possible to suppress the disappearance. That is, Sc is filled with metal Sc.
It is possible to suppress the loss of I _3, whereby it is possible to suppress a decrease in luminous flux maintenance factor, which promotes the reaction between ScI ₃ and the quartz glass, devitrification facilitate contribute to the luminous flux maintenance factor decreases Will be done. Therefore, by replacing a part of ScI ₃ to ScBr _3, it is possible to suppress the reaction, i.e., the devitrification of ScI ₃ and the quartz glass.

[0015]

Next, embodiments of the present invention will be described in detail with reference to experimental examples.

[0016]

EXPERIMENTAL EXAMPLE 1 The external structure of an arc tube for a discharge lamp is the same as the conventional structure shown in FIG. 5, but is characterized by a substance sealed in a sealed glass bulb 4a made of quartz glass. That is, in the first experimental example, Xe gas, mercury, and a predetermined amount of N
aI, a predetermined amount of ScI ₃ , a predetermined amount of metal Sc with respect to the amount of metal iodide, and a predetermined amount of Sc _{3 with} respect to ScI ₃ .
cBr ₃ is enclosed.

The inner volume of the closed glass bulb 4a is about 30 μl,
The distance between the electrode rods 5a is 3.8 to 4.2 mm, which is enclosed.
NaI and ScI_ThreeAnd ScBr_ThreeIs NaI: Sc
I_Three: ScBr_Three= 75: 10: 15% by weight
A) and NaI: ScI _Three: ScBr_Three= 75: 2
Two types of 0: 5% by weight (Invention Example B) were prepared.
In addition, the amount of the metal Sc to be filled is the same as that of the invention examples A and B.
0.004mg (ScI_ThreeAnd ScBr_ThreeTotal weight
2% by weight of the amount). Also, the pressure of the sealed gas (Xe)
Is 6 atm, the density of mercury is 2.7 × 10^-2(Mg / μ
l).

Then, a test is performed in a blinking mode in which lighting power is set to 35 W and on and off are repeated at predetermined time intervals, and the test results are shown in FIGS. In addition,
As test samples, in addition to Invention Examples A and B, the amount of metal iodide encapsulated was NaI: ScI ₃ = 75: 25% by weight.
Comparative Example 1 in which ScBr ₃ was not encapsulated at all and metal Sc was encapsulated in 0.004 mg (2% by weight of ScI ₃ ).

[0019]

EXPERIMENTAL EXAMPLE 2 The external structure of the arc tube (dimensions such as the volume of the sealed glass sphere and the distance between the electrodes) in the second experimental example is the same as the structure of the arc tube in the first experimental example. However, there are some differences in the substance sealed in the quartz glass sealed glass sphere.

That is, as in the first embodiment, Xe gas, mercury, NaI and ScI
₃ and ScBr ₃ are encapsulated, but no metal Sc is encapsulated at all. In addition, the enclosed NaI and S
The ratio of cI ₃ to ScBr ₃ is NaI: ScI ₃ : Sc
Br ₃ = 75: 10: 15% by weight (Invention Example C)
And NaI: ScI ₃ : ScBr ₃ = 75: 20: 5% by weight (Invention Example D). Then, a test was performed under the same conditions as in the case of the first experimental example described above,
The test results are shown in FIGS. As test samples, in addition to Invention Examples C and D, the amount of metal iodide enclosed was NaI: ScI ₃ = 75: 25% by weight.
A sample in which ScBr ₃ and metal Sc were not encapsulated at all was shown as Comparative Example 2.

FIG. 1 shows the test samples (Inventive Examples AD)
And the temporal change of the luminous flux maintenance rate of Comparative Examples 1 and 2). In this figure, the luminous flux at the start of the test is shown as 100%. As is evident from the results shown in FIG. 1, the luminous flux retention ratios of Invention Examples A and B decrease with time as in Comparative Example 1 in which ScBr ₃ is not encapsulated.
The target value that is a sufficient standard (8 hours after 1000 hours)
5% or more).

In the invention example A, 130 minutes from the start of lighting.
The decrease in the luminous flux maintenance rate until about 0 hours is smaller than in Invention Example B and Comparative Example 1. In the invention example B, the decrease in the luminous flux maintenance ratio in the initial stage (0 to 200 hours) is substantially equal to that in the comparative example 1, but the decrease in the luminous flux maintenance ratio in about 300 to 1200 hours is smaller than that in the comparative example 1.

The specific values of the luminous flux maintenance rate after 1000 hours have passed are 100% at the start of the test, 90.4% for Invention Example A, 89.0% for Invention Example B, and 99.0% for Comparative Example 1. 8
It is 6.8%, and it can be seen that, in the invention examples A and B, the luminous flux maintenance ratio is slightly reduced as compared with the comparative example 1, though slightly. Inventive examples C and D in which metal Sc is not enclosed
The luminous flux maintenance factor of Invention Example A,
B is slightly inferior in about 200 to 1200 hours after the start of the test, but the decrease in luminous flux maintenance factor is clearly smaller than that in Comparative Example 2 in which ScBr ₃ and metal Sc are not encapsulated, and ScBr ₃ is encapsulated. Although not shown, the luminous flux maintenance factor of the comparative example 1 in which the metal Sc is encapsulated exhibits substantially the same characteristics as that of Comparative Example 1, and the luminous flux maintenance factor does not become 80% or less until about 2000 hours, and is a practical target which is a sufficient standard. The value has been cleared.

FIG. 2 shows the test samples (Inventive Examples A to D).
5 shows changes over time in the color temperature of Comparative Examples 1 and 2. In FIG. 2, the color temperature of Inventive Example A is 4400.
K, the color temperature of Invention Example B changes around 4100K.
B is almost the same as Comparative Example 1, and the initial performance level can be maintained for a long time.

In about 1000 hours after the start of lighting, the color temperature of Comparative Example 2 sharply decreases from 4200 K to about 3400 K, whereas in Invention Example C, the color temperature gradually decreases from 4400 K to 4300 K within 2000 hours after the start of lighting. In the invention example D, it tends to sharply decrease by about 5 to 10% in about 200 hours after the start of lighting. However, after 200 to 400 hours, the same level is maintained, and it is more appropriate than before. There is no practical problem at a value close to 4400K.

FIG. 3 shows the change over time in the average color rendering index Ra of the test samples (Inventive Examples A to D and Comparative Examples 1 and 2). In this figure, in Examples A and B, as in Comparative Example 1, there is almost no change in Ra over time. In addition, Comparative Example 2 rapidly decreased in 200 hours immediately after the start of lighting, and continued to decrease thereafter, and was maintained substantially constant after 800 hours, whereas Invention Example C slightly increased until 2000 hours. Inventive Example D
, Has changed even after lapse of 2000 hours with the initial characteristics.

That is, Comparative Example 2 in which ScBr ₃ and metal Sc were not encapsulated exhibited a large change in light color and could not be put to practical use. On the other hand, Invention Examples A and B in which ScBr ₃ and metal Sc were encapsulated, In each of Invention Examples C and D in which Sc was not encapsulated but ScBr ₃ was encapsulated, the change in light color was small and there was no practical problem. FIG. 4 shows the change over time of the tube voltage of the test samples (Inventive Examples A to D and Comparative Examples 1 and 2).

[0028] In this figure, the tube voltage of the Invention Example A~D is a 86V or less at the time of 2,000 hours after either case, since the large increase is not observed, the ScBr ₃ 1
Even if 5% by weight or 5% by weight is enclosed, there is no practical problem. In addition, the inventors have determined that after 1000 hours and 20
Inventive Examples A, B, C, D and Comparative Example 1,
Photographs were taken of the appearance of each of the two.

As a result, the blackening of Comparative Example 2 was most intense,
Although the inside of the closed glass sphere is hardly visible, Invention Example A,
The degree of blackening of B, C, and D was substantially the same as that of Comparative Example 1, and the details inside the closed glass sphere were visible. In addition, the devitrification phenomenon is smaller in the inventive examples A, B, C, and D after the lapse of 1000 hours than in the comparative example 1, and this is considered to be a factor that the luminous flux maintenance ratio becomes better after the lapse of 1000 hours.

The deformation of the electrodes is described in Invention Examples A, B, C,
D, and none of Comparative Examples 1 and 2.

[0031]

As is clear from the above description, according to the first or second aspect , the devitrification phenomenon is suppressed by enclosing a predetermined amount of ScBr ₃ , and the luminous flux maintenance rate does not decrease for a long time. Thus, an actuating tube suitable for an automobile headlamp free from problems such as a change in chromaticity and unstable lighting can be obtained.
In particular, when the metal Sc is not sealed, the manufacturing process of the arc tube is simplified accordingly. Further, according to the second aspect , by recycling scandium iodide by enclosing a predetermined amount of metal Sc and suppressing devitrification by enclosing a predetermined amount of ScBr ₃ , the luminous flux maintenance factor does not decrease for a long time. Thus, an arc tube that is optimal for a headlamp for an automobile without problems such as a change in chromaticity and unstable lighting can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temporal change of a luminous flux maintenance factor of an arc tube according to the present invention.

FIG. 2 is a diagram showing a change over time of a color temperature of an arc tube according to the present invention.

FIG. 3 is a diagram showing a change over time of an average color rendering index of the arc tube according to the present invention.

FIG. 4 is a diagram showing a change over time of a tube voltage of the arc tube according to the present invention.

FIG. 5 is an overall structural view of the present invention and a conventional discharge lamp.

[Explanation of symbols]

 4 Arc tube 4a Closed glass bulb 5a Electrode rod

Continuation of front page (56) References JP-A-4-289654 (JP, A) JP-A-6-162994 (JP, A) JP-A-50-152578 (JP, A) JP-A-1-227347 (JP) , A) JP-A-61-163553 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 61/16

Claims (2)

(57) [Claims] An electrode is provided oppositely in a sealed glass sphere, and an Xe gas, mercury,
When NaI and ScI ₃ is a metal iodide Ru encapsulated
Both a predetermined amount discharge electric lamp arc tube enclosing a ScBr ₃ relative to the ScI _3, wherein Sc
Amount of the enclosed br ₃ shall be the being in the range of 20 to 80% by weight relative to the total weight of ScI ₃ and ScBr ₃
Arc tube for discharge electric lamps. 2. A has opposed the installed electrodes sealed inside glass bulb, and Xe gas into the glass bulb, and mercury, are NaI and ScI ₃ is a metal iodide is enclosed Rutoto
In addition, a predetermined amount of metal Sc with respect to the metal iodide,
A predetermined amount discharge electric lamp arc tube enclosing a ScBr ₃ relative to cI _3, the amount of the enclosed metal Sc is in the range of 1 to 5% by weight relative to the total weight of the metal iodide And the amount of ScBr ₃ enclosed is between ScI ₃ and S
discharge electric lamp arc tube you characterized in that the total weight of the CBR ₃ is in the range of 20 to 80 wt%.