JPH09223481A - Arc tube for discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an arc tube for a discharge lamp whose lumen maintenance factor is heightened by suppressing devitrification of a bulb wall of a closed quartz glass bulb. SOLUTION: In the inside of a closed glass bulb 4a (of about 30μl volume capacity), Xe gas (at 6 atmospheric pressure), mercury (in 2.7×10<-2> mg/μl), prescribed amounts of metal iodides (NaI, ScI3 ), and a prescribed amount of ScBr3 are sealed. The ratio (wt.%) of NaI and ScI3 and ScBr3 is set to be NaI:ScI3 : ScBr3 =75:(25-X):X wherein X is defined as 5<=X<=20. If necessary, 0.002mg (1wt.% of the total weight of ScI3 and ScBr3 ) to 0.010mg (5wt.% of the total weight of ScI3 and ScBr3 ) of metal Sc may be sealed in the glass bulb 4a.

Description

Detailed Description of the Invention

[0001]

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

[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 has been studied, and in this type of discharge lamp, a metal halide arc tube is used as the light source. In the structure of this type of discharge lamp, as shown in FIG. 5, the arc tube 4 is supported by a pair of metal lead supports 2 and 3 protruding from an insulating base (base) 1.

In the arc tube 4, both open ends of a quartz glass tube are pinch-sealed, and a hermetically sealed glass bulb 4a serving as a discharge part is formed at the center in the longitudinal direction. Pinch seal part 4
In b, a tungsten electrode rod 5a and a molybdenum foil 5 are provided.
The electrode assembly 5 in which b and the lead wire 5c made of molybdenum are integrated is sealed, and the tip of the electrode rod 5a projects into the sealed glass ball 4a to form a pair of electrodes facing each other.

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, the conventional discharge lamp having such a structure is not always satisfactory in the luminous flux maintenance factor as a headlamp for an automobile.

Therefore, the present inventors have conducted various experiments,
As a result of proceeding with the analysis, the cause of the decrease in the luminous flux maintenance factor is
It is known that the metal iodide enclosed in the closed glass sphere 4a, in particular, is caused by a decrease in light emission of scandium iodide (ScI ₃ ). I also learned. That is, the above-described decrease in the scandium iodide emission is caused by the disappearance of scandium iodide due to a chemical reaction between scandium iodide and quartz glass (SiO ₂ ). The disappearance of scandium iodide causes the reaction of scandium iodide and quartz glass represented by the following chemical formula, and as a result, scandium iodide is converted into an oxide, which causes a decrease in Sc vapor pressure and causes a decrease in luminous flux. Is reduced.

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

SiI ₄ + nW → SiW _n + 4I ⁻ (2) Furthermore, the reaction between scandium iodide and quartz glass is 2ScI ₃ + 2SiO ₂ + 3H ₂ O + 3Hg → Sc _{2 in} the presence of water (H ₂ O). Si ₂ O ₇ + 3HgI ₂ + 3H ₂ (is released to the outside as a gas) (3), and scandium iodide changes to silicon oxide, causing a problem such as a decrease in Sc vapor pressure as described above. .

Further, the reaction between scandium iodide and quartz glass becomes 4ScI ₃ + 4SiO ₂ + 3O ₂ + 6Hg → 2Sc ₂ Si ₂ O ₇ + 6HgI ₂ (4) in the presence of oxygen (O ₂ ). As in the above case, scandium chloride is changed to silicon oxide, causing problems such as a decrease in Sc vapor pressure and erosion of quartz glass.

Furthermore, the electrode rod 5a made of tungsten is used.
In order to improve the discharge performance, a material doped with ThO ₂ (thia) as an auxiliary substance for improving the electron emission property is used in the above discharge lamp, and the electrode rod 5a having such a structure is adopted. In this case, the free iodine (4I ⁻ ) shown in the formula (2) reacts with this ThO ₂ as shown in the formula below, ThO ₂ disappears from the electrode rod 5a, and the temperature of the electrode rises. Then, there was a problem that blackening proceeded. ThO ₂ + 4I ⁻ → ThI ₄ +20 ^{2 −} (5) By the way, it seems that the above problems can be solved by increasing the amount of scandium iodide enclosed, for example. Even if the amount of scandium iodide enclosed is increased, the amount of the above-mentioned reaction with quartz glass is only increased, and scandium once converted to oxide or silica is chemically stable. Therefore, it does not contribute to the improvement of the luminous flux maintenance factor.

Therefore, the inventor paid attention to a metal Sc having a strong reactivity with halogen and a strong chemical affinity with H ₂ O and O _2, and enclosing the metal Sc in a predetermined amount in a closed glass bulb of an arc tube. By doing so, a replenishing action of scandium iodide, a vanishing preventive action and a vanishing preventive action of ThO ₂ are obtained, and the generation of Sc oxides and sulfates, the decrease of the Sc spectrum intensity and the disappearance of ThO _{2 at} the electrode are suppressed. Proposals were made (Japanese Patent Laid-Open No. Hei 6-162994) that the problems such as reduction of luminous flux, change of chromaticity and instability of lighting can be solved by suppressing each.

[0011]

However, the above-mentioned Japanese Unexamined Patent Application Publication No.
In the arc tube according to No. 162992, the metal Sc
Compared with an arc tube that does not include a lamp, problems such as a decrease in luminous flux maintenance rate, a change in chromaticity, and instability of lighting are solved, but after 1000 hours have elapsed due to 6 blinks per hour (SAE standard) There is still room for improvement because a devitrification phenomenon occurs in which the inner wall of the quartz glass tube of the arc tube becomes cloudy, which leads to a decrease in luminous flux.

Therefore, the main cause of devitrification is that the inner wall of the quartz glass tube is eroded by the reactions represented by the above equations (1), (3) and (4). Is
The inventor has paid attention to bromine (Br), which has a stronger binding energy with Sc than iodine (I), because the reaction amount between quartz glass and ScI ₃ is 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 of (1), (3), and (4) will be alleviated, the amount of ScI ₃ enclosed is reduced, and ScBr ₃ is enclosed by that amount. It was confirmed that devitrification was suppressed in both cases of encapsulation and non-encapsulation, so that 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 consideration of the inventor, and an object thereof is to suppress devitrification on the tube wall of the closed quartz glass sphere. An object is to provide an arc tube for a discharge lamp having an improved luminous flux maintenance factor.

[0014]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
In the arc tube for a discharge lamp according to claim 1,
Have electrodes placed opposite to each other in a sealed glass bulb.
Then, in the glass sphere, Xe gas, mercury, and metal iodide
NaI and ScI_ThreeDischarge lamp
Arc tube for use in the ScI_ThreePrescribed against
Amount of ScBr_ThreeWas to be enclosed. Further, claim 3
The arc tube for discharge lamps related to
The glass plate has electrodes placed opposite to each other,
Xe gas, mercury, and metal iodide NaI
And ScI_ThreeArc lamp for discharge lamp in which
In the furnace, a predetermined amount of metal S is added to the metal iodide.
c and the ScI_ThreeA certain amount of ScBr_ThreeEnclose
It was to so. In addition, in claim 1 and claim 3
ScBr_ThreeThe enclosed amount is_ThreeAnd ScBr_ThreeTotal
Desirable to set within the range of 20 to 80% by weight
New Where ScBr_ThreeIs less than 20% by weight
Is ScBr_ThreeEncapsulation effect (ScI_ThreeReaction with glass
80%) and the effect of suppressing
%, The Br presenting strong chemical activity is excessive.
Will cause damage to the electrodes, such as erosion and scattering.
ScBr_ThreeEncapsulation amount of ScI _ThreeAnd S
cBr_ThreeBe in the range of 20-80% by weight of the total weight of
Is desirable. In addition, inclusion of the metal Sc in claim 3
The amount is ScI to be enclosed._Three1 to 5% by weight with respect to the weight of
It is desirable to set within the range. That is, the seal of metal Sc
When the amount added is 1% by weight or less based on the weight of the metal iodide,
Encapsulation effect of metal Sc is not fully exerted, and 5 weight
%, The defects such as electrode deformation will increase.
That's why. Next, the operation of the present invention will be described. Contract
In the arc tube for a discharge lamp according to claim 1 and claim 3.
According to ScI_ThreeA certain amount of ScBr_ThreeIs enclosed
Is, ScBr_ThreeIs ScI_ThreeThan binding energy
Is large, S near the tube wall where the temperature of the closed glass bulb is low
cBr_ThreeIs difficult to dissociate, and the above (1), (3),
The progress of the reaction of (4) is moderated. That is, ScI_ThreeOne
ScBr is difficult to react with quartz glass_ThreeReplaced by
Therefore, the reaction with quartz glass is relaxed, and the tube
Devitrification of the wall is suppressed. The discharge lamp adapter according to claim 3
According to the arc tube, a predetermined amount of metal iodide is
The metal Sc is enclosed, and this metal Sc is reactive.
Rich, highly reactive with halogen, and H_TwoO, O_Two
Since it has a strong chemical affinity with, as detailed below,
Scandium iodide replenishment action and its elimination prevention action, T
hO_TwoCan be obtained. Scandium iodide
The replenishment action is based on the above formulas (1) and (2).
When the free iodine and the metal Sc are generated,
A reaction as shown by the formula occurs, and this reaction causes an iodide scan.
It is possible to suppress the decrease in Sc emission due to the generation of nitrogen.
Wear. Metal Sc + 3I^-+ 3e^-→ ScI_Three (6) However, scandium iodide was replenished in this way.
Then, the reactions of equations (1) and (2) continue to proceed to the right,
Therefore, glass erosion (Si0_Two→ SiI_Four) Change of electrode
Shape (nW → SiW_n) Is larger than usual. this
Therefore, if the metal Sc is excessively enclosed, such a problem will occur.
Since the amount of metal iodide is
On the other hand, it is desirable to limit the content to 5% by weight or less. Also,
If a predetermined amount of metal Sc is enclosed, the above formula (3),
In (4), before these reactions occur, H_TwoO,
O_TwoIs adsorbed on the metal Sc and H_TwoO, O_TwoThe amount of
You. Therefore, the reaction in the right direction in equations (3) and (4)
Is suppressed and the loss of scandium iodide is minimized.
It is possible to suppress the decrease of Sc spectrum intensity.
it can. Furthermore, in the above equations (1), (2), and (6)
By recycling free iodine to reach, shown in equation (5)
Since the free iodine itself decreases,
ThO for electrode_TwoSuppresses its disappearance even if doped with
It becomes possible. That is, the inclusion of metal Sc causes Sc
I_ThreeCan be suppressed, which helps maintain the luminous flux.
Although the decrease in the rate can be suppressed, ScI_ThreeAnd quartz glass
This is one of the reasons why the luminous flux maintenance factor is lowered by promoting the reaction with
The devitrification will be promoted. So ScI_ThreePart of
To ScBr_ThreeTo replace ScI_ThreeAnd quartz glass
The reaction with the soot, that is, devitrification can be suppressed.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail based on experimental examples.

[0016]

[Experimental Example 1] The external structure of the arc tube for a discharge lamp is the same as that of the conventional structure shown in FIG. 5, but is characterized by the substance enclosed in the closed glass bulb 4a made of quartz glass. That is, in the first experimental example, Xe gas, mercury, and a predetermined amount of N as a metal iodide are contained in the closed glass sphere 4a.
aI and 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 S with respect to ScI ₃ .
cBr ₃ is enclosed.

The internal 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_ThreeThe ratio of NaI: Sc
I_Three: ScBr_Three= 75: 10: 15% by weight
Clear example A) and NaI: ScI _Three: ScBr_Three= 75: 2
Two kinds of 0: 5% by weight (Invention Example B) were prepared.
In addition, the amount of the metal Sc enclosed in each of Invention Examples A and B
However, 0.004 mg (ScI_ThreeAnd ScBr_ThreeTotal weight of
2% by weight). Also, the pressure of the enclosed gas (Xe)
Is 6 atm and the encapsulation density of mercury is 2.7 × 10.^-2(Mg / μ
l).

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

[0019]

[Experimental Example 2] The external structure of the arc tube in this second experimental example (dimensions such as the volume of the closed glass bulb and the distance between electrodes) is the same as that of the arc tube in the first experimental example described above. However, the substances enclosed in the quartz glass closed glass sphere are partially different.

That is, as in the first embodiment, Xe gas, mercury, NaI and ScI are contained in the closed glass bulb.
₃ and ScBr ₃ are encapsulated, but metal Sc is not encapsulated at all. Also, the enclosed NaI and S
The ratio of cI ₃ to ScBr ₃ is NaI: ScI ₃ : Sc.
Br ₃ = 75: 10: 15 wt% (Invention Example C)
And NaI: ScI ₃ : ScBr ₃ = 75: 20: 5 wt% (Invention Example D). Then, a test is conducted 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.
In Comparative Example 2, ScBr ₃ and metal Sc were not encapsulated at all.

FIG. 1 shows the above test samples (Invention Examples A to D).
2 shows the changes over time in the luminous flux maintenance factor of Comparative Examples 1 and 2, and in this figure, the luminous flux at the start of the test is shown as 100%. As is clear from the results shown in FIG. 1, in Invention Examples A and B, the luminous flux maintenance factor decreases with the passage of time, almost in the same manner as Comparative Example 1 in which ScBr ₃ is not encapsulated.
Sufficient target value (8 after 1000 hours
5% or more).

In the invention sample A, 130 seconds from the start of lighting.
The decrease in the luminous flux maintenance factor up to about 0 hours is smaller than that of the invention sample B and the comparative example 1. Further, in Invention Example B, the decrease in the luminous flux maintenance factor in the initial period (0 to 200 hours) is substantially equal to that in Comparative Example 1, but the decrease in the luminous flux maintenance factor in about 300 to 1200 hours is smaller than that in Comparative Example 1.

The specific values of the luminous flux maintenance factor after 1000 hours are 90.4% for Inventive Example A, 89.0% for Inventive Example B, and Comparative Example 1 when the test start time is 100%. 8
It is 6.8%, and it can be seen that the invention examples A and B show a slight decrease in the luminous flux maintenance factor as compared with the comparative example 1, although it is slight. Inventive Examples C and D in which metal Sc is not enclosed
The luminous flux maintenance rate of the invention example A, in which the metal Sc is enclosed,
Compared to B, it is slightly inferior in about 200 to 1200 hours after the start of the test, but the decrease in luminous flux maintenance rate is obviously 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, it exhibits substantially the same characteristics as the luminous flux maintenance factor of Comparative Example 1 in which metal Sc is enclosed, and the luminous flux maintenance factor does not fall below 80% by about 2000 hours, which is a sufficient practical target. The value has been cleared.

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

Approximately 1000 hours after the start of lighting, the color temperature of Comparative Example 2 drops sharply from 4200K to 3400K, whereas in Inventive Example C, the color temperature slowly changes from 4400K to 4300K within 2000 hours after the start of lighting. In Inventive Example D, there is a tendency for it to decrease sharply by about 5 to 10% about 200 hours after the start of lighting, but after 200 to 400 hours have passed, it remains approximately the same level, and it is considered more appropriate than before. The value is close to 4400K which is present, and there is no practical problem.

FIG. 3 shows changes with time in the average color rendering index Ra of the test samples (Invention Examples A to D and Comparative Examples 1 and 2). In this figure, in each of Invention Examples A and B, as in Comparative Example 1, almost no change in Ra occurs over time. Further, Comparative Example 2 sharply decreases after 200 hours immediately after the start of lighting, continues to decrease thereafter, and maintains substantially constant after 800 hours have passed, whereas Invention Example C slightly increases until 2000 hours have passed. Inventive Example D
Shows that the initial characteristics remain unchanged even after 2000 hours.

That is, in Comparative Example 2 in which ScBr ₃ and metal Sc are not encapsulated, the change in light color is large and it cannot be put to practical use, whereas invention examples A and B in which ScBr ₃ and metal Sc are encapsulated and metal In each of Inventive Examples C and D in which Sc is not enclosed but ScBr ₃ is enclosed, the change in light color is small and there is no practical problem. FIG. 4 shows the changes over time in the tube voltage of the test samples (Invention Examples A to D and Comparative Examples 1 and 2).

In this figure, the tube voltages of Invention Examples A to D are 86 V or less even after 2000 hours in any case, and a large increase is not observed. Therefore, ScBr _{3 is set} to 1
There is no practical problem even if 5% by weight or 5% by weight is enclosed. In addition, the inventors have found that after 1000 hours and 20
Inventive Examples A, B, C and D and Comparative Example 1, after 00 hours
Photographs of the appearances of 2 were taken.

As a result, the blackening of Comparative Example 2 was the strongest,
Although the inside of the closed glass bulb is hardly visible, invention example A,
The degree of blackening of B, C, and D was almost the same as in Comparative Example 1, and the internal details of the closed glass sphere were visually observable. Further, the devitrification phenomenon was smaller in Comparative Examples 1 and 2 in Invention Examples A, B, C, and D after 1000 hours, which is considered to be one of the reasons why the luminous flux maintenance factor becomes good after 1000 hours.

Further, the deformation of the electrodes is carried out by the invention examples A, B, C,
Neither in D nor in Comparative Examples 1 and 2.

[0031]

As is apparent from the above description, according to the first or third aspect, the devitrification phenomenon is suppressed by enclosing a predetermined amount of ScBr ₃ , and the luminous flux maintenance factor does not decrease for a long period of time. Thus, it is possible to obtain an actuated tube suitable for automobile headlamps that does not have problems such as chromaticity change and unstable lighting.
In particular, when the metal Sc is not enclosed, the manufacturing process of the arc tube is simplified accordingly. Further, according to the third or fourth aspect, the luminous flux maintenance factor is reduced for a long period of time by recycling scandium iodide by enclosing a predetermined amount of metal Sc and suppressing the devitrification phenomenon by enclosing a predetermined amount of ScBr _3. It is possible to obtain an arc tube that is most suitable for automobile headlamps that does not have problems such as chromaticity change and lighting instability.

[Brief description of drawings]

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

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

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

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

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

[Explanation of symbols]

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

Claims (4)

[Claims] 1. An Xe gas and mercury are provided in the glass sphere, the electrodes being oppositely installed in a sealed glass sphere.
In NaI and for discharge lamps arc tubes ScI ₃ is enclosed is a metal iodide discharge lamp arc tube, wherein the encapsulating ScBr ₃ of a predetermined amount with respect to the ScI _3. 2. The arc tube for a discharge lamp according to claim 1, wherein the enclosed amount of ScBr ₃ is in the range of 20 to 80% by weight based on the total weight of ScI ₃ and ScBr ₃ . 3. An arc for a discharge lamp, which has electrodes installed opposite to each other in a sealed glass bulb, and Xe gas, mercury, and metal iodides NaI and ScI ₃ are enclosed in the glass bulb. In the tube, a predetermined amount of metal Sc and ScI ₃ are added to the metal iodide.
An arc tube for a discharge lamp, characterized in that a predetermined amount of ScBr ₃ is filled therein. 4. The amount of the metal Sc enclosed is within the range of 1 to 5 wt% with respect to the total weight of the metal iodide, and the Sc
The arc tube for a discharge lamp according to claim ₃ , wherein the enclosed amount of Br ₃ is within a range of 20 to 80 wt% with respect to the total weight of the ScI ₃ and ScBr ₃ .