JPH09320524A - Light emitting tube for discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long-life light emitting tube for discharge lamp with enhanced linear transmissivity by providing a translucent tube formed of a polycrystalline alumina sintered body, which has specified alumina content and relative density, and having a translucent property whose linear transmissivity of visible light per specified thickness is specified. SOLUTION: The translucent tube 2 of a light emitting tube 1 for discharge lamp has a substantially cylindrical form having a curved protruding part 2a in the center, and it is formed of a polycrystalline alumina sintered body which has an alumina content of 99.98wt.% or more and a translucent property such that the linear transmissivity of visible light per thickness of 5mm is 30% or more. Thus, the reaction with a light emitting material sealed in the translucent tube is minimzed, and a long-life light emitting tube for discharge lamp having excellent coloring property can be provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a xenon lamp,
The present invention relates to an arc tube for a discharge lamp such as a sodium lamp, a halogen lamp, and a metal halide lamp.

[0002]

2. Description of the Related Art Conventionally, high-pressure sodium lamps have been used for lighting such as roads and tunnels, and xenon lamps and halogen lamps having high luminous efficiency have been used for lights such as automobiles. Discharge lamps such as metal halide lamps having excellent color rendering properties are used for illumination, and backlights for OHP and liquid crystal projectors.

For example, a metal halide lamp is one in which a discharge lamp arc tube 1 (hereinafter abbreviated as arc tube) constituting a light emitting portion is disposed inside a bottomed cylindrical body 11 as shown in FIG. As shown in the detailed structure of the arc tube 1 in FIG. 1, a metal halide and a noble gas as a light emitting material are placed inside a substantially cylindrical light-transmitting tube 2 having a curved protrusion 2a in the center. In addition to being sealed, both ends of the light-transmitting tube 2 were sealed with the closing bodies 3 each having the electrode mandrel 5 and the lead mandrel 6.

Further, the light-transmitting tube 2 constituting such an arc tube 1 has a high linear transmittance of light (visible light), has a bending strength of 35 kg / mm ² or more, and is a light-emitting material. Since it is required that the corrosion due to the reaction with the metal halide is small, it is formed of a translucent polycrystalline alumina sintered body containing 0.1% by weight of an auxiliary component such as MgO. There was (Japanese Patent Laid-Open No. 59-
184450, Japanese Patent Publication No. 60-22670).

[0005]

However, since MgO added as an auxiliary component is precipitated in the crystal grain boundaries of the alumina sintered body that constitutes the above-mentioned light-transmitting tube 2, these precipitates are formed. The birefringence of light was large, and the linear transmittance of light (visible light: 600 nm) per wall thickness of 0.5 mm was about 10%, which was not sufficient for the light-transmitting tube 2.

Further, since the auxiliary component added to the alumina sintered body has a low melting point, in a state where the inside of the light-transmitting tube 2 reaches about 1000 ° C. like a metal halide lamp, the auxiliary component and the auxiliary component are transparent. There is a problem that the metal halide sealed inside the light tube 2 reacts with the light tube 2 to corrode the light tube 2.

For example, Mg is used as an auxiliary component of the alumina sintered body.
When O was used and ScI ₃ —NaI was used as the metal halide, the translucent tube 2 was corroded because the reaction shown in Chemical formula 1 occurred.

[0008]

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For this reason, light is scattered on the inner wall surface of the light-transmitting tube 2, the linear transmittance is lowered, and the mechanical strength is lowered.

On the other hand, although the transparent tube 2 made of sapphire has a high linear transmittance, sapphire is a hard material and is difficult to process, so that the shape of the transparent tube 2 is restricted. However, there is a problem that the transparent tube 2 having a complicated shape such as No. 1 cannot be manufactured.

[0011]

In view of the above-mentioned problems, the present invention provides a light-transmitting tube which constitutes an arc tube for a discharge lamp with an alumina content of 99.98% by weight or more and a relative density of 9%.
It is characterized by being formed of a polycrystalline alumina sintered body having a transmissivity of 9.8% or more and a linear transmittance of visible light per 0.5 mm thickness of 30% or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION That is, according to the present invention, a light-transmitting tube which constitutes an arc tube for a discharge lamp is formed of a polycrystalline alumina sintered body which is substantially composed of alumina crystals without adding any auxiliary component. Specifically, it is formed of an alumina sintered body having an alumina content of 99.98% by weight or more, and further 99.99% by weight or more. Therefore, except for alumina, only impurities are contained in the sintered body, and even if these impurities are deposited in the grain boundaries, light absorption and diffusion by these are small, and the linear transmittance of light (visible light) is reduced. It can be increased to 30% or more.

In order to increase the linear transmittance of light (visible light) while maintaining the strength required for the light-transmitting tube 2 (flexural strength: 35 kg / mm ² ), the alumina sintered body is It is necessary to set the relative density to 99.8% or more.

That is, when the relative density is less than 99.8%, the number of defects (holes) between alumina crystals becomes too large, and the light incident on the defects (holes) is attenuated, so that the linear transmission of 30% or more is performed. This is because if the ratio is not obtained and the relative density becomes smaller, the strength required for the light-transmitting tube 2 cannot be maintained.

The relative density of the alumina sintered body is 99.
In order to achieve 8% or more, the average crystal grain size of alumina needs to be 20 μm or less, and preferably 15 μm or less.

Furthermore, the inventors of the present invention have found that the amount of impurities contained in the alumina sintered body is important when the light-transmitting tube is used for a metal halide lamp, and the content thereof is 200 ppm or less. , Preferably 100
It is below ppm.

That is, the transparent tube of the present invention is characterized by being formed of an alumina sintered body to which no auxiliary component is added, but impurities are contained in the alumina raw material or manufactured. May be mixed during the process. And impurities other than alumina, especially Mg, Ca, etc.
Group elements and oxides thereof are used as light emitting materials for metal halide lamps, such as DyI ₃ , LiI, and ScI.
_Since it easily reacts with metal halides such as ₃ and so on, if it is contained in the alumina sintered body in an amount of more than 200 ppm, the translucent tube is largely eroded due to the reaction with the metal halide which is a light emitting material, and the light transmission tube is short-term. This is because it will reach the end of its life.

Next, a method of manufacturing a light-transmitting tube which constitutes the arc tube for a discharge lamp according to the present invention will be described.

First, an alumina raw material having a purity of 99.99% or higher is prepared as a starting raw material. At this time, it is preferable that the alumina raw material used has an average particle diameter of 0.5 μm or less and a BET specific surface area of 10 m ² / g or more. This is because when the average particle size of the alumina raw material is larger than 0.5 μm or the BET specific surface area is less than 10 m ² / g, the activity of the alumina cannot be increased, and the grain growth is sufficiently suppressed. Because you cannot do it.

Next, the alumina raw material slurry is produced,
The slurry is filled in a mold made of resin or metal and pressure is applied to mold it into a predetermined shape. At this time, the green density of the molded body is preferably 2.6 g / cm ³ or more in order to reduce grain growth and porosity during firing. Further, the resin or metal is used for the mold material in order to suppress the mixing of impurities. That is, when gypsum used in cast molding or the like is used as the mold material, impurities are mixed in a large amount, so that the alumina purity of the alumina sintered body is lowered.

Then, the obtained molded body is calcined in the atmosphere at a temperature of about 1200 to 1300 ° C. to densify it to a relative density of 99.0% or more, and further to 1500 to 18
The main part of the transparent tube of the present invention can be obtained by subjecting the inner and outer surfaces to mirror-finishing after main firing in a hydrogen atmosphere at 00 ° C., a vacuum atmosphere, or a reducing atmosphere.

As described above, by using a high-purity alumina raw material, making a mold for molding a resin or a metal, and performing firing in two steps, it is possible to obtain a high-quality material without adding an auxiliary component. A polycrystalline alumina sintered body of high purity can be manufactured. In particular, the temperatures of calcination and main calcination are important for producing the alumina sintered body of the present invention. That is, when the calcination temperature is 1200 ° C. or the main calcination temperature is lower than 1500 ° C., it is difficult to sufficiently densify, and the relative density of the alumina sintered body cannot be 99.8% or more, In addition, when the calcination temperature is 1300 ° C or the main calcination temperature is higher than 1800 ° C, the crystal grows abnormally to cause sintering, and the linear transmittance of light (visible light) and the mechanical strength are all observed. Because it cannot raise.

As described above, in the arc tube for a discharge lamp according to the present invention, since the light-transmitting tube is formed of the high-purity alumina sintered body containing no auxiliary component, the linear transmittance of light is greatly increased. The linear transmittance of light (visible light: 600 nm) per thickness of 0.5 mm can be increased to 30% or more.

Further, since the total content of impurities mixed in the alumina sintered body, especially elements of Group 2a of the periodic table such as Mg and Ca and their oxides is 200 ppm or less, even if it is used for a metal halide lamp. , Little reaction with the metal halide enclosed inside the translucent tube,
The light-emitting tube for discharge lamps of the present invention formed by using this light-transmitting tube has a high luminous efficiency and has a characteristic that the light-transmitting tube has almost no decrease in linear transmittance even after being used for 3000 hours. A highly reliable arc tube with little deterioration can be obtained.

Furthermore, since the polycrystalline alumina sintered body can be formed by a general ceramic forming method, it is possible to easily form a transparent tube having a complicated shape such as a metal halide lamp.

[0026]

EXAMPLES An arc tube for a discharge lamp which constitutes a metal halide lamp will be described below as an example of the present invention.

FIG. 1 is a vertical sectional view showing an arc tube 1 for a discharge lamp according to the present invention. A transparent tube 2 has a curved projection 2 at its center.
It has a substantially cylindrical shape with a and has an alumina content of 9
It is formed of a polycrystalline alumina sintered body having a relative density of 9.99% by weight and a relative density of 99.9%.

Inside the transparent tube 2, ScI ₃ -NaI as a light emitting material and a rare gas are enclosed, and both ends of the transparent tube 2 are closed by an Al ₂ O ₃ -Mo cermet material. It is sealed with the body 3. As a method of fixing the closing body 3, the closing body 3 at the lower end is fixed to the translucent tube 2 by integral sintering, and the closing body 3 at the upper end is fixed by attaching glass 4.

An electrode mandrel 5 is provided at one end of each closing body 3.
And a lead rod 6 is embedded at the other end so as not to come into contact with the electrode mandrel 5 inside, and a voltage is applied to the lead rod 6 to generate a discharge between the electrode mandrels 5. ScI ₃ -NaI enclosed in the arc tube 2 is gasified to emit light.

Next, a method of manufacturing the discharge lamp arc tube 1 shown in FIG. 1 will be described.

First, in order to manufacture the light-transmitting tube 2, ion-exchanged water and a dispersant are put into a pot mill, high-purity alumina balls are added to these to disperse the dispersant uniformly, and then the average particle diameter is 0. 0.2 μm, BET specific surface area 15 m ² /
An alumina raw material having a purity of 99.99% is added and mixed and pulverized for about 5 hours. Then, the slurry from which the high-purity alumina balls had been removed was filled in a porous resin mold, pressure was applied, and then the mold was removed to form a cylindrical body 2 having a curved projection 2a in the center. This time,
The green density of the molded body was 2.61 g / m ³ . And
After drying the molded body at a temperature of 80 ° C., 1250
It was calcined at a temperature of ° C for about 2 hours to form a calcined body having a density of about 99.2%.

Next, after inserting the closing body 3 made of an Al ₂ O ₃ —Mo cermet material in which the electrode mandrel 5 and the lead rod 6 are embedded into one end of the calcined body, the calcined body is obtained. Put in a vacuum furnace, baking temperature 1650 ℃, vacuum degree 1 ×
The light-transmitting tube 2 in which the closing body 3 is integrally sintered at one end by performing main firing for about 6 hours in an atmosphere of 10 ⁻⁵ torr.
Was formed.

Next, the inside and outside of the light-transmitting tube 2 is made into a mirror surface by polishing, and the inside of the light-transmitting tube 2 is ScI ₃ -NaI which is a light emitting material.
Al ₂ O ₃ -Mo in which the electrode mandrel 5 and the lead rod 6 are embedded in the other end of the light-transmitting tube 2 after sealing the rare gas.
By sealing the closing body 3 made of a system cermet material via glass, the arc tube 1 for discharge and the like shown in FIG. 1 was obtained.

When the characteristics of the alumina sintered body forming the light-transmitting tube 2 were analyzed, it was confirmed that Si
O ₂ , MgO, CaO, Na ₂ O, K ₂ O, Fe ₂ O ₃
Was contained in a total of 100 ppm, of which the content of the oxide of the Group 2a element of the periodic table was about 19 ppm. Further, the relative density of the alumina sintered body is 99.9.
%, Bending strength is 36 kg / mm ² , average crystal particle size is 1
4 μm and visible light (60
The linear transmittance at 0 nm) was 36%.

(Experimental Example 1) Here, the discharge lamp arc tube 1 of the above-described embodiment and the conventional discharge lamp arc tube 1 were prepared, and the emission characteristics of the arc tube 1 were measured.

An alumina sintered body containing 400 ppm of MgO and an alumina content of 99.95% by weight was used for the light-transmitting tube 2 which constitutes the conventional discharge lamp arc tube 1.

Then, the maintenance factor in the lighting time was measured when the initial luminous efficiency (color rendering) of each arc tube 1 was 100%, and the luminous efficiency was 70% or more of the initial value even after lighting for 3000 hours. What was done was considered good.

The respective results are shown in FIG.

As a result, in the conventional discharge lamp arc tube 1, 400 ppm of M is contained in the alumina sintered body forming the light transmitting tube 2.
Since gO was included, the maintenance ratio was less than 70% after lighting for about 1000 hours.

Then, when the inner surface of the light-transmitting tube 2 was observed, AlScO ₃ which is a compound of the light emitting material was precipitated along the grain boundaries of the alumina crystal, and this compound (AlSc
It was found that the light emission was reduced due to the scattering of light due to the precipitation of O ₃ ).

On the other hand, the discharge lamp arc tube 1 of the embodiment
In the alumina sintered body forming the light-transmitting tube 2, only about 100 ppm of impurities are contained, and since MgO and CaO which easily react with the light-emitting material are about 19 ppm, even during lighting for 3000 hours. It had a high maintenance rate and had a maintenance rate of 70% or more even after lighting for 4000 hours.

As described above, the discharge lamp arc tube 1 of the embodiment
It can be seen that the high luminous efficiency can be obtained over a long period of time.

(Experimental Example 2) Next, an alumina sintered body constituting the light-transmitting tube 2 of the present invention and an alumina sintered body used in the conventional light-transmitting tube 2 were prototyped, and linear transmission of light was performed. The rate and the bending strength were measured.

In the measurement of the linear transmittance, each alumina sintered body was formed into a plate having a diameter of 20 mm and a thickness of 0.5 mm, and the linear transmittance was measured when the plate was irradiated with light having a wavelength of 600 nm. It was measured.

The respective results are shown in Table 1.

[0046]

[Table 1]

As a result, the sample No. In Nos. 12, 13 and 15, since the alumina content was less than 99.98% by weight, even the highest linear transmittance of light was only 19%. In particular, the sample No. 15 has a relative density of 99.
Since it was too small as 4%, it was not possible to satisfy the bending strength of 35 kg / mm ² or more required for constructing the transparent tube 2.

Sample No. Nos. 11 and 14 have an alumina content of 99.98% by weight or more, but the relative density is less than 99.8%, and therefore the linear light transmittance is 12 or less.
It was as low as about 15%.

On the other hand, the sample No. 1 to
No. 10 had an alumina content of 99.98% by weight or more and a relative density of 99.8% or more, so that it was possible to satisfy the linear transmittance of 30% or more. Also, the transparent tube 2
Satisfies the strength required for (breaking strength: 35 kg / mm ² or more), and the highest strength is 90 kg / mm ²
Was obtained.

In the embodiment of the present invention, the discharge lamp arc tube 1 for a metal halide lamp has been described, but other sodium lamps, mercury lamps, xenon lamps,
It goes without saying that it can be preferably used as a halogen lamp.

[0051]

As described above, according to the present invention, the translucent tube constituting the arc tube for a discharge lamp has an alumina content of 99.
It is formed of a polycrystalline alumina sintered body having a light transmittance of 98% by weight or more and a relative density of 99.8% or more and a linear transmittance of visible light per 0.5 mm thickness of 30% or more. As a result, the linear transmittance of light (visible light) can be increased to 30% or more, and since there is little reaction with the light-emitting material enclosed inside the light-transmitting tube, it has excellent color rendering properties and long life. It can be used as an arc tube for a discharge lamp.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an arc tube for a discharge lamp according to the present invention.

FIG. 2 is a schematic view showing a general discharge lamp.

FIG. 3 is a graph showing the light emission characteristics of the arc tube for a discharge lamp according to the present invention.

[Explanation of symbols]

 1 Light emitting tube for discharge lamp 2 Light transmitting tube 3 Closure body 4 Glass 5 Electrode core rod 6 Lead rod

Claims (1)

[Claims] 1. An arc tube for a discharge lamp in which a luminescent material is enclosed in a translucent tube, wherein the translucent tube has an alumina content of 9
It is made of a polycrystalline alumina sintered body having a relative density of 9.98% by weight or more and a relative density of 99.8% or more, and has a translucency such that the linear transmittance of visible light per 0.5 mm thickness is 30% or more. Arc tube for discharge lamp.