JP4134926B2 - Super high pressure mercury lamp - Google Patents

Description

The present invention relates to an ultrahigh pressure mercury lamp (hereinafter also simply referred to as a lamp) used mainly as a light source for a backlight of a liquid crystal projector or the like. In particular, the present invention relates to an ultra-high pressure mercury lamp in which 0.15 mg / mm ³ or more of mercury is sealed in a discharge vessel, and the mercury vapor pressure at the time of lighting reaches 150 atm or more.

  In recent years, a projector device that projects a screen on a personal computer on a large screen in a presentation, a seminar, a meeting, a school lesson, or the like has attracted attention. Such projector apparatuses can be roughly classified into two types according to the video system: a liquid crystal system and a DLP (digital light processing) system.

Among these, the liquid crystal system is the most popular as the specification of the projector device. In the liquid crystal system, an image is projected by applying light from a light source to an RGB (red / green / blue) liquid crystal panel. Projector apparatuses that employ a liquid crystal system are often three-panel projectors that use RGB panels. The three-type projector device has an advantage that the resolution is high because the number of pixels is tripled.
On the other hand, the DLP system has a track record of performing movie screening and the like, and the market has been rapidly expanding in recent years because of its high image quality and high brightness. The DLP system is a mechanism for projecting an image by digitally controlling a DMD (digital micromirror device) chip in which hundreds of thousands to hundreds of thousands of micromirrors are arranged on a substrate. The DLP method has an advantage that it has higher luminance than the liquid crystal method, and further, the projector device itself can be miniaturized because a liquid crystal panel is not required.

Since the projector device described above needs to illuminate an image uniformly and sufficiently with respect to the screen, a metal halide lamp in which mercury or a halide is enclosed is used as a light source. In recent years, the projector apparatus, in particular, the DLP projector apparatus, has a tendency to achieve higher brightness and smaller size, and thus there is a strong demand for higher brightness and smaller size of the light source.
For this reason, it has been proposed to use, as a light source for a projector device, an ultra-high pressure mercury lamp in which the mercury vapor pressure during lighting reaches 200 bar (about 197 atmospheres) or more instead of a metal halide lamp. This lamp suppresses the spread of the arc by increasing the mercury vapor pressure at the time of lighting, and further improves the light output (see Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 2-148561 JP-A-6-52830

  It is known that quartz glass is used as a material constituting the discharge vessel of the ultra high pressure mercury lamp. It is known that there are roughly two types of quartz glass, fused quartz glass containing metal impurities and synthetic quartz glass not containing such impurities. The ultra-high pressure mercury lamp is small in size and has extremely severe thermal conditions such that the mercury vapor pressure during lighting reaches 150 atm or more, so it has excellent heat resistance as a material constituting the discharge vessel. For example, it is common to use fused silica glass containing aluminum.

  However, it has been found that, with the elapse of lighting time, the ultra high pressure mercury lamp frequently causes blackening in the light emitting part due to the electrode constituent material evaporated from the electrode adhering to the inner surface of the light emitting part. When blackening occurs, there is a problem that the amount of light transmitted through the light emitting portion is significantly reduced and the illuminance is lowered.

  An object of the present invention is to provide an ultrahigh pressure mercury lamp that does not cause a decrease in illuminance by preventing blackening occurring in a light emitting portion of a discharge vessel made of fused silica glass.

  In order to solve the above problems, the present inventor examined the factors that cause the blackening phenomenon in the light emitting portion. As described later, the aluminum contained in the fused silica glass, which is a material constituting the discharge vessel, inhibits the halogen cycle. It has been found that the light emission part of the discharge vessel has a concentration distribution of aluminum in the thickness direction, and the concentration is higher on the inner surface side. In view of this, the present invention was completed by focusing on the aluminum concentration on the inner surface of the light emitting portion and defining the concentration.

  That is, in the ultrahigh pressure mercury lamp of the present invention, a pair of electrodes are disposed opposite to each other inside a discharge vessel having a light emitting portion made of fused silica glass and a sealing portion, and mercury is sealed therein. The aluminum concentration in the region from the inner surface to a depth of 5 μm is 1 to 25 wt. It is characterized by being in ppm.

  Furthermore, the ultra high pressure mercury lamp of the present invention is characterized in that the aluminum concentration of the electrode is 10 wt · ppm or less.

  Furthermore, the ultra high pressure mercury lamp of the present invention is characterized in that the bulk density of the electrode is 99.4% or more.

  In the ultrahigh pressure mercury lamp of the present invention, the aluminum concentration in the region from the inner surface of the light emitting portion of the discharge vessel made of fused silica glass to a depth of 5 μm is 1 to 25 wt. It is specified in the ppm range. Therefore, even when fused silica glass having excellent heat resistance is used for the discharge vessel, the halogen cycle is not hindered by the aluminum released from the inner surface of the light emitting portion to the discharge space, and thus, during lamp lighting. It can suppress that blackening arises in a light emission part.

FIG. 1 is a diagram for explaining an extra-high pressure mercury lamp of the present invention.
The ultra high pressure mercury lamp 10 includes a discharge vessel 13 made of fused silica glass, which includes a substantially spherical light emitting portion 11 and rod-shaped sealing portions 12 formed continuously at both ends of the light emitting portion 11. Have. In the discharge space 14 in the light emitting unit 11, an anode 15 and a cathode 16 made of, for example, tungsten are arranged to face each other. A metal foil 17 made of, for example, molybdenum is hermetically embedded in the sealing portion 12 by a pinch seal or the like. The metal foil 17 is electrically connected to a base end portion of an electrode rod 18 having an anode 15 and a cathode 16 at one end thereof at one end thereof by welding or the like, and extends to the other end from the sealing portion 12. The external lead 19 is electrically connected by welding or the like.

  In the discharge space 14 inside the light emitting unit 11, mercury for obtaining a necessary visible light wavelength, for example, radiation light of 360 to 780 nm, and a rare gas such as argon and xenon for improving lighting startability, In order to prevent blackening of the discharge vessel 13, for example, a halogen gas such as chlorine or bromine is enclosed.

  The ultra-high pressure mercury lamp 10 is very small as shown in the numerical examples described later, and the mercury vapor pressure at the time of lighting reaches 150 atm or higher, so that the thermal conditions are extremely severe. Therefore, as the material constituting the discharge vessel 13, it is preferable to use fused silica glass containing aluminum rather than synthetic quartz glass containing almost no impurities. This is because the aluminum atoms present in the fused silica glass are excellent in heat resistance because they capture alkali metals that adversely affect the bonding strength at the interface between the glass and the electrode. More specifically, when aluminum atoms are replaced with silica (Si) atoms in fused silica glass to form a negative ion region, alkali metal migration can be suppressed by trapping alkali in fused silica glass in this region. it is conceivable that.

  As will be described in detail later, the discharge lamp 10 of the present invention has an aluminum concentration in the region from the inner surface 20 of the light emitting portion 11 to a depth of 5 μm of 1 to 25 wt. Processing is performed so that it becomes ppm, and this is the greatest feature of the present invention. The inner surface 20 of the light emitting unit 11 refers to all portions that are the inner surface of the discharge vessel 13 and face the discharge space 14. The aluminum concentration in the region up to a depth of 5 μm means the average aluminum concentration in the depth region as described later.

Here, a numerical example of the ultra high pressure mercury lamp 10 will be described below. The maximum outer diameter of the light emitting unit 11 is selected from a range of 9 mm to 14 mm, and is 11.3 mm, for example. Internal volume of the arc tube 11 ^is selected from a range of 60 mm 3 to 300 mm ^3, for example, 100 mm ^3. The distance between the electrodes is selected from the range of 0.8 mm to 2 mm, for example, 1.1 mm. Wall load is selected from a range of ^{0.5W / mm 2 ~2W / mm 2} , such as 1.1 W / mm ^2. The rated voltage is selected from the range of 60V to 90V and is, for example, 75V. The rated power is selected from the range of 130 W to 350 W, for example, 200 W.

Further, numerical examples regarding the inclusions in the light emitting unit 11 will be described below. The amount of mercury enclosed is selected from the range of 10 to 50 mg, for example, 22 mg. In this case, the mercury vapor pressure at the time of lighting the lamp reaches 130 to 250 atmospheres, and the higher the mercury vapor pressure at the time of lighting, the more suitable the light source for the projector device. The amount of argon used as the rare gas is selected from the range of 5 to 20 kPa at the time of sealing, and is, for example, 13.3 kPa. The amount of bromine used as the halogen gas is selected from the range of 2 × 10 ⁻⁴ μmoles / mm ^{3 to} 7 × 10 ⁻³ μmoles / mm ³ at the time of sealing, for example, 1.2 × 10 ⁻³ μmoles. / Mm ³ . By appropriately adjusting the amount of enclosed halogen and utilizing the halogen cycle, blackening of the discharge vessel 13 can be prevented and the life of the discharge lamp 10 can be extended.

  According to the ultrahigh pressure discharge lamp 10 of the present invention as described above, the aluminum concentration in the region from the inner surface 20 of the light emitting portion 11 to the depth of 5 μm is 1 to 25 wt. Since it is specified in the range of ppm, it is possible to suppress the occurrence of blackening in the light emitting unit 11 during lamp lighting. The reason for this will be discussed below in 0020 to 0027.

  Conventionally, it is known that an ultrahigh pressure mercury lamp prevents blackening of a light emitting part by using a halogen cycle by a halogen gas introduced into a discharge vessel. The halogen cycle means that tungsten bromide is formed by combining tungsten atoms evaporated when the electrode is in a high temperature state when the lamp is turned on, and bromine atoms enclosed as halogen gas, for example. Refers to a series of flows until the tungsten atoms are returned to the electrode by dissociating into bromine and tungsten in the vicinity of the electrode in a high temperature state after being moved by convection in the discharge vessel. If such a halogen cycle exhibits its original function, the light emitting portion will not easily be blackened. Therefore, in the conventional ultra-high pressure mercury lamp, the light emitting portion is frequently blackened because of the halogen cycle. It is thought that it is inhibited and does not exhibit its original function.

  Then, when this inventor examined the factor which inhibits a halogen cycle, it discovered that the aluminum in the fused silica glass which comprises a discharge vessel was the cause. That is, it is considered that aluminum contained in the fused silica glass has an adverse effect on the halogen cycle while contributing to improvement in heat resistance by suppressing the movement of alkali metal in the discharge vessel if it is in an appropriate amount. The reason for this will be described in detail in the following 0022 to 0024.

  In order for the halogen cycle to perform well, the solubility of tungsten in the vicinity of the inner surface 21 on the upper side (upward in the drawing) of the light emitting portion 11 must be greater than that in the vicinity of the anode 15 or the cathode 16. That is, in order for tungsten to evaporate from the anode 15 or the cathode 16 and return again to the vicinity of the anode 15 or the cathode 16, tungsten adheres to the inner surface 21 on the upper side which is a lower temperature than the anode 15 or the cathode 16. It must exist as a gas phase without precipitation. In other words, the evaporated tungsten needs to be dissolved in the discharge space 14. When this solubility is higher in the vicinity of the upper inner surface 21 than in the vicinity of the anode 15 or the cathode 16, it is considered that tungsten does not adhere to the upper inner surface 21.

FIG. 2 is a graph showing the relationship between temperature and tungsten solubility at various aluminum concentrations. In FIG. 2, the horizontal axis represents temperature (K) and the vertical axis represents tungsten solubility (mol). Specifically, it is assumed that the following atoms are present in the discharge space 14 of the ultrahigh pressure mercury lamp 10 having the above numerical example, and the lamp 10 is turned on by changing the amount of aluminum atoms present in the discharge space 14 in four ways. In this case, the relationship between the amount of tungsten present in the gas phase and the temperature is obtained by theoretical calculation.
<Atoms assumed to exist in the discharge space 14>
Mercury: 5 × 10 ⁻⁵ mol
Bromine: 1 × 10 ⁻⁸ mol
Oxygen: 1 × 10 ⁻⁹ mol
Hydrogen: 1 × 10 ⁻⁹ mol
Aluminum: 1 × 10 ⁻⁹ mol, 2 × 10 ⁻⁹ mol, 5 × 10 ⁻⁹ mol, 1 × 10 ⁻⁸ mol, 4 × internal pressure at lighting: 200 atm

An ultra-high pressure mercury lamp whose mercury vapor pressure reaches 150 atm or more when turned on generally has a temperature of the upper inner surface 21 of about 1300 K (Kelvin) and a temperature of the tip of the anode 15 or the cathode 16 of 3000 K. Is.
As shown in FIG. 2, at 1300 K corresponding to the temperature of the inner surface 21 on the upper side, it can be seen that the solubility of tungsten decreases as the aluminum concentration increases. As a result, when the aluminum concentration in the discharge space 14 increases, the amount of aluminum atoms that can be dissolved in the space near the upper inner surface 21 decreases, so that tungsten is deposited on the upper inner surface 21. It is considered that blackening occurs in the light emitting portion 11 due to the adhesion. On the other hand, it can be seen that at 3000 K, which corresponds to the temperature of the tip of the anode 15 or the cathode 16, the solubility of tungsten is hardly affected by the change in the aluminum concentration.

  Upon further examination, the present inventor has found that the fused quartz glass tube 30 (hereinafter also referred to as the original tube 30) used for manufacturing the discharge vessel shown in FIG. If not, the aluminum concentration changes as the depth L1 from the inner surface 32 of the portion 31 corresponding to the light emitting portion changes. Specifically, the aluminum concentration increases toward the inner surface 32 side. I found it.

Accordingly, it is considered effective to scrape a region having a high aluminum concentration on the original tube 30 made of fused silica glass used for manufacturing the ultra-high pressure mercury lamp 10, specifically, the inner surface. It is desirable to scrape 32 to 20 μm or more. According to the ultrahigh pressure mercury lamp 10 of the present invention in which the original tube 30 previously subjected to such processing is used for the discharge vessel 13, the amount of aluminum released into the discharge space 14 when the lamp is turned on can be reduced. It is considered that the possibility of blackening in the portion 11 is extremely low.
On the other hand, when a raw tube that has not been subjected to any processing such as a conventional ultra-high pressure mercury lamp is used, a large amount of aluminum is released into the discharge space when the lamp is lit, and the halogen cycle occurs. It is considered that blackening is likely to occur in the light emitting portion due to the inhibition.

According to the ultra high pressure mercury lamp 10 of the present invention, as shown in FIG. 3, the depth from the surface 34 (inner surface 20 in FIG. 1) of the original tube 30 formed after scraping the fused silica glass from the inner surface 32. Defines the aluminum concentration in the region up to 5 μm as an average value. The reason for defining the region up to 5 μm is as follows.
In FIG. 1, when the light emitting part 11 becomes high temperature while the lamp is lit, aluminum contained in the fused silica glass moves toward the inner surface 20 which is the high temperature part by thermal diffusion. The moving distance is determined by the diffusion coefficient at the temperature (1000 ° C. or higher) of the light emitting unit 11 when the lamp is turned on. Here, assuming that the temperature of the light emitting unit 11 is 1200 ° C., the diffusion coefficient of aluminum is about 3 × 10 ⁻¹⁴ cm ² / s. When the lamp life is set to 2000 hours, the distance traveled in the fused silica glass when it is turned on can be estimated to be about 4.8 μm. Therefore, by defining the amount of aluminum existing in the region 5 μm deep from the inner surface 20 of the light emitting portion 11, aluminum atoms are prevented from being released into the discharge space, and the halogen cycle is prevented from being inhibited. It is considered possible.

  Here, a method of analyzing the aluminum concentration in a region having a depth of 5 μm from the inner surface 20 of the light emitting portion 11 will be described below with reference to 0029 to 0031.

  The analysis method was flameless atomic absorption (FL-ASS), and a commercial product (manufactured by HITACHI) was used. The measurement principle is a generally well-known method, in which each element absorbs light of a specific wavelength, that is, the light absorbance (light attenuation) is used. Specifically, the light peculiar to the subject is transmitted and the absorbance at that time is measured, and the content of each element contained in the subject is evaluated based on the magnitude of the absorbance.

  As an analysis method of this case, a calibration curve is first created. Prepare several solvents of known concentration of the target element and create a calibration curve of concentration versus absorbance. Next, pure water is added to a hydrofluoric acid (HF) solution in which high-purity glass (synthetic quartz glass) is dissolved, and diluted to an HF concentration of 5%. Then, an arbitrary concentration of aluminum is added, and the absorbance of the solution is measured. Next, the change in absorbance with respect to the amount of added aluminum is plotted, and a calibration curve is created. Based on this calibration curve, the aluminum content in the sample is determined.

(A) Fill the inside of the glass tube with an etching solution and uniformly etch the inside surface of the tube. At this time, the outside of the tube should not be etched. 47% HF (28 ± 1 ° C.) is used as an etching solution.
(B) The difference in weight of the glass tube before and after etching is measured to determine the etching weight. For the glass weight, a microbalance and an electronic balance are used.
(C) On the other hand, before and after etching, the inner diameter of the glass tube is measured with a micrometer, and the amount of change in the thickness direction is obtained. At that time, the glass tube is placed in a refractive index adjusting liquid, and the influence of the refractive index on the glass surface (curved surface) is corrected.
(D) The correlation between the etching weight and the change in thickness is derived from the above (b) and (c).
(E) Based on the relationship (d) above, the inner surface of the glass tube is etched so that the thickness change amount is 5 μm, and the aluminum concentration contained in the etching solution corresponding to the thickness change amount of 5 μm is evaluated. . This value is the aluminum concentration in a region having a depth of 5 μm from the inner surface 20 of the light emitting portion 11.

  The unit of aluminum concentration calculated by the above method is ng / μm. The method for converting to ppm is as follows. In this case, the weight per 1 μm thickness of the glass was estimated to be 4 mg. Therefore, ng / μm to wt. Conversion to ppm is obtained by dividing the value by 4 mg.

  In the present invention, the anode 15 or the cathode 16 has an aluminum concentration of 10 wt. It is specified in ppm or less. As a result, the amount of aluminum released into the discharge space 14 when the ultrahigh pressure mercury lamp 10 is turned on can be further reduced, so that the occurrence of blackening in the light emitting portion 11 can be prevented. Specifically, the pure tungsten content is 99.99% or more, and the aluminum component is 10 wt. A tungsten electrode made of tungsten or a tungsten alloy obtained by performing plastic working on an ingot manufactured from tungsten powder having a high purity of ppm or less is used.

Further, in the present invention, the bulk density (mass / volume) of the anode 15 or the cathode 16 is specified to be 99.4% or more. As a result, since the anode 15 or the cathode 16 has a high density, the ratio of the grain boundaries is reduced, so that a space for an impurity that inhibits a halogen cycle such as aluminum is reduced, and the anode 15 or the cathode 16 is manufactured. There is an effect that impurities such as aluminum are not easily mixed. Specifically, as described above, a tungsten compact having the above-described bulk density is sintered by sintering a compact obtained by pressing high-purity tungsten powder with a pressing pressure of 2000 kgf / cm ² or higher at a high temperature of 3000 ° C. or higher. An ingot is obtained. After cutting and cutting those ingots to desired dimensions, those recrystallized at a high temperature are used as electrode materials.

Here, the first experiment for demonstrating the effect of the present invention will be described. In order to confirm the influence of the aluminum concentration in the region from the inner surface 20 of the light emitting portion 11 to 5 μm on the occurrence of blackening, 14 experimental lamps having different average aluminum concentrations in the region were prepared. Details of the experimental lamp are shown below. The discharge vessels of these lamps were obtained by adjusting the inner surface 32 of the original tube 30 shown in FIG. 3 to various aluminum concentrations by chemical etching by the method described above.
<Experimental lamp>
Maximum outer diameter of the light emitting part 11: 11 mm
Internal volume of discharge vessel 13: 100 mm ³
Distance between electrodes: 1.2mm
Encapsulated mercury amount: 0.25 mg / mm ³
Encapsulated halogen and encapsulated amount: 1.3 × 10 ⁻³ μmoles / mm ^{3 of} bromine
Tube wall load: 1.1 W / mm ²
Rated voltage: 70V
Rated power: 200W

  Experimental conditions will be described. After each lamp was lit continuously for 50 hours, the presence or absence of blackening in the light emitting part 11 and the presence or absence of rupture in the light emitting part 11 were visually confirmed. The results are shown in Table 1.

In Table 1, “◯” shown in the “Blackening” column indicates that no blackening occurred in the light emitting unit 11, and “Δ” indicates blackening occurred in a part of the light emitting unit 11. “X” indicates that the light emitting unit 11 is entirely blackened. Further, “◯” shown in the “rupture” column indicates that the light-emitting portion 11 has not been ruptured, and “x” indicates that the light-emitting portion 11 has been ruptured.
From the experimental results shown in Table 1, in the lamps of Examples 1 to 8, no blackening occurred in the light emitting portion 11 and the light emitting portion 11 did not burst. On the other hand, in the lamps of Comparative Examples 1 and 2 in which the aluminum concentration is lower than the numerical range of the present invention, the light emitting portion 11 is ruptured, and in the lamps of Comparative Examples 3 to 6 in which the aluminum concentration exceeds the numerical range of the present invention, the light emitting portion 11 is blackened. Occurred. Therefore, it was shown that when the amount of aluminum contained in the light emitting portion 11 is too small, there is a problem in terms of heat resistance, and when it is too large, it becomes a factor inhibiting the halogen cycle.

  A second experiment for demonstrating the effect of the present invention will be described. In order to confirm the influence of the average aluminum concentration of the electrodes on the blackening of the light emitting portion 11, 14 experimental lamps having different average aluminum concentrations of the anode 15 were prepared. The details of the lamp and the experimental conditions are the same as in the first experiment. The results are shown in Table 2.

In Table 2, “◯” shown in the “Blackening” column indicates that no blackening occurred in the light emitting unit 11, and “Δ” indicates blackening occurred in a part of the light emitting unit 11. “X” indicates that the light emitting unit 11 is entirely blackened.
From the experimental results shown in Table 2, in the lamps of Examples 1 to 8 having an average aluminum concentration within the range of the present invention, no blackening occurred in the light emitting portion 11. On the other hand, in the lamps of Comparative Examples 1 to 6 in which the average aluminum concentration exceeded the numerical range of the present invention, blackening occurred in the light emitting portion 11.

  As described above, the super high pressure mercury lamp of the present invention has been described with respect to a DC lighting, but is not limited thereto, and can be applied to an AC lighting. This is because the blackening of the light-emitting portion caused by aluminum contained in the fused silica glass is not a phenomenon that occurs peculiar to DC lighting but can also occur in AC lighting.

  The super high pressure mercury lamp of the present invention can be applied to various lighting postures such as when the longitudinal axis of the lamp is vertically arranged, horizontally arranged, or obliquely arranged.

  Furthermore, the ultrahigh pressure mercury lamp of the present invention has an aluminum concentration of 1 to 25 wt. Although it is specified within the range of ppm, it is assumed that the aluminum concentration after the lamp is manufactured and after the lamp is turned on for a predetermined time is also within this range.

It is a figure for demonstrating the ultrahigh pressure mercury lamp of this invention. It is a figure which shows the relationship between the temperature in various aluminum concentration, and tungsten solubility. It is a figure for demonstrating the structure of the original tube used as a discharge vessel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Super high pressure mercury lamp 11 Light emission part 12 Sealing part 13 Discharge vessel 14 Discharge space 15 Anode 16 Cathode 17 Metal foil 18 Electrode rod 19 External lead 20 Inner surface

Claims (3)

In an ultra-high pressure mercury lamp in which a pair of electrodes are arranged opposite to each other in a discharge space inside a discharge vessel having a light emitting part and a sealing part made of fused silica glass, and mercury is enclosed,
The aluminum concentration in the region from the inner surface of the light emitting portion to a depth of 5 μm is 1 to 25 wt. An ultra-high pressure mercury lamp characterized by being in the ppm range. The aluminum concentration of the electrode is 10 wt. The ultra-high pressure mercury lamp according to claim 1, wherein the pressure is not more than ppm. The ultrahigh pressure mercury lamp according to claim 1 or 2, wherein a bulk density of the electrode is 99.4% or more.

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