JP2012150951A - Xenon short arc lamp for digital projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a xenon short arc lamp with a long service life capable of restraining a flicker phenomenon for a long time by preventing projections and bumps on a tip face of a cathode for a long time after a lamp is lit on.SOLUTION: A xenon short arc lamp for a digital projector comprises: an anode; a cathode having a cathode body made of tungsten with an electron radioactive material; and a luminous tube made of quartz glass. The cathode has a stripe-like phase of tungsten carbide in a phase of tungsten (W) on a surface layer on the tip face. Carbon and/or carbide is provided inside the luminous tube, and a concentration of an OH group on an inner surface of the luminous tube is 100wt-ppm or higher, and a getter having a hydrogen selectivity property is provided inside the luminous tube.

Description

  The present invention relates to a xenon short arc lamp for a digital projector used as a light source in a digital projector using DLP (Digital Light Processing: registered trademark) technology using, for example, DMD (digital micromirror device: registered trademark).

Conventionally, in a movie theater screening system, a film projector that normally projects a 35 mm film through an aperture and projects it onto a screen has been used. FIG. 11 is a diagram illustrating the configuration of a film projector. The film 71 is a film in which video frames (hereinafter simply referred to as frames) representing continuous contents are recorded at regular intervals. The film 71 is transported by a traveling mechanism (not shown) and passes through the picture gate portion 72 from the upper part toward the lower part. The light condensed from the light source device 73 passes through the aperture formed in the picture gate portion 72 and irradiates the frame recorded on the film 71.
The size of one frame on the film 71 is, for example, about 24 × 18 mm and a diagonal of about 30 mm. Therefore, the light source device 73 must have a configuration capable of efficiently condensing light from the light source lamp so as to be a circle having a diameter of about 30 mm in order to efficiently irradiate the film area.

  Therefore, the light source device 73 includes a xenon short arc lamp 73a (hereinafter also referred to as a xenon lamp) as a light source lamp, and a reflecting mirror 73b disposed in the rear part thereof. The reflecting mirror 73b is configured to include a reflecting surface composed of a spheroid that condenses the light emitted from the xenon lamp 73a into the size of the circle having a diameter of about 30 mm. The light emitted from the xenon lamp 73a is reflected by the reflecting mirror 73b, condensed at the second focal point (F2), passes through the film 71, and magnified by the projection lens 74 as shown in the ray path shown in FIG. And projected onto the screen 75.

  However, the ray path shown in the figure is an ideal system, and actually, the arc of the xenon lamp 73a is not a point light source but has a finite size. For this reason, all the light rays from the arc are not collected at one point, and the inside of a circle of a certain size is irradiated even at the position of the second focal point. It is known that the irradiation area at the position of the second focal point increases in proportion to the cross-sectional area of the arc (the area of the arc when viewed from the side) if the elliptical mirror is the same.

For this reason, a xenon lamp having an arc length of about 3 to 7 mm is used as a light source for a film projector in order to irradiate a circle having a diameter of about 30 mm. The “arc length” is equal to the distance between the electrodes when the lamp is steadily lit.
Furthermore, when a numerical example is given about the specification of the xenon lamp for such a film projector, for example, the rated power consumption is 0.9 to 6.0 kW, the cathode tip diameter is 0.6 to 1 mm, and the enclosed xenon pressure is Is 0.6 to 0.9 MPa, the current density at the cathode tip is 76 to 110 A / mm ² , and the tube wall load is 18 to 29 W / cm ² .
Regarding these numerical examples, specific numerical values are enumerated taking as an example a xenon lamp for a film projector with a rated power consumption of 4 kW. The arc length is 6 mm, the cathode tip diameter is 0.9 mm, the enclosed xenon pressure is 0.7 MPa, and the current is The density is 108 A / mm ² and the tube wall load is 25 W / cm ² .
In the above, the “current density” is the current density obtained by dividing the lamp current by the cross-sectional area at a position of 0.5 mm from the cathode tip, and “tube wall load” is the lamp surface area of the arc tube portion. The power per unit area divided by.

  Since the xenon lamp emits high-luminance light, the electrode tip temperature becomes extremely high. For this reason, wear is severe at the tip of the cathode that emits electrons. When the electrode tip is worn and irregularities are formed on the tip surface of the cathode, a phenomenon in which the starting point of arc discharge moves between the convex portions, so-called flickering, occurs. When this flicker occurs, the luminance distribution of the lamp fluctuates and appears on the screen as flicker.

In order to avoid the occurrence of such flicker, that is, in order to obtain stable radiation for a long time, the xenon lamp has been improved.
For example, the cathode uses tungsten doped with tria (ThO ₂ ) having a high melting point among electron-emitting materials, and a carbide layer made of tungsten carbide (W ₂ C) excluding the tip side region is, for example, 8 to 30 μm. It is formed with a thickness. By forming this carbonized layer, an electron-emitting material (for example, tria (ThO ₂ )) added to the cathode is reduced by carbon during the lamp operation, and thorium (Th) is generated. Thorium (Th) can be supplied efficiently.
Such a technique is disclosed, for example, in JP-A-10-283921.

The reason why the carbonized layer is not formed at the tip of the cathode (the reason why it should not be formed) is that the region of the tip of the cathode reaches a high temperature of about 2900 ° C., so that tungsten carbide (W ₂ C) having a low melting point is used. The reason for this is that the lamp is melted early and the electrode is worn out, or the arc tube is blackened and the intensity of the emitted light is lowered, so that the lamp life comes to an early stage.
In the xenon lamp optimized by adopting such a technique for the lamp for the film projector described above, the carbon amount per lamp volume is in the range of 0.5 to 1.8 μmol / cm ³ .

In addition, quartz glass is usually used for the arc tube. When water is released into the lamp based on OH groups contained in the quartz glass as the lamp is turned on, the starting voltage rises and the arc tube Since a problem such as blackening may occur, an arc tube having a low OH group concentration is typically used. Such an arc tube maintains the OH group concentration at the level of the raw material before molding by using a dry gas (N ₂ ) in a molding process for expanding the arc tube.

  The xenon lamp thus improved has a flicker life of about 3500 hours, can realize a sufficiently long service life, has good startability, and has improved blackening.

JP-A-10-283921

  By the way, in the screening system of a movie theater, in recent years, it has become possible to perform advanced CG using digital technology that improves video quality, there is no film degradation, and the cost of film production can be reduced. Cinema has become widespread, and along with this, replacement with digital projectors using DLP (Digital Light Processing: registered trademark) technology is rapidly progressing.

  A configuration example of such a digital projector (DLP projector) is shown in FIG. In this digital projector 80, the light from the xenon lamp 81 is collected by a reflecting mirror 82 having an elliptical reflecting surface, and DMD (digital micromirror) is passed through a color filter 83, an integrator rod 84, and collecting lenses 85a and 85b. An image element called a device (registered trademark) is irradiated. Then, the light reflected by the DMD 86 is projected onto the screen 88 by the projection lens 87 to display an image.

  In such a digital projector 80, the light from the xenon lamp 81 must be collected with high efficiency and incident on the end face of the integrator rod 84. The reason why the light should be collected with high efficiency in this way is that the end face of the integrator rod 84 is usually the same size as that of the DMD 86 and is 0.7 to 1 inch diagonal (17.8 to 25. 4mm) is small, so that it is possible to display an image with the same brightness as that of a conventional film projector on the screen. It is because it must be made to do.

Since the irradiation area by the reflecting mirror 82 is substantially proportional to the cross-sectional area of the arc, the xenon lamp 81 for the digital projector has a higher xenon pressure in order to shorten the arc length and make the arc thinner. Must be used.
As a result, the arc length of the xenon lamp 81 is about 2 to 7 mm, and the sealed pressure of the xenon gas is required to be 1 MPa or more, specifically in the range of 1 to 2 MPa in terms of normal temperature.
In order to withstand the high operating pressure when the lamp is lit, it is necessary to make the arc tube smaller than before, and as a result, the tube wall load of a xenon lamp for a digital projector reaches 30 W / cm ² or more. More specifically, a range of 30 to 40 W / cm ² is required. This is much higher than the conventional xenon lamp for a film projector.

  Here, as a method for reducing the irradiation area by the reflecting mirror 82, it is conceivable to shorten the distance between the focal points of the elliptical reflecting surface (distance between F1 and F2). However, in this case, the proportion of light rays having a large angle with respect to the optical axis 89 increases, the number of light rays that do not reach the DMD element increases, and the light utilization rate decreases, and this method cannot be employed. In other words, when the irradiation area is reduced, it is difficult to increase the light collection efficiency only by devising the optical system.

Furthermore, the xenon lamp 81 needs to increase the light output of the lamp because of the demand for a brighter image in the digital projector. For this reason, from the viewpoint of reducing the light rays from the arc that are blocked by the cathode, those having a smaller cathode tip diameter than the conventional one are required, and the cathode tip diameter in the lamp for the digital projector is smaller than the conventional one. For example, it is 0.35-0.7 mm.
As a result, the current density at the cathode tip is also increased, specifically 119 A / mm ² or more, and 119 to 210 A / mm ² in a practical range.
With regard to such a specification, specific examples of numerical values for a xenon lamp for a digital projector with a rated power consumption of 4 kW are given as examples. The arc length is 3.5 mm, the cathode tip diameter is 0.6 mm, and the enclosed xenon pressure is 1 0.8 MPa, the current density is 119 A / mm ² , and the tube wall load is 37.5 W / cm ² .
The “current density” is the current density obtained by dividing the lamp current by the cross-sectional area at a position 0.5 mm from the cathode tip as described above, and “tube wall load” is the lamp power of the arc tube section. The power per unit area divided by the inner surface area.

Summarizing the characteristics of the above xenon short arc lamps for digital projectors, the pressure of the enclosed xenon gas is high, and the arc tube has been downsized to withstand high operating pressure. The value obtained by dividing the inner surface area in the swollen portion is high, and the current density is increased as a result of reducing the cathode tip diameter. To describe such matters using specific numerical values, the enclosed pressure of xenon gas is 1 MPa or more, the tube wall load is 30 W / cm ² or more, and the current density of the cathode end face is 119 A / mm ² or more. Very strict specifications are required.
When trying to satisfy the specifications as described above, the tip temperature of the xenon lamp further rises, and the cathode tip wears out and deforms very rapidly. It becomes large and unevenness is formed, and flicker is generated at an early stage.
Even if the flicker life of the xenon lamp is improved by a conventionally known technique such as the formation of a carbonized layer or the shape of the tip of the cathode, the life will be reached in a very short period of only 200 to 350 hours after lighting. .

  The present invention has been made to solve such a problem, and prevents the tip end surface of the cathode from being uneven for a long time after the lamp is turned on, and suppresses the occurrence of flicker phenomenon for a long time. It is to provide a xenon short arc lamp for a long-life digital projector.

In order to solve the above problems, the present invention is characterized by comprising the following configuration.
(1)
The anode,
A cathode with a cathode body made of tungsten with an electron-emitting material;
A xenon short arc lamp for a digital projector comprising an arc tube made of quartz glass,
The cathode has a striped phase of tungsten carbide in the phase of tungsten (W) on the surface layer on the tip surface,
In the arc tube, carbon and / or carbide is provided,
The OH group concentration on the inner surface of the arc tube is 100 wt-ppm or more,
The arc tube includes a getter having hydrogen selectivity inside.
(2)
The hydrogen-selective getter includes a hydrogen-permeable airtight container and a getter material enclosed in the airtight container.
The hermetic container is made of any one of palladium (Pd), nickel (Ni), iron (Fe), 400 series stainless steel, iron / nickel alloy, and nickel / copper (Cu) alloy.
(3)
The hydrogen-selective getter includes a getter material and a plating layer that covers the surface of the getter material.
(4)
The getter material may be made of at least one of zirconium (Zr), zirconium alloy, titanium (Ti), tantalum (Ta), and yttrium (Y).
(5)
The hydrogen-selective getter is provided in a sealed tube portion of the arc tube.

According to the xenon short arc lamp for a digital projector according to the present invention, the cathode has a striped phase of tungsten carbide in the phase of tungsten (W) on the surface layer on the front end surface, and carbon inside the arc tube And / or carbide, and the OH group concentration on the inner surface of the arc tube is 100 wt-ppm or more, so that unevenness is not easily formed at the cathode tip, and the occurrence of flicker phenomenon caused by arc flickering is prolonged. The lamp can be suppressed for a long time, the service life of the lamp can be extended, and the arc tube has a hydrogen-selective getter that selectively absorbs hydrogen. Thus, it is possible to suppress a decrease in lighting startability caused by including a large amount of. In addition, oxygen and oxide, which play a role in supplying carbon to the tip of the cathode, are not occluded and reduced by the getter, and carbon can be smoothly supplied to the cathode.
As a result, during lamp operation, tungsten carbide melts and only the cathode tip part melts to reshape a smooth spherical surface by surface tension, so that the shape of the tip can be adjusted to the desired smooth shape, After the lamp is extinguished, a plurality of linear tungsten carbides appear in a striped phase in the tungsten (W) phase on the surface of the cathode tip. According to such a xenon short arc lamp, it is difficult for irregularities to be formed at the cathode tip, and the occurrence of flicker phenomenon caused by arc flickering can be suppressed for a long time, and the xenon short for a digital projector having a long service life. It can be an arc lamp.

It is sectional drawing explaining the structure of the xenon short arc lamp for digital projectors explaining embodiment of this invention. It is explanatory drawing explaining the behavior of the carbon of the front-end | tip part of the cathode structure based on this invention. It is a figure which shows the electron micrograph of the cathode front-end | tip which concerns on this invention. It is sectional drawing for description which shows an example of the hydrogen selective getter which concerns on this invention. It is sectional drawing for description which shows the other example of the hydrogen selective getter which concerns on this invention. It is the table | surface which put together the permeability | transmittance of hydrogen and oxygen of various substances. It is a table | surface which shows collectively the specification of each lamp | ramp of an Example and a reference example, and the flicker lifetime of each lamp | ramp in this experiment example. It is a figure which shows the mode of the change of the cathode tip shape of the lamp | ramp 2 concerning the reference example 2. FIG. It is a figure which shows the mode of the change of the cathode tip shape of the lamp | ramp 6 concerning the reference example 6. FIG. It is a figure which shows the mode of the change of the cathode tip shape of the lamp | ramp 7 concerning the reference example 7. FIG. It is a figure explaining the structure of the projector for films. It is a figure explaining the structure of the projector for DLP.

FIG. 1 is a cross-sectional view for explaining the configuration of a xenon short arc lamp for a digital projector (hereinafter also referred to as “xenon lamp” or simply “lamp”) for explaining an embodiment of the present invention.
The xenon lamp 10 includes an arc tube portion 12 made of a swelled glass tube provided near the center, and an arc tube 11 made of quartz glass having a sealing tube portion 13 connected to both ends thereof, and an arc tube Inside the portion 12, it is constituted by a cathode 14 and an anode 15 that are provided so that their tips face each other.
The main body portion 14a of the cathode 14 is made of tungsten including an electron-emitting material, and the main body portion 15a of the anode 15 is made of tungsten. As described above, tungsten is mainly used as the material constituting the main body portions 14a and 15a of the electrode because it has a high melting point, a low vapor pressure, and a high thermal conductivity. This is because the substance is superior in the invention. Of course, the material of the electrode cathode main bodies 14a and 15a mentioned here is not limited to those having 100% of each material component, and of course includes the case of containing inevitably mixed impurities. 14a and / or the anode main body 15a may be additionally provided with a carbonized layer or other substances.
The cathode body 14a and the anode body 15a are mounted and held on the electrode rods 14b and 15b, respectively, so as to be positioned at the center of the arc tube portion 12.
The electrode rods 14b and 15b are respectively inserted into holes in a thick cylindrical quartz glass body 16 fixed in a narrowed portion 13a between the arc tube portion 12 and the sealing tube portion 13, and the sealing tube portion. 13 are hermetically sealed and held at the step glass portions 13b formed at both ends of the plate. The electrode rods 14 b and 15 b extend outward from the outer end portion of the arc tube 11, and also serve as a lead portion for supplying power to supply power to the xenon lamp 10. The arc tube 11 is filled with xenon gas as a luminescent material.

Such a xenon short arc lamp for a digital projector according to the present invention typically satisfies the following specifications.
The enclosed pressure of xenon is 1 MPa or more, the tube wall load is 30 W / cm ² or more, and the current density on the tip surface of the cathode is 119 A / mm ² or more. All of these specifications are required as a light source used in a digital projector for DLP, an irradiation area comparable to that of a DMD element, specifically 0.7 to 1 inch (17.8 to 25 inches diagonally). It is necessary at least to satisfy both of the purpose of condensing light with high efficiency in a small area (about 4 mm) and illuminating the screen more brightly.
In order to realize the above-described large current density, it is desirable to use tria (ThO ₂ ) as the electron-emitting material contained in the cathode 14, and the cathode main body portion 14 a is preferably composed of triated tungsten. .
Also in the anode 15, the anode body 15 a is subjected to an arc and becomes high temperature by receiving electrons, so that the anode body 15 a is preferably made of high melting point tungsten.

  Further, in the xenon short arc lamp 10 according to the present invention, a getter 17 is provided inside the arc tube 11 for the purpose of improving the startability of the lamp. In this embodiment, the getter 17 is composed of an airtight container 17B having hydrogen permeability and a getter material (17A) enclosed in the container 17B. For example, as shown in FIG. It is made to adhere to 15b and is fixed with a metal wire. The role of the getter 17 will be described in detail later.

  FIG. 2 shows an embodiment of the tip portion of the cathode structure according to the present invention. The tip portion of the cathode main body 14a has a cone angle of 60 ° virtually connecting the surface taper surface (ridge line), a tip diameter of 0.35 to 1.0 mm, and a large diameter. The diameter of the part is 4 to 12 mm. By making the diameter of the cathode tip small in this way, the light output from the lamp can be reduced by reducing the number of rays from the arc that are blocked by the cathode itself.

In order to supply carbon (C) to a portion taken into the arc at the tip of the cathode, the xenon lamp 10 is provided with carbon inside the arc tube 11. As one form thereof, for example, as shown in FIG. 2, carbon can be arranged by providing a tungsten carbide (W ₂ C) layer 141 in the vicinity of the tip of the cathode 14a.
The portion where the tungsten carbide layer 141 is formed is, for example, a position that is retracted by at least 2 mm along the axis L of the electrode from the tip surface of the cathode 14a, and the thickness of the layer is 30 to 100 μm. The reason why the tungsten carbide layer 141 is not formed at the tip of the cathode in this way (cannot be formed) is that tungsten carbide (W ₂ C) having a low melting point is formed in a thickness range of about 30 μm or more. The problem is that the melting point of the cathode tip becomes excessive, the cathode tip diameter increases in a short time and the brightness decreases, and the inside surface of the arc tube becomes black due to evaporation of tungsten carbide (W ₂ C), and the intensity of the emitted light This is because there is a problem that the lifetime of the lamp comes early due to the decrease in.

The means for disposing carbon or a carbon-containing compound as a carbon supply source inside the arc tube 11 is not limited to the above-described form, and may be a method of attaching to a metal portion inside the arc tube. Any form may be used. For example, a tungsten carbide (W ₂ C) layer may be provided on the anode main body 15 a, or it can be realized by arranging carbide on the shaft portions 14 b and 15 b of the electrodes 14 and 15. In addition, when providing a carbonized layer in the anode main body 15a, it is desirable to arrange | position except the front-end | tip part area | region similarly to the case where it provides in the cathode main body 14a.

It is difficult to realize stable supply of carbon to the tip of the cathode 14a as a gas phase only by disposing solid state carbon or a compound containing carbon in the arc tube 11.
Various methods can be considered as means for bringing carbon into a gas phase state such as carbon dioxide gas. As an example, CO is produced by providing oxygen (O) in the arc tube 11. Thus, carbon can be reliably supplied to the cathode tip surface.
One form thereof is to contain a large amount of OH groups in the quartz glass constituting the arc tube 11. In a preferred embodiment, a layer having an OH group concentration of 100 wt-ppm or more is formed on the inner surface of the arc tube 11. The OH group concentration in the inner surface layer is defined by the average concentration in the thickness range from the inner surface to 150 μm.
Furthermore, as a more preferable form, the amount of OH groups contained in the arc tube 11 is 0.15 μmol or more per 1 cm ³ of the internal volume of the lamp.

According to such a xenon short arc lamp, the OH group contained in the quartz glass of the inner surface layer of the arc tube 11 is released into the discharge space as, for example, water (H ₂ O) during lamp operation, and the arc tube 11 It reacts with a carbon source (ie, carbon or carbon compound) provided therein to produce carbon monoxide gas (CO). A part of the CO enters the arc by diffusing in a gas phase state in the arc tube 11. CO is decomposed in the arc due to the high temperature, producing C ⁺ ions. The C ⁺ ions are carried to the cathode tip surface by the electric field in the arc, where they react with tungsten on the cathode 14a to produce tungsten carbides such as W ₂ C and WC. The tungsten carbide melts when exposed to the high temperature of the cathode 14a, but the amount of melting is extremely small because C is derived from the gas phase. Therefore, there is no problem that the tip end of the cathode 14a becomes large in a short time and the luminance is lowered, or that the inner surface of the arc tube is blackened by evaporation of tungsten carbide.

  When such a small amount of carbon is present, when the lamp is turned off, a plurality of linear tungsten carbides are formed in a striped pattern on the tip of the tungsten cathode. Even if the tungsten carbide generated to such an extent that it remains in the minute area of the cathode tip surface melts during lamp operation, even if irregularities are formed on the cathode tip, the tip of the cathode has a smooth spherical surface due to surface tension. Mold to form a smooth surface again.

  In FIG. 3, the electron micrograph which expands and shows the surface layer part of a cathode front-end | tip is shown. Here, (a) in the figure is an enlarged photograph of the tip part, and (b) shows an enlarged photograph of a part surrounded by a circle P in the figure. Specifically, as shown in FIG. 3, the tungsten carbide is formed in a number of lines on the tungsten (W) phase, which is the main component of the main body portion, so that a striped phase is formed. Forming. The stripe tungsten carbide phase has a width of about 0.1 to 0.5 μm, and a large number of phases are formed at intervals of about 0.5 to 3 μm. The proportion of carbon at the tip of the cathode is about 1 wt%, and as the proportion of carbon, the surface layer at the tip of the cathode is the largest, and becomes smaller as the position recedes from the tip. This confirms that carbon has been carried by the gas phase at the tip of the cathode, and that the cathode tip has a striped phase of tungsten carbide through the gas phase during lamp operation. It is possible to say that carbon has been carried to the cathode tip.

In order to reliably realize C supply in the gas phase, the amount of carbon (C) provided in the arc tube is preferably 2.4 μmol / cm ³ or more with respect to the internal volume of the arc tube. By providing 2.4 μmol or more of carbon per 1 cm ³ of the internal volume of the lamp, it becomes possible to always supply the carbon in the vapor phase reaching the cathode tip, and the flicker life can be extended.
The “carbon amount” referred to here is the total amount of carbon (C) from all carbon and carbon compounds adhering to the metal member in the arc tube including the arc tube portion and the sealing tube portion. Is converted to a molar amount and divided by the inner volume of the arc tube.

As described above, in order to supply carbon to the cathode tip by the gas phase, it is necessary to contain a large amount of OH groups in the quartz glass constituting the arc tube. However, if a large amount of OH groups are contained inside the arc tube, H ₂ is generated from the OH groups in the course of the reaction, and there is no problem with discharge during lamp operation. It makes you worse.
Therefore, in the present invention, a getter material capable of absorbing and H ₂ as described above above, by providing the inside of the arc tube in a state sealed in the selective hydrogen permeable in the hermetic container, a getter having a hydrogen-selective It is functioning.

FIG. 4 shows an example of a getter having hydrogen selectivity in the present invention. This figure is a cross-sectional view cut in the axial direction of the tube of the airtight container.
The getter material 17A for occluding H ₂ is a substance that can absorb and remove hydrogen gas satisfactorily. Specifically, zirconium alloys such as zirconium (Zr) and Zr-V-Fe, titanium (Ti), tantalum (Ta), yttrium (Y), or the like can be used. Such a getter material may be composed of a single substance or a combination of a plurality of substances.

In the present invention, the reason why such a getter material (17A) is enclosed in an airtight container is as follows. That is, the getter material (17A) having the hydrogen storage property has the property of absorbing CO and O ₂ in the same manner as H ₂ . For this reason, when the amount of the getter material 17A is increased to such an extent that improvement of the starting characteristics of the lamp can be expected, oxygen for transporting C to the cathode tip decreases, and the function of supplying C to the cathode tip is hindered. End up. On the other hand, if importance is attached to the function for carrying C, the absolute amount of the getter material 17A becomes insufficient, and the deterioration of the startability cannot be improved.

Therefore, in the present invention, the getter material as described above is hermetically sealed in an airtight container 17B made of a material that easily permeates H ₂ but does not easily absorb and permeate CO and O _2. A getter having hydrogen selectivity that selectively permeates is formed and disposed inside the arc tube. As a result, the wall of the hermetic container 17B is permeable to H ₂ , so that H ₂ passes through this wall and is absorbed by the getter 17A, but CO and O ₂ cannot be transmitted or are hardly absorbed. Therefore, the original function as a carbon carrier can be exhibited without CO or O ₂ being absorbed by the internal getter 17A. As a result, H ₂ can be selectively removed with CO and O ₂ remaining inside the arc tube, and OH can be maintained while maintaining the function of carrying C to the cathode tip via the gas phase. It is possible to greatly improve the deterioration of the starting characteristic of the lamp that is inevitably generated by the provision.

As shown in FIG. 4, when the getter having such hydrogen selectivity is constituted by an elongated tubular airtight container 17B and a getter material 17 enclosed therein, the getter is particularly used for the airtight container 17B. The material to be formed is preferably made of a material having a H ₂ transmittance of 10 ⁻⁵ cc (NTP) / cm ² · s or more at 500 ° C.

FIG. 5 shows a summary of the transmittances of the substances hydrogen (H ₂ ) and oxygen (O ₂ ). The hydrogen permeability and oxygen permeability shown in the figure are as follows: (1) “Hiroo Kumagai, Goro Tominaga, Yasushi Sakai, Genichi Horikoshi,“ Physics and Applications of Vacuum ”published by Saika Huabo, October 25, 1980 Issued on the same day, and (2) “WH Kohl“ HANDBOOK of MATERIALS and TECHNIQUES for VACUUM DEVICES ””. The permeability of gas molecules is a gas in a standard state (= NTP: 1 atm-0 ° C.) per 1 cm ² per 1 cm ² when the pressure difference between both surfaces of a 1 mm thick material is 1 atm. Expressed in terms of molecular volume (cc). In the case where the transmittance of the same substance is described in the two documents cited in FIG. 5, both values are described. Specifically, palladium (Pd), for example, has a hydrogen permeability of 10 ⁻⁵ cc (NTP) / cm ² · s according to Kohl literature and 8 according to Kumagaya literature. It was 0.7 × 10 ⁻³ cc (NTP) / cm ² · s.

In the case of the substances described above, CO and O ₂ absorbed by the material constituting the hermetic container are very small. This is because some CO and O ₂ are decomposed into atoms on the surface of the container and dissolved in the material of the container, but the diffusion coefficients of C and O in these materials are small enough to be ignored ( This is because, after being dissolved in the surface layer of the container, it is not further dissolved. Here, oxygen (O) is also absorbed into the container by reacting with the material of the container to form an oxide. However, since the diffusion coefficient of oxygen (O) is small as described above, the above oxidation is performed. The formation of objects is limited to the very surface layer of the container. Only a small amount of oxygen is lost from the discharge space by this process.

Here, specific materials as the material of the hermetic container having a high hydrogen permeability are listed. Palladium (Pd), nickel (Ni), iron (Fe), 400 series stainless steel, iron / nickel alloy (Fe—Ni), Nickel: a copper (Ni-Cu) alloy. Of course, in addition to the substances listed here, a substance having hydrogen permeability with the above-described H ₂ permeability as one may be used.
In an airtight container made of palladium (Pd), nickel (Ni), iron (Fe), 400 series stainless steel, iron-nickel alloy, nickel-copper (Cu) alloy, zirconium (Zr), Zr-Al or Zr By enclosing a getter material such as zirconium alloy such as -V-Fe, titanium (Ti), tantalum (Ta), or yttrium (Y), a hydrogen selective getter can be configured.

  Further, in the hydrogen selective getter described above, as shown in FIG. 6, it is possible to provide hydrogen selectivity by providing a plating layer on the entire surface of the getter material. In such a case, nickel (Ni), palladium (Pd), or the like can be suitably used as a substance that covers the surface of the getter material 17.

The getter having the hydrogen selectivity described above is preferably provided at a position where the temperature is 500 to 800 ° C. when the lamp is turned on. This is because if the temperature is too low, the rate at which hydrogen (H ₂ ) permeates through the hermetic vessel is reduced, resulting in insufficient hydrogen removal, while if the temperature is too high, hydrogen is transferred from the getter material to the discharge space. Because it will be released. In the lamp, by providing a hydrogen-selective getter inside the sealed tube portion, the temperature condition of the getter material is satisfied, and the expected action and effect are efficiently achieved.

Hereinafter, the present invention will be described based on experimental examples.
Based on the basic configuration shown in FIG. 1, xenon short arc lamps 1 to 9 having different specifications were produced. The specifications of the lamps 1 to 9 are summarized in Table 1 shown in FIG.
The lamp 1 is a lamp according to a reference example of the present invention, and is a conventional xenon lamp for a film projector. The rated power consumption is 3500 W, the cathode tip diameter is 0.9 mm, the current density is 104 A / cm ² , the tube wall load is 20.6 A / cm ² , and the cone angle at the cathode tip is 40 °. The arc tube had an inner surface area of 170 cm ³ and an inner volume of 217 cm ³ , and the xenon gas filling pressure was 0.6 MPa in terms of normal temperature (25 ° C.).
The lamps 2 to 9 are all xenon lamps for DLP digital projectors, and the basic specifications are the same. That is, the rated power consumption was 4000 W, the cathode tip diameter was 0.6 mm, the current density was 119 A / cm ² , the tube wall load was 37.5 A / cm ² , and the cone angle at the cathode tip was 60 °. The arc tube had an inner surface area of 107 cm ³ and an inner volume of 135 cm ³ , and the xenon gas filling pressure was 1.6 MPa in terms of normal temperature (25 ° C.). Such a specification makes it possible to efficiently collect light in a small area of 0.7 to 1 inch (17.8 to 25.4 mm) diagonally, and is suitable as a light source for a digital projector. It is an essential requirement to obtain a short arc lamp.

Each item in the table of FIG. 6 is defined as follows.
The “current density” is a current density obtained by dividing the lamp current by the cross-sectional area at a position of 0.5 mm from the cathode tip, and the unit is A / mm ² .
The “tube wall load” is a value obtained by dividing the lamp power by the inner surface area of the value obtained by dividing the lamp power by the inner surface area in the swollen portion (the arc tube portion) of the arc tube, and the unit is W / cm ² .
“The arc tube inner surface OH concentration” is an average OH group concentration in a thickness range of 150 μm from the inner surface of the arc tube.
The “OH concentration in the arc tube” is the OH group concentration at the center (about ½ part of the thickness) of the inner and outer surfaces of the arc tube.
The OH group concentration in the quartz glass of such an arc tube can be calculated from the relationship between the etching depth and the infrared absorbance after etching the inside of the arc tube with hydrofluoric acid.
“OH group amount / internal volume” means the OH group amount existing on the inner surface (150 μm) of the arc tube portion (only the bulging portion of the arc tube), and the entire content of the lamp including the arc tube portion and the sealing tube portion. The number of moles per unit volume divided by the product.
In addition, the “flicker life” is that the fluctuation of the luminance distribution of the lamp due to the occurrence of flicker correlates with the fluctuation of the lamp voltage, and when the fluctuation width of the lamp voltage exceeds 1 V, it is visually recognized as flicker on the screen. It was uniformly measured as the lighting time when the fluctuation range of the lamp voltage reached 1V.

[Reference Example 1]
The lamp 1 (Reference Example 1) is a xenon short arc lamp used as a light source of a film projector.
The arc tube was manufactured using dry gas (N ₂ ) when the arc tube was expanded in the molding process. As can be seen from the fact that the OH concentration inside the arc tube and the OH concentration inside the arc tube are both equal to 5 wt-ppm, the OH group concentration on the inner surface of the arc tube is maintained at the level of the raw material before molding. Met.
In addition, a tantalum getter is formed on the cathode of the lamp 1 for the purpose of forming a carbonized layer on the surface of the tapered portion excluding the tip of the main body portion by a conventionally known method and occluding H ₂ to improve the startability of the lamp. Were attached at positions immediately behind the cathode shaft portion, the cathode body of the anode shaft portion, and the anode body 15a. Tantalum was composed of a single substance.
When this lamp 1 was turned on, the flicker life was 3500 h, and a long service life could be obtained.
Furthermore, when the lamp 1 was analyzed, the inside of the arc tube included a carbonized layer at the cathode tip, and 1.8 μmol / cm per inner volume of the arc tube (including both the arc tube portion and the sealing tube portion). It was revealed that ³ carbons were present.

[Reference Example 2]
The lamp 2 (Reference Example 2) is a xenon short arc lamp for a digital projector for DLP, and has a high sealing pressure, a cathode tip current density, and a tube wall load in order to obtain a high-intensity lamp. Specific specifications are as described above.
In the arc tube forming process, when the arc tube is inflated, a dry gas (N ₂ ) is used in the same manner as the lamp 1, and the concentration of OH groups on the inner surface of the arc tube maintains the level of the raw material before molding, It was as low as 5 wt-ppm. Similarly to the lamp 1, a carbonized layer was formed on the surface of the tapered portion of the cathode body by a conventionally known method, and a tantalum getter was disposed inside the arc tube. Tantalum was composed of a single substance.
When such a lamp 2 was turned on, the flicker life was 260 hours, which was extremely short compared to the lamp 1.
Further, when the lamp 2 was analyzed, the total amount of carbon inside the arc tube was 2.1 μmol per 1 cm ³ of the arc tube inner volume. The molar ratio of tantalum constituting the getter to carbon was 31.

FIG. 8 schematically shows how the cathode tip is deformed by observing the flicker phenomenon of the xenon short arc lamp in the lamp 2 (Reference Example 2). A smooth state is maintained after lighting for 200 hours, but when the cathode tip is eventually deformed to form irregularities, the discharge start point moves between the convex parts (arc jump), and flicker occurs. Confirmed to start.
In other words, the discharge is stable even if the cathode tip is consumed and the tip surface becomes large, but if the deformation further progresses and the tip surface becomes uneven, the discharge starting point moves between the protrusions. Flicker. In the lamp of the high load specification for the lamp according to this reference example, the temperature at the tip of the cathode is high, and such deformation progresses quickly, so that the flicker life is considered to be short.

  Further, a plurality of lamps having the same specifications as the lamp 2 were turned on, and the cathode of the lamp before flickering and the cathode of the lamp after flickering were analyzed by an X-ray photoelectron spectrometer (XPS). As a result, tungsten carbide was present at the cathode tip of the lamp before the former flickering, but not at the cathode tip of the lamp after the latter flickering. From this, the inventors have found that when carbon is transported to the cathode tip and tungsten carbide is produced, the cathode tip surface is not uneven, but when tungsten carbide is no longer produced, the cathode tip surface is uneven and flickers. I guessed that it would occur.

In other words, this phenomenon is summarized as follows. Water in the arc tube reacts with carbon in the arc tube to generate CO, which diffuses in the gas phase in the discharge space and is transported to the cathode tip. More specifically, as CO diffuses through the air and enters the arc, decomposition and ionization occur due to the high temperature, and C ⁺ ions are transported to the cathode tip by the electric field in the arc. Therefore, in order to improve the flicker life, it is necessary to maintain the production of CO for a long time.

[Reference Example 3]
The lamp 3 (Reference Example 3) is a lamp using an arc tube having a high OH group concentration in the inner surface layer as a water supply source for a long time. The lamp 3 was manufactured in the same manner as the lamp 2 except for the structure related to the OH group concentration.

  Here, the layer having a high OH group concentration can be formed on the inner surface of the arc tube glass as follows, for example. That is, in the arc tube forming step for expanding the arc tube, a layer having a high OH group concentration is formed on the inner surface of the arc tube glass by blowing a pressurized gas containing water vapor into the quartz glass tube heated to a working temperature or higher. be able to. The pressurized gas can contain water vapor by passing through the water, and the water content of the pressurized gas and the OH group concentration of the inner surface layer of the arc tube can be controlled by adjusting the water temperature. For example, when a quartz glass tube heated to 2500 ° C. is expanded using pressurized gas (nitrogen) passed through water at 25 ° C., an average OH group concentration of about 150 μm in thickness is obtained in about 2 minutes. An inner surface layer of the arc tube that is increased to about 100 wt-ppm can be formed. When the water temperature is 80 ° C., the average OH group concentration with a thickness of about 150 μm is about 350 wt-ppm when other processing conditions are the same.

By such means, an average OH group concentration having a thickness of about 150 μm was produced by increasing the OH group concentration of the arc tube to 100 wt-ppm. Details are shown in the table of FIG.
However, in this lamp 3 as well, the effect of improving the flicker life is limited. The reason for this is thought to be that although the supply of water for generating CO increased, the amount of carbon was insufficient.

[Reference Example 4]
Therefore, a lamp 4 (Reference Example 4) with an increased amount of carbon in the arc tube was manufactured.
The lamp 4 (Reference Example 4) is the same as the lamp 3 (Reference Example 3) in that an arc tube having a high OH group concentration in the inner surface layer is used as a source of water for a long time.
Here, various methods for increasing the amount of carbon are studied. In this example, the area for carbonizing the cathode surface was increased. The amount of carbon existing inside the arc tube, that is, the amount of carbon disposed at the cathode or anode of the cathode tip is, for example, the amount of coating agent containing carbon, the region where the carbonized layer is formed in the carbonized layer forming step. It can be adjusted according to the surface area and the temperature of the high-temperature carburizing treatment.
When the lighting test of the lamp 4 was carried out, the flicker life was extended to 470 hours, and an unprecedented improvement was recognized. This is presumably because the generation of CO and the supply of carbon to the cathode tip are maintained for a long time by a sufficient amount of carbon and moisture released from the inner surface of the arc tube.
As a result of further analysis of the lamp 4, the amount of carbon present in the arc tube was 2.4 μmol with respect to the inner volume of 1 cm ³ of the arc tube.

[Reference Example 5]
A lamp 5 (reference example 5) having the same configuration as that of the lamp 4 (reference example 4) except that the amount of carburizing to the cathode was further increased was produced. When this lamp 5 was turned on, the flicker life was 540 hours, and the service life could be further extended. When the amount of carbon in the lamp 5 was analyzed, it was 3.0 μmol with respect to the inner volume of 1 cm ³ of the arc tube.

[Reference Example 6]
Subsequently, a lamp 6 (Reference Example 6) having the same configuration as that of the lamp 5 (Reference Example 5) except that the OH group concentration in the surface layer inside the arc tube was further increased. The OH group concentration on the inner surface of the arc tube of the lamp 6 was 350 wt-ppm. FIG. 9 shows how the shape of the cathode tip of the lamp 6 (Reference Example 6) changes.
The lamp 6 had a flicker life of 650 h, and the service life could be further extended.
When the amount of carbon in the lamp 6 was analyzed, it was 0.54 μmol / cm ³ with respect to the inner volume of the arc tube.

[Reference Example 7]
A lamp 7 (Reference Example 7) having the same configuration as that of the lamp 6 (Reference Example 6) except that the amount of carburizing to the cathode was further increased. FIG. 10 shows a change in the shape of the cathode tip in the lamp 7 (Reference Example 7).
The lamp 7 had a flicker life of 910 hours, and the service life could be further extended.
When the amount of carbon in the lamp 6 was analyzed, it was 5.2 μmol / cm ³ with respect to the inner volume of the arc tube.

  Examination of the above lamps 4 to 7 (Reference Examples 4, 5, 6, and 7) shows that the flicker life becomes longer as the amount of carbon increases and the OH group concentration further increases. Further, as can be seen from the comparison between FIGS. 8 and 9, it can be seen that the lamp 7 having a larger amount of carbon (Reference Example 7) has a slower occurrence of unevenness at the cathode tip.

By the way, in the said lamp | ramp 1-lamp 7, the getter which consists of a single-piece | unit tantalum was equipped normally. This tantalum getter is provided in order to prevent this because H ₂ is generated when moisture is present in the lamp and the startability of the lamp deteriorates. However, since the tantalum getter occludes CO and O _{2 in} addition to hydrogen, it is considered that the function of supplying carbon to the cathode tip is also hindered.
Therefore, the present inventors tried to enclose a getter material constituting a single getter such as tantalum in an airtight container having a high hydrogen permeability and disposing it inside the arc tube.

[Example 1]
The lamp 8 (Example 1) is a xenon short arc lamp in which a hydrogen-permeable getter configured by sealing tantalum as a getter material in an airtight container is disposed inside the arc tube. The basic specifications other than the getter were the same as those of the lamp 6.
In the getter 17 according to the present embodiment, a nickel (Ni) elongated tube sealed at both ends is used as the hermetic container 17B, and powdered yttrium (Y) as a getter material is enclosed therein. did. This airtight container was fixed to the anode shaft portion and disposed inside the sealed tube portion. The amount of tantalum sealed inside the nickel pipe constituting the airtight container 17B was 22 in terms of the molar ratio to carbon.
When the lamp 8 (Example 1) was evaluated, the flicker life could be extended up to 820 h. That is, it was 170 hours longer than the lamp 6 having substantially the same specifications except for the getter. This is because the getter material occludes hydrogen gas (H ₂ ) and removes hydrogen from the discharge space, so that the startability is improved and the getter material is sealed in an airtight container having low permeability to oxides. As a result, the amount of CO occluded in the getter material is reduced, and carbon is reliably supplied to the cathode tip. As a result, deformation of the cathode tip shape can be suppressed for a long time. In addition, in the lamp 8, the increase of the dielectric breakdown voltage is suppressed, and the startability can be maintained well compared with the lamp 6 and the lamp 7 arranged in the arc tube with the getter material exposed.

Furthermore, the inventors changed the structure of the getter as compared with the lamp 6 (Reference Example 6), and manufactured the lamp 9 (Example 2) having the same specifications as the others.
In the getter according to Example 2, an elongated tube made of palladium (Pd) sealed at both ends was used as the hermetic container 17B, and powdered tantalum serving as a getter material was enclosed therein. In addition, the quantity with respect to carbon of the tantalum enclosed with the inside of the palladium pipe | tube which comprises the airtight container 17B was 22 in the ratio converted into the mole.
According to the lamp of this lamp 9 (Example 2), the flicker life is about 780 h longer than that of the lamp 6, and it is confirmed that the life is improved by using a hydrogen selective getter in this example as well. It was. Furthermore, it was confirmed that the increase in dielectric breakdown voltage was suppressed and the startability was excellent.
When the amount of carbon in the lamp 9 was analyzed, it was 3.0 μmol / cm ³ with respect to the inner volume of the arc tube.

In the lamps 8 and 9 according to the above-described embodiments, yttrium and tantalum are used as the getter materials. However, the present invention is not limited to this, and other materials such as zirconium (Zr), zirconium alloy, titanium (Ti), and the like are employed. You can also. In addition to the nickel (Ni) and palladium (Pd) described above, the airtight container includes iron (Fe), 400 series stainless steel, iron / nickel alloy, nickel / copper (Cu) alloy, etc. It is also possible to use substances. As the material constituting the airtight container, it shall have desirable transmittance of _{H 2} is ^{10 -5 cc (N.T.P) / cm} 2 · s or more at 500 ° C.. Further, the structure is not limited to the configuration in which the getter material is sealed in the airtight container, and a plating layer can be applied to the entire surface of the getter material.

By the way, in the lamps 1 to 9 according to the above reference examples and examples, the carbon (C) supply source was provided mainly by forming a carbonized layer on the surface layer of the cathode. The present inventors further examined whether or not a carbon supply source is disposed in a metal part inside the lamp such as an anode body, a cathode shaft portion, an electrode portion such as an anode shaft portion, etc., and the flicker life can be extended. As a result, it was confirmed that the same effect as that obtained when the carbonized layer was provided on the cathode was obtained.
And it goes without saying that the location where such a hydrogen-selective getter is attached is not limited to the configuration shown in FIG. The hydrogen-selective getter according to the present invention may be appropriately adjusted in the arrangement position in the arc tube in consideration of the relationship between the gas storage characteristics and temperature of the hermetic container, the plating layer and the getter material constituting the hydrogen-selective getter. However, it is not limited to the scope described in this specification.

DESCRIPTION OF SYMBOLS 10 Xenon short arc lamp 11 Light emission tube 12 Light emission tube part 13a Restriction part 13 Sealing tube part 13b Sealing part 14 Cathode 14a Cathode main body 14b Cathode axial part 15 Anode 15a Anode main body 15b Anode axial part 16 Glass body 17 Getter 17A Getter material 17B Airtight container 18 Getter 18A Getter material 18B Plating layer L Electrode shaft

Claims (6)

The anode,
A cathode with a cathode body made of tungsten with an electron-emitting material;
A xenon short arc lamp for a digital projector comprising an arc tube made of quartz glass,
The cathode has a striped phase of tungsten carbide in the phase of tungsten (W) on the surface layer on the tip surface,
In the arc tube, carbon and / or carbide is provided,
The OH group concentration on the inner surface of the arc tube is 100 wt-ppm or more,
A xenon short arc lamp for a digital projector, comprising a getter having hydrogen selectivity inside the arc tube.
2. The xenon short arc lamp for a digital projector according to claim 1, wherein the hydrogen-selective getter comprises an air-tight container having hydrogen permeability and a getter material enclosed in the air-tight container.
The airtight container is made of any one of palladium (Pd), nickel (Ni), iron (Fe), 400 series stainless steel, iron-nickel alloy, and nickel-copper (Cu) alloy. Xenon short arc lamp for the digital projector described.
The xenon short arc lamp for a digital projector according to claim 1, wherein the hydrogen-selective getter comprises a getter material and a plating layer covering the surface of the getter material.
The getter material is made of at least one of zirconium (Zr), zirconium alloy, titanium (Ti), tantalum (Ta), and yttrium (Y), according to any one of claims 1 to 4. Xenon short arc lamp for digital projector.
The xenon short arc lamp for a digital projector according to claim 1, wherein the hydrogen-selective getter is provided inside a sealed tube portion of the arc tube.

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