JPH11135066A - Metal vapor discharge lamp - Google Patents

Abstract

(57) [Abstract] [Object] The present invention suppresses the corrosive action of molybdenum foil by gallium, which is an additive in the arc tube, and has a long life without fear of leakage of the arc tube throughout the life of the lamp. An object of the present invention is to provide a metal vapor discharge lamp which is excellent as a light source for photochemical reaction and has excellent lamp life characteristics and optical characteristics. The present invention is characterized in that sealing portions are formed at both ends of an arc tube made of quartz glass, an electrode connected through molybdenum foil and an external lead wire are embedded in the sealing portion, and an inside of the arc tube is formed. Gallium is sealed together with mercury, rare gas and halogen.
The surface of the molybdenum foil exposed in a gap formed around the connection between the electrode mandrel and the molybdenum foil in the sealing portion is covered with tantalum, tungsten or a composite of tantalum and tungsten.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source for a photochemical reaction, and more particularly to an improvement in an arc tube for a metal vapor discharge lamp used in a plate making apparatus.

[0002]

2. Description of the Related Art Photochemical light sources are used in various industrial fields. For example, in the printing field, a photosensitive ink or resin is applied to printed matter, and the printed matter is irradiated with ultraviolet light or visible light having a short wavelength to cause a chemical reaction of the ink or resin, thereby drying and curing. In addition, a plate-making printing apparatus called a plate making machine for producing a plate by forming a pattern by irradiating a light-irradiated or unirradiated part with a positive film and forming a pattern on a photosensitive agent is commercially available.

[0003] Various light sources such as a water-cooled ultra-high pressure mercury lamp, a xenon lamp, and a metal halide lamp have been used as light sources for a printing plate machine. Among them, the radiation efficiency of light having a wavelength effective for a photochemical reaction is excellent. Metal halide lamps are used.

In the case of utilizing a photochemical reaction, it is important from the viewpoint of efficiency to irradiate light having a wavelength suitable for the sensitivity of the photosensitive agent. A PS plate in which a photosensitive agent is applied to a thin aluminum plate is used as an irradiation target used in the printing plate machine. This type of photosensitizer absorbs light having a wavelength of 350 nm to 450 nm and causes a photochemical reaction. Therefore, gallium (Ga) is sealed as a luminescent metal in a metal halide lamp for a printing plate, and the light having a wavelength of 350 nm to 450 nm is efficiently emitted. It radiates well.

[0005] However, gallium metal or gallium halide has a property of corroding molybdenum foil as a metal foil which is an electrode sealing material at both ends of a quartz arc tube. When the molybdenum foil used for the sealing portion reacts with gallium as a light emitting metal to make the inside of the arc tube airtight, an alloy of molybdenum and gallium is generated. The reaction of gallium to molybdenum varies, and greatly affects lamp characteristics. For example, molybdenum foil becomes brittle and its mechanical strength is reduced, so that the molybdenum foil breaks due to the thermal expansion of the electrode when the lamp is turned on and off, causing the lamp to become inconsistent and alloying with the molybdenum foil at a high concentration. Thus, the volume expansion of the molybdenum foil is promoted, a crack is generated in the sealing portion, and finally the arc tube leaks. Thus, there is a problem that the lamp to which gallium is added has a short life.

[0006]

The present inventor has made various studies on the corrosion effect of the molybdenum foil due to gallium. As a result, it has been found that the above-mentioned effect occurs as follows. In general, metal halide lamp is
As disclosed in Japanese Patent No. 8228, it is well known that a luminescent metal is encapsulated in excess of iodine in order to suppress generation of iodine as free halogen in an arc tube.

[0007] The metal halide lamp for the plate printing machine is also designed in the same manner as described above, but the excess gallium added to the arc tube causes the bottom of the innermost end of the arc tube, which is the coldest portion of the lamp, during lamp operation. It accumulates, and then passes through a gap between the electrode mandrel of the sealing portion and the quartz glass, and accumulates in a gap formed around the connection between the electrode mandrel and the molybdenum foil. This is because gallium becomes a liquid at about 29 ° C. or higher, and surface tension is applied to narrow places in the gaps, especially around the connection between the electrode mandrel and the molybdenum foil and around the sealing part between the quartz glass and the molybdenum foil. This is because they have the property of accumulating.

[0008] As gallium accumulates in such a location, the corrosive action of gallium on the molybdenum foil increases. Around the connection between the electrode mandrel and the molybdenum foil,
Gallium reacts with molybdenum to form a gallium-molybdenum alloy. This alloy is initially deposited on the surface of the molybdenum foil, but gradually corrodes the molybdenum foil and grows as granular crystals, and finally, the molybdenum foil around the connection portion is changed to granular crystals of a gallium-molybdenum alloy.

[0009] Since the molybdenum foil in this state is no longer an aggregate of granular substances, the bonding strength between crystals, that is, the mechanical strength is weak. For this reason, the electrical coupling is broken due to the stress due to the thermal expansion of the electrodes accompanying the turning on and off of the lamp. Then, electric energy is no longer supplied to the electrodes, so that the discharge cannot be maintained.

[0010] Further, gallium reacts with molybdenum around the sealing portion between the quartz glass and the molybdenum foil, and granular crystals precipitate on the surface of the molybdenum foil in the same manner as described above. Then, as the granular crystals gradually grow, a stress is generated that peels off the sealing portion from the end of the sealing portion between the quartz glass and the molybdenum foil,
Its power increases as the alloy grows. Eventually, a phenomenon occurs in which the sealing portion cannot withstand the stress, glass cracks occur, and the airtightness of the arc tube cannot be maintained.

[0011] The present invention has been made in view of the above, and suppresses the corrosive action of molybdenum foil by gallium, which is an arc tube additive, and has a long life without fear of leakage of the arc tube throughout the life of the lamp. It is another object of the present invention to provide a metal vapor discharge lamp which is optimal as a light source for photochemical reaction and has excellent lamp life characteristics and optical characteristics.

[0012]

In order to achieve the above object, a metal vapor discharge lamp according to the present invention has sealing portions formed at both ends of a quartz glass arc tube, and a molybdenum foil is formed on the sealing portions. An electrode and an external lead-in connected through the buried electrode are buried, and mercury, a rare gas, and gallium are sealed together with halogen inside the arc tube, and a connection portion between the electrode mandrel and the molybdenum foil in the sealing portion is formed. The surface of the molybdenum foil exposed in the gap formed in the periphery is covered with tantalum, tungsten or a composite of tantalum and tungsten.

[0013] By coating the surface of the molybdenum foil with tantalum or tungsten, the gallium and the molybdenum foil do not come into direct contact with each other, so that the reaction between the gallium and the molybdenum does not occur. Further, since tantalum and tungsten do not react with gallium, a molybdenum alloy is not generated, and no granular crystals are generated. In addition, there is no inconvenience of the lamp due to leakage or crack of the arc tube.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing one embodiment of a metal vapor discharge lamp according to the present invention, and FIG. 2 is an enlarged view of a main part. In a metal halide lamp 1 shown in FIG. 1, sealing portions 3 are formed at both ends of an arc tube 2 made of quartz glass, and molybdenum foil 4 is embedded in the sealing portions. An electrode 5 made of a refractory metal such as tungsten is connected to one end of the molybdenum foil, and an external lead wire 6 made of tungsten is connected to the other end. The arc tube is filled with mercury, rare gas, halogen and gallium. Then, when power is supplied from outside the lamp, a discharge occurs between both electrodes of the arc tube,
The vapors of the mercury and gallium halides are excited by the electrons and emit mainly 350 nm to 450 nm light.

FIG. 2 is an enlarged view of the vicinity of the electrode portion and the sealing portion of the arc tube 2. Before encapsulating the additive in the arc tube, a pair of electrode mounts including the molybdenum foil 4, the tungsten electrode mandrel 5a of the electrode 5, and the external lead wire 6 are inserted into a quartz glass tube to melt the portion. The sealing is performed by performing a so-called pinch seal, but as shown in the drawing, a void 7 is formed around the connection portion due to the viscosity of the fused quartz glass. After that, the vacuum tube is connected to a vacuum exhaust device (not shown) formed in the center of the arc tube,
After exhausting the impure gas in the tube, the additive and a rare gas at a predetermined pressure are sealed.

Next, specific structures of the arc tube and the electrode mount will be described. The dimensions of the arc tube 2 are 19 mm in inner diameter, the distance between the electrodes 5 and 5 is 232 mm, and 100 mg
Of mercury, 18 mg of mercury iodide and 5 mg of gallium are sealed with 4 × 10 ⁴ Pa xenon gas. The electrode 5 has a 0.8 mm diameter tungsten wire wound around the tip of a 2 mm diameter thoriated tungsten electrode mandrel 5a.

The molybdenum foil 4 has a width of 5 mm, a length of 20 mm,
This is a metal foil for sealing glass having a thickness of about 35 μm and having a substantially rectangular edge and a knife edge 4a. Further, tantalum 8 is coated with a thickness of about 1 micrometer from the end of the molybdenum foil 4 on the side to which the electrode mandrel 5a is connected to a position of about 10 mm. In addition, the PVD method (particularly, the sputtering method) is effective as a coating method of tantalum, but rolling joining is also possible.

Further, an external lead wire 6 made of tungsten having a diameter of 2 mm is connected to the other end of the molybdenum foil 4. The metal halide lamp thus configured starts discharging to the external introduction lines at both ends of the arc tube, and a ballast for stably supplying power is connected. When the lamp is stably operated, the lamp power is 6 kW, the lamp voltage is 400V, lamp current 16
A is lit.

When the lamp having the above configuration is turned on, mercury and gallium sealed in the arc tube become halide vapors, dissociate in the discharge plasma, and excite to emit light having a spectrum unique to mercury and gallium. . Also, a part of the excessively filled gallium accumulates in the coldest part of the arc tube and accumulates in the space around the connection between the electrode mandrel and the molybdenum foil as the lighting time elapses. Since the surface of the molybdenum foil exposed in the void (gap) is coated with tantalum, gallium does not react with molybdenum,
No gallium-molybdenum alloy is formed. Thereby, stable life characteristics can be maintained.

Further, the gallium in the coldest part remains as a metal, and the amount consumed by lighting the lamp can be supplemented, so that the gallium concentration in the plasma becomes constant, and a good ultraviolet radiation intensity throughout the lifetime is obtained. Can be maintained.

Generally, in the case of a plate making light source, it is used under the condition that the frequency of blinking is high, that is, the lighting (time required for printing) is repeated for 20 to 30 seconds and the light is repeatedly turned on in a cycle of about 40 seconds. In order to confirm the life characteristics of the discharge lamp according to the present invention, ten metal halide lamps according to the present invention and ten conventional lamps were prepared, and a blinking test was performed in a cycle of 20 seconds on and 40 seconds off. FIG. 3 shows the residual ratio characteristics.

FIG. 3 shows the life characteristics measured by the remaining ratio of the lamp with respect to the number of blinks. Here, the residual rate is ((the number of test pieces−the number of cracks, the number of spots where defects have occurred) / the number of test pieces × 10
0). In the figure, the solid line shows the residual ratio curve of the lamp of the present invention, and the broken line shows the residual ratio curve of the conventional lamp. As is clear from FIG. 3, the lamp of the present invention has a number of blinks of 1000 × 1.
Even at 0 ³ (about 5000 hours), there was no lamp defect associated with leaks and cracks in the arc tube.

In the above embodiment, the case where tantalum is used as the metal to be coated on the molybdenum foil has been described. However, tungsten or a composite of tantalum and tungsten also has a reaction resistance to gallium.
It can be used similarly to tantalum. Further, in the above-described embodiment, the connection portion between the electrode mandrel and the molybdenum foil is coated with tantalum. However, even if the entire surface of the molybdenum foil is coated, similar characteristics can be obtained and workability is good.

[0024]

As described above, according to the present invention, since the surface of the molybdenum foil exposed at least in the gap formed at the connection between the electrode mandrel and the molybdenum foil is coated with tantalum or tungsten, gallium and molybdenum do not come into contact with each other. Since no alloy is formed, no breakage of the molybdenum foil or cracks in the quartz glass of the sealing portion occurs with the passage of the lighting time, and as a light source for optical devices with good lamp characteristics such as life characteristics and ultraviolet radiation characteristics. An optimal metal vapor discharge lamp can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view of a metal vapor discharge lamp showing one embodiment of the present invention.

2 is an enlarged view of a main part showing a connection portion and a sealing portion between an electrode mandrel and molybdenum foil of the arc tube of FIG. 1;

FIG. 3 is a characteristic diagram showing a change in a remaining rate in a life test by blinking of a metal halide lamp according to the present invention and a conventional lamp.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal halide lamp 2 Arc tube 3 Sealing part 4 Molybdenum foil 5 Electrode 5a Electrode mandrel 6 External introduction wire 7 Void 8 Tantalum coating part

Claims (1)

[Claims] 1. A sealed portion is formed at both ends of an arc tube made of quartz glass, an electrode connected via a molybdenum foil and an external lead wire are embedded in the sealed portion, and mercury is introduced into the arc tube. In a metal vapor discharge lamp in which gallium is sealed together with a rare gas and a halogen, the surface of the molybdenum foil exposed in a gap formed around the connection between the electrode mandrel and the molybdenum foil in the sealing portion is tantalum, tungsten or tantalum. A metal vapor discharge lamp characterized by being coated with a composite of tungsten and tungsten.