KR101373872B1 - Short arc type discharge lamp - Google Patents

Abstract

The present invention relates to a short-arc discharge lamp in which a pair of cathodes and anodes are disposed opposite to each other in a light tube, in particular, full standby lighting that repeats normal lighting at rated power and standby lighting lighting at a smaller power than this. Also in the city, the electrode structure is provided so that the center portion of the anode tip does not protrude from the peripheral annular portion thereof and the blackening of the lamp due to evaporation of the electrode material does not occur.
A concave portion is formed in the front end surface of the anode, an insert made of the same material as the anode is inserted into the concave portion, and a space is formed between the rear end of the insert and the concave portion.

Description

Short arc type discharge lamp {SHORT ARC TYPE DISCHARGE LAMP}

TECHNICAL FIELD This invention relates to a short arc type discharge lamp. Specifically, It is related with the short arc type discharge lamp applied to the light source for exposures, such as the manufacturing field of a semiconductor and a liquid crystal, and the light source for backlight of a projector.

The short arc type discharge lamp is used as a light source for an exposure apparatus or a backlight of a projector by combining with an optical system because the distal end distance of the pair of electrodes disposed in the light emitting tube is short and close to the point light source.

Japanese Patent Laid-Open No. 10-188890 discloses a conventional short arc type discharge lamp.

The conventional short arc type discharge lamp is shown by FIG. 4, The light emitting tube 10 of the short arc type discharge lamp 1 has the light emitting part 11 formed in the substantially spherical shape located in the center, and The sealing part 12 is provided. In the light emitting tube 10, a cathode 21 made of tungsten or the like and an anode 31 are disposed to face each other, and a light emitting material such as mercury and xenon is enclosed in the light emitting space S therein.

Electrode shafts 22 and 32 provided after the cathode 21 and anode 31 are sealed by the sealing portion 12 via a metal foil (not shown).

In recent years, however, in the short arc type discharge lamp used in the manufacturing process of a semiconductor or a liquid crystal panel, as shown in Japanese Patent Laid-Open No. 2000-181075, the lamp is always lit with a constant power to save power. The lighting method is to turn on (normal lighting) at rated power only during exposure, and to turn on (standby lighting) at a minimum power smaller than the rated power when waiting for substrate movement, etc. (hereinafter referred to as full standby lighting). Is adopted.

For example, it is repeated to light 0.1-10 second at rated power at the time of exposure, and to light 0.1-100 second at standby power smaller than rated power at the time of standby.

By the way, when the lamp is turned on or off, or when the input power is changed at the time of full standby lighting, the heat flux flowing from the arc to the anode changes, so that the anode temperature changes, and the anode has an internal stress. Occurs.

At this time, as shown to FIG. 5 (A), (B), the center part 50 of the anode front end surface which faces an arc is the part with the largest temperature change, and also thermal expansion becomes large. In contrast, the annular portion 51 around the central portion 50 has a smaller temperature change than the central portion 50, and its thermal expansion is also smaller.

Therefore, the center part 50 is subjected to compressive stress from the peripheral annular part 51 by such thermal expansion, and as a result, it deform | transforms so that it may protrude from a front end surface.

Such projection remains even after the temperature at the tip of the anode is stabilized at the rated lighting time, without returning to the original shape completely. In addition, in the case of the full standby lighting in particular, such deformation occurs repeatedly, and the protrusions accumulate and enlarge.

Then, the discharge concentrates on the enlarged protrusion, the protrusion abnormally overheats, the electrode material evaporates, adheres to the inner wall of the light emitting tube, and the inner wall of the light emitting tube is blackened, causing a rapid decrease in illuminance.

Japanese Patent Laid-Open No. 10-188890 Japanese Patent Publication No. 2000-181075

The problem to be solved by the present invention is to solve the problems of the prior art, in particular, in a short arc discharge lamp employing a full standby lighting method, to reduce the thermal stress generated at the tip of the anode, the center portion of the tip of the anode It is an object of the present invention to provide a short arc type discharge lamp having an anode structure capable of preventing this deformation and preventing blackening.

In order to solve the said subject, in the short arc type discharge lamp which concerns on this invention, the recessed part is formed in the front-end surface of the said anode, the insert which consists of the same material as the anode is inserted in the recessed part, and this insert A space is formed between the rear end of the and the concave portion.

The space is characterized in that at least part of the space exists within the range of the thermal diffusion length from the tip of the anode.

The space is characterized by being in the range of S ≦ πL ² when the distance from the positive electrode end face to the space is L and the maximum cross-sectional area of the space in the vertical cross section with respect to the electrode axis is S.

According to the short arc type discharge lamp of the present invention, an insert made of the same material as the anode is inserted into a recess formed at the tip of the anode, and a space is formed between the rear end of the insert and the recess. In particular, even when the temperature of the tip portion of the anode changes during full standby lighting or the like, the thermal change is not transmitted linearly to the rear as it is due to the presence of the space, and the space permits the insert to thermally expand and contract. It functions as a release area of, suppressing deformation of the tip of the anode, that is, the insert so as to protrude. As a result, it is possible to prevent blackening of the light emitting tube due to evaporation of the electrode and to prevent a decrease in illuminance retention.

BRIEF DESCRIPTION OF THE DRAWINGS It is partial sectional drawing of the front end of the anode of the short arc type discharge lamp which concerns on this invention.
2 is a partial cross-sectional view of another embodiment.
3 is a partial cross-sectional view of yet another embodiment.
4 is a general view of the prior art.
FIG. 5 is an explanatory diagram of a main part of FIG. 4. FIG.

FIG. 1: shows 1st Embodiment, (A) is insertion part sectional drawing, (B) is explanatory drawing of an insertion process.

In the figure, at the tip of the anode 3 made of tungsten or the like, a concave portion 4 opening in the tip end surface 3A is formed. An insert 5 made of the same material as the anode 3 is inserted into the recess 4 by press-fitting or the like, and the tip end face thereof is flush with the tip end face 3A of the anode 3. Consists of

A space 6 is formed between the rear end of the insert 5 inserted in this way and the recess 4.

In FIG. 1A, the position L of the space 6 formed in the concave portion 4 is formed so that at least part thereof is within the range of the thermal diffusion length from the front end surface 3A.

In addition, the thermal diffusion length is an index indicating how far the wavelength remains when the heat (temperature) applied alternatingly diffuses in a substance, and is given by the following equation.

L = √ (α / f)

  L: thermal diffusion length (m)

  α: thermal diffusion rate (m 2 / s)

  f: repetition frequency (㎐)

Here, the thermal diffusion rate α is defined below.

α = k / (ρ × Cp)

  k: Heat transfer rate 120 (J / smK) ※ In the case of tungsten W

ρ: Density 19.1 × 10 ³ (㎏ / ㎥) * For W

  Cp: Specific heat 134.4 (J / kgK) * For W

Here, as an example, the anode 3 is made of tungsten (W),

When the repetition frequency f = 1 (Hz), L = 6.84 mm

            When f = 1000 (Pa), it is L = 0.216 mm.

The heat from the tip of the anode 3 can only be expected to be a direct-current thermal effect in the region beyond the above range, and the region exhibits no periodic temperature change. In other words, thermal distortion tends to accumulate in comparison with other portions in the region subject to periodic temperature fluctuations due to full standby lighting, resulting in irreversible deformation of the electrode.

However, due to the presence of the space formed in the anode, the thermal conduction from the tip of the anode to the rear is hindered, and the temperature difference hardly occurs and becomes almost uniform in the rear region from the space, so that the thermal distortion based on the thermal expansion difference Becomes smaller.

On the other hand, thermal expansion occurs at the tip of the anode, but since the space itself functions as a release area for distortion that allows free expansion and contraction inside the electrode, deformation of the electrode is suppressed as a result.

That is, although compressive stress occurs due to thermal expansion at the electrode tip, the compressive stress is released to the space side, so that deformation toward the electrode tip is suppressed.

On the other hand, if the space is too large, the cross-sectional area of heat conduction from the electrode tip to the rear end becomes small and the temperature near the electrode tip rises, so that the evaporation of the electrode material is promoted, and as a result, the roughness retention rate is increased. It causes a decrease.

Therefore, the size of the space 6 is preferably formed so as to satisfy the relationship of S ≦ πL ² when the cross sectional area, that is, the maximum cross sectional area in the vertical section with respect to the electrode axis is S.

FIG. 2 is a partial sectional view of the second embodiment, (A) is an insertion sectional view, and (B) is an explanatory view of an insertion step.

In this embodiment, the recessed part 4 consists of two opening 4A, 4B. 4 A of 1st openings are about the same diameter as the insert 5, and the 2nd opening 4B which is smaller than this is formed in the inside.

The insert 5 is press-fitted into the first opening 4A, and the depth is determined by the second opening 4B. The second opening 4B forms a space 6.

3 is a partial sectional view of the third embodiment, (A) is an insertion sectional view, and (B) is an insertion explanatory diagram.

In this embodiment, 5 A of annular ribs protrude from the rear end of the insert 5, and circular recessed part 5B is formed in the rear end surface. When this insert 5 is press-fitted into the recessed part 4, 5 A of annular ribs abut the bottom surface of the recessed part 4, and the said recessed part 5B forms the space 6.

According to the two embodiments shown in FIG. 2 and FIG. 3, when the insert 5 is inserted into the recess 4, the space 6 is automatically formed in contact with the bottom of the recess 4. do.

In order to compare this invention and the conventional anode, the lighting test with respect to the illumination intensity retention based on Example 1 was done.

The lamp used for the experiment has the amount of 2 mg / cc of encapsulated mercury, about 3.5 atmospheres of Ar, and the size of the positive electrode (tungsten) having a diameter of 29 mm, a total length of 50 mm, and a tip diameter of 10 mm. The cathode was 12 mm in diameter, tapered angle of 60 degrees, and tip diameter of 1 mm, and the gap before lighting was 6.5 mm.

For this test, three types of anodes were prepared, and among them, the anode of the present invention formed a concave portion 4 having a diameter of 3.5 mm and a depth of 10 mm on the tip end surface of the anode, and the concave portion 4 ), An insert 5 having a diameter of 3.5 mm and a thickness of 8 mm was press-fitted. As a result, a space 6 having a height of 2 mm is formed between the insert 5 and the bottom of the recess 4.

Moreover, as a comparative product, the thickness of the said insert was made the same as the depth of a recessed part, it pressed in in the recessed point, and the thing without space was prepared. In addition, the prior art prepared what did not perform these shaping | molding.

These lamps were subjected to an acceleration test for evaluating illuminance retention in a short time (100 hours) under periodic thermal loads of severe input modulation widths in which the lighting currents 50A and 140A were switched at 1 second intervals (0.5 mA). In addition, the illumination intensity retention calculated the illumination intensity retention after 100 hours on the basis of the ultraviolet ray intensity of wavelength 365nm (i line) at the time of lighting start in the same lighting conditions.

The results of these tests are shown in Table 1.

As can be seen from Table 1, the prior art was deformed so that the center portion of the tip end of the positive electrode protruded badly, and the tip melted. Because of the risk of rupture, the lighting test was stopped midway. The illuminance retention at this point was 52%.

The comparative product was deformed so that the press-inserted body popped out, the tip was raised, and the roughness retention was 65%.

On the other hand, this invention product had little deformation | transformation of the insert which forms a tip center part, and the roughness retention was also favorable at 85%.

As described above, in the short arc discharge lamp according to the present invention, an insert made of the same material as the anode is inserted into a recess formed at the tip of the anode, and the rear end of the insert and the recess are Since a space is formed between the bottom portions, especially when the full standby lighting method is employed, when the central portion of the tip of the anode is periodically heated, the thermal distortion is released into the space, so that it protrudes locally toward the tip. There is no deformation | transformation, and the effect that the fall of the roughness based on blackening by evaporation of a positive electrode material can be suppressed.

3: anode 3A: tip section
4: concave point 5: insert
6: Space
L: distance from the front end surface 3A of the space 6
S: cross section of the space 6

Claims (3)

In a short arc discharge lamp in which a pair of anodes and cathodes are disposed opposite to each other in a light emitting tube, and full standby is lit,
A recess is formed in the front end surface of the anode, an insert made of the same material as the anode is inserted into the recess, and a space is formed between the rear end of the insert and the recess.
The space is in the range of S ≦ πL ² when the distance from the tip surface of the anode to the space is L and the maximum cross-sectional area of the space in the vertical section with respect to the electrode axis is S. lamp. The method according to claim 1,
The space is a short arc discharge lamp, characterized in that at least part of the space is within the range of the thermal diffusion length from the tip of the anode. delete

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