JP2012038658A - Discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp which can maintain illuminance for a long time by enhancing startability of lighting.SOLUTION: In a discharge lamp, i.e., an excimer lamp, a foil electrode 30 is arranged along a tube axis C in a discharge tube 20. The foil electrode 30 is covered with a dielectric 50. Meanwhile, external electrodes 40 having a polarity different from that of the foil electrode 30 are arranged on the external surface of the discharge tube 20. Edges 30K1, 30K2 of the foil electrode 30 are formed in the shape of knife edge which becomes thinner toward the edge.

Description

  The present invention relates to an electrodeless discharge lamp such as an excimer lamp or an external electrode type fluorescent lamp that emits light by dielectric barrier discharge or capacitively coupled high-frequency discharge, and more particularly to an electrode configuration of the lamp.

  In the double cylindrical tube type excimer lamp, the light emitting portion is constituted by two coaxial cylindrical tubes that are long in the axial direction, and high-pressure gas is enclosed in the light emitting tube, and the inner tube inner surface and the outer tube outer surface along the axial direction. A pair of electrodes are arranged to face each other. Then, discharge light emission is performed by applying a high-frequency voltage of several kV between the electrodes (see, for example, Patent Document 1).

  Also, in a discharge lamp adopting a single tube structure such as an external electrode type fluorescent lamp, a strip electrode covered with a dielectric is disposed along the axial direction inside the discharge tube and disposed on the outer surface of the discharge tube. Discharge light emission between the external electrodes (see Patent Document 2).

JP-A-6-275242 JP-A-11-283579

  In the conventional discharge lamp, the electrode inside the discharge tube has a columnar shape or a thin plate shape, and its cross-sectional shape is circular or rectangular. In such a cross-sectional shape, in order to discharge between the electrode in the dielectric and the electrode outside the discharge tube, a very large electric power is required, and the start-up of the lamp is slow.

  When high power is supplied to the lamp, the electrode is likely to be peeled off from the dielectric due to the difference in thermal expansion between the dielectric covering the electrode and the electrode, and electrode oxidation may occur due to exposure of the electrode material to the discharge space. .

  The discharge lamp of the present invention is a discharge lamp that emits light by dielectric barrier discharge, capacitively coupled high frequency discharge, or the like, and includes a discharge tube in which a discharge gas is sealed, and at least one strip-shaped member disposed in the discharge vessel. An electrode, and at least one dielectric covering the electrode. A strip electrode such as a foil electrode is embedded in a dielectric and is not exposed to the discharge space. The gas to be enclosed in the discharge space is arbitrary, and a rare gas alone, a halogen alone such as chlorine, or a mixed gas of halogen and rare gas may be enclosed.

  In the present invention, the thickness of at least one of both edges along the longitudinal direction of the electrode is thinner than the central portion of the electrode. As a result, electric field concentration occurs in the thin electrode edge portion, and the electric field strength is increased. As a result, discharge occurs between the electrodes even with a relatively low input voltage.

  Several electrodes may be covered together with one dielectric, or may be covered with different dielectrics. It is desirable that the thickness of both edges of the strip electrode is made thinner than the thickness of the central portion of the electrode to improve the lighting startability at both ends of the electrode.

  Various shapes that sharpen toward the edge can be applied as the electrode shape, but it is desirable to use a knife edge shape as a shape that is smoothly pointed toward the edge. As a result, the cross-section of the edge portion is linear in the axial direction, so that the discharge start voltage level can be further reduced, and a gap is less likely to occur at the boundary portion with the dielectric covered by the knife edge shape. Etc. are less likely to occur.

  Regarding the electrode arrangement, one electrode may be disposed outside the discharge tube, or the electrode may be configured only inside the discharge tube. For example, a plurality of strip electrodes having the same polarity are arranged in the discharge tube, and the electrodes are arranged outside the discharge tube. In this case, in consideration of uniformly emitting light from the entire discharge tube, it is preferable to arrange a plurality of strip electrodes in a state where their width directions are parallel to each other. Or you may arrange | position a some strip | belt-shaped electrode in a symmetrical position about a discharge tube axis | shaft.

  On the other hand, a plurality of strip electrodes having different polarities may be arranged in the discharge tube. In this case, in consideration of radiation as uniformly as possible from the entire discharge tube, it is preferable to arrange the plurality of strip electrodes at symmetrical positions with respect to the discharge tube axis. The overall radiation can also be realized by making the width directions of the plurality of strip-like electrodes the same direction, that is, parallel to each other.

  For example, in the case of a lamp configuration in which an electrode is disposed outside the discharge tube, in order to increase the electric field strength with the electrode edge, a strip electrode is disposed coaxially within the discharge tube, and the width direction of the electrode is the diameter inside the discharge tube. It is better to match the direction. Thereby, the extension direction of the electrode edge becomes the maximum electric field intensity, and the lighting start voltage can be suppressed.

  The electrode material may be formed of a highly conductive metal or alloy. The thickness of the electrode is preferably determined in consideration of the current capacity and the expansion coefficient, and is determined in any range of 20 μm to 50 μm, for example. The width of the electrode is preferably determined in consideration of the current capacity, for example, it is preferably determined within a range of 1.2 mm to 10 mm.

  The thickness of the discharge tube has a thickness that prevents deterioration of the discharge tube due to excimer light. On the other hand, it is preferable that the thickness be set to a thickness that increases the discharge start voltage and the lighting sustain voltage. For example, the thickness of the discharge tube is determined in the range of 0.8 mm to 1.5 mm. The inner diameter of the discharge tube is desirably set within a range of 8 mm to 20 mm, for example, so that the discharge distance is short and illuminance is not insufficient, while the discharge distance is long and the discharge is not unstable.

  What is necessary is just to comprise a dielectric material with the columnar dielectric material with a circular cross section, for example. It is desirable to use an insulating material that approximates the coefficient of thermal expansion of the electrode at the operating temperature. The thickness of the dielectric is preferably in the range of 0.1 mm to 2 mm in consideration of preventing the discharge start voltage from being increased while maintaining insulation.

  The discharge distance between the electrode and another electrode having a different polarity is determined by the type of discharge gas and the applied voltage. In order to prevent the discharge interval from becoming narrow and insufficient illuminance, in order to prevent the discharge distance from becoming longer and causing the discharge to become unstable, the discharge distance is preferably set in a range of 3 mm to 10 mm.

  When the width of the strip electrode is w and the inner diameter of the discharge tube is d, it is desirable that the ratio satisfies “1.6 ≦ d / w ≦ 13.4”. If the value of d / w is smaller than 1.6, the area of the foil occupying the discharge vessel is increased, the discharge distance is shortened, the discharge light is blocked by the strip electrode, and the illuminance is insufficient. If the value of d / w is greater than 13.4, the width of the strip electrode may be small, causing overheating due to overcurrent, or increasing the discharge distance, which may result in unstable discharge.

  ADVANTAGE OF THE INVENTION According to this invention, the discharge lamp which can improve lighting startability and can maintain illumination intensity for a long time can be provided.

It is a schematic plan view of the discharge lamp which is 1st Embodiment. It is sectional drawing along II-II of FIG. It is sectional drawing to which the electrode edge part vicinity of FIG. 2 was expanded. It is the figure which showed the manufacturing process of the discharge lamp. It is a schematic sectional drawing of the discharge lamp in 2nd Embodiment. It is a schematic sectional drawing of the discharge lamp which is 3rd Embodiment. A discharge lamp according to a fourth embodiment will be described.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic plan view of a discharge lamp according to the first embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG.

  A discharge lamp 10 which is an excimer lamp includes a discharge tube 20 having a circular cross section made of a dielectric material such as quartz glass. In the discharge tube 20, a rare gas such as xenon gas or a mixed gas thereof is used as a discharge gas. It is enclosed. The sealed pressure of the discharge gas is set to, for example, 5 kPa to 150 kPa.

  Inside the discharge tube 20, one foil electrode 30 extending in a strip shape along the tube axis C is disposed. The foil electrode 30 is covered with a columnar dielectric 50 having a substantially circular cross section, and is embedded in the dielectric 50 without being exposed to the discharge space.

  The foil electrode 30 is coaxially arranged with the center position of the dielectric 50 aligned with the center position in the width direction. The dielectric 50 is disposed coaxially with the discharge tube 20. Therefore, the foil electrode 30 is disposed at a coaxial position with respect to the discharge tube 20 and is disposed at a symmetrical position with respect to the tube axis C.

  As will be described later, the edges 30K1 and 30K2 which are both edges along the tube axis direction of the foil electrode 30 are configured in a knife edge shape. Therefore, the thickness of the foil electrode 30 is reduced from the center in the width direction toward the edge, and the electrode cross-sectional shape is tapered and sharp. In FIG. 2, the width direction of the foil electrode 30 is defined as the Y direction, and the direction orthogonal to the width direction (thickness direction) is defined as the X direction.

  The external electrode 40 disposed on the outer surface of the discharge tube 20 has a configuration in which a plurality of electrode portions are disposed in a net shape, and are arranged along the tube axis C in a spiral manner at predetermined intervals. The power supply line 70 connected to the end of the foil electrode 30 is connected to a power supply unit (not shown) installed outside, and power is supplied to the discharge lamp 10 via the power supply line 70.

  The polarities of the foil electrode 30 and the external electrode 40 are determined as an anode and a cathode, respectively. When a voltage of several kV is supplied to the discharge lamp 10, dielectric barrier discharge occurs between the foil electrode 30 and the external electrode 40, and excimer light having a predetermined spectrum (for example, 172 nm) is emitted.

  The axial length of the discharge tube 20 is set to 100 mm to 250 mm. On the other hand, the thickness of the discharge tube 20 is set to 0.8 mm to 1.5 mm in order to prevent discharge tube deterioration due to excimer light and to suppress an increase in the discharge start voltage. The inner diameter of the discharge tube 20 is set to 8 mm to 20 mm so as to prevent both unstable discharge due to a long discharge distance and insufficient illuminance due to a short discharge distance.

  The thickness of the foil electrode 30 is set to 20 μm to 50 μm in consideration of current capacity, ease of manufacture, and prevention of peeling due to thermal expansion. Further, the width of the foil is set to 1.2 mm to 10 mm in consideration of current capacity, ease of manufacture, and prevention of blocking of discharge light due to enlargement of the electrode area. As the electrode material, molybdenum or an alloy containing the same is used.

  The dielectric 50 is made of a dielectric material (such as SiO 2) that approximates the thermal expansion coefficient of the electrode as much as possible. The thickness of the dielectric 50 is set to 0.1 mm to 2 mm in consideration of the limit for maintaining insulation and prevention of increase in the discharge start voltage.

A discharge distance, that is, a distance interval between the dielectric 50 and the inner diameter of the discharge tube 20 is set to 3 mm to 10 mm in consideration of prevention of insufficient illuminance and discharge stability. Further, when the width of the foil electrode 30 is w and the inner diameter of the discharge tube is d, the electrode width and the inner diameter of the discharge tube are determined so as to satisfy the following conditional expressions.

1.6 ≦ d / w ≦ 13.4 (1)

  FIG. 3 is an enlarged cross-sectional view of the vicinity of the electrode edge in FIG. However, the sizes and relative positional relationships of the electrodes, dielectrics, and discharge tubes are partially different from those in FIG.

  As described above, the edges 30K1 and 30K2 of the foil electrode 30 have a knife edge shape. The foil electrode 30 is sharpened from the center in the width direction toward the edge, the thickness thereof is thinner than the thickness T at the center in the width direction, and the edge 30T1 is sharp. The edge 30K2 (not shown) has a similar shape.

  Such an electrode shape causes electric field concentration at the edge 30T1. In other words, the electric field intensity becomes maximum in the region near the edge 30T1 (see the broken line E), and the region is narrow due to the sharp shape of the edge 30T1. This is because, in the conventional rectangular cross section having no sharp edge, electric field concentration occurs over the entire plane portion of the edge, that is, the potential gradient increases. In this embodiment, the edge 30T1 is substantially axial. This is because the electric field concentration occurs only at the edge.

  The foil electrode 30 is coaxially disposed with respect to the dielectric 50 and the discharge tube 20, and the width direction thereof is along the radial direction. Therefore, the distances (discharge distances) between the edges 30K1 and 30K2 of the foil electrode 30 and the inner surface of the discharge tube 20 are equal. Therefore, light is radiated from the discharge tube 20 as a whole with good balance.

  FIG. 4 is a diagram showing a manufacturing process of the discharge lamp.

  A power supply line 80 is connected to the foil electrode 70 by resistance welding or the like, and is inserted into a glass tube 60 serving as a dielectric coating material. After inserting the electrode 70, the inside of the tube is evacuated, and then the dielectric coating material 60 is heated from the outside and welded to the foil electrode 70 (step (1)). Note that the step of coating the dielectric may be performed instead.

  A so-called abacus-shaped sealing part 85 having a bowl shape is formed at the position of the glass tube corresponding to the electrode edge (step (2)). Then, a discharge tube 90 made of quartz glass or the like having an exhaust tube at one end and an insertion port at the other end is formed (step (3)), the electrode 70 is inserted into the discharge tube 90, and the insertion port of the discharge tube 70 is inserted. Is welded to the abacus-shaped sealing portion 85 (step (4)).

  While heating the whole, evacuation through the exhaust tube of the discharge tube 90 is performed to remove impurities. Then, after the discharge gas is sealed, the exhaust tube is sealed, and the external electrode 95 is disposed on the outer surface of the discharge tube 90 (step (5)).

  Thus, according to the present embodiment, the foil electrode 30 covered with the dielectric 50 inside the discharge tube 20 is disposed along the tube axis C. In addition, external electrodes 40 having different polarities are disposed on the outer surface of the discharge tube 20. The edges 30K1 and 30K2 of the foil electrode 30 are formed in a knife edge shape.

  Since the electrode edge is sharp, the electrolytic strength locally increases at the electrode edge, and discharge at the start of lighting occurs at a low voltage. The electrode edge serves as a trigger for starting discharge, and the illuminance is maintained even when the lamp is lit for a long time.

  Further, since the electrode edge is smoothly sharpened, a gap is not easily formed between the electrode and the dielectric, and the electrode is not exposed to the discharge space due to a difference in thermal expansion during lighting, thus avoiding oxidation.

  Next, the discharge lamp which is 2nd Embodiment is demonstrated using FIG. In the second embodiment, two foil electrodes having different polarities are arranged inside the discharge tube.

  FIG. 5 is a schematic cross-sectional view of a discharge lamp according to the second embodiment.

  The discharge lamp 100 includes two foil electrodes 130A and 130B inside the discharge tube 120 and is covered with columnar dielectrics 150A and 150B, respectively. The foil electrodes 130A and 130B have different polarities. Here, the foil electrode 130A is defined as an anode, and the foil electrode 130B is defined as a cathode.

  Further, the foil electrodes 130A and 130B are arranged at symmetrical positions with respect to the tube axis C, and both the width directions are parallel to the Y axis. Both edge portions of the foil electrodes 130A and 130B have a knife edge shape as in the first embodiment. With such an electrode arrangement, symmetrical discharge light emission occurs with respect to the discharge tube 20, and light is emitted from the entire discharge tube 20.

  FIG. 6 is a schematic cross-sectional view of a discharge lamp according to the third embodiment. In the third embodiment, a plurality of foil electrodes are arranged in the discharge tube.

  In the discharge lamp 200, nine foil electrode buried dielectrics 220A to 220C are two-dimensionally arranged in the discharge tube 210 along the X and Y axes. Each foil electrode has its width direction in the Y-axis direction. External electrodes 250 having different polarities are disposed on the outer surface of the discharge tube 210. Due to the symmetrical arrangement of the electrodes, light is uniformly emitted from the entire discharge tube.

  FIG. 7 illustrates a discharge lamp according to a fourth embodiment. The discharge lamp 300 includes three foil electrode embedded dielectrics 320 in a discharge tube 310 and is arranged in a row. External electrodes 350 having different polarities are arranged on both sides of the discharge tube 300 having a rectangular cross section. With such an electrode arrangement, light is irradiated from below the discharge tube.

  The dielectric may have a shape other than a circular cross section, and for example, the foil electrode may be coated so as to have a coaxial arrangement relationship. The electrode edge is not limited to the knife edge shape, and may be any shape as long as the electric field is concentrated so as to be thinner than the central portion in the width direction. Alternatively, only one electrode edge may be sharpened. Furthermore, the position of the electric field concentration is set by making the shape of the electrode a saw with a non-uniform width, or by arranging the center position of the dielectric and the center position of the foil electrode not to match. May be. Moreover, the stress in the thickness direction that separates the electrode foil and the dielectric may be dispersed by twisting the width direction of the electrode foil with respect to the axial direction of the discharge tube to form a spiral foil electrode.

  As a discharge method, instead of the dielectric barrier discharge excimer lamp that can stably generate a uniform discharge along the axis of the discharge space, for example, an external electrode type fluorescent lamp used in a scanner light source or the like is used. Therefore, it may be applied as a relatively low voltage capacitively coupled (capacitance type) high frequency discharge type lamp. In the case of the capacitively coupled high-frequency discharge method, a high voltage can be easily applied by making the final part of the power supply unit an LC resonance circuit.

  The discharge lamp of the Example equivalent to 1st Embodiment is demonstrated. The axial length of the discharge tube is 300 mm, the thickness is 1 mm, the inner diameter is 12.8 mm, and the thickness of the dielectric having a circular cross section is 1 mm in the direction parallel to the width of the foil electrode, and is parallel to the thickness of the foil electrode. In this direction, the discharge distance is set to 1.5 mm and the discharge distance is set to about 5 mm. The foil electrode has a thickness of 20 μm and a width of 1.5 mm. If the inner diameter of the discharge tube is d and the width of the foil electrode is w, the ratio d / w is 8.5.

  Xe gas was enclosed as a discharge gas, and a lighting experiment was performed at an applied voltage of 6.5 kV and a gas pressure of 47 kPa. When the lamp lighting operation that radiates spectrum light of 172 nm was continued for 2500 hours, a maintenance rate of 90% was obtained for the illuminance.

10 Discharge lamp 20 Discharge tube 30 Foil electrode (band electrode)
40 External electrode 50 Dielectric

Claims (12)

A discharge tube filled with discharge gas;
At least one strip electrode disposed in the discharge vessel;
And at least one dielectric covering the electrode,
The discharge lamp according to claim 1, wherein the thickness of at least one of both edges along the longitudinal direction of the electrode is thinner than the central portion of the electrode.   The discharge lamp according to claim 1, wherein an edge of the belt-like electrode has a knife edge shape.   The discharge lamp according to any one of claims 1 to 2, wherein the strip electrode is coaxially arranged in the discharge tube.   The discharge lamp according to any one of claims 1 to 3, wherein a thickness of both edges of the belt-like electrode is thinner than a thickness of a central portion of the electrode.   The discharge lamp according to claim 1, wherein a plurality of strip electrodes having different polarities are arranged in the discharge tube. A plurality of strip electrodes having the same polarity are arranged in the discharge tube,
The discharge lamp according to claim 1, wherein an external electrode having a polarity different from that of the strip electrode is disposed outside the discharge tube.   The discharge lamp according to any one of claims 5 to 6, wherein the plurality of strip-like electrodes are disposed at symmetrical positions with respect to the discharge tube axis.   The discharge lamp according to any one of claims 5 to 6, wherein the plurality of strip electrodes are arranged in a state where their width directions are parallel to each other.   The discharge lamp according to any one of claims 1 to 8, wherein the plurality of electrodes are respectively covered with different dielectrics.   2. The discharge lamp according to claim 1, wherein a thickness of the belt-like electrode is set within a range of 20 μm to 50 μm and a width of the belt-like electrode is within a range of 1.2 mm to 10 mm.   The discharge tube has a thickness of 0.8 mm to 1.5 mm, the inner diameter of the discharge tube is 8 mm to 20 mm, the thickness of the dielectric is 0.1 mm to 2 mm, and the discharge distance is 3 mm to 10 mm. The discharge lamp according to claim 1. The discharge lamp according to any one of claims 10 to 11, wherein the following expression is satisfied, where w is a width of the strip electrode and d is an inner diameter of the discharge tube.
1.6 ≦ d / w ≦ 13.4

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