JP2024142377A - Discharge lamp - Google Patents

Abstract

To provide a discharge lamp with a long life.SOLUTION: A discharge lamp comprises: an arc tube; a pair of electrodes which are disposed to face each other inside the arc tube; and two lead rods each of which is connected to each of the pair of electrodes. The discharge lamp comprises: a hydrogen getter in which a getter material for adsorbing hydrogen inside the arc tube is contained in a sealed container; a cover which covers the hydrogen getter and is fixed to the lead rod; and a contact prevention member which is located between the hydrogen getter and the cover so as to prevent the hydrogen getter from making contact with the cover.SELECTED DRAWING: Figure 2

Description

This invention relates to a discharge lamp.

It is known to place a hydrogen getter inside the light-emitting tube of a discharge lamp. The getter material contained in the hydrogen getter absorbs hydrogen inside the light-emitting tube, thereby stabilizing the illuminance of the discharge lamp.

Patent document 1 discloses a short-arc type discharge lamp having a hydrogen getter and a cover (referred to as a "casing" in patent document 1) that covers the hydrogen getter and is fixed to the lead rod.

JP 2011-100588 A

There is a market demand for longer-life discharge lamps. Our goal is to provide a long-life discharge lamp to meet this market demand.

The present invention provides a discharge lamp comprising an arc tube, a pair of electrodes arranged opposite each other within the arc tube, and two lead rods connected to each of the pair of electrodes, the discharge lamp comprising:
a hydrogen getter, the getter material for adsorbing hydrogen in the light emitting tube being sealed in a sealed container;
a cover that covers the hydrogen getter and is fixed to the lead rod;
and a contact prevention member that is positioned between the hydrogen getter and the cover to prevent the hydrogen getter from contacting the cover.

As will be described in detail later, in conventional discharge lamps, the hydrogen getter sometimes comes into contact with the cover. As a result of the inventor's analysis, it was found that if the hydrogen getter continues to be lit while in contact with the cover, the hydrogen getter is diffusion bonded to the cover, damaging the sealed container of the hydrogen getter, and the risk of leakage of the getter material increases. The leaked getter material adheres to the light-emitting tube, causing a decrease in the illuminance of the discharge lamp. However, the discharge lamp of the present invention is equipped with the contact prevention member. The contact prevention member prevents the hydrogen getter from contacting the cover, so that the contact area between the hydrogen getter and the cover is reduced or there is no contact. As a result, even if the discharge lamp is used for a long time, the diffusion bonding between the sealed container of the hydrogen getter and the cover is unlikely to progress, and the risk of leakage of the getter material due to damage to the sealed container is reduced. If the getter material leaks, the hydrogen getter will adhere to the light-emitting tube, causing a decrease in the illuminance of the discharge lamp, but since the risk of leakage is reduced, the illuminance of the discharge lamp is less likely to decrease.

The contact prevention member may be in sheet form.

The surface of the contact prevention member may be embossed, meshed, or have multiple perforations or multiple recesses.

The contact prevention member may be made of the same material as the sealed container of the hydrogen getter.

The contact prevention member may be made of at least one of tantalum and niobium.

The cover may be made of at least one of molybdenum and tungsten.

This allows for the provision of long-life discharge lamps.

1 is an overall view of a discharge lamp according to a first embodiment; FIG. 2 is an enlarged cross-sectional view of the periphery of a hydrogen getter. FIG. 2 is a perspective view of a hydrogen getter. FIG. 1 is an enlarged cross-sectional view of the periphery of a hydrogen getter in a discharge lamp having no contact-preventing member. FIG. 13 is a diagram showing a sheet-shaped contact prevention member. FIG. 6 is an enlarged cross-sectional view of the periphery of a hydrogen getter in a discharge lamp of a second embodiment. FIG. 11 is an enlarged cross-sectional view of the periphery of a hydrogen getter in a discharge lamp of a third embodiment. FIG. 10 is an enlarged cross-sectional view of the periphery of a hydrogen getter in a discharge lamp according to a fourth embodiment.

The embodiments of the present invention will be described with reference to the drawings. Note that the drawings disclosed in this specification are merely schematic illustrations. The dimensional ratios on the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match.

Some of the drawings are shown in an XYZ Cartesian coordinate system. The vertical direction is the Z direction, and the two directions that are perpendicular to each other in a horizontal plane perpendicular to the vertical direction are the X and Y directions. When expressing a direction, if a distinction is made between positive and negative, it is written with a positive or negative sign, such as "+Z direction" and "-Z direction", but when expressing a direction without distinguishing between positive and negative, it is simply written as "Z direction". The -Z direction is the direction of gravity.

First Embodiment
[Discharge Lamp Overview]
With reference to FIG. 1, an outline of a discharge lamp of the first embodiment will be described. A discharge lamp 10 (here, a short-arc type ultra-high pressure mercury lamp) shown in FIG. 1 includes an arc tube 2, a pair of electrodes (anode 3 and cathode 4) arranged opposite each other in the arc tube 2, two lead rods 7 connected to the anode 3 and the cathode 4, respectively, and two side tubes 5 connected to both ends of the arc tube 2. In this embodiment, the arc tube 2 and the two side tubes 5 are arranged along the Z1 axis. The Z1 axis is an axis parallel to the Z direction. The arc tube 2 is formed by expanding in the X direction and the Y direction from the Z1 axis. The arc tube 2, the two side tubes 5, the anode 3, and the cathode 4 have a shape of a revolution body centered on a common Z1 axis. However, the arc tube 2 and the two side tubes 5 do not have to be arranged along the Z1 axis, and do not have to have a shape of a revolution body. A base 6 is attached to each of the two side tubes 5. The discharge lamp 10 further includes a hydrogen getter (not shown in FIG. 1) and covers (8a, 8b) that cover the hydrogen getter.

[Hydrogen getter]
The hydrogen getter will be described with reference to Figures 2 and 3. Figure 2 is an enlarged cross-sectional view of the hydrogen getter and its periphery. Figure 3 is a perspective view of the hydrogen getter. As shown in Figure 2, a cover (8a, 8b) that covers the hydrogen getter 9 is fixed to a lead rod 7 that is connected to the cathode 4 (see Figures 1 and 2).

As shown in FIG. 2, the hydrogen getter 9 has a sealed container 13 and a getter material 12 filled inside the sealed container 13. The sealed container 13 is sealed so that the getter material 12 does not leak. There is a space inside the sealed container 13 that is not filled with the getter material 12 so that the getter material 12 does not leak from the sealed container 13 even if the getter material 12 thermally expands due to a rise in temperature.

When the temperature of the getter material 12 rises due to heat generated by lighting the discharge lamp 10 and reaches a temperature at which hydrogen molecules can be adsorbed, the getter material 12 adsorbs the hydrogen molecules in the light-emitting tube 2. Examples of the getter material 12 include metals such as yttrium and zirconium, but are not limited to these metals. The purity of the metal used in the getter material 12 is preferably, for example, 90 at% or more, but may be less than 90 at%.

Figure 3 is a perspective view of the appearance of the hydrogen getter 9. The sealed container 13 in this embodiment is rod-shaped. Both ends of the sealed container 13 in the longitudinal direction are tapered. By having both ends of the sealed container 13 in the longitudinal direction have a tapered shape, the contact area between the bottom of the sealed container 13 and the cover 8a can be reduced. The sealed container 13 is permeable to hydrogen molecules. The material used for the sealed container 13 is a material that does not melt even when exposed to high temperatures and can be processed into a container. Examples of the material for the sealed container 13 include tantalum (Ta) and niobium (Nb). The purity of the metal used for the sealed container 13 is preferably, for example, 90 at% or more.

The size of the hydrogen getter 9, i.e., the longitudinal dimension of the sealed container 13, may be 5 mm or more and 30 mm or less, and preferably 15 mm or more and 25 mm or less. The maximum width of the cross section perpendicular to the longitudinal direction of the sealed container 13 may be 2 mm or more and 10 mm or less, and preferably 3 mm or more and 8 mm or less. The thickness of the sheet constituting the sealed container 13 may be 3 μm or more and 300 μm or less, and preferably 5 μm or more and 200 μm or less. The shape and dimensions of the sealed container 13 are not limited to those described above, and other shapes and dimensions may be used.

[Hydrogen getter cover]
The covers (8a, 8b) will now be described. Fig. 4 is an exploded perspective view of the covers (8a, 8b). The two covers 8a are arranged to sandwich the lead rod 7. The two covers 8a are then fixed to the lead rod 7 by fixing them together with screws or the like (not shown). The two covers 8b are fitted into the cover 8a, respectively, with the hydrogen getter 9 (not shown in Fig. 4) housed therein. This isolates the hydrogen getter 9 from the outside of the covers (8a, 8b).

The function of the covers (8a, 8b) will be explained. Without the covers (8a, 8b), abnormal discharge may occur from the hydrogen getter 9 when the discharge lamp 10 is turned on, which may damage the hydrogen getter 9. The covers (8a, 8b) cover the hydrogen getter 9, preventing abnormal discharge from occurring from the hydrogen getter 9.

Although not shown in Figures 2 and 4, the fitted covers (8a, 8b) have gaps that allow hydrogen to pass through. These gaps need only be small enough that abnormal discharge does not occur from the hydrogen getter 9. For example, the gaps may be large enough to be visible to the naked eye.

The covers (8a, 8b) do not melt even when exposed to high temperatures caused by lighting the discharge lamp 10. The covers (8a, 8b) are made of a material different from that of the sealed container 13. Examples of materials for the covers (8a, 8b) include metals such as molybdenum (Mo) and tungsten (W). The purity of the metal used for the covers (8a, 8b) may be low. For example, the covers (8a, 8b) may be an alloy in which the main metal is 70 at% or less.

In this embodiment, two hydrogen getters 9 are contained within one set of covers (8a, 8b), but more hydrogen getters 9 may be contained within one set of covers (8a, 8b), or one hydrogen getter 9 may be contained within one set of covers (8a, 8b). In addition, this embodiment in which two covers 8a are arranged to sandwich the lead rod 7 is merely an example, and is not limited to this. For example, one cover may be present to surround the lead rod 7, or more than two covers may be lined up along the lead rod 7. It is sufficient that the covers cover the hydrogen getter 9 so as to suppress the occurrence of abnormal discharge from the hydrogen getter 9.

[Contact prevention member]
The contact prevention member of this embodiment will be described. As shown in Fig. 2, the discharge lamp 10 has a contact prevention member 11. The contact prevention member 11 is located between the hydrogen getter 9 and the cover (8a, 8b). The contact prevention member 11 prevents the hydrogen getter 9 from contacting the cover (8a, 8b).

The function of the contact prevention member 11 will be described in detail by comparing it with a discharge lamp without the contact prevention member 11. FIG. 5 shows a discharge lamp without the contact prevention member 11. Since the discharge lamp shown in FIG. 5 does not have the contact prevention member 11, the sealed container 13 of the hydrogen getter 9 is in contact with the cover (8a, 8b) at the contact point C1. In a high-temperature environment during lamp lighting, if the sealed container 13 is in contact with the cover (8a, 8b), diffusion bonding between the material of the sealed container 13 and the material of the cover (8a, 8b) progresses. As a result, the sealed container 13 and the cover (8a, 8b) are welded at the contact point C1. If the contact point C1 is welded, when the discharge lamp 10 is repeatedly turned on and off, stress due to the difference in the amount of thermal expansion between the sealed container 13 and the cover (8a, 8b) is repeatedly applied near the contact point C1. As a result, the sealed container 13 may be locally penetrated, and the getter material 12 in the sealed container 13 may leak from the sealed container 13. If the getter material 12 leaks from the sealed container 13, the getter material 12 adheres to the light-emitting tube 2, reducing the light transmittance of the light-emitting tube 2. In other words, this leads to a decrease in the illuminance of the discharge lamp 10.

In contrast, as shown in FIG. 2, when a contact prevention member 11 is placed between the hydrogen getter 9 and the cover (8a, 8b), no contact points are formed between the hydrogen getter 9 and the cover (8a, 8b), or at least the contact area is reduced. As a result, diffusion between the material of the sealed container 13 of the hydrogen getter 9 and the material of the cover (8a, 8b) is less likely to proceed, preventing damage (penetration) of the sealed container 13 and reducing the risk of leakage of the getter material 12. As a result, the illuminance of the discharge lamp 10 is less likely to decrease even when the discharge lamp 10 is used for a long time, so the life of the discharge lamp 10 can be extended.

When the contact prevention member 11 is placed between the hydrogen getter 9 and the cover (8a, 8b), the contact prevention member 11 comes into contact with the cover (8a, 8b). Diffusion bonding may progress between the contact prevention member 11 and the cover (8a, 8b), and the contact prevention member 11 and the cover (8a, 8b) may be welded together. Even if stress is repeatedly applied to the contact prevention member 11, distortion accumulates, causing deformation and breakage, the function of preventing the sealed container 13 from coming into contact with the cover (8a, 8b) is not lost, and this does not lead to breakage of the sealed container 13.

In this embodiment, the contact prevention member 11 has a sheet shape. By wrapping such a sheet-shaped contact prevention member 11 around multiple hydrogen getters 9, the contact prevention member 11 is arranged as shown in the cross-sectional view of FIG. 2. It is better to wrap the hydrogen getter 9 with the contact prevention member 11 so that it softly envelops it, rather than wrapping the hydrogen getter 9 so that it is bound and fixed. By allowing the hydrogen getter 9 to freely expand thermally within the contact prevention member 11, damage to the contact prevention member 11 and the sealed container 13 of the hydrogen getter 9 can be prevented.

The thickness of the sheet that is the contact prevention member 11 should be thinner than the thickness of the covers (8a, 8b). The thickness of the sheet should be 5 μm or more and 1 mm or less. Preferably, the thickness should be 10 μm or more and 500 μm or less, and more preferably, the thickness should be 15 μm or more and 100 μm or less. The contact prevention member 11 should be made of a tough material that is not easily damaged even if it is deformed by use of the discharge lamp.

In principle, the contact prevention member 11 is made of a different material than the covers (8a, 8b). However, if the contact prevention member 11 is in a state where it is more easily deformed than the sealed container 13, such as when the thickness of the contact prevention member 11 is thinner than the thickness of the sheet that constitutes the sealed container 13, the contact prevention member 11 may be made of the same material as the covers (8a, 8b). Even if the contact prevention member 11 and the covers (8a, 8b) are welded together, deformation due to thermal expansion is concentrated in the contact prevention member 11, making it difficult to deform the sealed container 13 and not leading to leakage of the getter material 12.

The material of the contact prevention member 11 may be different from that of the sealed container 13 of the hydrogen getter 9, or it may be the same material. If the material of the contact prevention member 11 is the same as that of the sealed container 13, the thermal expansion coefficient of the sealed container 13 and that of the contact prevention member 11 are the same, and diffusion bonding does not occur, making it easier to prevent damage to the contact prevention member 11 and the sealed container 13.

Figure 6 is a diagram showing a sheet-shaped contact prevention member 11. One side of the sheet is shown in Figure 6. In this embodiment of the contact prevention member 11, multiple protrusions 21 (hatched areas in Figure 6) are formed on the surface of a flat sheet. The height of each protrusion 21 is within 2 mm. In this specification, such multiple protrusions 21 are sometimes referred to as embossed, but embossed protrusions do not only refer to those obtained by embossing a flat sheet, but also include those in which multiple protrusions 21 are formed from a sheet-shaped material by other processing methods.

When the sheet-shaped contact prevention member 11 is wrapped around the multiple hydrogen getters 9, the contact prevention member 11 is wrapped so that the multiple protrusions 21 are located on the inside. This reduces the contact area between the contact prevention member 11 and the sealed container 13 of the hydrogen getter 9. The contact prevention member 11 is less likely to weld to the sealed container 13 than the cover (8a, 8b), but it may weld slightly. However, by providing protrusions on the contact prevention member 11, the contact area between the contact prevention member 11 and the sealed container 13 can be reduced, making it more difficult for them to weld. In addition, if the same material as the sealed container 13 (e.g., tantalum (Ta)) is selected for the contact prevention member 11, the thermal expansion coefficients of the two will be the same, and the weld prevention effect will be high.

The contact prevention member 11 shown in FIG. 6 has protrusions 21 that are long in one direction and arranged in a lattice shape with each protrusion facing in an alternating direction. However, the shape of the protrusions 21 and the arrangement of the multiple protrusions 21 are not particularly limited. The contact prevention member 11 may be simply a flat sheet. The contact prevention member 11 may also be in the form of a mesh in which multiple wires are woven. The contact prevention member 11 may also be an array in which strip-shaped sheets are lined up in one direction. The contact prevention member 11 may have multiple perforations or multiple recesses.

Second Embodiment
A discharge lamp according to the second embodiment will be described with reference to Fig. 7. The following description will focus on the differences from the first embodiment. Descriptions of the same aspects as those in the first embodiment will be omitted. The same applies to the third and subsequent embodiments.

In FIG. 7, the contact prevention member 11 is formed in a bag shape and surrounds the entire hydrogen getter 9. In FIG. 2, the contact prevention member 11 contacts the cover 8a at the end on the -Z side, but in FIG. 7, the bag-shaped contact prevention member 11 surrounds the entire hydrogen getter 9, and there is no contact point between the hydrogen getter 9 (sealed container 13) and the cover (8a, 8b).

Third Embodiment
A discharge lamp of the third embodiment will be described with reference to Fig. 8. In Fig. 8, a cover 8a does not cover the lead rod 7. A contact prevention member 11 is provided between the hydrogen getter 9 (sealed container 13) and the lead rod 7 to prevent diffusion bonding between the sealed container 13 and the lead rod 7.

<Fourth embodiment>
A discharge lamp of the fourth embodiment will be described with reference to Fig. 9. In Fig. 9, the contact prevention member 11 is coil-shaped. In Fig. 9, the hydrogen getter 9 is not shown in order to clearly show the shape of the contact prevention member 11. In reality, the hydrogen getter 9 is disposed inside the coil-shaped contact prevention member 11. The coil-shaped contact prevention member 11 can reduce the contact area between the hydrogen getter 9 and the cover (8a, 8b). Furthermore, when the coil-shaped contact prevention member 11 is self-supporting, it does not contact the inner surface of the cover (8a, 8b), and the contact area between the contact prevention member 11 and the cover (8a, 8b) can also be reduced.

Each embodiment of the discharge lamp has been described above. The present invention is not limited to the above-described embodiments, and various modifications or improvements can be made to each of the above-described embodiments, or each embodiment can be combined, without departing from the spirit of the present invention.

Examples of discharge lamps include short-arc discharge lamps, such as ultra-high pressure mercury lamps and xenon lamps. Furthermore, examples of discharge lamps include long-arc metal halide lamps.

In each of the above embodiments, the contact prevention member 11 is shown as being separate from the sealed container 13, but the contact prevention member may be in contact with the sealed container 13. For example, a film that prevents contact between the sealed container 13 and the cover (8a, 8b) may be formed on the surface of the sealed container 13. As a specific example of such a film, a coating film made of a ceramic material may be formed by application or the like. The coating film should have a thickness that does not prevent the permeation of hydrogen molecules. For example, the thickness of the coating film should be 10 μm or more and 100 μm or less. Also, instead of forming the coating film on the entire surface of the sealed container 13, the coating film may be formed intermittently or on a portion where the sealed container 13 is likely to come into contact with the cover (8a, 8b).

The outer surface of the sealed container 13 may be formed with irregularities (protrusions and/or recesses) to reduce the contact area between the sealed container 13 and the contact prevention member 11 and cover (8a, 8b).

The following experiment was carried out. First, the following three sample discharge lamps were prepared.
Sample 1: A metal sheet was arranged as the contact prevention member 11 as shown in Fig. 2. The metal sheet was made of high-purity tantalum (tantalum content of 95 at% or more) and had a thickness of 50 µm. The sheet had no protrusions.
Sample 2: A metal sheet was arranged as the contact prevention member 11 as shown in Fig. 2. The metal sheet was made of high-purity tantalum (tantalum content of 95 at% or more) and had a thickness of 50 µm. The sheet was provided with a plurality of protrusions 21 as shown in Fig. 6.
Sample 3: A discharge lamp without a contact-preventing member 11.
For the three samples (1, 2, 3), all other conditions (eg, conditions of the hydrogen getter 9 and the discharge lamp 10) were the same.

The three sample discharge lamps shown above were inspected after being used for a specified period of time (including repeated turning on and off). The inspection results are shown in Table 1.

In Table 1, "adhesion of getter material" indicates the result of visual inspection of whether or not getter material 12 is attached to the light emitting tube 2. Since the light emitting tube 2 is transparent and the getter material 12 is brown, it can be visually confirmed when a certain amount of getter material 12 is attached. In Samples 1 and 2, adhesion of getter material 12 to the light emitting tube 2 could not be confirmed (i.e., "not attached") even after the discharge lamp 10 was used for a specified period of time, whereas in Sample 3, adhesion of getter material 12 to the light emitting tube was confirmed (i.e., "attached"). Sample 3 indicates that the sealed container 13 of the hydrogen getter 9 was damaged, and the leaked getter material 12 adhered to the light emitting tube, reducing the light transmittance and reducing the illuminance.

In Table 1, "welding between hydrogen getter and cover" is inspected by determining whether the sealed container 13 of the hydrogen getter 9 is welded to the cover (8a, 8b) by disassembling the cover (8a, 8b) and judging the pulling force when manually pulling the hydrogen getter 9 away from the cover (8a, 8b). If the hydrogen getter 9 can be pulled away from the cover (8a, 8b) without applying pulling force, it is judged as "not welded". If the hydrogen getter 9 cannot be pulled away from the cover (8a, 8b) without applying force, it is judged as "welded". Sample 3 was judged as "welded". Samples 1 and 2 were judged as "not welded".

In Table 1, "welding between hydrogen getter and contact prevention member" is inspected by determining whether the sealed container 13 of the hydrogen getter 9 is welded to the contact prevention member 11 by judging the tensile force when manually pulling the hydrogen getter 9 away from the contact prevention member 11. If the hydrogen getter 9 can be pulled away from the contact prevention member 11 without applying tensile force, it is judged as "no welding." In sample 1, slight welding was observed, to the extent that it could be pulled away (peeled off) with a light force, whereas in sample 2, the hydrogen getter 9 could be pulled away from the contact prevention member 11 without applying tensile force, and no welding was observed. Note that sample 3 does not use a contact prevention member 11, so this item for sample 3 is not evaluated.

The "Overall Rating" in Table 1 was derived from the results of "Adhesion of Getter Material," "Welding of Hydrogen Getter to Cover," and "Welding of Hydrogen Getter to Contact Prevention Member." The overall rating is judged from AA, A, and B in descending order of superiority. B is an unfavorable rating, while A is a favorable rating. AA is an even more favorable rating. Samples 1 and 2 were rated A or higher because no leakage of getter material 12 was observed even after a specified period of use. Sample 1 was rated A because there was no leakage of getter material 12, but there was slight adhesion due to welding between the welding prevention member and the hydrogen getter. Sample 2 was rated AA because there was no leakage of getter material 12, and furthermore there was no welding between the hydrogen getter 9 and the cover (8a, 8b) or between the hydrogen getter 9 and the contact prevention member 11. It was predicted that the sealed container 13 would not break even if the lamp was turned on for a longer period of time, and sample 2 was rated AA.

2: Arc tube 3: Anode 4: Cathode 5: Side tube 6: Base 7: Lead rod 8a: Cover 8b: Cover 9: Hydrogen getter 10: Discharge lamp 11: Contact prevention member 12: Getter material 13: Sealed container 21: Protrusion C1: Contact point

Claims (6)

A discharge lamp comprising an arc tube, a pair of electrodes arranged opposite each other within the arc tube, and two lead rods connected to each of the pair of electrodes, the discharge lamp comprising:
a hydrogen getter, the getter material for adsorbing hydrogen in the light emitting tube being sealed in a sealed container;
a cover that covers the hydrogen getter and is fixed to the lead rod;
a contact prevention member positioned between the hydrogen getter and the cover to prevent the hydrogen getter from contacting the cover. The discharge lamp according to claim 1, characterized in that the contact prevention member is sheet-shaped. The discharge lamp according to claim 2, characterized in that the surface of the contact prevention member has an embossed shape, a mesh shape, or a plurality of perforations or a plurality of recesses. The discharge lamp according to any one of claims 1 to 3, characterized in that the contact prevention member is made of the same material as the sealed container of the hydrogen getter. The discharge lamp according to claim 4, characterized in that the contact prevention member is made of at least one of tantalum and niobium. 4. The discharge lamp according to claim 1, wherein the cover is made of at least one of molybdenum and tungsten.