EP2626889A1

EP2626889A1 - Ceramic tube and method for producing same

Info

Publication number: EP2626889A1
Application number: EP11830531.7A
Authority: EP
Inventors: Sugio Miyazawa; Keiichiro Watanabe; Tsuneaki Ohashi
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2010-10-08
Filing date: 2011-09-27
Publication date: 2013-08-14
Also published as: EP2626889A4; WO2012046598A1; CN103155092A; JPWO2012046598A1

Abstract

In the present invention, a first ceramic tube (10A) for a high-brightness discharge lamp has a light-emitting unit (12) that emits light therewithin and an electrode-sealing first tubule (14a) and second tubule (14b) respectively formed integrally to the two ends of the light-emitting unit (12). Of the light-emitting unit (12), a position towards the first tubule (14a) is provided with a through-hole (16) wherein the direction from the inside of the light-emitting unit (12) to the outside of the light-emitting unit (12) is the same as the direction of extension of the first tubule (14a).

Description

Technical Field

The present invention relates to a method for producing a ceramic tube usable in a high-intensity discharge lamp such as a high-pressure sodium vapor lamp or a metal halide lamp, and further relates to the ceramic tube.

Background Art

In ceramic metal halide lamps, a pair of electrodes are inserted into a ceramic tube for a high-intensity discharge lamp, and a metal halide is ionized by the electrodes to show discharge emission.
Such a ceramic tube has a pair of capillaries, and the axis lines of the capillaries extend toward a light-emitting portion. Each capillary has an electrode insertion hole, into which the electrode is inserted. Various types of the ceramic tubes (such as those produced by assembling a plurality of members, those composed of a single integrally formed member, and those produced by bonding two members) are disclosed in e.g. Japanese Laid-Open Patent Publication Nos. 63-143738 , 5-334962 , 7-021990 , 8-055606 , 2010-514125 (PCT), and 2010-514127 (PCT), US Patent Application Publication No. 2006/0001346 , and Japanese Laid-Open Patent Publication Nos. 2009-530127 (PCT) and 2008-044344 .
For example, one electrode is inserted into the electrode insertion hole in one of the two capillaries
(small holes) in the ceramic tube, the electrode insertion hole is sealed with a fritted glass or the like, a light-emitting material is introduced from the other electrode insertion hole into a light-emitting container, the other electrode is inserted into the other electrode insertion hole, and then the other electrode insertion hole is sealed by the fritted glass or the like, to obtain an arc tube. In another known example, the ceramic tube has a third capillary or small hole in addition to the above two capillaries for electrode insertion, and the light-emitting material is introduced through the third capillary or small hole into the light-emitting container after the electrodes are sealed.
Specifically, Japanese Laid-Open Patent Publication No. 63-143738 discloses a ceramic discharge lamp containing an arc tube bulb composed of a translucent ceramic and closure members composed of a conductive cermet. The arc tube bulb has openings at either end, and the openings are sealed by solid-phase-bonding the closure members having electrodes. The arc tube bulb further has a small hole for discharging an exhaust gas from the tube and for supplying an inclusion, and the small hole is closed by welding a ceramic cover.
Japanese Laid-Open Patent Publication No. 5-334962 discloses a translucent bulb composed of a polycrystalline alumina. The translucent bulb has cylindrical openings at either end, and closure members are attached to the cylindrical openings. Each closure member has a hole at the center, and an electrode is inserted into the hole. The translucent bulb further has an opening, and a light-emitting material is introduced from the opening into the translucent bulb. The opening is formed in a position eccentrically with respect to the center of one of the closure members.
Japanese Laid-Open Patent Publication No. 7-021990 discloses a discharge tube, wherein pin-like current conductors having a diameter of 300 µm are inserted into the ends of the discharge tube, and plugs are directly bonded to the ends by sintering. Especially, as shown in FIGS. 3 and 4 of this patent document, a filling hole having a diameter of 1 mm or more may be formed, for introducing a light-emitting material into the discharge tube, in a wall of the discharge tube around the second end or in the second plug.
Japanese Laid-Open Patent Publication No. 8-055606 discloses an arc tube having an infundibular portion, which is formed integrally with a small-diameter tube having a closed lower end. The small-diameter tube extends downward from the center of the infundibular portion, and a liquid metal halide is stored in a lower portion (coldest portion, which is coldest during lighting) of the small-diameter tube. The liquid metal halide is not vaporized and remains in the arc tube. In particular, this patent document describes that one opening formed on a flange-like intermediate portion may be used as an inlet for the metal halide and mercury, and the small-diameter tube may be used as an inlet tube.
Japanese Laid-Open Patent Publication No. 2010-514125 (PCT) discloses a ceramic burner containing a discharge vessel. One end of the discharge vessel is formed integrally with a wall of the tube, and the other end of the discharge vessel is sealed with a ceramic plug. Particularly, in an example of this patent document, a tube extends outward from a ceramic wall of the discharge vessel, and is used for introducing an ionizing filler into the discharge vessel in the manufacture of the ceramic burner. Incidentally, the tube is air-tightly sealed.
Japanese Laid-Open Patent Publication 2010-514127 (PCT) discloses a discharge vessel having a substantially spherical or oval shape containing two independent portions (separated by a dashed line in FIG. 2A of this patent document). A tube is formed only on the first portion of the discharge vessel, extends outward from a ceramic wall of the discharge vessel, and is used for introducing an ionizing filler into the discharge vessel in the manufacture of a ceramic burner. Incidentally, the tube is air-tightly sealed.
US Patent Application Publication No. 2006/0001346 discloses a structure containing a tube portion and end members bonded to either end of the tube portion. An electrode is disposed at the center of each end member, and extends toward the inside of the tube portion. Particularly one end member has an inlet hole, which extends from the outer surface of the member to the inner surface (the surface facing the tube portion). A metal halide or the like is introduced from the inlet hole into the tube portion, and then the inlet hole is sealed with a plug member.
Furthermore, a production method containing preparing a plurality of inorganic powder compacts, applying a slurry to the joining surfaces of the compacts, and integrating and sintering the compacts to obtain a strongly-bonded sintered body is known from e.g. Japanese Laid-Open Patent Publication No. 2009-530127 (PCT), and a bonded assembly of inorganic powder compacts that can be produced while preventing or avoiding the deformation of the joining portion and the increase of surface roughness is known from e.g. Japanese Laid-Open Patent Publication No. 2008-044344 .
Specifically, Japanese Laid-Open Patent Publication No. 2009-530127 (PCT) discloses a method for producing a sintered body suitable for use in an arc tube of a discharge lamp. The method uses an inorganic powder, an organic dispersion medium having a reactive functional group, and a gelling agent, and contains the steps of performing a chemical solidification reaction between the organic dispersion medium and the gelling agent to obtain first and second inorganic powder compacts, applying a slurry containing a powder and an organic dispersion medium to the joining surface of the first inorganic powder compact, bringing the inorganic powder compacts into contact with each other with the slurry applied therebetween to obtain an integrated bonded assembly, and sintering the bonded assembly to produce the sintered body.
Japanese Laid-Open Patent Publication No. 2008-044344 discloses a sintered body suitable for use in an arc tube of a discharge lamp. The sintered body is derived from a bonded assembly of two or more inorganic powder compacts, and has a first portion corresponding to the two or more inorganic powder compacts in the bonded assembly and a second portion corresponding to a joining portion in the bonded assembly. The sintered body has one or both of the flowing properties (a) and (b).

(a) The surface roughness of the second portion is equal to or lower than that of the first portion.
(b) The translucency of the second portion is equal to higher than that of the first portion in the vicinity of the width-direction center.

Summary of the Invention

In Japanese Laid-Open Patent Publication Nos. 63-143738 , 7-021990 , 8-055606 , 2010-514125 (PCT ), and 2010-514127 (PCT ), the first and second capillaries are formed to introduce and seal the electrodes into the light-emitting portion and seal the electrodes, and the third capillary (or the third small hole) is formed to introduce the light-emitting material into the light-emitting portion. The first, second, and third capillaries have first, second, and third through-holes extending in the axis directions respectively. Specifically, the axis directions of the first and second capillaries are different from that of the third capillary (or the third small hole). Therefore, in a case where the compacts for producing the ceramic tube are prepared by injection molding, gel casting, or the like, the drawing directions of pins for forming the first and second through-holes are different from that of a pin for forming the third through-hole (or the third small hole). Thus, this process requires a molding apparatus having a mechanism suitable for the drawing directions and a production equipment having an expensive complicated structure, thereby resulting in high production cost.
In the light-emitting portion, a portion having the third capillary or small hole exhibits a light transmittance lower than those of the other portions. Therefore, in a case where the third capillary or small hole is located in a position corresponding to the discharge area around the electrode end, the lamp efficiency and the light distribution are deteriorated due to the lowered light transmittance. Meanwhile, in a case where the third capillary or small hole is located in the vicinity of the first or second electrode-sealing capillary, the third capillary or small hole is likely to act as the coldest portion during lighting. In this case, when the light-emitting material is stored in the third capillary or small hole, the ceramic may be corroded to reduce the lifetime of the tube.
Furthermore, as described in Japanese Laid-Open Patent Publication No. 5-334962 and US Patent Application Publication No. 2006/0001346 , in a case where the disc-shaped portion (plug) having the third small hole is formed in advance separately from the first and second electrode-sealing capillaries and attached to the tube body, the axis direction of the third small hole being parallel to the axis directions of the first and second electrode-sealing capillaries, the third small hole is located in a thick portion in the vicinity of the electrode in the assembled lamp, and is disadvantageously corroded by the coldest portion.
When the axis lines of the third capillary and the light-emitting portion form an excessively low angle, an edge having a sharp cross-sectional angle is formed at the boundary between the through-hole of the third capillary and the inner surface of the light-emitting portion. The edge is easily chipped off in the production, transport, or the like. Consequently, waste may be generated, and the chipped portion may be cracked.
In addition, when the third capillary is excessively long, the third capillary is not sufficiently heated and acts as the coldest portion during the lighting, whereby the ceramic may be corroded undesirably as described above.
In view of the above problems, an object of the present invention is to provide a ceramic tube for a high-intensity discharge lamp, which has a third small hole or capillary for introducing a light-emitting material into a light-emitting portion and can be highly reliably produced at low production cost and high productivity while preventing light transmittance deterioration without using a production equipment having a complicated structure.
Another object of the present invention is to provide a method capable of easily producing a ceramic tube for a high-intensity discharge lamp, which has a third small hole or capillary for introducing a light-emitting material into a light-emitting portion, at low production cost, high productivity, and high yield by using a simple production equipment.

[1] A ceramic tube for a high-intensity discharge lamp according to a first aspect of the present invention, comprising a light-emitting portion, a first capillary, and a second capillary that are formed integrally, wherein the light-emitting portion is adapted to emit a light inside the ceramic tube, the first and second capillaries are disposed on either side of the light-emitting portion, the first and second capillaries being provided for sealing electrodes, the light-emitting portion has a through-hole formed in a position close to the first capillary, and the through-hole extends from an inside to an outside of the light-emitting portion in a direction parallel to the extending direction of the first capillary.
[2] The ceramic tube according to the first aspect, wherein the axis line of the through-hole is parallel to the axis line of the first capillary.
[3] The ceramic tube according to the first aspect, wherein in the light-emitting portion, the through-hole is formed in the position closer to the first capillary than a position corresponding to an end of an electrode sealed in the first capillary.
[4] The ceramic tube according to the first aspect, wherein in the light-emitting portion, a distance between the axis lines of the through-hole and the first capillary is 0.55 or more times as large as the outer diameter of the first capillary.
[5] The ceramic tube according to the second aspect, wherein the light-emitting portion has a curved surface between a portion corresponding to a discharge area and the first or second capillary, and the through-hole is formed on the curved surface.
[6] A ceramic tube for a high-intensity discharge lamp according to a second aspect of the present invention, comprising a light-emitting portion, a first capillary, and a second capillary that are formed integrally, wherein the light-emitting portion is adapted to emit a light inside the ceramic tube, the first and second capillaries are disposed on either side of the light-emitting portion, electrodes being sealed therein, the light-emitting portion has a third capillary formed in a position close to the first capillary, the third capillary protrudes in a direction parallel to an extending direction of the first capillary, and a through-hole extends from an end of the third capillary to an inside of the light-emitting portion.
[7] The ceramic tube according to the second aspect, wherein an axis line of the third capillary is parallel to an axis line of the first capillary.
[8] The ceramic tube according to the second aspect, wherein in the light-emitting portion, the third capillary is formed in the position closer to the first capillary than a position corresponding to an end of an electrode sealed in the first capillary.
[9] The ceramic tube according to the second aspect, wherein in the light-emitting portion, a distance between the axis lines of the third capillary and the first capillary is 0.55 or more times as large as the outer diameter of the first capillary.
[10] The ceramic tube according to the second aspect, wherein an inner surface of the light-emitting portion has a cross-sectional outline in a plane containing the axis line of the third capillary, and the axis line and a tangent line at an intersection between the outline and the axis line form an angle of 30° or more.
[11] The ceramic tube according to the second aspect, wherein the third capillary has a base point, which is a reference point of a maximum length of the third capillary along the axis line, and the maximum length of the third capillary is 1/10 to 5/10 of a length between the base point and an end of the first capillary along the axis line of the first capillary.
[12] The ceramic tube according to the second aspect, wherein the light-emitting portion has a curved surface between a portion corresponding to a discharge area and the first or second capillary, and the third capillary is formed on the curved surface.
[13] A method according to a third aspect of the present invention, for bonding a plurality of ceramic compacts to produce one ceramic tube for a high-intensity discharge lamp, comprising a compact preparation step of preparing a first ceramic compact containing a first curved portion and a first cylindrical portion formed integrally and a second ceramic compact containing a second curved portion and a second cylindrical portion formed integrally, and a compact bonding step of bonding an end surface of the first curved portion in the first ceramic compact and an end surface of the second curved portion in the second ceramic compact to each other to prepare a bonded assembly, wherein the first curved portion has a through-hole extending along an axis direction of the first cylindrical portion, and an axis line of the through-hole is parallel to an axis line of the first cylindrical portion in the first ceramic compact.
[14] A method according to a fourth aspect of the present invention, for bonding a plurality of ceramic compacts to produce one ceramic tube for a high-intensity discharge lamp, comprising a compact preparation step of preparing a first ceramic compact containing a first curved portion and a first cylindrical portion formed integrally and a second ceramic compact containing a second curved portion and a second cylindrical portion formed integrally, and a compact bonding step of bonding an end surface of the first curved portion in the first ceramic compact and an end surface of the second curved portion in the second ceramic compact to each other to prepare a bonded assembly, wherein the first curved portion has a capillary extending along the axis direction of the first cylindrical portion, a through-hole extends from an end of the capillary to an inside of the first curved portion, and an axis line of the capillary and the through-hole is parallel to an axis line of the first cylindrical portion in the first ceramic compact.

Brief Description of the Drawings

FIG. 1 is a perspective view of a ceramic tube according to a first embodiment of the present invention (a first ceramic tube);
FIG. 2 is an exploded perspective view of a combination example of first and second ceramic compacts used in production of the first ceramic tube;
FIG. 3 is a cross-sectional view of first and second electrodes sealed in the first ceramic tube;
FIG. 4 is a cross-sectional view of a ceramic tube according to a comparative example;
FIG. 5A is a cross-sectional view of a casting mold (having a stationary mold and a movable mold) for producing the ceramic tube of the comparative example, FIG. 5B is a cross-sectional view of the casting mold with a pin drawn out, and FIG. 5C is a cross-sectional view of the stationary mold and the movable mold separated therefrom;
FIG. 6A is a cross-sectional view of a casting mold (having a stationary mold and a movable mold) for producing the first ceramic tube, and FIG. 6B is a cross-sectional view of the stationary mold and the movable mold separated therefrom;
FIG. 7 is a block flow diagram of a method for producing the first ceramic tube;
FIG. 8 is a cross-sectional view of a first bonded assembly;
FIG. 9 is a perspective view of a ceramic tube according to a second embodiment of the present invention (a second ceramic tube);
FIG. 10 is a cross-sectional view of first and second electrodes sealed in the second ceramic tube;
FIG. 11A is a cross-sectional view of a casting mold (having a stationary mold and a movable mold) for producing the second ceramic tube, and FIG. 11B is a cross-sectional view of the stationary mold and the movable mold separated therefrom;
FIG. 12 is an enlarged schematic view of main features illustrating a preferred angle between an inner surface of a light-emitting portion and an extending direction of a third capillary in the second ceramic tube;
FIG. 13 is a cross-sectional view for illustrating a maximum length of the third capillary in the second ceramic tube;
FIG. 14 is a block flow diagram of a method for producing the second ceramic tube;
FIG. 15 is an exploded perspective view of a combination example of first and second ceramic compacts used in production of the second ceramic tube;
FIG. 16 is a cross-sectional view of a second bonded assembly; and
FIG. 17 is a cross-sectional view of a ceramic tube according to Comparative Example 3.

Description of Embodiments

Several embodiment examples of the ceramic tube and its production method of the present invention will be described below with reference to FIGS. 1 to 17. It should be noted that, in this description, a numeric range of "A to B" includes both the numeric values A and B as the lower limit and upper limit values.
The following embodiments are described with respect to production of one ceramic tube. It is to be understood that the embodiments are applicable to production of a large number of the ceramic tubes.
The ceramic tube is preferably used as an arc tube in a discharge lamp. A high-pressure discharge lamp containing the ceramic tube can be used in various illumination devices such as road illuminations, store illuminations, car headlamps, and liquid-crystal projectors. The arc tube may be used in a metal halide lamp or a high-pressure sodium vapor lamp.
As shown in FIG. 1, a ceramic tube according to a first embodiment (hereinafter referred to as a first ceramic tube 10A) contains a light-emitting portion 12, a first capillary 14a, and a second capillary 14b that are formed integrally. The light-emitting portion 12 is adapted to emit a light inside the first ceramic tube 10A. The first capillary 14a and the second capillary 14b are disposed on either side of the light-emitting portion 12, and electrodes are sealed therein. The light-emitting portion 12 has a through-hole 16 formed in a position close to the first capillary 14a, and the through-hole 16 extends from the inside to the outside of the light-emitting portion 12 in a direction parallel to the extending direction of the first capillary 14a. In the case of producing the first ceramic tube 10A as the arc tube, the through-hole 16 is used as an inlet hole for introducing a light-emitting material or the like into the light-emitting portion 12. Therefore, the through-hole 16 is sealed after the introduction of the light-emitting material or the like. In addition to an inert start gas such as an argon gas, mercury and metal halide additives are contained in the light-emitting portion 12. Incidentally, the mercury additive is not an essential component.
As shown in FIG. 2, the first ceramic tube 10A is produced by bonding and firing a first ceramic compact 22A containing a first curved portion 18a and a first cylindrical portion 20a formed integrally and a second ceramic compact 22B containing a second curved portion 18b and a second cylindrical portion 20b formed integrally. As shown in FIG. 1, the first ceramic tube 10A has an expanded portion obtained by bonding and firing the first curved portion 18a and the second curved portion 18b (the light-emitting portion 12) at the center, and further has the first capillary 14a and the second capillary 14b that are formed integrally with either end of the light-emitting portion 12. A hollow portion 24 is formed in the first ceramic tube 10A, and extends from the first capillary 14a to the second capillary 14b.
As shown in FIG. 3, a first electrode 26A and a second electrode 26B are inserted into and sealed in the first capillary 14a and the second capillary 14b respectively. The first electrode 26A has a first electrode shaft 28a, a first coil 30a wound around the inner end of the first electrode shaft 28a, and a first lead 32a connected to the outer end of the first electrode shaft 28a by welding or the like. The first lead 32a is sealed in the inner wall of the first capillary 14a, whereby the entire first electrode 26A is sealed in the first capillary 14a. Similarly, the second electrode 26B has a second electrode shaft 28b, a second coil 30b wound around the inner end of the second electrode shaft 28b, and a second lead 32b connected to the outer end of the second electrode shaft 28b by welding or the like. The second lead 32b is sealed in the inner wall of the second capillary 14b, whereby the entire second electrode 26B is sealed in the second capillary 14b. A region between the first coil 30a and the second coil 30b in the light-emitting portion 12 acts as a discharge area 34 for emitting a light.
In the light-emitting portion 12, a first curved surface 36a is formed between a portion corresponding to the discharge area 34 and the first capillary 14a, and the diameter thereof decreases continuously from the portion corresponding to the discharge area 34 to the first capillary 14a. Similarly, a second curved surface 36b is formed between the portion corresponding to the discharge area 34 and the second capillary 14b, and the diameter thereof decreases continuously from the portion to the second capillary 14b.
In the light-emitting portion 12, the through-hole 16 is formed on the first curved surface 36a closer to the first capillary 14a than a position corresponding to the inner end of the first electrode 26A (the first coil 30a). Specifically, as shown in FIG. 3, in the light-emitting portion 12, when the inner opening of the through-hole 16 has a point 35 farthest from the axis line n1 of the first capillary 14a, the axis line n1 has a position Pa on a perpendicular line Ln (perpendicular to the axis line n1) extending from the point 35, the axis line n1 has a position Pb on the inner end of the first electrode 26A, the direction from the position Pb toward the first capillary 14a is considered as the positive direction, and the direction from the position Pb toward the second capillary 14b is considered as the negative direction, it is preferred that the position Pa is equal to the position Pb or is shifted from the position Pb in the positive direction. In this case, the axis line m1 of the through-hole 16 is preferably parallel to the axis line n1 of the first capillary 14a.
As in a ceramic tube shown in FIG. 4 according to a comparative example, the axis line m1 of the through-hole 16 may be perpendicular to the axis line n1 of the first capillary 14a. However, such a structure has the following disadvantage.
As shown in FIG. 2, the first ceramic tube 10A is produced by bonding and firing the first and second ceramic compacts 22A and 22B. For example, in the case of using a gel casting process for preparing the first ceramic compact 22A having the above structure with the through-hole 16, this process requires a casting mold shown in FIG. 5A, which has a stationary mold 38 and a movable mold 40 for forming the first curved portion 18a and the first cylindrical portion 20a, and further has a pin 42 for forming the through-hole 16. Furthermore, a hole 44, into which the pin 42 is inserted, has to be formed in the stationary mold 38, and a clearance hole 46, into which the end of the pin 42 is inserted, has to be formed in the movable mold 40. In addition, when the casting mold is removed, the pin 42 is drawn out as shown in FIG. 5B, and then the movable mold 40 is separated as shown in FIG. 5C. Thus, the process requires a mechanism and a control system for controlling the reciprocating movements of the movable mold 40 and the pin 42. Consequently, the production equipment has a large complicated structure, resulting in high production cost.
In contrast, in a case where the axis line m1 of the through-hole 16 is parallel to the axis line n1 of the first capillary 14a in the first ceramic tube 10A, the above problem is not caused. In this case, a simple first casting mold can be used for forming the first ceramic compact 22A without significant design change. Thus, as shown in FIGS. 6A and 6B, in the first casting mold, a pin 48 for forming the through-hole 16 is formed on a surface of the movable mold 40 facing the stationary mold 38, and a clearance hole 50, into which the pin 48 is inserted, is formed on the stationary mold 38. In addition, the first casting mold can be removed only by drawing out the movable mold 40 as shown in FIG. 6B. Therefore, the specific mechanism and control system for controlling the pin are not required. Thus, only the mechanism and control system for controlling the reciprocating movement of the movable mold 40 is required, and the large complicated structure of the production equipment is not required.
In the first ceramic tube 10A, the through-hole 16 is preferably closer to the first capillary 14a than the position corresponding to the inner end of the first electrode 26A (the first coil 30a) in the light-emitting portion 12, and is further preferably closer by 0.5 mm or more to the first capillary 14a than the inner end of the first electrode 26A. Consequently, the light transmittance of the first ceramic tube 10A is not affected by the through-hole 16, and the light-emitting efficiency and the light distribution are not deteriorated by the through-hole 16.
In the light-emitting portion 12, the distance La between the axis line m1 of the through-hole 16 and the axis line n1 of the first capillary 14a is preferably 0.55 or more times as large as the outer diameter Da of the first capillary 14a. In this case, when the first ceramic tube 10A is used as the arc tube, the sealing portion of the through-hole 16 can be prevented from acting as the coldest portion and from being corroded, during the lighting. In the structure of the first ceramic tube 10A, a portion around the first capillary 14a may have a high heat capacity, and thereby may act as the coldest portion during the lighting. Even when the portion does not act as the coldest portion, the portion is likely to have a low temperature. If the through-hole 16 is formed in this portion, a large amount of the light-emitting material is not vaporized and is stored in the vicinity of the through-hole 16 even during the lighting, whereby the corrosion is rapidly caused. Therefore, the through-hole 16 is preferably formed in a portion, which has a low heat capacity and exhibits a relatively high temperature during the lighting, e.g. on the first curved surface 36a. The distance La is preferably 1.6 or less times as large as the outer diameter Da of the first capillary 14a. When the distance La is more than 1.6 times as large as the outer diameter Da, the light-emitting portion 12 is readily cracked due to solidification shrinkage of a gelling agent in the molding process.
A method for producing the first ceramic tube 10A will be described below with reference to FIG. 7.
In step S1 of FIG. 7, the first and second ceramic compacts 22A and 22B are prepared as shown in FIG. 2. The first ceramic compact 22A has a through-hole 52, which acts as the through-hole 16 when in the sintered body (the first ceramic tube 10A). The second ceramic compact 22B does not have through-holes.
Specifically, in step 51a, a ceramic powder, a dispersion medium, a gelling agent, and the like are mixed to prepare a gel casting slurry (hereinafter referred to as a molding slurry). In step S1b, the molding slurry is cast into and then solidified in a first casting mold for forming the first ceramic compact 22A and a second casting mold for forming the second ceramic compact 22B. As shown in FIGS. 6A and 6B, in the first casting mold, the movable mold 40 has the pin 48 for forming the through-hole 16, and the stationary mold 38 has the clearance hole 50, which the pin 48 is inserted into. In the second casting mold, the pin 48 and the clearance hole 50 are not formed. Then, in step S1c, the first and second casting molds are separated to obtain the first and second ceramic compacts 22A and 22B shown in FIG. 2.
The first and second ceramic compacts 22A and 22B each have a cylindrical shape with a hollow portion 54. More specifically, the shapes of the first and second ceramic compacts 22A and 22B are similar to shapes obtained by dividing the first ceramic tube 10A as a final product (see FIG. 1) into two parts at the length-direction center of the axis line p1. As shown in FIGS. 2 and 8, the first ceramic compact 22A has a shape containing the first curved (bowl-shaped) portion 18a and the first cylindrical portion 20a integrally formed. The through-hole 52 is formed on the first curved portion 18a, and the axis line m2 of the through-hole 52 is parallel to the axis line n2 of the first cylindrical portion 20a. The second ceramic compact 22B has a shape containing the second curved (bowl-shaped) portion 18b and the second cylindrical portion 20b integrally formed.
Joining surfaces 56a and 56b of the first and second ceramic compacts 22A and 22B are positioned at the ends of the first and second curved portions 18a and 18b, and are parallel to a plane perpendicular to the axis direction of the first and second ceramic compacts 22A and 22B. Though not shown in the drawings, the outer and inner peripheries of the joining surfaces 56a and 56b of the first and second ceramic compacts 22A and 22B may be chamfered to form e.g. an R- or C-surface.
In step S2 of FIG. 7, the first and second ceramic compacts 22A and 22B are bonded to each other to prepare a first bonded assembly 58A.
Specifically, in step S2a, a ceramic powder, a solvent, a binder, and the like are mixed to prepare a bonding slurry (hereinafter referred to as a bonding slurry 60, see FIG. 8). In step S2b, the bonding slurry 60 is applied (supplied) e.g. to the joining surface 56a of the first ceramic compact 22A. Then, in step S2c, the joining surface 56a of the first ceramic compact 22A is pressed toward the joining surface 56b of the second ceramic compact 22B to obtain the first bonded assembly 58A shown in FIG. 8. The shape of the first bonded assembly 58A (see FIG. 8), which is obtained by bonding the first and second ceramic compacts 22A and 22B, is geometrically similar to the shape of the first ceramic tube 10A, which is obtained by firing the first bonded assembly 58A. The first bonded assembly 58A is shrunk to produce the first ceramic tube 10A.
In step S3 of FIG. 7, the first bonded assembly 58A is fired to produce the sintered body (the first ceramic tube 10A).
In the method for producing the first ceramic tube 10A, the through-hole 52, formed on the first curved portion 18a of the first ceramic compact 22A, extends along the axis direction of the first cylindrical portion 20a. Therefore, in the first ceramic tube 10A produced by bonding and firing the first and second ceramic compacts 22A and 22B, the through-hole 16 can be easily formed in the position closer to the first capillary 14a in the light-emitting portion 12. The through-hole 16 extends from the inside to the outside of the light-emitting portion 12 in the direction parallel to the extending direction of the first capillary 14a. Furthermore, the through-hole 52 can be formed on the first curved portion 18a in the first ceramic compact 22A by using the simple first casting mold without the significant design change and the additional mechanism. Therefore, the first ceramic tube 10A can be produced without using the large complicated structure of the production equipment. Thus, the first ceramic tube 10A, which has the through-hole 16 for introducing the light-emitting material or the like into the light-emitting portion 12, can be easily produced by using a simple production equipment at low production cost, high productivity, and high yield.
A ceramic tube according to a second embodiment (hereinafter referred to as a second ceramic tube 10B) will be described below with reference to FIGS. 9 to 16.
The second ceramic tube 10B is approximately equal to the first ceramic tube 10A, and is different from the first ceramic tube 10A in that, as shown in FIG. 9, the light-emitting portion 12 has a third capillary 70 formed in a position close to the first capillary 14a, the third capillary 70 protrudes in a direction parallel to the extending direction of the first capillary 14a, and a through-hole 72 extends from the end of the third capillary 70 to the inside of the light-emitting portion 12. In the case of producing the second ceramic tube 10B as the arc tube, the third capillary 70 is used as the inlet hole for introducing the light-emitting material or the like into the light-emitting portion 12. Therefore, the through-hole 72 in the third capillary 70 is sealed after the introduction of the light-emitting material or the like.
As shown in FIG. 10, in the light-emitting portion 12, the third capillary 70 is formed on the first curved surface 36a closer to the first capillary 14a than the position corresponding to the inner end of the first electrode 26A (the first coil 30a). Also in the second ceramic tube 10B, as in the first ceramic tube 10A, when the inner opening of the through-hole 72 has the point 35 farthest from the axis line n1 of the first capillary 14a, the axis line n1 has the position Pa on the perpendicular line Ln (perpendicular to the axis line n1) extending from the point 35, the axis line n1 has the position Pb on the inner end of the first electrode 26A, the direction from the position Pb toward the first capillary 14a is considered as the positive direction, and the direction from the position Pb toward the second capillary 14b is considered as the negative direction, it is preferred that the position Pa is equal to the position Pb or is shifted from the position Pb in the positive direction. In addition, it is preferred that the axis line m3 of the third capillary 70 is parallel to the axis line n1 of the first capillary 14a.
In this case, a simple first casting mold can be used for forming the first ceramic compact 22A without significant design change. Thus, as shown in FIGS. 11A and 11B, in the first casting mold, a pin 74 for forming the through-hole 72 is formed on a surface of the movable mold 40 facing the stationary mold 38, and a cavity 76 for forming the third capillary 70 and a clearance hole 78, into which the pin 74 is inserted, are formed on the stationary mold 38. The specific mechanism and control system for controlling the pin 74 are not required. Thus, only the mechanism and control system for controlling the reciprocating movement of the movable mold 40 is required, and the large complicated structure of the production equipment is not required.
In the second ceramic tube 10B, the third capillary 70 is preferably positioned closer to the first capillary 14a than the position corresponding to the inner end of the first electrode 26A (the first coil 30a) in the light-emitting portion 12, and is further preferably positioned closer by 0.5 mm or more to the first capillary 14a than the inner end of the first electrode 26A. Consequently, the light transmittance of the second ceramic tube 10B is not affected by the third capillary 70, and the light-emitting efficiency and the light distribution are not deteriorated by the third capillary 70.
In the light-emitting portion 12, the distance Lb between the axis line m3 of the third capillary 70 and the axis line n1 of the first capillary 14a is 0.55 or more times as large as the outer diameter Da of the first capillary 14a. In this case, when the second ceramic tube 10B is used as the arc tube, the sealing portion of the through-hole 72 in the third capillary 70 can be prevented from acting as the coldest portion and from being corroded, during the lighting. In the structure of the second ceramic tube 10B, a portion around the first capillary 14a may have a high heat capacity, and thereby may act as the coldest portion during the lighting. Even when the portion does not act as the coldest portion, the portion is likely to have a low temperature. If the third capillary 70 is formed in this portion, the heat capacity is often further increased, and the temperature is often further lowered, so that a large amount of the light-emitting material is not vaporized and is stored in the vicinity of the third capillary 70 even during the lighting, whereby the corrosion is rapidly caused. Therefore, the third capillary 70 is preferably formed in a portion, which has a low heat capacity and exhibits a relatively high temperature during the lighting, e.g. on the first curved surface 36a. The distance Lb is preferably 1.6 or less times as large as the outer diameter Da of the first capillary 14a. When the distance Lb is more than 1.6 times as large as the outer diameter Da of the first capillary 14a, the light-emitting portion 12 is readily cracked due to solidification shrinkage of a gelling agent in the molding process.
As shown in FIG. 12, when the inner surface of the light-emitting portion 12 has a cross-sectional outline 80 in a plane containing the axis line m3 of the third capillary 70, it is preferred that the axis line m3 and a tangent line 84 at an intersection 82 between the outline 80 and the axis line m3 form an angle θ of 30° or more. When the angle θ is excessively lowered, an edge having a sharp cross-sectional angle is formed at the boundary between the through-hole 72 in the third capillary 70 and the inner surface of the light-emitting portion 12. The edge is easily chipped off in the production, transport, or the like, so that waste may be generated, and the chipped portion may be cracked. When the angle θ is 30° or more, this problem is not caused.
As shown in FIG. 13, when the third capillary 70 has a base point 88, which is a reference point of the maximum length Lc of the third capillary 70 along the axis line m3, it is preferred that the maximum length Lc of the third capillary 70 is 1/10 to 5/10 of the length Ld between the base point 88 and the end of the first capillary 14a along the axis line n1. When the maximum length Lc of the third capillary 70 is excessively reduced, it is difficult to seal the through-hole 72 in the third capillary 70. When the maximum length Lc of the third capillary 70 is excessively increased, the third capillary 70 is easily deformed in the firing step, and the third capillary 70 is likely to act as the coldest portion and thereby readily corroded during the lighting.
A method for producing the second ceramic tube 10B will be described below with reference to FIG. 14.
In step S101 of FIG. 14, the first and second ceramic compacts 22A and 22B are prepared as shown in FIG. 15. The first ceramic compact 22A has a third cylindrical portion 90 and a through-hole 92, which acts as the third capillary 70 and the through-hole 72 in the sintered body (the second ceramic tube 10B). The second ceramic compact 22B does not have the third cylindrical portion 90 and the through-hole 92.
Specifically, the ceramic powder, the dispersion medium, the gelling agent, and the like are mixed to prepare the molding slurry (step S101a of FIG. 14), the molding slurry is cast into and then solidified in the first casting mold (see FIG. 11A) and the second casting mold (not shown) (step S101b), and then the first and second casting molds are separated (step S101c), to obtain the first and second ceramic compacts 22A and 22B shown in FIG. 15.
As shown in FIG. 15, the first ceramic compact 22A has a shape containing the first curved (bowl-shaped) portion 18a and the first cylindrical portion 20a integrally formed. The first curved portion 18a has the third cylindrical portion 90 protruding in the direction parallel to the extending direction of the first cylindrical portion 20a, and the through-hole 92 extends from the end of the third cylindrical portion 90 to the inside of the first curved portion 18a. The axis line m4 of the third cylindrical portion 90 is parallel to the axis line n2 of the first cylindrical portion 20a. The second ceramic compact 22B has a shape containing the second curved (bowl-shaped) portion 18b and the second cylindrical portion 20b integrally formed.
In step S102 of FIG. 14, the first and second ceramic compacts 22A and 22B are bonded to each other to prepare a second bonded assembly 58B shown in FIG. 16. Specifically, the ceramic powder, the solvent, the binder, and the like are mixed to prepare the bonding slurry 60 (step S102a), the bonding slurry 60 is applied (supplied) e.g. to the joining surface 56a of the first ceramic compact 22A (step S102b), and then the joining surface 56a of the first ceramic compact 22A is pressed toward the joining surface 56b of the second ceramic compact 22B, to obtain the second bonded assembly 58B shown in FIG. 16.
In step S103 of FIG. 14, the second bonded assembly 58B is fired to produce the sintered body (the second ceramic tube 10B).
In the method for producing the second ceramic tube 10B, the third cylindrical portion 90, formed on the first curved portion 18a of the first ceramic compact 22A, extends along the axis direction of the first cylindrical portion 20a. Therefore, in the second ceramic tube 10B produced by bonding and firing the first and second ceramic compacts 22A and 22B, the third capillary 70 can be easily formed in the position closer to the first capillary 14a in the light-emitting portion 12. The third capillary 70 extends from the inside to the outside of the light-emitting portion 12 in the direction parallel to the extending direction of the first capillary 14a. Furthermore, the third cylindrical portion 90 and the through-hole 92 can be formed on the first curved portion 18a in the first ceramic compact 22A by using the simple first casting mold without the significant design change and the additional mechanism. Therefore, the second ceramic tube 10B can be produced without using the large complicated structure of the production equipment. Thus, the second ceramic tube 10B, which has the third capillary 70 and the through-hole 72 for introducing the light-emitting material or the like into the light-emitting portion 12, can be easily produced by using a simple production equipment at low production cost, high productivity, and high yield.
Preferred embodiments of materials and the like used in the production method of this invention will be described below. When it is not necessary to distinguish the above first and second ceramic compacts 22A and 22B, they may be referred to simply as the ceramic compacts 22. When it is not necessary to distinguish the joining surfaces 56a and 56b, they may be referred to simply as the joining surfaces 56.

(Ceramic compact)

In the above-described production method, the ceramic compact 22 is prepared. The ceramic compact 22 can be easily produced by various known method. For example, the ceramic compact 22 may be produced by a gel casting method. In the gel casting method, the molding slurry containing an inorganic powder and an organic compound is cast into the casting mold, a chemical reaction of the organic compound (such as a reaction between the dispersion medium and the gelling agent or a reaction of the gelling agent) is carried out to solidify the slurry, and the casting mold is separated. The molding slurry contains the dispersion medium and the gelling agent in addition to the raw material powder, and may further contain a dispersing agent or catalyst for controlling the viscosity or the solidification. The components will be described below.

(Raw material powder)

The ceramic powder used for the ceramic compact 22 may contain alumina, aluminum nitride, zirconia, YAG, or a mixture of two or more thereof. A sintering aid such as magnesium oxide may be used to improve the sintering or the property. Preferred examples of the sintering aids include ZrO₂, Y₂O₃, La₂O₃, and SC₂O₃.

(Dispersion medium)

The dispersion medium is preferably a reactive medium such as an organic dispersion medium having a reactive functional group. It is preferred that the organic dispersion medium having the reactive functional group is a liquid substance that can be chemically bonded to the gelling agent to solidify the molding slurry and can be used for preparing the molding slurry with a high fluidity suitable for the casting. The organic dispersion medium, which can be chemically bonded to the gelling agent to solidify the molding slurry, preferably has a functional group capable of forming a chemical bond with the gelling agent (such as a hydroxyl, carboxyl, or amino group) in the molecule.
In view of preparing the molding slurry with a high fluidity suitable for the casting, the organic dispersion medium preferably has a lower viscosity, and particularly preferably has a viscosity of 20 cps or less at 20°C.
A small amount of a polyol or a polybasic acid can be effectively used for improving the strength as long as it does not act to greatly increase the viscosity of the molding slurry.

(Gelling agent)

The gelling agent can be reacted with the reactive functional group of the dispersion medium to solidify the slurry. The gelling agent may be as follows.
The gelling agent preferably has a viscosity of 3000 cps or less at 20°C. The gelling agent preferably has a highly reactive isocyanate group (-N=C=O) and/or an isothiocyanate group (-N=C=S).
Examples of the gelling agents having an isocyanate group and/or an isothiocyanate group include MDI (4,4'-diphenylmethane diisocyanate) based agents (resins), HDI (hexamethylene diisocyanate) based agents (resins), TDI (tolylene diisocyanate) based agents (resins), IPDI (isophorone diisocyanate) based agents (resins), and isothiocyanates (resins). In the solidification, the slurry containing the gelling agent is shrunk by a condensation reaction of the resin. Particularly in the molding of the first ceramic compact 22A for the second ceramic tube 10B, in a case where the slurry exhibits a high shrinkage ratio in the solidification, a force acts on a portion between the first capillary 14a and the third capillary 70 due to the shrinkage, and the portion is often cracked. From the viewpoint of preventing the cracking, it is preferred that the slurry exhibits a lower shrinkage ratio (of 3% or less) in the solidification. The MDI based agent can be preferably used to achieve a low dry shrinkage ratio (of 3% or less).
The molding slurry for preparing the ceramic compact 22 may be selected from examples described in Japanese Laid-Open Patent Publication No. 2008-044344 , International Publication No. WO 2002/085590 , etc. For example, the molding slurry may be prepared in the following manner. Thus, the raw material powder may be dispersed first in the dispersion medium, and then the gelling agent may be added thereto to prepare the molding slurry. Alternatively, the raw material powder and the gelling agent may be simultaneously added to and dispersed in the dispersion medium to prepare the molding slurry. In view of workability in the casting or the like, the viscosity of the molding slurry is preferably 30000 cps or less, more preferably 20000 cps or less, at 20°C. The viscosity of the molding slurry can be controlled by changing the viscosities of the above reactive dispersion medium and the gelling agent, and also by changing the type of the powder, the amount of the dispersing agent, and the concentration of the slurry (the volume ratio % of the powder to the entire slurry). In general, the concentration of the molding slurry is preferably 25% to 75% by volume. In view of reducing the cracking due to the dry shrinkage, the concentration is more preferably 35% to 75% by volume.

(Bonding slurry)

In the preparation of the bonded assembly, the bonding slurry 60 is used to bond the ceramic compacts 22 to each other. The bonding slurry 60 is preferably a non-self-curable slurry, which is not solidified by a chemical reaction. The non-self-curable bonding slurry 60 can be easily maintained under a surface tension to obtain a joining portion with a small surface roughness (after drying and after sintering). Furthermore, the non-self-curable bonding slurry 60 can form a layer under the surface tension. Therefore, the shape of the layer of the bonding slurry 60 can be easily controlled, and thus the cross-sectional shape of the joining portion can be controlled (after sintering).
The bonding slurry 60 may contain the raw material powder used in the molding slurry and the unreactive dispersion medium, and may further contain a binder such as a polyvinyl acetal or ethyl cellulose resin, or the like. In addition, the bonding slurry 60 may contain a dispersing agent such as DOP (bis(2-ethylhexyl) phthalate) and an organic solvent such as acetone or isopropanol, or the like for controlling the viscosity in the mixing step.
The bonding slurry 60 can be prepared by mixing the raw material powder, the solvent, and the binder in a common ceramic paste or slurry production method using a triroll mill, a pot mill, etc. The dispersing agent or the organic solvent may be appropriately added to the bonding slurry 60. Specifically, butyl carbitol, butyl carbitol acetate, terpineol, or the like may be used in the bonding slurry 60.

(Preparation of bonded assembly)

Two or more ceramic compacts 22 are bonded to each other by the bonding slurry 60 to prepare the bonded assembly.

(Bonding slurry layer formation step)

In the preparation of the bonded assembly, first the layer of the bonding slurry 60 is formed, while maintaining the surface tension, between the joining surfaces 56 of the two or more ceramic compacts 22 to be bonded.
The bonding slurry 60 may be applied between the joining surfaces of the ceramic compacts 22 by a known method such as a dispenser, screen printing, or metal mask printing method.
To form the layer of the bonding slurry 60 while maintaining the surface tension, after the bonding slurry 60 is applied between the joining surfaces 56 of the ceramic compacts 22 or to the joining surface 56 of the ceramic compact 22, before the applied bonding slurry 60 is dried, the joining surfaces 56 may be maintained at a predetermined distance. In a case where the bonding slurry 60 is the non-self-curable slurry, after the bonding slurry 60 is applied to the joining surface 56, before the drying, the shape of the bonding slurry 60 is maintained due to the surface tension for a certain time.
The shape of the layer of the bonding slurry 60 can be controlled while maintaining the surface tension by controlling or changing the distance between the joining surfaces 56 of the ceramic compacts 22, by vibrating the bonding slurry 60, by rotating the bonding slurry 60, or by relatively displacing the ceramic compact 22 in the direction parallel to the joining surface 56. Especially, the shape of the layer of the bonding slurry 60 can be easily controlled by changing the load acting in the direction perpendicular to the joining surfaces 56 and/or the distance between the joining surfaces 56, to obtain the sintered body (the ceramic tube) without defects such as air bubbles.

(Drying)

The layer of the bonding slurry 60, formed between the joining surfaces 56 of the ceramic compacts 22 facing each other, is dried. The drying step may be appropriately controlled depending on the composition and the application amount of the bonding slurry 60. In general, the drying is carried out at a temperature of 40°C to 200°C for about 5 to 120 minutes.
In thus obtained bonded assembly, at least two ceramic compacts 22 are bonded by a joining portion (dried layer) formed by drying the layer of the bonding slurry 60. Though the two ceramic compacts 22 are bonded in the preparation of the bonded assembly, the preparation is not limited thereto. Three or more ceramic compacts 22 may be bonded by the layers of the bonding slurry 60 simultaneously or successively, to obtain the bonded assembly.

(Production of sintered body (ceramic tube))

The bonded assembly is fired, whereby sinterable components in the ceramic compacts 22 and the joining portion (the dried layer) are sintered to obtain the sintered body. Before the sintering step, the bonded assembly may be degreased or calcined.

Examples

[First Example]

Sintered bodies (ceramic tubes) were produced by production methods according to Examples 1 and 2 and Comparative Examples 1 to 3 respectively. The cracking of each sintered body and the leakage of the light-emitting portion were measured.

(Example 1)

Ten first ceramic tubes 10A shown in FIG. 1 were produced by the production method of FIG. 7.
The molding slurry for forming the first and second ceramic compacts 22A and 22B (see FIG. 2) was prepared in the following manner. A raw material powder containing 100 parts by weight of an alumina powder and 0.025 parts by weight of a magnesia, 30 parts by weight of a dispersion medium of a polybasic acid ester, 4 parts by weight of a gelling agent of an MDI resin, 2 parts by weight of a dispersing agent, and 0.2 parts by weight of a triethylamine catalyst were mixed to obtain the molding slurry.
The molding slurry was cast at the room temperature into the first casting mold (see FIG. 6A) and the second casting mold (not shown), composed of an aluminum alloy, and solidified at the room temperature for 1 hour. Then, the molds were separated from the solidified slurries, and the resultant solids were left at the room temperature for 2 hours and at 90°C for 2 hours. Ten first ceramic compacts 22A and ten second ceramic compacts 22B were prepared in this manner. The outer and inner peripheries of the joining surfaces 56a and 56b of the first and second ceramic compacts 22A and 22B were chamfered (to form e.g. an R-surface) within a radius range of 0.05 to 0.15 mm.
The bonding slurry 60 was prepared in the following manner. 100 parts by weight of a raw material powder of an alumina powder, 0.025 parts by weight of a magnesia, 100 parts by weight of terpineol, 30 parts by weight of butyl carbitol, and 8 parts by weight of a polyvinyl acetal resin were mixed to obtain the bonding slurry 60.
A screen plate having an emulsion thickness of 100 µm and a mesh of #290 was prepared. The screen plate had a ring-shaped pattern (having an inner diameter of 12.8 mm and an outer diameter of 13.7 mm) corresponding to the joining surface 56a of the first ceramic compact 22A. The first ceramic compact 22A was positioned, for example, on a stage of a screen printer such that the joining surface 56a
(having an inner diameter of 12.5 mm and an outer diameter of 14.0 mm) was parallel to the screen plate. The bonding slurry 60 was applied to the joining surface 56a of the first ceramic compact 22A by the screen printer using the screen plate. Then, the joining surface 56a of the first ceramic compact 22A was pressed toward the joining surface 56b of the second ceramic compact 22B, and dried by a dryer at 95°C for 15 minutes. Ten first bonded assemblies 58A having the through-holes 52 on the first curved portions 18a (see FIG. 8) were prepared in this manner.
Each of the prepared first bonded assemblies 58A was calcined in the air at 1200°C, and fired at 1800°C in a hydrogen/nitrogen (3/1) atmosphere, to increase the density and translucency. Consequently, the sintered body (the first ceramic tube 10B) shown in FIG. 1 was obtained. In the sintered body, the light-emitting portion 12 had the through-hole 16 formed in a position close to the first capillary 14a, the through-hole 16 extended from the inside to the outside of the light-emitting portion 12 in a direction parallel to the extending direction of the first capillary 14a, the light-emitting portion 12 had an outer diameter of 11 mm, and the first and second capillaries had a length of 17 mm. The through-hole 16 was formed such that the position Pa was shifted by 0.5 mm from the position Pb in the positive direction as shown in FIG. 3.
Thus produced ten sintered bodies (the first ceramic tubes 10A) of Example 1 did not have a cracked or deformed portion. The thermal shock resistances of the sintered bodies were evaluated by an in-water rapid cooling method. As a result, in all the sintered bodies, any cracking was not caused even at 150°C. Thus, the sintered bodies had resistances equal to that of a ceramic tube having the same shape except for the through-hole 16. Furthermore, after the thermal shock resistance evaluation, the through-holes 16 on the light-emitting portions 12 of the sintered bodies were closed, and the leakages of the light-emitting portions 12 were measured by an He (helium) leakage measuring apparatus. As a result, the sintered bodies each exhibited a leakage of 1×10^-8 atm·cc/sec or less. The sintered bodies were each used as an arc tube, and it was confirmed that the light transmittances of the sintered bodies were not affected by the through-holes 16. In this confirmation test, the practical luminance of each sintered body was measured, to evaluate whether the measured value was at least 98% of the designed luminance (the design value) or not. In Example 1, the measured values of the sintered bodies were 99.5% of the design value.

(Example 2)

Ten sintered bodies of Example 2 (second ceramic tubes 10B) shown in FIG. 9 were produced by the production method of FIG. 14.
The molding slurry was prepared in the same manner as Example 1. The molding slurry was cast at the room temperature into the first casting mold (see FIG. 11A) and the second casting mold (not shown), composed of an aluminum alloy, and solidified at the room temperature for 1 hour. Then, the molds were separated from the solidified slurries, and the resultant solids were left at the room temperature for 2 hours and at 90°C for 2 hours. Ten first ceramic compacts 22A and ten second ceramic compacts 22B were prepared in this manner. Also in this example, the outer and inner peripheries of the joining surfaces 56a and 56b of the first and second ceramic compacts 22A and 22B were chamfered (to form e.g. an R-surface) within a radius range of 0.05 to 0.15 mm.
The bonding slurry 60 was prepared in the same manner as Example 1, and was applied to the joining surface 56a of the first ceramic compact 22A by a screen printer using a screen plate. The screen plate had the same structure as that of Example 1.
Then, the joining surface 56a of the first ceramic compact 22A was pressed toward the joining surface 56b of the second ceramic compact 22B, and dried by a dryer at 95°C for 15 minutes. Ten second bonded assemblies 58B having the third cylindrical portions 90 and the through-holes 92 on the first curved portions 18a (see FIG. 16) were prepared in this manner.
Each of the prepared second bonded assemblies 58B was calcined and fired in the same manner as Example 1, to increase the density and translucency. Consequently, the second ceramic tube 10B shown in FIG. 9 was obtained. In the second ceramic tube 10B, the light-emitting portion 12 had an outer diameter of 11 mm, the first and second capillaries 14a and 14b had a length of 17 mm, the light-emitting portion 12 had the third capillary 70 formed in a position close to the first capillary 14a, the third capillary 70 protruded in a direction parallel to the extending direction of the first capillary 14a, and the through-hole 72 extended from the end of the third capillary 70 to the inside of the light-emitting portion 12. The maximum length Lc (see FIG. 13) of the third capillary 70 was 8 mm (Ld = 21 mm). The through-hole 72 was such that the position Pa was shifted by 0.5 mm from the position Pb in the positive direction as shown in FIG. 10.
Thus produced ten sintered bodies of Example 2 did not have a cracked or deformed portion. The thermal shock resistances of the sintered bodies were evaluated by an in-water rapid cooling method. As a result, in all the sintered bodies, the cracking was not caused even at 150°C. Thus, the sintered bodies had resistances equal to that of an arc tube having the same shape except for the third capillary 70. Furthermore, after the thermal shock resistance evaluation, the leakages of the sintered bodies were measured by an He leakage measuring apparatus. As a result, the sintered bodies each exhibited a leakage of 1×10^-8 atm·cc/sec or less. The sintered bodies were each used as an arc tube, and it was confirmed that the light transmittances of the sintered bodies were not affected by the third capillaries 70 and the through-holes 72. In this confirmation test, the practical luminance of each sintered body was measured, to evaluate whether the measured value was at least 98% of the designed luminance (the design value) or not. In Example 2, the measured values of the sintered bodies were 99.5% of the design value.

(Comparative Example 1)

Ten sintered bodies of Comparative Example 1 were produced as follows. First, the molding slurry was prepared in the same manner as Example 1. The molding slurry was cast at the room temperature into the second casting mold composed of an aluminum alloy, and solidified at the room temperature for 1 hour. Then, the mold was separated from the solidified slurry, and the resultant solid was left at the room temperature for 2 hours and at 90°C for 2 hours. Twenty second ceramic compacts 22B were prepared in this manner. One of each pair of the second ceramic compacts 22B was subjected to a hole forming processing using a drill or the like, whereby a through-hole having a diameter of 0.3 mm was formed on the second curved portion 18b.
The bonding slurry 60 was prepared in the same manner as Example 1, and was applied to the joining surface 56b of the one second ceramic compact 22B by a screen printer using a screen plate. Then, the joining surfaces 56b of each pair of the second ceramic compacts 22B were pressed toward each other, and dried by a dryer at 95°C for 15 minutes. Ten bonded assemblies were prepared in this manner. Each of the prepared bonded assemblies was calcined and fired in the same manner as Example 1. Consequently, ten sintered bodies of Comparative Example 1 were obtained.
Thus produced ten sintered bodies of Comparative Example 1 did not have a cracked or deformed portion. The thermal shock resistances of the sintered bodies were evaluated by an in-water rapid cooling method. As a result, the sintered bodies were cracked at 150°C. Furthermore, after the thermal shock resistance evaluation, the leakages of the sintered bodies were measured by an He leakage measuring apparatus. As a result, each sintered body exhibited a leakage of 1×10^-8 atm·cc/sec or less.

(Comparative Example 2)

Ten sintered bodies of Comparative Example 2 were produced as follows. First, twenty second ceramic compacts 22B were prepared in the same manner as Comparative Example 1. One of each pair of the second ceramic compacts 22B was subjected to a hole forming processing using a drill or the like, whereby a through-hole having a diameter of 0.9 mm was formed on the second curved portion 18b.
Then, each pair of the second ceramic compacts 22B were bonded to each other, and a ceramic pipe was connected to the through-hole portion. Ten bonded assemblies were prepared in this manner. Each of the prepared bonded assemblies was calcined and fired in the same manner as Example 1. Consequently, ten sintered bodies of Comparative Example 2 were obtained.
Thus produced ten sintered bodies of Comparative Example 2 did not have a cracked or deformed portion. The thermal shock resistances of the sintered bodies were evaluated by an in-water rapid cooling method. As a result, the sintered bodies were cracked at 140°C. Furthermore, after the thermal shock resistance evaluation, the leakages of the sintered bodies were measured by an He leakage measuring apparatus. As a result, a leakage was caused in two of the ten sintered bodies.

(Comparative Example 3)

Ten sintered bodies shown in FIG. 17 of Comparative Example 3 were produced in the same manner as Example 1. In Comparative Example 3, the third capillary 70 was formed on the light-emitting portion 12 such that the axis line m3 of the third capillary 70 was perpendicular to the axis line n1 of the first capillary 14a. The third capillary 70 had a maximum length of 9 mm.
Thus produced ten sintered bodies of Comparative Example 3 were bent in the step of sintering the third capillaries 70. Therefore, the light-emitting material could not introduced into the light-emitting portions 12 in the process of producing arc tubes.

[Second Example]

In Examples 11 to 13 and Reference Examples 1 and 2 (similar to Example 1) and Examples 14 to 16 and Reference Examples 3 and 4 (similar to Example 2), a property was evaluated under various distances La between the axis line m1 of the through-hole 16 and the axis line n1 of the first capillary 14a and various distances Lb between the axis line m3 of the third capillary 70 and the axis line n1 of the first capillary 14a.

(Example 11)

Ten sintered bodies of Example 11 were produced in the same manner as Example 1 except that the distance La between the axis line m1 of the through-hole 16 and the axis line n1 of the first capillary 14a was 0.55 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Example 12)

Ten sintered bodies of Example 12 were produced in the same manner as Example 1 except that the distance La was 0.7 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Example 13)

Ten sintered bodies of Example 13 were produced in the same manner as Example 1 except that the distance La was 0.85 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Example 14)

Ten sintered bodies of Example 14 were produced in the same manner as Example 2 except that the distance Lb between the axis line m3 of the third capillary 70 and the axis line n1 of the first capillary 14a was 0.55 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Example 15)

Ten sintered bodies of Example 15 were produced in the same manner as Example 2 except that the distance Lb was 0.7 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Example 16)

Ten sintered bodies of Example 16 were produced in the same manner as Example 2 except that the distance Lb was 0.85 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Reference Example 1)

Ten sintered bodies of Reference Example 1 were produced in the same manner as Example 1 except that the distance La was 0.5 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Reference Example 2)

Ten sintered bodies of Reference Example 2 were produced in the same manner as Example 1 except that the distance La was 0.4 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Reference Example 3)

Ten sintered bodies of Reference Example 3 were produced in the same manner as Example 2 except that the distance Lb was 0.5 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

(Reference Example 4)

Ten sintered bodies of Reference Example 4 were produced in the same manner as Example 2 except that the distance Lb was 0.4 times as large as the outer diameter Da of the first capillary on the light-emitting portion 12.

The produced sintered bodies were evaluated as follows. An arc tube was produced using each sintered body, and subjected to a continuous lighting test. The lamp effective time of each arc tube (the time from the start of lighting until the luminance is reduced to 80%) was measured.
The effective time of Example 11 was considered as h (hour), and the effective times of Examples 12 to 16 and Reference Examples 1 to 4 were represented as ratios to h.

(Evaluation results)

The evaluation results are shown in Table 1.

Table 1

	Basic structure	Distance La	Distance Lb	Effective time
Reference Example 1	Example 1	Da × 0.4	-	0.7h
Reference Example 2	Example 1	Da × 0.5	-	0.8h
Reference Example 3	Example 2	-	Da × 0.4	0.7h
Reference Example 4	Example 2	-	Da × 0.5	0.8h
Example 11	Example 1	Da × 0.55	-	h
Example 12	Example 1	Da × 0.7	-	1.2h
Example 13	Example 1	Da × 0.8	-	1.3h
Example 14	Example 2	-	Da × 0.55	h
Example 15	Example 2	-	Da × 0.7	1.2h
Example 16	Example 2	-	Da × 0.8	1.3h

As is clear from the evaluation results, the effective times and thus the lifetimes of Examples 12 to 16 were equal to or longer than those of Example 11. In contrast, the effective times of Reference Examples 1 to 4 were shorter than that of Example 11. This was considered to be caused because the sealing portion of the through- hole 16 or 72 acted as the coldest portion and thus corroded during the lighting. Thus, in the light-emitting portion 12, it is preferred that the distance La between the axis line m1 of the through-hole 16 and the axis line n1 of the first capillary 14a or the distance Lb between the axis line m3 of the third capillary 70 and the axis line n1 of the first capillary 14a is 0.55 or more times as large as the outer diameter Da of the first capillary.

[Third Example]

In Examples 21 to 23 and Reference Examples 11 and 12 (similar to Example 2), cracking was evaluated under various angles θ. As shown in FIG. 12, when the inner surface of the light-emitting portion 12 has the cross-sectional outline 80 in the plane containing the axis line m3 of the third capillary 70, the axis line m3 and the tangent line 84 at the intersection 82 between the outline 80 and the axis line m3 form the angle θ.

(Example 21)

Ten sintered bodies of Example 21 were produced in the same manner as Example 2 except that the shape of the curved surface was changed, whereby the angle θ between the axis line m3 and the tangent line 84 (at the intersection 82 between the outline 80 and the axis line m3) was 30°.

(Example 22)

Ten sintered bodies of Example 22 were produced in the same manner as Example 2 except that the angle θ was 35°.

(Example 23)

Ten sintered bodies of Example 22 were produced in the same manner as Example 2 except that the angle θ was 45°.

(Reference Example 11)

Ten sintered bodies of Reference Example 11 were produced in the same manner as Example 2 except that the angle θ was 20°.

(Reference Example 12)

Ten sintered bodies of Reference Example 11 were produced in the same manner as Example 2 except that the angle θ was 25°.

Whether cracking was caused or not at the boundary 86 between the through-hole 72 of the third capillary 70 and the inner surface of the light-emitting portion 12 was evaluated immediately after the production of the sintered body and in a thermal shock resistance test using an in-water rapid cooling method (at 150°C). In each of Reference Examples 11 and 12 and Examples 21 to 23, the number of cracked sintered bodies was measured among the ten sintered bodies.

(Evaluation results)

The evaluation results are shown in Table 2. Table 2

Angle θ Cracking

Reference Example 11 20° 5/10

Reference Example 12 25° 4/10

Example 21 30° Not observed

Example 22 35° Not observed

Example 23 40° Not observed
As is clear from the evaluation results, in Examples 21 to 23, the cracking was not caused at the boundary 86. In contrast, in Reference Example 11, five of the ten sintered bodies were cracked. In Reference Example 12, four of the ten sintered bodies were cracked. Thus, it is preferred that the angle θ between the axis line m3 and the tangent line 84 (at the intersection 82 between the outline 80 and the axis line m3) is 30° or more.

[Fourth Example]

In Examples 31 to 35 and Reference Examples 21 and 22 (similar to Example 2), a property was evaluated under various maximum lengths Lc. As shown in FIG. 13, the maximum length Lc is a length along the axis line m3 of the third capillary 70.

(Example 31)

Ten sintered bodies of Example 31 were produced in the same manner as Example 2 except that the maximum length Lc of the third capillary 70 was 1/10 of the length Ld between the base point 88 and the end of the first capillary 14a along the axis line n1.

(Example 32)

Ten sintered bodies of Example 32 were produced in the same manner as Example 2 except that the maximum length Lc of the third capillary 70 was 2/10 of the length Ld.

(Example 33)

Ten sintered bodies of Example 33 were produced in the same manner as Example 2 except that the maximum length Lc of the third capillary 70 was 3/10 of the length Ld.

(Example 34)

Ten sintered bodies of Example 34 were produced in the same manner as Example 2 except that the maximum length Lc of the third capillary 70 was 4/10 of the length Ld.

(Example 35)

Ten sintered bodies of Example 35 were produced in the same manner as Example 2 except that the maximum length Lc of the third capillary 70 was 5/10 of the length Ld.

(Reference Example 21)

Ten sintered bodies of Reference Example 21 were produced in the same manner as Example 2 except that the maximum length Lc of the third capillary 70 was 0.5/10 of the length Ld.

(Reference Example 22)

Ten sintered bodies of Reference Example 22 were produced in the same manner as Example 2 except that the maximum length Lc of the third capillary 70 was 6/10 of the length Ld.

The produced sintered bodies were evaluated as follows. In the same manner as Second Example, an arc tube was produced using each sintered body, and subjected to a continuous lighting test. The lamp effective time of each arc tube (the time from the start of lighting until the luminance is reduced to 98%) was measured.
The effective time of Example 35 was considered as h (hour), and the effective times of Examples 31 to 34 and Reference Examples 21 and 22 were represented as ratios to h.

(Evaluation results)

The evaluation results are shown in Table 3.

Table 3

	Maximum length Lc of third capillary	Effective time	Note
Reference Example 21	Ld × 0.5/10	-	Unsealable
Example 31	Ld × 1/10	1.5h
Example 32	Ld × 2/10	1.4h
Example 33	Ld × 3/10	1.3h
Example 34	Ld × 4/10	1.2h
Example 35	Ld × 5/10	h
Reference Example 22	Ld × 6/10	0.8h	Deformed

As is clear from the evaluation results, the effective times and thus the lifetimes of Examples 31 to 34 were longer than those of Example 35. In contrast, the effective time of Reference Example 22 was shorter than that of Example 35. This was considered to be caused because the sealing portion of the through- hole 16 or 72 acted as the coldest portion and thus corroded during the lighting. In Reference Example 21, it was difficult to seal the through-hole, so that the leakage was caused in an early stage of the lifetime test.
Thus, it is preferred that the maximum length Lc of the third capillary 70 is 1/10 to 5/10 of the length Ld between the base point 88 and the end of the first capillary 14a along the axis line n1.

[Fifth Example]

In Examples 41 to 43 and Reference Examples 21 and 22 (similar to Example 1) and Examples 44 to 46 and Reference Examples 23 and 24 (similar to Example 2), the effect of the through-hole 16 or the third capillary 70 and the through-hole 72 on the light transmittance was evaluated under various positions Pa relative to the position Pb shown in FIGS. 3 and 10.

(Example 41)

Ten sintered bodies of Example 41 were produced in the same manner as Example 1 except that the through-hole 16 was formed such that the position Pa was equal to the position Pb. As shown in FIG. 3, in the light-emitting portion 12, the inner opening of the through-hole 16 had the point 35 farthest from the axis line n1 of the first capillary 14a, the axis line n1 had the position Pa on the perpendicular line Ln extending from the point 35, the axis line n1 had the position Pb on the inner end of the first electrode 26A, the direction from the position Pb toward the first capillary 14a was considered as the positive direction, and the direction from the position Pb toward the second capillary 14b was considered as the negative direction.

(Example 42)

Ten sintered bodies of Example 42 were produced in the same manner as Example 1. The through-hole 16 was formed such that the position Pa was shifted by 0.5 mm from the position Pb in the positive direction in the same manner as Example 1.

(Example 43)

Ten sintered bodies of Example 43 were produced in the same manner as Example 1 except that the through-hole 16 was formed such that the position Pa was shifted by 2 mm from the position Pb in the positive direction.

(Reference Example 21)

Ten sintered bodies of Reference Example 21 were produced in the same manner as Example 1 except that the through-hole 16 was formed such that the position Pa was shifted by 0.5 mm from the position Pb in the negative direction.

(Reference Example 22)

Ten sintered bodies of Reference Example 22 were produced in the same manner as Example 1 except that the through-hole 16 was formed such that the position Pa was shifted by 2 mm from the position Pb in the negative direction.

(Example 44)

Ten sintered bodies of Example 44 were produced in the same manner as Example 2 except that the third capillary 70 and the through-hole 72 were formed such that the position Pa was equal to the position Pb as shown in FIG. 10.

(Example 45)

Ten sintered bodies of Example 45 were produced in the same manner as Example 2. The third capillary 70 and the through-hole 72 were formed such that the position Pa was shifted by 0.5 mm from the position Pb in the positive direction in the same manner as Example 2.

(Example 46)

Ten sintered bodies of Example 46 were produced in the same manner as Example 2 except that the third capillary 70 and the through-hole 72 were formed such that the position Pa was shifted by 2 mm from the position Pb in the positive direction.

(Reference Example 23)

Ten sintered bodies of Reference Example 23 were produced in the same manner as Example 2 except that the third capillary 70 and the through-hole 72 were formed such that the position Pa was shifted by 0.5 mm from the position Pb in the negative direction.

(Reference Example 24)

Ten sintered bodies of Reference Example 24 were produced in the same manner as Example 2 except that the third capillary 70 and the through-hole 72 were formed such that the position Pa was shifted by 2 mm from the position Pb in the negative direction.

The produced sintered bodies were evaluated as follows. An arc tube was produced using each sintered body, the practical luminance of the arc tube was measured, and the reduction of the measured value from the designed luminance (the design value) was evaluated. The arc tube was evaluated as "A" when the measured value was 99% or more of the design value, as "B" when the measured value was 98% or more but less than 99% of the design value, as "C" when the measured value was 97% or more but less than 98% of the design value, and as "D" when the measured value was less than 97% of the design value.

(Evaluation results)

The evaluation results are shown in Table 4.

Table 4

	Basic structure	Relation of position Pa to position Pb	Evaluation
Example 41	Example 1	0	B
Example 42	Example 1	+0.5 mm	A
Example 43	Example 1	+2 mm	A
Reference Example 21	Example 1	-0.5 mm	C
Reference Example 22	Example 1	-2 mm	D
Example 44	Example 2	0	B
Example 45	Example 2	+0.5 mm	A
Example 46	Example 2	+2 mm	A
Reference Example 23	Example 2	-0.5 mm	C
Reference Example 24	Example 2	-2 mm	D

As is clear from the evaluation results, in Examples 41 to 46, the light transmittance was hardly affected by the through-hole 16 (or the third capillary 70 and the through-hole 72) on the light-emitting portion 12. Thus, in the light-emitting portion 12, it is preferred that the through-hole 16 (or the third capillary 70 and the through-hole 72) be closer to the first capillary 14a than the position corresponding to the inner end of the first electrode 26A in the first capillary 14a, and it is more preferred that the through-hole 16 (or the third capillary 70 and the through-hole 72) be closer by 0.5 mm or more to the first capillary 14a than the position corresponding to the inner end of the first electrode 26A in the first capillary 14a.
It is to be understood that the ceramic tube and the production method of the present invention are not limited to the above embodiments, and various changes and modifications may be made therein without departing from the scope of the invention.

Claims

A ceramic tube for a high-intensity discharge lamp, comprising a light-emitting portion (12), a first capillary (14a), and a second capillary (14b) that are formed integrally,
wherein
the light-emitting portion (12) is adapted to emit a light inside the ceramic tube,
the first capillary (14a) and the second capillary (14b) are disposed on either side of the light-emitting portion (12), the first and second capillaries being provided for sealing electrodes,
the light-emitting portion (12) has a through-hole (16) formed in a position close to the first capillary (14a), and
the through-hole (16) extends from an inside to an outside of the light-emitting portion (12) in a direction parallel to the extending direction of the first capillary (14a).
The ceramic tube according to claim 1,
wherein the axis line (m1) of the through-hole (16) is parallel to the axis line (n1) of the first capillary (14a).
The ceramic tube according to claim 1,
wherein in the light-emitting portion (12), the through-hole (16) is formed in the position closer to the first capillary (14a) than a position (Pb) corresponding to an end of an electrode (26A) sealed in the first capillary (14a).
The ceramic tube according to claim 1,
wherein in the light-emitting portion (12), a distance (La) between the axis line (m1) of the through-hole (16) and the axis line (n1) of the first capillary (14a) is 0.55 or more times as large as the outer diameter (Da) of the first capillary (14a).
The ceramic tube according to any one of claims 1 to 4, wherein the light-emitting portion (12) has a curved surface between a portion corresponding to a discharge area (34) and the first capillary (14a) or the second capillary (14b), and the through-hole (16) is formed on the curved surface.
A ceramic tube for a high-intensity discharge lamp, comprising a light-emitting portion (12), a first capillary (14a), and a second capillary (14b) that are formed integrally, wherein
the light-emitting portion (12) is adapted to emit a light inside the ceramic tube,
the first capillary (14a) and the second capillary (14b) are disposed on either side of the light-emitting portion (12), the first and second capillaries being provided for sealing electrodes,
the light-emitting portion (12) has a third capillary (70) formed in a position close to the first capillary (14a),
the third capillary (70) protrudes in a direction parallel to the extending direction of the first capillary (14a), and
a through-hole (72) extends from an end of the third capillary (70) to an inside of the light-emitting portion (12).
The ceramic tube according to claim 6,
wherein an axis line (m3) of the third capillary (70) is parallel to an axis line (n1) of the first capillary (14a).
The ceramic tube according to claim 6,
wherein in the light-emitting portion (12), the third capillary (70) is formed in the position closer to the first capillary (14a) than a position (Pb) corresponding to an end of an electrode (26A) sealed in the first capillary (14a).
The ceramic tube according to claim 6,
wherein in the light-emitting portion (12), a distance (Lb) between the axis line (m3) of the third capillary (70) and the axis line (n1) of the first capillary (14a) is 0.55 or more times as large as the outer diameter (Da) of the first capillary (14a).
The ceramic tube according to claim 6,
wherein
an inner surface of the light-emitting portion (12) has a cross-sectional outline (80) in a plane containing the axis line (m3) of the third capillary (70), and
the axis line (m3) and a tangent line (84) at an intersection (82) between the outline (80) and the axis line (m3) form an angle (θ) of 30° or more.
The ceramic tube according to claim 6, wherein
the third capillary (70) has a base point (88), which is a reference point of a maximum length (Lc) of the third capillary (70) along the axis line (m3), and
the maximum length (Lc) of the third capillary (70) is 1/10 to 5/10 of a length (Ld) between the base point (88) and an end of the first capillary (14a) along the axis line (n1) of the first capillary (14a).
The ceramic tube according to any one of claims 6 to 11, wherein the light-emitting portion (12) has a curved surface between a portion corresponding to a discharge area (34) and the first capillary (14a) or the second capillary (14b), and the third capillary (70) is formed on the curved surface.
A method for bonding a plurality of ceramic compacts to produce one ceramic tube for a high-intensity discharge lamp, comprising
a compact preparation step of preparing a first ceramic compact (22A) containing a first curved portion (18a) and a first cylindrical portion (20a) formed integrally and a second ceramic compact (22B) containing a second curved portion (18b) and a second cylindrical portion (20b) formed integrally, and
a compact bonding step of bonding an end surface (56a) of the first curved portion (18a) in the first ceramic compact (22A) and an end surface (56b) of the second curved portion (18b) in the second ceramic compact (22B) to each other to prepare a bonded assembly (58A), wherein
the first curved portion (18a) has a through-hole (16) extending along an axis direction of the first cylindrical portion (20a), and
an axis line (m2) of the through-hole (16) is parallel to an axis line (n2) of the first cylindrical portion (20a) in the first ceramic compact (22A).
A method for bonding a plurality of ceramic compacts to produce one ceramic tube for a high-intensity discharge lamp, comprising
a compact preparation step of preparing a first ceramic compact (22A) containing a first curved portion (18a) and a first cylindrical portion (20a) formed integrally and a second ceramic compact (22B) containing a second curved portion (18b) and a second cylindrical portion (20b) formed integrally, and
a compact bonding step of bonding an end surface (56a) of the first curved portion (18a) in the first ceramic compact (22A) and an end surface (56b) of the second curved portion (18b) in the second ceramic compact (22B) to each other to prepare a bonded assembly (58B), wherein
the first curved portion (18a) has a capillary (90) extending along an axis direction of the first cylindrical portion (20a),
a through-hole (92) extends from an end of the capillary (90) to an inside of the first curved portion (18a), and
an axis line (m4) of the capillary (90) and the through-hole (92) is parallel to an axis line (n2) of the first cylindrical portion (18a) in the first ceramic compact (22A).