JP2011034840A - Cold cathode discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold cathode discharge lamp maintaining an effect of improvement in lamp characteristics by an emitter for a long period of time. <P>SOLUTION: In the cold cathode discharge lamp, electrodes 32 having a side wall are arranged in each inner end of a glass tube 1, a roughened surface 322 configured of fine unevennesses 323 is formed on a surface of an inner wall of each electrode 32, and an emitter 35 made from, for example, cesium sulfate is formed at least in a part of the roughened surface 322. The emitter 35 is composed with an emitter material such as cesium sulfate and liquid such as pure water, and is formed by evaporating a liquid component after an emitter aqueous solution 35' is applied on the roughened surface 322 wherein the emitter aqueous solution dropped on the smooth electrodes 32 has a contact angle θ of larger than 0° and less than 90°. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a cold cathode discharge lamp used for a light source of a backlight of a liquid crystal television or a notebook computer.

  Currently, cold cathode discharge lamps are the mainstream of light sources used for backlights. This cold cathode discharge lamp has a structure in which an electrode mount made of an electrode, a lead or the like is sealed at an end of a glass tube in which mercury or a rare gas is sealed.

  In this cold cathode discharge lamp, for example, as disclosed in Patent Documents 1 to 3, it is known to apply an emitter to an inner wall surface of an electrode. This is to improve lamp characteristics such as luminous efficiency by the excellent electron emission property of the emitter.

JP-A-10-144255 JP 2002-25499 A JP 2005-183172 A

  However, when the emitter is applied to the electrode, there is a problem that if the emitter disappears during the lifetime due to sputtering or the like, the lamp characteristics are rapidly deteriorated. Therefore, when the emitter is applied to the electrode, the point is how to maintain the effect of the emitter for a long time.

  An object of the present invention is to provide a cold cathode discharge lamp that can sustain the effect of improving lamp characteristics by an emitter for a long period of time.

  In order to achieve the above object, a cold cathode discharge lamp of the present invention is a cold cathode discharge lamp in which an electrode having a side wall is disposed at the inner end of a glass tube, and the inner wall surface of the electrode has minute irregularities. A structured rough surface portion is formed, and an emitter is formed on at least a part of the rough surface portion.

  According to the present invention, the effect of improving the lamp characteristics by the emitter can be maintained for a long time.

BRIEF DESCRIPTION OF THE DRAWINGS The whole figure for demonstrating the cold cathode discharge lamp of the 1st Embodiment of this invention. The figure for demonstrating the range of X enclosed with the dashed-dotted line of FIG. The figure for demonstrating the enlarged photograph (photographed with the electron microscope with a magnification of 500 times) of the rough surface part cross section formed in the electrode surface. The figure for demonstrating the manufacturing method of an electrode mount. The figure for demonstrating the contact angle of emitter aqueous solution. The figure for demonstrating the change of the lamp voltage during the lifetime of the lamp | ramp of an Example, the prior art example 1, and the prior art example 2. FIG. The figure for demonstrating the change of the tube wall temperature of the electrode part during the lifetime of the lamp | ramp of an Example, the prior art example 1, and the prior art example 2. FIG. The figure for demonstrating the emitter on the rough surface part in the cold cathode discharge lamp of the 2nd Embodiment of this invention.

(First embodiment)
Hereinafter, a cold cathode discharge lamp of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining a cold cathode discharge lamp according to a first embodiment of the present invention, and FIG. 2 is a diagram for explaining a range of X surrounded by an alternate long and short dash line in FIG.

  The container of the cold cathode discharge lamp is composed of a glass tube 1 made of hard glass or soft glass. The glass tube 1 has an elongated cylindrical shape, and both ends thereof are sealed, and a discharge space 11 is formed inside. A discharge medium made of mercury and a rare gas is enclosed in the discharge space 11. As the rare gas, a simple substance such as neon, argon, xenon, krypton, or a mixed gas can be used. On the inner surface of the glass tube 1, a phosphor layer 2 made of RGB three-wavelength phosphor is formed in a range covering at least the light emission region of the lamp.

  Electrode mounts 3 are sealed at both ends of the glass tube 1. As shown in FIG. 2, the electrode mount 3 includes an inner lead 31, an electrode 32, an outer lead 33, a bead 34 and an emitter 35.

  The inner lead 31 is sealed at the end of the glass tube 1, and one end thereof is led out to the discharge space 11 and the other end is led to the space outside the glass tube 1 along the tube axis. As the inner lead 31, it is desirable to use a material having a thermal expansion coefficient close to that of the glass tube 1, for example, molybdenum, Kovar (an alloy containing nickel Ni, iron Fe, cobalt Co, etc.), an iron-nickel alloy, or the like is preferable. It is.

  The electrodes 32 have a bottomed opening shape (cup shape) having a bottom wall and a side wall, and a pair of electrodes 32 are arranged on both sides of the discharge space 11 so that the opening faces the center side of the glass tube 1. As the electrode 32, it is desirable to use a material excellent in sputtering resistance. For example, nickel, molybdenum, tungsten or the like is suitable. Note that the bottom wall of the electrode 32 is joined to the inner lead 31, and when the electrode and the inner lead are made of different materials as in the present embodiment, both are disposed between the inner lead 31 and the electrode 32. The alloy layer 321 in a state where the members are mixed is formed.

  A rough surface portion 322 is formed on the inner wall surface and the outer wall surface of the electrode 32. As can be seen from FIG. 3, the rough surface portion 322 includes innumerable minute irregularities 323 formed on the surface. The arithmetic average roughness Ra of the rough surface portion 322 constituted by the minute irregularities 323 is preferably 0.50 to 0.60 μm. Note that the arithmetic average roughness Ra of the rough surface portion 322 is a value when the average roughness of the range of 100 μm × 50 μm is measured in a non-contact manner with a laser microscope.

  The outer lead 33 is made of, for example, jumet, and is connected to the inner lead 31 so as to extend in the external space direction along the lamp axis.

  The beads 34 are glass balls made of substantially the same material as the thermal expansion coefficient of the glass tube 1 formed on the shaft member of the inner lead 31, and are hermetically sealed at both ends of the glass tube 1.

  The emitter 35 is a thin film made of an emitter material such as cesium sulfate having excellent electron emission properties, and is formed on the rough surface portion 322 on the tip end side of the inner surface of the electrode 32, that is, on a part of the minute irregularities 322 shown in FIG. Is formed.

  Here, a method for manufacturing the electrode mount 3, particularly a method for forming the rough surface portion 322 and the emitter 35, will be described with reference to FIG. 4.

First, as shown in FIG. 4A, the electrode 32 portion of the electrode mount 3 in which the inner lead 31, the electrode 32, the outer lead 33 and the bead 34 are integrated is placed in the etching tank 4 into which the etching solution 41 is poured. The rough surface portion 322 is formed on almost the entire inner and outer wall surfaces of the electrode 32 as shown in FIG. Next, after removing and drying the etching solution 41 remaining on the surface of the electrode 32, the syringe 5 is inserted through the opening of the electrode 32, and the concentration of cesium sulfate obtained by mixing fine powder of cesium sulfate and pure water is 10 wt. % Emitter solution 35 ′ is dropped on the rough surface portion 322 near the tip of the electrode 32 by 4 μl. The emitter solution 35 ′ is dropped on the rough surface portion 322 because the contact angle θ when dropped on the smooth surface, for example, the electrode 32 before roughening, is 0 ° <θ <90 °. Then, the liquid film spreads thinly on the rough surface. The contact angle θ of the emitter solution 35 ′ is a value measured from the θ / 2 method, that is, the angle θ ₁ (= θ / 2) with respect to the solid surface of the straight line connecting the end point and the apex of the droplet as shown in FIG. And

  Then, as shown in (d), warm air from the dryer 6 is applied to the periphery of the electrode 32 portion where the emitter solution 35 'has been dropped to evaporate almost all of the liquid components of the emitter solution 35'. Thereby, as shown in (e), the electrode mount 3 having the emitter 35 thinly spread on the rough surface portion 322 of the inner wall surface of the electrode 32 can be obtained.

  An example of the cold cathode discharge lamp of the present embodiment is shown below.

(Example)
Glass tube 1; made of borosilicate glass, lamp length = 400 mm, outer diameter = 4.0 mm, inner diameter = 3.0 mm, wall thickness = 0.5 mm,
Discharge medium; mixed gas of mercury, 80% neon and 20% argon = 30 torr,
Phosphor layer 2; composed of RGB phosphors;
Inner lead 31; made of molybdenum, diameter = 0.8 mm,
Electrode 32; made of nickel, tube axial length = 10 mm, outer diameter = 2.7 mm, cup shape with inner diameter = 2.5 mm, arithmetic average roughness Ra = 0.55 μm of rough surface portion 322,
Outer lead 33; made of Jumet, diameter = 0.6mm,
Emitter 35: Cesium sulfate is formed on the rough surface portion 322 of the inner wall surface near the tip of the electrode, the amount of formation = about 0.4 mg.

  The lamp of this example, and a conventional lamp (hereinafter, Conventional Example 1) in which the same amount of emitter as that of the Example was formed on the inner wall surface of an electrode whose surface was not roughened (arithmetic average roughness Ra = 0.13 μm), For the lamp of Conventional Example 1 (hereinafter referred to as Conventional Example 2) in which no emitter was formed, a test for comparing the lamp voltage during the lifetime and a test for comparing the tube wall temperature near the electrode portion during the lifetime were performed. The results are shown in FIGS. 6 and 7, respectively. These tests are based on the assumption that actual impacts will be applied during transportation, installation in the backlight, after being mounted on a liquid crystal television, etc., and each completed lamp will be baked five times from a height of 150 mm. The test is conducted after an impact test that allows natural fall.

  As can be seen from the results, even when the lamp of the example is lit for about 2000 hours, the lamp voltage and the tube wall temperature of the electrode part are little changed, and the lamp voltage and the tube wall temperature are only slightly increased from the initial values. As described above, the lamp voltage and the tube wall temperature of the electrode portion increase during the lifetime because the emitter disappeared due to sputtering of the electrode member by ions such as rare gas sealed in the glass tube. When the emitter disappears completely from the electrode member, the characteristics of the lamp are almost the same as the lamp without the emitter. On the other hand, the lamp of the conventional example 1 starts to increase the lamp voltage and the tube wall temperature of the electrode portion from an early time, and changes to characteristics close to that of the conventional example 2 when it is lit for 2000 hours. That is, it can be said that the working effect of the emitter has been maintained for a long time as compared with the lamp of the first example.

  As described above, the cause of the large difference between the example and the conventional example 1 is related to the remaining amount of the emitter 35 on the inner wall surface of the electrode 32 after the impact test. That is, as a result of the impact, the emitter 35 peeled from the electrode 32 does not contribute to the lamp characteristics, but the remaining amount of the emitter 35 after the impact test is considered to be larger in the example.

The cause of the difference in the remaining amount of the emitter 35 after the impact test will be described in detail. In the embodiment, the contact angle θ on the smooth surface on the rough surface portion 322 of the electrode 32 is 0 ° <θ <90 °. A certain emitter solution 35 'is dropped. Thus, the Wenzel equation, ie cos θ _W = r (γ _SG −γ _SL ) / γ _LG = r cos θ (where θ _W = contact angle on the rough surface, γ _SG = solid / gas interface energy, γ _SL As shown in (= solid / liquid interfacial energy, γ _LG = liquid / gas interfacial energy, r = roughness factor), on the rough surface portion 322, the roughness factor r representing the actual surface area / apparent surface area is 1. Therefore, the emitter solution 35 ′ having a contact angle θ of 0 to 90 ° has a contact angle θ _W on the rough surface of θ _W <θ, and is thinner on the rough surface portion 322 than when dropped on a smooth surface. Will spread. That is, on the rough surface portion 322, the wettability of the emitter solution 35 ′ is improved. Along with this, the emitter 35 obtained by evaporating the liquid component from the emitter solution 35 ′ also becomes a thin film spread on the rough surface portion 322. As a result, it became strong against impact, and the adhesion effect with the electrode member was improved by the anchor effect caused by the emitter 35 entering the plurality of minute irregularities 323. Therefore, it is considered that it was difficult to peel off even if an impact test was performed.

  On the other hand, the conventional example 1 is the emitter 35 which has the same amount of emitter formation but is less spread and thicker than the example, so that it is weak against impact and the anchor effect cannot be obtained. It is thought that many peeled off by performing the test.

  Even when the inner wall surface of the electrode 32 is roughened, when the contact angle θ of the emitter solution 35 ′ with respect to the smooth electrode material is 90 ° or more, the thin film emitter 35 as in the embodiment is used. I can't get it. In this case, as is apparent from the Wenzel equation, the film is thicker on the rough surface than on the smooth surface, and rather easily peeled off due to impact or the like. In Japanese Patent Application Laid-Open No. 2002-25499, unevenness is formed on the inner wall surface of the electrode. Even though such macroscopic unevenness has the effect of widening the range in which the emitter can be formed, it is microscopically. Since it is a smooth surface, the effect of suppressing the peeling of the emitter cannot be obtained. In other words, in the present invention, the combination of the properties of the emitter solution 35 'and the rough surface having minute irregularities is important. Here, the contact angle θ of the emitter solution 35 ′ can be adjusted by the type of the emitter material and the solvent, the concentration of the emitter material in the emitter solution 35 ′, and the like.

  When the emitter solution 35 ′ in which the emitter material is substantially dissolved in the liquid is used as the emitter solution as in this embodiment, the arithmetic average roughness Ra of the rough surface portion 322 of the electrode 32 is 0.50 μm to 0.60 μm. It is desirable. Within this range, it has been confirmed that a stable effect can be obtained. The emitter solution 35 ′ is not limited to a state in which the emitter material is completely dissolved in the solvent, but may be in a state in which most of the emitter material is dissolved in the solvent. As the emitter material of the emitter solution 35 ', an alkali metal element, an alkaline earth metal element, a rare earth element, or a compound thereof can be used. As the solvent, an organic solvent such as ethanol or butyl acetate may be used, and if desired, a binder such as a dispersant or nitrocellulose may be added. However, in consideration of handling and the like, it is desirable to use pure water or the like as the solvent. Examples of water-soluble emitter materials include cesium carbonate and cesium chloride in addition to cesium sulfate.

  Therefore, in the present embodiment, a rough surface portion 322 composed of minute irregularities 323 is formed on the inner wall surface of the electrode 32, and the contact angle θ when dropping onto the smooth electrode 32 is 0 ° < After dropping the cesium sulfate aqueous solution with θ <90 °, the moisture in the cesium sulfate aqueous solution is evaporated to form the emitter 35, so that the impact resistance and adhesion of the emitter 35 are increased, and therefore, impact or the like is added. However, it becomes difficult to peel off from the electrode 32, and the effect of improving the lamp characteristics by the emitter 35 can be maintained for a long time. Therefore, the present invention can also solve problems such as an increase in electrode temperature and power saving due to the application of a high current to a lamp in recent years. In addition, the arithmetic mean roughness Ra of the rough surface part 322 can acquire a high effect in it being 0.50-0.60 micrometer.

(Second Embodiment)
A cold cathode discharge lamp according to a second embodiment of the present invention will be described.

  In the second embodiment, an emitter suspension composed of yttrium oxide and pure water is dropped onto the rough surface portion 322, and then the emitter 35 is formed on the rough surface portion 322 by substantially evaporating the pure water component. The yttrium oxide particles 351 are in a state where they enter the minute unevenness 323.

  The emitter suspension as in the present embodiment is a state in which the emitter material, which is a solute, is dispersed as particles in the liquid. Therefore, as shown in FIG. 8, the particles 351 are allowed to enter the minute irregularities 323. For example, the width W of the minute irregularities 323 is larger than the average particle diameter R of the particles 351 of the emitter material. By adjusting the roughness, it is possible to realize the emitter 35 that is difficult to peel off even when an impact is applied, as in the first embodiment. Examples of the emitter suspension include an emitter solution in which lanthanum oxide or magnesium oxide is mixed with water.

  The embodiment of the present invention is not limited to the above, and may be modified as follows, for example.

  The rough surface portion 322 does not need to be formed on almost the entire electrode 32 and may be formed on at least a part of the inner wall surface of the electrode 32. Further, the method for forming the rough surface is not limited to chemical polishing such as etching, but may be polishing by blasting or laser.

  The emitter 35 does not need to be formed on the entire rough surface portion 321 and may be at least a part.

  In the step of FIG. 4D, the liquid component of the emitter solution 35 'is evaporated by drying, but may be evaporated by baking.

DESCRIPTION OF SYMBOLS 1 Glass tube 11 Discharge space 2 Phosphor layer 3 Electrode mount 31 Inner lead 32 Electrode 322 Rough surface part 323 Minute unevenness 35 Emitter

Claims (5)

A cold cathode discharge lamp in which an electrode having a side wall is disposed at the inner end of a glass tube,
A cold cathode discharge lamp, wherein an inner wall surface of the electrode is formed with a rough surface portion constituted by minute irregularities, and an emitter is formed on at least a part of the rough surface portion.   The emitter includes an emitter material and a liquid, and an emitter liquid having a contact angle θ of 0 ° <θ <90 ° when dropped onto the smooth electrode is applied to the rough surface portion, and then the liquid component is evaporated. The cold cathode discharge lamp according to claim 1, wherein the cold cathode discharge lamp is formed.   The emitter liquid is an emitter solution in which the emitter material is substantially dissolved in the liquid, and the arithmetic average roughness Ra of the rough surface portion is 0.50 to 0.60 μm. 2. The cold cathode discharge lamp according to 2.   The cold cathode discharge lamp according to claim 3, wherein the emitter material is cesium sulfate.   The emitter liquid is an emitter suspension liquid in which the emitter material is dispersed in the liquid, and the rough surface portion is rough enough for particles of the emitter material to enter the minute unevenness. Item 3. The cold cathode discharge lamp according to Item 2.

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