JP2012190550A - Electrode for cold cathode fluorescent lamp and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for cold cathode fluorescent lamp in which the bonding strength between a lead wire and a glass bead has been improved.SOLUTION: An electrode for cold cathode fluorescent lamp comprises an electrode part 1 and a lead wire part 2 that has an inner lead part 2a and an outer lead part 2b and is connected to the end part of the electrode part 1. The inner lead part 2a is made of iron-containing metal at least on a front surface side, and a glass part 3 is bonded with the circumference of the inner lead part 2a. The glass part 3 has a Fe diffused layer with an average thickness of 5 to 25 μm toward the inside from the boundary face with the inner lead part 2a. The Fe diffused layer is divided into a Fe high-concentration layer and a Fe low-concentration layer located inner than it, with the average thickness of the Fe high-concentration layer being 1 to 4 μm. If the section of the boundary face between the glass part and the inner lead part is observed with an SEM, the average number of recessed portions having a depth of 3 μm or above into the inner lead part per 100 μm of the boundary line, which is formed by the boundary faces between the glass part and the inner lead part, is 4 or lower.

Description

  The present invention relates to an electrode for a cold cathode fluorescent lamp (CCFL) and a method for manufacturing the same.

  Liquid crystal display devices (LCDs) such as liquid crystal displays and liquid crystal televisions incorporate a backlight for illuminating the display screen, and a cold cathode fluorescent lamp is generally used as a light source for the backlight. Yes. The cold cathode fluorescent lamp is also used as a reading light source for a scanner, a light source for irradiating a document in a copying machine, and a light guide plate light source for an electronic signboard.

  The cold cathode fluorescent lamp includes a cylindrical glass tube coated with phosphor on the inner surface and filled with mercury and a rare gas, and a pair of electrodes attached to both ends of the glass tube. Typically, the electrode includes a bottomed cup-shaped electrode part and a lead wire connected to the bottom part of the electrode part. The lead wire is composed of an inner lead wire and an outer lead wire. The inner lead wire is disposed inside the glass tube, while the outer lead wire is disposed outside the glass tube. In order to improve the adhesion to the glass tube, glass beads are bonded to the outer periphery of the inner lead wire. The glass beads are inserted into the glass tube together with the inner lead wire and heat-sealed, so that the airtightness in the glass tube is maintained.

  Here, if the bonding between the lead wire and the glass bead is insufficient, a gap is formed in the sealing portion of the glass tube, and air, water vapor, etc. enter from here, and the gas filled in the glass tube leaks. As a result, there arises a problem that the life of the fluorescent lamp is shortened. Accordingly, the lead wire and the glass bead are required to have high bonding strength.

  As a method for improving the bondability between the lead wire and the glass bead, a method of heating the outer periphery of the lead portion and forming an oxide film on the surface of the lead portion has been known so far. For example, in Japanese Patent Laid-Open No. 11-238489 (Patent Document 1), a portion to be sealed of a lead wire is heated with an oxygen burner or the like, and an oxide film having a thickness of 1.0 to 3.0 μm is formed on the surface of the lead wire. It is described that by providing the film, the glass is well wetted and airtightly bonded. Moreover, in Unexamined-Japanese-Patent No. 2003-229060 (patent document 2), the oxide film is formed by heating a wire to about 600 to 1000 degreeC with a burner in air | atmosphere.

Furthermore, in Japanese Patent Application Laid-Open No. 2008-130396 (Patent Document 3), an oxidizing step in which at least the surface side of the lead portion is made of an iron-containing metal and the lead portion is heated in an oxidizing atmosphere to form an oxide film; A two-step heating method is described in which a lead portion is heated in a non-oxidizing atmosphere after the oxidizing step to perform a non-oxidizing step for generating FeO in the oxide film (claim 4 etc.). In the first stage heating, an oxide film of Fe ₂ O ₃ or Fe ₃ O ₄ is formed, and in the second stage heating, Fe, which is a constituent element of the lead portion, is diffused into the oxide film. The atomic ratio of Fe is increased, and FeO is formed in the film. It is described that the oxide film containing FeO has improved bonding strength with the glass part as compared with an oxide film made of Fe ₂ O ₃ and Fe ₃ O ₄ (paragraph 0009). The thickness of the oxide film is preferably 1 μm or more and less than 10 μm (paragraph 0019).

  Further, in this publication, the lead part is also heated by the heating for forming the glass part, and the elements constituting the lead part and the oxide film diffuse to the glass side, and the components of the glass part and the lead part It is described that the ion diffusion layer mixed with is formed on the side of the glass portion in contact with the oxide film. And, since the ion diffusion layer has a different thermal expansion coefficient from other parts of the glass part, if it is too thick, the glass part and the glass tube will be cracked. Therefore, it is preferable that the ion diffusion layer is as thin as possible. It describes what to do (paragraph 0026).

JP-A-11-238489 JP 2003-229060 A JP 2008-130396 A

  However, there is still room for improvement in the bonding strength between the lead wire and the glass bead. Therefore, an object of the present invention is to provide a cold cathode fluorescent lamp electrode in which the bonding strength between the lead wire and the glass bead is improved. Moreover, this invention makes it another subject to provide the manufacturing method of such an electrode for cold cathode fluorescent lamps.

  The present inventor has intensively studied to solve the above-mentioned problems. When an iron-containing metal is used as a material constituting the inner lead wire, the Fe component is a glass bead when the glass bead is melt-bonded to the outer periphery of the inner lead wire. It was found that the degree of diffusion of the Fe component plays an important role in the bonding strength between the inner lead wire and the glass bead.

In one aspect, the present invention completed on the basis of the above knowledge is for a cold cathode fluorescent lamp having an electrode portion, an inner lead portion and an outer lead portion, and a lead portion connected to an end portion of the electrode. An electrode,
The inner lead portion is made of an iron-containing metal at least on the surface side, and a glass portion is bonded to the outer periphery of the inner lead portion. The glass portion has an average thickness of 5 to 25 μm from the interface with the inner lead portion toward the inside. Fe diffusion layer, Fe diffusion layer is divided into Fe high concentration layer and Fe low concentration layer inside it, the average thickness of Fe high concentration layer is 1 to 4 μm,
When the cross section of the interface between the glass part and the inner lead part is observed with an SEM, a recess having a depth of 3 μm or more to the inner lead part per 100 μm length of the boundary line between the glass part and the inner lead part formed by the interface is formed. This is an electrode for a cold cathode fluorescent lamp having an average number of 4 or less.

  In one embodiment of the electrode for a cold cathode fluorescent lamp according to the present invention, when the cross section of the interface between the glass portion and the inner lead portion is observed by SEM, the length of the boundary line between the glass portion and the inner lead portion formed by the interface is long. On the other hand, the cumulative length of the oxide layer along the boundary line is less than 5%.

  Another aspect of the present invention is a lead portion before joining to a glass portion for manufacturing an electrode for a cold cathode fluorescent lamp, the inner lead portion and the outer lead portion, and the surface of the inner lead portion The lead portion is formed with an oxide layer, and the average thickness of the oxide layer is 0.2 to 1.5 μm.

In one embodiment of the lead portion according to the present invention, the ratio of the total mass of FeO and Fe ₃ O _{4 to} the total mass of Fe, FeO, Fe ₃ O ₄ and Fe ₂ O _{3 in} the oxide layer is 90% or more. is there.

  In another aspect of the present invention, the inner lead portion and the outer lead portion are joined to form the lead portion 1 and the inner lead portion is 800 to 1000 in an inert gas atmosphere having a dew point of −5 to 30 ° C. Step 2 of oxidizing the surface of the inner lead part by heating at 5 ° C. for 5 to 15 minutes, placing a glass part on the outer periphery of the inner lead part, and in an inert gas atmosphere having a dew point of −60 to −10 ° C. A method of manufacturing an electrode for a cold cathode fluorescent lamp, comprising a step 3 of joining the inner lead part and the glass part by heating the inner lead part at 800 to 1000 ° C. for 1 to 10 minutes.

  In one embodiment, the method for manufacturing an electrode for a cold cathode fluorescent lamp according to the present invention includes, after step 3, a step 4 of reducing the surface of the lead portion by heating in a reducing atmosphere, and an inner lead portion side of the lead portion. The process 5 of joining the edge part of this to an electrode part is further included.

  In still another aspect, the present invention is a cold cathode fluorescent lamp equipped with the cold cathode fluorescent lamp electrode according to the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for cold cathode fluorescent lamps which the joining strength of a lead wire and glass beads was improved can be provided.

It is the schematic which shows the electrode for cold cathode fluorescent lamps concerning one Embodiment of this invention. It is an example of the Fe concentration curve and Si concentration curve near the interface between the inner lead portion 2a and the glass portion 3. It is the schematic which shows an example of the manufacturing method of the electrode for cold cathode fluorescent lamps concerning one Embodiment of this invention. It is the schematic which shows the cold cathode fluorescent lamp which concerns on one Embodiment of this invention. Invention Example No. 5 and Comparative Example No. 10 is a SEM photograph of the boundary cross section between the inner lead part and the glass part for No. 10; It is a figure explaining the test method when evaluating the joint strength of a glass bead and an inner lead wire. It is a photograph example when the cross section of the interface of a glass part and an inner lead part is observed by SEM (magnification: 1,700 times). The average thickness of the oxide layer is about 0.6 μm. It is a photograph example when the cross section of the interface of a glass part and an inner lead part is observed by SEM (magnification: 1,700 times). The thickness of the oxide layer is zero μm. It is a photograph example when the cross section of the interface of a glass part and an inner lead part is observed by SEM (magnification: 1,700 times). The average thickness of the oxide layer is about 2.3 μm.

(Cold cathode fluorescent lamp electrode)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a cold cathode fluorescent lamp electrode according to an embodiment of the present invention. This cold cathode fluorescent lamp electrode is formed by joining an electrode part 1, an inner lead part 2a and an outer lead 2b in this order, and a glass part 3 is joined so as to surround the outer periphery of the inner lead 2a. The inner lead portion 2 a and the outer lead portion 2 b form the lead portion 2.

  The shape of the electrode portion 1 can be any known shape and is not particularly limited, and examples thereof include a filament, a rod, and a plate. From the viewpoint of suppressing sputtering, the shape is generally a bottomed cylinder (cup). The material of the electrode part 1 is not limited, but nickel (Ni), niobium (Nb), nickel alloy (Ni, Al, Si, Ti, V, Mn, Fe, Y, Zr, Nb, Mo, W) A metal material such as an alloy to which etc. are added can be used. In order to improve the heat resistance of the electrode part 1, you may form with refractory metals, such as tungsten (W) and molybdenum (Mo). A discharge characteristic improving agent or the like for improving the discharge characteristics may be sealed inside the electrode portion 1 as necessary.

  The lead part 2 plays a role of supplying electric power to the electrode part 1 and is generally a wire. The inner lead portion 2a and the outer lead portion 2b constituting the lead portion 2 are joined to each other by resistance welding or the like. In order to position the glass portion 3 in assembling the CCFL electrode component, it is preferable that the diameter of the inner lead 2a is larger than the diameter of the outer lead 2b.

As the material of the inner lead portion 2a, at least the surface side uses iron-containing metal. This is because the Fe component of the inner lead part 2a is thermally diffused into the glass part 3 to increase the bonding strength between the inner lead part 2a and the glass part 3. The entire inner lead portion 2a may be an iron-containing metal wire, or the surface of a wire made of Cu or Cu alloy may be plated with an iron-containing metal layer.
As an iron-containing alloy, for example, Fe: 54% by mass, Ni: 29% by mass, and Co: 17% by mass are main components, and optionally a small amount of other elements such as Si and Mn are added. In addition to Kovar having 40 to 55 × 10 ⁻⁷ / K (30 to 400 ° C.), 42 alloy (Fe-42 mass% Ni) can be used, and Kovar is preferable because it has a thermal expansion coefficient close to that of glass. Examples of the composition of Kovar include a composition containing 28 to 30% by mass of Ni and 16 to 18% by mass of Co with the balance being Fe and inevitable impurities. Kovar can contain a total of 0.5% by mass of additive elements such as Si and Mn as optional components.

  An oxide layer for improving wettability with the glass part 3 is formed on the surface of the inner lead part 2a before joining to the glass part 3 by an oxidation process of the inner lead part described later. The Fe component is easily diffused into the glass portion by being oxidized. If the oxide layer becomes too thin, the diffusion of the Fe component into the glass part 3 tends to proceed excessively, and the bonding strength between the glass part 3 and the inner lead part 2a is lowered. On the other hand, if the oxide layer becomes too thick, the oxide layer remains and lowers the bonding strength. Therefore, the average thickness of the oxide layer is preferably 0.2 to 1.5 μm, more preferably 0.4 to 1.2 μm, and still more preferably 0.6 to 0.9 μm.

  Here, in paragraph 0020 of Japanese Patent Application Laid-Open No. 2008-130396 (Patent Document 3), in the case of an electrode member having a glass part, the oxide film formed on the lead part is oxidized by heating at the time of joining the glass part. The element constituting the film diffuses to the glass side to reduce the thickness, so that the thickness of the oxide film of the electrode member after forming the glass part is in the above range (1 to 10 μm). The oxide film to be formed on the lead part before forming the film is formed to be thicker than this range. Specifically, it is preferably 6 to 20 μm ”, and as in the present invention, it is bonded to the glass part. It should be noted that there is no suggestion that the average thickness of the previous oxide layer should be 0.2-1.5 μm.

The oxide layer can be visually observed by SEM observation of the cross section of the interface between the glass portion 3 and the inner lead portion 2a, and an average value can be obtained from the measured values of the thickness at a plurality of locations.
Since the oxide layer diffuses toward the glass part 3 during the joining process with the glass part 3, it disappears after joining. In one embodiment of the present invention, the thickness of the oxide layer after bonding with glass is zero μm. Note that zero means that the cross section of the interface between the glass bead and the inner lead wire is exposed and the SEM observation reveals that the oxide layer has a length relative to the length of the boundary line between the glass portion and the inner lead portion formed by the interface. The cumulative length is less than 5% (specifically, the total length of the oxide layer along the boundary per 100 μm of the boundary is less than 5 μm). On the other hand, when the cumulative length of the oxide layer along the boundary line occupies 5% or more of the length of the boundary line, the thickness of the oxide layer is not zero μm, but the average value is calculated from the measured values of the thickness at multiple locations. By doing so, it is possible to measure the average thickness.

  7 to 9 are examples of photographs when the cross section of the interface between the glass portion and the inner lead portion is observed by SEM (magnification: 1,700 times). In FIG. 7, the cumulative length of the oxide layer occupies about 78% of the length of the boundary line, and the thickness of the observed oxide layer is separately calculated based on the SEM photograph (1,700 times). When five points are measured every 2 μm in the direction, the average thickness is about 0.6 μm. In FIG. 8, since the oxide layer cannot be confirmed, the thickness of the oxide layer is zero μm. In FIG. 9, the cumulative length of the oxide layer occupies 100% of the length of the boundary line, and the thickness of the observed oxide layer is separately determined based on the SEM photograph (1,700 times). When 5 points were measured every 2 μm, the average thickness was about 2.3 μm.

  Even if granular oxide of about 1 μm size remains in the recesses of the inner lead (the number of recesses per 100 μm boundary length between the glass part and the inner lead part is 4 or less), there is an adverse effect on the bonding strength. Since this does not occur, this is not taken into account in the calculation of the thickness of the oxide layer.

It is preferable that Fe is present in the form of FeO and / or Fe ₃ O _{4 in} the oxide layer present on the surface of the inner lead portion 2a before joining with the glass portion 3. This is because once Fe ₂ O ₃ having poor adhesion to the base material is generated in the process of oxidizing the inner lead portion, a void is generated between the base material and the oxide layer. In this state, even if Fe ₂ O ₃ is reduced to Fe ₃ O ₄ or FeO, the above voids remain, and when the glass part is formed, the bonding strength between the glass part and the lead part decreases. The ratio of the oxidized form of Fe constituting the oxide layer can be measured by an X-ray diffraction quantitative analysis technique. In one embodiment of the present invention, the oxide layer is quantitatively analyzed by X-ray diffraction, and the ratio of the total mass of FeO and Fe ₃ O _{4 to} the total mass of Fe, FeO, Fe ₃ O ₄ and Fe ₂ O ₃ is It is 90% or more, preferably 95% or more.

  The material of the outer lead portion 2b can be any known material. For example, a nickel (Ni) wire, a wire made of an alloy of Ni and manganese (Mn), jumet (iron (Fe) and nickel (Ni Or the like) can be used.

  The material of the glass part 3 can be any known material, and examples thereof include borosilicate glass and aluminosilicate glass. In the glass part 3, an Fe diffusion layer is formed from the interface with the inner lead part 2a toward the inside of the glass part 3. As will be described later, the Fe diffusion layer is formed by thermally diffusing an Fe component that is a constituent element of the inner lead portion 2a, and contributes to an improvement in bonding strength between the inner lead portion 2a and the glass portion 3.

  The Fe diffusion layer is divided into an Fe high concentration layer closer to the interface and an Fe low concentration layer inside thereof. The Fe high-concentration layer has a steep Fe concentration gradient and is a layer in which the Fe concentration rapidly decreases toward the inside of the glass portion 3. On the other hand, the Fe low-concentration layer is a layer in which the Fe concentration gradient is gentle and the Fe concentration gradually decreases toward the inside of the glass portion 3. The break point where the Fe concentration gradient changes suddenly becomes the boundary between the two. The Fe high-concentration layer and the Fe low-concentration layer are relatively determined from the transition of the Fe concentration in the Fe diffusion layer. For example, it does not mean that the Fe high-concentration layer must contain a certain concentration or more of Fe. .

  If the Fe high-concentration layer is too thick, it causes an increase in the thermal expansion coefficient of the glass portion 3 and a decrease in mechanical strength. On the other hand, if it is too thin, the effect of improving the bonding strength with the inner lead portion 2a cannot be obtained. Therefore, in this invention, the average thickness of Fe high concentration layer is prescribed | regulated as 1-3 micrometers. The average thickness of the Fe high concentration layer is preferably 1 to 2 μm.

  The thickness of the Fe diffusion layer, which is the total thickness of the Fe high-concentration layer and the Fe low-concentration layer, is 5 to 25 μm on average from the viewpoint of obtaining a high bonding strength while suppressing a decrease in the mechanical strength of the glass. It is preferable that it is 10 to 20 μm.

The average thickness of the Fe high-concentration layer and the average thickness of the Fe diffusion layer are obtained by performing an elemental line analysis of the cross section of the interface between the glass part 3 and the inner lead part 2a with an electron beam microanalyzer (EPMA). Can be measured.
Specifically, the average thickness of the Fe high-concentration layer is a Fe concentration curve drawn by EPMA line analysis, with the thickness direction from the surface of the glass portion 3 toward the inside being the X axis and the Fe mass concentration being the Y axis. When the inner lead portion 2a is a boundary between the Fe high-concentration layer and the Fe low-concentration layer, the thickness point corresponding to the break point between the steep concentration curve portion of the high Fe-containing layer and the low-concentration concentration curve portion of the low Fe-containing layer. The length of the thickness direction from the interface of the glass part 3 to the said boundary is calculated | required, and it gives as an average value of the measured value in multiple places. When the Fe concentration curve near the folding point is rounded and the boundary is unclear, the boundary is the depth point where the tangent angle is 135 ° with respect to the X axis in the concentration curve of the Fe content.
The average thickness of the Fe diffusion layer refers to the length in the thickness direction from the interface between the glass portion 3 and the inner lead portion 2a to the Fe detection lower limit (location where the Fe concentration is 2 mass%) on the glass side.
The interface between the glass part 3 and the inner lead part 2a is set to a position where the Si concentration rapidly rises in the EPMA line analysis.
An example of the Fe concentration curve and the Si concentration curve is shown in FIG.

  In one embodiment of the electrode for a cold cathode fluorescent lamp according to the present invention, when the cross section of the interface between the glass part 3 and the inner lead part 2a is observed with an SEM, the glass part 3 and the inner lead part 2a formed by the interface are formed. The number of recesses having a depth of 3 μm or more to the inner lead portion 2a per 100 μm of the boundary line on average is 4 or less, preferably 2 or less. By suppressing the number of recesses, the bonding strength between the glass part 3 and the inner lead part 2a can be increased.

In order to suppress the number of recesses, it is important not to generate Fe ₂ O ₃ having poor adhesion to the base material during the oxidation process of the inner lead portion. When Fe ₂ O ₃ is generated, voids are generated between the base material and the oxide layer and appear as concave portions. In this state, even if Fe ₂ O ₃ is reduced to Fe ₃ O ₄ or FeO, the above voids remain, and when the glass part is formed, the bonding strength between the glass part and the lead part decreases. Since it is easy to produce Fe ₂ O ₃ when oxidized in the atmosphere, in order to prevent the formation of Fe ₂ O ₃ , an atmosphere in which water vapor is added to an inert atmosphere such as nitrogen gas or argon gas when oxidizing the inner lead part When the oxidation treatment is performed, a dense oxide layer (FeO and Fe ₃ O ₄ ) with few defects can be formed on the inner lead surface. Specific oxidation treatment conditions will be described later.

(Method for producing electrode for cold cathode fluorescent lamp)
With reference to FIG. 3, an embodiment of a method for manufacturing a cold cathode fluorescent lamp electrode according to the present invention will be described below.

(1) Formation of electrode portion The bottomed cup-shaped electrode portion 1 is formed by subjecting a flat metal plate to deep drawing, pressing, swaging, or the like.

(2) Lead welding The inner lead part 2a and the outer lead part 2b are prepared, and these end parts are joined together by resistance welding, laser welding, ultrasonic welding or the like. At this time, if the welding bump 4 is formed at the joint portion, it is useful for positioning when the glass beads are arranged on the outer periphery of the inner lead portion 2a.

(3) Oxidation treatment The inner lead portion 2 a oxidizes the surface in order to improve wettability with the glass portion 3. This oxidation treatment is preferably performed by steam oxidation performed by heating at 800 to 1000 ° C. for 5 to 15 minutes in an inert gas atmosphere having a dew point of −5 to 30 ° C.
The merit of controlling the form and growth rate of the oxide layer can be obtained by adjusting the dew point of the atmospheric gas during the oxidation treatment, that is, the amount of water vapor. An oxidation treatment using oxygen in the atmosphere is not preferable because an Fe ₂ O ₃ oxide layer is formed, causing defects and peeling. The dew point in the above range is based on experimental facts for producing an oxide layer having a desired thickness. The dew point is more preferably 0 to 25 ° C.
Examples of the inert gas include nitrogen, rare gases (He, Ne, Ar, Kr, Xe, Rn) or a mixed gas thereof. Nitrogen is more preferred because of its low cost.
The heating temperature within the above range is based on experimental facts for producing an oxide layer having a desired thickness. The heating temperature is more preferably 840 to 950 ° C.
The oxidation treatment process may be performed at any stage before or after lead welding, but the positioning accuracy is reduced in welding between the outer lead and the glass-bonded inner lead. It is preferable to do. When oxidation is performed after lead welding, the surfaces of both the inner lead portion 2a and the outer lead portion 2b are oxidized.

(4) Arrangement of Glass Part The glass part 3 is arranged so as to surround the outer periphery of the inner lead part 2a after the oxidation treatment. For example, a glass bead having a through hole is inserted and arranged at a predetermined position. For example, by making the diameter of the through hole of the glass bead larger than the diameter of the inner lead part 2a and smaller than the diameter of the welding cob 4, the glass bead inserted into the inner lead part 2a becomes the welding cove of the inner lead part 2a. Can be positioned at.

(5) Bonding of glass part After the glass part 3 is disposed on the outer periphery of the inner lead part 2a, heat treatment is performed for bonding the glass part 3 to the outer periphery of the inner lead part 2a. By performing the heat treatment, the glass portion 3 is fused to the outer periphery of the inner lead portion 2a. At this time, the Fe component of the inner lead portion 2 a diffuses into the glass portion 3, thereby increasing the bonding strength between the inner lead portion 2 a and the glass portion 3. This heat treatment is preferably performed by heating the inner lead portion at 800 to 1000 ° C. for 1 to 10 minutes in an inert gas atmosphere having a dew point of −60 to −10 ° C.
The dew point of the atmospheric gas during the heat treatment is set lower than that during the oxidation treatment. This is to suppress an increase in the oxide layer of the inner lead. In this case, too, heat treatment in an air atmosphere is not preferable because the thickness of the oxide layer is too thick and it becomes difficult to join the glass. The dew point is more preferably -60 to -20 ° C.
Examples of the inert gas include nitrogen, rare gases (He, Ne, Ar, Kr, Xe, Rn) or a mixed gas thereof. Nitrogen is more preferred because of its low cost.
The reason why the heating temperature is in the above range is based on the experimental facts for obtaining the desired profile of the diffusion state of Fe in the glass. The heating temperature is more preferably 820 to 950 ° C.
This heat treatment may be performed at any stage before and after lead welding, but is preferably performed after lead welding because the inner lead portion 2a and the glass portion 3 are easily positioned.

(6) Reduction treatment After the heat treatment of (5), the surface of the lead portion is reduced by heating in a reducing atmosphere in order to remove an unnecessary oxide layer of the inner lead portion 2a. The method of the reduction treatment is not particularly limited. For example, hydrogen gas is put in an electric furnace and heated in a reducing atmosphere at a heating temperature of 600 to 700 ° C. for a heating time of about 5 to 20 minutes. There is a method of reducing and removing the oxide layer on the inner lead 2a that does not contribute to the bonding with the glass part 3. Since the heat treatment temperature is low and the time is short, it hardly affects the Fe diffusion state in the glass.
The reduction treatment may be performed at any stage before and after lead welding, but is preferably performed after lead welding in view of the productivity of the welding apparatus. When reduction treatment is performed after lead welding, the surfaces of both the inner lead portion 2a and the outer lead portion 2b are reduced.

(7) Joining of electrode part After formation of the electrode part 1, the bottom part of the electrode part 1 and the end part of the inner lead part 2a are joined by laser welding, resistance welding, ultrasonic welding or the like by resistance welding or the like. Although there is no restriction | limiting in particular in the order which implements this joining process, it implements at the end for the reason that favorable joining strength is obtained by removing the stain | pollution | contamination and oxide film of the junction part of the electrode part 1 and the inner lead part 2a. It is preferable.

Through the steps (1) to (7), the cold cathode fluorescent lamp electrode according to the present invention can be produced. The order of the steps is free except as described above, and is not particularly limited. For example, the following order can be considered. Step (1) may be performed anywhere before step (7).
(2) → (3) → (4) → (5) → (6) → (7)
(3) → (4) → (5) → (6) → (2) → (7)
The electrode for a cold cathode fluorescent lamp according to the present invention can be mounted on a cold cathode fluorescent lamp. A method of attaching the cold cathode fluorescent lamp electrode to the cold cathode fluorescent lamp is known per se and need not be explained in particular. For example, it can be attached by the following procedure. Referring to FIG. 4, first, a glass tube 22 having a phosphor 21 disposed therein is prepared. Then, with the glass tube 22 filled with mercury and a rare gas, cold cathode fluorescent lamp electrodes are inserted facing both ends of the glass tube 22, and both ends of the glass tube 22 are sealed with the glass portion 3. Sealing can be performed by heat fusion of the glass portion 3 and the glass tube 22. The temperature at the time of heat fusion is 800 or more and less than 1000 ° C, and typically 850 to 950 ° C. The heating time is 1 to 10 minutes, typically 2 to 7 minutes. Under such temperature and time conditions, the Fe diffusion layer hardly changes. On the contrary, when heat-sealing at a high temperature of 1000 ° C. or higher, the Fe diffusion layer is changed, and the bonding strength between the inner lead portion 2a and the glass portion 3 may be reduced, and should be avoided.

  Examples for better understanding of the present invention and its advantages are shown below, but the present invention is not limited to these examples.

<Lead welding>
Inner lead wire (φ0.75 mm, length 3.0 mm) made of Kovar (54 mass% Fe-29 mass% Ni-17 mass% Co) and Ni-Mn alloy (98 mass% Ni-2 mass% Mn) A manufactured outer lead wire (φ0.60 mm, length 12 mm) was prepared. The end portions of the inner lead wire and the outer lead wire were resistance welded to produce a lead wire. Welding bumps (φ1.1 mm) were formed at these joints. Sufficient lead wires were prepared for manufacturing various invention examples and comparative examples.

<Oxidation treatment>
The obtained lead wires were put in an electric furnace and heated in the atmosphere, oxygen partial pressure, dew point, material temperature and heating time shown in Table 1, respectively, and an oxide layer was formed on the surface of the inner lead wire by steam oxidation. This process also oxidizes the surface of the outer lead wire. No. No. 10 corresponds to an example of Japanese Patent Application Laid-Open No. 2008-130396 (Patent Document 3), and the oxidation treatment was performed in two stages. The cooling time from the material temperature during heating to 100 ° C. was 6 to 8 minutes.
<Evaluation of oxide layer thickness>
The surface of the inner lead wire subjected to the oxidation treatment was exposed with a FIB-SEM composite device (SMI3050SE, manufactured by SII Nano Technology Co., Ltd.), and subjected to SEM observation (magnification: 15,000 times). Then, the thickness of the observed oxide layer was measured at intervals of 2 μm in the direction of the boundary line based on the SEM photograph. Observation was performed for any three visual fields, and the average value was taken as the measured value. The results are shown in Table 1.
<Oxidation form of Fe>
The total mass of FeO and Fe ₃ O ₄ with respect to the total mass of Fe, FeO, Fe ₃ O ₄ and Fe ₂ O ₃ in the oxide layer by quantitative analysis by X-ray diffraction (Model RINT-2200, manufactured by Rigaku Corporation) The ratio (Fe oxide ratio) was determined. The average value for any three locations of the inner lead wire (φ0.85mm × 20mm length, 20 pieces, fixed to the plate glass with double-sided tape and made into a plate shape of about 20mm × 20mm) formed with an oxide layer The measured value was used. The results are shown in Table 1.

<Glass beads insertion>
Next, glass beads made of borosilicate glass having a through hole of φ0.85 mm were prepared. The glass beads were inserted into each lead wire after steam oxidation from the inner lead wire side. Since the diameter of the through hole of the glass bead is larger than the diameter of the inner lead wire and smaller than the diameter of the welding bump, the glass bead inserted through the lead wire was naturally positioned at the welding lead of the inner lead wire.

<Glass part bonding>
While holding the position of the glass beads, each lead wire inserted with the glass beads is put into an electric furnace and heated in the atmosphere, oxygen partial pressure, dew point, material temperature and heating time shown in Table 2 to melt the glass beads. As a result, it was joined to the oxide layer of the inner lead wire. No. No. 10 was divided into two stages according to the example of Patent Document 3. The cooling time from the material temperature during heating to 100 ° C. was 6 to 8 minutes.

<Reduction treatment>
After joining the glass beads, each lead wire was placed in an electric furnace and heated at a material temperature of 650 ° C. for 10 minutes in a hydrogen atmosphere.

<Junction of electrode part>
A bottomed cup-shaped electrode part (φ2.0 mm, length 5.0 mm) is formed by deep-drawing a flat Ni plate, and the bottom part is formed at the end of the lead wire on the inner lead wire side. Laser welding was performed to produce a cold cathode fluorescent lamp electrode.

<Evaluation of Fe diffusion state>
Each of the cold cathode fluorescent lamp electrodes thus obtained was fixed by being embedded in an epoxy resin and polished with water-resistant abrasive paper to expose the cross section of the interface between the glass beads and the inner lead wire. And by EPMA (JEOL Co., Ltd. model JXA-8500F), elemental line analysis was performed in a direction perpendicular to the interface, and based on the above-mentioned definition, “average thickness of Fe high concentration layer” and “Fe diffusion layer The “average thickness” was measured. Each measured value was an average value at five locations.
The operating conditions of EPMA were as follows.
Acceleration voltage: 15.0kV
Irradiation current: 3.0 × 10 ⁻⁸ A
Beam diameter: 0.1 μm

<Evaluation by SEM observation of interface>
(I) Average number of recesses in the boundary line Similar to the evaluation of the Fe diffusion state, the cross section of the interface between the glass beads and the inner lead wire was exposed and subjected to SEM observation (magnification: 1,000 times). Then, the number of concave portions having a depth of 3 μm or more to the Kovar side per 100 μm length of the boundary line between the observed glass beads and the inner lead wire was counted based on the SEM photograph. Observation was performed for any 10 visual fields, and the average value was taken as the measured value. For reference, Invention Example No. 5 SEM photograph and Comparative Example No. Ten SEM photographs are shown in FIG.

<Evaluation of bonding strength>
For each cold cathode fluorescent lamp electrode, the bonding strength between the glass beads and the inner lead wire was evaluated. Fix a jig with a φ1.5mm through hole on a metal plate with a thickness of 2mm, pass the outer lead through it from the bottom, pull the outer lead upward with a tensile tester, and the strength of breaking the glass. Was evaluated (see arrows in FIG. 6).

<Evaluation of the thickness of the lead oxide layer after glass bonding>
Similarly to the evaluation of the Fe diffusion state, the cross section of the interface between the glass beads and the inner lead wire was exposed and SEM observation (magnification: 1,000 times) was performed. The thickness of the oxide (layer) remaining at the interface between the glass beads and the inner leads was measured at 10 points every 10 μm in the direction of the boundary line. Observation was performed for any three visual fields, and the average value was taken as the measured value. When the length of the oxide layer along the boundary line per 100 μm length of the boundary line between the glass part and the inner lead part formed by the interface is less than 5 μm in total (with respect to the boundary line length) The total thickness of the oxide layer was less than 5%), and the average thickness of the oxide layer was set to “0”, and the length ratio of the oxide layer was entered in parentheses.

  Table 3 shows the results of the evaluation test.

<Discussion>
No. which is a comparative example. No. 1 was an oxidation treatment in the atmosphere, so the oxidized layer after the oxidation treatment was thick, the Fe oxide ratio was small, the Fe high concentration layer was short, and the entire Fe diffusion layer was also short. In addition, the number of recesses having a boundary line depth of 3 μm or more was large. Therefore, high bonding strength was not obtained.
No. which is a comparative example. Since No. 2 is an oxidation treatment in the atmosphere, the oxidized layer after the oxidation treatment was thick, the Fe oxide ratio was small, the Fe high concentration layer was long, and the Fe diffusion layer was also long. In addition, the number of recesses having a boundary line depth of 3 μm or more was large. Therefore, high bonding strength was not obtained.
Inventive example No. In No. 3, the Fe high-concentration layer was appropriately controlled, and a higher bonding strength was obtained compared to the comparative example.
Inventive example No. In No. 4, since the Fe high concentration layer was appropriately controlled and the thickness of the Fe diffusion layer was also suitable, Invention Example No. Compared to 3, a high bonding strength was obtained.
Inventive example No. No. 5 further had a small number of recesses having a boundary line depth of 3 μm or more. Compared to 4, a higher bonding strength was obtained.
Inventive example No. No. 6, the thickness of the oxidized layer after the oxidation treatment is thicker within the specified range, but the thickness of the Fe high-concentration layer and the Fe diffusion layer is appropriately controlled by selecting appropriate glass bonding conditions, and the high bonding Strength was obtained.
Inventive example No. No. 7 is that the thickness of the oxidized layer after the oxidation treatment is thin within a specified range, but the thickness of the Fe high concentration layer and the Fe diffusion layer is appropriately controlled by selecting appropriate glass bonding conditions, and the high bonding Strength was obtained.
Invention Example No. 8 and no. No. 9 is an oxidation treatment performed in an argon atmosphere. The thickness of the oxidized layer after the oxidation treatment is appropriate, the Fe high concentration layer and the Fe diffusion depth are appropriately controlled, and a high bonding strength is obtained. It was.
No. which is a comparative example. 10 corresponds to the example of Patent Document 1, but the oxidized layer after the oxidation treatment was thick. Although the Fe high concentration layer was appropriate, the Fe diffusion depth was long. Although the Fe oxide ratio was high, since the oxidation treatment was once performed in the air, the number of recesses having a boundary line depth of 3 μm or more was large, and a high bonding strength was obtained compared to the present invention. I couldn't.
No. which is a comparative example. No. 11 has a low glass bonding temperature, so the Fe high-concentration layer is short, the entire Fe diffusion layer is short, and the oxide layer remains. Therefore, the bonding strength was low.

DESCRIPTION OF SYMBOLS 1 Electrode part 2 Lead part 2a Inner lead part 2b Outer lead part 3 Glass part 4 Welding edge 21 Phosphor 22 Glass tube

Claims (7)

An electrode for a cold cathode fluorescent lamp, comprising an electrode portion, a lead portion having an inner lead portion and an outer lead portion and connected to an end portion of the electrode,
The inner lead portion is made of an iron-containing metal at least on the surface side, and a glass portion is bonded to the outer periphery of the inner lead portion. The glass portion has an average thickness of 5 to 25 μm from the interface with the inner lead portion toward the inside. It has an Fe diffusion layer, and the Fe diffusion layer is divided into an Fe high concentration layer and an Fe low concentration layer inside thereof, and the average thickness of the Fe high concentration layer is 1 to 4 μm. When the cross section of the interface with the lead part is observed by SEM, the number of recesses with a depth of 3 μm or more to the inner lead part per 100 μm length of the boundary line between the glass part and the inner lead part formed by the interface is averaged. 4 or less cold cathode fluorescent lamp electrodes.   When the cross section of the interface between the glass part and the inner lead part is observed with an SEM, the total number of oxide layers along the boundary line is the length of the boundary line between the glass part and the inner lead part formed by the interface. The electrode for a cold cathode fluorescent lamp according to claim 1, having a length of less than 5%.   A lead part before joining to a glass part for manufacturing a cold cathode fluorescent lamp electrode, having an inner lead part and an outer lead part, and an oxide layer is formed on the surface of the inner lead part, The lead part whose average thickness of an oxide layer is 0.2-1.5 micrometers. The lead part according to claim 3, wherein the ratio of the total mass of FeO and Fe ₃ O _{4 to} the total mass of Fe, FeO, Fe ₃ O ₄ and Fe ₂ O _{3 in} the oxide layer is 90% or more.   Step 1 for forming the lead portion by joining the inner lead portion and the outer lead portion, and heating the inner lead portion at 800 to 1000 ° C. for 5 to 15 minutes in an inert gas atmosphere having a dew point of −5 to 30 ° C. Step 2 of oxidizing the surface of the inner lead part by the above, and placing a glass part on the outer periphery of the inner lead part, and the inner lead part at 800 to 1000 ° C. in an inert gas atmosphere having a dew point of −60 to −10 ° C. The manufacturing method of the electrode for cold cathode fluorescent lamps which includes the process 3 which joins an inner lead part and a glass part by heating for 1 to 10 minutes.   6. The method according to claim 5, further comprising, after Step 3, Step 4 of reducing the surface of the lead portion by heating in a reducing atmosphere, and Step 5 of joining the end portion of the lead portion on the inner lead portion side to the electrode portion. Of manufacturing an electrode for a cold cathode fluorescent lamp.   A cold cathode fluorescent lamp equipped with the cold cathode fluorescent lamp electrode according to claim 1.