JP2005285587A - Electrode for cold cathode tube and cold cathode tube using this electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a cold cathode tube and a cold cathode tube suppressing blackening on the inside of a glass tube, having long life being required to a television receiver or the like, and obtaining prescribed characteristics at relatively low temperature sintering. <P>SOLUTION: A cup electrode 4 of electrode parts 2 at both ends of a cold cathode fluorescent tube 1 uses a tungsten and/or molybdenum substrate containing 4-10 wt% at least one selected from the group comprising lanthanum oxide, yttrium oxide, cerium oxide, strontium oxide, hafnium oxide, and barium oxide and furthermore containing 0.05-0.5 wt% at least one of nickel, iron, cobalt, and palladium. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrode for a cold cathode tube used as a backlight of a liquid crystal display (LCD) such as a television receiver or a personal computer, and a cold cathode tube using the electrode.

  A liquid crystal display (LCD) used for OA equipment such as a personal computer and a word processor incorporates a backlight having a cold cathode fluorescent tube as a light source for illuminating the LCD. The cold cathode fluorescent tube of this light source is roughly composed of an electrode portion and a glass tube portion.

  The electrode part is composed of a cup electrode, a sealing rod, and a lead wire. Conventionally, nickel is used as a material for the cup electrode, and in recent years, niobium, molybdenum, tungsten, and the like have been used. Since the sealing rod is glass-sealed, Kovar, tungsten, or molybdenum whose thermal expansion coefficient behavior is similar to that of glass is used. Further, as the external lead wire, a dimet wire or a nickel wire is used. And these each part is joined by normal resistance welding or laser welding, and comprises the electrode part. The glass tube portion is coated with a fluorescent paint on the inner surface, has an outer diameter of about 2 mm, and a length of about 100 to 1000 mm. The glass tube is sealed with a sealing rod wrapped with glass beads.

There has also been proposed a cathode tube electrode that suppresses the influence of sputtering and has a long life and high output (for example, see Patent Document 1).
Japanese Patent No. 2792543

  In recent years, liquid crystal display devices have been used for television receivers. However, this television receiver has a longer lifespan and a higher life for liquid crystal display devices than conventional OA devices such as personal computers. Brightness is required. That is, the backlight of the liquid crystal display device and the cold cathode tube as the light source are also required to have a long life and high luminance. In addition, with the increase in the size of the display screen, the cold cathode fluorescent lamps have become longer and the operating voltage has become higher.

  Here, it is the blackening of the inner surface of the glass tube near the electrode that determines the lamp life. This is because the electrode material is knocked out from the cup electrode surface by mercury ions, etc., and this knocked-out electrode material adheres to the inner surface of the glass tube in the vicinity of the electrode, thereby blackening the inner surface of the glass tube. The life of the tube is shortened.

  As a countermeasure against the above blackening, molybdenum or tungsten having excellent sputter resistance against mercury ions is used instead of conventional nickel as an electrode material. However, even when these materials are used, blackening measures are not sufficient, and a desired lifetime cannot be obtained.

  On the other hand, an electrode in which a relatively small amount of a low work function substance such as lantana is added to a molybdenum or tungsten electrode has been proposed. Although this electrode has improved suppression of blackening as compared with molybdenum and tungsten electrodes, it has still not been sufficient for the life of a cold cathode tube required for a television receiver.

  An object of the present invention is to provide an electrode for a cold cathode tube that can suppress blackening of the inner surface of the glass tube and can meet a long life required for a television receiver or the like, for example, a reduction in luminance of 50% or less in 60,000 hours. It is to provide a cold cathode tube using an electrode.

  In order to achieve the above object, the present invention employs the following configuration.

  4-10 wt% of one or more of the group consisting of lanthanum oxide, yttrium oxide, cerium oxide, strontium oxide, hafnium oxide and barium oxide is contained in the base material of tungsten and / or molybdenum, and further It is characterized by containing one or more of nickel, iron, cobalt and palladium in a ratio of 0.05 to 0.5 wt%.

  Further, the cold cathode tube electrode is formed by a metal powder injection molding method.

  According to the present invention, in the cold-cathode tube electrode, 4 or more of one or more of the group consisting of lanthanum oxide, yttrium oxide, cerium oxide, strontium oxide, hafnium oxide and barium oxide are added to tungsten and / or molybdenum. By containing -10 wt%, blackening of the inner surface of the glass tube can be suppressed, and a cold cathode tube having a long life required for a television receiver or the like can be provided.

  Further, in addition to the oxide, it contains 0.05 to 0.5% by weight of nickel, iron, cobalt and palladium, so that it can be sintered at a relatively low temperature. Thus, a cold cathode tube electrode having the following characteristics can be obtained.

  Embodiments of the present invention will be specifically described below with reference to the drawings.

  FIG. 1 is a (partly) sectional view showing the structure of a cold cathode fluorescent tube according to the present invention. The cold cathode fluorescent tube 1 has, for example, a straight tube shape having an outer diameter of about 2.6 mm, an inner diameter of 1.6 mm, and a length of about 400 mm. A tube made of Kovar glass (Nippon Electric Glass Co., Ltd .: code number BFK) having a linear expansion coefficient of 5.1 ppm or tungsten glass (Nippon Electric Glass Co., Ltd .: code number BFW) having a linear expansion coefficient of 3.8 ppm. The electrode part 3 is provided at both ends of the glass bulb 2, and the electrode part 3 is composed of a cup electrode 4, an enclosure rod 5 and a lead wire 6, and is sealed with the enclosure rod 3 through the glass coating layer 7. Yes. A phosphor film 8 is provided on the inner surface of the glass bulb 2.

  The cup electrode 4 is made of tungsten, and 7 wt% of lanthanum oxide is added to the cup electrode 4 in order to improve electron emission. Further, in order to improve the sintering characteristics, for example, 0.2% nickel by weight is added. The cup electrode 4 has an outer diameter of 1.2 mm, an inner diameter of 0.9 mm, and a length of about 5 mm. The enclosure rod 5 made of molybdenum has an outer diameter of about 0.8 mm and is sealed with a glass coating layer 7 made of Kovar glass as shown in FIG. Moreover, the lead wire 6 to be connected externally uses a jimet wire.

  The cup electrode 4 and the molybdenum enclosure rod 5 are joined by laser welding. The molybdenum enclosure rod 5 and the jimet wire as the lead wire 6 are joined by resistance welding.

  Here, in the present embodiment, the following configuration is adopted. That is, tungsten and / or molybdenum is used as the base metal. Tungsten, molybdenum and their alloys are well-known high melting point materials, and sputter resistance, which is an index of blackening resistance, belongs to the most excellent metal category. That is, the sputtering resistance is superior to nickel used in conventional electrodes.

  Also, with respect to tungsten and / or molybdenum, lanthanum oxide, yttrium oxide, cerium oxide, strontium oxide, hafnium oxide and barium oxide up to more than 4 wt% and up to 10 wt% improve the electron emission property on the electrode surface, and tungsten, molybdenum It has the effect of further improving the excellent spatter resistance.

  If it is 4 wt% or less, the sputtering resistance is inferior, and a predetermined effect cannot be obtained. This is presumably because the area occupied by an oxide phase such as lanthanum oxide on the electrode surface is insufficient. On the other hand, if it is 10 wt% or more, the ratio of the oxide becomes large, the electrode strength becomes insufficient, and the assembly becomes impossible.

  In order to improve the density by improving the sinterability of tungsten and molybdenum, 0.05 to 0.5 wt% of one or more metals selected from nickel, iron, cobalt, and palladium are contained. When 0.05 to 0.5% nickel or the like is added to tungsten and / or molybdenum in a weight ratio, the sinterability is improved, and a high-density sintered body can be obtained at an economical sintering temperature. .

  Further, if the amount of nickel, iron, cobalt and palladium is less than 0.05%, the sinterability is not improved. If it exceeds 0.5%, the electrical conductivity and the thermal conductivity are lowered, and the electrode performance is lowered.

FIG. 2 is a graph showing the relationship between the La ₂ O ₃ (lanthanum oxide) content and the light transmission intensity in the vicinity of the electrode with respect to the tungsten substrate, the horizontal axis is the La ₂ O ₃ content [wt%], and Relative transmission intensity. As shown in the figure, when the content of La ₂ O ₃ is 4 wt% or less, the transmission strength is extremely lowered. Further, if the content of La ₂ O ₃ is 10 wt% or less, the sinterability is poor.

Further, when the amount of nickel with respect to tungsten is about 0.03%, sintering proceeds remarkably at both 1200 ° C. and 1300 ° C. At 0.05%, densification is achieved. When the amount of nickel is more than this, all of them are densified by sintering at 1200 ° C and 1300 ° C. Even if it is 0.05% or less and (0.02 to 0.03%), if the sintering temperature is about 2000 ° C., it becomes dense, but it is not economical. When Ni is 0%, it is not densified unless it exceeds 2600 ° C. If it exceeds 0.5%, it becomes dense, but the amount of nickel increases, the amount of Ni ₄ W that is an intermetallic compound layer increases, and the electrical conductivity and thermal conductivity decrease. That is, Ni ₄ W itself has low electrical conductivity. If the densification is insufficient (0.05 or less), the bonding force between the tungsten particles is insufficient, and the sputtering resistance is insufficient. Moreover, since there are many voids, electrical conductivity and thermal conductivity are also reduced. When the amount of nickel is too large (0.5% or more), both the electrical conductivity and the thermal conductivity decrease as described above. The amount of nickel is preferably 0.1 to 0.3%.

  Here, the above-mentioned cup electrode 4 is manufactured as follows, for example. First, 0.2 wt% nickel is first added to tungsten powder having a particle size of micron order, and then 7 wt% lanthanum oxide is added. And an organic binder is added and the feedstock for injection molding is created. Next, the feedstock is heated and injection molded into a predetermined mold to obtain a molded body having a predetermined shape. The obtained molded body is heated in a hydrogen stream and degreased and pre-sintered. By subjecting the obtained pre-sintered body to main sintering at 1600 ° C. in a hydrogen stream, an electrode having a relative density of about 98% can be obtained.

  The cup electrode 4 thus obtained is laser welded with a molybdenum sealing rod 5 which is resistance-welded in advance to a dimet wire which is an external lead wire 6, and then glass beads made of Kovar glass are passed through the sealing portion. Then, the glass coating layer 7 is formed by heating in a non-oxidizing atmosphere and welding the glass beads to the molybdenum sealing rod 5. And the edge part of the glass bulb | bulb 2 is welded and sealed to the said glass winding part, and an annealing process is performed subsequently.

  Subsequently, the cold cathode fluorescent tube 1 is completed through an exhaust process in the glass bulb 2, a mercury introduction process, and a lead wire solder finishing process. In the cold cathode fluorescent tube 1 thus obtained, a cathode voltage drop of 20 to 30 V was obtained regardless of the length of the tube. Furthermore, as a result of the life acceleration test, the spatter resistance was improved and the blackening was significantly reduced.

Nickel nitrate was dissolved in water or ethanol and added to tungsten powder having an average particle size of 0.8 microns so that the nickel amount was 0.2 wt%. The powder was dried and then heated at 600 ° C. in a hydrogen stream to remove nitrate radicals. 7 wt% of lanthanum oxide (La ₂ O ₃ ) was added to the tungsten powder added with nickel as a discharge characteristic improver and mixed uniformly.

  The above mixed powder was kneaded with a copolymer of ethylene vinyl acetate / butyl methacrylate / polystyrene, which is an organic binder for injection molding, paraffin wax, butyl phthalate and stearic acid to obtain a feedstock for metal powder injection molding. The feedstock was put into an injection molding machine, heated to 150 to 160 ° C., and then injection molded into a predetermined mold. The dimensions of the obtained molded body were an outer diameter of 2.21 mm, an inner diameter of 1.82 mm, and a total length of 6.5 mm.

  Next, the obtained molded body was gradually heated to 800 ° C. in a hydrogen atmosphere and degreased. Thereafter, sintering was performed in hydrogen at 1600 ° C. for 30 minutes to obtain a cup electrode having an outer diameter of 1.7 mm, an inner diameter of 1.4 mm, and a total length of 5 mm. The shape is shown in FIG. The relative density of the obtained sintered body was 99%.

  The cup electrode 4 obtained as described above was laser-welded with a molybdenum sealing rod 5 which had been resistance-welded in advance with a zimet wire as the external lead wire 6. Thereafter, glass beads made of Kovar glass were inserted into the sealing portion and heated in a non-oxidizing atmosphere to weld the glass beads to the molybdenum enclosure rod 5.

  The end of the arc tube (glass bulb) was welded and sealed to the glass winding part, followed by annealing treatment. Subsequently, a cold cathode fluorescent lamp was completed through an exhaust process in the arc tube, a mercury introduction process, and a lead wire solder finishing process. In this cold cathode fluorescent lamp, a cathode voltage drop of 20 to 30 V was obtained regardless of the length, and as a result of performing a life acceleration test, the sputtering resistance was improved and the blackening was remarkably reduced.

4 wt% of lanthanum oxide (La ₂ O ₃ ) was added as a discharge characteristic improver to tungsten powder having an average particle size of 0.8 microns, and wet mixed using ethyl alcohol as a solvent in a ball mill. After mixing, the slurry was dried to obtain a mixed powder.

  The above powder was kneaded with ethylene vinyl acetate / butyl methacrylate / polystyrene copolymer, which is an organic binder for injection molding, paraffin wax, butyl phthalate and stearic acid to obtain a feedstock for metal powder injection molding. This was put into an injection molding machine maintained at 150 to 160 ° C. and injection molded into a predetermined mold. The dimensions of the obtained molded body were an outer diameter of 1.6 mm, an inner diameter of 1.2 mm, and a total length of 6.8 mm.

  The obtained molded body was gradually heated to 800 ° C. in a hydrogen atmosphere, degreased and pre-sintered. Thereafter, the pre-sintered body was sintered at 2200 ° C. for 30 minutes in hydrogen to obtain a cup electrode 4 having an outer diameter of 1.2 mm, an inner diameter of 0.9 mm, and a total length of 5 mm. The relative density of the obtained sintered body was 98.5%.

  The cup electrode 4 thus obtained was laser-welded with a tungsten sealing rod 5 which had been resistance-welded in advance with a nickel wire as the external lead wire 6. Thereafter, glass beads made of tungsten glass were inserted into the sealing portion and heated in a non-oxidizing atmosphere to weld the glass beads to the tungsten sealing rod 5.

  The end portion of the arc tube was welded and sealed to the above-described glass winding portion, followed by annealing treatment. Subsequently, a cold cathode fluorescent lamp was completed through an exhaust process in the arc tube, a mercury introduction process, and a lead wire solder finishing process. In this cold cathode fluorescent lamp, a cathode voltage drop of 20 to 30 V was obtained regardless of the length, and as a result of performing a life acceleration test, the sputtering resistance was improved and the blackening was remarkably reduced.

  Nickel nitrate was dissolved in water or ethanol and added to tungsten powder having an average particle size of 1.2 microns so that the nickel amount was 0.2 wt%. The powder was dried and then heated at 600 ° C. in a hydrogen stream to remove nitrate radicals.

  7 wt% of yttrium oxide powder as a discharge characteristic improver was added to the tungsten powder to which nickel was added, and wet mixed using ethyl alcohol as a solvent in a ball mill. After mixing, the slurry was dried to obtain a mixed powder.

  The obtained powder was kneaded with ethylene vinyl acetate / butyl methacrylate / polystyrene copolymer, paraffin wax, butyl phthalate, and stearic acid, which are organic binders for injection molding, and used as a feedstock for metal powder injection molding. . This was put into an injection molding machine maintained at 150 to 160 ° C. and injection molded into a predetermined mold. The dimensions of the obtained molded body were an outer diameter of 1.6 mm, an inner diameter of 1.2 mm, and a total length of 6.8 mm.

  The obtained molded body was gradually heated to 800 ° C. in a hydrogen atmosphere, degreased and pre-sintered. Thereafter, the pre-sintered body was sintered at 1600 ° C. for 30 minutes in hydrogen to obtain a cup electrode 4 having an outer diameter of 1.2 mm, an inner diameter of 0.9 mm, and a total length of 5 mm. The relative density of the obtained sintered body was 98.5%.

  The cup electrode 4 thus obtained was laser-welded with a molybdenum sealing rod 5 which had been resistance-welded in advance with a nickel wire as an external lead wire 6. Thereafter, glass beads made of Kovar glass were inserted into the sealing portion and heated in a non-oxidizing atmosphere to weld the glass beads to the molybdenum enclosure rod 5.

  The end portion of the arc tube was welded and sealed to the above-described glass winding portion, followed by annealing treatment. Subsequently, a cold cathode fluorescent lamp was completed through an exhaust process in the arc tube, a mercury introduction process, and a lead wire solder finishing process. As a result of an accelerated test using the cold cathode fluorescent lamp, the spatter resistance was improved and the blackening was significantly reduced. Further, a cathode voltage drop of 20 to 30 V was obtained regardless of the length of the tube.

Nickel nitrate was dissolved in water or ethanol and added to tungsten powder having an average particle size of 0.8 microns so that the nickel amount was 0.2 wt%. The powder was dried and then heated at 600 ° C. in a hydrogen stream to remove nitrate radicals. 2 wt% of lanthanum oxide (La ₂ O ₃ ) and 2 wt% of cerium oxide (CeO ₂ ) were added to the tungsten powder added with nickel as a discharge characteristic improver and mixed uniformly. A cup electrode was prepared and used for the test in the same manner as in Example 1 below. Similar results were obtained.

6 wt% of lanthanum oxide (La ₂ O ₃ ) was added to molybdenum powder having an average particle size of 0.8 μm as a discharge characteristic improving agent, and wet mixed using ethyl alcohol as a solvent in a ball mill. After mixing, the slurry was dried to obtain a mixed powder.

  1.5 wt% of polyvinyl alcohol and stearic acid, which are organic binders for press molding, were added to the powder, and the mixture was made cloudy in ethyl alcohol and granulated with a spray granulator to obtain a granulated powder. The granulated powder was press-molded in a predetermined press mold. The dimensions of the obtained press-molded body were an outer diameter of 2.64 mm, an inner diameter of 1.92 mm, and a total length of 4.8 mm.

  The obtained molded body was gradually heated to 800 ° C. in a hydrogen atmosphere, degreased and pre-sintered. Thereafter, the pre-sintered body was main sintered in hydrogen at 1850 ° C. for 30 minutes to obtain a cup electrode 4 having an outer diameter of 2.2 mm, an inner diameter of 1.6 mm, and a total length of 4 mm. The relative density of the obtained sintered body was 98%.

  The cup electrode 4 thus obtained was laser-welded with a molybdenum-enclosed rod 5 which had been resistance-welded in advance with a nickel wire as the external lead wire 6. Thereafter, glass beads made of Kovar glass were inserted into the sealing portion and heated in a non-oxidizing atmosphere to weld the glass beads to the molybdenum enclosure rod 5.

  The end portion of the arc tube was welded and sealed to the above-described glass winding portion, followed by annealing treatment. Subsequently, a cold cathode fluorescent lamp was completed through an exhaust process in the arc tube, a mercury introduction process, and a lead wire solder finishing process. In the cold cathode fluorescent lamp, a cathode voltage drop of 20 to 30 V was obtained regardless of the length, and as a result of performing a life acceleration test, the sputter resistance was improved and the blackening was remarkably reduced.

Sectional drawing which shows the structure of the cold cathode fluorescent tube which concerns on this invention Explanatory view showing a relationship between a light transmission intensity in the vicinity of the content of La ₂ O ₃ and the electrode

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cold cathode fluorescent tube 2 Glass bulb 3 Electrode part 4 Cup electrode 5 Enclosing rod 6 Lead wire 7 Glass coating layer 8 Phosphor film

Claims (3)

  4-10 wt% of one or more of the group consisting of lanthanum oxide, yttrium oxide, cerium oxide, strontium oxide, hafnium oxide and barium oxide is contained in the base material of tungsten and / or molybdenum, and further An electrode for a cold cathode tube, comprising one or more of nickel, iron, cobalt and palladium in a ratio of 0.05 to 0.5 wt%.   The cold cathode tube electrode according to claim 1, wherein the electrode is formed by a metal powder injection molding method.   A cold cathode tube comprising the cold cathode tube electrode according to claim 1.

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