JP2004319511A - Electrode for low-pressure discharge lamp and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a low pressure discharge lamp having a low scattering rate, in which the sealed gas is contaminated least or is not contaminated at all during use, with a discharge tube least blackened or is not blackened at all. <P>SOLUTION: The electrode for the low pressure discharge lamp comprises tungsten or a tungsten alloy whose average carbon content is <5 μg/g, having a maximum cross-sectional area of 30mm<SP>2</SP>which is perpendicular to the axial line of electrode. The manufacturing method of the same includes a manufacturing process of a plasticized powder material, composed of plasticizer and tungsten alloy powder or tungsten powder, having Fisher average particle size KG of 0.3 μm<KG<5 μm; a shaping process which uses a plasticized powder material; a thermal process in the temperature range of at least 100-500°C in the atmosphere, having a composition of 10 volume %<(H<SB>2</SB>+H<SB>2</SB>O)<100 volume %, 0 volume %<(N<SB>2</SB>and/or rare gas) <90 volume %, with a volume ratio of H<SB>2</SB>O/H<SB>2</SB>being 0.003<H<SB>2</SB>O/H<SB>2</SB><0.15; and a thermal process which is performed at a thermal process temperature T of 1,600°C<T<2,800°C in an atmosphere, having the composition of 10 volume %<(H<SB>2</SB>+H<SB>2</SB>O)<100 volume %, 0 volume %<(N<SB>2</SB>and/or rare gas)<90 volume %, with a volume ratio for H<SB>2</SB>O/H<SB>2</SB>being H<SB>2</SB>O/H<SB>2</SB><0.002. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a low-pressure discharge lamp electrode made of tungsten or a tungsten alloy and a method of manufacturing the same.

  The light source that excites the atoms of the fill gas so that the electrons emanating from the electrodes emit electromagnetic radiation is called a discharge lamp. Discharge lamps are classified into low-pressure discharge lamps and high-pressure discharge lamps according to the filling pressure. Low pressure discharge lamps are usually divided into fluorescent lamps and low pressure sodium lamps. Further, fluorescent lamps are divided into hot cathode fluorescent lamps and cold cathode fluorescent lamps.

  In the case of hot-cathode fluorescent lamps, a sufficient emission electron density is obtained by heat emission at a correspondingly high temperature. For that purpose, the electrode material needs to have a high melting point, a low vapor pressure, and a chemical resistance to the filling gas. Of all metallic and ceramic materials, tungsten and tungsten alloys meet the requirements most. An oxide emitter material is also typically provided on the tungsten electrode to enhance electron emission. The tungsten electrode body is usually formed as a pin, and a tungsten wire is wound around the pin in the area of the electrode tip. An oxide emitter material is provided in the area of the wound coil.

  In the case of a cold cathode fluorescent lamp, secondary electrons are generated by ions that collide with the electrodes. Until now, mainly nickel materials have been used because of their relatively low operating temperatures. Cold cathode fluorescent lamps are commonly used for backlighting flat displays. Particularly in the case of a TFT flat display (TFT = Thin Film Transistor), high requirements for the illumination constant and lifetime and requirements for realizing a large-sized display cause an excessive electric field strength. This results in unacceptably high splash rates. The use of refractory metals such as tungsten, molybdenum, tantalum or niobium has been proposed to reduce the splattering rate. Of the materials mentioned above, tungsten has the lowest scattering rate. There are various electrode shapes depending on the type of cold cathode fluorescent lamp. Pin-shaped electrodes are usually made from drawn wires or rolled or forged bars. The pot-shaped electrode is made from a sheet metal or a strip by deep drawing. The pot-shaped electrode is subsequently vitrified, preferably by welding W.Ni pins.

  The development trend in low pressure discharge lamps has become increasingly demanding on the lamp components. It has been found that many useful electrodes today do not meet that requirement. In particular, the interaction between the electrode and the filling gas component results in poor arc stability and blackening of the discharge vessel. This is evident, for example, by a reduction in the luminous flux during the use of the lamp.

  Patent Document 1 discloses that W is a main component composition, Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Sn, Na, K, Mo, U, and Th are subcomponent compositions, and a subcomponent composition. A tungsten electrode material for a discharge lamp which is refined so that the total content of each element is 0.001% or less with respect to the content of W as a main component composition is described. The low content of subcomponent composition is obtained by heat treatment of the electrode in vacuum. However, the high heat treatment temperatures required for this make the particles noticeably coarser, and the coarsening of the particles makes the material significantly more brittle.

Patent Literature 2 describes a deformed ingot made of tungsten or a tungsten alloy having a purity of 99.99% or more. The deformed ingot has a total content of nitrogen, oxygen and carbon of 500 μg / g or less. When the deformation rate is at least 30% and the final heat treatment temperature is 2600 ° C., the average particle size of the tungsten particles is 20 μm to 600 μm. The values given correspond to the usual standard properties for tungsten until recently and do not improve the working properties of the electrode. Manufacturing techniques are also known in which a plasticizing powder material is used to perform a molding process such as metal powder die casting or powder injection molding. However, these methods have not heretofore been used, particularly for lamp electrodes, because the carbon content of the parts so produced is too high.
JP-A-9-165641 JP 2001-226735 A

  An object of the present invention is to provide an electrode for a low-pressure discharge lamp having a low scattering rate, in which a sealed gas is not or hardly contaminated during use and the discharge tube is not or hardly blackened, and a method of manufacturing the same.

The problem with the electrodes for low-pressure discharge lamps is, according to the invention, for low-pressure discharge lamps made of tungsten or a tungsten alloy with an average carbon content of <5 μg / g and having a transverse area of at most 30 mm ² at right angles to the electrode axis. In the electrode, the production is at least the next step,
A process for producing a plasticized powder material comprising a tungsten powder or a tungsten alloy powder having a Fisher average particle size KG of -0.3 μm <KG <5 μm and a plasticizer, a ratio PM of the plasticizer to the plasticized powder material; Is 40% by volume <PM <70% by volume,
A shaping step using a plasticized powder material,
Optionally performing at least the following heat treatment in one step or in separate steps;
-10 _{vol% <(H 2 + H 2} O) <100 vol%, 0 vol% <(N ₂ and / or noble gas) <has the composition 90% by volume, the volume ratio of H ₂ O / H ₂ is Heat treatment performed in an atmosphere of 0.003 <H ₂ O / H ₂ <0.15 at least in a temperature range of 100 ° C. to 500 ° C., at least a heating rate from ambient temperature to 500 ° C. is 0.05 ° C./s Is the following,
-10 _{vol% <(H 2 + H 2} O) <100 vol%, 0 vol% <(N ₂ and / or noble gas) <has the composition 90% by volume, the volume ratio of H ₂ O / H ₂ is A heat treatment performed in an atmosphere of H ₂ O / H ₂ <0.002 or optionally in a vacuum of pressure <0.0001 mbar at a heat treatment temperature T of 1600 ° C. <T <2800 ° C.
It is solved by including.

According to the present invention, at least the following steps are performed based on the present invention,
A process for producing a plasticized powder material comprising a tungsten powder or a tungsten alloy powder having a Fisher average particle size KG of -0.3 μm <KG <5 μm and a plasticizer, a ratio PM of the plasticizer to the plasticized powder material; Is 40% by volume <PM <70% by volume,
A shaping step using a plasticized powder material,
Optionally performing at least the following heat treatment in one step or in separate steps;
-10 _{vol% <(H 2 + H 2} O) <100 vol%, 0 vol% <(N ₂ and / or noble gas) <has the composition 90% by volume, the volume ratio of H ₂ O / H ₂ is Heat treatment performed in an atmosphere of 0.003 <H ₂ O / H ₂ <0.15 at least in a temperature range of 100 ° C. to 500 ° C., at least a heating rate from ambient temperature to 500 ° C. is 0.05 ° C./s Is the following,
-10 _{vol% <(H 2 + H 2} O) <100 vol%, 0 vol% <(N ₂ and / or noble gas) <has the composition 90% by volume, the volume ratio of H ₂ O / H ₂ is A heat treatment performed in an atmosphere of H ₂ O / H ₂ <0.002 or optionally in a vacuum with a pressure of <0.0001 mbar at a heat treatment temperature T of 1600 ° C. <T <2800 ° C.
It is solved by including.

  The average carbon content includes the carbon component that has been melted or precipitated and surface absorbed or combined in the base material. It should be noted that the conditions under which the test strips are analyzed must correspond to the conditions under which the electrodes are used in the lamp. The specimen does not need to be corroded or pickled before chemical analysis. This is because such things are not possible at sites near the surface.

  As in the case of the tungsten parts used hitherto, the base material carbon content was 5 to 15 μg / g. However, this matrix carbon content does not include the carbon content of the portion near the edge. The average carbon content is detected because the specimen is analyzed in an uncorroded state. The volume at the near edge relative to the average carbon content depends on the specimen diameter or wall thickness. The smaller the diameter or wall thickness of the specimen, the greater the concentration of carbon at sites near the edges. The typical average carbon content of a tungsten pin electrode in the electropolished state is 16 μg / g for a diameter of 1 mm and 25 μg / g for a diameter of 0.2 mm. In the case of a tungsten pot-type electrode having a wall thickness of 0.1 mm, the average carbon content is 20 μg / g or more. Thus, a significantly higher average carbon content compared to the base carbon content reveals that carbon-containing lubricants or carbon-containing impurities are concentrated at sites near the surface and can no longer be completely removed by conventional refining processes. I have. Also, heat treatment does not provide sufficient purity near the surface.

An average carbon content of <5 μg / g is obtained by the process of claim 1. Tungsten powder with a usual metal purity of 99.95% is used as raw material, which guarantees economical production. For particularly stringent requirements, so-called UHP powders (UHP = Ultra High Purity) with a purity of> 99.999% are used, at which values the inclusion of C, N, O, H, Mo is not considered. In addition, tungsten powders are used, each having a usual powder particle size of 0.3 μm to 5 μm based on Fisher. Effective carbon reduction during sintering takes place through open pores because the diffusion rate in the tungsten lattice is not large enough. The higher the density, the more the transition from open pores to closed pores takes place during sintering. This transition point is shifted toward higher temperatures due to the lower density in the green state (unprocessed state). Correspondingly low green densities are obtained by processing plasticized powdered materials in which the proportion of plasticizer is between 40% and 70% by volume. In the case of an electrode having a transverse area of at most 30 mm ² at right angles to the electrode axis, its gas discharge path is short enough to obtain a carbon content according to the invention.

The shaping of the plasticized powder material to a shape close to the final shape or the shaping of the final shape is performed by metal powder die casting, powder extrusion molding, or a similar manufacturing method. An important factor for setting the average carbon content <5 μg / g is the effect of the sintering atmosphere. The sintering process must include at least the following heat treatment steps, optionally in one step or separate steps. In the green state, the electrode compact firstly has a composition of 10% by volume <(H ₂ + H ₂ O) <100% by volume, 0% by volume <(N ₂ and / or rare gas) <90% by volume, The heat treatment is performed in a first atmosphere in which the volume ratio H ₂ O / H _{2 of} steam and hydrogen is 0.003 <H ₂ O / H ₂ <0.15. The temperature at which the electrode compact is heat-treated in the first atmosphere reaches at least 100 ° C. to 500 ° C. at a heating rate from room temperature to at least about 500 ° C. of 0.05 ° C./s or less. Thereafter, it has a composition of 10% by volume <(H ₂ + H ₂ O) <100% by volume, 0% by volume <(N ₂ and / or rare gas) <90% by volume, and H ₂ O / H ₂ <0. The heat treatment is performed in the second atmosphere 002. Optionally, a vacuum with a pressure <0.0001 mbar is also used as the second atmosphere. The temperature at which the electrode compact is heat treated in the second atmosphere is 1700 ° C. to 2800 ° C., depending on the powder size used. Since no other forming process is required, there is no contamination by the carbon-containing lubricant. Electrodes manufactured in this process sequence have a significantly lower average carbon content than, for example, the same shaped electrodes manufactured by rolling, forging, drawing, electropolishing and cutting or rolling and deep drawing as described in the literature. Having. When the electrode emitting and / or absorbing sites of the electrode have a surface roughness <1.5 μm, local evaporation is reduced to a minimum.

  In the case of an electrode for a cold cathode fluorescent lamp, it is particularly advantageous if a pin-like extension is provided at the bottom of the pot-like part of the electrode and a Ni pin is further connected to the pin-like extension. The pot-like portion and the pin-like extension are integrally formed. Since a portion of the tungsten pin interacts with the fill gas, the lamp characteristics are advantageously affected when the site is also comprised of low carbon content tungsten. Further, since the welding between the pot-like portion and the tungsten pin is omitted, the manufacturing cost is reduced. The tungsten pot and the tungsten pin are integrally manufactured by metal powder die casting.

  The Fisher method for measuring the particle size is a standardized measuring method for determining the average particle size. The grain size determined in this way is called a Fisher-based grain size or a Fisher grain size.

  In the following examples, the average carbon content of conventionally conventionally used electrodes is compared with the electrodes according to the invention.

The pot-shaped electrode shown in FIGS. 1 and 2 and integrally formed with pins was manufactured by metal powder die casting. To this end, a 2.1 μm particle size tungsten powder based on fisher was mixed with a wax-based binder by means of a grinding mixer and homogenized. The binder content was 52% by volume and the mixing time was 5 hours. The mixture was compressed in a screw extruder into the starting material for powder die casting. This starting material was heated to a temperature of 160 ° C. and poured into a mold at a pressure of 500 bar. The temperature of the mold was 70 ° C. The die-cut test piece had a pot length L1 of 5.3 mm, a pin length L2 of 3.2 mm, a pot outer diameter D1 of 2.8 mm, a pin diameter D2 of 1.3 mm, and a wall thickness d of 0.2 mm. Thus, a mold was formed. This cylindrical test piece was heated to a temperature of 800 ° C. at a heating rate of 0.009 ° C./s in a H ₂ —N ₂ —H ₂ O atmosphere in a resistance heating type cold wall furnace. The volume ratio of H ₂ / N ₂ was set to 5.7, and the volume ratio of H ₂ O / N ₂ was set to 0.01. At a temperature T = 800 ° C., the furnace atmosphere was replaced with H ₂ (H ₂ O / H ₂ = 0.0005) having a volume content of 0.05% H ₂ O, and the test piece was heated at 0.1 ° C./s. Heated at a rate to a sintering temperature of 2250 ° C. The maintenance time at a temperature T = 2250 ° C. was 4 hours. Thereafter, the furnace was cooled. The pot length L1 was 4.1 mm, the pin length L2 was 2.5 mm, the pot outer diameter D1 was 2.1 mm, the pin diameter D2 was 1.0 mm, and the wall thickness d was 0.15 mm. Further, an average density of 98.6% and an average number of particles of 5950 / mm ² were obtained. The average carbon content of the test piece so formed was detected by combustion analysis and resulted in a value of 1.0-3 μg / g. In that case, the specimen was not corroded before analysis. Pots produced by deep drawing from rolled steel have a value of 18-63 μg / g.

Front view of tungsten pot-type electrode with integral extension pin Sectional view along the line AA in FIG.

Explanation of reference numerals

L1 Pot length L2 Pin length D1 Pot diameter D2 Pin diameter D Wall thickness

Claims (8)

In a low pressure discharge lamp electrode comprising tungsten or a tungsten alloy having an average carbon content of <5 μg / g and having a cross-sectional area of up to 30 mm ² at right angles to the electrode axis, the production of the electrode is at least the following steps:
A process for producing a plasticized powder material comprising a tungsten powder or a tungsten alloy powder having a Fisher average particle size KG of -0.3 μm <KG <5 μm and a plasticizer, a ratio PM of the plasticizer to the plasticized powder material; Is 40% by volume <PM <70% by volume,
A shaping step using a plasticized powder material,
Optionally performing at least the following heat treatment in one step or in separate steps;
-10 _{vol% <(H 2 + H 2} O) <100 vol%, 0 vol% <(N ₂ and / or noble gas) <has the composition 90% by volume, the volume ratio of H ₂ O / H ₂ is Heat treatment performed in an atmosphere of 0.003 <H ₂ O / H ₂ <0.15 at least in a temperature range of 100 ° C. to 500 ° C., at least a heating rate from ambient temperature to 500 ° C. is 0.05 ° C./s Is the following,
-10 _{vol% <(H 2 + H 2} O) <100 vol%, 0 vol% <(N ₂ and / or noble gas) <has the composition 90% by volume, the volume ratio of H ₂ O / H ₂ is A heat treatment performed in an atmosphere of H ₂ O / H ₂ <0.002 or optionally in a vacuum with a pressure of <0.0001 mbar at a heat treatment temperature T of 1600 ° C. <T <2800 ° C.
An electrode for a low pressure discharge lamp, comprising:   2. The electrode according to claim 1, wherein the purity is 99.999% or more excluding the components containing Mo, C, N, O, and H.   The electrode according to claim 1, wherein the electrode is formed in a pot shape.   The electrode according to claim 3, wherein the pot and the pin are formed integrally.   5. Electrode according to claim 1, wherein the site for emitting and / or absorbing electrons has a surface roughness of <1.5 [mu] m.   6. The electrode according to claim 1, wherein the electrode is used for a cold cathode fluorescent lamp. In order to produce an electrode according to one of claims 1 to 5, at least the following steps:
A process for producing a plasticized powder material comprising a tungsten powder or a tungsten alloy powder having a Fisher average particle size KG of -0.3 μm <KG <5 μm and a plasticizer, a ratio PM of the plasticizer to the plasticized powder material; Is 40% by volume <PM <70% by volume,
A shaping step using a plasticized powder material,
Optionally performing at least the following heat treatment in one step or in separate steps;
-10 _{vol% <(H 2 + H 2} O) <100 vol%, 0 vol% <(N ₂ and / or noble gas) <has the composition 90% by volume, the volume ratio of H ₂ O / H ₂ is Heat treatment performed in an atmosphere of 0.003 <H ₂ O / H ₂ <0.15 at least in a temperature range of 100 ° C. to 500 ° C., at least a heating rate from ambient temperature to 500 ° C. is 0.05 ° C./s Is the following,
-10 _{vol% <(H 2 + H 2} O) <100 vol%, 0 vol% <(N ₂ and / or noble gas) <has the composition 90% by volume, the volume ratio of H ₂ O / H ₂ is A heat treatment performed in an atmosphere of H ₂ O / H ₂ <0.002 or optionally in a vacuum with a pressure of <0.0001 mbar at a heat treatment temperature T of 1600 ° C. <T <2800 ° C.
A method for producing an electrode for a low pressure discharge lamp, comprising:   The method of claim 7, wherein the shaping step is performed by metal powder die casting using a plasticized powder material.

Images