Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J61/00—Gas-discharge or vapour-discharge lamps
  • H01J61/02—Details
  • H01J61/24—Means for obtaining or maintaining the desired pressure within the vessel
  • H01J61/26—Means for absorbing or adsorbing gas, e.g. by gettering; Means for preventing blackening of the envelope
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J61/00—Gas-discharge or vapour-discharge lamps
  • H01J61/02—Details
  • H01J61/12—Selection of substances for gas fillings; Specified operating pressure or temperature
  • H01J61/18—Selection of substances for gas fillings; Specified operating pressure or temperature having a metallic vapour as the principal constituent
  • H01J61/20—Selection of substances for gas fillings; Specified operating pressure or temperature having a metallic vapour as the principal constituent mercury vapour

Definitions

• This invention relates to mercury gas discharge devices, in particular mercury vapour fluorescent lamps including hot cathode and cold cathode fluorescent lamps (CCFLs).
• mercury vapour fluorescent lamps including hot cathode and cold cathode fluorescent lamps (CCFLs).
• CCFLs cold cathode fluorescent lamps
• CCFLs are often used as miniature high luminous intensity light sources. They feature simple construction, are miniature in size, have high luminous intensity, exhibit small increases in lamp temperature during operation, and have a relatively long operating life. Because of these characteristics, CCFLs have been widely used as a light source in various backlit light units and scanners.
• CCFLs are mass produced and have great difficulty meeting these ever increasing demands.
• Figure 1 shows a glass envelope 2 with a fluorescent powder film 4 coated onto its interior wall.
• Gas 5 such as a neon and argon mixture with a source of mercury vapour are confined in glass envelope 2.
• Electrodes 1 are disposed at opposing ends of glass envelope 2.
• Electrodes 1 are a key component of the CCFL. They are responsible for conducting electricity, emitting electrons, forming a magnetic field, and for other lamp and heating functions. To a large extent, lamp performance depends upon the choice of the electrode material.
• Electrodes commonly used in CCFLs include an electrode wire 6 formed of tungsten, dumet or kovar and a cathode in the form of a nickel tube or nickel bucket 3 welded onto the part of electrode wire 6 which is inside glass envelope 2.
• Conventional nickel tubes or nickel buckets are made using high-ratio compression.
• the operating surface area of the nickel tube or nickel bucket 3 is limited by the inner diameter of glass envelope 2 and the length of the electrode. Accordingly, any increase in the lamp's luminous intensity during operation is limited by the surface area of the nickel tube or nickel bucket and the melting point of nickel which is approximately 1453°C. As a result of these limitations, current CCFL's are not able to withstand a large lamp electric current and the impact of a strong electron stream.
• the limited surface area of the nickel tube or nickel bucket also limits the amount of active alkaline metals such as barium, calcium, strontium and cesium that can be added. These metals can be added to the cathode to enhance electron emission efficiency.
• waste gases such as water, oxygen, nitrogen, carbon monoxide and carbon dioxide
• waste gases develop and proliferate from the materials used.
• These waste gases enter into the interior of the lamp. They result in an increase in resistance to electrical conductivity within the lamp, and cause damage to the cathode by reacting with the active alkaline metals that can be added to the cathode. This reduces the functioning of the lamp and is known to present difficulties when attempting to produce high quality, small sized, high luminous intensity and high performance fluorescent lamps and CCFLs.
• a mercury gas discharge device such as a cold cathode fluorescent lamp (CCFL) with a construction that overcomes or at least ameliorates the problems of prior art mercury gas discharge devices.
• Another object of the invention is to provide a mercury gas discharge device such as a CCFL that operates under a larger operating electric current without affecting the device's operational lifetime.
• a mercury gas discharge device such as a CCFL that provides greater intensity and longer operational lifetime when compared with current mercury gas discharge devices.
• a mercury gas discharge device constructed according to an embodiment of the present invention comprises an envelope with inert gas and mercury vapour confined within the envelope.
• the gas discharge device includes a pair of electrodes which may be located inside or outside of the envelope.
• One or more sintered metal portions are also located in the envelope. The sintered metal portions have high gettering characteristics with respect to waste gases, but low gettering characteristics with respect to the mercury vapour.
• Figure 1 is a schematic diagram illustrating the construction of known CCFLs.
• Figure 2 is a schematic diagram illustrating a CCFL constructed in accordance with an embodiment of the present invention.
• Figure 3 is a graph showing the typical life span of a CCFL constructed in accordance with an embodiment of the present invention.
• Figure 4 is a schematic diagram illustrating a CCFL constructed in accordance with another embodiment of the present invention.
• Figure 5 is a schematic diagram illustrating a CCFL constructed in accordance with a further embodiment of the present invention.
• Figure 6 is a schematic diagram illustrating an external electrode fluorescent lamp according to another embodiment of the invention.
• a fluorescent lamp 10 comprising a tube 2 with an interior wall and an exterior wall and a fluorescent powder film coating 4 on the interior wall.
• Inert gas and mercury vapour 5 are confined within the tube and the lamp includes a pair of electrodes 1.
• One or more sintered metal portions 11 are also located in tube 2. Sintered metal portions 11 have high gettering characteristics with respect to waste gases such as water, oxygen, nitrogen, carbon monoxide and carbon dioxide, but low gettering characteristics with respect to the mercury vapour.
• One or more sintered metal portions 11 may be placed anywhere within tube 2. It is preferred that sintered metal portions 11 are welded in the tube, preferably welded to one or more of electrodes 1, although welding to electrodes is not essential. In an embodiment where one or more sintered metal portions 11 are welded to an electrode, they may be welded to any part of the electrode which is inside tube 2.
• the number of sintered metal portions 11 included is preferably determined by the size of tube 2. When tube 2 is small, only one sintered metal portion 11 may be required to achieve the advantages of the invention.
• tube 2 may be any appropriate type of tube and is preferably a glass tube.
• the sintered metal portion is a sintered metal tube (or bucket) 7 or plate 8 (which can be in a pair as shown in Figure 5) which is welded on to the part of each electrode wire 6 which extends inside the tube.
• the sintered metal tube (or bucket) 7 or plate 8 may be manufactured using typical metal powder metallurgy techniques or ultrasonic moulding press or any other appropriate methodology.
• the sintered metal tube 7 or plate 8 (which may also be provided in the form of a bucket, not shown) preferably includes at least one metal element which is selected from a first group of metal elements which have high gettering characteristics with respect to waste gases and low gettering characteristics with respect to the mercury vapour within tube 2.
• a first group of metal elements which have high gettering characteristics with respect to waste gases and low gettering characteristics with respect to the mercury vapour within tube 2.
• metal elements have very low gettering characteristics with respect to mercury vapour.
• the first group of metal elements includes but is not limited to ferrous family metals such as iron, nickel and cobalt. These metal elements react chemically with waste gases such as water, oxygen, nitrogen, carbon monoxide and carbon dioxide under operating temperatures of the lamp 10 but not with the mercury vapour. Therefore, the gettering characteristics of the sintered metal tube 7 or plate 8 is enhanced by the inclusion of one or more of the metal elements included in the first group.
• sintered metal tube 7 or plate 8 is a combination of metal elements which also includes one or more metals from a second group that exhibit high temperature resistance in combination with low or very low gettering characteristics with respect to the mercury vapour, thereby reducing the possibility of sputtering.
• Metals such as molybdenum, tungsten, tantalum and niobium are appropriate for inclusion in the second group of metals.
• FIG. 6 illustrates a further arrangement in which the electrodes 12 are entirely outside of tube 2.
• This type of arrangement is known as an external electrode fluorescent lamp (EEFL).
• EEFL external electrode fluorescent lamp
• each end of tube 2 is capped with an electrode 12, each of which has an electrical connector 13.
• tube 2 has a powder film coating 4 on the interior wall, and inert gas and mercury vapour 5 are confined within the tube 2.
• One or more sintered metal portions may be located anywhere within the tube.
• a sintered metal portion in the form of sintered tube 7 is located at one end of the EEFL tube 2, held in place by a neck portion of EEFL tube 2.
• sintered metal tube 7 or plate 8 is a metallic combination comprising between 2 and 5 metal elements with at least one of the metal elements being selected from the first group (high gettering characteristics with respect to waste gases but not mercury vapour) and at least one of the metal elements being selected from the second group (resistant to high temperatures with low or very low gettering characteristics with respect to mercury vapour). It is preferred that the sintered metallic combination is porous with a porosity of 50% to 4% and a relative density of 50% to 96%.
• the metal portion further includes one or more active alkaline metals for enhancing the efficiency with which electrons are emitted from the cathode.
• the active alkaline metals may include but are not limited to barium, calcium, strontium, and cesium.
• a graph shows brightness or luminous intensity versus life span for a CCFL constructed with a sintered porous metal tube or plate according to the present invention.
• the graph of Figure 3 shows a distinct drop in luminous intensity of around 3 to 5%. This is due to the proliferation of waste gases derived from the glass, fluorescent powder and the electrodes. The proliferation of these waste gases results in contamination and sputtering inside the lamp. Meanwhile, during operation the sintered porous metal tube or plate continues to attempt to increase absorption of the waste gases.
• the sintered metal selected does not react with or absorb mercury vapour during operation.
• the content of the mercury vapour within the tube is maintained at a higher level for longer, thereby reducing the rate at which the lamp's luminous intensity decreases when compared with conventional lamps.
• the fluorescent lamp of the present invention is capable of withstanding twice the operational electric current of conventional fluorescent lamps.
• the operational electric current of a conventional CCFL with an outer diameter of 2.6mm is 5mA.
• a CCFL constructed in accordance with the present invention with the same outer diameter and with a sintered porous metallic combination tube can withstand an operational electric current of up to 10mA, achieving an increased luminous intensity of 8,000 to 10,000cd/m 2 whilst maintaining comparable lamp life (approximately 15,000 to 20,000 hours).
• the operational life of the inventive CCFL may exceed 50,000 hours.
• FIG. 4 shows a schematic illustration of a CCFL constructed according to an embodiment of the present invention. It comprises glass envelope 2, fluorescent powder film 4 coated onto the interior wall of glass envelope 2 and inert gas and mercury vapour 5 confined inside glass envelope 2. Electrodes 1 are located at the ends of the lamp (only one shown). Electrodes 1 include electrode wire 6 sealed at the end of envelope 2 and extending from the interior to the exterior of envelope 2.
• the inventive CCFL has a sintered metal tube 7 composed of a combination of 2 to 5 metal elements welded onto electrode wires 6 and used as a cathode, although sintered metal tube 7 may be welded anywhere in glass envelope 2. This replaces the conventional nickel tube 3 illustrated in Figure 1.
• the inventive sintered metal tube 7 is produced by metallic powder processes using typical powder metallurgy and is, therefore, a porous product. As a result, its surface area is 2 to 20 times greater than that of the high density compacted nickel tube of conventional lamps.
• the sintered metal tube 7 can therefore absorb or accommodate more of active alkaline metals such as barium, calcium, strontium and cesium etc. which act as activating elements for electron emission, thereby reducing the resistance to electron emission at cathode.
• the inventive sintered metal portion composition is preferably chosen from the following group of compositions:
• the inventive sintered metal portion is not necessary for the inventive sintered metal portion to be composed only of elements in the aforementioned first and second groups of metal elements. However, it is preferred that the proportion of metal elements selected from the first group in combination with the proportion of metal elements selected from the second group comprises between 50% and 100% of the total sintered metal composition.
• a linear CCFL is produced with an outer diameter of 2.6mm, an inner diameter of 2.0mm, a lamp length of 243mm and uses a sintered porous metal tube composed of tungsten, molybdenum, iron and cobalt and welded onto a tungsten electrode.
• the composition is: tungsten + molybdenum: 10 to 40% iron + cobalt: 90 to 60%
• the electrode tube is sealed in a borosilicate (hard glass) tube, the interior wall of which is coated with fluorescent powder film with a color temperature of 5800°K.
• the borosilicate tube is filled with an appropriate neon/argon gas combination and a mercury vapour source, and is ignited with circuitry known in the art.
• the CCFL of Case Study 1 has performance characteristics as shown in Table 1 below.
• a linear cold cathode fluorescent lamp (CCFL) is produced with an outer diameter of 1.8mm, an inner diameter of 1.2mm and lamp length of 72.5mm as illustrated in Figure 5.
• the feature distinguishing the CCFL of Figure 5 from that of Figure 4 is the use of porous sintered metal plate 8 in place of tube 7.
• the sintered porous metal plate is composed of tungsten, molybdenum, iron, nickel and cobalt and is welded onto a tungsten electrode.
• the composition is: tungsten + molybdenum: 10 to 40% iron + nickel + cobalt: 90 to 60%
• the electrode plate is sealed in a borosilicate (hard glass) tube, the interior wall of which is coated with fluorescent powder film with a color temperature of 6500°K.
• the borosilicate tube is filled with an appropriate neon/argon gas combination and a mercury vapour source, and is ignited with circuitry, as known in the art.
• the CCFL of Case Study 2 has performance characteristics as shown in Table 2 below.
• a linear cold cathode fluorescent lamp (CCFL) is produced with an outer diameter of 2.6mm, an inner diameter of 2.0mm and a lamp length of 243mm. It uses a sintered porous metal tube composed of tungsten, molybdenum, iron and cobalt and welded onto a tungsten electrode.
• the composition is: tungsten + molybdenum: 70 to 90% iron + cobalt: 30 to 10%
• the electrode tube is sealed in a borosilicate (hard glass) tube, the interior wall of which is coated with fluorescent powder film with a color temperature of 5800°K.
• the borosilicate tube is filled with an appropriate neon/argon gas combination and a mercury vapour source, and is ignited with circuitry, as known in the art.
• the CCFL of Case Study 3 has performance characteristics as shown in Table 3 below.
• a linear CCFL is produced with an outer diameter of 4.0mm, an inner diameter of 2.9mm, a lamp length of 264mm and uses a sintered porous metal tube composed of niobium, molybdenum, iron, nickel and cobalt and welded onto a tungsten electrode.
• the composition is: niobium + molybdenum: 30% iron + nickel + cobalt: 70%
• the electrode tube is sealed in a borosilicate (hard glass) tube, the interior wall of which is coated with fluorescent powder film with a color temperature of 5200°K.
• the borosilicate tube is filled with an appropriate neon/argon gas combination and a mercury vapour source, and is ignited with circuitry known in the art.
• the CCFL of Case Study 4 has performance characteristics as shown in Table 4 below.
• CCFL constructed using the described porous sintered metal combination will achieve a lamp life of 50,000 or more hours of continuous operation at 8.2mA, and a lamp life of 10,000 to 15,000 hours of continuous operation at 16.4mA.
• a linear CCFL is produced with an outer diameter of 1.8mm, an inner diameter of 1.4mm, a lamp length of 38.5mm and uses a sintered porous metal tube composed of tungsten, tantalum, iron and cobalt and welded onto a tungsten electrode.
• the composition is: tungsten + tantalum: 80% iron + cobalt: 20%
• the electrode tube is sealed in a borosilicate (hard glass) tube, the interior wall of which is coated with fluorescent powder film with a color temperature of 12000°K.
• the borosilicate tube is filled with an appropriate neon/argon gas combination and a mercury vapour source, and is ignited with circuitry known in the art.
• the CCFL of Case Study 5 has performance characteristics as shown in Table 5 below.
• the mercury gas discharge device (such as a CCFL) constructed according to the present invention uses sintered metal portions (such as tubes, buckets or plates) to improve gettering with respect to waste gases within the device envelope, thus increasing intensity, extending lifetime of the device and significantly improving performance.
• the inventive sintered metal portion is porous. Therefore, it has an increased operational surface area when compared with the getters of conventional mercury gas discharge devices or CCFLs. Accordingly, the device is able to withstand higher operating currents whilst maintaining steady operating conditions and intensity; when the operating current increases, so too does the intensity or luminous intensity.
• a CCFL with a porous sintered portion when used as the cathode and constructed according to an embodiment of the present invention, exhibits a significantly higher luminous intensity index than conventional fluorescent lamps.
• a mercury gas discharge device (such as a CCFL) constructed according to an embodiment of the present invention would also exhibit an increase in temperature during operation. The increase in temperature will release any mercury vapour which has become physically trapped within the sintered metal portion, but will not release waste gases as they will be chemically bound to the "gettering" metal.
• a sintered metal portion according to an embodiment of the present invention forms compounds with waste gases in the device envelope and absorbs them. These sintered metal portions become more active when protected in a vacuum or inert gas environment.
• inventive sintered metal portion is ideal for use in multi-functional, high efficiency and long life CCFLs.
• a CCFL according to the present invention exhibits a life span which is among the longest of all CCFLs.

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• 2002
  • 2002-09-12 US US10/242,504 patent/US6825613B2/en not_active Expired - Fee Related
• 2003
  • 2003-04-30 EP EP03009949A patent/EP1398822B1/en not_active Expired - Lifetime
  • 2003-04-30 AT AT03009949T patent/ATE356427T1/de not_active IP Right Cessation
  • 2003-04-30 DE DE60312273T patent/DE60312273T2/de not_active Expired - Fee Related
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  • 2003-09-12 AU AU2003258391A patent/AU2003258391B2/en not_active Ceased
  • 2003-09-12 JP JP2004534868A patent/JP2005538515A/ja active Pending
  • 2003-09-12 CA CA002496178A patent/CA2496178A1/en not_active Abandoned
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