JP2010073333A - Electrode for cold cathode fluorescent tube, and cold cathode fluorescent tube using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a cold cathode fluorescent tube having improved sputtering resistance while suppressing the degradation of brightness, and to provide the cold cathode fluorescent tube using the same. <P>SOLUTION: The cold cathode fluorescent tube 1 comprises a glass tube 2 whose internal space is filled with at least rare gas and mercury gas and on the inner face of which a fluorescent layer 2a is formed, and a pair of cup electrodes 5 arranged at both ends thereof with their opening portions 5a opposing each other. The cup electrodes 5 are each formed of iridium (Ir) having a smaller sputtering rate than molybdenum (Mo), or of an alloy containing iridium (Ir). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode for a cold cathode fluorescent tube and a cold cathode fluorescent tube using the same.

  A liquid crystal display (LCD) used in a display device such as a television receiver or a personal computer incorporates a backlight having a cold cathode fluorescent tube as a light source.

  Such a cold cathode fluorescent tube includes a glass tube portion and electrode portions provided at both ends of the glass tube portion (see, for example, Patent Document 1). The glass tube is sealed with a fluorescent paint applied on the inner surface, and a rare gas such as argon (Ar) or neon (Ne), which is a discharge gas, and mercury (Hg) for phosphor excitation. Has been. The electrode part is composed of a cup-type electrode, a sealing rod, and a lead wire. As a material for the cup-type electrode, nickel (Ni) has been conventionally used, and in recent years, niobium (Nb), molybdenum (Mo), tungsten (W) and the like are generally used.

  When a voltage is applied to the electrode portion, electrons are emitted from one electrode, collide with mercury atoms, and ultraviolet rays are generated. Ultraviolet light is converted into visible light by a phosphor formed on the surface of the glass tube, and visible light is emitted from the inside of the glass tube.

Here, for cold cathode fluorescent tubes using mercury, reduction of mercury is required for the purpose of reducing the environmental load. In response to this, it is common to reduce the number of cold cathode fluorescent tubes in the backlight and cover the decrease in luminance by increasing the discharge current.
JP-A-2005-285587

  However, in order to increase the discharge current, it is necessary to increase the density of the rare gas and mercury that are enclosed in accordance with this, and therefore the following problems arise.

  First, when the encapsulated rare gas gives an impact to the electrode, sputtering in which a part of the electrode material is knocked out and scattered increases. The scattered electrode material takes in mercury and becomes amalgam, reducing the effective amount of mercury that contributes to the generation of ultraviolet rays, and as a result, lowering the luminance. Furthermore, the scattered electrode material and the amalgam incorporating the electrode material adhere to the surface of the phosphor, further reducing the luminance.

  In view of the above circumstances, an object of the present invention is to provide a cold cathode fluorescent tube electrode capable of enhancing the sputtering resistance of the electrode and suppressing a decrease in luminance, and a cold cathode fluorescent tube using the same. .

  The electrode for a cold cathode fluorescent tube of the present invention is disposed with both openings facing each other at both ends of a glass tube in which at least a rare gas and a mercury gas are sealed in an internal space and a phosphor layer is formed on the inner surface. A pair of cup-type electrodes, characterized by being made of iridium (Ir) or an alloy containing the iridium (Ir) having a sputtering rate smaller than that of molybdenum (Mo).

  In the cold cathode fluorescent tube, the present inventors use a metal having a smaller sputtering rate than molybdenum (Mo) or nickel (Ni) generally used as the electrode material or an alloy thereof, so that the electrode material is formed by sputtering. I found out that it was prevented from scattering.

  Based on this knowledge, the electrode for the cold cathode fluorescent tube of the present invention uses iridium (Ir) or an alloy thereof as an electrode material having an electrical property close to that of molybdenum or nickel and having a smaller sputtering rate than these. As a result, it is possible to increase the sputter resistance of the electrode and suppress a decrease in luminance.

  In particular, when an iridium alloy is used as the electrode material, the composition of iridium (Ir) is preferably 0.5 wt% or more and 30 wt% or less. Since iridium has high sputter resistance, for example, even when 0.5 wt% is contained in molybdenum or nickel, the sputter resistance can be improved more than any of these simple substances. And the spatter resistance can be improved as the content rate is increased, but the effect is not so changed even if it exceeds 30% by weight. Therefore, by setting the content of iridium in the alloy to 0.5 wt% or more and 30 wt% or less, it is possible to effectively increase the sputtering resistance and suppress the decrease in luminance.

  Further, by using the cold cathode fluorescent tube electrode having the above-described configuration as a cold cathode, it is possible to suppress a decrease in luminance and to provide a long-life cold cathode fluorescent tube.

  First, the overall configuration of the cold cathode fluorescent tube 1 of the present embodiment will be described with reference to FIG. The cold cathode fluorescent tube 1 is a light source used for a backlight of a liquid crystal display device (LCD) used in a display device such as a television receiver or a personal computer, and includes a glass tube 2 and both ends of the glass tube 2. The electrode part 3 is provided.

  The glass tube 2 is made of boro-silicate glass, for example, a straight tube type glass tube having an outer diameter of about 3.0 mm, an inner diameter of 2.4 mm, and a length of about 300 mm. Hermetically sealed.

  A phosphor layer 2a is formed on the inner surface of the glass tube 2 over substantially the entire circumference. The phosphor forming the phosphor layer 2a can be appropriately selected from existing or new phosphors such as halophosphate phosphors and rare earth phosphors according to the purpose and application of the cold cathode fluorescent tube 1. Furthermore, the phosphor layer 2a can also be constituted by a phosphor in which two or more kinds of phosphors are mixed.

  A predetermined amount of rare gas such as discharge gas such as argon (Ar) and neon (Ne) and phosphor excitation mercury (Hg) is sealed in the internal space of the glass tube 2, and the internal pressure is a predetermined pressure below atmospheric pressure. The pressure is reduced to In this embodiment, a mixed gas of argon (Ar) and neon (Ne) is enclosed.

  The electrode portions 3 provided at both ends of the glass tube 2 include a cup-type electrode 5 (corresponding to the cold cathode fluorescent tube electrode of the present invention), an enclosing rod 6 and a lead wire 7, and the enclosing rod 6 is a glass bead 4. It penetrates.

  The cup-shaped electrode 5 has a bottomed cylindrical shape in which one side in the longitudinal direction is opened as an opening 5a and the other is closed by a bottom 5b, and a metal plate made of an electrode material is cylindrical (cup-shaped). It is molded by pressing. For example, the cup-type electrode 5 has an outer diameter of 2.1 mm, an inner diameter of 1.8 mm, a length of 5 mm, and a driving current of 6 mA. The enclosing rod 6 is made of molybdenum (Mo), nickel (Ni), or an alloy thereof, and is joined to the cup-type electrode 5 by laser welding. Furthermore, the lead wire 7 is made of a conductive material such as Kovar.

  In the above configuration, the cup-type electrode 5 is made of iridium (Ir) having a smaller sputtering rate than molybdenum or an alloy containing the iridium (Ir). The reason why the use of iridium as the material of the cup-type electrode 5 can increase the spatter resistance and suppress the decrease in luminance to extend the life of the cold cathode fluorescent tube 1 will be described below.

  First, referring to FIG. 2, the simulation results of the sputtering rate of iridium (Ir) and the sputtering rates of molybdenum (Mo) and nickel (Ni) are shown in comparison. FIG. 2 (a) shows the sputtering of these metals against the kinetic energy of neon (Ne) ions enclosed in the glass tube 2, and FIG. 2 (b) shows argon (Ar) enclosed in the glass tube 2. The sputtering rate of these metals with respect to the kinetic energy of The sputtering rate indicates how many electrode materials are ejected (atoms / ion) in response to collision of one ion.

  As shown in FIGS. 2 (a) and 2 (b), the sputtering rate increases as the kinetic energy of each rare gas increases, but in any energy state, sputtering of molybdenum (Mo) rather than nickel (Ni). The sputtering rate of iridium (Ir) is lower than that of molybdenum (Mo). Therefore, iridium (Ir) has the highest sputtering resistance among the simple substances of molybdenum (Mo), nickel (Ni) and iridium (Ir), and is suitable as the cup-type electrode 5.

Next, with reference to FIG. 3A, changes in luminance of the cold cathode fluorescent tube 1 over time when iridium (Ir) and molybdenum (Mo) are used as electrodes of the cold cathode fluorescent tube 1 are shown. The horizontal axis is a lighting elapsed time (h), and the vertical axis is the luminance maintenance rate in the central portion of the glass tube 2 (luminance B with respect to the initial value B ₀ of the luminance,%). In the measurement of FIG. 3, a rod-shaped electrode having a diameter of 1.5 mm and a length of 15 mm was used as the electrode of the cold cathode fluorescent tube 1.

  As shown in FIG. 3 (a), the luminance maintenance ratio of iridium (Ir) and molybdenum (Mo) decreases from 100% with the passage of time, but at any elapsed time, iridium ( Ir) shows a higher luminance maintenance rate.

Here, the luminance maintenance ratio B / B _{0 with} respect to the elapsed time t is expressed by the following general formula using the time constant τ.

_{B / B 0 = exp [-} (t / τ) 1/2] ······· (1)

Then, by taking the logarithm of the above formula (1) and arranging it, the following formula is obtained.

log (B / B ₀ ) = (− τ ^−1/2 ) · (t ^1/2 ) (2)

Here, in the above equation (2), if y = log (B / B ₀ ), a = (− τ ^−1/2 ), x = (t ^1/2 ), equation (2) It is deformed as follows.

y = a · x (3)

From here, the logarithm of the data corresponding to FIG. 3A is taken and re-plotted so as to match the above equation (3), and FIG. 3B is obtained. In FIG. 3B, the horizontal axis is the square root t ^1/2 (h ^1/2 ) of the elapsed time, and the vertical axis is the logarithm log (B / B ₀ ) of the luminance maintenance ratio B / B _0. . In FIG. 3B, the constant a can be obtained as the slope of the linear approximation formula based on the least square method.

Here, assuming that the lifetime (h) of the cold cathode fluorescent tube 1 is the elapsed time t _{1/2 when the} luminance B is halved from its initial value B ₀ , the elapsed time when the luminance B is halved from its initial value B _0. t _1/2 is expressed by the following equation.

t _1/2 = [log (0.5) / a] ² (4)

The lifetimes of iridium (Ir) and molybdenum (Mo) calculated from the above equation (4) are shown in the table below.

  Similarly, the table below shows the calculation results of the lifetime of iridium (Ir) and molybdenum (Mo) when the drive current is 9 mA.

  In this case, if the life time (h) of 6 mA molybdenum is 1, the normalized life of molybdenum (Mo) with a drive current of 9 mA decreases to 0.8, whereas the standard of iridium (Ir) The lifetime is not as low as 1.7. Therefore, when iridium (Ir) is used as the electrode of the cold cathode fluorescent tube 1, a long life can be maintained even when the drive current is increased.

  Next, with reference to FIG. 4, the time-dependent change of the brightness | luminance of the cold cathode fluorescent tube 1 at the time of using the alloy containing iridium (Ir) and molybdenum (Mo) as the cup type electrode 5 is shown, respectively. The measurement conditions are that the cup-type electrode 5 has an outer diameter of 2.1 mm, an inner diameter of 1.8 mm, a length of 5 mm, and a driving current of 6 mA.

  As shown in FIG. 4 (a), the luminance maintenance ratio of the alloy having the iridium (Ir) content of 0.5 wt%, 3 wt%, and 30 wt% in nickel (Ni) and the luminance of molybdenum (Mo). The maintenance factor decreases from 100% with the passage of time, but by adding 0.5% by weight or more of iridium (Ir), a luminance maintenance factor higher than that of molybdenum (Mo) is obtained at any elapsed time. Can do.

  Furthermore, according to the above formulas (1) to (3), the logarithm of the data corresponding to FIG. 4A is taken and replotted to obtain FIG. 4B. Further, the life time of the alloy having the iridium (Ir) content in nickel (Ni) of 0.5 wt%, 3 wt%, and 30 wt% calculated from FIG. 4B and the above formula (4) is used. And the lifetime of molybdenum (Mo) is shown in the table below.

  In Table 3, when the life time (h) of molybdenum (Mo) is normalized to 1, an alloy in which the content of iridium (Ir) in nickel (Ni) is 0.5 wt%, 3 wt%, and 30 wt% The lifetime is equivalent to 1.4 to 1.5. By including iridium (Ir) in nickel (Ni) or the like as the cup-type electrode 5, it is possible to increase the spatter resistance, suppress a decrease in luminance, and extend the life of the cold cathode fluorescent tube 1. On the other hand, the lifetime of an alloy containing iridium (Ir) does not extend so much even if its content is increased. In particular, even if the content of iridium (Ir) exceeds 30% by weight, it is not expected that the lifetime will be dramatically extended. Therefore, when iridium (Ir) is contained, the content is preferably within 0.5 to 30% by weight.

  As described above, the use of an alloy containing iridium (Ir) or iridium (Ir) having a sputtering rate smaller than that of nickel (Ni) or molybdenum (Mo) as an electrode of the cold cathode fluorescent tube 1 reduces luminance. Therefore, the life of the cold cathode fluorescent tube 1 can be extended.

  In the present embodiment, the alloy of nickel (Ni) and iridium (Ir) has been described as the electrode of the cold cathode fluorescent tube 1 in particular, but the composition of the alloy is not limited to this, and iridium An alloy of (Ir) and rhodium (Rh) (IrRh) or an alloy of iridium (Ir) and platinum (Pt) (IrPt) may be used.

The figure which shows the structure of the cold cathode fluorescent tube of this embodiment. The graph which shows the sputtering rate of iridium (Ir), molybdenum (Mo), and nickel (Ni). The graph which shows a time-dependent change of the brightness | luminance maintenance factor at the time of using iridium as an electrode of a cold cathode fluorescent tube. The graph which shows a time-dependent change of the brightness | luminance maintenance factor at the time of using an iridium alloy as an electrode of a cold cathode fluorescent tube. DESCRIPTION OF SYMBOLS 1 ... Cold cathode fluorescent tube, 2 ... Glass tube, 2a ... Phosphor layer, 3 ... Electrode part, 4 ... Glass bead, 5 ... Cup type electrode (electrode for cold cathode fluorescent tube), 5a ... Opening part, 5b ... Bottom part, 6 ... enclosed rod, 7 ... lead wire.

Claims (3)

  A pair of cup-shaped electrodes disposed at opposite ends of a glass tube in which at least a rare gas and a mercury gas are sealed in an internal space and a phosphor layer is formed on an inner surface, with openings facing each other. An electrode for a cold cathode fluorescent tube comprising iridium (Ir) or an alloy containing the iridium (Ir) having a sputtering rate smaller than that of molybdenum (Mo).   2. The alloy according to claim 1, wherein the alloy is an alloy of nickel (Ni) and iridium (Ir), and the composition of the iridium (Ir) is not less than 0.5 wt% and not more than 30 wt%. Cold cathode fluorescent tube electrode.   A cold cathode fluorescent tube comprising the cold cathode fluorescent tube electrode according to claim 1 or 2 as a cold cathode.

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