JP2005302660A - Cold cathode fluorescent lamp and backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold cathode fluorescent lamp which is more improved than, a cold cathode fluorescent lamp in which mixed gas with neon/argon as the body is sealed in both the lamp efficiency and starting voltage (especially in starting voltage near 0°C). <P>SOLUTION: In the cold cathode fluorescent lamp 26 provided with a tube state glass bulb 32 in which a noble gas mixture is sealed and is formed with a fluorescent film 34 on its interior surface and a pair of electrodes 36 and 38 installed facing each other on both ends of the glass bulb 32, the mixed gas is constituted of 95% neon and 5% krypton (mole ratio). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cold cathode fluorescent lamp and a backlight unit, and more particularly to a backlight unit used in an LCD (liquid crystal display) device and the like and a cold cathode fluorescent lamp used as a light source of the backlight unit and the like.

Among the fluorescent lamps, cold cathode fluorescent lamps, in which a phosphor is coated on the inner surface of a straight tube-shaped glass bulb and cold cathodes are provided as internal electrodes at both ends, are suitable for reducing the diameter and are therefore thin. It is suitably used as a light source of a backlight unit that requires (downsizing).
A rare gas and a small amount of mercury are enclosed in the glass bulb of the cold cathode fluorescent lamp. The rare gas is sealed mainly for the purpose of lowering the discharge start voltage, and conventionally, the rare gas to be sealed is basically argon alone.

  However, as the LCD device including the backlight unit is further reduced in size, a further reduction in the discharge start voltage has been required under the demand for downsizing the power supply unit that drives the cold cathode fluorescent lamp. In order to meet this demand, a cold cathode fluorescent lamp mainly composed of neon and argon as a rare gas to be filled has been developed (see Patent Document 1, Patent Document 2, etc.).

  The present inventor also conducted experiments on the starting voltage characteristics when the molar ratio of neon and argon to be sealed was changed. The experimental results are shown in FIG. FIG. 8A is a characteristic diagram in which the horizontal axis represents the molar ratio [%] of neon (Ne) and argon (Ar), and the vertical axis represents the starting voltage. This figure merely shows the tendency of the change in the starting voltage with respect to the mixing ratio of the rare gas, and does not show an absolute value or the like.

As can be seen from FIG. 8 (a), it can be seen that the starting voltage gradually decreases as the neon ratio is increased (decreasing the argon ratio) from argon alone (100%). FIG. 8A shows that if only the starting voltage is improved, the ratio should be close to that of neon alone (100%).
However, it has been confirmed by experiments that the lamp efficiency is lowered when neon alone or at a ratio close thereto. FIG. 8B is a characteristic diagram showing the relationship between the mixing ratio of neon and argon and the lamp efficiency. As can be seen from FIG. 8 (b), although the lamp efficiency gradually increases as the argon ratio is decreased, it turns out that the vicinity of argon 5% (neon 95%) becomes the peak and then decreases. This is because the glass bulb surface temperature (Ts) is 60 ° C. at which an optimum mercury vapor pressure can be obtained when the mixing ratio is 95% neon to 5% argon.

Therefore, neon 95% -argon 5% is set to an optimum mixing ratio that improves the starting voltage and improves the lamp efficiency as compared with the case of argon alone.
Japanese Patent No. 3141411 Japanese Patent No. 3068659

  By the way, with the increase in size and brightness of liquid crystal televisions, the number of cold cathode fluorescent lamps provided per one direct-type backlight unit attached to the LCD panel for the liquid crystal television is also increasing. As the number of cold-cathode fluorescent lamps increases, the temperature in the unit also rises, exceeding 60 ° C. at which an optimum mercury vapor pressure is obtained, and rising to nearly 70 ° C. As a result, the lamp efficiency is reduced, and the required luminance cannot be obtained.

  For the decrease in lamp efficiency due to the rise in unit internal temperature, it is conceivable to raise the argon ratio to more than 5%, lower the glass bulb surface temperature, and lower the unit internal temperature to around 60 ° C. Then, as can be seen from FIG. 8 (a), the starting voltage increases. In this case, even in a temperature environment where a liquid crystal television is used, the starting voltage becomes a problem particularly at a low temperature (about 0 ° C.) at which the mercury vapor pressure is low.

  The present invention relates to a cold cathode fluorescent lamp in which both the lamp efficiency and the starting voltage (particularly, the starting voltage at a low temperature) are improved compared to a fluorescent lamp mainly composed of neon / argon gas, and the cold cathode fluorescent lamp. It aims at providing the backlight unit used for the light source.

In order to achieve the above object, a cold cathode fluorescent lamp according to the present invention has a tubular glass bulb in which a mixed gas of rare gas is enclosed and a phosphor film is formed on the inner surface, and is opposed to both ends of the glass bulb. A cold cathode fluorescent lamp having a pair of electrodes arranged, wherein the constituent gas of the mixed gas includes at least neon and krypton.
Further, the constituent gas of the mixed gas further contains argon.

  In order to achieve the above object, a backlight unit according to the present invention includes the above-described cold cathode fluorescent lamp as a light source.

  According to the cold cathode fluorescent lamp of the present invention, since at least neon and krypton are included as constituent gases of the mixed gas sealed in the glass bulb, a mixed gas mainly composed of neon and argon is sealed. As compared with the conventional cold cathode fluorescent lamp, the starting voltage at 0 ° C. and in the vicinity thereof can be lowered, and high lamp efficiency can be realized in an ambient temperature environment higher than that of the conventional cold cathode fluorescent lamp.

Furthermore, the same effect as described above can be obtained by including argon and using a mixed gas composed of three kinds of rare gases, neon, argon, and krypton.
Further, according to the backlight unit according to the present invention, since the cold cathode fluorescent lamp described above is provided as a light source, the starting voltage is lowered as compared with the backlight unit provided with the conventional cold cathode fluorescent lamp as a light source. Therefore, it is possible to reduce the size of the power supply unit provided in the backlight unit. Furthermore, even if the number of cold cathode fluorescent lamps provided in the backlight unit is increased and the temperature in the unit at the time of lighting is higher than before, the cold cathode fluorescent lamp has the same or higher lamp efficiency than the conventional one. The lamp emits light, and the luminance of the entire backlight unit is improved.

FIG. 1 is a perspective view showing a schematic configuration of a direct-type backlight unit 10 according to an embodiment. In addition, FIG. 1 is the figure which fractured | ruptured the translucent board 16 mentioned later. The backlight unit 10 is arranged and used on the back of an LCD (liquid crystal display) panel (not shown), and constitutes an LCD device.
The backlight unit 10 includes an envelope 18 including a rectangular reflecting plate 12, a side plate 14 surrounding the reflecting plate 12, and a translucent plate 16 provided in parallel to the reflecting plate 12. The reflecting plate 12 and the side plate 14 are both reflecting films (not shown) in which silver or the like is vapor-deposited on one main surface (the inner surface when assembled as the envelope 18) of a plate material made of PET (polyethylene terephthalate) resin. Is formed.

The light transmissive plate 16 is formed by laminating a light diffusing plate 20, a light diffusing sheet 22, and a lens sheet 24 in order from the reflecting plate 12 side.
In the envelope 18, a plurality of (14 in this example) cold cathode fluorescent lamps 26 (hereinafter simply referred to as “lamps 26”) have short sides parallel to the long sides of the reflector 12. It is stored at equal intervals in the direction. Note that the envelope 18 has a sealed structure in order to prevent intrusion of dust or the like into the inside thereof.

FIG. 2A is a longitudinal sectional view showing a schematic configuration of the lamp 26.
The lamp 26 has a glass bulb 32 in which both ends of a glass tube having a circular cross section are hermetically sealed with lead wires 28 and 30. The glass bulb 32 is made of hard borosilicate glass and has a total length of 450 mm, an outer diameter of 4.0 mm, and an inner diameter of 3.0 mm.
A phosphor film 34 is formed on the inner surface of the glass bulb 32. The phosphor film 34 includes three kinds of rare earth phosphors such as red-emitting Y ₂ O ₃ : Eu, green-emitting LaPO ₄ : Ce ³ , Tb ^3, and blue-emitting BaMg ₂ Al ₁₆ O ₂₇ : Eu ² .

The glass bulb 32 is filled with a mixed gas composed of about 3 mg of mercury (not shown) and a plurality of kinds of rare gases. The type and mixing ratio of the rare gas constituting the mixed gas will be described in detail later.
The lead wires 28 and 30 are connections between the internal lead wires 28A and 30A made of tungsten and the external lead wires 28B and 30B made of nickel, respectively, and the glass tube is airtight at the internal lead wires 28A and 30A at both ends. It is hermetically sealed. The internal lead wires 28A and 30A and the external lead wires 28B and 30B both have a circular cross section. The inner lead wires 28A and 30A have a wire diameter of 1 mm and a total length of 3 mm. The outer lead wires 28B and 30B have a wire diameter of 1 mm. Is 0.8 mm and the total length is 10 mm.

  Electrodes 36 and 38 are joined to the inner end portions of the internal lead wires 28A and 30A supported on the end portions of the glass bulb 32 by laser welding or the like, respectively. The electrodes 36 and 38 are so-called hollow electrodes having a bottomed cylindrical shape, and are formed by processing a niobium rod. The reason why the hollow type electrodes are used as the electrodes 36 and 38 is that they are effective in suppressing sputtering in the electrodes caused by discharge during lamp lighting (for details, refer to JP-A-2002-289138). ).

  The electrodes 36 and 38 have the same shape, and the dimensions of each part shown in FIG. 2B are as follows: electrode length L = 5.2 mm, outer diameter p1 = 2.7 mm, wall thickness t = 0.2 mm, (inner diameter p2 = 2.3 mm). Since the electrodes 36 and 38 are provided so that the center thereof is aligned with the tube axis of the glass bulb (glass tube) 32, the gap between the outer circumference of the electrodes 36 and 38 and the inner circumference of the glass bulb 32 is determined from the above dimensional relationship. The spacing is about 0.15 mm. Thus, the gap between the electrode outer periphery and the glass bulb inner periphery is set to a narrow interval such as 0.15 mm so that the lamp current does not flow into the gap. In other words, when the lamp is turned on, discharge is generated only on the inner surfaces (the inner peripheral surface and the bottom surface of the cylindrical portion) of the hollow electrodes 36 and 38.

The inventor of the present application, in the cold cathode fluorescent lamp having the above-described configuration, uses [neon (Ne) + argon (Ar) + krypton (Kr)], [neon (Ne) + For each of the krypton (Kr)], a comparative experiment was performed on the starting voltage and the like with the conventional one of [neon (Ne) + argon (Ar)]. Hereinafter, experimental conditions and experimental results are described for each mixed gas configuration.
[1] Neon (Ne) + Argon (Ar) + Krypton (Kr)
Starting with a mixed gas of neon + argon + krypton (hereinafter referred to as “type B”) and a conventional mixed gas, that is, 95% neon and 5% argon (hereinafter referred to as “type A”). A voltage comparison experiment was performed. In the present specification, the mixing ratio (%) of the mixed gas is expressed in molar ratio. For Type B, five types with different mixing ratios of the mixed gases composed of the above three types of rare gases were prepared. The five types are distinguished by attaching serial numbers such as B-1, B-2,..., B-5. A specific mixing ratio will be described later.

For each of Type A and Types B-1 to B-5, five of each with sealed gas pressures of 40 Torr (5320 Pa), 50 Torr (6650 Pa), and 60 Torr (7980 Pa) are manufactured. The starting voltage at an ambient temperature of 25 ° C. was measured.
The measurement results are shown in Tables 1 to 6.

上記表１〜表６に基づき、周囲温度０℃における実験結果を示すグラフを図３に示す。また、タイプＢ−１〜Ｂ−５における混合ガスの混合比率を図３のグラフ左上にも示す。なお、上記５本の測定結果（Ｎｏ．１〜５）全てをグラフにプロットすると煩雑になるため、図３では５本の測定結果の相加平均を代表値としてプロットしている。

Based on the said Table 1-Table 6, the graph which shows the experimental result in ambient temperature 0 degreeC is shown in FIG. Moreover, the mixing ratio of the mixed gas in types B-1 to B-5 is also shown in the upper left of the graph of FIG. In addition, since it will become complicated when all the said 5 measurement results (No. 1-5) are plotted on a graph, in FIG. 3, the arithmetic mean of the 5 measurement results is plotted as a representative value.

  As can be seen from FIG. 3, it can be seen that the type B lamp has a lower starting voltage than the type A lamp at any gas pressure in an environment where the ambient temperature is 0 ° C. That is, by adding krypton to a conventional lamp type A mixed gas to form a mixed gas consisting of neon, argon, and krypton, the starting voltage at low temperature (at 0 ° C.) was successfully reduced. It is.

FIG. 4 is a graph showing experimental results in an environment at an ambient temperature of 25 ° C. based on Tables 1 to 6 above.
As can be seen from FIG. 4, the type B starting voltage is generally the type A starting voltage except that the starting voltage of the type B-1 lamp is lower than the starting voltage of the type A lamp at a gas pressure of 60 Torr. It is equal to or higher than the voltage. However, the maximum value of type B starting voltage is about 1250 V for type B-5 at a gas pressure of 60 Torr. This value of 1250 V is lower than the lowest starting voltage of Type A at an ambient temperature of 0 ° C. (see FIG. 3). That is, by using the mixed gas of type B, the starting voltage can be improved under the most severe conditions of the temperature environment in which the liquid crystal display device is used. As a result, the power circuit can be downsized. Become.
[2] Neon (Ne) + Krypton (Kr)
A lamp having a mixed gas composition of 95% neon and 5% krypton (hereinafter referred to as “type C”) was manufactured, and a comparison experiment with the type A lamp was performed. The experimental conditions are the same as in the case of Type B described above.

  Table 7 shows the experimental results.

表１および表７に基づき、周囲温度０℃における始動電圧の測定結果のグラフを図５に、周囲温度２５℃における始動電圧の測定結果のグラフを図６にそれぞれ示す。なお、図５、図６では、５本の測定結果（Ｎｏ．１〜５）を全てプロットしている。

Based on Table 1 and Table 7, a graph of the measurement result of the starting voltage at an ambient temperature of 0 ° C. is shown in FIG. 5, and a graph of the measurement result of the starting voltage at an ambient temperature of 25 ° C. is shown in FIG. 5 and 6, all five measurement results (Nos. 1 to 5) are plotted.

5 and 6, the starting voltage of the type C lamp is lower than the starting voltage of the type A lamp under any conditions (ambient temperature, gas pressure), and the starting voltage is improved. I understand. In other words, the starting voltage was successfully reduced by using a mixed gas of neon and krypton without using argon as the mixed gas.
[3] Lamp efficiency The inventor of the present application also examined the lamp efficiency (lm / W) of the above-mentioned type A, type B, and C lamps with respect to the ambient temperature (° C.). Detailed data on the ambient temperature and lamp efficiency are omitted, and only the tendency of the relationship between them is shown in FIG.

FIG. 7 is a graph in which the horizontal axis indicates the ambient temperature and the vertical axis indicates the lamp efficiency. In the figure, the broken line indicates the type A lamp, and the solid lines indicate the types B and C.
Both type A and types B and C have the highest lamp efficiency at a certain optimum temperature. It has been confirmed that this optimum temperature is about 60 ° C. for Type A, while it is about 10 ° C. higher for Types B and C. Moreover, the maximum value of the lamp efficiency is slightly higher in types B and C than in type A.

In a direct-type backlight unit, where the number of lamps further increases as the size of the LCD device increases, the temperature inside the unit rises to about 70 ° C. during lighting. Therefore, in Type A, the maximum value of the lamp efficiency cannot be obtained. On the other hand, in types B and C, the highest lamp efficiency can be obtained near the temperature in the unit when the temperature is raised to the maximum.
As described above, according to the cold cathode fluorescent lamp according to the present invention, the starting voltage at 0 ° C. and in the vicinity thereof is lowered as compared with the conventional cold cathode fluorescent lamp in which a mixed gas mainly composed of argon and neon is sealed. Therefore, it is possible to reduce the size of the power supply unit and the like. Furthermore, the highest lamp efficiency can be obtained in the temperature environment in the unit where the cold cathode fluorescent lamp is installed.

Although the present invention has been described based on the embodiment, the present invention is not limited to the above-described form, and for example, the following form may be employed.
(1) In the above embodiment, an example in which a cold cathode fluorescent lamp is used as a light source of a direct type backlight unit has been introduced. However, a cold cathode fluorescent lamp according to the present invention has an edge light type (side light type or conductive type). It can also be suitably used as a light source.
The edge light type backlight unit is a unit having a structure in which a light guide plate is placed on the back surface of an LCD panel and a fluorescent lamp is arranged on an end surface of the light guide plate. Edge light type backlight units include a type in which 2 to 4 cold cathode fluorescent lamps are arranged in close contact with the end face of the light guide plate. In such a type, the ambient temperature of the cold cathode fluorescent lamp is just below the above-mentioned level. This is because the temperature is raised to the same level as in the case of the backlight unit of the system.

  (2) Although the bottomed cylindrical hollow electrode is used as the electrode (cold cathode) of the cold cathode fluorescent lamp in the above embodiment, the shape of the electrode is not limited to this. For example, a cylindrical shape or a strip-shaped plate shape may be used. The material is not limited to niobium, and for example, nickel, molybdenum, or tantalum may be used. In addition, as the use of mercury progresses due to environmental issues, the use of niobium, molybdenum, and tantalum as the electrode material will reduce the consumption of the electrode compared to the case of using nickel. Can be extended.

  The cold cathode fluorescent lamp according to the present invention can be used, for example, as a light source of a direct type backlight unit, and the backlight unit according to the present invention can be used, for example, for a liquid crystal display device.

It is a figure which shows schematic structure of the backlight unit which concerns on embodiment. It is a longitudinal cross-sectional view which shows the cold cathode fluorescent lamp used as a light source of the said backlight unit. FIG. 6 is a characteristic diagram of a starting voltage when the type of mixed rare gas and the mixing ratio change at an ambient temperature of 0 ° C. FIG. 6 is a characteristic diagram of a starting voltage when the kind of mixed rare gas and the mixing ratio change at an ambient temperature of 25 ° C. FIG. 6 is a characteristic diagram of a starting voltage when the type of mixed rare gas and the mixing ratio change at an ambient temperature of 0 ° C. FIG. 6 is a characteristic diagram of a starting voltage when the kind of mixed rare gas and the mixing ratio change at an ambient temperature of 25 ° C. It is a characteristic view which shows the change of the lamp efficiency with respect to ambient temperature. In a cold cathode fluorescent lamp in which a mixed gas mainly composed of argon and neon is sealed, (a) is a characteristic diagram of the starting voltage and (b) is a graph showing lamp efficiency when the mixing ratio of argon and neon is changed. FIG.

Explanation of symbols

10 Backlight Unit 26 Cold Cathode Fluorescent Lamp 32 Glass Bulb 34 Phosphor Film 36, 38 Electrode

Claims (3)

A cold cathode fluorescent lamp having a tubular glass bulb in which a mixed gas of rare gas is sealed and a phosphor film is formed on the inner surface, and a pair of electrodes arranged opposite to each other at both ends of the glass bulb,
A cold cathode fluorescent lamp comprising at least neon and krypton as constituent gases of the mixed gas.   The cold cathode fluorescent lamp according to claim 1, further comprising argon as a constituent gas of the mixed gas.   A backlight unit comprising the cold cathode fluorescent lamp according to claim 1 as a light source.

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