JP4150349B2 - Cold cathode fluorescent lamp and backlight unit - Google Patents

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.

In recent years, as the development of LCD devices for notebook personal computers and the like has become full-scale, the demand for backlight units installed therein has further increased.
The backlight unit is roughly classified into an edge light method (also referred to as a side light method or a light guide plate method) in which a light guide plate is placed on the back surface of the LCD panel, and a fluorescent lamp is disposed on an end surface of the light guide plate. There are two types, a direct type in which a plurality of fluorescent lamps are arranged in parallel on the back surface of the LCD panel. When comparing the two, in general, the edge light method is excellent in thinning and luminance uniformity of the light emitting surface, but it is disadvantageous in terms of high luminance, while the direct method is excellent in terms of high luminance, but thin. It can be said that it is disadvantageous in terms of conversion.

Therefore, the LCD device used in a notebook personal computer or the like where emphasis is placed on thinning often employs an edge light system.
The edge light type backlight unit will be described in more detail. In the edge light type, an elongated cold cathode fluorescent lamp is disposed in parallel to one side of the light guide plate disposed on the back of the LCD panel. The light emitted from the fluorescent lamp is introduced into the light guide plate from the one side surface, reflected inside the light guide plate, and emitted from the main surface on the side facing the LCD panel. The back of the LCD panel is irradiated with light emitted from the LCD panel. The edge light type backlight unit having such a configuration has a structure in which a cold cathode fluorescent lamp is disposed on one side surface of the light guide plate. Therefore, the thickness of the entire backlight unit can be reduced, and the entire LCD device is thin. Contribute to

  By the way, in a backlight unit that is required to be compact as a whole as well as thin, an electronic ballast connected to the cold cathode fluorescent lamp is disposed on one end side of the cold cathode fluorescent lamp, and from here, In some cases, the cold cathode fluorescent lamp may be wired to the electrode lead wires at both ends. In the case of adopting this configuration, in order to achieve assembling workability of the backlight unit and further downsizing of the whole, wiring to the electrode lead wire far from the electronic ballast (hereinafter referred to as “long wiring”) The thing using a flat cable is known (for example, refer patent document 1). That is, when a general circular cross-section cable is used for long wiring, the assembly becomes complicated during assembly, and the workability is reduced. The flat cable having a thickness smaller than the outer diameter of the general cable is used. By adopting the cable, for example, it becomes possible to attach the flat cable to one side surface of the frame to which the cold cathode fluorescent lamp is attached, and to lay it out. The necessary space can be reduced.

In this case, in the cold cathode fluorescent lamp, the electrode closer to the electronic ballast is the high voltage side, the electronic ballast and the electrode lead wire are connected by a high voltage cable, and the electrode far from the electronic ballast is the ground side. The lead wire of the ground side electrode and the electronic ballast are connected by the flat cable having a smaller cross-sectional area of the conductor portion than the high-voltage cable.
JP-A-9-55112

However, when the backlight unit configured as described above is continuously lit, there is a problem that the life of the cold cathode fluorescent lamp is shortened.
As will be described later, the present inventors have confirmed that the above-described problems can occur not only in the edge light type backlight unit but also in the direct type backlight unit.

  An object of this invention is to provide the cold cathode fluorescent lamp which can extend the lifetime at the time of making it light continuously, and a backlight unit using the same in view of the above-mentioned subject.

  The cold cathode fluorescent lamp according to claim 1 of the present invention is a glass tube having a phosphor film formed on its inner surface, a first lead wire sealed at a first end of the glass tube, and the glass A second lead wire sealed to a second end portion of the tube, a first electrode joined to the glass tube inner side end portion of the first lead wire, and the second lead wire A second electrode joined to an end portion on the inner side of the glass tube, an end portion side of the first lead wire outside the glass tube is connected to a high-voltage side wiring from an external power source, and the second electrode In the cold cathode fluorescent lamp, an end portion side of the lead wire outside the glass tube is connected to a ground side wiring from the external power source and a wiring having lower thermal conductivity than the high voltage side wiring. As the second electrode, the amount of heat generated when the cold cathode fluorescent lamp is turned on is greater than that of the second electrode. Wherein the what is more the first electrode is higher is selected.

The cold cathode fluorescent lamp according to claim 2 of the present invention is characterized in that the effective electrode surface area of the first electrode is smaller than the effective electrode surface area of the second electrode.
In the cold cathode fluorescent lamp according to claim 3 of the present invention, the area ratio obtained by dividing the value of the effective electrode surface area of the first electrode by the value of the effective electrode surface area of the second electrode is 0.5 or more. It is characterized by being set in a range of 0.9 or less.

The cold cathode fluorescent lamp according to claim 4 of the present invention is characterized in that the metal material forming the first electrode has a higher work function than the metal material forming the second electrode.
In the cold cathode fluorescent lamp according to claim 5 of the present invention, nickel is selected as the metal material for forming the first electrode, and niobium, tantalum, or molybdenum is used as the metal material for forming the second electrode. One metal material is selected.

  The cold cathode fluorescent lamp according to claim 6 of the present invention is a glass tube having a phosphor film formed on its inner surface, a first lead wire sealed at a first end of the glass tube, and the glass A second lead wire sealed to a second end portion of the tube, a first electrode joined to the glass tube inner side end portion of the first lead wire, and the second lead wire A second electrode joined to an end portion on the inner side of the glass tube, an end portion side of the first lead wire outside the glass tube is connected to a high-voltage side wiring from an external power source, and the second electrode In the cold cathode fluorescent lamp, an end portion side of the lead wire outside the glass tube is connected to a ground side wiring from the external power source and a wiring having lower thermal conductivity than the high voltage side wiring. As the second lead wire, the first lead wire has a lower thermal conductivity than the second lead wire. Wherein the but has been selected.

The cold cathode fluorescent lamp according to claim 7 of the present invention is characterized in that the cross-sectional area of the first lead wire is smaller than the cross-sectional area of the second lead wire.
In the cold cathode fluorescent lamp according to claim 8 of the present invention, the first and second lead wires have a circular cross section, and an outer diameter of the first lead wire is set to be outside of the second lead wire. The wire diameter ratio obtained by dividing by the diameter is set in the range of 0.65 or more and 0.85 or less.

The backlight unit for a liquid crystal display device according to claim 9 of the present invention has the cold cathode fluorescent lamp described above as a light source, a high-voltage side wiring connecting the power circuit and the first lead wire, the power circuit, It is a wiring for connecting the second lead wire, and has a ground side wiring having a lower thermal conductivity than the high voltage side wiring.
In the backlight unit for a liquid crystal display device according to claim 10 of the present invention, a pair of electrodes is enclosed in a glass tube, and a first lead wire joined to one electrode extends from one end of the glass tube. A backlight unit for a liquid crystal display device provided with a cold cathode fluorescent lamp as a light source, the second lead wire being connected to the other electrode and extending from the other end of the glass tube A high-voltage side wiring connected to the first lead wire for supplying power from the power supply circuit, and a wiring connected to the second lead wire for supplying power from the power supply circuit. An electrical contact that is in close contact with the ground-side wiring having a lower thermal conductivity than the high-voltage side wiring and the glass tube end on the first lead wire side and covers the glass tube end and the first lead wire. Insulation A first bush, a second bushing that is in close contact with the end of the glass tube on the second lead wire side and that covers the end of the glass tube, and is more electrically conductive than both bushes. And a support member that supports both the bushes, and the thermal conductivity between the first bush and the support member is between the second bush and the support member. It is characterized by being comprised so that it may become lower than thermal conductivity of this.

The backlight unit according to claim 11, wherein a thermal insulation medium having lower thermal conductivity than the first bush is interposed between the first bush and the support member, and the second bush and The support member is in direct contact with the support member.
The backlight unit according to claim 12, wherein a contact area between the first bush and the support member is smaller than a contact area between the second bush and the support member. .

The backlight unit according to claim 13, wherein a contact pressure between the first bush and the support member is lower than a contact pressure between the second bush and the support member. .
The backlight unit according to claim 14 is characterized in that the first and second bushes are made of silicon rubber, and the support member is made of a metal plate.

  The backlight unit for a liquid crystal display device according to claim 15, wherein a pair of electrodes is enclosed in a glass tube, and a first lead wire joined to one electrode is extended from one end of the glass tube, A backlight unit for a liquid crystal display device comprising, as a light source, a cold cathode fluorescent lamp having a configuration in which a second lead wire joined to the other electrode is extended from the other end of the glass tube, A high-voltage side wiring connected to the first lead wire for supplying power from the power supply circuit, and a wiring connected to the second lead wire for supplying power from the power supply circuit, A ground-side wiring having a lower thermal conductivity than the high-voltage side wiring, and a first bush having electrical insulation that is in close contact with the glass tube end portion on the first lead wire side and covers the glass tube end portion; The above And a second bush having electrical insulation that is in close contact with the end portion of the glass tube on the lead wire side and covers the end portion of the glass tube, and the glass tube is turned on when the cold cathode fluorescent lamp is turned on. The heat dissipation of heat absorbed from the surface is configured such that the first bush is lower than the second bush.

The backlight unit according to claim 16 is characterized in that the heat dissipation area of the first electrically insulating bush is smaller than the heat dissipation area of the second electrically insulating bush.
The backlight unit according to claim 17, wherein the first electrically insulating bush is formed of a material having a lower thermal conductivity than a material forming the second electrically insulating bush. .

  In the cold cathode fluorescent lamp according to the present invention, the end portion of the first lead wire outside the glass tube is connected to the high voltage side wiring from the external power source, and the end portion outside the glass tube of the second lead wire is connected to the outside In a cold cathode fluorescent lamp connected to a ground side wiring from a power source and having a lower thermal conductivity than the high voltage side wiring, the first electrode joined to the first lead wire and the second electrode As the second electrode joined to the lead wire, the first electrode is selected so that the amount of heat generated when the cold cathode fluorescent lamp is turned on is higher than that of the second electrode. It becomes possible to extend the lamp life by eliminating the temperature imbalance between both ends.

  In the cold cathode fluorescent lamp according to the present invention, the end portion outside the glass tube of the first lead wire is connected to the high voltage side wiring from the external power source, and the end portion outside the glass tube of the second lead wire is In a cold cathode fluorescent lamp connected to a ground side wiring from an external power source and having a lower thermal conductivity than the high voltage side wiring, the first and second lead wires are more than the second lead wires. Since the first lead wire having a lower thermal conductivity is selected, the temperature non-equilibrium between both ends of the glass tube is eliminated, and the lamp life can be extended.

  The backlight unit according to the present invention is connected to the first lead wire and connected to the high-voltage side wiring for supplying power from the power supply circuit and the second lead wire and supplies power from the power supply circuit. And is in close contact with the ground-side wiring having a lower thermal conductivity than the high-voltage side wiring and the glass tube end portion on the first lead wire side, and the glass tube end portion and the first lead wire are connected to each other. A first bush having electrical insulation to cover, a second bush having electrical insulation that is in close contact with the glass tube end on the second lead wire side and covers the glass tube end, and both bushes Is also made of a material having high thermal conductivity, and has a support member that supports the bushes. The thermal conductivity between the first bush and the support member is greater than that of the second bush. Lower than the thermal conductivity to the support member Which is configured as, it is possible to non-equilibrium temperature between both the ends of the glass tube is eliminated extend lamp life.

  The backlight unit according to the present invention is connected to the first lead wire and connected to the high-voltage side wiring for supplying power from the power supply circuit and the second lead wire and supplies power from the power supply circuit. Wiring that is lower in thermal conductivity than the high-voltage side wiring, and is in close contact with the glass tube end portion on the first lead wire side and covers the glass tube end portion. A cold-cathode fluorescent lamp, and a first bush having an electrical insulating property, which is in close contact with the end portion of the glass tube on the second lead wire side and covers the end portion of the glass tube Since the heat dissipation of the heat absorbed from the surface of the glass tube when the light is turned on is configured so that the first bush is lower than the second bush, between both ends of the glass tube The temperature non-equilibrium in the lamp is eliminated Life it is possible to extend the.

Hereinafter, an embodiment of the present invention will be described. Before entering a specific description of an embodiment according to the present invention, a basic configuration serving as a basis of the embodiment will be described.
FIG. 1 is an exploded perspective view showing a schematic configuration of a backlight unit 2 for a 15-inch LCD (Liquid Crystal Display) device.
The backlight unit 2 is arranged and used on the back surface 4A of an LCD (liquid crystal display) panel 4, and is an edge portion of the light guide plate 6 made of transparent acrylic or the like (in this example, the lower side of the light guide plate 6). This is a so-called edge light type backlight unit in which a cold cathode fluorescent lamp (hereinafter simply referred to as “lamp”) 8 is disposed as a light source at the end.

FIG. 2A is a sectional view mainly showing a schematic configuration of the lamp 8.
The lamp 8 has a glass bulb 10 in which both ends of a glass tube having a circular cross section are sealed, and a pair of electrodes 12 and 14 are provided at both ends of the glass bulb 10.
The electrodes 12 and 14 are so-called hollow electrodes having a bottomed cylindrical shape, and lead wires 16 and 18 are joined to the outer bottom by laser welding or the like, respectively. The electrodes 12 and 14 are formed by processing a nickel plate.

  The lead wires 16 and 18 are joints of the internal lead wires 16A and 18A made of tungsten and the external lead wires 16B and 18B made of nickel, respectively. The glass tube is sealed at both ends of the internal lead wires 16A and 18A. It is hermetically sealed. The internal lead wires 16A, 18A and the external lead wires 16B, 18B both have a circular cross section. The internal lead wires 16A, 18A have a wire diameter of 0.8 mm and a total length of 3.0 mm. 18B has a wire diameter of 0.6 mm and a total length of 1.5 mm.

The glass bulb 10 is made of hard borosilicate glass and has an overall length of 298 mm, an outer diameter of 1.8 mm, and an inner diameter of 1.4 mm.
A phosphor film 20 is formed on the inner surface of the glass bulb 10 shown in FIG. The phosphor film 20 is made of a mixture of three kinds of red, green and blue emitting Y ₂ O ₃ : Eu, LaPO ₄ : Ce ³ , Tb ³ and BaMg ₂ Al ₁₆ O ₂₇ : Eu ² phosphors. The body is applied, dried and solidified.

Further, the inside of the glass bulb 10 is filled with about 1200 μg of mercury (not shown) and a rare gas (not shown) composed of a neon-argon mixed gas having a composition (Ne 95% + Ar 5%) and a pressure of 10 kPa at 20 ° C. ing.
Of the above configuration, the electrodes 12 and 14 will be described in more detail. As described above, hollow electrodes are used as the electrodes 12 and 14. This is because it is effective in suppressing sputtering in the electrode caused by the discharge when the lamp is lit (for details, see JP-A-2002-289138).

The electrodes 12 and 14 in the basic configuration have the same shape, and the dimensions of each part shown in FIG. 2B are as follows: electrode length L = 3.5 mm, outer diameter p1 = 1.1 mm, wall thickness t = 0.1 mm. (Inner diameter p2 = 0.9 mm). Since the electrodes 12 and 14 are provided so that the center thereof is aligned with the tube axis of the glass bulb (glass tube) 10, the gap between the outer periphery of the electrodes 12 and 14 and the inner circumference of the glass bulb 10 is determined from the dimensional relationship described above. 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 (cylindrical inner peripheral surface and inner bottom surface) of the hollow electrodes 12 and 14. Here, in the electrode, the surface that substantially contributes to the discharge is defined as the “effective electrode surface”, and the area is defined as the “effective electrode surface area”. In the hollow-type electrode having the bottomed cylindrical shape described above, the inner peripheral surface and the inner bottom surface of the cylindrical portion are the effective electrode surfaces. The effective electrode surface area of the electrode shown in FIG. 2 (b) = {p2 × π × (L−t) + (p2 / 2) ² × π}, and the effective electrode surface area of the electrodes 12 and 14 is about 10.2 mm ² .

Wires for supplying power from the power supply circuit unit 22 (FIG. 1) including the electronic ballast are connected to the lead wires 16 and 18 of the lamp 8 having the above-described configuration. The wiring mode will be described with reference to FIG.
As shown in FIG. 3A, bushes 24 and 26 made of silicon rubber are fitted into both ends of the lamp 8, respectively. The bushes 24 and 26 will be described later. The wiring and the lead wires 16 and 18 are connected within the respective bushes 24 and 26.

FIG. 3B shows a view in which the bush 24 is cut. The lead wire 16 is connected to a high voltage cable 28 (withstand voltage of 3 kVrms) which is a high voltage side wiring from the power supply circuit unit 22. The connection is made by joining the lead wire 28A of the high voltage cable 28 with the solder 30 in a state where the lead wire 28A is entangled with the external lead wire 16B. The lead wire 28A of the high-voltage cable 18 is made of copper plated with tin and has a wire diameter of 1.5 mm (cross-sectional area: 1.77 mm ² ). The total length of the high voltage cable 28 is 60 mm.

FIG. 3C shows a view in which the bush 26 is cut. The other lead wire 18 is connected to a flat cable 32 that is formed in a generally elongated tape shape as a ground side wiring from the power supply circuit. As shown in FIG. 3 (d), the flat cable 32 is configured by sandwiching a conductive foil 32C made of copper between two insulating films 32A and 32B made of vinyl chloride. At both ends, a part of the conductive foil 32C is exposed, and one of the exposed portions is bonded to the external lead wire 18B in the direction indicated by the arrow in FIG. The conductive foil 32C has a width of 2.5 mm and a thickness of 0.2 mm (cross-sectional area: 0.5 mm ² ). The total length of the flat cable 32 is 320 mm.

  3A of the bush 24 that covers the end of the lamp 8 on the lead wire 16 side are as follows: L1 = 6.0 mm, W1 = 2.8 mm, H1 = 7.5 mm, L3 = 2.0 mm, H3 = 2.8 mm. The bush 24 has a circular storage hole 24B for storing the end portion of the lamp 8. The hole diameter of the storage hole 24B is set slightly smaller than the outer diameter of the glass bulb 10, and the lamp 8 is press-fitted into the storage hole 24B. As a result, the bush 24 comes into close contact with the outer periphery of the glass bulb 10.

  The dimensions of each part shown in FIG. 3A of the bush 26 covering the end of the lead wire 18 side lamp 8 are L2 = 6.0 mm, W2 = 2.8 mm, and H2 = 2.8 mm. The bush 26 has a circular storage hole 26 </ b> A for storing the end portion of the lamp 8. The hole diameter of the storage hole 26A is also set slightly smaller than the outer diameter of the glass bulb 10, and the lamp 8 is press-fitted into the storage hole 26A. As a result, the bush 24 comes into close contact with the outer periphery of the glass bulb 10. At this time, the flat cable 32 is deformed (bent) along the outer periphery of the glass bulb 10.

Silicone rubber used for the bushes 24 and 26 has moderate elasticity, is known as a synthetic resin material having relatively good thermal conductivity, in addition to excellent electrical pressure resistance and heat resistance. It has been.
Returning to FIG. 1, the lamp 8 to which the high-voltage cable 28 and the flat cable 32 are connected and the bushes 24 and 26 are attached as described above is disposed at the lower end of the light guide plate 6 as described above. . At this time, a reflector 36 having a “U” -shaped cross section is fitted into the bushes 24 and 26. The reflector 36 is formed by bending a long metal plate into a “U” shape, and a reflective film (not shown) is formed on the inner surface (the surface surrounding the lamp 8 from three sides). In addition, the distance between the inner surfaces of two opposing surfaces in the “U” cross section is about 3.8 mm.

Two diffusion sheets 38 and 40 and two prism sheets 42 and 44 are arranged on the LCD panel 4 side of the light guide plate 6. On the other hand, a reflection sheet 46 is disposed on the opposite side of the light guide plate 6 from the LCD panel 4.
Diffusion sheets 38 and 40, prism sheets 42 and 44, and a reflection sheet 46 are overlapped on the light guide plate 6 and fitted into a frame-shaped resin support frame 48. At this time, the lamp 8 and the reflector 36 are also fitted together with the light guide plate 6.

After the above members are fitted, a metal back plate 50 made of aluminum or the like is fixed to the resin support frame 48 by screwing or the like.
In FIG. 4, sectional drawing of the state which attached the metal back cover board 50 is shown. The cross-sectional view is a view cut at a location where the glass bulb 10 is inserted into the bush 24. In FIG. 4, the resin support frame 48 is not shown. As shown in the figure, the reflector 36 sandwiching the bush 24 (26) also serves as a support member for the bush 24 (26).

  Returning to FIG. 1, the resin support frame 48 has a storage portion 48 </ b> A for storing the power supply circuit unit 22 at a lower right portion (a portion close to one end portion of the lamp 8). And stored in the storage portion 48A. The high voltage cable 28 is connected to the high voltage side output terminal 22 </ b> A of the power supply circuit unit 22. Further, the flat cable 32 is connected to the ground-side terminal 22 </ b> B of the power circuit unit 22 through the connection line 52. The connecting line 52 is a covered wire having a copper wire having a wire diameter of 1.0 mm, and the total length is 40 mm.

The lamp 8 constituting the backlight unit 2 having the above configuration is lit by the power supply circuit unit 22 at a rated current of 7.0 mA and a lighting frequency of 58 kHz. The rated life is defined as 10,000 hours.
However, when the LCD panel 4 is continuously turned on in combination with the LCD panel 4, there is a case where the light is not turned on in about 5,000 hours, for example, before reaching the rated life.

The inventor has collected the lamp 8 that has been short-lived and tried to find out the cause.
First, when the collected lamp 8 was observed, in the glass bulb 10, there was a difference between the degree of blackening occurring on the inner wall of one end and the degree of blackening occurring on the inner wall of the other end. (This phenomenon is hereinafter referred to as “blackening bias”). Further, in a lamp with blackening bias, the end portion on the lead wire 18 side to which the flat cable 32 is connected (hereinafter referred to as “ground side end portion”) is always connected to the high voltage cable 28. It has also been found that the degree of blackening is more severe than the end portion on the lead wire 16 side (hereinafter referred to as “high-pressure side end portion”).

The present inventor presumes that the blackening bias is a cause of short life, and the blackening bias is because different types of cables are joined to the lead wires 16 and 18. I thought that it might occur.
Therefore, both lead wires 16 and 18 of the lamp 8 are connected to the same type of wiring (general-purpose coated copper stranded wire) with the same length, through which power is supplied from the power supply circuit unit 22 to perform a continuous lighting test. Conducted (Comparative Test 1). As a result of the comparative test 1, the rated life was achieved and no blackening bias was observed.

  In addition, the inventor measured the temperature on the surface of both tube end portions (surface at a position corresponding to the electrode on the outer periphery of the glass bulb 10) when the lamp 8 having a short life was continuously lit. As a result, the surface temperature of the high-pressure side end (hereinafter referred to as “high-pressure side end surface temperature”) and the surface temperature of the ground-side end (hereinafter referred to as “grounding side”) immediately before the lighting failure (end of life). It has been found that there is a considerable difference between them (referred to as “end surface temperature”) (this phenomenon is hereinafter referred to as “temperature non-equilibrium”). Specifically, the surface temperature of the high-pressure side end portion was about 103 ° C., whereas the surface temperature of the ground-side end portion was about 118 ° C. This cause was presumed to be due to the difference in thermal conductivity of the cables connected to both the lead wires 16 and 18. Therefore, although not practical, a test was conducted in which both the lead wires 16 and 18 were supplied with power from the power supply circuit unit 22 using the flat cable 32 to continuously light the lamp 8 (Comparative Test 2). As a result of Comparative Test 2, although there was no difference that the surface temperature on the ground side end was about 118 ° C, the surface temperature on the high pressure side end was also increased to about 117 ° C, and it was confirmed that the temperature imbalance was almost eliminated. It was done. Further, in the lamp 8 subjected to the comparative test 2, no blackening bias was observed.

  Next, the present inventor connects the same type of wiring (general-purpose coated copper stranded wire) with the same length to both the lead wires 16 and 18 of the lamp 8, and supplies power from the power supply circuit unit 22 through this. At the same time, a continuous lighting test was carried out with only one end of the glass bulb 10 forcedly cooled (Comparative Test 3). As a result of the comparative test 3, the lamp 8 was turned off before reaching the rated life. Further, when the lamp 8 which was turned off was observed, the forced air cooling was not forced air cooled more than the forced air cooled end side regardless of whether the forced air cooled end portion was the high pressure end portion side or the ground side end portion. It turned out that the end side became darker.

Based on Comparative Tests 1 to 3, the present inventor analyzed the cause of the lamp 8 introduced as a basic configuration not being lit when continuously lit as follows. The analysis result will be described with reference to FIG. In FIG. 2, the high-voltage cable 28, the flat cable 32, and the power supply circuit unit 22 are all simplified as compared with the lamp 8.
(A) At the time of steady lighting, mercury ions strike the effective surfaces of both electrodes 12 and 14, thereby releasing electrons and maintaining the discharge. At this time, the electrode generates heat, and the generated heat moves mainly to the outside of the glass bulb 10 via the lead wires 16 and 18. The heat transferred to the lead wires 16 and 18 is further transferred by the high voltage cable 28 and the flat cable 32. Here, the high voltage cable 28 and the flat cable 32 have different thermal conductivities due to the difference in the cross-sectional area of the conductor portion. In other words, the conductor cross-sectional area as compared with the high-voltage cable 28 of 1.78 mm ^2, the thermal conductivity of the flat cable 32 of conductor cross-sectional area is 0.5 mm ² is low. Therefore, even if the calorific value is the same, the electrode 14 has poor heat outflow compared to the electrode 12, and the temperature of the electrode 14 is higher than the temperature of the electrode 12. As a result, the ambient temperature of the electrode 14 in the glass bulb 10 (hereinafter referred to as “ground side end portion temperature”) is higher than the ambient temperature of the electrode 12 (hereinafter referred to as “high pressure side end portion temperature”). As described above, this difference appears as a difference between the high-pressure side end surface temperature and the ground-side end surface temperature.

(B) As described above, when a temperature difference occurs between the both end portions of the glass bulb 10, the mercury in the glass bulb 10 gradually moves to the lower end portion (high pressure side end portion) as a whole. (Aggregation) At the end portion with the higher temperature (the end portion on the ground side), a mercury deficient state in which mercury becomes more diluted (hereinafter referred to as “mercury distribution bias”) is obtained.
(C) At the end on the ground side where mercury is diluted, the cathode fall voltage rises.

  (D) As a result, electrode scattering due to sputtering increases at the ground side end, and the blackening of the inner wall of the glass bulb 10 becomes severe. This phenomenon was observed as the blackening bias described above. Since the electrode scattering material traps the rare gas in the glass bulb 10 and adheres to the inner wall, the rare gas is consumed. In addition, the amount of heat generated in the ground-side electrode 14 increases (the electrode temperature increases) due to the increase in the cathode fall voltage.

  (E) The following cycle is repeated: promotion of bias in mercury distribution → increase in cathode fall voltage at the end on the ground side → increase in exhaustion of noble gas due to scattered material and increase in heat generation at the ground side electrode (electrode temperature rise) As a result, exhaustion of rare gas is promoted. As a result, the lamp impedance gradually decreases, an overcurrent flows at a certain point in time, the fuse in the power supply circuit unit 22 is blown, and the lamp 8 is not lit.

As is clear from the above analysis, the root cause of the accelerated rare gas consumption that causes the lamp to turn off is the distribution of mercury distribution, and this is caused by the temperature non-equilibrium between both ends of the glass bulb.
Therefore, the present inventor decided to solve the above-described problem by eliminating the temperature non-equilibrium between both ends of the glass bulb. The solution is as follows: 1. improvement of the lamp itself; We examined from both aspects of the improvement of the entire backlight unit. In this case, since it is a backlight unit used in an LCD device that is particularly required to be thin and compact, the wiring to one lead wire is a high voltage cable and the wiring to the other lead wire is a flat cable. Based on the premise that the above-mentioned basic configuration is maintained, that is, the configuration, that is, the wiring having a difference in thermal conductivity is used for power feeding to both lead wires, the means for solving the problem was examined.

Hereinafter, a specific form which is the solution means will be described.
As described above, since the mercury distribution bias is observed as a blackening bias as a result, in the following embodiments, whether or not the mercury distribution bias has occurred is determined. It will be evaluated by.
1. Improvement of lamp (Embodiment 1)
FIG. 5 is a cross-sectional view showing a schematic configuration of the lamp 54 according to the first embodiment.

The lamp 54 according to the first embodiment has basically the same configuration as the lamp 8 described above except that the shape (size) of the hollow electrode arranged at the high-pressure side end is different. Therefore, in the lamp 54, the same components as those in the lamp 8 are denoted by the same reference numerals, and the description thereof will be omitted, or only a brief description will be given, and different points will be mainly described.
In the lamp 8 in the basic configuration, the ground-side electrode 14 and the high-voltage side electrode 12 are the same material and have the same shape (see FIG. 2). However, in the lamp 54 according to the first embodiment, the ground-side electrode is the basic electrode. The structure was left as it was, and a high-voltage side electrode shorter than the electrode 12 in the tube axis direction of the glass bulb 10 was employed. That is, by shortening the overall length and reducing the effective electrode surface area of the high-pressure side electrode 56, the amount of heat generated in the electrode 56 is increased, and the temperature imbalance between both ends of the glass bulb 10 is eliminated. Is. Further, by shortening the overall length, the heat capacity of the electrode 56 becomes smaller than that of the electrode 12 (electrode 14), and the heat generation temperature of the electrode 56 can be increased also by a synergistic effect.

Specifically, the electrode 56 on the high voltage side in the lamp 54 has a total length L shortened from 3.5 mm to 2.5 mm in the dimensions of each part of the electrode shown in FIG. Other dimensions are the same as those of the electrode 12 (electrode 14). In this case, the effective electrode surface area Sh of the high-voltage side electrode 56, 7.4 mm ^2, and the area ratio obtained by dividing the effective electrode area Se of the electrode 14 of the Sh ground (= 10.2mm ²⁾ Re Is 0.73.

A backlight unit is constructed by mounting the lamp 54 having the above configuration, and the lamp 54 is subjected to a continuous lighting test under the same conditions (lighting frequency 58 kHz, lamp current 7.0 mA) as described in the basic configuration. did.
As a result, the surface temperature at the high-pressure end was about 116 ° C. and the surface temperature at the ground-side end was about 118 ° C., and the temperature imbalance that was a problem could be almost eliminated, and no blackening bias was observed. Moreover, the rated life was satisfied.

  The area ratio Re is not limited to 0.73 described above. The inventor has found that if the area ratio Re is set in the range of 0.50 or more and 0.90 or less, the short life of the lamp can be prevented. If it is set within this range, it has been confirmed that the difference between the surface temperature on the high-pressure side end surface with respect to the surface temperature on the ground-side end portion falls within about ± 5 ° C., and blackening bias can be prevented. Incidentally, when the area ratio Re is less than 0.5, on the contrary, a blackening bias in which the blackening at the high-pressure side end portion becomes intense occurs.

In the above example, the electrode on the high voltage side in the lamp 8 having the basic configuration is shortened. On the contrary, the electrode on the ground side may be elongated. Alternatively, the electrode on the high voltage side may be shortened and the electrode on the ground side may be extended. In short, it is possible to extend the lamp life by relatively reducing the effective electrode surface area of the high-voltage side electrode than the ground side, and the optimum range thereof is the above-described range.
(Embodiment 2)
In the first embodiment, the problem is solved by devising the shape of the electrode. On the other hand, in the second embodiment, the shape of the electrode remains the basic configuration, and the problem is solved by devising the selection of the material for forming the electrode.

The lamp 58 according to the second embodiment will be described with reference to FIG. 2 because the overall shape of the lamp itself is the same as the basic configuration as described above.
In the lamp 8 in the basic configuration, the ground side electrode 14 and the high voltage side electrode 12 are made of the same material. However, in the lamp 58 according to the second embodiment, the high voltage side electrode is left in the basic configuration, and the ground side electrode A material having a work function lower than that of the material forming the high-voltage side electrode 12 was selected as a material for forming the high-voltage side electrode 12. If a material with a low work function is used, the cathode fall voltage at the electrode, that is, the electrode loss is reduced, and the heat generation amount at the electrode is reduced. That is, by using a material having a work function lower than that of the high-voltage side electrode for the ground-side electrode, the amount of heat generated in the ground-side electrode is reduced, and temperature non-equilibrium between both pipe ends is eliminated. It is.

Specifically, the material of the high-voltage side electrode 12 in the lamp 58 is nickel Ni (work function: 4.50 eV), whereas the material of the ground-side electrode 60 is niobium Nb (work function: 4.01 eV). It was.
A backlight unit was constructed by mounting the lamp 58 having the above configuration, and a continuous lighting test was performed on the lamp 58 under the same conditions as described in the basic configuration.

As a result, the surface temperature at the high-pressure end was about 103 ° C. and the surface temperature at the ground-side end was about 101 ° C., and the temperature imbalance that was a problem could be almost eliminated, and no blackening bias was observed. Moreover, the rated life was satisfied.
The material of the ground-side electrode 60 is not limited to the niobium Nb described above. For example, tantalum Ta (work function: 4.30 eV) or molybdenum Mo (work function: 4.23 eV) may be selected. The inventor has found that if the work function difference between the material used for the high-voltage side electrode and the material used for the ground-side electrode is at least 0.20 eV, the short life of the lamp can be prevented and the rated life can be satisfied. Therefore, if the work function difference between the materials used for both electrodes is 0.2 eV or more, the materials for both electrodes are not limited to those described above, or the combinations of the materials used for both electrodes are not limited to those described above. For example, in combination, either tantalum Ta or molybdenum Mo may be selected as the material for the high-voltage side electrode, and niobium Nb may be selected as the material for the ground-side electrode.

The work function is a value measured by a thermal method.
(Embodiment 3)
In the first and second embodiments, the problem is solved by devising the electrode. In contrast, in the third embodiment, the shape and material of the electrode remain the basic configuration, and the problem is solved by devising the lead wire.

FIG. 6 is a sectional view showing a schematic configuration of the lamp 62 according to the third embodiment.
The lamp 62 according to Embodiment 3 has basically the same configuration as the lamp 8 described above except that the shape (thickness) of the internal lead wire joined to the high-voltage side electrode is different. Therefore, in the lamp 62, the same components as those in the lamp 8 are denoted by the same reference numerals, and the description thereof will be omitted or only briefly mentioned, and different points will be mainly described.

  In the lamp 8 in the basic configuration, an internal lead wire joined to the ground side electrode 14 (hereinafter referred to as “ground side internal lead wire”) and an internal lead wire joined to the high voltage side electrode 12 (hereinafter referred to as “high voltage side internal lead”). (Refer to FIG. 2), in the lamp 62 according to the third embodiment, the ground-side internal lead wire remains in the basic configuration, and the high-pressure side internal A lead wire having a smaller cross-sectional area than the internal lead wire 16A (FIG. 2) was used. That is, by reducing the cross-sectional area and reducing the thermal conductivity of the high-voltage side lead wire, the fluidity of heat generated in the high-voltage side electrode 12 to the high-voltage cable 28 is reduced, and the heat generation temperature of the high-voltage side electrode 12 is reduced. The temperature non-equilibrium between the both ends of the glass bulb 10 is eliminated by raising the temperature.

Specifically, the wire diameter of the high-pressure side internal lead wire in the lamp 62 was reduced to 0.6 mm. In this case, the wire diameter ratio Rw obtained by dividing the wire diameter Wh (= 0.6 mm) of the high-voltage-side internal lead wire 64A by the wire diameter We (= 0.8 mm) of the ground-side internal lead wire 18A is 0. 75.
A backlight unit was configured by mounting the lamp 62 having the above configuration, and a continuous lighting test was performed on the lamp 62 under the same conditions as described in the basic configuration.

As a result, the high-temperature side end surface temperature was about 103 ° C., the ground-side end surface temperature was about 105 ° C., and the temperature imbalance that was a problem could be almost eliminated, and no blackening bias was observed. Moreover, the rated life was satisfied.
The wire diameter ratio Rw is not limited to 0.75 described above. The present inventor has found that the short life of the lamp can be prevented by setting the wire diameter ratio Rw in the range of 0.65 to 0.85. If it is set within this range, it has been confirmed that the difference between the surface temperature on the high-pressure side end surface with respect to the surface temperature on the ground-side end portion falls within about ± 5 ° C., and blackening bias can be prevented. Incidentally, when the wire diameter ratio Rw is less than 0.65, on the contrary, a blackening bias in which the blackening at the high-pressure side end portion becomes intense occurs.

In the above example, the cross-sectional area of the high-voltage side internal lead wire in the lamp 8 having the basic configuration is reduced, but conversely, the cross-sectional area of the ground-side internal lead wire may be extended. . Alternatively, the cross-sectional area of the high-voltage side internal lead wire may be reduced and the cross-sectional area of the ground-side internal lead wire may be expanded. In short, by making the cross-sectional area of the high-voltage-side internal lead wire relatively smaller than the ground-side internal lead wire, it is possible to extend the lamp life, and the optimum range is the above-mentioned range. .
2. Improvement in the entire backlight unit In the first to third embodiments, the problem is solved by devising the lamp itself. However, in the embodiment described below, the problem is solved by devising the backlight unit. I try to plan. Specifically, the problem is solved by adjusting the fluidity of heat from the bushes mounted on both ends of the lamp to the reflector (support member) 36 and then to the metal back plate 50 (FIGS. 1 and 4). It was decided.
(Embodiment 4)
In the fourth embodiment, a heat insulating medium is interposed between the bush 24 attached to the high-pressure side end and the reflector 36 (FIGS. 1 and 4). That is, by interposing a heat insulating medium between the bush 24 and the reflector 36, the fluidity of heat moving from the surface of the high pressure side end of the glass bulb 10 to the bush 24, the reflector 36 and the metal back plate 50 is inhibited. Thus, the temperature inside the high pressure side end is increased to eliminate the temperature imbalance between both ends of the glass bulb 10. FIG. 7 shows a diagram of the backlight unit according to Embodiment 4 cut at a location where the glass bulb 10 is inserted into the bush 24. FIG. 7 corresponds to FIG. The backlight unit according to Embodiment 4 has basically the same configuration as the backlight unit 2 having the basic configuration described above, except that the thermal insulation medium is added. Therefore, in the backlight unit according to Embodiment 4, the same components as those of the backlight unit 2 are denoted by the same reference numerals and the description thereof will be omitted or only briefly mentioned, and the description will focus on the different points. To do.

In this example, two resin film tapes 66 were used as the heat insulating medium.
Specifically, a polyethylene terephthalate film having a thickness of 350 μm, a length of 6 mm, and a width of 3 mm was used. The resin film tape 66 is attached to one end face 24A (see FIG. 3) facing the reflector 36 and the end face opposite to the end face 24A, and the resin film is interposed between the bush 24 and the reflector 36 as shown in FIG. The tape 66 is interposed.

In the backlight unit having the above configuration, the lamp 8 was subjected to a continuous lighting test under the same conditions as described in the basic configuration.
As a result, the surface temperature at the high-pressure end was about 116 ° C. and the surface temperature at the ground-side end was about 118 ° C., and the temperature imbalance that was a problem could be almost eliminated, and no blackening bias was observed. Moreover, the rated life was satisfied.

The thermal insulation medium is not limited to the polyethylene terephthalate film described above. In short, any material having lower thermal conductivity than either the bush 24 or the reflector 36 may be used. Therefore, “thermal insulation” does not mean that the flow of heat is completely blocked, but means that it is in the flow path of heat and decreases the fluidity of heat.
(Embodiment 5)
In the fifth embodiment, the contact area between the bush 24 attached to the high-pressure side end and the reflector 36 (FIGS. 1 and 4) is reduced. That is, by reducing the contact area between the bush 24 and the reflector 36, the fluidity of heat moving from the surface of the high pressure side end of the glass bulb 10 to the bush, the reflector 36, and the metal back plate 50 is reduced. The temperature inside the high pressure side end is increased to eliminate the temperature non-equilibrium between both ends of the glass bulb 10. FIG. 8 shows the lamp 8 in a state where the bush 68 and the bush 26 are attached to both ends in the backlight unit according to the fifth embodiment. FIG. 8 is a diagram corresponding to FIG. The backlight unit according to Embodiment 5 has basically the same configuration as the backlight unit 2 having the above-described basic configuration, except that the shape of the bush attached to the high-pressure side end is different. Therefore, in the backlight unit according to Embodiment 5, the same components as those of the backlight unit 2 are denoted by the same reference numerals, and the description thereof will be omitted or only briefly mentioned, and the description will be focused on the different points. To do.

  In the fifth embodiment, in the bush 68 attached to the high-pressure side end, one end face 68A of the two end faces sandwiched between the reflectors 36 (FIGS. 1 and 4) has a width of 1.0 mm and a length of 6. A convex portion 68B having a height of 0.6 mm from the end face 68A at 0 mm was provided. As a result, the end face 68A side of the two end faces comes into contact with the reflector 36 (FIGS. 1 and 4) only at the top of the convex portion 68B. As a result, when the convex portion 68B is not provided, the contact area is reduced as compared to the case where the substantially entire surface of the end surface 24A (FIG. 3A) of the bush 24 is in contact with the reflector 36. In addition, each part dimension shown with a symbol in FIG. 8 is the same as that of the basic composition shown to Fig.3 (a).

In the backlight unit according to Embodiment 5 having the above-described configuration, the lamp 8 was subjected to a continuous lighting test under the same conditions as described in the basic configuration.
As a result, the surface temperature at the high-pressure end was about 116 ° C. and the surface temperature at the ground-side end was about 118 ° C., and the temperature imbalance that was a problem could be almost eliminated, and no blackening bias was observed. Moreover, the rated life was satisfied.
(Embodiment 6)
In the sixth embodiment, the contact pressure between the bush 24 attached to the high-pressure side end and the reflector 36 (FIGS. 1 and 4) is set between the bush 26 attached to the ground-side end and the reflector 36. It was decided to make it lower than the contact pressure. That is, by lowering the contact pressure between the bush 24 and the reflector 36, the fluidity of the heat moving from the bush 24 to the reflector 36 is lowered, the internal temperature of the high pressure side end is increased, and both ends of the glass bulb 10 are The temperature non-equilibrium between the parts is eliminated.

Specifically, in the basic configuration shown in FIG. 3A, W1 = W2 = 3.8 mm is shortened to W1 = 3.4 in the high pressure side bush 24, and the ground side bush 26 is reduced. In this case, it was assumed that W2 = 4.2 mm. Other dimensions are the same as the basic configuration.
As described above, the distance between the inner surfaces of the two opposing surfaces in the reflector 36 having the “U” -shaped cross section is about 3.8 mm, and the width (W1, W2) direction is sandwiched between the two surfaces. Thus, both bushes 24 and 26 are supported. Therefore, with the above dimensional configuration, the ground-side bush 26 is elastically deformed by the dimensional difference (0.4 mm), and the contact pressure is improved by the restoring force. On the other hand, the bush 24 on the high pressure side has a so-called backlash corresponding to the dimensional difference (0.4 mm) between the reflector 36 and the bush 36. As a result, the high-pressure side bush 24 comes into contact with only one of the bottom surface of the reflector 36 having a “U” -shaped cross section and two opposing surfaces, but the contact pressure is grounded due to elastic deformation of silicon rubber. It becomes lower than the contact pressure of the side bush 26.

In the backlight unit according to Embodiment 6 having the above-described configuration, the lamp 8 was subjected to a continuous lighting test under the same conditions as described in the basic configuration.
As a result, the high-temperature side end surface temperature was about 110 ° C. and the ground-side end surface temperature was about 112 ° C., and the temperature imbalance that was a problem could be almost eliminated, and no blackening bias was observed. Moreover, the rated life was satisfied.
3. Direct-type backlight unit Up to this point, the present invention has been described by taking an example in which the present invention is applied to an edge-light type backlight unit, but the present invention is also applicable to a direct-type backlight unit. Hereinafter, the direct-type backlight unit will be described as a seventh embodiment.
(Embodiment 7)
FIG. 9 is a perspective view showing a schematic configuration of the backlight unit 70 according to Embodiment 7. In FIG. FIG. 9 is a diagram in which a diffusing plate 80, a diffusing sheet 82, and a lens sheet 84 described later are broken.

The backlight unit 70 includes an envelope 76 including a rectangular reflection plate 72 and a side plate 74 surrounding the reflection plate 72. Both the reflecting plate 72 and the side plate 74 are 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 76) of a plate material made of PET (polyethylene terephthalate) resin. Is formed.
A plurality (eight in this example) of cold cathode fluorescent lamps 78 are accommodated in the envelope 76 at equal intervals in the short side direction in parallel with the long side of the reflector 72. The cold cathode fluorescent lamp 78 has the same basic configuration as the lamp 8 except for the size.

A diffusion plate 80, a diffusion sheet 82, and a lens sheet 84 are provided at the opening of the envelope 76.
FIG. 10 is a view showing an installation mode of the lamp 78 in the envelope 76.
FIG. 10 shows a part on the reflection plate 72 in a state where the side plate 74, the diffusion plate 80, the diffusion sheet 82, and the lens sheet 84 are removed. What can be seen in FIG. 10 is the ground-side end of the lamp 78.

On the reflection plate 72, a pair of printed wiring board holding members (hereinafter simply referred to as "holding members") 86 and 88 having a "U" -shaped cross section are erected facing each other. A printed wiring board 90 is fitted into 88.
Each lamp is provided with a bush 92 made of silicon rubber, and a lead wire 96 (FIG. 11) protruding from the bush 92 is supported on the printed wiring board 90 as will be described later. Note that the high voltage side end of the lamp 78 is also supported by the printed wiring board 104 (FIG. 11).

FIG. 11 is a view taken along a plane including the tube axis of the lamp 78 in FIG.
As described above, the bush 92 is attached to the end of the lamp 78 on the ground side. A lead wire 96 made up of an internal lead wire 96B and an external lead wire 96A is led out from the end of the glass bulb 94, and the external lead wire 96A is inserted into a through hole 90A provided in the printed wiring board 90 to be the tip. The part is protruding. The protruding tip portion is soldered to the wiring 90B formed on the printed wiring board 90.

  The other high-pressure side end is attached in the same manner. That is, the bush 100 is attached to the high pressure side end of the lamp 78. A lead wire 102 consisting of an internal lead wire 102B and an external lead wire 102A is led out from the end of the glass bulb 94, and the external lead wire 102A is inserted into a through hole 104A provided in the printed wiring board 104, and the tip The part is protruding. The protruding tip portion is soldered to the wiring 104B formed on the printed wiring board 104. The cross-sectional shapes of the bush 92 and the bush 100 are the same.

  Here, the area of the cross section of the high voltage side wiring 104B connected to the high voltage side lead wire 102 is set larger than the area of the cross section of the ground side wiring 90B connected to the ground side lead wire 96. Has been. That is, the ground side wiring 90B has lower thermal conductivity than the high voltage side wiring 104B. Therefore, as in the case of the backlight unit according to the basic configuration of the edge light system described above, the problem of short lamp life due to temperature imbalance can also occur in the direct backlight system.

  Therefore, in the present embodiment, the heat dissipation area of the ground side bush 92 is made larger than the heat dissipation area of the high pressure side bush 100 (the heat dissipation area of the high pressure side bush 100 is smaller than the heat dissipation area of the ground side bush 92. did.). That is, the heat dissipating property from the surface of the ground side end portion is improved and the temperature in the ground side end portion is lowered, thereby eliminating the temperature imbalance between both ends of the glass bulb 94.

Between the bushes 92 and 100 having the same cross-sectional shape, the total length Le of the ground-side bush 92 is made longer than the total length Lh of the high-pressure side bush 100.
Thereby, the short life due to temperature non-equilibrium is improved, and the life can be extended.
In the above example, the heat release area between the bushes is made different by changing the heat release area of the high pressure side bush and the ground side bush. However, as a means for making a difference in heat release, Not limited to. For example, even if bushes of the same shape and size are used, a material having lower thermal conductivity than that of the ground side bush may be used for the high pressure side bush. A material having higher thermal conductivity than the bush on the high pressure side may be used for the bush.) For example, fluorine rubber can be used as the material of the high-pressure side bush, and silicone mixed with a highly heat conductive filler can be used as the material of the bush on the ground side.

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

It is a disassembled perspective view which shows schematic structure of a backlight unit. (A) is sectional drawing which shows the cold cathode fluorescent lamp which concerns on a basic composition, (b) is a figure which shows each part dimension of the hollow type electrode which comprises the said cold cathode fluorescent lamp. (A) is a perspective view which shows the state in which the bush was mounted | worn with the said cold cathode fluorescent lamp both ends. (B) is sectional drawing which cut | disconnected the bush of the high voltage | pressure side edge part. (C) is sectional drawing which cut | disconnected the bush of the grounding side edge part. (D) is a perspective view showing a flat cable connected to a ground side end of the cold cathode fluorescent lamp and a lead wire of the ground side end. It is a figure which shows a part of cross section which cut | disconnected the backlight unit in the position corresponding to a high voltage | pressure side bush. 1 is a cross-sectional view illustrating a schematic configuration of a cold cathode fluorescent lamp according to Embodiment 1. FIG. 6 is a cross-sectional view showing a schematic configuration of a cold cathode fluorescent lamp according to Embodiment 3. FIG. 6 is a cross-sectional view showing a part of a backlight unit according to Embodiment 4. FIG. FIG. 9 is a perspective view showing a state where bushes are attached to both ends of a cold cathode fluorescent lamp in a backlight unit according to Embodiment 5. FIG. 10 is a perspective view with a part cut away showing a schematic configuration of a direct-type backlight unit according to Embodiment 7. FIG. 10 is a diagram showing a cold cathode fluorescent lamp holding structure in a seventh embodiment. FIG. 10 is a diagram showing a cold cathode fluorescent lamp holding structure in a seventh embodiment.

Explanation of symbols

2,70 Backlight unit 10 Glass bulb 12, 14, 56, 60 Hollow type electrode 16, 18 Lead wire 24, 26, 68 Bush 28 High voltage cable 32 Flat cable 36 Reflector (support member)
54, 58, 62 Cold cathode fluorescent lamp 66 Resin film tape

Claims (17)

A glass tube having a phosphor film formed on the inner surface;
A first lead wire sealed to a first end of the glass tube;
A second lead wire sealed to a second end of the glass tube;
A first electrode joined to the inside end portion of the glass tube of the first lead wire;
A second electrode joined to the inside end portion of the glass tube of the second lead wire;
Have
An end portion outside the glass tube of the first lead wire is connected to a high voltage side wiring from an external power supply, and an end portion outside the glass tube of the second lead wire is connected to a ground side from the external power supply. In the cold cathode fluorescent lamp connected to the wiring and the wiring having a lower thermal conductivity than the high-voltage side wiring,
The first electrode and the second electrode are selected so that the amount of heat generated when the cold cathode fluorescent lamp is turned on is higher in the first electrode than in the second electrode. Cathode fluorescent lamp.   The cold cathode fluorescent lamp according to claim 1, wherein the effective electrode surface area of the first electrode is smaller than the effective electrode surface area of the second electrode.   The area ratio obtained by dividing the value of the effective electrode surface area of the first electrode by the value of the effective electrode surface area of the second electrode is set in the range of 0.5 to 0.9. The cold cathode fluorescent lamp according to claim 2.   2. The cold cathode fluorescent lamp according to claim 1, wherein the metal material forming the first electrode has a higher work function than the metal material forming the second electrode.   Nickel is selected as the metal material forming the first electrode, and one metal material of niobium, tantalum, and molybdenum is selected as the metal material forming the second electrode. The cold cathode fluorescent lamp according to claim 4. A glass tube having a phosphor film formed on the inner surface;
A first lead wire sealed to a first end of the glass tube;
A second lead wire sealed to a second end of the glass tube;
A first electrode joined to the inside end portion of the glass tube of the first lead wire;
A second electrode joined to the inside end portion of the glass tube of the second lead wire;
Have
An end portion outside the glass tube of the first lead wire is connected to a high voltage side wiring from an external power supply, and an end portion outside the glass tube of the second lead wire is connected to a ground side from the external power supply. In the cold cathode fluorescent lamp connected to the wiring and the wiring having a lower thermal conductivity than the high-voltage side wiring,
A cold cathode fluorescent lamp, wherein the first and second lead wires are selected such that the first lead wire has a lower thermal conductivity than the second lead wire.   7. The cold cathode fluorescent lamp according to claim 6, wherein a cross-sectional area of the first lead wire is smaller than a cross-sectional area of the second lead wire.   The first and second lead wires have a circular cross section, and a wire diameter ratio obtained by dividing the outer diameter of the first lead wire by the outer diameter of the second lead wire is 0.65. The cold cathode fluorescent lamp according to claim 7, wherein the cold cathode fluorescent lamp is set in a range of 0.85 or less. It has the cold cathode fluorescent lamp of any one of Claims 1-8 as a light source,
High-voltage side wiring connecting the power supply circuit and the first lead wire;
A wiring connecting the power supply circuit and the second lead wire, the ground side wiring having a lower thermal conductivity than the high voltage side wiring;
A backlight unit for a liquid crystal display device. A pair of electrodes are enclosed in a glass tube, a first lead wire joined to one electrode is extended from one end of the glass tube, and a second lead wire joined to the other electrode is A backlight unit for a liquid crystal display device provided with a cold cathode fluorescent lamp having a configuration extending from the other end of the glass tube as a light source,
High-voltage side wiring connected to the first lead wire for supplying power from the power supply circuit;
A ground-side wiring connected to the second lead wire for supplying power from a power supply circuit and having lower thermal conductivity than the high-voltage side wiring;
A first bushing that is in close contact with the end portion of the glass tube on the first lead wire side and has an electrical insulation property covering the end portion of the glass tube and the first lead wire;
A second bushing that is in close contact with the end portion of the glass tube on the second lead wire side and has an electrical insulation property covering the end portion of the glass tube;
Made of a material having higher thermal conductivity than the both bushes, and a support member for supporting the bushes;
Have
The thermal conductivity between the first bush and the support member is configured to be lower than the thermal conductivity between the second bush and the support member. Backlight unit to be used.   A thermal insulation medium having a lower thermal conductivity than the first bush is interposed between the first bush and the support member, and the second bush and the support member are in direct contact with each other. The backlight unit according to claim 10.   The backlight unit according to claim 10, wherein a contact area between the first bush and the support member is smaller than a contact area between the second bush and the support member.   The backlight unit according to claim 10, wherein a contact pressure between the first bush and the support member is lower than a contact pressure between the second bush and the support member.   The backlight unit according to any one of claims 10 to 13, wherein the first and second bushes are made of silicon rubber, and the support member is made of a metal plate. A pair of electrodes are enclosed in a glass tube, a first lead wire joined to one electrode is extended from one end of the glass tube, and a second lead wire joined to the other electrode is A backlight unit for a liquid crystal display device provided with a cold cathode fluorescent lamp having a configuration extending from the other end of the glass tube as a light source,
High-voltage side wiring connected to the first lead wire for supplying power from the power supply circuit;
A ground-side wiring connected to the second lead wire for supplying power from a power supply circuit and having lower thermal conductivity than the high-voltage side wiring;
A first bush having electrical insulation that is in close contact with the glass tube end on the first lead wire side and covers the glass tube end;
A second bushing that is in close contact with the end portion of the glass tube on the second lead wire side and has an electrical insulation property covering the end portion of the glass tube;
Have
When the cold cathode fluorescent lamp is turned on, heat dissipation from the surface of the glass tube is configured such that the first bush is lower than the second bush. The backlight unit.   The backlight unit according to claim 15, wherein the heat dissipation area of the first electrically insulating bush is smaller than the heat dissipation area of the second electrically insulating bush.   16. The backlight unit according to claim 15, wherein the first electrically insulating bush is formed of a material having a lower thermal conductivity than a material forming the second electrically insulating bush.

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