JP2005332813A - Backlight unit, and liquid crystal display apparatus including it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit capable of suppressing luminance irregularity as compared with a conventional one. <P>SOLUTION: This direct type backlight unit 2 is composed by housing, in an outer container 4, curved fluorescent lamps 6 each composed by forming electrodes at both ends of a glass bulb 32 having a folded portion 34 formed by folding a glass tube nearly at the middle part in its longitudinal direction and linear portions 36 and 38 that extend in parallel with each other from both the sides of the folded portion 34. Each curved fluorescent lamp 6 is housed in the outer container 4 in an attitude where both the electrodes (bushes 46) are disposed on the lower side and the folded portion 34 is disposed on the upper side in a state where the backlight unit 2 is used. An inverter device for supplying power for lighting to the curved fluorescent lamps 6 is disposed outside the outer container 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a backlight unit and a liquid crystal display device, and more particularly to a backlight unit disposed on the back surface of a liquid crystal panel or the like and constituting an LCD (liquid crystal display) device, and a liquid crystal display device having the backlight unit.

In recent years, as the development of LCD devices for liquid crystal televisions and the like has become full-fledged, 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.

In view of this, an LCD device used in a liquid crystal television set with an emphasis on high brightness often employs a direct method.
The direct-type backlight unit will be described in a little more detail. The direct-type backlight unit, like a liquid crystal television screen, is arranged between a horizontally-long rectangular reflector and a translucent plate including a light diffusing plate provided in parallel therewith. A plurality of fluorescent lamps are arranged on the LCD panel, and the light emitted from the fluorescent lamps is taken out from the translucent plate side, so that the LCD panel provided in parallel with this is irradiated from the back side. Further, in order to prevent dust and dust from entering the unit, the four sides of the reflecting plate and the translucent plate, that is, the four sides surrounding the fluorescent lamp are closed by side plates or the like (see Patent Document 1).

Various types of direct-type backlight units having the above-described configurations have been put into practical use depending on the shape and arrangement direction of the fluorescent lamp. Up to now, straight tube fluorescent lamps are laid horizontally and arranged at equal intervals in the vertical direction (hereinafter referred to as “straight tube horizontal type”), and straight tube fluorescent lamps are vertically aligned. And a fluorescent lamp that is arranged at equal intervals in the horizontal direction (hereinafter referred to as “straight pipe vertical type”) (see Patent Document 1) or a bent fluorescent lamp bent in a U shape. A material that has been laid down and arranged at equal intervals in the vertical direction (hereinafter referred to as “bent tube horizontal type”) (see Patent Document 2) has been put into practical use.
Japanese Patent Laid-Open No. 2002-214605 JP-A-7-270786

  By the way, with the increase in size and brightness of liquid crystal televisions, the number of fluorescent lamps provided per one direct-type backlight unit attached to the LCD panel for the liquid crystal television is increasing. As the number of fluorescent lamps increases, the temperature in the unit rises, and the temperature distribution in the unit becomes more uneven. That is, in a liquid crystal television that is normally used with a horizontally long screen, the temperature is higher on the upper side in the unit and lower on the lower side.

  Therefore, in the horizontal type backlight unit, a luminance difference occurs between the fluorescent lamps, such that the fluorescent lamp arranged at the upper portion has a higher luminance and the fluorescent lamp arranged at the lower portion has a lower luminance. Luminance unevenness occurs in the entire backlight unit. In the straight tube vertical type, there is no difference in luminance between fluorescent lamps. However, in individual fluorescent lamps, the brightness is higher at the top and lower at the bottom, and uneven brightness occurs in the entire backlight. Yes.

  In view of the above-described problems, an object of the present invention is to provide a backlight unit in which luminance unevenness is suppressed more than ever and a liquid crystal display panel having the backlight unit.

  In order to achieve the above object, a backlight unit according to the present invention includes an envelope, a folded portion that is housed in the envelope, and is formed by folding the glass tube in the middle in the longitudinal direction. A bent fluorescent lamp in which electrodes are provided at both ends of a glass bulb having a linear portion extending in parallel from both sides of the folded portion, and power for lighting is supplied to the bent fluorescent lamp A backlight unit of a direct type having an inverter device, wherein the bent fluorescent lamp is arranged in a state where the inverter device is arranged outside the envelope and the backlight unit is used. The electrodes are housed in the envelope in such a posture that the electrodes are on the lower side and the folded portion is on the upper side.

Moreover, it has the folding | returning part support member which supports the said folding | returning part in the said envelope, and the heat insulation member inserted between the said folding | returning part and the said folding | returning part support member, It is characterized by the above-mentioned.
Furthermore, a reflection member that reflects light from the folded portion in the extending direction of the linear portion is attached to the heat insulating member.
Further, a heat radiating member made of a material having a higher thermal conductivity than the gas filling at least the inside of the envelope is attached to the outer periphery closer to the end than the center in the longitudinal direction of each linear portion. And

  Alternatively, a linear portion support member that supports a portion closer to the folded portion than the center in the longitudinal direction of each linear portion within the envelope, and an end corresponding to the center in the longitudinal direction of each linear portion A heat dissipating member that releases more heat than heat that escapes through the linear portion support member among the heat generated in the bent fluorescent lamp when lighting is attached to the outer periphery of the portion. .

  In order to achieve the above object, a liquid crystal display device according to the present invention includes a liquid crystal display panel and the backlight unit in which the envelope is disposed on the back surface of the liquid crystal display panel. To do.

  According to the backlight unit of the present invention, the bent fluorescent lamp is housed in the envelope in a state where both electrodes are in the lower side and the folded part is in the upper side in the used state. The heat generated from a certain electrode convects upward in the glass bulb, and is exclusively used for heating the rare gas normally enclosed in the glass bulb. As a result, the gas (air) filling the unit is not heated as much as in the conventional backlight unit, and the temperature rise in the unit is suppressed. The uneven temperature distribution in the direction is reduced. Therefore, uneven brightness in the backlight unit due to the uneven temperature distribution is suppressed.

In addition, since the inverter device, which is a useless heat source, is arranged outside the envelope, the backlight unit is caused by temperature unevenness in the envelope that occurs when the inverter device is arranged inside the envelope. Overall brightness unevenness can be avoided.
According to the liquid crystal display device according to the present invention, since the envelope of the backlight unit is arranged on the back surface of the liquid crystal display panel, an image with less luminance unevenness is formed on the liquid crystal display panel.

  FIG. 1 is a plan view showing a schematic configuration of a direct-type backlight unit 2 according to the embodiment, and FIG. 2A is a cross-sectional view taken along line AA in FIG. FIG. 1 shows a state in which a translucent plate 12 to be described later and a mounting frame 22 to which the translucent plate 12 is attached are removed. The backlight unit 2 is arranged and used on the back of an LCD (liquid crystal display) panel (not shown), and constitutes an LCD device serving as a display unit of a liquid crystal television.

The configuration of the backlight unit 2 will be described with reference to FIG. 1 and FIG.
The backlight unit 2 is configured by storing a plurality of bent cold cathode fluorescent lamps 6 (hereinafter simply referred to as “fluorescent lamps 6”) in a flat box-shaped envelope 4. When the backlight unit 2 is used as a constituent unit such as a liquid crystal television, the X-axis direction shown in FIG. 1 is in the horizontal direction and the Y-axis direction is in the vertical direction. Here, in this specification, the X-axis direction is described as a horizontal direction or a horizontal direction, and the Y-axis direction is described as a vertical direction or a vertical direction.

  The envelope 4 basically includes a horizontally-long rectangular reflecting plate 8, a side plate 10 surrounding the reflecting plate 8, and a translucent plate 12 provided in parallel with the reflecting plate 8. Here, as shown in FIG. 1, the portions corresponding to the sides of the side plate 10 that looks like a rectangular frame in plan view are referred to as an upper side portion 14, a lower side portion 16, a left side portion 18, and a right side portion 20, respectively. And The translucent plate 12 is fitted in an attachment frame 22 attached to the side plate 10. The mounting frame 22 is made of a non-translucent material, and light emitted from the fluorescent lamp 6 is extracted from a region surrounded by a two-dot chain line in FIG. 1 where only the translucent plate 12 exists.

The light transmissive plate 12 is formed by laminating a light diffusion plate 24, a light diffusion sheet 26, and a lens sheet 28 in this order from the reflection plate 8 side (fluorescent lamp 6 side).
In addition, a metal plate 30 for reinforcement is attached to the reflecting plate 8.
A pair of ribs 16 </ b> A and 16 </ b> B that are erected from the side wall of the lower side portion 16 of the side plate 10 toward the inside of the unit are arranged at predetermined intervals in the lateral direction. The ribs 16A and 16B are for supporting the fluorescent lamp 6 at the ends thereof, which will be described later.

Next, a schematic configuration of the fluorescent lamp 6 will be described.
The fluorescent lamp 6 has a glass bulb 32. The glass bulb 32 has a folded portion 34 formed by folding a glass tube having a circular cross-section in the middle, and linear portions 36 and 38 extending in parallel from both sides of the folded portion 34. The ends of the straight portions 36 and 38 are hermetically sealed.

As shown in FIG. 1, the glass bulb 32 has a “U” -shaped bent shape. The glass bulb 32 is made of hard borosilicate glass.
The end of the glass bulb 32 is hermetically sealed with a lead wire 40 as shown in FIG.
A phosphor film 42 is formed on the inner surface of the glass bulb 32. The phosphor film 42 has red [Y ₂ O ₃ : Eu ³⁺ ], green [LaPO ₄ : Ce ³⁺ , Tb ³⁺ ] and blue [BaMg ₂ Al ₁₆ O ₂₇ : Eu ^2+]. Including three types of rare earth phosphors. In order to improve the color rendering properties, a high color purity phosphor may be used instead of these phosphors. In this case, changing the green phosphor to one having a high color purity is most effective in improving the color rendering properties. Examples of the high color purity green phosphor include [BaMg ₂ Al ₁₆ O ₂₇ : Eu ²⁺ , Mn ²⁺ ], [Ce (Mg, Zn) Al ₁₁ O ₁₉ : Eu ²⁺ , Mn ²⁺ ], [CeMgAl ₁₁ O ₁₉ : Tb ³⁺ , Mn ²⁺ ] can be selected. In order to further improve the color rendering properties, the red phosphor may be replaced with one having a high color purity. As the high-purity red phosphor, for example, [Y (P, V) O ₄ : Eu ³⁺ ] or [Y ₂ O ₂ S: Eu ³⁺ ] can be selected. Also, the blue phosphor may be replaced with one having high color purity. As the blue phosphor with high color purity, for example, [CaMgSi ₂ O ₈ : Eu ²⁺ ] can be used.

The glass bulb 32 is filled with a mixed gas of about 3 mg of mercury (not shown), 92% of neon (Ne), and the balance of argon (Ar) and krypton (Kr). The kind of rare gas constituting the mixed gas, the mixing ratio, and the like are not limited to this, and can be selected from a range described in detail later.
The lead wire 40 is a connection between an internal lead wire 40A made of tungsten and an external lead wire 40B made of nickel, and the glass bulb 32 is hermetically sealed at the internal lead wire 40A portion. Both the inner lead wire 40A and the outer lead wire 40B have a circular cross section.

  An electrode 44 is joined to the inner end portion of the internal lead wire 40A supported on the end portion of the glass bulb 32 by laser welding or the like. The electrode 44 is a so-called hollow electrode having a bottomed cylindrical shape, and is obtained by processing a niobium rod. The reason why the hollow electrode is used as the electrode 44 is that it is effective in suppressing sputtering in the electrode caused by discharge when the lamp is lit (for details, refer to JP-A-2002-289138).

  Bushes 46 made of silicon rubber are fitted into both ends of the fluorescent lamp 6. As shown in the cross-sectional view of FIG. 2A, the lead wire 40 is connected with a covered electric wire 48 wired from an inverter device 204 (not shown in FIG. 2A, see FIG. 25) as a power circuit unit. Is done. The connection is made by joining with the solder 50 in a state where the conductive wire 48A of the covered electric wire 48 is entangled with the external lead wire 40B. The covered electric wire 48 is led out of the unit through a communication hole 60 that extends across the reflecting plate 8 and the metal plate 30.

  A perspective view of the bush 46 in a state where it is mounted on the fluorescent lamp 6 is shown in FIG. As shown in FIG. 2B, a plurality of ribs 46 </ b> A protrude from the outer peripheral surface of the bush 46. Both ends of the fluorescent lamp 46 are attached to the envelope 4 through the bush 46. That is, as shown in FIG. 1, the bush 46 is press-fitted and attached between the pair of ribs 16A and 16B. At this time, the bush 46 is elastically deformed a little and is firmly fixed with its restoring force. Further, in the mounted state, the bush 46 is in contact with the ribs 16A and 16B, the lower side portion 16, and the reflector 8 only at the top of the rib 46A. In the above example, a plurality of ribs 46A (six in this example) are provided. However, the number of ribs 46A is not limited to this, and may be at least one. The reason for providing the rib 46A will be described later.

  The folded portion 34 side is shown in FIG. As shown in FIG. 2A, the folded portion supporting member 62 attached to the upper side portion 14 is supported. The folded-back support member 62 is made of PET resin. As shown in FIG. 2A, the folded-back support member 62 has a “C” -shaped cross section, and the glass bulb 32 (folded section 34) having a circular cross section is fitted into the C-shaped cross section. At this time, the folded portion 34 is firmly supported by the elastic deformation of the C-shaped cross section.

  A reflective sheet 64 and a heat insulating sheet 66 are inserted between the support member 62 and the folded portion 34. The reflection sheet 64 exhibits the function of a reflection member that reflects light from the folded portion 34 in the extending direction of the linear portions 36 and 38, that is, downward. As a result, the light from the folded portion 34 that cannot be directly extracted due to the presence of the mounting frame 22 can be indirectly extracted outside the unit, which contributes to the improvement of the luminance of the unit. . Moreover, the heat insulation sheet 66 exists between the folding | returning part 34 and the folding | returning part support member 62, and has played the role of the heat insulating material literally. In addition, although the material used as a heat insulating material can consider Teflon (trademark), it is not restricted to this, What is necessary is just the material whose thermal conductivity is lower than the gas which fills the inside of a unit, ie, air. The reason for providing the heat insulating material (heat insulating sheet 66) will be described later. The heat insulating sheet 66 and the reflection sheet 64 are integrally attached to the folded portion support member 62.

As described above, the backlight unit 2 (hereinafter, this type is referred to as a “bent tube vertical installation type”) in which the bent fluorescent lamp 6 is configured such that the electrode 44 faces downward and the folded portion 34 faces upward. ), The brightness unevenness (brightness unevenness on the plate surface of the translucent plate 12) in the whole unit was improved as compared with the conventional unit.
The reason why the luminance unevenness occurs in the conventional backlight unit and the reason why the luminance unevenness is improved in the backlight unit according to the present embodiment will be described with reference to FIGS.

  FIGS. 3A and 3B each show a horizontal type backlight unit. In the fluorescent lamp, heat is generated from the plasma and the electrodes. The temperature of the electrode is higher than that of plasma. Naturally, the heat generated in the electrode is dissipated upward. In the horizontal type, the heat generated in the electrode is immediately dissipated outside the glass bulb through the thickness of the glass bulb as shown by three arrows in the figure, and heats the air in the unit. . That is, the heat generated in the electrodes is exclusively used for heating the air in the unit. This causes the temperature in the unit to rise excessively and causes the non-uniformity in the unit temperature as described above. . As a result, a luminance difference is generated between fluorescent lamps having different arrangement positions in the vertical direction, and uneven luminance occurs in the entire unit. Although detailed data is omitted, in the bent tube horizontal type shown in FIG. 3 (b), not only between the fluorescent lamps but also the upper linear portion and the lower linear shape in one fluorescent lamp. The inventor of the present application has found that a luminance difference occurs with respect to the part.

  In the case of the straight pipe vertical type shown in FIG. 4 (a), most of the heat generated in the lower electrode rises as it is inside the glass bulb, and is used exclusively for heating the enclosed gas and the glass bulb. Again, the heat generated in the upper electrode is immediately dissipated out of the glass bulb and exclusively heats the air in the unit. As a result, similarly to the horizontal type described above, the temperature in the unit is non-uniform, and a luminance difference occurs in the vertical direction in each fluorescent lamp, resulting in uneven luminance in the entire unit.

  On the other hand, in the bent tube vertical type shown in FIG. 4B, both heat generated by the electrodes rises in the glass bulb and is exclusively used for heating the sealed gas and the glass bulb. That is, as compared with any of the conventional types such as the straight pipe horizontal type, the bent pipe horizontal type, and the straight pipe vertical type, it is possible to suppress an increase in the internal temperature of the unit, thereby reducing nonuniformity of the internal temperature of the unit. As a result, the luminance difference in one fluorescent lamp as well as between fluorescent lamps is reduced, and the luminance unevenness in the entire unit is suppressed as compared with the conventional case.

The inventor of the present application confirmed by experiments (referred to as a first experiment) that the difference in luminance in one fluorescent lamp is small in the bent tube vertical type. Further, separately from the experiment, an experiment (second experiment) in which the temperature of the glass bulb surface of the fluorescent lamp is measured in a state where it is not housed in the unit, that is, with the bent cold cathode fluorescent lamp in the vertical direction in a sufficiently wide space. ).
First, the second experiment will be introduced.

FIG. 5 shows a model of the second experiment. As shown in FIG. 5, the bent portion of the bent cold cathode fluorescent lamp was turned on by hanging a thread around the folded portion, and the temperature at each measurement point <1> to <17> was measured. The position of each measurement location is shown in FIG.
The measurement position in FIG. 6 is a distance [mm] measured in the Y-axis direction from the lower end of the glass bulb. The experiment was performed with the ambient temperature set to 25 ± 1 ° C.

The experimental results are shown in FIG.
As shown in FIG. 7, the temperature is almost constant in the linear portions (<2> to <8>, <10> to <16>) regardless of the positions of the electrodes (<1>, <17>). Thus, it can be seen that there is not much difference in luminance. This is natural because it is not lighting in a closed space as in the unit. In addition, it turns out that the temperature in a folding | turning part (<9>) is lower than any other location.

Next, the first experimental result is shown in FIG.
In the first experiment, the same fluorescent lamp as that in the second experiment was suspended in the unit in the same manner with a thread. From FIG. 8, it can be seen that the temperature in the linear portions (<2> to <8>, <10> to <16>) is increased by about 10 ° C. compared to the case of the second experiment. This is because, even if the bent tube vertical type does not raise the temperature inside the unit, it rises to such an extent that no uneven brightness occurs. However, in the linear portions (<2> to <8>, <10> to <16>), it can be seen that there is almost no temperature difference in the vertical direction and no luminance difference. Even if it is said that the temperature in the vertical direction in the unit is not uneven, the heat is also slightly accumulated in the vicinity of the uppermost part in the unit. As a result, the folded portion (<9>) is raised by about 20 ° C., which is about 10 ° C. higher than other portions. As a result, all the remaining portions (<2> to <16>) except for the electrode positions (<1>, <17>) have a substantially uniform temperature.

  When the lamp is lit under the conditions as in the second experiment, the coldest spot appears at the position of the folded portion (<9>) (FIG. 7), and since the coldest spot temperature is too lower than the appropriate temperature, sufficient mercury vapor Pressure cannot be obtained. However, as can be seen from the first experiment, when arranged in the unit, the temperature of the folded portion (<9>) is changed to other linear portions (<2> to <8>, <10> to <16). >), This point will be improved.

  By the way, in the conventional bent tube horizontal type backlight unit, the folded portion is supported by the same method as shown in FIG. However, if the conventional method is adopted as it is, the heat of the folded portion is taken away via the support member, the temperature of the folded portion is lowered, and this portion becomes the coldest point, and the appropriate mercury The vapor pressure cannot be obtained. Therefore, in the above-described embodiment, a heat insulating member (heat insulating sheet 66 (FIG. 2)) is inserted between the folded portion support member 62 and the glass bulb 32 so that the temperature of the folded portion does not decrease. .

  The reason why the rib 46A is formed on the bush 46 (FIG. 2) is as follows. That is, in the vertical type of bent tube, in addition to the above-mentioned effect that the heat generated in the electrode is not dissipated into the unit internal space, the mercury vapor is heated by heating the sealed gas with the heat. There is also an effect of increasing the pressure to an appropriate pressure. In other words, the heat generated in the electrode is actively used for heating the sealed gas, thereby obtaining an appropriate mercury vapor pressure with a small amount of electric power. Therefore, the rib 46A is provided on the bush 46, and the contact area between the bush 46 and the ribs 16A and 16B provided on the side plate 10 (lower side portion 16) and the lower side portion 16 is reduced, so that the heat from the electrode is enclosed by the envelope. The amount of escape to 4 is to be reduced. This improves the rate used to heat the encapsulated heat generated by the electrodes.

  Moreover, even if the high-color purity phosphor is used as the phosphor constituting the phosphor film, it is possible to obtain a desired luminance without significantly increasing the input power to the fluorescent lamp. Become. Although the high color purity phosphor has the advantage of expanding the NTSC triangle in the chromaticity diagram, the luminance is lower than other types of phosphors. Therefore, if the high color purity phosphor is used to obtain the same brightness as other types of phosphors, it is necessary to increase the input power to the fluorescent lamp accordingly. Therefore, as described above, a desired luminance can be obtained without significantly increasing the input power to the fluorescent lamp because a proper mercury vapor pressure can be obtained with a small amount of electric power.

  In addition, although it did not mention so far until the size of the backlight unit 2 and the fluorescent lamp 6, etc., the backlight unit according to the present invention is preferably used as a constituent unit of a liquid crystal television having a size of 14 to 52 inches. In this case, the number of fluorescent lamps housed in the unit is in the range of 6 to 20 in the aspect ratio 4: 3 and 6 to 23 in the aspect ratio 16: 9. Further, the total length L1 of the fluorescent lamp shown in FIG. 1 is 130 to 600 mm, and the preferred range of the length W1 of the folded portion (that is, the interval between the linear portion 36 and the linear portion 38) is 15 to 35 mm. The reason why the lower limit is set to 15 mm is that if it is shorter than this, it is difficult to stably fold the glass tube during the production. The upper limit is set to 35 mm. If the upper limit exceeds 35 mm, the diffusibility of mercury collected in the central portion of the folded portion in the glass bulb 32 to the linear portion decreases, and this causes the linear portion of the fluorescent lamp 6 to This is because the luminance is lowered. That is, W1 = 15 to 35 mm is a suitable range in which the glass tube can be stably folded and the luminance is not lowered.

Moreover, the form of embodiment which concerns on this invention is not restricted above, For example, the following modifications can also be considered.
(Modification 1)
FIG. 9A shows a part of a plan view of the backlight unit 70 according to the first modification. Moreover, FIG.9 (b) is an expanded sectional view along the BB line in Fig.9 (a).

The backlight unit 70 according to the modification 1 has basically the same configuration as the backlight unit 2 of the first embodiment except that the heat radiating member 72 is added. Therefore, common portions are denoted by the same reference numerals as those of the backlight unit 2, and description thereof is omitted, and the heat radiating member 72 will be mainly described.
The heat dissipating member 72 functions as a literal heat dissipating member that effectively dissipates part of the heat generated by the fluorescent lamp 6 from the fluorescent lamp 6, and as shown in FIG. It functions as a support member that supports the inside.

  The heat dissipating member 72 is formed of white PET resin, has a C-shaped cross section that opens to the light transmitting plate 12 (see FIG. 2A), and the outer periphery of the glass bulb 32 at the inner periphery of the C-shaped cross section. It is attached so as to come into surface contact with. The heat radiating member 72 has the effect | action which takes heat from the contact surface with the glass bulb | bulb 32, and cools the corresponding glass bulb | bulb 32 part. The heat dissipating member 72 is attached for the purpose of stably forming the coldest spot in the vicinity of the electrode, increasing the distribution density of mercury in the vicinity of the electrode, and thereby extending the life of the electrode and hence the life of the fluorescent lamp.

Since the heat dissipating member 72 is attached for the above purpose, the attachment position (distance in the Y-axis direction from the end of the glass bulb 32) L2 shown in FIG. 9 is a position closer to the electrode than the center with respect to the lamp full length L1. (L2 ≦ (L1) / 2)) is preferable, more preferably in a range of L2 ≦ (L1) / 3), and still more preferably a position within 50 mm from the upper end of the electrode.
In addition, since the heat radiating member is mainly intended for heat radiating as described above, the heat radiating member may not be used as a support member like the heat radiating member 72. For example, as shown in FIG. 9C, the heat radiating member 72 may be the heat radiating member 74 except for the leg portion 72A.

Further, the material is not limited to PET resin, and may be, for example, translucent silicon. In short, any material having higher thermal conductivity than the gas (air) that fills the inside of the unit may be used.
(Modification 2)
FIG. 10 shows a part of a plan view of the backlight unit 80 according to the second modification. The backlight unit 80 according to the modification 2 is basically the same as the modification 1 except that the backlight unit 80 includes a linear portion support member 82 including a pair of support members 82A and 82B instead of the folded-back support member 62 (FIG. 9). It is the same configuration. Therefore, description of common parts is omitted, and different parts will be mainly described.

  As described above, in the backlight unit 80, the linear portions 36 and 38 support the folded portion 34 side. By doing so, it is possible to improve the positioning accuracy of the fluorescent lamp 6 in the left-right direction as compared with the case where the folded portion 34 is supported. Both of the support members 82A and 82B have the same shape, and an enlarged cross-sectional view cut along the line C / C in FIG. 10 is the same as that of the heat radiation member 72 shown in FIG. 9B. . The linear portion support member 82 is formed of the same white PET resin as the heat dissipation member 72. Here, since the linear portion support member 82 is provided for the purpose of supporting the upper portion of the fluorescent lamp 6, it is located at a position closer to the turn-up portion 34 than the center (L3 ≦ (L1) / 2) is preferred.

Further, since the heat from the fluorescent lamp 6 escapes even through the linear portion support member 82, it is necessary to prevent the coldest spot from occurring at a location corresponding to this portion. Therefore, in the second modification, the vertical length L4 (Y-axis direction length) of the support members 82A and 82B is greater than the vertical length (Y-axis direction length) L5 of the heat dissipation member 72. It is shortened. That is, by providing a difference in contact area with the glass bulb 32 between the two members, heat from the heat radiating member 72 rather than heat escaping through the linear portion support member 82 out of heat generated in the fluorescent lamp 6 at the time of lighting. The heat that traveled away escaped more. The above is an example in which both members are formed of the same material (PET resin). However, in the case of the same shape, both members may be formed of materials having different thermal conductivities. For example, the linear portion support member 82 may be formed of acrylic resin, and the heat dissipation member 72 may be formed of translucent silicon having higher thermal conductivity.
(About sealed gas)
The inventor of the present application has developed a lamp that is improved in lamp efficiency and starting voltage as compared with a conventional cold cathode fluorescent lamp by devising the composition of the mixed gas sealed in the glass bulb. Along with the development process, we will explain below.

As described above, 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 response to this demand, a cold cathode fluorescent lamp mainly composed of neon and argon as a rare gas to be filled has been developed.

  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. 11A 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. 11 (a), it can be seen that the starting voltage gradually decreases as the neon ratio is increased from the argon alone (100%) (when the argon ratio is decreased). From FIG. 11A, it can be seen 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. 11B 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. 11 (b), although the lamp efficiency gradually increases as the argon ratio is decreased, the vicinity of argon 3 to 10% (neon 90 to 97%) becomes the peak and then decreases. I understand that. This is because the glass bulb surface temperature (Ts) becomes 60 ° C. at which an optimum mercury vapor pressure can be obtained when the mixing ratio is 90 to 97% neon and 3 to 10% argon.

Therefore, neon 90 to 97% -argon 3 to 10% 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.
By the way, with the increase in size and brightness of liquid crystal televisions, the number of cold cathode fluorescent lamps provided per backlight unit attached directly to the LCD panel for the liquid crystal television is also increasing. Is as described above. 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 necessary 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. 11 (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 inventor of the present application has developed various cold cathode fluorescent lamps that are improved in both lamp efficiency and starting voltage (particularly, starting voltage at a low temperature) over fluorescent lamps mainly composed of neon / argon gas. The experiment was conducted.
FIG. 12A is a longitudinal sectional view showing a schematic configuration of a cold cathode fluorescent lamp 100 (hereinafter simply referred to as “lamp 100”) subjected to the experiment. Although the experiment was performed with a straight tube type lamp, the experimental result can be applied to a bent type lamp.

The lamp 100 has a glass bulb 106 in which both ends of a glass tube having a circular cross section are hermetically sealed with lead wires 102 and 104. The glass bulb 106 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 108 is formed on the inner surface of the glass bulb 106. The phosphor film 108 includes red-emitting [Y ₂ O ₃ : Eu ³⁺ ], green-emitting [LaPO ₄ : Ce ³⁺ , Tb ³⁺ ] and blue-emitting [BaMg ₂ Al ₁₆ O ₂₇ : Eu ^2+]. Including three types of rare earth phosphors.

Further, inside the glass bulb 106, a mixed gas composed of about 3 mg of mercury (not shown) and plural kinds of rare gases is sealed. The type and mixing ratio of the rare gas constituting the mixed gas will be described in detail later.
The lead wires 102 and 104 are connections between the internal lead wires 102A and 104A made of tungsten and the external lead wires 102B and 104B made of nickel, respectively, and the glass tube is airtight at the internal lead wires 102A and 104A at both ends. It is hermetically sealed. The internal lead wires 102A and 104A and the external lead wires 102B and 104B both have a circular cross section. The internal lead wires 102A and 104A have a wire diameter of 1 mm and a total length of 3 mm. The wire diameters of the external lead wires 102B and 104B Is 0.8 mm and the total length is 10 mm.

Electrodes 110 and 112 are joined to the inner end portions of the internal lead wires 102A and 104A supported by the end portions of the glass bulb 106 by laser welding or the like, respectively. The electrodes 110 and 112 are so-called hollow electrodes having a bottomed cylindrical shape, and are obtained by processing a niobium rod.
The electrodes 110 and 112 have the same shape, and the dimensions of each part shown in FIG. 12B are as follows: electrode length L6 = 5.2 mm, outer diameter p1 = 2.7 mm, wall thickness t = 0.2 mm, (inner diameter p2 = 2.3 mm). Since the electrodes 110 and 112 are provided so that the center thereof is aligned with the tube axis of the glass bulb (glass tube) 106, the gap between the outer periphery of the electrodes 110 and 112 and the inner circumference of the glass bulb 106 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 lit, discharge is generated only on the inner surfaces (cylindrical inner peripheral surface and bottom surface) of the hollow electrodes 110 and 112.

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 FIGS.
FIG. 19 shows a graph showing experimental results at an ambient temperature of 0 ° C. based on FIGS. 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 plotting all the five measurement results (Nos. 1 to 5) on the graph is complicated, in FIG. 19, an arithmetic average of the five measurement results is plotted as a representative value.

  As can be seen from FIG. 19, in an environment with an ambient temperature of 0 ° C., it can be seen that the start voltage of the type B lamp is lower than that of the type A lamp at any gas pressure. 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. 20 is a graph showing experimental results in an environment at an ambient temperature of 25 ° C. based on FIGS.
As can be seen from FIG. 20, 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 minimum starting voltage of type A at an ambient temperature of 0 ° C. (see FIG. 19). 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.

FIG. 21 shows the experimental results.
Based on FIGS. 13 and 21, a graph of the measurement result of the starting voltage at an ambient temperature of 0 ° C. is shown in FIG. 22, and a graph of the measurement result of the starting voltage at an ambient temperature of 25 ° C. is shown in FIG. 22 and 23, all five measurement results (Nos. 1 to 5) are plotted.
22 and 23, 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 of the ambient temperature and lamp efficiency are omitted, and only the tendency of the relationship between them is shown in FIG.

FIG. 24 is a graph in which the horizontal axis represents the ambient temperature, and the vertical axis represents 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 embodiment, 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 enclosed. Therefore, the power supply unit or the like can be downsized. Furthermore, the highest lamp efficiency can be obtained in the temperature environment in the unit where the cold cathode fluorescent lamp is installed.

Next, the example which used the said backlight unit 2 (FIG. 1, FIG. 2) for the liquid crystal television shown as an example of a liquid crystal display device is shown.
FIG. 25 is a diagram showing the liquid crystal television 200 with a part of the front surface thereof cut away. A liquid crystal television 200 shown in FIG. 25 is, for example, a 32-inch size liquid crystal television, and includes a liquid crystal display panel 202, a backlight unit 2, and the like. In FIG. 25, the inverter device 204 is one of the components of the backlight unit 2.

The liquid crystal display panel 202 includes a color filter substrate, a liquid crystal, a TFT substrate, and the like, and is driven by a drive module (not shown) based on an external image signal to form a color image.
The backlight unit 2 is provided on the back surface of the liquid crystal display panel 202 and irradiates the liquid crystal display panel 202 from the back surface. As shown in FIG. 25, the envelope 4 having a flat box that constitutes the backlight unit 202 in a state in which the backlight unit 202 is used stands. Needless to say, each fluorescent lamp 6 (FIG. 1) is housed in the envelope 4 that is used in an upright state, with the electrode 44 positioned downward and the folded portion 34 positioned upward.

  The inverter device 204 supplies high-frequency power to each fluorescent lamp 6 (FIG. 1) constituting the backlight unit 2 to turn on each fluorescent lamp 6. The inverter device 204 is disposed inside the casing 206 of the liquid crystal television 200 and outside the envelope 4. During operation of the liquid crystal television 200, that is, when each fluorescent lamp 6 in the backlight unit 2 is turned on, the inverter device 204 becomes a heat source that generates heat at a considerable temperature. When such a heat source is installed inside the envelope 4, the temperature unevenness in the envelope 4 is further increased, and consequently the luminance unevenness of the entire backlight unit 2 is increased. Therefore, in the backlight unit 2, the inverter device 204 is arranged outside the envelope 4 in order to eliminate unnecessary heat sources in the envelope 4 as much as possible.

As mentioned above, although this invention has been demonstrated based on embodiment, it cannot be overemphasized that this invention is not restricted to an above-described form, For example, it can also be set as the following forms.
(1) In the above embodiment, the fluorescent lamps 6 are arranged such that the linear portions are arranged in the left-right direction. However, the present invention is not limited to this, and in FIG. 1, the linear portions are arranged in a direction perpendicular to the paper surface. It may be arranged.
(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. In the case of lighting at a low current, it is not particularly necessary to use a hollow electrode. 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 amount of mercury used has been regulated due to environmental issues, the use of niobium, molybdenum, and tantalum as the electrode material reduces the consumption of the electrode compared to the case where nickel is used. Can be extended.

  The backlight unit according to the present invention can be used, for example, for a liquid crystal display device, and the liquid crystal display device according to the present invention can be used, for example, as a liquid crystal television.

It is a top view of the backlight unit (state which excluded the translucent board etc.) concerning an embodiment. (A) is the sectional view on the AA line in FIG. 1, (b) is a perspective view which shows the bush of the state with which the cold cathode fluorescent lamp was mounted | worn. Both (a) and (b) are diagrams showing a conventional fluorescent lamp horizontal type backlight unit. (A) is a figure which shows the conventional straight tube | pipe vertical installation type backlight unit, (b) is a figure which shows the bending pipe vertical installation type backlight unit which concerns on this Embodiment. It is a figure which shows the experimental model of the surface temperature measurement experiment of a glass bulb. It is a figure which shows the temperature measurement position in the said experimental model. It is a figure which shows the temperature measurement result at the time of making it light without the said experimental model being accommodated in a unit. It is a figure which shows the temperature measurement result at the time of making it light with the said experimental model accommodated in the unit. It is a figure which shows a part of backlight unit which concerns on the modification 1. FIG. FIG. 11 is a diagram showing a part of a backlight unit according to Modification 2. 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. It is a longitudinal cross-sectional view which shows the cold cathode fluorescent lamp used for experiment. In a cold cathode fluorescent lamp in which a mixed gas in which neon gas and argon gas are mixed at a predetermined ratio is enclosed, the starting voltage at an ambient temperature of 0 ° C. and the ambient temperature at 25 ° C. when the pressure of the mixed gas is changed It is a figure which shows the result of having measured the starting voltage. In a cold cathode fluorescent lamp in which a mixed gas obtained by mixing neon gas, argon gas, and krypton gas at a predetermined ratio is sealed, the starting voltage and the ambient temperature at an ambient temperature of 0 ° C. when the pressure of the mixed gas is changed It is a figure which shows the result of having measured the starting voltage in temperature 25 degreeC. In a cold cathode fluorescent lamp in which a mixed gas obtained by mixing neon gas, argon gas, and krypton gas at a predetermined ratio is sealed, the starting voltage and the ambient temperature at an ambient temperature of 0 ° C. when the pressure of the mixed gas is changed It is a figure which shows the result of having measured the starting voltage in temperature 25 degreeC. FIG. 16 is a diagram showing measurement results of the same items as those in FIG. 15 in a cold cathode fluorescent lamp in which a mixed gas having a different ratio from that shown in FIG. 15 is sealed. FIG. 16 is a diagram showing measurement results of the same items as those in FIG. 15 in a cold cathode fluorescent lamp in which a mixed gas having a different ratio from that shown in FIG. 15 is sealed. FIG. 16 is a diagram showing measurement results of the same items as those in FIG. 15 in a cold cathode fluorescent lamp in which a mixed gas having a different ratio from that shown in FIG. 15 is sealed. 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. In a cold cathode fluorescent lamp in which a mixed gas in which neon gas and krypton are mixed at a predetermined ratio is enclosed, a starting voltage at an ambient temperature of 0 ° C. and a starting at an ambient temperature of 25 ° C. when the pressure of the mixed gas is changed It is a figure which shows the result of having measured the voltage. 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. It is a figure which shows schematic structure of the liquid crystal television using the backlight unit which concerns on the said embodiment.

Explanation of symbols

2, 70, 80 Backlight unit 4 Envelope 6 Bent cold cathode fluorescent lamp 32 Glass bulb 34 Folded part 36, 38 Linear part 44 Electrode 62 Folded part support member 64 Reflective sheet 66 Teflon (registered trademark) sheet 72, 74 Heat Dissipation Member 82 Linear Part Support Member 200 Liquid Crystal Television 202 Liquid Crystal Display Panel 204 Inverter Device

Claims (6)

An envelope,
A glass bulb having a folded portion that is housed in the envelope and formed by folding a glass tube in the middle in the longitudinal direction thereof, and a linear portion that extends in parallel from both sides of the folded portion. A bent fluorescent lamp in which electrodes are provided at both ends;
A direct-type backlight unit having an inverter device for supplying power for lighting to the bent fluorescent lamp,
In the state where the inverter device is arranged outside the envelope and the backlight unit is used, the bent fluorescent lamp has a posture in which both the electrodes are downward and the folded portion is upward. The backlight unit is housed in the envelope. A folded portion support member for supporting the folded portion in the envelope;
A heat insulating member inserted between the folded portion and the folded portion support member;
The backlight unit according to claim 1, comprising:   The backlight unit according to claim 2, wherein a reflection member that reflects light from the folded portion in an extending direction of the linear portion is attached to the heat insulating member.   A heat dissipating member made of a material having a higher thermal conductivity than the gas filling at least the inside of the envelope is attached to the outer periphery closer to the end than the center in the longitudinal direction of each linear portion. The backlight unit according to claim 1. A linear portion support member that supports a portion of the linear portion closer to the folded portion than the center in the longitudinal direction in the envelope;
Of the heat generated by the bent fluorescent lamp at the time of lighting, more heat than the heat that escapes through the linear portion support member is formed on the outer periphery from the end corresponding to the longitudinal center of each linear portion. The backlight unit according to claim 1, further comprising a heat dissipating member for releasing the light. A liquid crystal display panel;
A liquid crystal display device comprising the backlight unit according to claim 1, wherein the envelope is disposed on a back surface of the liquid crystal display panel.

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