JP2006127833A - Backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit used as a backlight having an emission surface having a uniform luminance distribution by improving a luminance distribution of a discharge lamp with a bent part formed thereon. <P>SOLUTION: A heat-retention space 8 is formed around the bent part 2 of each discharge lamp 1 used by this backlight unit by using a support plate 10 supporting the discharge lamp 1 and a reflective casing 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a backlight unit having a uniform light emitting surface, which is used for a backlight of a large liquid crystal TV or a display device of a personal computer.

  A backlight unit is used in a display device such as a personal computer, a liquid crystal television, or a liquid crystal meter. This backlight unit usually uses a cold cathode discharge lamp as a light source, and displays a liquid crystal surface by applying substantially uniform light in plan view from the back of a liquid crystal panel such as a small liquid crystal television or a liquid crystal meter.

  FIG. 12 is an exploded perspective view showing an example of a conventional backlight unit. In the case of the direct type, the backlight unit has a shallow dish shape, an opening 21a is formed, a bottom wall surface 21b has a reflecting surface, and a cold cathode low-pressure discharge lamp 22 that is straight tubed or bent (curved) is fixedly installed. The reflection type casing 21 is disposed, and a diffuse transmission plate 25 is detachably attached to the opening 21a. Further, a diffusion sheet 31, a lens sheet 32, and a polarizing sheet 33 are sequentially arranged on the upper surface side of the diffusion transmission plate 25.

  In the exploded perspective view shown in FIG. 13, the vicinity of the reflective casing will be further described. The reflective casing 21 formed with a white or mirror-like reflective surface has a shallow dish shape with an open front surface, and a plurality of the casings are formed inside. The cold cathode low-pressure discharge lamp 22 is electrically connected and held in a plane by holding the power supply terminal side with a lamp holder 24 made of an elastic material such as rubber. A synthetic resin-based diffuse transmission plate 25 is detachably attached to the opening of the reflective casing 21.

  The cold cathode low-pressure discharge lamp 22 is formed, for example, by connecting a plurality of U-shaped cold cathode discharge lamps 22 and 22 in series at a connection terminal portion 23 and using both ends as power supply terminals.

  The reflective casing 21 is made of, for example, a polycarbonate resin or a weather resistant resin of a polycarbonate resin mixed system. Further, the bottom wall surface 21a of the reflective casing 21 has a concavo-convex surface in a certain direction (stripe-shaped projections 21b are formed). The concavo-convex surface functions as a reflective surface, while the cold cathode low-pressure discharge lamp 22 is Then, the bent portion 22a and the like are locked by a locking piece 21c and are arranged and mounted in a planar manner inside the reflective casing 21. Further, the cold cathode low-pressure discharge lamp 22 has a lamp holder 24 made of an elastic material such as rubber and a connection terminal 23 by means of a support groove 26a of a support member 26 that is integrally installed on the side wall portion 21d of the reflective casing 21. It is supported in a sandwiched manner and fixed and mounted inside the reflective casing 21.

In these configurations, the both ends of the cold cathode low-pressure discharge lamp 22 are fitted and supported in the support groove 26a of the support member 26 via the lamp holder 24. The deformation and use of a minute bulb accompanying thermal expansion that occurs during lighting are used. The external force due to the impact or vibration at the time is absorbed by the rubber-based elastic material holder 23 to prevent the cold cathode low-pressure discharge lamp 22 from being damaged, while providing electrical insulation. (For example, see Patent Document 1)
14 (a) and 14 (b) are explanatory diagrams showing a lamp fixing method in a backlight unit configured by arranging a plurality of bent fluorescent lamps (U-shaped or U-shaped) as cold cathode low-pressure discharge lamps. (A) is side sectional drawing, (b) is a top view. 14 (a) and 14 (b), the same reference numerals are given to the same functional portions as those in FIG. 13, and the description thereof is omitted. That is, the bent portion 22a of the cold cathode low-pressure discharge lamp 22 arranged in the reflective casing 21 is sandwiched and supported by the lamp holder 24 made of an elastic body such as silicon rubber, thereby forming the bent portion 22a. The fluorescent lamp is securely fixed.
JP-A-10-39808 (paragraph numbers 0003 to 0005)

  The backlight unit used for the backlight is a light source that emits substantially uniform light in a planar manner from the back surface of the liquid crystal panel, and thus is required to be a light source having a uniform brightness (luminance) in a planar manner.

  A cold cathode fluorescent lamp used as a light source uses ultraviolet radiation from excitation of mercury vapor in a tube for light emission. Therefore, the brightness of the lamp is determined by the correlation between the vapor pressure of mercury sealed in the tube and the temperature. Moreover, since the vapor pressure of mercury changes depending on the temperature in the tube, the light output (brightness) changes sensitively to the ambient temperature.

  As shown in the explanatory diagram of FIG. 15, at the time of lighting, the electrode portion to which a high voltage is applied generates heat by becoming a starting point of discharge, and is heated to a higher temperature than other portions in the tube. In addition, since this high temperature causes deterioration of the member, heat dissipation is enhanced by using a metal for the back frame or the like as a countermeasure for preventing the deterioration. However, since the heat of the whole lamp is lowered by this, the internal temperature of the cold cathode fluorescent lamp does not rise, and the luminance is partially reduced as shown in the graph of the luminance distribution in the conventional backlight unit in FIG. Was.

  Further, when the current flowing through the cold cathode fluorescent lamp 22 is increased in order to increase the overall brightness of the cold cathode fluorescent lamp 22, the temperature of the electrode portion held by the lamp holder 24 also increases, and the ambient temperature of the tube The luminance decreases beyond the optimum temperature of the characteristics of brightness and luminance.

  Therefore, it is necessary to radiate the heat generated in the vicinity of the electrode part to the outside and suppress the temperature from exceeding the optimum value. Note that there is a problem that the influence of the brightness on the lamp temperature increases in proportion to the tube length of the cold cathode fluorescent lamp 22.

  Generally, for a backlight with a relatively small display screen size of 20 inches or less, a sidelight type backlight using a light guide plate and a direct type formed by arranging a plurality of straight pipes in parallel are adopted. There are many cases.

  However, in recent years, there is an increasing demand for the use of a direct type backlight using a plurality of large bent tubes. The direct type backlight using a plurality of large bent tubes reduces the number of lamps used by half, reduces the number of lighting circuits, and can consolidate the electrode parts at both ends in the same direction. In addition, there is a merit that the high voltage wiring can be shortened by adopting a both high voltage application lighting system in which positive and negative inverted voltages are applied simultaneously.

  However, when a U-shaped tube with a total length almost twice as long as a straight tube is used as a direct backlight using a plurality of large bent tubes, the temperature difference in the axial direction of a single tube The resulting unevenness (luminance) in the brightness (luminance) of the tube becomes noticeable. Therefore, there is a problem of eliminating unevenness of the brightness (luminance) of the tube and a luminance difference.

  In the conventional lamp fixing method, the straight tube fluorescent lamp is fixed to the case using a silicon rubber holder or the like in which electrode portions at both ends are molded. On the other hand, in the case of a fluorescent lamp in which a U-shaped or U-shaped bent portion is formed, the fluorescent lamp cannot be reliably supported by fixing only the electrode portions at both ends. For this reason, three-point fixing is performed together with the electrode portion using a silicon rubber holder or the like molded corresponding to the bent portion.

  However, the U-shaped or U-shaped bent part is located at a position away from the electrode part side where the temperature becomes high when the lamp is lit, and the temperature is difficult to rise even when the lamp is lit, and the bent part is fixed with a molded silicone rubber rubber holder. Then, heat is radiated to the metal frame that also serves as a noise countermeasure through the rubber holder.

  As a result, as shown in the explanatory diagram of FIG. 15, when the tube temperature near the low-pressure side bent portion 22a and the tube temperature near the high-pressure side electrode portion are compared, the low-pressure side becomes low temperature, and the high-pressure side Becomes hot. As a result, the temperature difference increases and the temperature gradient of the entire tube increases.

  The temperature difference between the vicinity of the electrode portion and the vicinity of the bent portion affects the luminance of the lamp, and the luminance distribution of the lamp becomes non-uniform. Therefore, particularly in a backlight using a bent lamp having a long overall length, a problem to be solved is that the temperature difference between the vicinity of the electrode portion where the temperature is high and the vicinity of the bent portion where the temperature is difficult to rise must be as small as possible. Has been.

  The present invention has been made based on these circumstances, and provides a backlight unit used as a backlight having a light emitting surface with a uniform luminance distribution by improving the luminance distribution of a discharge lamp having a bent portion. It is aimed.

According to the present invention, a reflective casing having an opening formed on the front surface and a reflecting surface formed on the bottom wall surface, and a straight pipe portion that is supported and arranged on the bottom wall surface of the reflective casing by a supporting means. A backlight unit for a direct type backlight, comprising: a discharge lamp that forms a flat light-emitting portion by a bent portion; and a diffusion transmission plate attached to the opening of the casing,
The discharge unit and the bent portion of the discharge lamp are backlight units characterized in that the temperatures are substantially equal when the discharge lamp is lit.

  According to the invention, the member forming the low wall surface of the reflective casing is formed of a material having a plurality of different heat dissipation characteristics.

  According to the present invention, the member forming the low wall surface of the reflective casing is formed by changing the plate thickness along the axial direction of the discharge lamp that is supported. This is a backlight unit.

  According to the present invention, the lamp luminance distribution can be made uniform and mercury condensation can be prevented, and a backlight unit for a backlight having a uniform light emitting surface can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  In the present invention, in order to form a backlight unit having a uniform light emitting surface, the luminance distribution of a cold cathode fluorescent lamp having a bent portion is improved. Improvement of the luminance distribution of the cold cathode fluorescent lamp with the bent portion is achieved by a new holding structure for the lamp and a new structure of the back frame portion of the reflective casing.

  The basic structure of the backlight unit in the case of the direct type is as described above with reference to FIG. 12 in the background art section. The opening 21a is formed in a shallow dish shape, the bottom wall surface 21b has a reflective surface, A reflective casing 21 having a straight tube or a curved and bent cold cathode low-pressure discharge lamp 22 fixed thereto is disposed, and a diffuse transmission plate 25 is detachably attached to the opening 21a. Further, a diffusion sheet 31, a lens sheet 32, and a polarizing sheet 33 are sequentially arranged on the upper surface side of the diffusion transmission plate 25.

  Next, the relationship between the reflection type casing of the backlight unit and the arrangement of the cold cathode discharge lamp 1 having a bent portion will be described. That is, FIG. 1 is a perspective plan view showing the configuration of the vicinity of the reflective casing of the backlight unit, which is a direct type backlight, and FIG. 2 is a cross-sectional view taken along the line AA in FIG. It is.

  In a backlight unit that is a direct type backlight, two straight tube portions 1a and 1b are formed in parallel on the same plane as a light source, and one end of each of the straight tube portions 1a and 1b is a U-shaped bent portion 2 (note that the In the case of using an integrated cold cathode discharge lamp 1 (hereinafter simply referred to as a discharge lamp) communicated by a straight bent portion 2 having a straight portion 2a at the center thereof, the discharge lamp 1 is supplied with power. A terminal 1t is held by a lamp holder 3 made of an elastic material such as rubber, and a plurality of terminals are arranged and stored in a flat plate-like reflection casing 4 having an opening 4a on the front surface. ing. A light diffusing and transmitting plate 5 is attached to the opening side of the reflective casing 4 so as to be freely attached.

  The reflective casing 4 is made of, for example, polycarbonate resin and is formed in a shallow dish shape having an opening (opening 4b) on the front surface. The bottom wall surface 4b of the reflective casing 4 is formed with a reflection surface of a specular reflection layer formed by silver deposition. The light diffusing and transmitting plate 5 is milky white made of, for example, an acrylic resin and has a light diffusing action.

  As in the conventional example shown in FIG. 13, each discharge lamp 1 is connected in series with a power feeding terminal 1 t and held by the lamp holder 3, and power feeding portions 6 are formed at both ends of the lamp holder 3. It is connected to a boost lighting circuit (not shown). That is, the discharge lamp 1 has a power supply terminal 1t formed on one end side of the pair of straight tube portions 1a and 1b, and a bent portion 2 formed on the opposite side to the power supply terminal 1t. In addition, a phosphor layer (not shown) is formed on the inner wall surface of the discharge lamp 1, and discharge electrodes 7 as cold cathodes are sealed in both ends of the straight tube portions 1a and 1b, respectively, and required inside. A quantity of rare gas and mercury are enclosed.

  The discharge lamp 1 is fixed to the reflective casing 4 by holding the power supply terminal 1t side of the discharge lamp 1 on the lamp holder 3 (supporting means). FIG. 3 (a) is a side sectional view, and FIG. As shown in the plan view of the B1-B1 cross section, on the bent portion 2 side, the straight portion 2a is locked and fixed to the extending portion 10a of the support plate 10 (support means). Therefore, the discharge lamp 1 has a structure that is fixedly supported at three or more locations as a whole. In addition, the fixing support other than the peripheral portion of the discharge electrode 7 is fixed so as to reduce heat conduction and heat dissipation by using a fixing component having a structure in which the contact area with the surface of the discharge lamp 1 is made as small as possible. Further, a narrow heat retaining space 8 is formed in a part of the reflective casing 4. As a result, the bent portion 2, where the temperature of the tube wall tends to be low because it is farther from the discharge electrode 7, is housed in a narrow heat-retaining space 8 to prevent the temperature from decreasing. As a result, a backlight unit which is a backlight unit which prevents mercury suspecting and improves the lamp luminance distribution to form a uniform light emitting surface is formed.

  The backlight unit having such a configuration is turned on, and the light distribution characteristic emitted through the diffuser transmission plate 5 provides a luminance distribution with almost no luminance unevenness as a surface light source. Therefore, when used as a backlight of a liquid crystal display device, the luminance distribution radiated through the diffusing and transmitting plate 5 has substantially uniform luminance (no luminance unevenness) on the entire surface and good visibility. A liquid crystal display surface can be irradiated.

  Next, a modification of the above-described backlight unit will be described. In the following modifications, the same reference numerals are given to the same functional portions as those in the above-described embodiment, and the description thereof is omitted.

(Modification 1)
4A is a cross-sectional side view, and FIG. 4B is a plan view at A2-A2. The bottom wall surface 4a of the reflective casing 4 is compared with the discharge lamp 1 and the vicinity of the discharge electrode 7. FIG. A lighting circuit or other circuit board 9 is disposed at a position corresponding to the vicinity of the bent portion 2 having a low temperature. Thereby, the bottom wall surface 4a in the vicinity of the bent portion 2 is heated by heat generated when an electronic component (not shown) mounted on the circuit board 9 is operated. Thereby, the temperature difference between the bent portion 2 and the bottom wall surface 4a is reduced, and the temperature drop due to heat radiation near the bent portion 2 is reduced.

  As a result, the temperature difference between the vicinity of the discharge electrode 7 and the vicinity of the bent portion 2 of the discharge lamp 1 can be reduced. Thereby, a backlight unit which is a backlight having a uniform lamp luminance distribution with a small luminance gradient can be realized.

(Modification 2)
As shown in the plan view of FIG. 5A and the side sectional view of FIG. 5B, the bottom wall surface 4a of the reflective casing 4 facing the discharge lamp 1 is connected to the bottom wall surface 4a in the axial direction of the discharge lamp 1. Are formed of a material having a plurality of different heat dissipation characteristics.

  That is, as shown in the explanatory diagram of FIG. 6, the bottom wall surface 4 a of the reflective casing 4 facing the discharge lamp 1 faces the vicinity of the discharge electrode 7 on the high pressure side where the cold discharge lamp 1 generates a large amount of heat. The part uses aluminum (metal) or the like, which is a member 4b having good heat dissipation (high thermal conductivity), while the part facing the lamp central part (bent part 2) where the lamp on the low pressure side is difficult to warm is radiating heat. A molding resin such as polycarbonate, which is a member 4c having poor properties (low thermal conductivity), is used. Thereby, as shown in the graph of FIG. 7, the temperature balance in the axial direction of the discharge lamp 1 can be made uniform, and the overall brightness of the discharge lamp 1 is improved.

  As a result, the temperature difference between the vicinity of the discharge electrode 7 and the vicinity of the bent portion 2 of the discharge lamp 1 can be reduced. Thereby, a backlight unit having a uniform lamp luminance distribution with a small luminance gradient can be realized.

(Modification 3)
As shown in the plan view of FIG. 8A and the side sectional view of FIG. 8B, the bottom wall surface 4a of the reflective casing 4 facing the discharge lamp 1 of the reflective casing 4 is discharged to the bottom wall surface 4a. The plate thickness is changed along the axial direction of the lamp 1.

  That is, as illustrated in FIG. 9, the bottom wall surface 4 a facing the discharge lamp 1 of the reflective casing 4 is a portion facing the vicinity of the discharge electrode 7 on the high-pressure side where the discharge lamp 1 generates a large amount of heat. Is formed with a thick plate so as to have good heat dissipation (high thermal conductivity). On the other hand, the portion facing the lamp central portion (bent portion 2) where the lamp on the low pressure side is difficult to warm is poor in heat dissipation. The member 4d formed so as to have a thin plate thickness (small thermal conductivity) is used. Thereby, as shown in the graph of FIG. 7, the temperature balance in the axial direction of the discharge lamp 1 can be made uniform, and the overall brightness of the discharge lamp 1 is increased.

  As a result, a temperature difference between the vicinity of the discharge electrode 7 and the vicinity of the bent portion 2 of the discharge lamp 1 can be reduced, and a backlight unit having a uniform lamp luminance distribution with a small luminance gradient can be realized.

(Modification 4)
As shown in a plan view in FIG. 10 (a) and a side sectional view in FIG. 10 (b), the bottom wall surface 4a of the reflective casing 4 facing the discharge lamp 1 of the reflective casing 4 is discharged. Along the axial direction of the lamp 1, the size of the space formed in a stepwise manner is changed.

  That is, as shown in the explanatory diagram of FIG. 11, the bottom wall surface 4a of the reflective casing 4 facing the discharge lamp 1 is a portion facing the vicinity of the discharge electrode 7 on the high-pressure side where the discharge lamp 1 generates a large amount of heat. Is formed by reducing the size of the holes 11a, 11b, 11c,..., 11n so as to improve heat dissipation (large thermal conductivity). On the other hand, the large holes 11a, 11b, 11c,... 11n are sparse so that the portion facing the lamp central portion (bent portion 2) where the lamp on the low pressure side is difficult to warm is deteriorated in heat dissipation (low thermal conductivity). The hole is formed in the hole.

  The holes 11a, 11b, 11c,..., 11n can have shapes such as a circle, a square, a triangle, and an ellipse corresponding to the temperature gradient in the axial direction of the discharge lamp 1. If the fine temperature balance is adjusted by gradually changing the sizes of the holes 11a, 11b, 11c... 11n, finer temperature adjustment is possible.

  As described above, the bottom wall surface 4a is formed by changing the size of the space provided in a stepwise manner along the axial direction of the discharge lamp 1, as shown in the graph of FIG. By making the temperature balance in the axial direction of the discharge lamp 1 uniform, the brightness of the entire lamp is increased.

  As a result, the temperature difference between the vicinity of the discharge electrode 7 and the vicinity of the bent portion 2 of the discharge lamp 1 can be reduced. Thereby, a backlight unit which is a backlight having a uniform lamp luminance distribution with a small luminance gradient can be realized.

  In addition, this invention is not limited to what was illustrated above, A various deformation | transformation can be taken in the range which does not deviate from the meaning of invention. For example, the discharge lamp is not limited to a U-shaped shape, and in the case of a flat shape such as a U or W shape having a bent portion and a straight portion, the discharge electrode is a hot cathode instead of a cold cathode. Even if it exists, the same effect | action and effect can be acquired.

The top view which shows the structure of the reflection type casing part in the backlight unit which is an Example of this invention. It is sectional drawing along the AA line of FIG. It is a figure which shows the structure of the principal part in the backlight unit of FIG. 1, (a) is side sectional drawing which shows fixation to the reflective casing of a discharge lamp, (b) is the top view. It is a figure which shows the backlight unit of this invention, (a) is a sectional side view of a modification, (b) The top view. (A) Side sectional drawing of the modification of this invention, (b) The top view. Explanatory drawing of the modification of this invention. The graph which shows the temperature balance of the axial direction of a discharge lamp. (A) Side sectional drawing of the modification of this invention, (b) The top view. Explanatory drawing of the modification of this invention. (A) Side sectional drawing of the modification of this invention, (b) The top view. Explanatory drawing of the modification of this invention. The disassembled perspective view which shows an example of the conventional backlight unit. The disassembled perspective view of the reflection type casing in the conventional backlight unit. It is a figure which shows the fixing method of the lamp | ramp in the conventional backlight unit, (a) is a sectional side view, (b) is a top view. Explanatory drawing of the temperature distribution in the conventional backlight unit. The graph which shows the luminance distribution in the conventional backlight unit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Discharge lamp, 1a, 1b ... Straight pipe | tube part, 2 ... Bending part, 2a ... Straight part, 3 ... Lamp holder, 4 ... Reflection type casing, 4a ... Bottom wall surface, 4b ... Opening part, 5 ... Light diffuse transmission board , 6 ... power feeding part, 7 ... discharge electrode, 8 ... heat insulation space, 9 ... circuit board, 10 ... support plate, 10a ... extension part, 11a, 11b, 11c to 11n ... hole

Claims (3)

A reflection-type casing having an opening formed on the front surface and a reflection surface formed on the bottom wall surface, and a straight pipe portion and a bent portion that are supported and arranged on the bottom wall surface of the reflection-type casing by support means. A backlight unit for a direct type backlight, comprising: a discharge lamp that forms a light emitting portion of the light source; and a diffusion transmission plate attached to the opening of the casing.
The discharge unit of the discharge lamp and the bent portion are formed so that the temperatures are substantially equal when the discharge lamp is lit.   The backlight unit according to claim 1, wherein the member forming the low wall surface of the reflective casing is formed of a plurality of materials having different heat dissipation characteristics.   The member forming the low wall surface of the reflective casing is formed by changing the plate thickness along the axial direction of the discharge lamp that is supported. 2. The backlight unit according to 2.

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