JPH11224517A - Surface light source device and flat display device using the same - Google Patents

Abstract

(57) [Summary] In an edge light type surface light source device 500 and a flat panel display device using the same, by reducing the number of parts, it is possible to reduce the cost of the device, and to form a tube forming an edge light. An object is provided in which electromagnetic noise or leakage current from a light source (fluorescent tube) 711 is sufficiently suppressed. A reflection sheet 721 made of a three-layer laminated film sandwiching a conductive film 725 covers the back surface of a light guide plate 701 and is bent at the periphery thereof to cover a tubular light source 711. Thus, the reflection sheet 721 also functions as a lamp reflector for the tubular light source 711. In order to suppress the leakage current, the conductive film 725 of the reflection sheet 721 is omitted on the upper side and the outer peripheral side of the bent portion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an edge light type surface light source device and a flat panel display device using the same.

[0002]

2. Description of the Related Art A flat display device such as a liquid crystal display device has been used as an image display device for a television, various computers, a car navigation system, etc. by taking advantage of features such as thinness, light weight, and low power consumption. Have been.

For example, a light transmission type liquid crystal display device includes a liquid crystal panel having a liquid crystal layer held between a pair of transparent substrates,
A surface light source device disposed on the back surface of the liquid crystal panel (surface opposite to the image display surface) to guide light source light to the liquid crystal panel;

In order to further reduce the thickness and size of such a flat display device, it is necessary to reduce the thickness of the surface light source device. Therefore, the surface light source device (backlight) has been replaced with a sidelight type (edge light type) from a direct type.

As disclosed in Japanese Utility Model Laid-Open Publication No. 63-24529, an edge light type surface light source device has a tubular light source and a thin plate made of an acrylic resin or the like having a milky white scattering pattern printed on the back side. One end face of the light guide plate is disposed close to the tubular light source including the light guide plate. The light source light from the tubular light source propagates through the light guide plate, is scattered by the scattering pattern on the back surface of the light guide plate, and is emitted from the main surface of the light guide plate on the liquid crystal panel side.

[0006]

The above-described surface light source device generally includes a lamp reflector for efficiently guiding light from the tubular light source into the light guide plate, and furthermore, light leakage from the light guide plate to the back side thereof. Various members have been used to improve light use efficiency, such as a reflection plate disposed on the back surface of the light guide plate to prevent the occurrence of light. Therefore, it has been difficult to reduce the price of the surface light source device.

Further, with the increase in the effective display area of the flat panel display, electromagnetic noise from the tubular light source has a direct adverse effect on the display.

Furthermore, depending on the configuration of the surface light source device, there has been a problem that a leakage current and a reduction in luminance or a waste of power due to the leakage current.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and achieves a reduction in the cost of an apparatus.
It is an object of the present invention to provide a surface light source device capable of sufficiently suppressing electromagnetic noise or leakage current from a tubular light source, and a flat display device using the same.

[0010]

According to the first aspect of the present invention,
A tubular light source and a light source, which is disposed with the side end face close to the tubular light source, propagates light from the tubular light source incident from the side end face, and emits light from the propagated light in each section of the propagation path. A light guide plate for distributing the light from the upper surface thereof, and a reflection sheet covering the lower surface of the light guide plate, in an edge light type surface light source device, wherein the reflection sheet has the tubular light source at its peripheral portion. A bent portion that covers the lower side, the outer peripheral side, and the upper side, and the bent portion forms a light source reflector that reflects light from the tubular light source to the side end surface of the light guide plate. In the light source device.

According to such a configuration, the lamp reflector and the reflection plate arranged on the back surface of the light guide plate to prevent light leakage from the light guide plate are integrally formed, so that the number of parts is reduced.

According to a third aspect of the present invention, in the surface light source device, the reflection sheet includes the conductive layer over substantially the entire surface including the bent portion.

According to such a configuration, the reflection sheet has:
Including the conductive layer, the tubular light source is covered and bent, so that the influence of electromagnetic noise from the tubular light source can be reduced.

According to a fourth aspect of the present invention, in the surface light source device, the reflection sheet is substantially composed of only a non-conductive layer in a region at the tip of the bent portion which covers the tubular light source from above. Features.

According to such a configuration, a leak current from the tubular light source can be suppressed.

According to a ninth aspect of the present invention, there is provided a flat display device including a light transmission type display panel and a surface light source device disposed below the display panel.
A tubular light source, a light guide plate arranged with the side end face close to the tubular light source, and emitting the light source light to the upper surface while propagating light from the tubular light source incident from the side end face; A reflection sheet that covers the lower surface of the light plate, the reflection sheet includes, at its peripheral edge, a bent portion that covers the tubular light source from the lower side, the outer peripheral side, and the upper side, and the bent portion is formed from the tubular light source. The flat panel display device is characterized in that the flat panel display device comprises a light source reflector for reflecting light to the side end surface of the light guide plate.

According to such a configuration, the number of parts can be reduced, and the cost of the apparatus can be reduced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a light transmission type liquid crystal display device will be described as an example.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS.

The liquid crystal display device 1 of the first embodiment has a diagonal
It is capable of performing color display with an inch size and a wide effective display area having an aspect ratio of 16: 9. As shown in FIG. 1, a liquid crystal panel 100 and a metal sandwiching the liquid crystal panel 100 are provided. Bezel 500, a resin frame 600 including a surface light source unit, and a circuit board (PCB) 80 disposed on the back surface of the frame 600.
And a flexible circuit board TCP 900 for electrically connecting the PCB 800 and the liquid crystal panel 100.

The liquid crystal panels 100 are mutually sealed.
1 and an array substrate 110 and a counter substrate 2
10, a twisted nematic (TN) type liquid crystal layer 300 is held between a pair of transparent substrates 110 and 210 via a pair of transparent substrates 311 and 313, respectively.

Although not shown, the array substrate 110 has a plurality of scanning lines and signal lines arranged in a matrix on a glass substrate, and a thin film transistor (TFT) is disposed near each intersection between the scanning lines and the signal lines. ITO (Indium Ti
n Oxide).
The TFT includes a gate electrode electrically connected to the scanning line,
A gate insulating film disposed thereon, a semiconductor film of hydrogenated amorphous silicon (a-Si: H) thereon, and a drain integrally formed with the signal line and electrically connected to the semiconductor film Electrodes, a source electrode for electrically connecting the pixel electrode and the semiconductor film, and doped hydrogenated amorphous silicon (n ⁺ -type a-Si) disposed between the source and drain electrodes and the semiconductor film, respectively. H) membrane.

The counter substrate 210 is formed on a glass substrate by forming a matrix-shaped light-shielding film for shielding a gap between a scanning line or a signal line and a pixel electrode, a TFT, and a matrix-shaped light-shielding film. A color filter layer including red, green, and blue color filters is disposed in the region, and a counter electrode made of ITO is disposed to cover the light-shielding film and the color filter layer.

The surface light source unit includes a light guide plate 701 made of an acrylic resin housed in a frame 600 and, as shown in FIG.
The light guide plate 701 includes a U-shaped tubular light source 711 having a diameter of 2.5 mm arranged along a pair of long sides 701a and 701b and a short side 701c.

On the back side of the light guide plate 701, the light guide plate 701
A diffusion groove 703 for selectively diffusing the light source light propagating through the inside and emitting the light is formed.
It is formed so that its density increases as it goes away from 1, thereby achieving uniform luminance. Instead of the diffusion groove 703, a projection may be formed or a diffusion pattern may be printed.

On the light exit side (the liquid crystal panel side, in this specification, this direction is described as the upper side) of such a light guide plate 701, a diffusion sheet 751 slightly larger than the effective exit area, And a lens sheet 755 for providing directivity. These optical sheets may be appropriately changed depending on the purpose of use of the surface light source device and the like.

A reflection sheet 721 is provided on the back side of the light guide plate 701 in order to prevent light leakage from the light guide plate 701 to the back side and to effectively use light from the tubular light source.
Is arranged.

The reflection sheet 721 has a reflectance of 9 made of a polycarbonate film in order from the light guide plate 701 side.
7% of insulating reflective film 723 and aluminum (A
1) and an insulating film 727 made of polyethylene terephthalate (PET) are laminated. These insulating reflective films 72
3. The thicknesses of the conductive film 725 and the insulating film 727 are 0.19 mm, 0.1 mm, and 0.05 mm, respectively.

The reflection sheet 721 covers the U-shaped tubular light source 711 disposed along the three sides of the light guide plate 701 so as to cover the U-shaped tubular light source 711 from the lower side (the back side of the light guide plate 701), the outer peripheral side, and the upper side. Three sides 701a, 701b, 701 of light guide plate 701
It is bent and arranged along c. In this example,
Although not shown, a dot-shaped cutout is provided along a predetermined bending line to facilitate bending of the reflection sheet 721. Further, in order to further facilitate bending, two corner portions of the reflection sheet 721 are cut out corresponding to the locations where the tubular light source 711 bends along the corners of the light guide plate 701.

If the conductive film 725 has a uniform specular reflection characteristic, the insulating film 723 is not provided with a separate insulating reflection film 723, or the insulating film 723 is formed in consideration of a leak current between the light source 711 and the tubular light source 711. Alternatively, a transparent insulating sheet can be provided. Further, the conductive film 725 may be made of copper (Cu) or the like in addition to aluminum (Al).

In this embodiment, the reflection sheet 721 includes
The insulating film 72 is exposed so as to partially expose the conductive film.
A window 728 from which 7 has been removed is provided. A connection wiring 729 extending from the window 728 to the PCB 800 is arranged.
25 and the ground wiring 810 on the PCB 800 are electrically connected.

Further, the tubular light source 711 is provided with a ring-shaped gap member 713 made of transparent insulating resin.
The three sides 701a, 701b, and 701c are arranged and fitted in each region of the tubular light source 711. Thereby, the shape of the reflection sheet 721 is made uniform, and the occurrence of variations in luminance among products of the liquid crystal display device is suppressed. In addition, this ensures the insulation between the tubular light source 711 and the reflection sheet 721.

According to this embodiment, as described above, the reflecting sheet 721 is disposed so as to cover the tubular light source 711 from the lower side, the outer peripheral side, and the upper side, thereby having the function of the lamp reflector. . Therefore, the number of parts can be reduced.

Moreover, the tubular light source 711 is covered by the reflection sheet 721 including the conductive film 725, and
Since the conductive film is maintained at a predetermined potential, electromagnetic noise from the tubular light source is generated by the liquid crystal panel 100 or the PCB 80.
There is no adverse effect such as 0 on surrounding circuits.

Further, the reflection sheet 721 is used for the light guide plate 70.
Since the first effective region is not covered, the light use efficiency is not reduced.

In the above-described embodiment, the substantially U-shaped tubular light source 711 corresponding to the two long sides and one short side of the light guide plate 701 is used. The light guide plate 701 may have a linear shape corresponding to any one of the long sides, a substantially L-shaped shape corresponding to one long side and one short side of the light guide plate 701, or surround the light guide plate 701 from all around. It may be in the shape of a mouth.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIGS.

The liquid crystal display device 2 of the second embodiment has the same configuration as that of the first embodiment, except for the following points.

As shown in FIG. 3, the reflection sheet 721 is
In a substantially horizontal flange portion (hereinafter, referred to as an A region) that covers the tubular light source 711 from above, and a substantially vertical portion (hereinafter, referred to as a B region) that covers the tubular light source 711 from the outer peripheral side,
It does not include the conductive film 725 and the insulating film 727. That is, the reflection sheet 721 is a single-layer film including only the insulating reflection film 723 in the region A and the region B.

The light guide plate 7 below the tubular light source 711
A portion continuing from 01 (hereinafter, referred to as a C region) and a B region are substantially perpendicular to each other.

This configuration is particularly effective when the distance between the tubular light source 711 composed of a fluorescent tube and the reflection sheet 721 cannot be sufficiently set, and the tubular film light source 711 and the conductive film 725 of the reflection sheet 721 can be combined with each other. This is for suppressing a leak current caused by a floating capacitance formed between the two.

The leakage current will be described with reference to the schematic circuit diagram of the tubular light source shown in FIG.

The tubular light source 711 of the embodiment is a fluorescent tube such as a cold cathode tube, and uses a high-frequency alternating current as a power source. A current from a DC power supply that drives the liquid crystal display device 100 is converted into a high-frequency AC current by an inverter transformer 910 and input to the tubular light source 711 through a capacitor 920 of a ballast (ballast). Capacitor 920
The input wiring 930 to which is not arranged is connected to the ground wiring 940 for the light source system.

Normally, a high-voltage current flows through the tubular light source 711 of the liquid crystal display device. Therefore, when the conductive film 725 is arranged close to the tubular light source 711, the tubular light source is placed in each of such closely arranged regions. The electric charges are accumulated on the inner surface of 711 to form a minute capacitor. The conductive film 72 extends over substantially the entire length of the tubular light source 711.
If 5 are arranged close to each other, a capacitor having a large stray capacitance C is formed as a whole. Here, since a high-frequency current is input to the tubular light source 711, the stray capacitance C causes a leakage current.

As for the leak current, the frequency of the alternating current naturally increases. However, particularly in a small liquid crystal display device such as a portable or vehicle-mounted type, the inverter transformer 910 is used.
It is difficult to reduce the oscillation frequency because the size cannot be increased. Therefore, if the stray capacitance C is large, the leakage current increases.

The stray capacitance C follows the basic formula for the capacitance of the capacitor, that is, capacitance C = (dielectric constant ε) × (capacitor area S) ÷ (distance d between electrodes). In the embodiment, the total electric capacity is reduced by reducing the area S. That is, by omitting the conductive films 725 in the A region and the B region, the capacitor area S is reduced accordingly.

As a first modification of this embodiment, the reflection sheet 721 is provided only in the region A by using the insulating reflection film 723.
Of a single layer film. Further, as a second modification of the present embodiment, the reflection sheet 721 is configured such that the insulating reflection film 7 is provided not only in the region A and the region B but also in the region C.
It is also possible to adopt a configuration of 23 single-layer films.

<Measurement of Leakage Current and the Like> The result of specifically measuring the magnitude of the leakage current and the like will be described below. Tables 1 and 2 collectively show measurement results performed on the liquid crystal display devices of the second embodiment, the first and second modified examples, and the liquid crystal display device of the first embodiment.

The model of the liquid crystal display device used for the measurement is as follows.
Toshiba Corporation's TFD58W03-MM (ES sample,
Diagonal 7 inches), and the model number of the surface light source device here is:
B / L1P. Here, the gap between the tubular light source 711 and the reflection sheet 721 is set to 0.5 by the gap member 713.
mm. That is, the inner diameter of the ring of the gap member 713 is 2.5 mm, which is the same as the outer shape of the tubular light source 711, and the outer diameter of the ring is 3.5mm. Reflective sheet 72
The structure of the three-layer film and the thickness of each film are as described in the first embodiment.

The electromagnetic noise prevention level in the measurement results of Tables 1 and 2 was subjectively determined based on observation of image display of the liquid crystal display device.

Table 1 below shows, as the inverter transformer 910, a BLC manufactured by Tokosha having an oscillation frequency of about 60 KHz.
It is a measurement result in the case of using 216 825TG-120 (rating 5W).

[0052]

[Table 1] As shown in Table 1, when the oscillation frequency was a high frequency of about 60 KHz, in the first embodiment and the first modified example, the leak current and the decrease in luminance due to this were remarkable. In the case of the second modified example, it was considered that the leak current was zero, but it was observed that the electromagnetic noise prevention level was slightly inferior. The second embodiment is more preferable than the other embodiments because there is little leakage current and a reduction in luminance due to this, and there is no concern about electromagnetic noise as in the case of the second modification.

Table 2 below shows the measurement results obtained when Harrison HIU-733 (rated at 7 W) having an oscillation frequency of 34.3 KHz was used as the inverter transformer 910.

[0054]

[Table 2] As shown in Table 1, when the oscillation frequency of the inverter transformer 910 was about 34 KHz, no leakage current was observed. In this case, the electromagnetic noise prevention level is
The first example was better than the others. Therefore, when the oscillation frequency is at this level or lower, the first embodiment is considered to be most preferable.

As described above, in each of the above-described embodiments and modified examples, the lamp reflector can be configured by simply bending the reflection sheet on the back surface of the light guide plate, so that the number of parts and the number of assembly steps can be reduced, and the apparatus can be reduced. Can be reduced.

In particular, according to the first embodiment, it is possible to sufficiently reduce the electromagnetic noise from the tubular light source to the liquid crystal panel, PCB and the like.

Further, according to the second embodiment, a power source for a tubular light source having a high oscillating frequency is used, and a bent portion of a reflection sheet which functions as a lamp reflector is provided.
Even in the case where the tubular light source is arranged in close proximity, it is possible to sufficiently suppress the reduction in luminance due to the leak current or the waste of power.

[0058]

According to the flat display device of the present invention, since it is not necessary to separately arrange a lamp reflector, the number of parts and the number of assembling steps can be reduced, and the cost of the device can be reduced.

In particular, according to the flat display device of claim 3,
Electromagnetic noise can be sufficiently reduced.

According to the flat display device of the fourth aspect,
It is possible to sufficiently suppress a leak current, a reduction in luminance and a waste of power due to the leakage current.

[Brief description of the drawings]

FIG. 1 is a schematic sectional perspective view of a liquid crystal display device according to a first embodiment.

FIG. 2 is a schematic perspective view of a light guide plate provided with a reflection sheet and a tubular light source according to the first embodiment.

FIG. 3 is a cross-sectional perspective view of a bent portion of a peripheral edge of a reflection sheet in the liquid crystal display device according to the second embodiment.

FIG. 4 is a schematic circuit diagram of a tubular light source system for explaining a leak current.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device 100 ... Liquid crystal panel 600 ... Bezel 701 ... Light guide plate 711 ... Tubular light source 721 ... Reflection sheet 725 ... Conductive film

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shuichi Matsumoto 50, Kamiyube, Yobe-ku, Himeji-shi, Hyogo Pref.

Claims (10)

[Claims] 1. A tubular light source having a side end face disposed close to the tubular light source, and propagating light from the tubular light source incident from the side end face in each section of the propagation path. A light guide plate that distributes outgoing light from the light and emits the light from the upper surface, and a reflective sheet that covers the lower surface of the light guide plate.In the edge light type surface light source device, the reflective sheet has a peripheral portion, A bent portion that covers the tubular light source from the lower side, the outer peripheral side, and the upper side, and the bent portion forms a light source reflector that reflects light from the tubular light source to the side end surface of the light guide plate. A surface light source device characterized by the above-mentioned. 2. The surface light source device according to claim 1, wherein the reflection sheet includes a conductive layer at least in a region covering a lower surface of the light guide plate. 3. The surface light source device according to claim 2, wherein the reflection sheet includes the conductive layer over substantially the entire surface including the bent portion. 4. The reflection sheet according to claim 2, wherein the reflection sheet is substantially composed of only a non-conductive layer in a region at the tip of the bent portion which covers the tubular light source from above. Surface light source device. 5. The reflective sheet comprises substantially only a non-conductive layer in a region covering the tubular light source from the upper side and the outer peripheral side, and includes a conductive layer in a region covering the tubular light source from the lower side. The surface light source device according to claim 4, wherein: 6. The surface light source device according to claim 1, wherein an insulating gap member is disposed between the reflection sheet and the tubular light source. 7. The surface light source device according to claim 2, wherein the conductive layer is sandwiched between a first insulating layer on a side of the light guide plate and a second insulating layer. 8. The surface light source device according to claim 7, wherein said first insulating layer includes a light reflecting layer. 9. A flat display device comprising a light-transmitting display panel and a surface light source device disposed below the display panel, wherein the surface light source device includes a tubular light source and the tubular light source. A light guide plate that emits the light source light to an upper surface while propagating light from a tubular light source incident from the side end surface, and a reflection sheet that covers a lower surface of the light guide plate The reflection sheet includes, at a peripheral edge thereof, a bent portion that covers the tubular light source from the lower side, the outer peripheral side, and the upper side, and the bent portion transmits light from the tubular light source to the light guide plate. A flat panel display device comprising a light source reflector for reflecting light to the side end surface. 10. The reflection sheet includes a conductive layer at least in a region covering a lower surface of the light guide plate, wherein the conductive layer is electrically connected to a ground conductor or a conductor set to a predetermined common potential. 10. The flat display device according to claim 9, wherein the display panel is held at a predetermined potential for driving the display panel.