JPH1152372A - Surface light source device and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve luminance by providing the uppermost part of a surface light source device with a polarizing sheet, thereby making it possible to approximately completely utilizing the light from a surface light source part. SOLUTION: The polarizing sheet 34 which allows the transmission of the light made substantially linearly polarized light approximately aligned to the transmission axis of the polarizing sheet 34, i.e., an optical sheet among light rays transmitting a lens sheet 32, and reflects the other light is disposed atop a lens sheet 32. The diffused light 42 made incident on the polarizing sheet 34 is transmitted as the substantially linearly polarized light by the effect of the sheet 34 and is transmitted as it its through the polarizing plate 18. The light of the component exclusive of the linearly polarized light 44 is reflected by the effect of the sheet 34 and is made incident on a light transmission plate 2, is diffused by the effect of scattering pattern dots 26 or diffusion sheet 30 and is emitted again as the diffused light 46, which is then made incident on the sheet 34. The exit light from the light transmission plate 20 is eventually efficiently utilized by repeating the same, by which the exit light is approximately completely utilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a surface light source device such as a backlight and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art A recent liquid crystal display device is required to have low power consumption. For this purpose, it is effective to reduce the power consumption of a backlight, which occupies a large part of the power consumption of the liquid crystal display device.

By the way, since the liquid crystal cell has polarizing plates on its upper and lower surfaces, half of the light emitted from the backlight is necessarily absorbed by the polarizing plate. Therefore, there is a problem that the light utilization rate of the backlight is poor.

For this reason, only a certain polarization component is transmitted,
A liquid crystal display device using a polarizing sheet that reflects other polarized components has been proposed (JP-A-8-146416).
No., JP-A-9-146092).

In these liquid crystal display devices, as shown in FIG. 7, a line light source 104 is disposed on a side surface of a light guide plate 102, and a light guide plate 10 is provided.
2, a reflection plate 106 and the like are provided on the lower surface. Further, the above-described polarizing sheet 108 is disposed on the upper surface of the light guide plate 102, and the diffusion sheet 110 is disposed thereon. A liquid crystal cell (not shown) is provided on the backlight 100.

Accordingly, there is an effect that the brightness of the backlight 100 can be increased by effectively using the light emitted from the light guide plate 102 by the polarizing sheet 108.

[0007]

However, the polarizing sheet 108 is disposed on the upper surface of the light guide plate 102 as described above,
Further, even in the method of disposing the diffusion sheet 110 thereon, the light utilization rate is slightly improved as compared with the conventional method, and the light emitted from the light guide plate 102 cannot be completely utilized.

Accordingly, the present invention provides a surface light source device capable of almost completely utilizing light emitted from a light guide plate, and a liquid crystal display device using the same.

[0009]

According to the present invention, there is provided a surface light source unit,
A diffusion plate disposed on the surface light source unit and diffusing light source light from the surface light source unit, and an optical sheet disposed on the diffusion plate and transmitting a predetermined component of the light source light and reflecting the other component. It is provided with.

The present invention will be described.

[0011] Of the light emitted from the surface light source section such as the light guide plate or the lamp house, the light having the component that is coincident with the polarization transmission axis of the optical sheet is transmitted by the action of the optical sheet, and the other light components are reflected. The light enters the surface light source again. This incident light is reflected by the surface light source unit and emitted again.

By repeating this, all the emitted light passes through the optical sheet. At this time, by arranging the transmission axis of the optical sheet so as to match the transmission axis of the polarizing plate of the liquid crystal cell, the light emitted from the surface light source device can efficiently contribute to the liquid crystal image device.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG.

FIG. 1 shows a liquid crystal display device 10 according to this embodiment.
FIG.

The liquid crystal display device 10 comprises a liquid crystal cell 12 and a backlight 14 arranged on the lower surface thereof.

On the upper and lower surfaces of the liquid crystal cell 12, polarizing plates 16 and 18 are provided.

The backlight 14 is provided with a fluorescent lamp 22 as a linear light source on one side surface of a transparent flat light guide plate 20. In order to effectively use the light of the fluorescent lamp 22,
A lamp reflecting mirror 24 is provided on the outer peripheral surface of the fluorescent lamp 22.

On the lower surface of the light guide plate 20, scattering pattern dots 26 for uniformly scattering the light emitted from the fluorescent lamp 22 are scattered, and a reflection sheet 28 for reflecting the light is disposed on the lower surface. ing.

On the upper surface of the light guide plate 20, a diffusion sheet 30 for uniformly diffusing light is provided. This eliminates uneven brightness of the surface light source. On an upper surface of the diffusion sheet 30, a lens sheet 32 for condensing light in a vertical direction of a light emitting surface (upper surface) of the light guide plate 20 for improving front luminance is arranged.

On the upper surface of the lens sheet 32, of the light transmitted through the lens sheet, substantially linearly polarized light substantially coincident with the transmission axis of the polarizing sheet, which is an optical sheet, is transmitted. A polarizing sheet 34 that reflects light is provided.

The fluorescent lamp 22 comprises a bar-type hot cathode tube lamp or a cold cathode tube lamp. The light guide plate 20 is formed of a transparent resin plate or a transparent glass plate having a high light transmittance, such as acrylic resin, polycarbonate, AS, or PET.
The diffusion sheet 30 is made of a plate made of translucent polycarbonate having a high transmittance, or a plate obtained by stacking a plurality of layers of this plate. The scattering pattern dots 26 are formed by scattered points such as flaws, embossing, and screen printing.
Further, the reflection sheet 28 thereunder is made of white polyester or a polyester film in which a silver vapor-deposited film is adhered to the inner surface of the polyester film.

Next, the polarizing sheet 34 will be described.

As described above, the polarizing sheet 34 transmits substantially only linearly polarized light and reflects other components. However, the following three types of polarizing sheets 32 are currently known. Although any of them can be used in the present invention, the second and third polarizing sheets are particularly useful.

In the first polarizing sheet, a multilayer interference layer is formed between sheets having a mountain-shaped cross section having a vertex angle of 90 °, which is covered with a separate sheet and flattened into a plate shape ( JP-A-6-508449).

The second polarizing sheet is a quarter of a polarizing separator having two or more cholesteric liquid crystal layers having different central wavelengths of selective reflection and a superimposed body of two or more retardation films having different phase differences. A polarizing plate comprising a laminate with a wavelength plate, a polarizing plate containing a dichroic dye on the quarter-wave plate side thereof, and a laminate further comprising a laminated plate (Japanese Patent Application Laid-Open No. 8-271732).

The third polarizing sheet is obtained by laminating a plurality of sheets having different refractive indexes (WO95 / 17691, WO95 / 17691).
WO 95/17692).

Each of the three polarizing sheets is formed of a thin film,
It separates the incident light beam into one component passing through the polarizing sheet 32 and the reflected light component.

The backlight 14 having the above-described structure includes:
When the liquid crystal cell 12 is arranged as shown in FIG. 1, a gap 36 of about 1 mm is provided between the lower surface of the liquid crystal cell 12 and the upper surface of the backlight 14. The space 36 is formed when the liquid crystal cell 12 and the backlight 14 are housed in a frame.

The reason why such a gap 36 is provided is that the coefficient of thermal expansion of the polarizing sheet 34 is different from the coefficients of thermal expansion of the other light guide plates 20, the diffusion sheet 30 and the lens sheet 32, and that the polarizing sheet 34 is polarized on the lens sheet 32. This is because a phenomenon in which the sheet 34 warps on the lens sheet 32 due to a temperature change may occur. This is because the polarizing sheet 34 is formed by laminating a plurality of materials.

Therefore, a gap 36 is provided so that even if such a warping phenomenon occurs, it can be absorbed.

The transmission axis of the polarizing sheet 34 and the polarizing plate 1
8 and the transmission axis are matched.

The function of light of the liquid crystal display device 10 will be described with reference to FIG.

In FIG. 2, the left side of the dotted line is the conventional example, and the right side is the structure of the present embodiment.

First, a conventional example will be described.

The diffused light 3 emitted from the lens sheet 32
8 enters the polarizing plate 18 of the liquid crystal cell 12 and
, The linearly polarized light 40 of 50% of the diffused light 38
Contribute to the display of the liquid crystal.

Next, this embodiment will be described.

The diffused light 42 incident on the polarizing sheet 34 is
By the action of the polarizing sheet 34, the substantially linearly polarized light 44
And the light passes through the polarizing plate 18 as it is.

Here, the reason why the linearly polarized light is substantially used is that elliptically polarized light close to linearly polarized light is included due to the configuration of the polarizing sheet.

Light of components other than the linearly polarized light 44 is reflected by the action of the polarizing sheet 34, enters the light guide plate 20, is diffused by the action of the scattering pattern dots 26 and the diffusion sheet 30, and is emitted again as diffused light 46. Polarizing sheet 34
Incident on. By repeating this, the light emitted from the light guide plate 20 is efficiently used, and is almost completely used.

The graph of FIG. 3 shows the rate of increase in the brightness of the liquid crystal screen depending on the order of lamination of the sheets used for the backlight 14.

The uppermost row is that of the present embodiment, and the diffusion sheet 30, the lens sheet 32, and the
The polarizing sheet 34 is provided. In the second stage, the diffusion sheet 30, the polarizing sheet 34, and the lens sheet 32 are arranged in this order. The third stage is a lens sheet 32,
In this example, a diffusion sheet 30 and a polarizing sheet 34 are provided.
In the fourth row, the polarizing sheet 34, the diffusion sheet 30, and the lens sheet 32 are arranged in this order. In the fifth stage, the diffusion sheet 30 and the lens sheet 32 are arranged as in the related art without using the polarizing sheet 34.

Here, the polarizing sheet is DBEF manufactured by 3M Company.
(Trade name) and the lens sheet is 3M BEF
90HP (trade name) was used, and PCM1 (trade name) of Tsujimoto Electric Co., Ltd. was used as a diffusion sheet.

As is apparent from FIG. 3, when the luminance using only the lens sheet 32 and the diffusion sheet 30 is set to 1, the maximum value in this embodiment is 1.6 times, and the polarizing sheet is used. If you put 34 in the middle, 1.3 times,
When the order of the lens sheet 32, the diffusion sheet 30, and the polarizing sheet 34 is the order, the magnification is 1.2 times, and when the polarizing sheet 34 is placed at the bottom, the magnification is 1.1 times.

That is, as in the present embodiment, the diffusion sheet 3
Light is efficiently used by using 0, the lens sheet 32, and the polarizing sheet 34 in this order. This is because, by using the polarizing sheet 34 at the top, the polarized light is disturbed when the light transmitted through the polarizing sheet 34 passes through the lens sheet 32 or the diffusion sheet 30 as compared with the case where the polarizing sheet 34 is disposed in other places. This prevents the polarizing plate 18
Is not efficiently transmitted.

The positional relationship between the lens sheet and the polarizing sheet can be polarized if the disturbance of the polarization component can be sufficiently suppressed.

(Second Embodiment) FIG. 4 shows a liquid crystal display 1
0 is a second example.

The difference between the present embodiment and the first embodiment is that no gap 36 is provided between the liquid crystal cell 12 and the backlight 14, and an anti-sticking sheet 50 is provided instead.

By providing the sticking prevention sheet 50, the polarizing plate 18 and the polarizing sheet 34 do not stick to each other, and display trouble does not occur.

(Third Embodiment) FIG. 5 shows a liquid crystal display device 10 according to a third embodiment.

The difference between this embodiment and the first embodiment is that
Instead of the air gap 36 between the liquid crystal cell 12 and the backlight 14, the lower surface of the
2 are provided. When an anti-glare polarizing plate (trade name) manufactured by Nitto Denko is used as the polarizing plate 18 as an example of the height difference of the unevenness 52, the thickness is 6 μm.

By providing the irregularities 52 as described above,
Adhesion between the polarizing sheet 34 and the polarizing plate 18 can be prevented, and display problems do not occur.

(Fourth Embodiment) FIG. 6 shows a liquid crystal display device 10 according to a fourth embodiment.

The difference between the present embodiment and the first embodiment is that the light guide plate 20 is not a simple flat plate but has a wedge-shaped cross section as shown in FIG.

(Modification) In the above-described first to fourth embodiments, the light guide plate 20 is used. However, instead of this, a surface using a light source in a parallel hexahedral lamp house is used. A light source may be used.

[0055]

As described above, according to the surface light source device of the present invention, the light from the surface light source unit can be used almost completely by providing the polarizing sheet on the top of the surface light source device.

Therefore, a liquid crystal display device using the same can increase the luminance as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is an explanatory view showing an action of light.

FIG. 3 is a graph showing a rate of increase in the luminance of a liquid crystal screen according to the order of the configuration of sheets used for a backlight.

FIG. 4 is a liquid crystal display device according to a second embodiment.

FIG. 5 is a liquid crystal display device according to a third embodiment.

FIG. 6 shows a liquid crystal display device according to a fifth embodiment.

FIG. 7 is a liquid crystal display device according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 12 Liquid crystal cell 14 Backlight 16 Polarizer 18 Polarizer 20 Light guide plate 22 Fluorescent lamp 24 Lamp reflector 26 Scattering pattern dot 28 Reflection sheet 30 Diffusion sheet 32 Lens sheet 34 Polarization sheet 36 Gap 50 Adhesion prevention sheet 52 Unevenness

Claims (7)

[Claims] A surface light source unit; a diffusion plate disposed on the surface light source unit for diffusing light source light from the surface light source unit; and a light of a predetermined component of the light source light disposed on the diffusion plate. An optical sheet that transmits light and reflects others. 2. The surface light source device according to claim 1, further comprising a lens sheet disposed between said diffusion plate and said optical sheet, for adjusting a light flux of said light source light. 3. The surface light source unit comprises an optically transparent flat plate or a light guide plate having a wedge-shaped longitudinal section, and a light source disposed on one side of the light guide plate. 2. The surface light source device according to 1. 4. The surface light source device according to claim 1, wherein the surface light source unit comprises a flat parallel hexahedral lamp house and a light source disposed inside the lamp house. 5. A liquid crystal display device comprising a surface light source device according to claim 1, 2, 3 or 4, wherein a liquid crystal cell is provided with a predetermined gap provided on an upper surface thereof. 6. A liquid crystal display device comprising a surface light source device according to claim 1, 2, 3 or 4, wherein an adhesion preventing sheet is disposed between the upper surface of the surface light source device and the liquid crystal cell. 7. The surface light source device according to claim 1, wherein irregularities are provided on the lower surface side of the polarizing plate disposed in the lowermost layer of the liquid crystal cell, and the lower surface of the polarizing plate is provided. A liquid crystal display device comprising: