JPH05297366A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce electric power consumption and to enhance brightness by forming antireflection films for relieving reflectivity respectively on the light transmission boundaries of a liquid crystal display plate, diffusion sheet and light transmission plate. CONSTITUTION:This liquid crystal display device is constituted by forming the antireflection films 21 to 23 for relieving the reflectivity on at least one of the light transmission boundaries of the front surface or rear surface of the liquid crystal display plate 10 which is disposed with transparent electrode plates on both the front and rear surfaces of a liquid crystal layer and is further laminated with a polarizing plate 10a, the front or light incident end face of the light transmission plate 11 and the front surface or rear surface of the diffusion sheet 14. The light form a light source 12 is diffused by the diffusion sheet 14 or diffusion plate via the light transmission plate 11 and the reflection sheet 13 or reflection plate and is projected to the rear surface of the liquid crystal display plate 10. The light reflectivity at the light transmission boundaries of the respective members 11, 13, 14 is relieved by the antireflection films 21 to 23 at this time, by which the light loss is decreased. The antireflection films 21 to 23 are formed by using a solvent soluble transparent fluororesin, etc., and are coated at prescribed film thicknesses.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-receiving type liquid crystal display device having back lighting, and more particularly to a high brightness liquid crystal display device.

[0002]

2. Description of the Related Art Generally, liquid crystal display devices having back lighting (back light system) are roughly classified into a direct type and a light guide type.

The direct type is a liquid crystal display panel 1 as shown in FIG.
A plurality of light sources 2 are provided behind the light source 2, a light adjusting film 3 and a diffuser plate 4 for equalizing the brightness are provided between the light source 2 and the liquid crystal display plate 1, and the light source 2 is provided behind the light source 2. The reflection plate 5 that effectively reflects the light from 2 to the diffusion plate 4 side is provided.

On the other hand, in the light guide system, as shown in FIG. 7, a diffusion film 7 is provided on the front surface of the light guide plate 6 (light guide) mainly made of polymethylmethacrylate (PMMA), and the rear surface of the light guide plate 6 is provided. The ink material 8 (TiO ₂ ) having a light scattering effect is applied to the back surface of the high-reflection film 9
And the light source 2 is covered with a reflector 2a.

Reference numeral 1a in the figure denotes a polarizing plate of the liquid crystal display plate 1.

[0006]

In the conventional backlight system, the direct type can realize high brightness, but uneven brightness occurs due to the lamp stripes of the light source 2 and the unit thickness of the liquid crystal display device is reduced. There are drawbacks such as becoming large. From this, in order to achieve uniform brightness,
Multiple (eg, four or more when using cold cathode lamps) light sources 2
Must be used, which results in high power consumption.

Further, in the light guide system, this system has a good luminance uniformity and can be made thin, but it is difficult to realize a back light compatible with high luminance as compared with the direct type system. It is difficult to achieve high brightness unless power is consumed.

In view of the above problems, it is an object of the present invention to provide a liquid crystal display device capable of realizing high brightness with low power consumption.

[0009]

The means for solving the problems according to claims 1 to 5 of the present invention are as shown in FIGS.
And the light guide plate 1 arranged in parallel behind the liquid crystal display plate 10.
1, a light source 12 arranged at both ends of the light guide plate 11, a reflection sheet 13 for reflecting the backward light from the light guide plate 11 to the liquid crystal display plate 10 side, and the brightness of the illumination surface over the entire surface. In the liquid crystal display device including the diffusion sheet 14 for uniformizing the front surface and the rear surface of the liquid crystal display plate 10, the front surface or the light incident end surface of the light guide plate 11, and the front surface or the rear surface of the diffusion sheet 14. , An antireflection film 21 for relaxing the reflectance on at least one light transmitting interface,
22, 23, and 24 are formed.

A means for solving the problems according to claims 6 to 8 of the present invention is, as shown in FIG. 4, a liquid crystal display plate 10 and the liquid crystal display plate 10.
A plurality of light sources 12 arranged at a predetermined distance behind the
A reflector 33 for reflecting the backward light from the light source 12 to the liquid crystal display panel 10 side, the light source 12 and the liquid crystal display panel 1
In a liquid crystal display device including a diffusion plate 34 that diffuses light between 0, at least one light transmission interface among the front surface or the rear surface of the liquid crystal display plate 10 and the front surface or the rear surface of the diffusion plate 34, Antireflection films 21 and 22 for relaxing the reflectance are formed.

According to a ninth aspect of the present invention, there is provided a means for solving the problems, wherein the antireflection films 21 to 24 according to the first or sixth aspects are:
A solvent-soluble transparent fluorine compound is used.

[0012]

In the means for solving the problems according to claims 1 to 9, the light from the light source 12 is guided by the light guide plate 11 and the reflection sheet 13.
Alternatively, after passing through the reflection plate 33, the light is diffused by the diffusion sheet 14 or the diffusion plate 34 and is irradiated to the rear surface of the liquid crystal display plate 10.

At this time, the antireflection films 21 to 24 alleviate the light reflectance at the light transmitting interfaces of the members 11, 13, 14, 33, 34 and reduce the light loss.

[0014]

【Example】

(First Embodiment) FIG. 1 is a schematic cross-sectional view of a light guide type liquid crystal display device according to the first embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of an essential part showing a light path in an antireflection film, and FIG. It is a figure which shows the relationship of the light incident angle and light transmittance in an interface.

As shown in the figure, the light guide type liquid crystal display device of this embodiment includes a liquid crystal display plate 10, a light guide plate 11 arranged in parallel behind the liquid crystal display plate 10, and both end portions of the light guide plate 11. A light source 12 disposed on the light guide plate, a reflection sheet 13 for reflecting the backward light from the light guide plate 11 toward the liquid crystal display panel 10, and a diffusion sheet 14 for uniformizing the brightness of the illumination surface over the entire surface. An antireflection film 21 for relaxing the reflectance at the interface on at least one of the front surface and the rear surface of the liquid crystal display panel 10, at least one of the front surface and the rear surface of the diffusion sheet 14 and the light incident end surface of the light guide plate 11. , 22, and 23 are formed respectively.

The liquid crystal display panel 10 is formed by disposing transparent electrode plates on both front and rear surfaces of a liquid crystal layer and further laminating polarizing plates 10a. The liquid crystal display panel 10 comprises a plurality of transparent picture element electrodes arranged in a grid pattern. The molecules in the layer are driven by rotating them around the light distribution axis.

As shown in FIG. 1, the light guide plate 11 is made of acrylic resin having a total light transmittance of 93% and a refractive index of n = 1.49, and has a length dimension of 205 mm and a width dimension of 155 mm.
It is formed in a flat plate shape with a thickness dimension of 6.0 mm.

The light source 12 has a power consumption of 5 W, for example.
A straight tube type hot cathode tube including a luminous body such as a driving filament and an outer tube covering the luminous body is used, and the diameter thereof is set to 4.1 mm and the tube surface brightness is set to 15000 nt. In FIG. 1, reference numeral 12 a is a light source reflector that reflects light from the light source 12 to the side opposite to the light guide plate 11 to the light guide plate 11 side.

As the reflection sheet 13, a resin sheet coated with a light scattering material 13a such as TiO ₂ is used, and is adhered to the rear surface of the light guide plate 11.

The diffusion sheet 14 is made of a milky white resin film.

The antireflection films 21, 22, and 23 are made of a solvent-soluble transparent fluorine resin or the like having a refractive index of 1.34, and are coated with a thin thickness of 2 μm.

Here, the transmittance with and without the antireflection films 21, 22, and 23 will be described using a diffusion sheet as an example.

First, in the prior art shown in FIG. 7, since a single layer film is formed on the diffusion sheet, the relationship between the incident angle θ1 when light enters the air from the diffusion sheet and the refraction angle θ2 is the same. When the refractive index of the film is 1.58 and the refractive index of air is 1.00, Snell's law gives the following.

Sin θ1 = (1 / 1.58) × sin θ2 (1) Further, in general, the light ray reflectance ρ at the interface between two media is expressed by the following equation (2).

[0025]

[Equation 1]

In the equation (2), the conventional light reflectance ρ ₀ may be calculated by substituting θ1 for θi and θ2 for θo and solving a simultaneous equation with the equation (1).

Next, the case of this embodiment shown in FIG. 1 will be considered.
Here, when the transparent fluorine resin 22 has a refractive index of 1.34, light enters the antireflection film 22 from the diffusion sheet at the interface between the diffusion sheet 14 and the antireflection film 22 as shown in FIG. The relationship of the expression (3) is established between the incident angle θ1 and the refraction angle θH.

Sin θ1 = (1.34 / 1.58) × sin θH (3) Further, θ1 is substituted for θi and θH is substituted for θo in the equation (2),
The light reflectance ρ _A at the interface between the diffusion sheet 14 and the antireflection film 22 is calculated by solving the simultaneous equation with the equation (3).

Next, the relationship of the equation (4) is established between the incident angle θH when light enters the air from the antireflection film 22 and the refraction angle θ2.

Sin θH = (1 / 1.34) × sin θ2 (4) Substituting θH for θi and θ2 for θo in the equation (2),
The light reflectance ρ _B at the interface between the antireflection film 22 and the air is calculated by solving a simultaneous equation with the equation (4).

Then, the total light transmittance T is determined by the equation (5).

T = (1-ρ _A ) · (1-ρ _B ) × 100 (5) When the relationship between this T and the final emission angle θ2 is illustrated,
It becomes like FIG. In the figure, A is the transmittance in this embodiment, and B is
Indicates the transmittance in the conventional example. As described above, the fluorocarbon resin coating can increase the incident angle range of light transmitted through the interface by about 3.3% as compared with the conventional one, and the transmittance of light at each incident angle is 25% as a whole. I was able to improve.

This applies not only to the antireflection film 22 on the diffusion sheet 14, but also to the antireflection film 21 formed on the liquid crystal display plate 10 and the antireflection film 23 formed on the light incident end face of the light guide plate 11. Is.

As described above, the antireflection treatments 21 to 23 can reduce the reflection loss at the interface between the members 10, 11, and 14 and increase the transmittance of the light from the light source 12.
To that extent, the light utilization efficiency can be improved. Therefore, it is possible to realize a liquid crystal display device with the same low power consumption and high brightness as the conventional one.

(Second Embodiment) FIG. 4 is a schematic sectional view of a direct type liquid crystal display device according to the second embodiment of the present invention. As shown in the figure, the direct type liquid crystal display device according to the present embodiment includes a liquid crystal display panel 10.
And two light sources 12 arranged behind the liquid crystal display panel 10.
An aluminum reflector 33 for reflecting the backward light from the light source 12 toward the liquid crystal display panel 10, and the light source 1
2 and the liquid crystal display panel 10 diffuses the light between the diffusion plate 34
And the antireflection films 21 and 22 for relaxing the reflectance at the interface are formed on the rear surface of the liquid crystal display plate 10 and the front or rear surface of the diffusion plate 34, respectively. Note that reference numeral 35 in the figure denotes a light amount adjuster that limits the local brightness due to the direct light from the light source 12.

It goes without saying that the same effects as those of the first embodiment can be obtained in this embodiment as well.

(Third Embodiment) FIG. 5 is a schematic sectional view of a light guide type liquid crystal display device according to a third embodiment of the present invention. As shown in the figure, in the liquid crystal display device of this embodiment, an antireflection film 24 made of a solvent-soluble transparent fluorine resin having a thickness of 0.1 μm is formed on the front surface of the light guide plate 11. Also, in the figure, 21,2
Reference numerals 2 and 23 are the same antireflection film 24 as described in the first embodiment, but the thickness thereof is set to 0.1 μm here in order to increase the light transmittance. Other configurations are similar to those of the first embodiment.

In the above structure, the light entering from the light incident end surface of the light guide plate 11 strikes the front and rear surfaces in the light guide plate 11 and is totally reflected.

Of these, a part of the light applied to the front surface of the light guide plate 11 is emitted to the front. By providing the antireflection film 24, the light transmitted through the light transmitting interface is incident as shown in FIG. Since the angular range can be increased by about 3.3% as compared with the conventional case, the light radiated at an angle close to the critical angle to the front surface of the light guide plate 11 can be transmitted forward. Here, in the light guide system, since the light source 12 is generally arranged on the side of the light guide plate 11, most of the light inside the light guide plate 11 is inside the light guide plate 11 at an angle close to the critical angle with respect to the front surface. It will proceed. Therefore, most of the light traveling inside can be emitted from the front surface, and the amount of light can be significantly improved by the antireflection film 24.

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, as the antireflection films 21 to 24, the refractive index thereof is 1.34 in the above embodiment, but other than this, for example, MgF ₂ having a refractive index of 1.38 may be used. The film thickness is 2 μm or 0.
It is not limited to 1 μm.

Further, in the above embodiment, each antireflection film 2 is provided.
Although any two or more of 1 to 24 are combined, only one of them may be formed.

[0043]

As is apparent from the above description, according to claims 1 to 9 of the present invention, the reflection loss at the light transmitting interface of each member is reduced by the antireflection treatment, and the transmittance of the light from the light source is reduced. Therefore, regardless of whether it is a direct type or a light guide type, it is possible to realize a high-brightness liquid crystal display device with the same low power consumption as the conventional one.

In particular, the antireflection film can widen the incident angle range of light transmitted through the light transmitting interface as compared with the conventional case. Therefore, most of the light that has entered the light guide plate from the light incident end surface is emitted at an angle close to the critical angle, so most of this light can be transmitted forward, and a significant increase in brightness can be achieved. When you get it, it has a great effect.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a light guide type liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of an essential part showing the path of light through an antireflection film.

FIG. 3 is a diagram showing a relationship between a light incident angle and a light transmittance at an interface.

FIG. 4 is a schematic sectional view of a direct type liquid crystal display device according to a second embodiment of the present invention.

FIG. 5 is a schematic sectional view of a light guide type liquid crystal display device according to a third embodiment of the present invention.

FIG. 6 is a cross-sectional view of a conventional direct type liquid crystal display device.

FIG. 7 is a sectional view of a conventional light guide type liquid crystal display device.

[Explanation of symbols]

 10 liquid crystal display plate 11 light guide plate 12 light source 13 reflection sheet 14 diffusion sheets 21 to 24 antireflection film 33 reflection plate 34 diffusion plate

Claims (9)

[Claims] 1. A liquid crystal display plate, a light guide plate arranged in parallel behind the liquid crystal display plate, light sources arranged at both ends of the light guide plate, and a rear light on the light guide plate for liquid crystal display. At least one of the liquid crystal display plate, the light guide plate, and the diffusion sheet in a liquid crystal display device including a reflection sheet for reflecting the light toward the plate side and a diffusion sheet for making the brightness of the illumination surface uniform over the entire surface. A liquid crystal display device, wherein an antireflection film for reducing the reflectance is formed on one light transmitting interface. 2. A liquid crystal display device, wherein the antireflection film according to claim 1 is formed on at least one of a front surface and a rear surface of a liquid crystal display plate. 3. The liquid crystal display device according to claim 1, wherein the antireflection film is formed on at least one of a front surface and a rear surface of the diffusion sheet. 4. A liquid crystal display device, wherein the antireflection film according to claim 1 is formed on a light incident end surface of a light guide plate. 5. A liquid crystal display device, wherein the antireflection film according to claim 1 is formed on a front surface of a light guide plate. 6. A liquid crystal display plate, a plurality of light sources arranged behind the liquid crystal display plate with a predetermined interval, and a reflection plate for reflecting backward light from the light sources to the liquid crystal display plate side. In a liquid crystal display device including a diffuser plate that diffuses light between the light source and the liquid crystal display plate, an antireflection film for relaxing a reflectance at a light transmission interface of at least one of the liquid crystal display plate and the diffuser plate. A liquid crystal display device, wherein a liquid crystal display device is formed. 7. A liquid crystal display device, wherein the antireflection film according to claim 6 is formed on at least one of a front surface and a rear surface of a liquid crystal display plate. 8. A liquid crystal display device, wherein the antireflection film according to claim 6 is formed on at least one of a front surface and a rear surface of a diffusion plate. 9. A liquid crystal display device, wherein the antireflection film according to claim 1 or 6 uses a solvent-soluble transparent fluorine compound.