JPH08160203A - Picture quality improving film for liquid crystal display - Google Patents

Abstract

PURPOSE: To attain bright, easily visible and excellent picture feeling by arranging such a picture quality improving film between a liquid crystal display element and a prism sheet, that consists essentially of a colorless, transparent plastic, and controlling its full light transmissivity to a specific value and diffusion half value angle of vertical incident light to the range of a specific angle. CONSTITUTION: The picture quality improving film 21 is arranged between a liquid crystal display element 11 and a prism sheet 18 and consists eassentially of the colorless, transparent plastic. The full light transmissivity in the picture qunality improving film 21 is >=80% and the diffusion half value angle of the vertical incident light is 5-15 deg.. When the full light transmissivity is under 80 deg., light utilization efficiency is decreased. And the diffusion half value and in diffusing power is preferably 8-20 deg., in the case of being under 5 deg., light emission is not converted into a desired state and the picture feeling is not improved and in the case of exceeding 15 deg., the quantity of light is decreased. And the purpose is attained by inserting the picture improving film 21 between the prism sheet 18 and the liquid crystal display element 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image quality improving film for a liquid crystal display device which improves the image quality of the liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display element that constitutes a liquid crystal display device such as a personal computer or a small word processor is
Since it does not have a self-luminous property, a planar light source device is used as its back light source in order to meet the demand for improved visibility.

At the beginning of development, the planar light source device had a structure (direct type) in which a light source such as a fluorescent lamp was arranged directly on the back surface of a liquid crystal display element. On the other hand, in recent years, in order to reduce the thickness of the entire liquid crystal display device and reduce the size of the structure, a light guide plate is used as a planar light source device, and a structure called an edge light system in which a fluorescent lamp is arranged on at least one end surface thereof is used. Is often taken.

FIG. 1 is a schematic diagram showing the basic structure of an edge light type planar light source device. In FIG. 1, 1 is a liquid crystal display element and 2 is a planar light source device. In the planar light source device 2, the fluorescent lamp 3 as the linear light source is provided with the light guide plate 4.
It is provided by the side of. A dot-printed paint (light-scattering ink) 5 is provided on the back surface of the light guide plate 4, a reflection plate 6 is provided on the back surface of the light guide plate 4, and a light diffusion sheet 7 is provided on the front surface of the light guide plate 4. Has been.

A light beam emitted from the fluorescent lamp 3 enters inside from the end surface of the light guide plate 4, and paint 5 on the back surface of the light guide plate 4.
Is diffusely reflected by and is emitted from the surface of the light guide plate 4.
The paint 5 is a printed pattern of a light-scattering ink for causing the light entering the light guide plate 4 from the fluorescent lamp 3 to be uniformly emitted from any position on the surface of the light guide plate 4, and can also be called a pseudo light source. However, as it is, the brightness required for the liquid crystal display device is not sufficient, and the printed pattern of the paint 5 on the back surface of the light guide plate 4 is visually recognized from the front surface of the liquid crystal display element 1. Therefore, the light diffusion sheet 7 enables uniform light emission without observing the pseudo light source on the back surface, that is, the above-mentioned coating pattern of the paint 5 through the liquid crystal display element 1 when observing the screen of the liquid crystal display device. It works.

In the edge light type planar light source device as described above, in order to increase the amount of light emission toward the observer, a prism sheet (light collecting sheet) is provided between the liquid crystal display element 1 and the light diffusing sheet 7. 8) is provided. As described in JP-A-62-144102, JP-A-2-93401 and JP-A-2-257188, the prism sheet 8 is provided with a concavo-convex shape on one side of a transparent plastic sheet, The light is condensed in an arbitrary direction by the prism effect.

[0007]

The prism sheet 8 is
Although it has the function of significantly increasing the amount of light emitted in the direction of the observer, the sharp prism shape is used, so the more the light emission is concentrated in the direction of the observer, the less the light emission in the other direction decreases. As shown in FIG. 2, there is a direction in which no light is emitted. When a planar light source device having such a light emission characteristic is mounted on a liquid crystal display device, even if the relative position of the observer moves even slightly, there will be a situation where a bright part and an extremely dark part exist at the same time in the screen. Will not be able to withstand. Therefore, the user is forced to use the positional relationship without changing the positional relationship as much as possible, which causes a problem of fatigue of the user.

In order to solve this problem, a light diffusing member based on a conventionally supported technique is arranged between the liquid crystal display element 1 and the prism sheet 8 to avoid the extreme concentration of light emitting directions as described above. However, as a result that the light emission amount in the main viewing direction is significantly reduced, the original light collecting function of the prism sheet 8 is impaired, and overall image quality is not improved.

An object of the present invention is to realize a liquid crystal display device which changes the light emission state of a prism sheet, is bright, is easy to see, and has a good image quality without fatigue.

[0010]

The present invention according to claim 1 is configured by providing a planar light source device on a back surface of a liquid crystal display element, and the planar light source device includes a light guide plate and a side portion of the light guide plate. A linear light source provided in, and a light diffusion sheet provided on the front surface of the light guide plate,
An image quality improving film for a liquid crystal display device, comprising a prism sheet provided on the front surface of a light diffusion sheet, wherein the image quality improving film is disposed between the liquid crystal display element and the prism sheet and is a colorless transparent plastic. As the main component, the total light transmittance is 80% or more, and the half-value angle of diffusion of vertically incident light is 5 to 15 degrees.

According to a second aspect of the present invention, in addition to the first aspect of the present invention, at least one surface of the image quality improving film has a surface shape of fine irregular disordered shape. .

[0012]

In solving the above-mentioned problems, as a result of examining the light emission state that the observer perceives as a good image quality and the light diffusing ability of the light diffusing member that has been conventionally used, the observer finds that I feel uncomfortable with the sudden drop.
The observer feels uncomfortable when there is no light emission and the display is invisible. Conventional light diffusing members aim to diffuse light uniformly in all angular directions.
It is concluded that the conventional light diffusing member allows the loss of light for the purpose. Therefore, if a conventional light diffusing member is added in an attempt to improve the above, the light emission range concentrated by the prism sheet will be converted into diffused light again, and the light reaching the observer will be significantly reduced. The light utilization efficiency itself will also decrease. Therefore, the present invention has conducted a study for an optical functional film that significantly improves the image quality without deteriorating the light concentration function of the prism sheet. We have found that it is possible. That is, "An image quality improving film, which is composed mainly of colorless and transparent plastic, has a total light transmittance of 80% or more and a diffusion incident half-value angle of vertically incident light of 5 to 15 degrees, is used for liquid crystal display elements and prism sheets. It should be placed between and. "

The image quality improving film of the present invention contains a colorless and transparent plastic as a main component, and as the plastic, for example, polymethylmethacrylate, polycarbonate, polyvinyl chloride, polyvinyl alcohol, polyester can be adopted.

The total light transmittance of this image quality improving film is 80.
% Or more, and the half-value angle of divergence of vertically incident light is 5 degrees ~
It must be 15 degrees. When the total light transmittance is less than 80%, the light utilization efficiency is lowered, and it is preferably 90% or more. With respect to the diffusing ability, if the half-value angle of divergence of a vertically incident light beam is less than 5 degrees, the desired light emission state is not converted, and the image quality is not improved. Above 15 degrees,
The concentration of light rays by the prism sheet is eliminated, and the number of light rays reaching the observer is reduced. It is preferably 8 to 12 degrees. This image quality improving film achieves the object of the present invention by being used by being inserted between the prism sheet and the liquid crystal display element.

Any means may be used to obtain the image quality improving film of the present invention, but it can be realized relatively easily by providing at least one surface of the plastic film with fine irregular disordered shapes. . In order to further improve the light diffusing property, at least one surface may be coated with a light-diffusing particle as a main component in addition to the above-mentioned concavo-convex shape.

[0016]

EXAMPLES Liquid crystal display element 1 constituting liquid crystal display device 10
1 as a back light source, a planar light source device 1 as shown in FIG.
Configured 2.

The planar light source device 12 is provided with a fluorescent lamp 13 as a linear light source near the side of the light guide plate 14. A dot-printed paint (light-scattering ink) 15 is provided on the back surface of the light guide plate 14, and a reflection plate 16 is provided on the back surface of the light guide plate 14.
The light diffusing sheet 17 is provided on the front surface of the light guide plate 14, and the prism sheet (light collecting sheet) 18 is provided on the front surface of the light diffusing sheet 17. Further, in the planar light source device 12, the liquid crystal display element 1 and the prism sheet 18 are used.
The image quality improving film 21 of the present invention is disposed between

The concrete results of the present invention will be described below together with a conventional example and a comparative example. (Example 1) (FIG. 3) The planar light source device 12 has a light guide plate 14 having a thickness of 4 mm, and the fluorescent lamp 13 has one cold cathode tube.
Diagonal 10.5 inches (diagonal length), coating type light diffusion sheet as light diffusion sheet 17, prism sheet 18
As the back light module for a color liquid crystal display device, a back light module equipped with a prism sheet having an apex angle of 90 degrees was used.

Further, the image quality improving film 21 is constructed as follows (FIG. 3). That is, a film having a thickness of 200 μm was obtained by extrusion molding of a polycarbonate resin. An image-improving film 21 of Example 1 was obtained by using an embossing roll on one side of this film to provide fine and irregular irregularities. In FIG. 3, 21A indicates fine irregular disorderly projections and depressions.

The total light transmittance of the image quality improving film 21 was measured by Murakami Color Research Laboratory Co., Ltd. Haze Meter HR-10.
It was 94% as measured by 0. In addition, the diffusion half-value angle can be calculated using the ellipsometer NPDM-1000 manufactured by Nikon Corporation.
It was 8 degrees when measured by.

(Example 2) (FIG. 4) In the planar light source device 12 of Example 1, the image quality improving film 21 was changed as follows (FIG. 4). That is, a film having a thickness of 200 μm was obtained by extrusion molding of a polycarbonate resin. Using a embossing roll on one side of this film, fine and irregular irregularities were applied, and a coating with an average film thickness of 7μ was formed on both sides of the film with an acrylic resin containing 5 parts by weight of styrene beads with a particle size of 10μ. The image quality improving film 21 of Example 2 was used. In FIG. 4, 21A indicates fine and irregular irregularities.
1B is a coating and 21C is a light diffusion particle.

The total light transmittance of the image quality improving film 21 is measured by Murakami Color Research Laboratory Co., Ltd. haze meter HR-10.
It was 92% as measured by 0. In addition, the diffusion half-value angle was measured by Nikon Ellipsometer NPDM-10.
It was 10 degrees when measured by 00.

(Conventional Example) The image quality improving film 21 was removed from the planar light source device 12 of Example 1 to obtain a conventional example.

(Comparative Example) The image quality improving film 21 was removed from the planar light source device 12 of Example 1, and a conventional light diffusing member was placed in place of the image quality improving film 21. This light diffusing member was a 200 μm-thick acrylic resin sheet containing 60 parts by weight of titanium white, and had a total light transmittance of 70% and a half value angle of diffusion of 60 °.

With respect to the above-mentioned Examples 1 and 2, the conventional example, and the comparative example, the following three points were evaluated: the brightness in the direction of the screen normal, the presence or absence of the ray non-emission angle, and the quality of the image by the observer. Table 1 was obtained.

[Table 1]

From the results shown in Table 1, according to the image quality improving film 21 of the present invention, the light emission state of the planar light source device using the prism sheet as the light condensing sheet is changed, and the image quality is bright, easy to see, and good in image quality without fatigue. It is recognized that a liquid crystal display device having a feeling can be realized. Further, as a secondary effect, there is an effect of protecting the prism sheet that is easily scratched during the process, and the yield due to scratches can be improved.

[0027]

As described above, according to the present invention, it is possible to realize a liquid crystal display device which changes the light emission state of the prism sheet, is bright, is easy to see, and has a good image quality without fatigue.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a conventional planar light source device.

FIG. 2 is a schematic diagram showing a light emission characteristic of a conventional planar light source device.

FIG. 3 is a schematic view showing an example of an image quality improving film of the present invention.

FIG. 4 is a schematic view showing another example of the image quality improving film of the present invention.

FIG. 5 is a schematic view showing a planar light source device according to the present invention.

[Explanation of symbols]

 10 Liquid Crystal Display Device 11 Liquid Crystal Display Element 12 Planar Light Source Device 13 Fluorescent Lamp (Light Source) 14 Light Guide Plate 17 Light Diffusing Sheet 18 Prism Sheet 21 Image Quality Improvement Film 21A Fine and Irregular Concavo-convex

Claims (2)

[Claims] 1. A planar light source device is provided on the back surface of a liquid crystal display element, wherein the planar light source device is provided on a front surface of the light guide plate, a linear light source provided near the side of the light guide plate. An image quality improving film for a liquid crystal display device comprising a light diffusing sheet and a prism sheet provided in front of the light diffusing sheet, the image quality improving film being disposed between the liquid crystal display element and the prism sheet. An image quality improving film for a liquid crystal display device, which is mainly composed of colorless and transparent plastic, has a total light transmittance of 80% or more, and has a half-value angle of diffusion of vertically incident light of 5 to 15 degrees. 2. The surface shape of at least one surface of the image quality improving film is a fine irregular disordered shape.
An image quality improving film for the described liquid crystal display device.