JP2007201997A - Image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To view a television image to be viewed under a variety of environments as a real image with little tired feeling even under any environment by adjusting the image suitably and automatically fitting the image to a nature to which human eyes are adapted according to a brightness of the environment when an image display apparatus (especially, liquid crystal television set) is viewed. <P>SOLUTION: The image display apparatus combines a light scattering film having grainy fine areas (internal scattering bodies) with different refractive indexes so as to scatter the light in a visible ray wavelength area more intensively according to a grain size (Mie scattering) to a polarizing film and applies it to a liquid crystal display element. The apparatus has a change of gamma of 0.5 or less in a range of 45° from a front face, keeps a contrast of 1:50 or more and is provided with a measuring device which measures an illuminance of a viewing environment. The apparatus is provided with a means to change a gradation characteristic according to the measured illuminance. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color-correctable diffuser that can suppress a decrease in luminance of a liquid crystal display device by diffusing light and can form a liquid crystal display device with little color change depending on the viewing angle, and is particularly vertically aligned. When used with a liquid crystal cell, it compensates for color changes due to changes in gamma characteristics when the liquid crystal display is viewed from an oblique direction, scatters light on the short wavelength side more strongly, and has high parallel light transmittance and high backscattering. The present invention relates to a diffuser having a small scattering angle (Mie scattering), and further to a polarizing element using this diffuser, and applying this, there is little blur, high contrast, bright, gradation change, color The present invention relates to a liquid crystal display device with little change, and more particularly to a thin liquid crystal display device that can easily watch high-quality images such as a liquid crystal television.

  A transmissive liquid crystal display device is a display element typified by a flat panel display and is widely used in liquid crystal televisions, car navigation systems, personal computer monitors, notebook PCs, FAs, etc. because it is light, thin, and has low power consumption. In particular, in recent years, it has been widely used as a television application.

To date, alignment type liquid crystal such as TN mode, OCB mode, VA mode, and IPS mode has been developed.
Among them, TN (twisted nematic) type liquid crystal has a twisted orientation, and therefore, there is a disadvantage that even if the polarization is corrected in the retardation film, contrast inversion occurs in only one direction. It is not very suitable for TVs that are supposed to be viewed from.
In the TN system, the liquid crystal is twisted by 90 ° and aligned.

On the other hand, there is an OCB method in which the liquid crystal is twisted 180 °.
This method has a wide viewing angle, high responsiveness, and good optical characteristics.
However, since the vent orientation has two stable states of the spray orientation, it is very difficult to produce a stable operation.

In addition, in order to solve the problem of the viewing zone, an IPS type liquid crystal display with an orientation is known.
However, IPS is said to be relatively low in responsiveness, easily dark areas are crushed, and expensive to manufacture.

Similarly, in order to solve the problem of the viewing zone, a vertical alignment type (VA type) liquid crystal display is known.
In this VA type liquid crystal, TN and IPS are aligned horizontally, whereas they are aligned vertically, so that the contrast is high and the gradation of the black portion is easy to reproduce.
Also, in terms of responsiveness, transmittance, and manufacturing cost, it is said that it is relatively easy to manufacture than IPS, although it is inferior to TN type.
However, the gamma changes depending on the viewing angle, and when viewed from an oblique angle, the gamma changes and the color changes depending on the viewing angle.

  Gamma is a numerical value that represents the characteristics of the gradation. If this gamma characteristic is not displayed correctly, gray scales may be colored or subtle intermediate colors may not be accurately reproduced. Invite.

Unlike a monitor, a television needs to display a video with many intermediate gradations from various angles. Therefore, there is a demand for a display device that has little gradation and no color change from any direction. .
On the other hand, an increase in the size of a flat-screen television is remarkable, and viewing an image with a sense of incongruity directly leads to eye fatigue.

Such a large-screen television has the main purpose of easily enjoying high-quality video, and the viewing environment varies depending on the mood of the day, the viewing time zone, and the content.
On the other hand, human feeling is known to be very affected by external brightness, and the optimal image display varies depending on the brightness of the environment, so there is a feeling of fatigue depending on the viewing environment. An image suitable for all viewing environments cannot be displayed because it may be a video or an image with no sharpness.

Some research reports indicate that it is more natural to make the gamma when displaying movies and slides about 1.5 times the gamma that you want to express, and that the contrast between white and black is about 1: 1000. (See Non-Patent Document 1)
“The Theory of the Photographic Process” THJames

In a bright room, only a density of 2, that is, 1: 100 can be recognized. Therefore, if the gamma is set too high and a color is displayed in a dark part, the display of the dark part is crushed and the sense of depth is lost.
It is said that this is because stimulation from the periphery of the retina is transmitted to the nerve near the center of the retina through the inhibitory nerve.
In view of this, it is conceivable that the user adjusts the image quality appropriately. However, in view of the fact that the television is used by various people, it becomes very complicated and it is difficult to think that all people can appropriately perform the adjustment.

Here, the bright room refers to a room of about 100 to 300 lux / cm 2, and the dark room refers to a room mainly composed of indirect illumination of 50 lux / cm 2 or less.
Furthermore, when a television is displayed at a store, it is placed in a very bright environment, and it is necessary to attract the attention of the buyer. Therefore, a highly saturated image is desired. However, when such an image is brought into the living room as it is, it becomes a very tired image.

Conventionally, efforts have been made to improve the visual image quality in consideration of the film density when watching movies, slides, etc. in a dark room. There is no suggestion to control to improve image quality.
According to the present invention, when a video display device (particularly, a liquid crystal television) is viewed, various images can be obtained by automatically adjusting an image in accordance with the property that the human eye adapts according to the brightness of the environment. The main objective is to make the TV watched below less tiring in any environment and make it possible to see more realistic images. In bright storefront display conditions, brightness, contrast, and blur are suppressed. At the same time, it provides a video display device capable of displaying a suitable image quality (color) using a diffuser capable of color correction that suppresses changes in gradation and color depending on the viewing angle, and improves users' willingness to purchase. It is something that you want to encourage.

An image display device according to the present invention includes:
A light-scattering film with a fine particle area (inner surface scatterer) with different refractive index that scatters light in the visible wavelength range more strongly according to the particle diameter (Mie scattering) is combined with a polarizing film to produce liquid crystal A video display device applied to a display element,
In the range of 45 ° from the front, the change in gradation gamma is within 0.5 and the contrast is kept at 1:50 or more,
A measuring instrument capable of measuring the illuminance of the viewing environment is provided, and means for changing gradation characteristics according to the measured illuminance is provided.

As a diffuser with relatively high parallel light transmittance, visible light wavelength range depending on the particle size under various illumination conditions such as dark room, indirect lighting, bright room, storefront display, etc. Using a light scattering film having a fine particle area (inner scatterer) with a different refractive index that scatters light (Mie scattering) more strongly,
By applying the above film to a liquid crystal display element in combination with a polarizing film and disposing it further on the front side of the polarizing layer on the viewer side,
Color change according to the viewing angle of the video display device (liquid crystal television), contrast reduction, blur, and brightness reduction at the front are so small that they cannot be recognized. A liquid crystal television that takes advantage of features such as cost will be realized.

When a TV is placed in a bright room (bright room environment of 100 to 300 lux / cm 2), the contrast should be set to about 1:50 and display can be performed with the same gamma as the gamma to be displayed. preferable.
In order to perform such display, if the contrast is not sufficiently maintained even when viewed from an oblique direction, there is a problem in that the black float becomes larger when viewed from an oblique direction.
Also, if the gamma characteristic has a tendency to fall, a desirable characteristic cannot be obtained.

In a room with dim indirect lighting (a dark room environment of 50 lux / cm 2 or less), it is appropriate to set the gamma to be about 1.3 to 1.6 times the gradation to be displayed.
In that case, it is more desirable to suppress the brightness of 100 cd / m 2 or less because it is considered that the black float is suppressed and the burden on the eyes can be suppressed.

  In an environment (300 lux / cm 2 or more) such as that displayed at a store, it is desirable to make the purchaser's eye-catching by displaying with higher saturation.

  Conventional LCD TVs and plasma TVs are not equipped with such a gradation adjustment mechanism, and are designed to express the gradation to make the most of the contrast in any environment. When I looked, the black part was crushed.

On the other hand, it can be said that such gradation expression functioned effectively in a dark room environment, but in reality, it is presumed to be visible in a bright room environment. It becomes an expression.
Such an expression can feel a little uncomfortable on a small display and not so much fatigue, but if the display becomes larger, the feeling of discomfort and fatigue will become stronger.
A desirable gradation characteristic (input signal = NTSC) in a bright room environment and a dark room environment is shown in the graph of FIG.

<Embodiment 1>
Vertically-aligned liquid crystal televisions with light-scattering films that have particulate regions (inner surface scatterers) with different refractive indices that scatter light in the visible wavelength range more strongly (Mie scattering) depending on the particle diameter FIG. 2 is a graph showing the contrast change corresponding to the change in angle when arranged in the graph.

  For a liquid crystal having such a sufficient contrast characteristic, it is assumed that at 50 lux or less, the gamma is equivalent to 1.5 times the conventional value using full gradation, and the NTSC signal is 2.2. The input signal should be 3.3.

Further, in 150 lux / cm 2 to 250 lux / cm 2, it was assumed to be 2.2 which is a gamma assumed for the original NTSC signal.
It was assumed that the gamma varied asymptotically between 1.5 and 2.2 between 50 lux / cm 2 and 150 / cm 2.

Further, at 250 lux / cm 2 or more, by setting so as to increase the saturation and display a more desirable image than reality, it is possible to display a video with a higher eye-catching effect even during store display.
In order to display such a gamma characteristic, it is necessary to provide a display device in which the gamma characteristic does not change from any angle and the black floating is suppressed to some extent. This was realized by placing an optical film that satisfies the following conditions on the front surface of the polarizing layer of the front polarizing plate of the liquid crystal panel.

When such a diffusion film is arranged, the contrast in the front direction decreases, and falls to about 1: 300.
However, if it is in a dim light such as under indirect lighting, even if the luminance of black is reduced further, it cannot be recognized. In terms of density, 2.5 is maintained, so even in a dark environment ,It is enough.
Rather, the point that the contrast is lowered to about 1:20 at the maximum when viewed from an oblique direction is considered to be problematic in view of the viewing environment of the television, and this point should be improved.

・ Backscattering Under the bright room is recommended for TV viewing. When talking about contrast, when considering the conditions under the bright room, light is diffused and the liquid crystal display device is under the bright room. In order to ensure sufficient contrast, in contrast to the dark room, in the bright room, considering that the sensitivity to the dark part of the display becomes dull, contrast of 100: 1 or higher is hardly perceivable. Therefore, 100: 1 is sufficient as the contrast.
By the way, the current liquid crystal television has a white luminance of 400 cd / m ² or more.
At this time, in order to obtain the contrast 100, the luminance of black may be suppressed to 4 cd / m ² or less.

Here, an increase in black luminance due to external light is considered.
In a normal indoor environment, it is 100 to 300 lux / m ^2. Considering the case of a bright room, if the reflection from the display is an ideal diffuser, 300 / 3.14 = 95 cd / m ^2. .
On the other hand, when black is displayed on the liquid crystal display, the luminance is about 1/400 of the white luminance, which is about 1 cd / m ² .
Here, when the reflectance of the liquid crystal display is 3% of the ideal diffusion plate, the luminance is 2.9 cd / m ^{2. In} this case, sufficient contrast is obtained even in a bright room such as a normal living room. Is obtained.
In a normal living room or the like, an illumination light source is generally located near the center of the room, and a television is generally placed near the wall of the room.
From this, about 45 degree illumination is considered appropriate as the incident angle of the illumination light incident on the assumed display. When combined with the above conditions, if the reflectivity of 45 degree illumination and 0 degree measurement is 3% or less with respect to the standard white plate, sufficient contrast can be obtained even in a bright room.

It is said that the contrast in a dark room is not sufficient in a liquid crystal television, and usually, it is often made assuming that a program such as a drama, news, sports, etc. is viewed in a bright room.
On the other hand, there is a desire to easily watch movies in a calm environment, but for such applications, LCD TVs have a slightly blurred impression because the gamma characteristics are lightly touched from the above points. I will receive it.
Similarly, if the luminance is the same as that under the bright room, the luminance of black tends to float, and it is necessary to use a liquid crystal panel with high contrast, but the luminance of the backlight is lowered in dark places. As a result, high image quality can be obtained even when the luminance of the liquid crystal panel remains low.

The vertical alignment type liquid crystal looks different when it is viewed from the front and when viewed from an oblique direction, and when viewed from an oblique direction, the gamma becomes smaller and the color appears pale.
Also, it tends to look blue at the front and yellow from the side.
In order to correct this, a retardation film having negative uniaxial anisotropy is used, but this has a specific orientation, and is effective only in the black part, so it can be used for correction at intermediate gradations. Is not enough.

-Color change By arranging the optical film to which the diffuser of the present invention is applied on the front polarizing plate of a vertically aligned liquid crystal, light in each direction is sufficiently mixed, and due to the effect of wavelength dependence of diffusion The color can be corrected, and by making the color difference between the front and the periphery to be 0.04 or less in ΔU′V ′, a display that does not substantially perceive a color change can be obtained.
For those demanding more stringent quality, ΔU′V ′ is preferably 0.03 or less.
At this time, as test colors, for example, colors in the vicinity of 8 test colors defined in CIE1974 can be used.
Further, colors in the vicinity of 15 test colors of JIS Z 8726 may be used.
When measuring this color change, it is virtually impossible to measure all colors, so measuring a representative color and measuring the color change in this way is what evaluates the display. Is considered reasonable.
Moreover, generally the brightness | luminance of a front surface falls by adding the optical film which applied this diffuser. Although it is possible to correct this with a backlight, it cannot be corrected if it is extremely reduced, so it is suppressed to within 40% of the original luminance compared to before adding an optical film to which this diffuser is applied. It is considered reasonable. More preferably, it should be kept within 20%.

In addition, on the surface opposite to the diffusion layer of the optical film using the diffuser of the present invention, which also serves as a protective film, the purpose is hard coat treatment, antireflection treatment, anti-sticking, antifouling, antistatic, and diffusion or antiglare. It may be the one that has been subjected to the processing.
It can also be used with a retardation film having refractive index anisotropy.

In such a liquid crystal display device, a contrast of 1: 300 was actually obtained, and a contrast of 1:50 was obtained even in the range up to 60 °.
In the liquid crystal display device thus obtained, even when the brightness of the viewing environment is different by changing the gamma of the gradation according to the surrounding luminance, it was possible to view a good image.

<Embodiment 2>
As a thin display device capable of such display, an IPS liquid crystal television can be given.
However, when this display is also viewed from an oblique direction, the contrast becomes about 1:10 to 1:20 due to light leaking obliquely through the polarizing plate.
In such a display as well, it is desirable to ensure sufficient contrast by using a retardation film or a diffusion film to suppress black float.
Further, in IPS, the gradation does not become soft when viewed from an angle as in the case of the VA liquid crystal, and in this respect, it is easy to display a desirable gradation.
For liquid crystal with such a sufficient contrast characteristic, it is assumed that at 50 lux or less, gamma is equivalent to 1.5 times the conventional using full gradation, and the NTSC signal is assumed to be 2.2. The signal should be 3.3.
Further, it was assumed that 150 lux / cm 2 to 250 lux / cm 2 is set to 2.2, which is the gamma assumed for the original NTSC signal.
It was assumed that the gamma varied asymptotically between 1.5 and 2.2 between 50 lux / cm 2 and 150 / cm 2.
Further, at 250 lux / cm 2 or more, by setting the saturation to be more desirable and displaying a more desirable image, it is possible to display a video with a higher eye-catching effect even during store display.
In order to display such a gamma characteristic, it is necessary to provide a display device in which the gamma characteristic does not change from any angle and the black floating is suppressed to some extent. This was realized by placing an optical film that satisfies the following conditions on the front surface of the polarizing layer of the front polarizing plate of the liquid crystal panel.

<Embodiment 3>
In a plasma TV, for example, by using a layer that absorbs light on the outermost surface, contrast in a bright room can be improved. With such a panel, sufficient contrast can be obtained in a living room at home. Since the obtained gradation characteristics do not change depending on the angle, it can be used for such a display.

<Light scattering film>
Vinyl acetate SN-12T dissolved in MEK (Polymer product name: Poval Osaka Organic Chemical Co., Ltd.) and acrylic monomer M-110 (Product name: Aronix Toagosei Co., Ltd.) in a mass ratio of 5: 1 The TAC Fujitak (80 μm thickness) manufactured by Fuji Photo Film Co., Ltd. was applied, the solvent was evaporated by heating, and the polymer layer was applied to a film thickness of 18 μm. After irradiation at 500 mJ / cm ² , the mixture was heated at 120 ° C. for 10 minutes to obtain a phase-separated light diffuser. This film was bonded to the surface of KLV-15AP (trade name: Vega Sony) of a 15-screen type liquid crystal television.
The average particle diameter of the inner scatterer is 0.4 μm.
From the mass ratio of the solid content of the entire coating liquid, the content of the inner surface scatterer was about 30%, but sufficient scattering properties were obtained. Further, by arranging such an optical film on the outermost surface of the liquid crystal television, it was possible to suppress the color change to about 0.04 at ΔU′V ′.

  By adapting such a light scattering film to the vertical alignment type liquid crystal used for the upper polarizing plate, it can be used in any audio-visual environment with less fatigue and a beautiful and clear image. It can be used as a TV.

The graph which shows the desirable gradation characteristic (input signal = NTSC) in a bright room environment and a dark room environment about a television image. The graph which shows the contrast change according to an angle change at the time of arrange | positioning the light-scattering film of this invention to the vertical alignment type liquid crystal television.

Claims (3)

A light-scattering film with a fine particle area (inner surface scatterer) with different refractive index that scatters light in the visible wavelength range more strongly according to the particle diameter (Mie scattering) is combined with a polarizing film to produce liquid crystal A video display device applied to a display element,
In the range of 45 ° from the front, the change in gradation gamma is within 0.5 and the contrast is kept at 1:50 or more,
An image display device comprising a measuring instrument capable of measuring the illuminance of a viewing environment, and comprising means for changing gradation characteristics in accordance with the measured illuminance. In a dark room environment of 50 lux / cm2 or less, the gradation is displayed so that it is approximately 1.5 with respect to the original gamma of the gradation to be expressed.
2. An image display apparatus according to claim 1, wherein in a bright room environment of 100 to 300 lux / cm @ 2, gradation display is performed so that the original gradation to be expressed is approximately 1 with respect to gamma.   3. The video display device according to claim 1, wherein when the illuminance is 300 lux / cm <2> or higher, the image is displayed with higher saturation than the input signal.

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