JPH09127878A - Picture display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture display device capable of making a visual field angle larger without deteriorating image equality by arranging a phase grating in the display optical path of a picture display unit, so as to turn the grating surface of the phase grating to an observer side. SOLUTION: The phase grating is arranged on the observer side being the opposite side to a light source and light after transmitting picture elements is diffracted by the phase grating. At this time, an equation I is satisfied to make the visual field angle larger, while keeping high image quality. Where, T in the equation I is given by an equation II, and in the equations I and II, the periods of the grating of the phase grating and the picture elements of the picture display unit are denoted as P and L respectively and the level difference between recessed and projecting parts in the grating part of the phase grating is denoted as D. Then, the refractive index of the grating part of the phase grating is denoted as n, the number of layers and the refractive index of each layer up to the base material part of the phase grating from the surfaces on the observer side of the picture elements of the picture display unit are denoted as M and ni respectively and the thickness of each layer is denoted as ti. Further, the refractive index of air is assumed to be one.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device using an image display represented by a liquid crystal panel.

[0002]

2. Description of the Related Art An image display device using an image display device in which pixels are arranged in a dot shape, which is represented by a light emitting diode array, a liquid crystal panel of a TFT active matrix system, or the like, is known. Being developed. In such an image display device, the angle formed by the direction in which the image display device is observed and the direction perpendicular to the display surface of the image display device (that is, the direction in which the observer is viewed from the display surface of the image display device is , The angle of deviation from the front direction of the image display device) greatly changes the contrast of the image displayed on the image display device,
Good image quality can be obtained only when the observer observes the image display device from the front or near the front. That is, in such an image display device, there is a problem that the viewing angle for obtaining good image quality is narrow. Therefore, it is difficult for a large number of people to simultaneously observe one display surface of the image display device. Further, when a large screen of such an image display device is closely observed, a difference in contrast is recognized between the central portion and the peripheral portion of the display surface, which causes a problem that image quality is deteriorated.

The above problems are particularly remarkable in an image display device using a liquid crystal panel as an image display. In order to solve this problem, a liquid crystal display device in which a polyhedron lens is arranged on the observer side of the liquid crystal panel (see JP-A-56-65175) and a display device in which a concave lens array is arranged (JP-A-53-25399). , Etc. have been developed. However, although these conventional image display devices can enlarge the viewing angle, they have not yet achieved sufficient image quality.

An object of the present invention is to solve the above problems and to provide an image display device capable of enlarging the viewing angle without deteriorating the image quality.

[0005]

A first image display device of the present invention for solving the above-mentioned problems comprises an image display in which pixels are arranged in a dot shape, and a phase grating having a grating surface,
The phase grating is arranged in the display optical path of the image display so that the grating surface of the phase grating faces the viewer side, and the viewing angle of the image display is enlarged by the phase grating. Further, a second image display device of the present invention which solves the above-mentioned problems is provided with an image display having a phase grating on the display surface such that the grating surface faces the viewer side, and the image display is performed by the phase grating. It is characterized in that the viewing angle of the vessel is expanded.

In the first image display device or the second image display device of the present invention, the period of the grating of the phase grating consisting of the base material and the grating part is P, the period of the pixels of the image display is L, The step difference between the concave portion and the convex portion in the grating portion of the phase grating is D, the refractive index of the grating portion of the phase grating is n, and the number of layers from the observer side surface of the pixel of the image display to the base portion of the phase grating M, the refractive index of each layer from the surface of the pixel of the image display on the observer side to the base portion of the phase grating is ni, and the thickness of each layer is ti
, L / 12 <T · D · (n−1) / P <4 · L (1) where T is given by the following formula (2).

(Equation 2) It is preferable that the above condition (2) be satisfied, because higher image quality can be obtained. The grating portion of the phase grating means a portion from the apex of the convex portion of the grating to the bottom of the concave portion, and the base portion of the phase grating is
The part from the bottom of the concave portion of the lattice to the flat surface side (the surface on which the lattice is not formed). Further, the number of layers from the observer side surface of the pixel of the image display to the base portion of the phase grating means, for example, a liquid crystal panel having a structure in which the pixel is sandwiched between glass protective plates as the image display. Polyvinyl alcohol (vinylon) film is used for triacetyl cellulose (T
AC) a polarizing plate sandwiched between films and an image display device in combination with the above liquid crystal panel, an observer side protective plate, a TAC film, a polyvinyl alcohol film, and an adhesive layer for adhering the TAC film and polyvinyl alcohol , The number of layers having different refractive indexes such as air layers (that is, when a plurality of materials having substantially the same refractive index are laminated, this is counted as one layer). However, when the thickness of the adhesive layer or the air layer is extremely small, it may be ignored in the calculation.

In the present invention, the light emitted from the pixel of the image display is diffracted by the phase grating provided on the display optical path of the image display or the display surface of the image display and is bent and diffused. Spreads. As a result, the viewing angle of the image display device is expanded.

The image display device used in the present invention includes:
Examples include CRTs, light emitting diodes, liquid crystal panels, and the like. Examples of liquid crystal panel systems include a simple matrix drive system and an active matrix drive system.
Typical liquid crystal modes include a twist nematic type and a super twist nematic type.

The phase grating according to the present invention includes, for example, a mold (or stamper) provided with an uneven pattern corresponding to the grating of the phase grating, polycarbonate, acrylic,
Manufactured by placing a transparent film or transparent plate made of TAC etc., thermally deforming the transparent film etc. within the mold (or on the stamper), cooling the heat deformed transparent film etc., and then removing the mold or stamper To be done. Further, the phase grating in the present invention is obtained by applying a UV-curable transparent resin on a transparent film or a transparent plate and UV-curing a mold (or stamper) provided with an uneven pattern corresponding to the grating of the phase grating. It is also manufactured by irradiating ultraviolet rays while curing the transparent resin while it is placed on the coated surface of the transparent resin. Instead of the ultraviolet curable transparent resin, a thermosetting transparent resin may be applied and the transparent resin may be thermoset. Further, an ultraviolet curable transparent resin is applied on a transparent film or a transparent plate, and the transparent resin is irradiated with ultraviolet rays through a photomask on which a concavo-convex pattern corresponding to the grating of the phase grating is printed, and then,
The phase grating in the present invention can also be manufactured by subjecting the ultraviolet curable transparent resin to a development treatment. Further, the phase grating according to the present invention can be manufactured by injection molding using a thermoplastic transparent resin such as polycarbonate or acrylic.

The plane side of the phase grating in the present invention (the surface on which the grating is not formed) is on the pixel side of the image display, but this surface can be bonded to the protective plate of the image display. This eliminates the air layer between the image display and the phase grating, and can suppress the reflection of light generated at the interface between the image display and the air and the interface between the phase grating and the air. It is possible to increase the proportion of light emitted to the outside through the phase grating. The same effect can be obtained by directly forming the phase grating on the protective plate of the liquid crystal panel or the polarizing plate of the liquid crystal panel.

Generally, an image display device is required to have high brightness. However, when a phase grating is installed in front of the image display (display optical path of the image display or display surface of the image display), an interface between the phase grating and air is provided. As described above, the brightness of the image display device may decrease because the number of surfaces on which the light from the image display device is reflected increases. This problem can be solved by bonding the phase grating and the protective plate or the like as described above.
If higher brightness is required, an antireflection film may be provided on the observer side of the phase grating (the surface having the grating). In addition,
It is preferable that the light transmittance of the phase grating is 97% or more in the wavelength range of 450 to 650 nm from the viewpoint of obtaining high brightness.

It is also preferable to use a phase grating having a continuous curved cross-sectional shape so that a discontinuous cross-sectional shape (for example,
This is preferable in that a higher contrast can be obtained than when a phase grating having a rectangular shape is used. Furthermore, the period of the phase grating is smaller than the period of the pixels of the image display,
This is preferable in that the grating pattern of the phase grating is not observed. The grating depth of the phase grating (the step between the concave portion and the convex portion) is preferably 1 μm or more because the diffraction efficiency of the phase grating is high.

In a small television receiver or the like, the image quality is deteriorated due to the screen becoming dirty during use. This problem can be solved by applying an antifouling coat to the grating surface of the phase grating using a fluorine resin or the like. The contact angle of water on the surface of the phase grating is 70 by applying the antifouling coating.
Good antifouling performance can be obtained by setting it to be at least °.

Although the image quality is deteriorated due to scratches on the screen during use, the grating surface of the phase grating (observer side)
It is preferable to apply a hard coat agent to the above and make the pencil hardness of this surface H or more.

When a fluorescent lamp or the like is reflected on the screen, the image overlaps with the original image, resulting in deterioration of contrast and visibility. This problem can be solved without causing deterioration of the image by performing non-glare processing on the uneven surface of the phase grating.

[0016]

1 shows a schematic structure of an example of a first image display device of the present invention. This image display device includes an image display 2 in which pixels 1 are arranged in a dot shape, and a phase grating 4 having a grating surface. The phase grating 4 is arranged in the display optical path of the image display 2 so that the grating surface of the phase grating 4 faces the viewer side 3. The pixel 1 of the image display controls light emitted from the pixel itself, light incident on the pixel from a light source provided on the side opposite to the observer side, or light incident on the pixel from a light source provided on the observation side. The image display 2 displays an image by controlling the pixels. The phase grating in the image display device shown in FIG. 1 has a continuous curved cross-sectional shape, and the cross-sectional shape is substantially sinusoidal as shown in FIG.

By arranging the phase grating in the display optical path of the image display as in the above-mentioned image display device, the light emitted from the pixel of the image display is displayed by the display optical path of the image display or the display of the image display. Since the phase grating provided on the surface diffracts and bends and diffuses it, the viewing angle of the image display device is expanded, but on the other hand, the image quality may deteriorate due to whitening of the image. The degree of this image quality deterioration changes depending on the position where the phase grating is installed, the period of the phase grating, the depth of the phase grating, and the like. Further, considering the case where the phase grating is arranged on the viewer side of the liquid crystal panel as an example, from the pixel of the liquid crystal panel to the phase grating, a glass substrate for protecting the pixels of the liquid crystal panel, a TAC film of the polarizing plate, and a polarizing plate of the polarizing plate. It has a multilayer structure such as a polyvinyl alcohol film, an adhesive layer for adhering a TAC film and polyvinyl alcohol, and an air layer, and the thickness and refractive index of each of these layers also greatly affect the image quality. Therefore, images were evaluated using samples of various phase gratings produced by changing the grating depth and the period of the phase grating.

Here, FIG. 2 shows a schematic configuration of the image display device used for the evaluation. In this image display device, the light source 5
The light emitted by the polyvinyl alcohol film is TAC
The polarizing plate 6 sandwiched between the films enters the TFT type liquid crystal panel 7 arranged on both the front and back sides, and the pixels of the liquid crystal panel 7 are controlled to transmit or block the light, thereby displaying an image. It The phase grating 4 is arranged on the side of the viewer 3 opposite to the light source 5, as shown in FIG.
As shown in, the light transmitted through the pixel is diffracted by the phase grating and the viewing angle is expanded. In this image display device, a glass substrate (this is one of the components of the liquid crystal panel and is not shown) is provided from the surface of the pixel of the image display on the observer side to the base portion of the phase grating. , TAC film,
There are 5 layers of polyvinyl alcohol film, TAC film and air layer. The period of the phase grating is 50μ
A phase grating was prepared by changing the thickness to m or 100 μm. The step between the concave portion and the convex portion in the unevenness of the phase grating (that is,
Thickness of the grating part of the phase grating. ) Was changed in the range of 1.4 to 294 μm to produce a phase grating. The refractive index of the base material of the phase grating is 1.53. The image evaluation results are shown in Table 1. The thickness of the adhesive layer for adhering the TAC film and polyvinyl alcohol was extremely small and was ignored in the calculation.

[0019]

[Table 1]

In Table 1, α is a value given by the following equation. α = T · D · (n−1) / (P · L) Further, in the image quality evaluation result, ◯ indicates that the image quality is not deteriorated, Δ indicates that the image quality is not significantly deteriorated, and × indicates that the image quality is significantly deteriorated. Mean respectively. In the evaluation results of the viewing angle expansion, ◯ means that the viewing angle expansion property is large, Δ means that the viewing angle expansion property is small, and x means that there is no viewing angle expansion property.

From these results, it was found that the viewing angle can be expanded while maintaining high image quality when the following expression (1) is satisfied. Here, in the formula (1) and the following formula (2), as shown in FIG. 3, the period of the grating of the phase grating is P, the period of the pixel of the image display is L, and the concave portion in the grating part of the phase grating is Is D, the refractive index of the grating portion of the phase grating is n, the number of layers from the surface of the pixel of the image display on the observer side to the base portion of the phase grating is M, and Let n be the refractive index of each layer from the surface of the pixel on the observer side to the base material of the phase grating.
i, the thickness of each layer is represented by ti. Further, the refractive index of air is 1. L / 12 <T * D * (n-1) / P <4 * L (1) However, in Formula (1), T is given by the following Formula (2).

(Equation 3)

In the present invention, in place of the equation (1), the following equation (3), L / 10 <T · D · (n−1) / P <3 · L (3), must be satisfied. This is preferable in that higher image quality can be obtained, and is even higher if a phase grating that satisfies the formula (4), L / 8 <T · D · (n−1) / P <2 · L (4) is used. Image quality can be obtained.

FIG. 4 shows a schematic configuration of an example of the second image display device of the present invention. In this image display device, a TFT type liquid crystal panel 7 is used as an image display, and the grating portion 4 of the phase grating is directly provided on the polarizing plate 6 on the side opposite to the light source 5 side. The polarizing plate 6 has a polyvinyl alcohol film sandwiched between TAC films. That is, the TAC film on the viewer side of the polarizing plate corresponds to the base portion of the phase grating. On the viewer side of the phase grating, a hard coat layer 8 and then an antireflection film 9 are provided from the grating section 4 side of the phase grating. According to this embodiment, it is possible to obtain a display image with high brightness and a display screen that is not easily scratched. In this image display device, if the adhesive layer for adhering the TAC film and polyvinyl alcohol is neglected in the calculation, the glass substrate is provided from the surface of the pixel of the image display on the observer side to the base portion of the phase grating. (This is one of the components of the liquid crystal panel and is not shown.), TAC
Film, polyvinyl alcohol film and TAC
It is four layers of film (base material of phase grating).

[0024]

According to the image display device of the present invention, the viewing angle can be widened and a good image with little deterioration in image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a first image display device of the present invention.

FIG. 2 is a schematic configuration diagram showing an image display device used for evaluation.

FIG. 3 is a diagram schematically showing a cross section of a first image display device of the present invention.

FIG. 4 is a schematic configuration diagram showing an example of a second image display device of the present invention.

[Explanation of symbols]

 1 Pixel 2 Image Display 4 Phase Grating 5 Light Source 6 Polarizing Plate 7 Liquid Crystal Panel

 ──────────────────────────────────────────────────続 き Continued on front page (72) Katsuhiko Hayashi 1621 Sazu, Kurashiki-shi, Okayama Pref.

Claims (9)

[Claims] 1. An image display device in which pixels are arranged in a dot shape, and a phase grating having a grating surface, and is provided in a display optical path of the image display device so that the grating surface of the phase grating faces the observer side. An image display device, wherein a phase grating is arranged, and the viewing angle of the image display is expanded by the phase grating. 2. An image characterized by comprising an image display having a phase grating on the display surface such that the grating surface faces the observer, and the viewing angle of the image display is enlarged by the phase grating. Display device. 3. The image display device according to claim 2, wherein the image display is a liquid crystal panel provided with a protective plate, and a phase grating is formed on the protective plate. 4. The image display device according to claim 2, wherein the liquid crystal display is a liquid crystal panel having a polarizing plate, and a phase grating is formed on the polarizing plate. 5. A period of a grating of a phase grating composed of a base portion and a grating portion is P, a period of pixels of an image display is L, a step between a concave portion and a convex portion of the lattice portion of the phase grating is D, a phase. The refractive index of the grating portion of the grating is n, the number of layers from the viewer side surface of the pixel of the image display to the base portion of the phase grating is M, and the phase grating from the viewer side of the pixel of the image display In the case where the refractive index of each layer up to the base material part is represented by ni and the thickness of each layer is represented by ti, the following formula (1), L / 12 <T · D · (n−1) / P <4 -L (1) However, T is given by the following formula (2). (Equation 1) The image display device according to any one of claims 1 to 4, which satisfies the above condition. 6. The image display device according to claim 1, wherein a phase grating having a continuous curved cross-sectional shape is used. 7. The image display device according to claim 1, wherein the period of the phase grating is smaller than the period of the pixels of the image display. 8. The image display device according to claim 1, wherein a phase grating having a contact angle of water on the grating surface of 70 ° or more is used. 9. A phase grating having a pencil hardness of H or more on the grating surface is used.
Item 10. The image display device according to Item 1.