JP2002350618A - Optical film and liquid crystal display device using the same - Google Patents

Abstract

(57) [Problem] To eliminate the overlap between a display image and specular reflection of external light source light and to obtain a bright and high-contrast display image even when there is no special illumination light source such as a backlight or an edge light. thing. An optical film 1 having a plurality of regions 2 and 3 having different refractive indexes inside a film, wherein each region 2 and 3 has
On the surface, it has an elongated shape in one direction, is arranged in stripes, and has a structure in which it is distributed in a layered manner with respect to the thickness direction of the film, and the light incident on the film is inclined. For light incident obliquely from a direction substantially along the direction, the direction of the light is changed by total reflection at the inclined interface between the layers 2 and 3 having different refractive indices in the film. For light incident from the direction of
The light is transmitted as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical film used for a liquid crystal display device for defining a display pattern by transmission / non-transmission of light and a liquid crystal display device using the same, and more particularly to an optical film such as a backlight or an edge light. The present invention relates to an optical film capable of observing a display image in a bright and high-contrast state even when there is no special illumination light source, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Heretofore, it has been possible to observe a bright display image by collecting illumination light in the direction of an observer on the front or back of a liquid crystal cell which defines a display pattern by transmission / non-transmission of light. Optical films are known.

As an example of this type of optical film, there is a film using a prism sheet. In addition, “Japanese Patent Laid-Open No. 2000-3
Japanese Patent Application Publication No. 9507 "also discloses one using a similar prism sheet.

In particular, the latter prism sheet has
A transparent substrate sheet in which a plurality of unit prisms are arranged at a constant pitch in a one-dimensional or two-dimensional direction, and external light incident on the transparent substrate sheet from the surface side is inclined to the inclined surface of the unit prism. , And the light is emitted internally through the transparent substrate sheet.

[0005]

However, an optical film having such a prism sheet needs to be used as a reflective layer on the back surface.

Therefore, it cannot be applied to a liquid crystal display device in which a reflective layer and a liquid crystal cell are integrated as in recent years.

Further, in such a reflective layer, when illumination light is illuminated at an angle almost perpendicular to the reflection surface, the light is reflected in the same direction as the illumination.

Therefore, the angle of observation and the angle of the illumination light are the same, and there is a problem that the illumination light source is hidden behind the observer.

On the other hand, the holographic technique is used as an optical film that changes the direction of only the incident light into the liquid crystal cell and transmits the light emitted from the liquid crystal cell as it is without changing the direction of the light. Applications are known.

However, in the method using such a holographic technique, a change in the direction of light differs depending on the wavelength of light.

For this reason, there is a problem that the color is added or the angle at which the optical effect can be obtained is limited.

An object of the present invention is to change the direction of light incident from a wide angle to an appropriate direction so that when applied to a display device, a display image and regular reflection of external light source light overlap. It is an object of the present invention to provide an optical film capable of obtaining a bright and high-contrast display image even when there is no special illumination light source such as a backlight or an edge light.

Further, an object of the present invention is to change the direction of light incident from a wide angle to an appropriate direction so as to eliminate the overlap between the display image and the specular reflection of the external light source light, and to improve the backlight and the like. An object of the present invention is to provide a liquid crystal display device capable of obtaining a bright and high-contrast display image even when there is no special illumination light source such as an edge light.

[0014]

In order to achieve the above object, according to the first aspect of the present invention, a film is provided inside a film.
An optical film having a plurality of regions having different refractive indices, each region having a shape elongated in one direction on the surface,
It is arranged in a stripe shape, and has a structure that is distributed in a layered manner with an inclination to the thickness direction of the film,
Light incident on the film is obliquely incident from a direction substantially along the inclined direction, and is totally reflected at an inclined interface between layers having different refractive indices in the film, thereby changing the direction of the light. This is changed so that light incident from other directions is transmitted as it is.

Therefore, in the optical film according to the first aspect of the present invention, by taking the above means, the direction of light incident from a wide angle can be changed to an appropriate direction. When applied to a display device, eliminate the overlap between the display image and the specular reflection of the external light source light, and obtain a bright and high-contrast display image even when there is no special illumination light source such as a backlight or an edge light. Can be. Further, by arranging the regions having different refractive indices in a stripe shape, it is possible to easily manufacture the optical film.

According to a second aspect of the present invention, there is provided an optical film having a plurality of regions having different refractive indices inside the film, wherein each region has a shape elongated in one direction on the surface, It is arranged randomly, and has a structure that is distributed in a layered manner with inclination to the thickness direction of the film, and light incident on the film is obliquely incident from a direction substantially along the inclination direction. In this case, the direction of the light is changed by total reflection at an inclined interface between layers having different refractive indices in the film, and the light is transmitted as it is for light incident from other directions. Like that.

Therefore, in the optical film of the invention corresponding to claim 2, by taking the above-described means, by changing the direction of light incident from a wide angle to an appropriate direction, When applied to a display device, eliminate the overlap between the display image and the specular reflection of the external light source light, and obtain a bright and high-contrast display image even when there is no special illumination light source such as a backlight or an edge light. Can be. In addition, by randomly arranging the regions having different refractive indexes, it is possible to suppress the influence of coloring due to light diffraction and interference due to the regularity of the arrangement of the regions, and prevent a color change of a display image. it can. further,
According to the invention corresponding to claim 3, an optical film having a plurality of regions having different refractive indexes inside the film, wherein each region is distributed in a layered manner inclining with respect to the thickness direction of the film. The angle α between the film surface and the inclined interface between regions having different refractive indices in the film, the angle between light incident on the film and the normal to the film surface is θ, and the respective refractive indices are n1, n2 (however,
n1 and n2 are n1> n2),

(Equation 2) I am trying to be.

Therefore, in the optical film according to the third aspect of the present invention, by taking the above measures, the direction of light incident from a wide angle can be changed to an appropriate direction. When light enters from a region with a high refractive index to a region with a low refractive index, the light is totally reflected at the interface between the regions having different refractive indexes, and is emitted while being shifted from the direction of the regular reflection in the front direction to the display device. When applied, the overlap between the display image and the specular reflection of the external light source light is eliminated, and a bright and high-contrast display image can be obtained even when there is no special illumination light source such as a backlight or an edge light.

According to a fourth aspect of the present invention, in the optical film of the third aspect of the present invention, the angle θ formed between the light incident on the film and the normal to the film surface.
Is set to satisfy 0 ° <θ <55 °.

According to a fifth aspect of the present invention, in the optical film according to the third aspect, an angle θ between light incident on the film and a normal line of the film surface.
Is set to satisfy 0 ° <θ <45 °.

Further, in the invention according to claim 6, in the optical film according to the invention described in claim 3, the angle θ between the light incident on the film and the normal to the film surface is 0 ° <θ <. 30 °.

Therefore, in the optical film of the invention corresponding to claims 4 to 6, the angle θ between the light incident on the film and the normal to the film surface is 0 ° <θ <5.
5 °, or 0 ° <θ <45 °, or 0 ° <θ <30 °
By applying such a size, when applied to a display device, more incident light can be reflected at the interface between regions having different refractive indices. The function can be achieved more effectively.

According to a seventh aspect of the present invention, in the optical film according to the first aspect of the present invention, the difference in refractive index in the film is set to 0.06 or less. I have.

According to an eighth aspect of the present invention, in the optical film according to any one of the first to sixth aspects, the refractive index difference in the film is set to 0.04 or less. I have.

According to a ninth aspect of the present invention, in the optical film according to any one of the first to sixth aspects, the refractive index difference in the film is 0.02.
It is to be as follows.

Therefore, in the optical film of the invention corresponding to claims 7 to 9, the refractive index difference in the film is set to 0.06 or less, or 0.04 or less, or 0.02 or less. When applied to a display device, more incident light can be reflected at the interface between regions having different refractive indices, so that the operation of the invention corresponding to any one of claims 1 to 6 can be achieved. Can be achieved even more effectively.

According to a tenth aspect of the present invention, in the optical film according to the first aspect of the present invention, the pitch at which the regions are arranged is randomly changed. I have to.

Therefore, in the optical film of the invention corresponding to claim 10, when the pitch for arranging each region is randomly changed, when applied to a display device,
Since the wavelength selectivity and the angle selectivity can be reduced to suppress the influence of chromatic dispersion and the like, the effect of the invention corresponding to any one of claims 1 to 6 can be more effectively achieved. Can be played.

According to an eleventh aspect of the present invention, in the optical film according to any one of the first to tenth aspects, of the layers having different refractive indexes,
The layer having a higher refractive index is made wider than the layer having a lower refractive index.

Therefore, in the optical film according to the present invention, the interval between the high refractive index layer and the low refractive index layer is increased so that
When applied to a display device, the light is transmitted through the optical film before the light that has been totally reflected once is completely reflected again, so that it is possible to prevent the light that has been totally reflected once from being totally reflected again. The operation of the invention corresponding to any one of the first to tenth aspects can be more effectively achieved.

Furthermore, in the invention corresponding to claim 12,
In the optical film according to any one of the first to tenth aspects, among layers having different refractive indices, the width of a layer having a high refractive index is low on a front side (back side). The spacing should be wide relative to the width of the layer,
On the back side (front side), the width of the high refractive index layer is smaller than the width of the low refractive index layer.

Therefore, in the optical film according to the twelfth aspect of the present invention, the width of the high refractive index layer is wider than that of the low refractive index layer on the front side (back side), On the side (front side), the width of the high-refractive-index layer is narrower than the width of the low-refractive-index layer, so that when applied to a display device, the light once totally reflected However, light is incident at an angle that is almost perpendicular than the angle at which total reflection occurs again, and light is transmitted without being totally reflected, so that once reflected light is prevented from being totally reflected again Accordingly, the effect of the invention corresponding to any one of claims 1 to 11 can be further effectively achieved.

On the other hand, the invention according to claim 13 corresponds to any one of claims 1 to 12 on the observer side of the liquid crystal cell which defines a display pattern by transmission / non-transmission of light. The optical film of the invention is arranged.

Therefore, in the liquid crystal display device according to the present invention, the optical film exhibiting the effect of the invention according to any one of the above-mentioned inventions is transmitted / non-transmitted by light. By arranging it on the observer side of the liquid crystal cell that defines the display pattern, by changing the direction of the light incident from a wide angle to an appropriate direction, the display image and the external reflection of the external light source light are reflected. , And even when there is no special illumination light source such as a backlight or an edge light, a bright and high-contrast display image can be observed. That is,
For light that is obliquely incident on the optical film as described above, the direction of the light is changed by performing total reflection at the boundary between layers having different refractive indices, and for light emitted from the liquid crystal cell. , And has the property of transmitting light. Also,
When light is incident on the optical film as described above from a direction substantially perpendicular to the film surface, the light is reflected at an interface of a layered distribution having different refraction in the film and emitted in an oblique direction. The angles described above are conditions that are in good agreement with normal viewing conditions, and the illumination light is emitted in such a direction and is diffused by the diffusion layer, so that a display with extremely high brightness under normal viewing conditions is obtained. A liquid crystal display device capable of observing an image can be realized.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION The optical film of the present invention totally reflects illumination light incident on the film at the interface between regions having different refractive indexes inside the film.

That is, an optical film having a plurality of regions having different refractive indices inside the film, wherein each region has an elongated shape in one direction on the surface, and is arranged in stripes or randomly. It has a structure that is distributed in a layered manner with inclination to the thickness direction of the film, and light incident on the film is obliquely incident from a direction substantially along the inclination direction. By changing the direction of the light by total reflection at an inclined interface between layers having different refractive indices, the light is transmitted as it is for light incident from other directions. It is.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a partial perspective view showing a configuration example of an optical film according to the present embodiment.

That is, as shown in FIG. 1, in the optical film 1 according to the present embodiment, a plurality of regions having different refractive indexes (2 is a high refractive index region (layer)) and 3 is a refractive index Low areas (layers) are arranged in stripes on the surface, having a shape elongated in one direction, and inclined at a certain inclination to the film thickness direction. It is a film having a structure distributed in a layered manner, and light incident on the film is inclined with respect to light incident obliquely from a direction substantially along the inclination direction. The direction of the light is changed by total reflection at the interface, and the light incident from other directions is transmitted as it is.

Next, the optical film 1 according to the present embodiment configured as described above was applied to a display device by changing the direction of light incident from a wide angle to an appropriate direction. At this time, the overlap between the display image and the specular reflection of the external light source light is eliminated, and a bright and high-contrast display image can be obtained even when there is no special illumination light source such as a backlight or an edge light.

That is, when light enters the interface between the regions 2 and 3 having different refractive indices on the optical film 1 as shown in FIG. 1, the angle between the traveling direction of the light and the interface becomes small. In this case, even if the difference in the refractive index between the two layers 2 and 3 having different refractive indices is small, the layer 2 having a higher refractive index and the layer 3 having a lower refractive index are different.
When light enters, the light is totally reflected.

Here, the reflectance at the interface between the different regions 2 and 3 when light is incident from the region 3 having a lower refractive index to the region 2 having a higher refractive index of the optical film 1 will be described with reference to FIG. .

FIG. 3 is a sectional view for explaining a coordinate system used in the optical film of the present invention.

In FIG. 3, the angle of the light beam from the refractive index n0 to the film surface having the refractive index n1 with respect to the film surface is shown as θ.
Incident on the film surface is refracted at the film surface, and the angle θ ′ formed with the film surface inside the film has a relationship of n1 sin (θ ′) = n0 sin (θ), which is established by Snell's law.

Here, the angle is expressed in radians.

In the following equations, all are expressed in radians.

The angle between the light beam and the interface is the angle between the direction vector (straight line) of the light beam and the normal to the interface.

The angle between the interface and the film surface is the angle between the two planes.

The angle at which a light ray incident on the low refractive index area 3 of the film at an angle θ is incident from the high refractive index area 2 on the film to the low refractive index area 3 is ρ1 = π / 2. − (Sin-1 (n0 / n1 sin (θ)) −α).

Here, n0 is the refractive index on the side where the light beam enters the film, n1 is the refractive index of the region 2 having a high refractive index, and α is FIG.
Is the angle of the interface between the regions 2 and 3 having different refractive indexes in the film.

The angle ρ2 between the light beam boundary and the light beam in the low refractive index region 3 is ρ2 = sin-1 (n1 / n2 sin (ρ1)).

Here, n2 is the refractive index of the region 3 having a low refractive index.

The reflectivity of the p-polarized light at this interface is (tan (ρ1−ρ2) / tan (ρ1 + ρ2)) 2 FIG. FIG. 4 is a characteristic diagram illustrating a reflectance when p-polarized light is incident on a medium.

The reflectance of the s-polarized light at the interface is (-sin (ρ1−ρ2) / sin (ρ1 + ρ2)) 2 FIG. FIG. 4 is a characteristic diagram showing a reflectance when s-polarized light is incident on a medium having a ratio of 1.5.

As shown in FIGS. 4 and 5, when both p-polarized light and s-polarized light have ρ1>ρ1> sin-1 (n2 / n1), the light rays are totally reflected and reflectivity is high. Becomes 1.

When the incident angle is deeper than this, the reflectivity is extremely reduced as shown in the graphs of FIGS.

Therefore, in a film having a region having a slightly different refractive index, all light rays are reflected with respect to light that enters the interface at an angle smaller than the angle at which total reflection occurs.
At other angles, light rays are transmitted with little reflection.

When the regions 2 and 3 having slightly different refractive indices are arranged to be inclined, a light beam incident from a direction substantially along the inclination direction is shallow with the interface between the regions 2 and 3 having different refractive indices. Since the light is incident at an angle, the light is totally reflected at the boundary surface and its direction is bent.

FIG. 6 is a sectional view showing a configuration example of a liquid crystal display device using the optical film 1 according to the present embodiment.
FIG. 6 shows a case where illumination light is obliquely incident on the optical film 1 and is observed from a substantially vertical direction. That is, as shown in FIG. 6, in the liquid crystal display device, the optical film 1 according to the present embodiment is arranged on the viewer side of the liquid crystal cell 4, and further, the reflection layer is provided on the side opposite to the viewer side of the liquid crystal cell 4. 5 are arranged. For example, as shown in FIG. 6, the incident light beam is bent in a direction substantially perpendicular to the direction, is reflected by the reflection layer 5, and is formed at a boundary surface between the regions 2 and 3 having different refractive indexes at a deeper angle. Since the light is incident, it is not totally reflected, and most of the light is transmitted and reflected toward the observer.

Therefore, by applying the optical film 1 according to the present embodiment to a reflection type liquid crystal display device, it is possible to change the direction of an obliquely incident light beam and emit it. Similarly, a light beam incident from the front is also reflected on the boundary surface between the regions 2 and 3 having different refractive indexes and emitted obliquely.

That is, the light incident obliquely on the optical film 1 having the above-mentioned structure is changed in direction by being totally reflected at the boundary between the layers 2 and 3 having different refractive indexes. It has a property of transmitting light emitted from the liquid crystal cell 4.

When light is incident on the optical film 1 as described above from a direction substantially perpendicular to the film surface, the light is reflected at the interface of the layered distribution having different refraction in the film,
It is emitted in an oblique direction.

The angle as described above is a condition which is in good agreement with the normal observation condition. The illumination light is emitted in such a direction and diffused by the diffusion layer, so that the luminance is extremely high under the normal observation condition. A liquid crystal display device capable of observing a display image with a high level can be realized.

As described above, in the optical film 1 and the liquid crystal display device according to the present embodiment, the direction of light incident from a wide angle is changed to an appropriate direction, so that the present invention is applied to the display device. In this case, the overlap between the display image and the specular reflection of the external light source light is eliminated, and a bright and high-contrast display image can be obtained even when there is no special illumination light source such as a backlight or an edge light. .

Further, since the regions 2 and 3 having different refractive indices are arranged in a stripe shape, it is possible to easily manufacture the optical film 1. (Second Embodiment) FIG. 2 is a partial perspective view showing a configuration example of an optical film according to the present embodiment, and the same elements as those in FIG. 1 are denoted by the same reference numerals. That is, as shown in FIG. 2, in the optical film 1 according to the present embodiment, a plurality of regions having different refractive indexes (2 is a high refractive index region (layer), 3 is a low refractive index region ( Each of which has an elongated shape in one direction on the surface, is randomly arranged, and is distributed in a layered manner with a certain inclination with respect to the thickness direction of the film. It is a film having a structure, and light incident on the film is incident on light obliquely from a direction substantially along the inclination direction.
The direction of the light is changed by total reflection at the inclined interface between the three, and the light incident from other directions is transmitted as it is.

Next, in the optical film 1 according to the present embodiment configured as described above, similarly to the operation of the optical film 1 according to the above-described first embodiment, light incident from a wide angle is provided. By changing the direction to an appropriate direction, when applied to the display device, the display image and the regular reflection of the external light source light are eliminated, and there is no special illumination light source such as a backlight or an edge light. In this case, a bright and high-contrast display image can be obtained.

Furthermore, by randomly arranging the regions 2 and 3 having different refractive indexes, the influence of coloring due to light diffraction and interference due to the regularity of the arrangement of the regions 2 and 3 is suppressed. Thus, color change of the display image can be prevented. Therefore, by applying the optical film 1 according to the present embodiment to a reflection type liquid crystal display device, a normal liquid crystal display device using the optical film 1 according to the first embodiment is used. It is possible to realize a liquid crystal display device capable of observing a display image with extremely high luminance under observation conditions.

As described above, also in the optical film 1 and the liquid crystal display device according to the present embodiment, the direction of light incident from a wide angle is changed to an appropriate direction, so that the present invention is applied to the display device. In this case, the overlap between the display image and the specular reflection of the external light source light is eliminated, and a bright and high-contrast display image can be obtained even when there is no special illumination light source such as a backlight or an edge light. .

(Third Embodiment) As described above, in the optical film according to the present embodiment, a plurality of regions having different refractive indexes are inclined in the film thickness direction inside the film. In an optical film having a structure distributed in a layered manner, an angle α between an inclined interface between regions 2 and 3 having different refractive indices in the film and the film surface is an angle between light incident on the film and a normal to the film surface. To θ
And the respective refractive indices are n1 and n2 (where n1 and n2 are n1>
n2)

(Equation 3) I am trying to be.

Next, in the optical film according to the present embodiment configured as described above, similarly to the operation of the optical film 1 according to the first or second embodiment described above,
For light incident from a wide angle, the direction is changed to an appropriate direction. That is, when light is incident from the high refractive index region 2 to the low refractive index region 3 in the film, regions having different refractive indexes are changed. By applying total reflection at the interfaces of the two or three and emitting light with a shift in the front direction from the direction of the regular reflection, when applied to a display device, the overlap between the display image and the regular reflection of the external light source light is eliminated, and the backlight and the Even without a special illumination light source such as an edge light, a bright and high-contrast display image can be obtained.

Accordingly, by applying the optical film 1 according to the present embodiment to a reflection type liquid crystal display device, the liquid crystal display device using the optical film 1 according to the first or second embodiment described above can be used. Similarly to the above, it is possible to realize a liquid crystal display device capable of observing a display image with extremely high luminance under normal observation conditions.

That is, when light enters the optical film as in the present embodiment from an oblique direction almost parallel to the interface between the regions 2 and 3 having different refractive indices, the refractive indices differ at a shallower angle than a certain angle. When the light is incident on the boundary between the layers, the light is totally reflected, and is emitted from the film at an angle almost perpendicular to the incident light.

When this light is reflected by the reflective layer 5 and then enters the film again, it is incident at a deeper angle than when it first enters the film, so that it is transmitted without being totally reflected (FIG. 6). ).

For this reason, when light enters obliquely from the same direction as the inclination direction of the layers 2 and 3 having different refractive indexes, the light exits at an angle that is almost perpendicular to regular reflection.

Similarly, when light is incident from a direction almost perpendicular to the film surface, the light is totally reflected and emitted obliquely at the interface of the layered distribution having a different refractive index in the film, and is reflected by the reflection layer 5. And emit in an oblique direction (FIG. 7).

Further, when light is incident on the optical film as in the present embodiment almost in parallel with the layers 2 and 3 having different refractive indexes, the effect on the light is small and the visibility is almost the same as the conventional one. Can be obtained.

As described above, also in the optical film 1 and the liquid crystal display device according to the present embodiment, the direction of light incident from a wide angle is changed to an appropriate direction, so that the present invention is applied to the display device. In this case, the overlap between the display image and the specular reflection of the external light source light is eliminated, and a bright and high-contrast display image can be obtained even when there is no special illumination light source such as a backlight or an edge light. .

(Fourth Embodiment) Next, the appropriate refractive index difference between the layers having the different refractive indices of the optical film having different refractive indices as described above and the angle thereof will be examined.

The greater the difference in the refractive index, the wider the range of angles at which total reflection occurs at the interface between the layers 2 and 3 having different refractive indexes with respect to incident light.

At this time, however, the range of angles at which the light is reflected by the reflection layer 5 and totally reflected again upon entering the optical film becomes wider. Therefore, an appropriate difference in the refractive index can be obtained when the layers 2 and 3 having different refractive indexes in the film are formed at a certain angle.

Since the refractive index of a normal film is around 1.5, in the following examination, the refractive index of the film is 1.5.
And

Even when the refractive indices are different, almost the same results as in the following case can be obtained.

That is, when the layers 2 and 3 having different refractive indices are arranged at an inclination of 10 ° with respect to the thickness direction of the film, 30.2 ° to 1.0 ° when the refractive indices are 1.5 and 1.52. Is totally reflected at the boundary of the layer.

Similarly, when the layers 2 and 3 having different refractive indices are arranged at an inclination of 10 ° with respect to the thickness direction of the film, the refractive indices of 1.5 and 1.53 denote −33.9 °.
Light incident at 2.1 ° is totally reflected at the boundary of the layer.

The light of -2.1 ° to 2.1 ° is reflected again by this film.
The light of 33.1 ° is transmitted as it is. Therefore, the light incident on the liquid crystal display device at 33.1 ° to 2.0 ° can be bent by the film of the present embodiment, and the light emitted from the liquid crystal cell 4 can be transmitted.

For this reason, when the layers 2 and 3 having different refractive indexes are arranged at an inclination of 10 ° with respect to the thickness direction of the film, the difference in refractive index is preferably about 0.02.

When the layers 2 and 3 having different refractive indices are arranged at an inclination of 14 degrees with respect to the thickness direction of the film, and when the refractive indices are 1.5 and 1.54, light is emitted at the interface. The range for total reflection is 44.5 ° to 1.4 °.

Similarly, when the layers 2 and 3 having different refractive indices are arranged at an inclination of 14 ° with respect to the thickness direction of the film, and when the refractive indices are 1.5 and 1.55, a light Is totally reflected from 47.8 ° to -0.9 °.

However, at this time, the light of -0.9 ° to 0.9 ° is
The light is reflected from the liquid crystal cell 4 and again reflected from the film. Therefore, about 0.04 is appropriate as the refractive index difference in this case.

Similarly, when the layers 2 and 3 having different refractive indices are arranged at an inclination of 15 ° with respect to the thickness direction of the film, and when the refractive indices are 1.5 and 1.55, light is emitted at the interface between the layers. Is totally reflected from 49.9 ° to 0.6 °.

Similarly, when the layers 2 and 3 having different refractive indexes are arranged at an inclination of 15 degrees, and the refractive indexes are 1.5 and 1.56, the range in which light is totally reflected at the interface is 53.3 °. From -1.5 °.

However, at this time, the light of -1.5 ° to 1.5 ° is
The light is reflected from the liquid crystal cell 4 and reflected from the film. Therefore, about 0.05 is appropriate as the difference in refractive index in this case.

Further, when the layers having different refractive indices are arranged at an inclination of 16 °, when the refractive indices are 1.5 and 1.52, the range in which light is totally reflected at the interface is from 40.5 ° to 10.2 °.
It is.

Similarly, the layers 2 and 3 having different refractive indices are arranged at 16 °
1.5 and 1.55 when arranged at an inclination of
The total reflection of light at the interface is 52.0 °
From 2.2 °.

Similarly, the layers 2 and 3 having different refractive indices are arranged at 16 °
1.5 and 1.56 when arranged at an inclination of
The total reflection of light at the interface is 55.6 °
From 0.1 °.

Similarly, the layers 2 and 3 having different refractive indices are arranged at 16 °
1.5 and 1.57 when arranged at an inclination of
The total reflection of light at the interface is 59.2 °
From -1.8 °.

However, at this time, the light of -1.8 ° to 1.8 °
The light is reflected from the liquid crystal cell 4 and again reflected from the film. Therefore, about 0.06 is appropriate as the refractive index difference in this case.

On the other hand, as a method for producing such an optical film, there is a method of recording regions having different refractive indices using, for example, a polymer or the like whose refractive index is modulated by light or the like. In such a polymer, regions 2 and 3 having different refractions can be formed in a film in a stripe shape by two-beam interference or the like.

Examples of such a polymer include “RT Ingwall and Mark Troll,“ Mechanism of Holo ”
gram formation in DMP-128 photopolymer, ”OPTICAL
ENGINEERING June1989 Vol. 28 No. 6 p586-591 ".

This photopolymer has a refractive index modulation of 0.1.
06 or less. In the above-mentioned polymer, regions having different refractive indexes can be formed in the film by two-beam interference or the like.

As described above, layers 2 and 3 having different refractive indices were used.
By using such a photopolymer, it is possible to easily realize an optical film in which the high refractive index region 2 and the low refractive index region 3 have a refractive index of 1.5 and 1.56, respectively. Such an optical film has an effect in the range of 55.6 ° to 3.2 °, and a practically sufficient effect can be expected.

As an illumination condition for viewing a reflection type object, illuminating light is applied to JIS Z 8722 from an oblique direction of 45 ° and observation is performed from almost the front, or illumination is incident from the front.
The conditions for observation are described such that observation is performed from an angle of 45 °.

Under these conditions, based on the above consideration, the layers 2 and 3 having different refractive indices are arranged at an inclination of 14 °, and the refractive indices of the high refractive index region 2 and the low refractive index region 3 are determined. Is 1.54 and 1.5, respectively, the present optical film is effective for light rays of 45 ° or less with respect to a substantially perpendicular line of the film.

Since such an optical film has a smaller difference in refractive index, it can be formed more easily, and is extremely advantageous in terms of cost and the like.

Further, even when the difference in the refractive index is low, an optical film which is effective for illumination from, for example, 30 ° has a refractive index of 1.5 and 1.52 with a slope of 1 °.
It can be realized with the arrangement at 0 °, and under such conditions, it can be realized with many polymers,
It is possible to produce an optical film having a wider application range.

As described above, in the optical film and the liquid crystal display device according to the present embodiment, the refractive index difference in the film is set to 0.06 or less, or 0.04 or less, or 0.02 or less. When applied, more of the incident light can be reflected at the interface between the regions 2 and 3 having different refractive indices.
The functions of the optical film and the liquid crystal display device according to the embodiment can be further effectively achieved. Further, the angle θ between the light incident on the film and the normal to the film surface is 0 ° <θ <55 °, or 0 ° <θ <45 °,
Alternatively, since 0 ° <θ <30 °, when applied to a display device, more incident light can be reflected at the interface between the regions 2 and 3 having different refractive indexes. The functions of the optical film and the liquid crystal display device according to the third embodiment described above can be exhibited more effectively. (Other Embodiments) The present invention is not limited to the above embodiments, and can be variously modified and implemented without departing from the scope of the invention at the stage of implementation. (A) In each of the embodiments described above, the case where the light incident on the film is totally reflected at the interface from the higher refractive index to the lower one has been described, but the present invention is not limited to this. .

FIG. 8 is a sectional view showing a case where illumination light is incident on the optical film 1 obliquely and the light is totally reflected twice.

That is, as shown in FIG. 8, when the layers 2 and 3 having different refractive indices are arranged almost in parallel, the light incident on the film is changed from the interface having the higher refractive index to the interface having the lower refractive index. And may be totally reflected when the light is again emitted from a region having a high refractive index to a region having a low refractive index.

Thus, for example, as shown in FIG. 9, of the layers 2 and 3 having different refractive indices, the front side (rear side) has the width of the high refractive index layer 2 smaller than that of the low refractive index layer 3. On the other hand, the interval is made wider, and on the back side (front side), the width of the high refractive index layer 2 is made smaller than that of the low refractive index layer 3, that is, High refractive index layer 2
Has a trapezoidal cross-sectional shape such that the area on the observer side is large and the area on the liquid crystal cell 4 side is small. Since light is incident at an angle that is almost perpendicular to the angle at which total reflection occurs, light is transmitted because it is not totally reflected, so that it is possible to prevent light that has been totally reflected once from being totally reflected again. .

As a result, the functions of the optical film and the liquid crystal display device according to the first to fourth embodiments described above can be exhibited more effectively. (B) Also, as shown in FIG. 10, for example, of the layers 2 and 3 having different refractive indices, the band 2 having a higher refractive index is formed in a band shape so that the distance between the layer 2 and the layer 3 having a lower refractive index becomes wider. By adopting a structure, when applied to a display device, the light transmitted through the optical film before the light that has been totally reflected once is totally reflected again, so that the light that has been once totally reflected is prevented from being totally reflected again. Can be.

As a result, the functions of the optical film and the liquid crystal display device according to each of the above-described embodiments can be more effectively exerted. (C) In the optical films of the above-described embodiments, a sufficient effect cannot be obtained unless much of the incident light is reflected at the interface between the regions 2 and 3 having different refractive indexes. Therefore, it is necessary to arrange the layered structures at a fine pitch.

However, when the layered structure is arranged at a fine pitch, light that has passed through the layered structure causes interference, and wavelength selectivity and angle selectivity appear. A sufficient effect cannot be obtained.

Therefore, by adopting a structure in which the pitch at which the regions 2 and 3 having different refractive indices are arranged is changed randomly, the wavelength selectivity and the angle selectivity can be reduced when applied to a display device. Thus, the influence of color dispersion and the like can be suppressed.

As a result, the functions of the optical film and the liquid crystal display according to each of the above-described embodiments can be more effectively achieved. On the other hand, in order to obtain the same effect, it is also possible to make the optical film have a diffusivity by diffusing a diffusible material into the inside of the optical film of each of the embodiments described above.

Further, the diffusivity may be added by disposing a film having diffusivity on the film surface or by controlling the shape of the film surface.

On the other hand, the above-described embodiments may be implemented in appropriate combinations as much as possible. In that case, the combined functions and effects can be obtained. Furthermore, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent features. For example, even if some components are deleted from all the components shown in the embodiment, at least one of the problems described in the section of the problem to be solved by the invention can be solved, and In the case where (at least one of) the effects described in the section is obtained, a configuration from which this component is deleted can be extracted as an invention.

[0117]

As described above, according to the optical film of the present invention, the direction of light incident from a wide angle is changed to an appropriate direction. In addition, the overlap between the display image and the specular reflection of the external light source light is eliminated, and a bright and high-contrast display image can be obtained even when there is no special illumination light source such as a backlight or an edge light.

As described above, according to the liquid crystal display device of the present invention, the direction of light incident from a wide angle is changed to an appropriate direction. The overlap with regular reflection is eliminated, and a bright and high-contrast display image can be obtained even when there is no special illumination light source such as a backlight or an edge light.

[Brief description of the drawings]

FIG. 1 is a partial perspective view showing a first embodiment of an optical film according to the present invention.

FIG. 2 is a partial perspective view showing a second embodiment of the optical film according to the present invention.

FIG. 3 is a sectional view for explaining a coordinate system used in the optical film according to the present invention.

FIG. 4 is a characteristic diagram showing a reflectance when p-polarized light is incident from a medium having a refractive index n1 of 1.52 to a medium having a refractive index n2 of 1.5.

FIG. 5 is a characteristic diagram showing a reflectance when s-polarized light is incident from a medium having a refractive index n1 of 1.52 to a medium having a refractive index n2 of 1.5.

FIG. 6 is a sectional view showing a configuration example of a liquid crystal display device using the optical film according to the first embodiment.

FIG. 7 is a sectional view showing a configuration example of a liquid crystal display device using an optical film according to a third embodiment of the present invention.

FIG. 8 is a cross-sectional view showing a configuration example of a liquid crystal display device using an optical film according to another embodiment of the present invention.

FIG. 9 is a cross-sectional view showing another configuration example of a liquid crystal display device using an optical film according to another embodiment of the present invention.

FIG. 10 is a cross-sectional view showing another configuration example of a liquid crystal display device using an optical film according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical film 2 ... High refractive index area | region (layer) 3 ... Low refractive index area | region (layer) 4 ... Liquid crystal cell 5 ... Reflection layer.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H042 BA04 BA20 2H091 FA14X FA37X FA50X FB02 FC08 FC09 FD06 FD23 KA01 LA03 LA16 LA17 LA20 5G435 AA02 AA03 BB12 BB16 FF02 FF03 GG11

Claims (13)

[Claims] 1. An optical film having a plurality of regions having different refractive indexes inside a film, wherein each of the regions has a shape elongated in one direction on a surface,
It is arranged in a stripe shape, and has a structure in which the light is incident on the film obliquely from a direction substantially along the inclined direction, and has a structure in which the light is incident on the film obliquely with respect to the thickness direction of the film. For light, the direction of the light is changed by total reflection at an inclined interface between layers having different refractive indexes in the film, and for light incident from other directions, the light is An optical film characterized by being transmitted as it is. 2. An optical film having a plurality of regions having different refractive indices inside the film, wherein each of the regions has a shape elongated in one direction on a surface,
It is arranged randomly, and has a structure in which the light is incident on the film obliquely from a direction substantially along the inclined direction, and has a structure in which the light is incident on the film and is distributed in a layered manner with respect to the thickness direction of the film. For, the direction of the light is changed by total reflection at an inclined interface between layers having different refractive indices in the film, and the light incident from other directions is left as it is. An optical film characterized by being transmitted. 3. An optical film having a plurality of regions having different refractive indices inside a film, wherein each of the regions has a structure in which the regions are distributed in a layered manner with respect to a thickness direction of the film. An angle α between an inclined interface between regions having different refractive indexes in the film and the film surface is an angle between light incident on the film and a normal to the film surface, and the respective refractive indices are n1 and n2. (However, n1,
When n2 is n1> n2), An optical film, characterized in that: 4. The optical film according to claim 3, wherein an angle θ between light incident on the film and a normal to the film surface is set to 0 ° <θ <55 °. Optical film. 5. The optical film according to claim 3, wherein an angle θ between light incident on the film and a normal to the film surface is set to 0 ° <θ <45 °. Optical film. 6. The optical film according to claim 3, wherein an angle θ between light incident on the film and a normal to the film surface is set to 0 ° <θ <30 °. Optical film. 7. The method according to claim 1, wherein
The optical film according to claim 1, wherein a difference in refractive index in the film is 0.06 or less. 8. The method according to claim 1, wherein
The optical film according to claim 1, wherein a difference in refractive index in the film is 0.04 or less. 9. The method according to claim 1, wherein
The optical film according to claim 1, wherein the difference in the refractive index in the film is 0.02 or less. 10. The optical film according to claim 1, wherein a pitch at which the regions are arranged is changed at random. 11. The optical film according to claim 1, wherein, among the layers having different refractive indices, a layer having a higher refractive index corresponds to a layer having a lower refractive index. An optical film characterized by having a large interval. 12. The optical film according to claim 1, wherein, of the layers having different refractive indices, a width of a layer having a high refractive index is larger on a front side (back side). The interval between the layers having a lower refractive index is set to be wider than the width of the layer having a lower refractive index. An optical film characterized in that: 13. An optical film according to claim 1, wherein the optical film according to claim 1 is arranged on a viewer side of a liquid crystal cell which defines a display pattern by transmitting / non-transmitting light. Characteristic liquid crystal display device.