JP2002189105A - Off-axis anisotropic light scattering film and display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-scattering film having both of scattering anisotropy and scattering directivity and having not only the light-scattering property without causing changes in colors of the display light by the observation position but also the off-axis scattering directivity, and to provide a display device which uses the light-scattering film. SOLUTION: In the film, portions with different refractive indices are distributed while having irregular forms and thickness to form stripes of densities with different refractive indices. In a specified film cross section, the running direction of the density stripes is tilted from the principal plane of the film and a referable tilt angle is 13 deg.±4 deg.. To make the off-axis light-scattering characteristics significant, the tilt angle is gradually changed along the thickness direction of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a characteristic that the scattering property varies (or has an incident angle selectivity) depending on the incident angle of light, that is, "anisotropic". “Angle” is the “off-axis” light scattering property that causes strong light scattering in the direction where the center of the optical axis is different, and a light-scattering film that has directivity in the light-scattering property. The present invention relates to a display device capable of improving performance (brightness, contrast, and the like) and reducing power consumption.

[0002] The above-mentioned display device does not require a special light source such as a backlight or an edge light, and uses a reflection type liquid crystal display of a type in which reflected light from ambient light (such as sunlight or indoor illumination light) is used as display light. Device, a “transmissive liquid crystal display device” of the type having the special light source built in the display device, or a “reflective / transmissive liquid crystal display device (a transflective liquid crystal display) Device). Hereinafter, in this specification, a liquid crystal display device will be mainly described. However, the present invention is not limited to this, and may be applied to a type in which a pixel emits light, such as a plasma display (PDP) or electroluminescence (EL). It is needless to say that the present invention is also applied to the display device described above and the CRT television screen.

In the present invention, when the terms "scatter" and "diffusion" are used for light, they are synonymous. Also, the terms “film” and “sheet” are used as synonyms in the present invention.

[0004]

2. Description of the Related Art In a liquid crystal display device, a viewing angle at the time of observation is secured (that is, a display image is brightly displayed on the front surface of the display device), and uniform brightness is provided over the entire display screen. In order to make a display image visible, a light scattering film is arranged on the front of the device.
As a conventional light scattering film, a resin film whose surface is processed into a mat shape, a resin film containing a diffusing material inside, and the like are used.

However, in the case of the above-mentioned film, a function of changing the scattering property depending on the incident angle of the incident light (hereinafter referred to as a function).
(Referred to as scattering anisotropy) is difficult in principle, and does not actually have such a function.
When used in a display device, there is a problem that unnecessary scattered light is generated, resulting in a decrease in display brightness and contrast or blurring of a displayed image.

In the case of a light-scattering film whose surface is processed into a mat shape, the film surface is physically processed like a sand blaster treatment to form a matte surface, or the film surface is chemically treated by dissolution treatment with an acidic or alkaline solution. A mat surface is formed. It is possible to control the scattered light emission range / direction (hereinafter referred to as scattering directivity) by controlling the matte surface (shape of unevenness, etc.), but it is the principle to control even the scattering anisotropy. Difficult.

[0007] In a light-scattering film containing a diffusing material therein, attempts have been made to control the refractive index, size and shape of the diffusing material in order to control the scattering anisotropy. At present, it is technically difficult and not sufficiently practical.

[0008] In particular, the above-mentioned film has no scattering anisotropy or off-axis light scattering characteristics, has low light scattering directivity,
Even when applied to a display device, unnecessary scattered light is generated in a direction due to reflection from the outermost surface of the display device (specular reflection direction) or in a direction inappropriate for observing a display image, resulting in a decrease in display brightness and contrast. Or blurring of the displayed image.

On the other hand, there is little backscattering property and strong forward scattering property (light scattering occurs only when ambient light enters the display device, and light scattering does not occur when display light is emitted from the device). Patent application for a reflective liquid crystal display device using a scattering plate having scattering anisotropy is disclosed in Japanese Patent Application Laid-Open No. 8-201.
No. 802.

[0010] In the invention described in the above publication, the structure of the scattering plate is not specifically described, but only "transparent fine particles hardened with a transparent polymerizable polymer". In such a scattering plate, even if the scattering anisotropy (forward or backward) can be controlled, even the scattering directivity can be controlled in the same manner as the “light scattering film containing a diffusing material inside”. It is difficult.

A patent application for a transmission type liquid crystal display device using a hologram as a scattering plate is disclosed in Japanese Patent Laid-Open No. 9-152.
No. 602. The above application scatters display light emitted from a liquid crystal display device having a backlight, and employs a hologram as a scattering plate, so that it is easy to control scattering anisotropy and scattering directivity. However, since the spectrum (wavelength dispersion) is inevitably involved, the color of the display light changes and is visually recognized as the viewpoint to be observed is moved.

[0012]

As described above, the various prior arts according to the above-mentioned application have light scattering properties of both scattering anisotropy and scattering directivity, and change the color of display light depending on the observation position. There is no report on light scattering sheets that do not.

According to the present invention, it is easy to provide scattering anisotropy (forward or backward and selectivity of incident angle) and to control even scattering directivity (vertical and horizontal scattering ranges and directions). It is an object of the present invention to provide a light-scattering film having a characteristic in which the color of display light does not change depending on an observation position, and a display device using the same.

In particular, an object of the present invention is to make the above-mentioned light-scattering film have "off-axis" light-scattering characteristics so that scattered light can be emitted in a direction suitable for observation, thereby increasing the efficiency of use of light contributing to observation. And

[0015]

The light-scattering film according to the first aspect of the present invention is such that portions having different refractive indices are distributed in an irregular shape and thickness inside the film, and have a high or low refractive index. A band-like shading is formed, and in a specific film cross section, the direction in which the band-like shading extends is inclined with respect to the main surface of the film, and the inclination direction gradually extends over the thickness direction of the film. This is a modified configuration, and the light incident at a specific range of angles according to the above-mentioned inclination direction causes light scattering, and has the strongest intensity distribution in the direction having the center of the optical axis different from the incident direction. An off-axis anisotropic light-scattering film having a light-scattering property having an incident-angle selectivity and an off-axis function such that light emitted at a different angle is transmitted without causing light scattering. The inclination direction Is off-axis anisotropic light-scattering film which is characterized in that the angle range including 13 ° ± 4 ° with respect to the normal to the beam.

According to a second aspect of the present invention, a portion having a different refractive index is distributed in an irregular shape and thickness inside the film to form a band-like shading having a high and low refractive index.
In a specific film cross section, the direction in which the band-like shading extends is inclined with respect to the main surface of the film, and the inclination direction is an angle in a range including 13 ° ± 4 ° with respect to the normal to the film. In accordance with the above-mentioned inclination direction, for light incident at a specific range of angles, light is scattered and emitted with the strongest intensity distribution in the direction having the center of the optical axis different from the incident direction, An off-axis anisotropic light-scattering film characterized by having light-scattering properties having an incident-angle selectivity and an off-axis function, for light incident at other angles, transmitting without causing light scattering. .

According to a third aspect of the present invention, light incident obliquely with respect to the normal to the film has scattered transmitted light having a strong intensity distribution in a direction closer to the normal to the film than the incident angle. The light is emitted.
The off-axis anisotropic light-scattering film according to 1.

According to the fourth aspect of the present invention, the portions having different refractive indices forming the band-like shading are irregular in size, and are exposed in a vertically long (or horizontally long) shape on the film surface. In addition, according to the shape exposed on the surface of the film, the light scattering characteristic has directivity such that the range / direction in which light is scattered and emitted is horizontally (or vertically) long. An off-axis anisotropic light-scattering film according to claim 1.

According to a fifth aspect of the present invention, the light emission /
The off-axis anisotropic light-scattering film according to any one of claims 1 to 4 is disposed on the front side (observer side) of an image display element whose display pattern is changed by modulating non-emission. It is a display device having a configuration.

According to a sixth aspect of the present invention, there is provided an image display device in which a display pattern is changed by modulating transmission / non-transmission (or transparency / scattering) of each pixel according to an applied voltage. A display device having a configuration in which the off-axis anisotropic light-scattering film according to any one of claims 1 to 4 is disposed at any position on the front side (observer side) or the back side (opposite to the observer). is there.

According to the present invention, a liquid crystal panel in which a display pattern is changed by modulating transmission / non-transmission (or transparency / scattering) of each pixel in accordance with an applied voltage is provided. Front side of the panel (observer side)
A display device having a configuration in which the off-axis anisotropic light-scattering film according to any one of claims 1 to 4 is disposed at any position on the front surface (the observer side) or the back surface (the side opposite to the observer) of the glass. It is.

<Operation> The light-scattering film of the present invention can easily control scattering anisotropy (incident angle selectivity) and scattering directivity in the production thereof. The observation range (viewing range) of the image can be appropriately set, and the display luminance in the setting range can be improved.

In particular, since it has an "off-axis" scattering directivity, when applied to a reflection type liquid crystal display device, display light other than the direction in which incident ambient light (sunlight or illumination light) is specularly reflected. It is possible to emit scattered light that

Since the light-scattering film has the above-mentioned characteristics, even if the light-scattering film has scattering anisotropy (incidence angle selectivity), if light scattering occurs in accordance with the scattering anisotropy, incident light is With respect to the scattered emission light, the center optical path of each other has a relationship of regular reflection.

In the reflection type liquid crystal display device, the display light having the highest luminance is emitted in the direction in which the ambient light is specularly reflected. At the same time, the direction of the specular reflection is the same as that of the transparent member disposed outside the display surface. This is the direction in which the effect of glare on the surface of (generally, glass) is the strongest, and conversely, display light may be difficult to see.

By providing the off-axis scattering directivity, it is possible to emit the display light having the highest luminance in a direction other than the direction in which the ambient light is specularly reflected (generally in the front direction of the display device). The adverse effects of glare are avoided.

In applications other than the reflection type liquid crystal display device, the display image light is scattered to an appropriate range due to the incident angle selectivity of the light scattering film. Light) is directly transmitted without being scattered, so that a decrease in contrast due to light other than display image light does not occur.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. <Embodiment 1> FIGS. 1A and 1B are explanatory views showing an example of the light scattering film of the present invention. FIG. 1A is a plan view, and FIG.

As shown in the figure, inside the light scattering film, portions having different refractive indices are distributed in an irregular shape and thickness, and a band-like shading having a high and low refractive index (in FIG.
(Expressed in black).

In FIG. 1B showing a specific film cross section,
The portions having different refractive indexes are distributed in a state where the direction in which the band-shaped shading extends is inclined leftward and downward with respect to the main surface of the film.

Further, the inclination direction is gradually changed in the thickness direction of the film (the direction in which the shading extends closer to the main surface of the film is closer to the lower side in the figure). It has become.

First, the optical characteristics of the light scattering film 1 shown in FIG. 1 will be considered with reference to FIG. The portion having a different refractive index is distributed, and the angle substantially along the direction in which the band-like shading extends inclining (the angle 2 is an angle θ from the perpendicular of the film 1, and the arrow 2 in the figure)
Light), light scattering occurs.

For light incident at an angle (almost perpendicular) different from the above direction (direction of arrow 4 in the figure), it functions as a mere transparent film, and the incident light exits without being scattered.

In the light scattering film 1, the direction in which the portion having a different refractive index extends obliquely changes gradually in the thickness direction of the film, and the incident light has such a characteristic that light scattering is strongly generated along the direction. In the case where light rays enter the film at an angle at which light scattering occurs, the scattered light emitted from the film spreads in a direction different from the incident angle of the incident light (the direction of arrow 3 in the drawing).

Next, referring to FIG. 1 (a), the portions having different refractive indices are irregularly distributed on the film surface and thus do not have the regularity of a hologram. No induced chromatic dispersion occurs. Therefore, according to the light scattering film of the present invention, the color of emitted light does not change depending on the observation position, and an ideal white color is exhibited.

When the shape of the portion having a different refractive index is vertically long (or horizontally long), when light incident on the portion is scattered and emitted, the light scattering characteristic of the light emitted from each portion is horizontally long (or long). Or, it has directivity such that it is vertically long.

The above shape is generally elliptical,
The smaller the size, the wider the scattering range, and the larger the size, the narrower the scattering range. In order to control the scattering characteristics in the vertical and horizontal directions, the vertical / horizontal length ratio is selected from about 30: 1 to 1:30, and the size is in the range of 1 μm to 100 μm. It is chosen to be an angle. FIG.
In (a), the emitted light is scattered vertically because the shape is horizontally long. This will be described later in the manufacturing process of the light scattering film 1.

FIG. 2 is a graph showing an example of scattering anisotropy (incident angle selectivity) of the light scattering film 1 of the present embodiment. In the figure, as shown by a solid line 5, the haze value is 80% or more for light in a specific incident angle range (0 ° to 60 ° in the figure), and conversely, the incident angle is symmetrical to that (− in the figure). The haze value for light of 60 ° to 0 °) is 20% or less, which indicates the light scattering anisotropy (incident angle selectivity) referred to in this specification.

FIG. 3 is a graph showing an example of the off-axis function of the light scattering film 1 of the present invention. The figure shows that, when the illumination light is incident on the light-scattering film 1 of the present invention at an incident angle of 30 ° (in FIG. 2, one of the angles at which the haze value is 80% or more), the emitted scattered light is It is a graph which shows an intensity distribution.

As shown in FIG.
The strongest scattered light is generated in the direction. In other words, the optical axis is shifted in a direction different from the incident angle of 30 °, which indicates the off-axis function referred to in the present invention.

Further, as described above, when the shape of the portion having a different refractive index on the film surface is horizontally long (or vertically long), when light incident on the portion is scattered and emitted, each portion has a different shape. Has a directivity such that the light scattering characteristic of the outgoing light becomes vertically long (or horizontally long). For example, when the shape is horizontally long as shown in FIG. 1A, the scattered light emitted from the light scattering film shows the intensity distribution of the scattered light.
As can be seen from FIG.

<Embodiment 2> FIG. 8 is an explanatory view showing an example of the light-scattering film of the present invention. FIG.
FIG. 8B is a cross-sectional view of a specific cross section. In the present embodiment, the light scattering film according to <Embodiment 1> described with reference to FIGS. 1 to 4 has substantially the same structure and optical characteristics based thereon, and uses the same reference numerals for the same components. And the same explanation holds.

In the present embodiment, as shown in FIG. 8 (b), the angle at which the portions having different refractive indices are distributed and the band-shaped shading extends obliquely (the angle at which the incident light causes light scattering), as shown in FIG.
The structure is inclined in an angle range including 3 °. Further, in the present embodiment, unlike the first embodiment, a configuration in which the inclination angle gradually changes in the thickness direction of the film is not essential.

As in the case of the first embodiment, it is assumed that light is scattered with respect to light incident in the direction of arrow 2 shown in FIG. In the figure, the angle of arrow 2 is larger than 13 ° within a range in which scattering anisotropy occurs.

FIG. 9 is an enlarged view showing a specific portion having a substantially elliptical shape having a different refractive index. The optical path through which the incident light is scattered and emitted will be described with reference to FIG. 9. At this time, when viewed microscopically, the incident light 2 is regularly reflected at the interface of the elliptical portion.

As a result, the centers of the optical axes of the incident light 2 and the scattered emission light 3 are shifted, the scattered emission light 3 has an angle close to the normal direction of the film, and the light scattering film 1 has an off-axis function. Become. That is, the angle of the incident light 2 is slightly larger than 13 °, and the center of the optical axis of the scattered emitted light 3 is slightly smaller than 13 ° and close to the normal direction of the film.

When considering the use form of a standard reflection type liquid crystal display device, the user faces almost vertically to the display screen, and the ambient light (room light or daylight) from obliquely above.
Is most often used for observation. The user is required to make sure that the ambient light to the device is incident between approximately 20 ° and 40 °.
Usually, the relative relationship between the device and the direction of the incident light is set.

In consideration of standard observation conditions, it is necessary that the above-mentioned angle of inclination in the film has a certain width, and the refraction of light at the interface of the film 1 at the time of input / output is required. As a result of experimental confirmation in consideration, it was found that a range of ± 4 ° with 13 ° as the center was preferable.

The description in the plan view of FIG. 8A is exactly the same as in the first embodiment. In order to make the off-axis light scattering characteristics remarkable, it is preferable to gradually change the inclination angle even in the film as in the first embodiment. It is preferable to adopt the form 2 and these can be used arbitrarily.

FIG. 5 is a sectional view conceptually showing a main part of a reflection type liquid crystal display device to which the light scattering film 1 of the present invention is applied. The display device includes a liquid crystal panel 6, a specular or scattering reflector 7 disposed on the back surface (non-observer side), and a light scattering film disposed on the front surface of the liquid crystal panel 6 (observer side). 1 and 1.

The reflecting plate 7 is not a separate member from the liquid crystal panel 6 as shown in the figure, but may be of a type in the liquid crystal panel 6 as a reflector (referred to as a reflecting electrode) which also serves as a liquid crystal driving electrode. When the reflector 7 is semi-transmissive (both reflection and transmission functions) and a backlight is required on the back side (non-observer side) of the reflector 7, a reflection / transmission type liquid crystal display device (semi-transmissive) (Transmissive liquid crystal display device) is also possible.

Although the light scattering film 1, the liquid crystal panel 6, and the reflection plate 7 are shown separated from each other for convenience of explanation, they are actually integrally laminated. Depending on the type of liquid crystal, a polarizing plate, a retardation plate or other optical film, a color filter, an alignment film, a transparent electrode, or the like may be used, but is not shown.

The liquid crystal panel 6 has a general structure, modulates incident light according to the presence or absence of an applied voltage, and performs switching display between white / black (transmission / non-transmission).

As shown in the figure, the light scattering film 1 causes light scattering when the incident light 8 enters the light scattering film 1 from the front side of the liquid crystal display device, and scattered light whose optical axis is shifted from the incident light. 9 is emitted. The scattered light 9 is reflected by the reflection plate 7 on the back side of the liquid crystal panel 6, passes through the light scattering film 1, and is emitted to the front. At this time, the light scattering film 1 transmits the scattered light 10 to be emitted without secondary scattering.

As described above, due to the scattering anisotropy (incident angle selectivity) of the light scattering film 1, unnecessary scattering at the time of emitting display light does not occur, and a so-called double image due to reflection of pixels is obtained. Therefore, blurring of the display image can be reduced. In addition, the scattering directivity (especially off-axis function) can reduce unnecessary scattering and improve the brightness and contrast of the display in front of the display device.

The liquid crystal display panel 6 of the liquid crystal display device includes:
Either a color display panel or a monochrome display panel equipped with a color filter corresponding to the R, G, and B pixels may be used. The liquid crystal display device is a TN type,
STN system, guest host system, polymer dispersion type, etc.
The driving method of the liquid crystal is not limited.

Next, the structure of the light scattering film 1 of the present invention will be described in more detail. As described above, the light-scattering film 1 of the present invention has a light and shade pattern having a high or low refractive index by distributing portions having different refractive indexes in irregular shapes and thicknesses.

If the difference in the refractive index is too small, the scattering property deteriorates. On the other hand, if the difference is too large, light scattering occurs regardless of the incident angle of the light. It becomes difficult to have characteristics. Therefore, light scattering does not occur only by the refractive index difference on the surface, and the film 1 needs to have an optimal refractive index difference such that the film 1 has a sufficient scattering property due to its thickness.

In the present invention, the following conditions are satisfied:
The refractive index difference is appropriately selected in the range of 0.001 to 0.2,
The film thickness ranges from 1000 μm to 1 μm depending on the refractive index
m is appropriately selected.

Since the refractive index difference that can be recorded is limited by the method of producing the film and the recording material, the film is made thinner when the refractive index difference is large, and thicker when the refractive index difference is small. It is possible to realize the light scattering film of the present invention.

For example, a portion having a refractive index of 1.56 (refractive index difference 0.04) is distributed in a film having an average refractive index of 1.52 and a thickness of 20 μm to form a light and shade pattern. As a result, a light scattering film having sufficient scattering properties and incident angle selectivity could be obtained.

The distribution of shading in the film (in a specific section,
The direction in which the band-shaped shading extends obliquely varies depending on the application of the light scattering film. However, taking the front scattering plate for a reflection type liquid crystal display device shown in FIG. 5 as an example, the direction perpendicular to the display device (0). Function that scatters light incident from 60 ° (upward from the front of the device) to 60 ° (downward from the front of the device), and conversely, does not scatter light from the normal direction to -60 ° (downward from the front of the device). It is desirable in practical use.

As described above, it is necessary to generate light scattering most efficiently for incident light at an angle of 20 ° to 40 ° (obliquely upward). On the other hand, it is often observed at an angle between −20 ° from the perpendicular direction (0 ° = front).

The incident light at an angle of 20 ° to 40 ° is
In order to transmit the scattered light mainly in the direction of °, the above-mentioned inclination angle in the film is optimally in the range of 13 ° ± 4 °.

The direction (angle) of the light beam is assumed to be 0 ° perpendicular to the reference plane, and + in the clockwise direction and − in the counterclockwise direction.
It is common in the field of optics. Therefore, in FIG. 5, considering the incident light, the incident light 8 is
The angle of incidence is + because the light is incident from above from the incident surface in a clockwise direction with respect to a vertical line on the observer side. Considering the outgoing light, the scattered light 9 has a positive outgoing angle because the scattered light 9 is emitted clockwise downward from a vertical line standing on the reflecting plate 7 side from the outgoing surface. Since the scattered light 10 is emitted counterclockwise downward from a vertical line on the viewer side from the emission surface, the scattered light 10 has a negative emission angle.

In order to remarkably realize the off-axis function as shown in FIG. 3, the light-scattering film according to the first embodiment has a structure in which the inclination angle is gradually changed with respect to the thickness direction of the film. Has become.

Taking the front scattering plate for a reflection type liquid crystal display device shown in FIG. 5 as an example, the liquid crystal display device is approximately -20 ° from the perpendicular direction (0 ° = front) (downward from the front of the device).
Therefore, it is desirable that the incident light 8 having an incident angle of 30 ° be scattered light 9 whose center of the optical axis is shifted. (The emission angle of the scattered light 9 is centered at + 20 °, and the emission angle of the scattered light 10 is centered at −20 °.)

For this reason, the light scattering film 1 shown in FIG.
Means that the incident light from the 30 ° direction is shifted by -10 ° with respect to the center of the optical axis.
The structure has a structure in which the inclination angle of a portion having a different refractive index with respect to the film thickness direction is gradually changed so that the light is scattered in a shifted direction.

In this example, considering the refraction of light at the film interface, the inclination angle is about 19 ° from the direction perpendicular to the film in the vicinity of the film surface (upper section in FIG. 1) as described above. The angle of inclination gradually decreases toward the rear surface of the film (the lower side in the cross-sectional view of FIG. 1), and the structure is inclined approximately 6.5 ° from the direction perpendicular to the film near the rear surface of the film.

The size of the portions having different refractive indices is random and non-regular in order to cause light scattering, but in order to have the required scattering, the average size is 0.1 mm in diameter.
It is appropriately selected from the range of 1 μm to 300 μm according to the scattering property required for each application.

As an example, a light and shade pattern having an average size of 12 μm and having a high and low refractive index can provide about ± 4%.
A scattering property having a scattering spread of about 0 ° was obtained.

In order to make the light scattering have directivity,
In the vertical direction and the horizontal direction of the film (the plan view of FIG. 1), the average size of the portions having different refractive indexes is different. As an example, in order to generate light scattering in an elliptical shape extending in the vertical direction, the average size in the vertical direction is 12 μm, but the average size in the horizontal direction is 50 μm, so that the shape is elongated in the vertical direction. Thus, a light scattering film having a scattering directivity of about ± 40 ° in the horizontal direction and about ± 10 ° in the horizontal direction was obtained.

Although the light scattering film of the present invention has been described in the specification as a film in the present specification, for example, it is a sheet formed on a hard substrate such as a glass substrate or a resin substrate. Is also good.

Therefore, in the liquid crystal display device shown in FIG. 5, the light scattering film 1 of the present invention is not necessarily a film separate from the liquid crystal panel 6 as shown in FIG. 11 may be formed.

At this time, the light scattering film 1 of the present invention
The functions described above can be used regardless of whether the front glass 11 is on the viewer side or the liquid crystal layer side.

Hereinafter, means for producing the light scattering film of the present invention will be described. The light scattering film of the present invention can be produced by an optical exposure means.

FIG. 6 is an explanatory view showing an example of an optical system for producing the light scattering film 1 having the structure shown in FIG. 1 using a speckle pattern. A ground glass 16 is irradiated with a laser beam 15 emitted from a laser light source 14. A photosensitive material 19 is disposed at a predetermined distance F on the surface of the frosted glass 16 opposite to the laser irradiation side, and a speckle pattern, which is a complex interference pattern generated by laser light transmitted and scattered by the frosted glass 13, is applied to the photosensitive material 19. Exposure is recorded.

At this time, since the laser beam 15 and the photosensitive material 19 are arranged at a predetermined angle α as shown in the figure, the speckle pattern is exposed and recorded at a predetermined angle in the photosensitive material. Become.

Since this angle corresponds to the inclination of the portion having a different refractive index in the light scattering film 1 (that is, the scattering peak angle θ of the incident angle selectivity shown in FIG. 2),
The angle is appropriately selected within a range of about 0 to 60 ° depending on the application. As a matter of course, the inclination of the portion having a different refractive index in the light scattering film 1 and the scattering peak angle θ of the incident angle selectivity are different angles due to the refraction of light at the film interface.

Further, the inclination angle α between the laser beam 15 and the photosensitive material 19 and the scattering peak angle θ of the incident angle selectivity may be different depending on the processing steps such as recording and development depending on the photosensitive material used.

The laser light source 14 used for exposure recording can be appropriately selected and used from the wavelengths of 514.5 nm, 488 nm and 457.9 nm of an argon ion laser depending on the sensitivity of the photosensitive material. In addition, other than an argon ion laser, any laser light source having good coherence can be used. For example, a helium neon laser, a krypton ion laser, or the like can be used.

The photosensitive material 19 used here is a photosensitive material capable of recording the form of change in the refractive index between an exposed portion and an unexposed portion by a laser beam, and has a higher resolution than a light and shade pattern to be recorded. The material must be capable of recording a pattern in the direction of its thickness.

As such a recording material, a photosensitive material for a volume hologram can be used, and a silver salt photosensitive material 8E56 for hologram manufactured by Agfa, an HRF film for a hologram manufactured by DuPont or gelatin dichromate, Polaroid Co., Ltd. DMP-128 recording material can be used.

Description of “Optical Measurement Handbook, Asakura Shoten, written by Toshiharu Tada et al., Published on November 25, 1994” (p.266-p.26)
According to 8), in a speckle pattern in which the density and the phase show random values depending on the position, the size of the pattern is inversely proportional to the angle at which the diffusion plate is viewed from the photosensitive material, and the average diameter of the pattern is determined. Is done. Therefore, when the size of the diffusion plate is made larger in the vertical direction than in the horizontal direction,
The pattern recorded on the photosensitive material is finer in the vertical direction than in the horizontal direction.

In the speckle pattern according to the manufacturing method using the optical system shown in FIG. 6, the wavelength λ of the laser beam 15 to be used, the size D of the ground glass 16, and the distance F between the ground glass 16 and the photosensitive material 19 are recorded. The average size d of the pattern is determined. Generally, d is expressed by the following equation. d = 1.2λF / D

The average length t of the speckle pattern in the depth direction is represented by t = 4.0λ (F / D) ² .

As described above, by optimizing the values of λ and F / D, the light scattering layer 2 having a desired three-dimensional refractive index distribution so as to have a desired scattering property can be obtained. As an example, if λ = 0.5 μm and F / D = 2, d =
1.2 μm, t = 8 μm, the light and shade pattern on the film surface is distributed at an average of 1.2 μm, and in the thickness direction of the film, it is distributed at an average of 8 μm in a direction according to the inclination angle. .

However, these sizes are merely average sizes. Actually, the sizes are variously large and small with respect to these sizes, and portions having different refractive indexes are inclined on the surface and in the depth direction. Will be distributed.

In the light scattering film produced by the above-described means, portions having different refractive indexes are distributed at the same inclination angle φ which does not change in principle in the thickness direction of the film as it is. (See FIG. 7a)

In order to realize an anisotropic light-scattering film having a large off-axis function as in Embodiment 1, it is necessary to gradually change the tilt angle over the thickness direction of the film. The means will be described below.

Varying the inclination angle φ of the portion having a different refractive index is achieved by changing the film thickness L of the light scattering film 1 on which the portion having a different refractive index is recorded. That is, the same inclination angle φ as shown in FIG.
The film thickness L of the light scattering film recorded in FIG.
As shown in (1), when the inclination angle φ is increased to L ′, the principle that the inclination angle φ changes to φ ′ is used.

In the thickness direction of the film, the film thickness was not changed uniformly over the entire surface, and as shown in FIG. If the increase in the thickness is large near (in the figure, near Y), the off-axis anisotropic light-scattering film of the present invention can be realized.

Depending on the material constituting the light scattering film,
Because the processing method to change the thickness is different, as an example,
"HRF film", a hologram photosensitive material manufactured by DuPont
The case where is used will be described.

The HRF film is obtained by laminating a “CTF film” commercially available from DuPont after exposure recording of the hologram, and changing the thickness of the photosensitive material itself by a predetermined process (heating and UV exposure fixing). And has the property of changing the reproduction color of the hologram.

Although this is known in the art, it is possible to control the variation in thickness by the processing step.

"PROCEEDINGS OF SPIE", Volume 3637,
p196, “Holographic Diffusive Reflectors for Refle
As described in Fig. 7 in “Ctive color LCDs” and its description, the mechanism of film thickness increase is that the monomer in CTF diffuses into the HRF film and increases its thickness. Therefore, by controlling the diffusion time of the monomer after laminating the CTF and the HRF, the film thickness is greatly increased on the side of the HRF facing the CTF, and is increased on the opposite side where the CTF is not laminated. There may be conditions that do not increase so much.

Taking the front scattering plate for a reflection type liquid crystal display device as an example, the anisotropic light scattering film is exposed and recorded on the HRF film by the above-mentioned means (tilt angle: 19 °).
Laminate the TF film on the back side of the HRF film,
By heating and leaving at 40 ° C. for about 40 seconds and fixing by UV exposure, the inclination angle of the portion having a different refractive index in the film thickness direction is about 19 ° near the film surface and about 6.5 near the back surface. ° off-axis anisotropic light-scattering film can be obtained.

In order to impart scattering directivity to the light scattering film 1, the size of the ground glass used in the optical system shown in FIG. Can be realized by:

As an example, the size D of the frosted glass 16 differs between the vertical (y) direction and the horizontal (x) direction, and
Assuming that (Dx) = 2, (F / Dy) = 20 and other conditions are the same as above, the average size dx in the horizontal direction of the speckle pattern is 1.2 μm, and the average size dy = 1 in the vertical direction.
The speckle pattern has an average size of 2 μm and an aspect ratio of 1:10.

By performing exposure recording in this way, a light scattering film having scattering anisotropy having different scattering properties in the vertical and horizontal directions can be obtained.

The above manufacturing means is merely an example,
The present invention is not limited to this, and the light-scattering film of the present invention may be realized by a manufacturing method other than optical exposure means.

[0102]

As described above, according to the present invention, not only the color of the display light does not change depending on the observation position, but also the off-axis scattering A light-scattering film having a property is provided.

That is, in the light scattering film of the present invention,
Light incident on the film at an angle within a predetermined range causes light scattering, and light incident at a different angle functions as a mere transparent film. When light is incident at an angle at which scattering occurs, it has scattering directivity in which scattered light is generated in a direction different from the incident angle off the optical axis. Therefore, light that requires light scattering and light that does not require light scattering can be separated according to the angle of incidence on the film, and the required scattered light can be deflected in a desired direction.

In particular, considering the standard viewing conditions of the display device, the ambient light incident on the device at an angle of approximately 20 ° to 40 ° makes it possible to view a bright display image in front of the device. It is preferable to set the inclination angle at which the portions having different refractive indices are distributed within a range of ± 4 ° around 13 °.

When the light-scattering film of the present invention is applied to a display device, an appropriate observation position (approximately in front of the device) can be obtained without unnecessary scattering due to light incident on the display device.
This has the effect of improving the brightness, definition, visibility, and contrast of the display, and reducing the blur of the displayed image.

Further, since the portions having different refractive indices in the light scattering film are irregularly distributed on the film surface, there is no change in the color of the emitted light according to the observation position as seen in the hologram.

In addition, when light is incident at an incident angle at which light scattering occurs, it is possible to also have a scattering directivity in which the spread of the scattered light differs vertically and horizontally. As a result, scattered light can be emitted only in a necessary range and direction, and as a result, when used in a display device, the effect of improving display brightness and contrast without generating unnecessary scattering can be obtained. is there.

[0108]

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a light scattering film of the present invention. (Plan view and sectional view)

FIG. 2 is a graph showing an example of incident angle selectivity of the light scattering film of the present invention.

FIG. 3 is a graph showing an example of an emitted light intensity distribution showing scattering anisotropy (off-axis function) of the light scattering film of the present invention.

FIG. 4 is an explanatory view showing the scattering directivity of the light scattering film of the present invention.

FIG. 5 is a sectional view conceptually showing a main part of a reflection type liquid crystal display device using the light scattering film of the present invention.

FIG. 6 is an explanatory view showing an example of an optical system for producing the light scattering film shown in FIG. 1 using a speckle pattern.

FIG. 7 is an explanatory view conceptually showing a production means for imparting an off-axis function to the light scattering film of the present invention.

FIG. 8 is an explanatory view showing a light scattering film of the present invention. (Plan view and sectional view)

FIG. 9 is a partially enlarged explanatory view showing the inside of the light scattering film of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light-scattering film 2 ... Illumination light incident from a scattering direction 3 ... Emitted scattered light from a light-scattering film 4 ... Illumination light incident from a transmission direction 5 ... Plot of measured haze value 6 ... Liquid crystal panel 7 ... Reflector 8 ... peripheral illumination light 9 ... scattered light 10 ... emitted scattered light 11 ... front glass plate of liquid crystal panel 12 ... liquid crystal layer 13 ... rear glass plate of liquid crystal panel 14 ... laser light source 15 ... laser light 16 ... ground glass 17 ... beam expander 18 ... Collimator 19: photosensitive material

 ──────────────────────────────────────────────────続 き Continued on front page F-term (reference) 2H042 BA01 BA15 BA20 2H091 FA23Z FA32Z FB04 FC10 FC24 FC26 FC29 FC30 FD06 FD22 LA16 5G435 AA01 AA02 BB12 BB16 DD14 FF02 FF03 FF05 FF06

Claims (7)

[Claims] 1. In a film, portions having different refractive indices are distributed in an irregular shape and thickness to form a band-like shading composed of high and low refractive indices. The direction in which the shading extends is inclined with respect to the main surface of the film, and the inclination direction is gradually changed over the thickness direction of the film. For light incident at, the light is scattered and emitted with the strongest intensity distribution in the direction having the center of the optical axis different from the incident direction,
For light incident at other angles, an off-axis anisotropic light-scattering film having a light-scattering property having an incident-angle selectivity and an off-axis function such that the light is transmitted without causing light scattering. The direction is 13 ° ± 4 with respect to the film normal.
An off-axis anisotropic light-scattering film having an angle in a range including °. 2. Within the film, portions having different refractive indices are distributed in an irregular shape and thickness to form a band-like shading consisting of high and low refractive indices. The direction in which the shading extends is inclined with respect to the main surface of the film, and the inclination direction is an angle in a range including 13 ° ± 4 ° with respect to the normal line of the film. For light incident at a specific range of angles, light is scattered and emitted with the strongest intensity distribution in a direction having the center of the optical axis different from the incident direction,
An off-axis anisotropic light-scattering film characterized by having an incident angle selectivity and a light-scattering property having an off-axis function so that light incident at other angles is transmitted without causing light scattering. 3. A light transmitted obliquely with respect to a normal line of a film emits scattered transmitted light having a strong intensity distribution in a direction closer to the normal line of the film than the incident angle. The off-axis anisotropic light-scattering film according to claim 1. 4. A portion having a different refractive index for forming a band-like shading is irregular in size, and is exposed in a vertically long (or horizontally long) shape on the film surface, and is exposed on the film surface. Depending on the above shape, the range / direction in which light is scattered and emitted is horizontally long (or vertically long).
The off-axis anisotropic light-scattering film according to claim 1, wherein the film has directivity in light scattering characteristics. 5. An image display device whose display pattern is changed by modulating light emission / non-light emission of each pixel.
A display device having a configuration in which the off-axis anisotropic light-scattering film according to any one of claims 1 to 4 is arranged on a front side (viewer side). 6. An image display device in which a display pattern is changed by modulating transmission / non-transmission (or transparency / scattering) of each pixel according to an applied voltage, so that a front side (observer side) is provided. A display device having a configuration in which the off-axis anisotropic light-scattering film according to any one of claims 1 to 4 is disposed at any position on the back side (the side opposite to the observer). 7. A liquid crystal panel whose display pattern is changed by modulating transmission / non-transmission (or transparency / scattering) of each pixel according to an applied voltage. Either on the surface of the glass (observer side) or on the back side (on the side opposite to the observer),
A display device comprising the off-axis anisotropic light-scattering film according to claim 1.