JP2001141912A - Colored light-diffusing sheet and liquid crystal display device using the sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-scattering sheet which controls the wavelength (color) of the scattered light exiting from the sheet and if necessary, which can easily control the scattering anisotropy and scattering directivity, and to provide a liquid crystal display device using that sheet. SOLUTION: The light scattering sheet has such a structure in the sheet that a part having a different refractive index is distributed, and the part having a different refractive index is formed within the size of the visible ray wavelength (380 to 780 nm). The scattering anisotropy and scattering directivity are controlled by changing the shape and distribution (direction) of the aforementioned part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet having a function to scatter and emit incident light, and more particularly to a light scattering sheet in which the wavelength (color) of scattered and emitted light is controlled. Also, if necessary, by imparting the incident angle selectivity to the sheet, such that the scattering properties vary according to the incident angle of light, such as `` scattering anisotropy '', and when light scattering occurs, The present invention relates to a light scattering sheet in which “scattering directivity” having directivity in its direction and range is also controlled. In addition, the present invention relates to a liquid crystal display device in which the above-described sheet is applied to improve visibility (brightness, contrast, and the like) of a display image and reduce power consumption of the display device.

The above-mentioned liquid crystal display device does not require a special light source such as a backlight or an edge light, and uses a reflection type liquid crystal of a type in which reflected light from ambient light (sunlight, indoor illumination light, etc.) is used as display light. Display device "and a" transmission type liquid crystal display device "of the type having the above-mentioned special light source.

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, it is difficult in principle to provide a function of changing the scattering property (scattering anisotropy) depending on the incident angle of the incident light, and such a function is actually provided. When used for display devices,
There is a problem that unnecessary scattered light is generated, which causes a decrease in display brightness and contrast, or a blurred display 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 in principle difficult to control the scattering anisotropy by controlling the matt surface (shape of irregularities, etc.).

[0007] Even in a light scattering film containing a diffusing material therein, in order to control the scattering property, the refractive index of the diffusing material,
Attempts have been made to control the size, shape, etc., but at present it is technically difficult and not sufficient for practical use.

Accordingly, the above-mentioned light-scattering film has no selectivity of incident angle of light-scattering and has little or no anisotropy of light-scattering, so that unnecessary scattered light is generated when used in a display device. As a result, there is a problem that the brightness and contrast of display are reduced or a displayed image is blurred.

[0009] In addition to the above-mentioned scattering anisotropy, a function required for the light scattering film relates to control of “scattering directivity” such as an emission direction and an emission range of light emitted by generating light scattering. Function.

Hereinafter, known documents relating to a liquid crystal display device using a light scattering film will be introduced. The scattering anisotropy is that there is almost no backscattering property and strong forward scattering properties (light scattering occurs only when the ambient light enters the display device, and no light scattering occurs when the display light is emitted from the device). Japanese Patent Application Laid-Open No. Hei 8-201802 is known as a proposal for a reflection type liquid crystal display device using a scattering plate.

[0011] In the above publication, the structure of the scattering plate is not specifically described, but is merely described as "solid 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”. Is difficult.

As a proposal for a transmission type liquid crystal display device using a hologram as a scattering plate, Japanese Patent Application Laid-Open No. 9-152
No. 602 is known. The above proposal 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.

As a proposal for a light-scattering film having scattering anisotropy and scattering directivity, and having no color change of scattered light observed with movement of the viewpoint, the present applicant has proposed a Japanese Patent Application No. 10-346743. Has filed.

The above application discloses a spectroscopic pattern (light and dark spots generated when light with good coherence is scattered and reflected or transmitted by a rough surface or a light diffuser) on a photosensitive material, thereby obtaining a spectroscopy unique to a hologram. (Wavelength dispersion) is solved, and the outline thereof is as follows.

In the film, portions having different refractive indices are distributed in irregular shapes and thicknesses to form a light and shade pattern having high and low refractive indices.
And a second region having a substantially different refractive index from the second region. The first and second regions have an irregular but roughly band-like shape, and the scattering directivity is determined by the shape and distribution exposed on the film surface, and the scattering anisotropy is determined by the distribution form in the cross section of the film. It is determined.

According to the above-mentioned application, a light-scattering film having no change in color of scattered light observed with movement of a viewpoint is realized, and the emission direction and emission range of display light are controlled. It is white (colorless). When a full-color image is displayed on a liquid crystal display device or the like, the display image is colored by another member different from the light scattering film (generally, a color filter adjacent to the liquid crystal panel in the display device). Will contribute.

[0017]

The main object of the present invention is to provide an unreported "wavelength (color) of scattered emitted light".
A light-scattering sheet that can control the scattering anisotropy and the scattering directivity, if necessary, and a liquid crystal display device to which the sheet is applied. Is to provide.

[0018]

According to a first aspect of the present invention, there is provided a light-scattering sheet having a structure in which portions having different refractive indexes are distributed inside the sheet. Within a range of 380 nm to 780 nm, a range of ± 100 nm centered on a specific value, and selectively and strongly scatters light in a specific wavelength range (specific color) equal to the size of the above-described portion of incident light. It is characterized by making it.

In the light scattering sheet according to the second aspect, the shape of the portion having a different refractive index is an ellipsoid, and in the sheet, the elliptical portion is arranged inside the sheet with its major axis and minor axis aligned in the same direction. Dispersed, formed as a shade of high and low refractive index, light is transmitted by generating light scattering at a specific range of angles along the direction of the long axis, and for light incident at angles other than the above. 2. The colored light-scattering sheet according to claim 1, wherein the sheet has a scattering anisotropy that allows the light to pass through without causing light scattering.

According to a third aspect of the present invention, the light scattering sheet has a scattering directivity such that a direction and a range of light scattering and transmission are controlled according to the shape of the ellipsoid.
It is a colored light-scattering sheet of the description.

According to a fourth aspect of the present invention, in the liquid crystal panel for performing full-color display, wavelengths at which light scattering occurs are set in a pattern corresponding to the arrangement of the liquid crystal cells of R, G, and B colors. The colored light-scattering sheet according to any one of claims 1 to 3, wherein the colored light-scattering sheet is configured to be divided into regions as described above, and to have a pattern in which shading having a high or low refractive index is patterned.

Further, in the liquid crystal display device according to the present invention, the light-scattering sheet according to any one of claims 1 to 4 is arranged on the front surface (on the observer side) or the back surface (on the side opposite to the observer) of the liquid crystal panel. It becomes.

<Function> The light scattering sheet of the present invention is most functionally characterized in that the wavelength (color) of the scattered emission light can be controlled. When the light scattering sheet is applied to a liquid crystal display device to display an image, In addition to controlling the direction and range of the scattered emission of the display light, the incident light from a predetermined direction can be colored as desired and emitted as full-color display light.

Further, structurally, it is a remarkable feature that an element constituting a shade having a high or low refractive index in a sheet is an elliptical small piece of a predetermined size. In the volume hologram, interference fringes are recorded in a form in which layers having different refractive indexes and transmittances are laminated (around 1000 layers / mm) in the thickness direction of the sheet (photosensitive material). In the pattern, the part with different refractive index has irregular shape and
In this configuration, the thickness is distributed as a speckled pattern.

As described above, as a proposal for a light scattering film using a speckle pattern, the present applicant
We have filed Japanese Patent Application No. 10-346743. The shape in which the “region consisting of portions having different refractive indices” in the above application is exposed on the film surface is approximately band-like, but the incident light is scattered in the minor axis direction, and their distribution is dense. The more the degree, the greater the degree of scattering. In the cross section of the film, the first and second regions are approximately layered, but when the incident light is incident on the layer at an angle close to parallel, light scattering occurs, but when the incident light is incident on the layer at an angle close to perpendicular, light scattering occurs. It simply transmits.

According to the present invention, a portion having a different refractive index, which is “approximately band-shaped” in the above-mentioned application, is defined as “an elliptical small piece having a major axis and a minor axis”, and by controlling the size thereof,
The color tone of the scattered emission light can be controlled together with the scattering directivity.

It is well known that the size of particles in the scattering phenomenon is related to light scattering characteristics or light diffusion characteristics when traveling in a medium. Numerous examples have been described in the literature relating to the difference between the color of smoke rising from a lit cigarette and the color of smoke of a cigarette exhaled from a human mouth.

According to this, the smoke coming directly from the tip of the cigarette looks blue on a dark background. This is because the particles constituting the smoke are sufficiently smaller than the wavelength of the ambient light. In contrast, the color of cigarette smoke emanating from a person's mouth appears white. In this case, water droplets sufficiently larger than the wavelength of the ambient light exist in the particles constituting the smoke, and the particles non-selectively reflect and refract at all wavelengths (colors).

With respect to the color of light caused by the light scattering phenomenon, the size of the particles can be divided into the following three. It is smaller than the wavelength of the incident light. It is larger than the wavelength of the incident light. Close to the wavelength of the incident light.

Rayleigh scattering is known as light scattering without wavelength change caused by particles whose size is 1/10 or less of the wavelength (of the incident light), and corresponds to the above case.

If the particle size is larger than the wavelength of light, the phenomenon of reflection and refraction exists (non-selectively) for every wavelength (color). Therefore, the diffusion effect is the same for all wavelengths, and therefore, when white light enters, white diffused light is observed.

On the other hand, when the size of the particles is close to the wavelength of the incident light, the scattered light has a remarkable color. In the present invention, the wavelength (color) of the scattered light is controlled by utilizing the phenomenon in this case.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a graph showing the scattering efficiency calculated by Mie.
DCHogg co-authored "Effects of precipitation on propag
ationat 0.63, 3.5 and 10.6 microns "(Bell Laboratories, Technical Journal 47, p723-759 1968), showing the scattering characteristics for three wavelengths (0.63 μm, 3.5 μm, 10.5 μm). The vertical axis in the figure is the value of the “scattering coefficient” with respect to the radius of the water droplet (on the horizontal axis), and the larger the value, the more light scattering occurs. From the figure, 0.63μm (630nm ≒ red) and 3.5μm (3500nm =
It can be seen that the light scattering at a wavelength (outside visible) has a higher “scattering coefficient” when the size of the water droplet is close to the value of the wavelength.

FIG. 2 is an example of a graph in which the scattering efficiency is plotted. The graph in this figure is very similar to the waveform shown in FIG. 1, but the scattering efficiency of Mie is plotted against a parameter x defined by the following equation (1). x = kr = 2πr / λ (1) where k is the amplitude of the wavelength vector, r is the radius of the small piece, and λ is the wavelength of the radiation.

From the two viewpoints, the following analysis is made from the graph. It is a viewpoint of whether the “scattering coefficient K” functions so as to change the wavelength while keeping the size of the small piece, or functions as the size of the small piece when the wavelength has only a single value. Focus on the first perspective. Mie's rigorous analysis is used for the case where the calculation is complicated and the wavelength change is abrupt as illustrated in FIG. It is difficult for even a skilled person to approximate sudden vibrations and gentle convergence to mathematical expressions, but the general behavior shown in FIG. 2 has been experimentally proved and phenomena confirmed. ing.

If the diffuser is composed of small pieces of a size close to the selected wavelength size as described above, a "colored diffuser" is obtained. FIG. 3 is an explanatory diagram showing the relationship between the size of a small piece and the wavelength when scattering occurs. When a small piece extending in one direction is illuminated, the size is close to the size of the small piece (the size of the short axis; a). Light scattering at the wavelength (λ ≒ a) will occur.

The extended shape of the small piece has other effects besides causing light scattering at a specific wavelength. FIG. 4 is a graph showing an example of the scattering anisotropy (incident angle selectivity) of the light scattering sheet of the present invention.

As shown in the figure, the diffusion efficiency is low for incident light having an incident angle of about -60 ° to 0 ° on the light scattering sheet, and for incident light in that angle range, The sheet does not cause light scattering and functions simply as a transparent sheet. On the other hand, the diffusion efficiency is high for incident light in a specific incident angle range (+ 30 ° to + 60 °), and the sheet causes light scattering, and exhibits a diffusion efficiency of about 90% at the maximum. Depending on the characteristics (use) required of the light scattering sheet, its parameters, for example,
The diffusion efficiency, diffusion angle, etc. are changed.

FIG. 5 shows that small pieces (portions having different refractive indices) that cause light scattering inside the main surface of the light scattering sheet are dispersed with their major and minor axes aligned in the same direction.
It is sectional drawing which shows notably the state formed as the shading which has a high and low refractive index. In FIG. 5A, the elliptical small pieces 2 having different refractive indexes are parallel to the main surface of the sheet 1 without being inclined in the thickness direction of the sheet 1 (the major axis is indicated by an arrow 3).
(a state aligned in the direction of a). FIG.
In (b), the elliptical small pieces 2 having different refractive indices are
In the thickness direction of the sheet 1, the sheet 1 is inclined with respect to the main surface of the sheet 1 and is distributed non-parallel (in a state where the long axes are aligned in the direction of the arrow 3b).

The light scattering characteristics of the light scattering sheet 1 will be described. For light incident on the main surface of the light scattering sheet 1 at an angle along the direction in which the major axes of the elliptical small pieces 2 having different refractive indexes are distributed (arrow 3b in FIG. 5B), the small piece 2 Light scattering occurs at a wavelength (color) corresponding to the size of the light beam. For light incident at an angle different from the above direction,
It functions simply as a transparent sheet, and emits incident light without being scattered.

The above will be described with reference to the cross-sectional view of FIG. 6. The light scattering sheet 62 has an angle A (arrow 3b in FIG. 5B).
When the incident light 61 is incident at an angle corresponding to
Thus, light of a component having a wavelength (color) corresponding to the size of the internal small piece is scattered and emitted as colored diffused light 63. Light having a component other than the wavelength (color) does not scatter and is emitted as colored non-diffused light 64.

When the incident light 61 is incident at an angle B different from the above-mentioned A, the light of any wavelength (color) is not scattered on the sheet 62, and only the uncolored transmitted light is emitted. It will be emitted as 65.

Regarding the scattering directivity, if the shape of a portion having a different refractive index on the surface (not shown) of the film is vertically long (or horizontally long), light incident on the portion is scattered and emitted. Each of the portions has a directivity such that the light scattering characteristic of the light emitted from each portion becomes horizontally long (or vertically long). In the present invention, the portions having different refractive indices are elliptical (sp
heroid = spheroid), and the above “vertical or horizontal” corresponds to the major axis or minor axis of the ellipse.

An example of a method for manufacturing such a light scattering sheet will be described below. By recording a light and dark spot pattern (speckle pattern) generated when light with good coherence is scattered and reflected or transmitted by a rough surface or a light diffuser on a photosensitive material, a light scattering sheet based on the speckle pattern is exposed and recorded. . For example, a standard speckle pattern is recorded by irradiating frosted glass (rough surface) with light having good coherence, such as laser light, and exposing the light passing through the frosted glass to a photosensitive material.

In the present invention, the size and the shape are controlled instead of the random spot pattern, and the portions having different refractive indices are formed.
As shown in FIG. 7, a mask having an opening is arranged close to the photosensitive material in order to form the shading in the sheet, and the opening of a predetermined pattern formed in the mask is irradiated with recording light from a predetermined angle. To record on a photosensitive material. The pattern formed on the mask is a group of a plurality of holes having the same size, and the size is set according to the wavelength at which diffusion occurs selectively as described above. The arrangement of the holes is random to avoid other diffraction phenomena.

Exposure recording is performed by irradiating ultraviolet parallel light. When the mask is irradiated with the parallel light of the ultraviolet light, a portion having a different refractive index (an elliptical shape corresponding to the shape of the opening) in the photosensitive material is inclined with respect to the main surface of the photosensitive material according to the irradiation angle. Distributed and formed. This angle is
This corresponds to the inclination angle of a portion having a different refractive index in the light scattering sheet.

The photosensitive material used here is a photosensitive material capable of recording an exposed portion and an unexposed portion of a laser beam in the form of a change in the refractive index. The photosensitive material has a higher resolving power than the density to be recorded and has a thickness direction. Must be a material that can record patterns.

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, gelatin dichromate, polaroid DMP-128 recording material can be used.

FIG. 8 shows three types of cells (a red cell 81 and a green cell 8 whose wavelengths to be selectively diffused are R, G, and B).
2, the colored diffusion sheet 8 of the present invention composed of blue cells 83)
FIG. 4 is an explanatory diagram showing an example of 0. As shown in the figure, each part (red cell 81, green cell 82, and blue cell 83) divided into regions on a cell basis receives diffused light corresponding to the corresponding color when white light enters at a predetermined angle. Is emitted in a predetermined direction, and light of other wavelengths is transmitted without being diffused.

The case where the light scattering sheet of FIG. 8 is applied to a liquid crystal display will be described. FIG. 9 is an explanatory view conceptually showing an example of a transmission type liquid crystal display device using the light scattering sheet of the present invention.

When the incident light 91 is incident on the light scattering sheet 92 at an angle that matches the scattering anisotropy (incident angle selectivity), light is scattered by the sheet 92 and is incident on the liquid crystal panel 93. The light is emitted as display light (diffused light). In FIG. 9, the liquid crystal panel 93 has R, R for color display.
This is a configuration in which three types of liquid crystal cells of G and B are arranged, and a configuration in which the light scattering sheet 92 selectively diffuses three types of wavelengths is in a 1: 1 correspondence. The light scattering sheet 92 and the liquid crystal panel 93 are disposed in close contact with each other in order to prevent the diffused outgoing light from the light scattering sheet 92 from entering the liquid crystal cell of an uncorresponding color. The liquid crystal panel 93 has a general structure, and modulates incident light in accordance with the presence or absence of an applied voltage, and switches between white and black (transmission / non-transmission).

In general, description of polarizing plates used before and after a liquid crystal panel is omitted, and a retardation plate or another optical film may be used depending on the type of liquid crystal, but is omitted here. I do.

As described above, the light scattering sheet of the present invention can be applied to a transmission type liquid crystal display device. in this case,
The light scattering sheet is designed to have scattering anisotropy (incidence angle selectivity) so as to cause light scattering when light from a light source such as a backlight or an edge light incorporated in the display device is incident. By arranging the above light scattering sheet between the liquid crystal panel and the light source, the light scattering sheet of the present invention functions to make only light of a predetermined wavelength incident on a liquid crystal cell of a predetermined wavelength. It is also possible to have a function similar to a color filter that emits light.

[0054]

As described above, according to the present invention,
A novel light scattering sheet in which the wavelength (color) of the scattered light is controlled is provided. Further, by applying / controlling the scattering anisotropy and the scattering directivity to the sheet, it is more preferable for application to a liquid crystal display device. The liquid crystal display device using the above sheet has the effects of improving the brightness, fineness, and contrast of the display without causing unnecessary scattering, reducing the blur of the display image, and displaying full-color images. For the purpose, the display light of the desired color can be diffused and emitted in the direction of the observer to make it visible.

[0055]

[Brief description of the drawings]

FIG. 1 is a graph showing scattering efficiency calculated by Mie.

FIG. 2 is an example of a graph plotting scattering efficiency.

FIG. 3 is an explanatory diagram showing a wavelength at which light scattering occurs and a size of a small piece by the light scattering sheet of the present invention.

FIG. 4 is a graph showing an example of scattering anisotropy (incident angle selectivity) of the light scattering sheet of the present invention.

FIG. 5 is a diagram showing a light scattering sheet in which small pieces that cause light scattering inside the light scattering sheet are dispersed with their major and minor axes aligned in the same direction, and formed as shades of high and low refractive indexes. Sectional drawing which shows a state notionally.

FIG. 6 is a cross-sectional view illustrating scattering anisotropy (incident angle selectivity) of the light scattering sheet.

FIG. 7 is an explanatory view showing an example of an optical system for producing the light scattering sheet of the present invention.

FIG. 8 is an explanatory view showing an example of the colored diffusion sheet of the present invention composed of three types of cells in which wavelengths to be selectively diffused are three types of R, G, and B.

FIG. 9 is an explanatory view conceptually showing an example of a transmission type liquid crystal display device using the light scattering sheet of the present invention.

[Explanation of symbols]

 1, 62, 92 light scattering sheet 2 small pieces (different refractive index) 61, 91 incident light 63 colored diffused light 64 non-diffused light 65 transmitted light 93 liquid crystal panel

Claims (5)

[Claims] 1. A light scattering sheet having a structure in which portions having different refractive indexes are distributed inside the sheet, wherein the size of the portions having different refractive indexes is from 380 nm to 780.
A range of ± 100 nm centered on a specific value within a range of nm, and selectively and strongly scatters light in a specific wavelength range (specific color) equal to the size of the above portion of incident light. A colored light scattering sheet characterized by the following. 2. The shape of a portion having a different refractive index is an ellipsoid. In the sheet, the elliptical portion is dispersed in the sheet with its major axis and minor axis aligned in the same direction. The light incident at a specific range of angles along the direction of the long axis causes light scattering and transmits, and the light incident at other angles does not cause light scattering as it is. 2. The colored light-scattering sheet according to claim 1, wherein the sheet has a scattering anisotropy that allows transmission. 3. The colored light-scattering sheet according to claim 2, wherein the sheet has a scattering directivity such that the direction and range of light scattering and transmission are controlled according to the shape of the ellipsoid. 4. A liquid crystal panel for performing full-color display is divided into regions such that wavelengths at which light scattering occurs are set in a pattern corresponding to the arrangement of liquid crystal cells of R, G, and B colors. The colored light-scattering sheet according to any one of claims 1 to 3, wherein a shade having a high or low refractive index is patterned. 5. A liquid crystal display device, wherein the light scattering sheet according to claim 1 is disposed on the front side (observer side) or the back side (opposite side of the observer) of a liquid crystal panel. .