JPH1082910A - Optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently cut the zero-order light in a hologram cut filter and to prevent problems of decrease in contrast or decrease in chromaticity in a display device, by using long-chain dye molecules which has absorptivity to the component of light parallel to the axis of the molecule but have no absorptivity to the component of light in the normal direction of the molecular axis. SOLUTION: The long-chain dye molecules in the dichroic dye show different absorptivities of light depending on the direction of the molecular axis. The molecules have almost no absorptivity to the component of light in the normal direction of the molecular axis and transmit the light, but the molecules have absorptivity to the component of light in the parallel direction to the molecular axis and does not transmit light. Therefore, in a hologram color filter 5 with <=40 deg. incident angle of back light 3, for example, the diffracted light 15 with wavelength dispersion by the optical film 19 can be condensed into a liquid crystal display device without cutting, while the zero-order transmitted light 14 can be completely cut.

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 field-of-view selection film for a display, a stray light cut filter, a zero-order light cut filter for a HOE, and the like.

[0002]

2. Description of the Related Art In recent years, direct-view displays using liquid crystals have been commercialized mainly for color notebook PCs in the OA field. In such a liquid crystal display device, since the energy of a battery serving as a power source of a display backlight is limited, it is necessary to increase the light use efficiency of the entire liquid crystal panel in order to use it for a long time.

A color filter for a color liquid crystal display device will be described as an example. Compared to the conventional wavelength absorption type,
The present applicant has disclosed in Japanese Patent Application No. 5-12170 and the like that a hologram color filter can be used to allow each wavelength component of the backlight to be incident on each liquid crystal cell without waste and without absorption, thereby greatly improving the efficiency of use of the backlight. Proposed.
There are two types of configurations, the first type is composed of an eccentric Fresnel zone plate-shaped micro-hologram array. The second type consists of a hologram or diffraction grating composed of parallel and uniform interference fringes and a microlens array superimposed thereon. Less than,
These hologram color filters will be briefly described.

A liquid crystal display device using a hologram color filter of the first type will be described with reference to the sectional view of FIG. In this figure, the liquid crystal cell 6 'is regularly arranged.
Backlight 3 of liquid crystal display element 6 divided into (pixels)
A hologram array 5 constituting the hologram color filter is arranged at a distance from the incident side. On the back surface of the liquid crystal display element 6, a black matrix 4 provided between the liquid crystal cells 6 'is arranged. In addition to the above, polarizing plates (not shown) are arranged on both sides of the liquid crystal display element 6. In addition, between the black matrix 4, similarly to the conventional color liquid crystal display device, an absorption type color filter that transmits light of colors corresponding to R, G, and B color separation pixels is additionally arranged. You may do so.

The hologram array 5 has a repetition period of R, G, and B color pixels, that is, a set of three liquid crystal cells 6 ′ adjacent to each other in the direction of the liquid crystal display element 6 in the plane of the drawing. The micro holograms 5 'are arranged in an array at the same pitch as the repetition pitch. The micro holograms 5' are aligned with each set of three liquid crystal cells 6 'adjacent to each other in the direction of the plane of the liquid crystal display element 6, and each hologram 5' Each of the micro holograms 5 ′ corresponds to the light of the green component in the backlight 3 that enters at an angle θ with respect to the normal to the hologram array 5 and corresponds to the micro hologram 5 ′. It is formed in a Fresnel zone plate shape so that light is condensed on the liquid crystal cell G at the center of the three color separation pixels R, G, and B. The micro hologram 5 ′ has a relief type, which has no or little wavelength dependence of the diffraction efficiency.
It consists of transmission holograms such as phase type and amplitude type. Here, the fact that there is no or little wavelength dependence of the diffraction efficiency is not a type that diffracts only a specific wavelength and does not diffract other wavelengths like a Lippman hologram,
Means that one diffraction grating diffracts any wavelength,
The diffraction grating having a small wavelength dependence of the diffraction efficiency diffracts at different diffraction angles according to the wavelength.

With such a configuration, when the white backlight 3 which is incident at an angle θ with respect to the normal line from the surface of the hologram array 5 opposite to the liquid crystal display element 6 is incident, the wavelength is reduced. Accordingly, the diffraction angle of the minute hologram 5 'is different, and the condensing position for each wavelength is dispersed in a direction substantially parallel to the surface of the hologram array 5. Among them, the red wavelength component is located at the position of the liquid crystal cell R displaying red, the green component is located at the position of the liquid crystal cell G displaying green, and the blue component is located at the position of the liquid crystal cell B displaying blue. By arranging the hologram array 5 so as to diffract and condense, each color component passes through each liquid crystal cell 6 'with little attenuation by the black matrix 4, and the color components of the liquid crystal cell 6' at the corresponding position. Color display according to the state can be performed.

As described above, by using the hologram array 5 as a color filter, each wavelength component of the conventional backlight for a color filter can be made incident on each liquid crystal cell 6 'without waste and without absorption. Can be greatly improved.

A liquid crystal display device using a hologram color filter of the second type will be described with reference to the sectional view of FIG. In the figure, a hologram color filter 10 of the second type comprises a hologram 7 and a condensing microlens array 8, and microlenses 8 'constituting the microlens array 8 are R, G, B color separation. The pixels are arranged in an array at the same pitch as the repetition cycle of the pixels, that is, each set of three liquid crystal cells 6 ′ adjacent to each other in the direction of the paper surface of the liquid crystal display element 6. The hologram 7 is composed of parallel and uniform interference fringes acting as a diffraction grating, and is formed of a transmission hologram such as a relief type, a phase type, and an amplitude type having little or no wavelength dependence of diffraction efficiency. On the back surface of the liquid crystal display element 6, a black matrix 4 provided between the liquid crystal cells 6 'is arranged. In addition to the above, polarizing plates (not shown) are arranged on both sides of the liquid crystal display element 6. In addition, between the black matrix 4, similarly to the conventional color liquid crystal display device, an absorption type color filter that transmits light of colors corresponding to R, G, and B color separation pixels is additionally arranged. You may do so.

With such a structure, the hologram 7
When the backlight 3 is incident on the surface opposite to the liquid crystal display element 6 at an angle θ with respect to the normal line, the light is diffracted at different angles depending on the wavelength and dispersed on the exit side of the hologram 7. . Due to the microlenses 8 ′ arranged on the entrance side or the exit side of the hologram 7, this dispersed light
The light is separated and focused on the focal plane for each wavelength. Among them,
The red wavelength component is diffracted and condensed at the position of the liquid crystal cell R for displaying red, the green component is diffracted and condensed at the position of the liquid crystal cell G for displaying green, and the blue component is condensed at the position of the liquid crystal cell B for displaying blue. As described above, by arranging the color filter 10, each color component passes through each liquid crystal cell 6 'with little attenuation by the black matrix 4, and corresponds to the state of the liquid crystal cell 6' at the corresponding position. Color display can be performed.

In such an arrangement, a hologram 7 can be a transmission-type hologram having uniform interference fringes and having a small wavelength dependence of diffraction efficiency, instead of a light-collecting property. And the pitch of the microlens array 8 is different from that of each liquid crystal cell 6 '.
It is three times as large as the conventional case where one microlens is arranged corresponding to each, and is characterized in that it is easy to manufacture and easy to align.

In such a color filter for a color liquid crystal display device, when natural polarized light or elliptically polarized light is used as the backlight 3, the light is not diffracted by the hologram color filters 5, 10 proposed by the present applicant. There is a considerable component (0th order diffracted light) that passes through the
This becomes stray light, which is one of the causes of a decrease in contrast and chromaticity of the color liquid crystal display device.

[0012]

Such zero-order light is:
In order to be incident at an angle from the normal direction to the display device, cutting has been performed by using a louver film with view selectivity. However, the louver film has the following problems. (1) The cost is high because the fabrication is difficult. (2) Since the strength is not sufficient only in the louver portion, it is necessary to sandwich the both surfaces with the base material, so that the entire louver film becomes thick. (3) Since a certain film thickness is required in the louver portion for oblique light cutting, the aperture ratio is low, and the light transmittance is low. (4) Distortion during manufacturing tends to remain and defects such as tilting of the louvers and deviation of the pitch are likely to occur. Particularly in the case of a display, poor uniformity in the plane is a major problem. (5) Unless the pitch is made smaller than the pitch of the display, pitch moiré occurs.

The present invention is an optical film which does not have such a problem, and efficiently cuts the zero-order light in a hologram color filter and does not cause problems such as a decrease in contrast and a decrease in chromaticity in a display device. The task is to provide optical films.

[0014]

The optical film of the present invention is an optical film in which a long-chain dye molecule is dispersed in a polymer film, wherein the long-chain dye molecule is converted into a light component parallel to its molecular axis. While it has absorptivity to light, it has almost no absorptivity to light components normal to the molecular axis, and is oriented and dispersed in a certain direction within the film plane. And

The optical film of the present invention is characterized in that the long-chain dye molecules are dichroic dyes.

The optical film of the present invention is characterized in that the long-chain dye molecules are oriented by stretching the polymer film.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A long-chain dye molecule in the optical film of the present invention will be described. As long-chain dye molecules,
And dichroic dyes. Such long-chain dye molecules,
For example, a dichroic dye is a dye that absorbs light differently depending on the direction of the molecular axis.Light components in the direction normal to the direction of the molecular axis of the dye molecule have little absorption and transmit light. On the other hand, the light component in the direction parallel to the direction of the molecular axis has absorptivity and does not transmit light. Such dichroic dyes include anthraquinone-based, azo-based,
Bisazo dyes are exemplified.

As the polymer for dispersing such long-chain dye molecules, polyvinyl alcohol, polyurethane,
Polymethyl methacrylate, polyvinyl carbazole,
Polyvinyl chloride and the like. The long-chain dye molecule may be dispersed in the polymer in an amount of 1% by weight to 50% by weight, preferably 1% by weight to 20% by weight, and if it is more than 50% by weight, it is difficult to dissolve or disperse. In addition, a plasticizer, a film-forming aid, a thickener, and the like may be added to the optical film of the present invention.

The optical film of the present invention is obtained by dissolving or dispersing the above-mentioned constituents in a solvent such as methyl ethyl ketone, forming a film by a casting method, a coating method or the like, and then uniaxially stretching the film at a stretching ratio of 10% to 50%. Produced. The thickness of the optical film is 1 μm to 20 μm, preferably 3 μm to
The thickness is preferably 10 μm.

In the state where the long-chain dye molecules are dispersed in a random manner in the polymer film, the polymer film only shows light absorption in the isotropic direction. By dispersing in an oriented state, anisotropy of light absorption ability can be exhibited.

Next, a hologram color filter system using the optical film of the present invention will be described.

FIG. 1 is a diagram for explaining the configuration and operation of a hologram color filter system using the optical film of the present invention. In the figure, 3 is a backlight, 5 is a hologram color filter, 5 'is a minute hologram, 1
Reference numeral 4 denotes a zero-order light, 15 denotes a diffracted light, and 19 denotes an optical film.

As shown in FIG. 1, the optical film 19 of the present invention is disposed on the exit side of the hologram color filter 5, and removes the zero-order transmitted light 14 in front of the focal point of the minute hologram 5 '. . The optical film of the present invention,
Only the light component from the normal direction is transmitted. Therefore, in the case of the hologram color filter 5 in which the incident angle θ of the backlight 3 is set to, for example, 40 °, the wavelength-dispersed diffracted light 15 is not blocked at all by the optical film 19 and the liquid crystal display layer (FIG. (Not shown), and the zero-order transmitted light 1 which causes stray light.
4 can be completely shut off. This liquid crystal display device, as it is as a direct-view type liquid crystal display device, or
It can also be used as a liquid crystal projection display device by using it as a spatial modulation element for a projection display device. Hereinafter, the present invention will be described with reference to examples.

[0024]

EXAMPLES Polyvinyl alcohol (average degree of polymerization 500,
Saponification degree 88%, manufactured by Kuraray Co., Ltd., Poval 20 (trade name)
5) The dichroic dye {S-428 (manufactured by Mitsui Toatsu Chemicals, Inc.)} was dissolved in isopropyl alcohol at a ratio of 2% by weight, and a coating solution having a concentration of 30% by weight (solid content) was prepared. Prepared.

The coating solution was dried to form a film having a thickness of 5 μm using a wire bar, and then uniaxially stretched at a stretching ratio of 20% to produce an optical film of the present invention.

When the obtained optical film is applied to the hologram color filter system shown in FIG. 1, the optical film completely blocks the 0th-order transmitted light 14 and prevents a decrease in contrast and chromaticity in a display device. Met.

[0027]

The optical film of the present invention makes it possible to substantially block the 0th-order transmitted light that is not diffracted by the hologram color filter, so that the wavelength-dispersed diffracted light is hardly blocked and the stray light is hardly blocked. The zero-order transmitted light, which is the cause, can be almost completely blocked, and a decrease in contrast of a liquid crystal display device using this hologram color filter can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the configuration and operation of a hologram color filter system using an optical film of the present invention.

FIG. 2 is a cross-sectional view of a conventional liquid crystal display device using a first type of hologram color filter.

FIG. 3 is a cross-sectional view of a conventional liquid crystal display device using a second type of hologram color filter.

[Explanation of symbols]

In the figure, 3 is a backlight, 5 is a hologram color filter, 5 'is a small hologram, 14 is 0th order (transmitted) light, 1
5 is diffracted light, 19 is an optical film, 20 is a polymer, 2
5 indicates a long-chain dye molecule.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29L 7:00 11:00

Claims (3)

[Claims] 1. An optical film in which a long-chain dye molecule is dispersed in a polymer film, wherein the long-chain dye molecule has absorptivity to a light component parallel to its molecular axis.
An optical film characterized in that it has substantially no absorptivity to a light component in a direction normal to a molecular axis, and is oriented and dispersed in a certain direction in a film plane. 2. The optical film according to claim 1, wherein the long-chain dye molecule is a dichroic dye. 3. The method according to claim 1, wherein the long-chain dye molecules are oriented by stretching the polymer film.
The optical film as described.