JP2001264535A - Optical member and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop an optical member capable of forming a liquid crystal display device excellent in brightness and contrast and less in coloring at a wide visual field angle in front and diagonal viewing. SOLUTION: The optical member consists of a laminated body of an optical compensation polarizing plate 1 wherein a double refraction layer 11 consisting of a discotic liquid crystal polymer is supported by a transparent protective layer 12 with which a polarizing film 13 is coated and a polarized light separating plate 3 for separating incident natural light into reflected light and transmitted light both consisting of polarized light. The liquid crystal display device is formed by disposing the optical member having the polarizing film positioned between the double refraction layer and the polarized light separating plate on at least one side of a liquid crystal cell via the double refractive layer side. Thereby, the liquid crystal display device capable of thinning its size and enhancing light transmittance and excellent in display quality can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical member capable of forming a liquid crystal display device which is excellent in brightness and contrast and has little coloring at a wide viewing angle in front and in perspective.

[0002]

BACKGROUND OF THE INVENTION Conventionally, a polarized light separating plate for separating incident natural light into reflected light and transmitted light composed of polarized light (Japanese Patent Laid-Open No. 59-1270).
19, JP-A-61-122626, JP-A-63-121821, JP-A-3-45906, etc.) and a birefringent layer comprising a discotic liquid crystal polymer supported by a transparent substrate. Optical compensator (Japanese Unexamined Patent Publication No.
-214116). According to the above, a polarization separation plate and an optical compensator are laminated with a polarization plate to form an optical member, which is disposed on a sidelight type light guide plate forming a backlight to polarize linearly polarized light through the polarization separation plate. It is expected that a liquid crystal display device having excellent brightness and a wide viewing angle by supplying the liquid crystal to a plate to suppress absorption loss and compensating for a phase difference due to birefringence of a liquid crystal cell via an optical compensator is obtained.

However, in the above-described optical member including the polarization splitting plate, the polarizing plate, and the optical compensator, the light transmittance is greatly reduced, and the hue is greatly changed (colored) when viewed in the front and oblique directions. There was a point.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to develop an optical member capable of forming a liquid crystal display device which is excellent in brightness and contrast and has little coloring at a wide viewing angle in a frontal and oblique view.

[0005]

According to the present invention, there is provided an optically compensating polarizing plate comprising a transparent protective layer for covering a polarizing film and supporting a birefringent layer comprising a discotic liquid crystal polymer; The optical member, comprising a laminate with a polarization separation plate that separates light into light, and the optical member, in which a polarizing film is located between the birefringence layer and the polarization separation plate, at least a liquid crystal cell via the birefringence layer side. A liquid crystal display device characterized by being arranged on one side is provided.

[0006]

According to the optical member of the present invention, the transparent protective layer of the polarizing film and the supporting substrate of the discotic liquid crystal polymer layer can be used in common, and therefore, the supporting transparent substrate in the conventional optical compensator can be omitted. In addition, the light transmittance can be improved together with the reduction in thickness, and coloring due to visual recognition in the front and oblique directions can be significantly suppressed. As a result, it is possible to form a liquid crystal display device which is excellent in display quality such as luminance and contrast at a wide viewing angle in a frontal and oblique view while improving luminance and suppressing coloring.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical member according to the present invention comprises an optically compensating polarizing plate comprising a transparent protective layer covering a polarizing film and supporting a birefringent layer comprising a discotic liquid crystal polymer; It is made of a laminate of a light and a polarized light separating plate that separates light into transmitted light. An example is shown in FIG. 1 is an optical compensation polarizing plate, 3 is a polarization separation plate, and 2 is an adhesive layer as required.

As an optical compensation polarizing plate, a birefringent layer 11 made of a discotic liquid crystal polymer is supported by a transparent protective layer 12 covering a polarizing film 13 as shown in FIG.
What used the transparent protective layer of the polarizing film and the support base material of the discotic liquid crystal polymer layer together is used.

As the polarizing film, an appropriate film that transmits linearly polarized light having a predetermined polarization axis and absorbs other light can be used, and the type thereof is not particularly limited. By the way, as an example, iodine and / or a dichroic dye is adsorbed on a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, and an ethylene / vinyl acetate copolymer-based partially saponified film. Examples of the film include a stretched film, a polyene-oriented film such as a polyvinyl alcohol dehydration product and a polyvinyl chloride dehydrochlorination product. Above all, a polarizing film composed of a polyvinyl alcohol-based stretched film containing iodine and / or a dichroic dye is preferably used from the viewpoint of the degree of polarization.

On the other hand, as shown in the figure, the transparent protective layers 12 and 14, which cover one or both sides of the polarizing film 13 to protect the polarizing film, can be formed of an appropriate transparent polymer. In particular, a polymer excellent in transparency, mechanical strength, heat stability, moisture shielding property and the like can be preferably used. Incidentally, examples thereof include cellulosic polymers such as cellulose diacetate and cellulose triacetate, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, acrylic polymers such as polycarbonate polymers and polymethyl methacrylate, and polystyrene and acrylonitrile / styrene. Examples include styrene-based polymers such as polymers, polyethylene and polypropylene, polyolefins having a cyclo- or norbornene structure, olefin-based polymers such as ethylene-propylene copolymers, vinyl chloride-based polymers, and amide-based polymers such as nylon and aromatic polyamides. Can be

Also, imide polymers, sulfone polymers, polyethersulfone polymers, polyetheretherketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, Oxymethylene-based polymers, epoxy-based polymers and blends of the above-mentioned polymers, or polyester-based, acrylic-based, urethane-based or amide-based, silicone-based or epoxy-based polymers that are cured by heat or ultraviolet irradiation, and the like are also the transparent protective layers. Can be used to form The transparent protective layer, which is preferable from the viewpoint of suppression of coloring and the like, has excellent isotropy like a cellulose film. The transparent protective layer can be formed by an appropriate method such as a method of applying a polymer liquid or an adhesive lamination method of a film.

The optically compensating polarizing plate is formed by supporting a birefringent layer made of a discotic liquid crystal polymer with a transparent protective layer covering the above-mentioned polarizing film. The birefringent layer 11 is provided outside the transparent protective layer 12 on one side to be coated.

The optically compensating polarizing plate can be formed by a method in which the birefringent layer is provided on a transparent protective layer covering the polarizing film, or the birefringent layer is provided on a film for forming the transparent protective layer. However, the method can also be performed by bonding the film to a polarizing film. The birefringent layer made of a discotic liquid crystal polymer can be formed by a method according to the related art such as a method of applying a solution of a liquid crystal polymer on an alignment film.

As the polarization separation plate, an appropriate one that reflects linearly polarized light in a predetermined polarization direction or circularly polarized light in a predetermined direction when natural light is incident and that transmits other light can be used. Incidentally, as an example, a linearly polarized light having a characteristic of transmitting linearly polarized light in a predetermined polarization direction and reflecting other light, such as a multilayer thin film of a dielectric or a multilayered laminate of thin films having different refractive index anisotropy. Circularly polarized light separating plates, such as a separating plate and a cholesteric liquid crystal layer, exhibiting a characteristic of reflecting left and right circularly polarized light and transmitting other light.

By using a polarization separating plate exhibiting such reflection and transmission characteristics, light from a light source such as a backlight is made incident to obtain transmitted light of a predetermined polarization state, which is supplied in a state where it is hardly absorbed by the polarizing plate. As a result, the amount of light that can be used for a liquid crystal display or the like can be increased to improve the luminance. Further, in this case, when the light reflected by the polarization separation plate is inverted through a reflection layer or the like and re-incident on the polarization separation plate, a part or all of the light can be transmitted as light having a predetermined polarization state, so that the reflected light is transmitted. By utilizing the light, the amount of light transmitted through the polarization separation plate can be increased to further improve the brightness of a liquid crystal display or the like.

The above-mentioned circularly-polarized light separating plate made of cholesteric liquid crystal can be obtained as an alignment film of a liquid crystal polymer or the like. In general, as shown in FIG. It is obtained as a liquid crystal polymer layer 33 having a Grand Jean orientation. In that case, one or two or more cholesteric liquid crystal polymer layers can be provided on one or both sides of the transparent substrate.

In the case where two or more cholesteric liquid crystal polymer layers are provided in the above, it is preferable to use a combination of those having different helical pitches of the Grandian orientation and therefore different reflection wavelengths. By superimposing by such a combination, it is possible to expand the wavelength range of reflection and obtain circularly polarized light in a wide wavelength range such as a visible light range, and to obtain transmission circularly polarized light in a wide wavelength range based thereon. .

The superposed layer of the cholesteric liquid crystal polymer layer can be formed by a recoating method or the like. When superimposing cholesteric liquid crystal polymer layers having different helical pitches of the Grandian orientation, it is preferable to superimpose the cholesteric liquid crystal polymer layers so that the helical pitches are in the order of magnitude from the viewpoint of improving light use efficiency and, in turn, improving luminance. Further, as the transparent base material supporting the cholesteric liquid crystal polymer layer, an appropriate one made of the polymer exemplified in the above-mentioned transparent protective layer can be used.

In the above description, since the circularly polarized light separating plate provides circularly polarized light, it can be used in combination with a quarter-wave plate for the purpose of converting the circularly polarized light into linearly polarized light. That is, as shown in the figure, the circularly polarized light by the circularly polarized light separating layer 33 is linearly polarized by the quarter-wave plate 31, and the optical axis is set so that the transmission axis of the polarizing film 13 coincides with the vibration plane of the linearly polarized light as much as possible. By arranging the compensating polarizing plate 1, it is possible to prevent the absorption loss by the polarizing film and to further increase the luminance. Therefore, as shown in FIG.
Is disposed between the optical compensation polarizing plate 1 and the circularly polarized light separating layer 33.

Examples of the quarter-wave plate include a birefringent film made of a stretched polymer of the polymer exemplified as the transparent protective layer, an alignment film of a nematic liquid crystal polymer, and an alignment liquid crystal layer formed of a transparent substrate. An appropriate material according to the related art such as a material supported on a material can be used. Those that function as quarter-wave plates in a wide wavelength range such as the visible light range
For example, a phase difference layer functioning as a 波長 wavelength plate and a phase difference layer exhibiting other phase difference characteristics, for example, a phase difference layer functioning as a 波長 wavelength plate are superimposed on monochromatic light such as light having a wavelength of 550 nm. It can be obtained by such a method. Therefore 1 /
The four-wavelength plate may be composed of one or two or more retardation layers.

The above-mentioned stretched film may be processed by an appropriate method such as uniaxial or biaxial, for example, by applying a shrinking force and / or a stretching force while adhering to the heat shrinkable film. A birefringent film in which the refractive index in the thickness direction of the film is controlled may be used. When the circularly polarized light separating plate is formed by superimposing the above cholesteric liquid crystal layer so that the helical pitch thereof is in the order of magnitude, a 波長 wavelength plate is arranged on the side where the helical pitch of the superposed body is small. This is preferable from the viewpoint of reduction of coloring due to oblique view.

The optical member according to the present invention may be one in which an optical compensation polarizing plate and a polarization separating plate are simply stacked,
Preferably, the optically compensating polarizing plate 1 and the polarizing separating plate 3 are adhered to each other via an adhesive layer 2 as shown in the figure for the purpose of stabilizing the quality by preventing the deviation of the optical axis and improving the assembling efficiency of the liquid crystal display device. It is integrated. In the case where the 波長 wavelength plate 31 is provided, it is preferable that the １ ／ wavelength plate 31 is also laminated and integrated with the circularly polarized light separating plate via the adhesive layer 32.

For the formation of the above-mentioned adhesive layer, an appropriate adhesive substance such as an adhesive based on an appropriate polymer such as an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyether or a synthetic rubber as a base polymer. Can be used. Among them, those which are excellent in optical transparency, weather resistance, heat resistance and the like and are hardly caused to float or peel off under the influence of heat or humidity, such as acrylic adhesives, can be preferably used.

Incidentally, examples of the above-mentioned acrylic pressure-sensitive adhesive include those having a carbon number of 2 such as methyl group, ethyl group and butyl group.
An acrylic monomer comprising an alkyl ester of (meth) acrylic acid having an alkyl group of 0 or less and an improving component such as (meth) acrylic acid or hydroxyethyl (meth) acrylate has a glass transition temperature of 0 ° C. or less. Examples thereof include, but are not limited to, an acrylic polymer having a weight-average molecular weight of 100,000 or more obtained by copolymerization in combination as a base polymer.

The pressure-sensitive adhesive layer may have a light diffusing property by containing transparent particles. The transparent particles include, for example, silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide, and the like, and inorganic particles that may be conductive, and organic materials, such as a crosslinked or uncrosslinked polymer. One or more appropriate particles such as particles may be used.

The adhesive layer is formed by bonding an adhesive material to an optically compensating polarizing plate or a polarizing separating plate by an appropriate method such as a rolling method using a calender roll method or a coating method using a doctor blade method or a gravure roll coater method. It can be carried out by an appropriate method such as a method of attaching to a surface, or a method of forming an adhesive layer on a separator according to the above and transferring it to a predetermined adhesive surface. In addition, an adhesive layer for the purpose of bonding to another member such as a liquid crystal cell can be provided on the outer surface of the optical member, if necessary. If the adhesive layer is exposed on the surface, the surface may be temporarily covered with a separator or the like for the purpose of protection such as contamination prevention until practical use.

The optical member according to the present invention can be used for various applications according to the related art. In particular, it can be preferably used for improving luminance and expanding a viewing angle in a liquid crystal display device. The liquid crystal display device includes, for example, a method in which an optical member in which a polarizing film 13 is located between a birefringent layer 11 and a polarization separating plate 3 is arranged on at least one side of a liquid crystal cell via the birefringent layer side as shown in the figure. Can be formed. Therefore, the optical member is arranged such that the birefringent layer 11 is located between the polarizing film and the liquid crystal cell.

In forming a liquid crystal display device, any liquid crystal cell can be used. For example, an active matrix driving type represented by a thin film transistor type, a TN
Various types of liquid crystal display devices can be formed using appropriate types of liquid crystal cells, such as a simple matrix drive type represented by a liquid crystal or STN type, and a liquid crystal cell provided with a color filter. In addition, the liquid crystal display device may include, for example, an appropriate optical sheet used for forming the liquid crystal display device, such as an anti-reflection sheet, an anti-glare sheet, a light diffusion sheet, a condensing sheet such as a prism sheet or a lens sheet, and a backlight. The species or two or more species can be arranged at appropriate positions.

[0029]

EXAMPLE 1 A cellulose triacetate film provided with a birefringent layer composed of a discotic liquid crystal polymer was attached to one side of a polarizing film composed of an iodine-containing stretched polyvinyl alcohol film such that the birefringent layer was on the outside. Then, a cellulose triacetate film was adhered to the other side of the polarizing film to obtain an optically compensating polarizing plate. On the other hand, a reflection center wavelength of 760 nm, 6
A cholesteric liquid crystal polymer having a thickness of 50 nm, 550 nm or 430 nm is superposed and coated to form a four-layered circularly-polarized light separating plate, and a quarter-wavelength plate made of polycarbonate is adhered thereto via an acrylic adhesive layer to separate the polarized light. I got a board. Then, an optical member was obtained by bonding and laminating a polarization separation plate to the side of the optically compensating polarizing plate having no birefringent layer via an acrylic adhesive layer via a quarter wavelength plate side.

Comparative Example 1 Instead of the optical compensation polarizing plate, a birefringent layer made of a discotic liquid crystal polymer was formed on a cellulose triacetate film on one side of a polarizing plate obtained by adhering cellulose triacetate films on both sides of a polarizing film. An optical member was obtained in the same manner as in Example 1 except that the provided optical compensator was bonded and laminated via an acrylic pressure-sensitive adhesive layer such that the birefringent layer was on the outside.

Comparative Example 2 An optical member was obtained in the same manner as in Example 1 except that the birefringent layer made of a discotic liquid crystal polymer was omitted.

Evaluation Test The thickness, light transmittance, hue b (NBS), viewing angle and luminance improvement rate of the optical members obtained in the examples and comparative examples were examined. The viewing angle was evaluated based on a viewing area having a contrast ratio of 10: 1 or more in the case of a liquid crystal display device. The luminance improvement rate is based on the luminance when a liquid crystal cell having polarizing plates on both sides is arranged on a backlight, and the polarizing plate on the backlight side is replaced with the optical members obtained in the examples and comparative examples. Was evaluated and evaluated.

The results are shown in the following table. Thickness (μm) Light transmittance Hue b Viewing angle Brightness improvement rate Example 1 430 43.9% 4.89 120 degrees 146% Comparative example 1 555 43.4% 5.31 120 degrees 143% Comparative example 2 425 44 .2% 4.87 90 degrees 149%

From the table, it can be seen that in the embodiment, the thickness and the light transmittance are improved while improving the luminance and the viewing angle, and the coloring which is almost equal to that in the case where the polarization separator is not used (Comparative Example 2) is obtained. You can see that it has been achieved

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment.

[Explanation of symbols]

 1: Optically compensating polarizing plate 11: Birefringent layer 12, 14: Transparent protective layer 13: Polarizing film 2: Adhesive layer 3: Polarization separating plate 31: 1/4 wavelength plate 33: Cholesteric liquid crystal polymer layer 34: Transparent substrate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA03 BA05 BA06 BA07 BA27 BA28 BA42 BB03 BB43 BB44 BB49 BB51 BC03 BC22 2H091 FA08X FA08Z FA11X FA11Z FA26X FA26Z FA41Z FB02 JA01 LA16 LA17 LA19

Claims (5)

[Claims] 1. An optically compensating polarizing plate comprising a birefringent layer made of a discotic liquid crystal polymer supported by a transparent protective layer covering a polarizing film, and polarized light for separating incident natural light into reflected light and transmitted light. An optical member comprising a laminate with a separation plate. 2. The birefringent layer according to claim 1, wherein the optically compensating polarizing plate has a birefringent layer outside a transparent protective layer made of a cellulose-based film covering a polarizing film made of a polyvinyl alcohol-based stretched film containing iodine or a dichroic dye. An optical member comprising: 3. A circularly polarized light separating plate according to claim 1, wherein the polarized light separating plate is provided with one or more cholesteric liquid crystal polymer layers on one or both sides of a transparent substrate.
An optical member comprising a / 4 wavelength plate. 4. The optical member according to claim 1, wherein the optical compensation polarizing plate and the polarization separating plate are bonded via an adhesive layer. 5. The optical member according to claim 1, wherein a polarizing film is located between the birefringent layer and the polarizing beam splitter, wherein the optical member is disposed on at least one side of the liquid crystal cell via the birefringent layer side. Liquid crystal display device.