JP2002116322A - Polarizing member and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polarizing member which hardly causes decrease in the separation function of circularly polarized light or in the improving rate of luminance or which hardly causes elimination of polarized light or decrease in the front face luminance, and to obtain a liquid crystal display device having high luminance which hardly causes color unevenness in a wide viewing angle including the front direction and oblique viewing directions. SOLUTION: The polarizing member (1) is obtained by incorporating particles for diffusion of light in a cholesteric liquid crystal layer having Grandjean alignment. The liquid crystal display device is obtained by using the above polarizing member. The Grandjean alignment in the cholesteric liquid crystal layer can be maintained in a high level, and color irregularity can be further improved by reusing reflected light. The obtained liquid crystal display device is excellent in the display quality in a wide viewing angle including the front direction and oblique viewing directions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing member capable of forming a high-brightness liquid crystal display device in which color unevenness hardly occurs at a wide viewing angle in a frontal and oblique view.

[0002]

BACKGROUND OF THE INVENTION A polarizing member composed of a cholesteric liquid crystal layer of Grand Jean orientation and a quarter-wave plate is disposed on a side light type light guide plate for forming a backlight for the purpose of increasing the brightness of a liquid crystal display device or the like. Has been proposed. This utilizes the property of the cholesteric liquid crystal layer of the Grand Jean orientation that separates the incident natural light into reflected light and transmitted light composed of one of left and right circularly polarized lights, and circularly polarizes the outgoing light from the light guide plate, thereby reducing it to 1/4. By supplying linearly polarized light through a wavelength plate and supplying the linearly polarized light to the polarizing plate, absorption loss due to the polarizing plate can be suppressed and luminance can be improved.

[0003] However, the conventional polarizing member has a problem that color unevenness occurs in various colors in the oblique direction, such as coloring in yellow in the horizontal direction and blue in the vertical direction. It is considered that such a color unevenness problem is that since a quarter-wave plate or a polarizing plate is arranged with the optical axis adjusted centering on the front direction, the optical axis relationship is shifted in perspective and various colors are caused. ing.

In view of the above, there has been proposed a method of diffusing transmitted light, confusing various kinds of color light, making the same color in all directions, preventing color unevenness, and reducing color intensity. There has been known a method in which disclination (alignment defect) serving as a diffusion source is caused in the Grand Jean alignment of the cholesteric liquid crystal layer, and a method in which a light diffusion plate is additionally arranged. However, in the former, the degree of disclination required to prevent color unevenness is strong, and the original circularly polarized light separating function is greatly reduced, and the luminance improvement rate is also reduced. In the latter, the front diffuser is reduced because the light is diffused by the light diffusion plate. There was a point.

[0005]

SUMMARY OF THE INVENTION The present invention is to obtain a polarizing member which is less likely to cause a problem of a circularly polarized light separating function, a reduction in a luminance improvement rate, elimination of polarized light, and a reduction in a front luminance. An object is to develop a high-brightness liquid crystal display device that is unlikely to occur.

[0006]

According to the present invention, there is provided a polarizing member characterized in that particles for light diffusion are contained in a cholesteric liquid crystal layer having a Grandian orientation, and a liquid crystal display comprising the polarizing member. An apparatus is provided.

[0007]

According to the polarizing member of the present invention, the method of blending particles for diffusing light into the liquid crystal layer allows the cholesteric liquid crystal layer to maintain a high level of the Grand Jean orientation, thereby deteriorating the circularly polarized light separating function and causing the deterioration. It is possible to suppress a decrease in the luminance improvement rate, and to suppress a decrease in the front luminance due to depolarization. Further, when the light reflected by the polarizing member is reused through a reflection layer or the like, the light reflected by the polarizing member is diffused light, which also contributes to further improvement in color unevenness. As a result, light can be efficiently diffused, various color lights can be mixed, and the same color can be obtained in all directions, color unevenness can be prevented, color intensity can be reduced, and color unevenness due to perspective can be prevented while improving brightness. As a result, a liquid crystal display device having excellent brightness and display quality with a wide viewing angle in front and in a perspective can be formed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A polarizing member according to the present invention has at least a cholesteric liquid crystal layer having a Grand Jean orientation containing particles for diffusing light, and, if necessary, a quarter-wave plate and further a polarizing plate. Consisting of An example is shown in FIG. Reference numeral 1 denotes a cholesteric liquid crystal layer (polarizing member) having a Grand Jean orientation. The figure shows a liquid crystal display device, wherein 2 is a quarter-wave plate, 3 and 5 are polarizing plates, 4 is a liquid crystal cell, and 8 is a light source.

There is no particular limitation on the cholesteric liquid crystal layer of the Grand Jean orientation, and an appropriate layer exhibiting the characteristic of transmitting incident natural light on one of left and right circularly polarized lights and reflecting the other can be used. By using a cholesteric liquid crystal layer exhibiting such reflection / transmission characteristics, light from a light source such as a backlight is made incident to obtain transmitted light in a predetermined polarization state, and the transmitted light is supplied to a polarizing plate in a state where it is hardly absorbed by a liquid crystal. Brightness can be improved by increasing the amount of light available for display and the like.

In the above, when the light reflected by the cholesteric liquid crystal layer is inverted through the reflection layer or the like and re-enters the cholesteric liquid crystal layer, part or all of the light can be transmitted as light having a predetermined polarization state. By utilizing the reflected light, the amount of light transmitted through the cholesteric liquid crystal layer can be increased to further improve the brightness of a liquid crystal display or the like.

The cholesteric liquid crystal layer may have an arrangement structure in which two or three or more layers are overlapped in a combination of those having different helical pitches of the Grandian orientation, and therefore different reflection wavelengths. With such superimposition, it is possible to obtain circularly polarized light that reflects in a wide wavelength range such as the visible light range, and based on this, it is possible to obtain transmitted circularly polarized light in a wide wavelength range. When superimposing cholesteric liquid crystal layers having different helical pitches of the Grandian orientation, it is preferable to superimpose the cholesteric liquid crystal layers so that the helical pitches are in the order of magnitude from the viewpoint of improving light use efficiency and, consequently, improving brightness. Is 1 / to the side where the helical pitch of the superimposed body is smaller.
It is preferable to dispose a four-wavelength plate from the viewpoint of, for example, reducing coloration due to perspective.

The cholesteric liquid crystal layer exhibiting the above-mentioned reflection / transmission characteristics can be obtained as a liquid crystal polymer film or the like. However, in general, a liquid crystal polymer obtained by subjecting a transparent substrate to a Grand Jean alignment through an alignment film formed by rubbing or the like is used. It can be obtained as a layer or the like. The superposed layer can be formed by a recoating method or the like.

Further, in the above case, the light-diffusing particles are mixed with a solution of a liquid crystal polymer or a solution of a solvent or the like, and the mixture is developed in a layered form. A cholesteric liquid crystal layer with a Jean alignment can be formed. The thickness of the cholesteric liquid crystal layer can be determined as appropriate, but is generally 100 μm or less, preferably 0.5 to 50 μm, particularly 1 to 20 μm based on the layer unit from the viewpoint of the efficiency of the alignment treatment and the like. .

The material for forming the transparent substrate is not particularly limited, but generally a polymer is used.
Examples of the polymer 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; polystyrene and acrylonitrile / styrene. Styrene polymers such as copolymers, polyethylene and polypropylene, polyolefins having a cyclo or norbornene structure, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, and amide polymers such as nylon and aromatic polyamides. can give.

Further, 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, and polyester-based, acrylic-based, urethane-based and amide-based, silicone-based and epoxy-based polymers and the like that are cured by heat or ultraviolet irradiation, etc. are also used as the transparent substrate. Can be used to form A transparent substrate having excellent isotropy, such as a cellulosic film, is preferably used.

The purpose of the light diffusing particles contained in the cholesteric liquid crystal layer is to mix various colored lights into the same color to prevent color unevenness due to perspective as described above. The particles include, for example, silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide, and the like, inorganic particles that may be conductive, and organic particles that include a crosslinked or uncrosslinked polymer. One or more suitable materials such as the above may be used.

From the viewpoint of obtaining a material having excellent light diffusion efficiency without deteriorating the Grand Jean orientation of the cholesteric liquid crystal, particles having an average particle size of 0.5 to 30 μm, especially 20 μm or less, particularly 1 to 15 μm, It can be preferably used. Also, the content of the light diffusing particles in the cholesteric liquid crystal layer is 0.1 to 20% by weight, preferably 0.3 to 15% by weight from the viewpoint of obtaining a light diffusion efficiency without deteriorating the Grand Jean orientation. %, Especially 0.5 to 10% by weight
It is preferred to adjust to.

If necessary, the polarizing member may be 1/4 as shown in FIG.
One or more other appropriate optical layers such as the polarizing plate 3 and the retardation plate may be provided on the wavelength plate 2 and further on the outside thereof. Such a quarter-wave plate is disposed on one side or both sides of the cholesteric liquid crystal layer, and aims to linearly polarize reflected light and / or transmitted light composed of circularly polarized light by the cholesteric liquid crystal layer. Its transmission axis is 1 /
By arranging as much as possible with the vibration plane of the linearly polarized light transmitted through the four-wavelength plate, absorption loss can be prevented and luminance can be further increased.

As the quarter-wave plate, a birefringent film composed of a stretched film of various polymers, an oriented film of a liquid crystal polymer such as discotic or nematic, and an oriented liquid crystal layer are supported on a transparent substrate. An appropriate one such as a conventional one can be used. The polymer forming the birefringent film may be any suitable polymer such as those exemplified above for the transparent substrate. Above all, a polymer having excellent crystallinity, such as a polyester-based polymer or polyetheretherketone, can be preferably used. The stretched film may be processed by an appropriate method such as uniaxial or biaxial. Further, a birefringent film in which the refractive index in the thickness direction of the film is controlled by a method of applying a contraction force and / or a stretching force while bonding to the heat-shrinkable film may be used.

The quarter-wave plate may be a laminate of two or more retardation layers for the purpose of controlling optical characteristics such as retardation. Incidentally, 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 板 wavelength plate are superimposed on monochromatic light such as light having a wavelength of 550 nm. According to such a method, a plate functioning as a quarter-wave plate in a wide wavelength range such as a visible light region can be obtained. 1/4 which can be preferably used from the viewpoint of preventing color unevenness and the like
When the in-plane main refractive index is nx and ny and the main refractive index in the thickness direction is nz, the wave plate has the formula: (nx-nz) / (nx-n).
Nz defined in y) is from +0.5 to -2.5.

On the other hand, a polarizing plate aims to obtain linearly polarized light for achieving a liquid crystal display and the like, and a retardation plate compensates a phase difference due to birefringence of a liquid crystal cell to improve display quality. Aim. When providing a polarizing plate, usually
As shown in the figure, 1/4 is applied to only one side of the cholesteric liquid crystal layer 1.
The wave plate 2 is provided, and the polarizing plate 3 is provided via the quarter wave plate. Thereby, the transmitted light of the cholesteric liquid crystal layer can be converted into a highly linearly polarized state.

As the polarizing plate, an appropriate one 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. Generally, a polarizing film or a film having one or both surfaces protected by a transparent protective layer is used. Incidentally, as an example of the polarizing film, iodine and / or a dichroic dye is applied to 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 thereof include films that have been adsorbed and stretched, and polyene-oriented films such as polyvinyl alcohol dehydration products and polyvinyl chloride dehydrochlorination products.

The transparent protective layer provided on one side or both sides of the polarizing film, if necessary, can be formed of the polymer exemplified for the above transparent substrate. Above all, a transparent protective layer made of a polymer having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like is preferable. 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.

On the other hand, as the retardation plate, a birefringent film or an oriented liquid crystal layer having an appropriate retardation according to the above-mentioned 波長 wavelength plate can be used, and the optical characteristics such as the retardation can be controlled. It may be a laminate of two or more retardation layers for the purpose. The compensating retardation plate is usually arranged so as to be located between the polarizing plate and the liquid crystal cell.

In the above description, the cholesteric liquid crystal layer and, if necessary, a quarter-wave plate, a polarizing plate, a retardation plate and the like may be simply placed one on top of another. It is laminated and integrated via an adhesive layer such as an adhesive layer for the purpose of stabilizing and improving the assembling efficiency of the liquid crystal display device. Further, on the outer surface of the polarizing member, if necessary, an adhesive layer for the purpose of bonding to another member such as a liquid crystal cell can be provided. 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.

For the formation of the above-mentioned pressure-sensitive adhesive layer, a suitable pressure-sensitive adhesive substance such as a pressure-sensitive adhesive having an appropriate polymer such as an acrylic polymer, a silicone-based polymer, polyester, polyurethane, polyether or synthetic rubber as a base polymer is used. 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.

Examples of the acrylic pressure-sensitive adhesive include an alkyl ester of (meth) acrylic acid having an alkyl group having 20 or less carbon atoms such as a methyl group, an ethyl group, and a butyl group; Based on an acrylic polymer having a weight average molecular weight of 100,000 or more, obtained by copolymerizing an acrylic monomer comprising an improving component such as hydroxyethyl (meth) acrylate in a combination having a glass transition temperature of 0 ° C. or lower. Examples thereof include polymers, but are not limited thereto.

The adhesive layer may be formed by an appropriate method such as a rolling method using an adhesive substance by a calender roll method or a coating method using a doctor blade method or a gravure roll coater method. , A method of attaching to a supporting substrate composed of a polarizing plate, a retardation plate, or the like, or forming an adhesive layer according to the above on a separator using a separator on the supporting substrate and forming it with a cholesteric liquid crystal layer or the like. It can be performed by an appropriate method such as a method of transferring to a supporting base material. The pressure-sensitive adhesive layer can also be formed as a superposed layer of different pressure-sensitive adhesives.

The polarizing member according to the present invention can be used for various applications according to the prior art. In particular, it can be preferably used for forming a surface light source or a liquid crystal display device for the purpose of improving luminance or the like. In the liquid crystal display device, for example, a polarizing member (cholesteric liquid crystal layer) 1 is disposed on one side of a liquid crystal cell 4 via a quarter-wave plate 2 or a polarizing plate 3 as shown in FIG. 5 can be formed.

The surface light source has a light source 82 on the side as shown in FIG.
On the light emission side of the side light type light guide plate 81 in which
The polarizing member can be formed by a method in which the cholesteric liquid crystal layer 1 is disposed on the light guide plate side or the like. In the illustrated surface light source 8, a light source 82 is surrounded by a holder 83, and a polarizing member is provided on a light exit side of a light guide plate 81 provided with a reflective layer 9 on the bottom surface via a light diffusion sheet 7 and a light collection sheet 6. Is arranged.

According to the liquid crystal display device shown in the figure, the light emitted from the surface light source 8 is diffused by the light diffusion sheet 7, the optical path is controlled by the light collection sheet 6, and enters the cholesteric liquid crystal layer 1.
The liquid crystal cell is separated into reflected light and transmitted light to become diffused light, and the transmitted circularly polarized light enters the quarter-wave plate 2, is linearly polarized therethrough and passes through the polarizing plate 3 with little absorption loss, and the liquid crystal cell 4 and the display light is emitted through the polarizing plate 5 on the viewing side.

In the above, the absorption loss due to the polarizing plate 3 is small, and the reflected light from the cholesteric liquid crystal layer 1 is inverted by the reflecting layer 9 on the lower surface side of the light guide plate, re-enters the cholesteric liquid crystal layer and transmits, and the reflected light The brightness of the liquid crystal display device can be improved, for example, by improving the light use efficiency by using the light emitting device.

In forming the liquid crystal display device, any liquid crystal cell can be used. For example, an active matrix drive 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.

When a liquid crystal display device or a surface light source is formed as shown in the above-mentioned example, for example, a polarizing plate 5 and a light diffusing sheet 7 on the viewing side, a condensing sheet 6 such as a prism sheet and a lens sheet, and a backlight 8 are formed. One or more appropriate optical layers used for forming a liquid crystal display device can be arranged at appropriate positions, and a retardation plate for compensation can be arranged on the viewing side.

As the above-mentioned polarizing plate 5 on the viewing side, any suitable one such as the above-mentioned polarizing member can be used, and if necessary, an antiglare layer, an anti-reflection layer and the like are provided on the surface on the viewing side. be able to. The anti-glare layer scatters the external light reflected on the surface, and the anti-reflection layer suppresses the surface reflection of the external light, preventing the surface reflected light from causing glare or the like to impair the visibility of the transmitted light of the display device. It is performed for the purpose. Therefore, both the anti-glare layer and the anti-reflection layer can be provided to further improve the prevention of visual impairment due to surface reflected light.

The antiglare layer and the antireflection layer are not particularly limited, and can be formed as appropriate having the above functions. Incidentally, the antiglare layer can be formed by imparting a light-scattering and reflecting fine uneven structure by an appropriate method such as a method of forming a resin containing transparent particles into a film or a method of coating a support film. In addition, the antireflection layer is formed by a vapor deposition method such as a vacuum deposition method, an ion plating method, or a sputtering method, a plating method, or a suitable coating method such as a sol-gel method. It can be formed by an interference film made of a coating film of a low refractive material such as.

On the other hand, a light diffusion layer such as a light diffusion sheet can also be formed by an appropriate method according to the above-mentioned antiglare layer. In the present invention, a light diffusion type in which particles for light diffusion are mixed with an adhesive layer. It can be provided as an adhesive layer. According to such a light-diffusion-type pressure-sensitive adhesive layer, a light-diffusing function can be imparted by using the light-diffusion-type pressure-sensitive adhesive layer with another member, and there is an advantage that the thickness can be reduced.

[0038]

EXAMPLES Reference Example A polarizing plate (SEG1425Du, manufactured by Nitto Denko Corporation) was used.

Example 1 Silicone resin particles having an average particle size of 2 μm were mixed and dispersed on a cellulose triacetate (TAC) film having a thickness of 40 μm via a rubbing alignment film made of polyvinyl alcohol having a thickness of 0.1 μm. The cholesteric liquid crystal polymer solution is superimposed, and the reflection center wavelength obtained by the alignment treatment is 70.
A cholesteric liquid crystal layer having a three-layer structure of 0 nm, 550 nm or 400 nm has a thickness of 25 μm on the 400 nm side of the reflection center wavelength.
A polarizing member was obtained by bonding a 1/4 wavelength plate made of a uniaxially stretched polycarbonate film through an acrylic pressure-sensitive adhesive layer of m. Each of the cholesteric liquid crystal layers having the above-described Grand Jean orientation has a thickness of about 3 μm, and contains silicone resin particles in a ratio of 1% by weight.

Comparative Example 1 A polarizing member was obtained in the same manner as in Example 1 except that silicone resin particles were not added to each layer of the cholesteric liquid crystal layer.

Comparative Example 2 Silicone resin particles were not blended in each layer of the cholesteric liquid crystal layer, and the refractive index was 1.4 as an acrylic adhesive layer.
3. Polarizing member according to Example 1, except that a light diffusion type (particle content: 20% by weight) having a refractive index of 1.47 and a thickness of 25 μm containing uncolored transparent particles having an average particle size of 4 μm was used. I got

Evaluation Test The polarizing plate of the reference example and the polarizing members obtained in the examples and comparative examples were examined for the total light transmittance, the luminance improvement rate, the haze, the degree of polarization, and the viewing angle characteristics. The total light transmittance and haze were measured with a haze meter (HGM-2DP, manufactured by Suga Test Instruments Co., Ltd.), and the degree of polarization was measured with DOT-3 (manufactured by Murakami Color LAB).

Regarding the brightness of the polarizing member, the polarizing member is disposed on the backlight composed of a sidelight type light guide plate having a reflective layer on the lower surface via the cholesteric liquid crystal side, and the polarizing member is placed on the quarter wavelength plate. The plate was arranged so as to exhibit the maximum luminance, the front luminance was measured with a luminance meter (BM7, manufactured by Topcon Corporation), and the luminance improvement rate was calculated based on the reference example of only the polarizing plate. Regarding the viewing angle characteristics, the degree of coloring by the viewing angle was visually evaluated in three stages.

The results are shown in the following table. Total light transmission Brightness improvement Haze Polarization degree Visual angle excess ratio (%) Ratio (%) Characteristic reference example 43 100 0 99.9 ○ Example 1 50 141 60 90.4 ○ Comparative example 1 50 142 2 91.0 × Comparison Example 2 48 135 80 85.7 △

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a liquid crystal display device (polarizing member).

[Explanation of symbols]

 1: cholesteric liquid crystal layer 2: quarter wavelength plate 3, 5: polarizing plate 4: liquid crystal cell

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ikuo Kawamoto 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H049 BA02 BA05 BA07 BA43 BA44 BB03 BB51 BB65 BC22 2H088 HA17 HA18 HA28 HA30 JA14 MA05 2H090 KA09 LA08 LA09 MA17 2H091 FA08X FA08Z FA11X FA11Z FA23Z FA41Z HA11 LA16 LA20

Claims (7)

[Claims] 1. A polarizing member characterized in that particles for light diffusion are contained in a cholesteric liquid crystal layer having a Grandian orientation. 2. The polarizing member according to claim 1, wherein the light diffusion particles are composed of one or more of inorganic or organic particles. 3. The polarizing member according to claim 1, wherein the particles for light diffusion have an average particle diameter of 0.5 to 30 μm. 4. The polarizing member according to claim 1, wherein the content of the light diffusing particles is 0.1 to 20% by weight. 5. The method according to claim 1, wherein at least 1 /
A polarizing member formed by laminating four-wavelength plates. 6. The method according to claim 1, wherein 1 /
A polarizing member formed by laminating polarizing plates via a four-wave plate. 7. A liquid crystal display device comprising the polarizing member according to claim 1.