JP4401511B2 - Composite retardation plate, optical compensation polarizing plate, and liquid crystal display device - Google Patents

Description

【図面の簡単な説明】
【図１】液晶表示装置例の断面図
【図２】実施例１及び比較例の等コントラスト曲線
【符号の説明】
１：複合位相差板
１１，１４：位相差層（Ａ）
１２，１５：位相差層（Ｂ）
１３，１６：位相差層（Ｃ）
２：偏光板
３：液晶セル[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a composite phase difference plate and an optical compensation polarizing plate that can form a liquid crystal display device having excellent viewing angle and contrast by highly compensating birefringence due to TN liquid crystal.
[0002]
[Prior art]
While TFT-LCDs (liquid crystal display devices) using TN liquid crystals are widely used in televisions, personal computer monitors, etc., paying attention to high-speed response and high contrast in the front direction, there is a significant decrease in contrast in the perspective direction. Improvement of narrowness of good viewing angle by inversion of tone display (gradation inversion), etc. is required. High contrast, wide viewing angle, suppression of display color change by viewing angle and uniform screen display. This is a particularly important issue as the screen size increases.
[0003]
Conventionally, as the above-mentioned improvement measures, a proposal has been made to expand the viewing angle by compensating for the phase difference due to the birefringence of the TN liquid crystal by using a retardation plate. Wide view film (trade name, manufactured by Fuji Photo Film Co., Ltd.) showing negative refractive index anisotropy made of Tik liquid crystal, and NH film (trade name, made of nematic liquid crystal with tilted optical axis) (Made by Nippon Petrochemical Co., Ltd.), a retardation plate composed of a uniaxially stretched film made of a polymer exhibiting positive birefringence characteristics, and the refractive index of the retardation plate in combination with the optical axis being in-plane and inclined with respect to the plane Superposition type compensation plates (JP-A-7-306406, JP-A-7-35924, JP-A-10-123506) laminated so that the directions are orthogonal to each other have been known.
[0004]
However, the wide-view film has a problem that the contrast is remarkably lowered at a viewing angle inclined by 60 degrees or more from the front direction, and a coloring phenomenon occurs in a white display state where no voltage is applied. In addition, the NH film has a problem in that when the viewing angle is changed in a black display state where a voltage is applied, the color changes and the color is not black. Further, the superposed compensation plate has a problem that a remarkable coloring phenomenon occurs due to a change in viewing angle. Therefore, the conventional compensator cannot sufficiently cope with the phase difference characteristic of the TN liquid crystal, and has a problem that it cannot satisfy the improvement of the visual recognition characteristic.
[0005]
[Technical Problem of the Invention]
The present invention can highly compensate the phase difference due to the birefringence of the TN liquid crystal even in the case of a large screen, has excellent viewing angle and contrast that does not invert the gradation, suppresses the display color change due to the viewing angle, and makes the screen display uniform. The purpose is to develop a retardation plate capable of forming an excellent liquid crystal display device.
[0006]
[Means for solving problems]
In the present invention, the in-plane refractive index is nx, ny, the thickness direction refractive index is nz, the layer thickness is d, nx−ny = Δnxy and (nx−nz) / (nx−ny) = Q. (A) a retardation layer composed of a polymer film satisfying nx>ny> nz, (B) a retardation layer satisfying nx ≧ ny> nz and an optical axis inclined with respect to the normal direction of the layer plane; (C) A laminate comprising an oriented film of norbornene-based polymer and having one or more retardation layers each satisfying Δnxy · d ≦ 70 nm and 1 ≦ Q ≦ 4, and in-plane in the laminate Nx, Ny, the refractive index in the thickness direction is Nz, the thickness is D, and Nx ≧ Ny, (Nx−Ny) = ΔNxy and {(Nx + Ny) / 2−Nz} · D = Rth when, based on the monochromatic light of wavelength 590 nm △ Nxy · D is at 25 to 100 nm, birefringence which Rth is characterized by the Dearuko 100~300nm There is provided a retardation plate.
[0007]
The present invention also includes an optical compensation polarizing plate comprising a laminate of the composite retardation plate and the polarizing plate, and the composite retardation plate between the polarizing plate and a liquid crystal cell. Provided is a liquid crystal display device.
[0008]
【The invention's effect】
According to the present invention, the birefringence of the TN liquid crystal is achieved by achieving the retardation characteristics of ΔNxy and Rth by combining the retardation of the retardation layers (A), (B), and (C). A phase difference plate that can compensate for the phase difference due to the azimuth at all azimuth angles can be obtained, and even in the case of a large screen, the viewing angle that does not invert the gradation is wide and the display color does not easily change depending on the viewing angle. A liquid crystal display device with excellent uniformity can be formed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The composite phase difference plate according to the present invention has an in-plane refractive index of nx, ny, a thickness direction refractive index of nz, a layer thickness of d, nx−ny = Δnxy and (nx−nz) / (nx−ny). ) = Q, (A) retardation layer made of a polymer film satisfying nx>ny> nz, (B) nx ≧ ny> nz satisfying optic axis tilted with respect to the normal direction of the layer plane And (C) a norbornene polymer oriented film, and a laminate having one or more retardation layers each satisfying Δnxy · d ≦ 70 nm and 1 ≦ Q ≦ 4, and The in-plane refractive index of the laminate is Nx, Ny, the refractive index in the thickness direction is Nz, and the thickness is D. Nx ≧ Ny, (Nx−Ny) = ΔNxy and {(Nx + Ny) / 2−Nz} When D = Rth, ΔNxy · D based on monochromatic light with a wavelength of 590 nm is 25 to 100 nm, and Rth is 100 to 300 nm. And consist of angle of the normal line and Nz for lamination body surface β is 5 to 30 degrees.
[0010]
An example of the composite retardation plate is shown in FIG. Reference numeral 1 denotes a composite retardation plate made of a laminate of retardation layers (A), (B), and (C), 11 and 14 are retardation layers (A), and 12 and 15 are retardation layers (B), Reference numerals 13 and 16 denote retardation layers (C). The figure shows a liquid crystal display device, 2 is a polarizing plate, and 3 is a liquid crystal cell.
[0011]
The retardation layer (A) is a polymer film satisfying nx>ny> nz, that is, having an in-plane refractive index anisotropy (nx> ny), and having a thickness direction larger than the in-plane refractive index. Is formed of a polymer film exhibiting a refractive index characteristic (ny> nz) having a small refractive index. A phase difference layer (A) preferable from the viewpoint of the compensation effect has a phase difference based on monochromatic light having a wavelength of 590 nm: Δnxy · d is more than 0 to 50 nm or less, and the formula: (nx + ny) / 2−nz} · d The birefringence characteristic in which rth is defined as 30 to 100 nm is shown. In the above, nx and ny are in-plane refractive indices, nz is the refractive index in the thickness direction, d is the layer thickness, and Δnxy = nx−ny (the same applies hereinafter).
[0012]
As the polymer film, one made of an appropriate transparent polymer exhibiting the above-described refractive index characteristics can be used, and there is no particular limitation. Incidentally, examples thereof include films made of various polymers and stretched films obtained by orienting polymers by stretching the films by an appropriate method such as uniaxial or biaxial. In particular, those having excellent light transmittance and less alignment unevenness and phase difference unevenness can be preferably used.
[0013]
Incidentally, specific examples of the polymer forming the polymer film include polycarbonate, polyarylate, polysulfone, polyolefin, polyethylene terephthalate, polyethylene naphthalate, norbornene polymer, acrylic polymer, styrene polymer, cellulose polymer, and polymers of these polymers. Examples thereof include polymers in which two or three or more are mixed.
[0014]
In addition, by forming the retardation layer (A) with a polymer film, it can also serve as a transparent protective layer for the polarizing film. As shown in FIG. 1, optical compensation in which the composite retardation plate 1 and the polarizing plate 2 are laminated in a state where the retardation layers (A) 11 and 14 forming the composite retardation plate 1 also serve as a transparent protective layer of the polarizing film. By using a polarizing plate, the thickness can be reduced and the manufacturing process can be shortened.
[0015]
The retardation layer (B) is formed by satisfying nx ≧ ny> nz (negative refractive index anisotropy) and having an optical axis inclined with respect to the normal direction of the layer plane. This makes it possible to efficiently compensate for the state in which the optical axis is inclined with respect to the TN liquid crystal exhibiting positive refractive index anisotropy, particularly the cell substrate in the cell in black display by applying the voltage. If the retardation layer (B) satisfies only the negative refractive index anisotropy and does not satisfy the condition that the optical axis is inclined with respect to the normal direction of the layer plane, the object of the present invention cannot be achieved.
[0016]
That is, in a retardation layer that satisfies only negative refractive index anisotropy, if the normal direction is the reference (incidence angle 0 degree) and the incident angle of monochromatic light is tilted from the reference to the in-plane maximum refractive index direction, nxy · d has a symmetric shape centered on the maximum value when incident at 0 °, and Δnxy · d is incident at 0 ° when the incident angle is tilted in a direction perpendicular to the in-plane maximum refractive index azimuth. In this case, the minimum value is taken as a symmetric shape around the center, and the compensation effect is insufficient.
[0017]
On the other hand, by adding a characteristic that the optical axis is inclined from the normal line, it is possible to avoid the Δnxy · d from reaching the maximum value and the minimum value when incident at 0 degree, thereby improving the compensation effect. . Note that the minimum value of Δnxy · d does not become 0 when the gradient type with negative refractive index anisotropy forms a hybrid orientation, but the minimum value of Δnxy · d does not become 0 when a tilt orientation is formed. Sometimes it becomes zero.
[0018]
The retardation layer (B) having the above characteristics can be formed by, for example, a method of rolling a film made of a thermoplastic polymer with rolls having different peripheral speeds, applying a liquid crystal polymer under an electric field or a magnetic field, or using an alignment film or the like. It is possible to form the molecules in a tilted orientation with respect to the layer surface by an appropriate method such as a method of orienting via a layer.
[0019]
In addition, as said thermoplastic polymer, appropriate things, such as what was illustrated by said retardation layer (A), can be used. In addition, as the liquid crystal polymer, one or two or more suitable ones such as discotic, nematic, cholesteric, and smectic can be used. In particular, a discotic liquid crystal polymer such as that in the above-mentioned wide view film can be preferably used from the viewpoint of the processability of tilt alignment.
[0020]
The retardation layer (C) is composed of a norbornene-based polymer oriented film, and is formed to satisfy Δnxy · d ≦ 70 nm and 1 ≦ Q ≦ 4. Q = (nx-nz) / (nx-ny) (the same applies hereinafter). The retardation layer (C) is formed by, for example, a method in which a norbornene polymer film is uniaxially stretched at a magnification of 1.1 to 3 times in the width direction at a temperature 30 to 60 ° C. higher than the glass transition temperature via a tenter or the like. Can be performed. There is no particular limitation on the norbornene-based polymer that forms the retardation layer (C), and any suitable commercially available product may be used alone or in admixture of two or more.
[0021]
The composite retardation plate is formed by using Nx and Ny as the in-plane refractive index of the laminate, Nz as the refractive index in the thickness direction, and D as the thickness, and Nx ≧ Ny, (Nx−Ny) = ΔNxy and {( Nx + Ny) / 2−Nz} · D = Rth, where ΔNxy · D based on monochromatic light with a wavelength of 590 nm is 25 to 100 nm and Rth is 100 to 300 nm. ), (B), and (C) can be performed by laminating so that the angle β formed by the normal to the laminate surface and Nz is 5 to 30 degrees. In the lamination, one or more of the retardation layers A, B, and C can be used.
[0022]
By satisfying the above-mentioned ΔNxy and Rth, it is possible to form a TN liquid crystal display device that exhibits good contrast without change in display color at an omnidirectional angle of approximately 80 degrees with respect to the normal (front direction). is there. The control of ΔNxy and Rth in the composite retardation plate can be performed by changing the combination of the retardation layers (A), (B), and (C) and the number of the combinations.
[0023]
In the stacking of the retardation layers (A), (B), and (C), the arrangement angle and arrangement order of the slow axis or the fast axis are arbitrary, and the above ΔNxy can be controlled by controlling the arrangement angle. And Rth can be adjusted. Lamination that is more advantageous than the compensation effect is one in which the tilt direction of the optical axis of the retardation layer (B) intersects with the maximum refractive index direction in the laminate surface as orthogonally as possible (90 degrees). It is.
[0024]
In addition, the lamination which is advantageous from the viewpoint of reducing the thickness of the composite retardation plate while achieving the compensation effect described above is to use the retardation layers (A), (B) and (C) as a single layer, respectively. The layers are laminated so that (B) is located between (A) and (C). An appropriate adhesive such as an adhesive can be used for laminating the retardation layer, and the liquid crystal polymer layer can be adhered and supported by the retardation layer (A) or the like.
[0025]
As described above, a new retardation property can be provided by combining the retardation layers (A), (B), and (C), and the phase difference due to the birefringence of the TN liquid crystal, the change due to its viewing angle, etc. An abundant retardation plate exhibiting various types of retardation characteristics that can be compensated can be obtained, and it is possible to compensate for the difference in birefringence characteristics due to the difference in the alignment state of the TN liquid crystal with high accuracy.
[0026]
That is, only the retardation layers (A) and (B) such as the conventional wide-view film and NH film described above, for example, the contrast at a viewing angle of 60 degrees or more is greatly reduced, and coloring occurs in white display. By compensating for at least three of the retardation layers by compensating the retardation layer (C), such as a point or a point that is discolored by black display and becomes non-black, a wide viewing angle can be obtained. It is possible to obtain a TN liquid crystal display device that is excellent in contrast, low display color change, and the like.
[0027]
The thicknesses (A), (B), and (C) of the retardation layer can be appropriately determined according to the target retardation characteristics and the like. In general, in the case of a polymer film, the thickness is 1 to 500 μm, especially 3 to 350 μm, especially 5 to 250 μm, and in the case of a liquid crystal polymer layer, the thickness is 100 μm or less, especially 20 μm or less, especially 0.1 to 10 μm. However, it is not limited to this.
[0028]
The composite retardation plate according to the present invention can be used as it is, or can be used as an optical compensation polarizing plate by being laminated with the polarizing plate 2 as shown in the figure. For the formation of the optical compensation polarizing plate, an appropriate polarizing plate can be used, and the type thereof is not particularly limited. In particular, an absorptive polarizing plate that transmits linearly polarized light having a predetermined vibration surface and absorbs other light can be used more preferably because of its high degree of polarization.
[0029]
Incidentally, examples of the polarizing plate include a film of a hydrophilic polymer such as polyvinyl alcohol, partially formalized polyvinyl alcohol, or partially saponified ethylene / vinyl acetate copolymer, and iodine and / or dichroic dye. For example, a polarizing film obtained by adsorbing a chromatic substance and subjected to stretching and orientation treatment, a polyene-oriented polarizing film, and the like are used.
[0030]
The polarizing plate may be one in which a transparent protective layer is provided on one side or both sides of a polarizing film. The transparent protective layer is provided for various purposes such as reinforcing the polarizing film, improving heat resistance and moisture resistance. The transparent protective layer can be formed as a resin coating layer, a resin film laminate layer, or the like, and may contain fine particles for diffusion and roughening. The transparent protective layer may be provided as the retardation layer (A) as described above.
[0031]
In the above case, as shown in the figure, the retardation layers (A) 11 and 14 forming the composite retardation plate according to the present invention also serve as a transparent protective layer on one side of the polarizing film in the polarizing plate 2, so that the optical compensation polarization This is advantageous in reducing the thickness of the plate and improving the assembly efficiency of the liquid crystal display device. When the transparent protective layer provided separately from the composite retardation plate exhibits a retardation, the composite retardation plate satisfies the above-described ΔNxy and Rth as characteristics in a state in which at least the transparent protective layer adjacent thereto is added. It is preferable from the viewpoint of the compensation effect.
[0032]
The polarizing plate to be used may further be provided with an antireflection layer or an antiglare layer for the purpose of preventing surface reflection on the side where the composite retardation plate is not provided. The antireflection layer can be suitably formed, for example, as a light interference film such as a fluorine polymer coat layer or a multilayer metal vapor deposition film. On the other hand, the anti-glare treatment layer is also an appropriate method for diffusing the surface reflected light by providing a fine concavo-convex structure on the surface by an appropriate method such as a resin coating layer containing fine particles, embossing, sand blasting or etching, etc. It may be formed by.
[0033]
Examples of the fine particles include inorganic materials having an average particle diameter of 0.5 to 20 μm, such as silica, calcium oxide, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, and antimony oxide. One kind or two or more kinds of fine particles, such as crosslinked or uncrosslinked organic fine particles made of a suitable polymer such as polymethyl methacrylate and polyureta can be used.
[0034]
The arrangement relationship between the fast axis of the composite retardation plate and the transmission axis of the polarizing plate in the optical compensation polarizing plate is not particularly limited and can be determined as appropriate. In general, arranging the transmission axis of the polarizing plate and the in-plane maximum refraction direction of the composite retardation plate in a parallel or orthogonal relationship causes the viewing angle to change without affecting the front (vertical) direction characteristics. It is preferable from the point of controlling the above-mentioned characteristics to increase the viewing angle.
[0035]
The layers such as the retardation layer and the polarizing plate forming the composite retardation plate and the optical compensation polarizing plate according to the present invention may be in a separated state, but the reflection is suppressed by adjusting the refractive index difference between layers and the optical system is shifted. It is preferable that a part, especially, all of them are fixedly treated for prevention of foreign matter such as dust.
[0036]
For the fixing treatment, an appropriate material such as a transparent adhesive can be used, and the type of the adhesive is not particularly limited. From the standpoint of preventing changes in the optical characteristics of the constituent members, those that do not require a high-temperature process during curing and drying during the adhesion treatment are preferable, and those that do not require a long curing treatment or drying time are desirable. From this point, an adhesive layer can be preferably used.
[0037]
For the formation of the pressure-sensitive adhesive layer, for example, a transparent pressure-sensitive adhesive using an appropriate polymer such as an acrylic polymer, a silicone-based polymer, polyester, polyurethane, polyether, or synthetic rubber can be used. In particular, acrylic pressure-sensitive adhesives are preferred from the viewpoints of optical transparency, pressure-sensitive adhesive properties, weather resistance, and the like.
[0038]
In addition, an adhesion layer can also be provided as needed on one side or both sides of a composite phase difference plate, an optical compensation polarizing plate, etc. for the purpose of adhesion to an adherend such as a liquid crystal cell. When the pressure-sensitive adhesive layer is exposed on the surface, it is preferable to temporarily attach a separator or the like to prevent contamination of the pressure-sensitive adhesive layer surface until it is put to practical use.
[0039]
The composite retardation plate and the optical compensation polarizing plate according to the present invention can be preferably used for forming a liquid crystal display device as a compensation plate for birefringence by a liquid crystal, particularly TN liquid crystal. In general, a liquid crystal display device is formed by appropriately assembling components such as a polarizing plate, a liquid crystal cell, a compensation plate, and a backlight or a reflector as necessary, and incorporating a drive circuit. There is no particular limitation except that the above-described composite retardation plate and optical compensation polarizing plate are used, and a liquid crystal display device can be formed according to the conventional art.
[0040]
Therefore, when forming a liquid crystal display device, for example, an optical path control plate such as a light diffusing plate, an antiglare layer, a prism sheet, an antireflection film, a protective layer, a protective plate provided on the polarizing plate on the viewing side, a prism sheet provided on the backlight, etc. Appropriate optical elements such as can be appropriately arranged. The compensation plate is usually arranged between the liquid crystal cell 3 and the polarizing plate 2 on the viewing side or / and the backlight side as shown in the figure. Therefore, the composite retardation plate or optical compensation polarizing plate according to the present invention may be disposed on at least one side of the liquid crystal cell.
[0041]
【Example】
Example 1
A norbornene polymer film having a thickness of 100 μm (manufactured by JSR, Arton, the same applies hereinafter) is stretched at 175 ° C. with a tenter stretching machine, has a refractive index characteristic of nx>ny> nz, and is monochromatic with a wavelength of 590 nm A retardation layer A1 with light (hereinafter the same) Δnxy · d of 10 nm and rth of 80 nm was obtained. The refractive index and the like were measured with an automatic birefringence meter (manufactured by Oji Scientific Instruments, KOBRA-21ADH, the same shall apply hereinafter).
[0042]
Next, only the tilted orientation layer of the discotic liquid crystal polymer of the wide view film (WV02A) is transferred onto the retardation layer A1 by a method of transferring through an adhesive under a humidification process, and the retardation layer B1 is transferred. A laminated body was obtained in which Δnxy · d by monochromatic light having a wavelength of 590 nm was 30 nm and rth was 130 nm. In the transfer lamination, the direction of the in-plane maximum refractive index (nx) of the retardation layer A1 and the tilt direction of the discotic liquid crystal were processed in parallel.
[0043]
Next, Δnxy · d by monochromatic light having a wavelength of 590 nm obtained by uniaxially stretching a norbornene-based polymer film having a thickness of 100 μm on the retardation layer B1 with a tenter at 210 ° C. is 20 nm, and Q is 1. .6 retardation layer C1 was laminated through an acrylic adhesive layer to obtain a composite retardation plate having ΔNxy · D of 50 nm and Rth of 160 nm by monochromatic light having a wavelength of 590 nm.
[0044]
Next, a polyvinyl alcohol film having a thickness of 75 μm is dyed in an aqueous solution containing iodine, and then uniaxially stretched 6 times between rolls having different peripheral speeds in an aqueous solution containing boric acid. A triacetyl cellulose film having a thickness of 80 μm is bonded through an alcohol adhesive, and the composite retardation plate is bonded and laminated on the other surface of the polarizing film through a retardation layer A1 through a polyvinyl alcohol adhesive. A compensation polarizing plate was obtained.
[0045]
Comparative Example An optical compensation polarizing plate according to Example 1 except that instead of the composite retardation plate, a laminate of the above-described retardation layer A1 and retardation layer B1 was used and bonded and laminated through the retardation layer A1. Got.
[0046]
Evaluation test Example 1 and the optical compensation polarizing plate obtained in Comparative Example were adhered to both sides of the TN type liquid crystal cell so that the polarizing plate was on the outer side to obtain a liquid crystal display device, and a contrast measuring device (ELDIM, EZContrast) The viewing angle characteristics of the display contrast were examined. The results are shown in FIG. 2 as isocontrast curves. The viewing angle characteristics based on contrast 10 in the vertical and horizontal directions are shown in the following table. From the above results, it can be seen that in the embodiment, the viewing angle for good visual recognition is greatly enlarged in almost all directions.
[0047]

[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an example of a liquid crystal display device. FIG. 2 is an isocontrast curve of Example 1 and a comparative example.
1: Composite retardation plates 11, 14: Retardation layer (A)
12, 15: Retardation layer (B)
13, 16: Retardation layer (C)
2: Polarizing plate 3: Liquid crystal cell

Claims (4)

When the in-plane refractive index is nx, ny, the refractive index in the thickness direction is nz, the layer thickness is d, nx−ny = Δnxy and (nx−nz) / (nx−ny) = Q, (A A retardation layer comprising a polymer film satisfying nx>ny> nz, (B) a retardation layer satisfying nx ≧ ny> nz and an optical axis inclined with respect to the normal direction of the layer plane, and (C) norbornene It is composed of a laminated body made of an oriented film of a polymer and having one or more retardation layers each satisfying Δnxy · d ≦ 70 nm and 1 ≦ Q ≦ 4, and the in-plane refractive index in the laminated body is Nx, Ny, refractive index Nz, thickness D, Nx ≧ Ny, (Nx−Ny) = ΔNxy and {(Nx + Ny) / 2−Nz} · D = Rth, wavelength 590 nm based on the monochromatic light △ Nxy · D is at 25 to 100 nm, the composite retardation plate Rth is characterized by the Dearuko 100~300nm An optical compensation polarizing plate comprising a laminate of the composite retardation plate according to claim 1 and a polarizing plate. A liquid crystal display device comprising the composite retardation plate according to claim 1 between a polarizing plate and a liquid crystal cell. In Claim 3, a composite phase difference plate has a phase difference layer (B) between a phase difference layer (A) and a phase difference layer (C), and (A) and (B) ( A liquid crystal display device using one layer each of C).

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