JP2009036860A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display excellent in display quality that can be manufactured highly efficiently. <P>SOLUTION: The liquid crystal display comprises a liquid crystal cell, and polarizing plates disposed on both sides of the liquid crystal cell and made up of polarizers and polarizing plate protection films disposed on both sides of the polarizer. A uniaxial retardation film having properties as a negative-C plate optically, and a biaxial retardation film having properties as a B-plate optically are used for the polarizing plate protection films. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device in which a retardation film is used to improve viewing angle characteristics.

  The liquid crystal display device has features such as power saving, light weight, thinness, and the like, and has rapidly spread in recent years in place of the conventional CRT display. As shown in FIG. 8, a typical liquid crystal display device 100 may include an incident-side polarizing plate 102 </ b> A, an outgoing-side polarizing plate 102 </ b> B, and a liquid crystal cell 101. The polarizing plates 102A and 102B are configured to selectively transmit only linearly polarized light having a vibration surface in a predetermined vibration direction, and crossed Nicols so that the vibration directions are perpendicular to each other. It is arranged to face each other. The liquid crystal cell 101 includes a large number of cells corresponding to the pixels, and is disposed between the polarizing plates 102A and 102B.

  Various types of liquid crystal display devices have been put into practical use depending on the arrangement form of the liquid crystal molecules constituting the liquid crystal cell. At present, the VA (Vertical Alignment) method is mainly used. Such a VA liquid crystal display device has been widely used mainly for liquid crystal television applications. In recent years, an OCB (Optically Compensated Bend) type liquid crystal display device, which has a faster response speed, has been put to practical use. I'm bathing.

  In the liquid crystal cell used in the VA mode and OCB mode liquid crystal display devices, since the liquid crystal molecules are vertically aligned, the liquid crystal cell as a whole has optical characteristics that act as an optically positive C plate. Become. For example, if the liquid crystal cell 101 of the liquid crystal display device 100 shown in FIG. 8 has such optical characteristics, the linearly polarized light that has passed through the polarizing plate 102A on the incident side is the non-driven cell portion of the liquid crystal cell 104. At the time of transmission, the light is transmitted without being phase-shifted and is blocked by the output-side polarizing plate 102B. On the other hand, the linearly polarized light is phase-shifted when passing through the driven cell portion of the liquid crystal cell 101, and an amount of light corresponding to the amount of this phase shift is transmitted through the exit-side polarizing plate 102B and emitted. The Thereby, the drive voltage of the liquid crystal cell 101 can be appropriately controlled for each cell, and a desired image can be displayed on the exit-side polarizing plate 102B side.

  Considering the case where linearly polarized light is transmitted through the portion of the liquid crystal cell 101 that is not driven, as described above, the liquid crystal cell 101 has an optical characteristic that acts as an optically positive C plate. Therefore, although the light incident along the normal line of the liquid crystal cell 101 of the linearly polarized light transmitted through the incident side polarizing plate 102A is transmitted without being phase-shifted, the linearly polarized light transmitted through the incident side polarizing plate 102A is transmitted. Among them, light incident in a direction inclined from the normal line of the liquid crystal cell 101 has a phase difference when passing through the liquid crystal cell 101 and becomes elliptically polarized light. Along with this, even when a certain cell in the liquid crystal cell 101 is in a non-driven state, the linearly polarized light is essentially transmitted as it is and should be blocked by the output-side polarizing plate 102B. A part of the light emitted in the direction inclined from the normal line leaks from the polarizing plate 102B on the emission side. For this reason, in the conventional liquid crystal display device 100 as described above, the display quality of the image observed from the direction inclined from the normal line of the liquid crystal cell 101 is lower than the image observed from the front. There was a problem that it worsened by (viewing angle dependency problem).

  In order to improve the problem of viewing angle dependency in such a liquid crystal display device, various techniques have been developed so far, and a representative method is a method using a retardation film. As a method for improving the viewing angle dependency of a liquid crystal display device employing the VA mode and OCB mode liquid crystal cells using a retardation film, a retardation having properties as an optically negative C plate is usually used. A method using two retardation films of a film and a retardation film optically having properties as an A plate is used (for example, Patent Document 1). As a method of using such two retardation films, for example, a liquid crystal cell 101 as shown in FIG. 9A is used as a retardation film 103 having properties as an optically negative C plate and an optical film. In particular, it is sandwiched between the retardation film 104 having the property as an A plate, or has a property as an optically negative C plate on the polarizing plate 102A on the incident side as shown in FIG. 9B. A method of laminating the phase difference film 103 and the phase difference film 104 having optical properties as an A plate has been used. As described above, the method of improving the viewing angle dependency problem using two retardation films can be achieved by changing the combination of the retardation films in a liquid crystal display device using liquid crystal cells having various optical characteristics. It is useful in that it can improve the problem of viewing angle dependency and is still widely used today.

By the way, the retardation film used for improving the viewing angle characteristics of the liquid crystal display device is generally used as a polarizing plate protective film. However, the retardation having the properties of the optically A plate is used. When the film is bonded to the polarizer, it is required to bond the film so that the light absorption axis of the polarizer and the slow axis of the retardation film are perpendicular to each other. In addition, as a method for industrially producing a polarizing plate, it is desirable to continuously bond a polarizer and a retardation film in a long state.
Here, when the polarizer is formed in a long shape, the direction of the light absorption axis is parallel to the longitudinal direction due to its property. For this reason, when laminating a polarizer and a retardation film optically having properties as an A plate in a long state, the slow axis of the retardation film is oriented in a direction perpendicular to the longitudinal direction. It will be required to be.
In this respect, the retardation film having the property as an optically A plate, which is widely used at present, has a property as an optically positive A plate using a material having positive uniaxiality in general. Therefore, in order to orient the direction of the slow axis in the direction perpendicular to the longitudinal direction, it is necessary to perform a transverse stretching process in which the retardation film is stretched in the direction perpendicular to the longitudinal direction in the production process. It was.
However, when a transversely stretched retardation film is applied to a long retardation film, stress is applied not only in the direction perpendicular to the longitudinal direction but also in a direction parallel to the longitudinal direction. Therefore, there is a problem that it is difficult to realize desired optical characteristics.
Therefore, conventionally, after producing a retardation film having a slow axis oriented in a direction parallel to the longitudinal direction by subjecting the retardation film to a longitudinal direction in which the retardation film is stretched in a direction parallel to the longitudinal direction, It was necessary to cut it into a predetermined shape and attach it to a polarizer. For this reason, display defects due to variations in bonding positions and poor productivity have been problems.

  In addition, with the recent improvement in quality of liquid crystal display devices, a method of combining a retardation film having properties as a conventional A plate and a retardation film having properties as a negative C plate can achieve a desired display quality. It has been pointed out that it has become difficult to obtain.

Japanese Patent No. 3746050

  The present invention has been made in view of such circumstances, and a main object of the present invention is to provide a liquid crystal display device that can be manufactured with high efficiency and has excellent display quality. .

  In order to solve the above problems, the present invention provides a liquid crystal display comprising a liquid crystal cell and a polarizing plate disposed on both sides of the liquid crystal cell and comprising a polarizer and a polarizing plate protective film disposed on both sides of the polarizer. In the apparatus, a uniaxial retardation film having properties as an optically negative C plate and a biaxial retardation film having properties as an optical B plate are used as the polarizing plate protective film. Provided is a liquid crystal display device.

According to the present invention, the biaxial retardation film optically having the property as a B plate is used as the polarizing plate protective film, whereby the biaxial retardation film and the polarizer are used. It becomes possible to stick together continuously in a long state.
Further, according to the present invention, the biaxial retardation film is used in combination with a uniaxial retardation film having properties as an optically negative C plate, so that the viewing angle is simply expanded. Instead, it is possible to prevent the color of the image from changing even when the screen is viewed from an oblique direction.
Therefore, according to the present invention, a liquid crystal display device that can be manufactured with high efficiency and has excellent display quality can be obtained.

  In this invention, it is preferable that the said uniaxial retardation film has a base material and the uniaxial retardation layer which is formed on the said base material and contains a rod-shaped compound. Since the uniaxial retardation film has such a configuration, the optical characteristics can be adjusted in a wide range according to the optical characteristics of the liquid crystal cell and the biaxial retardation film used in the present invention. This is because it becomes easy.

  In the present invention, the biaxial retardation film is preferably made of a cycloolefin polymer. This is because it becomes easy to arbitrarily adjust the optical characteristics of the biaxial retardation film according to the optical characteristics of the liquid crystal cell and the uniaxial retardation film used in the present invention.

Moreover, in this invention, the said liquid crystal cell is a VA type liquid crystal cell provided with the optical characteristic which satisfies the following formula | equation (A-1)-(A-2), The said biaxial retardation film is the following. The optical properties satisfying the formulas (B-1) to (B-3) are satisfied, and the uniaxial retardation film satisfies the following formulas (C-1) to (C-3): It is preferable to have optical characteristics.
(A-1) 270 nm <Rth (550)
(A-2) Rth (450) / Rth (550)> 1
(B-1) 80 nm <Re ⁰ <110 nm
(B-2) 0.9 ≦ Re ⁴⁰ (450) / Re ⁴⁰ (550) ≦ 1.01
(B-3) 1.5 <Nz <1.9
(C-1) 0.98 ≦ Re ⁴⁰ (450) / Re ⁴⁰ (550) ≦ 1.10.
(C-2) 0 nm ≦ Re ⁰ <5 nm
(C-3) 150 nm <Rth (550) <200 nm
Because a liquid crystal cell having such optical characteristics, a uniaxial retardation film, and a biaxial retardation film are used in combination, a VA liquid crystal display device with further excellent display quality can be obtained. is there.

Here, Re ⁰ means in-plane retardation (Re) measured by making measurement light incident from the direction of the normal to the plane, and Re ⁴⁰ is inclined by 40 ° with respect to the normal to the plane. It means in-plane retardation (Re) measured by making measurement light incident from the measured direction. In-plane retardation (Re) is represented by Re = (nx−ny) × d. The Rth means retardation in the thickness direction (the numerical value in parentheses is the wavelength of the measurement light), and Rth = ((nx + ny) / 2−nz) × d. Further, the Nz is represented by Nz = (nx−ny) / (nx−nz). Here, nx is the refractive index in the slow axis direction x in the plane, ny is the refractive index in the fast axis direction y in the plane, nz is the refractive index in the thickness direction, and d is the thickness. .

  The liquid crystal display device of the present invention can be manufactured with high efficiency and has the effect of being excellent in display quality.

  Hereinafter, the liquid crystal display device of the present invention will be described.

  As described above, the liquid crystal display device of the present invention includes a liquid crystal cell, and a polarizing plate that is disposed on both sides of the liquid crystal cell and includes a polarizer and a polarizing plate protective film disposed on both sides of the polarizer. As the polarizing plate protective film, a uniaxial retardation film having properties as an optically negative C plate and a biaxial retardation film having properties as an optically B plate are used. It is characterized by that.

Such a liquid crystal display device of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing an example of the liquid crystal display device of the present invention. As illustrated in FIG. 1, the liquid crystal display device 10 of the present invention includes a liquid crystal cell 1 and polarizing plates 2 and 3 disposed on both surfaces of the liquid crystal cell 1.
In such an example, in the liquid crystal display device 10 of the present invention, the polarizing plate 2 includes a polarizer 2a, a polarizing plate protective film 2b disposed on one surface of the polarizer 2a, and the polarizer. 2a, and a biaxial retardation film 20 optically having a property as a B plate. The polarizing plate 3 includes a polarizer 3a and the polarizer 3a. And a uniaxial retardation film 30 having properties as an optically negative C plate and disposed on the other surface of the polarizer 3a. Is.

According to the present invention, the biaxial retardation film optically having the property as a B plate is used as the polarizing plate protective film, whereby the biaxial retardation film and the polarizer are used. It becomes possible to stick together continuously in a long state. This is because when the biaxial retardation film optically having the property as a B plate is formed in a long shape, the direction of the slow axis in the plane is perpendicular to the longitudinal direction. This is because the optical properties can be expressed.
Further, according to the present invention, the biaxial retardation film is used in combination with a uniaxial retardation film having properties as an optically negative C plate, so that the viewing angle is simply expanded. Instead, it is possible to prevent the color of the image from changing even when the screen is viewed from an oblique direction.
Therefore, according to the present invention, a liquid crystal display device that can be manufactured with high efficiency and has excellent display quality can be obtained.

  The liquid crystal display device of the present invention has at least a liquid crystal cell and two polarizing plates. Hereafter, each structure used for this invention is demonstrated in order.

1. Polarizing plate First, the polarizing plate used in the present invention will be described. The polarizing plate used for this invention has a polarizer and the polarizing plate protective film arrange | positioned on both surfaces of the said polarizer. The polarizing plate used in the present invention can be roughly divided into the following four modes depending on the difference in the configuration.
The polarizing plate of a 1st aspect has a polarizer, the polarizing plate protective film arrange | positioned on one surface of the said polarizer, and the uniaxial retardation film arrange | positioned on the other surface of the said polarizer. It is an aspect.
The polarizing plate of the second aspect includes a polarizer, a polarizing plate protective film disposed on one surface of the polarizer, and a biaxial retardation film disposed on the other surface of the polarizer. It is the aspect which has.
The polarizing plate of the third aspect includes a polarizer, a polarizing plate protective film disposed on one surface of the polarizer, a uniaxial retardation film and a biaxial film disposed on the other surface of the polarizer. It is an aspect which has a property retardation film. In the polarizing plate of this embodiment, the order in which the uniaxial retardation film and the biaxial retardation film are arranged on the polarizer is not particularly limited. Therefore, the uniaxial retardation film and the biaxial retardation film may be arranged in this order on the polarizer, or may be arranged in the reverse order.
The polarizing plate of the 4th aspect is an aspect which has a polarizer and the polarizing plate protective film arrange | positioned on both surfaces of the said polarizer.

The polarizing plate of each aspect is demonstrated referring a figure. FIG. 2 is a schematic sectional view showing an example of the polarizing plate of each embodiment used in the present invention. As illustrated in FIG. 2A, the polarizing plate 3 of the first embodiment used in the present invention includes a polarizer 3a, a polarizing plate protective film 3b disposed on one surface of the polarizer 3a, It has the uniaxial retardation film 30 arrange | positioned on the other surface of the said polarizer 3a.
Moreover, as illustrated in FIG. 2B, the polarizing plate 2 of the second embodiment used in the present invention includes a polarizer 2a and a polarizing plate protective film 2b disposed on one surface of the polarizer 2a. And a biaxial retardation film 20 disposed on the other surface of the polarizer 2a.
Moreover, as illustrated in FIG. 2C, the polarizing plate 4 of the third embodiment used in the present invention includes a polarizer 4a and a polarizing plate protective film 4b disposed on one surface of the polarizer 4a. And a uniaxial retardation film 30 and a biaxial retardation film 20 disposed on the other surface of the polarizer 4a.
Furthermore, as illustrated in FIG. 2D, the polarizing plate 5 of the fourth embodiment used in the present invention is a polarizer 5a and a polarizing plate protective film 5b disposed on one side of the polarizer 5a. It has.

  In the liquid crystal display device of the present invention, two polarizing plates are used, and the combination of the two polarizing plates used is at least a uniaxial retardation film and two of the four polarizing plates described above. The combination is not particularly limited as long as the axial retardation film is used one by one. The combination of polarizing plates used in the present invention will be described in detail in the section “3. Liquid crystal display device” described later.

  Hereinafter, the uniaxial retardation film, the biaxial retardation film, the polarizing plate protective film, and the polarizer used for the polarizing plate of each aspect described above will be described in detail.

(1) Uniaxial retardation film First, the uniaxial retardation film will be described. The uniaxial retardation film used in the present invention has properties as an optically negative C plate.
Here, in the present invention, “the property as an optically negative C plate” means that the refractive indexes in the x and y directions perpendicular to each other in the in-plane direction of the uniaxial retardation film are nx and ny, respectively, and the thickness direction When the refractive index in the (z direction) is nz, it means that the relationship of nx = ny> nz is established.
In addition, the uniaxial retardation film used in the present invention can be measured by the parallel Nicol rotation method using, for example, KOBRA-WR manufactured by Oji Scientific Instruments.

  The uniaxial retardation film used in the present invention is not particularly limited as long as it has properties as an optically negative C plate. Examples of such a uniaxial retardation film include a base material and a uniaxial retardation layer formed on the base material and containing a rod-like compound, and for example, Japanese Patent Application Laid-Open No. 2004-347698. A transparent substrate having at least one surface having a liquid crystal alignment regulating force, a surface modified layer, and an optically anisotropic layer containing a liquid crystal compound, wherein the surface modified layer is the transparent Examples of the optically anisotropic layer that are laminated on the surface of the substrate having a liquid crystal alignment regulating force and that are laminated on the transparent substrate through the surface modification layer can be given. Further, as described in JP-A-2004-347698, a transparent substrate, an alignment layer formed on the transparent substrate and made of a polymer compound having alignment ability of liquid crystal molecules, and the alignment layer And a retardation layer formed of a polymerizable liquid crystal compound having a (meth) acryloyl group. In the present invention, any uniaxial retardation film having any of these configurations can be suitably used as long as it can exhibit desired optical characteristics. It is preferable to use one having a uniaxial retardation layer containing a rod-like compound. This is because the uniaxial retardation film having such a configuration is excellent in the expression of optical characteristics.

Here, the uniaxial retardation film having such a configuration can be classified into two modes according to the arrangement form of the rod-shaped compounds in the uniaxial retardation layer. The first aspect is an aspect in which the rod-shaped compound forms a random homogeneous orientation, and the second aspect is an aspect in which the rod-shaped compound forms a cholesteric orientation. In the present invention, it is possible to use any of these embodiments, but it is preferable to use an embodiment in which the rod-like compound forms a random homogeneous orientation. Since the uniaxial retardation film of such an embodiment can be formed so that the uniaxial retardation layer is in direct contact with the base material, the adhesion between the base material and the uniaxial retardation layer is improved. Because it is excellent.
Therefore, hereinafter, a uniaxial retardation film having a base material and a uniaxial retardation layer containing a rod-like compound formed on the base material and having a random homogeneous orientation will be described in detail.

a. Uniaxial retardation layer First, the uniaxial retardation layer will be described. As described above, the uniaxial retardation layer contains a rod-shaped compound in which a random homogeneous orientation is formed.

(Bar compound)
The rod-shaped compound used in the present invention has an electric dipole efficiency that can be imparted to the uniaxial retardation film as an optically negative C plate by being arranged in the uniaxial retardation layer. It is not particularly limited.
Here, the “rod-like compound” means that the main skeleton of the molecular structure is rod-like.

As the rod-like compound used in the present invention, a compound having a relatively small molecular weight is preferably used. This is because the smaller molecular weight can improve the affinity with the material constituting the substrate described later, and therefore the adhesion between the substrate and the uniaxial retardation layer can be improved. Specifically, the molecular weight is preferably in the range of 200 to 1200, and particularly preferably in the range of 400 to 800.
In addition, when using the compound which has a polymeric functional group mentioned later as a rod-shaped compound, the said molecular weight shall show the molecular weight before superposition | polymerization.

  Moreover, it is preferable that the rod-shaped compound used for this invention is a liquid crystalline material which shows liquid crystallinity. This is because, when the rod-like compound is a liquid crystalline material, the uniaxial retardation layer used in the present invention can be made excellent in the development of optical characteristics per unit thickness.

  The liquid crystalline material is not particularly limited as long as it can form a random homogeneous alignment, but it is preferable to use a liquid crystalline material exhibiting a nematic phase. This is because a liquid crystalline material exhibiting a nematic phase is easier to form random homogeneous alignment than liquid crystalline materials exhibiting other liquid crystal phases.

  Further, as the liquid crystalline material exhibiting the nematic phase, it is preferable to use a compound having spacers at both mesogenic ends. This is because the liquid crystalline material having spacers at both ends of the mesogen is excellent in flexibility and can effectively prevent the uniaxial retardation layer from becoming clouded.

In addition, as the rod-shaped compound used in the present invention, those having a polymerizable functional group in the molecule are preferably used, and those having a polymerizable functional group capable of three-dimensional crosslinking are particularly preferably used. Since the rod-shaped compound has a polymerizable functional group, the rod-shaped compound can be polymerized and fixed. Therefore, the rod-shaped compound has excellent alignment stability and hardly changes in optical properties. It is because it can obtain.
Here, the above “three-dimensional crosslinking” means that liquid crystal molecules are polymerized three-dimensionally to form a network (network) structure.

  In the present invention, the rod-shaped compound having the polymerizable functional group may be mixed with the rod-shaped compound having no polymerizable functional group.

Examples of the polymerizable functional group include various polymerizable functional groups that are polymerized by the action of ionizing radiation such as ultraviolet rays and electron beams, or heat. Typical examples of these polymerizable functional groups include radical polymerizable functional groups or cationic polymerizable functional groups.
A representative example of the radical polymerizable functional group is a functional group having at least one addition-polymerizable ethylenically unsaturated double bond. Specific examples thereof include a vinyl group having or not having a substituent, and an acrylate group (generic name including an acryloyl group, a methacryloyl group, an acryloyloxy group, and a methacryloyloxy group).
On the other hand, specific examples of the cationic polymerizable functional group include an epoxy group. In addition, examples of the polymerizable functional group include an isocyanate group and an unsaturated triple bond. Among these, in the present invention, a functional group having an ethylenically unsaturated double bond is preferably used from the viewpoint of the process.

  The rod-shaped compound used in the present invention is particularly preferably a liquid crystalline material exhibiting liquid crystallinity and having the above-mentioned polymerizable functional group at the terminal. For example, if nematic liquid crystalline materials having polymerizable functional groups at both ends are used, they can be polymerized three-dimensionally to form a network structure, have alignment stability, and have optical properties. This is because a uniaxial retardation layer having excellent expression can be obtained. Moreover, even if it has a polymerizable functional group at one end, it can be crosslinked with other molecules to stabilize the sequence.

  Specific examples of such rod-shaped compounds include compounds represented by the following formulas (1) to (6).

  Here, the liquid crystalline materials represented by the chemical formulas (1), (2), (5) and (6) are D.I. J. et al. Broer et al., Makromol. Chem. 190, 3201-3215 (1989); J. et al. Broer et al., Makromol. Chem. 190, 2250 (1989), or by methods analogous thereto. The liquid crystal material represented by the chemical formulas (3) and (4) can be prepared by the method disclosed in DE 195, 04, 224, for example.

  Moreover, what is shown to following formula (7)-(17) can also be mentioned as a specific example of the nematic liquid crystalline material which has an acrylate group at the terminal.

  In addition, the rod-shaped compound used for this invention may be only 1 type, or 2 or more types may be sufficient as it. For example, when the rod-shaped compound is used by mixing a liquid crystalline material having one or more polymerizable functional groups at both ends and a liquid crystalline material having one or more polymerizable functional groups at one end, The polymerization density (crosslinking density) and optical characteristics can be arbitrarily adjusted by adjusting the ratio, which is preferable.

(Sequence form of rod-shaped compound)
Next, random homogeneous alignment formed by the rod-shaped compound in the uniaxial retardation layer will be described. The random homogeneous orientation has at least the following three characteristics. That is, the random homogeneous orientation in the present invention is
First, when the uniaxial retardation layer is viewed from the direction perpendicular to the surface of the uniaxial retardation layer, the arrangement direction of the rod-like compounds is random (hereinafter simply referred to as “irregularity”). )
Second, the size of the domain formed by the rod-shaped compound in the uniaxial retardation layer is smaller than the wavelength in the visible light region (hereinafter sometimes simply referred to as “dispersibility”).
Third, the rod-shaped compound molecules in the uniaxial retardation layer are present in a plane parallel to the surface of the uniaxial retardation layer (hereinafter, sometimes simply referred to as “in-plane orientation”). ,
At least.

  Such random homogeneous orientation will be specifically described with reference to the drawings. FIG. 3 is a schematic perspective view showing an example of a uniaxial retardation film suitably used in the present invention. As illustrated in FIG. 3, the uniaxial retardation film 30 preferably used in the present invention is formed of a base 31 and a rod-shaped compound that is formed so as to be in direct contact with the base 31 and has a random homogeneous orientation. A uniaxial retardation layer 32 containing A.

  FIG. 4 is a schematic view for explaining the random homogeneous alignment. Here, FIG. 4A shows a case where the uniaxial retardation film 30 in FIG. 3 is viewed from the perpendicular direction with respect to the surface (xy plane) of the uniaxial retardation layer 32 represented by Z in FIG. FIG. 4B and 4C are cross-sectional views taken along line Y-Y 'in FIG. 4A.

First, the “irregularity” of the random homogeneous orientation will be described with reference to FIG. As shown in FIG. 4A, the “irregularity” is obtained when the uniaxial retardation film 30 is viewed from the perpendicular direction (Z direction in FIG. 3) with respect to the surface of the uniaxial retardation layer 32. This shows that the rod-like compounds A are randomly arranged in the uniaxial retardation layer 32.
Here, in the present invention, in order to explain the arrangement direction of the rod-shaped compound A, the major axis direction (hereinafter referred to as molecular axis) represented by a in FIG. For this reason, the fact that the rod-shaped compounds A are arranged at random means that the direction of the molecular axis a of the rod-shaped compound A included in the uniaxial retardation layer 32 is random.

  Here, in addition to the arrangement state illustrated in FIG. 4A, even if the rod-shaped compound has a cholesteric structure, the direction of the molecular axis a is random as a whole. Although it corresponds to the “irregularity”, the “irregularity” in the present invention does not include a form caused by a cholesteric structure.

  Next, the “dispersibility” of the random homogeneous alignment will be described with reference to FIG. As shown in FIG. 4A, the above “dispersibility” indicates that when the rod-shaped compound A forms the domain A ′ in the uniaxial retardation layer 32, the size of the domain A ′ is in the visible light region. This indicates that it is smaller than the wavelength. In the present invention, the smaller the size of the domain A ′ is, the more preferable, and the state where the rod-shaped compound A is dispersed in a single molecule is the most preferable.

  Next, the “in-plane orientation” possessed by the random homogeneous orientation will be described with reference to FIG. As shown in FIG. 4B, the above-mentioned “in-plane orientation” indicates that the rod-shaped compound A in the uniaxial retardation layer 32 has the molecular axis a in the normal direction of the uniaxial retardation layer 32 (in FIG. 3). This means that the film is oriented so as to be substantially perpendicular to the Z direction) (substantially parallel to the xy plane in FIG. 3). Here, as the “in-plane orientation” in the present invention, as shown in FIG. 4B, the molecular axes a of all the rod-shaped compounds A in the uniaxial retardation layer 32 are in the normal direction Z. For example, as shown in FIG. 4 (c), the uniaxial retardation layer 32 has a rod shape in which the molecular axis a ′ is not perpendicular to the normal direction Z. Even when the compound A is present, the case where the average direction of the molecular axis a of the rod-shaped compound A existing in the uniaxial retardation layer 32 is substantially perpendicular to the normal direction A is included. That is, even if the molecular axis direction of each rod-shaped compound A has a distribution, the molecular axis direction averaged over all the molecules of the rod-shaped compound A may be substantially in the xy plane.

  Thus, since the rod-shaped compound forms a random homogeneous orientation, the refractive index nx in the x direction, the refractive index ny in the y direction, and the refractive index nz in the z direction shown in FIG. Since it is easy to establish a relationship of> nz, the uniaxial retardation layer used in the present invention expresses properties as an optically negative C plate. For this reason, when the said rod-shaped compound forms random homogeneous orientation, there exists an advantage that it becomes easy to provide the property as an optically negative C plate to a uniaxial retardation film.

  As described above, the random homogeneous orientation is characterized by exhibiting the “irregularity”, “dispersibility”, and “in-plane orientation”, but the rod-like compound exhibits random homogeneous orientation. The formation can be confirmed by the following method.

First, a method for confirming “irregularity” possessed by the random homogeneous orientation in the present invention will be described. The “irregularity” can be confirmed by evaluating the in-plane retardation (Re) of the uniaxial retardation layer and the presence / absence of a selective reflection wavelength due to the cholesteric structure.
That is, the in-plane retardation (Re) evaluation of the uniaxial retardation layer can confirm that the rod-like compound is randomly oriented, and the rod-like compound does not form a cholesteric structure depending on the presence or absence of the selective reflection wavelength. Can be confirmed.

It is confirmed that the rod-shaped compound is randomly oriented by the in-plane retardation (Re) value of the uniaxial retardation layer being within a range indicating that the rod-shaped compound is randomly oriented. can do. In particular, in the present invention, the in-plane retardation (Re) of the uniaxial retardation layer is preferably in the range of 0 nm to 5 nm. Here, the in-plane retardation (Re) includes the refractive index nx in the slow axis direction (direction with the highest refractive index) and the fast axis direction (with the smallest refractive index) in the plane of the uniaxial retardation layer. Direction) and the thickness d (nm) of the uniaxial retardation layer is a value represented by the equation Re = (nx−ny) × d.
Unless otherwise specified, the value of in-plane retardation (Re) in this specification refers to a value measured at a measurement wavelength of 589 nm in an environment of 23 ° C. and 55% RH.

  The in-plane retardation (Re) of the uniaxial retardation layer may be originally measured for a uniaxial retardation layer single layer. However, in many cases, in many cases, the uniaxial retardation layer is thin and is in close contact with the substrate, so that it is often difficult to measure only the uniaxial retardation layer. Therefore, it is usually obtained by subtracting the in-plane retardation (Re) exhibited by layers other than the uniaxial retardation layer from the in-plane retardation (Re) of the entire uniaxial retardation film. That is, by measuring in-plane retardation (Re) of the whole uniaxial retardation film and the uniaxial retardation film cut out from the uniaxial retardation film, and subtracting the latter measurement value from the former measurement value. The in-plane retardation (Re) of the uniaxial retardation layer can be obtained. In-plane retardation (Re) can be measured by, for example, a parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

  Next, a method for confirming “dispersibility” possessed by the random homogeneous orientation will be described. The above “dispersibility” means that the haze value of the uniaxial retardation layer constituting the uniaxial retardation film is within a range indicating that the domain size of the rod-shaped compound is not more than the wavelength in the visible light region. Can be confirmed. Among them, in the present invention, the haze value of the uniaxial retardation layer is preferably in the range of 0% to 5%, particularly preferably in the range of 0% to 1%, and more preferably 0% to It is preferable to be within the range of 5%.

  Here, the haze value of the uniaxial retardation layer may be originally measured for the uniaxial retardation layer single layer. However, in many cases, in many cases, the uniaxial retardation layer is thin and is in close contact with the substrate, so that it is often difficult to measure only the uniaxial retardation layer. Therefore, it is usually obtained by subtracting the haze value of a layer other than the uniaxial retardation layer from the haze value of the entire uniaxial retardation film. That is, the haze value is measured for the whole uniaxial retardation film and the uniaxial retardation film cut out from the uniaxial retardation film, and the uniaxial retardation is obtained by subtracting the latter haze value from the former haze value. The haze value of the layer can be determined. As the haze value, a value measured according to JIS K7105 is used.

  The size of the domain in the present invention is not more than the wavelength of visible light, but the specific size is preferably 380 nm or less, more preferably 350 nm or less, particularly 200 nm or less. It is preferable. In the present invention, since the rod-shaped compound is preferably monomolecularly dispersed, the lower limit value of the domain size is the size of a single molecule of the rod-shaped compound. The size of such a domain can be evaluated by observing the uniaxial retardation layer with a polarizing microscope, AFM, SEM, or TEM.

Next, a method for confirming the “in-plane orientation” possessed by the random homogeneous orientation will be described. The above-mentioned “in-plane orientation” means that the in-plane retardation (Re) of the uniaxial retardation layer is in the above-described range, and that the uniaxial retardation layer exhibits properties as an optically negative C plate. It can be confirmed by having a retardation (Rth) in the thickness direction to the extent possible. In particular, in the present invention, the thickness direction retardation (Rth) of the uniaxial retardation layer is preferably in the range of 50 nm to 400 nm, and more preferably in the range of 75 nm to 300 nm. It is preferable to be in the range of 100 nm to 250 nm.
Here, the retardation in the thickness direction (Rth) is determined by the refractive index nx in the slow axis direction (the direction in which the refractive index is the largest) and the fast axis direction (the refractive index is in the plane of the uniaxial retardation layer). The refractive index ny in the smallest direction), the refractive index nz in the thickness direction, and the thickness d (nm) of the uniaxial retardation layer are expressed by the formula Rth = {(nx + ny) / 2−nz} × d. Value.
Unless otherwise specified, the value of retardation (Rth) in the thickness direction in this specification refers to a value measured at a measurement wavelength of 589 nm in an environment of 23 ° C. and 55% RH.

  In addition, the retardation (Rth) in the thickness direction of the uniaxial retardation layer may be originally measured for a uniaxial retardation layer single layer. However, in many cases, since the uniaxial retardation layer is thin and is in close contact with the substrate, it is often difficult to measure only the uniaxial retardation layer. Therefore, it is usually obtained by subtracting the retardation (Rth) in the thickness direction indicated by the layers other than the uniaxial retardation layer from the retardation (Rth) in the thickness direction of the entire uniaxial retardation film. That is, the retardation in the thickness direction (Rth) is measured for the whole uniaxial retardation film and the uniaxial retardation film cut out from the uniaxial retardation film, and the latter measurement value is subtracted from the former measurement value. Thus, the retardation (Rth) in the thickness direction of the uniaxial retardation layer can be obtained. The retardation in the thickness direction (Rth) can be measured by, for example, a parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

(Other arbitrary compounds)
The uniaxial retardation layer may contain any other compound in addition to the rod-shaped compound. Examples of such an arbitrary compound include a photopolymerization initiator, a polymerization inhibitor, a leveling agent, a chiral agent, and a silane coupling agent.

  Moreover, it is preferable that the material which comprises the base material mentioned later is contained in the uniaxial retardation layer in this invention. For example, when the base material described later is made of triacetyl cellulose, the uniaxial retardation layer in the present invention preferably contains the triacetyl cellulose. This is because it becomes easy to randomly and uniformly align the rod-shaped compound in the uniaxial retardation layer, and the adhesion between the uniaxial retardation layer and the substrate can be improved.

(Uniaxial retardation layer)
The thickness of the uniaxial retardation layer is not particularly limited as long as it is within a range in which desired optical characteristics can be imparted to the uniaxial retardation layer, depending on the type of the rod-shaped compound. In particular, in the present invention, the thickness of the uniaxial retardation layer is preferably in the range of 0.5 μm to 10 μm, more preferably in the range of 0.5 μm to 8 μm, particularly 0.5 μm to 6 μm. It is preferable to be within the range.

  In addition, the configuration of the uniaxial retardation layer in the present invention is not limited to a configuration composed of a single layer, and may have a configuration in which a plurality of layers are stacked. When it has the structure by which the several layer was laminated | stacked, the layer of the same composition may be laminated | stacked, and the several layer which has a different composition may be laminated | stacked.

  Furthermore, although the uniaxial retardation layer used in the present invention is directly formed on the substrate described later, as an aspect in which the uniaxial retardation layer is laminated on the substrate, The substrate and the uniaxial retardation layer may be laminated so as to form a clear interface, or there may be a clear interface between the substrate and the uniaxial retardation layer. Alternatively, the rod-like compound may be laminated such that the concentration of the rod-like compound continuously changes.

b. Next, the base material will be described. The base material used for the uniaxial retardation film has a function of supporting the uniaxial retardation layer.

The transparency of the substrate used in the present invention may be arbitrarily determined according to the transparency required for the uniaxial retardation film, but usually the transmittance in the visible light region is 80% or more. Is preferable, and 90% or more is more preferable. This is because if the transmittance is low, the haze of the uniaxial retardation film may be larger than a desired value.
Here, the transmittance | permeability of a base material can be measured by JISK7361-1 (the test method of the total light transmittance of a plastic transparent material).

  As long as the base material used for this invention has the said transparency, even if it is a flexible material which has flexibility, it can also be used by the rigid material which does not have flexibility. In particular, in the present invention, it is preferable to use a flexible material. It is because the manufacturing process of a uniaxial retardation film can be made into a roll to roll process by using a flexible material.

  Examples of the flexible material include cellulose derivatives, cycloolefin polymers, acrylic resins such as polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyarylate, and other polyesters, polyvinyl alcohol, polyimide, polysulfone, polyethersulfone, Examples of the base material include amorphous polyolefin, modified acrylic polymer, polystyrene, epoxy resin, and polycarbonate. In particular, in the present invention, it is preferable to use a substrate derived from cellulose or a cycloolefin polymer. This is because the cellulose derivative is particularly excellent in optical isotropy, so that a uniaxial retardation film excellent in optical characteristics can be obtained. In addition, since the cycloolefin polymer has high durability under a high temperature and high humidity atmosphere, a uniaxial retardation film having excellent optical properties can be obtained.

  As the cellulose derivative used in the present invention, a cellulose ester is preferably used, and among the cellulose esters, cellulose acylates are preferably used. This is because cellulose acylates are advantageous in terms of availability because they are widely used industrially.

  As the cellulose acylates, C 2-4 lower fatty acid esters are preferably used. Such a lower fatty acid ester may contain only a single lower fatty acid ester, for example, cellulose acetate, and a plurality of fatty acid esters such as cellulose acetate butyrate and cellulose acetate propionate may be used. It may be included.

  In the present invention, cellulose acetate can be particularly preferably used among the above lower fatty acid esters. Among cellulose acetates, it is most preferable to use triacetyl cellulose having an average acetylation degree of 57.5 to 62.5% (substitution degree: 2.6 to 3.0). Here, the degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation can be determined by measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like). In addition, the acetylation degree of the triacetyl cellulose which comprises a triacetyl cellulose film can be calculated | required by said method, after removing impurities, such as a plasticizer contained in a film.

  On the other hand, the cycloolefin polymer used in the present invention is not particularly limited as long as it is a resin having a monomer unit composed of a cyclic olefin (cycloolefin). Examples of such a monomer comprising a cyclic olefin include norbornene and polycyclic norbornene monomers.

  In addition, as a cycloolefin type polymer used for this invention, any of a cycloolefin polymer (COP) or a cycloolefin copolymer (COC) can be used conveniently.

  The cycloolefin-based polymer used in the present invention may be a homopolymer of a monomer composed of the above cyclic olefin or a copolymer.

In addition, the cycloolefin polymer used in the present invention preferably has a saturated water absorption at 23 ° C. of 1% by mass or less, and in particular, has a range of 0.1% by mass to 0.7% by mass. preferable. This is because, by using such a cycloolefin polymer, the retardation film of the present invention can be made less susceptible to changes in optical properties and dimensions due to water absorption.
Here, the said saturated water absorption is calculated | required by immersing in 23 degreeC water for 1 week based on ASTMD570, and measuring an increase weight.

  Further, the cycloolefin polymer used in the present invention preferably has a glass transition point in the range of 100 ° C to 200 ° C, particularly preferably in the range of 100 ° C to 180 ° C, and in particular, 100 ° C. What is in the range of -150 degreeC is preferable. This is because when the glass transition point is within the above range, the uniaxial retardation film can be made more excellent in heat resistance and processability.

  Specific examples of the base material composed of cycloolefin polymer used in the present invention include, for example, Topas manufactured by Ticona, Arton manufactured by JSR, ZEONOR manufactured by Nippon Zeon, ZEONEX manufactured by Nippon Zeon, Apel manufactured by Mitsui Chemicals, Inc. And those obtained by subjecting these substrates to stretching treatment.

  Examples of rigid (rigid) materials having poor flexibility include glasses such as soda glass, potash glass, and borosilicate glass.

The thickness of the substrate used in the present invention is not particularly limited as long as it can provide the necessary self-supporting property for the uniaxial retardation film, but in the case of the flexible flexible material, it is usually 25 μm. It is preferable to be in the range of ˜1000 μm, and it is particularly preferable to be in the range of 20 μm to 100 μm. This is because if the thickness of the substrate is thinner than the above range, the self-supporting property necessary for the uniaxial retardation film may not be imparted. Moreover, when thickness is thicker than said range, when cutting a uniaxial phase difference film, for example, a process waste may increase or abrasion of a cutting blade may become quick.
On the other hand, in the case of the rigid material, a material having a thickness of about 0.5 mm to 5 mm is usually used.

  The structure of the base material in the present invention is not limited to a structure composed of a single layer, and may be a structure in which a plurality of layers are laminated. When it has the structure by which the several layer was laminated | stacked, the layer of the same composition may be laminated | stacked, and the several layer which has a different composition may be laminated | stacked.

  Moreover, the base material used in the present invention may be subjected to a stretching treatment. This is because the adhesion between the base material and the uniaxial retardation layer may be improved by using the base material that has been subjected to the stretching treatment. Here, the stretching treatment is not particularly limited, and may be arbitrarily determined according to the material constituting the substrate. Examples of such a stretching process include a uniaxial stretching process and a biaxial stretching process.

  Further, the form of the substrate used in the present invention may be a sheet having a certain size, or may be a long film having a certain length. When making a base material into the said elongate film, it is preferable that it is the roll wound form generally used industrially.

c. Next, a method for producing the uniaxial retardation film will be described. Examples of the uniaxial retardation film include a method of coating a uniaxial retardation layer forming composition prepared by dissolving the rod-shaped compound in a solvent on the substrate.

  The uniaxial retardation layer-forming composition usually comprises the rod-like compound and a solvent, and may contain other compounds as necessary.

  The solvent used in the uniaxial retardation layer forming composition is not particularly limited as long as it can dissolve the rod-like compound at a desired concentration. Examples of the solvent used in the present invention include hydrocarbon solvents such as benzene and hexane, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ether solvents such as tetrahydrofuran and 1,2-dimethoxyethane, chloroform, List alkyl halide solvents such as dichloromethane, ester solvents such as methyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, amide solvents such as N, N-dimethylformamide, and sulfoxide solvents such as dimethyl sulfoxide. Can do. In the present invention, among these solvents, a ketone solvent is preferably used, and cyclohexane is preferably used.

  The solvent used in the present invention may be one kind or a mixed solvent of two or more kinds of solvents.

  As the content of the rod-like compound in the uniaxial retardation layer forming composition, the uniaxial retardation layer formation is performed according to a coating method for applying the uniaxial retardation layer formation on a substrate. If it is in the range which can make the viscosity of the composition for desired value into a desired value, it will not be limited especially. Especially in this invention, it is preferable that content of the said rod-shaped compound exists in the range of 0.1 mass%-60 mass% in the said composition for uniaxial phase difference layer formation, Especially 1 mass%-50. It is preferable to be in the range of mass%, and it is particularly preferable to be in the range of 10 mass% to 40 mass%.

  The uniaxial retardation layer forming composition may contain a photopolymerization initiator as necessary. In particular, when a treatment for curing the uniaxial retardation layer by ultraviolet irradiation is performed, it is preferable to include a photopolymerization initiator. Examples of the photopolymerization initiator used in the present invention include benzophenone, methyl o-benzoylbenzoate, 4,4-bis (dimethylamine) benzophenone, 4,4-bis (diethylamine) benzophenone, α-amino acetophenone, 4, 4-dichlorobenzophenone, 4-benzoyl-4-methyldiphenyl ketone, dibenzyl ketone, fluorenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone P-tert-butyldichloroacetophenone, thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, diethylthioxanthone, benzyldimethyl ketal, benzylmethoxyethyl acetal Benzoin methyl ether, benzoin butyl ether, anthraquinone, 2-tert-butylanthraquinone, 2-amylanthraquinone, β-chloroanthraquinone, anthrone, benzanthrone, dibenzsuberone, methyleneanthrone, 4-azidobenzylacetophenone, 2,6-bis (p- Azidobenzylidene) cyclohexane, 2,6-bis (p-azidobenzylidene) -4-methylcyclohexanone, 2-phenyl-1,2-butadion-2- (o-methoxycarbonyl) oxime, 1-phenyl-propanedione-2 -(O-ethoxycarbonyl) oxime, 1,3-diphenyl-propanetrione-2- (o-ethoxycarbonyl) oxime, 1-phenyl-3-ethoxy-propanetrione-2- (o-benzoy ) Oxime, Michler's ketone, 2-methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone, Naphthalene sulfonyl chloride, quinoline sulfonyl chloride, n-phenylthioacridone, 4,4-azobisisobutyronitrile, diphenyl disulfide, benzthiazole disulfide, triphenylphosphine, camphorquinone, Adeca N1717, carbon tetrabromide, Examples include combinations of photoreducing dyes such as tribromophenylsulfone, benzoin peroxide, eosin, and methylene blue with reducing agents such as ascorbic acid and triethanolamine. In this invention, these photoinitiators can be used 1 type or in combination of 2 or more types.

  Furthermore, when using the said photoinitiator, a photoinitiator adjuvant can be used together. Examples of such photopolymerization initiation assistants include tertiary amines such as triethanolamine and methyldiethanolamine, and benzoic acid derivatives such as ethyl 2-dimethylaminoethylbenzoate and ethyl 4-dimethylamidebenzoate. Yes, but not limited to these.

  The coating method for coating the uniaxial retardation layer forming composition on the substrate is not particularly limited as long as the desired planarity can be achieved. Specifically, gravure coating method, reverse coating method, knife coating method, dip coating method, spray coating method, air knife coating method, spin coating method, roll coating method, printing method, dip pulling method, curtain coating method, die coating Examples thereof include, but are not limited to, a method, a casting method, a bar coating method, an extrusion coating method, and an E-type coating method.

  The thickness of the coating film of the uniaxial retardation layer forming composition is not particularly limited as long as the desired flatness can be achieved, but is usually within a range of 0.1 μm to 50 μm. It is preferable that it is within a range of 0.5 μm to 30 μm, and particularly preferably within a range of 0.5 μm to 10 μm. If the thickness of the coating film of the composition for forming a uniaxial retardation layer is thinner than the above range, the planarity of the formed uniaxial retardation layer may be impaired, and if the thickness is larger than the above range, This is because the drying load increases and the productivity may decrease.

  As a method for drying the coating film of the uniaxial retardation layer forming composition, a commonly used drying method such as a heat drying method, a reduced pressure drying method, or a gap drying method can be used. In addition, the drying method in the present invention is not limited to a single method, and a plurality of drying methods may be employed, for example, by changing the drying method sequentially according to the amount of solvent remaining.

  When a polymerizable material is used as the rod-shaped compound, a method for polymerizing the polymerizable material is not particularly limited, and may be arbitrarily determined according to the type of polymerizable functional group of the polymerizable material. . In particular, in the present invention, a method of curing by irradiation with actinic radiation is preferable. The actinic radiation is not particularly limited as long as it is a radiation capable of polymerizing a polymerizable material, but it is usually preferable to use ultraviolet light or visible light from the viewpoint of the ease of the device, etc. Among them, it is preferable to use irradiation light having a wavelength of 150 to 500 nm, preferably 250 to 450 nm, more preferably 300 to 400 nm.

  As the light source of this irradiation light, low pressure mercury lamp (sterilization lamp, fluorescent chemical lamp, black light), high pressure discharge lamp (high pressure mercury lamp, metal halide lamp), short arc discharge lamp (super high pressure mercury lamp, xenon lamp, mercury xenon) Lamp). Of these, use of metal halide lamps, xenon lamps, high-pressure mercury lamps, etc. is recommended. The irradiation intensity can be appropriately adjusted according to the content of the photopolymerization initiator.

(2) Biaxial retardation film Next, the biaxial retardation film used in the present invention will be described. The biaxial retardation film used in the present invention optically has properties as a B plate.
Here, “the property as an optically negative B plate” in the present invention means that the refractive index in the slow axis direction x in the in-plane direction of the biaxial retardation film is nx, and the refraction in the fast axis direction y When the rate is ny and the refractive index in the thickness direction (z direction) is nz, it means that the relationship of nx>ny> nz is established.
In addition, the biaxial retardation film used in the present invention can be measured by the parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments Co., Ltd., for example.

  The biaxial retardation film used in the present invention is not particularly limited as long as it has properties as an optically negative B plate. Examples of such a biaxial retardation film include a base material and a biaxial retardation layer formed on the base material and containing a rod-like compound, or a thermoplastic norbornene resin. Examples thereof include those obtained by biaxially stretching a raw film at a stretching ratio of 1.3 times or more in both the longitudinal direction and the transverse direction. Specific examples of such a biaxial retardation film include those described in JP-A-2006-221140 and JP-A-2005-43740. In the present invention, any biaxial retardation film having any of these configurations can be suitably used as long as it can exhibit desired optical characteristics. It is preferable to use a layer having a biaxial retardation layer containing a rod-shaped compound formed above and having an irregular random homogeneous orientation. This is because the biaxial retardation film having such a configuration is excellent in the expression of optical characteristics.

The irregular random homogeneous orientation will be described. The irregular random homogeneous orientation has at least the following three characteristics. That is, the anomalous random homogeneous orientation in the present invention is
First, when the biaxial retardation layer is viewed from the direction perpendicular to the surface of the biaxial retardation layer, the arrangement direction of the rod-shaped compounds has anisotropy (hereinafter simply referred to as “anisotropic”). ”),
Second, the size of the domain formed by the rod-shaped compound in the biaxial retardation layer is smaller than the wavelength in the visible light region (hereinafter sometimes simply referred to as “dispersibility”);
Third, in the biaxial retardation layer, rod-like compound molecules are present on a plane parallel to the surface of the biaxial retardation layer (a plane parallel to the xy plane in the example of FIG. 1) , Sometimes simply referred to as “in-plane orientation”).
At least.

  Such an irregular random homogeneous orientation will be specifically described with reference to the drawings. FIG. 5 is a schematic perspective view showing an example of a biaxial retardation film suitably used in the present invention. As illustrated in FIG. 5, the biaxial retardation film 20 suitably used in the present invention contains a base material 21 and a rod-shaped compound A formed on the base material 21 and having an irregular random homogeneous orientation. The biaxial retardation layer 22 is provided.

6 shows the biaxial retardation film 20 from the direction perpendicular to the surface (xy plane) of the biaxial retardation layer 22 represented by Z in FIG. 5 described above (normal direction, ie, Z direction). It is the schematic at the time of looking straight. Here, the “anisotropy” possessed by the irregular random homogeneous orientation will be described with reference to FIG. As shown in FIG. 6, the “anisotropy” refers to the biaxial retardation layer 22 when the biaxial retardation film 20 is viewed from the direction perpendicular to the surface of the biaxial retardation layer 22. 1 shows that rod-shaped compounds A are arranged in one direction on average.
That is, when the probability distribution function (probability density function) of each rod-shaped compound A oriented in each direction in the xy plane (biaxial retardation layer surface) is obtained, the probability distribution function peaks in a specific direction in the xy plane. (Average orientation direction), and the orientation direction is distributed so as to have a predetermined dispersion (variation width in the orientation direction). Furthermore, in other words, the orientation direction of the long axis of the rod-shaped compound A is not completely aligned in parallel, nor is it completely messy. An example of this is shown in FIG.
Here, in order to explain the arrangement direction of the rod-shaped compound A in the present invention, since the major axis direction represented by a in FIG. 6 (hereinafter referred to as a molecular axis) is considered as a reference, the rod-shaped compound A is Arranging in one direction means that the molecular axis a of the rod-shaped compound A contained in the biaxial retardation layer 22 is oriented in one direction on average.

  The “dispersibility” and “in-plane orientation” possessed by the irregular random homogeneous orientation are the same as those explained in the section of “1. Uniaxial retardation film”, and are therefore explained here. Is omitted.

  In the biaxial retardation film used in the present invention, the rod-shaped compound forms an irregular random homogeneous orientation, so that the refractive index nx in the x direction, the refractive index ny in the y direction, and z shown in FIG. Since it becomes easy to establish the relationship of nx> ny> nz to the refractive index nz in the direction, the property as a B plate is optically expressed.

  As described above, the irregular random homogeneous orientation is characterized by exhibiting the above-mentioned “anisotropy”, “dispersibility” and “in-plane orientation”, but the rod-like compound is irregular random homogeneous. The formation of the orientation can be confirmed by the following method.

  A method for confirming “anisotropy” possessed by the irregular random homogeneous orientation in the present invention will be described. The “anisotropy” can be confirmed by evaluating the in-plane retardation of the biaxial retardation layer (hereinafter sometimes simply referred to as “Re”).

  The rod-shaped compound has the above “anisotropy” because the in-plane retardation (Re) value of the biaxial retardation layer is an A plate in which the biaxial retardation layer is optically positive. It can be confirmed by being within a range in which the properties can be shown. In particular, in the present invention, the in-plane retardation (Re) of the biaxial retardation layer is preferably in the range of 5 nm to 300 nm, and more preferably in the range of 10 nm to 200 nm. It is particularly preferable that the thickness is in the range of 40 nm to 150 nm.

  The in-plane retardation (Re) of the biaxial retardation layer may be originally measured for a biaxial retardation layer single layer. However, in many cases, in many cases, the biaxial retardation layer is thin and is in close contact with the base material, so that it is often difficult to measure only the biaxial retardation layer. Therefore, it is usually obtained by subtracting the in-plane retardation (Re) exhibited by layers other than the biaxial retardation layer from the in-plane retardation (Re) of the entire biaxial retardation film. In other words, in-plane retardation (Re) measurement was performed on the entire biaxial retardation film and the biaxial retardation layer excised from the biaxial retardation film, and the latter measurement value was calculated from the former measurement value. By subtracting, the in-plane retardation (Re) of the biaxial retardation layer can be obtained. In-plane retardation (Re) can be measured by, for example, a parallel Nicol rotation method using KOBRA-WR manufactured by Oji Scientific Instruments.

  The method for confirming the above “dispersibility” and “in-plane orientation” is the same as the method described in the section “1. Uniaxial retardation film”, and the description here is omitted. .

  The biaxial retardation layer may contain any other compound in addition to the rod-shaped compound. Examples of such an arbitrary compound include a photopolymerization initiator, a polymerization inhibitor, a leveling agent, a chiral agent, and a silane coupling agent.

  Moreover, it is preferable that the material which comprises the base material mentioned later is contained in the biaxial retardation layer in this invention. For example, when the base material to be described later is made of triacetyl cellulose, the biaxial retardation layer in the present invention preferably contains the triacetyl cellulose. This is because it becomes easy to irregularly and homogeneously align the rod-like compound in the biaxial retardation layer, and the adhesion between the biaxial retardation layer and the substrate can be improved.

  The thickness of the biaxial retardation layer is not particularly limited as long as it is within a range in which desired optical characteristics can be imparted to the biaxial retardation layer, depending on the type of the rod-shaped compound. In particular, in the present invention, the thickness of the biaxial retardation layer is preferably in the range of 0.5 μm to 10 μm, more preferably in the range of 0.5 μm to 8 μm, particularly 0.5 μm to 6 μm. It is preferable to be within the range.

  In addition, the configuration of the biaxial retardation layer in the present invention is not limited to a configuration composed of a single layer, and may have a configuration in which a plurality of layers are stacked. When it has the structure by which the several layer was laminated | stacked, the layer of the same composition may be laminated | stacked, and the several layer which has a different composition may be laminated | stacked.

  Furthermore, although the biaxial retardation layer used in the present invention is directly formed on the substrate described later, as an aspect in which the biaxial retardation layer is laminated on the substrate. The base material and the biaxial retardation layer may be laminated so as to form a clear interface, or between the base material and the biaxial retardation layer. There may be a mode in which there is no clear interface and the layers are laminated so that the concentration of the rod-like compound continuously changes.

  In addition, about the base material used for the said biaxial retardation film, since the thing similar to what was demonstrated in the above-mentioned "1. Uniaxial retardation film" can be used, description here is abbreviate | omitted. To do.

  The biaxial retardation film having the above-described configuration is produced by, for example, producing a uniaxial retardation film by the method described in the section “1. Uniaxial retardation film” and then stretching the uniaxial retardation film. be able to.

(3) Polarizing plate protective film Next, the polarizing plate protective film used for this invention is demonstrated. The polarizing plate protective film used in the present invention has a function of preventing the polarizer from being exposed to moisture in the air in the polarizing plate used in the present invention and a function of preventing dimensional change of the polarizer. Is.

The polarizing plate protective film used for this invention will not be specifically limited if the polarizer mentioned later can be protected and it has desired transparency. Among them, the polarizing plate protective film used in the present invention preferably has a transmittance in the visible light region of 80% or more, and more preferably 90% or more.
Here, the transmittance of the polarizing plate protective film can be measured by JIS K7361-1 (Testing method of total light transmittance of plastic-transparent material).

As a material constituting the polarizing plate protective film used in the present invention, for example, cellulose derivative, cycloolefin resin, polymethyl methacrylate, polyvinyl alcohol, polyimide, polyarylate, polyethylene terephthalate, polysulfone, polyethersulfone, amorphous polyolefin, Examples thereof include modified acrylic polymers, polystyrene, epoxy resins, polycarbonates and polyesters.
Especially in this invention, it is preferable to use a cellulose derivative or a cycloolefin type polymer as said resin material.

  Examples of the cellulose derivative and the cycloolefin-based polymer are the same as those described as constituting the base material used for the uniaxial retardation film in the section “1. Uniaxial retardation film”. be able to.

  Specific examples of the polarizing plate protective film made of cycloolefin resin used in the present invention include, for example, Ticona Topas, JSR Arton, ZEON Corporation ZEONOR, ZEON Corporation ZEONEX, Mitsui Chemicals. A company-made appel can be mentioned.

(4) Polarizer Next, the polarizer used in the present invention will be described. The polarizer used in the present invention has a function of imparting polarization characteristics to the polarizing plate used in the present invention.

  The polarizer used in the present invention is not particularly limited as long as it has desired polarization characteristics, and those generally used for polarizing plates of liquid crystal display devices can be used without particular limitation. In the present invention, as such a polarizer, a polyvinyl alcohol film is usually stretched, and a polarizer containing iodine is preferably used.

2. Liquid crystal cell As the liquid crystal cell used in the present invention, one driven by a VA method and an OCB method is usually used. As such a liquid crystal cell, generally known ones can be used, and thus description thereof is omitted here.

3. Liquid crystal display device The liquid crystal display device of the present invention comprises at least the liquid crystal cell and a polarizing plate. As described above, since the polarizing plate used in the present invention can be divided into four modes, the liquid crystal display device of the present invention can be classified into the following three modes depending on the combination of polarizing plates.
The first mode is a mode in which the polarizing plate of the first mode and the polarizing plate of the second mode are used as two polarizing plates.
A 2nd aspect is an aspect by which the polarizing plate of the 1st aspect and the polarizing plate of the 3rd aspect were used as two polarizing plates.
A 3rd aspect is an aspect by which the polarizing plate of the 3rd aspect and the polarizing plate of the 4th aspect were used as two polarizing plates.

These aspects will be specifically described with reference to the drawings. FIG. 7 is a schematic diagram illustrating a liquid crystal display device of each aspect of the present invention. As illustrated in FIG. 7, the liquid crystal display device of the present invention is a liquid crystal display of the first mode in which the polarizing plate 3 of the first mode and the polarizing plate 2 of the second mode are used as two polarizing plates. Device 10A (FIG. 7A),
A liquid crystal display device 10B of the second mode in which the polarizing plate 3 of the first mode and the polarizing plate 4 of the third mode are used as two polarizing plates;
It can be divided into the liquid crystal display device 10C (FIG. 7C) of the third mode in which the polarizing plate 4 of the third mode and the polarizing plate 5 of the fourth mode are used as two polarizing plates. .

  The liquid crystal display device of the present invention can be suitably used in any of these modes, but usually the first mode or the third mode is used from the viewpoint of reducing the thickness and cost of the panel. Preferably used.

  In the liquid crystal display device of the present invention, at least a uniaxial retardation film and a biaxial retardation film are used one by one. The uniaxial retardation film used in the present invention and The optical characteristics of the biaxial retardation film are appropriately determined according to the optical characteristics of the liquid crystal cell used in the present invention so that the display quality of the liquid crystal display device can be set to a desired level.

For example, when the liquid crystal cell used in the present invention is a VA liquid crystal cell having optical characteristics satisfying the following formulas (A-1) to (A-3), the biaxial position used in the present invention. As the phase difference film, those having optical characteristics satisfying the following formulas (B-1) to (B-3) are used, and as the uniaxial phase difference film, the following formulas (C-1) to (C It is preferable to use those having optical characteristics satisfying -4).
(A-1) 270 nm <Rth (550)
(A-2) Rth (450) / Rth (550)> 1
(B-1) 80 nm <Re ⁰ <110 nm
(B-2) 0.9 ≦ Re ⁴⁰ (450) / Re ⁴⁰ (550) ≦ 1.01
(B-3) 1.5 <Nz <1.9
(C-1) 0.98 ≦ Re ⁴⁰ (450) / Re ⁴⁰ (550) ≦ 1.10.
(C-2) 0 nm ≦ Re ⁰ <5 nm
(C-3) 150 nm <Rth (550) <200 nm
By using a liquid crystal cell having such optical characteristics, a uniaxial retardation film and a biaxial retardation film in combination, it is possible to obtain a VA liquid crystal display device with further excellent display quality according to the present invention. Because it can.

Here, Re ⁰ means in-plane retardation (Re) measured by allowing measurement light to enter from the direction of the normal to the plane, and Re ⁴⁰ is a direction inclined by 40 ° from the normal to the plane. It means in-plane retardation (Re) measured by making measurement light incident more. Here, since the definition of the in-plane retardation (Re) and the measuring method are as described above, the description thereof is omitted here. In the present invention, Re ⁰ and Re ⁴⁰ mean values measured with measurement light having a wavelength of 589 nm.

  The Rth means retardation in the thickness direction. The numerical value in the parenthesis means the wavelength of the measurement light. For example, Rth (550) means the Rth value measured by the measurement light having a wavelength of 550 nm. The above Rth is a value measured by making measurement light incident from the direction of the normal to the plane.

  Further, the Nz means an Nz factor. Here, the Nz factor is Nz = when the refractive index in the slow axis direction x in the plane is nx, the refractive index in the fast axis direction y in the plane is ny, and the refractive index in the thickness direction z is nz. It is represented by (nx-ny) / (nx-nz).

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the technical idea described in the claims of the present invention has substantially the same configuration and exhibits the same function and effect regardless of the case. It is included in the technical scope of the invention.

1. Example 1
(1) Method for producing upper polarizing plate Using a PVA film previously dyed and stretched as a polarizer, a polarizing plate protective film (Fujifilm TF80UL) is bonded to one side of the polarizer, and optically negative on the opposite side. The upper polarizing plate was produced by laminating a biaxial retardation film (-B plate) having properties as a B plate. In this case, the -B plate was heated by JSR Arton to 150 ° C., and in a plane parallel to the surface of the substrate, stretched by 1.50 times in the direction perpendicular to the longitudinal direction of the substrate. What was produced by doing was used.
At this time, since the -B plate can be produced by lateral uniaxial stretching, it can be arranged by roll-to-roll so that the slow axis of the -B plate and the absorption axis of the PVA film intersect perpendicularly. there were.

(2) Production method of lower polarizing plate Using a PVA film previously dyed and stretched as a polarizer, a polarizing plate protective film (TF80UL manufactured by Fuji Film) is bonded to one side of the polarizer, and optically applied to the opposite side. A lower polarizing plate was produced by laminating a uniaxial retardation film (-C plate) having properties as a negative C plate. Here, the -C plate uses a triacetyl cellulose film (TF80UL manufactured by Fuji Film Co., Ltd.) having a thickness of 80 μm as a base material, and a photopolymerizable liquid crystal compound represented by the following formula (I) as a refractive index anisotropic material. A coating solution for forming a retardation layer obtained by dissolving Irgacure 907 (manufactured by Ciba Geigy Co., Ltd.) as a polymerization initiator in a photopolymerizable liquid crystal compound at 5 wt% and dissolving them in cyclohexanone at 15 wt% In addition, after coating by a bar coating method and drying in an oven at 40 ° C. for 2 minutes, m produced by irradiation with 100 mJ / m ² of ultraviolet rays in a nitrogen atmosphere was cured.

(3) Evaluation method as a liquid crystal display An optical simulation is performed on a liquid crystal display device having a configuration in which an upper polarizing plate, a liquid crystal cell, and a lower polarizing plate are stacked from the observation direction (upper) and a backlight light source is arranged. Was confirmed. For the optical calculation, LCD Master Ver 6.08 manufactured by Shintech Co., Ltd. was used. The values of materials conventionally used for liquid crystal displays were used as they were for glass substrates and polarizing plates.
Here, the spectrum of the color filter used in # 2659 by Corning Japan Co., Ltd. as a glass substrate and LC26GD3 by Sharp Corporation as a color filter was used. As the PVA in the polarizing plate, G1220DU manufactured by Nitto Denko Corporation was used.

As the liquid crystal material in the liquid crystal cell, a liquid crystal material having negative dielectric anisotropy and Δε = −4.1 was used. The alignment of the liquid crystal cell is almost vertical with a pretilt angle of 89.9 degrees, the cell gap of the substrate is 3.85 μm, the retardation of the liquid crystal (that is, the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy). The product Δn · d) with Δn was 331 nm at a wavelength of 450 nm, 316 nm at a wavelength of 550 nm, and 306 nm at a wavelength of 650 nm. The chromatic dispersion of the -B plate was set to the values shown in Table 1 for Re and Nz at a wavelength of 550 nm with Re ⁴⁰ (450) / Re ⁴⁰ (550) = 1.0. The specifications of the -C plate are shown in the table. As the light source, the spectrum of the light source used in LC26GD3 manufactured by Sharp Corporation was used.

<Measurement of leakage light of liquid crystal display device>
Table 1 shows the result of optical simulation using the above values and the calculation of oblique contrast and oblique color shift.
CR indicates oblique contrast with a polar angle of 60 ° and an azimuth angle of 45 °. In the oblique color shift, in the CIE standard color system (XYZ color system), the color change when tilted from the front (normal direction to the display) to a polar angle of 60 ° and an azimuth angle of 45 ° is Δx and Indicated by Δy.
As a liquid crystal display with a high oblique contrast and a small oblique color shift, the required specifications are, from experience, a comparison with the front in all directions when CR ≧ 60, Δx ≦ 0.15, and Δy ≦ 0.11. It has been found that the image does not deteriorate significantly.

2. Example 2
A liquid crystal display device was produced in the same manner as in Example 1 except that the wavelength dispersion of the -C plate was changed to reverse wavelength dispersion, and the same evaluation as in Example 1 was performed. Here, the -C plate used was prepared by stacking three TAC films (TF80UL manufactured by Fuji Film).
The results are shown in Table 2.

3. Comparative Example A liquid crystal display device as in Example 1 except that a uniaxial retardation film (+ A plate) having properties as an optically positive A plate was used instead of the -B plate used for the upper polarizing plate. Was made. Here, the + A plate is obtained by heating Arton manufactured by JSR to 150 ° C., and in a plane parallel to the surface of the base material, a 1.50 times longitudinal axis in a direction parallel to the longitudinal direction of the base material What was produced by extending | stretching was used. At this time, since the slow axis of the + A plate is parallel to the film transport direction, it was necessary to perform batch bonding to make the absorption axis of the PVA film and the slow axis of the + A plate orthogonal. For this reason, polarizing plate preparation cannot be performed by roll-to-roll, but it became a big demerit in cost.

It is a schematic sectional drawing which shows an example of the liquid crystal display device of this invention. It is the schematic which shows an example of the polarizing plate used for this invention. It is a schematic perspective view which shows an example of the uniaxial retardation film suitably used for this invention. It is the schematic explaining the random homogeneous orientation in this invention. It is a schematic perspective view which shows an example of the biaxial retardation film suitably used for this invention. It is the schematic explaining the irregular random homogeneous orientation in this invention. It is a schematic sectional drawing explaining each aspect of the liquid crystal display device of this invention. It is a schematic sectional drawing showing an example of a common liquid crystal display device. It is a schematic sectional drawing which shows an example of the liquid crystal display device using two retardation films.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal cell 2, 3, 4, 5 ... Polarizing plate 2a, 3a, 4a, 5a ... Polarizer 2b, 3b, 4b, 5b ... Polarizing plate protective film 10, 10A, 10B, 10C ... Liquid crystal display device 20 ... Two Axis retardation film 21 ... base material 22 ... biaxial retardation layer 30 ... uniaxial retardation film 31 ... base material 32 ... uniaxial retardation layer 100 ... liquid crystal display device 101 ... liquid crystal cell 102A, 102B ... polarizing plate 103, 104 ... retardation film A ... rod-shaped compound

Claims (4)

A liquid crystal display device comprising: a liquid crystal cell; and a polarizing plate that is disposed on both sides of the liquid crystal cell and includes a polarizer and a polarizing plate protective film disposed on both surfaces of the polarizer,
As the polarizing plate protective film, a uniaxial retardation film having properties as an optically negative C plate and a biaxial retardation film having properties as an optically B plate are used. A liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the uniaxial retardation film has a base material and a retardation layer formed on the base material and containing a rod-shaped compound.   The liquid crystal display device according to claim 1, wherein the biaxial retardation film is made of a cycloolefin-based polymer. The liquid crystal cell is a VA liquid crystal cell having optical characteristics satisfying the following formulas (A-1) to (A-2):
The biaxial retardation film has optical properties satisfying the following formulas (B-1) to (B-3),
Furthermore, the said uniaxial retardation film is provided with the optical characteristic which satisfies the following formula | equation (C-1)-(C-3), Any of Claim 1 to 3 characterized by the above-mentioned. A liquid crystal display device according to any one of the claims.
(A-1) 270 nm <Rth (550)
(A-2) Rth (450) / Rth (550)> 1
(B-1) 80 nm <Re ⁰ <110 nm
(B-2) 0.9 ≦ Re ⁴⁰ (450) / Re ⁴⁰ (550) ≦ 1.01
(B-3) 1.5 <Nz <1.9
(C-1) 0.98 ≦ Re ⁴⁰ (450) / Re ⁴⁰ (550) ≦ 1.10.
(C-2) 0 nm ≦ Re ⁰ <5 nm
(C-3) 150 nm <Rth (550) <200 nm
(Here, Re ⁰ means in-plane retardation (Re) measured by making measurement light incident from the direction of the normal to the plane, and Re ⁴⁰ is 40 ° to the normal to the plane. This means in-plane retardation (Re) measured by allowing measurement light to enter from an inclined direction, which is represented by Re = (nx−ny) × d. The Rth means retardation in the thickness direction (the value in parentheses is the wavelength of the measurement light), and is expressed by Rth = ((nx + ny) / 2−nz) × d. Further, the Nz is represented by Nz = (nx−ny) / (nx−nz), where nx is the refractive index in the in-plane slow axis direction x, and ny is Refractive index in the in-plane fast axis direction y nz the refractive index in the thickness direction is further d is representative of the thickness.)

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