JP2009244770A - Optical compensation film and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical compensation film which has an excellent front contrast ratio when applied to a liquid crystal display device, and further has an excellent contrast ratio even at a wide view angle. <P>SOLUTION: The optical compensation film includes a first optical anisotropic layer and a second optical anisotropic layer which are disposed so that the respective in-plane slow axes are orthogonal to each other. Each of the first optical anisotropic layer and the second anisotropic layer includes a liquid crystal compound. In each of the first optical anisotropic layer and the second anisotropic layer, an average inclination that is a mathematical average value of the inclination formed by the optical axis of the liquid crystal compound and a plane of the optical anisotropic layer in the thickness direction of the optical anisotropic layer is 0-20°. In each of the first optical anisotropic layer and the second optical anisotropic layer, a retardation value defined by Δn×d satisfies 90 nm<Δn×d≤200 nm in a light of wavelength 550 nm (wherein Δn represents birefringence, and is calculated by ne-no, d represents the thickness of the first optical anisotropic layer or the second optical anisotropic layer, ne represents abnormal light refractive index, and no represents ordinary light refractive index). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical compensation film and a liquid crystal display device.

Optical compensation films in which liquid crystal compounds are highly oriented and fixed are being developed in various applications such as optical compensation films for liquid crystal display devices, brightness enhancement films, and optical compensation films for projection display devices. The development of display devices as an optical compensation film is remarkable.
Usually, the liquid crystal display device includes a polarizing plate and a liquid crystal cell. In a TN mode TFT liquid crystal display device which is currently mainstream, an optical compensation film is inserted between the polarizing plate and the liquid crystal cell to realize a liquid crystal display device with high display quality. A method for producing an optical compensation film is described in Patent Document 1, for example.

Recently, the demand for liquid crystal televisions for TN liquid crystal display devices is increasing. However, liquid crystal television applications are required to maintain a high contrast ratio and to eliminate a decrease in contrast ratio due to viewing angle. By controlling the conventionally known optical parameters, a good front contrast ratio and a good contrast ratio are required. It has been difficult to obtain a contrast ratio in a wide viewing angle.
Patent Document 2 discloses a viewing angle in a TN mode of a liquid crystal display device, particularly a viewing angle when viewed from the vertical direction, by controlling a tilt angle of a positive birefringent material and a retardation value defined by Δn · d. An optical compensation film that can improve the above is disclosed.
Non-Patent Document 1 discloses an optical compensation film that can improve the viewing angle in a TN mode of a liquid crystal display device by laminating an optically anisotropic layer using a positive birefringent material.
However, by controlling the tilt angle, controlling the retardation value defined by Δn · d, or simply laminating an optically anisotropic layer, a good front contrast ratio and a good contrast ratio at a wide viewing angle. It was difficult to obtain.

  Therefore, when applied to a liquid crystal display device, an optical compensation film excellent in front contrast ratio and excellent in contrast ratio even in a wide viewing angle, and a liquid crystal display device using the same are still satisfactory. The current situation is not.

Japanese Patent Laid-Open No. 8-15681 Special table 2006-504146 EURODISPLAY 2002 10-3 (p183-186), Journal of the SID 11/3, 2003 (p519-524)

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, the present invention is an optical compensation film having an excellent front contrast ratio when applied to a liquid crystal display device, and also having a wide viewing angle, particularly a horizontal viewing angle, and an excellent contrast ratio. An object is to provide a liquid crystal display device to be used.

Means for solving the above problems are as follows. That is,
<1> At least a first optically anisotropic layer and a second optically anisotropic layer, and an in-plane slow axis of the first optically anisotropic layer and the second optically anisotropic layer. An optical compensation film arranged in a direction perpendicular to the in-plane slow axis of the isotropic layer,
The first optical anisotropic layer and the second optical anisotropic layer each comprise a liquid crystalline compound,
The first optical anisotropic layer and the second optical anisotropic layer each have an optical anisotropy having an inclination angle formed by the optical axis of the liquid crystalline compound and the surface of the optical anisotropic layer. The average inclination angle which is an arithmetic average value in the thickness direction of the layer is 0 ° to 20 °,
Each of the first optical anisotropic layer and the second optical anisotropic layer has a retardation value defined by Δn · d of 90 nm <Δn · d ≦ 200 nm in light having a wavelength of 550 nm. It is an optical compensation film characterized by satisfying.
[However, Δn represents birefringence and is calculated by ne-no. The d represents the thickness of the first optical anisotropic layer or the second optical anisotropic layer. The ne represents an extraordinary light refractive index, and the no represents an ordinary light refractive index. ]
<2> Each of the first optical anisotropic layer and the second optical anisotropic layer has a retardation value defined by Δn · d of 120 nm <Δn · d ≦ 180 nm in light having a wavelength of 550 nm, It is an optical compensation film as described in <1> which satisfy | fills.
<3> In any one of <1> to <2>, in the first optical anisotropic layer and the second optical anisotropic layer, the liquid crystalline compounds are arranged in a twisted manner in the thickness direction. It is an optical compensation film as described.
<4> The first optical anisotropic layer and the second optical anisotropic layer are composed of two or more liquid crystalline compounds having different numbers of polymerizable groups contained in one molecule, and each of the liquid crystalline compounds described above. Is an optical compensation film according to any one of <1> to <3> having one or more polymerizable groups in one molecule.
<5> The support according to any one of <1> to <4>, including a support, wherein the first optical anisotropic layer and the second optical anisotropic layer are laminated on one surface of the support. It is an optical compensation film as described.
<6> The in-plane retardation value Re of the support measured using light with a wavelength of 550 nm is −190 to 190 nm, and the retardation in the thickness direction of the support is measured using light with a wavelength of 550 nm. The optical compensation film according to <5>, wherein the value Rth is −60 to 170 nm.
<7> The in-plane retardation value Re of the support measured using light having a wavelength of 550 nm is −170 to 170 nm, and the retardation in the thickness direction of the support is measured using light having a wavelength of 550 nm. The optical compensation film according to <5>, wherein the value Rth is −40 to 160 nm.
<8> A liquid crystal display device comprising the optical compensation film according to any one of <1> to <7>, a liquid crystal cell, and a pair of polarizing plates sandwiching the optical compensation film and the liquid crystal cell,
The optical compensation film is disposed between the liquid crystal cell and at least one of the polarizing plates, and an in-plane slow axis of the optical compensation film and an in-plane slow axis of the one polarizing plate. Is a liquid crystal display device arranged in parallel or orthogonally.
<9> The liquid crystal cell includes a liquid crystal layer containing a liquid crystal compound, and a pair of substrates arranged in parallel with the liquid crystal layer interposed therebetween,
At least one of the substrates has a transparent electrode;
The liquid crystalline compound of the liquid crystal layer is in a state in which no voltage is applied, the liquid crystal compound is aligned parallel to the surface of the substrate, and twisted in the thickness direction of the liquid crystal layer, and the twist angle in the thickness direction is It is a liquid crystal display device as described in <8> which is 180 degrees or less.

  According to the present invention, when applied to a liquid crystal display device, an optical compensation film excellent in front contrast ratio and having a wide viewing angle, particularly a horizontal viewing angle, and a contrast ratio, and the same are used. A liquid crystal display device can be provided.

The optical compensation film and the liquid crystal display device according to the present invention will be described in detail below.
In the present specification, “orthogonal” and “parallel” mean that the angle is within an exact range of ± 5 °. The error from the exact angle is preferably less than 4 °, more preferably less than 3 °.
Regarding the angle, unless otherwise specified, “+” means a counterclockwise direction, and “−” means a clockwise direction.
In the present specification, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at the wavelength λ, respectively. Re (λ) is measured with KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments Co., Ltd.) by making light of wavelength λ nm incident in the normal direction of the film.
When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is the film surface when Re (λ) is used and the in-plane slow axis (determined by KOBRA 21ADH or WR) is the tilt axis (rotation axis) (if there is no slow axis) Measurement is performed at a total of 6 points by injecting light of wavelength λ nm from each inclined direction in steps of 10 degrees from the normal direction to 50 ° on one side with respect to the film normal direction (with any rotation direction as the rotation axis). Then, KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed value of the average refractive index, and the input film thickness value.
In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.
The retardation value is measured from any two directions with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), and the value Rth can also be calculated from the following formulas (1) and (2) based on the assumed average refractive index and the input film thickness value.
... (1)
Rth = ((nx + ny) / 2−nz) xd (2)
In the formula (1), Re (θ) represents a retardation value (Re) in a direction inclined by an angle θ from the normal direction. nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, nz represents the refractive index in the direction perpendicular to nx and ny, and d represents the thickness. To express.
When the film to be measured is a film that cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film without a so-called optical axis, Rth (λ) is calculated by the following method.
Rth (λ) is from −50 ° to the normal direction of the film, with Re (λ) being the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotary axis). Measured at 11 points by making light of wavelength λ nm incident in 10 ° steps up to + 50 °, and based on the measured retardation value, average refractive index assumption value and input film thickness value. KOBRA 21ADH or WR is calculated.
In the above measurement, the assumed value of the average refractive index is the polymer handbook (JOHN
WILEY & SONS, INC), catalog values of various optical films can be used. If the average refractive index is not known, it can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). The KOBRA 21ADH or WR calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

(Optical compensation film)
The optical compensation film of the present invention has at least a first optical anisotropic layer and a second optical anisotropic layer, and further includes other structures such as a support and an alignment film as necessary. .

<First optical anisotropic layer, second optical anisotropic layer>
[Optical characteristics]
The first optical anisotropic layer and the second optical anisotropic layer include a slow axis in the plane of the first optical anisotropic layer and a surface of the second optical anisotropic layer. The slow axis is arranged orthogonally.
The optical compensation film is obtained by arranging the slow axis in the plane of the first optical anisotropic layer and the slow axis in the plane of the second optical anisotropic layer orthogonal to each other. When combined with a liquid crystal display device, light leakage in front of black display can be suppressed.

  In addition, the first optical anisotropic layer and the second optical anisotropic layer use an average inclination angle and a retardation value defined by Δn · d of the optical anisotropic layer, respectively. It is prescribed.

-Orientation order-
The degree of orientation order is generally used as an index representing the degree of orientation of the polymer film and the degree of orientation of the liquid crystal, and can be a value from 0 to 1. When the degree of orientational order is 0, it shows a completely random state like a liquid state. When the degree of orientational order is 1, it indicates a state in which molecules are not fluctuated like crystals and are completely oriented in one direction.
The degree of alignment order is a mixture of two or more liquid crystal compounds having different numbers of polymerizable groups contained in one molecule, the type and amount of additive are changed, the type of alignment film and the rubbing strength are changed. It can be easily adjusted by changing.
The degree of orientation order is measured, for example, using “Nanofinder” manufactured by Tokyo Instruments Inc. under the measurement conditions in which the excitation laser wavelength is 532 nm, the excitation laser output is about 400 uW at the sample portion, and a depolarizer is attached in front of the spectrometer. can do.
More specifically, the film is cut obliquely at about 1 to 2 degrees, and the polarization Raman measurement near the surface or interface is performed in the optically anisotropic layer in the film. Rotate the film, change the angle between the orientation of the film surface and the electric field direction of the incident laser polarization, and measure at several angles. Among the scattered light components, the polarization component I is parallel to the incident laser polarization electric field. The parallel and the polarization component I perpendicular to the incident laser polarization electric field are spectrally detected using an analyzer. Further, by performing fitting analysis based on the least square method with respect to the band having a peak derived from the skeleton of the liquid crystalline compound, using the orientation order parameters P2 and P4 as parameters by a theoretically derived formula, Is calculated. The above is described on pages 651 to 654 of Proceedings of IDW'04, 651 (2004).

  The degree of orientation order of the first optically anisotropic layer and the second optically anisotropic layer is 0.3 to 1 and preferably 0.5 to 1, respectively. When the degree of orientation order is less than 0.3, light leakage in front of black display may increase when the optical compensation film is combined with a liquid crystal display device. When the degree of orientation order is 0.5 or more, it is advantageous in that light leakage in front of black display can be suppressed when the optical compensation film is combined with a liquid crystal display device.

-Average tilt angle-
FIG. 1 is a diagram showing an example of a cross section of the first optical anisotropic layer and the second optical anisotropy when the optical anisotropic layer is made of a rod-like liquid crystalline compound.
The optically anisotropic layer 23 is provided on the alignment film 22 formed on the support 21. The tilt angle (hereinafter also referred to as “tilt angle” or “pretilt angle”) of the rod-like liquid crystalline compounds 23a, 23b, and 23c constituting the optically anisotropic layer 23 is the bottom surface of the optically anisotropic layer. As the distance in the depth (thickness) direction increases, the entire layer generally increases in order. In FIG. 1, N represents the normal line of the support.

In an optically anisotropic layer in which rod-like liquid crystalline compounds are aligned, the tilt angle on one surface of the optically anisotropic layer (the physical target axis in the discotic liquid crystalline compound or rod-like liquid crystalline compound is the optically anisotropic layer It is difficult to directly and accurately measure θ1 and the tilt angle θ2 of the other surface. Therefore, in this specification, θ1 and θ2 are calculated by the following method. Although this method does not accurately represent the actual orientation state of the present invention, it is effective as a means for expressing the relative relationship between some optical properties of the optical film.
In this method, the following two points are assumed and the tilt angle at the two interfaces of the optically anisotropic layer is assumed for easy calculation.
1. The optically anisotropic layer is assumed to be a multilayer body composed of rod-shaped compounds or layers containing rod-shaped compounds. Further, it is assumed that the minimum unit layer (the tilt angle of the rod-like liquid crystal compound is uniform in the layer) constituting it is optically uniaxial.
2. It is assumed that the tilt angle of each layer changes monotonically with a linear function along the thickness direction of the optically anisotropic layer.
The specific calculation method is as follows.
(1) In a plane in which the tilt angle of each layer changes monotonically with a linear function along the thickness direction of the optically anisotropic layer, the incident angle of the measurement light to the optically anisotropic layer is changed, and three or more The retardation value is measured at the measurement angle. In order to simplify the measurement and calculation, it is preferable to measure the retardation value at three measurement angles of −40 °, 0 °, and + 40 °, with the normal direction to the optically anisotropic layer being 0 °. . Such measurement is performed by, for example, KOBRA-21ADH, KOBRA-WR (manufactured by Oji Scientific Instruments), transmission type ellipsometer AEP-100 (manufactured by Shimadzu Corporation), M150, M520 (JASCO Corporation) )), ABR10A (manufactured by UNIOPT Co., Ltd.) and the like.
(2) The refractive index of ordinary light in each layer is no, the refractive index of extraordinary light is ne (no and ne are the same values in all layers), and the thickness of the entire multilayer body is d. Furthermore, based on the assumption that the tilt direction in each layer and the optical axis direction of one axis of the layer coincide with each other, the calculation of the polar angle dependency of the retardation value of the optically anisotropic layer coincides with the measured value. Fitting is performed using the tilt angle θ1 on one surface of the optically anisotropic layer and the tilt angle θ2 on the other surface as variables, and θ1 and θ2 are calculated.
Here, known values such as literature values and catalog values can be used for no and ne. If the value is unknown, it can also be measured using an Abbe refractometer. The thickness of the optically anisotropic layer can be measured by an optical interference film thickness meter, a cross-sectional photograph of a scanning electron microscope, or the like.

For example, in FIG. 1, the tilt angle (θa in the illustrated example) of the rod-shaped liquid crystal compound on the support 21 side corresponds to a substantially minimum value, and the tilt angle of the rod-shaped liquid crystal compound on the side farthest from the support 21. (Θc in the illustrated example) substantially corresponds to the maximum value, and the tilt angle (θb in the illustrated example) of the rod-like liquid crystal compound therebetween substantially corresponds to the average tilt angle. Here, the inclination angle of the rod-like liquid crystal compound means the inclination of the major axis of the liquid crystalline compound with respect to the surface of the optically anisotropic layer.
The average inclination angle means an arithmetic average value of the inclination angle in the thickness direction of the optically anisotropic layer.
The average tilt angle can be easily adjusted by changing the type and addition amount of the liquid crystalline compound, changing the type and addition amount of the additive, or changing the type and rubbing strength of the alignment film. .

  The average tilt angle of the liquid crystal compound in the first optical anisotropic layer and the second optical anisotropic layer is not particularly limited as long as it is 0 ° or more, and is appropriately selected according to the purpose. 0 ° to 20 ° is preferable, and 0 ° to 15 ° is more preferable. When the average tilt angle exceeds 20 °, a sufficient viewing angle, particularly a horizontal viewing angle, cannot be obtained when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device. There is. When the average tilt angle is within the more preferable range, a sufficient viewing angle, particularly a horizontal viewing angle, can be obtained when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device. This is advantageous.

Δn · d of the optically anisotropic layer is a retardation value defined by the extraordinary refractive index ne, the ordinary refractive index no of the liquid crystal compound, and the thickness d of the optically anisotropic layer.
The Δn · d can be easily adjusted by changing the type and addition amount of the liquid crystalline compound, changing the type and addition amount of the additive, or changing the type and rubbing strength of the alignment film. .
The retardation value defined by Δn · d in the first optically anisotropic layer and the second optically anisotropic layer is not particularly limited and can be appropriately selected according to the purpose. 90 nm <Δn · d ≦ 200 nm is preferable, and 120 nm <Δn · d ≦ 180 nm is more preferable. When the Δn · d is 90 nm or less, a sufficient viewing angle, particularly a horizontal viewing angle, may not be obtained when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device. is there. When the Δn · d is 200 nm, a sufficient viewing angle, particularly a horizontal viewing angle, may not be obtained when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device. . When the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device, when the Δn · d is in the more preferable range, a sufficient viewing angle, particularly a horizontal viewing angle, can be obtained. This is advantageous.

[Constitution]
The material of the first optical anisotropic layer and the second optical anisotropic layer is not particularly limited as long as it has the above optical characteristics, and can be appropriately selected depending on the purpose. It is preferable to include a compound.

-Liquid crystalline compounds-
Examples of the liquid crystal compound include a disk-like discotic liquid crystal compound or a rod-like liquid crystal compound, and among these, a rod-like liquid crystal compound is preferable.
There is no restriction | limiting in particular as an alignment form of the said liquid crystalline compound, According to the objective, it can select suitably, Homeotropic alignment, homogeneous alignment, hybrid alignment, uniaxial inclination alignment etc. are mentioned. Among these, hybrid alignment, uniaxial tilt alignment, and homogeneous alignment are preferable, and hybrid alignment and homogeneous alignment are more preferable.
The hybrid alignment is, for example, an angle between the optical axis of the liquid crystal compound (the discotic liquid crystal compound is a disc surface and the rod-like liquid crystal compound is a long axis) and the surface of the support, that is, an inclination. The angle increases or decreases in the direction of the depth (perpendicular to the support) of the optically anisotropic layer. The uniaxial tilt orientation refers to, for example, the angle between the optical axis of the liquid crystal compound and the surface of the support, that is, the tilt angle θ (0 <θ <90 °) is the depth of the optically anisotropic layer (support It is constant in the direction (perpendicular to).

The liquid crystalline compound is composed of two or more types of liquid crystalline compounds having different numbers of polymerizable groups contained in one molecule, and each of the liquid crystalline compounds has one or more polymerizable groups in one molecule. Is preferred.
There is no restriction | limiting in particular as a kind of the said liquid crystalline compound which has a polymeric group, According to the objective, it can select suitably, The liquid crystalline compound which has 1-5 acrylate groups and / or methacrylate groups is preferable. 1 to 4 liquid crystal compounds are more preferable, and liquid crystal compounds having 1 to 2 acrylate groups and / or methacrylate groups are more preferable. Each of them is particularly preferably a rod-like liquid crystal compound having an acrylate group. By using one or more, the degree of orientational order is reduced, but the number of polymerizable groups increases, which is preferable because adhesion is improved. The number of 5 or less is preferable because the orientation degree tends to increase. The optically anisotropic layer preferably contains liquid crystal compounds having the same polymerizable group, and has two or more rod-like liquid crystal compounds having different acrylate groups and 1 to 4 polymerizable groups. It is preferable to have two or more rod-like liquid crystal compounds having different one or two polymerizable groups.

The liquid crystal compound preferably contains two types of liquid crystal compounds in which the number of polymerizable groups of the liquid crystal compound is m and n. Here, m and n are each a positive integer and m> n.
The content of the compound having n polymerizable groups is preferably 50% by weight or less, more preferably 1.0 to 10% by weight, based on the compound having m polymerizable groups. In particular, even if a liquid crystal compound having one acrylate group is added to a rod-like liquid crystal compound having two acrylate groups in an amount of more than 50% based on the total weight of the rod-like liquid crystal compound, the degree of alignment order is improved. As the content of the rod-like liquid crystal compound having an acrylate group is decreased, the degree of polymerization of the optically anisotropic layer is decreased, and the adhesion with the support tends to be deteriorated. Therefore, it is preferable to add 0.5 to 50% by weight of a rod-like liquid crystal compound having one acrylate group with respect to the total weight of the rod-like liquid crystal compound in order to maintain adhesion, and 0.5 to 20% by weight is preferable. More preferably, the degree of polymerization is preferably at least 85% or more, and more preferably 90% or more.
The liquid crystalline compound may be a high molecular liquid crystalline compound or a low molecular liquid crystalline compound. Furthermore, it is preferable that the alignment state is maintained and fixed. Examples of the liquid crystalline compound include those that are cross-linked when forming the optically anisotropic layer and then no longer show liquid crystal.

-Rod-like liquid crystalline compound-
Examples of the rod-like liquid crystalline compound include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, and alkoxy-substituted compounds. Examples include phenylpyrimidines, phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles. The rod-like liquid crystalline compound includes a metal complex. Moreover, the liquid crystal polymer which contains a rod-shaped liquid crystalline compound in a repeating unit can also be used as a rod-shaped liquid crystalline compound. In other words, the rod-like liquid crystalline compound may be bonded to a (liquid crystal) polymer. As for rod-like liquid crystalline compounds, for example, Quarterly Chemistry Review Volume 22 Liquid Crystal Chemistry (1994) Chapter 4, Chapter 7 and Chapter 11 of the Chemical Society of Japan, and Liquid Crystal Device Handbook, Japan Society for the Promotion of Science, 142nd member Those described in Chapter 3 of the meeting can be adopted.
There is no restriction | limiting in particular as a birefringence of a rod-shaped liquid crystalline compound, Although it can select suitably according to the objective, 0.001-0.7 are preferable.

--A rod-like liquid crystalline compound having a polymerizable group--
The rod-like liquid crystalline compound having a polymerizable group is not particularly limited as long as it is fixed by a polymerization reaction, and can be appropriately selected according to the purpose. For example, paragraphs of JP-A-2004-339193 Examples thereof include liquid crystalline compounds having a polymerizable group of [Chemical Formula 11] and [Chemical Formula 12] of numbers [0049] to [0050]. Among these, liquid crystal compounds having an acrylate group and / or a methacrylate group are particularly preferable.

  Specific examples of the rod-like liquid crystalline compound having one or two acrylate groups and / or methacrylate groups include paragraph numbers [0082] to [0105] of JP-A-8-3111 and JP-A-9-281331. Paragraph numbers [0022] to [0040], Paragraph numbers [0115] to [0128] of JP-A No. 2000-281628, Paragraph numbers [0250] to [0400] of JP-A No. 2002-220421, JP-A 2003-2003 And compounds described in paragraph Nos. [0056] to [0075] of Japanese Patent No. 48903.

  Specific examples of the liquid crystal compound having two or more polymerizable acrylate groups and / or methacrylate groups include compounds described in JP-A-2002-30042.

  The liquid crystal compound is usually used by dissolving in a solvent to form a solution and coating on a support. Therefore, the liquid crystal compound is preferably a compound exhibiting a nematic liquid crystal phase in the range of 50 to 150 ° C. in the process of removing the solvent.

There is no restriction | limiting in particular as an alignment film for aligning the said liquid crystalline compound, Although it can select suitably according to the objective, Usually, a polymer is utilized. As the polymer, any of a polymer that can be crosslinked by itself, a polymer that is crosslinked by a crosslinking agent, and a combination thereof can be used.
Examples of the polymer used for the alignment film include compounds described in paragraph [0022] of JP-A-8-338913. Among these, water-soluble polymers (for example, poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol, and modified polyvinyl alcohol) are preferable, gelatin, polyvinyl alcohol, and modified polyvinyl alcohol are more preferable, and polyvinyl alcohol and modified polyvinyl alcohol are preferable. Further preferred.

There is no restriction | limiting in particular as a saponification degree of polyvinyl alcohol, Although it can select suitably according to the objective, 70-100% is preferable, 80-100% is more preferable, 85-95% is still more preferable.
There is no restriction | limiting in particular as a polymerization degree of polyvinyl alcohol, Although it can select suitably according to the objective, It is preferable that it is 100-3000.

  The modifying group of the modified polyvinyl alcohol can be introduced by copolymerization modification, chain transfer modification or block polymerization modification. Examples of the modifying group include a hydrophilic group (carboxylic acid group, sulfonic acid group, phosphonic acid group, amino group, ammonium group, amide group, thiol group, etc.), a hydrocarbon group having 10 to 100 carbon atoms, and a fluorine atom. Substituted hydrocarbon groups, thioether groups, polymerizable groups (unsaturated polymerizable groups, epoxy groups, azirinidyl groups, etc.), alkoxysilyl groups (trialkoxy, dialkoxy, monoalkoxy) and the like can be mentioned. Specific examples of the modified polyvinyl alcohol compound include, for example, paragraph No. [0074] of JP-A No. 2000-56310, paragraph Nos. [0022] to [0145] of JP-A No. 2000-155216, and No. 2002-62426. In paragraph Nos. [0018] to [0022].

The liquid crystal compound is in a state in which the first optically anisotropic layer and the second optically anisotropic layer are twisted and arranged in the thickness direction of the liquid crystal compound, respectively. When combined with a liquid crystal display device, particularly a TN mode liquid crystal display device, a sufficient viewing angle, particularly a horizontal viewing angle, can be obtained.
There is no restriction | limiting in particular as a twist angle | corner in the thickness direction of the said liquid crystalline compound, According to the objective, it can select suitably.

  The optically anisotropic layer may contain other additives in addition to the liquid crystalline compound and the cellulose ester. Examples of other additives include plasticizers, surfactants, polymerizable monomers and polymers. These additives are preferably compatible with essential components such as a liquid crystal compound and contribute to control of the tilt angle of the liquid crystal compound or do not inhibit alignment.

<Method for producing optically anisotropic layer>
The optical compensation film is obtained by applying a composition (usually a coating solution) containing a liquid crystalline compound and optionally other additives to, for example, a support surface, preferably an alignment film surface, to form molecules of the liquid crystalline compound. Can be prepared by fixing the alignment state.
As a solvent used for preparation of a coating liquid, an organic solvent is preferable. Examples of organic solvents include amides (eg N, N-dimethylformamide), sulfoxides (eg dimethyl sulfoxide), heterocyclic compounds (eg pyridine), hydrocarbons (eg benzene, hexane), alkyl halides (eg , Chloroform, dichloromethane, tetrachloroethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane), alkyl halides and ketones Is preferred. The said organic solvent may be used individually by 1 type, and may use 2 types together. When producing an optical compensation film with high uniformity, the surface tension of the coating solution is preferably 25 mN / m or less, and more preferably 22 mN / m or less.

  Application | coating of a coating liquid can be performed by a well-known method (For example, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method). Among these, application by a wire bar coating method or a die coating method is preferable.

  The immobilization is preferably performed by a polymerization reaction. Examples of the polymerization reaction include a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator, and among these, a photopolymerization reaction is preferable. The coating liquid preferably contains a polymerizable monomer or a polymerization initiator that contributes to fixing the liquid crystalline compound. As the polymerizable monomer, for example, a compound having a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group is preferable. As addition amount of the said compound, 1-50 mass% is preferable with respect to a liquid crystalline compound, and it is more preferable that it is 3-30 mass%. In addition, it is more preferable to use a monomer having a polymerizable reactive functional group number of 3 or more in admixture because the adhesion between the alignment film and the optically anisotropic layer can be improved.

  Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Description), acridine and phenazine compounds (JP-A-60-105667, US Pat. No. 4,239,850) and oxadiazole compounds (US Pat. No. 4,221,970). The addition amount of the photopolymerization initiator is preferably 0.01 to 20% by mass and more preferably 0.5 to 5% by mass with respect to the solid content of the coating solution.

Ultraviolet light is preferably used for light irradiation for fixing the alignment of the liquid crystal compound (liquid crystal molecule). The irradiation energy is not particularly limited ^but is preferably ^{20mJ / cm 2 ~50J / cm 2} , more preferably ^{20mJ / cm 2 ~5000mJ / cm 2} , 100mJ / cm 2 ~800mJ / cm 2 is more preferable. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions. Although there is no restriction | limiting in particular as temperature for fixing orientation, In order to make Rth / d 0.12 or more, 100 degrees C or less is preferable and 80 degrees C or less is more preferable. Moreover, in order to maintain the adhesiveness of an optically anisotropic layer and a support body, it is preferable to harden | cure at 40 degreeC or more.

  The thickness of the optically anisotropic layer is preferably from 0.1 to 20 μm, more preferably from 0.5 to 15 μm, still more preferably from 1 to 10 μm. A protective layer may be provided on the optically anisotropic layer.

<Support>
When the optical compensation film includes a support, the first optical anisotropic layer and the second optical anisotropic layer are laminated on one surface of the support.
Any order may be sufficient as the order in which the said 1st optically anisotropic layer and the said 2nd optically anisotropic layer are laminated | stacked on a support body.

[Optical characteristics]
-In-plane retardation value Re-
The in-plane retardation value Re of the support is a retardation value measured when light having a wavelength of 550 nm is incident from the normal direction of the surface of the support.
The in-plane retardation value Re can be easily adjusted by changing the stretching conditions, changing the kind and amount of the support material, or changing the film thickness of the support.
Here, the in-plane retardation value Re can be measured by KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments).
There is no restriction | limiting in particular as in-plane retardation value Re in the said support body, Although it can select suitably according to the objective, -190-190 nm is preferable and -170-170 nm is more preferable. When the Re is less than -190 nm, when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device, a sufficient viewing angle, particularly a horizontal viewing angle, may not be obtained. . When the Re exceeds 190 nm, when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device, a sufficient viewing angle, particularly a horizontal viewing angle, may not be obtained. When the Re is in the more preferable range, it is advantageous in that a sufficient viewing angle, particularly a horizontal viewing angle, can be obtained when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device. It is.
Here, the in-plane retardation value Re of the support is the closest of the first or second optically anisotropic layer based on the value measured by KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments). The case where the slow axis and the support slow axis are arranged orthogonally is defined as “+”, and the case where they are disposed in parallel is defined as “−”.

-Right-direction retardation Rth-
The retardation Rth in the thickness direction can be easily adjusted by changing the stretching conditions, changing the kind and amount of support material, or changing the thickness of the support.
There is no restriction | limiting in particular as retardation Rth of the thickness direction in the said support body, Although it can select suitably according to the objective, -60-170 nm is preferable and -40-160 nm is more preferable. When the Rth is less than −60 nm, when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device, a sufficient viewing angle, particularly a horizontal viewing angle, may not be obtained. . When the Rth exceeds 170 nm, when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device, a sufficient viewing angle, particularly a horizontal viewing angle, may not be obtained. When the Rth is in the more preferred range, it is advantageous in that a sufficient viewing angle, particularly a horizontal viewing angle, can be obtained when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device. It is.

[Constitution]
The support is preferably made of a transparent member. Specifically, the support is preferably made of a member having a light transmittance of 80% or more.
The support for the optically anisotropic layer may be a part of the retardation film or the entire retardation film. Moreover, the support body of the said optically anisotropic layer may function as a protective film (polarizing plate protective film) of the said polarizing plate.

The polymer film to be a support is not particularly limited and may be appropriately selected depending on the intended purpose. However, a film of cellulose ester, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, cycloolefin polymer, etc. Is mentioned. Among these, cellulose acetate is preferable in that the production cost can be reduced. Moreover, a cycloolefin type polymer is preferable from a viewpoint of a retardation humidity change.
The polymer film is preferably formed by a solvent cast method. The thickness of the support is preferably 20 to 500 μm, and more preferably 40 to 200 μm. In order to improve the adhesion between the support and the layer (adhesive layer or optically anisotropic layer) provided thereon, the support is subjected to surface treatment (for example, glow discharge treatment, corona discharge treatment, ultraviolet (UV) treatment, flame) Processing) may be performed. An adhesive layer (undercoat layer) may be provided on the support. Further, the case where the support is a film of a polymer having a polymerizable group is also preferable because the adhesion to the optically anisotropic layer is improved. The average particle size is 10 to 100 nm in order to give the support or the long support a slippery property in the transporting process or to prevent the back surface and the surface from sticking after winding. It is preferable to use a polymer layer in which 5% to 40% of the solid particles are mixed by coating or co-casting with a support on one side of the support.

(Liquid crystal display device)
The liquid crystal display device of the present invention includes the optical compensation film, a liquid crystal cell, and a pair of polarizing plates, and includes other configurations as necessary.

-Liquid crystal cell-
The liquid crystal cell includes a liquid crystal layer containing a liquid crystal compound, and a pair of substrates arranged in parallel with the liquid crystal layer interposed therebetween. At least one of the pair of substrates has a transparent electrode.
The liquid crystalline compound in the liquid crystal layer is preferably aligned in parallel to the surface of the substrate in a state in which no voltage is applied. The liquid crystal compound in the liquid crystal layer is preferably twisted and arranged in the thickness direction of the liquid crystal layer when no voltage is applied. There is no restriction | limiting in particular as the twist angle, Although it can select suitably according to the objective, 180 degrees or less are preferable. When the liquid crystalline compound in the liquid crystal layer is aligned and aligned as described above, it is advantageous in that a sufficient viewing angle, particularly a horizontal viewing angle, can be obtained.

-Polarizing plate-
In this specification, the term “polarizing plate” is used to include both a long polarizing plate and a polarizing plate cut into a size incorporated in a liquid crystal display device unless otherwise specified. In this specification, “polarizing film” and “polarizing plate” are distinguished from each other, and “polarizing plate” is a laminate having a transparent protective film for protecting the polarizing film on at least one surface of the “polarizing film”. It means that.

  A polarizing plate generally has a polarizing film produced by adsorbing and orienting a dichroic substance on a base film, and a protective film bonded to at least one surface of the polarizing film. As the polymer used for the base film of the polarizing film, a polyvinyl alcohol (hereinafter referred to as PVA) polymer is generally used. As the dichroic substance, iodine or a dichroic dye is used alone or in combination.

  Here, the PVA used for the polarizing film is usually saponified polyvinyl acetate, but can be copolymerized with vinyl acetate such as unsaturated carboxylic acid, unsaturated sulfonic acid, olefins, and vinyl ethers. You may contain a component. In addition, modified PVA containing an acetoacetyl group, a sulfonic acid group, a carboxyl group, an oxyalkylene group, or the like can also be used. The degree of saponification of PVA is not particularly limited, but is preferably 80 to 100 mol%, particularly preferably 90 to 100 mol% from the viewpoints of solubility, polarization, heat resistance, moisture resistance and the like. Moreover, although the polymerization degree of PVA is not specifically limited, 1000-10000 are preferable and 1500-5000 are more preferable from film strength, heat resistance, moisture resistance, stretchability, etc. Moreover, it does not specifically limit about the syndiotacticity of PVA, It can also take arbitrary values according to the objective.

In the liquid crystal display device, the pair of polarizing plates are arranged with the optical compensation film and the liquid crystal cell interposed therebetween. The optical compensation film is disposed between the liquid crystal cell and at least the polarizing plate.
The slow axis in the plane of the optical compensation film and the slow axis in the plane of one of the polarizing plates are arranged either in parallel or orthogonally. When the positional relationship between the optical compensation film and the polarizing plate is as described above, when the optical compensation film is combined with a liquid crystal display device, particularly a TN mode liquid crystal display device, a sufficient viewing angle, particularly horizontal It is preferable in that the viewing angle in the direction can be obtained.

  The type of the liquid crystal display device is not particularly limited and may be appropriately selected according to the purpose. For example, a TN (Twisted Nematic) mode, an ECB (Electrically Controlled Birefringence) mode, an OCB (Optically Compensated Bend) mode, etc. Liquid crystal display device. Among them, a TN mode liquid crystal display device is preferable in that a sufficient viewing angle, in particular, a horizontal viewing angle can be obtained.

FIG. 2 is an exploded perspective view showing an example of the liquid crystal display device of the present invention. In FIG. 2, it is assumed that all the layers are arranged in parallel.
As shown in FIG. 2, the liquid crystal display device 1 includes an optical compensation film 2, a liquid crystal cell 3, and a deflection plate 4. The liquid crystal display device 1 shown in FIG. 2 includes a pair of optical compensation films 2. The optical compensation film 2 and the deflecting plate 4 are laminated on the upper surface and the lower surface of the liquid crystal cell 3 in this order. That is, the liquid crystal cell 3 is sandwiched between a pair of optical compensation films 2, and the pair of optical compensation films is sandwiched between a pair of deflection plates 4.
The optical compensation film 2 includes a first optical anisotropic layer 2a, a second optical anisotropic layer 2b, and a support 21. The optical compensation film 2 is disposed so that the first optical anisotropic layer 2 a is in contact with the liquid crystal cell and the support 21 is in contact with the deflection plate 4.
The liquid crystal cell 3 includes a liquid crystal layer containing a liquid crystal compound and a pair of substrates that sandwich the liquid crystal layer (not shown). Each of the pair of substrates has an alignment film on the liquid crystal layer side. The two alignment films of the liquid crystal cell 3 are rubbed in directions orthogonal to each other.
Here, the optical compensation film 2 and the liquid crystal cell 3 include the slow axis in the plane of the first optical anisotropic layer 2a and the first optical anisotropy of the two alignment films of the liquid crystal cell 3. The rubbing direction of the alignment film closer to the conductive layer 2a is arranged in parallel.
In the optical compensation film 2 and the deflecting plate 4, the slow axis in the plane of the second optical anisotropic layer 2 a and the absorption axis of the deflecting plate 4 are arranged in parallel.

Hereinafter, the present invention will be described in detail with reference to examples. However, the following examples are not intended to limit the present invention, and all the techniques of the present invention can be modified without departing from the spirit of the preceding and following descriptions. To be included in the scope.
In this example, the degree of alignment order was adjusted by changing the addition amount of the liquid crystal compounds having different polymerizable groups. The average inclination angle was adjusted by changing the UV irradiation condition and the rubbing condition in the film formation process of the optically anisotropic layer. Δn · d was adjusted by changing the thickness of the optically anisotropic layer in the step of forming the optically anisotropic layer. The in-plane retardation value Re and the retardation value Rth in the thickness direction were adjusted by changing the stretching conditions in the film forming process.

(Comparative Example 1)
<Production of optical compensation film>
-Production of support-
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.

[Material / solvent composition]
――――――――――――――――――――――――――――――――――――――
Cellulose acetate (acetylation degree 60.9%, polymerization degree 300, Mn / Mw = 1.5)
··· 100 parts by mass · Triphenyl phosphate (plasticizer) ·············· 7.8 parts by mass · Biphenyl diphenyl phosphate (plasticizer) ··· -3.9 parts by mass-Methylene chloride (first solvent) ... 300 parts by mass-Methanol (second solvent) ... ... 54 parts by mass 1-butanol (third solvent) ... 11 parts by mass ――――――――――――――――――――――――――――――

  In another mixing tank, 16 parts by mass of the following retardation increasing agent A, 8 parts by mass of retardation increasing agent B, 0.28 parts by mass of silicon dioxide fine particles (average particle size: 100 nm), 80 parts by mass of methylene chloride and A solution A was prepared by adding 20 parts by mass of methanol and stirring while heating. 40 parts by mass of the solution A was mixed with 474 parts by mass of the cellulose acetate solution, and stirred well to prepare a dope.

  The obtained dope was cast using a band casting machine. A film having a residual solvent amount of 15% by mass was stretched transversely at a stretch ratio of 20% using a tenter under the conditions of 130 ° C., held at 50 ° C. for 30 seconds with the stretched width, and then clipped to remove cellulose. An acetate film was prepared. The residual solvent amount at the end of stretching was 5% by mass, and further dried to prepare a film with the residual solvent amount being less than 0.1% by mass. The resulting polymer substrate had a thickness of 80 μm.

<Preparation of first alignment film>
The surface of the produced polymer substrate was subjected to saponification treatment, and an alignment film coating solution (adjusted to pH 6.0 with potassium hydroxide) having the following composition was applied onto this film with a wire bar coater at 20 ml / m ² . . The alignment film was obtained by drying with warm air of 60 ° C. for 60 seconds and further with warm air of 100 ° C. for 120 seconds.

[Alignment film coating solution composition]
――――――――――――――――――――――――――――――――――――――
・ The following modified polyvinyl alcohol ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 20 parts by mass ・ Potassium hydroxide ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・・ 0.05 parts by mass ・ Glutaraldehyde ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 0.5 parts by mass ・ Water ・ ・ ・ ・ ・ ・ ・ ・・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 360 parts by mass ・ Methanol ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 120 parts by mass ―――――――――――――――――――――――――――――――――――――

<Formation of first optically anisotropic layer>
The following composition was dissolved in 102 parts by mass of methyl ethyl ketone to prepare an optically anisotropic layer coating solution.

[Optical anisotropic layer coating composition]
――――――――――――――――――――――――――――――――――――――
-Rod-like liquid crystalline compound having the following two acrylate groups (Ac-2)
···· 45.07 parts by mass · Photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) ··· 1.35 parts by mass · Sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.)・ ・ ・ ・ ・ ・ 0.45 parts by mass ――――――――――――――――――――――――――――――――――――――

Compound Ac-2

  After rubbing the first alignment film surface in a fixed direction, the optically anisotropic layer coating solution was applied to the surface of the first alignment film with a wire bar. This was affixed to a metal frame and heated in a thermostatic bath at 70 ° C. for 1.5 minutes to align the rod-like liquid crystalline compound. Next, UV irradiation was performed at 60 ° C. with a 120 W / cm high-pressure mercury lamp for 20 seconds to crosslink the rod-like liquid crystalline compound, and then allowed to cool to room temperature to produce a first optical anisotropic layer. The rod-like liquid crystalline compound of the first optically anisotropic layer was confirmed using KOBRA 21ADH (manufactured by Oji Scientific Instruments Co., Ltd.). As a result, it showed a hybrid orientation and was tilted from the surface of the support. confirmed.

<Formation of second alignment film>
On the coating surface of the optically anisotropic layer coating liquid in the first optically anisotropic layer, a second alignment film was provided in the same manner as the first alignment film.

<Formation of Second Optically Anisotropic Layer>
After rubbing the second alignment film surface in a certain direction in a direction perpendicular to the direction in which the first alignment film surface is rubbed, the second optical anisotropic layer is formed in the same manner as the first optical anisotropic layer. And an optical compensation film of Example 1 was obtained. In addition, about the rod-shaped liquid crystalline compound of the second optically anisotropic layer, it was confirmed using KOBRA 21ADH (manufactured by Oji Scientific Instruments Co., Ltd.). It was confirmed that it was tilted from the surface of the support.

(Examples 1-3)
In Comparative Example 1, Comparative Example 1 except that the addition amount of Compound Ac-2 containing one acrylate and the addition amount of Compound Ac-1 containing one acrylate described below were set to the values shown in Table 1. In the same manner, optical compensation films of Examples 1 to 3 were produced.

Compound Ac-1

Table 1 shows the optical properties of the first optically anisotropic layer, the second optically anisotropic layer, and the support used in the production of the optical compensation films of Examples 1 to 3 and Comparative Example 1.
Each optical characteristic was measured by the following procedure.

-Orientation order-
The degree of orientation order was measured using “Nanofinder” manufactured by Tokyo Instruments Inc. under the measurement conditions in which the excitation laser wavelength was 532 nm, the excitation laser output was about 400 uW at the sample portion, and a depolarizer was attached in front of the spectrometer.
More specifically, the film was cut obliquely at about 1 to 2 degrees, and the polarization Raman measurement near the surface or interface was performed among the liquid crystal material layers in the film. Rotate the film, change the angle between the orientation of the film surface and the electric field direction of the incident laser polarization, and measure at several angles. Among the scattered light components, the polarization component I is parallel to the incident laser polarization electric field. The parallel and the polarization component I perpendicular to the incident laser polarization electric field were spectroscopically detected using an analyzer. Further, by performing fitting analysis based on the least square method with respect to the band having a peak derived from the skeleton of the liquid crystalline compound, using the orientation order parameters P2 and P4 as parameters by a theoretically derived formula, Was calculated.

-Average tilt angle-
Within the plane in which the tilt angle of each layer varies monotonically with a linear function along the thickness direction of the optically anisotropic layer, the incident angle of the measurement light to the optically anisotropic layer is changed, and retardation is achieved at three measurement angles. The value was measured. In order to simplify the measurement and calculation, the normal direction with respect to the optically anisotropic layer was set to 0 °, and the retardation value was measured at three measurement angles of −40 °, 0 °, and + 40 °. The measurement was performed using KOBRA-21ADH (manufactured by Oji Scientific Instruments).
The refractive index of ordinary light of each layer is no, the refractive index of extraordinary light is ne (no and ne are the same values in all layers), and the thickness of the entire multilayer body is d. Furthermore, based on the assumption that the tilt direction in each layer and the uniaxial optical axis direction of that layer coincide with each other, the calculation of the angular dependence of the retardation value of the optically anisotropic layer agrees with the measured value. Fitting was performed using the tilt angle θ1 on one surface of the anisotropic layer and the tilt angle θ2 on the other surface as variables, and θ1 and θ2 were calculated.
Here, no and ne were measured using an Abbe refractometer. The thickness of the optical anisotropic layer was measured using an optical interference film thickness meter.

-In-plane retardation value Re-
Measurement was performed using KOBRA 21ADH (manufactured by Oji Scientific Instruments).
Specifically, Re was measured by making light having a wavelength of 550 nm incident from the normal direction of the optically anisotropic layer or the surface of the support.

-Right-direction retardation Rth-
Measurement was performed using KOBRA 21ADH (manufactured by Oji Scientific Instruments).
Specifically, with the in-plane slow axis as the tilt axis (rotation axis), light with a wavelength of 550 nm is emitted from the tilted direction in a 10 degree step from the normal direction to 50 degrees on one side with respect to the film normal direction. Incidence was performed, and Re was measured at six points in total, and Rth was calculated by inputting the measured Re, an assumed value of average refractive index, and a film thickness value into KOBRA 21ADH.
The in-plane slow axis was determined using KOBRA 21ADH or WR.

The optical compensation films of Examples 1 to 3 and Comparative Example 1 were evaluated as follows.
(1) Measurement of front transmittance The analyzer of the polarizing microscope was fixed, and the opposite polarizer was rotated to determine the direction in which the transmitted light was minimized. The optical compensation film prepared between the analyzer and the polarizer was inserted, and the optical compensation film was rotated to determine the direction in which the transmitted light was minimized. The front transmittance at this time was measured using a polarizing microscope. The results are shown in Table 1.
[Evaluation criteria]
A: The front transmittance is significantly lower than that of Comparative Example 1.
○: The front transmittance is lower than that of Comparative Example 1.
(Triangle | delta): Front transmittance is comparable as the comparative example 1.
X: Front transmittance is higher than Comparative Example 1.

[In Table 1, Examples 1 to 3 and Comparative Example 1 show that the in-plane slow axis of the first optical anisotropic layer and the in-plane slow axis of the second optical anisotropic layer have Are arranged orthogonally. ]

  From the results of Table 1, it was confirmed that the front transmittance of the optical compensation film having a high degree of orientation order was low. When the front transmittance of the optical compensation film is low, the front contrast ratio of the liquid crystal display device becomes high when the optical compensation film is applied to the liquid crystal display device.

Example 4
<Manufacture of liquid crystal display devices>
-Oval polarizing plate-
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film. The surface on the support side of the optical compensation film of Example 1 and one surface of the polarizing film were attached using a polyvinyl alcohol-based adhesive. A commercially available cellulose acetate film (trade name “Fujitac”, manufactured by Fuji Film Co., Ltd.) was saponified and then attached to the other surface of the polarizing film using a polyvinyl alcohol adhesive to obtain an elliptically polarizing plate. .

-TN liquid crystal cell-
A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and the alignment film was rubbed. The obtained two glass substrates were opposed to each other so that the rubbing directions were orthogonal to each other, and the thickness of the liquid crystal cell was set to 4.0 μm. A liquid crystal compound (ZLI-4792, manufactured by Merck & Co., Inc.) having a positive dielectric anisotropy and a refractive index anisotropy Δn of 0.099 was injected into the gap between the liquid crystal cells to produce a TN liquid crystal cell. The Δn · d of the liquid crystal cell was about 400 nm.

-Liquid crystal display device-
A liquid crystal display device was prepared by combining the TN liquid crystal cell and the pair of polarizing plates.
The arrangement of the liquid crystal cell and the pair of polarizing plates was such that the rubbing direction of the liquid crystal cell and the absorption axis direction of the polarizing plate opposed thereto were parallel.
Polarizing plates were attached to separate transparent substrates on the display side and the light source side, respectively, so as to sandwich the prepared liquid crystal cell.

(Examples 4 to 11)
In Example 4, the same as Example 4 except that the average inclination angle and / or Δn · d of the first optically anisotropic layer and the second optically anisotropic layer were changed to the values shown in Table 2. Thus, liquid crystal display devices of Examples 4 to 11 were produced.

(Examples 12 to 18)
In Example 4, the liquid crystal of Examples 12 to 18 was used in the same manner as Example 4 except that the in-plane retardation value Re and the thickness direction retardation value Rth of the support were changed to the values shown in Table 2. A display device was manufactured.

Example 19
In Example 17, Example 19 was performed in the same manner as in Example 17 except that Δn · d of the first optically anisotropic layer and the second optically anisotropic layer was changed to the values shown in Table 2. A liquid crystal display device was manufactured.

(Example 20)
In Example 18, except that the average inclination angle and Δn · d of the first optically anisotropic layer and the second optically anisotropic layer were changed to the values shown in Table 2, the same as Example 18 was performed. A liquid crystal display device of Example 20 was manufactured.

(Comparative Example 2)
In Example 4, the first optical anisotropic layer and the second optical anisotropic layer were not provided, and the in-plane retardation value Re and the thickness direction retardation value Rth of the support were expressed as follows. A liquid crystal display device of Comparative Example 2 was produced in the same manner as in Example 4 except that the value shown in 2 was changed.

(Comparative Examples 3-5)
In Example 4, the same as Example 4 except that the average inclination angle and / or Δn · d of the first optically anisotropic layer and the second optically anisotropic layer were changed to the values shown in Table 2. Thus, liquid crystal display devices of Comparative Examples 3 to 5 were manufactured.

(Comparative Examples 6-8)
In Example 4, the in-plane retardation value Re and the thickness direction retardation value Rth of the support were changed to the values shown in Table 2 in the same manner as in Example 4, but the liquid crystals of Comparative Examples 6 to 8 A display device was manufactured.

(Comparative Example 9)
Example 4 is the same as Example 4 except that the in-plane slow axis of the first optical anisotropic layer and the in-plane slow axis of the second optical anisotropic layer are arranged in parallel. Similarly, a liquid crystal display device of Comparative Example 9 was produced.

The optical characteristics of the first optically anisotropic layer, the second optically anisotropic layer, the support and the liquid crystal cell used in the production of the optical compensation films of Examples 4 to 20 and Comparative Examples 2 to 9 are shown. It is shown in 2.
In addition, the measuring method of each optical characteristic in a 1st optically anisotropic layer, a 2nd optically anisotropic layer, and a support body is the same as what was mentioned above.

The following evaluation was performed about the liquid crystal display device of Examples 4-20 and Comparative Examples 2-9.
(2) Measurement of contrast viewing angle After the liquid crystal display devices of Examples 4 to 20 and Comparative Examples 2 to 9 were placed on the backlight in an environment of 25 ° C. and a relative humidity of 60%, a voltage was applied to the TN liquid crystal cell. Applied. While adjusting the voltage, the black luminance was measured using a luminance meter (BM-5A, manufactured by TOPCON) installed in front of the screen, and the voltage with the smallest black luminance was determined.
With this voltage applied, black luminance and white luminance at the center of the screen were measured. When measuring the black luminance and the white luminance, the luminance meter was measured in the range of −80 to 80 ° by tilting the front of the screen by 0 ° in increments of 10 °. The measured results were evaluated based on the following evaluation criteria with reference to Comparative Example 2 in which optical compensation was not performed, while tracking the change in viewing angle (contrast ratio> 10) in the horizontal direction of the screen. The results are shown in Table 2.
[Evaluation criteria]
A: The viewing angle is significantly wider than that of Comparative Example 2.
○: The viewing angle is considerably wider than that of Comparative Example 2.
Δ: The viewing angle is wider than that of Comparative Example 2.
X: The viewing angle is equivalent to that of Comparative Example 2.

[In Table 2, Examples 4 to 20 and Comparative Examples 3 to 8 are the slow axis in the plane of the first optical anisotropic layer and the slow axis in the plane of the second optical anisotropic layer. Are arranged orthogonally. In Comparative Example 9, the in-plane slow axis of the first optical anisotropic layer and the in-plane slow axis of the second optical anisotropic layer are arranged in parallel. ]

  From the results in Table 2, it was confirmed that the TN mode liquid crystal display devices of Examples 4 to 20 were good in viewing angle characteristics.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Optical compensation film 2a 1st optical anisotropic layer 2b 2nd optical anisotropic layer 3 Liquid crystal cell 4 Polarizing plate 21 Support body 22 Orientation film 23a, 23b, 23c Rod-like liquid crystalline compound

FIG. 1 is a diagram showing an example of a cross section of a first optical anisotropic layer and a second optical anisotropic layer when the optical anisotropic layer is made of a rod-like liquid crystal compound. FIG. 2 is an exploded perspective view showing an example of the liquid crystal display device of the present invention.

Claims (9)

A first optically anisotropic layer and at least a second optically anisotropic layer; an in-plane slow axis of the first optically anisotropic layer; and the second optically anisotropic layer. An optical compensation film arranged in a direction orthogonal to the slow axis in the plane of
The first optical anisotropic layer and the second optical anisotropic layer each comprise a liquid crystalline compound,
The first optical anisotropic layer and the second optical anisotropic layer each have an optical anisotropy having an inclination angle formed by the optical axis of the liquid crystalline compound and the surface of the optical anisotropic layer. The average inclination angle which is an arithmetic average value in the thickness direction of the layer is 0 ° to 20 °,
Each of the first optical anisotropic layer and the second optical anisotropic layer has a retardation value defined by Δn · d of 90 nm <Δn · d ≦ 200 nm in light having a wavelength of 550 nm. An optical compensation film characterized by satisfying.
[However, Δn represents birefringence and is calculated by ne-no. The d represents the thickness of the first optical anisotropic layer or the second optical anisotropic layer. The ne represents an extraordinary light refractive index, and the no represents an ordinary light refractive index. ]   The first optically anisotropic layer and the second optically anisotropic layer each have a retardation value defined by Δn · d satisfying 120 nm <Δn · d ≦ 180 nm in light having a wavelength of 550 nm. Item 5. The optical compensation film according to Item 1.   3. The optical compensation film according to claim 1, wherein each of the first optical anisotropic layer and the second optical anisotropic layer is in a state in which the liquid crystalline compounds are twisted and arranged in the thickness direction. .   The first optically anisotropic layer and the second optically anisotropic layer are composed of two or more liquid crystalline compounds having different numbers of polymerizable groups contained in one molecule, and each of the liquid crystalline compounds is 1 The optical compensation film according to claim 1, which has one or more polymerizable groups in the molecule.   The optical compensation film according to any one of claims 1 to 4, comprising a support, wherein the first optical anisotropic layer and the second optical anisotropic layer are laminated on one surface of the support. .   The in-plane retardation value Re of the support measured using light having a wavelength of 550 nm is -190 to 190 nm, and the retardation value Rth in the thickness direction of the support measured using light having a wavelength of 550 nm is The optical compensation film according to claim 5, which has a wavelength of -60 to 170 nm.   The in-plane retardation value Re of the support measured using light having a wavelength of 550 nm is -170 to 170 nm, and the retardation value Rth in the thickness direction of the support measured using light having a wavelength of 550 nm is The optical compensation film according to claim 5, which is -40 to 160 nm. A liquid crystal display device comprising the optical compensation film according to any one of claims 1 to 7, a liquid crystal cell, and a pair of polarizing plates sandwiching the optical compensation film and the liquid crystal cell,
The optical compensation film is disposed between the liquid crystal cell and at least one of the polarizing plates, and an in-plane slow axis of the optical compensation film and an in-plane slow axis of the one polarizing plate. Are arranged in either parallel or orthogonal. The liquid crystal cell includes a liquid crystal layer containing a liquid crystal compound, and a pair of substrates arranged in parallel with the liquid crystal layer interposed therebetween,
At least one of the substrates has a transparent electrode;
The liquid crystalline compound of the liquid crystal layer is in a state in which no voltage is applied, the liquid crystal compound is aligned parallel to the surface of the substrate, and twisted in the thickness direction of the liquid crystal layer, and the twist angle in the thickness direction is The liquid crystal display device according to claim 8, wherein the liquid crystal display device is 180 ° or less.