JP2006330268A - Liquid crystal display and optical film used for same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an IPS (in-plane switching) mode liquid crystal display having excellent display quality. <P>SOLUTION: In the IPS mode liquid crystal display of a normally black mode, a first polarizing plate, a liquid crystal cell, a negative nearly uniaxial optical film having an optical axis in its plane, a biaxial optical film whose refractive index in its thickness direction is higher than the refractive index in any direction in its plane and a second polarizing plate are laminated in this order. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device excellent in viewing angle characteristics, and an optical film suitable for the liquid crystal display device.

  In recent years, the performance of liquid crystal display devices has improved, and in particular, the vertical alignment mode and in-plane switching (hereinafter referred to as IPS) mode are superior in performance. Therefore, liquid crystal televisions using these have the potential to replace conventional CRT televisions. Hidden. A retardation film, which is an optical film having optical anisotropy, plays an important role in improving the performance of these liquid crystal display devices, particularly in widening the viewing angle. Although the IPS mode has conventionally been characterized by a wide viewing angle without using a retardation film for widening the viewing angle, it is widely used in recent years based on optical design technology using a retardation film. With the advance of viewing angle technology, it is difficult to differentiate from other modes. In such a background, there is an increasing need for development of an optical design technique using a retardation film aiming at further expansion of the viewing angle even in the IPS mode. For example, Non-Patent Document 1 describes a method of performing optical compensation using a biaxial retardation film.

  In addition, the polarizing plate viewing angle expansion technique described in Non-Patent Document 2 described below by combining a positive uniaxial A plate and a positive uniaxial C plate may be used to expand the viewing angle of IPS. Are known.

Yukita Saitoh, Shinichi Kimura, Kaoru Kusafuka, Hidehisa Shimizu, Japanese Journal of Applied Physics 37 1998 4822-4828 J. Chen, K. -H. Kim, J.-J. Jyu, J. H. Souk, J. R. Kelly, P. J. Bos, Society for Information Display '98 Digest, 1998 p. 315

  As a result of examining the techniques of Non-Patent Documents 1 and 2, it was found that when these methods are used to expand the viewing angle of an IPS mode liquid crystal display device, the color shift of black display is one problem. The color shift of black display here means that the color tone of black changes depending on the azimuth angle when the liquid crystal display device during black display is observed from an oblique direction rather than a normal direction. In the present invention, this problem is referred to as an azimuth angle dependency problem of color shift at oblique incidence. In other words, when the liquid crystal display device is observed from an oblique direction, the state changes from a strong reddish black color to a bluish black color depending on the viewing direction. In general, the above-described color shift in black display causes a color shift problem even in halftone display. Here, the azimuth angle is an angle set in the surface of the liquid crystal display device. On the other hand, the polar angle is an angle set with the normal of the surface of the liquid crystal display device as 0 °, and therefore the incident angle is defined by the polar angle and the azimuth angle.

  The phase difference value of the liquid crystal cell in the in-plane switching mode of the normally black mode is designed considering not only the viewing angle but also the transmittance and response speed, so the optimum phase difference value is not necessarily a half wavelength. It will not be. Here, the phase difference value of the liquid crystal cell is a phase difference value of the liquid crystal cell including the liquid crystal. Therefore, the viewing angle of the liquid crystal display device in the normally black mode in-plane switching mode is mainly determined by the optical anisotropy between the retardation film and the liquid crystal cell. In the said nonpatent literature 1, although a biaxial optical film is used, the relationship between the phase difference value of a liquid crystal cell and the phase difference value of a biaxial optical film is not disclosed. Similarly, Non-Patent Document 2 does not disclose the relationship between the liquid crystal cell and the retardation film.

  Furthermore, since the biaxial optical film and the positive uniaxial C plate used in Non-Patent Documents 1 and 2 are complicated in manufacturing method, the optical axis accuracy and phase difference accuracy can be obtained in a large area. It has the problem of being difficult. As a result, when these are used in a liquid crystal display device, defects such as display unevenness are likely to occur, and it is difficult to improve display quality.

An object of the present invention is to provide an IPS mode liquid crystal display device having excellent display quality.
It is a further object of the present invention to provide a liquid crystal display device having a wide viewing angle and excellent display quality that solves the above-mentioned color shift problem even if the retardation value of the IPS liquid crystal cell changes.

  A negative substantially uniaxial optical film having an optical axis in the plane can be obtained, for example, by forming a polymer material having negative molecular polarizability anisotropy into a film and performing a normal uniaxial stretching process. Therefore, such a film has a very simple manufacturing process and is excellent in the uniformity of optical anisotropy required for a liquid crystal television or the like. In addition, the biaxial optical film having a refractive index in the thickness direction larger than the refractive index in any direction in the in-plane direction is, for example, a film of a polymer material having negative molecular polarizability anisotropy as a raw material, It can be obtained by a normal biaxial stretching process or the like, and can be obtained by a simple manufacturing process.

  The present inventors conducted optical design using these optical films and intensively studied the method of expanding the viewing angle of the IPS mode liquid crystal display device. Even if the retardation value of the liquid crystal cell changes due to the design convenience. It was found that an IPS mode liquid crystal display device with a wide viewing angle and suppressed azimuth angle dependency of color shift at oblique incidence can be realized.

That is, the present invention is as follows.
[1] First polarizing plate, liquid crystal cell, negative substantially uniaxial optical film having an optical axis in the plane, biaxiality having a refractive index in the thickness direction larger than the refractive index in any direction in the plane A normally black mode in-plane switching mode liquid crystal display device in which an optical film and a second polarizing plate are laminated in this order, wherein the absorption axis of the first polarizing plate and the liquid crystal cell in the black state The angle formed by the in-plane slow axis is approximately 90 °, the angle formed by the in-plane slow axis of the liquid crystal cell in the black state and the slow axis of the negative approximately uniaxial optical film is approximately 90 °, and is approximately negative. The angle formed by the slow axis of the uniaxial optical film and the in-plane slow axis of the biaxial optical film is approximately 90 °, and the in-plane slow axis of the biaxial optical film and the absorption of the second polarizing plate A liquid crystal display device having an angle formed by an axis of approximately 0 °.
[2] The in-plane retardation values of the negative substantially uniaxial optical film, the liquid crystal cell in the black state, and the biaxial optical film are Γ ₁ (λ), Γ _LC (λ), and Γ ₂ (λ), respectively. When each of the first and second polarizing plates has a polarizing layer protective film on the liquid crystal cell side, the retardation values in the thickness direction of the polarizing layer protective film are Rth ₁ (λ) and Rth, respectively. ₂ (λ), the liquid crystal display device as described above, wherein the relationship of the following formulas (1) and (2) is satisfied.
−120 <Γ ₂ (λ) + Rth ₂ (λ) / 2 <30 nm (1)
45 <Γ _LC + Γ ₁ (λ) + Rth ₁ (λ) <155 nm (2)
(However, λ = 550 nm)
[3] The in-plane retardation values of the negative substantially uniaxial optical film, the liquid crystal cell in the black state, and the biaxial optical film were Γ ₁ (λ), Γ _LC (λ), and Γ ₂ (λ), respectively. In the case, the liquid crystal display device as described above, wherein the relationship of the following formula (3) and / or (4) is satisfied.
| Γ ₂ (λ ₁ ) | <| Γ ₂ (λ ₂ ) | (3)
| Γ _LC (λ ₁ ) + Γ ₁ (λ ₁ ) | <| Γ _LC (λ ₂ ) + Γ ₁ (λ ₂ ) | (4)
(However, λ represents the measurement wavelength, and 400 nm ≦ λ ₁ <λ ₂ ≦ 700 nm.)
[4] A negative substantially uniaxial optical film having an optical axis in a plane used for the liquid crystal display device.
[5] A biaxial optical film in which the refractive index in the thickness direction used in the liquid crystal display device is larger than the refractive index in any direction in the plane.
[6] The optical film as described above, comprising a polycarbonate having a fluorene skeleton.
[7] A laminated polarizing plate in which the optical film described above and a polarizing plate are integrated, and is a negative substantially uniaxial optical film having an optical axis in the plane, and the refractive index in the thickness direction is any in-plane A biaxial optical film having a refractive index larger than the refractive index in the direction of, and a polarizing plate are laminated in this order, and an in-plane slow axis of the negative substantially uniaxial optical film and an in-plane retardation of the biaxial optical film are laminated. A laminated polarizing plate, characterized in that an angle formed with a phase axis is approximately 90 °, and an in-plane slow axis of the biaxial optical film and an absorption axis of the polarizing plate are approximately 0 °.

In the present invention, an optically anisotropic film having refractive index anisotropy is referred to as a retardation film or an optical film. A uniaxial optical film and a biaxial optical film are classified according to their three-dimensional refractive index, and these are also categories of retardation films. The retardation film is expressed by a refractive index ellipsoid, and only the case where the orientations of the three main refractive indexes are parallel or perpendicular to the film plane is considered here. Here consider the orthogonal coordinate system axes are parallel or perpendicular to the surface of the film as shown in FIG. 3, it defines three refractive index corresponding to the orientation of the coordinate n _x, n _y, and n _z. When the slow axis direction in the plane is set as the x axis, the y axis is set in the plane and the z axis is set in the thickness direction. Accordingly, the negative substantially uniaxial optical film having an optical axis in plane of the present invention, with three refractive _{index, n z ≒ n x> n} y , and the late phase n _x is the film plane It becomes an axis. All three biaxial optical films are defined as having different refractive indexes. Therefore, the thickness direction of the refractive index of the biaxial optical film larger than the refractive index in either direction in the plane, is defined as _{n z> n x> n y} . The positive uniaxial A plate described above refers to a positive uniaxial medium (uniaxial optical film in the case of a film) having an optical axis in the plane, and in this definition, n _x > _ny = _Nz . On the other hand, the positive uniaxial C plate is a positive uniaxial medium (uniaxial optical film in the case of a film) having an optical axis in the thickness direction, and in this definition, n _x = n _y < _nz .

The in-plane retardation value Γ in the present invention is defined by the following formula (5) or (6).
When the optical film of the n _z ≧ _{n x} is
_{Γ (λ) = (n y} -n x) × d (5)
When the optical film of the n _{z <n x} is
_{Γ (λ) = (n x} -n y) × d (6)
Here, d is the thickness (nm) of the film.

Strictly speaking, it is preferable that the negative substantially uniaxial optical film having an in-plane optical axis in the present invention satisfies the relationship of n _z = n _x > _ny , but n _z ≈n _x > _ny . If you can, you can use it without any problems. In addition, since an actual retardation film also has a variation in refractive index, the range of the term of substantially negative uniaxiality is defined using the following formula (7) using these three refractive indexes.
_{Nz = (n x -n z)} / (n x -n y) (7)

What is a negative substantially uniaxial optical film having an optical axis in a plane in the present invention?
−0.4 <Nz <0.1 (8)
Is preferably defined as
−0.35 <Nz <0.05 (9)
And more preferably
−0.20 <Nz <0.03 (10)
More preferably,
−0.10 <Nz <0.02 (11)
It is. Rth is defined as follows.
Rth (λ) = {(n _x + _ny ) / 2−n _z } × d (12)
In the above formula (12), d (nm) is the thickness of the optical film. In the present invention, the phase difference value Γ (λ), Rth (λ), and Nz value are measured at a wavelength of 550 nm unless otherwise specified.

Moreover, the biaxial optical film in which the refractive index in the thickness direction in the present invention is larger than the refractive index in any direction in the plane is the following formula (13).
−5 ≦ Nz ≦ −0.4 (13)
And preferably, the following formula (14)
-4 <Nz ≦ −0.5 (14)
It is. When Nz is smaller than −5, biaxiality is poor, and it becomes close to a positive uniaxial C plate. As a result, a vertically symmetric structure sandwiching the liquid crystal cell is lost, and color shift is suppressed. May be difficult. Further, even when Nz is close to 0, it is optically uniaxial, which falls outside the scope of the present invention.

  The black state and the black display in the present invention are the darkest states in the gradation display, and specifically, the state where the transmittance measured by entering light from the normal direction of the surface of the liquid crystal display device is the lowest. Is defined.

  The optical axis alignment angle between the optically anisotropic elements needs to be the above-mentioned angle, but the allowable range is within ± 3 °, preferably within ± 2 °, more preferably centered on the set angle. Is within ± 1 °, more preferably within ± 0.5 °. That is, the expression of approximately 90 ° is defined as 90 ° ± 3 °.

  In the present invention, particularly when two retardation films are used on one side of the liquid crystal cell and the in-plane retardation value thereof and the in-plane retardation value of the liquid crystal cell in the black state are taken into consideration, a wide field of view is particularly excellent. The reason why keratinization can be realized is described below. Here, the wide viewing angle of the liquid crystal display device means that the phenomenon that the contrast changes depending on the viewing angle is improved, and the angular region having a high contrast is widened. In general, widening the viewing angle of a liquid crystal display device is aimed at making the transmittance during black display as close to 0 as possible regardless of the incident angle to the liquid crystal display device. It will be described below that the present invention can reduce the transmittance with respect to light having various incident angles.

  An example of the configuration of the liquid crystal display device according to the present invention is shown in FIG. The principle of wide viewing angle according to the present invention will be described with reference to FIG. In FIG. 1, the second polarizing plate is on the light source side, but the light source may be disposed on either side of the first or second polarizing plate.

  The configuration of FIG. 1 can be regarded as optically almost equivalent to FIG. 2 under certain conditions. First, since the liquid crystal display device in the present invention is in the IPS mode, the liquid crystal cell can be regarded as a positive uniaxial medium having an optical axis in the plane during black display. The negative uniaxial optical film having an optical axis in the plane and the slow axis of the liquid crystal cell are orthogonal to each other, and the absolute value of the in-plane retardation value of the liquid crystal cell is substantially negative uniaxial. Under the condition that it is larger than the absolute value of the retardation value of the diffractive optical film, the combination of the two elements can be regarded as optically substantially equivalent to the positive substantially uniaxial optical film [11] shown in FIG. . Therefore, the wide viewing angle in the liquid crystal display device of the present invention is examined by first considering widening the viewing angle in the configuration of FIG. 2, and based on the result, the optimum position of the optical anisotropic medium used in the present invention is determined. What is necessary is just to obtain | require a phase difference value and its relationship.

Realizing a wide viewing angle in FIG. 2 is to make the transmittance as close to 0 as possible for incident light having any incident angle. Therefore, the in-plane retardation of the positive substantially uniaxial optical film [11] in FIG. 2 and the biaxial optical film [12] whose refractive index in the thickness direction is larger than the refractive index in any direction in the plane. The values were set to Γ ₄ (λ) and Γ ₃ (λ), respectively, and optimum phase difference values were examined. It was found that the following expressions (15) and (16) were preferably satisfied. By satisfying the following formulas (15) and (16), the transmittance can be reduced when the incident angle of incident light is in the range of polar angle 0 to 80 ° and azimuth angle 0 to 360 °.
−120 <Γ ₃ (λ) <30 nm (15)
45 <Γ ₄ (λ) <155 nm (16)

The preferable range of the phase difference value is preferably to satisfy the following formulas (17) and (18). In this case, the incident angle of incident light is a polar angle of 0 to 80 ° and an azimuth angle of 0 to 360 °. In this range, the transmittance can be further reduced.
−100 <Γ ₃ (λ) <10 nm (17)
70 <Γ ₄ (λ) <140 nm (18)

A more preferable range of the phase difference value is to satisfy the following formulas (19) and (20). In this case, the incident angle of incident light is a polar angle of 0 to 80 ° and an azimuth angle of 0 to 360 °. In the range, the transmittance can be further reduced.
−80 <Γ ₃ (λ) <− 10 nm (19)
90 <Γ ₄ (λ) <130 nm (20)

Although the optimum value varies depending on the Nz value of the biaxial optical film and the refractive index of the optical film used, it is preferable to satisfy the above relationship.
As described above, from the comparison of the configurations of FIG. 1 and FIG. 2, it is newly found that the following equations (21) and (22) may be satisfied in order for both to be equivalent.
Γ ₃ (λ) = Γ ₂ (λ) (21)
Γ ₄ (λ) = Γ _LC (λ) + Γ ₁ (λ) (22)

  As described above, the reason why the above formula (22) is established is that both the liquid crystal cell and the first negative substantially uniaxial optical film having an optical axis in the plane are optically substantially uniaxial, In addition, since the slow axes are orthogonal to each other, both of them can be optically regarded as one uniaxial medium. Here, when the refractive indexes of all anisotropic media are equal, the above formulas (21) and (22) can be regarded as equal signs, but in general, the material used as an optically anisotropic medium in a liquid crystal display device is an organic substance. Even if the materials are different, the refractive index is not greatly different, so even if they are considered to be almost equal, there are few problems in practical use. If the above equations (21) and (22) are satisfied, the configuration of FIGS. 1 and 2 is optical. Can be considered equivalent to.

On the other hand, the polarizing plate in this invention contains the form by which the protective film for polarizing layers was installed in order to protect a polarizing layer only on a polarizing layer or the single side | surface or both surfaces of a polarizing layer. When the polarizing layer protective film is disposed on at least one surface of the polarizing layer and the polarizing layer protective film is present on the liquid crystal cell side, the polarizing layer protective film generally has an in-plane anisotropy. Although negligibly small, a retardation Rth (λ) in the thickness direction, which will be described later, cannot be ignored in the design of a liquid crystal display device. Then, the influence of this protective film for polarizing layers was examined. As a result, in order for FIG. 1 and FIG. 2 to be optically substantially equal, it has been found that the relationship between the above formulas (21) and (22) is approximately as follows.
Γ ₃ (λ) ≈Γ ₂ (λ) + Rth ₂ (λ) / 2 (23)
Γ ₄ (λ) ≈Γ _LC (λ) + Γ ₁ (λ) + Rth ₁ (λ) (24)

Here, Rth ₁ (λ) and Rth ₂ (λ) are respectively the retardation value in the thickness direction of the polarizing layer protective film on the liquid crystal cell side in the first polarizing plate and the retardation in the second polarizing plate in FIG. The retardation value in the thickness direction of the polarizing layer protective film on the film side is represented. From the definition of the optical anisotropy of the present invention, the value of Rth (λ) of a commonly used polarizing layer protective film is positive. On the other hand, the retardation value of the negative substantially uniaxial optical film having the optical axis in the plane of the present invention and the biaxial optical film of the present invention is negative. Therefore, they cancel each other out of anisotropy. The above equation shows that the value of Γ ₁ (λ) needs to be increased in absolute value by Rth (λ) as compared with the case where there is no polarizing layer protective film under the condition that Γ _LC (λ) is constant. The relationship between (22) and the above equation (24) is shown. On the other hand, the relationship between the above formula (21) and the above formula (23) indicates that the value of Γ ₂ (λ) needs to be increased in absolute value by Rth (λ) / 2. Therefore, from the relations of the above formulas (15), (16) and the above formulas (23), (24), in order to realize a wide viewing angle in the liquid crystal display device of the present invention, the above formulas (1), ( It is derived that it is preferable to satisfy 2).

  In general, in the normally black mode in-plane switching mode liquid crystal display device, the phase difference of the liquid crystal cell is usually about one-half wavelength or more, which takes into account the brightness and response speed. It is determined. In the liquid crystal display device of the present invention, a negative substantially uniaxial optical film having an optical axis in a plane and a liquid crystal cell which is a positive uniaxial medium are combined into one positive one as described above. Since it can be regarded as an axial medium, the prospect of optical design can be easily established, and even if the phase difference value of the liquid crystal cell changes due to the convenience of design, the above formulas (1) and (2) are satisfied. The fact that it is possible to obtain a liquid crystal display device with a wide viewing angle is also an excellent point not found in other methods.

In order to further improve the performance, it is preferable to consider the wavelength dependence of the retardation value of the optical element. That is, realizing a wider viewing angle and a wider band aiming at further performance improvement in FIG. 2 is to make the transmittance as close to 0 as possible with respect to incident light in the visible light band having all incident angles. . First, as a result of investigation, the two retardation films in FIG. 2 are not mutually compensated for the wavelength dispersion of the respective retardations, so that the wavelength dispersion of the retardation values of these retardation films is at least It has been found that one of them preferably has a wider bandwidth. Unless otherwise specified, the phase difference value is defined in nanometers as a unit of length. The broadening of the phase difference value referred to here is defined as approaching a state where the phase difference value becomes constant without depending on the wavelength when the phase difference value is displayed in an angle. When the phase difference value is converted into a unit of length, it is necessary at least that the absolute value of the phase difference value Γ (λ) be monotonously increased with respect to the wavelength. In other words, it can be said to approach the state of Expression (25).
Γ (λ) / λ = C (25)
Where Γ (λ) is a phase difference value (nm) at the measurement wavelength λ, λ is in the range of 400 to 700 nm, and C is a constant.

Therefore, when the retardation values of the positive substantially uniaxial retardation film and the biaxial optical film in FIG. 2 are Γ ₄ (λ) and Γ ₃ (λ), respectively, the following formula (26) and / or It is preferable to satisfy (27).
| Γ ₃ (λ ₁ ) | <| Γ ₃ (λ ₂ ) | (26)
| Γ ₄ (λ ₁ ) | <| Γ ₄ (λ ₂ ) | (27)
Here, λ represents the measurement wavelength, and 400 nm ≦ λ ₁ <λ ₂ ≦ 700 nm.

More preferably, the above expressions (26) and (27) are satisfied at the same time.
Therefore, the following formulas (3) and (4) are derived from the relationship between the above formulas (26) and (27) and the above formulas (21) and (22). The liquid crystal display device of the present invention preferably satisfies the following formulas (3) and / or (4), and more preferably satisfies both.
| Γ ₂ (λ ₁ ) | <| Γ ₂ (λ ₂ ) | (3)
| Γ _LC (λ ₁ ) + Γ ₁ (λ ₁ ) | <| Γ _LC (λ ₂ ) + Γ ₁ (λ ₂ ) | (4)
Here, λ represents the measurement wavelength, and 400 nm ≦ λ ₁ <λ ₂ ≦ 700 nm.

  Optically designed using a negative substantially uniaxial optical film having an optical axis in the plane of the present invention and a biaxial optical film having a refractive index in the thickness direction larger than the refractive index in any direction in the plane. The liquid crystal display device can easily design a wide viewing angle according to the change even if the phase difference value of the liquid crystal cell when no voltage is applied changes to various values in consideration of other characteristics. It has excellent performance such that the viewing angle is small and the azimuth angle dependency of the color shift at oblique incidence is small.

In order to obtain the effect of the invention, the first polarizing plate, the liquid crystal cell, and a negative substantially uniaxial optical film having an optical axis in the plane (hereinafter, sometimes simply referred to as a negative substantially uniaxial optical film) These are laminated in the order of a biaxial optical film having a refractive index in the thickness direction larger than the refractive index in any direction in the plane (hereinafter sometimes simply referred to as a biaxial optical film) and a second polarizing plate. A normally black mode in-plane switching mode liquid crystal display device, wherein the angle formed between the absorption axis of the first polarizing plate and the in-plane slow axis of the liquid crystal cell in the black state is approximately 90 °, black The angle formed by the in-plane slow axis of the liquid crystal cell in the state and the slow axis of the negative substantially uniaxial optical film is about 90 °, and the slow axis of the negative substantially uniaxial optical film and the biaxial optical film The angle formed by the in-plane slow axis is approximately 90 ° and the biaxial optical Angle between the absorption axis of the in-plane slow axis and a second polarizing plate of Lum is approximately 0 °,
And,
The in-plane retardation values of the negative substantially uniaxial optical film, the liquid crystal cell in the black state, and the biaxial optical film are Γ ₁ (λ), Γ _LC (λ), and Γ ₂ (λ), respectively. When a polarizing layer protective film is disposed on each of the liquid crystal cell sides of the first and second polarizing plates, the retardation values in the thickness direction of the polarizing layer protective film are Rth ₁ (λ), When Rth ₂ (λ), it is preferable that the liquid crystal display device satisfy the relationship of the following formulas (1) and (2).
−120 <Γ ₂ (λ) + Rth ₂ (λ) / 2 <30 nm (1)
45 <Γ _LC (λ) + Γ ₁ (λ) + Rth ₁ (λ) <155 nm (2)

The above range is more preferably
−100 <Γ ₂ (λ) + Rth ₂ (λ) / 2 <10 nm (28)
70 <Γ _LC (λ) + Γ ₁ (λ) + Rth ₁ (λ) <140 nm (29)
Even more preferably,
−80 <Γ ₂ (λ) + Rth ₂ (λ) / 2 <−10 nm (30)
90 <Γ _LC (λ) + Γ ₁ (λ) + Rth ₁ (λ) <130 nm (31)
It is.

More preferably, the in-plane retardation values of the negative substantially uniaxial optical film, the liquid crystal cell in the black state, and the biaxial optical film are Γ ₁ (λ), Γ _LC (λ), and Γ ₂ (λ), respectively. and, when the first and second polarizing plate has a protective film for a polarizing layer in the liquid crystal cell side, a retardation value in the thickness direction thereof polarizing layer protective film, respectively, Rth ₁ ( When λ) and Rth ₂ (λ), the relationship of the following formulas (3) and / or (4) is satisfied. In the following formulas (3) and (4), the influence of Rth (λ) is negligible because of the wavelength dependence.
| Γ ₂ (λ ₁ ) | <| Γ ₂ (λ ₂ ) | (3)
| Γ _LC (λ ₁ ) + Γ ₁ (λ ₁ ) | <| Γ _LC (λ ₂ ) + Γ ₁ (λ ₂ ) | (4)
However, λ represents a measurement wavelength, and 400 nm ≦ λ ₁ <λ ₂ ≦ 700 nm.
Preferably, the relationship of the above formulas (3) and (4) is satisfied at the same time.

The wavelength dispersion of the phase difference absolute value of the biaxial optical film is preferably to satisfy the following formulas (32) and (33) for the above formula (3):
0.4 <Γ ₂ (450) / Γ ₂ (550) <0.98 (32)
1.01 <Γ ₂ (650) / Γ ₂ (550) <1.50 (33)
More preferably, the following expressions (34) and (35) are satisfied.
0.6 <Γ ₂ (450) / Γ ₂ (550) <0.95 (34)
1.03 <Γ ₂ (650) / Γ ₂ (550) <1.40 (35)
In the above formulas (32) to (35), the number in () after Γ represents the measurement wavelength (nm).

The above formula (4) preferably satisfies the following formulas (36) and (37):
0.4 <(Γ _LC (450) + Γ ₁ (450)) / (Γ _LC (550) + Γ ₁ (550))
<0.98 (36)
1.01 <(Γ _LC (650) + Γ ₁ (650)) / (Γ _LC (550) + Γ ₁ (550))
<1.50 (37)
More preferably, the following expressions (38) and (39) are satisfied.
0.6 <(Γ _LC (450) + Γ ₁ (450)) / (Γ _LC (550) + Γ ₁ (550))
<0.95 (38)
1.03 <(Γ _LC (650) + Γ ₁ (650)) / (Γ _LC (550) + Γ ₁ (550))
<1.40 (39)
In the above formulas (36) to (39), the number in () after Γ represents the measurement wavelength (nm).

In general, the retardation value of the liquid crystal cell in the black state of the IPS mode decreases as the wavelength increases, and has a positive retardation value. Therefore, in order to satisfy the above formulas (4) and (36) to (39), the absolute value of the retardation of the first negative substantially uniaxial optical film having the optical axis in the plane increases with the wavelength increase. It is preferable to decrease. More specifically, in order to satisfy the relationship of the above formula (4), it is preferable to satisfy the following formulas (40) and (41).
Γ _LC (450) / Γ _LC (550) <Γ ₁ (450) / Γ ₁ (550) (40)
Γ _LC (650) / Γ _LC (550)> Γ ₁ (650) / Γ ₁ (550) (41)

  The negative substantially uniaxial optical film and the biaxial optical film may each be configured by laminating one film alone or two or more films as long as they have necessary characteristics. Each of them is preferable from the viewpoint of productivity because the thickness of the entire liquid crystal display device can be reduced, and a laminating process between films is unnecessary.

  IPS is a mode in which a liquid crystal director changes in a plane by a lateral electric field. A normally black mode in which black is displayed when the voltage is almost not applied and a normally white mode in which black is displayed when the voltage is applied are conceivable. In the IPS mode, the disorder of the liquid crystal alignment during voltage application is controlled. Therefore, in order to obtain high contrast, it is necessary to be in a normally black mode.

  As a phase difference of the liquid crystal cell in this invention, it is preferable that it is 200-450 nm, More preferably, it is 250-400 nm, More preferably, it is 270-390 nm. The phase difference value of the liquid crystal cell is a value (in-plane value) at the front incidence in a non-voltage applied state. The phase difference value of the liquid crystal cell varies depending on the cell structure, driving conditions, setting of desired transmittance, and the like, but it is preferable to satisfy these values. As the material used for the liquid crystal, known nematic liquid crystal and smectic liquid crystal having positive dielectric anisotropy and positive refractive index anisotropy are used, and nematic liquid crystal is preferable. Further, in order to drive the liquid crystal in the IPS mode, it is necessary to generate a lateral electric field in the plane, but a known comb electrode arrangement, an electrode forming method, or the like can be used.

The negative substantially uniaxial optical film and the biaxial optical film used in the present invention are preferably made of the same material. In this case, productivity can be improved by mass production effect.
As a material for providing a negative uniaxial optical film and a biaxial optical film having an optical axis in the plane (hereinafter sometimes referred to simply as an optical film), thermoplastic and curable polymers such as polycarbonate are used. , Polystyrene, syndiotactic polystyrene, amorphous polyolefin, polymer having norbornene skeleton, organic acid-substituted cellulose, polyethersulfone, polyarylate, polyester, olefin maleimide, copolymerized olefin maleimide having phenyl group, liquid crystalline polymer It is done. Further, among those obtained by aligning a polymerizable liquid crystal and cured, those having a negative molecular polarizability anisotropy are also included. These materials can be made into a negative uniaxial optical film having an in-plane optical axis by, for example, forming a film and then uniaxially stretching the material. Also, a biaxial optical film having a refractive index in the thickness direction larger than any refractive index in the in-plane direction can be produced by forming a film using these materials and biaxially stretching.

  Preferred as the material is a polycarbonate having a fluorene skeleton. Since the fluorene skeleton is oriented perpendicular to the polymer main chain by a stretching operation or the like, it can have a large negative molecular polarizability anisotropy.

ここで、Ｒ^１〜Ｒ^８は、互いに独立に、水素原子、ハロゲン原子、炭素数１〜６の炭化水素基および炭素数１〜６の炭化水素−Ｏ−基よりなる群から選ばれる基であり、そしてＸは下記式（１）−１

で表わされる基であり、Ｒ^３０およびＲ^３１は、互いに独立に、ハロゲン原子または炭素数１〜３のアルキル基であり、そしてｎおよびｍは互いに独立に、０〜４の整数である。 A preferable chemical structure of the polycarbonate having a fluorene skeleton is composed of a polymer or a polymer mixture containing a repeating unit represented by the following formula (I).

Here, R ^{1 to} R ⁸ are each independently a group selected from the group consisting of a hydrogen atom, a halogen atom, a hydrocarbon group having 1 to 6 carbon atoms, and a hydrocarbon group having 1 to 6 carbon atoms. And X is the following formula (1) -1

R ³⁰ and R ³¹ are each independently a halogen atom or an alkyl group having 1 to 3 carbon atoms, and n and m are each independently an integer of 0 to 4.

Here, the polymer and the polymer mixture preferably contain 50 to 95 mol%, more preferably 60 to 95 mol% of the repeating units represented by the above formula (I), respectively, based on the total repeating units of the polymer or polymer mixture. More preferably, it is 70-90 mol%.
These polycarbonates having a fluorene skeleton have excellent physical properties as an optical film in the present invention in terms of high glass transition temperature, handling, stretch moldability, and the like.

で示される繰返し単位からなり、かつ上記式（Ｉ）および（ＩＩ）の合計に基づき上記式（Ｉ）で表される繰返し単位は５０〜９５モル％含有する共重合体または混合物が好ましく、より好ましい範囲は６０〜９５モル％、さらに好ましくは７０〜９０モル％である。 More preferred polycarbonates include the repeating unit represented by the above formula (I) and the following formula (II):

And a copolymer or mixture containing 50 to 95 mol% of the repeating unit represented by the above formula (I) based on the sum of the above formulas (I) and (II), A preferable range is 60 to 95 mol%, more preferably 70 to 90 mol%.

よりなる群から選ばれる少なくとも一種の基である。ここで、Ｙ中のＲ^１７〜Ｒ^１９、Ｒ^２１およびＲ^２２は、それぞれ独立に、水素原子、ハロゲン原子、またはアルキル基、アリール基の如き炭素数１〜２２の炭化水素基であり、Ｒ^２０およびＲ^２３はアルキル基、アリール基の如き炭素数１〜２０の炭化水素基であり、また、Ａｒ^１〜Ａｒ^３は、それぞれ独立に、フェニル基の如き炭素数６〜１０のアリール基である。 In the above formula (II), R ^{9 to} R ¹⁶ are each independently at least one group selected from the group consisting of a hydrogen atom, a halogen atom, and a hydrocarbon group having 1 to 22 carbon atoms, and Y represents the following formula: Groups represented by each of the groups:

And at least one group selected from the group consisting of: Here, R ^{17 to} R ¹⁹ , R ²¹ and R ²² in Y are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group having 1 to 22 carbon atoms such as an alkyl group or an aryl group, and R ²⁰ and R ²³ are each a hydrocarbon group having 1 to 20 carbon atoms such as an alkyl group or an aryl group, and Ar ^{1 to} Ar ³ are each independently an aryl group having 6 to 10 carbon atoms such as a phenyl group. is there.

  Further, a biaxial optical film having a refractive index in the thickness direction larger than the refractive index in any direction in the plane, and the absolute value of the phase difference increases with increasing wavelength, Preference is given to polymers or polymer mixtures containing the repeating units represented by III). Here, the polymer and the polymer mixture are preferably a copolymer or a mixture containing 50 to 95 mol% of the repeating units represented by the following formula (III), respectively, based on the total repeating units of the polymer or polymer mixture, and a more preferable range is 60. It is -95 mol%, More preferably, it is 70-90 mol%. More preferably, the repeating unit is composed of repeating units represented by the following formula (III) and the above formula (II), and the repeating unit represented by the following formula (III) based on the sum of the above formulas (III) and (II) is 50 to What contains 95 mol% is preferable, More preferably, it is 60-95 mol%, More preferably, it is 70-90 mol%.

ここでＲ^４０、Ｒ^４１は炭素数１〜３のアルキル基またはアルコキシ基、またはニトロ基またはハロゲン原子を表し、そしてｌおよびｋは互いに独立に、０〜３の整数である。

Here, R ⁴⁰ and R ⁴¹ each represents an alkyl group or alkoxy group having 1 to 3 carbon atoms, or a nitro group or a halogen atom, and l and k are each independently an integer of 0 to 3.

  The above-mentioned polycarbonate is suitably produced by a method by polycondensation of a dihydroxy compound and phosgene, a melt polycondensation method, a solid phase polymerization method or the like. In the case of a polymer mixture (blend), a compatible blend is preferable, but even if it is not completely compatible, it is possible to suppress light scattering between components and improve transparency by adjusting the refractive index between components. .

  Another preferred material for the biaxial optical film is to use a blend of polyphenylene oxide and polystyrene. The stereoregularity of polystyrene may be any of atactic, syndiotactic and isotactic. The blend of polyphenylene oxide and polystyrene is a biaxial optical film whose refractive index in the thickness direction is larger than any refractive index in the in-plane direction, and the absolute value of the retardation is monotonous with respect to the wavelength, depending on the blend ratio. It is possible to make an increase.

  The optical film of the present invention may further contain an ultraviolet absorber such as phenyl salicylic acid, 2-hydroxybenzophenone, triphenyl phosphate, a bluing agent for changing the color, an antioxidant and the like.

  The thickness of the optical film is preferably 1 μm to 400 μm. In addition, the optical film in this invention is used by the meaning containing both what is called a "sheet" and a "board". Considering the handling of the film, the thickness is preferably 20 to 130 μm, more preferably 30 to 100 μm, still more preferably 40 to 90 μm.

  In general, the polarizing plate preferably has a structure in which a polarizing layer is sandwiched between a pair of films made of cellulose acetate or the like as a film for protecting the polarizing layer (hereinafter sometimes referred to as a protective film for a polarizing layer). It is used for. As the polarizing layer of the polarizing plate, an appropriate layer capable of obtaining light in a predetermined polarization state can be used. In particular, those capable of obtaining transmitted light in a linearly polarized state are preferable. Examples of polarizing layers include iodine and / or dichroic dye adsorbed on hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films. And a polarizing layer composed of a polyene-oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride.

  When a protective film for a polarizing layer is present on the polarizing plate, the optical anisotropy is preferably as small as possible. Specifically, the in-plane retardation is 10 nm or less, more preferably 7 nm or less, and most preferably 5 nm or less. Rth is preferably 70 nm or less, more preferably 50 nm or less, and most preferably 40 nm or less. Furthermore, it is preferable that the slow axis in the film plane of the protective film for polarizing layers is orthogonal or parallel to the absorption axis of a polarizing plate, and it is more preferable when performing parallel production of a polarizing plate that it is parallel. Examples of the protective film for the polarizing layer include polycarbonate, polystyrene, syndiotactic polystyrene, amorphous polyolefin, polymer having norbornene skeleton, organic acid substituted cellulose, polyethersulfone, polyarylate, polyester, olefin maleimide And a copolymerized olefin maleimide-based organic acid-substituted cellulose having a phenyl group are used, and cellulose acetate is preferred.

  In the present invention, the biaxial optical film having a refractive index in the thickness direction larger than the refractive index in any direction in the plane and the negative substantially uniaxial optical film having an optical axis in the plane are included. A negative substantially uniaxial optical film integrated with a polarizing plate and having an optical axis in the plane; a biaxial optical film having a refractive index in the thickness direction larger than the refractive index in any direction in the plane; The angle formed by the in-plane slow axis of the negative substantially uniaxial optical film and the in-plane slow axis of the biaxial optical film is approximately 90 °. A laminated polarizing plate having an in-plane slow axis and an absorption axis of the polarizing plate of about 0 ° is provided.

In the laminated polarizing plate of the present invention, the protective film for the polarizing layer on the side in contact with the biaxial optical film may be omitted, and the biaxial optical film may also serve as the protective film for the polarizing layer. This also has the advantage that the optical design becomes easier. In this case, Rth ₂ (λ) may be considered as 0 in the above formula (1). Similarly, when the protective film for the polarizing layer on the liquid crystal cell side of the first polarizing plate is not used, Rth ₁ (λ) may be considered to be 0 in the above formula (2).

  The laminated polarizing plate of the present invention can be formed by an appropriate method such as a method of sequentially laminating a retardation film and a polarizing plate in the course of manufacturing a liquid crystal display device, or a method of using it as a laminate in advance. The latter pre-lamination method has advantages such as excellent quality stability and laminating workability, and can improve the manufacturing efficiency of the liquid crystal display device.

  As a method for producing a negative uniaxial optical film having an optical axis in the plane, it is preferable to produce a material having negative molecular polarizability anisotropy by uniaxial stretching. By continuously producing a film made of a material having a negative molecular polarizability anisotropy in the transverse uniaxial direction, the optical axis is parallel to the in-plane direction with respect to the film width direction, and the slow axis is in the direction perpendicular thereto. Will exist. Similarly, a biaxial optical film can be obtained by biaxially stretching or uniaxially stretching a film made of a material having negative molecular polarizability anisotropy. And roll-to-roll pasting. In addition, a material having a negative molecular polarizability anisotropy is, for example, a polymer liquid crystal and subjected to an alignment treatment, or a polymerized liquid crystal that has been aligned and then cured is used as the optical film of the present invention. Also good.

  When laminating the polarizing plate and the optical film, they can be fixed via an adhesive or the like as necessary. From the standpoint of preventing axial misalignment, it is preferable to bond and fix. For the adhesion, for example, a transparent adhesive such as polyvinyl alcohol, modified polyvinyl alcohol, organic silanol, acrylic or silicone, polyester or polyurethane, polyether or rubber can be used. There is no particular limitation on. From the standpoint of preventing changes in optical properties, those that do not require high-temperature processes during curing and drying are preferred, and those that do not require long-time curing or drying treatments are desirable. Moreover, what does not produce peeling | exfoliation etc. on heating or humidification conditions is preferable.

  When triacetyl cellulose (TAC) is used as the protective film for the polarizing layer, TAC and retardation film adhesives include butyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate and ( An acrylic pressure-sensitive adhesive composed of an acrylic polymer having a weight average molecular weight of 100,000 or more and a glass transition temperature of 0 ° C. or less, which contains a monomer such as (meth) acrylic acid, can be particularly preferably used. An acrylic pressure-sensitive adhesive is also preferable from the viewpoint of excellent transparency, weather resistance, heat resistance, and the like.

  Adhesives may be appropriately selected from fillers and pigments made of natural or synthetic resins, glass fibers and glass beads, metal powders and other inorganic powders, colorants, antioxidants, and the like as required. Additives can also be blended. In addition, each layer such as the above polarizer, retardation film, polarizing plate protective film, adhesive layer is, for example, a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex compound, etc. An ultraviolet absorbing function can be provided by a method of treating with an ultraviolet absorber.

  The method for producing the liquid crystal display device of the present invention may be a normal method. That is, the liquid crystal display device is formed by appropriately assembling components such as a liquid crystal cell, a polarizing plate, an optical film, and an illumination system as necessary, and incorporating a drive circuit.

  The forming parts of the liquid crystal display device may be laminated and integrated, or may be in a separated state. In forming the liquid crystal display device, for example, appropriate optical elements such as a diffusion plate, an antiglare layer, an antireflection film, a protective layer, a protective plate, and a color filter can be appropriately disposed.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
(Evaluation method)
The material characteristic values and the like described in the present specification are obtained by the following evaluation methods.
(1) Measurement of retardation value (Γ (λ) = Δn · d (nm)), Rth (λ), Nz (λ) value A retardation value Γ value which is a product of birefringence Δn and film thickness d, and Nz was measured by a trade name “M150” manufactured by JASCO Corporation, a spectroscopic ellipsometer. The Γ (λ) value was measured in a state where the incident light beam and the film surface were orthogonal. In addition, Nz (λ) and Rth (λ) values (nm) are measured by measuring the phase difference value at each angle by changing the angle between the incident light beam and the film surface, and by using a known refractive index ellipsoidal equation, curve fitting seek _{n x, n y, n z} is a three-dimensional refractive index by packaging the following formula (7) was obtained by substituting (12).
_{Nz (λ) = (n x} -n z) / (n x -n y) (7)
Rth (λ) = {(n _x + _ny ) / 2−n _z } × d (12)

(2) Method 1 for producing negative substantially uniaxial optical film and biaxial optical film
A copolymer polycarbonate having a fluorene skeleton was used as the resin material for the optical film. The polymerization of the polycarbonate was performed by an interfacial polycondensation method using a known phosgene. A reaction vessel equipped with a stirrer, a thermometer and a reflux condenser was charged with an aqueous sodium hydroxide solution and ion-exchanged water, and the monomers [A] and [B] having the above structure were dissolved in this at a molar ratio of 86:14, A small amount of hydrosulfite was added. Next, methylene chloride was added thereto, and phosgene was blown in at about 20 ° C. over about 60 minutes. Further, p-tert-butylphenol was added to emulsify, and then triethylamine was added and stirred at 30 ° C. for about 3 hours to complete the reaction. After completion of the reaction, the organic phase was collected, and methylene chloride was evaporated to obtain a polycarbonate copolymer. The composition ratio of the obtained copolymer was almost the same as the charged amount ratio.

  This copolymer was dissolved in methylene chloride to prepare a dope solution having a solid concentration of 18% by weight. A cast film was produced from this dope solution to obtain an unstretched film. The residual solvent amount of this unstretched film was 0.9% by weight. The film was stretched at a stretching temperature of 225 ° C., and the stretching ratio was set so that the retardation value shown in Table 1 was obtained, and the film was uniaxially stretched, whereby a first negative substantially uniaxial property having an in-plane optical axis. An optical film was obtained. Similarly, a biaxial optical film was obtained by setting the stretching ratio so that the retardation values shown in Table 1 were obtained and biaxially stretching.

(3) Production method 2 of biaxial optical film
Polystyrene and polyphenylene oxide were adjusted to a weight ratio of 74.5 to 25.5, respectively, and dissolved in a chloroform solvent to prepare a dope solution having a concentration of 23% by weight. A cast film was produced from this dope solution to obtain an unstretched film. The residual solvent amount of this unstretched film was 1.4% by weight. The biaxial optical film used in Example 5 was produced by biaxially stretching the film at a stretching temperature of 130 ° C.

[Examples 1 to 3]
In the liquid crystal display device having the structure shown in FIG. 4, a negative substantially uniaxial optical film having an in-plane optical axis, a liquid crystal cell in a black state, a refractive index in the thickness direction in any direction in the plane The in-plane retardation values of the biaxial optical film larger than the ratio are respectively Γ ₁ (λ), Γ _LC (λ), Γ ₂ (λ), and the liquid crystal cell side of the first and second polarizing plates Are present, the retardation values in the thickness direction of the protective films for polarizing layers are Rth ₁ (λ) and Rth ₂ (λ), respectively, and the optical axis is in-plane. Nz values of a negative substantially uniaxial optical film having a refractive index and a biaxial optical film in which the refractive index in the thickness direction is larger than the refractive index in the direction in the plane are Nz ₁ and Nz ₂ , respectively. Change the value as shown in Table 1 In the black state of the PS liquid crystal cell, the incident angle dependence of the transmittance at a wavelength 450,550,650Nm (about light leakage) was calculated and compared to the actual liquid crystal display device. Here, the purpose is to enlarge the viewing angle and to suppress the color shift, and in order to show the effect, the result of calculating the wavelength dependence of the transmittance when the azimuth is changed at a polar angle of 60 ° is shown. To. The calculation conditions of Examples 1 to 3 are shown in Table 1, and the results correspond to FIGS. The case where Rth (λ) is 0 is the case where the protective film for the polarizing layer is not used. In this calculation, the retardation wavelength dispersion and retardation value of this retardation film were measured data of a retardation film made of a polycarbonate copolymer polymerized by the above production method 1. As for the retardation wavelength dependency of the liquid crystal cell, in Examples 1 to 3, a liquid crystal of a product name “W32-L7000” manufactured by Hitachi, Ltd., which is a commercially available normally black mode and IPS mode liquid crystal television. The phase difference chromatic dispersion of the cell was measured and used for the calculation. The polarization degree of the polarizing plate was 100%, and the transmittance of each polarizing plate was 50%. The definition of the azimuth is shown in FIG.

  From the above calculation results, the transmittance at 550 nm, which has the highest human eye visibility, is low, less than 0.2%, and the transmittance at all three wavelengths is less than 1%. It can be seen that the system has been realized. In addition, it can be seen that the wavelength 450 nm, which is the wavelength representative of the three primary colors of light, is always large with respect to the change in azimuth, and the color change such as blue and red does not occur depending on the azimuth. Further, it can be seen that the difference in the azimuth angle dependency of the incident angle depending on the wavelength is remarkably small as compared with a comparative example described later. This result indicates that the color tone hardly changes depending on the azimuth angle, and indicates that the color shift is greatly suppressed.

  Actually, the calculation shown in Table 1 was performed using a liquid crystal cell having a product name “W32-L7000” manufactured by Hitachi, Ltd., which is a commercially available liquid crystal television having substantially the same retardation value as the liquid crystal cells of Examples 1 to 3. A liquid crystal display device having the same configuration and each phase difference value was produced, and the viewing angle and color shift in the black state were confirmed by visual observation. It was confirmed that the color shift was extremely small. It was also found that these liquid crystal display devices have little color shift even in halftone and white display.

[Example 4]
As in Examples 1 to 3, in the liquid crystal display device having the structure shown in FIG. 8, the first negative substantially uniaxial optical film having an in-plane optical axis, the liquid crystal cell in the black state, the thickness direction The parameters relating to the retardation value of the biaxial optical film in which the refractive index of the biaxial optical film is larger than the refractive index in any direction in the plane are set as shown in Table 1, and the wavelength in the black state of the normally black mode IPS liquid crystal cell is set. The incident angle dependence of the transmittance (degree of light leakage) at 450, 550 and 650 nm was calculated and compared with an actual liquid crystal display device. In this calculation, the measurement data of the optical film made of the polycarbonate copolymer polymerized by the production method 1 was used for the retardation wavelength dispersion and retardation value of these optical films. Moreover, the phase difference wavelength dispersion of the liquid crystal cell of the brand name "W28-L5000" by Hitachi, Ltd. which is a commercially available liquid crystal television was measured, and they were used for calculation. The results are shown in FIG. The transmittance of 550 nm, which has the highest human eye visibility, is as low as less than 0.1%, and the transmittance at all three wavelengths is less than 0.5%, realizing a wide viewing angle. I understand that. In addition, it can be seen that the wavelength 450 nm, which is the wavelength representative of the three primary colors of light, is always large with respect to the change in azimuth, and the color change such as blue and red does not occur depending on the azimuth. Further, it can be seen that the difference in the azimuth angle dependency of the incident angle depending on the wavelength is remarkably small as compared with a comparative example described later. This result indicates that the color tone hardly changes depending on the azimuth angle, and indicates that the color shift is greatly suppressed.

  Next, using a liquid crystal cell having a product name “W28-L5000” manufactured by Hitachi, Ltd., which is a commercially available normally black mode and IPS mode liquid crystal television having substantially the same retardation value as the calculated liquid crystal cell, Table 1 A liquid crystal display device having the same configurations and phase difference values as those described above was actually manufactured, and the viewing angle and the color shift in the black state were confirmed by visual inspection. It was confirmed that the color shift was remarkably small with a wide viewing angle. It was also found that this liquid crystal display device has little color shift even in halftone and white display.

[Example 5]
Using the product name “W32-L7000” manufactured by Hitachi, Ltd., which is a commercially available normally black mode and IPS mode liquid crystal television as the liquid crystal cell used for the calculation and the liquid crystal cell used for the actual measurement, the configuration of FIG. Evaluation was performed in the same manner as in Example 4 except that the measurement value of the optical film produced by the production method 2 was used as the biaxial optical film. The calculation results are shown in FIG. Compared with Examples 1 to 4 and the comparative example described later, it can be seen that the transmittance is significantly reduced for all three wavelengths.

  Next, using a liquid crystal cell having a product name “W32-L7000” manufactured by Hitachi, Ltd., which is a commercially available normally black mode and IPS mode liquid crystal television having substantially the same retardation value as that of the calculated liquid crystal cell. The liquid crystal display device having the same configuration and each phase difference value as in Table 1 was prepared in the same manner as in No. 4, and the viewing angle and color shift in the black state were visually confirmed. Compared to Comparative Example 1 to be described later As with the calculation results, it was confirmed that the viewing angle was wide and the color shift was remarkably small. It was also found that this liquid crystal display device has little color shift even in halftone and white display. In FIG. 11, the dependency of the transmittance of each wavelength depending on the azimuth angle is different, but since each transmittance is remarkably low, it seems that color shift is not a problem. That is, it was confirmed that a wide viewing angle and a wide band can be realized.

[Comparative example]
The liquid crystal cell and the optical film used in the product name “W28-L5000” manufactured by Hitachi, Ltd., which is a commercially available liquid crystal television having the configuration of FIG. 12, were measured, and these physical properties were used in the same manner as in the examples. FIG. 13 shows the results of wavelength dependence of transmittance obtained by calculation. Table 2 shows the physical property values used for the calculation. The definition of the azimuth is shown in FIG. In the calculation, a biaxial optical film having an Nz (λ) of 0.3 and an in-plane retardation value of 135 nm was used in the same manner as the retardation film used in the product. The wavelength dependence of the retardation of the biaxial optical film was Γ (450) / Γ (550) = 1.08 and Γ (650) / Γ (550) = 0.98. From FIG. 13, it can be seen that the azimuth angle dependence of the maximum transmittance varies greatly depending on the wavelength, and the color tone varies depending on the azimuth angle. The commercially available product was visually checked for black viewing angle and color shift. When viewed from an oblique direction, depending on the azimuth angle, black changed to bluish black or reddish black, and it was found that the color shift was very large compared to the examples.

  The liquid crystal display device of the present invention is excellent in display quality, particularly viewing angle performance, and is useful for, for example, a liquid crystal television, a liquid crystal monitor, a display for mobile terminals, a display for mobile phones, a display for car navigation, and the like.

It is an example of the schematic of the liquid crystal display device of the normally black mode in-plane switching system of this invention. It is an example of a structure optically substantially equivalent to the normally black mode in-plane switching type liquid crystal display device of the present invention. It is a figure explaining the orthogonal coordinate for the definition of the three-dimensional refractive index of the phase difference film in this invention. FIG. 3 is a layout diagram of optical elements of liquid crystal display devices in Examples 1 to 3. It is the figure which showed the azimuth and wavelength dependence of the transmittance | permeability of the incident light of the polar angle of 60 degrees in Example 1. FIG. It is the figure which showed the azimuth and wavelength dependence of the transmittance | permeability of the incident light of the polar angle of 60 degrees in Example 2. FIG. It is the figure which showed the azimuth and wavelength dependence of the transmittance | permeability of the incident light of the polar angle of 60 degrees in Example 3. FIG. 10 is a layout diagram of optical elements of a liquid crystal display device in Example 4. It is the figure which showed the azimuth and wavelength dependence of the transmittance | permeability of the incident light of the polar angle of 60 degrees in Example 4. FIG. 10 is a layout diagram of optical elements of a liquid crystal display device in Example 5. It is the figure which showed the azimuth and wavelength dependence of the transmittance | permeability of incident light with a polar angle of 60 degrees in Example 5. It is an arrangement view of optical elements of a liquid crystal display device in a comparative example. It is the figure which showed the azimuth and wavelength dependence of the transmittance | permeability of the incident light of the polar angle of 60 degrees in a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st polarizing plate 2 IPS mode liquid crystal cell 3 Negative substantially uniaxial optical film 4 which has an optical axis in a plane 2 Biaxial whose refractive index of thickness direction is larger than the refractive index of any direction in a plane Optical film 5 Second polarizing plate 6 Absorption axis 7 of polarizing plate Slow axis 8 in phase of retardation film Slow axis 9 in IPS mode liquid crystal cell in black state Emitted from light source, liquid crystal display Light incident on the device 10 First polarizing plate 11 Positive having an optical axis in a plane that can be regarded as equivalent to a combination of a negative substantially uniaxial optical film having an optical axis in the plane and an IPS mode liquid crystal cell Substantially uniaxial optical film 12 biaxial optical film 13 whose refractive index in the thickness direction is larger than the refractive index in any direction in the plane second polarizing plate 14 absorption axis 15 of polarizing plate in plane of retardation film Slow axis 30 in Phase difference film 3 DESCRIPTION OF SYMBOLS 1 Surface 41 of retardation film 2nd polarizing plate 42 Bipolar optical film side polarizing layer protective film 43 Biaxial optical film 44 Negative substantially uniaxial optical film 45 having an optical axis in the plane IPS liquid crystal Cell 46 Polarizing layer protective film 47 on the IPS liquid crystal cell side First polarizing plate 48 Light emitted from the light source and incident on the liquid crystal display device 49 Absorption axis 50 of the polarizing plate In-plane retardation of the polarizing layer protective film Axis 51 Slow axis 52 in the plane of the retardation film Slow axis 55 in the plane of the IPS liquid crystal cell in the black state Transmittance 56 at a polar angle of 60 ° and a wavelength of 450 nm in the black state of the liquid crystal display device of Example 1 Polarity 60 in the black state of the liquid crystal display device of Example 1 and transmittance 57 at a wavelength of 550 nm Polarity angle in the black state of the liquid crystal display device of Example 1 at 60 ° and wavelength 650 nm Transmittance 61 Polarity 60 ° in the black state of the liquid crystal display device of Example 2 and transmittance 62 at a wavelength of 450 nm Transmittance 62 in the black state of the liquid crystal display device of Example 2 transmittance 63 at a wavelength of 550 nm in Example 2 The liquid crystal display device of Example 3 has a polar angle of 60 ° and a transmittance of 71 at a wavelength of 650 nm. The liquid crystal display device of Example 3 has a polar angle of 60 ° and a transmittance of 72 at a wavelength of 450 nm. Polarity 60 in state and transmittance 73 at wavelength 550 nm Polarity 60 in black state of liquid crystal display device of Example 3 and transmittance at wavelength 650 nm 81 First polarizing plate 82 IPS mode liquid crystal cell 83 In plane Negative substantially uniaxial optical film 84 having an optical axis Biaxial optical film 85 having a refractive index in the thickness direction larger than any in-plane refractive index Second polarizing plate 86 Absorption axis 87 of polarizing plate Slow axis 88 in plane of retardation film Slow axis 89 in plane of IPS mode liquid crystal cell in black state Emitted from light source and incident on liquid crystal display device Light 91 Polarity 60 ° in the black state of the liquid crystal display device of Example 4 and transmittance 92 at a wavelength of 450 nm The transmittance of the liquid crystal display device of Example 4 in the black state 60 ° and transmittance at wavelength 550 nm 93 Example 4 Transmittance of the liquid crystal display device in the black state at a polar angle of 60 ° and a wavelength of 650 nm 101 Second polarizing plate 102 A biaxial optical film 103 having a refractive index in the thickness direction larger than any in-plane refractive index Negative uniaxial optical film 104 having an optical axis in the IPS mode liquid crystal cell 105 First polarizing plate 106 Absorption axis 107 of polarizing plate In the plane of the retardation film Phase axis 108 Slow axis 109 in the plane of the IPS mode liquid crystal cell in the black state 111 Light emitted from the light source and incident on the liquid crystal display device Polar angle 60 ° in the black state of the liquid crystal display device of Example 5, wavelength Transmittance 112 at 450 nm Polarity 60 ° in the black state of the liquid crystal display device of Example 5 and transmittance 113 at the wavelength 550 nm 113 Polarity 60 ° in the black state of the liquid crystal display device of Example 5 Transmittance 141 at the wavelength 650 nm Polarization Plate 142 Protective film for polarizing layer 143 Biaxial optical film 144 IPS liquid crystal cell 145 Protective film for polarizing layer 146 Polarizing plate 147 Light 148 emitted from light source and incident on liquid crystal display device Absorption axis 149 of polarizing plate For polarizing layer Slow axis 150 in the plane of the protective film Slow axis 151 in the plane of the biaxial optical film In the black state The slow axis 161 in the plane of the PS liquid crystal cell The transmittance 162 at a black angle of 60 ° and a wavelength of 450 nm of the liquid crystal display device of the comparative example The polar angle of 60 ° and the wavelength of 550 nm at the wavelength of 450 nm of the liquid crystal display device of the comparative example Transmittance 163 Transmittance at a polar angle of 60 ° and a wavelength of 650 nm in the black state of the liquid crystal display device of the comparative example.

Claims (7)

  A first polarizing plate, a liquid crystal cell, a negative substantially uniaxial optical film having an optical axis in the plane, a biaxial optical film having a refractive index in the thickness direction larger than the refractive index in any direction in the plane, A normally black mode in-plane switching mode liquid crystal display device in which these are laminated in the order of a second polarizing plate, the absorption axis of the first polarizing plate and the in-plane retardation of the liquid crystal cell in the black state The angle formed by the phase axis is approximately 90 °, the angle formed by the in-plane slow axis of the liquid crystal cell in the black state and the slow axis of the negative approximately uniaxial optical film is approximately 90 °, and the approximately negative uniaxial property. The angle formed by the slow axis of the optical film and the in-plane slow axis of the biaxial optical film is approximately 90 °, and the in-plane slow axis of the biaxial optical film and the absorption axis of the second polarizing plate A liquid crystal display device having an angle of approximately 0 °. The in-plane retardation values of the negative substantially uniaxial optical film, the liquid crystal cell in the black state, and the biaxial optical film are Γ ₁ (λ), Γ _LC (λ), and Γ ₂ (λ), respectively. When the first and second polarizing plates each have a polarizing layer protective film on the liquid crystal cell side, the retardation values in the thickness direction of the polarizing layer protective film are Rth ₁ (λ) and Rth ₂ (λ ), The relationship of the following formulas (1) and (2) is satisfied.
−120 <Γ ₂ (λ) + Rth ₂ (λ) / 2 <30 nm (1)
45 <Γ _LC + Γ ₁ (λ) + Rth ₁ (λ) <155 nm (2)
(However, λ = 550 nm) When the in-plane retardation values of the negative substantially uniaxial optical film, the liquid crystal cell in the black state, and the biaxial optical film are Γ ₁ (λ), Γ _LC (λ), and Γ ₂ (λ), respectively, 3. The liquid crystal display device according to claim 1, wherein the relationship of the formula (3) and / or (4) is satisfied.
| Γ ₂ (λ ₁ ) | <| Γ ₂ (λ ₂ ) | (3)
| Γ _LC (λ ₁ ) + Γ ₁ (λ ₁ ) | <| Γ _LC (λ ₂ ) + Γ ₁ (λ ₂ ) | (4)
(However, λ represents the measurement wavelength, and 400 nm ≦ λ ₁ <λ ₂ ≦ 700 nm.)   The negative substantially uniaxial optical film which has an optical axis in the surface used for the liquid crystal display device in any one of Claims 1-3.   The biaxial optical film whose refractive index of the thickness direction used for the liquid crystal display device in any one of Claims 1-3 is larger than the refractive index of any direction in a surface.   6. The optical film according to claim 4 or 5, comprising a polycarbonate having a fluorene skeleton.   A laminated polarizing plate in which the optical film according to claim 4, 5 or 6 and a polarizing plate are integrated, a negative substantially uniaxial optical film having an optical axis in a plane, and a refractive index in a thickness direction. A biaxial optical film having a refractive index larger than the refractive index in any direction in the plane and a polarizing plate are laminated in this order, and the in-plane slow axis of the negative substantially uniaxial optical film and the biaxial optical film A laminated polarizing plate, characterized in that the angle formed by the in-plane slow axis is about 90 °, and the in-plane slow axis of the biaxial optical film and the absorption axis of the polarizing plate are about 0 °.

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