JP3203490B2 - Phase difference plate and liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel retardation plate used for a liquid crystal display or the like.

[0002]

2. Description of the Related Art A phase difference plate is disclosed in JP-A-63-189804, JP-A-1-96623, and JP-A-1-118.
No. 805, etc., a polymer film having optical homogeneity and durability and having uniaxial orientation, which is used as an optical compensator for improving the display quality of a liquid crystal display device. ing. STN using phase difference plate
A (super twisted nematic) type liquid crystal display device has advantages such as lightness, thinness, and low cost as compared with a two-layer STN type liquid crystal display device in which two liquid crystal cells are stacked, but has poor viewing angle characteristics. It had disadvantages such as inferior black and white levels. These disadvantages have been considerably improved by a method such as laminating two retardation plates, but the viewing angle characteristics have not yet reached a satisfactory level.

The viewing angle characteristics of a liquid crystal display device not only depend on the angle dependence of the birefringence of a liquid crystal cell, but also the birefringence of a retardation plate.
That is, it depends on the angle dependence of the retardation, and it is known that the smaller the angle change of the retardation is, the more preferable in the conventional retardation plate. In recent years,
As described in JP-A-191914, JP-A-2-285303, etc., a method of shrinking a film in a direction perpendicular to a stretching axis at the time of uniaxial stretching, or a method of forming a liquid polymer material under application of an electric field. By using various methods such as a method of controlling the birefringence characteristics by stretching the film that has been stretched, it has been studied to improve the viewing angle characteristics by reducing the angle change of the retardation of the retardation plate,
Many of these methods have problems in mass productivity, and few of them can be expected to greatly improve the viewing angle characteristics.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a retardation plate having not only excellent viewing angle characteristics but also mass productivity.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, have found that a birefringent film having an optically positive refractive index anisotropy and a negative refractive index anisotropic material. By using a birefringent film having the property to be laminated so that the slow axis in each film plane is in the same direction,
Discovered that a phase difference plate with good viewing angle characteristics can be obtained,
This has led to the present invention.

In order to evaluate the viewing angle characteristics of a birefringent film, a polarizing microscope equipped with a Senarmont compensator is used to set a slow axis for a birefringent film having a positive refractive index anisotropy. In the case of a birefringent film having a negative refractive index anisotropy, the retardation (R) measured in a state where the fast axis is inclined with respect to each of the rotation axes.
And the tilt angle (θ _1.10 ) when the ratio (R / R ₀ ) of the retardation (R ₀ ) measured in a horizontal state is 1.10, and this value is referred to as the viewing angle of the film. The smaller the angle change of the retardation, the larger this θ _1.10 , that is, the better the viewing angle characteristics.

The viewing angle of the conventional retardation plate is 37 to 42 ° when stretched by the longitudinal uniaxial stretching method, 42 ° even when complete uniaxial orientation is provided, and 20 ° when stretched by the tenter stretching method. Only those of ~ 37 ° were obtained.

The present inventors have found that the retardation change of a birefringent film having a positive refractive index anisotropy is positive when measured with the slow axis in the plane of the film as the rotation axis. On the other hand, a birefringent film having a negative refractive index anisotropy is negative, and similarly a birefringent having a positive refractive index anisotropy when measured with the fast axis as an axis. Focusing on the phenomenon that the change in the retardation of the birefringent film is negative while that of the birefringent film having a negative refractive index anisotropy is positive, the slow axes of the two films are the same. When the films are stacked so that they are oriented in the same direction, the change in retardation that occurs in each film due to the tilting compensates each other, so that the change in overall retardation is very small, and the viewing angle characteristics are excellent. The retarder is It was found that to be. That is, the present invention, the birefringent film having an optically positive refractive index anisotropy and the birefringent film having a negative refractive index anisotropy, the slow axis in each film plane is the same And a retardation (R ₀ ) measured from a direction perpendicular to the film surface and a retardation measured from a direction inclined from the vertical axis by θ degrees with the slow axis as a rotation axis (R ₀ ). R) and (R / R ₀ ) is 1.
10, the angle (θ _1.10 ) is 42 ° or more, and at least one of a birefringent film having an optically positive refractive index anisotropy and a birefringent film having a negative refractive index anisotropy. The refractive film has a retardation (R ₀ ) measured from a direction perpendicular to the film surface, a slow axis in the case of a birefringent film having a positive refractive index anisotropy, and a negative refractive index anisotropy. In the case of a birefringent film having properties, the ratio (R / R ₀ ) to the retardation (R) measured from a direction inclined by θ degrees from the vertical axis with the fast axis as the rotation axis is 1.10. The retardation plate is a birefringent film having an anisotropy of refractive index having a biaxial orientation of 37 ° or less (θ _1.10 ).

Examples of the birefringent film having a positive refractive index anisotropy used in the present invention include polyester resins such as polycarbonate resins, polyethylene terephthalate and polyester copolymers, nylon 6, nylon 6
And a film made of a polyamide resin such as No. 6, a polysulfone, a polyethersulfone, a polyarylate, or a modified product thereof, which is oriented by stretching or the like. Further, the birefringent film having a negative refractive index anisotropy used in the present invention is obtained by, for example, copolymerizing another ethylene comonomer with polymethyl methacrylate and methyl (meth) acrylate as main components ( Poly (meth) acrylate resins such as methyl (meth) acrylate copolymer, polystyrene resins such as styrene copolymers obtained by copolymerizing polystyrene, styrene as a main component and other ethylene comonomers, and these And those obtained by orienting a film made of a modified product of the above by stretching or the like. Above all, in view of the manifestation of birefringence, strength, heat resistance, etc., birefringent films having a positive refractive index anisotropy include polycarbonate, polysulfone, polyether sulfone, and a negative refractive index anisotropy. Polystyrene and polymethyl methacrylate are preferred as the birefringent film having

As a stretching method for orienting a film having a positive or negative refractive index anisotropy used in the present invention to obtain a birefringent film, any stretching method capable of obtaining uniform retardation can be used. Any of known methods such as a tenter stretching method, a roll-to-roll stretching method, and a roll-to-roll compression stretching method may be used, but the tenter stretching method is most preferable in terms of homogeneity and imparting biaxial orientation.

In the present invention, a laminated film obtained by laminating birefringent films having positive and negative anisotropy of refractive index is used. As an adhesive or pressure-sensitive adhesive for lamination, Any known materials having excellent transparency and durability can be used. FIG. 1 shows an example of a retardation plate according to the present invention using one birefringent film having positive and negative refractive index anisotropy.

The retardation of the retardation plate according to the present invention
Is birefringent with positive and negative refractive index anisotropy
Retardation (R₁, R_Two)
(R ′ = R₁+ R_Two). Also,
θ_1.10Is a composite with positive and negative refractive index anisotropy
Retardation value of each refractive film
(R ₁, R_Two) And adjust the viewing angle characteristics of each
By stacking, each of the individual retardation plates has θ
_1.10Can be set to any value from
You.

At this time, when a film having a relatively good viewing angle characteristic with a viewing angle of 37 to 42 ° is used as the birefringent film having positive and negative refractive index anisotropy, any arbitrary In order to obtain a retardation plate having viewing angle characteristics, it is necessary to laminate films having a significant difference in retardation between films having positive and negative refractive index anisotropy. In particular, in order to obtain a retardation plate having a retardation of 500 nm or less with a viewing angle of 42 to 60 ° when laminated, a birefringent film having either a positive or negative refractive index anisotropy is used. It is necessary to use a material having a date of 40 nm or less.
Since it is very difficult to obtain a birefringent film having the following retardation with uniformity by a normal stretching method, there is a problem in mass productivity.

On the other hand, in the present invention, as a birefringent film having a positive or / and negative refractive index anisotropy, a film having a viewing angle of 20 to 37 ° and a biaxial orientation with a not so good viewing angle characteristic. By using, since it is possible to freely adjust the viewing angle characteristics of the laminated product in a wide range even if the difference in retardation of each film is not large, any viewing angle characteristics, particularly 42 to 60 ° A retardation plate having a viewing angle can be easily obtained. From this, it is possible to ensure the uniformity of the orientation of the film, but when using a birefringent film produced by the tenter stretching method in which in-plane biaxial orientation was inevitable, the optical homogeneity and good arbitrary This technique is very effective because a very excellent retardation plate having the same viewing angle characteristics can be obtained.

The method of mounting the retardation plate of the present invention on a liquid crystal display device is not particularly limited. For example, one or both sides of the retardation plate shown in FIG. And / or a method such as lamination with a polarizing plate may be used. The thus obtained liquid crystal display device (STN type liquid
FIG. 2 shows an example of the crystal display device).

[0016]

【The invention's effect】

As the birefringent film having positive and negative refractive index anisotropy used in the present invention, good viewing angle characteristics can be obtained only by laminating two types of birefringent films having similar viewing angle characteristics. Therefore, the viewing angle characteristics of each film need not be particularly good. For this reason, there is no need to provide complete uniaxial orientation to control the viewing angle characteristics of the conventional retardation plate or to control the orientation in the thickness direction. Conversely, the conventional viewing angle is only 20 to 37 °. Even when using a birefringent film having in-plane biaxial orientation, which was said to have poor viewing angle characteristics, the viewing angle can be easily increased to 42 ° or more compared to the case of each film alone. The viewing angle characteristics can be dramatically improved, and by using this as an optical compensator, the display characteristics of the liquid crystal display device can be significantly improved.

[0018]

EXAMPLES The present invention will be described in detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

The retardation (R ₁ , R ₂ , R ′) of each film and laminate was measured using the polarizing microscope described above. According to the above-mentioned method, the viewing angle is set to the slow axis in the case of a birefringent film having a positive refractive index anisotropy, and to the advance in the case of a birefringent film having a negative refractive index anisotropy. The value of the ratio (R / R) of the retardation (R) measured in a state where the phase axes are each rotated as an axis of rotation and the retardation (R ₀ ) measured in a horizontal state.
R ₀ ) is represented by an inclination angle (θ _1.10 ) when the inclination angle is 1.10.
For films with R ₀ less than 1.10, the ratio value (R ₄₀ / R ₀ ) when the tilt angle was 40 ° was used.

Example 1 A polycarbonate film was stretched for 20 times by a tenter stretching method.
Stretched 1.7 times at 0 ° C., R ₁ = 222 nm, θ _1.10 = 2
A birefringent film having a degree of 6.5 ° and a thickness of 72 μm was obtained. Further, the polystyrene film was stretched 2.5 times at 125 ° C. by a tenter stretching method, and R ₂ = 220 nm, θ _1.10
= 27.5 ° and a thickness of 174 µm. When these two films were laminated such that their slow axes were in the same direction, R ′ = 443 nm, R ₄₀ /
A retardation plate having a very small angle dependence of retardation, R ₀ = 1.02, was obtained.

Example 2 A polycarbonate film was stretched for 20 times by a tenter stretching method.
Stretched 2.1 times at 0 ° C., R ₁ = 392 nm, θ _1.10 = 2
A birefringent film having a thickness of 5.0 ° and a thickness of 75 μm was obtained. Further, the polystyrene film was stretched 2.0 times at 125 ° C. by a tenter stretching method, and R ₂ = 198 nm, θ _1.10
= 27.3 ° and a thickness of 196 µm. When these two films were laminated such that their slow axes were in the same direction, R ′ = 592 nm, θ _1.10
= 45.2 ° was obtained.

Example 3 A polysulfone film was prepared by a tenter stretching method.
At 1.5 ° C., R ₁ = 379 nm, θ _1.10 = 31.
A birefringent film having a thickness of 3 ° and a thickness of 115 μm was obtained.
Further, the polymethyl methacrylate sheet was stretched 2.0 times at 130 ° C. by a tenter stretching method, and R ₂ = 148 nm,
A birefringent film having θ _1.10 = 25.0 ° and a thickness of 1142 μm was obtained. When these two films were laminated such that their slow axes were in the same direction, R '= 527n
A retardation plate with m, θ _1.10 = 50.0 ° was obtained.

Example 4 A polycarbonate film was stretched to 20 by a tenter stretching method.
Stretched 1.7 times at 0 ° C., R ₁ = 227 nm, θ _1.10 = 2
A birefringent film having a degree of 5.2 ° and a thickness of 80 μm was obtained. Further, a polystyrene film was stretched 1.5 times at 122 ° C. by a longitudinal uniaxial stretching method, and R ₂ = 373 nm, θ _1.10 =
A birefringent film having a thickness of 39.5 ° and a thickness of 175 μm was obtained. When these two films were laminated such that their slow axes were in the same direction, R ′ = 549 nm, θ _1.10 =
A phase difference plate of 47.3 ° was obtained.

Example 5 A polycarbonate film was stretched to 197 by a longitudinal uniaxial stretching method.
Stretching at 1.7 ° C., R ₁ = 308 nm, θ _1.10 = 40.
A birefringent film having a thickness of 2 ° and a thickness of 67 μm was obtained. Further, a polystyrene film is stretched to 12 by a tenter stretching method.
Stretched 2.5 times at 5 ° C., R ₂ = 242 nm, θ _1.10 = 2
A birefringent film having a thickness of 8.0 ° and a thickness of 153 μm was obtained. When these two films were laminated such that their slow axes were in the same direction, R ′ = 530 nm and θ _1.10 = 4
A 9.1 ° retardation plate was obtained.

Comparative Example 1 A polycarbonate film was stretched to 198 by a longitudinal uniaxial stretching method.
The film was stretched 1.8 times at ℃ to obtain a birefringent film. The film had θ _1.10 = 41.0 ° at R = 437 nm.

Comparative Example 2 A polycarbonate film was prepared by a tenter stretching method.
The film was stretched 2.0 times at 5 ° C. to obtain a birefringent film. This film had θ _1.10 = 31.9 ° at R = 590 nm.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing a configuration of an example of a phase difference plate according to the present invention.

FIG. 2 is a vertical sectional view showing an example of an STN type liquid crystal display device using a retardation plate according to the present invention.

[Explanation of symbols]

 1. 1. Birefringent polymer film having positive refractive index anisotropy 2. Birefringent polymer film having negative refractive index anisotropy 3. adhesive or pressure-sensitive adhesive Phase difference plate 5. Polarizing plate 6. STN liquid crystal cell

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Higashi 2-10-1, Tsukahara, Takatsuki-shi, Osaka Sumitomo Chemical Industries, Ltd. (72) Akiko Shimizu 2- 10-1 Tsukahara, Takatsuki-shi, Osaka Sumitomo Sumitomo Chemical Industry Co., Ltd. (56) References Yamamoto, et al., 3 phase difference films for LCD, Nitto Giho, October 1990, Vol. 28, No. 2, p. 105-113

Claims (5)

(57) [Claims] 1. A birefringent film having an optically positive refractive index anisotropy and a birefringent film having a negative refractive index anisotropy, wherein the slow axes in the respective film planes are in the same direction. And a retardation (R ₀ ) measured from a direction perpendicular to the film surface and a retardation (R ₀ ) measured from a direction inclined from the vertical axis by θ degrees with the slow axis as a rotation axis. ) And 1.1 (R / R ₀ )
The angle (θ _1.10 ) at which it becomes 0 is at least 42 °, and at least one of a birefringent film having an optically positive refractive index anisotropy and a birefringent film having a negative refractive index anisotropy. The refractive film has a retardation (R ₀ ) measured from a direction perpendicular to the film surface and a positive refractive index anisotropy.
In the case of a birefringent film having
In the case of a birefringent film having a refractive index anisotropy of
With each phase axis as a rotation axis, the ratio (R) to the retardation (R) measured from a direction inclined by θ degrees from the vertical axis.
/ R ₀ ) is a birefringent film having an anisotropy of refractive index having a biaxial orientation of not more than 37 ° at an angle (θ _1.10 ) of _1.10 . 2. The ratio (R / R) of the retardation (R ₀ ) measured from a direction perpendicular to the film surface to the retardation (R) measured from a direction inclined by θ degrees from the vertical axis with the slow axis as a rotation axis. R ₀ ) is 1.10, the birefringent film having a positive refractive index anisotropy having a biaxial orientation of 37 ° or less (θ _1.10 ), and a letter measured from a direction perpendicular to the film surface The ratio (R / R ₀ ) of the retardation (R ₀ ) to the retardation (R) measured from the direction inclined from the vertical axis by θ degrees with the fast axis as the rotation axis is 1.
10 become an angle (theta _1.10) is a retardation plate according to claim 1, characterized by using a birefringent film having a negative refractive index anisotropy having a 37 ° or less of biaxial orientation. 3. theta _1.10 and birefringent film having positive refractive index anisotropy with the 37 ° following the biaxial orientation, theta _1.10
The retardation plate according to claim 1, wherein a birefringent film having a negative refractive index anisotropy having a uniaxial orientation of 37 ° or more and 42 ° or less is used. A birefringent film having positive refractive index anisotropy wherein theta _1.10 is having a 37 ° or 42 ° or less of the uniaxial orientation, theta _1.10 is negative with biaxial orientation of 37 ° or less The retardation plate according to claim 1, wherein a birefringent film having a refractive index anisotropy is used. 5. A liquid crystal display device comprising the retardation plate according to claim 1.