JP2003075635A - Optical film, polarizing plate and display device - Google Patents

Abstract

(57) [Summary] [Problem] A liquid crystal display device having a good display quality by maintaining a good intersection relationship between optical axes (slow axes) even when the viewpoint changes.
Development of an optical film that can form a four-wavelength plate. The in-plane and thickness directions of a film and the refractive indexes thereof are respectively X axis, Y axis, Z axis, nx, ny, nz, film thickness is d, (nx-ny) d = Re, and (nx -nz) / (nx-n
y) = Nz, the birefringent film A having Re of 200 to 350 nm and Nz of 0.1 to 0.4 and Re of 100 to
Birefringent film B having 175 nm and Nz of 0.3 to 0.7
And a polarizing plate obtained by laminating a film having a polarizing function on the side of the birefringent film A in the above-mentioned optical film, and polarizing the polarizing plate with the polarizing plate. A liquid crystal display device or a display device which is disposed on at least one side or the outermost surface of a liquid crystal cell such that a film having a function is on the outside.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical film suitable for forming a liquid crystal display device having good display quality, a circularly polarizing plate or an elliptic polarizing plate, and an antireflection plate, in which axial displacement of a laminated body hardly occurs due to a change in viewpoint. Regarding

[0002]

2. Description of the Related Art Conventionally, in order to improve the display quality of a liquid crystal display device, a phase difference plate disposed between a polarizing plate and a liquid crystal cell, a circular polarizing plate, an antireflection plate, or the like has been formed. In a / 4 wavelength plate or the like, if it is formed of a single birefringent film, the birefringence will also be dispersed according to the wavelength based on the dispersion inherent in the material, and the birefringence will increase as the wavelength becomes shorter. In consideration of the fact that the phase difference differs depending on the wavelength and the change in the polarization state is not uniform, two birefringent films having different birefringence wavelength dispersion characteristics are laminated so that their slow axes are orthogonal to each other. An optical film formed by the above method has been proposed (JP-A-5-27118, JP-A-1).
0-239518).

In the above, by laminating the birefringent film, the wavelength dispersion characteristic of birefringence is controlled so that the birefringence becomes smaller on the shorter wavelength side, and a uniform polarization state change is realized over a wide wavelength band. As a result, it is possible to obtain a uniform compensation effect. On the other hand, it is also known that two retardation plates that give 1/2 wavelength and 1/4 wavelength in monochromatic light are laminated to give a predetermined phase difference in a wide wavelength range (Japanese Patent Laid-Open No. 5-100114). Gazette)

However, although the orthogonal relationship is maintained on the optical axis and a predetermined effect is exhibited, when observed from an oblique direction in a direction deviated from the optical axis, the apparent axial angle is changed and the orthogonal relationship is broken. There is a problem that the polarization state is changed without exerting a predetermined effect. Even if the Nz of the birefringent film is controlled to compensate the axial misalignment with the polarizing plate as in JP-A-5-27118, it is not effective in compensating the axial misalignment of the laminate itself of the birefringent film.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a liquid crystal display device or a quarter-wave plate which has a good display quality because the cross relationship of the optical axes (slow axes) is maintained well even if the viewpoint is changed. The challenge is to develop an optical film that can be formed.

[0006]

According to the present invention, the film thickness direction is set to Z.
Axis, the refractive index in the axial direction is nz, the maximum refractive index direction in the plane perpendicular to the Z axis is the X axis, the refractive index in the axial direction is nx, the direction perpendicular to the X axis and the Z axis is the Y axis, and The refractive index in the axial direction is n
y, film thickness d, (nx-ny) d = Re, and (nx-nz)
When / (nx-ny) = Nz, Re is 200 to 350 nm
So that the optical axes of the birefringent film A having Nz of 0.1 to 0.4 and the birefringent film B having Re of 100 to 175 nm and Nz of 0.3 to 0.7 are intersected. The present invention provides an optical film which is characterized by being laminated on.

The present invention also provides a polarizing plate characterized by laminating a film having a polarizing function on the side of the birefringent film A in the optical film, and the polarizing plate having the polarizing function. A liquid crystal display device characterized by being arranged on at least one side of a liquid crystal cell so that the film is on the outside, and the polarizing plate is arranged on the outermost surface so that the film having the polarizing function is on the outside. The present invention provides a display device characterized by the following.

[0008]

According to the present invention, the birefringent film A
Due to the above-mentioned combination and arrangement of B and B, it is possible to obtain an optical film in which the axial angle is hard to change in the azimuths on which the optical axis and the viewpoint are changed and the phase difference due to birefringence is hard to change in a wide viewing angle range. . As a result, it is possible to obtain a circularly polarizing plate or the like whose polarization characteristics do not easily change depending on the viewing angle or wavelength, or an antireflection plate with little viewing angle dependency.

Further, by using the circularly polarizing plate or elliptic polarizing plate whose polarization characteristics are hard to change over a wide azimuth and a wide wavelength band, it is possible to form a liquid crystal display device or the like which exhibits good display quality in a wide viewing angle. . Further, various display devices having good display quality can be obtained by using the antireflection plate whose circular polarization characteristics and the like are hard to change in a wide azimuth and a wide wavelength band.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The optical film according to the present invention has a Z-axis in the thickness direction of the film and a refractive index of nz, Z in the axial direction.
The maximum refractive index direction in the plane perpendicular to the axis is the X axis, the refractive index in the axial direction is nx, the direction perpendicular to the X and Z axes is the Y axis, the refractive index in the axial direction is ny, and the film thickness is d. , (Nx-ny) d =
When Re and (nx-nz) / (nx-ny) = Nz (hereinafter the same), Re is 200 to 350 nm and Nz is 0.1 to 0.4.
Birefringent film A, with Re of 100-175 nm and Nz
Of the birefringent film B of 0.3 to 0.7 are laminated so that their optical axes intersect.

The optical film can be formed by laminating the birefringent films A and B such that their optical axes intersect. In that case, as the birefringent film A, Re is 200 to 350 nm and Nz is 0.1 to 0.
4, preferably 0.2 to 0.3 is used. The birefringent film B has Re of 100 to 175n.
m, Nz is 0.3 to 0.7, preferably 0.4 to 0.6
What is used.

In the combination of A and B of the birefringent film, there is no particular limitation on the characteristics other than Re and Nz. Therefore, the forming materials of A and B of the birefringent film may be the same or different. When A and B of the birefringent film are made of the same forming material, the wavelength dispersion characteristics of the refractive index or the birefringence are the same,
A combination of those functioning as a ½ wavelength plate (A) and a ¼ wavelength plate (B) for the same wavelength light,
This optical film can be preferably used for forming a circularly polarizing plate and the like. When the birefringent film A and B are made of different forming materials, a combination of materials having different refractive index or birefringence wavelength dispersion characteristics can be used.

Further, each of the birefringent films A and B may be a single layer product, or may be one in which two or three or more retardation films are laminated to adjust the above-mentioned characteristics. Good. Also in that case, the retardation films to be laminated may be made of the same material or different materials.

Further, in each of the birefringent films A and B, two or more layers of retardation films forming the birefringent film A or the like are, for example, another birefringent film B or the like or two layers or more forming the same. It may be laminated by a method of alternately arranging with the retardation film of, and the retardation film of two or more layers may not be laminated adjacently.

There is no particular limitation on the film forming the birefringent film, for example, a film made of a polymer such as polycarbonate, polypropylene, polyester, polyvinyl alcohol, polymethylmethacrylate, polyethersulfone, polyarylate or polyimide,
Appropriate materials such as a material having a refractive index anisotropy such as an inorganic material or a liquid crystalline material coated on an isotropic or anisotropic substrate can be used.

Above all, a birefringent film excellent in transparency (light transmittance) is preferable. The birefringent film made of a polymer film can be obtained as a film that has been subjected to an appropriate orientation treatment, such as a film obtained by stretching the film by a uniaxial or biaxial method.

The crossing angle of the optical axis (fast axis or slow axis) between A and B of the birefringent film is not particularly limited.
It can be arbitrarily determined as an orthogonal relationship or an intersection angle of 45 degrees, or an intersection angle other than them. When the crossing angle of the optical axes of A and B of the birefringent film is set to a predetermined value, for example, an orthogonal relationship or the like, an axis deviation or the like due to a work error is allowed. When there are variations in the direction of the optical axis in the birefringent film, the slow axis and the like are determined based on the average direction.

The above Nz can be controlled by adjusting the orientation state of a polymer, such as polycarbonate, which exhibits a positive birefringence with a slow axis appearing in the orientation direction of molecules, by applying an electric field in the thickness direction. It can be performed by a method of changing the refractive index in the thickness direction of the film, such as a method of curing while simultaneously curing and stretching the film. The control of Re is
For example, it can be performed by a forming material, a stretching condition of the film, a method of changing the film thickness, or the like.

Although the birefringent films A and B in the optical film may be simply placed, they are preferably laminated in an adhesively fixed state from the viewpoint of preventing deviation of the optical axis. The lamination method is not particularly limited, and an appropriate method such as an adhesion method using an adhesive or a pressure-sensitive adhesive having excellent transparency can be adopted, and the kind of the adhesive is not particularly limited. From the viewpoint of preventing changes in the optical properties of the birefringent film, those that do not require a high temperature process at the time of curing or drying are preferable, and those that do not require a long curing treatment or drying time are desirable.

As described above, the birefringent film can be formed as a coating film of a material having a refractive index anisotropy, and in that case, A or B of the birefringent film which can serve as a supporting base material. On the other hand, another layer B or A is provided as the coating film, and the birefringent film A
It is also possible to form an optical film comprising B and B.

In the above case, by using the lyotropic liquid crystal as the material having the refractive index anisotropy for forming the coating film, the alignment direction can be controlled by the coating direction based on the shear alignment property, and the predetermined optical axis can be controlled. An optical film having a crossing angle can be formed by a simple operation, which is excellent in manufacturing efficiency. Further, in the case where the coating method is used for adhesion and lamination, a separate adhesive or the like can be omitted, which is advantageous for thinning. As the lyotropic liquid crystal, an appropriate liquid crystal exhibiting the above shear alignment can be used.

The optical film may be formed with a polarizing plate such as a circular polarizing plate or an elliptically polarizing plate or an antireflection plate in accordance with a conventional retardation plate or a wave plate according to the phase difference characteristics thereof.
It can be used for various purposes such as rotation of azimuth (vibration plane) of linearly polarized light, improvement of viewing angle of liquid crystal display and display quality.

In the above case, the optical film can be put to practical use as a polarizing plate laminated with a film having a polarizing function. Such a polarizing plate is capable of reducing changes in polarization characteristics due to viewing angle and wavelength, forming a liquid crystal display device showing good display quality in a wide viewing angle such as all directions, and as an antireflection plate with little characteristic changes due to wavelength. It can be preferably used.

A film having a polarizing function in forming the polarizing plate may be laminated on the side of the birefringent film B in the optical film, but the birefringence is reduced from the viewpoint of reducing the change of the polarization characteristics depending on the viewing angle and the wavelength. It is preferable to laminate it on the side of the conductive film A. In that case, by using an absorption type film having a polarizing function and laminating the film so that its absorption axis is orthogonal to the slow axis of the birefringent film A, the change of the polarization characteristics depending on the viewing angle. It is possible to obtain a particularly small number of circular polarizing plates or elliptically polarizing plates.

Further, in the above, when the polarizing plate is used for a specific purpose such as a circularly polarizing plate, from the viewpoint of preventing the change of the polarization characteristic, the birefringent film A forming the optical film is used.
It is preferable that the crossing angles of the optical axes of B and B are in the range of 40 to 50 degrees, especially 45 degrees, and 1 / for the same wavelength light.
A combination of the two-wave plate (A) and the one functioning as the quarter-wave plate (B) is preferable.

Any appropriate film can be used as the above-mentioned film having a polarizing function and is not particularly limited. Generally, for example, a film made of a hydrophilic polymer such as polyvinyl alcohol is adsorbed with a dichroic substance such as iodine or a dichroic dye and stretched, or a film made of a polymer such as polyvinyl chloride is treated. For example, an absorption type polarizing film that absorbs one linearly polarized light component whose vibration plane is orthogonal and transmits the other linearly polarized light component, such as one in which polyene is oriented, is used. The absorptive polarizing film may have a transparent protective layer made of a triacetyl cellulose film or the like on one surface or both surfaces thereof.

An appropriate method can be applied to the lamination of the optical film and the film having a polarizing function, and the method is not particularly limited. Various methods using an adhesive or the like can be applied according to the lamination of the birefringent films A and B described above. The optical film can also be provided as a transparent protective layer in the absorptive polarizing film.

If desired, a resin coating layer, an antireflection layer, an antiglare layer or the like may be provided on one side or both sides of the polarizing plate for the purpose of protecting water resistance and the like. Further, the orthogonal relationship between the slow axis of the birefringent film and the absorption axis of the polarizing film described above is preferably as parallel as possible, although axial misalignment due to a work error is allowed. If there are variations in the directions of the slow axis and the absorption axis, the slow axis or the absorption axis is determined based on the average direction.

The polarizing plate can be used for various purposes such as formation of a liquid crystal display device according to polarization characteristics such as circular polarization based on the retardation characteristics of the optical film. By the way, in a display device using a reflective TN liquid crystal, circularly polarized light may be incident on a liquid crystal cell for the purpose of improving display quality. At this time, by disposing the polarizing plate according to the present invention, which is a circularly polarizing plate, it is possible to achieve good display quality with less coloring during black display. It can also be used for the purpose of compensating for the phase difference due to the liquid crystal cell and improving the display quality such as widening the viewing angle.

The liquid crystal display device can be formed by disposing an optical film or a polarizing plate on one side or both sides of the liquid crystal cell. In that case, it is preferable to arrange the optical film so as to be located between the film having a polarizing function or the polarizing plate and the liquid crystal cell from the viewpoint of obtaining a liquid crystal display device having a wide viewing angle with good display quality.

Any liquid crystal cell may be used, for example, TN.
Type, STN type, VA type or the like can be used. Also as a liquid crystal display device, for example, a transmissive type or a reflective type,
It is possible to form various types such as an external light / illumination dual type. When a liquid crystal display device is formed, it may be used as an optical film or a polarizing plate laminated with appropriate optical components such as a retardation plate and a light diffusing plate that are used for the formation.

A circularly polarizing plate can be used as an antireflection plate, but in that case, it exhibits antireflection properties over a wide wavelength band, and thus obtains good properties with little coloring of reflected light. You can Further, it is possible to prevent the antireflection efficiency in the oblique direction from being lowered as in the conventional circularly polarizing plate.

The above antireflection property can be exhibited by arranging the polarizing plate on the outermost surface so that the film having the polarizing function is on the outer side, whereby various display devices can be formed. . The display device is not particularly limited, and various devices similar to the conventional display device provided with an antireflection film can be used.

[0034]

EXAMPLES Example 1 It consists of a stretched film of polycarbonate and has a Re of 270 n.
A birefringent film A1 having m and Nz of 0.25 and a birefringent film B1 having a Re of 135 nm and Nz of 0.5 and having a slow axis of 45
An optical film was obtained by adhering and laminating the adhesive film with a pressure sensitive adhesive.

Next, the side of the absorption type polarizing film which does not have the transparent protective layer formed by providing a transparent protective layer made of a triacetyl cellulose type film on one side of the polyvinyl alcohol type uniaxially stretched film for adsorbing iodine is absorbed on the side of A1. A circularly polarizing plate was obtained by bonding and laminating via an adhesive so that the axis was orthogonal to the slow axis of A1.

Comparative Example Consisting of a stretched film of polycarbonate and Re of 270 n
It is composed of a birefringent film X having m and Nz of 1.0 and a stretched film of polycarbonate and has Re of 135 nm and Nz of 1.
The birefringent film of 0 is adhered and laminated with an adhesive so that the slow axis of the birefringent film is 60 degrees to obtain an optical film. The birefringent film X is absorptive polarizing film according to Example 1. A circularly polarizing plate was obtained by adhering and laminating via. However, the crossing angle between the absorption axis of the absorptive polarizing film and the slow axis of X was set to 15 degrees.

Evaluation Test The polarization states of the light having a wavelength of 540 nm transmitted from the absorptive polarizing film of the circularly polarizing plates obtained in Example 1 and Comparative Example were measured, and the S0 component was normalized to 1 by the Stokes parameter. I asked. As a result, S in Example 1
The absolute values of the three components are the normal direction and the perspective direction (60 degrees from the normal direction in the direction of 45 degrees from the absorption axis of the absorptive polarizing film).
It was 0.99 or more in both cases.

However, the absolute value of the S3 component in Comparative Example 1 was 0.99 or more in the normal direction, but was 0.94 in the oblique direction, and there were many elliptically polarized components in the visible light region. Further, in the case of the comparative example, when the absorption axis of the absorptive polarizing film and the slow axis of the X were set to be orthogonal to each other, the performance became worse.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H049 BA02 BA03 BA04 BA06 BA07                       BA25 BA42 BB03 BC22                 2H091 FA08X FA08Z FA11X FA11Z                       FA37X FA37Z FB02 KA01                       KA10 LA16 LA19                 4F100 AT00A AT00B BA02 BA22                       GB41 JN10 JN18A JN18B                       YY00A YY00B                 5G435 AA02 BB12 FF02 FF05

Claims (7)

[Claims] 1. The thickness direction of the film is the Z axis, the refractive index in the axial direction is nz, the maximum refractive index direction in the plane perpendicular to the Z axis is the X axis, and the refractive index in the axial direction is nx, the X axis. And the direction perpendicular to the Z axis is the Y axis, the refractive index in the axial direction is ny, the film thickness is d, (nx-ny) d = Re, and (nx-nz) / (nx-ny) =
When Nz, Re is 200 to 350 nm and Nz is 0.1
~ 0.4 birefringent film A and Re 100-100
An optical film comprising a birefringent film B having an Nz of 0.3 to 0.7 at 5 nm, laminated such that their optical axes intersect. 2. The birefringent film A according to claim 1.
And a birefringent film B, which is a combination of those that function as a half-wave plate and a quarter-wave plate for light of the same wavelength. 3. A polarizing plate comprising a film having a polarizing function laminated on the side of the birefringent film A in the optical film according to claim 1 or 2. 4. The polarizing plate according to claim 3, wherein the film having a polarization function is an absorptive polarizing film, and the absorption axis thereof is orthogonal to the slow axis of the birefringent film A. 5. The circular polarizing plate or the elliptical polarizing plate according to claim 3, wherein the birefringent film forming the optical film has an optical axis crossing angle of A and B of 40 to 50 degrees. A polarizing plate that works. 6. A liquid crystal display device comprising the polarizing plate according to any one of claims 3 to 5 arranged on at least one side of a liquid crystal cell so that the film having the polarizing function is on the outside. 7. A display device, characterized in that the polarizing plate according to any one of claims 3 to 5 is arranged on the outermost surface so that the film having the polarizing function is on the outer side.