JP2003075641A - Optical retardation film, method for manufacturing the same and liquid crystal display device using optical retardation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical retardation film which enlarges a viewing angle of a liquid crystal display device with only one sheet thereof and a method for manufacturing the same. SOLUTION: The optical retardation film is effective in enlarging the viewing angle of the liquid crystal display device with only one sheet thereof. The optical retardation film has a maximum value and a minimum value respectively of the optical retardation of the film when observed from each of observation directions around the normal axis of the film surface with a constant inclined angle with respect to the normal axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation film for improving display contrast and viewing angle characteristics of a display color of a liquid crystal display device and a manufacturing method thereof.

[0002]

2. Description of the Related Art Retardation films are films having birefringence that allow linearly polarized light components vibrating in mutually perpendicular principal axis directions to pass therethrough and give a required retardation between the two components.
By imparting specific optical characteristics, such a retardation film serves as an optical compensation film for expanding the viewing angle of a liquid crystal display device. Several conventional techniques for producing such a retardation film have been reported. For example, Japanese Patent Registration No. 2640083 describes a phase film in which discotic liquid crystals are obliquely arranged by a rubbing alignment film and an SiO oblique vapor deposition alignment film. In addition, JP-A-10-
No. 332933, a retardation film composed of a rubbing alignment film, a film in which a liquid crystal polymer having positive birefringence is obliquely arranged on a SiO oblique vapor deposition alignment film, and a layer of a negative refractive index ellipsoid. Is listed. Further, Japanese Patent Laid-Open No. 2000-121831 describes a retardation film in which biaxial refractive index ellipsoids obtained by obliquely vapor-depositing tantalum pentoxide are obliquely arranged. However, in these reports, in order to improve the viewing angle characteristics of the liquid crystal display device,
Two tilted uniaxial index ellipsoids or biaxial index ellipsoids are arranged between the liquid crystal cell and the polarizing plates on both sides, one in total.

[0003]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention In the retardation film of the uniaxial refractive index ellipsoid or the biaxial refractive index ellipsoid which is tilted and oriented according to the above-mentioned prior art, the effect of enlarging the viewing angle of the liquid crystal display device is obtained. To obtain the above, two optically anisotropic elements (retardation film) are required. The present invention provides a retardation film capable of obtaining an optical compensation effect even with one sheet.

[0004]

According to the present invention, in the observation of the phase difference from each observation direction around the normal axis with a constant inclination angle with respect to the normal axis of the film surface, the phase difference has a maximum value and a minimum value. The method for producing a retardation film effective for enlarging the viewing angle of a liquid crystal display device is realized by using a retardation film having one observation direction around each normal axis.

The inventor has conducted an optical simulation for a layered medium having birefringence using the Mueller method.
A retardation film (index ellipsoid) required to obtain a viewing angle expansion effect for a 90 ° twisted nematic liquid crystal cell even with one sheet was calculated. As a result, such a retardation film has a constant inclination angle with respect to the normal axis of the film surface, and in the observation of the retardation from each observation direction around the normal axis, the retardation has a maximum value and a minimum value. The observation direction shown is a refractive index ellipsoid each having one around the normal axis, or a negative index such as a laminated film or a TAC film in which the refractive index ellipsoid and the biaxially stretched film are orthogonally bonded to each other. It has been found that the effect of enlarging the viewing angle of a 90 ° twisted nematic liquid crystal cell can be obtained by combining the layers having the refractive index ellipsoids.

Further, in the above-mentioned refractive index ellipsoid which can obtain the effect of enlarging the viewing angle of the 90 ° twisted nematic liquid crystal cell, two positive refractive index ellipsoids are inclined and oriented, and the length when projected onto each film surface is long. It has been found to be obtained when the axes or short axes are orthogonal to each other. Also, depending on the characteristics of the liquid crystal cell, the tilt angle of each index ellipsoid is 10 °.
It was found that even from 80 ° to 80 °, the effect of enlarging the viewing angle was obtained, and above all, it was preferable that the inclination angle was from 30 ° to 60 °. Although the effect of enlarging the viewing angle can be obtained even when the tilt angle is 80 ° or more, the larger the tilt angle, the more the film thickness of the retardation film is required, and the practicality is lacking. On the other hand, 10 °
In the case of the following, a sufficient viewing angle expansion effect cannot be obtained.
Furthermore, if the difference between the maximum value and the minimum value of the phase difference is between 30 nm and 200 nm, a viewing angle widening effect can be obtained, and more practically, it is preferably between 60 nm and 100 nm.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of the retardation film of the present invention.
And the normal axis of the film surface 11 of the retardation film 10.
With respect to P, each angle around the normal axis with the inclination angle α fixed
When observing the phase difference from the observation direction, the phase difference has a maximum value.
And the observation direction showing the minimum value (L _MAX, L_min), One for each
Shows the state of

To manufacture the retardation film of the present invention, the inventor of the present invention disclosed in JP-A-11-189665 and Japanese Patent Application No.
0-400356, which is produced by irradiating a film with linearly polarized light whose electric field vibration planes are orthogonal to each other, using a material that causes birefringence by irradiation with light and heating and cooling. can do. In addition, an alignment film is formed on the base material to bend-align the liquid crystalline material
It is also possible by forming two films which are obliquely oriented and films which are obliquely vapor-deposited with a dielectric material and are made to be obliquely oriented at right angles to each other, or by forming obliquely oriented layers on the front and back surfaces of the substrate so as to be orthogonal to each other. The retardation film of the present invention is illustrated in FIG. 2 (two positive refractive index ellipsoids are inclined and oriented at an inclination angle of 50 °, and the long axis or the short axis when projected onto each film surface is orthogonal to each other. As described above), the retardation film has one observation direction showing the maximum value and the minimum value of the retardation around the normal axis of the film surface.

On the other hand, used in the prior art,
Ordinary tilted uniaxial index ellipsoid or 2
The retardation film having an axial refractive index ellipsoid has a maximum value of the retardation around the normal axis as illustrated in FIG. 3 (when the positive refractive index ellipsoid is inclined and oriented at an inclination angle of 50 °). And a retardation film having two observation directions each exhibiting a minimum value. When such a film is used for optical compensation of a 90 ° twisted nematic liquid crystal cell, two retardation films are required.

FIG. 4 shows the observation results of the phase difference from each observation direction around the normal to the cell surface of a general 90 ° twisted nematic liquid crystal cell when a voltage is applied. From the figure, it can be seen that in the 90 ° twisted nematic liquid crystal cell, the phase difference changes depending on the azimuth angle, which causes the viewing angle dependence of the liquid crystal display device. FIG. 5 shows the incident angle and cell surface normal of a 90 ° twisted nematic liquid crystal cell under the application of this voltage, the retardation film of the present invention and a negative birefringent layer of an appropriate thickness. The simulation result in each observation direction around the direction is shown. From this figure, it is understood that the change in the magnitude of the retardation due to each observation direction around the cell surface normal direction is suppressed, and the viewing angle dependence of the liquid crystal display device can be improved by the retardation film of the present invention.

The optical characteristics of such a retardation film are
It is designed according to the optical characteristics of the liquid crystal display device on which the retardation film is mounted. Further, for optical compensation of the liquid crystal display device, it is necessary to adjust the phase difference of the optical anisotropic element in consideration of the phase difference of all the optical systems constituting the device including the polarizing plate. The combination of a layer having a negative refractive index ellipsoid such as a TAC film can improve the viewing angle expansion effect. The following example is an example in which a retardation film having one maximum and one minimum of the present invention was produced.

(Example) 3.75% by weight of poly (4-methyl)
Tacryloyloxyhexyloxy-4'-cinnamoy
Luoxyethyloxybiphenyl) and 1.25 weight
% 4,4'-bis (methacryloyloxyhexyl o
Xyhexyloxy) biphenyl ortho-dichloroben
Dissolves in Zen and inclines 40 ° to the normal direction of the film surface
On a TAC film with a phase difference of 20 nm in the vertical direction
To a thickness of about 1.5 μm. The film is horizontal
It is arranged so that it is tilted at 45 degrees with respect to the Grand Tailor Puri
UV rays converted into linearly polarized light using
From the vertical direction at room temperature on both the back and coated surfaces of the TAC film
100 mJ / cm from each side²Irradiate each. Next
Then, rotate the film 90 degrees to make linearly polarized light in the same way.
Convert the converted ultraviolet light from the direction perpendicular to the horizontal plane at room temperature.
100 mJ / cm from the front and back sides of the board ²Irradiation one by one
did. Then, after heating to 100 ° C., cooling to room temperature
It was The angle of the phase difference of the optical anisotropic element manufactured in this way
Dependence is 4 from the normal direction of the film surface as shown in FIG.
The magnitude of the phase difference is maximum in each observation direction tilted by 0 degree.
And each has one direction that indicates the minimum, and the difference between the maximum and the minimum ΔRe
Was approximately 85 nm.

The obtained retardation film was peeled off from the polarizing sheet of the liquid crystal color television set EV-510 manufactured by Casio, and one sheet was attached to the upper surface or the lower surface of the liquid crystal cell.
I stuck them one by one. The axial arrangement of each optical element was as shown in FIG. In FIG. 7, 61 is the retardation film of the present invention, a and a ′ indicate the irradiation direction of the ultraviolet rays converted into the irradiated linearly polarized light, 62 is a liquid crystal cell, and b and b ′.
Indicates the pretilt direction, 63 and 63 ′ indicate polarizing sheets, and c and c ′ indicate the respective light absorption axis directions. When the liquid crystal color television was driven with such a configuration and the contrast ratio at the time of white display and black display became 5, the viewing angle was defined, and the viewing angle in the vertical and horizontal directions was observed. BM-5A made by Topcon for observation of contrast ratio
Was used.

[0014]

[Table 1] From the table, it was proved that the retardation film of the present invention can widen the viewing angle of a liquid crystal display device with one sheet.

[0015]

EFFECTS OF THE INVENTION Conventionally, a retardation film having a uniaxial refractive index ellipsoid or a biaxial refractive index ellipsoid which is inclined and oriented has required two retardation films. With the retardation film, it is possible to provide a retardation film effective for expanding the viewing angle of the liquid crystal display device even with one sheet, and the manufacturing process of the liquid crystal display device with the expanded viewing angle can be simplified.

[0016]

[Brief description of drawings]

FIG. 1 shows a retardation film of the present invention.

FIG. 2 is a simulation result of retardation from each observation direction around the normal axis with a constant inclination angle with respect to the normal axis of the film surface in the retardation film of the present invention.

FIG. 3 is a tilted uniaxial index ellipsoid or 2
Simulation results of retardation from each observation direction around the normal axis with a constant inclination angle with respect to the normal axis of the film surface in the retardation film having an axial refractive index ellipsoid.

FIG. 4 is a simulation result of the phase difference from each observation direction around the normal axis with a constant inclination angle with respect to the normal axis of the TN liquid crystal cell when a voltage is applied.

FIG. 5: From each observation direction around the normal axis, when the TN liquid crystal cell at the time of applying a voltage, the retardation film of the present invention and the birefringent layer are laminated, with a constant inclination angle with respect to the normal axis Simulation result of phase difference

FIG. 6 is a retardation from each observation direction around a normal axis having an inclination angle of 50 ° with respect to the normal axis of the film surface in the retardation film of the example.

FIG. 7: Optical system when evaluating viewing angle characteristics

[Explanation of symbols]

10 ... Retardation film 11 ... Film surface P ... Normal axis L _MAX ... Observation direction (maximum phase difference) L _min ... Observation direction (minimum phase difference) α ... On normal axis Inclination angle with respect to

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Claims (6)

[Claims] 1. In the observation of the phase difference from each observation direction around the normal axis with a constant inclination angle with respect to the normal axis of the film surface, the observation direction showing the maximum value and the minimum value of the phase difference is A retardation film having one each around the normal axis. 2. The phase difference according to claim 1, wherein the observation directions of the phase difference for observing the maximum value and the minimum value are 180 degrees relative to each other about the normal axis of the film surface. the film. 3. A difference ΔRe between the maximum value and the minimum value of the phase difference.
Is in the range of 30 nm <ΔRe <300 nm. 4. The retardation film according to claim 1, wherein 4. A laminated retardation film comprising the retardation film according to claim 1 and a uniaxial refractive index ellipsoid layer and / or a biaxial refractive index ellipsoid layer. 5. A process in which the retardation film according to any one of claims 1 to 3 includes an operation of irradiating light or irradiating with heat and cooling to a material which induces birefringence by irradiating light or irradiating with heat and cooling. A method for producing a retardation film, which is produced by: 6. The twisted nematic liquid crystal cell and the two retardation plates disposed on both sides of the twisted nematic liquid crystal cell, wherein the retardation film according to any one of claims 1 to 4 is placed. A liquid crystal display device characterized by the above.