JP3165178B2 - Polarizing 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 polarizing plate which compensates for a shift of a transmission axis due to an azimuth angle, and a liquid crystal display device using the same, which has a wide viewing angle.

[0002]

2. Description of the Related Art In a liquid crystal display having a remarkable performance improvement such as a large screen and a high display density, a narrow viewing angle is still a concern, and a polarized light for realizing a liquid crystal display device having a wide viewing angle is required. It has been a long time since a board has been required. Conventionally, as a polarizing plate, a polarizing plate in which an isotropic sealing film made of a biaxially stretched triacetyl cellulose film or the like, that is, a birefringent hardly showing birefringence, is bonded to a polarizer has been known. The sealing film is for preventing the invasion of moisture and the like to improve the durability of the polarizer. However, as described above, there is a problem that the viewing angle of the obtained liquid crystal display device is narrow.

[0003]

An object of the present invention is to develop a polarizing plate capable of obtaining a liquid crystal display device having a wide viewing angle. In view of the foregoing, the present inventors have conducted intensive research and determined that the transmission axis of the polarizing plate changes depending on the viewing angle, particularly the azimuth thereof, which is a cause of narrowing the viewing angle of the liquid crystal display device. Further research was carried out to overcome the problems, and the present invention was accomplished.

[0004]

The present invention SUMMARY OF THE INVENTION may, on both sides <br/> polarizer phase difference indicates the birefringence of 200～320Nm, the
Slow axis direction, fast axis direction and thickness direction in birefringence
Is the refractive index of nx, ny, and nz, respectively, the formula:
Q = (nx−nz) / (nx−ny)
A polarizing plate, wherein a sealing film of 0.1 to 0.9 is adhered, and a fast axis of the sealing film is arranged in parallel to an absorption axis of the polarizer; It is an object of the present invention to provide a liquid crystal display device wherein a polarizing plate is arranged on at least one side of a liquid crystal cell.

[0005]

According to the above arrangement, the change in the transmission axis of the polarizer due to the azimuth (inclination angle) can be compensated for by the phase difference caused by the sealing film. In other words, by utilizing the fact that the fast axis changes with the azimuth angle even in the birefringent sealing film, the change is set as a combination that cancels the change in the transmission axis of the polarizer, and the transmission of the polarizer by the azimuth angle is performed. Compensate for shaft misalignment.

[0006]

FIG. 1 illustrates a polarizing plate of the present invention. 1 is a sealing film, 2 is an adhesive layer, and 3 is a polarizer. As the sealing film 1, a birefringent film having a phase difference of 200 to 320 nm is used. The retardation is determined by multiplying the product (△ n) of the difference (△ n) in the refractive index between the slow axis direction and the fast axis direction in the birefringence of the sealing film and the thickness (d) of the sealing film.
nd).

A sealing film having a retardation can be obtained, for example, as a birefringent film obtained by stretching a polymer film uniaxially or biaxially. Also,
It can also be obtained as a laminate of a birefringent film. The type of the polymer forming the birefringent film is not particularly limited, and those having excellent transparency are preferable. Examples of commonly used polymers include, for example, polycarbonate, triacetyl cellulose, polymethyl methacrylate, polyethylene terephthalate, polyarylate, and polyimide. When the sealing film is formed as a laminate of various films, there is no particular limitation on the number of layers, but it is preferable that the number is smaller than the transparency due to suppression of reflection loss.

[0008] sealing film used Te present invention smell, upper
In addition to the above retardation , the slow axis direction in its birefringence,
The refractive indices in the fast axis direction and the thickness direction are nx and n, respectively.
When y and nz are used, the formula: Q = (nx−nz) / (nx−
ny), the Q value (hereinafter the same) is 0.1 to 0.1.
9, especially 0.1 to 0.5.

The formation of a sealing film having such a Q value, particularly a birefringent film, is performed by using a polymer having a positive birefringence such as polycarbonate, that is, a polymer having a slow axis in the molecular orientation direction. The film can be cured by controlling the orientation by applying an electric field in the thickness direction and then stretching the film.

In the above description, in the case of a film made of a polymer having a positive birefringence, n
_{When y} and _nz are equal, the Q value becomes 1, and in the case of biaxial orientation, the Q value becomes larger than 1. Meanwhile, a film made of a polymer exhibiting negative birefringence as polystyrene, that is, when the full uniaxial orientation intended to fast axis appears in the orientation direction of the molecule, Q value n _x and n _z is equal to 0 In the case of biaxial orientation, the Q value is negative (minus). Therefore, in any case, it is difficult for a single-layer film to exhibit a compensation effect that is effective in widening the viewing angle and has excellent visibility.

That is, in the polarizer arranged in crossed Nicols, the transmission axis changes in the direction perpendicular to the tilt axis (the tilt angle from the vertical upright surface). In the oriented film, the change in the fast axis is in the opposite direction to the change in the absorption axis of the polarizer, and the compensation effect due to birefringence does not appear. In a biaxially oriented film of a positive birefringence system, the birefringence has an adverse effect, and no compensation effect is exhibited. On the other hand, in a completely biaxially oriented film of a negative birefringence system, the change in the fast axis and the change in the absorption axis of the polarizer are almost the same, and the compensation effect due to the phase difference is hardly exhibited. In a negative birefringent biaxially oriented film, the change in the fast axis is larger than the change in the absorption axis of the polarizer, and the birefringence has the opposite effect.

In the present invention, an appropriate polarizer can be used, and there is no particular limitation. In general, a film made of a hydrophilic polymer such as polyvinyl alcohol is stretched by treating with a dichroic dye such as iodine, or a film obtained by treating a plastic film such as polyvinyl chloride and orienting a polyene. Polarizing film is used.

In the polarizing plate of the present invention, the sealing film 1 is bonded to the polarizer 3 such that the fast axis is parallel to the absorption axis of the polarizer. The sealing films are provided on both sides of the polarizer. The above-mentioned parallel state of the fast axis and the absorption axis does not mean a completely parallel state in terms of working accuracy and the like, but it is preferable that the intersection angle is smaller than the point of compensation effect. In this case, the fast axis of the sealing film and the absorption axis of the polarizer are based on the front (azimuth angle: 0).

Adhesion of sealing film 1 and polarizer 3 (2)
Can be performed using, for example, a transparent adhesive or a pressure-sensitive adhesive. There is no particular limitation on the type of the adhesive or the like. From the viewpoint of preventing a change in the optical properties of the polarizer and the sealing film, those which do not require a high-temperature process for curing and drying are preferable, and those which do not require a long curing treatment or drying time are desirable.

In the liquid crystal display device of the present invention, the above-mentioned polarizing plate is disposed on one side or both sides of a liquid crystal cell. FIG. 2 illustrates such a liquid crystal display device. 4 is a polarizing plate and 5 is a liquid crystal cell. The liquid crystal cell used is arbitrary. For example,
Examples thereof include an active matrix driving type represented by a thin film transistor type, and a simple matrix driving type represented by a twisted nematic type and a super twisted nematic type.

[0016] After curing while applying an electric field in Example 1 15 kv, 155 ° C. at 10% stretch is not uniaxially stretched polycarbonate film was (a thickness of about _{50μm, n x: 1.5869, n} y: 1.582
4, _nz : 1.5858, Q value: 0.247) was adhered to both sides of a polarizer obtained by dyeing a polyvinyl alcohol film with iodine and then stretching, via an acrylic pressure-sensitive adhesive to obtain a polarizing plate. Was. The uniaxially stretched polycarbonate film was arranged such that the fast axis (the direction perpendicular to the stretching axis) was parallel to the absorption axis of the polarizer.

Comparative Example 1 The polarizer of Example 1 was directly used as a polarizing plate without bonding a sealing film.

Comparative Example 2 A biaxially stretched triacetyl cellulose film (about 80 μm thick,
_{n x: 1.5303, n y:} 1.5302, n z: 1.529
5, Q value: 8.000), except that a polarizing plate was obtained in the same manner as in Example 1.

COMPARATIVE EXAMPLE 3 A uniaxially stretched polycarbonate film (thickness: about 50%) cured by applying 15% at 155 ° C. after curing without applying an electric field.
_{μm, n x: 1.5890, n} y: 1.5834, n z: 1.
5826, Q value: 1.131), and a polarizing plate was obtained in the same manner as in Example 1.

Evaluation Test Change in Transmittance The polarizing plates obtained in Examples and Comparative Examples were placed at an angle of 45 ° with respect to the tilt axis, and the transmittance of the polarizing plate was measured with respect to the analyzer arranged in crossed Nicols. The ratio of the transmittance when tilted by 60 degrees with respect to the case where the tilt was not tilted was determined, and this was evaluated as a change in polarization performance. Therefore, the smaller the value, the greater the effect of compensating the change in the transmission axis of the polarizing plate.

The results are shown in Table 1. Table 1 also shows the phase difference (product of the film thickness and the refractive index difference) of the sealing film used for the polarizing plate.

[Table 1]

Viewing Angle A polarizing plate obtained in Example 1 or Comparative Example 2 was adhered to both sides of a twisted nematic liquid crystal cell to form a display device, and a contrast ratio was obtained in the left-right (horizontal) direction and the up-down (vertical) direction. Was examined in a range where the ratio was 10: 1 or more.

As a result, in the liquid crystal display device using the polarizing plate of Example 1, the range was +65 degrees to -60 degrees in the horizontal direction, and the range was +35 degrees to -55 degrees in the vertical direction. On the other hand, in the liquid crystal display device using the polarizing plate of Comparative Example 2, the range from +55 degrees to −50 degrees in the left-right direction,
The range was +25 degrees to -40 degrees in the vertical direction.

[0024]

According to the present invention, a change in the transmission axis of the polarizer due to the azimuth angle can be compensated for by using a sealing film having birefringence exhibiting a specific retardation and a Q value. Accordingly, a polarizing plate whose deflection performance is hard to change can be obtained. As a result, by applying such a polarizing plate to a liquid crystal cell, it is possible to obtain a liquid crystal display device exhibiting good contrast and having a wide viewing angle.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of a polarizing plate.

FIG. 2 is a sectional view of an embodiment of a liquid crystal display device.

[Explanation of symbols]

 1: sealing film 3: polarizer 4: polarizing plate 5: liquid crystal cell

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yasuo Fujimura 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nippon Denko Corporation (56) Reference JP-A-2-125224 (JP, A) JP 63-85705 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 5/30 G02F 1/1335 510

Claims (2)

(57) [Claims] 1. A phase difference between 200 and 32 on both sides of a polarizer.
Shows the birefringence of 0 nm, the slow axis direction in the birefringent
Direction, the fast axis direction and the refractive index in the thickness direction are nx,
where ny and nz, the equation: Q = (nx−nz) / (nx
A sealing film having a Q value calculated from -ny) of 0.1 to 0.9 is adhered, and the fast axis of the sealing film is arranged parallel to the absorption axis of the polarizer. A polarizing plate, characterized in that: 2. A liquid crystal display device comprising the polarizing plate according to claim 1 disposed on at least one side of a liquid crystal cell.