JPH0527119A - Phase difference plate and elliptical polarizing plate and liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the phase difference plate and elliptical polarizing plate which can easily control the wavelength dispersion of double refracted light and the liquid crystal display device which prevents the coloration of a black and white display. CONSTITUTION:This phase difference plate 5 consists of the laminate of a double refractive film 1 having 1.00 to 1.05 retardation to light of 450nm wavelength/retardation to light of 550nm wavelength and a double refractive film 3 having 1.05 to 1.20. This elliptical polarizing plate 6 consists of the laminate of the phase difference plate 5 and a polarizing plate 4. This liquid crystal display device is provided with the polarizing plate 4 via the phase difference plate 5 on at least one side of a liquid crystal cell 7. The phase difference plate 5 and elliptical polarizing plate 6 which can compensate the phase difference of the double refracted light over the wide band of a visible light region, etc., are easily obtd. in this way and the liquid crystal display device with which the coloration is prevented at a high degree and which has the excellent contrast of the black and white display is obtd. by using these plates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate having controlled wavelength dispersion of retardation of birefringent light, an elliptically polarizing plate using the retardation plate, and a liquid crystal display device having excellent contrast and excellent coloration prevention.

[0002]

2. Description of the Related Art A high contrast liquid crystal display device utilizing birefringence such as STN type is used for displaying various screens of personal computers and word processors.
In such a liquid crystal display device, elliptically polarized light based on the birefringence of a liquid crystal cell is used, and a display via a polarizing plate is usually colored yellow or blue. Therefore, in order to return elliptically polarized light to linearly polarized light and prevent coloring, an FTN method has been proposed in which a retardation plate made of a birefringent film is interposed between a liquid crystal cell and a polarizing plate to compensate for the retardation due to the liquid crystal cell.
The FTN method is a D-STN that compensates by superimposing a liquid crystal cell.
It is superior in thinness and lightness compared to the method.

However, the liquid crystal display device in which the phase difference is compensated by the above-mentioned conventional FTN method has a problem that white in the monochrome display is bluish or black is brownish. Such a problem is presented as a serious problem that causes discoloration when colorizing a display through a color filter or the like, in addition to the problem of coloring in black and white display.

[0004]

As a result of earnest research by the present inventors, the coloring of the black and white display described above is caused by the wavelength dispersion of birefringent light in the liquid crystal cell and the retardation plate. Clarified that it is necessary to compensate for the phase difference of birefringent light which differs depending on the wavelength due to the liquid crystal cell. Therefore, an object of the present invention is to develop a retardation plate capable of arbitrarily controlling the wavelength dispersion of birefringent light, or an elliptical polarizing plate, and a liquid crystal display device which compensates for coloring of black and white display by compensating over the entire visible light. To do.

[0005]

The present invention has a wavelength of 450 nm.
Of a birefringent film having a retardation of 1.05 to 1.05 and a retardation of 1.05 to 1.20 and a birefringent film of 1.05 to 1.20. A phase difference plate is provided.

The present invention also provides an elliptically polarizing plate comprising a laminate of the above retardation plate and a polarizing plate.

Further, the present invention provides a liquid crystal display device characterized in that a polarizing plate is provided on at least one side of a liquid crystal cell via the retardation plate.

[0008]

By laminating birefringent films having the above-mentioned characteristics, which have different retardations defined by the product (Δnd) of the refractive index difference (Δn) of birefringent light and the thickness (d), among them, By setting the optical axes in the parallel state or the orthogonal state, the wavelength dispersion of the retardation in each birefringent film can be superimposed or adjusted, and the retardation can be controlled. Therefore,
It is possible to obtain a retardation plate having a retardation in the light of wavelength 450 nm / retardation in the light of wavelength 550 nm of 1.2 or more and 1 or less, which cannot be realized by a single-layer birefringent film, and the ratio can be controlled arbitrarily. can do.

[0009]

EXAMPLES The retardation plate of the present invention is R ₄₅₀ / R ₅₅₀ , where R ₄₅₀ is the retardation in the light of wavelength ₄₅₀ nm and R ₅₅₀ is the retardation in the light of wavelength 550 nm.
With a birefringent film of 1.00 to 1.05 and 1.05 to
It is a laminate of 1.20 birefringent films. The retardation plate (5) according to FIG. 1 is illustrated. Reference numerals 1 and 3 are birefringent films, and 2 is a transparent adhesive layer.

From the viewpoint of easily forming a retardation plate having a desired wavelength dispersion characteristic of retardation, the preferred birefringent film laminating method is such that their optical axes are in a parallel state or an orthogonal state as much as possible. It is a method of stacking so as to be. The birefringent film can be obtained by, for example, a method in which a polymer film is uniaxially or biaxially stretched.

The birefringent film having R ₄₅₀ / R ₅₅₀ of 1.00 to 1.05 is, for example, a polyolefin-based polymer such as polyethylene or polypropylene, a polyvinyl alcohol-based polymer, a cellulose acetate-based polymer, or a polyvinyl chloride-based polymer. It can be formed using a polymer such as a polymer or a polymethylmethacrylate-based polymer having an absorption edge in the vicinity of a wavelength of 200 nm.

The birefringent film having R ₄₅₀ / R ₅₅₀ of 1.05 to 1.20 is, for example, a polycarbonate polymer, a polyester polymer such as polyarylate, a polyimide polymer, a polysulfone polymer, or a polyether. Like the sulfone-based polymer and polystyrene-based polymer, the absorption edge is 20
It can be formed by using a polymer having a wavelength longer than 0 nm.

In FIG. 2, a birefringent film (PES) made of polyether sulfone, a birefringent film (PC) made of polycarbonate, a birefringent film made of polymethylmethacrylate (PMMA), and polyvinyl alcohol. Birefringent film (PVA)
The wavelength dispersion characteristics of Wavelength is on the horizontal axis and wavelength is 5 on the vertical axis.
It is the ratio (Δn / Δn ₅₅₀ ) of the refractive index difference at each wavelength to the refractive index difference of the birefringent light in the light of 50 nm.

In the present invention, a retardation plate having an appropriate retardation characteristic can be used. The retardation characteristics can be controlled, for example, by combining the birefringent films to be laminated or changing the crossing state of the optical axes. When laminated so that the optical axes are parallel to each other, the retardation is the sum of retardations of the respective birefringent films. When laminated with the optical axes orthogonal to each other, the retardation is the difference in retardation between the birefringent films. The inclination of the wavelength dispersion can be controlled by changing the film thickness, the stretching conditions and the like to adjust the retardation of the birefringent film.

In the present invention, in particular, when the birefringent films are laminated with their optical axes orthogonal to each other, at least one of the birefringent films is n _x > n from the viewpoint of suppressing the change in retardation due to the viewing angle. _y and, (n _x -n _z) /
(N _x -n _y) <it is preferable to use those satisfying 1. The above n _x and n _y are the refractive index in the direction of the orthogonal axis of the film plane, and _nz is the refractive index in the thickness direction of the film. By suppressing the change of the phase difference depending on the viewing angle, there is an advantage that the visibility from an oblique direction can be improved and a liquid crystal screen with a wide viewing angle can be achieved.

The elliptically polarizing plate of the present invention is a laminate of the above retardation plate and a polarizing plate. The elliptically polarizing plate 6 is illustrated in FIG. Reference numeral 4 is a polarizing plate, and 5 is a retardation plate. Two
Is a transparent adhesive layer. The number of retardation plates (5) used may be one, or may be two or more. When two or more retardation plates are used, the retardation plates (5) may be arranged so that their various optical axes are at appropriate angles. Further, in the case of using two or more sheets, the retardation plate (5) of the present invention may be combined with the other retardation plate. A quarter-wave plate may be used as the retardation plate (5) to form a circularly polarizing plate. The circularly polarizing plate is obtained by intersecting the optical axis of one birefringent film with the transmission axis of the polarizing plate at an angle of 45 degrees or 135 degrees.

An appropriate polarizing plate can be used for forming the elliptically polarizing plate, and there is no particular limitation. Generally, a film made of a hydrophilic polymer such as polyvinyl alcohol is treated with a dichroic dye such as iodine and stretched, or a plastic film such as polyvinyl chloride is oriented with polyene. And a polarizing film covered with a sealing film for protection.

In the liquid crystal display device of the present invention, a polarizing plate is provided on one side or both sides of the liquid crystal cell via the above-mentioned retardation plate (5). The retardation plate and the polarizing plate may be attached as the above-mentioned elliptically polarizing plate (6). 4 and 5 illustrate the liquid crystal display device of the present invention. 6 is an elliptically polarizing plate, and 7 is a liquid crystal cell. In addition, 2 is a transparent adhesive layer, and 4 is a polarizing plate.

The retardation plate preferably used for forming the liquid crystal display device compensates the retardation in the birefringent liquid crystal cell over the entire visible light region. This allows
A high or complete black and white display can be achieved. Also, high contrast can be realized.

The lamination of birefringent films, the lamination of retardation plates and polarizing plates, the adhesion of elliptical polarizing plates and liquid crystal cells, etc.
For example, it can be performed using a transparent adhesive or a pressure-sensitive adhesive. The type of the adhesive or the like is not particularly limited. From the viewpoint of preventing changes in the optical properties of the constituent members, those that do not require a high temperature process during curing or drying are preferable, and those that do not require a long curing process or drying time are desirable.
The retardation plate and the elliptically polarizing plate are provided with an adhesive layer or the like, if necessary, so that they can be adhered to each other.

Example 1 A polypropylene film having a thickness of 70 μm was heated at 140 ° C. for 6 hours.
Birefringent film obtained by 0% stretching treatment (wavelength 550 nm
Retardation in light of 800 nm) and thickness 50
A birefringent film (retardation: 400 nm for light having a wavelength of 550 nm) obtained by uniaxially stretching a polycarbonate film of μm at 160 ° C. by 15% is laminated via an acrylic adhesive so that the optical axes thereof are orthogonal to each other. ,
The retardation plate of the present invention was obtained.

Example 2 A birefringent film (wavelength: 55) obtained by subjecting a polypropylene film having a thickness of 100 μm to 100% stretching treatment at 140 ° C.
Retardation at 0 nm light: 1200 nm) and a polycarbonate film with a thickness of 50 μm at 160 ° C.
Birefringent film obtained by 0% uniaxial stretching treatment (wavelength 55
Retardation at 0 nm light: 800 nm) was laminated via an acrylic pressure-sensitive adhesive so that their optical axes were orthogonal to each other to obtain a retardation plate of the present invention.

Example 3 A 70 μm thick polypropylene film was heated at 140 ° C. for 3 hours.
Birefringent film obtained by stretching 5% (wavelength 550 nm
In light of 470 nm) and a thickness of 50
A birefringent film (retardation for light with a wavelength of 550 nm: 70 nm) obtained by uniaxially stretching a polycarbonate film of μm at 2% at 160 ° C. is laminated with an acrylic adhesive so that their optical axes are orthogonal to each other. The retardation plate of the present invention was obtained.

Example 4 A birefringent film (wavelength: 550) obtained by subjecting a polypropylene film having a thickness of 100 μm to 90% stretching treatment at 140 ° C.
Retardation in the light of nm: 1000 nm) and a polycarbonate film of 90 μm in thickness at 160 ° C. for 30 minutes.
% Birefringent film (wavelength 550
Retardation in light of nm: 1400 nm) was laminated via an acrylic pressure-sensitive adhesive so that their optical axes were orthogonal to each other to obtain a retardation plate of the present invention.

Example 5 A polyvinyl alcohol film having a thickness of 75 μm was placed at 40 ° C.
Birefringent film obtained by stretching 50% in warm water (retardation in the light of wavelength 550nm: 250n
m) and a polyarylate film with a thickness of 50 μm
Birefringent film (wavelength 5
Retardation in light of 50 nm: 300 nm) was laminated via an acrylic pressure-sensitive adhesive so that their optical axes were parallel to each other to obtain a retardation plate of the present invention.

Regarding the retardation plate obtained in the above embodiment, R
₄₅₀ / _R550 was investigated and the results are shown in Table 1. In addition, R ₄₅₀ / R ₅₅₀ of each birefringent film used in the examples is 1.0 from the polypropylene film of Examples 1 to 4.
13, consisting of polycarbonate film 1.0
85, 1.005 for the polyvinyl alcohol film of Example 5, and 1.102 for the polyarylate film.

[0027]

[Table 1]

From Table 1, it can be seen that the wavelength dispersion can be controlled by changing the combination of laminated birefringent films based on their phase difference (retardation). It is also understood that the wavelength dispersion can be controlled by changing the type of birefringent film and the relationship of the optical axes.

[0029]

According to the present invention, it is possible to easily obtain a retardation plate or an elliptically polarizing plate capable of compensating the retardation of birefringent light over a wide band such as a visible light region, and using it, highly colored. It is possible to obtain a black-and-white display which is prevented, and to obtain a liquid crystal display device having excellent contrast.

[Brief description of drawings]

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

FIG. 2 is a graph showing wavelength dispersion of retardation in a birefringent film.

FIG. 3 is a sectional view of an example of an elliptically polarizing plate.

FIG. 4 is a sectional view of an embodiment of a liquid crystal display device.

FIG. 5 is a cross-sectional view of another embodiment of the liquid crystal display device.

[Explanation of symbols]

1,3: birefringent film 2: Adhesive layer 4: Polarizing plate 5: Retardation plate 6: Elliptical polarizing plate 7: Liquid crystal cell

Claims (4)

[Claims] 1. The retardation of light having a wavelength of 450 nm / the retardation of light having a wavelength of 550 nm is 1.0.
Birefringent film of 0 to 1.05 and 1.05 to 1.20
A retardation plate comprising a laminate with the birefringent film of. 2. At least one birefringent film,
When the refractive indices in the direction of the axis orthogonal to the plane of the film and the thickness direction of the film are n _x , n _y , and n _z , respectively, n _x >
n _y, and _{(n x -n z) / (} n x -n y) < retardation plate according to claim 1 is intended to satisfy one. 3. An elliptically polarizing plate comprising a laminated body of the retardation plate according to claim 1 and a polarizing plate. 4. The liquid crystal cell according to claim 1, which is provided on at least one side thereof.
A liquid crystal display device, characterized in that a polarizing plate is provided via the retardation plate described in (3).