JPH0821997A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the angle of visibility by forming two kinds of optical anisotropic elements as optical compensating sheets and controlling the sum of retardations of the optical anisotropic elements to be less than a specified value. CONSTITUTION:This device consists of a liquid crystal cell comprising two electrode substrates and a twisted nematic liquid crystal inserted between these substrates, two polarizing elements disposed on both sides of the cell, an optical anisotropic element (A) which is optically negative uniaxial and has the optical axis in the normal direction, and an optical anisotropic element (B) which is optically negative uniaxial and has the optical axis tilted by 5-50 deg. from the normal line. Both of the optical anisotropic elements (A) and (B) are disposed between the liquid crystal cell and the polarizing element. One of the polarizing elements has a protective film on the surface facing the liquid crystal cell. The sum of retardations expressed by {(nx+ny)/2-nz}xd of the optical anisotropic element (A) and the protective film on the polarizing element facing the liquid crystal is specified to <100nm, wherein nx and ny are the principal refractive indices in the film plane, nz is the refractive index in the thickness direction, and d is thickness of the element (A) or the protective film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
In particular, the present invention relates to a liquid crystal display device having improved display contrast and display color viewing angle characteristics of a TN-LCD.

[0002]

2. Description of the Related Art Display devices for OA equipment such as Japanese word processors and desktop personal computers are mainly used in CRTs.
Therefore, it is being converted to a liquid crystal display element (hereinafter referred to as LCD) which has great advantages of thin and light weight and low power consumption. Many of the currently widespread LCDs use twisted nematic liquid crystals. The display method using such a liquid crystal can be roughly classified into a birefringence mode and an optical rotation mode.

A display element using a birefringence mode (STN type LCD) has a twist angle of a liquid crystal molecule arrangement of 90 ° or more and has a steep electro-optical characteristic, so that there is no active element (thin film transistor or diode). However, a large-capacity display can be obtained by time-division driving with a simple matrix electrode structure. However, it has a drawback that response speed is slow (several hundred milliseconds) and gradation display is difficult, and it does not exceed the display performance of a liquid crystal display element (TFT-LCD or MIM-LCD) using active elements. .

For the TFT-LCD and the MIM-LCD, an optical rotation mode display mode (TN type LCD) in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method is the most effective method compared with other LCDs because it has a high response speed (several tens of milliseconds), can easily obtain a monochrome display, and has a high display contrast. But,
Since the twisted nematic liquid crystal is used, there is a problem in view angle characteristics that the display color and the display contrast change depending on the viewing direction due to the principle of the display system, and the display performance of the CRT cannot be exceeded.

Japanese Unexamined Patent Publication Nos. 4-229828 and 4-2.
As disclosed in Japanese Patent No. 58923, a method has been proposed in which a viewing angle is increased by disposing a retardation film between a pair of polarizing plates and a TN type liquid crystal cell. The retardation film proposed in the above-mentioned patent publication has a phase difference in the direction perpendicular to the liquid crystal cell of almost zero, exerts any optical action from directly in front, and was observed from an inclined direction. Sometimes, a phase difference appears, and it is intended to compensate for the phase difference appearing in the liquid crystal cell. However, even by these methods, the viewing angle of the LCD, specifically, the phenomenon of coloring (coloring phenomenon) or black and white inversion of the display image when tilted from the screen normal direction to the normal viewing angle direction or the left-right direction (reversal phenomenon) ) Is remarkable, and in particular, when it is considered as a vehicle-mounted type or a CRT alternative, the current situation is that it cannot be dealt with at all.

In JP-A-4-366808 and JP-A-4-366809, a viewing angle is improved by using a liquid crystal cell containing a chiral nematic liquid crystal having an inclined optical axis as a retardation film. This is a layer liquid crystal system, which is expensive and very heavy. Further, in JP-A-4-113301, JP-A-5-80323, and JP-A-5-157913, a retardation film in which a polymer chain, an optical axis or an optical elastic axis is inclined with respect to a liquid crystal cell is used. However, there is a problem that it is difficult to obtain a large-area retardation film at low cost, such as by slicing uniaxial polycarbonate obliquely. Further, although reference is made to the improvement of the viewing angle of the STN-LCD, no specific effect is shown for the improvement of the viewing angle of the TN-LCD. Further, Japanese Patent Laid-Open No. 5-215921 proposes a method for optically compensating an LCD by a birefringent plate in which a rod-shaped compound exhibiting liquid crystallinity is sandwiched between a pair of substrates subjected to alignment treatment. This plan is no different from the so-called double-cell type compensator that has been proposed in the past, and it causes a great increase in cost and is practically unsuitable for mass production.
Further, no effect has been shown on improving the omnidirectional viewing angle of a TN type LCD. In addition, JP-A-3-9326,
Also, Japanese Patent Laid-Open No. 3-291601 discloses a plan to apply a polymer liquid crystal to a film-shaped substrate provided with an alignment film to form an optical compensator for an LCD. Since it is impossible to orient the TN-type LCD, it is not possible to improve the omnidirectional viewing angle of the TN LCD.

Further, EP0576304A1 describes a method for improving viewing angle characteristics by using a retardation plate whose refractive index characteristic shows negative uniaxiality and whose optical axis is inclined. Although this method certainly improves the viewing angle significantly compared to the conventional one, it was still impossible to improve the viewing angle to the extent that a CRT alternative is considered.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a TN
It is an object of the present invention to provide a liquid crystal display device in which a viewing angle characteristic of a type LCD, that is, a coloring phenomenon and a reversal phenomenon depending on the viewing angle are improved.

[0009]

Means for Solving the Problems The above-mentioned problems are (1) at least a liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between two electrode substrates, two polarizing elements arranged on both sides of the liquid crystal cell, The optical anisotropic element (A) having negative uniaxiality and an optical axis in the normal direction, and the optical anisotropic element (A) having negative uniaxiality and having the optical axis inclined from the normal direction by 5 ° to 50 ° A liquid crystal display device having an optically anisotropic element (B), wherein both the optically anisotropic elements (A) and (B) are between a liquid crystal cell and a polarizing element, and at least one of the polarizing elements is a liquid crystal cell. Has a protective film on the side, the main in-plane refractive index of the protective film on the liquid crystal cell side of the optical anisotropic element (A) and the polarizing element is nx, ny, the main refractive index in the thickness direction is nz, and the thickness is d Then, the retardation represented by {(nx + ny) / 2−nz} × d The sum of, respectively the liquid crystal display device comprising it is less than 100 nm. (2) The main in-plane refractive index of the optically anisotropic element (B) is nx ′,
ny ', the main refractive index in the thickness direction is nz', and the thickness is d ', the retardation represented by {(nx' + ny ') / 2-Nz'} xd 'is 50 nm to 250 nm,
The liquid crystal display device according to the above (1) is characterized in that the optical axis is inclined by 15 ° to 40 ° from the normal direction.

The operation of the present invention will be described below with reference to the drawings, taking a TN type liquid crystal display element as an example. 1 and 2 show polarization states of light propagating in a liquid crystal cell when a sufficient voltage equal to or higher than a threshold voltage is applied to the liquid crystal cell. Since the transmittance characteristic of light particularly when a voltage is applied greatly contributes to the viewing angle characteristic of the contrast, a case where a voltage is applied will be described as an example. FIG. 1 is a diagram showing a polarization state of light when light is vertically incident on a liquid crystal cell. When natural light L0 is perpendicular to polarizing plate A having polarization axis PA, polarizing plate P
The light transmitted through A becomes linearly polarized light L1.

When a sufficient voltage is applied to the TN type liquid crystal cell, the alignment state of the liquid crystal molecules is schematically shown as a model with one liquid crystal molecule, which is represented by LC in the schematic diagram. Modeling the liquid crystal molecules in a liquid crystal cell, when the LC major axis in the schematic diagram is parallel to the light path, a difference in refractive index occurs on the incident surface (in the plane perpendicular to the light path). Since it does not exist, linearly polarized light propagates even when it passes through the liquid crystal cell. Polarization axis P of polarizing plate B
When B is set to be perpendicular to the polarization axis PA of the polarizing plate A, the linearly polarized light L2 that has passed through the liquid crystal cell cannot pass through the polarizing plate B and is in a dark state.

FIG. 2 is a diagram showing a polarization state of light when the light obliquely enters the liquid crystal cell. When the natural light L0 is obliquely incident, the polarized light L1 transmitted through the polarizing plate A becomes almost linearly polarized light. (In the actual case, it becomes elliptically polarized light due to the characteristics of the polarizing plate.) In this case, a difference in refractive index occurs at the incident surface of the liquid crystal cell due to the refractive index anisotropy of the liquid crystal, and the light L2 that passes through the liquid crystal cell becomes elliptically polarized light. It is modulated and is not completely blocked by the polarizing plate B. As described above, in oblique incidence, light is not sufficiently blocked in a dark state, resulting in a significant decrease in contrast, which is not preferable.

The present invention is intended to prevent such a reduction in contrast due to oblique incidence and improve viewing angle characteristics. In the present invention, an optically negative uniaxial optically anisotropic element (A) whose optical axis is in the direction normal to the film surface and an optically anisotropic element whose optical axis is inclined from the direction normal to the film surface are used. A negative uniaxial optically anisotropic element (B) is used. The optical anisotropic elements (A) and (B) may be arranged on one side of the liquid crystal cell, or may be arranged on both sides in a separate manner.

The fact that the present invention has greatly improved the viewing angle of the liquid crystal display device is estimated as follows. Most TN-LCDs adopt a normally white mode. In this mode, the transmittance of light from the black display portion is significantly increased as the viewing angle is increased, resulting in a sharp drop in contrast. The black display is the state when a voltage is applied. At this time, the liquid crystal molecules in the TN type liquid crystal cell are aligned as in the model of FIG. When the arrangement of the liquid crystal molecules is approximated by an optically positive uniaxial refractive index ellipsoid, it becomes as shown in FIG. 3B, and the optical axis of the TN type liquid crystal cell is slightly tilted from the direction normal to the cell surface. A total of four laminated bodies can be regarded as two positive uniaxial positive optical anisotropic bodies and two positive uniaxial positive optical anisotropic bodies whose optical axes are in the same direction as the normal direction.

If the liquid crystal cell can be regarded as a laminate of four positive uniaxial optical anisotropic bodies, in order to compensate for it, negative uniaxial optics composed of the same combination of optical axis tilt angles as the laminate is used. It is preferable to use four anisotropic plates. For these reasons, it is estimated that the optical compensation film of the present invention has significantly improved the viewing angle characteristics.

The optical anisotropic element (A) used in the present invention is required to have a good light transmittance as well as a plane orientation. The plane orientation referred to in the present invention is a state in which the relationship of the triaxial refractive index of the film satisfies nx = ny> nz. However, nx and ny are main refractive indices in the film plane, and nz is a main refractive index in the thickness direction of the film. Also, the values of nx and ny need not be exactly equal,
Almost equal is enough. Specifically, if | nx-ny | / | nx-nz | ≦ 0.2, there is no practical problem. Further, when the thickness of the base film is d, it is preferable that the condition of 0 ≦ n · d <100 (nm) is satisfied. However, n = (nx +
ny) / 2-nz. Specifically, a film formed of a material having a small intrinsic birefringence value, which is sold under the trade name of ZEONEX (Nippon Zeon), ARTON (Nippon Synthetic Rubber), Fujitac (Fuji Photo Film Co., Ltd.) is preferable. However, even with materials having a large intrinsic birefringence value such as polycarbonate, polyarylate, polysulfone, and polyethersulfone, by controlling the molecular orientation during film formation, a plane-oriented film with n · d of less than 100 nm is formed. It is also possible to use them suitably.

The polarizing element usually has a protective film. The protective film is preferably optically isotropic, but generally has a slight optical anisotropy. If this protective film is on the outside of the liquid crystal cell,
Although it does not affect the viewing angle characteristics of the liquid crystal display device, since protective films are usually used on both sides of the polarizing element, the protective film on the liquid crystal cell side has the same effect as the optical anisotropic element (A) of the present invention. For this reason, it is important that the retardation of each of the protective film on the liquid crystal cell side of the polarizing element and the optical anisotropic element (A) is within 100 nm.

The optically anisotropic element (B) used in the present invention, which has an optically negative uniaxial property and its optical axis is inclined 5 ° to 50 ° from the normal direction of the film, has a light transmittance of 80. % Or more, and at the same time, the main refractive index in the film plane is nx ′, n
Letting y ′ be the main refractive index in the thickness direction be nz ′ and the film thickness be d ′, the relationship between the triaxial main refractive indices is nx ′ = n.
satisfying y ′> nz ′, 50 nm ≦ {(nx ′ + ny ′) / 2−nz ′} × d ′
It is preferable that ≦ 400 nm. However, the values of nx 'and ny' do not have to be exactly equal, and it is sufficient if they are almost equal. Specifically, there is no practical problem as long as the following. | Nx'-ny '| / | nx'-nz' | ≤0.2 Further, regarding the angle formed by the optical axis and the normal direction of the film,
It is more preferably 10 ° to 40 °. As a method for producing the optical anisotropic element (B) of the present invention, Japanese Patent Application No. 6-
As described in No. 126521, a discotic compound is obliquely oriented, a shearing force is applied to both sides of the film to impart strain, and a compound such as azobenzene is irradiated with polarized light. .

The optically anisotropic element (B) is preferably an embodiment characterized by containing an oriented discotic compound.
The discotic compound of the present invention is, for example, C.I. Destra
de et al., Mol. Cryst. 71 volumes, 11
Benzene derivatives described on page 1 (1981); Kohne et al., Angew. Che
m. Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. Lehn et al.,
J. Chem. Commun. , P. 1794 (1985).
Year), J. Research report by Zhang et al. Am. Che
m. Soc. 116, pp. 2655 (1994), such as azacrown-based and phenylacetylene-based macrocycles. Generally, these are used as the mother nucleus of the molecular center, and straight-chain alkyl groups, alkoxy groups, and substituted It has a structure in which a benzoyloxy group or the like is linearly substituted as its straight chain, exhibits liquid crystallinity, and includes what is generally called discotic liquid crystal. However, the molecule is not limited to the above description as long as the molecule itself has negative uniaxiality and can give a certain orientation. Further, in the present invention, the layer formed of the discotic compound does not require that the finally formed layer is the above compound, and for example, the low molecular weight discotic liquid crystal has a group that reacts with heat, light, etc. Therefore, as a result, those which are polymerized or crosslinked by reaction with heat, light or the like to have a high molecular weight and lose liquid crystallinity are also included.

The discotic compound in the present invention is a reaction product of discotic liquid crystal as listed below, or a discotic liquid crystal which does not show liquid crystallinity anymore due to reaction with other low molecular weight compounds or polymers. And the like mean a compound in which the molecule itself has optically negative uniaxiality.

[0021]

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[0022]

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[0023]

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[0024]

[Chemical 4]

The discotic liquid crystal typified by the above discotic compound is applied after rubbing an organic alignment film provided on a transparent support, or applied on an inorganic alignment film, and then heated in an isotropic phase. By keeping the liquid crystal phase for a certain period of time, it is possible to perform the oblique alignment.

The organic alignment film may be a polyimide film or a polystyrene derivative, and the water-soluble film may be a gelatin film or polyvinyl alcohol. By subjecting all of them to rubbing treatment, the discotic liquid crystal can be oriented obliquely.
Of these, the alkyl-modified polyvinyl alcohol is particularly preferable, and the present inventors have discovered that it has an excellent ability to uniformly align the discotic liquid crystal. It is speculated that this is due to the strong interaction between the alkyl chains on the alignment film surface and the alkyl side chains of the discotic liquid crystal. The above alkyl-modified polyvinyl alcohol has an alkyl group at the terminal as listed below, and has a saponification degree of 80%.
As described above, the polymerization degree is preferably 200 or more. Further, polyvinyl alcohol having an alkyl group in a side chain can also be used effectively. As a commercial item, Kuraray MP103, M
P203, R1130, etc. are available.

A polyimide film, which is widely used as a liquid crystal alignment film for LCDs, is also preferable as the organic alignment film,
This is a polyamic acid (for example, LQ / L manufactured by Hitachi Chemical
X series, SE series manufactured by Nissan Chemical Co., Ltd.) is applied to the surface of the substrate, baked at 100 to 300 ° C. for 0.5 to 1 hour, and then rubbed.

The rubbing treatment is the same method widely used as a liquid crystal alignment treatment process for LCDs, and the surface of the alignment film is made of paper, gauze, felt, rubber,
Alternatively, it is a method of obtaining orientation by rubbing nylon or polyester fibers in a certain direction. In general, rubbing is performed several times using a cloth or the like in which fibers of uniform length and thickness are evenly flocked.

As a vapor deposition material for the inorganic oblique vapor deposition film, metal oxides such as TiO ₂ , MgF ₂ and ZnO ₂ and fluorides, and metals such as Au and Al can be cited as a representative of SiO.
The metal oxide can be used as the oblique vapor deposition material as long as it has a high dielectric constant, and is not limited to the above. Both a fixed substrate type method and a continuous vapor deposition type method on a film can be used to form a vapor deposition film.
For example, when the vapor deposition angle α is about 65 to 88 °, the discotic liquid crystal is uniformly aligned in a direction whose optical axis is substantially perpendicular to the direction of the vapor deposition particle column.

The above-mentioned alignment film has a function of determining the alignment direction of the discotic liquid crystal molecules coated thereon.
However, since the alignment of the discotic liquid crystal depends on the alignment film, it is necessary to optimize the combination. Next, the uniformly aligned discotic liquid crystal molecules are aligned at a certain angle with the film normal, but the tilt angle does not change much depending on the seed of the alignment film, and often takes a value specific to the discotic liquid crystal molecules. . Further, when two or more kinds of discotic liquid crystals or a compound similar to the discotic liquid crystal is mixed, the tilt angle can be adjusted within a certain range by the mixing ratio. Therefore, a method of selecting or mixing discotic liquid crystals is more effective for controlling the tilt angle of the oblique alignment.

The optical anisotropic body (B) in the present invention requires a process for obtaining a uniform oblique orientation in the manufacturing process. Specifically, a rubbing-treated organic alignment film,
Alternatively, the discotic liquid crystal is applied to the substrate on which the inorganic alignment film is formed, and then the temperature is raised to a temperature at which a discotic nematic phase is formed, more preferably a discotic nematic phase. As a result, the liquid crystal is obliquely aligned, and remains in the solid state at room temperature while maintaining the alignment by subsequent cooling. Further, the discotic nematic liquid crystal phase forming temperature is unique to the discotic liquid crystal, but can be arbitrarily adjusted by mixing two or more different types. The discotic liquid crystal used in the present invention has a discotic nematic liquid crystal phase-solid phase transition temperature of preferably 70 ° C. or higher and 300 ° C. or lower, particularly preferably 70 ° C. or higher.
It is above 150 ° C.

Magnetic field orientation and electric field orientation are available as methods other than the above for orienting the discotic compound coated on the substrate obliquely. In this method, after the discotic compound is coated on the support, the discotic compound can be obliquely oriented at a desired angle by using a magnetic field, an electric field or the like.

In order to maintain the oblique orientation of the discotic compound thus obtained under high temperature and high humidity conditions, a polymerizable unsaturated group, an epoxy group, a hydroxyl group, an amino group, and Radical polymerization of a polymerizable unsaturated group with a thermal or photopolymerization initiator that has a functional group such as a carboxyl group, or ring-opening polymerization of an epoxy group with a photo-acid generator, polyvalent isocyanate, crosslinking with a polyvalent epoxy compound It is preferable to crosslink the discotic compound itself by a reaction or the like. At this time, another compound having the same functional group may be contained.

The optically anisotropic element (B) having negative uniaxiality and having an inclined optical axis in the present invention can be obtained by subjecting at least a step of applying a shearing force to both surfaces of the transparent film. Specifically, a film made of a thermoplastic resin and having a light-transmitting property is sandwiched between two rolls having different peripheral speeds, and a shearing force is applied to the film to efficiently obtain the film. The thermoplastic resin used here has a light transmittance of 70%, more preferably 85%.
%, There is no problem at all, and there are no other restrictions, but specifically, polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyethylene ether sulfone, Polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyvinyl alcohol, polyamide, polyimide, polyolefin, polyvinyl chloride, cellulose polymer, polyacrylonitrile, polystyrene, binary system,
Various ternary polymers, graft copolymers, blends and the like are preferably used.

The photoisomerizable substance in the present invention is a substance which causes stereoisomerization or structural isomerization by light,
Preferably, the reverse isomerization is caused by light having a different wavelength or heat. In general, these compounds, which are accompanied by structural change and color tone change in the visible region, are often well known as photochromic compounds, and are azobenzene compounds, benzaldoxime compounds, azomethine compounds, fulgide compounds, diary compounds. −
Examples thereof include ruethene compounds, cinnamic acid compounds, retinal compounds, hemithioindigo compounds and the like.

The present invention will be described in detail below based on examples. Example 1 <Preparation of Optically Anisotropic Elements A1, A2, A3> Triacetyl cellulose having a styrene-equivalent weight average molecular weight of 130,000 was dissolved in methylene chloride, cast on a metal band, and stripped in a width direction with a tenter. A1, A corresponding to the optical anisotropic element (A) of the present invention having various plane orientations by stretching, MD stretching and relaxation of orientation by heat.
2 and A3 were created.

Example 2 <Preparation of Optically Anisotropic Element B1> A polycarbonate film (Iupilon; manufactured by Mitsubishi Gas Chemical Co., Ltd.) having a thickness of 54 μm was used.
After passing through a pair of metal peripheral speed rolling rollers (speed ratio 1: 1.003) heated to 2 ° C., stretching in the transverse direction,
B1 corresponding to the optically anisotropic element (B) of the present invention was prepared.

Example 3 <Preparation of Optically Anisotropic Element B2> Alkyl-modified PVA (trade name MP20) was prepared using A1 prepared in Example 1 as a support.
3: made by Kuraray Co., Ltd.) to a thickness of 0.5 μ,
Rubbing was carried out by a rubbing machine, and the coating liquid prepared by dissolving 0.4 g of the above-mentioned discotic liquid crystal TE-8 (m = 4), 0.04 g of trimethylolpropane triacrylate, and 0.004 g of Irgacure 907 in 1.6 g of methyl ethyl ketone was applied. After coating with a spin coater and drying, heat from room temperature to 145 ° C for 15 minutes to orient the discotic liquid crystal, and then irradiate for 1 minute with a high pressure mercury lamp at 147 ° C, slowly cool to room temperature, and spin the disc. An optically anisotropic element B2 having a layer D1 containing a crystalline compound was prepared.

Example 4 <Evaluation of optical characteristics of optical anisotropic elements A1, A2, B1, B2, A0> Optical anisotropic elements A1, A produced in Examples 1 to 3
For 2, B1, B2, and A0 described later, the film thickness of the film was measured with a film thickness meter, and the retardation value and the tilt angle formed by the optical axis and the normal line direction of the film were obtained using an ellipsometer. . However, the optical anisotropic element B
For 2, the optical characteristics of the support and the coating layer containing the discotic compound were determined separately. The results are summarized in Tables 1 and 2.

[0040]

[Table 1]

[0041]

[Table 2]

Example 5 <Preparation of Polarizing Plates P0, P1, P2 and P3> An optical anisotropic film having a thickness of 100 μm was prepared by using an acrylic adhesive on both sides of the polarizing element S1 in which iodine was adsorbed in stretched polyvinyl alcohol. A non-functional film A0 (trade name: Arton, made by Japan Synthetic Rubber) is laminated as a protective film, and a polarizing plate P0 is used.
It was created. As the protective film, the polarizing plates P1 and P1 were prepared in exactly the same manner as above except that the optical anisotropic element A1, A2 or A3 prepared in Example 1 was used instead of A0.
2 and P3 were created.

Example 6 <Production of liquid crystal display devices H1 to H5> The product of the difference in the refractive index of the ordinary light and the extraordinary light of the liquid crystal and the gap size of the liquid crystal cell is 465.
The optically anisotropic elements B1 or B2 prepared in Examples 2 and 3 are provided on both sides of a TN type liquid crystal cell having a twist angle of 90 ° in nm.
Was pasted as an optical compensation film, on which Example 5 was applied.
The liquid crystal display devices H1, H2, H3, H4, and H5 were prepared by laminating the polarizing plates P0, P1, P2, and P3 prepared in (1). With respect to the liquid crystal display devices H1 to H5, a voltage of 40 Hz square wave and a range of 0 V to 5 V was applied to the liquid crystal cell, and the angle dependence of the transmittance (T) was measured by Otsuka Electronics LCD-
It was measured at 5000. The viewing angle was determined by defining the position where the contrast ratio (T0 / T5) of white display and black display was 10 as the viewing angle. The results are shown in Table 3.

[0044]

[Table 3]

[0045]

As is apparent from Table 3, as in the present invention, two types of optical anisotropic elements (A) and (B) are provided as optical compensation sheets, and the retardation of the optical anisotropic element (A) is set. In a liquid crystal display device having a total value of less than about 100 nm, a significant improvement in viewing angle has been achieved.

[0046]

[Brief description of drawings]

FIG. 1 is a diagram illustrating a polarization state of light when natural light is vertically incident on a liquid crystal cell.

FIG. 2 is a diagram illustrating a polarization state of light when natural light is obliquely incident on a liquid crystal cell.

FIG. 3 is a model view showing an arrangement of liquid crystal molecules in a TN liquid crystal cell.

[Explanation of symbols]

TNC: TN type liquid crystal cell A, B: Polarizing plate PA, PB: Polarization axis L0: Natural light L1: Linearly polarized light L2: Modulated light after passing through the liquid crystal cell LC: When a sufficient voltage is applied to the TN type liquid crystal cell State of liquid crystal molecules in BL: Backlight

Claims (2)

[Claims] 1. A liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between at least two electrode substrates, two polarizing elements arranged on both sides of the liquid crystal cell, which are optically negative uniaxial and have an optical axis. Liquid crystal display device having an optically anisotropic element (A) in the normal direction and an optically anisotropic element (B) which is optically uniaxial and has an optical axis inclined 5 ° to 50 ° from the normal direction. Both of the optically anisotropic elements (A) and (B) are between the liquid crystal cell and the polarizing element, and at least one of the polarizing elements has a protective film on the liquid crystal cell side. When (A) and the in-plane main refractive index of the protective film on the liquid crystal cell side of the polarizing element are nx, ny, the main refractive index in the thickness direction is nz, and the thickness is d {(nx + ny) / 2-n
A liquid crystal display device, wherein the sum of the retardations represented by z} × d is less than 100 nm. 2. When the main in-plane refractive index of the optically anisotropic element (B) is nx ', ny', the main refractive index in the thickness direction is nz ', and the thickness is d', {(nx '+ ny) ′) / 2-Nz ′} ×
retardation represented by d'is 50 nm to 250 nm
2. The liquid crystal display device according to claim 1, wherein the optical axis is tilted by 15 ° to 40 ° from the normal direction.