JPH0735924A - Optically anisotropic element and liquid crystal display device formed by using the same - Google Patents

Abstract

PURPOSE:To provide the optically anisotropic element which is relatively easily produced, effectively prevents the degradation in display contrast particularly in diagonal incidence and is capable of greatly improving the visual sensation characteristics of display colors and the liquid crystal display element using the same. CONSTITUTION:This optically anisotropic element consists of a laminate of the following optically anisotropic layer (a) and optically anisotropic layer (b) and has the optical axis inclining in a 10 to 40 deg. range from the direction normal to the surface of the laminate: (a) The optically anisotropic layer which exhibits positive uniaxiality and has the optical axis inclining from the direction normal to the surface of the laminate; (b) the optically anisotropic layer which exhibits positive uniaxialiy and has the optical axis within the plane parallel with the surface of the laminate. The liquid crystal display element is obtd. by using the optically anisotropic element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical anisotropic element and a liquid crystal display element using the same, and particularly to an optical anisotropic element useful for improving the visual characteristics of display contrast and display color, and the optical anisotropic element. The liquid crystal display element used.

[0002]

2. Description of the Related Art A CRT has been conventionally used as a display device for equipment representative of office automation such as a Japanese word processor and a desktop personal computer. However, since the CRT is large and heavy and consumes a large amount of power, liquid crystal display elements have recently been attracting attention, and various researches, developments, and commercializations have been conducted. Liquid crystal display elements (hereinafter, also referred to as LCDs) that are generally used at present use twisted nematic liquid crystals, and the mainstream display methods are broadly classified into STN (super twisted nematic). ) Birefringence mode using liquid crystal and T
N (twisted nematic) liquid crystal is used, and it can be divided into optical rotation modes called TFT-LCD and MIM-LCD using active elements.

The LCD based on the birefringence mode uses STN liquid crystal having a twist angle of 90 degrees or more in the alignment of liquid crystal molecules and has steep electric characteristics. Therefore, it is necessary to use active elements such as thin film transistors and diodes. Without
Even with a simple matrix electrode structure, there is an advantage that a large capacity display can be realized by time-division driving. However, it is disadvantageous in that the response speed is slow (about several hundreds of milliseconds) and that gradation display is difficult. TFT
-L based on the rotation mode of LCD or MIM-LCD
The CD uses a TN liquid crystal in which the alignment state of liquid crystal molecules is twisted by 90 degrees. With this display method, a fast response speed (about several tens of milliseconds), a black and white display can be easily obtained, and a high display contrast is exhibited. It is said to be the most effective method as compared with other types of LCDs. However, since the twisted nematic liquid crystal is used, there is an unfavorable visual characteristic that the viewing angle is narrow and the display color and the display contrast are changed depending on the viewing direction due to the principle of the display method, and its improvement has been attempted.

That is, liquid crystal molecules have different refractive indices in the major axis direction and the minor axis direction of the liquid crystal molecule, and when a certain polarized light is incident on the liquid crystal molecule exhibiting such anisotropy of the refractive index, The polarized light changes the polarization state depending on the angle of liquid crystal molecules. The molecular arrangement of the liquid crystal cell of the twisted nematic liquid crystal has a structure in which the arrangement of the liquid crystal molecules is twisted in the thickness direction of the liquid crystal cell. Sequentially polarized light propagates depending on the orientation of liquid crystal molecules. Therefore, the polarization state of the light propagating in the liquid crystal cell is different between the case where the light is vertically incident on the liquid crystal cell and the case where the light is obliquely incident, and as a result, the display pattern depends on the viewing direction and the angle. It may not be visible at all, which is not preferable for practical use as a display device.

As a method for improving the above-mentioned unfavorable visual characteristics, for example, Japanese Patent Laid-Open No. 4-229828.
There is a method using a retardation film disclosed in Japanese Patent Laid-Open No. 4-258923 and Japanese Patent Laid-Open No. 4-258923. That is,
A liquid crystal display element usually comprises a liquid crystal cell in which a TN type liquid crystal is sandwiched between two electrode substrates, and two polarizing elements arranged on both sides of the liquid crystal cell. It is a method of disposing a film (retardation film) for adjusting the retardation between the two. The retardation film proposed in the above-mentioned publication has a phase difference in the direction perpendicular to the surface of the liquid crystal cell which is almost zero, and has no optical effect on light from the front. On the other hand, on the other hand, when the tilted light is incident, the phase difference is expressed and the phase difference generated in the liquid crystal cell is compensated. However, in the compensation of the phase difference by this method,
The improvement in the viewing angle of LCDs achieved is not sufficient.
Especially when mounted on vehicles such as automobiles, or CR
When used as an alternative display device for T, it is necessary to improve the viewing angle to a high degree, and the above method cannot be said to be sufficient.

In the inventions disclosed in JP-A-4-366808 and JP-A-4-366809, the viewing angle is improved by using a chiral nematic liquid crystal layer having an inclined optical axis as a retardation film. But
This system is a two-layer liquid crystal system, which has drawbacks such as an extremely high cost and a significant increase in the weight of the entire display device.

[0007]

DISCLOSURE OF THE INVENTION The present invention effectively prevents a decrease in display contrast particularly at oblique incidence and significantly improves the visual characteristics of display colors while the cost is small and the weight is light. Optical anisotropic element capable of
And to provide a liquid crystal display device using the same. Another object of the present invention is to provide an optical anisotropic element which is particularly useful as a retardation film for a liquid crystal display element using a TN type liquid crystal.

[0008]

The present invention comprises a laminate of the following optical anisotropic layer (a) and optical anisotropic layer (b), the optical axis of which is 10 to 10 in the direction normal to the surface of the laminate. The optical anisotropic element is tilted in the range of 40 degrees (preferably 20 to 30 degrees). (A) An optical anisotropic layer having positive uniaxiality, the optical axis of which is inclined from the direction normal to the surface of the laminate; (b) Positive uniaxiality, whose optical axis is parallel to the surface of the laminate. In-plane optically anisotropic layer. The present invention also provides a liquid crystal cell in which a TN type liquid crystal is sandwiched between two electrode substrates, two polarizing elements arranged on both sides of the liquid crystal cell, and a liquid crystal cell and a polarizing element. There is also a liquid crystal display element including the above-mentioned optically anisotropic element.

Preferred embodiments of the present invention are listed below. 1) The above optical anisotropic element, wherein the optical anisotropic layer (a) is a layer containing a nematic liquid crystal. 2) The optical anisotropic element, wherein the optical anisotropic layer (a) is made of a thermoplastic resin obtained by passing between two rolling rolls having different peripheral speeds. 3) The optical anisotropic element, wherein the optical anisotropic layer (b) is a uniaxially stretched thermoplastic resin having a positive intrinsic birefringence value. 4) The above-mentioned optical anisotropic element in which the optical anisotropic layer (a) and the optical anisotropic layer (b) are laminated so that the directions of the main refractive indices are orthogonal (including substantially orthogonal) to each other. 5) A liquid crystal cell in which a TN type liquid crystal is sandwiched between two electrode substrates, two polarizing elements arranged on both sides of the liquid crystal cell, and the above-mentioned one disposed between the liquid crystal cell and the polarizing element. A liquid crystal display element comprising the optically anisotropic element described in any one of 1) to 4).

The optical anisotropic element of the present invention exhibits negative uniaxiality due to the above-mentioned constitution, and when this is used in a liquid crystal display device, even if light is obliquely incident on a liquid crystal cell and is taken out as elliptically polarized light. , The elliptically polarized light passes through the optically anisotropic element and is modulated into the original linearly polarized light. Therefore, by using the optical anisotropic element of the present invention, the liquid crystal display element (device) as a whole exhibits the same transmittance for various oblique incidences, and the viewing angle dependency is remarkably improved. (That is, the viewing angle is greatly increased).

The reason why the optical anisotropic element of the present invention can realize a large increase in viewing angle is estimated as follows. A liquid crystal display device using a TN-LCD generally employs a normally white mode. According to the viewing angle characteristics in this mode, the transmittance of light from the black display portion is significantly increased as the viewing angle is increased, which causes a sharp decrease in contrast. This black display corresponds to the state when a voltage is applied. At this time, the TN type liquid crystal cell becomes a positive uniaxial optical anisotropic body in which the optical axis is slightly tilted from the direction normal to the surface of the liquid crystal cell. Further, when displaying a halftone, the optical axis is further inclined from the normal direction of the liquid crystal cell. When the optical axis of the liquid crystal cell is tilted from the direction of the normal line to the surface of the liquid crystal cell, the retardation film having the optical axis in the normal direction is insufficient in compensation. On the other hand, the optical anisotropic element of the present invention has (a) an optical anisotropic layer having positive uniaxiality, the optical axis of which is inclined from the direction normal to the surface of the laminate, and (b) a positive anisotropic layer. Negative uniaxiality is obtained by forming a laminate by combining an optically anisotropic layer having uniaxiality and an optical axis of which is in a plane parallel to the surface of the laminate, and the optical axis of the laminate is Since the tilt is adjusted within a range of 10 to 40 degrees from the direction normal to the body surface, it is possible to sufficiently compensate for the phase difference generated in the light incident on the liquid crystal cell in the oblique direction, resulting in a large visual field. It is thought that the enlargement of the corner will be realized.

The optical anisotropic layer (a) and the optical anisotropic layer (b) constituting the optical anisotropic element of the present invention are both thermoplastic resins having a positive intrinsic birefringence value or a positive intrinsic birefringence value. It can be produced by using a combination of a low molecular weight compound having γ and a compound for fixing orientation.

Examples of thermoplastic resins having a positive intrinsic birefringence value include polycarbonate resins, polyarylate resins, polyester resins, polyamide resins, polyimide resins, and polysulfone resins. , Especially polycarbonate, polyarylate,
Polyethylene terephthalate, polyamide, polyimide, polysulfone, and polyether sulfone are preferred. In any case, a resin material having a large intrinsic birefringence value and capable of easily forming a film having a uniform surface state by a solution film forming method or a melt extrusion method is preferable. The above-mentioned polymer is not limited to a homopolymer, and it goes without saying that it may be a copolymer, a homopolymer or a derivative of a copolymer, or a mixture thereof. When the thermoplastic resin having a positive intrinsic birefringence value is classified from the position of the functional group having an intrinsic birefringence value, it can be classified into a main chain type and a side chain type. Further, as the functional group, a mesogen group which is a functional group of ordinary liquid crystals is preferable. In consideration of the orientation, the side chain type is preferable. The skeleton of the side chain type resin (side chain type polymer compound) is preferably any one of vinyl type polymer, polysiloxane, polypeptide, polyphosphazene, polyethyleneimine, and cellulose.

The low molecular weight compound having a positive intrinsic birefringence value preferably has a mesogenic group, and examples thereof include Schiff liquid crystals, azoxy liquid crystals, cyanobiphenyl liquid crystals, cyanophenylcyclohexane liquid crystals,
Examples thereof include low molecular weight liquid crystals such as cyanophenyl ester liquid crystals, benzoic acid phenyl ester liquid crystals, cyclohexanecarboxylic acid phenyl ester liquid crystals, phenylpyrimidine liquid crystals, and phenyldioxane liquid crystals. When the low molecular weight compound having a positive intrinsic birefringence value is contained in the optically anisotropic layer, the low molecular weight compound is mixed with the low molecular weight compound, or the polymer matrix and the low molecular weight compound which are coexistent to fix the orientation are crosslinked. Therefore, it is preferable to introduce a reactive substituent such as a substituent having an unsaturated bond or a substituent having active hydrogen into the above-mentioned low molecular weight compound. Examples of such a substituent include a vinyl group, an aryl group, a mercapto group, an amino group, a carboxyl group, a hydroxyl group and an epoxy group.

Further, in order to fix the orientation of the low molecular weight compound having a positive intrinsic birefringence value, a matrix formed of a high molecular weight compound can be used. The polymer compound forming this matrix is not particularly limited, but it should be a substantially transparent and colorless layer having a light transmittance of 60% or more in the state of containing the above low molecular compound. preferable. That is, in the optically anisotropic layer, the polymer matrix and the low molecular weight compound having a positive intrinsic birefringence value are compatible with each other, or the low molecular weight compound in the polymer matrix has a particle size of 0.08 μm or less. Particles (or oil droplets)
Is preferably dispersed as. To disperse the low molecular weight compound in the polymer matrix, a surfactant, a polymer compound that increases compatibility, or the like can be used as a dispersion aid. Examples of the polymer matrix material used for the above purpose include natural polymer compounds such as gelatin, agarose, pectin, and carrageenan, and polyvinyl alcohol, polyvinyl butyral, polymethyl vinyl ether, polyhydroxy acrylate, hydroxyethyl cellulose, hydroxypropyl cellulose. ,
Methyl cellulose, polycarbonate, polyacrylate, polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyamide, polyimide, polyolefin, polyvinyl chloride, cellulose derivative, polyacrylonitrile, Mention may be made of synthetic polymer compounds such as polystyrene. Further, other binary or ternary copolymers, graft copolymers, mixtures of various polymers and the like can also be used.

The optically anisotropic layer (a) is obtained by, for example, melt-extruding a thermoplastic resin having the above positive intrinsic birefringence value,
A solution casting method or a calendar method is used to form a film, and the film is passed between a pair of rollers having different peripheral speeds to give a shearing force difference between both surfaces of the film. It can be obtained by orienting the angle of the polymer compound molecule. A detailed description of this method is given in Japanese Patent Application No. 4-324116.
In addition, since a film made of a thermoplastic resin having a positive intrinsic birefringence value oriented in this manner is less likely to undergo orientation relaxation, it is usually unnecessary to perform a special orientation fixing treatment. However, if necessary, an orientation fixing treatment that is used when the orientation is performed using a low molecular weight compound having a positive intrinsic birefringence value, which will be described later, may be performed. Optically anisotropic layer (a)
Or, by applying a magnetic field, an electric field, or polarized light to a low-molecular weight compound having a positive intrinsic birefringence value applied on a support to orient the low-molecular weight compound, and then fixing the orientation. Can also be manufactured. In addition, the same material as the alignment film used for aligning the liquid crystal during the production of the liquid crystal cell is used, and a liquid crystalline low-molecular compound having a positive intrinsic birefringence value is applied and aligned to fix it. The optical anisotropic layer (a) can also be produced by the method described above.

As a method of fixing the orientation of a low molecular weight compound having a positive intrinsic birefringence value, for example, the low molecular weight compound and an immobilizing agent (such as a monomer having an unsaturated bond),
Then, a method of preparing a reactive composition comprising a photopolymerization initiator or a thermal polymerization initiator, and at the same time as orienting the film formation thereof, or immediately afterward, applying light or heat to cause a polymerization reaction to form a resin film Is used. Alternatively, a compound having a reactive group is selected as a low molecular weight compound having a positive intrinsic birefringence value, and this is mixed with a material forming a polymer matrix to prepare a film-forming composition, which is then formed into a film. A film in which the orientation is fixed by reacting the low molecular weight compound with the polymer matrix material by using a method of applying heat, application of light, or change of pH immediately after or immediately after the orientation can be obtained. Further, only a compound having a reactive group is used as a low molecular weight compound having a positive intrinsic birefringence value, at the same time as film-forming orientation of this, or immediately after that, cross-linking polymerization is performed by a method such as application of heat or application of light, It is also possible to obtain a film having a fixed orientation. In addition, it is also possible to use various other known orientation fixing methods.

Examples of the thermal polymerization initiator used for the above purpose include azo compounds, organic peroxides, inorganic peroxides, sulfinic acids and the like. Details of these compounds are described on pages 6 to 18 of “Addition Polymerization / Ring-Opening Polymerization” edited by The Society of Polymer Science, Editorial Committee for Polymer Experiments. Examples of the photopolymerization initiator include benzophenones, acetophenones, benzoins, thioxanthones and the like. Details thereof are described on pages 63 to 147 of "Ultraviolet curing system" (1989, published by General Technology Center).

The optically anisotropic layer (b) is oriented in the plane direction by, for example, a method of stretching (uniaxially stretching or biaxially stretching) a film produced from a thermoplastic resin having a positive intrinsic birefringence value. Can be given and manufactured.

The optical anisotropic element comprising the optical anisotropic layer (a) and the optical anisotropic layer (b) of the present invention can be used alone (one sheet) as a retardation film, but if desired, it can be used as a retardation film. It is also possible to use a combination of more than one sheet (such as lamination).

[0021]

【Example】

Example 1 Preparation of Optically Anisotropic Element (KI-1) A photopolymerizable oligomer (UN900PEP, manufactured by Negami Kogyo Co., Ltd.) 1 on a uniaxially stretched polycarbonate film.
Parts by weight, tetrahydrofuran 19 parts by weight, and a small amount of benzophenone.
After drying for a minute, a nematic liquid crystal (ZL14
788-100, manufactured by Merck Japan Co., Ltd., and a magnetic field of 5 kG is applied while applying a magnetic field of 5 kG at an angle inclined by 70 degrees from the normal direction of the coating film surface to the direction perpendicular to the stretching axis in the film surface. The nematic liquid crystal was aligned and fixed by irradiating it with ultraviolet rays from a lamp. Then, it was covered with a cellulose triacetate film to obtain an optically anisotropic element (KI-1) according to the present invention.

Example 2 Production of Optically Anisotropic Element (KI-2) Between two heating rollers having different peripheral speeds (clearance:
100 μm, heating temperature: 145 ° C.), thickness 115 μm
Of the polycarbonate film (Upilon, manufactured by Mitsubishi Gas Chemical Co., Inc.) to produce a tilted polycarbonate film (KS-1). The peripheral speed ratio of the heating roller was 7: 8, and the peripheral speed of the slower roller was 1.9 m / min. Separately, by uniaxially stretching a polycarbonate film, the thickness is 100 μm.
Then, an optically anisotropic film (CO-1) having a retardation value of 300 nm was produced. Then, the tilted polycarbonate film (KS-1) and the optically anisotropic film (CO-1) were laminated in an orthogonal manner to obtain an optical anisotropic element (KI-2) according to the present invention.

Example 3 Preparation of Optically Anisotropic Element (KI-3) Polysulfone (Udel P-350) was formed on a flat temporary support.
0, manufactured by Amoco Japan Co., Ltd.) was cast to form a casting film, which was dried to produce a polysulfone film. Next, this polysulfone film was stretched at 200 ° C. by 14% to have a thickness of 100 μm and a retardation value of 300 n.
m optically anisotropic film (FO-1) was produced. The optically anisotropic element (KI-3) according to the present invention is obtained by orthogonally laminating the optically anisotropic film (FO-1) and the graded polycarbonate film (KS-1) produced in Example 2. It was

Example 4 Production of Optically Anisotropic Element (KI-4) On a uniaxially stretched polycarbonate film, SiO was used as a vapor deposition material and oblique vapor deposition was performed at a vapor deposition angle of 70 degrees.
Nematic liquid crystal (MBBA, Merck.
Japan Co., Ltd.) methylene chloride solution (concentration: 1% by weight) is applied, dried and then heated to 70 ° C.,
By cooling, a fixed nematic layer having a thickness of 0.5 μm was formed. After that, it was covered with a cellulose triacetate film to obtain an optically anisotropic element (KI-4) according to the present invention.

Optically anisotropic elements (K
Table 1 shows the optical characteristics of I-1 to KI-4).

Table 1 ──────────────────────────────────── Optical anisotropic optical axis tilt Angle element Optical anisotropic layer (a) Optical anisotropic layer (b) Optical anisotropic element ────────────────────────────── ─────── KI-1 70 degrees (liquid crystal layer) 0 degrees (stretched film) 20 degrees KI-2 60 degrees (different rolling speed) 0 degrees (stretched film) 20 degrees KI-3 60 degrees (same as above) ) 0 degree (stretched film) 30 degree KI-4 70 degree (liquid crystal layer) 0 degree (stretched film) 20 degree ──────────────────────── ─────────────

When measuring the inclination of the optical axis, an ellipsometer AEP-100 manufactured by Shimadzu Corporation was used in the transmission mode, and the film to be measured was AEP-
It was mounted on a goniometer placed between a 1000 λ / 4 plate and an analyzer, the film was rotated, and the direction in which the values of the ordinary light refractive index and the extraordinary light refractive index were equal was set as the optical axis.

Example 5 Preparation of Optically Anisotropic Element (KI-5) Two optical anisotropic elements (KI-1) obtained in Example 1 were prepared, and they were used in the directions of their respective main refractive indices. Were laminated so as to be different from each other by 90 degrees (that is, orthogonal to each other) to obtain an optically anisotropic element (KI-5) according to the present invention.

Example 6 Fabrication of Optically Anisotropic Element (KI-5) Three optical anisotropic elements (KI-1) obtained in Example 1 were prepared, and they were made to have the main refractive index of each other. Direction 45
The optical anisotropic element (KI-6) according to the present invention was obtained by sequentially stacking them with different degrees.

An ordinary liquid crystal display device (Liquor made by Otsuka Electronics Co., Ltd.) consisting of a liquid crystal cell in which a TN type liquid crystal is sandwiched between two electrode substrates and two polarizing elements arranged on both sides of the liquid crystal cell.
CD-5000) was prepared, and the optical anisotropic elements of Examples 1 to 6 were arranged between the liquid crystal cell and the polarizing element, and the viewing angle characteristics of 0V / 5V contrast were measured.
Table 2 shows the measured values of the vertical and horizontal viewing angle characteristics based on the contrast of 10.

Table 2 ──────────────────────────────────── Optical anisotropic viewing angle Characteristic element ~ Bottom left ~ Right ──────────────────────────────────── KI-1 48 degrees-46 degrees 45 Degree ~ 46 degree KI-2 40 degree ~ 38 degree 42 degree ~ 40 degree KI-3 42 degree ~ 40 degree 44 degree ~ 40 degree KI-4 48 degree ~ 46 degree 45 degree ~ 46 degree KI-5 51 degree ~ 52 degree Degree 50 degree ~ 49 degree KI-6 53 degree ~ 54 degree 55 degree ~ 54 degree ───────────────────────────────── ───── None (Comparative example) 29 degrees to 18 degrees 33 degrees to 36 degrees ────────────────────────────── ──────

From the above results, it is apparent that the addition of the optical anisotropic element of the present invention can realize a large increase in viewing angle.

[0033]

By using the optically anisotropic element of the present invention, the viewing angle characteristics of a liquid crystal display element (particularly a liquid crystal display element using a TN type liquid crystal) are significantly improved, and a high-quality display liquid crystal with excellent visibility is obtained. A display element can be obtained. The optical anisotropic element of the present invention is particularly useful when applied to an active matrix liquid crystal display element using a TFT or MIM type three-terminal or two-terminal active element.

Claims (6)

[Claims] 1. A laminated body of the following optical anisotropic layer (a) and optical anisotropic layer (b), the optical axis of which is tilted within a range of 10 to 40 degrees from the direction normal to the surface of the laminated body. Optically anisotropic element: (a) Optically anisotropic layer having positive uniaxiality, the optical axis of which is tilted from the direction normal to the surface of the laminate; (b) Positive uniaxiality, and its optical axis is laminated. An optically anisotropic layer in a plane parallel to the body surface. 2. The optically anisotropic element according to claim 1, wherein the optically anisotropic layer (a) is a layer containing a nematic liquid crystal. 3. The optical anisotropic element according to claim 1, wherein the optical anisotropic layer (a) is made of a thermoplastic resin obtained by passing between two rolling rolls having different peripheral speeds. 4. The optically anisotropic element according to claim 1, wherein the optically anisotropic layer (b) is a uniaxially stretched thermoplastic resin having a positive intrinsic birefringence value. 5. The optical anisotropic element according to claim 1, wherein the optical anisotropic layer (a) and the optical anisotropic layer (b) are laminated so that the directions of the main refractive indexes thereof are orthogonal to each other. 6. A liquid crystal cell in which a TN liquid crystal is sandwiched between two electrode substrates, two polarizing elements arranged on both sides of the liquid crystal cell, and arranged between the liquid crystal cell and the polarizing element. 6. A liquid crystal display element comprising the optically anisotropic element according to claim 1.