JP3434346B2 - Optical compensatory sheet made of discotic compound and liquid crystal display device using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensatory sheet made of at least a discotic compound and having a remarkably improved heat resistance, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art CRTs, which are the mainstream display devices for office automation equipment such as Japanese word processors and desktop personal computers
Have been converted into liquid crystal display elements which have the great advantages of thinness, light weight, and low power consumption. Most of the liquid crystal display elements (hereinafter, referred to as LCDs) that are currently popular 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.

An LCD using the birefringence mode has a twisted angle of 90 ° or more in the alignment of liquid crystal molecules and has steep electro-optical characteristics, so that it has a simple matrix without active elements (thin film transistors or diodes). A large-capacity display can be obtained by the time-divisional behavior with the electrode structure in the shape of a circle. But,
The response speed is slow (hundreds of milliseconds), and gradation display is difficult, and a liquid crystal display element (TFT-
It does not exceed the display performance of LCD and MIM-LCD.

For the TFT-LCD and MIM-LCD, a display system (TN type liquid crystal display element) of optical rotation mode 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. However, since the twisted nematic liquid crystal is used, there is a problem in the viewing angle characteristics that the display color and the display contrast change depending on the viewing direction due to the principle of the display system.
It does not exceed the display performance of T.

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 retardation of almost zero in the direction perpendicular to the liquid crystal cell, and does not exert any optical action from the front.
A phase difference appears when tilted, and the phase difference that appears in the liquid crystal cell is compensated. However, even with these methods, the viewing angle of LCD is still insufficient, and further improvement is desired. In particular, when considered as a vehicle-mounted type or as a substitute for a CRT, it is the current situation that the current viewing angle cannot support at all.

Further, 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. It is a layered liquid crystal system, which is expensive and very heavy. Further, JP-A-5-80323 proposes a method of using a retardation film having an optical axis inclined with respect to a liquid crystal cell. However, since uniaxial polycarbonate is obliquely sliced and used. However, there is a problem that it is difficult to obtain a large area retardation film at low cost.

Further, Japanese Patent Application No. 5-5823 describes a method of using a photoisomerizable substance and a retardation film having an inclined optical axis. According to this method, a liquid crystal display device having a wide viewing angle characteristic, a light weight, and a low cost can be realized. However, the drawback of this method is that the retardation film is not sufficiently stable against heat and light.

Japanese Unexamined Patent Publication (Kokai) 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. However, this plan is no different from the so-called double-cell type compensator that has been proposed in the past, which results in a great increase in cost and is practically unsuitable for mass production. Further, as long as a rod-shaped compound is used, the birefringent plate has a T
It is impossible to improve the viewing angle in all directions of N-type LCD.

Further, in JP-A-3-9326 and JP-A-3-291601, L is obtained by applying a polymer liquid crystal to a film-like substrate provided with an alignment film.
Although an optical compensating plate for CD is described, it is impossible to improve the viewing angle in all directions of the TN type LCD because it is impossible to align the molecules obliquely by this method.

On the other hand, the inventor of the present invention has filed Japanese Patent Application No. 5-23653.
According to the specification of No. 9, when a triphenylene compound is oriented on a plane-oriented transparent film, the optical axis of a thin film made of the triphenylene compound is inclined, and optical compensation is performed by interaction of different optical characteristics of these two layers. It was shown to be useful as a sheet. However, high temperature (80
Since it lacks orientation stability at (° C to 100 ° C) and its optical characteristics change with isothermal aging, there is a problem that it is not suitable for use in a high temperature state such as in a vehicle.

[0011]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical compensation sheet which is excellent in heat resistance and remarkably improves the viewing angle characteristics of a conventional LCD, and a liquid crystal display device using the same. Especially.

[0012]

As a result of intensive studies, the present inventor has (1) at least a disk on a transparent film having an optically negative uniaxial property and an optical axis in the normal direction of the film. An optical compensation sheet having a layer containing a crystalline compound, and a layer formed of the discotic compound having optical anisotropy. (2) The optical compensation system according to (1), wherein the discotic compound is represented by the following general formula (1) and has a reactive functional group P at the end of its radial side chain. -G. In the general formula (1) R _nk -D- (L-P) _k , D is at the center of the molecule, and a total of n substituents R and substituents (P-L)-are n-functionally arranged radially. Represents the group of. Each of the k P's independently represents an isocyanate group, a thiocyanate group, an amino group, an alkylamino group, an arylamino group, a mercapto group, a formyl group, an acyl group, a hydroxyl group, a carboxyl group, a sulfo group, a phosphoryl group, a halocarbonyl group. , A halosulfonyl group, a halophosphoryl group, an acryloyl group, a vinyloxy group, an epoxy group, and a propargyl group, each of (n−k) R independently represents a functional group that does not contribute to the formation of the polymerization composition, and L represents Each independently, P
Represents a group or a chemical bond connecting D and D, n represents an integer of 3 to 8, and k represents an integer of 1 to n. (3) A polymerizable composition comprising a disk-shaped compound represented by the general formula (1), wherein the layer formed of the disk-shaped compound has a reactive functional group P at the end of its radial side chain. The optical compensation sheet according to (2), which is a polymerized product. (4) The layer formed of the discotic compound has an optically negative uniaxial property, and the optical axis is 5 ° from the normal direction of the film.
The optical compensation sheet according to (1), wherein the optical compensation sheet is inclined by 85 °. (5) Re value defined by the following equation (2) is 20 nm to 3
The optical compensation sheet according to (4), which is in the range of 00 nm. Formula (2) Re = | ne-no | × d ne: Refractive index in the optical axis direction no: Refractive index in the direction perpendicular to the optical axis d: Film thickness (μm) (6) Between two electrode substrates In a liquid crystal display device including a liquid crystal cell having a liquid crystal sandwiched between two polarizing elements and two polarizing elements disposed on both sides of the liquid crystal cell, at least one optical compensation sheet according to (1) is provided between two polarizing plates. A liquid crystal display device having. It has been found that the present invention can be achieved by

The present invention will be described in detail below. The discotic compound of the present invention generally means benzene or 1,3,5
-A structure in which a cyclic mother nucleus such as triazine and calixarene is arranged at the center of the molecule, and a linear alkyl group, an alkoxy group, a substituted benzoyloxy group, etc. are radially substituted as its side chain, The discotic compound that is preferably used is a polymerization composition of a discotic liquid crystal compound that easily moves when heated, molecules are easily oriented, that is, liquid crystal properties are physically exhibited.

Typical examples of the discotic liquid crystal compound include C.I. Research report of Destrade et al.,
Mol. Cryst. Liq. Cryst. Volume 71, 1
Benzene derivative, triphenylene derivative, truxene derivative, phthalocyanine derivative described in p. 11 (1981); Research Report by Kohne et al., An
gew. Chem. 96, 70 (1984), and cyclohexane derivatives described in J. M. Lehn et al., J. Chem. Soc. Chem. Com
mun. , Pp. 1794 (1985), J. Zhang
Et al., J. Am. Chem. Soc. 116
Vol. 2, pp. 2655 (1994). Examples include azacrown-based and phenylacetylene-based macrocycles.

The general formula (1) of the present invention is as follows:
The details will be described. The multi-functional group D having a discoid structure is the above-mentioned discotic liquid crystal compound group. A triphenylene ring, a truxene ring, an inositol ring, an azacrown ring and a phenylacetylene macrocycle are preferable, and a triphenylene ring and a truxene ring are more preferable.

Each of the k P's independently represents an isocyanate group, a thiocyanate group, an amino group, an alkylamino group,
It represents an arylamino group, a mercapto group, a formyl group, an acyl group, a hydroxyl group, a carboxyl group, a sulfo group, a phosphoryl group, a halocarbonyl group, a halosulfonyl group, a halophosphoryl group, an acryloyl group, a vinyloxy group, an epoxy group and a propargyl group. Preferably, a mercapto group,
Formyl group, hydroxyl group, halocarbonyl group, acryloyl group, vinyloxy group and epoxy group. More preferred are a hydroxyl group and an acryloyl group.

Each of the (nk) R independently represents a functional group that does not contribute to the formation of the polymerized composition, but whether or not it contributes depends on the functional group of the condensation partner. But,
Generally, an alkyl group, an alkoxy group, an oligooxyethylene group, an acyl group, an acyloxy group, a benzoyloxy group and a benzoyl group are preferably used. But,
It may have a structure in which adjacent Rs are linked to each other to form a ring, and one or two side chains are radially substituted.

Each L independently represents a group or a chemical bond connecting P and D. For example, an alkylene group (for example,
Ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene), alkyleneoxy group (for example, ethyleneoxy, propyleneoxy, butyleneoxy, pentyleneoxy, hexyleneoxy, heptyleneoxy, octyleneoxy, nonyleneoxy), phenylene And a group having a carbonyl group on one side of the group and the alkylene group (for example, 1-oxononylene). An alkyleneoxy group is preferable, and an ethyleneoxy group and a hexyleneoxy group are more preferable. However, a structure in which adjacent Ls are linked to each other to form a ring, and further 1 or 2 side chains are radially substituted, and P is substituted at the terminal may be used. n represents an integer of 3 to 8, and k represents an integer of 1 to n.

Specific examples of the compound of the present invention represented by the general formula (1) are shown below, but the present invention is not limited thereto.

[0020]

[Chemical 1]

[0021]

[Chemical 2]

[0022]

[Chemical 3]

[0023]

[Chemical 4]

[0024]

[Chemical 5]

[0025]

[Chemical 6]

[0026]

[Chemical 7]

[0027]

[Chemical 8]

[0028]

[Chemical 9]

[0029]

[Chemical 10]

[0030]

[Chemical 11]

[0031]

[Chemical 12]

[0032]

[Chemical 13]

When polymerizing or cross-linking these low molecular weight compounds having a reactive substituent, the low molecular weight compounds are easier to move and the alignment time is faster. Therefore, after coating on the transparent film of the present invention, It is preferably performed on the transparent film. Therefore, at least one of the interfaces is in contact with the gas phase, that is, the liquid crystal thin film is formed on a suitable support by a general coating method, and after drying, the discotic nematic phase is formed at a temperature within the liquid crystal phase formation temperature range. Alternatively, an optical anisotropy having desired optical properties and high thermal durability by heat-treating for a certain period of time while forming a uniaxial columnar phase and then directly performing thermal polymerization or photocrosslinking polymerization and then cooling. A conductive material can be obtained.

The polymerization process used in the present invention is generally carried out after the liquid crystal exhibits a preferable optical anisotropy, that is, the monodomain is uniaxially aligned by heating on the alignment film. In the case of an epoxy group, cationic type polymerization by ultraviolet rays is also possible, but after orientation in a short time, the temperature can be further raised by several tens of degrees and fixed by thermal polymerization. However, radical polymerization or cationic polymerization using a photopolymerization initiator with ultraviolet rays generally has a very high polymerization rate and is preferable in terms of productivity in the manufacturing process.

Examples of the photopolymerization initiator in the present invention include US Pat. Nos. 2,367,661 and 2,367,67.
No. 0 α-carbonyl compounds described in each specification,
Acyloin ethers described in US Pat. No. 2,448,828, US Pat. No. 2,722,512
.Alpha.-hydrocarbon substituted aromatic acyloin compounds described in U.S. Pat. No. 3,046,127.
No. 2,951,758, a polynuclear quinone compound, a combination of a triarylimidazole dimer / p-aminophenyl ketone described in US Pat. No. 3,549,367, JP-A-6
0-105667, acridine and phenazine compounds described in US Pat. No. 4,239,850, oxadiazole compounds described in US Pat. No. 4,212,970, and the like. . The content concentration of these photopolymerization initiator systems in the composition of the present invention is usually low, and when the content is inappropriately high, undesired results such as blocking of effective rays are produced. The amount of photoinitiator system in the present invention is 0.
The range of 01% to 20% is sufficient, and more preferably 0.5% to 5% to obtain good results. Further, in the present invention, various organic amine compounds can be used in combination, if necessary, thereby enhancing the effect. Examples of these organic amine compounds include triethanolamine, diethanolaniline, p-dimethylaminobenzoic acid ethyl ester, and Michler's ketone. The amount of the organic amine compound added is preferably 50 to 200% of the total amount of the photopolymerization initiator. Further, the photopolymerization initiator used in the present invention may contain N-phenylglycine or 2
The photopolymerization initiation ability can be further increased by adding a hydrogen donating compound such as -mercaptobenzothiazole or N, N-dialkylaminobenzoic acid alkyl ester. Further, in order to suppress polymerization inhibition by oxygen,
Adding a small amount of a surfactant is often effective.

For the polymerization of epoxy groups, allyldiazonium salts (hexafluorophosphate, tetrafluoroborate), diallyliodonium salts, VIa group allylonium salts (PF6, As) are used as UV-activated cation catalysts.
An allylsulfonium salt having an anion such as F6 or SbF6) is preferably used.

As the light rays for photopolymerization, electron rays, ultraviolet rays, visible rays and infrared rays (heat rays) can be used as required, but ultraviolet rays are generally used. The light sources are low-pressure mercury lamps (sterilization lamps, fluorescent chemical lamps, black lights), high-pressure discharge lamps (high-pressure mercury lamps, metal halide lamps), and short arc discharge lamps (ultra-high pressure mercury lamps, xenon lamps, mercury-xenon lamps). Can be mentioned.

In the case of the benzoyloxytriphenylene ring compound of the present invention, it generally has λmax at ˜270 nm and its large molecular extinction coefficient, so that short-wave ultraviolet rays of 254 nm and the like are not effectively used. Therefore, as the photopolymerization initiator, a compound having an absorption band in the near ultraviolet described below is preferably used, and a light source that can strongly emit near ultraviolet light, such as a high pressure mercury lamp or a metal halide lamp is also preferably used.

Further, a polymerization composition obtained by polymerizing the low molecular weight compound may be coated on the transparent film of the present invention. The term "polymer composition containing at least one discotic compound represented by the general formula (1)" means a compound containing two or more residues of the discotic liquid crystal compound, which are the same or different from each other. Examples of the state in which a plurality of dimers are included include so-called oligomers and so-called polymers of dimers, trimers and quanta. To form these states, for example, a method of reacting and linking polymerizable discotic compounds, a method of reacting and coupling a polymerizable discotic compound with another polymerizable compound, a polymer chain After the formation of the compound, a method of reacting it with a discotic compound, for example, a halogen atom, a polymer having a substituent active in a nucleophilic reaction such as aryl sulfonate, for example, a hydroxy group, an amino group, a mercapto group such as Examples thereof include reacting a discotic compound having a substituent capable of nucleophilic reaction. The state of the formed ones is, for example, a state in which the discotic molecule is crosslinked, the discotic molecule itself forms a part of the main chain of the polymer, and the discotic molecule is pendant to the polymer chain. It may be in the state of being bound together. Below, the specific example of a polymeric composition is shown.

[0040]

[Chemical 14]

[0041]

[Chemical 15]

[0042]

[Chemical 16]

The fact that the triphenylene discotic liquid crystal has a negative birefringence is described in B. Research report of Maurey et al. [Mol. Cryst. Liq. Cryst. , 8
4, p. 193 (1982)], in order to apply this property as an optically anisotropic material, all the molecules constituting the thin film are statistically oriented in one direction at room temperature. It is necessary to be lined up. Moreover, the discotic liquid crystal is composed of an alignment region (domain) having a specific directionality microscopically, and does not show optical anisotropy macroscopically, like the liquid crystal composed of conventional rod-shaped molecules. Due to the property of forming a so-called multi-domain, the thin film often does not exhibit favorable optical properties that can be used for an optical compensation sheet.

The above-mentioned polymerization composition often exhibits liquid crystallinity thermally, but it is often optically suspended in white, and even if it is transparent, it hardly has anisotropic properties. . However, these polymerization compositions are dissolved in a suitable solvent, and the method is disclosed in JP-A-3-9326 and JP-A-3-291601.
As described in JP-A-5-142510, coating on a polyimide film which is an alignment film for liquid crystal.
It was revealed that orientation can be easily achieved by heating. As the solvent, for example, chloroform,
Halogenated hydrocarbons such as dichloroethane, tetrachloroethane, trichloroethylene, orthodichlorobenzene, mixed solvents of these with phenolic solvents such as phenol, o-chlorophenol, cresol, dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, etc. An aprotic polar solvent, tetrahydrofuran, dioxane is used. The coating concentration varies depending on the coating method, the viscosity of the polymerization composition, etc., but is used in the range of 5 to 50 wt%, preferably 1
It is in the range of 0 to 30 wt%. As a coating method, a spin coating method, a roll coating method, a gravure coating method, a dipping method or the like can be adopted.

The solvent is removed by drying, and heat treatment is performed at a predetermined temperature for a predetermined time to complete the liquid crystal alignment in a monodomain, and then the temperature is cooled to a temperature not higher than the glass transition point. The heat treatment temperature at this time is selected from the temperature above the glass transition point of the polymerization composition. The viscosity of the polymer composition is preferably low in order to assist the orientation due to the interfacial effect of the orientation film, and thus the heat treatment temperature is preferably high, but if it is too high, the production cost increases and the workability deteriorates, which is not preferable. In general, a liquid crystalline polymer has an isotropic phase at a temperature higher than that of a nematic phase, but even if it is heat-treated in this temperature range, uniform alignment is often not obtained. As described above, the heat treatment temperature needs to be equal to or higher than the glass transition point of the polymerization composition of the present invention, and is preferably equal to or lower than the transition point to the isotropic phase. Generally 50-30
The range of 0 ° C is preferable, and the range of 100 to 250 ° C is particularly preferable. The time required to obtain sufficient alignment in the liquid crystal state on the alignment film varies depending on the composition and molecular weight of the polymerization composition and cannot be generally stated, but is preferably in the range of 10 seconds to 60 minutes, and particularly 20 seconds to 3 minutes. The range of minutes is preferred.
Further, the polymer composition of the present invention can obtain the same alignment state by applying a heat treatment to a substrate which has been subjected to the alignment treatment in a molten state and then performing a heat treatment. Further, surprisingly, an anisotropic film in which not only the monodomain property but also the optical axis of the thin film was often tilted was obtained only by the operations of coating on this alignment film, heating alignment, and cooling.

An inorganic or organic alignment film is used as the alignment film. A typical example of the metal oblique evaporation film is a SiO oblique evaporation film, and a typical example of an organic alignment film is a rubbed polyimide film. In addition, a glass treated with a rubbed alkyl-modified poval or a rubbed silylating agent. A substrate or a rubbed gelatin film is used. However, instead of rubbing, a method in which a polyvinyl alcohol thin film is stretched 4 to 5 times, or a glass substrate is directly rubbed without providing the above protective film can be used.

Even if an alignment film is not used, a thin-film polymerized composition obtained by coating or melting is applied to Helmut.
Ringsdorf, Macromol. Chem. ，
Rapid Commun. Volume 7, page 97 (1986
Year). As described in (1), an optically uniaxial anisotropic sheet can also be obtained by performing a stretching operation at a temperature near the glass transition point.

Further, the polymerization composition of the present invention is disclosed in Japanese Patent Laid-Open No.
-120512 gazette, Polymer, 26 volumes, 85
Page 3 (1985), Applied Physics
As described in Letter, 24, page 15 (1974), it can be oriented by placing it in a high electromagnetic field in a heated state at a temperature above its glass transition point. At that time, the optical axis can be tilted by placing it obliquely in a high electromagnetic field.

As another method of tilting the optical axis, the polymer composition sheet of the present invention obtained by coating and stretching on the alignment film is heated to a temperature higher than its glass transition point, and there is a difference in peripheral speed or reverse. This is possible by sandwiching the sheet between two rollers that rotate so as to advance the film in the direction and pulling it out.

Negative uniaxiality in the present invention means a relationship of nα <nβ = nγ, where nα, nβ, and nγ are the refractive indices of the sheet having optical anisotropy in the triaxial directions in ascending order. I have. Therefore, it has a characteristic that the refractive index in the optical axis direction is the smallest. However, it is not necessary that the values of nβ and nγ be exactly equal, and it is sufficient if they are almost equal. Specifically, (nβ-nγ) / (nβ-n
If α) <0.2, there is no practical problem. In addition, TFT,
As a condition for greatly improving the viewing angle characteristics of the TN type liquid crystal cell, the optical axis is preferably inclined by 5 to 85 degrees from the normal direction of the sheet surface, more preferably 10 to 40 degrees, and more preferably 10 degrees. Most preferred is -30 degrees. Further, when the thickness of the sheet is D, 50 <(nβ-nα) × D <300n
It is desirable to satisfy the condition of m.

The transparent film of the present invention preferably has good light transmittance. Specifically, the light transmittance is 80%
It is preferably at least 90%, more preferably at least 90%. Therefore, a support 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 Film), or the like is preferable. However, even if the material has a large intrinsic birefringence value such as polycarbonate, polyacrylate, polysulfone, and polyethersulfone, it is possible to form an optically isotropic support by controlling the molecular orientation during film formation. It is possible, and they are preferably used.
Specifically, the range of the Re value represented by the formula (2) is 20
nm to 300 nm, more preferably 30 nm to 15
It is 0 nm. By satisfying the condition of this plane orientation,
It has a remarkable effect on the improvement of the viewing angle characteristics.

A protective layer may be provided on the layer containing the discotic compound of the present invention. Specific examples include, for example, polymethylmethacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleic anhydride copolymer. , Polyvinyl alcohol, N-methylol acrylamide, styrene
Vinyltoluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, polyethylene, polypropylene, polycarbonate, etc. Polymeric substances; and organic substances such as silane coupling agents may be mentioned. In addition, Langmuir-Blodgett method (LB-method such as ω-tricosanoic acid, dioctadecyldimethylammonium chloride and methyl stearate)
A cumulative film formed by the method) can also be used.

[0053]

EXAMPLES The present invention will now be described based on examples. Example 1 Triacetyl cellulose 85 μm thick film coated with a gelatin thin film (0.1 μm) (Fuji Photo Film Co., Ltd.)
Made as a transparent support, on which long-chain alkyl-modified PV
A (MP-203 manufactured by Kuraray Co., Ltd.) was applied, dried with warm air, and then subjected to a rubbing treatment to form an alignment film. On this alignment film, 1 wt% of Michler's ketone + benzophenone (weight ratio 1: 1) was added to a 10 wt% methyl ethyl ketone solution of TP-38, and was applied by spin coating. This is heated to 130 ° C., and after 8 minutes, an ultraviolet irradiation device (ULTRA-VIOLET PRODUCTS).
UVSL-58) manufactured by the same company was used for exposure for 2 minutes, and then cooled to room temperature to prepare an optical compensation sheet RF-1. Examples 2 and 3 Two kinds of the polymerization compositions TP-85 and TP-30 were applied under the same conditions as in Example 1 instead of TP-38, and each was heated at the temperature shown in Table 1 below and treated with ultraviolet rays. Then, optical compensation sheets RF-2 and RF-3 were produced. Comparative Example 1 In Example 1, ND-25 was coated under the same conditions as in Example 1 instead of TP-38, and each was heated at the temperature shown in Table 1 below and treated with ultraviolet light to obtain an optical compensation sheet RF-. Four
Was produced.

[0054]

[Table 1]

[0055]

[Chemical 17]

Example 4 DP-14 as a 20 wt% dichloromethane solution was coated on the same alignment film as in Example 1 and dried. This was heated at 130 ° C. for 10 minutes and then cooled to room temperature to prepare an optical compensation sheet RE-5.

Comparative Example 2 An optically isotropic glass substrate coated with a gelatin thin film (0.1 μm) was used as a transparent support, and a long-chain alkyl-modified PVA (MP-produced by Kuraray Co., Ltd.) was formed on the transparent support. 203) was applied and dried with warm air, and then a rubbing treatment was performed to form an alignment film. On this alignment film, 10w of TP-38
1 wt% of Michler's-ketone + benzophenone (weight ratio 1: 1) was added to a t% methyl ethyl ketone solution and applied by spin coating. This is heated to 130 ° C., and after 8 minutes, an ultraviolet irradiation device (ULTRA-VIOLET PR
An optical compensation sheet RF-6 was prepared by exposing it for 2 minutes using UVSL-58 manufactured by ODUCTS and then cooling it to room temperature.

Regarding the optical characteristics of the optical compensation sheet, an ellipsometer AEP-100 manufactured by Shimadzu Corporation was used.
The Re value of the layer made of the discotic compound and the direction of the optical axis were calculated from the measured values. By the way, the Re value of the transparent support is 150 nm, and the optical axis is in the direction of the film normal.
Further, when the direction in which the Re value became 0 was examined, it was found that it was not present in all the optical compensation films. For heat resistance evaluation, 80 ° C, 1000h
After the forced test of r, the Re value and the direction of the optical axis of the layer made of the discotic compound were measured to examine the change from the value before the forced test. The results are summarized in Table 2. Further, the domain size of the discotic liquid crystal was observed with a polarization microscope.

[0059]

[Table 2]

(Incorporation into Liquid Crystal Display Element) A liquid crystal cell in which a nematic liquid crystal is sandwiched at a twist angle of 90 ° and a gap size of 4.5 μ is provided between a pair of polarizing elements. A liquid crystal display element was prepared by laminating two optical compensation sheets prepared in the above-mentioned examples between the polarizing element and the liquid crystal cell. However, the rubbing direction on the lower side of the liquid crystal cell, the projection direction of nγ of the upper optical anisotropic element on the film surface, and the rubbing direction on the upper side of the liquid crystal cell,
The projection direction of nγ of the lower optical anisotropic element on the film surface is made to coincide. Further, the polarization axes of the polarizing elements were made orthogonal to each other, and a normally white mode TN liquid crystal display element was obtained.

By applying a rectangular wave voltage of 55 Hz to this TN type liquid crystal display, the contrast from the direction tilted in the front direction and the up / down direction and the left / right direction is displayed by Otsuka Electronics LCD.
The measurement was performed using -5000, and the frontal contrast and the upper / lower and left / right viewing angles at which the contrast was 10 or more were obtained and summarized in Table 3.

[0062]

[Table 3]

As is clear from Tables 1 and 2, the optical compensation sheet of the present invention has the effect of widening the viewing angle and is extremely excellent in heat resistance.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-8-50204 (JP, A) JP-A-7-281028 (JP, A) JP-A-7-191217 (JP, A) JP-A-2- 47629 (JP, A) JP 63-279229 (JP, A) JP 6-75116 (JP, A) JP 3-276123 (JP, A) JP 6-3525 (JP, A) JP-A-2-292388 (JP, A) JP-A-56-90878 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 5/30

Claims (6)

(57) [Claims] 1. A layer having at least a discotic compound on a transparent film having an optically negative uniaxiality and an optical axis extending in a direction normal to the film, and a layer formed from the discotic compound. Is an optically anisotropic sheet. 2. The optical according to claim 1, wherein the discotic compound is represented by the following general formula (1) and has a reactive functional group P at the end of its radial side chain. Compensation sheet. In the general formula (1) R _nk -D- (L-P) _k , D is at the center of the molecule, and a total of n substituents R and substituents (P-L)-are n-functionally arranged radially. Represents the group of. Each of the k P's independently represents an isocyanate group, a thiocyanate group, an amino group, an alkylamino group, an arylamino group, a mercapto group, a formyl group, an acyl group, a hydroxyl group, a carboxyl group, a sulfo group, a phosphoryl group, a halocarbonyl group. , A halosulfonyl group, a halophosphoryl group, an acryloyl group, a vinyloxy group, an epoxy group, and a propargyl group, each of (n−k) R independently represents a functional group that does not contribute to the formation of the polymerization composition, and L represents Each independently, P
Represents a group or a chemical bond connecting D and D, n represents an integer of 3 to 8, and k represents an integer of 1 to n. 3. A layer formed of a discotic compound is represented by the general formula (1) and contains at least one reactive functional group P.
3. The optical compensation sheet according to claim 2, which is obtained by polymerizing a discotic compound having a group at the end of its radial side chain. 4. The layer formed of the discotic compound has an optically negative uniaxial property, and the optical axis is tilted by 5 ° to 85 ° from the normal direction of the film. The optical compensation sheet described in 1. 5. The Re value defined by the following formula (2) is 20 n.
The optical compensation sheet according to claim 4, which is in the range of m to 300 nm. Formula (2) Re = | ne-no | × d ne: Refractive index in the optical axis direction no: Refractive index in the direction perpendicular to the optical axis d: Film thickness (μm) 6. A liquid crystal display device including a liquid crystal cell formed by sandwiching liquid crystal between two electrode substrates and two polarizing elements arranged on both sides of the liquid crystal cell, wherein the two polarizing plates are arranged between the two polarizing plates.
A liquid crystal display device comprising at least one sheet of the optical compensation sheet described in 1.