JPH07168021A - Optical compensating sheet and liquid crystal display device using same - Google Patents

Abstract

PURPOSE:To provide an optical compensating sheet which can be manufactured through simple processes and at low cost and exhibit excellent visual characteristics by forming the sheet from a stack of two kinds of optical anisotropic substances, and containing at least one kind of photoisomeric compond in one of the substances. CONSTITUTION:An optical compensating sheet comprises a stack of an optical anisotropic substance (A) meeting n2<n1=n3 and an optical anisotropic substance (B) meeting n1>n2>=n3 i n which n1 and n2 are in-plane refractive indices and n3 is a perpendicular-direction refractive index, the optical anistropic substance (A) containing at least one kind of photoisomer. The photoisomer contained in the optical anisotropic substance (A) undergoes stereoisomerization or structural isomerization under light, and preferably undergoes reverse isomerization under light of other wavelengths or heat. A number of such compounds that undergo tone changes in the visible range as well as structural changes are generally well-known as photochromic compounds, examples of which are azobenzene componds, benzaldoxime componds, azomethine componds, and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensation sheet and a liquid crystal display device using the same, and more particularly, an optical compensation sheet useful for improving the viewing angle characteristics of display contrast and display color and a liquid crystal using the same. Regarding display element.

[0002]

2. Description of the Related Art Liquid crystal display devices have many features such as low voltage and low power consumption, which can be directly connected to an IC circuit, various display functions, and weight reduction. It is widely used as a display device for word processors and personal computers. inside that,
A twisted nematic liquid crystal display device (hereinafter STN-LCD) having a twist angle of liquid crystal molecules of 160 ° or more is capable of displaying a larger capacity than a conventional twisted nematic liquid crystal display device (TN-LCD) having a twist angle of 90 °. Because of its excellent high-speed response, it is currently the mainstream of liquid crystal display devices.

However, the STN-LCD has a drawback in that the background of the displayed image is colored blue or yellow (blue mode or yellow mode). Therefore, in black and white display, the contrast and the visibility are lowered, and colorization is extremely made. There was also the problem of difficulty.

As means for solving the above-mentioned problems, Japanese Patent Laid-Open No. 63-
No. 167303, No. 63-167304, No. 63-1
89804, 63-261302, 63-14.
9624, JP-A-1-201607 and 1-201.
608, 1-105217, JP-A-2-2853.
No. 03, No. 2-59702, No. 2-24406, No. 2-146002, No. 2-257103, JP-A-3.
-23404, 3-126012, 3-181.
As described in Japanese Patent Publication No. 905, No. 3194503, etc., a method using a retardation plate is proposed, and STN-L is used.
It was found that the coloring of the display image by the CD was significantly improved, but the viewing angle characteristics were hardly improved.

Therefore, in order to improve this viewing angle characteristic,
JP-A-2-385303 proposes a method in which a birefringent film having a refractive index in the thickness direction larger than at least one of main refractive indexes parallel to a surface is prepared by electric field orientation and used as a phase plate. Was done. According to this method
Although the change in contrast with viewing angle is reduced and the viewing angle characteristics are improved, the effect is still small, and it is necessary to apply a high voltage to the molten polycarbonate for a long time, which complicates the manufacturing process, resulting in cost reduction. Was difficult to reduce. In addition, Japanese Patent Laid-Open No. 2-16
No. 0204 discloses a method in which a rod-shaped polycarbonate obtained by extrusion molding is cut into a plate shape and polished and used as a retardation plate. In this method, a retardation plate having a subject area is manufactured at low cost. It was extremely difficult to produce. Further, in EP482620A2 publication,
A method of using a film obtained by laminating a heat-shrinkable film on a polycarbonate film and uniaxially stretching it and then peeling off the heat-shrinkable film as a retardation plate is the same as at least the retardation plate in this method. Alternatively, a heat-shrinkable film having a double or more area is required, and there is a problem that it cannot be produced at low cost.

Further, JP-A-2-256023, JP-A-3-141303, JP-A-3-14122 and JP-A-3-24.
In Japanese Patent No. 502, a method is proposed in which one film each having a positive and negative intrinsic birefringence or a laminated film is used as a retardation plate. According to this method, the viewing angle characteristics can be improved by adjusting the birefringence of the two films in accordance with the characteristics of the liquid crystal cell. However, two or more birefringent films prepared separately are used. Things are necessary and that alone adds to the cost.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical compensatory sheet having excellent visual angle characteristics which can be manufactured by a simple process at low cost and uses the optical compensatory sheet. An object of the present invention is to provide a liquid crystal display device having good viewing angle characteristics.

[0008]

The above-mentioned problems are solved when the in-plane refractive indices are n ₁ and n ₂ , and the refractive index in the thickness direction is n ₃ .
Optical anisotropic body (A) with n ₂ <n ₁ = n ₃ and n ₁ > n ₂ ≧ n
_An optical compensatory sheet comprising a laminate of the optical anisotropic body (B) of ₃ , wherein the optical anisotropic body (A) contains at least one photoisomerizable substance. And a liquid crystal cell in which a liquid crystal is sandwiched between two electrode substrates, two polarizing elements arranged on both sides of the liquid crystal cell, and at least one optical compensation sheet between the liquid crystal cell and the polarizing element. This is achieved by a liquid crystal display device characterized by being arranged.

The photoisomerizable substance contained in the optically anisotropic substance (A) in the present invention is one which causes stereoisomerization or structural isomerization by light, and preferably light or heat of another wavelength. It causes the reverse isomerization. Generally, as these compounds, those accompanied by a structural change and a color tone change in the visible region are often well known as photochromic compounds, and specifically,
Azobenzene compounds, benzaldoxime compounds,
Azomethine compounds, stilbene compounds, spiropyran compounds, spirooxazine compounds, fulgide compounds, diarylethene compounds, cinnamic acid compounds,
Examples thereof include retinal compounds and hemithioindigo compounds.

The photoisomerizable substance useful in the present invention, that is, the compound having a functional group capable of photoisomerization may be a low molecular weight compound or a polymer. In the case of a polymer, the photoisomerizable group may be the same in the main chain or the side chain. Can exert the function of. Further, the polymer may be a homopolymer or a copolymer, and the copolymerization ratio of the copolymer is appropriately set to a suitable value in order to appropriately control the physical properties of the polymer such as photoisomerization ability and Tg. Further, these compounds having a functional group capable of photoisomerization may be liquid crystal compounds at the same time. That is, a functional group capable of photoisomerization may be included in the molecule of the liquid crystal compound. For these, polymer, 41, (12),
(1992) p884, "Chromic Materials and Applications"
(CMC edition) p221, "Mechanochemistry"
(Maruzen Edition) p21, "Polymer Thesis Collection Vol. 147, No. 10"
(1991) p771 and the like.

Further, these photoisomerizable substances are, for example,
Alkyl group, alkenyl group, alkynyl group, aryl group, heterocyclic group, cyano group, carboxyl group, carbamoyl group, alkoxycarbonyl group, aryloxycarbonyl group, acyl group, halogen atom, amino group, alkylamino group, arylamino Group, acylamino group, alkylsulfonylamino group, arylsulfonylamino group, ureido group, alkoxy group, aryloxy group, acyloxy group, alkylsulfonyloxy group, arylsulfonyloxy group, alkylthio group, arylthio group, alkylsulfonyl group, arylsulfonyl group It may have a substituent such as a group, a sulfo group and a sulfamoyl group. The substitution position of these substituents is preferably substitution in the major axis direction of the photoisomerizable molecule, but is not particularly limited thereto.

From the above photoisomerizable substance, n ₁ <n ₂ = n
The optically anisotropic substance (A) of ₃ can be obtained by irradiating a photoisomerizable substance previously formed in a film shape with linearly polarized light from a direction perpendicular to the film surface. Conventionally,
It has been known that birefringence is exhibited by irradiating a photoisomerizable substance with linearly polarized light, but its three-dimensional optical characteristics have not been known. The present inventor analyzes the optical characteristics when irradiated with linearly polarized light from the angle dependence of the birefringence value, and thereby obtains negative uniaxial optical characteristics having an optical axis in the direction of linearly polarized light, that is, n ₂ <n ₁ The inventors of the present invention have completed the present invention by finding out that the characteristic of = n ₃ is exhibited.

The optically anisotropic substance (B) in the present invention is obtained by uniaxially stretching or unbalanced biaxially stretching a substantially transparent film made of a polymer having a positive intrinsic birefringence value. Further, conventionally known stretching methods can be used for the stretching. For example, horizontal uniaxial stretching with a longitudinal uniaxial stretching tenter between rolls having different peripheral speeds, uniaxial stretching with roll rolling, and the like can be preferably used.

The polymer having a positive intrinsic birefringence value is not particularly limited, but is particularly polycarbonate, polyarylate, polyethylene terephthalate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyamide imide, polyimide, polyolefin. , Polyacrylonitrile, cellulose, polyester, polysulfone and the like are preferable, and polycarbonate resin and polysulfone resin are particularly preferable.

Next, a preferred method for laminating the optically anisotropic body (A) and the optically anisotropic body (B) to prepare an optical compensation sheet will be described. First of all, an optical anisotropic body (B) is formed by the uniaxial stretching or unbalanced biaxial stretching, a solution containing a photoisomerizable substance is applied on the optical anisotropic body, and a linearly polarized light is obtained through a drying step. Irradiate. All of the above steps are carried out in a continuous process, and there is no need for complicated processes such as an adhesive step, and the production is extremely simple.

The solution to which the polymer is preferably applied as the photoisomerizable substance is prepared by dissolving the photoisomerizable substance in a solvent by a general method. The solvent used varies depending on the kind of the photoisomerizable substance and is not limited, but an organic solvent such as methylene chloride, acetone, methanol, methyl ethyl ketone or the like can be preferably used. Also,
The concentration of the solution is selected so as to obtain a viscosity suitable for coating and is not particularly limited, but is usually 1 to 50%. As the coating method, known coating methods such as bar coating and roll coating can be used.

The polarized light irradiation can be performed from the time when the coating layer is almost dried. Generally, the term “dry” means that the residual solvent in the coating layer is 30 wt% or less. The optimum temperature for polarized light irradiation depends on the amount of residual solvent.
Particularly preferred is g-50 ° to Tg + 30 °. The polarization axis is selected at an angle that does not match the maximum refractive index direction of the optically anisotropic body (B), and the optimum value of the angle made by them is 10 ° to 9 °.
It is 0 °, and more preferably 50 ° to 90 °.
The polarized light source is also not particularly limited, and a mercury lamp, a halogen lamp or the like is preferably used.

The optical compensatory sheet manufactured according to the present invention as described above can prevent the coloring and the contrast reduction due to the change of the viewing angle, which is peculiar to the liquid crystal display, and can provide the liquid crystal display with the improved viewing angle characteristics at a low cost. Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 <Preparation of Optically Anisotropic Body (A)> Makromal. Chem., Rapid C
According to the method disclosed in ommun. 10, 477-483 (1989), a compound (1) having an azobenzene side chain and a molecular weight of 20,000 was synthesized.

[0020]

[Chemical 1]

10 g of the polymer was dissolved in 100 g of a solvent of methanol: methylene chloride = 1: 9 to prepare an azobenzene polymer solution. The solution to a thickness of 0.5
It was applied to a glass substrate of mm by a wire bar. The coating film thickness after drying was 2.0 μm. While heating the substrate to 40 ° C., linearly polarized light having an illuminance of 10000 lux was irradiated from the vertical direction of the substrate to prepare an optically anisotropic body (A). The light source for linearly polarized light was a halogen lamp, which was linearly polarized with an iodine polarizing plate.

<Preparation of Optically Anisotropic Body (B)> Polycarbonate having a molecular weight of 80,000 obtained by condensation of phosgene and bisphenol A was dissolved in methylene chloride to prepare a 10% solution. The solution was cast on a steel drum and continuously peeled off to obtain a transparent polycarbonate film having a thickness of 60 μm and a width of 500 mm. The film was subjected to longitudinal uniaxial stretching with a stretching ratio of 3.5% and 7.2% between rolls having different peripheral speeds under a temperature condition of 170 ° C. to prepare optically anisotropic bodies (B) and (C).

Example 2 <Preparation of Optically Compensatory Sheet> The optically anisotropic body (A) and the optically anisotropic body (B) in Example 1 were irradiated to the optically anisotropic body (A), and the polarization axis of linearly polarized light was irradiated. An optical compensatory sheet (1) was produced by laminating with an acrylic pressure-sensitive adhesive so that the direction and the stretching axis of the optically anisotropic body (B) were orthogonal to each other.

Example 3 <Production of Optical Compensation Sheet> Optically anisotropic substance (B) of Example 1
A 1 μm barrier layer containing gelatin was coated thereon, and the azobenzene polymer solution prepared in Example 1 was coated thereon under the same conditions as in Example 1 to give a thickness on the optically anisotropic body (B). An azobenzene polymer layer having a thickness of 2 μm was formed to prepare an optical compensation sheet (2) which was a laminate of the optically anisotropic substance (B) and the azobenzene polymer. The laminate was irradiated with linearly polarized light having a plane of polarization from the vertical direction to the direction orthogonal to the stretching axis direction of the optically anisotropic body (B). Temperature at this time,
The light source, illuminance, and irradiation time are the same as in the first embodiment.

Example 4 <Measurement of triaxial refractive index> Optically anisotropic substance (A) of Example 1,
Regarding (B), (C), optical compensation sheet (1), (2),
The refractive index in the triaxial direction was determined from the angle dependence of the retardation at a wavelength of 632.8 nm. However, the average refractive index of the optically anisotropic bodies (A), (B) and (C) is 1.59, and among the optical elastic axes n ₁ , n ₂ and n ₃ , n ₁ and n ₂ are in-plane. It is an optical elastic axis and has a relationship of n ₁ ≧ n ₂ ,
₃ is the refractive index in the thickness direction. The results are shown in Table 1.

[0026]

[Table 1]

<Evaluation of viewing angle dependence in liquid crystal panel>
Commercially available liquid crystal display (Sharp word processor "Shoin" W
D551A) is disassembled, the optically anisotropic substance (C) is arranged on both sides of the liquid crystal cell, the optical compensation sheet (1) is arranged on both sides of the liquid crystal cell, and the optical compensation sheet (2) is arranged on both sides of the liquid crystal cell. The viewing angle at which the contrast ratio was 5: 1 or more in the driven state and the non-driven state of the liquid crystal panel was measured for the three cases arranged on the side. In this measurement, the optical axes of the optical compensation sheet and the like were the same as those of the product. The results are shown in Table 2.

[0028]

[Table 2]

As can be seen from Table 2, in the present invention, the viewing angle is widened in the vertical and horizontal directions.

Claims (2)

[Claims] 1. An optical anisotropic body (A) satisfying n ₂ <n ₁ = n ₃ and n ₁ > where n ₁ and n ₂ are in-plane refractive indices and n ₃ is a refractive index in the thickness direction. An optical compensatory sheet comprising a laminate of optical anisotropic bodies (B) satisfying n ₂ ≧ n ₃ , wherein the optical anisotropic body (A) contains at least one photoisomerizable substance. Sheet. 2. A liquid crystal cell in which a liquid crystal is sandwiched between two electrode substrates, and two polarizing elements arranged on both sides of the liquid crystal cell.
A liquid crystal display device comprising at least one optical compensation sheet according to claim 1 disposed between the liquid crystal cell and the polarizing element.