JPH07294903A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [Object] To provide a liquid crystal display device having excellent viewing angle characteristics. [Configuration] A liquid crystal display device having the following configuration. Composition: PL / (PLC / PC / PC / PLC) / Liquid crystal cell / PL where PL: Linearly polarized film (): Compensation retardation layer PC: Uniaxially composed of thermoplastic resin having positive refractive index anisotropy Alignment retardation film PLC: vertical alignment film selected from the following: After forming a polymer liquid crystal showing a nematic phase or a smectic phase, a crystalline phase (or glass phase) / liquid crystal phase transition temperature (Tg) or more liquid crystal phase / A vertical alignment film obtained by heat treatment at a temperature lower than the isotropic phase transition temperature (Ti) for vertical alignment, or after forming a polymerizable liquid crystal oligomer showing a nematic phase or a smectic phase, at a temperature of Tg or higher and lower than Ti. Vertical alignment film obtained by heat treatment for vertical alignment and polymerization while maintaining alignment

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FTN type liquid crystal display device (hereinafter referred to as FTN type LCD).

[0002]

2. Description of the Related Art A liquid crystal display device has a twist angle of the major axis of liquid crystal molecules of 180 to 2 degrees.
70 degree STN type liquid crystal display device (STN type LCD)
Has enabled a large liquid crystal display device of about 10 inches by a simple matrix drive system, and has come to be used for laptop type word processors, personal computers and the like which require a large display capacity. However, this STN type LC
Since D utilizes the birefringence of liquid crystal, it has drawbacks such as poor viewing angle characteristics, colored display, and low contrast.

In order to solve these problems, an FTN type LCD using a uniaxially oriented retardation film made of a thermoplastic resin as a compensating retardation layer for compensating the birefringence of liquid crystal has been developed, and a black and white display is provided. It has become possible to improve the contrast. However, the viewing angle characteristics such that the contrast is lowered or the hue is changed depending on the viewing angle have not yet been satisfied, and improvement of the viewing angle characteristics is desired.

[0004]

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have found that such problems can be solved by using a specific compensation retardation layer in a specific arrangement. .

That is, according to the present invention, nematic liquid crystal molecules having a positive dielectric anisotropy are arranged between a pair of transparent substrates having electrodes inside, and the long axes of the molecules are parallel to the substrates when no voltage is applied. And the long axis of the molecule is 180 in the direction perpendicular to the transparent substrate.
A liquid crystal cell configured to have a twisted structure of 1 to 270 degrees, a pair of linear polarizing films arranged outside a pair of transparent substrates, and a compensation unit arranged between the liquid crystal cell and the linear polarizing film. An FTN type liquid crystal display device comprising a phase difference layer, characterized by having the following configuration: PL / (PLC / PC / PC / PLC) / liquid crystal cell / PL, where PL: linearly polarized light Film (): Compensation retardation layer PC: Uniaxially oriented retardation film made of thermoplastic resin having positive refractive index anisotropy PLC: Vertical orientation film selected from the following: High nematic or smectic phase Vertical alignment obtained by forming a molecular liquid crystal film and then performing heat treatment at a temperature not lower than the crystalline phase (or glass phase) / liquid crystal phase transition temperature (Tg) and lower than the liquid crystal phase / isotropic phase transition temperature (Ti) to achieve vertical alignment. Membrane or Nema Click phase or at a temperature less than Tg than Ti after it is deposited a polymerizable liquid crystal oligomer showing a smectic phase is vertically aligned by heat treatment, to a vertical alignment film obtained by while polymerizing retaining the orientation.

As the polymer liquid crystal, either a main chain polymer liquid crystal or a side chain polymer liquid crystal can be used as long as it is a polymer liquid crystal having a nematic phase or a smectic phase in a liquid crystal state. The transition temperature (Ti) of the liquid crystal phase / isotropic phase of the polymer liquid crystal is, for example, about 200 ° C. or lower, preferably 150 ° C. or lower.

Examples of the main chain type polymer liquid crystal include a wholly aromatic polyester type polymer liquid crystal in which a group imparting liquid crystallinity (mesogen group) is linked by an ester bond, a mesogen group and polymethylene, polyethylene oxide, polysiloxane and the like. A semi-rigid polyester-based polymer liquid crystal composed of a main chain in which bent chains are alternately bonded to each other to impart flexibility is exemplified.

The side chain type polymer liquid crystal is, for example, a mesogen via a spacer consisting of a linear or cyclic skeleton chain composed of methacrylic acid, acrylic acid, polymethylene, polyethylene oxide, polysiloxane, etc. and a bent chain. Those having a side chain to which a group is bound are included. A polysiloxane type is preferable, and a cyclic type is preferable.

The polymerizable liquid crystal oligomer exhibiting a nematic phase or a smectic phase is not particularly limited, but a polymerizable side chain type liquid crystal oligomer is preferable.

The polymerizable side-chain type liquid crystal oligomer is, for example, a linear or cyclic oligomer composed of the following repeating units (I) and (II), and the repeating units (I) and ( When the numbers of II) are n and n ', respectively, a liquid crystal oligomer in which n and n'are each independently an integer of 1 to 20 and 4≤n + n'≤21 is mentioned.

[0011] [Wherein A is a group represented by the following formula (III) or (IV), and in formula (III), -Si-O- is represented by formula (I).
Or the main chain of (II), and in the formula (IV), -C
—CH ₂ — is the backbone of formula (I) or (II),
R ₁ or R ₂ is located on the opposite side of the OO group. Formula (I)
When A is the formula (III) and when A is the formula (III) in the formula (II), R ₁ and R ₂ are each independently hydrogen, an alkyl group having 1 to 6 carbon atoms or a phenyl group. In formula (I), when A is formula (IV), and in formula (II), A is formula (IV),
R ₁ and R ₂ are independently hydrogen or an alkyl group having 1 to 6 carbon atoms. k and k'independently represent an integer of 2 to 10, m and m'independently represent 0 or 1, and Ar ₁ , Ar ₂ , A
r ₃ and Ar ₄ are independently a 1,4-phenylene group, 1,
4-cyclohexane group, pyridine-2,5-diyl group,
Pyrimidine-2,5-diyl group, L and L '-CH ₂ -O- _{independently, -O-CH 2 -, -COO} -, - OCO-, -CH 2 -CH 2 -,
-CH = N-, -N = CH- or Is a divalent group represented by, p and p ′ are independently 0 or 1, R is a halogen, a cyano group, an alkyl group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, R'is hydrogen or an alkyl group having 1 to 5 carbon atoms. ]

The skeleton chain is preferably a cyclic structure, and A
For this, SiO is preferable. The ratio of n to n'is preferably in the range of 1: 3 to 3: 1. As k and k ′, an integer of 2 to 6 is preferable, and m and m ′ are preferably 1. Ar ₁ , Ar
1,2-phenylene group is preferable as ₂ , Ar ₃ and Ar ₄ , and -CH ₂ -CH _2- , -COO-, -OCO- group is preferable as L and L ', and -COO- group is particularly preferable. preferable. As R, a cyano group is preferable.

In the case of the polymerizable side chain type liquid crystal oligomer, the liquid crystal phase / isotropic phase transition temperature (Ti) is, for example, 200 ° C. or lower, preferably 170 ° C. or lower, more preferably 150 ° C. or lower. The crystal phase (or glass phase) / liquid crystal phase transition temperature (Tg) is preferably 25 ° C. or lower.

As a substrate for forming a polymer liquid crystal or a polymerizable liquid crystal oligomer, an optically transparent and isotropic resin substrate, a linear polarizing film, and a thermoplastic resin having a positive refractive index anisotropy. And a uniaxially oriented retardation film made of When a polymer liquid crystal or a polymerizable liquid crystal oligomer is formed on the surface of a uniaxially oriented retardation film made of a linearly polarized film or a thermoplastic resin having a positive refractive index anisotropy, it is subjected to heat treatment or the like to form a vertical film. After forming the alignment film, this is used as it is as PL / PLC, PLC / PC or PC / PLC
Can be incorporated into a liquid crystal display device.

When the vertical alignment film is formed on an optically transparent and isotropic resin substrate, the vertical alignment film is directly attached to a uniaxially oriented retardation film made of a thermoplastic resin without peeling the vertical alignment film from the substrate. PLC / PC or PC / PLC
Can be incorporated into a liquid crystal display device.

Optically isotropic means that nX is the maximum in-plane refractive index, nY is the minimum in-plane refractive index, nZ is the refractive index in the film thickness direction, and d is the film thickness. , (NX −nY) × d is 20 nm or less and ((nX +
nY) / 2-nZ) xd is 200 nm or less. Preferably, (nX-nY) * d is 10 nm or less and ((nX + nY) / 2-nZ) * d is 100 nm or less. The optically transparent and isotropic resin substrate is not particularly limited, but preferably has a glass transition temperature of 100 ° C. or higher, and more preferably 110 ° C. or higher. Examples of the resin include polycarbonate, polysulfone, polyarylate, polyether sulfone,
Examples thereof include cellulose diacetate, cellulose triacetate, polyethylene terephthalate, polyethylene naphthalate, polyvinyl alcohol, polystyrene, and polymethyl methacrylate. Among them, polycarbonate, polysulfone, polyarylate, cellulose triacetate, and polyethylene terephthalate are preferable.

A method for forming a vertical alignment film such as a polymer liquid crystal will be described below using a case of an optically transparent and isotropic resin substrate. A linear polarization film and a uniaxial alignment retardation film will be described below. The formation on the surface can be performed in the same manner. The surface of the transparent resin substrate is preferably hydrophilic or hydrophobic.

As the hydrophilic resin substrate, a hydrophilic polymer film such as polyvinyl alcohol or the like, a surface of a cellulose triacetate or cellulose diacetate film is saponified, or a surface of a polymer film is made hydrophilic. Can be mentioned. The hydrophilization treatment is not particularly limited, but treatment with oxygen plasma, a method of applying a hydrophilic polymer on the surface, a method of applying a surfactant, and the like can be used.

As the hydrophilic resin substrate, a film obtained by forming a film of a cellulose resin such as cellulose triacetate or cellulose diacetate by a solvent casting method and saponifying the surface is preferable.

As the hydrophobic treatment, a method of applying a fluoropolymer, a method of applying a surfactant such as lecithin,
A method of reacting a silane coupling agent, a titanium coupling agent or the like can be used.

The method for forming the polymer liquid crystal or the polymerizable liquid crystal oligomer is not particularly limited. For example, a liquid obtained by dissolving a polymer liquid crystal or a polymerizable liquid crystal oligomer in a solvent capable of dissolving a polymer liquid crystal or a polymerizable liquid crystal oligomer and having little dissolution or swelling of a substrate material is subjected to a roll coating method, a gravure coating method, a bar coating method. , Spin coating method, spray coating method, printing method, dipping method, etc., or heating a high molecular liquid crystal or a polymerizable liquid crystal oligomer to a crystal phase (or glass phase) / liquid crystal phase transition temperature (Tg) or higher. There is a method of applying the above by the same method as the above-mentioned method.

Among these, the roll coating method, gravure coating method, bar coating method, spin coating method and dipping method using a polymer liquid crystal solution or a polymerizable liquid crystal oligomer solution are preferable, and depending on the film thickness, R40 / R0, etc. The optical characteristics can be adjusted.

The heat treatment temperature (Tt) for orienting the polymer liquid crystal or the polymerizable liquid crystal oligomer after film formation in the direction perpendicular to the film surface is set to the crystal phase (or glass phase) of the polymer liquid crystal or the polymerizable liquid crystal oligomer / It is higher than or equal to the liquid crystal phase transition temperature (Tg) and lower than the liquid crystal phase / isotropic phase transition temperature (hereinafter referred to as Ti). It is preferably below the glass transition temperature of the substrate. In the case of the polymerizable liquid crystal oligomer, Tg + 30
C. ≦ Tt <Ti is preferable, and Tg + 40 ° C. ≦
It is more preferable that Tt <Ti.

The heat treatment time is not particularly limited, but is, for example, 1 minute or longer, preferably 2 minutes or longer.

In the case of the polymerizable liquid crystal oligomer, the liquid crystal oligomer is polymerized after being heat-treated while maintaining the vertical alignment. The polymerization method is not particularly limited, and photopolymerization, radiation polymerization of γ rays or the like, thermal polymerization and the like can be used, but photopolymerization is preferable. In the case of photopolymerization or thermal polymerization, a known polymerization initiator can be used.

As the uniaxially oriented retardation film, not only a perfect uniaxially oriented film but also a biaxially oriented film has a refractive index anisotropy in the film plane and is seen from a direction perpendicular to the film plane. If it exhibits a retardation similar to that of the uniaxially oriented film, it can be used.

The thermoplastic resin used for the uniaxially oriented retardation film made of a thermoplastic resin having a positive refractive index anisotropy includes polycarbonate, polysulfone, polyarylate, polyether sulfone, polyethylene terephthalate, polyvinyl alcohol, and acetic acid. Examples thereof include cellulose, and polycarbonate and polysulfone are preferable.

As the method for producing the raw film, a molding method such as a solvent casting method, an extrusion molding method, or a pressing method can be used. As a method of stretching the raw fabric film, a lateral stretching method using a tenter, a roll-roll stretching method, a roll-roll compression stretching method, or the like can be used. Preferred is a method of transversely stretching a raw film formed by a solvent casting method with a tenter. By combining such a vertical alignment film (PLC) and a uniaxially oriented retardation film (PC) made of a thermoplastic resin having a positive refractive index anisotropy, a retardation layer for compensation (PLC / PC / PC / PLC) and
By disposing it between the liquid crystal cell and the linear polarizing film on the upper side, it is possible to obtain an FTN directional liquid crystal display device having excellent viewing angle characteristics. Then, the slow axis of the two uniaxially oriented retardation films (PC) and the absorption axis of the linear polarizing film (PL) are adjusted so that the contrast and the like are optimal when incorporated in a liquid crystal display device. Two vertical alignment films (PLC
) Or a uniaxially oriented retardation film (PC) made of a thermoplastic resin having a positive refractive index anisotropy does not necessarily have the same optical characteristics.

The retardation measured by injecting the measuring light in the direction perpendicular to the surface was R0, and the retardation measured by injecting the measuring light at an inclination of 40 ° with the direction of the maximum in-plane refractive index being the inclination axis was R40. Then, PLC / PC and PC / PLC in the compensating retardation layer are respectively 1.10 ≧ R40 /
It is preferable that R0 ≥ 0.90, and 1.06 ≥ R40
It is more preferable that / R0 ≥ 0.94.

[0030]

The FTN LCD of the present invention has excellent viewing angle characteristics.

[0031]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The measurement of the isocontrast curve is LCD-700 manufactured by Otsuka Electronics Co., Ltd.
It was carried out by the transmission method using 0. The voltage applied to the liquid crystal display device was set to a state where the contrast was the best when the liquid crystal display device in the actual driving state was visually observed from the front. The retardation value of the uniaxially oriented retardation film is measured by a spectroscope (Otsuka Electronics Co., Ltd.) in which two polarizing prisms are arranged in parallel in the optical system.
MCPD-1000) manufactured by Mitsui Chemicals, Inc. was used to determine the maximum wavelength of the interference spectrum.

Example 1 The following were used as the vertical alignment film (PLC) and the uniaxially oriented retardation film (PC).・ Vertical alignment film (PLC) As a polymerizable liquid crystal oligomer, 4- (allyl-oxy)-
Benzoic acid-4'-cyanophenyl ester and 4- (allyloxy) -benzoic acid- (4'-methacryloyloxy-phenyl)
A non-polymerizable mesogen group and a polymerizable mesogen group obtained by reacting an ester with pentamethylcyclopentasiloxane at a mixing ratio of 1: 1 by the method described in JP-B-63-41400 in a ratio of about 1: 1. A cyclic pentasiloxane liquid crystal oligomer having a side chain was used (Tg 18.7 ° C., Ti 11
7.5 ° C). (NX −nY) × d is 6n at a thickness of 80 μm
m, ((nX + nY) / 2-nZ) × d cellulose acetate film having a thickness of 50 nm (Fujitac SH-80
Fuji Photo Film Co., Ltd.) was subjected to surface saponification treatment, and a 30% toluene solution of a polymerizable liquid crystal oligomer was formed by a gravure coating method so that the film thickness after drying was 1.8 μm. After heat treatment was carried out at 80 ° C. for 2 minutes to perform vertical alignment, ultraviolet rays were irradiated (integrated light amount of 500 mJ / cm ² ) while maintaining the alignment to form a vertical alignment film (PLC) on the cellulose triacetate film. Uniaxially oriented retardation film (PC) Uniaxially oriented retardation film obtained by uniaxially stretching a solvent cast film of polycarbonate (trade name Sumikalite SEF-360428 manufactured by Sumitomo Chemical Co., Ltd.,
In-plane retardation 428 nm).

PC was bonded onto a vertical alignment film (PLC) formed on a cellulose acetate film 3 using an adhesive to obtain two compensating retardation layer members (both R40 / R0 = 1). ．
0027). Compensation retardation layer (PLC
/ PC / PC / PLC) was obtained. This compensation retardation layer is used as a word processor (trade name: OASYS 30LX-401).
An FTN LCD mounted on Fujitsu Ltd.) and a liquid crystal cell on which a linear polarizing film (PL) is laminated using an adhesive (PL / (PLC / PC / PC / PLC) / liquid crystal Cell / PL). This FTN type LCD had a small change in contrast depending on the viewing angle, was bilaterally symmetric, and particularly had a good spread of the high contrast region. The isocontrast curve is shown in FIG.

Example 2 The thickness of the polymerizable liquid crystal oligomer after drying was 3.3 μm (R40 / R0 = 0.95 of the compensating retardation layer member).
In 52), an FTN type LCD was obtained in the same manner as in Example 1 (PL / (PLC / PC / PC / PLC) / liquid crystal cell / PL). This FTN type LCD had a small change in contrast depending on the viewing angle, was bilaterally symmetric, and particularly had a good spread of the high contrast region. The isocontrast curve is shown in FIG.

Comparative Example 1 Two PCs were used, and these were the same FTN type LCD as in Example 1.
Laminated between the upper polarizing film and the liquid crystal cell (PL / PC / PC
/ Liquid crystal cell / PL). Compared with the FTN type LCD according to the present invention, this FTN type LCD was not bilaterally symmetrical in viewing angle characteristics, and was particularly inferior in vertical viewing angle characteristics. The isocontrast curve is shown in FIG.

[Brief description of drawings]

FIG. 1 is a diagram showing isocontrast curves in Example 1.

FIG. 2 is a diagram showing isocontrast curves in Example 2.

FIG. 3 is a diagram showing isocontrast curves in Comparative Example 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akiko Shimizu 2-10-1 Tsukahara, Takatsuki City, Osaka Prefecture Sumitomo Kagaku Kogyo Co., Ltd. (72) Inventor Koji Higashi 2-10-1, Tsukahara, Takatsuki-shi Sumitomo Chemical Co., Ltd.

Claims (3)

[Claims] 1. A pair of transparent substrates having electrodes inside,
The nematic liquid crystal molecules having positive dielectric anisotropy have a structure in which the long axis of the molecule is parallel to the substrate and the long axis of the molecule is twisted by 180 to 270 degrees in the direction perpendicular to the transparent substrate when no voltage is applied. An FTN type liquid crystal display device comprising a liquid crystal cell configured as described above, a pair of linearly polarizing films arranged outside a pair of transparent substrates, and a retardation layer for compensation arranged between the liquid crystal cell and the linearly polarizing film. A liquid crystal display device having the following configuration. Composition: PL / (PLC / PC / PC / PLC) / Liquid crystal cell / PL where PL: Linearly polarized film (): Compensation retardation layer PC: Uniaxially composed of thermoplastic resin having positive refractive index anisotropy Alignment retardation film PLC: Vertical alignment film selected from the following: Crystalline phase (or glass phase) / Liquid crystal phase transition temperature (Tg) or higher after forming polymer liquid crystal showing nematic phase or smectic phase Liquid crystal phase / A vertical alignment film obtained by performing a vertical alignment by performing a heat treatment at a temperature lower than the isotropic phase transition temperature (Ti), or Vertical alignment film obtained by heat treatment for vertical alignment and polymerization while maintaining alignment 2. A vertical alignment film is formed by forming a side chain type polymer liquid crystal having a polysiloxane skeletal chain exhibiting a nematic phase or a smectic phase, and then heat-treating at a temperature of Tg or more and less than Ti for vertical alignment. The liquid crystal display device according to claim 1, which is a vertical alignment film obtained by the above. 3. A vertical alignment film is produced by forming a polymerizable side chain type liquid crystal oligomer having a skeleton chain composed of --SiO-- showing a nematic phase or a smectic phase, and then heat-treating at a temperature of Tg or more and less than Ti. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a vertical alignment film obtained by vertically aligning and polymerizing while maintaining the alignment.