JPH0667169A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve brittleness and cracking property of a film, to decrease changes in double refraction due to heat, and to obtain good characteristics for angle of view field for contrast. CONSTITUTION:This liquid crystal display device consists of, from the back light side, a polarizing plate, first phase contrast plate, supertwist-oriented liquid crystal cell second phase contrast plate, and polarizing plate. The first and second phase contrast plates consist of uniaxially oriented films having positive and negative, or negative and positive intrinsic double refractive indeces, respectively. The high-molecular materilal having a negative intrinsic double refractive index contains a graft-polymer obtd. by additional polymn. of one or more kinds of monomers including styrene monomer to polymers having at least unsatd. double bonds in the main or side chains.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using twisted nematic liquid crystal or cholesteric liquid crystal. Furthermore, the present invention relates to a retardation film used for color correction of the liquid crystal device and for increasing the viewing angle, and more specifically, it has improved brittleness / strength of the film and is excellent in the properties of color correction and viewing angle increase. Regarding the phase difference film.

[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, high productivity and light weight. And its applications have expanded. At present, a twisted nematic liquid crystal display device (hereinafter referred to as STN-LCD) in which a twist angle of liquid crystal molecules is 160 ° or more and 270 ° or less is practically used as a dot matrix type liquid crystal display device used in OA-related devices such as word processors and personal computers. It has become. This is because the STN-LCD can maintain high contrast even during high-multiplex driving, as compared with the conventional twisted nematic liquid crystal display device (TN-LCD) having a twist angle of 90 °.

However, in the STN-LCD,
It is difficult to make the background color of the display screen white, and the background usually has a green to yellow-red tint, which is insufficient as a display device. In order to solve this problem, a method has been proposed in which one or more retardation films are provided between a pair of polarizing plates.

There is also a patent application for the phase film plate used alone for removing color in STN-LCD. For example, JP-A-63-189804 discloses a retardation (product of birefringence value and film thickness) measured with a polarization microscope of 200 to 350 nm or 475 to 625 nm.
And a polycarbonate film uniaxially stretched so that

Further, Japanese Patent Laid-Open No. 63-167304 relates to a film laminate in which two or more films or sheets having birefringence which are stretched in a uniaxial direction are stacked so that their optical principal axes are orthogonal to each other. It is a thing. In the above invention, when two birefringent films (each having a retardation value of R ₁ and R ₂ ) are laminated at right angles, a retardation film having a retardation of | R ₁ −R ₂ | Utilizing the fact that | R ₁ −R ₂ | is 90 even if R ₁ and R ₂ have large retardation values.
~ 180 nm, 200-350 nm, 475-625n
This is aimed at the effect that it can be adjusted to a range such as m.

All of the above-mentioned inventions are aimed at removing coloration of STN-LCDs, and in that respect, they have been greatly improved, and a display close to white / black display has been obtained. In addition, the method of using a polymer birefringent film (hereinafter referred to as a retardation film) has a cost advantage and the demand is rapidly expanding.

However, with this retardation film, coloring can be almost removed when the liquid crystal display is viewed from the front, but when the display is viewed from an angle, coloring due to a slight angle change and the contents displayed on the screen disappear. However, the problem of viewing angle characteristics that occurs in STN-LCD in general has not been solved.
-It has become a serious issue for LCDs.

More specifically, a longitudinal uniaxially stretched film of a polymer having a positive intrinsic birefringence value has a refractive index n _{MD in} the stretching axis direction, a refractive index n _TD in the direction orthogonal to the stretching axis, and a film surface normal. Assuming that the refractive index in the linear direction is n _ND , the magnitude relationship between the respective refractive indexes is expressed by the following equation.

[0009]

[Equation 1]

[0010] Therefore, when the incident light enters perpendicular to the film plane, Re = a (n _MD -n _TD) d. Next, when the incident light passes through a plane orthogonal to the stretching direction, the birefringence value changes in the range of Δn = n _MD −n _TD to Δn = n _MD −n _ND with the change of the incident angle. Here, the relation of the following equation holds, so △
n does not change or increases due to oblique incidence.

[0011]

[Equation 2]

On the other hand, since the optical path length increases due to the oblique incidence, Re = Δn · d rapidly increases with the oblique incidence.

Further, when the incident light is incident while being inclined from the film normal direction to the stretching axis direction, Δn is from n _MD −n _ND to n _ND
Since a drastic change occurs up to −n _TD , even if the optical path length increases, the decrease cannot be compensated and Re = Δn due to oblique incidence.
・ D decreases sharply. In principle, the uniaxially stretched film with the smallest rate of change in retardation is n _MD > n _TD = n
_In the case of _ND as well, Re also greatly changes in this case due to the increase in the optical path length accompanying oblique incidence.

A method of changing the refractive index of the retardation film in the three-dimensional direction is proposed because the problem of the viewing angle of the STN-LCD is closely related to the change of the viewing angle of the retardation value of the film. ing. In this,
A method for controlling the three-dimensional orientation of molecules as seen in JP-A-2-160204 and JP-A-2-285303 and an optical axis substantially in the normal direction of the film as seen in JP-A-2-256023. A film having, specifically, a viewing angle by inserting a laminated film of a biaxially stretched film having a negative intrinsic birefringence value and a uniaxially stretched film having a positive intrinsic birefringence value between a liquid crystal cell and a polarizing plate. A method of significant improvement is disclosed.

Further, in JP-A-3-206422, a laminate of a uniaxially stretched polymer having a positive intrinsic birefringence value and a uniaxially stretched polymer having a negative intrinsic birefringence value is provided between a liquid crystal cell and a polarizing plate. It is disclosed that the viewing angle characteristics of the liquid crystal display device can be significantly improved by inserting the device into the liquid crystal display device. Similarly, regarding the improvement of the viewing angle problem based on the lamination of films having positive and negative intrinsic birefringence,
The disclosure is made in JP-A-3-24502 and JP-A-4-140722. All of the films disclosed as negative intrinsic birefringence films used in the above patents are homopolymers or copolymers using a styrene monomer.

The inventors of the present invention have made earnest efforts to improve the viewing angle characteristics, heat resistance and the like of styrene-based copolymers, and depending on the copolymerization structure and the copolymerization ratio, or the stretching conditions,
A patent application was filed for a retardation film using a film having a negative intrinsic birefringence with improved performance (Japanese Patent Application Nos. 2-316440, 2-410080, 3-4744).
2). However, the above-mentioned polymers mainly composed of styrene-based monomers are all fragile, and are easily broken during uniaxial stretching.
It has a problem that it is easily cracked by punching, and cracks easily occur due to a thermal history after the liquid crystal display device is assembled.

[0017]

The object of the present invention is, firstly, to comprise a styrene copolymer capable of remarkably improving the fragility and fragility of the film in film forming, processing and liquid crystal display products. An object is to provide a liquid crystal display device using a retardation film. Secondly, an object of the present invention is to provide a retardation film which has the excellent film physical properties described above, has a small change in birefringence value due to heat, and has an excellent effect of improving a viewing angle. Thirdly, an object of the present invention is to provide a liquid crystal display device having improved performance by using the retardation film having the above excellent properties.

[0018]

The above objects of the present invention have been achieved by the following means. (1) A liquid crystal display device in which a polarizing plate, a first retardation plate, a liquid crystal cell having a super twist orientation, a second retardation plate, and a polarizing plate are arranged in this order from the backlight side. The retardation plate is a uniaxially stretched polymer having a specific birefringence value of positive and negative, or a negative and positive polymer, respectively, and the material of the polymer having a negative intrinsic birefringence value of at least a main chain or a side chain. A liquid crystal display device comprising a graft polymer obtained by addition-polymerizing at least one monomer containing a styrene-based monomer to a polymer having an unsaturated double bond. (2) The crossing angle between the polarization axis of the backlight-side polarizing plate and the slow axis of the first retardation plate in contact with the polarizing plate is 20 to 40 degrees, and
The crossing angle between the slow axis of the retardation plate and the rubbing axis of the liquid crystal cell on the first retardation plate side is 70 to 90 degrees, and it is located on the opposite side of the first retardation plate through the liquid crystal cell. The crossing angle of the slow axis of the second retardation plate and the rubbing axis on the second retardation plate side is 70 to 90 degrees, the slow axis of the second retardation plate, and the polarization of the polarizing plate in contact with the second retardation plate. The liquid crystal display device according to (1), wherein the angle of intersection with the axis is 50 to 70 degrees.

The present invention will be described in detail below. The polymer used for the uniaxially stretched film having a negative intrinsic birefringence value of the present invention is at least a styrene-based monomer as compared with a polymer having an unsaturated double bond in the main chain or side chain (referred to as (A)). One or more monomers containing ((B)
Is referred to as “(), which is a graft polymer obtained by addition-polymerizing (hereinafter referred to as“ polymer (C) of the present invention ”).

First, the polymer (A) constituting the so-called trunk of the graft polymer (C) of the present invention will be described. The polymer (A) is specifically a polymer having a repeating unit of at least an unsaturated double bond in the main chain or side chain.
This repeating unit is preferably one derived by polymerization of a monomer having a conjugated diene structure.

Preferred examples of specific monomers having a conjugated diene structure include 1,3-butadiene, isoprene, 1,3-pentadiene, 2-ethyl-1,3-butadiene and 2-n-propyl-. 1,3-butadiene, 2,
3-dimethyl-1,3-butadiene, 2-methyl-1,
3-pentadiene, 1-phenyl-1,3-butadiene, 1-α-naphthyl-1,3-butadiene, 1-β-
Naphthyl-1,3-butadiene, 2-chloro-1,3-
Butadiene, 1-bromo-1,3-butadiene, 1-chlorobutadiene, 2-fluoro-1,3-butadiene,
2,3-dichloro-1,3-butadiene, 1,1,2-
Trichloro-1,3-butadiene, 2-cyano-1,3
-Butadiene and the like can be mentioned, of which 1,3
-Butadiene, isoprene, 2-chloro-1,3-butadiene are particularly preferred.

Further, the polymer (A) constituting the trunk of the polymer (C) of the present invention may be copolymerized with a hydrophobic monomer other than the above-mentioned monomer having a diene structure. Examples of such hydrophobic monomers include ethylene, propylene, 1-butene, isobutene, styrene, α-methylstyrene, vinyl ketone, monoethylenically unsaturated esters of aliphatic acids (eg vinyl acetate, allyl acetate). , Esters of ethylenically unsaturated monocarboxylic acids or dicarboxylic acids (for example, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, n-butyl acrylate, n-hexyl acrylate, 2- Ethylhexyl acrylate, t
-Butyl methacrylate, dodecyl methacrylate, 2
-Hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate)

And amides (eg t-butyl acrylamide, t-butyl methacrylamide), monoethylenically unsaturated compounds (eg acrylonitrile, methacrylonitrile) and the like. Of these, ethylene, propylene, styrene, α-methylstyrene, esters of acrylic acid or methacrylic acid, acrylonitrile, and methacrylonitrile are particularly preferable.

Two or more kinds of each of the above-mentioned monomer having a conjugated diene structure and other hydrophobic monomer may be used. The unsaturated structure introduced into the polymer (A) by polymerization of a monomer having a conjugated diene structure may be a cis-1,4 bond as well known in the art, or a trans structure. 1,4-bond or transformer 1,2-
It may be a bond.

The polymer (A) may be a homopolymer derived from a monomer having a diene structure,
It may be a copolymer with another hydrophobic monomer. In the case of a copolymer, it may be a so-called random copolymer in which each monomer is copolymerized at an arbitrary ratio, or a block copolymer. Regarding the polymer and the synthesis method of such a conjugated diene monomer, for example, “Synthetic Polymer II,” edited by Shunsuke Murahashi et al.
Published by Asakura Shoten, 1975, pp. 171-308.

A preferred specific example of the polymer (A) described above is a styrene-butadiene copolymer (generally referred to as SBR, which is solution-polymerized SBR or emulsion-polymerized SBR).
There is. As the solution-polymerized SBR, there are the above-mentioned block copolymers (for example, butadiene-styrene block copolymers and styrene-butadiene-styrene block copolymers) in addition to random polymers,

Butadiene homopolymer (eg cis-1,
4-butadiene, trans-1,2-butadiene, or rubber in which these and trans-1,4-butadiene structure are mixed), isoprene homopolymer (example of stereostructure is the same as butadiene polymer), styrene- Isoprene copolymer (random copolymer, block copolymer), ethylene-propylene-diene copolymer (as diene monomer, 1,4-hexadiene, dicyclopentadiene, ethylidene norbornene, etc.),

Acrylonitrile-butadiene copolymer,
Chloroprene copolymer, isobutylene-isoprene copolymer, butadiene-acrylic acid ester copolymer (as acrylic acid ester, ethyl acrylate, butyl acrylate, etc.), butadiene-acrylic acid ester-acrylonitrile copolymer (acrylic acid Examples of the ester include the same as above.

The glass transition temperature (T) of the polymer (A) itself
g) is important for improving the film physical properties of the retardation film, and Tg is 50 ° C. or lower, preferably 30 ° C. or lower, and particularly preferably 0 ° C. or lower. The ratio of the conjugated diene monomer component in the polymer (A) is not particularly limited as long as it is within the above glass transition temperature range, but a range of 10 to 100% by weight is preferable.

Next, the monomer (B) used to obtain the graft polymer (C) by addition-polymerizing the polymer (A) will be described. In the polymer (C) of the present invention, if the polymer (A) is referred to as a trunk,
The polymer of the monomer (B) can be referred to as a branch having a repeating unit extending in a comb shape from the origin (A).

In the present invention, the monomer (B) used in the graft polymerization is at least one monomer containing at least a styrene monomer. Specific examples of the styrene-based monomer include styrene and α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene,
Styrene derivatives such as p-nitrostyrene, p-aminostyrene, p-carboxylstyrene, p-phenylstyrene, 2,5-dichlorostyrene and p-t-butylstyrene are included, of which styrene or styrene and others Particularly preferred is a combination of the styrene derivatives.

Further, the monomer (B) may contain a monomer other than the above-mentioned styrene type monomer,
Examples of such a monomer include N-phenylmaleimidoacrylonitrile, methacrylonitrile, α-chloroacrylonitrile, methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic acid, and methacrylic acid. Examples thereof include acids, butadiene, isoprene, maleic anhydride, vinyl acetate, ethylene and propylene, and of these, acrylonitrile and methacrylonitrile are particularly preferable. These may be copolymerized alone with a styrene derivative,
Plural may be used.

The proportion of the trunk component polymer (A) in the graft copolymer (C) used in the present invention is difficult to uniquely determine because its structure may change the contribution to the physical properties of the membrane. Considering that the amount necessary for improving the physical properties of the film or the amount is too large, the film becomes too soft, and relaxation of the polymer molecular orientation due to heat may occur, preferably 1 to 30% by weight, particularly preferably 3 to 20% by weight. %.

The molecular weight of the graft polymer (C) is not particularly limited as long as it is not particularly small, but considering the viscosity of the polymer solution when forming a film from a solution, the weight average molecular weight is 100,000 to 1,000,000. Is preferable, and particularly preferably in the range of 150,000 to 500,000.
The proportion of the styrenic monomer component in all the constituent components of the graft polymer (C) is preferably 50% or more by weight from the viewpoint of manifesting birefringence characteristics, and particularly preferably 60.
% Or more.

The graft polymer (C) of the present invention can be synthesized by a commonly used radical polymerization method (eg, emulsion polymerization method, solution polymerization method). The graft polymer (C) of the present invention may be used as a mixture of two kinds having different compositions and structures. Further, a polymer other than the graft polymer (C) may be mixed. Further, the polymer obtained in the present invention may be a graft polymer and another polymer such as a polymer (A) which does not undergo a graft reaction or a styrene-based random copolymer which does not undergo a graft reaction, although it depends on the polymerization method. Polymers may be mixed.

Preferred specific examples of the graft polymer (C) of the present invention are as follows: (A) a polymer (stem) having at least an unsaturated double bond in its main chain or side chain (B) containing at least a styrene monomer It is exemplified in the form of a polymer portion (branch) to which one or more kinds of monomers are added, but the present invention is not limited thereto. That is, it represents a product obtained by graft-polymerizing (B) with respect to (A). The ratio of the numbers in parentheses in (A) and (B) represents the copolymerization ratio (weight) of the monomers in each component,
(A): (B) represents the weight percentage ratio of the polymer of the corresponding trunk component / branch component.

P-1,2 (A) Styrene / butadiene copolymer (20/80) (B) Styrene / acrylonitrile / α-methylstyrene (60/20/20) P-1 (A) :( B) = 10: 90 P-2 (A) :( B) = 5: 95 P-3,4 (A) Styrene / butadiene copolymer (2
0/80) (B) Styrene / acrylonitrile (80/20) P-3 (A) :( B) = 10: 90 P-4 (A) :( B) = 7: 93 P-5 (A) Styrene / Butadiene copolymer (5
0/50) (B) Styrene / acrylonitrile (75/25) (A) :( B) = 12.5: 87.5

P-6,7 (A) Styrene / butadiene copolymer (50/50) (B) Styrene / acrylonitrile / α-methylstyrene (60/30/10) P-6 (A) :( B) = 15: 85 P-7 (A) :( B) = 10: 90 P-8 (A) Styrene / butadiene copolymer (5
0/50) (B) Styrene / acrylonitrile (75/25) (A): (B) = 10: 90 P-9 (A) polybutadiene (B) Styrene / acrylonitrile (70/30) (A): (B ) = 5: 95 P-10 (A) Polybutadiene (B) Styrene / acrylonitrile / methacrylonitrile (75/15/10) (A) :( B) = 10: 90

P-11 (A) Styrene / butadiene copolymer (50/50) (B) Styrene (A) :( B) = 12: 88 P-12 (A) Styrene / butadiene copolymer (2)
3/77) (B) Styrene / methyl methacrylate / acrylonitrile (70/10/20) (A) :( B) = 10: 90 P-13 (A) Polyisoprene (B) Styrene / t-butylstyrene (70) / 30) (A) :( B) = 10: 90

P-14 (A) acrylonitrile / butadiene copolymer (50/50) (B) styrene / acrylonitrile (80/20) (A) :( B) = 10: 90 P-15 (A) acrylonitrile / Butadiene copolymer (25/75) (B) Styrene / acrylonitrile / α-methylstyrene (60/20/20) (A) :( B) = 12: 88 P-16 (A) Ethyl acrylate / butadiene co-polymer Polymer (50/50) (B) Styrene / methyl methacrylate (80/20) (A) :( B) = 10: 90 P-17 (A) Ethyl acrylate / styrene / butadiene copolymer (40/30) / 30) (B) Styrene / methacrylonitrile (75/25) (A) :( B) = 15: 85

There is no limitation as a polymer used for the film having a positive intrinsic birefringence value in the present invention, but specifically, polycarbonate, polyarylate, polyethylene terephthalate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, Polyamide-imide, polyimide, polyolefin, polyvinyl chloride, cellulose, polyester-based polymers and the like are preferable, and particularly polycarbonate-based polymers,
Polymers such as polyarylate-based polymers and polyester-based polymers, which have a large intrinsic birefringence value and can easily form a planar homogeneous film by solution casting, are preferred.

The above-mentioned polymer may be not only a homopolymer but also a copolymer, a derivative thereof, a blended product and the like. Further, the film having positive and negative intrinsic birefringence values in the present invention preferably has a light transmittance of 70% or more and is achromatic, and more preferably has a light transmittance of 85% or more and is achromatic. is there.

Even if the absolute value of the intrinsic birefringence value is small, it can be sufficiently utilized by increasing the thickness or the stretching ratio, but in order not to be restricted by them, the intrinsic birefringence value is preferably. Absolute value 0.02 or more,
It is more preferably 0.04 or more. Further, in order to prevent the molecules, which have been oriented by stretching, from relaxing the orientation due to the temperature rise during the LCD manufacturing process or during display, the Tg (glass transition point) of the material is 90 degrees or more, more preferably 100 degrees or more, and further preferably 110 degrees. More than a degree. The thickness of the uniaxially stretched film having a birefringence value is not particularly limited, but 10
The range of μ to 1 mm is preferred.

Now, the front contrast of the liquid crystal display device,
To improve display quality such as color and viewing angle characteristics
Is the liquid crystal properties (elastic constant, dielectric constant, anisotropy, intrinsic birefringence
Etc.), twist angle of liquid crystal, rubbing axis, retardation film
Consider many variables such as retardation value, slow axis, polarization axis, etc.
You need to be careful. We have the elastic constant K of the liquid crystal₁(Su
Play) 7.0 × 10^-12N ~ 2.5 x 10^-11N,
K₂(Twist) 3.0 × 10^-12N ~ 1.5 x 10
^-11N, K ₃(Bend) 1.0 × 10^-12N ~ 3.0
× 10^-11N, dielectric constant ε₁₁7 to 25, ε₂3 to 6,
Intrinsic birefringence Δn ° of 0.12 to 0.15
The thickness of the retardation film can be changed by changing the thickness within the range of 6 to 8 μm.
Retardation, polarization axis, retardation plate slow axis, Rabin
Optimization of the axis. As a result, the spectral fill
Retardation value of the liquid crystal is 350-500 nm,
Under the condition that the ist angle is 230 to 250 degrees, the following configuration
It has good head-on contrast, good color and viewing angle
A liquid crystal display device having good characteristics was obtained.

That is, the crossing angle between the polarization axis of the backlight side polarizing plate and the slow axis of the first phase plate in contact with the polarizing plate is 20 to.
40 degrees, the crossing angle between the slow axis of the first retardation plate and the rubbing axis of the liquid crystal cell on the first retardation plate side is 70 to
90 degrees, the crossing angle between the slow axis of the second retardation film located on the opposite side of the first retardation film and the rubbing axis on the second retardation film side is 70 to 90 degrees through the liquid crystal cell, The crossing angle between the slow axis of the retardation plate and the polarization axis of the polarizing plate in contact with the second retardation plate is 50 to 70 degrees. Hereinafter, the present invention will be described in detail with reference to examples.

[0046]

【Example】

Example 1 170 g of each polymer shown in Table 1 containing the above-mentioned graft polymer of the present invention was dissolved in 830 g of methylene chloride. This solution was cast on a glass plate so that the film thickness after drying was 100 μm, allowed to stand at room temperature for 5 minutes, and then at 45 ° C.
Was dried with warm air for 20 minutes and peeled from the glass plate. The peeled film was attached to a frame, dried at 70 ° C. for 1 hour, further dried at 110 ° C. for 15 hours, and then uniaxially stretched by a 200% uniaxial stretching under a temperature condition of 115 ° C. to obtain a sample. did. Next, the obtained sample was used for the following evaluations.

(1) Brittleness 10 mm in the stretching direction (MD), the direction perpendicular to the stretching direction (T
A 35 mm sample piece was cut out in D), and as shown in FIG.
Bend slowly so that a crease parallel to D can be made,
The angle θ at which it breaks was read. 0 ° if not damaged
And It is preferable that θ is small, and it is necessary that it is actually 10 ° or less.

(2) Punching suitability Using the 18 cm × 16 cm Thomson punching machine shown in FIG.
Five pieces were piled up so that D was 45 ° with the long side, punched, and cracks entering from the 4 corners were observed. The length of the longest crack in the four corners of the fifth sheet from the holding plate was measured. In practice, it should be 5 mm or less.

(3) Heat-resistant (2) The sample punched out was attached to a glass plate using an adhesive, and the MD of the sample was placed between two crossed Nicols polarizing plates.
Is placed at 45 ° with respect to the polarization axis, the retardation is measured from the wavelength dependence of the intensity of transmitted light, and then the heat treatment is performed at 90 ° C. for 4 hours and 70 ° C. for 120 hours, and then the retardation is measured again to obtain the retardation. The reduction rate (%) was calculated. In practice, it is required to be 3% or less. Also, the heat treatment should not cause cracks. Table 1 shows the above evaluation results. It can be seen that the present invention clearly improves brittleness, punching suitability, and heat resistance.

[0050]

[Table 1]

Example 2 The polymer of P-1 shown in Table 1 was dissolved in methylene chloride to prepare a 20% by weight solution. This solution is cast on a stainless steel band, continuously peeled off and dried, and the film is uniaxially stretched between rolls having different peripheral speeds under a temperature condition of 115 ° C. to obtain a roll film having a retardation value of 430 nm. Got An adhesive sheet was attached to one surface of the obtained styrene-based film, and a vinyl chloride protective film was laminated on the opposite surface to prepare a sample. The obtained sample was evaluated in the same manner as in Example 1, but it was confirmed that the film made of the graft polymer of the present invention was superior in brittleness and punching suitability to Comparative Example, and also had good heat resistance.

Example 3 A polycarbonate having a weight average molecular weight of 100,000 was dissolved in methylene chloride to prepare a 20% by weight solution. This solution was cast on a stainless steel band, continuously peeled off and dried to obtain a polycarbonate film. The film 1
Uniaxially stretched between rolls having different peripheral speeds under a temperature condition of 70 ° C. to obtain a uniaxially stretched polycarbonate film having a retardation value of 430 nm. A pressure-sensitive adhesive sheet and a protective film were attached to both surfaces of the obtained polycarbonate film in the same manner as in Example 2 to prepare a sample.

Example 4 <Production of Liquid Crystal Cell> SE-610, an alignment film material for liquid crystal manufactured by Nissan Chemical Industries, Ltd., was dissolved in a solvent to obtain 2 wt% of SE-61.
It was made with 0 solution. Further, a SiO ₂ true sphere having a diameter of 7 μm was mixed with the solution at a ratio of 0.03 with respect to SE-610 and sufficiently stirred. Next, the transparent electrode layer (ITO, indium tin oxide) is vapor-deposited on the transparent electrode side of a 100 mm × 100 mm glass electrode substrate, the SE-610 solution is applied by a spin coater to form an alignment film of about 1-2 μm. Formed.
Furthermore, the surface of the alignment film was rubbed with a commercially available rubbing device.

The transparent electrode substrates, each of which has been rubbed at a predetermined angle, are attached so that the transparent electrode surfaces face each other,
Next, the liquid crystal for STN made by Merck (Clearing point: +11
1, Viscosity: 23mm ² S ^-1 , △ n: 589 nm +0.1304 at 20 ℃, extraordinary light refractive index n _e : 589nm 1.6277 at 20 ℃, ordinary light refractive index n ₀ : 58
1.4973 at 9nm, 20 ℃, dielectric anisotropy △ ε: 1kHz, +6 at 20 ℃.
3, elastic constant k ₁ : ₁ : 68 × 10 ^-11 N at 20 ° C, k ₂ : 0.75 × 1 at 20 ° C
0 ⁻¹¹ N, k ₃ : 2.15 × 10 ⁻¹¹ N) at 20 ° C. was injected between the transparent electrode substrates and subjected to isotropic treatment at 120 ° C. for 60 minutes.

<Measurement of Display Quality> Next, the retardation film (D ₁ ) obtained in Example 3 was provided on the backlight side of the liquid crystal cell.
The retardation film (D ₂ ) obtained in Example 2 was attached to the viewing side of the liquid crystal cell, and polarizing plates were attached to both sides of the laminate of the LC cell and the retardation film to give a liquid crystal panel. Table 2 shows the shaft configuration at that time.

[0056]

[Table 2]

Connect a driver to the liquid crystal panel, and
A rectangular wave signal is applied at a duty of 200, and the viewing angle defined by contrast and contrast ratio 2 is directly up and down,
A Topcon luminance meter was used to measure the contrast measured on the left and right. The results are shown in Table 2.

Comparative Example 1 With the same configuration as in Example 4, the contrast and the viewing angle in front of each other were measured by changing only the axis. The results are shown in Table 2.

As can be seen from Table 2, it has been found that the axial configuration according to the present invention has a high front contrast and a wide viewing angle.

[Brief description of drawings]

FIG. 1 shows a sample mounted on a brittleness measuring machine.

FIG. 2 shows a cross section of a Thomson punching machine.

FIG. 3 (1) shows a configuration of a liquid crystal display device used in Examples.
(2) shows the configuration of the optical axis as seen from the front of 〃.

[Explanation of symbols]

θ: Bending angle a: Sample b: Presser plate (made of vinyl chloride) c: Hard iron blade d: Rubber mat e: Wooden table BL: Backlight P ₁ : Polarizing plate D ₁ : Later phase difference plate LC : Liquid crystal cell D ₂ : Front phase difference plate P ₂ : Polarizing plate R ₁ : Backlight side rubbing axis of liquid crystal cell R ₂ : Front side rubbing axis of liquid crystal cell

Claims (2)

[Claims] 1. A liquid crystal display device in which a polarizing plate, a first retardation film, a liquid crystal cell having a super twist orientation, a second retardation film, and a polarizing plate are arranged in this order from the backlight side. The second retardation plate is a polymer uniaxially stretched film having an intrinsic birefringence value of positive and negative or a negative and positive polymer, respectively, and a polymer material having a negative intrinsic birefringence value is attached to a main chain or a side chain. A liquid crystal display device comprising a graft polymer obtained by addition-polymerizing one or more monomers containing at least a styrene monomer to a polymer having at least an unsaturated double bond. 2. The crossing angle between the polarization axis of the backlight side polarizing plate and the slow axis of the first retardation plate in contact with the polarizing plate is 20 to 4.
0 degree, the crossing angle of the slow axis of the first retardation plate and the rubbing axis of the liquid crystal cell on the first retardation plate side is 70 to 9
0 degree, the crossing angle of the slow axis of the second retardation plate located on the opposite side of the first retardation plate through the liquid crystal cell and the rubbing axis on the second retardation plate side is 70 to 90 degrees, the second position The crossing angle between the slow axis of the retardation plate and the polarization axis of the polarizing plate in contact with the second retardation plate is 50 to 50.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device has an angle of 70 degrees.