JPH06130227A - Phase difference plate and liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the phase difference plate of a low cost which has an excellent angle of field characteristic, is improved in a front surface contrast and is further improved in the brittleness in a stretching or working stage or when the plate is further built as a liquid crystal display material and the liquid crystal display device which has the excellent angle of field characteristic, and is improved in the front surface contrast. CONSTITUTION:This phase difference plate is formed by laminating at least one sheet of films consisting of a polymer having a positive intrinsic double refractive index and at least one sheet of films consisting of a polymer having a negative intrinsic double refractive index. The phase difference plate is so formed that the wavelength dispersion value alpha(alpha=DELTAn(450nm)/DELTAn(600nm)) of the double refractive index DELTAn of at least one of two kinds of these films is >=1.10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate used for color correction and improvement of viewing angle characteristics of a liquid crystal display device. More specifically, by using the retardation plate, coloring or viewing angle characteristics can be improved. And an improved liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device has many characteristics such as low voltage and low power consumption, direct connection to an IC circuit, a variety of display functions, high productivity and light weight. And its applications have expanded. At present, a twisted nematic liquid crystal device (hereinafter referred to as STN-LCD) having a twist angle of liquid crystal molecules of 160 to 240 degrees or less has been put into practical use as a dot matrix type liquid crystal display device used in OA-related devices such as word processors and personal computers. Has become. This is because the STN-LCD can maintain a high contrast even at the time of high multiplex driving, as compared with the conventional twisted nematic liquid crystal display device (TN-LCD) having a twist angle of 90 degrees.

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), which results in low contrast and visibility in monochrome display, and colorization. There was also the problem of being extremely difficult.

As means for solving the above-mentioned problems, Japanese Patent Laid-Open No. 63-63
-167303, 63-167304, 63-
No. 189804, No. 63-261302, No. 63-1
49624, JP-A-1-201607 and 2-59.
No. 702, No. 2-24406, No. 2-146002
No. 2, No. 2-257103, No. 3-23404, No. 3
-126012, 3-181905, 3-19
A method using a retardation film as described in Japanese Patent No. 4503 and the like has been proposed, and it has been found that coloring of a display image by STN-LCD is significantly improved.

However, when the liquid crystal display is viewed from an oblique direction, a slight change in the angle causes the STN- such as coloration of the screen, deterioration of contrast, and inversion of black and white.
The problems of viewing angle characteristics found in LCDs in general have not been solved, and these problems are regarded as serious problems of STN-LCDs.

Therefore, in order to improve this viewing angle characteristic,
A method of producing a birefringent film having a refractive index in the thickness direction larger than that in the direction perpendicular to the optical axis of the birefringence by electric field orientation in JP-A-2-285303 and using this as a retardation plate Was proposed. According to this method, the change in contrast depending on the viewing angle is reduced, and the viewing angle characteristics are improved, but the effect is still small, and it is necessary to apply a high voltage to the molten polycarbonate for a long time. Since it becomes complicated, it was difficult to reduce the cost. 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 large-area retardation plate is manufactured at low cost. It was extremely difficult to produce in.

Further, EP 482620 A2 proposes a method in which a heat shrinkable film is laminated on a polycarbonate film, uniaxially stretched, and then the heat shrinkable film is peeled off to use a film as a retardation plate. This method requires at least a heat-shrinkable film having an area equal to or more than twice as large as that of the retardation plate, which is a problem that it is difficult to produce the film at low cost.
Furthermore, JP-A-2-256023 and JP-A-3-1413.
No. 03, No. 3-14122, and No. 3-24502, one intrinsic birefringence film and one negative film,
Alternatively, there has been proposed a method of using a laminated body as a retardation plate. These methods of controlling the refractive index in the thickness direction can significantly improve the viewing angle characteristics, but the contrast when viewed from the front cannot be said to be sufficiently high,
There was room for improvement.

Further, in Japanese Patent Laid-Open No. 4-51101,
A method for improving the viewing angle problem by using only a film having a negative intrinsic birefringence as a retardation film is disclosed. However, the film having a negative intrinsic birefringence used in the above-mentioned patent is a homopolymer or a copolymer using a styrene monomer, a polymer mainly composed of a styrene-based monomer is fragile, and in the uniaxial stretching step. Easy to break, easy to break during processing (cutting, punching) of the film after stretching,
Alternatively, there is a problem that cracks are likely to occur due to heat history after the liquid crystal display device is assembled. Moreover, the contrast when viewed from the front is not yet sufficiently high, and there is room for improvement.

[0009]

DISCLOSURE OF THE INVENTION An object of the present invention is to improve the viewing angle characteristics, improve the front contrast, and improve the brittleness when incorporated in a stretching or processing step and as a liquid crystal display material at a low cost. It is to provide a phase difference plate. Another object of the present invention is to have excellent viewing angle characteristics,
Another object of the present invention is to provide a liquid crystal display device having an improved front contrast.

[0010]

The above objects of the present invention have been achieved by the following means. (1) In a retardation plate in which at least one film made of a polymer having a positive intrinsic birefringence value and at least one film made of a polymer having a negative intrinsic birefringence value are laminated, Wavelength dispersion value α (α = Δn (450n
m) / Δn (600 nm)) is 1.10 or more. (2) A polymer having a negative intrinsic birefringence value is a graft polymer obtained by addition-polymerizing one or more monomers containing at least a styrene-based monomer to a polymer having an unsaturated double bond in a main chain or a side chain. The retardation plate according to (1) above, which is a styrene-based copolymer containing the same. (3) A liquid crystal element having a nematic liquid crystal sandwiched between two electrode substrates facing each other, and a pair of polarizing plates disposed on both sides of the liquid crystal element, and at least one sheet (1) above. Alternatively, a liquid crystal display device having the retardation plate according to (2). (4) A liquid crystal element formed by sandwiching a nematic liquid crystal in a twisted orientation between at least two electrode substrates facing each other, at least two retardation plates arranged on both sides of the liquid crystal element, and In a liquid crystal display device having a pair of polarizing plates arranged on both sides, one of the two retardation plates includes at least one film made of a polymer having a positive intrinsic birefringence value, and the other one. Includes at least one film made of a polymer having a negative intrinsic birefringence value, and a wavelength dispersion value α (α = Δn (450 nm) / Δ of birefringence Δn of at least one of the two kinds of films.
A liquid crystal display device, wherein n (600 nm) is 1.10 or more. (5) The polymer having the negative intrinsic birefringence value is a graft polymer obtained by addition-polymerizing one or more monomers including at least a styrene-based monomer to a polymer having an unsaturated double bond in the main chain or side chain. The liquid crystal display device according to (4) above, which is a styrene-based copolymer containing the same.

The present invention will be described in detail below. The cause of the low front contrast is not clear, but it is considered that the amount of transmitted light in the blue wavelength region does not reach a sufficiently low level in the black display portion of the liquid crystal display device, and a considerable amount is transmitted. From this, wavelength 450n
When the retardation value of the retardation plate for blue light of m was increased, that is, the wavelength dispersion value in the following formula was increased, it was found that the front contrast was remarkably improved, and the present invention was completed. Here, the wavelength dispersion value α of the birefringence Δn is defined as follows by the ratio of Δn for light with a wavelength of 450 nm and Δn for light with a wavelength of 600 nm. α = Δn (450 nm) / Δn (600 nm) In the present invention, in order to improve the contrast when the liquid crystal display is viewed from the front, the wavelength dispersion value α of the birefringence Δn of at least one of the birefringent films is set to 1 .1
It is preferably 0 or more.

Preferred examples of the polymer having a positive intrinsic birefringence value of the present invention include polycarbonate, polyarylate, polyethylene terephthalate, polyamide, polyimide, polysulfone, polyethersulfone, and the like, and particularly polycarbonate-based polymer and polyarylate. It is preferable to use a polymer having a large intrinsic birefringence value such as a system polymer or a polyester polymer, which can easily form a planar homogeneous film by solution casting. Further, the above-mentioned polymer may be not only a homopolymer but also a copolymer, a derivative thereof, a blended product and the like. Wavelength dispersion value α of birefringence Δn of a film made of a polymer having a positive intrinsic birefringence value
In order to achieve a value of 1.10 or higher, sulfur is added to the polymer.
It preferably contains a halogen (fluorine, chlorine, bromine, iodine) atom or the like, and specific examples of the polymer of this type include polysulfone, polyether sulfone and the like.

Examples of the polymer having a negative intrinsic birefringence value of the present invention include a polymer having at least an unsaturated double bond in the main chain or a side chain (referred to as (A)),
It is a graft polymer (referred to as the polymer (C) of the present invention) obtained by addition polymerization of a monomer (referred to as (B)) containing at least one styrene-based monomer. Birefringence Δ of a film made of a polymer having a negative intrinsic birefringence value
In order to set the wavelength dispersion value α of n to 1.10 or more, the above (A) or (B) includes sulfur, halogen (fluorine,
(Chlorine, bromine, iodine) atom is preferable, and as described later, (A) is 1 to 3 of the graft copolymer (C).
Since it is 0% by weight, it is more preferable to use (B) containing a sulfur or halogen (fluorine, chlorine, bromine, iodine) atom.

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 at least an unsaturated double bond repeating unit in its 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 the specific monomer 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)

Further, amides (eg t-butyl acrylamide, t-butyl methacrylamide), monoethylenically unsaturated compounds (eg acrylonitrile, methacrylonitrile) and the like can be mentioned. 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 called SBR, which is solution-polymerized SBR and 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, budadiene-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 contains at least a styrene monomer.
It is a monomer of at least one species. Specific examples of the styrene-based monomer include styrene and α-methylstyrene, o-methylstyrene, p-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2,5-
Dichlorostyrene, p-iodostyrene, pt-butylstyrene, sodium p-vinylbenzenesulfonate, potassium p-vinylbenzenesulfinate, β-
Examples thereof include styrene derivatives such as (p-vinylbenzenesulfonyl) propionic acid amide, p-styrenesulfonyl (β-chloroethyl) amide, and butyl β- (p-vinylbenzenesulfonyl) propionic acid.

Further, the monomer (B) may contain a monomer other than the above-mentioned styrene-based monomer,
As such a monomer, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, acrylic acid, methacrylic acid, β- Chloroethyl methacrylate,
p-bromophenyl acrylate, butadiene, isoprene, maleic anhydride, vinyl acetate, ethylene, propylene, β-phenylsulfonylaminoethyl acrylate, 1: 1 addition product of benzenesulfinic acid and methylenebisacrylamide, sodium vinyl sulfonate, etc. Can be mentioned.

In order to set the wavelength dispersion value α of the birefringence Δn of the film made of the polymer having a negative intrinsic birefringence value of the present invention to 1.1 or more, as described above, as (B), sulfur is used. , A monomer containing a halogen (fluorine, chlorine, bromine, iodine) atom, such as p-
Chlorostyrene, 2,5-dichlorostyrene, p-iodostyrene, sodium p-vinylbenzenesulfonate, potassium p-vinylbenzenesulfinate, β-
(P-Vinylbenzenesulfonyl) propionic acid amide, p-styrenesulfonyl (β-chloroethyl) amide, β- (p-vinylbenzenesulfonyl) propionic acid butyl, α-chloroacrylonitrile, β-chloroethyl methacrylate, p-bromophenyl Examples thereof include acrylate, β-phenylsulfonylaminoethyl acrylate, 1: 1 addition product of benzenesulfinic acid and methylenebisacrylamide, sodium vinylsulfonate and the like. The proportion of the monomer containing a sulfur atom or a halogen atom (fluorine, chlorine, bromine, iodine) in (B) is appropriately adjusted by the value of α.

The proportion of the backbone component polymer (A) in the graft copolymer (C) used in the present invention cannot be uniquely determined because its contribution to the physical properties of the membrane may change depending on its structure. Although difficult, it is preferably 1 to 30% by weight, particularly preferably 3 to 30% by weight in view of the fact that the amount necessary for improving the physical properties of the film or the amount too large causes the film to be too soft and the relaxation of polymer molecular orientation due to heat may occur. It is 20% by weight.

The molecular weight of the polymer 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 10
It is preferably in the range of 1,000,000 to 1,000,000, particularly preferably 15
It ranges from 10,000 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, particularly preferably 60% or more, from the viewpoint of manifesting birefringence characteristics.

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.

The preferred specific examples of the graft polymer (C) of the present invention include (A) a polymer having at least an unsaturated double bond in its main chain or side chain (stem) (B) containing at least a styrene monomer. Although illustrated in the form of a polymer portion (branch) to which one or more kinds of monomers are added, the present invention is not limited thereto. That is, (B) for (A)
Is graft-polymerized. (A), (B) The ratio of the numbers in parentheses represents the copolymerization ratio (weight) of the monomers in each component, and (A) :( B) is the corresponding trunk component / branch component. Represents the weight percentage ratio of the polymer.

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-3,4 (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 P-18 (A) Styrene / butadiene copolymer (5)
0/50) (B) Styrene / p-styrenesulfonyl (β-chloroethyl) amide / acrylonitrile (60/20/2
0) (A) :( B) = 10: 90 P-19 (A) Styrene / butadiene copolymer (2
0/80) (B) Styrene / β- (p-vinylbenzenesulfonyl) butyl propionate / acrylonitrile (50/3
0/20) (A) :( B) = 15: 85 P-20 (A) Styrene / butadiene copolymer (5
0/50) (B) Styrene / β-phenylsulfonylaminoethyl acrylate (80/20) (A) :( B) = 15: 85

In the case of the exemplary graft polymer of the present invention, the polymer represented by (A) is mainly prepared by the emulsion polymerization method or a commercially available product is purchased, which is in the form of an aqueous dispersion. An aqueous dispersion of the graft polymer obtained after polymerization was carried out at 65 ° C. using a redox initiator of potassium persulfate and sodium sulfite while adding or dropping the monomer represented by B) all at once. Was synthesized under a strong acid condition or by addition of a salt (for example, common salt), or by freeze-thawing of the liquid, followed by filtration and drying.

The film made of a polymer having a positive or negative intrinsic birefringence value used for the retardation plate of the present invention is
Using the polymer, a film is formed by a melt extrusion method, a solution casting method, a calender method, or the like, and then the film is further uniaxially stretched by the Denter method, or longitudinally uniaxially stretched (stretched by utilizing the difference in peripheral speed between rolls). It can be obtained by performing uniaxial stretching such as in the case of performing free shrinking in the width direction at any time and in the case of restricting it) or by biaxial stretching using both in combination.

The temperature in this stretching depends on the T of the polymer.
The range of g-20 ° C to Tg + 50 ° C is preferable. That is, when the stretching temperature is far lower than Tg, the optical characteristics are significantly deteriorated due to unevenness in stretching, clouding of the film, and the like. On the other hand, when the stretching temperature is considerably higher than Tg, thermal relaxation occurs even if the molecular chains are oriented, so that the anisotropy of the refractive index cannot be obtained.

The draw ratio is most closely related to the manifestation of the refractive index anisotropy of the raw material polymer, and a small draw ratio is sufficient for a polymer having a large developability, but a large draw ratio is required for a polymer having a small developability. And Also in the film made of a polymer having a positive or negative intrinsic birefringence value in the present invention, it is preferable that the light transmittance is 70% or more and achromatic, and the transmittance is 85% or more and achromatic. More preferable.

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 The absolute value is preferably 0.02 or more, 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 60 degrees or more, more preferably 90 degrees or more and further preferably 100 degrees. More than a degree. The thickness of the uniaxially stretched film having a birefringence value is not particularly limited, but 1
The range of 0 μ to 1 mm is preferable.

In the present invention, the retardation plate in which at least one film made of a polymer having a positive intrinsic birefringence value and at least one film made of a polymer having a negative intrinsic birefringence value are laminated, Retardations in the normal direction are added to each other, and retardation plates with extremely small changes in retardation with respect to omnidirectional grazing incidence, retardation plates with moderate retardation changes, etc. effective.

In the case where these effects are particularly remarkable, the uniaxially stretched film of the polymer having a positive intrinsic birefringence value and the uniaxially stretched film of the polymer having a negative intrinsic birefringence value have their stretching axes orthogonal to each other. , When the crossing angle is 90 ° ± 35 °.

Now, in a laminate of at least one film made of a polymer having a positive intrinsic birefringence and at least one film made of a polymer having a negative intrinsic birefringence value, the molecules of each film are By controlling the orientation level by stretching and the like, it is possible to almost eliminate the viewing angle dependence of the retardation of the laminate and to make an appropriate change. Therefore, depending on the optical characteristics of STN-LCD, It is recognized that the viewing angle characteristics of the STN-LCD can be greatly expanded when it is arranged as a retardation film between the polarizing plate and the liquid crystal cell in the STN-LCD because the viewing angle characteristic of the STN-LCD can be adapted.

More specifically, 90 ° or more, especially 1
The coloring phenomenon due to the birefringence of the liquid crystal element in the liquid crystal display device using the twisted nematic liquid crystal or the cholesteric liquid crystal with the twisted orientation of 80 ° to 330 ° is eliminated, and the viewing angle and the high contrast range can be expanded. The present invention relates to a liquid crystal display device, and with respect to retardation in the direction of the film normal, a retardation of a film formed from a polymer having a positive intrinsic birefringence value and a film formed from a polymer having a negative intrinsic birefringence value The added value of the retardation of is obtained.

However, when the uniaxially stretched film of the polymer having the positive and negative intrinsic birefringence values coincides with each other in the stretching axis, the retardation is canceled, which is not preferable. Therefore, it is preferable that the stretching axes of the film laminate are arranged substantially orthogonal to each other. Specifically, the angle formed by the stretching axis of the film is most preferably 55 ° to 125 °.

However, this is not the case when they are arranged on both sides through a retardation plate including a film made of a polymer having the positive and negative intrinsic birefringence values. That is, the films may not always be laminated and used, may be disposed on both sides of the liquid crystal element, or may serve as a protective film on the liquid crystal element side of the polarizing plate. In particular, when it is used as a polarizing plate protective film, there is a merit that the viewing angle can be expanded and the cost can be reduced. Further, the film in the present invention is not a generally considered film warp,
A film-like material applied to a certain substrate is also included.

Even in this case, the retardation values of the retardation plates arranged on both sides of the liquid crystal element, or the angle formed by the stretching axis thereof is adjusted according to the optical characteristics of the STN-LCD, so that the liquid crystal element has a composite film. The viewing angle characteristics can be improved by eliminating the coloring phenomenon due to the refractive property.

The present invention will be described in detail below with reference to examples.

【Example】

Film making example 1. Preparation of polysulfone film (F1) Polysulfone (trade name: Cordell (registered trademark) P-35)
00, manufactured by Amoco Japan Co., Ltd.) 51.0 g was dissolved in 249.0 g of methylene chloride to give a glass plate having a dry film thickness of 7
Cast to a thickness of 5 μm, dry at room temperature for 30 minutes, then 70 ° C.
And dried for 20 minutes to prepare a polysulfone film having a volatile content of about 2%. This film was cut into a size of 5 cm × 10 cm and stretched 14% under a pulling speed of 10 mm / min at a temperature of 193 ° C. to prepare a birefringent film (F1) used in the present invention. The retardation value of this film was 430 nm, and α was 1.17.

2. Preparation of Polysulfone Film (F2) Polyester film (trade name: FS-1200, manufactured by Sumitomo Bakelite Co., Ltd.) was cut into a size of 5 cm × 10 cm, and a pulling speed of 10 mm / min was applied at a temperature of 193 ° C. It was originally stretched by 12% to prepare a birefringent film (F2) used in the present invention. The retardation value of this film was 432 nm, and α was 1.16.

3. Preparation of polystyrene-based film (F3) 90 parts by weight of a monomer mixture consisting of styrene: acrylonitrile = 80: 20 (wt%) was graft-polymerized to 10 parts by weight of SBR, and a polystyrene copolymer P having a weight average molecular weight of about 300,000 was obtained. -3 51.0 g was dissolved in 249.0 g of methylene chloride, cast on a glass plate so that the dry film thickness was 100 μm, and dried at room temperature for 30 minutes,
It was dried at 70 ° C. for 20 minutes to prepare a polystyrene film having a volatile content of about 3%. This film is 5cm x 10cm
And cut it to size of 10 mm /
The birefringent film (F3) used in the present invention was prepared by stretching 150% under a pulling speed of min. The retardation value of this film was 432 nm and α was 1.07.

4. Preparation of Polycarbonate Film (F4) 102 g of polycarbonate (trade name: C-1400, manufactured by Teijin Chemicals Ltd.) was dissolved in 498 g of methylene chloride, and cast on a glass plate so that the dry film thickness was 80 μm. Then, it was dried at room temperature for 30 minutes and then at 70 ° C. for 30 minutes to prepare a polycarbonate film having a volatile content of about 1%. Cut this film into a size of 5 cm x 10 cm,
The birefringent film (F4) used in the present invention was prepared by stretching 11% under a temperature condition of 158 ° C. The retardation value of this film is 429 nm, and α is 1.0
It was 8.

5. Preparation of polystyrene film (F5) Polymer in which polystyrene-co-p-styrenesulfonyl (β-chloroethyl) amide (for synthetic method, see Yoshio Iwakura and Keisuke Kurita, “Reactive Polymer” page 111) was grafted to SBR. (P-18) 10.2 g was dissolved in methylene chloride 46.5 g to give a dry film thickness of 9 on a glass plate.
Cast to 0 μm and dry at room temperature for 30 minutes, then 70
It was dried at 30 ° C. for 30 minutes to prepare a polystyrene film having a volatile content of about 20%. This film is cut into a size of 5 cm × 10 cm and 10 mm / min at a temperature of 117 ° C.
The film was stretched 140% under the pulling speed of 2 to prepare a birefringent film (F5) used in the present invention. The retardation value of this film was 435 nm, and α was 1.12.

Example 1 (Invention) The retardation plate F1 is arranged on one side of the STN type liquid crystal cell used in the word processor WD-A551 manufactured by Sharp Corporation, and the other side of the liquid crystal cell is arranged. The retardation plate F3 is arranged at. The angle between the liquid crystal cell and the retardation plate F1 and the angle between the liquid crystal cell and the retardation plate F3 were adjusted so that the contrast when viewed from the front was maximized. In this embodiment, a contrast ratio of 25: 1 is obtained from the front,
The range of the contrast ratio of 5: 1 or more was 32 ° in the upper direction, 34 ° in the lower direction, 45 ° in the right direction, and 35 ° in the left direction, and had good viewing angle characteristics.

Example 2 (Invention) On one side of the STN type liquid crystal cell, a laminate of retardation plates F2 and F3 was arranged so that the retardation plate F2 was close to the liquid crystal cell. The angle formed by the liquid crystal cell and the retardation plate F2 and the angle formed by the liquid crystal cell and the retardation plate F3 were adjusted so that the contrast when viewed from the front was maximized. In this embodiment, a contrast ratio of 24: 1 from the front is obtained, and a range of the contrast ratio of 5: 1 or more is in the upward direction 3
The angle was 4 °, the downward direction was 37 °, the rightward direction was 36 °, and the leftward direction was 32 °, which had good viewing angle characteristics.

Example 3 (Invention) The retardation plate F4 was arranged on one side of the STN type liquid crystal cell, and the retardation plate F5 was arranged on the other side of the liquid crystal cell. The angle between the liquid crystal cell and the retardation plate F4 and the angle between the liquid crystal cell and the retardation plate F5 were adjusted so that the contrast when viewed from the front was maximized. In this embodiment, a contrast ratio of 22: 1 from the front is obtained, and the range of the contrast ratio of 5: 1 or more is 33 ° upward, 35 ° downward, 40 ° rightward, and 33 ° leftward. It had a good viewing angle characteristic.

Example 4 (Invention) The retardation plate F1 was arranged on one side of the STN type liquid crystal cell, and the retardation plate F5 was arranged on the other side of the liquid crystal cell. The angle between the liquid crystal cell and the retardation plate F1 and the angle between the liquid crystal cell and the retardation plate F5 were adjusted so that the contrast when viewed from the front was maximized. In this embodiment, a contrast ratio of 26: 1 from the front is obtained, and the range of the contrast ratio of 5: 1 or more is 37 ° upward, 38 ° downward, 46 ° right, and 40 ° left, It had a good viewing angle characteristic.

Comparative Example 1 The retardation plate F3 was arranged on one side of the STN type liquid crystal cell, and the retardation plate F4 was arranged on the other side of the liquid crystal cell. The angle formed by the liquid crystal cell and the retardation plate F3 and the angle formed by the liquid crystal cell and the retardation plate F4 were adjusted so that the contrast when viewed from the front was maximized. In this comparative example, the contrast ratio from the front was 15: 1, and the range of the contrast ratio of 5: 1 or more was 33 ° upward, 35 ° downward, 40 ° right, and 33 ° left.

Comparative Example 2 One retardation film F4 was arranged on both sides of the STN type liquid crystal cell. The angle formed by the liquid crystal cell and the two retardation plates F4 was adjusted so that the contrast when viewed from the front was maximized. In this comparative example, the contrast ratio from the front is 12: 1, and the range of the contrast ratio of 5: 1 or more is
Upward 13 °, downward 15 °, rightward 16 °, leftward 1
It was 5 °.

Comparative Example 3 One retardation film F1 was arranged on each side of the STN type liquid crystal cell. The angle formed by the liquid crystal cell and the two retardation films F1 was adjusted so that the contrast when viewed from the front was maximized. In this comparative example, the contrast ratio from the front is 24: 1, and the range of the contrast ratio of 5: 1 or more is
Upward 14 °, Downward 15 °, Rightward 15 °, Leftward 1
It was 4 °.

The above results are summarized in Table 1. In Examples 1 to 4 of the present invention, the front contrast is 20: 1.
It is understood that the above is favorable and the viewing angle characteristics are also favorable. On the other hand, in Comparative Examples 1 to 3, neither front contrast nor viewing angle characteristics are good.

[0061]

[Table 1]

[0062]

As described above, according to the present invention, an S having a high contrast when viewed from the front and an excellent viewing angle characteristic.
A TN liquid crystal display device can be obtained.

Claims (5)

[Claims] 1. A retardation plate in which at least one film made of a polymer having a positive intrinsic birefringence value and at least one film made of a polymer having a negative intrinsic birefringence value are laminated, Wavelength dispersion value α (α = Δn of birefringence Δn of at least one of the two types of films)
(450 nm) / Δn (600 nm)) is 1.10 or more. 2. A graft weight in which the polymer having a negative intrinsic birefringence value is obtained by addition-polymerizing one or more monomers including at least a styrene-based monomer to a polymer having an unsaturated double bond in a main chain or a side chain. The retardation plate according to claim 1, wherein the retardation plate is a styrene-based copolymer containing a combination. 3. A liquid crystal element comprising a nematic liquid crystal sandwiched between two electrode substrates facing each other, and a pair of polarizing plates arranged on both sides of the liquid crystal element, and at least one sheet. 1. A liquid crystal display device comprising the retardation plate according to 1 or 2. 4. A liquid crystal element comprising a nematic liquid crystal which is twisted and aligned and sandwiched between at least two electrode substrates facing each other, at least two retardation plates arranged on both sides of the liquid crystal element, and the phase difference. In a liquid crystal display device having a pair of polarizing plates arranged on both sides of the plate, one of the two retardation plates includes at least one film made of a polymer having a positive intrinsic birefringence value, and One includes at least one film made of a polymer having a negative intrinsic birefringence value, and a wavelength dispersion value α (α = Δn (450
nm) / Δn (600 nm)) is 1.10 or more. 5. A grafted polymer in which the polymer having a negative intrinsic birefringence value is obtained by addition-polymerizing at least one monomer containing at least a styrene-based monomer to a polymer having an unsaturated double bond in a main chain or a side chain. The liquid crystal display device according to claim 4, wherein the liquid crystal display device is a styrene-based copolymer containing a combination.