JP3938142B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device that enables a wide viewing angle.

  In recent years, due to various advantages such as low power consumption, low voltage operation, light weight, and thinness, liquid crystal display devices (LCDs) are used for information such as mobile phones, personal digital assistants (PDAs), personal computers and televisions. Applications as display devices have increased rapidly. With the development of LCD technology, LCDs in various modes have been proposed, and LCD problems such as response speed, contrast, and narrow viewing angle are being solved. However, it is pointed out that the viewing angle is still narrower than that of a cathode ray tube (CRT), and various measures for compensating the viewing angle have been proposed.

  As one of the countermeasures for viewing angle compensation, a liquid crystal cell capable of essentially expanding the viewing angle has been proposed. Examples include an optically compensated bend (OCB) mode, a vertical alignment (VA) mode, and an in-plane switching (IPS) mode.

  Whereas a conventional twisted nematic (TN) mode liquid crystal cell changes the alignment state of liquid crystal molecules by a vertical electric field applying a voltage in a direction perpendicular to the substrate surface, the IPS mode is parallel to the substrate surface. The orientation state of the liquid crystal molecules is changed by a lateral electric field in which a voltage is applied in any direction. In the IPS mode, the liquid crystal molecules are aligned in parallel to the substrate surface when no voltage is applied, but are not twisted as in the TN mode but are aligned in substantially the same direction.

  The principle of the IPS mode will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional view illustrating a configuration example of an IPS mode liquid crystal display device, and FIG. 2 is a schematic perspective view illustrating an example of normally black in order to explain the principle of the IPS mode. A) shows a state when no voltage is applied, and (B) shows a state when a voltage is applied. In FIG. 2B, reference numerals are given only to parts that are in a different state from (A), and parts in the same state as (A) are designated by reference numerals in order to avoid difficulty in viewing the drawing. Is also omitted.

  Referring to FIG. 1, a liquid crystal cell 10 that forms the center of this liquid crystal display device has a liquid crystal layer 14 sandwiched between upper and lower substrates 11 and 12. The liquid crystal molecules 15 constituting the liquid crystal layer 14 are aligned substantially parallel to the surfaces of the substrates 11 and 12. The polarizing plates 20 and 30 are respectively disposed above and below the liquid crystal cell 10. Of the light from the backlight 50 disposed on one outer side (back side) of the liquid crystal cell 10, the liquid crystal cell 10 and the backlight 50. Only linearly polarized light parallel to the transmission axis of the polarizing plate 30 in between is incident on the liquid crystal cell 10.

Next, in the state where no voltage is applied as shown in FIG. 2A, the liquid crystal molecules 15 are aligned parallel to the substrate surface and in substantially the same direction. In this example, the liquid crystal molecules 15 are aligned in a direction substantially parallel to the transmission axis 32 of the back side polarizing plate 30. One substrate (lower substrate in this example) 12 is provided with electrodes 13 and 13 in parallel in a comb shape. In this state, the linearly polarized light 16 transmitted through the back-side polarizing plate 30 passes through the liquid crystal layer 14 without changing its polarization state, and passes through the upper substrate 11 in the state of the linearly polarized light 17 in the same direction as the incident light. To do. The transmission axis 22 of the polarizing plate 20 disposed thereon, if are perpendicular to the transmission axis 32 of the back side polarizing plate 30, the linearly polarized light 17 passing through the upper substrate 11 to pass through the upper polarizer 2 0 Cannot be displayed, and a black state is displayed.

  On the other hand, as shown in FIG. 2B, when an electric field 18 indicated by a broken line is applied between the electrodes 13 and 13 arranged in parallel on the substrate surface, the long axis of the liquid crystal molecules 15 18 and is displaced from the transmission axis 32 of the back-side polarizing plate 30. As a result, the polarization state changes while the incident linearly polarized light 16 passes through the liquid crystal layer 14, and after passing through the liquid crystal layer, an elliptically polarized light 17 is generated, and a component that can pass through the transmission axis 22 of the upper polarizing plate 20 is generated. Thus, the bright state is displayed.

  In FIG. 2, the transmission axis 32 of the rear polarizing plate 30 is arranged so as to be substantially parallel to the long axis of the liquid crystal molecules 15, and the transmission axes of the upper polarizing plate 20 and the rear polarizing plate 30 are orthogonal to each other. In the example of the arrangement, the transmission axis 22 of the upper polarizing plate 20 is arranged so as to be substantially parallel to the long axis of the liquid crystal molecules 15, and the transmission axes of the upper and lower polarizing plates 20, 30 are arranged so as to be orthogonal to each other. The same result is obtained. In short, the liquid crystal molecules 15 may be arranged so that the major axis thereof is substantially parallel to the transmission axis of one of the polarizing plates. At this time, the major axis direction of the liquid crystal molecules 15 and the transmission axis of one of the polarizing plates do not need to be strictly parallel, but rather the liquid crystal molecules 15 rotate in a certain direction when the electric field 18 is applied. The angle may be shifted by a certain angle, for example, an angle within 10 °. Further, by arranging the transmission axes of the upper and lower polarizing plates 20 and 30 to be orthogonal, a black state is displayed when no voltage is applied, and a bright state is displayed when a voltage is applied. If the transmission axes of the upper and lower polarizing plates 20 and 30 are arranged in parallel, a bright state is displayed when no voltage is applied, and a black state is displayed when a voltage is applied.

  As described above, in the IPS mode, liquid crystal molecules are aligned in the same direction in parallel with the substrate surface, and therefore, the viewing angle characteristics are excellent compared to other modes. However, even in various liquid crystal display devices with improved viewing angle characteristics such as the IPS mode, viewing angle dependency still occurs. This viewing angle dependency will be described with reference to FIG. 3, taking the IPS mode as an example.

  FIG. 3 shows the relationship between the transmission axis direction of the upper and lower polarizing plates and the major axis direction of the liquid crystal molecules when the viewing angle is changed in the black display state of the IPS mode shown in FIG. ) Is a diagram when observed from the normal direction of the substrate, and (B) is a diagram when observed from an oblique direction with respect to the normal line of the substrate. When observed from the normal direction of the substrate as shown in FIG. 3A, the transmission axis 32 of the polarizing plate 30 on the back side (see FIG. 2) and the polarizing plate 20 on the opposite side (viewing side) (see FIG. 2) Is perpendicular to the transmission axis 22. The major axis of the liquid crystal molecules 15 is substantially in the same direction as the transmission axis 32 of the back side polarizing plate. On the other hand, when viewed from an oblique direction rather than the normal direction of the substrate as shown in FIG. 3B, that is, when observed from an oblique direction in the direction of arrow V in FIG. The transmission axes 22 and 32 of the polarizing plates do not have an orthogonal relationship, and a light leak 35 indicated by a white arrow occurs.

  Various measures have been proposed to compensate for the viewing angle dependency of the polarizing plate. As one of them, a method of compensating the viewing angle of the polarizing plate with a retardation plate is effective. For example, Japanese Patent Laid-Open No. 2-160204 (Patent Document 1) discloses that the ratio of the retardation when entering from the vertical direction and the retardation when entering from a direction inclined by 40 degrees from the normal is in a certain range. A retardation film, for example, a retardation film oriented in the thickness direction is described. JP-A-7-230007 (Patent Document 2) discloses a retardation film in which the uniaxially stretched thermoplastic resin film is caused to undergo thermal shrinkage in a predetermined form, and the retardation angle dependency is controlled, for example, A retardation film oriented in the thickness direction is also described. Such a retardation plate oriented in the thickness direction is transmitted through an adjacent polarizing plate between one of the two polarizing plates arranged with the liquid crystal cell interposed therebetween and the liquid crystal cell substrate. Arranging so that the axis and the slow axis of the phase difference plate are parallel is effective in compensating the viewing angle.

Also, SID 00 DIGEST, p.1094-1097 the (non-patent document 1), a slow axis direction of the refractive index n _x in the plane, the refractive index in the direction perpendicular to the slow axis in the plane n _y and the refractive index in the thickness direction is taken as _{n z, (n x -n z} ) / (n x -n y) Nz coefficient expressed by is thick oriented 0.25 and 0.8-positions It is described that the retardation film is more effective. Furthermore, in Japanese Patent Laid-Open No. 11-133408 (Patent Document 3), for the IPS mode, a retardation film (compensation) having an optical axis in the direction perpendicular to the substrate surface with positive uniaxiality between the liquid crystal cell substrate and the polarizing plate. Layer), that is, disposing a retardation film uniaxially oriented in the thickness direction.

  However, these thickness-oriented retardation plates have poor productivity and require precise processing, so that the product becomes expensive. In addition, the types of resins that can be thickness-oriented in this way are limited, and since only polycarbonate-based resins are currently mass-produced, the photoelasticity is particularly low (that is, the photoelastic coefficient is small). ) Is not always satisfactory for applications that require it.

  Further, for the IPS mode, the viewing angle dependency may be improved by mounting a negative uniaxial retardation plate (optical compensation sheet) between the liquid crystal cell substrate and at least one polarizing plate. JP-A-10-54982 (Patent Document 4). This publication shows an example in which the optical axis of a retardation film having negative uniaxiality, that is, the fast axis is arranged in parallel with the major axis of liquid crystal molecules. However, according to the experiments of the present inventors, when the phase difference plate is arranged so that the fast axis is parallel to the long axis of the liquid crystal molecules, sufficient viewing angle characteristics are not necessarily obtained (Comparative Example 1 described later). reference).

On the other hand, various proposals have been made for materials for retardation plates. For example, JP 2000-214325 A (Patent Document 5) discloses a copolymer of N-alkylmaleimide and α-olefin as a retardation plate. It is described to do. The maleimide copolymer itself is known in addition to this. For example, JP-A-5-117334 (Patent Document 6) discloses a copolymer of N-phenylmaleimide, N-alkylmaleimide and α-olefin. It is described that the combination is useful for an optical lens, an optical fiber, an optical disk substrate, and the like. JP 2003-2076 40 A (Patent Document 7) describes that a terpolymer of an acyclic olefin monomer, a cyclic olefin monomer, and an aromatic vinyl monomer is used as a retardation plate. .

JP-A-2-160204 (Claims) JP-A-7-230007 (Claim 1) JP-A-11-133408 (Claim 1, FIG. 1) JP-A-10-54982 (Claim 1, FIG. 3) JP 2000-214325 A (Claim 1) Japanese Patent Laid-Open No. 5-117334 (Claim 1, Paragraph 0034) JP 2003-207640 A (Claim 1) T. Ishinabe et al., ‘Novel Wide Viewing Angle Polarizer with High Achromaticity’, SID 00 DIGEST, p.1094-1097 (2000) (Table 1)

  An object of the present invention is to provide a liquid crystal display device provided with a retardation plate that is excellent in viewing angle characteristics and easy to manufacture.

  In order to achieve the above object, according to the present invention, a liquid crystal having two substrates and a liquid crystal layer sandwiched between them and aligned in parallel with the substrate in the vicinity of the substrate when no voltage is applied. A cell, a first polarizing plate disposed outside one substrate of the liquid crystal cell, a second polarizing plate disposed outside the other substrate of the liquid crystal cell, and any one substrate and the substrate The retardation plate is disposed between the polarizing plate on the side and has a negative uniaxial property, its optical axis is in the in-plane direction, and its slow axis is A liquid crystal display device is provided in which the transmission axis of adjacent polarizing plates and the major axis of liquid crystal molecules located on the adjacent substrate surface are arranged substantially parallel to each other.

In this liquid crystal display device, it is advantageous that the two polarizing plates are arranged normally black so that their transmission axes are orthogonal to each other. The retardation plate constituting the liquid crystal display device is a film in which a polymer having negative intrinsic birefringence is uniaxially stretched, or has a layer of a liquid crystalline discotic compound exhibiting negative uniaxiality. Is preferred. These phase difference plates are preferably plane retardation is 80 to 250 nm, further, the refractive indices n _x of the the three axial directions, based on the n _y and _{n z (n x -n z)} / (n _x -n _y) Nz coefficient expressed by is preferably a -0.2～0.2.

When the retardation plate is made of a polymer having negative intrinsic birefringence, the photoelastic coefficient is preferably 10 × 10 ⁻⁵ mm ² kg ⁻¹ or less. The polymer preferably has a glass transition temperature (Tg) of 120 ° C. or higher. From the viewpoint of such a photoelastic coefficient and glass transition temperature, as a preferred polymer, an acyclic olefin monomer selected from ethylene and an α-olefin compound having 3 to 20 carbon atoms and a cyclic olefin selected from a cyclic olefin compound are used. Mention may be made of terpolymers of a monomer and an aromatic vinyl monomer selected from vinyl compounds having an aromatic hydrocarbon ring. In this case, it is advantageous that the aromatic vinyl monomer is polymerized at a copolymerization ratio of 5 to 50 mol%, and the acyclic olefin monomer and the cyclic olefin monomer are 50 to 95 mol% in total.

  In this liquid crystal display device, the operation mode of the liquid crystal cell used is preferably the IPS mode.

  The liquid crystal display device according to the present invention has a negative uniaxial property between one of two polarizing plates sandwiching a liquid crystal cell and the liquid crystal cell, and the optical axis thereof is in the in-plane direction. Retardation by the liquid crystal layer and the polarizing plate by arranging the sheets so that the slow axis thereof is substantially parallel to the transmission axis of the adjacent polarizing plate and the long axis of the liquid crystal molecules located on the adjacent substrate surface, respectively. As compared with the conventional liquid crystal display device, the light leakage depending on the viewing angle can be suppressed. Further, if the retardation plate is made of a specific ternary copolymer, the photoelasticity is excellent.

  Hereinafter, the present invention will be described in detail with appropriate reference to the accompanying drawings. 4A and 4B show examples of the liquid crystal display device according to the present invention, in which FIG. 4A is a schematic sectional view and FIG. 4B is a perspective view for explaining an axial relationship. The liquid crystal display device is configured with a liquid crystal cell 10 as a center. The liquid crystal cell 10 has a liquid crystal layer 14 sandwiched between two substrates 11 and 12. A first polarizing plate 20 is disposed outside one substrate 11, and a second polarizing plate 30 is disposed outside the other substrate 12. The transmission axis 22 of the first polarizing plate 20 and the transmission axis 32 of the second polarizing plate 30 are generally arranged in a substantially perpendicular relationship and are normally black as described above. They can also be arranged in parallel so that they are normally white. Further, the transmission axis 32 of the other polarizing plate 30 is set so that the transmission axis 22 of one polarizing plate 20 is substantially orthogonal to the major axis direction 19 of the liquid crystal molecules 15 in the liquid crystal layer 14 when no voltage is applied. They are arranged so as to be almost parallel. In this specification, “substantially” when saying “substantially parallel” or “substantially orthogonal” means that it is allowed up to about ± 10 ° centering on the arrangement (parallel or orthogonal) described there. To do.

  In the present invention, the polarized light whose transmission axis is substantially parallel to the direction (major axis direction of the liquid crystal molecules) 19 in which the liquid crystal molecules in the liquid crystal layer 14 constituting the liquid crystal cell 10 are aligned when no voltage is applied. The phase difference plate 40 is disposed only between the plate 30 and the liquid crystal cell 10. This phase difference plate 40 has negative uniaxiality, and its optical axis is in the in-plane direction. The slow axis 42 of the phase difference plate 40 is disposed so as to be substantially parallel to the transmission axis 32 of the adjacent second polarizing plate 30. The phase difference plate 40 functions as an optical compensation plate. At least a retardation plate is not disposed between the other polarizing plate 20 and the liquid crystal cell 10. A backlight is disposed on the back surface of one of the polarizing plates 20 or 30 and serves as a light source for supplying light to the liquid crystal cell 10. The backlight may be arranged on either side.

Here the phase difference plate 40, three axial directions of the refractive indices n _x, has a n _y and n _z, the slow axis 42 direction of the refractive indices n _x in the plane, the fast axis direction (slow axis the refractive index of the direction) orthogonal in the plane and n _y, the refractive index in the thickness direction and n _z. FIG. 5 shows a state in which a retardation plate having a negative uniaxial property and having an optical axis in the in-plane direction is represented by a refractive index ellipsoid as defined in the present invention. FIG. 5A shows a state in which the slow axis 42 in the refractive index ellipsoid is taken in the horizontal direction, and FIG. 5B shows an axis (fast axis) orthogonal to the slow axis 42 in the plane. Is in the state of taking in the horizontal direction. It has a negative uniaxial property, and the phase difference plate whose optical axis is in plane direction, as shown in FIG. 5, the refractive index structure, a relation of n _x ≒ n _z> n _y are those, smallest n _y direction refractive index (fast axis direction) is the optical axis.

Then, the screen vertical thickness of the retardation plate 40 is taken as d, the properties of the retardation plate 40, the product of the difference and the thickness of the in-plane refractive index [(n _x -n _y) · d The in-plane retardation value represented by the formula is preferably 80 nm or more and 250 nm or less, more preferably 100 nm or more, 210 nm or less, particularly 100 nm or more, particularly 120 nm or more, and 160 nm or less. _{(n x -n z) / (} n x -n y) Nz coefficient expressed by is preferably in the range from -0.2 to 0.2. As a particularly preferred retardation plate, a negative uniaxial retardation plate obtained by uniaxially stretching a polymer having negative intrinsic birefringence and having an Nz coefficient of approximately 0, or a liquid crystalline discotic compound exhibiting negative uniaxiality In this case, the above-mentioned layer is formed.

Examples of the polymer used when uniaxially stretching a polymer having negative intrinsic birefringence to form the retardation plate include a styrene polymer, an acrylate ester polymer, a methacrylate ester polymer, an acrylonitrile polymer, Methacrylonitrile polymer, vinyl naphthalene polymer, vinyl pyridine polymer, vinyl carbazole polymer, phenyl acrylamide polymer, vinyl biphenyl polymer, vinyl anthracene polymer, acenaphthylene polymer, phenyl carbonyl Oxynorbornene polymer, biphenylcarbonyloxynorbornene polymer, naphthylcarbonyloxynorbornene polymer, anthracenylcarbonyloxynorbornene polymer, phenylcarbonyloxytetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene polymer, biphenylcarbonyloxytetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene polymer, naphthylcarbonyloxytetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene polymer, anthracenylcarbonyloxytetracyclo [4.4.0.1 ^2,5 . 1 ^7,10] -3-dodecene polymer, alpha-olefin / N- phenylmaleimide copolymer but are like, but is not limited thereto. Here, tetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene has the following structure and is also called dimethanooctahydronaphthalene.

  In addition, the above-mentioned polymers can be mixed with other polymers or copolymerized with other monomers so that the negative intrinsic birefringence is not impaired. Functions such as elasticity may be added.

The polymer used for producing the retardation plate is preferably composed of a copolymer having a glass transition temperature of usually 120 ° C. or higher and heat resistance in consideration of the use environment. The glass transition temperature of this copolymer is particularly preferably 130 ° C. or higher. The polymer preferably has a photoelastic coefficient of 10 × 10 ⁻⁵ mm ² kg ⁻¹ or less. Photoelasticity is a phenomenon in which, when an external force is applied to an isotropic substance to cause stress therein, it exhibits optical anisotropy and exhibits birefringence. When the stress (force per unit area) acting on the substance is σ and the birefringence is Δn, the stress σ and the birefringence Δn are theoretically proportional and can be expressed as Δn = Cσ. This C is the photoelastic coefficient. In other words, if the stress σ acting on the substance is taken on the horizontal axis and the birefringence Δn when the stress is applied on the vertical axis, the relationship between them is theoretically a straight line, and the gradient of this straight line is the photoelasticity. It is a coefficient.

  In view of the high glass transition temperature and low photoelasticity, preferred polymers having negative intrinsic birefringence include acyclic olefin monomers selected from ethylene and α-olefin compounds having 3 to 20 carbon atoms, and cyclic olefins. Examples include terpolymers using at least one cyclic olefin monomer selected from compounds and an aromatic vinyl monomer selected from vinyl monomers having an aromatic hydrocarbon ring.

  Next, each monomer component which comprises this ternary copolymer is demonstrated. The acyclic olefin monomer is selected from ethylene and an α-olefin compound having 3 to 20 carbon atoms. Here, examples of the α-olefin compound having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1- C3-C20 linear α-olefin such as hexadecene, 1-octadecene, 1-eicosene, 4-methyl-1-pentene, 3-methyl-1-pentene, 3-methyl-1-butene And branched α-olefins having 4 to 20 carbon atoms. Among these, ethylene having 2 carbon atoms and propylene or 1-butene, which is a linear α-olefin having 3 or 4 carbon atoms, is obtained when the resulting copolymer is formed into a film. In view of flexibility, ethylene is particularly preferable for the same reason. The above ethylene and α-olefin may be used alone or in combination of two or more.

The cyclic olefin monomer is a compound having a polymerizable carbon-carbon double bond in a carbocycle, and when copolymerized, a cyclobutane ring, a cyclopentane ring, a cyclohexane ring in the main chain of the copolymer, A monomer capable of introducing an alicyclic ring such as one or more bonded rings. Specifically, bicyclo [2.2.1] hept-2-ene, which is usually called norbornene, 6-alkylbicyclo [2.2.1] hept-2-ene, 5,6-dialkylbicyclo Such as [2.2.1] hept-2-ene, 1-alkylbicyclo [2.2.1] hept-2-ene, 7-alkylbicyclo [2.2.1] hept-2-ene, Tetracyclo [4.4.0.1 ^2,5 .norbornene derivatives into which an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, or a butyl group is introduced, or dimethanooctahydronaphthalene. 1 ^7,10 ] -3-dodecene and 8-alkyltetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene, 8,9-dialkyltetracyclo [4.4.0.1 ^2,5 . ^{Dimethanooctahydronaphthalene} derivative in which an alkyl group having 3 or more carbon atoms is introduced into the 8-position and / or 9-position of dimethanooctahydronaphthalene, such as 1 ^7,10 ] -3-dodecene, Examples thereof include norbornene derivatives in which one or more halogens are introduced, and dimethanooctahydronaphthalene derivatives in which halogens are introduced at the 8th and / or 9th positions. These cyclic olefins may be used alone or in combination of two or more.

  Aromatic vinyl monomers include styrene and its derivatives. Styrene derivatives are compounds in which other groups are bonded to styrene, such as o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, o-ethylstyrene, p-ethyl. Alkyl styrene such as styrene, hydroxy styrene, t-butoxy styrene, vinyl benzoic acid, vinyl benzyl acetate, o-chloro styrene, p-chloro styrene, benzene nucleus of styrene with hydroxyl group, alkoxy group, carboxyl group, Substituted styrene introduced with acyloxy group, halogen, etc., vinylbiphenyl compounds such as 4-vinylbiphenyl and 4-hydroxy-4'-vinylbiphenyl, and further 1-vinylnaphthalene and 2-vinylnaphthalene. And vinyl naphthalene compounds

  As for the amount of each monomer, when the amount of the aromatic vinyl monomer is too small, it has a positive intrinsic birefringence, which is not preferable. On the contrary, when the amount is too large, This is not preferable because the elastic modulus increases. Further, when the amount of the cyclic olefin monomer is too small, the glass transition temperature is lowered, which is not preferable. On the other hand, when the amount is too large, the copolymer becomes brittle, which is also not preferable. In view of this, it is suitable to polymerize the aromatic vinyl monomer at a copolymerization ratio of about 5 to 50 mol% and the total of the acyclic olefin monomer and the cyclic olefin monomer to be about 50 to 95 mol%.

More specifically, for example, the acyclic olefin monomer is ethylene, the aromatic vinyl monomer is styrene, and the cyclic olefin monomer is tetracyclo [4.4.0.1 ^2,5 . In the ternary copolymer composed of ^1,7,10 ] -3-dodecene, 15 to 25 mol% of styrene and tetracyclo [4.4.0.1 ^2,5 . It is particularly preferable that the content of 1 ^7,10 ] -3-dodecene is 25 to 35 mol%, since the resin exhibits negative birefringence, a high glass transition temperature, and a low photoelasticity.

  In addition, in consideration of the high glass transition temperature and low photoelasticity, another preferred polymer having negative intrinsic birefringence includes a copolymer containing N-phenylmaleimide units and α-olefin units. It is done. Specifically, this copolymer can have units of the following formulas (I) and (II).

In formula (I), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ each independently represent hydrogen, halogen, a carboxyl group or an alkyl group having 1 to 8 carbon atoms;
In formula (II), R ₈ , R ₉ and R ₁₀ each independently represent hydrogen or an alkyl group having 1 to 6 carbon atoms.

Formula (I) represents an N-phenylmaleimide unit, and R ₁ , R ₂ , R ₃ , R ₄ and R ₅ appearing on the benzene ring are each independently hydrogen, halogen, a carboxyl group (—COOH) or It is a C1-C8 alkyl group. When any of these is a halogen, examples of the halogen include fluorine, chlorine, bromine, iodine and the like. When any of R _{1 to} R ₅ is an alkyl group, the carbon number thereof is 1 to 8, which may be linear, and when it has 3 or more carbon atoms, isopropyl, isobutyl, sec-butyl , Tert-butyl and the like may be branched. Of the groups R ₁ , R ₂ , R ₃ , R ₄ and R ₅ on the benzene ring, at least one of them is preferably a group other than hydrogen, especially one or two are alkyl groups and the rest Is preferably hydrogen. In particular, it is preferable that R ₁ located at the 2-position and / or R ₅ located at the 6-position is an alkyl group.

In formula (I), R ₆ and R ₇ appearing on the carbon atom of maleimide are each independently hydrogen, halogen, a carboxyl group (—COOH 3) or an alkyl group having 1 to 8 carbon atoms. The same explanation as described above applies to the halogen and alkyl groups in this case. These R ₆ and R ₇ appearing on the carbon atom of maleimide are generally advantageously hydrogen, but on the other hand, it is also effective to use a polar halogen or carboxyl group.

Formula (II) represents an α-olefin unit, and R ₈ , R ₉ and R ₁₀ appearing there are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms. Regarding the alkyl group in this case, the same explanation as described above applies except for the number of carbon atoms. Among the α-olefins that give the unit of the formula (II), those having 4 or more carbon atoms and R ₈ and R ₉ being an alkyl group are preferred.

  Examples of the compound giving the N-phenylmaleimide unit of the formula (I) include N-phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-isopropylphenyl) ) Maleimide, N- (3-methylphenyl) maleimide, N- (3-ethylphenyl) maleimide, N- (4-methylphenyl) maleimide, N- (4-ethylphenyl) maleimide, N- (2,6- Dimethylphenyl) maleimide, N- (2,6-diethylphenyl) maleimide, N- (2,6-diisopropylphenyl) maleimide, N- (2,4,6-trimethylphenyl) maleimide, N- (2-, 3 -Or 4-carboxyphenyl) maleimide, N- (2,4-dimethylphenyl) maleimide and the like. . These may be used alone or in combination of two or more for polymerization.

  Examples of the compound giving an α-olefin unit of the formula (II) include isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, 2-methyl-1-hexene, 2-methyl-1-heptene. 2-methyl-1-octene, 2-ethyl-1-pentene, 2-methyl-2-butene, 2-methyl-2-pentene, 2-methyl-2-hexene, ethylene, propylene, 1-butene, 2 -Butene, 1-hexene and the like. These can also be used for polymerization individually or in combination of two or more.

  As described above, the compound that gives the N-phenylmaleimide unit of the formula (I) and the compound that gives the α-olefin unit of the formula (II) are polymerized by a known method to thereby define the negative defined in the present invention. N-phenylmaleimide / α-olefin copolymer used for a retardation film having a uniaxial property and an optical axis in the in-plane direction can be produced. At this time, if desired, other vinyl monomers can be copolymerized in a small amount within a range not impairing the object of the present invention. Examples of other vinyl monomers include styrene, α-methylstyrene, and vinyl toluene.

  The amount of each monomer in this case will be described. When the amount of N-phenylmaleimide is too small, positive intrinsic birefringence is exhibited and the glass transition temperature is lowered. If the amount is too large, the photoelastic coefficient increases and the copolymer becomes brittle. Accordingly, those obtained by polymerization at a copolymerization ratio such that the N-phenylmaleimide unit is about 5 to 50 mol% and the α-olefin unit is about 50 to 95 mol% are suitable. In order to prevent the glass transition temperature from being lowered, N-alkylmaleimide may be used as a monomer to the extent that the optical properties of the polymer are not impaired.

  A retardation plate can be obtained by forming a polymer as described above into a film and stretching it by an appropriate method. In order to obtain a retardation plate with small variations in retardation, it is important to use an optically uniform film for stretching. There are various known methods for forming a film, such as a melt extrusion method, a solvent casting method, and an inflation method. However, the film thickness variation is small, the retardation is small, and an optically isotropic film is obtained. Any method can be applied as long as it is.

  The film thus obtained can be subjected to an orientation treatment by a known stretching method to give a uniform retardation. As the stretching method, a uniaxial or biaxial thermal stretching method can be employed. When optical uniaxiality is important, free end longitudinal uniaxial stretching can be cited as a preferred stretching method.

  The retardation plate thus obtained exhibits negative uniaxiality and can be preferably used for compensation of viewing angle characteristics of a liquid crystal display device using the IPS liquid crystal operation mode.

  Next, a mode in which a layer of a liquid crystalline discotic compound exhibiting negative uniaxial property is formed to have a negative uniaxial property and the optical axis thereof is in the plane will be described. A liquid crystal discotic compound is a compound that exhibits liquid crystallinity and has a discotic molecular structure. In such a state that such a compound is melted or dissolved in an appropriate solvent, it is applied onto a transparent plastic film so that the disk surface is parallel to the film surface and in a predetermined direction. By aligning the disk surface upright on the film surface so that the disk surface is in a predetermined orientation, and solidifying while maintaining the orientation, or removing the solvent, the resulting liquid crystalline discotic compound layer is negative. Uniaxiality is exhibited, and the optical axis (fast axis) is in the plane. Also by such a method, a retardation plate having a refractive index ellipsoidal structure as shown in FIG. 5 can be manufactured. In order to align the liquid crystalline discotic compound, a general method such as use of an alignment film, rubbing, addition of a chiral dopant, or light irradiation can be used. Further, after aligning the liquid crystalline discotic compound, it is possible to cure the liquid crystalline compound in order to fix the alignment.

  Returning to FIG. 4, the polarizing plates 20 and 30 constituting the liquid crystal display device of the present invention transmit linearly polarized light that vibrates in one direction orthogonal to each other in the film plane and absorb linearly polarized light that vibrates in the other direction. It may be a known linearly polarizing plate of the type. Specifically, there are an iodine type polarizing plate in which iodine is adsorbed and oriented on a polyvinyl alcohol film and a dye type polarizing plate in which a dichroic organic dye is adsorbed and oriented on a polyvinyl alcohol film, both of which can be used. These polarizing plates are generally used in such a form that one or both surfaces of a polarizer made of a polyvinyl alcohol film are covered with a polymer protective film.

  As shown in FIG. 4A, an adhesive is used for laminating the retardation plate 40 and the polarizing plate 30, laminating the liquid crystal cell substrate 11 and the polarizing plate 20, and laminating the liquid crystal cell substrate 12 and the retardation plate 40. Alternatively, the adhesive 55 may be used. In general, an acrylic or other transparent adhesive is preferably used.

  When producing the retardation plate applied to the liquid crystal display device of the present invention and having the optical axis in the in-plane direction and having negative uniaxiality, in the case where the free end longitudinal uniaxial stretching is employed, the negative electrode thus obtained is obtained. Bonding of the uniaxial retardation plate and the polarizing plate can be performed by roll-to-roll, thereby reducing the number of manufacturing steps and efficiently manufacturing. In addition, a retardation plate is directly bonded to the side of the polarizing plate that is coated only on one side with a polymer protective film, and the phase difference plate is used as an alternative to the polymer protective film. You can also.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this invention is not limited by these examples.

Example 1
A phase difference plate and iodine linear polarizing plate are bonded to the back of the IPS mode liquid crystal cell [LCD monitor manufactured by EIZO NANAO CORPORATION] in order from the substrate side. Only the linear polarizing plate was bonded. The retardation plate is a uniaxially stretched polystyrene film having negative intrinsic birefringence and having an in-plane retardation value of 150 nm. The iodine linear polarizing plate is manufactured by Sumitomo Chemical Co., Ltd. SRW842AP1 "was used. The slow axis of the retardation plate is parallel to the transmission axis of the back side linear polarizing plate and the long axis direction of the liquid crystal molecules in the liquid crystal cell, and the front side linear polarizing plate and the back side linear polarizing plate. Were arranged so that their transmission axes were orthogonal. The layer configuration and the axial relationship of the liquid crystal display device manufactured here are as shown in FIG. A backlight was installed on the back of the liquid crystal display device, and the viewing angle dependency was measured with a luminance measuring device by viewing angle “EZ-Contrast” manufactured by ELDIM. The viewing angle dependency was evaluated based on the degree of light leakage due to a change in viewing angle in a black display state where no voltage was applied. The measurement results are shown in FIG.

  FIG. 9 shows the luminance distribution in this state, where the right direction of the screen is 0 °, and the azimuth is displayed with the counterclockwise direction being positive (every 45 ° from 0 ° to 315 °). Numbers are displayed), and “10”, “20”..., “70” on the horizontal axis means the inclination angle from the normal line at each azimuth angle. For example, the right end of the circle means the luminance in the direction in which the azimuth angle is 0 ° and tilted by 80 °. The scale on the right side represents luminance. The darker the color (black), the darker (no light leak), and the lighter the color (white), the brighter (light leaked). The + mark represents the brightest position (the largest light leak). The following FIGS. 10 to 12 also show the luminance distribution in the same meaning for different liquid crystal display devices. From FIG. 9, it was confirmed that the liquid crystal display device of this example has little light leakage in the front direction, the oblique direction, and the like.

Example 2
A liquid crystal display device was produced with the same configuration and angular arrangement as in Example 1 except that a uniaxially stretched polystyrene film having an in-plane retardation value of 200 nm was used as the retardation plate. With respect to this liquid crystal display device, the viewing angle dependency was measured in the same manner as in Example 1. The result is as shown in FIG. 10, and it was confirmed that this liquid crystal display device also has little light leakage in the front direction and the oblique direction.

Example 3
Ethylene, styrene and tetracyclo [4.4.0.1 ^2,5 . A copolymer obtained by copolymerizing 1 ^7,10 ] -3-dodecene at a molar ratio of 50:20:30 was formed into a film having a thickness of 100 μm by press molding. When this film was uniaxially stretched by an autograph, a retardation plate having negative birefringence and an in-plane retardation value of 140 nm was obtained. A liquid crystal liquid crystal display device was produced in the same manner as in Example 1 except that this retardation plate was used instead of the uniaxially stretched polystyrene film. With respect to this liquid crystal display device, the viewing angle dependency was measured by the same method as in Example 1. As a result, the same result as in Example 1 was obtained, and light leakage was suppressed in both the front direction and the oblique direction. confirmed.

Comparative Example 1
As shown in FIG. 6, the arrangement and the axis configuration of each layer are the same as those in the first embodiment, and the slow axis 42 of the retardation plate 40 is perpendicular to the major axis 19 of the liquid crystal molecules constituting the liquid crystal cell 10. A liquid crystal display device was produced in the same manner as in Example 1 except for the above. With respect to this liquid crystal display device, the viewing angle dependency was measured in the same manner as in Example 1. As a result, the light leakage due to the change in the viewing angle was remarkable.

Comparative Example 2
As shown in FIG. 7, the arrangement and the axis configuration of each layer are the same as those in the first embodiment, and the transmission axis 32 of the linearly polarizing plate 30 adjacent to the phase difference plate 40 has the liquid crystal molecules constituting the liquid crystal cell 10. A liquid crystal display device was produced in the same manner as in Example 1 with the arrangement being perpendicular to the long axis 19. With respect to this liquid crystal display device, the viewing angle dependency was measured in the same manner as in Example 1. As a result, as in Comparative Example 1, light leakage due to a change in viewing angle was significant.

Comparative Example 3
As shown in FIG. 8 showing the arrangement and axis configuration of each layer, the layer configuration is the same as in Example 1, the slow axis 42 of the phase difference plate 40 and the transmission axis 32 of the linearly polarizing plate 30 adjacent thereto are parallel, A liquid crystal display device was manufactured in the same manner as in Example 1 except that each axis was arranged to be perpendicular to the major axis 19 of the liquid crystal molecules constituting the liquid crystal cell 10. The viewing angle dependency of this liquid crystal display device was measured in the same manner as in Example 1. As a result, as in Comparative Examples 1 and 2, light leakage due to a change in viewing angle was significant.

Comparative Example 4
A liquid crystal display device was produced with only the iodine-based linearly polarizing plate used in Example 1 and no retardation plate. With respect to this liquid crystal display device, the viewing angle dependency was measured in the same manner as in Example 1. The result is as shown in FIG. 11 and there was little light leakage in the front direction, but there was much light leakage in the oblique direction, and the viewing angle dependency was high.

Comparative Example 5
“SEZ270135” manufactured by Sumitomo Chemical Co., Ltd. was prepared as a thickness-oriented retardation plate. This retardation plate is made of polycarbonate, has an in-plane retardation value of 135 nm, and has an in-plane slow axis direction refractive index of nx and an in-plane perpendicular direction of the slow axis to n _{x y,} the refractive index in the thickness direction is taken as n _z, those Nz = the _{(n x -n z) / (} n x -n y) = 0.2. A liquid crystal display device was produced in the same manner as in Example 1 except that this thickness-oriented retardation plate was used instead of the uniaxially stretched polystyrene film. With respect to this liquid crystal display device, the viewing angle dependency was measured in the same manner as in Example 1. The result is as shown in FIG. 12 and there was little light leakage in both the front direction and the oblique direction. However, compared with the result of Example 1, the maximum value of light leakage was smaller in Example 1. Compared with the results of Example 2, Example 2 had a smaller angle range showing light leakage.

  Table 1 summarizes the main conditions and results obtained in Examples 1 to 3 and Comparative Examples 1 to 5 described above.

It is a cross-sectional schematic diagram which shows the structural example of the liquid crystal display device of an IPS mode. In order to explain the principle of the IPS mode, it is a schematic perspective view showing an example of normally black, where (A) shows a state when no voltage is applied, and (B) shows a state when a voltage is applied. It is a figure which shows the relationship between the transmission-axis direction of an up-and-down polarizing plate at the time of changing a viewing angle, and the major-axis direction of a liquid crystal molecule about the black display state of IPS mode. An example of the liquid crystal display device concerning the present invention is shown, (A) is a mimetic diagram and (B) is a perspective view for explaining an axial relation. This also corresponds to the layer configuration and axial relationship of the liquid crystal display devices manufactured in Examples 1 to 3. FIG. 2A is a diagram showing a retardation plate having a negative uniaxial property and having an optical axis in the in-plane direction as a refractive index ellipsoid. FIG. 4A shows the slow axis of the refractive index ellipsoid in the horizontal direction. (B) is a state in which an axis (fast axis) orthogonal to the slow axis in the plane is taken in the lateral direction. 6 is a perspective view illustrating a layer configuration and an axial relationship of a liquid crystal display device manufactured in Comparative Example 1. FIG. 10 is a perspective view illustrating a layer configuration and an axial relationship of a liquid crystal display device manufactured in Comparative Example 2. FIG. 10 is a perspective view showing a layer configuration and an axial relationship of a liquid crystal display device manufactured in Comparative Example 3. FIG. It is a figure which shows the luminance distribution in the black display state of no voltage application about the liquid crystal display device produced in Example 1. FIG. It is a figure which shows the luminance distribution in the black display state of no voltage application about the liquid crystal display device produced in Example 2. FIG. It is a figure which shows the luminance distribution in the black display state of no voltage application about the liquid crystal display device produced in the comparative example 4. FIG. It is a figure which shows the luminance distribution in the black display state of no voltage application about the liquid crystal display device produced in the comparative example 5. FIG.

Explanation of symbols

10 ... Liquid crystal cell,
11, 12 ... substrate,
13 …… Electrodes on the substrate
14 ... Liquid crystal layer,
15 …… Liquid crystal molecules,
16: Polarized light incident on the liquid crystal cell,
17: Polarization state after passing through the liquid crystal cell,
18 ... Electric field,
19 …… Long axis direction of liquid crystal molecules when no voltage is applied,
20 …… First polarizing plate,
22: Transmission axis of the first polarizing plate,
30 …… Second polarizing plate,
32 …… Transmission axis of the second polarizing plate,
40 ... retardation plate,
42 …… Slow axis of retardation plate,
50 …… Backlight,
55: Adhesive or adhesive.

Claims (6)

And two substrates are sandwiched between them, the liquid crystal cell have a liquid crystal layer which is oriented substantially parallel to the substrate in the vicinity of the substrate in the absence of an applied voltage, operating in the transverse electric field mode,
A first polarizing plate disposed outside one substrate of the liquid crystal cell;
A second polarizing plate disposed outside the other substrate of the liquid crystal cell, and one retardation plate disposed only between any one of the substrates and the polarizing plate on the substrate side,
The retardation plate has negative uniaxiality, its optical axis is in the in-plane direction, and its slow axis is the length of the liquid crystal molecules located on the transmission axis of the adjacent polarizing plate and the adjacent substrate surface. It is characterized by being arranged so as to be substantially parallel to the axis,
Liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the first polarizing plate and the second polarizing plate are arranged so that transmission axes thereof are orthogonal to each other.   The liquid crystal display device according to claim 1, wherein the retardation plate is a film in which a polymer having negative intrinsic birefringence is uniaxially stretched.   The polymer having negative intrinsic birefringence includes at least one acyclic olefin monomer selected from ethylene and an α-olefin compound having 3 to 20 carbon atoms, at least one cyclic olefin monomer selected from cyclic olefin compounds, and At least one aromatic vinyl monomer selected from vinyl compounds having an aromatic hydrocarbon ring, the aromatic vinyl monomer is 5 to 50 mol%, and the total of the acyclic olefin monomer and the cyclic olefin monomer is 50 to 95 mol%. The liquid crystal display device according to claim 3, which is a copolymer polymerized at a copolymerization ratio of   The liquid crystal display device according to claim 1, wherein the retardation plate has a layer of a liquid crystal discotic compound exhibiting negative uniaxiality.   The liquid crystal display device according to claim 1, wherein the retardation plate has an in-plane retardation of 80 to 250 nm.