TW202020522A - Liquid crystal display device - Google Patents

Abstract

A liquid crystal display device which sequentially comprises a first polarizer, a refractive index anisotropic layer, a liquid crystal cell and a second polarizer in this order, and which is configured such that: the liquid crystal cell has a homogeneous alignment; the absorption axis of the first polarizer and the absorption axis of the second polarizer are at right angles to each other; the absorption axis of the second polarizer and the in-plane slow axis A1 of the liquid crystal cell, to which a voltage is not applied, are at right angles to each other; the refractive index anisotropic layer has a single layer structure, while having negative biaxiality; and the in-plane slow axis A2 of the refractive index anisotropic layer and the in-plane slow axis A1 are parallel to each other.

Description

Liquid crystal display device

The present invention relates to a liquid crystal display device.

The liquid crystal display device can be classified into a liquid crystal display device in a vertical electric field mode and a liquid crystal display device in a horizontal electric field mode according to the orientation direction of the liquid crystal molecules in the liquid crystal cell and the direction of the applied voltage. As a representative liquid crystal display device of the lateral electric field mode, a liquid crystal display device of a plane switching mode (IPS mode) can be mentioned. In the IPS mode liquid crystal display device, the liquid crystal molecules are aligned in a direction parallel to the in-plane direction of the alignment film of the liquid crystal cell (uniform alignment), and the liquid crystal molecules are rotated by generating an electric field in the in-plane direction of the alignment film to control the penetration The transmittance of light through the liquid crystal cell.

The IPS mode liquid crystal display device is generally considered to be superior in contrast, color, etc. compared to the twisted nematic mode (TN mode) liquid crystal display device in the lateral electric field mode, but there have been attempts to change the phase with refractive index anisotropy Differential layers are combined into IPS mode liquid crystal display devices (Patent Documents 1, 2 and 3) to improve image quality.

"Patent Literature" "Patent Document 1": Japanese Patent Publication No. 2009-092847 (corresponding bulletin: US Patent Application Publication No. 2009/103017 specification) "Patent Document 2": Japanese Patent Publication No. 2008-517322 (Corresponding Gazette: International Patent Publication No. 2007/013782) "Patent Document 3": International Patent Publication No. 2008/156011

In the technique of Patent Document 1, a high contrast is achieved by combining the specified retardation layers and allowing the transmittance of the two polarizing plates to be different.

In the technique of Patent Document 2, a high-contrast is achieved by disposing a biaxial thin film coated with a uniaxial C film between the polarizer and the liquid crystal cell as a retardation layer of a multilayer structure.

However, the technologies of Patent Documents 1 to 3 all require two types of polarizing plates or have to stack multiple retardation layers. As a result, the structure of the liquid crystal display device becomes complicated, and the manufacturing cost increases. Moreover, the more stacked layers are, the greater the risk of dust and the like being sandwiched between the layers, resulting in a decrease in the quality of the liquid crystal display device. In particular, with regard to large-area liquid crystal display devices that have been in high demand in recent years, it is desired to simplify the structure.

Therefore, a liquid crystal display device having a simple structure and having sufficient contrast is desired.

The inventor has made intensive studies to solve the aforementioned problems. As a result, it was found that by providing a layered body with a single-layer structure having a specified refractive index anisotropy between the first polarizer layer and the liquid crystal cell, the aforementioned problems can be solved, and the present invention has been completed.

That is, the present invention provides the following.

[1] A liquid crystal display device comprising a first polarizer, a refractive index anisotropic layer, a liquid crystal cell, and a second polarizer in sequence, wherein the liquid crystal cell is uniformly oriented, and the absorption axis of the first polarizer is the same as the foregoing The absorption axis of the second polarizer is orthogonal, the absorption axis of the second polarizer is orthogonal to the slow axis A _{1 in} the plane of the liquid crystal cell to which no voltage is applied, and the refractive index anisotropic layer is a single-layer structure and has With negative biaxiality, the slow axis A _{2 in} the plane of the refractive index anisotropic layer is parallel to the slow axis A ₁ .

[2] The liquid crystal display device according to [1], wherein the layered body having refractive index anisotropy included between the layered body of the first polarizer and the layered body of the second polarizer is only the liquid crystal The cell and the aforementioned refractive index anisotropic layer.

[3] The liquid crystal display device according to [1] or [2], wherein the maximum refractive index nx in the plane of the refractive index anisotropic layer is in the in-plane direction of the refractive index anisotropic layer and is The refractive index ny given in the direction perpendicular to the refractive index nx and the refractive index nz in the thickness direction of the aforementioned refractive index anisotropic layer satisfy the following formula (i): 1.1≦(nx-nz)/(nx-ny)≦1.9　　(i).

[4] The liquid crystal display device according to any one of [1] to [3], wherein the retardation Re in the in-plane direction of the refractive index anisotropic layer is 10 nm or more and 250 nm or less.

[5] The liquid crystal display device according to any one of [1] to [4], wherein the refractive index anisotropic layer is formed of a resin containing an alicyclic structure-containing polymer.

[6] The liquid crystal display device according to [5], wherein the alicyclic structure-containing polymer is selected from the group consisting of a hydride of a ring-opening polymer of a monomer having a reduced ene structure, and a monomer having a reduced ene structure. One or more of the group consisting of an addition copolymer with α-olefin, and a hydride of an addition copolymer of a monomer with a reduced olefin structure and an α-olefin.

[7] The liquid crystal display device according to any one of [1] to [6], wherein the average contrast at a polar angle of 60° is 30 or more.

[8] The liquid crystal display device described in any one of [1] to [7] further includes a backlight, and the backlight, the first polarizer, and the refractive index anisotropic layer are sequentially arranged , The liquid crystal cell and the second polarizer.

[9] The liquid crystal display device according to any one of [1] to [7], which further includes a backlight, and the first polarizer, the refractive index anisotropic layer, and the liquid crystal cell are sequentially arranged , The second polarizer and the backlight.

According to the present invention, it is possible to provide a liquid crystal display device having a simple structure and having sufficient contrast.

The embodiments and examples are disclosed below to explain the present invention in detail. However, the present invention is not limited by the embodiments and examples disclosed below, and can be implemented with any changes without departing from the scope of the patent application of the present invention and its equivalent scope.

In the following description, the so-called slow axis of a film or layer means the slow axis in the plane of the film or layer unless otherwise noted.

In the following description, the angle between the optical axis (slow axis, penetration axis, absorption axis, etc.) of each layer in a member with multiple layers, unless otherwise noted, means viewing the layer from the thickness direction Time angle.

In the following description, the frontal direction of a certain film means the normal direction of the main surface of the film unless otherwise noted, and specifically refers to the direction of the polar angle of the main surface and the azimuth angle of 0°.

In the following description, the so-called oblique direction of a film, unless otherwise noted, means the direction that is neither parallel nor perpendicular to the main surface of the film, specifically means that the polar angle of the main surface is greater than 0° and less than The direction of the 90° range.

In the following description, the retardation Re in the in-plane direction of the layer body is the value shown by Re=(nx-ny)×d unless otherwise noted. And the retardation Rth in the thickness direction of the layer body, unless otherwise noted, is the value shown by Rth={[(nx+ny)/2]-nz}×d. nx represents the refractive index in the direction perpendicular to the thickness direction of the layer body (in-plane direction) and the direction giving the maximum refractive index. ny represents the refractive index which is the aforementioned in-plane direction of the layer body and the direction orthogonal to the direction of nx. nz represents the refractive index in the thickness direction of the layer body. d represents the thickness of the layer body. Unless otherwise noted, the measurement wavelength is 590 nm.

In the following description, the so-called component directions are "parallel", "vertical" and "orthogonal". Unless otherwise noted, within the scope of not detracting from the effects of the present invention, for example, ±3°, ± Error within 2° or ±1°.

[1. Outline of liquid crystal display device]

A liquid crystal display device according to an embodiment of the present invention sequentially includes a first polarizer, a refractive index anisotropic layer, a liquid crystal cell, and a second polarizer.

[1.1. Liquid crystal cell]

The liquid crystal cell generally includes a substrate, two alignment films formed on the substrate, a liquid crystal compound disposed between the two alignment films, and electrodes. The liquid crystal cell may also include a control element that controls voltage.

The liquid crystal cell is preferably a liquid crystal cell driven by the IPS mode.

The liquid crystal cell is uniformly oriented when no voltage is applied. The so-called uniform alignment of the liquid crystal cell means that the alignment vector of the liquid crystal molecules existing between the alignment films coincides with the specified direction in the plane of the alignment film in a parallel alignment state. Here, a liquid crystal cell with an orientation vector of liquid crystal molecules and an orientation film surface at an angle exceeding 0° and below 3° is also regarded as uniformly oriented. The angle between the orientation vector and the orientation film surface is called the pretilt angle.

The pretilt angle of the liquid crystal molecules in the liquid crystal cell (hereinafter also referred to as the "pretilt angle of the liquid crystal cell.") The smaller the better, the ideal value is 0°. In the widely used friction treatment, it is usually not easy to make the pretilt angle 0°, but 3° or less is better. A liquid crystal display device including a liquid crystal cell with a pretilt angle exceeding 0°, when viewed from an oblique direction when the screen is displayed in black, tends to have a large color change due to the azimuth angle observed, but this embodiment type The liquid crystal display device can suppress the color change even when the pretilt angle exceeds 0°.

The pretilt angle of the liquid crystal molecules in the liquid crystal cell can be measured by a conventionally well-known method (such as the rotating crystal method).

The liquid crystal cell has a slow axis A ₁ in the plane when no voltage is applied. Thereto, so-called slow axis, means in a plane parallel to the alignment film of the liquid crystal cell, giving maximum refractive index n _e of the direction. The slow axis A ₁ generally coincides with the optical axis direction, and generally coincides with the alignment direction of the alignment film. The orientation direction of the alignment film refers to the direction in which the liquid crystal molecules are aligned in the case where liquid crystal molecules are aligned on the alignment film by performing a process (such as rubbing treatment) that imparts an alignment restriction force to the alignment film. In the case where the treatment performed by the orientation film is rubbing treatment, the orientation direction of the orientation film is usually the rubbing direction.

The direction of the slow axis A ₁ in the liquid crystal cell can be determined by measuring the refractive index of the liquid crystal cell in a plane parallel to the alignment film of the liquid crystal cell in the state where no voltage is applied. And the rubbing direction of the orientation of the film is known cases, the rubbing direction may be considered as the direction of the slow axis A _1.

As the liquid crystal cell, commercially available products can be used.

[1.2. Polarizer]

As the first polarizer and the second polarizer, a film that "transmits one of two linear polarized lights that intersect at a right angle in the vibration direction and transmits or absorbs the other" can be used. Here, the vibration direction of linearly polarized light means the vibration direction of the electric field of linearly polarized light. Such a film usually has a polarized light transmission axis (hereinafter also referred to as a polarized light transmission axis.), can penetrate linear polarized light having a vibration direction parallel to the transmission axis, and can absorb or reflect light Linear polarized light in the direction of vibration perpendicular to the transmission axis.

To give specific examples of polarizers, mention may be made of: polyvinyl alcohol resin films containing polyvinyl alcohols, partially formalized polyvinyl alcohols, and other vinyl alcohol-based polymers are applied in the appropriate order and manner. Appropriate treatments such as dyeing treatment of dichroic substances such as iodine and dichroic dyes, "extension treatment", and "crosslinking treatment". The polarizer preferably contains polyvinyl alcohol resin.

The first polarizer and the second polarizer may have different characteristics, but those having the same characteristics are preferred. By using members having the same characteristics as the first polarizer and the second polarizer, the manufacturing cost of the liquid crystal display device can be suppressed.

For example, the difference between the transmittance of the first polarizer and the second polarizer is preferably less than 0.5%, preferably less than 0.2%, and more preferably less than 0.1%, usually set to 0 %the above.

[1.3. Refractive index anisotropic layer]

The refractive index anisotropic layer is a layered structure having a single-layer refractive index and anisotropy, and has negative biaxiality. By making the refractive index anisotropic layer into such a structure, a liquid crystal display device with sufficient contrast must be realized with a simple structure.

A layer body having negative biaxiality means a layer body in which nx, ny, and nz satisfy the relationship of nx>ny>nz, and means a so-called negative B-plate in a layer system.

The retardation Re in the in-plane direction of the refractive index anisotropic layer is preferably 10 nm or more, preferably 30 nm or more, more preferably 50 nm or more, and preferably 250 nm or less, and 240 nm or less Preferably, 230 nm or less is more preferable. When the in-plane retardation Re is more than the aforementioned lower limit value, the contrast in the oblique direction (viewing angle contrast) can be effectively improved, and by viewing the screen showing the black state from the oblique direction below the aforementioned upper limit value Next, the color change caused by the azimuth angle can be effectively suppressed.

The refractive index anisotropic layer preferably satisfies the following formula (i) with a value of (nx-nz)/(nx-ny). In the following description, the value of (nx-nz)/(nx-ny) is also called NZ coefficient. 1.1≦(nx-nz)/(nx-ny)≦1.9　　(i)

The NZ coefficient is preferably 1.2 or more, more preferably 1.25 or more, and preferably 1.8 or less, and more preferably 1.75 or less.

By the NZ coefficient falling within the aforementioned range, the contrast can be effectively improved, especially when viewed from the oblique direction. The reason is considered to be that when the NZ coefficient is within the aforementioned range, the polarization state of the light emitted from the backlight side polarizer of the liquid crystal display device to the oblique direction changes when the screen displays black, and the light is highly efficient It is absorbed, but this does not limit the inventor.

The refractive index anisotropic layer is preferably a layered body formed of a thermoplastic resin.

As the thermoplastic resin that forms the refractive index anisotropic layer, a thermoplastic resin having a positive intrinsic birefringence value can be used. By extending "a layer formed from a thermoplastic resin having a positive intrinsic birefringence value by any method" in the in-plane direction, a layer having a negative biaxiality can be made. As the stretching method, any method such as a uniaxial stretching method, a sequential biaxial stretching method, and a simultaneous biaxial stretching method may be used.

A resin having a positive intrinsic birefringence value means a resin whose refractive index in the extending direction becomes larger than that in the direction orthogonal to it. The inherent birefringence is calculated from the dielectric constant distribution.

Examples of the polymer included in the resin having a positive intrinsic birefringence include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; and polyphenylene Polyarylene sulfide such as sulfide; Polyvinyl alcohol; Polycarbonate; Polyarylate; Cellulose ester; Polyether satin; Polysatin; Polyarylene satin; Polyvinyl chloride; Polymers containing alicyclic structures such as norbornene polymers Thing; rod-shaped liquid crystal polymer.

The resin that forms the refractive index anisotropy may include the aforementioned polymer alone or in combination of any ratio of two or more.

The resin forming the refractive index anisotropic layer has a photoelastic coefficient of preferably 30×10 ^{− 13} cm ² /dyn or less, preferably 10×10 ^{− 13} cm ² /dyn or less, 5×10 ^{− 13} cm ² /dyn or less is better, the smaller the better.

The photoelastic coefficient of resin can be measured by an ellipsometer. A film can be formed from resin, and the phase difference when a load of 50 g, 100 g, or 150 g is applied to the film is measured, and it is obtained from the slope of the graph of load and phase difference.

By obtaining the photoelastic coefficient of the resin forming the refractive index anisotropic layer below the upper limit, it is possible to suppress the application of external forces such as changes in the use environment, bending or shrinkage stress to the refractive index anisotropic layer formed of such a resin The display defects such as "uneven display of the liquid crystal display device" that may occur under the circumstances.

The refractive index anisotropic layer is preferably formed of a resin containing an alicyclic structure-containing polymer. The so-called alicyclic structure-containing polymer is a polymer whose structural unit contains an alicyclic structure.

The resin forming the anisotropic refractive index layer may contain a single type of alicyclic structure-containing polymer, or a combination of two or more types of alicyclic structure-containing polymer.

The polymer containing an alicyclic structure may have an alicyclic structure in the main chain, an alicyclic structure in the side chain, or an alicyclic structure in both the main chain and the side chain. Among them, from the viewpoint of mechanical strength and heat resistance, a polymer containing an alicyclic structure at least in the main chain is preferred.

Examples of the alicyclic structure include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structure. Among them, from the viewpoint of mechanical strength and heat resistance, a naphthenic structure and a cycloalkene structure are preferred, and among them, a naphthenic structure is particularly preferred.

The number of carbon atoms constituting the alicyclic structure is preferably 4 or more per alicyclic structure, preferably 5 or more, and preferably 30 or less, preferably 20 or less, 15 The following is particularly preferred. By setting the number of carbon atoms constituting the alicyclic structure within this range, the mechanical strength, heat resistance, and formability of the resin including the alicyclic structure-containing polymer can be highly balanced.

In the polymer containing an alicyclic structure, the proportion of structural units having an alicyclic structure is appropriately selected according to the purpose of use. The proportion of the structural unit having an alicyclic structure in the polymer containing an alicyclic structure is preferably 55 wt% or more, more preferably 70 wt% or more, more preferably 90 wt% or more, and usually 100 wt% or less . If the ratio of structural units having an alicyclic structure in the alicyclic structure-containing polymer is within this range, the transparency and heat resistance of the resin containing the alicyclic structure-containing polymer will be good.

Examples of the alicyclic structure-containing polymer include: norbornene-based polymers, monocyclic cyclic olefin-based polymers, cyclic conjugated diene-based polymers, vinyl alicyclic hydrocarbon polymers, and hydrogenation of these Compounds, and hydrides of vinyl aromatic polymers. Among these, since transparency and moldability are good, a norbornene-based polymer is preferable. The resin containing such a polymer has a low water vapor transmission rate and a small photoelastic coefficient, so it can suppress the application of external forces such as changes in the use environment, bending or shrinkage stress to the refractive index anisotropic layer formed by this resin Under the circumstances, the display defects such as uneven display of the liquid crystal display device may occur.

As examples of the reduced-ene-based polymers, there may be mentioned: ring-opened polymers and their hydrogenated products of monomers with a reduced-ene structure; and addition polymers and hydrogenated products of the monomers with a reduced-ene structure. And as an example of a ring-opening polymer having a monomer having a reduced ene structure, a ring-opening homopolymer having one type of monomer having a reduced ene structure and two or more types of monomers having a reduced ene structure can be cited. Ring-opening copolymers, as well as ring-opening copolymers of monomers with a reduced ene structure and any monomers that can be copolymerized therewith. In addition, as an example of an addition polymer of a monomer having a reduced ene structure, an addition homopolymer of one type of monomer having a reduced ene structure, or two or more types of having a reduced ene structure may be cited. Addition copolymers of monomers, as well as addition copolymers of monomers with a reduced ene structure and any monomers that can be copolymerized therewith.

Among these, hydrides of ring-opening polymers with monomers with a reduced ene structure, addition copolymers of monomers with a reduced ene structure and α-olefins, and monomers with a reduced ene structure The hydride of the addition copolymer with α-olefin is preferred.

Examples of monomers having a reduced pentene structure include bicyclo[2.2.1]hept-2-ene (common name: reduced pentene), tricyclo[4.3.0.1 ^2,5 ]dec-3,7-di Diene (common name: dicyclopentadiene), 7,8-benzotricyclo[4.3.0.1 ^2,5 ]dec-3-ene (common name: tetramethyltetrafluoromethylene bridge), tetracyclo[4.4.0.1 ^{2, 5.1 7,10]} dodeca-3-ene (common name: tetracyclododecene) and derivatives of such compounds (e.g., those having a substituent on the ring) and the like. Here, as a substituent, an alkyl group, an alkylene group, a polar group, etc. are mentioned, for example. These substituents may also be the same or different and may be bonded to multiple rings. Monomers with a reduced ene structure can be used alone or in combination of two or more at any ratio.

The ring-opening polymer having a monomer with a reduced ene structure, for example, can be produced by polymerizing or copolymerizing the monomer in the presence of a ring-opening polymerization catalyst.

In the addition copolymer of a monomer having a reduced ene structure and an α-olefin, examples of the α-olefin include: α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, and the like Etc. derivatives. Among these, ethylene is preferred. One type of α-olefin may be used alone, or two or more types may be used in combination at any ratio.

The addition polymer of a monomer having a reduced ene structure, for example, can be manufactured by polymerizing or copolymerizing the monomer in the presence of an addition polymerization catalyst.

The hydride of the ring-opening polymer and the addition polymer described above can be obtained by, for example, in the solution of the ring-opening polymer and the addition polymer by hydrogenation of transition metals including nickel and palladium. In the presence of a medium, it is better to hydrogenate the carbon-carbon unsaturated bond by more than 90%.

The resin to form the refractive index anisotropic layer may contain any admixture in addition to the polymer. Examples of admixtures include antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, near-infrared absorbers and other stabilizers; plasticizers; and the like. One type of admixture may be used, or two or more types may be combined in any ratio.

[1.4. Relationship between components]

In the liquid crystal display device of this embodiment, the absorption axis A _{a2 of} the second polarizer is orthogonal to the slow axis A _{1 in} the plane of the liquid crystal cell when no voltage is applied. Specifically, the angle between the absorption axis A _a2 and the slow axis A _{1 of} the second polarizer when viewing the second polarizer and the liquid crystal cell from the thickness direction is preferably 90°±1°, preferably 90°±0.8° It is better, or 90°±0.5° is better.

The absorption axis A _a1 of the first polarizer is orthogonal to the absorption axis A _{a2 of} the second polarizer. Specifically, the angle between the absorption axis A _a1 of the first polarizer and the absorption axis A _a2 of the second polarizer when viewing the first polarizer and the second polarizer from the thickness direction is 90°±1° It is better to use 90°±0.8° or 90°±0.5°.

Furthermore, in the liquid crystal display device of the present embodiment, the slow axis A _{2 in} the plane of the refractive index anisotropic layer is parallel to the slow axis A _{1 in} the plane of the liquid crystal cell when no voltage is applied. Specifically, the angle between the slow axis A ₂ and the slow axis A _{1 of the} refractive index anisotropic layer when viewing the refractive index anisotropic layer and the liquid crystal cell from the thickness direction is preferably 0°±1°, preferably 0 °±0.8° is better, or 0°±0.5° is better.

With each member having the aforementioned relationship, a liquid crystal display device with a simple structure and sufficient contrast can be realized.

In the case where the second polarizer is a polarizer on the backlight side, the absorption axis A _{a2 of} the second polarizer is orthogonal to the slow axis A _{1 of the} liquid crystal cell, and the liquid crystal display device is a so-called E-mode liquid crystal display device.

In the case where the first polarizer is a polarizer on the backlight side, the absorption axis A _{a1 of the} first polarizer is parallel to the slow axis A _{1 of the} liquid crystal cell, and the liquid crystal display device is a so-called O-mode liquid crystal display device.

[1.5. Arbitrary components]

The liquid crystal display device may include an arbitrary layer body in addition to the first polarizer, the refractive index anisotropic layer, the liquid crystal cell, and the second polarizer. Examples of such an arbitrary layered body include a polarizer protective film, a color filter, and a bonding layer to which each layered body is bonded.

However, it is preferable that only the liquid crystal cell and the refractive index anisotropic layer are included in the layer body having the refractive index anisotropy between the layer body of the first polarizer and the layer body of the second polarizer. That is, between the layered body of the first polarizer and the layered body of the second polarizer, it is preferable that there is no layered body having refractive index anisotropy except the liquid crystal cell and the refractive index anisotropic layer. In this way, it is possible to easily realize a liquid crystal that is “simple in structure and has sufficient contrast, even when viewed from the oblique direction of the screen when the screen is displayed in a black state, the color change due to the azimuth angle can be effectively suppressed” Display device.

The layer body having refractive index anisotropy is, for example, a layer body in which the retardation Re in the in-plane direction is 5 nm or more and/or the absolute value of the retardation Rth in the thickness direction is 3 nm or more.

[1.6. Characteristics of liquid crystal display devices]

The average contrast of the liquid crystal display device at a polar angle of 60° is preferably 30 or more, preferably 35 or more, more preferably 40 or more, and the larger the better.

The average contrast at a polar angle of 60° can be measured as follows. The azimuth angle in the direction of the slow axis in the plane of the liquid crystal cell is defined as 0° and 180°. Then, at the polar angle of 60° and the azimuth angles of 45°, 135°, 225°, and 315°, measure the brightness B1 when the screen is displayed in black and the brightness W1 when the screen is displayed in white, and calculate the brightness The ratio of W1 to brightness B1 (brightness W1/brightness B2) is taken as the average contrast at the polar angle of 60°. The brightness must be measured by, for example, a spectroradiometer.

[2. Configuration example of liquid crystal display device]

[2.1. First Embodiment]

FIG. 1 is an exploded schematic view of the liquid crystal display device related to the first embodiment. FIG. 1 illustrates a liquid crystal display device in a state where no voltage is applied. And the electrodes, circuits, control elements, etc. are omitted.

The liquid crystal display device 100 according to this embodiment includes a first polarizer 110, a refractive index anisotropic layer 120, a color filter 130, a liquid crystal cell 140, a second polarizer 150, and a backlight 160.

The first polarizer 110 and the second polarizer 150 have an absorption axis A _a1 and an absorption axis A _{a2, respectively} . The absorption axis A _{a1 is} orthogonal to the absorption axis A _a2 . The refractive index anisotropic layer 120 has a slow axis A ₂ . The liquid crystal cell 140 has a slow axis A ₁ . The slow axis A _{2 of the} refractive index anisotropic layer 120 is parallel to the slow axis A _{1 of the} liquid crystal cell 140. The absorption axis A _{a2 of} the second polarizer 150 is orthogonal to the slow axis A _{1 of the} liquid crystal cell 140, and the liquid crystal display device 100 is a so-called E-mode liquid crystal display device.

As the backlight 160, any structure may be adopted, and either an edge-light type method or a direct type method may be used.

As the color filter 130, any structure may be adopted, and for example, a red color filter, a green color filter, or a blue color filter may be used.

[2.2. Second Embodiment]

FIG. 2 is an exploded schematic diagram of a liquid crystal display device related to a second embodiment. FIG. 2 shows a liquid crystal display device in a state where no voltage is applied. And the electrodes, circuits, control elements, etc. are omitted.

The liquid crystal display device 200 according to this embodiment includes a backlight 260, a first polarizer 210, a refractive index anisotropic layer 220, a liquid crystal cell 240, a color filter 230, and a second polarizer 250 in this order.

The first polarizer 210 and the second polarizer 250 have an absorption axis A _a1 and an absorption axis A _{a2, respectively} . The absorption axis A _{a1 is} orthogonal to the absorption axis A _a2 . The refractive index anisotropic layer 220 has a slow axis A ₂ . The liquid crystal cell 240 has a slow axis A ₁ . The slow axis A _{2 of the} refractive index anisotropic layer 220 is parallel to the slow axis A _{1 of the} liquid crystal cell 240. The absorption axis A _{a1 of the} first polarizer 210 is parallel to the slow axis A _{1 of the} liquid crystal cell 240, and the liquid crystal display device 200 is a so-called O-mode liquid crystal display device.

As the backlight 260 and the color filter 230, the same structure as the backlight 160 and the color filter 130, respectively, can be adopted.

『Examples』

The following examples are disclosed to specifically illustrate the present invention. However, the present invention is not limited by the embodiments disclosed below, and can be arbitrarily changed and implemented without departing from the scope of the patent application of the present invention and its equivalent scope.

In the following description, "%" and "parts" indicating quantities are weight standards unless otherwise noted. And unless otherwise noted, the operations described below are performed under normal temperature and normal pressure.

〔Evaluation Method〕

(Thickness of film)

Measure the thickness of the film through a caliper.

(Refractive index of the film, retardation Re in the in-plane direction, retardation Rth and NZ coefficient in the thickness direction)

The refractive index (nx, ny, nz) of the film, the retardation Re in the in-plane direction, and the retardation Rth in the thickness direction were measured at a wavelength of 590 nm using a phase difference measuring device (manufactured by Axometrics, product name "AxoScan").

From the measured values of Re and Rth, the NZ coefficient of the film was obtained according to the following formula. NZ coefficient = Rth/Re + 0.5

(Pretilt angle)

The pretilt angle of the liquid crystal molecules in the liquid crystal cell is measured by a conventionally well-known method (such as the rotating crystal method).

(Color changes due to azimuth when the screen is displayed in black)

It is set to a state where the liquid crystal display device displays black. The azimuth angles of 0° and 180° are defined as the slow axis direction of the liquid crystal cell provided in the liquid crystal display device in the state where no voltage is applied. Then, visually observe the color of the picture in two directions from the polar angle 60° azimuth angle 45° and the polar angle 60° azimuth angle 135°.

(Compared)

It is set to display a black state or a white state on the liquid crystal display device. Then, using a brightness meter ("SR-LED" manufactured by Topcon), the brightness B1 when the screen is displayed in black and the brightness W1 when the screen is displayed in white are measured. The ratio of brightness W1 to brightness B1 (brightness W1/brightness B1) is obtained.

From the brightness measured from the normal direction (front direction) of the screen of the liquid crystal display device, the front direction contrast is obtained.

And from the brightness measured from the direction of the polar angle of the liquid crystal display device screen at 60°, the average contrast at the polar angle of 60° was obtained. Specifically, the slow axis direction of the liquid crystal cell included in the liquid crystal display device in the state where no voltage is applied is defined as azimuth angles of 0° and 180°. Then, find the contrast at the polar angle of 60° and the azimuth angles of 45°, 135°, 225°, and 315°, and add the average of the contrast at each azimuth angle as the average contrast value at the polar angle of 60°.

From the contrast in the frontal direction and the average contrast at the polar angle of 60°, the contrast of the liquid crystal display device was comprehensively evaluated by the following criteria. A: Average contrast ≧40　 and 　 frontal contrast ≧1100 B: Average contrast≧40　and　1100＞Front contrast≧1000 C: Average contrast<40

[Production Example 1]

It is obtained by melting and extruding a resin containing a polymer containing an alicyclic structure ("ZEONOR 1420" manufactured by Ruion Corporation, with a photoelastic coefficient of 2×10 ^{− 13} cm ² /dyn) and drawing it to a casting roll to obtain Raw material film with a thickness of 60 μm. The obtained raw material film was longitudinally extended 2.5 times at 142°C. The longitudinal extension is carried out by setting the speed difference of the peripheral speed of the conveying roller. Next, the longitudinally stretched film was transversely stretched 1.5 times at 142°C through a tenter stretching machine to obtain a compensation film 1 as a refractive index anisotropic layer. The thickness of the obtained compensation film 1 is 26 μm, the refractive index nx is 1.5328, the refractive index ny is 1.5293, the refractive index nz is 1.5280, the retardation Re in the in-plane direction is 90 nm, and the retardation Rth in the thickness direction is 79 nm, NZ The coefficient is 1.38.

[Production Example 2]

With the exception of changing the following items, according to Production Example 1, a raw material film having a thickness of 55 μm was obtained. ・The pulling speed to the casting roll was changed to 1.1 times the speed in Manufacturing Example 1.

The obtained raw material film was longitudinally extended 2.2 times at 141°C. The longitudinal extension is carried out by setting the speed difference of the peripheral speed of the conveying roller. Next, the longitudinally stretched film was transversely stretched 1.5 times at 141°C through a tenter stretching machine to obtain a compensation film 2 as a refractive index anisotropic layer. The thickness of the obtained compensation film 2 is 25 μm, the refractive index nx is 1.5330, the refractive index ny is 1.5293, the refractive index nz is 1.5277, the retardation Re in the in-plane direction is 92 nm, and the retardation Rth in the thickness direction is 86 nm, NZ The coefficient is 1.43.

[Production Example 3]

According to Manufacturing Example 2, a raw material film having a thickness of 55 μm was obtained. The obtained raw material film was longitudinally extended to 2.7 times at 141°C. The longitudinal extension is carried out by setting the speed difference of the peripheral speed of the conveying roller. Next, the longitudinally stretched film was transversely stretched 1.6 times at 141°C through a tenter stretching machine to obtain a compensation film 3 as a refractive index anisotropic layer. The thickness of the obtained compensation film 3 is 20 μm, the refractive index nx is 1.5338, the refractive index ny is 1.5289, the refractive index nz is 1.5273, the retardation Re in the in-plane direction is 99 nm, and the retardation Rth in the thickness direction is 80 nm, NZ The coefficient is 1.31.

[Production Example 4]

With the exception of changing the following items, according to Production Example 1, a raw material film with a thickness of 105 μm was obtained. ・The pulling speed to the casting roll was changed to 0.5 times the speed in Manufacturing Example 1.

The obtained raw material film was longitudinally extended to 3.7 times at 140°C. The longitudinal extension is carried out by setting the speed difference of the peripheral speed of the conveying roller. Next, the longitudinally stretched film was stretched laterally at 140°C by a tenter stretching machine to 1.9 times to obtain a compensation film 4 as a refractive index anisotropic layer. The thickness of the obtained compensation film 4 is 28 μm, the refractive index nx is 1.5332, the refractive index ny is 1.5290, the refractive index nz is 1.5279, the retardation Re in the in-plane direction is 118 nm, and the retardation Rth in the thickness direction is 89 nm, NZ The coefficient is 1.25.

[Production Example 5]

With the exception of changing the following items, according to Production Example 1, a raw material film having a thickness of 85 μm was obtained. ・The pulling speed to the casting roll was changed to 0.6 times the speed in Manufacturing Example 1.

The obtained raw material film was longitudinally extended at 3.4 times at 143°C. The longitudinal extension is carried out by setting the speed difference of the peripheral speed of the conveying roller. Next, the longitudinally stretched film was stretched laterally by a tenter stretching machine at 143°C to a factor of 1.8 to obtain a compensation film 5 as a refractive index anisotropic layer. The thickness of the obtained compensation film 5 is 26 μm, the refractive index nx is 1.5338, the refractive index ny is 1.5288, the refractive index nz is 1.5273, the retardation Re in the in-plane direction is 130 nm, and the retardation Rth in the thickness direction is 105 nm, NZ The coefficient is 1.31.

[Production Example 6]

By melting and extruding a thermoplastic resin ("ZEONOR 1420" manufactured by Japan Ruion Corporation with a photoelastic coefficient of 2×10 ^{− 13} cm ² /dyn), a raw material film with a thickness of 50 μm was obtained. The obtained raw material film was longitudinally extended to 1.5 times at 140° C. to obtain a compensation film C1. The longitudinal extension is carried out by setting the speed difference of the peripheral speed of the conveying roller. The thickness of the obtained compensation film C1 is 41 μm, the refractive index nx is 1.5315, the refractive index ny is 1.5293, the refractive index nz is 1.5293, the retardation Re in the in-plane direction is 90 nm, and the retardation Rth in the thickness direction is 45 nm, NZ The coefficient is 1.00.

[Example 1]

Prepare a commercially available IPS-type liquid crystal display device (manufactured by ADONIS, TS-430). In this liquid crystal display device, the pretilt angle of the liquid crystal cell is 2°, and the absorption axis of the backlight-side polarizer is orthogonal to the slow axis of the liquid crystal cell when no voltage is applied, which is a so-called E-mode device. The absorption axis of the viewing side polarizer is orthogonal to the absorption axis of the backlight side polarizer.

The liquid crystal display device was disassembled, and after the compensation film 1 was inserted between the viewing side polarizer and the color filter, it was reassembled to obtain a liquid crystal display device 1 for evaluation. At this time, the adjustment is made so that the slow axis of the compensation film 1 (direction given to nx) is parallel to the slow axis of the liquid crystal cell when no voltage is applied. The liquid crystal display device 1 includes, in order from the viewing side, a viewing side polarizer, a compensation film 1, a color filter, a liquid crystal cell, a backlight side polarizer, and a backlight. For the obtained liquid crystal display device 1, by the aforementioned method, the color change and contrast due to the azimuth angle in the state where the screen is displayed in black are evaluated. The results are shown in Table 1.

[Example 2]

Except that the compensation film 2 was used instead of the compensation film 1, the liquid crystal display device 2 for evaluation was obtained according to Example 1, and the color change and contrast caused by the azimuth angle in the state where the screen displayed black were evaluated. The results are shown in Table 1.

[Example 3]

Except that the compensation film 3 was used instead of the compensation film 1, the liquid crystal display device 3 for evaluation was obtained according to Example 1, and the color change and contrast due to the azimuth angle in the state where the screen was displayed in black were evaluated. The results are shown in Table 1.

[Example 4]

Except that the compensation film 4 was used instead of the compensation film 1, the liquid crystal display device 4 for evaluation was obtained according to Example 1, and the color change and contrast due to the azimuth angle in the state where the screen displayed black were evaluated. The results are shown in Table 1.

[Example 5]

Except that the compensation film 5 was used instead of the compensation film 1, the liquid crystal display device 5 for evaluation was obtained according to Example 1, and the color change and contrast due to the azimuth angle in the state where the screen displayed black were evaluated. The results are shown in Table 1.

[Example 6]

Prepare a commercially available IPS-type liquid crystal display device (manufactured by LG Display, 23M47). In this liquid crystal display device, the pretilt angle of the liquid crystal cell is 1.0°, and the absorption axis of the backlight-side polarizer is parallel to the slow axis of the liquid crystal cell when no voltage is applied, which is a so-called O-mode device. The absorption axis of the viewing side polarizer is orthogonal to the absorption axis of the backlight side polarizer.

The liquid crystal display device was disassembled, and the compensation film 1 was inserted between the backlight-side polarizer and the liquid crystal cell, and then reassembled to obtain a liquid crystal display device 6 for evaluation. At this time, the adjustment is made so that the slow axis of the compensation film 1 (direction given to nx) is parallel to the slow axis of the liquid crystal cell when no voltage is applied. The liquid crystal display device 6 includes, in order from the viewing side, a viewing side polarizer, a color filter, a liquid crystal cell, a compensation film 1, a backlight side polarizer, and a backlight. For the obtained liquid crystal display device 6, by the aforementioned method, the color change and contrast due to the azimuth angle in the state where the screen is displayed in black are evaluated. The results are shown in Table 2.

[Comparative Example 1]

The liquid crystal display device C1 for evaluation was obtained according to Example 1 except that the following items were changed. • Use compensation film C1 instead of compensation film 1.

For the obtained liquid crystal display device C1, the color change due to the azimuth angle and the contrast in the state where the screen is displayed in black are evaluated. The results are shown in Table 1.

[Comparative Example 2]

For a commercially available IPS-type liquid crystal display device (TS-430 manufactured by ADONIS), the color change and contrast caused by the azimuth angle when the screen is displayed in black are evaluated. The results are shown in Table 1.

In the table below, the so-called "color" means the color change due to azimuth when the screen is displayed in black.

"Table 1"

"Table 2"

From the above results, it can be seen that the liquid crystal display devices of Examples 1 to 5 have a frontal contrast of 1000 or more and an average contrast of 60° polar angle of 30 or more, which is sufficiently large. In addition, it can be seen that when viewing the screen displaying the black state from the oblique direction, the colors at the azimuth angle of 45° and the azimuth angle of 135° are homologous colors, and the color change due to the azimuth angle is suppressed.

On the other hand, it can be seen that the liquid crystal display device of Comparative Example 2 that does not include the compensation film and the liquid crystal display device of Comparative Example 1 that does not have the negative biaxiality of the compensation film have an average contrast of 60 degrees at a polar angle of less than 30. The contrast in the oblique direction is insufficient. Furthermore, it can be seen that in the case of viewing a screen displaying a black state from an oblique direction, the colors at an azimuth angle of 45° and an azimuth angle of 135° are heterochromatic colors, and the change in color due to the azimuth angle is not suppressed.

These results show that by arranging the designated refractive index anisotropy layer of a single-layer structure at the designated position of the so-called E-mode liquid crystal display device, it is possible to achieve a contrast not only in the front direction but also in the oblique direction Full liquid crystal display device.

Furthermore, it can be seen that the liquid crystal display device of Example 6 has a frontal contrast of 1000 or more, and an average contrast of a polar angle of 60° of 30 or more, which is quite large. In addition, it can be seen that when viewing the screen displaying the black state from the oblique direction, the colors at the azimuth angle of 45° and the azimuth angle of 135° are homologous colors, and the color change due to the azimuth angle is suppressed. This result shows that by arranging the designated refractive index anisotropic layer of a single-layer structure at the designated position of the so-called O-mode liquid crystal display device, it is possible to achieve sufficient contrast not only in the front direction but also in the oblique direction LCD device.

In addition, in Examples 1-6, a compensation film containing “use of a very small resin (ZEONOR 1420) such as a photoelastic coefficient of 2×10 ^{− 13} cm ² /dyn” is included, which shows little unevenness on the liquid crystal display device , Showing excellent uniformity.

100: liquid crystal display device 110: 1st polarizer 120: refractive index anisotropic layer 130: color filter 140: LCD unit 150: 2nd polarizer 160: backlight 200: LCD display device 210: 1st polarizer 220: refractive index anisotropic layer 230: color filter 240: LCD unit 250: 2nd polarizer 260: Backlight

<FIG. 1> FIG. 1 is an exploded schematic view of a liquid crystal display device related to a first embodiment.

<FIG. 2> FIG. 2 is an exploded schematic view of a liquid crystal display device related to a second embodiment.

100: liquid crystal display device

110: 1st polarizer

120: refractive index anisotropic layer

130: color filter

140: LCD unit

150: 2nd polarizer

160: backlight

A ₁ : Slow axis in the plane of the liquid crystal cell

A ₂ : Slow axis in the plane of the refractive index anisotropic layer

A _a1 : absorption axis of the first polarizer

A _a2 : absorption axis of the second polarizer

Claims (9)

A liquid crystal display device includes a first polarizer, a refractive index anisotropic layer, a liquid crystal cell, and a second polarizer in sequence, wherein the liquid crystal cell is uniformly oriented, the absorption axis of the first polarizer and the second polarized light The absorption axis of the device is orthogonal, the absorption axis of the second polarizer is orthogonal to the slow axis A _{1 in} the plane of the liquid crystal cell where no voltage is applied, and the refractive index anisotropic layer is a single-layer structure and has a negative double In the axial direction, the slow axis A _{2 in} the plane of the refractive index anisotropic layer is parallel to the slow axis A ₁ . The liquid crystal display device according to claim 1, wherein the layered body having refractive index anisotropy included between the layered body of the first polarizer and the layered body of the second polarizer includes only the liquid crystal cell and the layer Refractive index anisotropic layer. The liquid crystal display device according to claim 1 or 2, wherein the maximum refractive index nx in the plane of the refractive index anisotropic layer is in the in-plane direction of the refractive index anisotropic layer and is equal to the refractive index nx The refractive index ny in the direction perpendicular to the direction and the refractive index nz in the thickness direction of the refractive index anisotropic layer satisfy the following formula (i): 1.1≦(nx-nz)/(nx-ny)≦1.9　　(i) . The liquid crystal display device according to claim 1 or 2, wherein the retardation Re in the in-plane direction of the refractive index anisotropic layer is 10 nm or more and 250 nm or less. The liquid crystal display device according to claim 1 or 2, wherein the refractive index anisotropic layer is formed of a resin containing an alicyclic structure-containing polymer. The liquid crystal display device according to claim 5, wherein the alicyclic structure-containing polymer is selected from the group consisting of a hydride of a ring-opening polymer having a monomer with a reduced ene structure, a monomer with a reduced ene structure and α- One or more types of olefin addition copolymers, and hydrides of addition copolymers of monomers with a reduced olefin structure and α-olefins. The liquid crystal display device according to claim 1 or 2, wherein the average contrast at a polar angle of 60° is 30 or more. The liquid crystal display device according to claim 1 or 2, further comprising a backlight, and the backlight, the first polarizer, the refractive index anisotropic layer, the liquid crystal cell, and the second polarized light are sequentially arranged Pieces. The liquid crystal display device according to claim 1 or 2, further comprising a backlight, and the first polarizer, the refractive index anisotropic layer, the liquid crystal cell, the second polarizer, and the backlight are sequentially arranged source.

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