WO2020045287A1

WO2020045287A1 - Liquid crystal display device

Info

Publication number: WO2020045287A1
Application number: PCT/JP2019/033078
Authority: WO
Inventors: 貴道猪股
Original assignee: 日本ゼオン株式会社
Priority date: 2018-08-29
Filing date: 2019-08-23
Publication date: 2020-03-05
Also published as: TW202020522A; JPWO2020045287A1

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

<< The present invention relates to a liquid crystal display device.

Liquid crystal display devices are classified into a vertical electric field mode liquid crystal display device and a horizontal electric field mode liquid crystal display device according to the orientation direction of liquid crystal molecules in a liquid crystal cell and the direction of applied voltage. As a typical liquid crystal display device in the horizontal electric field mode, an in-plane switching mode (IPS mode) liquid crystal display device is exemplified. In the IPS mode liquid crystal display device, the liquid crystal molecules are aligned (homogeneous alignment) in a direction parallel to the in-plane direction of the alignment film of the liquid crystal cell, and the liquid crystal molecules are generated by generating an electric field in the in-plane direction of the alignment film. By rotating, the transmittance of light passing through the liquid crystal cell is controlled.
The IPS mode liquid crystal display device is said to be superior in contrast, color, etc. as compared with the liquid crystal display device in the twisted nematic mode (TN mode), which is a transverse electric field mode, but aims at further improving the image quality. Attempts have been made to combine a retardation layer having a refractive index anisotropy with an IPS mode liquid crystal display device (Patent Documents 1, 2, and 3).

Japanese Patent Application Laid-Open No. 2009-092847 (corresponding publication: US Patent Application Publication No. 2009/103017) Japanese Translation of PCT International Publication No. 2008-517322 (corresponding publication: International Publication No. 2007/013782) International Publication No. WO 2008/156011

In the technique of Patent Literature 1, a high contrast is realized by combining predetermined retardation layers and at the same time giving a difference in transmittance between two polarizing plates.
In the technique of Patent Document 2, high contrast is realized by disposing a retardation layer having a multilayer structure in which a biaxial film is coated with a uniaxial C film between a polarizer and a liquid crystal cell. I have.
However, any of the techniques of Patent Documents 1 to 3 requires two types of polarizing plates or needs to laminate a plurality of retardation layers. As a result, the configuration of the liquid crystal display device becomes complicated and the manufacturing cost increases. In addition, as the number of layers to be stacked increases, there is a greater possibility that dust or the like will be interposed between the layers, and the quality of the liquid crystal display device will be reduced. In particular, simplification of the configuration is desired for a large-area liquid crystal display device, which has been growing in demand in recent years.

Therefore, there is a demand for a liquid crystal display device having a simple configuration and sufficient contrast.

The inventors of the present invention have intensively studied to solve the above-mentioned problems. As a result, the inventors have found that the problem can be solved by providing a layer having a predetermined refractive index anisotropy and having a single-layer structure between the first polarizer layer and the liquid crystal cell, thereby completing the present invention.
That is, the present invention provides the following.

[1] including a first polarizer, a refractive index anisotropic layer, a liquid crystal cell, and a second polarizer in this order;
The liquid crystal cell has a homogeneous alignment,
The absorption axis of the first polarizer is orthogonal to the absorption axis of the second polarizer,
The slow axis A ₁ in the second polarizer absorption axis in the plane of the liquid crystal cell voltage is not applied of, are orthogonal,
The refractive index anisotropic layer has a single-layer structure and negative biaxiality,
Wherein the slow axis A ₂ in the plane of the refractive index anisotropic layer and the slow axis A ₁ is parallel, the liquid crystal display device.
[2] The layer according to [1], wherein the layer having the refractive index anisotropy contained between the first polarizer layer and the second polarizer layer is only the liquid crystal cell and the refractive index anisotropic layer. Liquid crystal display device.
[3] The maximum refractive index nx in the plane of the refractive index anisotropic layer, the refractive index ny in the in-plane direction of the refractive index anisotropic layer and a direction perpendicular to the direction giving the refractive index nx, and the refraction The liquid crystal display device according to [1] or [2], wherein the refractive index nz in the thickness direction of the anisotropic layer satisfies the following expression (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 refractive index anisotropic layer has an in-plane retardation Re of 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 alicyclic structure-containing polymer is a hydride of a ring-opening polymer of a monomer having a norbornene structure, an addition copolymer of a monomer having a norbornene structure and an α-olefin, and a norbornene structure Liquid crystal display device according to [5], which is at least one member selected from the group consisting of a hydride of an addition copolymer of a monomer having α 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] A backlight further comprising: the backlight, the first polarizer, the refractive index anisotropic layer, the liquid crystal cell, and the second polarizer are arranged in this order. The liquid crystal display device according to any one of [7].
[9] A backlight is further provided, wherein the first polarizer, the refractive index anisotropic layer, the liquid crystal cell, the second polarizer, and the backlight are arranged in this order. The liquid crystal display device according to any one of [7].

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

FIG. 1 is an exploded view schematically showing the liquid crystal display device according to the first embodiment. FIG. 2 is an exploded view schematically showing the liquid crystal display device according to the second embodiment.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the following embodiments and examples, and can be arbitrarily modified and implemented without departing from the scope of the claims of the present invention and equivalents thereof.

In the following description, the slow axis of the film or layer means the in-plane slow axis of the film or layer unless otherwise specified.

In the following description, an angle formed by an optical axis (slow axis, transmission axis, absorption axis, etc.) of each layer in a member including a plurality of layers is an angle when the layer is viewed from the thickness direction, unless otherwise specified. Represents

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

In the following description, the tilt direction of a certain film means a direction that is neither parallel nor perpendicular to the main surface of the film unless otherwise specified. Specifically, the polar angle of the main surface is greater than 0 ° and 90 °. Point in a direction smaller than °.

において In the following description, the retardation Re in the in-plane direction of the layer is a value represented by Re = (nx−ny) × d unless otherwise specified. The retardation Rth in the thickness direction of the layer is a value represented by Rth = [{(nx + ny) / 2} −nz] × d unless otherwise specified. nx represents the refractive index in the direction (in-plane direction) perpendicular to the thickness direction of the layer and in the direction giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the layer and in a direction perpendicular to the direction of nx. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer. The measurement wavelength is 590 nm unless otherwise specified.

In the following description, the directions of the elements are "parallel", "vertical" and "orthogonal", unless otherwise specified, within a range that does not impair the effects of the present invention, for example, ± 3 °, ± 2 ° or ± 1 °. May be included.

[1. Overview of Liquid Crystal Display]
A liquid crystal display device according to an embodiment of the present invention includes a first polarizer, a refractive index anisotropic layer, a liquid crystal cell, and a second polarizer in this order.

[1.1. Liquid crystal cell]
A 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 an electrode. The liquid crystal cell may include a control element for controlling a voltage.
The liquid crystal cell is preferably a liquid crystal cell driven in the IPS mode.
The liquid crystal cell has a homogeneous alignment when no voltage is applied. The fact that the liquid crystal cell is in a homogeneous alignment means that the alignment vector of the liquid crystal molecules existing between the alignment films is in an alignment state in which the alignment vectors are uniformly parallel to a predetermined direction in the plane of the alignment film. Here, it is assumed that the liquid crystal cell in which the alignment vector of the liquid crystal molecules forms an angle of more than 0 ° and 3 ° or less with the alignment film surface is also in a homogeneous alignment. The angle between the alignment vector and the alignment film surface is called a pretilt angle.

(4) The smaller 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 is preferable, and the ideal value is 0 °. It is usually difficult to set the pretilt angle to 0 ° in a widely used rubbing treatment, but it is preferable that the pretilt angle be 3 ° or less. In a liquid crystal display device including a liquid crystal cell having a pretilt angle exceeding 0 °, when observed from an inclined direction when black is displayed on the screen, the color change depending on the azimuth angle observed tends to be large. The liquid crystal display device according to the aspect can suppress such a change in tint even when the pretilt angle exceeds 0 °.

プレ The pretilt angle of liquid crystal molecules in a liquid crystal cell can be measured by a conventionally known method (for example, a crystal rotation method).

The liquid crystal cell has a slow axis A ₁ in plane when no voltage is applied. Here, the slow axis, in the orientation film in a plane parallel to the liquid crystal cell means the direction which gives a maximum refractive index n _e. The slow axis A ₁ is normally coincides with the optical axis direction, also coincides with the orientation direction of the normal alignment layer. The alignment direction of the alignment film is a direction in which the liquid crystal molecules are aligned when a process (eg, a rubbing process) for applying an alignment regulating force to the alignment film is performed to align the liquid crystal molecules on the alignment film. When the treatment performed on the alignment film is a rubbing treatment, the alignment direction of the alignment film is usually the rubbing direction.

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 the orientation film in a plane parallel to the liquid crystal cell in the absence of an applied voltage. Further, the rubbing direction of the alignment film in the case of known, good rubbing direction as the direction of the slow axis A _1.

市販 A commercially available liquid crystal cell can be used.

[1.2. Polarizer]
As the first polarizer and the second polarizer, a film capable of transmitting one of two linearly polarized lights whose vibration directions intersect at right angles and absorbing or reflecting the other can be used. Here, the oscillation direction of the linearly polarized light indicates the oscillation direction of the electric field of the linearly polarized light. Such a film usually has a polarization transmission axis (hereinafter, the polarization transmission axis is also referred to as a transmission axis), can transmit linearly polarized light having a vibration direction parallel to the transmission axis, and vibrates perpendicularly to the transmission axis. It can absorb or reflect linearly polarized light having a direction.

Specific examples of the polarizer include polyvinyl alcohol, including a vinyl alcohol-based polymer such as partially formalized polyvinyl alcohol, a polyvinyl alcohol resin film, iodine, dyeing treatment with a dichroic substance such as a dichroic dye, One obtained by performing an appropriate treatment such as a stretching treatment and a cross-linking treatment in an appropriate order and manner may be used. The polarizer preferably contains a polyvinyl alcohol resin.

１The first polarizer and the second polarizer may have different characteristics, but are preferably members having the same characteristics. 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 reduced.

For example, the difference in transmittance between the first polarizer and the second polarizer is preferably less than 0.5%, more preferably 0.2% or less, further preferably less than 0.1%, and usually 0%. Or more.

[1.3. Refractive index anisotropic layer]
The refractive index anisotropic layer is a layer having a single-layer structure with anisotropic refractive index, and has negative biaxiality. With such a configuration of the refractive index anisotropic layer, a liquid crystal display device having a sufficient contrast can be realized with a simple configuration.

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

The refractive index anisotropic layer has a retardation Re in the in-plane direction of preferably 10 nm or more, more preferably 30 nm or more, still more preferably 50 nm or more, preferably 250 nm or less, more preferably 240 nm or less, and still more preferably 230 nm. It is as follows. When the in-plane retardation Re is greater than or equal to the lower limit, the contrast in the inclined direction (viewing angle contrast) can be effectively improved. When the in-plane retardation is less than or equal to the upper limit, black is displayed from the inclined direction. When observing the screen in the state, the change in the tint due to the azimuth can be effectively suppressed.

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

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

When the NZ coefficient falls within the above range, the contrast, particularly the contrast when observed from an inclined direction, can be effectively improved. The reason is that when the NZ coefficient is within the above range, the polarization state of light in the tilt direction from the backlight side polarizer of the liquid crystal display device changes when black is displayed on the screen, and light is efficiently emitted. It is considered to be absorbed, but does not limit the present invention.

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

As a thermoplastic resin capable of forming the refractive index anisotropic layer, a thermoplastic resin having a positive intrinsic birefringence value can be used. By stretching a layer formed from a thermoplastic resin having a positive intrinsic birefringence value by an arbitrary method in an in-plane direction, a layer having negative biaxiality can be obtained. As the stretching method, for example, any method such as a uniaxial stretching method, a sequential biaxial stretching method, and a simultaneous biaxial stretching method can be used.

樹脂 A resin having a positive intrinsic birefringence value means a resin in which the refractive index in the stretching direction is higher than the refractive index in the direction perpendicular to the stretching direction. The intrinsic birefringence value can be calculated from the permittivity distribution.

Examples of polymers that can be included in the resin having a positive intrinsic birefringence value include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; Polyarylate; cellulose ester, polyether sulfone; polysulfone; polyaryl sulfone; polyvinyl chloride; alicyclic structure-containing polymer such as norbornene polymer; and rod-shaped liquid crystal polymer.

樹脂 The resin capable of forming the refractive index anisotropy may contain the polymer alone or in a combination of two or more kinds in any ratio.

The resin capable of forming the refractive index anisotropic layer has a photoelastic coefficient of preferably 30 × 10 ⁻¹³ cm ² / dyn or less, more preferably 10 × 10 ⁻¹³ cm ² / dyn or less, and still more preferably 5 × 10 5 ^-13 cm ² / dyn or less, and a smaller value is more preferable.
The photoelastic coefficient of the resin can be measured by an ellipsometer. A film is formed from a resin, and a phase difference when a load of 50 g, 100 g, or 150 g is applied to the film is measured, and the phase difference is obtained from a slope of a graph of the load and the phase difference.
Since the photoelastic coefficient of the resin capable of forming the refractive index anisotropic layer is equal to or less than the upper limit, a change in the use environment, an external force such as bending or shrinkage stress is applied to the refractive index anisotropic layer formed from the resin. Display defects such as display unevenness of the liquid crystal display device, which may occur in the case of the above.

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

樹脂 The resin forming the refractive index anisotropic layer may contain one kind of the alicyclic structure-containing polymer alone, or may contain two or more kinds thereof in combination.

The alicyclic structure-containing polymer may have an alicyclic structure in the main chain, may have an alicyclic structure in the side chain, and may have an alicyclic structure in both the main chain and the side chain. It may have a structure. Above all, a polymer containing an alicyclic structure in at least the main chain is preferable from the viewpoint of mechanical strength and heat resistance.

Examples of the alicyclic structure include a saturated alicyclic hydrocarbon (cycloalkane) structure and an unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structure. Above all, from the viewpoint of mechanical strength and heat resistance, a cycloalkane structure and a cycloalkene structure are preferable, and a cycloalkane structure is particularly preferable.

The number of carbon atoms constituting the alicyclic structure is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more preferably 20 or less, particularly preferably, per one alicyclic structure. Is in the range of 15 or less. By setting the number of carbon atoms constituting the alicyclic structure in this range, the mechanical strength, heat resistance and moldability of the resin containing the alicyclic structure-containing polymer are highly balanced.

において In the alicyclic structure-containing polymer, the ratio of the structural unit having an alicyclic structure can be appropriately selected depending on the purpose of use. The proportion of the structural unit having an alicyclic structure in the alicyclic structure-containing polymer is preferably at least 55% by weight, more preferably at least 70% by weight, particularly preferably at least 90% by weight, and usually at most 100% by weight. It is. When the proportion of the structural unit 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 are improved.

Examples of the alicyclic structure-containing polymer include, for example, a norbornene-based polymer, a monocyclic cycloolefin-based polymer, a cyclic conjugated diene-based polymer, a vinyl alicyclic hydrocarbon polymer, and hydrogenated products thereof, and vinyl. Examples include hydrides of aromatic hydrocarbon polymers. Among these, a norbornene-based polymer is more preferable because of its excellent transparency and moldability. Since the resin containing such a polymer has a low water vapor transmission rate and a small photoelastic coefficient, it occurs when an external force such as a change in use environment, bending or shrinkage stress is applied to the refractive index anisotropic layer formed from such a resin. Display defects such as display unevenness of the liquid crystal display device can be suppressed.

Examples of the norbornene-based polymer include a ring-opened polymer of a monomer having a norbornene structure and a hydride thereof; and an addition polymer of a monomer having a norbornene structure and a hydride thereof. Examples of the ring-opening polymer of a monomer having a norbornene structure include a ring-opening homopolymer of one kind of monomer having a norbornene structure and a ring-opening polymer of two or more kinds of monomers having a norbornene structure. Examples of the copolymer include a copolymer, a monomer having a norbornene structure, and a ring-opening copolymer of any monomer copolymerizable therewith. Further, examples of the addition polymer of a monomer having a norbornene structure include an addition homopolymer of one type of monomer having a norbornene structure and an addition copolymer of two or more types of monomers having a norbornene structure. And an addition copolymer of a monomer having a norbornene structure and an arbitrary monomer copolymerizable therewith.

Among these, hydrides of ring-opening polymers of monomers having a norbornene structure, addition copolymers of monomers having a norbornene structure and α-olefin, and monomers having a norbornene structure and α-olefin A hydride of an addition copolymer with an olefin is preferred.

Examples of the monomer having a norbornene structure include bicyclo [2.2.1] hept-2-ene (common name: norbornene) and tricyclo [4.3.0.1 ^2,5 ] deca-3,7. -Diene (common name: dicyclopentadiene), 7,8-benzotricyclo [4.3.0.1 ^2,5 ] dec-3-ene (common name: methanotetrahydrofluorene), tetracyclo [4.4. 0.1 ^2,5 . [ ^1,7,10 ] dodec-3-ene (common name: tetracyclododecene) and derivatives of these compounds (eg, those having a substituent on the ring). Here, examples of the substituent include an alkyl group, an alkylene group, and a polar group. Two or more of these substituents may be the same or different and may be bonded to the ring. As the monomer having a norbornene structure, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

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

In the addition copolymer of a monomer having a norbornene structure and an α-olefin, examples of the α-olefin include α-olefins having 2 to 20 carbon atoms, such as ethylene, propylene and 1-butene, and derivatives thereof. Is mentioned. Of these, ethylene is preferred. One type of α-olefin may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The addition polymer of a monomer having a norbornene structure can be produced, for example, 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 used, for example, in a solution of the ring-opening polymer and the addition polymer in the presence of a hydrogenation catalyst containing a transition metal such as nickel, palladium, etc. Saturated bonds may be produced by hydrogenating preferably 90% or more.

樹脂 The resin capable of forming the refractive index anisotropic layer may contain an optional compounding agent in addition to the polymer. Examples of the compounding agents include stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, near infrared absorbers, etc .; plasticizers. One type of compounding agent may be used, or two or more types may be used in combination at an arbitrary ratio.

[1.4. Relationship of each element]
In the liquid crystal display device of this embodiment, the absorption axis A _a2 of the second polarizer, and the slow axis A ₁ in the plane of the liquid crystal cell when no voltage is applied orthogonally. Specifically, the angle between the absorption axis A _a2 of the second polarizer and the slow axis A ₁ when the second polarizer and the liquid crystal cell are viewed from the thickness direction is preferably 90 ° ± 1 °, Preferably 90 ° ± 0.8 °, or preferably 90 ° ± 0.5 °.

The absorption axis A _a1 of the first polarizer is orthogonal to the absorption axis A _a2 of the second polarizer. Specifically, the absorption axis A _a1 of the first polarizer and the absorption axis A _a2 of the second polarizer, the angle when viewed first polarizer and the second polarizer from a thickness direction, preferably 90 ° ± 1 °, preferably 90 ° ± 0.8 °, or preferably 90 ° ± 0.5 °.

In the liquid crystal display device of this embodiment, the slow axis A ₂ in the plane of the refractive index anisotropic layer and the slow axis A ₁ in the plane of the liquid crystal cell when no voltage is applied is parallel. Specifically, the slow axis A ₂ of the refractive index anisotropic layer, the slow axis A _1, the angle when viewing the refractive index anisotropic layer and the liquid crystal cell in the thickness direction, preferably 0 ° ± 1 °, preferably 0 ° ± 0.8 °, or preferably 0 ° ± 0.5 °.

により Since each element has the above-described relationship, it is possible to realize a liquid crystal display device having a simple configuration and sufficient contrast.

When the second polarizer is a backlight-side polarizer, 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. A display device.
When the first polarizer is a backlight-side polarizer, 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 component]
The liquid crystal display device may include an arbitrary layer in addition to the first polarizer, the refractive index anisotropic layer, the liquid crystal cell, and the second polarizer. Examples of such optional layers include a polarizer protective film, a color filter, and an adhesive layer for bonding each layer.
However, it is preferable that the layer having the refractive index anisotropy included between the first polarizer layer and the second polarizer layer is only the liquid crystal cell and the refractive index anisotropic layer. That is, it is preferable that no layer having a refractive index anisotropy exists between the first polarizer layer and the second polarizer layer other than the liquid crystal cell and the refractive index anisotropic layer. Thus, it is possible to effectively suppress the change in color due to the azimuth angle even when the image is viewed from the tilt direction of the screen when black is displayed on the screen while having a simple configuration and sufficient contrast. A liquid crystal display device can be easily realized.

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

[1.6. Characteristics of liquid crystal display device]
The average contrast of the liquid crystal display device at a polar angle of 60 ° is preferably 30 or more, more preferably 35 or more, and still more preferably 40 or more.

平均 The average contrast at a polar angle of 60 ° can be measured as follows. The azimuthal angles in the slow axis direction in the plane of the liquid crystal cell are defined as 0 ° and 180 °. Then, when the polar angle is 60 ° and the azimuth angles are 45 °, 135 °, 225 °, and 315 °, the luminance B1 in a state where black is displayed on the screen and the luminance W1 in a state where white is displayed on the screen are measured. , The ratio of the luminance W1 to the luminance B1 (luminance W1 / luminance B2) can be calculated to obtain the average contrast at a polar angle of 60 °. Brightness can be measured, for example, by a spectroradiometer.

[2. Configuration example of liquid crystal display device]
[2.1. First Embodiment]
FIG. 1 is an exploded view schematically showing the liquid crystal display device according to the first embodiment. FIG. 1 shows the liquid crystal display device in a state where no voltage is applied. In addition, electrodes, circuits, control elements, and the like are omitted.
The liquid crystal display device 100 according to the 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 in this order.
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 and the absorption axis A _a2 are orthogonal to each other. 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 1} of the slow axis _{A 2} and the liquid crystal cell 140 of the refractive index anisotropic layer 120 are parallel. The slow axis _{A 1} of the absorption axis _{A a2} and the liquid crystal cell 140 of the second polarizer 150 are orthogonal, the liquid crystal display device 100 is a liquid crystal display device of the so-called E- mode.

The backlight 160 may have any configuration, and may be an edge light type or a direct type.

(4) The color filter 130 may have any configuration. 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 view schematically showing the liquid crystal display device according to the second embodiment. FIG. 2 shows the liquid crystal display device in a state where no voltage is applied. In addition, electrodes, circuits, control elements, and the like are omitted.
The liquid crystal display device 200 according to the present 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 second polarizer 250 each have an absorption axis _{A a1} and the absorption axis _{A a2.} The absorption axis A _a1 and the absorption axis A _a2 are orthogonal to each other. 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 1} of the slow axis _{A 2} and the liquid crystal cell 240 of the refractive index anisotropic layer 220 are parallel. The slow axis _{A 1} of the absorption axis _{A a1} and the liquid crystal cell 240 of the first polarizer 210 is parallel, the liquid crystal display device 200 is a liquid crystal display device of the so-called O- mode.
As the backlight 260 and the color filter 230, configurations similar to those of the backlight 160 and the color filter 130, respectively, can be adopted.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the embodiments described below, and may be arbitrarily modified and implemented without departing from the scope of the claims of the present invention and equivalents thereof.

において In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified. The operations described below were performed at normal temperature and normal pressure unless otherwise specified.

[Evaluation method]
(Film thickness)
The thickness of the film was measured with a snap gauge.

(Refractive index of film, retardation Re in in-plane direction, retardation Rth in thickness direction and NZ coefficient)
The refractive index (nx, ny, nz), the retardation Re in the in-plane direction, and the retardation Rth in the thickness direction of the film were measured at a wavelength of 590 nm using a phase difference measuring device (Axometric's product name “Axoscan”). .
The NZ coefficient of the film was determined from the measured values of Re and Rth 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 was measured by a conventionally known method (for example, a crystal rotation method).

(Color change due to azimuth angle when black is displayed on the screen)
The liquid crystal display was set to display black. The slow axis directions of the liquid crystal cell included in the liquid crystal display device when no voltage was applied were defined as azimuth angles 0 ° and 180 °. The color of the screen was visually observed from two directions: a polar angle of 60 ° azimuth 45 ° and a polar angle of 60 ° azimuth 135 °.

(contrast)
The liquid crystal display device was set to a state where black was displayed or a state where white was displayed. Then, using a luminance meter (“SR-LED” manufactured by Topcon), a luminance B1 in a state where black was displayed on the screen and a luminance W1 in a state where white was displayed on the screen were measured. The ratio of the luminance W1 to the luminance B1 (luminance W1 / luminance B1) was determined.
The front direction contrast was determined from the luminance measured from the normal direction (front direction) of the liquid crystal display screen.
The average contrast at a polar angle of 60 ° was determined from the luminance measured from the direction of the polar angle of 60 ° on the liquid crystal display screen. Specifically, the slow axis directions of the liquid crystal cell included in the liquid crystal display device when no voltage was applied were defined as azimuth angles of 0 ° and 180 °. Then, the contrast at the polar angle of 60 ° and the azimuth angles of 45 °, 135 °, 225 °, and 315 ° were obtained, and the arithmetic mean of the contrast at each azimuth angle was defined as the value of the average contrast at the polar angle of 60 °.

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

[Production Example 1]
A resin containing an alicyclic structure-containing polymer (“ZEONOR1420” manufactured by Zeon Corporation, photoelastic coefficient: 2 × 10 ⁻¹³ cm ² / dyn) is melted, extruded, and taken out by a cast roll to form a thickness. A 60 μm raw film was obtained. The obtained raw film was longitudinally stretched 2.5 times at 142 ° C. The longitudinal stretching was performed by providing a difference in the peripheral speed of the transport roll. Next, the longitudinally stretched film was horizontally stretched 1.5 times by a tenter stretching machine at 142 ° C. to obtain a compensation film 1 as a refractive index anisotropic layer. The obtained compensation film 1 has a thickness of 26 μm, a refractive index nx of 1.5328, a refractive index ny of 1.5293, a refractive index nz of 1.5280, an in-plane retardation Re of 90 nm, and a thickness direction. Had a retardation Rth of 79 nm and an NZ coefficient of 1.38.

[Production Example 2]
Except having changed the following matter, it carried out similarly to manufacture example 1, and obtained the 55-micrometer-thick raw film.
The take-up speed to the cast roll was changed to 1.1 times the speed in Production Example 1.
The obtained raw film was longitudinally stretched 2.2 times at 141 ° C. The longitudinal stretching was performed by providing a difference in the peripheral speed of the transport roll. Next, the longitudinally stretched film was transversely stretched 1.5 times by a tenter stretching machine at 141 ° C. to obtain a compensation film 2 as a refractive index anisotropic layer. The obtained compensation film 2 has a thickness of 25 μm, a refractive index nx of 1.5330, a refractive index ny of 1.5293, a refractive index nz of 1.5277, an in-plane retardation Re of 92 nm, and a thickness direction. Had a retardation Rth of 86 nm and an NZ coefficient of 1.43.

[Production Example 3]
A 55 μm thick raw film was obtained in the same manner as in Production Example 2. The obtained raw film was longitudinally stretched 2.7 times at 141 ° C. The longitudinal stretching was performed by providing a difference in the peripheral speed of the transport roll. Next, the longitudinally stretched film was horizontally stretched 1.6 times by a tenter stretching machine at 141 ° C. to obtain a compensation film 3 as a refractive index anisotropic layer. The obtained compensation film 3 has a thickness of 20 μm, a refractive index nx of 1.5338, a refractive index ny of 1.5289, a refractive index nz of 1.5273, a retardation Re in the in-plane direction of 99 nm, and a thickness direction. Had a retardation Rth of 80 nm and an NZ coefficient of 1.31.

[Production Example 4]
A 105 μm-thick raw film was obtained in the same manner as in Production Example 1 except for the following changes.
-The take-up speed to the cast roll was changed to 0.5 times the speed in Production Example 1.
The obtained raw film was longitudinally stretched 3.7 times at 140 ° C. The longitudinal stretching was performed by providing a difference in the peripheral speed of the transport roll. Next, the longitudinally stretched film was horizontally stretched 1.9 times by a tenter stretching machine at 140 ° C. to obtain a compensation film 4 as a refractive index anisotropic layer. The obtained compensation film 4 has a thickness of 28 μm, a refractive index nx of 1.5332, a refractive index ny of 1.5290, a refractive index nz of 1.5279, a retardation Re in the in-plane direction of 118 nm, and a thickness direction. Had a retardation Rth of 89 nm and an NZ coefficient of 1.25.

[Production Example 5]
An original film having a thickness of 85 μm was obtained in the same manner as in Production Example 1 except for the following changes.
-The take-up speed to the cast roll was changed to 0.6 times the speed in Production Example 1.
The obtained raw film was longitudinally stretched at 143 ° C. by 3.4 times. The longitudinal stretching was performed by providing a difference in the peripheral speed of the transport roll. Next, the longitudinally stretched film was transversely stretched 1.8 times by a tenter stretching machine at 143 ° C. to obtain a compensation film 5 as a refractive index anisotropic layer. The obtained compensation film 5 has a thickness of 26 μm, a refractive index nx of 1.5338, a refractive index ny of 1.5288, a refractive index nz of 1.5273, a retardation Re in the in-plane direction of 130 nm, and a thickness direction. Had a retardation Rth of 105 nm and an NZ coefficient of 1.31.

[Production Example 6]
A 50 μm thick raw film was obtained by melting and extruding a thermoplastic resin (“ZEONOR1420” manufactured by Zeon Corporation, photoelastic coefficient: 2 × 10 ⁻¹³ cm ² / dyn). The obtained raw film was longitudinally stretched 1.5 times at 140 ° C. to obtain a compensation film C1. The longitudinal stretching was performed by providing a difference in the peripheral speed of the transport roll. The obtained compensation film C1 has a thickness of 41 μm, a refractive index nx of 1.5315, a refractive index ny of 1.5293, a refractive index nz of 1.5293, a retardation Re in the in-plane direction of 90 nm, and a thickness direction. Had a retardation Rth of 45 nm and an NZ coefficient of 1.00.

[Example 1]
A commercially available IPS liquid crystal display device (TS-430 manufactured by ADONIS) was prepared. The liquid crystal display device has a so-called E-mode in which 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. Device. The absorption axis of the viewing side polarizer is orthogonal to the absorption axis of the backlight side polarizer.
The liquid crystal display was disassembled, the compensation film 1 was inserted between the viewing-side polarizer and the color filter, and reassembled to obtain the liquid crystal display 1 for evaluation. At that time, the slow axis of the compensating film 1 (the direction giving nx) was made parallel to the slow axis of the liquid crystal cell when no voltage was applied. The liquid crystal display device 1 includes a viewing side polarizer, a compensation film 1, a color filter, a liquid crystal cell, a backlight side polarizer, and a backlight in this order from the viewing side. With respect to the obtained liquid crystal display device 1, a change in tint and a contrast depending on an azimuth angle in a state where black was displayed on a screen were evaluated by the above method. Table 1 shows the results.

[Example 2]
A liquid crystal display device 2 for evaluation was obtained in the same manner as in Example 1 except that the compensating film 2 was used instead of the compensating film 1, and the color change and contrast depending on the azimuth angle in a state where black was displayed on the screen were measured. evaluated. Table 1 shows the results.

[Example 3]
A liquid crystal display device 3 for evaluation was obtained in the same manner as in Example 1 except that the compensating film 3 was used instead of the compensating film 1, and the color change and contrast due to the azimuth angle in a state where black was displayed on the screen were measured. evaluated. Table 1 shows the results.

[Example 4]
A liquid crystal display device 4 for evaluation was obtained in the same manner as in Example 1 except that the compensating film 4 was used instead of the compensating film 1, and the color change and contrast due to the azimuth angle in a state where black was displayed on the screen were measured. evaluated. Table 1 shows the results.

[Example 5]
A liquid crystal display device 5 for evaluation was obtained in the same manner as in Example 1 except that the compensating film 5 was used instead of the compensating film 1, and the color change and contrast due to the azimuth angle in a state where black was displayed on the screen were measured. evaluated. Table 1 shows the results.

[Example 6]
A commercially available IPS liquid crystal display device (23M47 manufactured by LG Display) was prepared. This liquid crystal display device has a so-called O-mode in which 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. Device. The absorption axis of the viewing side polarizer is orthogonal to the absorption axis of the backlight side polarizer.
The liquid crystal display was disassembled, the compensation film 1 was inserted between the backlight-side polarizer and the liquid crystal cell, and reassembled to obtain a liquid crystal display 6 for evaluation. At that time, the slow axis of the compensating film 1 (the direction giving nx) was made parallel to the slow axis of the liquid crystal cell when no voltage was applied. The liquid crystal display device 6 includes, 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 in this order. With respect to the obtained liquid crystal display device 6, a change in color and a contrast depending on the azimuth angle in a state where black was displayed on the screen were evaluated by the above-described method. Table 2 shows the results.

[Comparative Example 1]
A liquid crystal display device C1 for evaluation was obtained in the same manner as in Example 1 except for the following changes.
-The compensation film C1 was used instead of the compensation film 1.
With respect to the obtained liquid crystal display device C1, the color change and the contrast depending on the azimuth angle in the state where black was displayed on the screen were evaluated. Table 1 shows the results.

[Comparative Example 2]
With respect to a commercially available IPS type liquid crystal display device (TS-430 manufactured by ADONIS), the color change and the contrast depending on the azimuth angle when black was displayed on the screen were evaluated. Table 1 shows the results.

において In the table below, “color” means a change in color depending on the azimuth angle when black is displayed on the screen.

According to the above results, it is understood that the liquid crystal display devices of Examples 1 to 5 have sufficiently high front-side contrast of 1000 or more and an average contrast at a polar angle of 60 ° of 30 or more. In addition, when observing a screen in which black is displayed from the tilt direction, the colors at the azimuth angles of 45 ° and 135 ° are similar colors, and the change of the color due to the azimuth angle is suppressed. I understand.
On the other hand, in the liquid crystal display device of Comparative Example 2 not including the compensation film and the liquid crystal display device of Comparative Example 1 in which the compensation film did not have negative biaxiality, the average contrast at a polar angle of 60 ° was less than 30. It can be seen that the contrast in the tilt direction is insufficient. Further, when observing a screen in which black is displayed from the tilt direction, the colors at the azimuth angles of 45 ° and 135 ° are different colors, and the change of the color by the azimuth angle is not suppressed. You can see that.
These results show that by arranging a predetermined refractive index anisotropic layer having a single-layer structure at a predetermined position of a so-called E-mode liquid crystal display device, the contrast in the tilt direction as well as in the front direction can be sufficiently obtained. It is shown that a liquid crystal display device can be realized.

Further, it can be seen that the liquid crystal display device of Example 6 had a front direction contrast of 1000 or more and an average contrast at a polar angle of 60 ° of 30 or more, and was sufficiently large. In addition, when observing a screen in which black is displayed from the tilt direction, the colors at the azimuth angles of 45 ° and 135 ° are similar colors, and the change of the color due to the azimuth angle is suppressed. I understand. This result is obtained by arranging a predetermined refractive index anisotropic layer having a single-layer structure at a predetermined position of a liquid crystal display device in a so-called O-mode, so that the contrast in the tilt direction as well as in the front direction is sufficient. This shows that a certain liquid crystal display device can be realized.

Also, in Example 1-6, the liquid crystal display device has a small display unevenness, including a compensation film having a photoelastic coefficient of 2 × 10 ⁻¹³ cm ² / dyn and using a very small resin (ZEONOR1420). The uniformity was excellent.

Reference Signs List 100 liquid crystal display device 110 first polarizer 120 refractive index anisotropic layer 130 color filter 140 liquid crystal cell 150 second polarizer 160 backlight 200 liquid crystal display device 210 first polarizer 220 refractive index anisotropic layer 230 color filter 240 liquid crystal cell 250 second polarizer 260 backlight

Claims

Including a first polarizer, a refractive index anisotropic layer, a liquid crystal cell, and a second polarizer in this order;
The liquid crystal cell has a homogeneous alignment,
The absorption axis of the first polarizer is orthogonal to the absorption axis of the second polarizer,
The slow axis A 1 in the second polarizer absorption axis in the plane of the liquid crystal cell voltage is not applied of, are orthogonal,
The refractive index anisotropic layer has a single-layer structure and negative biaxiality,
Wherein the slow axis A 2 in the plane of the refractive index anisotropic layer and the slow axis A 1 is parallel, the liquid crystal display device.
2. The liquid crystal display according to claim 1, wherein a layer having a refractive index anisotropy included between the first polarizer layer and the second polarizer layer is only the liquid crystal cell and the refractive index anisotropic layer. apparatus.
The maximum refractive index nx in the plane of the refractive index anisotropic layer, the refractive index ny in the in-plane direction of the refractive index anisotropic layer, and a direction perpendicular to the direction giving the refractive index nx; The liquid crystal display device according to claim 1, wherein the refractive index nz in the thickness direction of the layer satisfies the following expression (i).
1.1 ≦ (nx−nz) / (nx−ny) ≦ 1.9 (i)
4. The liquid crystal display device according to claim 1, wherein the refractive index anisotropic layer has an in-plane retardation Re of 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 from a resin containing an alicyclic structure-containing polymer.
The alicyclic structure-containing polymer is a hydride of a ring-opened polymer of a monomer having a norbornene structure, an addition copolymer of a monomer having a norbornene structure and an α-olefin, and a monomer having a norbornene structure. 6. The liquid crystal display device according to claim 5, wherein the liquid crystal display device is at least one member selected from the group consisting of a hydride of an addition copolymer of a monomer and an α-olefin.
7. The liquid crystal display device according to claim 1, wherein the average contrast at a polar angle of 60 ° is 30 or more.
8. The liquid crystal display according to claim 1, further comprising a backlight, wherein the backlight, the first polarizer, the refractive index anisotropic layer, the liquid crystal cell, and the second polarizer are arranged in this order. 2. The liquid crystal display device according to claim 1.
8. The liquid crystal display according to claim 1, further comprising a backlight, wherein the first polarizer, the refractive index anisotropic layer, the liquid crystal cell, the second polarizer, and the backlight are arranged in this order. 2. The liquid crystal display device according to claim 1.