JP2009276618A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display having height front contrast, and the omnidirectionaly excellent visibility. <P>SOLUTION: The liquid crystal display includes: a liquid crystal cell 10 having a liquid crystal layer sandwiched between a pair of transparent substrates with electrodes; a first polarization plate 21 disposed on the viewing side of the liquid crystal cell; a first anisotropic optical element 31 disposed between the liquid crystal cell and the first polarization plate; and a second anisotropic optical element 41 disposed between the first anisotropic optical element and the liquid crystal cell. If the first anisotropic optical element 31 has an in-plane refractive index nx<SB>1</SB>in a phase delay axis, an in-plane refractive index ny<SB>1</SB>in an phase advance axis, and a refractive index nz<SB>1</SB>in the thickness direction, it satisfies nx<SB>1</SB>≥ny<SB>1</SB>>nz. The second anisotropic optical element 41 is formed of a liquid crystalline material, and has a portion in which an orientation direction of the liquid crystalline material is continuously varied in the thickness direction of the anisotropic optical elements. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device including a polarizing plate and an anisotropic optical element on the viewing side of a liquid crystal cell.

  A liquid crystal display device generally has a configuration in which at least one of the liquid crystal cells has a polarizing plate. By applying a voltage to the liquid crystal cell, the alignment state of the liquid crystal molecules in the liquid crystal cell changes, and the liquid crystal cell is transmitted accordingly. Using the conversion of the polarization state of the light, the brightness and darkness of each pixel is adjusted and characters and images are displayed. Such conversion of the polarization state by the liquid crystal cell utilizes a birefringence phenomenon or an optical rotation phenomenon of liquid crystal molecules.

  As a liquid crystal alignment method in the liquid crystal cell, for example, a VA (Vertical Alignment) method, an IPS (In Plane Switching) method, a TN (Twisted Nematic) method and the like are widely adopted. On the other hand, the ECB (Electrically Controlled Birefringence) method, which is also referred to as a field effect birefringence method, uses a birefringence phenomenon of liquid crystal, and does not require a special manufacturing process in forming a liquid crystal cell. It has the advantage of being easy and inexpensive.

  In particular, the transflective ECB mode, which uses a transmissive mode that uses a light source such as a backlight and a reflective mode that uses external light, has good display visibility even in the presence of external light such as outdoors. Widely used in mobile applications such as mobile phones. In such a transflective mode liquid crystal display device, a method has been proposed in which light incident on the liquid crystal cell is circularly polarized from the viewpoint of reducing the parallax between the transmissive mode and the reflective mode (see, for example, Patent Document 1). ).

  On the other hand, the ECB mode has a disadvantage that the front contrast is lower than that of the liquid crystal display device of other modes and that the viewing angle is small (visibility from an oblique direction is low). From the viewpoint of overcoming such disadvantages, those using a liquid crystal panel having an optical compensation film between a liquid crystal cell and a polarizing plate are generally employed (see, for example, Patent Document 2).

WO99 / 40480 international publication pamphlet JP2002-031717

  However, in a transflective ECB mode liquid crystal display device using a conventional compensation method, the front contrast and viewing angle characteristics are still insufficient. Therefore, there has been a demand for a liquid crystal display device with improved characteristics, high front contrast, and good visibility in all directions.

As a result of intensive studies, the present inventors have found that the above problems can be solved by adopting a predetermined optical compensation method, and have reached the present invention. That is, the present invention provides a liquid crystal cell in which a liquid crystal layer is sandwiched between a pair of transparent substrates having electrodes, a first polarizing plate disposed on the viewing side of the liquid crystal cell, the liquid crystal cell and the first polarization A first anisotropic optical element disposed between the plate and a second anisotropic optical element disposed between the first anisotropic optical element and the liquid crystal cell. The present invention relates to a liquid crystal display device provided. In the liquid crystal display device of the present invention, the first anisotropic optical element has an in-plane refractive index in the slow axis direction of nx ₁ , an in-plane refractive index in the fast axis direction of ny ₁ , and a thickness. When the refractive index in the direction is nz ₁ , nx ₁ > ny ₁ ≧ nz ₁ is satisfied. The second anisotropic optical element has a portion formed of a liquid crystalline material, and the orientation direction of the liquid crystalline material continuously changes in the thickness direction of the anisotropic optical element.

  In a preferred embodiment of the liquid crystal display device of the present invention, the first polarizing plate, the first anisotropic optical element, and the second anisotropic optical element are laminated so as to form a circular polarizing plate. ing. In this embodiment, the front retardation of the first anisotropic optical element is 200 to 300 nm, and the front retardation of the second anisotropic optical element is 50 to 200 nm. Is preferred.

  In a preferred embodiment of the liquid crystal display device of the present invention, the second anisotropic optical element compensates for birefringence of liquid crystalline molecules in the vicinity of the transparent substrate of the liquid crystal cell in the voltage application state of the liquid crystal cell. Are arranged as follows.

  Moreover, in one Embodiment of the liquid crystal display device of this invention, it has a circularly-polarizing plate on the opposite side to providing the said 1st polarizing plate of the said liquid crystal cell.

  In the liquid crystal display device of the present invention, it is preferable that the liquid crystalline material forming the second anisotropic optical element is a rod-shaped liquid crystalline compound having positive refractive index anisotropy.

  Furthermore, in one embodiment of the liquid crystal display device of the present invention, the liquid crystal cell is an ECB mode liquid crystal cell. Furthermore, as an embodiment of the present invention, a transflective liquid crystal display device including a transflective plate on the opposite side of the liquid crystal cell from the first polarizing plate can be cited.

  According to the present invention, an anisotropic optical element (so-called so-called so-called liquid crystal cell) has a portion that is formed of a liquid crystalline material and the orientation direction of the liquid crystalline material continuously changes in the thickness direction. O-plate) compensates for the birefringence of the liquid crystal molecules in the liquid crystal layer, particularly when a voltage is applied to the liquid crystal cell. Therefore, display characteristics in the front and oblique directions can be improved.

[Configuration overview of LCD panel]
FIG. 1 is a schematic sectional view of a liquid crystal panel in the liquid crystal display device of the present invention. The liquid crystal cell 10 has a structure in which a liquid crystal layer 13 is sandwiched between a pair of transparent substrates (first substrate 11 and second substrate 12) including electrodes. The liquid crystal display device includes a first polarizing plate 21 on the viewing side of the liquid crystal cell 10. Between the liquid crystal cell 10 and the first polarizing plate 21, there is a first anisotropic optical element 31, and between the first anisotropic optical element 31 and the liquid crystal cell 10, there is a second The anisotropic optical element 41 is provided. On the opposite side of the liquid crystal cell 10 from the first polarizing plate 21, means for supplying light to a polarizing plate, an anisotropic optical element, a light source, a liquid crystal panel such as a reflecting plate, etc. (Not shown).

  Hereinafter, the liquid crystal cell, the polarizing plate, and the anisotropic optical element constituting the liquid crystal panel will be sequentially described.

[Liquid Crystal Cell]
Referring to FIG. 1, the liquid crystal cell 10 includes a liquid crystal layer 13, a first substrate 11 disposed on the viewing side of the liquid crystal layer 13, and a second substrate 12 disposed on the opposite side. One substrate (active matrix substrate) preferably has a switching element (typically a TFT) for controlling the electro-optical characteristics of the liquid crystal, a scanning line for supplying a gate signal to the switching element, and a signal line for supplying a source signal. Are provided (both not shown). The other substrate (color filter substrate) is provided with a color filter (not shown). Note that the color filter may be provided on the active matrix substrate. Alternatively, as in the field sequential method, an RGB three-color light source (which may further include a multicolor light source) is used as the illumination means of the liquid crystal display device, or the birefringence of an ECB mode liquid crystal cell. A color filter in the case of a liquid crystal display device that performs color display using wavelength dependency, a monochrome liquid crystal display device, or the like can be omitted. Further, the distance (cell gap) between the two substrates can be controlled by a spacer or the like.

  As the first substrate and the second substrate, those subjected to alignment treatment are preferably used from the viewpoint of arranging liquid crystal molecules in the liquid crystal layer in a predetermined alignment state. The alignment treatment means may be any method as long as the liquid crystal molecules are arranged in a certain alignment state on the surface of the substrate, but the liquid crystal layer 13 side of each of the first substrate and the second substrate. It is preferable that an alignment film is provided on the substrate, and the alignment film is subjected to an alignment treatment. As the alignment film, a film coated with an alignment polymer such as polyimide or polyvinyl alcohol is preferable. Further, as the alignment means, a “rubbing method” in which the alignment film is rubbed in one direction with a fiber such as nylon or polyester is preferably used. For example, when the rubbing method is used as the alignment treatment, the alignment treatment direction is substantially equal to the rubbing direction.

  The liquid crystal layer is not particularly limited, but in the present invention, the liquid crystal cell is substantially parallel to the substrates 11 and 12, that is, has a homogeneous alignment when no voltage is applied to the liquid crystal cell, that is, when no electric field is present in the liquid crystal cell. Are preferably used. In an ECB type liquid crystal cell, also called a field effect birefringence type, nematic liquid crystal having positive dielectric anisotropy is used as a liquid crystal molecule forming a liquid crystal layer. When the voltage is applied to the liquid crystal cell, the liquid crystal molecules are aligned along the electric field, so the polarization state of the light passing through the liquid crystal cell differs depending on whether or not the voltage is applied. Is obtained.

  The angle formed by the alignment treatment direction of the first substrate 11 and the alignment treatment direction of the second substrate 12 is not limited, and for example, both can be parallel. Here, when both are made parallel, the directors of the liquid crystal molecules in the vicinity of the substrate interface may be in the same direction, or the directions may be opposite, that is, antiparallel. In an ECB mode liquid crystal cell, one having an alignment direction of the substrate antiparallel is widely used. However, as disclosed in, for example, JP-A-6-27467, the alignment direction of the substrate is (anti). Those arranged at an angle other than parallel can also be adopted.

  FIG. 2 is a diagram conceptually showing a schematic cross section of an ECB mode liquid crystal cell when no voltage is applied and when a voltage is applied. FIG. 2A shows the time when no voltage is applied, and FIG. 2B shows the time when a voltage is applied. As described above, when the liquid crystal molecules of the liquid crystal layer 13 have a positive dielectric anisotropy, when a voltage is applied between the electrodes, as shown in FIG. The first substrate 11 and the second substrate 12 are arranged in a direction perpendicular to the surfaces. In this state, when a predetermined polarized light is incident from the surface of the second substrate 12, the polarized light travels along the major axis direction of the vertically aligned liquid crystal molecules. Since birefringence does not occur in the major axis direction of the liquid crystal molecules, the polarization state of incident light reaches the viewing side of the liquid crystal cell without being converted. For example, when the polarizing plates are arranged so as to be crossed Nicols on the second substrate side and the first substrate of the liquid crystal cell, the light is viewed on the viewing side arranged on the first substrate side. Therefore, a black (dark) display can be obtained.

  On the other hand, when no voltage is applied, the liquid crystal molecules of the liquid crystal layer 13 are aligned in parallel (homogeneously) with the surfaces of the first substrate 11 and the second substrate 12 as shown in FIG. Therefore, when a predetermined polarized light is incident from the surface of the second substrate 12, the polarized light is affected by birefringence by the liquid crystal molecules, and the polarized state is converted, so that a translucent state is obtained. Further, by changing the strength of the applied voltage, the gray scale (intermediate color) can be obtained with the orientation of the liquid crystal in the intermediate state between the two.

  By the way, as shown in FIG. 2B, when a voltage is applied to the liquid crystal cell, the liquid crystal molecules 133 and 134 present in the central portion in the thickness direction of the liquid crystal cell are aligned along the electric field direction. Since the liquid crystal molecules 131, 132, 135, and 136 near the interface between the substrates 11 and 12 cannot completely exceed the alignment regulating force of the substrate, their alignment cannot be completely aligned with the electric field direction. Since this influence is greater as it is closer to the substrate interface, as a result, the alignment direction of the liquid crystal molecules in the direction of the interface of the substrate gradually changes along the thickness direction of the liquid crystal cell.

  Due to the alignment state of the liquid crystal molecules near the substrate interface, the polarization state of incident light is converted by the birefringence of the liquid crystal cell even when a voltage is applied to the liquid crystal cell. As a result, light leakage occurs in black display. In the present invention, from the viewpoint of suppressing this light leakage, an anisotropic optical element is used as described later.

[Polarizer]
In the present specification and claims, the term “polarizing plate” refers to an element that can convert natural light or polarized light into arbitrary polarized light. The polarizing plate used in the present invention is not particularly limited, but preferably converts natural light or polarized light into linearly polarized light. Such a polarizing plate has a function of transmitting one of the polarized components when incident light is divided into two orthogonal polarized components, and absorbing, reflecting, and scattering the other polarized component. At least one function selected from the functions to be performed.

  The transmittance of the polarizing plate at a wavelength of 440 nm (also referred to as single transmittance) is preferably 41% or more, and more preferably 43% or more. Note that the theoretical upper limit of the single transmittance is 50%. Further, the degree of polarization is preferably 99.8 to 100%, and more preferably 99.9 to 100%. If it is said range, the contrast of a front direction can be made still higher when it uses for a liquid crystal display device.

The single transmittance and the degree of polarization can be measured using a spectrophotometer. As a specific method for measuring the degree of polarization, the parallel transmittance (H ₀ ) and orthogonal transmittance (H ₉₀ ) of the polarizing plate are measured, and the formula: degree of polarization (%) = 100 × {(H ₀ − H ₉₀ ) / (H ₀ + H ₉₀ )} ^1/2 . The parallel transmittance (H ₀ ) is a transmittance value of a parallel laminated polarizing plate produced by superposing two identical polarizing plates so that their absorption axes are parallel to each other. The orthogonal transmittance (H ₉₀ ) is a value of the transmittance of an orthogonal laminated polarizing plate produced by superposing two identical polarizing plates so that their absorption axes are orthogonal to each other. Note that these transmittances are Y values obtained by correcting the visibility using the 2-degree field of view (C light source) of JlSZ8701-1982.

(Polarizer)
As the 1st polarizing plate 21 used for this invention, arbitrary appropriate polarizing plates are used according to the objective. For example, as a polarizer constituting a polarizing plate, a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, an ethylene / vinyl acetate copolymer partially saponified film, iodine or a dichroic dye. And uniaxially stretched by adsorbing a dichroic substance such as polyene-based oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Further, a guest / host type O-type polarizer in which a liquid crystalline composition containing a dichroic substance and a liquid crystalline compound disclosed in US Pat. No. 5,523,863 is aligned in a certain direction, US Pat. An E-type polarizer or the like in which lyotropic liquid crystals disclosed in US Pat. No. 6,049,428 are aligned in a certain direction can also be used. Among such polarizers, from the viewpoint of having a high degree of polarization, a polarizer made of a polyvinyl alcohol film containing iodine is preferably used.

(Protective film)
The polarizer preferably includes a transparent film as a protective film on one or both sides from the viewpoint of preventing the optical properties from being deteriorated due to scratches or sublimation of the dichroic substance. As such a transparent protective film, a film that is excellent in transparency, mechanical strength, thermal stability, moisture shielding properties, and the like and is less likely to cause optical unevenness due to strain is preferably used. As the film, a polymer film is preferably used.

  As such a transparent protective film, those which do not substantially convert the polarization state are preferable, and from this viewpoint, an optical isotropic film is preferable. As a material constituting such an optically isotropic film, polycarbonate resin, polyvinyl alcohol resin, cellulose resin, polyester resin, polyarylate resin, polyimide resin, cyclic polyolefin resin, polysulfone resin, Examples include polyethersulfone resins, polyolefin resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. Further, a thermosetting resin such as urethane, acrylic urethane, epoxy, or silicone, or an ultraviolet curable resin can also be used. One or more kinds of arbitrary appropriate additives may be contained in the optical isotropic film.

  Moreover, it can be set as the polarizer protective film which has the function as an anisotropic optical element by using the anisotropic optical element mentioned later as a protective film of a polarizer instead of using an optical isotropic film. This can contribute to thinning and cost reduction of the liquid crystal display device.

(Lamination of polarizer and isotropic optical element)
The method for laminating the polarizer and the transparent protective film is not particularly limited, but laminating via an adhesive is preferable. Examples of such adhesives include acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate / vinyl chloride copolymers, modified polyolefins, epoxy systems, fluorine systems, natural rubber systems, and synthetic rubbers. Those using a rubber-based polymer as a base polymer can be appropriately selected and used. In particular, a water-based adhesive is preferably used for laminating the polarizer and the optically isotropic film. Especially, what has polyvinyl alcohol-type resin as a main component is used suitably.

  It is preferable to apply the adhesive so that the thickness of the adhesive layer after drying is about 10 to 300 nm. The thickness of the adhesive layer is more preferably from 10 to 200 nm, and even more preferably from 20 to 150 nm, from the viewpoint of obtaining a uniform in-plane thickness and sufficient adhesive strength.

[First anisotropic optical element]
Referring to FIG. 1, the first anisotropic optical element 31 is disposed on the first polarizing plate 21 disposed on the viewing side of the liquid crystal cell and the second anisotropic optical element 41. .

The first anisotropic optical element 31 used in the liquid crystal display device of the present invention has an in-plane refractive index in the slow axis direction of nx ₁ , an in-plane refractive index in the fast axis direction of ny ₁ , and a thickness. When the refractive index in the direction is nz ₁ , nx ₁ ≧ ny ₁ > nz ₁ is satisfied. Here, a case where the anisotropic optical element satisfies nx ₁ > ny ₁ = nz ₁ is referred to as a “positive A plate”, and a case where the anisotropic optical element satisfies nx ₁ > ny ₁ > nz ₁ is referred to as a “biaxial plate”. However, it is particularly preferable to use a positive A plate in the liquid crystal display device of the present invention. In one embodiment of the present invention, it is preferable that the first anisotropic optical element has a retardation of approximately ½ of the wavelength. The preferred range and reason for retardation will be described in detail later.

  The thickness of the first anisotropic optical element is usually 0.5 μm to 100 μm. The light transmittance at a wavelength of 590 nm of the first anisotropic optical element is preferably 85% or more, more preferably 90% or more.

  The material and manufacturing method of the first anisotropic optical element are not particularly limited as long as the above optical characteristics are satisfied, and a stretched polymer film or a liquid crystal compound is aligned. A publicly known thing can be used. The first anisotropic optical element may be a single layer film or a laminate of two or more layers. Preferably, the first anisotropic optical element is a single layer film. This is because retardation shift and unevenness due to shrinkage stress of a polarizing plate or the like or heat from a light source can be reduced, and the liquid crystal display device can be made thin. When the first anisotropic optical element is a laminate, it may include an adhesive layer or an adhesive layer for attaching two or more retardation films. When the laminate includes two or more retardation films, these retardation films may be the same or different.

[Second anisotropic optical element]
Referring to FIG. 1, the second anisotropic optical element 41 is disposed between the first substrate 11 on the viewing side of the liquid crystal cell 10 and the first anisotropic optical element 31.

The second anisotropic optical element 41 used in the liquid crystal display device of the present invention is formed of a liquid crystalline material, and the orientation direction of the liquid crystalline material continuously changes in the thickness direction of the anisotropic optical element. Such an anisotropic optical element having a portion that has the same shape is generally referred to as an “O plate”. More specifically, it is a solidified layer or a cured layer of a liquid crystal compound aligned in a hybrid arrangement. “Hybrid alignment” refers to an alignment tilt angle (tilt angle) of a liquid crystal compound that increases or decreases continuously or intermittently in the thickness direction. As schematically shown in FIG. The tilt angle (θ ₁ ) at one interface is different from the tilt angle (θ ₂ ) at the other interface. Here, the tilt angle represents an angle formed by the adjacent layer surface and the rod-like liquid crystal compound molecules, and the case where the molecules are arranged in parallel in the plane is 0 °.

  Examples of the liquid crystalline material forming the second anisotropic optical element include those having a positive refractive index anisotropy represented by a rod-like liquid crystalline compound and negative negatives represented by a discotic liquid crystal compound. Examples include compounds having birefringence. Any one of them can be used in the present invention, but it has a positive refractive index anisotropy from the viewpoint of appropriately performing optical compensation of an ECB mode liquid crystal cell and improving front contrast and viewing angle characteristics. A thing can be used suitably.

  In the present specification and claims, the “rod-like liquid crystalline compound” has a mesogenic group in the molecular structure, and the refractive index in the major axis direction of the mesogenic group is larger than that in the minor axis direction. A compound that exhibits a liquid crystal phase by temperature change such as heating and cooling or by the action of a certain amount of solvent. The “solidified layer” refers to a softened, melted or solution-state liquid crystalline composition that has been cooled and solidified, and the “cured layer” refers to a part or all of the liquid crystalline composition that is composed of heat, a catalyst, This refers to those that have been crosslinked by light and / or radiation to become insoluble or insoluble or hardly soluble.

  Any appropriate compound can be selected as the rod-like liquid crystalline compound, and those that exhibit a crystal or glass state at room temperature and develop a nematic liquid crystal phase at high temperatures can be suitably used. The rod-like liquid crystalline compound exhibits a liquid crystal phase before film formation, but after the film formation, for example, a network structure may be formed by a crosslinking reaction and no liquid crystal phase may be exhibited. By using the rod-like liquid crystalline compound having the above properties, for example, the alignment state can be fixed by cooling or crosslinking after forming a hybrid alignment in a state exhibiting a liquid crystal phase.

  The mesogenic group is a structural part for forming a liquid crystal phase and usually contains a ring structural unit. Specific examples of the mesogenic group include a biphenyl group, a phenylbenzoate group, a phenylcyclohexane group, an azoxybenzene group, an azomethine group, an azobenzene group, a phenylpyrimidine group, a diphenylacetylene group, a diphenylbenzoate group, a bicyclohexane group, and a cyclohexylbenzene group. And terphenyl group. In addition, the terminal of these ring structural units may have substituents, such as a cyano group, an alkyl group, an alkoxy group, a halogen group, for example. Among them, those having a biphenyl group or a phenylbenzoate group as the mesogenic group are preferably used.

  The rod-like liquid crystal compound may be a polymer substance (polymer liquid crystal) having a mesogenic group in the main chain and / or side chain, or a low molecular substance (low molecular liquid crystal) having a mesogen group in a part of the molecular structure. ). The polymer liquid crystal is excellent in productivity because the molecular alignment state can be fixed by cooling from the liquid crystal state. On the other hand, a low molecular liquid crystal has high orientation and can easily obtain a highly transparent retardation layer.

  The rod-like liquid crystalline compound preferably has at least one crosslinkable functional group in a part of the molecular structure. This is because the cross-linking reaction increases the mechanical strength and provides a retardation layer having excellent durability. Examples of the crosslinkable functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group. A commercially available rod-like liquid crystalline compound can also be used as it is. Alternatively, other additives such as a liquid crystal compound, a polymerization initiator, and a leveling agent may be added to a commercially available or synthesized rod-like liquid crystal compound and used as a liquid crystal composition.

  The manufacturing method of the second anisotropic optical element is not particularly limited, and a known method can be applied, but a method of aligning the liquid crystalline compound as a solidified layer or a cured layer on the substrate can be suitably used. The substrate for forming the solidified layer or the cured layer is not particularly limited. However, in the case where the liquid crystal compound is applied on the substrate as a coating solution in which the liquid crystalline compound is dissolved or dispersed, Those not eroded by the solvent can be suitably used. The first anisotropic optical element, the polarizer protective film of the polarizing plate, and the like may also serve as a base material for forming a solidified layer or a cured layer of the liquid crystalline compound. In such a case, the first anisotropic optical element or the polarizer protective film of the polarizing plate may be subjected to an alignment treatment or may have an alignment film in order to align the liquid crystalline compound.

  When the first anisotropic optical element or the polarizer protective film for the polarizing plate is used as a substrate for forming a solidified layer or a cured layer of the liquid crystal compound, the substrate is used as it is in a liquid crystal display device. Can be used. When other films are used as the substrate, the substrate can be used as it is in the formation of the liquid crystal display device, or the substrate is removed and only the solidified layer or the cured layer of the liquid crystalline compound is used as the second layer. The anisotropic optical element may be used in a liquid crystal display device. When using for a liquid crystal display device, without removing a base material, what is excellent in this base material is preferable. In this case, the substrate is preferably optically isotropic from the viewpoint of appropriately performing optical compensation.

In the present invention, the tilt angle of the second anisotropic optical element can be appropriately designed according to the type of liquid crystal cell used. The tilt angle (θ ₁ ) at one interface is different from the tilt angle (θ ₂ ) at the other interface, but the difference between them (Δθ = θ ₂ −θ ₁ ) is preferably 20 ° to 90 °. More preferably, it is 40 ° to 85 °, and further preferably 60 ° to 80 °.

Further, the smaller one (θ ₁ ) of the tilt angles of the liquid crystal molecules at the interface is preferably 0 ° to 10 °, more preferably 0 ° to 5 °. On the other hand, the larger one of the tilt angles of liquid crystalline molecules at the interface (θ ₂ ) is preferably 20 ° to 90 °, more preferably 40 ° to 85 °, and further preferably 60 ° to 80 °. It is. The average tilt angle (θ _ave = (θ ₁ + θ ₂ ) / 2) expressed as the average of the tilt angles at both interfaces is preferably 10 ° to 45 °, more preferably 15 ° to 42 °, More preferably, the angle is 20 ° to 40 °. By making the average tilt angle in the above range, the optical compensation of the liquid crystal cell can be performed more appropriately.

Note that the tilt angle of the liquid crystal compound in the second anisotropic optical element can be measured using Journal of Applied Phisics Vol. 2 as shown in the following formulas (I) and (II). 38 (1999) p. The expression of Witte according to 748, _n e of the liquid crystal compounds was measured in advance, _{n o,} and the direction parallel to the retardation (slow axis, a polar angle of -40 ° ~ ten 40 ° (the normal direction 0 ° And each value measured in 5 ° increments). Here, θ _air represents the tilt angle of the liquid crystal compound at one interface (for example, air interface) of the anisotropic optical element, and θ _AL represents the tilt angle at the other interface (for example, a substrate or alignment film). Represents. d represents the thickness of the solidified layer or cured layer of the liquid crystal compound aligned in a hybrid arrangement. n _e represents an extraordinary refractive index of the rod-shaped liquid crystalline compounds, n _o represents an ordinary refractive index of the rod-shaped liquid crystalline compound.

  The transmittance at a wavelength of 590 nm of the liquid crystal layer as the second anisotropic optical element is preferably 85% or more, and more preferably 90% or more. Moreover, thickness is 0.1 micrometer-10 micrometers normally, Preferably it is 0.5 micrometer-5 micrometers.

[Retardation value and arrangement of anisotropic optical element]
The first anisotropic optical element 31 and the second anisotropic optical element 41 are provided between the liquid crystal cell 10 and the first polarizing plate 21. The retardation and arrangement angle of the first anisotropic optical element and the second anisotropic optical element are not particularly limited, but a transmission mode using a light source such as a backlight and a reflection mode using external light are used. In the transflective mode liquid crystal display device used in combination, the first polarizing plate, the first anisotropic optical element, and the second anisotropic optical element may be laminated so as to form a circularly polarizing plate. preferable.

  A polarizing plate and an anisotropic optical element form a circular polarizing plate when an arbitrary polarized light is incident on the laminate of the polarizing plate and the anisotropic optical element from the polarizing plate side. It means that it is emitted as circularly polarized light from the side. Here, “circularly polarized light” may include not only perfect circularly polarized light but also elliptically polarized light that is close to circularly polarized light, that is, whose ellipticity is close to 1. Further, it does not matter whether circularly polarized light and elliptically polarized light are clockwise or counterclockwise. Furthermore, the polarization state does not necessarily need to be completely polarized, and may be partially polarized including a state where it is not partially polarized.

  Generally, as a combination of such a polarizing plate and an anisotropic optical element, the anisotropic optical element has a front retardation corresponding to about ¼ of the wavelength, and the anisotropic optical element Examples include those in which the slow axis direction and the absorption axis direction of the polarizing plate form an angle of 45 °. As such an embodiment, for example, the first anisotropic optical element and the second anisotropic optical element are arranged so that the slow axis directions thereof are parallel to each other, and the sum of the front retardations of both is arranged. Is approximately ¼ of the wavelength (or an odd multiple of ¼), the slow axis direction of the first anisotropic optical element and the second anisotropic optical element, and the absorption of the polarizing plate Examples are those laminated so that the axial direction is 45 °.

  On the other hand, in the present invention, the slow axis direction of the first anisotropic optical element, the slow axis direction of the second anisotropic optical element, and the absorption axis direction of the first polarizing plate are all parallel. It is preferable that these layers are stacked so that they do not become so as to form a broadband circularly polarizing plate. As described above, in the circularly polarizing plate laminated so that the slow axis direction of the anisotropic optical element and the absorption axis direction of the polarizing plate form an angle of 45 °, the birefringence wavelength of the anisotropic optical element Due to the influence of dispersion, circularly polarized light is obtained in a wavelength region where visible light is present, but in other wavelength regions, retardation deviates from ¼ of the wavelength. There is a problem that it is difficult to obtain. On the other hand, when a broadband circularly polarizing plate is used, substantially circularly polarized light can be obtained in the entire visible light region, so that good display characteristics can be obtained.

  Examples of a method for forming a broadband circularly polarizing plate using two anisotropic optical elements as described above include, for example, JP-A-5-100114, JP-A-10-68816, and JP-A-11-149015. As disclosed in Japanese Laid-Open Patent Publication No. 2006-171713 and the like, a technique of laminating two anisotropic optical elements so that the slow axis forms an angle that is neither parallel nor orthogonal is preferably used. it can.

In order to obtain such a broadband circularly polarizing plate, the angle formed between the absorption axis direction of the first polarizing plate and the slow axis of the first anisotropic optical element and the second anisotropic optical element is It can be appropriately determined according to the retardation value of the anisotropic optical element. As an example, as disclosed in JP-A-5-100114, the first polarizing plate having a front retardation of approximately ½ with respect to the transmission axis direction of the first polarizing plate as a reference (0 °). The angle in the slow axis direction of the anisotropic optical element is (ψ ₁ ), and the angle in the slow axis direction of the second anisotropic optical element having a front retardation of approximately ¼ is (ψ ₂ ). In this case, it is preferable to arrange so that ψ ₂ = 2ψ ₁ ± 45 °. As a more specific example, when the angle formed by the absorption axis direction of the first polarizing plate and the slow axis of the first anisotropic optical element is 15 ° clockwise, the second The anisotropic optical element was emitted from the first polarizing plate by arranging the slow axis direction to be 75 ° clockwise with respect to the absorption axis direction of the first polarizing plate. Linearly polarized light can be converted into circularly polarized light in a wide band of visible light by two anisotropic optical elements.

  From this viewpoint, the front retardation of the first anisotropic optical element is preferably approximately ½ of the wavelength, and the front retardation of the second anisotropic optical element is approximately ¼ of the wavelength. It is preferable. Specifically, the front retardation at a wavelength of 590 nm of the first anisotropic optical element is preferably 200 to 300 nm, and more preferably 250 to 300 nm. Further, the front retardation of the second anisotropic optical element at a wavelength of 590 nm is preferably 50 to 200 nm, and more preferably 70 to 160 nm.

  The retardation value of the second anisotropic optical element is approximately ¼ wavelength from the viewpoint of forming the broadband circularly polarizing plate as described above, and at the same time, the liquid crystal cell in the voltage application state of the liquid crystal cell. It is preferable to select so as to compensate for the birefringence of liquid crystalline molecules in the vicinity of the transparent substrate. For example, as shown in FIG. 2B, when a voltage is applied to the ECB mode liquid crystal cell, the liquid crystal molecules near the interface between the substrates 11 and 12 are denoted by reference numerals 131, 132, 135, and 136. In order to obtain a black display with tilted orientation and less light leakage in the front and oblique directions, the retardation value of the second anisotropic optical element is set so as to optically compensate for these birefringence. It is preferable to select.

As described above, in the second anisotropic optical element, the tilt angle (θ ₁ ) at one interface is smaller than the tilt angle (θ ₂ ) at the other interface, and the front and back are not optically equivalent. . In the liquid crystal display device of the present invention, the side with the small tilt angle (θ ₁ ) of the second anisotropic optical element 21 is either the liquid crystal cell 10 side or the first anisotropic optical element 31 side. However, as described above, the liquid crystal cell is preferably arranged so as to compensate for the birefringence of the liquid crystal molecules in the vicinity of the transparent substrate in the voltage application state. Such an arrangement can be appropriately selected depending on the type of the liquid crystal cell or the like, but when the liquid crystal cell is in the ECB mode, the side with the smaller tilt angle (θ ₁ ) is the liquid crystal cell side and the angle with the larger tilt angle (θ ₂ ) Side is preferably arranged so as to face the first anisotropic optical element side.

  The present invention provides a transflective liquid crystal display by disposing a second anisotropic optical element having a portion in which the alignment direction of the liquid crystalline material continuously changes in the thickness direction on the viewing side of the liquid crystal cell. The optical compensation of the apparatus can be appropriately performed. That is, in the transmissive mode, the light from the light source disposed on the opposite side of the liquid crystal cell on the viewing side (the side on which the first polarizing plate 21 is disposed) is transmitted between the liquid crystal cell 10 and the second anisotropy. Each passes through the optical element 41 (and the first anisotropic optical element 31 and the first polarizing plate 21) once. On the other hand, in the reflection mode using external light, the external light is transmitted from the liquid crystal cell 10 and the second anisotropic optical element 41 (and the first anisotropic optical element 31 and the first polarizing plate 21). Will be passed twice each. Thus, in the configuration of the present application, the number of times of passing through the liquid crystal cell and the number of times of passing through the second anisotropic optical element are the same in both the transmission mode and the reflection mode. By making the retardation value of the liquid crystal cell and the retardation of the second anisotropic optical element substantially equal, the optical compensation of the liquid crystal cell can be suitably performed.

  In addition, since the orientation direction of liquid crystal molecules differs depending on the thickness direction of the O plate, the second anisotropic optical element does not have an optical axis as a whole, but the liquid crystal compound has a positive refractive index anisotropy. When the direction of the director direction of the liquid crystal compound projected onto the liquid crystal cell surface is parallel to the apparent slow axis direction and the liquid crystal compound has negative refractive index anisotropy, The direction in which the director direction of the compound is projected onto the liquid crystal cell surface is perpendicular to the apparent slow axis direction. In addition, the retardation value of the second anisotropic optical element is strictly a value obtained by calculating an in-plane refractive index at each coordinate in the thickness direction and integrating this in the thickness direction. As shown in Examples described later, a measurement value obtained by a commercially available automatic birefringence meter or the like is adopted as the retardation value of the second anisotropic optical element.

In the front retardation of the first anisotropic optical element, the in-plane slow axis direction refractive index is nx ₁ , the in-plane fast axis direction refractive index is ny ₁ , and the thickness direction refractive index is nz _1. When the thickness is d, (nx ₁ −ny ₁ ) × d. The thickness direction retardation is represented by (nx ₁ −nz ₁ ) × d. When the first anisotropic optical element is a positive A plate, strictly ny = nz, but in the present invention, not only when ny and nz are exactly the same, but also substantially the same. In some cases, ny = nz is included. Note that the both are substantially identical, generally _refers to those Nz coefficient expressed by _{Nz = (nx 1 -nz 1)} / (nx 1 -ny 1) is 1.2 or less, The Nz coefficient is preferably 1.1 or less, more preferably 1.05 or less. Further, when the first anisotropic optical element is a biaxial plate, the Nz coefficient is preferably 1.1 to 6.0, more preferably 1.1 to 4.0, and still more preferably. 1.2-2.0.

[Formation of liquid crystal display device]
The liquid crystal display device can be formed by any appropriate method using the liquid crystal cell 10, the first polarizing plate 21, the first anisotropic optical element 31, and the second anisotropic optical element 41. . In particular, the liquid crystal cell 10, the first polarizing plate 21, the first anisotropic optical element 31, and the second anisotropic optical element 41 are laminated via an adhesive layer, an adhesive layer, and the like, respectively. Is preferred. In laminating these, a method of sequentially laminating other layers on the liquid crystal cell can be adopted. From the viewpoint of handling properties, however, the polarizing plate, the first anisotropic optical element, and the second An optical compensation polarizing plate (circular polarizing plate) in which anisotropic optical elements are laminated in this order is formed, and a method of laminating this with a liquid crystal cell via an adhesive or the like can be suitably employed.

  In the liquid crystal display device of the present invention, as described above, the second anisotropic optical element is selected so as to compensate for the birefringence of the liquid crystal molecules in the vicinity of the transparent substrate of the liquid crystal cell in the voltage application state of the liquid crystal cell. It is preferable that the arrangement angle between the liquid crystal cell and the second anisotropic optical element is selected so as to achieve the above object. The angular relationship that can achieve such an object varies depending on the type of the liquid crystal cell to be used. For example, the alignment treatment direction (rubbing direction) of the first substrate 11 and the second substrate 12 of the liquid crystal cell 10 is parallel. Alternatively, when an antiparallel liquid crystal cell is used, the liquid crystal cell is arranged so that the alignment treatment direction of the liquid crystal cell and the projection of the second anisotropic optical element on the liquid crystal cell surface are parallel or antiparallel. It is preferable. Here, “parallel” includes not only the case of being completely parallel but also the case of being substantially parallel. The angle is generally in the range of 0 ° ± 10 °, preferably 0 ° ± 5 °, more preferably 0 ° ± 2 °, and even more preferably 0 ° ± 1 °.

  On the other hand, when the alignment process direction (rubbing direction) of the first substrate 11 and the second substrate 12 of the liquid crystal cell 10 forms a predetermined angle, the alignment process direction of one of the substrates and the second anisotropic direction It is preferable to arrange so that the projection on the liquid crystal cell surface in the director direction of the diffractive optical element is parallel or antiparallel. In addition, the projection direction of the liquid crystal layer 13 on the liquid crystal cell surface in the average director direction and the projection on the liquid crystal cell surface in the director direction of the second anisotropic optical element are arranged in parallel or antiparallel. Is also preferable.

(Adhesive)
In addition, when laminating each layer using a pressure-sensitive adhesive, the pressure-sensitive adhesive is not particularly limited. For example, an acrylic polymer, a silicone-based polymer, a polyester, a polyurethane, a polyamide, a polyether, a fluorine-based or rubber-based polymer, etc. A base polymer can be appropriately selected and used. In particular, those having excellent optical transparency, such as an acrylic pressure-sensitive adhesive, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and having excellent weather resistance, heat resistance and the like can be preferably used.

  In addition to the above, from the viewpoints of prevention of foaming and peeling phenomenon due to moisture absorption, deterioration of optical characteristics due to thermal expansion difference and the like, prevention of warpage of liquid crystal cells, and formation of liquid crystal display devices with high quality and excellent durability. An adhesive layer having a low moisture absorption rate and excellent heat resistance is preferred.

  The adhesive layer is, for example, natural or synthetic resins, in particular, tackifier resins, fillers or pigments made of glass fibers, glass beads, metal powders, other inorganic powders, colorants, antioxidants, etc. It may contain an additive to be added to the adhesive layer. Moreover, the adhesion layer etc. which contain microparticles | fine-particles and show light diffusibility may be sufficient. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, but is generally 1 to 500 μm, preferably 5 to 200 μm, and more preferably 10 to 100 μm.

[Other parts]
(Ellipse polarizing plate)
In the liquid crystal display device of the present invention, the optical layer and other members other than the liquid crystal cell 10, the first polarizing plate 21, the first anisotropic optical element 31, and the second anisotropic optical element 41 are provided. It can also be included. In particular, as shown in FIG. 4, it is preferable to have a second polarizing plate 22 on the side opposite to the first polarizing plate 21 of the liquid crystal cell 10. Further, from the viewpoint of performing optical compensation of the liquid crystal layer, it is preferable to have an anisotropic optical element between the second polarizing plate 22 and the liquid crystal cell 10. In particular, in the case of a transflective mode liquid crystal display device, it is preferable to dispose the second polarizing plate and the anisotropic optical element so that the combination acts as an elliptically polarizing plate.

  The elliptically polarizing plate 102 is the same as the circularly polarizing plate 101 disposed on the viewing side as a laminate of the first polarizing plate, the first anisotropic optical element, and the second anisotropic optical element. Things can also be used. In addition, an anisotropic optical element (for example, an A plate or a biaxial plate) made of a stretched polymer film or the like without using an anisotropic optical element in which the orientation direction of the liquid crystalline material continuously changes in the thickness direction. It is also preferable to use a circularly polarizing plate using only the same. In particular, as described above, when the retardation of the second anisotropic optical element is set to be substantially equal to the retardation value of the liquid crystal cell when a voltage is applied, the optical compensation of the liquid crystal layer is appropriately performed. From the viewpoint, it is preferable that the elliptically polarizing plate 102 disposed on the side opposite to the viewing side of the liquid crystal cell does not include an anisotropic optical element in which the alignment direction of the liquid crystalline material continuously changes in the thickness direction.

  The elliptically polarizing plate 102 is preferably a broadband circular polarizing plate. As such a broadband circularly polarizing plate, as an anisotropic optical element, a longer wavelength has a higher retardation as disclosed in Japanese Patent Application Laid-Open No. 2001-137116 and WO00 / 26705. / 4 wavelength plate arranged such that the slow axis direction forms an angle of 45 ° with the absorption axis direction of the polarizing plate, Japanese Patent Laid-Open Nos. 5-100114, 10-68816, and 11 -189015, JP-A 2006-171713, etc., wherein two anisotropic optical elements are laminated with a polarizing plate so that the slow axis forms an angle that is neither parallel nor orthogonal Can be suitably used.

  From the viewpoint of reducing the black luminance in the front direction in the transmission mode and increasing the front contrast, the elliptically polarizing plate 102 is preferably an ideal circularly polarizing plate having an ellipticity close to 1, but the white luminance That is, from the viewpoint of increasing the brightness of the liquid crystal display device, it is not necessarily optimal that the ellipticity is 1, and may be appropriately changed depending on the type of the liquid crystal cell. In this case, the ellipticity of polarized light at a wavelength of 590 nm by the elliptically polarizing plate is preferably 0.5 or more, more preferably 0.7 or more, and further preferably 0.8 or more.

(Semi-transmissive reflector)
When forming a transflective liquid crystal display device, as shown in FIG. 4, it is preferable to have a transflective plate 60 on the side opposite to the viewing side of the liquid crystal cell 10 of the liquid crystal display device. The transflective plate 60 is provided for the purpose of reflecting external light from the viewing side to the viewing side (liquid crystal cell side) while transmitting light from the light source to the liquid crystal cell side. In FIG. 4, the transflective plate is disposed immediately below the liquid crystal cell 10. However, the location of the transflective plate is not limited to the embodiment illustrated in FIG. 4. The polarizing plate 22 and the light source unit 200 can also be disposed. Further, the liquid crystal cell 10 can be provided integrally in the second substrate 12.

  The transflective plate reflects at a certain reflectance and transmits the remaining part. For example, a metal vapor-deposited film, a very narrow slit, or a metal film having a hole can be used. Such a metal film is not particularly limited, and a metal such as aluminum, silver, gold, chromium, or platinum, an alloy containing them, or an oxide such as magnesium oxide can be used. Further, as the transflective plate, a so-called “brightness enhancement film” that selectively reflects and transmits predetermined polarized light can be used. As such a brightness enhancement film, an isotropic multilayered film such as described in German Patent No. 3836955 and an optically anisotropic layer typified by a trade name “D-BEF” manufactured by 3M Corporation are isotropic. An alternating layered structure of a conductive layer is exemplified. In addition, a cholesteric liquid crystal layer, particularly an oriented film of a cholesteric liquid crystal polymer, or a film in which the oriented liquid crystal layer is supported on a film substrate can be used. The brightness enhancement film using such a cholesteric liquid crystal exhibits a characteristic of reflecting one of the left and right circularly polarized light and transmitting the other light. For example, the product name “PCF350” manufactured by Nitto Denko Corporation, manufactured by Merck For example, “Transmax”.

(light source)
When the liquid crystal display device is a transmissive or transflective liquid crystal display device, it is preferable to provide a light source unit 200 as a light source on the side opposite to the viewing side of the liquid crystal cell, as shown in FIG. Note that FIG. 4 shows a case where the direct light system is adopted as the light source unit, but this may be a side light system, for example.

  When the direct light system is adopted as the light source unit, the light source unit 200 preferably includes a light source 81, a reflection film 82, a diffusion plate 83, and a prism sheet 84. Although not shown, it is also preferable to have a brightness enhancement film. When the sidelight method is adopted, it is preferable that the light source unit further includes a light guide plate and a light reflector in addition to the above configuration. In addition, as long as the effect of this invention is acquired, the optical member illustrated in FIG. 4 may be partly omitted depending on the design of the illumination method or the like of the liquid crystal display device, or may be replaced with another optical member. Can be done.

(Surface treatment layer)
Further, the surface on the viewing side of the liquid crystal display device, for example, the surface on the opposite side of the first polarizing plate 21 where the first anisotropic optical element is disposed, or the anisotropy of the second polarizing plate. A surface treatment layer such as an antireflection layer, an antisticking layer, a diffusion layer or an antiglare layer can be provided on the surface opposite to the side where the optical element is disposed. The surface treatment layer can be provided by subjecting a polarizing plate (substantially the outermost polarizer protective film of the polarizing plate) to surface treatment, or can be provided separately from the polarizing plate.

  The hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate. For example, a hard film with an appropriate UV curable resin such as an acrylic type or a silicone type is applied to a protective film with excellent hardness and sliding properties. It can be formed by a method of adding to the surface. The antireflection treatment is performed for the purpose of preventing the reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the prior art. Further, the anti-sticking treatment is performed for the purpose of preventing adhesion with an adjacent layer.

  The anti-glare treatment is applied for the purpose of preventing the outside light from being reflected on the surface of the polarizing plate and obstructing the visibility of the light transmitted through the polarizing plate. For example, the surface is roughened by a sandblasting method or an embossing method. Or by applying a fine concavo-convex structure to the surface of the protective film by an appropriate method such as a blending method of transparent fine particles. The fine particles to be included in the formation of the surface fine concavo-convex structure are, for example, conductive materials made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide or the like having an average particle size of 0.5 to 50 μm. In some cases, transparent fine particles such as inorganic fine particles, organic fine particles composed of a crosslinked or uncrosslinked polymer, and the like are used. When forming a surface fine uneven structure, the amount of fine particles used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the transparent resin forming the surface fine uneven structure. The antiglare layer may also serve as a diffusion layer (viewing angle expanding function or the like) for diffusing the light transmitted through the polarizing plate to expand the viewing angle or the like.

  As described above, the liquid crystal display device of the present invention includes a first polarizing plate, a first optically anisotropic layer, and a second anisotropic layer on the viewing side of the liquid crystal cell, so Since refraction is optically compensated, front contrast and viewing angle characteristics can be enhanced. The liquid crystal display device of the present invention can be used for various applications. In particular, as a transflective ECB mode liquid crystal display device, mobile devices such as mobile phones, watches, digital cameras, personal digital assistants (PDAs), and portable game machines, It can be suitably used as a small and medium-sized liquid crystal display device that can be used outdoors, such as a back monitor, a car navigation system monitor, and an in-vehicle device such as a car audio.

  The present invention will be further described using examples and comparative examples, but the present invention is not limited to the following examples. In addition, the measured value etc. which were used in the Example were obtained by the following methods.

[Measuring method]
(Thickness)
The thickness of the liquid crystal cured layer was measured using a thin-film spectrophotometer [manufactured by Otsuka Electronics Co., Ltd., “instant multiphotometry system MCPD-2000”].

(Retardation)
Retardation at a wavelength of 590 nm was measured using a product name “Axioscan” manufactured by Axiometric. In the measurement, in order to eliminate the influence of birefringence due to the base material, the liquid crystal cured layer was peeled off from the base material and transferred onto a glass plate using an adhesive, and then the measurement was performed.

(Tilt angle at the interface of rod-like liquid crystalline compounds)
Journal of Applied Phisics, vol. 38 (1999), p. The expression of Witte according to _748, n e, _{n o,} and parallel to the retardation (slow axis, the polar angle -40 ° ~ ten 40 ° (the normal direction to 0 °) at 5 ° increments Each measured value) was substituted and determined.

(contrast)
After 30 minutes had passed since the backlight was turned on in a dark room at 23 ° C., measurement was performed using a trade name “Conoscope” manufactured by AUTRONIC-MELCHERS GmbH. Note that the right side (right azimuth) of the liquid crystal display device in the left-right direction of the screen is azimuth angle 0 °, the counterclockwise direction is positive, and the normal direction of the screen is polar angle 0 °.

[Production Example 1]
(Formation of O plate)
Formula (II) polymer represented by a liquid crystal (weight average molecular weight: 5,000) and 20 parts by weight, the polymerizable liquid crystal compound [BSAF's trade name "Paliocolor LC242" _(n e = 1.654, and n _o = 1.523)] 80 parts by weight, to prepare a cyclopentanone dissolved solids concentration of 30 wt% solution of 233 parts by weight. To this solution, 0.3 part by weight of a surface preparation agent [trade name “BYK375” manufactured by Big Chemie Co., Ltd.] is added, and further 7 parts by weight of a polymerization initiator [trade name “Irgacure 907” manufactured by Ciba Specialty Chemicals]. ] Was added. To this solution, 196 parts by weight of cyclopentanone was added to prepare a liquid crystal composition solution having a solid concentration of 20% by weight.
The numerical values “65” and “35” in the following formula (II) indicate that the copolymerization ratio is 65:35.

  A polyethylene terephthalate film [trade name “RC06” manufactured by Toray Industries, Inc., thickness 75 μm] was rubbed with a rayon rubbing cloth [trade name “YA181R” manufactured by Yoshikawa Processing Co., Ltd.] to obtain an alignment substrate. The liquid crystalline composition solution was uniformly applied to the rubbing treated surface of the alignment substrate using a wire bar to form a coating layer.

Thus, the said coating layer formed on the base material was dried with the orientation base material for 2 minutes with an 80 degreeC air circulation type thermostat oven, and the solidified layer by which the inclination orientation was carried out was formed. The surface of the obtained solidified layer is irradiated with ultraviolet rays in an air atmosphere at a room temperature (25 ° C.) so that the amount of irradiation light at a wavelength of 365 nm is 500 mJ / cm ² using a conveyor type ultraviolet irradiation device, and tilted orientation is performed. A cured liquid crystal layer was formed.

  In this way, an O plate provided with a base material and a liquid crystal cured layer was produced. When the cured liquid crystal layer was peeled from the substrate and measured for physical properties, the average tilt angle was 38 ° and the front retardation was 90 nm. Further, the tilt angle of the O plate was continuously changed in the thickness direction because the tilt angle on the air interface side was larger than the tilt angle on the substrate interface side.

  While removing the orientation base material of the O plate comprising the base material and the liquid crystal cured layer, an acrylic pressure-sensitive adhesive (thickness: on a 40 μm thick triacetylcellulose film [trade name “KC4UYW” manufactured by Konica Minolta, Inc.] 20 μm). In this way, the O plate in which the liquid crystal cured layer is formed on the triacetyl cellulose film is referred to as “O plate 1”.

(Polarizer)
A polarizing plate (trade name “NPF-L-CAT1465CU” manufactured by Nitto Denko Corporation) in which an acrylic transparent film having substantially no front retardation was laminated on both surfaces of the polarizer was used as it was.

(A plate)
A norbornene-based resin film [trade name “Zeonor Film” manufactured by Optes Co., Ltd.] having a retardation of 260 nm and a Nz coefficient of 1 was used as “A plate 1” as it was.

(Creation of circular polarizer)
The polarizing plate, the A plate 1 and the O plate 1 are arranged in this order so as to have the angular arrangement shown in Table 1 below via an acrylic adhesive (thickness: 20 μm) between the respective layers. It laminated | stacked and it was set as the circularly-polarizing plate. In addition, regarding the lamination | stacking of O plate 1, it laminated | stacked so that the triacetyl cellulose side might oppose A plate, ie, the tilt angle on the A plate side might become large.

  The angle in Table 1 above is the angle when viewed from the polarizing plate side (the counterclockwise direction is a positive angle with respect to the long side direction of the screen when forming a liquid crystal display device to be described later). Represents). The slow axis direction of the O plate 1 represents the projection of the liquid crystal director. The same angle reference was used in Tables 2 to 4 described later.

[Production Example 2]
In the above Production Example 1, a circularly polarizing plate was prepared in the same manner as in Production Example 1 except that the polarizing plate, the A plate 1 and the O plate 1 were laminated in this order so as to have the angular arrangement shown in Table 2. Created.

[Production Example 3]
(A plate)
A norbornene-based resin film [trade name “Zeonor Film” manufactured by Optes Co., Ltd.] having a retardation of 110 nm and a Nz coefficient of 1 was used as “A plate 2” as it was.

(Creation of circular polarizer)
In Production Example 1, a circularly polarizing plate was obtained by laminating to have the angular arrangement shown in Table 3 in the same manner as in Production Example 1 except that the A plate 2 was used instead of the O plate 1.

  In the above Production Example 3, the circularly polarizing plate was formed in the same manner as in Production Example 3 except that the polarizing plate, the A plate 1 and the A plate 2 were laminated in this order so as to have the angular arrangement shown in Table 4. Created.

[Example 1]
(Liquid crystal cell)
From the liquid crystal display device [trade name “iPod Classic” manufactured by Apple Inc.] having a transflective ECB mode liquid crystal panel, the liquid crystal panel is taken out, and all the optical films disposed above and below the liquid crystal cell are removed. The glass surface (front and back) was washed.

(Formation of liquid crystal panel)
The acrylic polarizing plate (thickness: 20 μm) was used for the circularly polarizing plate produced in Production Example 1 on the surface on the viewing side of the liquid crystal cell and the polarizing plate produced in Production Example 4 on the other surface of the liquid crystal cell. And laminated. The laminated structure and the arrangement angle of each layer in this liquid crystal panel are as shown in Table 5.

  The angle in Table 5 is an angle with the long side direction (right direction) of the screen as the reference of the angle (0 °) when the liquid crystal panel is observed from the viewing side (counterclockwise is the positive angle). Represents. The slow axis direction of the O plate 1 represents the projection of the director of the liquid crystal, and the rubbing direction of the liquid crystal cell substrate is equal to the director direction of the liquid crystal molecules near the substrate interface. The same angle reference was used in Tables 6 and 7 described later.

(Formation of liquid crystal display device)
A liquid crystal display device was formed by incorporating the liquid crystal panel formed above into the backlight system of the original liquid crystal display device again.

[Comparative Example 1]
Example 1 is the same as Example 1 except that the circularly polarizing plate produced in Production Example 3 was used instead of the circularly polarizing plate having the O plate produced in Production Example 1 as the polarizing plate on the viewing side. Thus, a liquid crystal panel and a liquid crystal display device were formed. The laminated structure and the arrangement angle of each layer in the liquid panel of Comparative Example 1 are as shown in Table 6.

[Comparative Example 2]
In Example 1 above, instead of using the circularly polarizing plate having the O plate prepared in Production Example 1 as the viewing side polarizing plate, the circularly polarizing plate having no O plate produced in Production Example 3 was used. In the same manner as in Example 1, a liquid crystal panel and a liquid crystal display device were formed. The laminated structure and the arrangement angle of each layer in the liquid panel of Comparative Example 2 are as shown in Table 7.

[Evaluation results]
The front contrast of the liquid crystal display devices obtained in Examples and Comparative Examples was 319 in Example 1, 172 in Comparative Example 1, and 124 in Comparative Example 2. Moreover, the isocontrast diagram showing the angle dependence of contrast is shown in FIGS. Further, FIG. 8 shows the contrast when the polar angle is changed in the azimuth angle 0-180 ° direction (left-right direction of the screen), and the polar angle is changed in the azimuth angle 90-270 ° direction (up-down direction of the screen). The contrast in each case is shown in FIG.

  In addition, Table 8 shows the viewing angles obtained in the upper, lower, left, and right sides of the screen based on the results of FIGS.

  As can be seen from the above results, the liquid crystal display device of Comparative Example 2 having the O plate on the opposite side (light source unit side) to the viewing side compared to the liquid crystal display device of Comparative Example 1 having no O plate is Although the front contrast and viewing angle characteristics were improved, it was not sufficient. On the other hand, according to the liquid crystal display device according to the embodiment of the present invention, it can be seen that the front contrast is high and the viewing angle characteristics are improved in all directions.

It is a schematic sectional drawing which represents typically the laminated structure of a liquid crystal cell, a polarizing plate, a 1st anisotropic optical element, and a 2nd anisotropic optical element in the liquid crystal display device of this invention. It is a figure which represents notionally the schematic cross section of the liquid crystal cell of ECB mode. FIG. 2A shows the time when no voltage is applied, and FIG. 2B shows the time when a voltage is applied. It is a schematic sectional drawing for demonstrating the tilt angle of a 2nd anisotropic optical element. It is a schematic sectional drawing showing one Embodiment of the liquid crystal display device of this invention. It is an isocontrast diagram of the liquid crystal display device of an Example. 6 is an isocontrast diagram of the liquid crystal display device of Comparative Example 1. FIG. 10 is an isocontrast diagram of the liquid crystal display device of Comparative Example 2. FIG. In the liquid crystal display device of an Example and a comparative example, it is a graph showing the contrast change at the time of changing a polar angle in an azimuth angle 0-180 degree direction. In the liquid crystal display device of an Example and a comparative example, it is a graph showing the contrast change at the time of changing a polar angle in an azimuth 90-180 degree direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal cell 11, 12 Substrate 13 Liquid crystal layer 21, 22 Polarizing plate 31, 32 Anisotropic optical element 41, 42 Anisotropic optical element 60 Transflective reflector 81 Light source 82 Reflective film 83 Diffuser plate 84 Prism sheet 100 Liquid crystal display Equipment 101 Circular polarizing plate 102 Elliptical polarizing plate (circular polarizing plate)
200 Light source unit

Claims (8)

A liquid crystal cell having a liquid crystal layer sandwiched between a pair of transparent substrates provided with electrodes;
A first polarizing plate disposed on the viewing side of the liquid crystal cell;
A first anisotropic optical element disposed between the liquid crystal cell and the first polarizing plate;
A second anisotropic optical element disposed between the first anisotropic optical element and the liquid crystal cell,
The first anisotropic optical element has an in-plane slow axis direction refractive index of nx ₁ , an in-plane fast axis direction refractive index of ny ₁ , and a thickness direction refractive index of nz ₁ . In this case, nx ₁ > ny ₁ ≧ nz ₁ is satisfied, the second anisotropic optical element is formed of a liquid crystalline material, and the orientation direction of the liquid crystalline material is the thickness direction of the anisotropic optical element. A liquid crystal display device having a continuously changing portion.   The liquid crystal display device according to claim 1, wherein the first polarizing plate, the first anisotropic optical element, and the second anisotropic optical element are stacked so as to form a circularly polarizing plate.   The liquid crystal display device according to claim 2, wherein the front retardation of the first anisotropic optical element is 200 to 300 nm, and the front retardation of the second anisotropic optical element is 50 to 200 nm. .   The liquid crystal display device according to claim 1, wherein the liquid crystalline material forming the second anisotropic optical element is a rod-like liquid crystalline compound having positive refractive index anisotropy.   The said 2nd anisotropic optical element is arrange | positioned so that the birefringence of the liquid crystalline molecule | numerator near the transparent substrate of the liquid crystal cell in the voltage application state of the said liquid crystal cell may be compensated. 2. A liquid crystal display device according to item 1.   The liquid crystal display device according to claim 1, further comprising a circularly polarizing plate on a side opposite to the first polarizing plate of the liquid crystal cell.   The liquid crystal display device according to claim 1, wherein the liquid crystal cell is an ECB mode liquid crystal cell.   The liquid crystal display device according to claim 1, further comprising a transflective plate on a side opposite to the first polarizing plate of the liquid crystal cell.