JP2012252084A - Liquid crystal panel and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal panel employing a VA (vertical alignment) system and having high luminance, high contrast and a wide viewing angle, and a liquid crystal display device.SOLUTION: The liquid crystal panel comprises: a first polarizer disposed in one side of a liquid crystal cell employing a multi-domain VA system; and a second polarizer disposed in the other side of the liquid crystal cell. A first quarter-wave plate is disposed between the first polarizer and the liquid crystal cell, and a second quarter-save plate is disposed between the second polarizer and the liquid crystal cell. Each of the first quarter-wave plate and the second quarter-wave plate preferably shows a frontal retardation of 90 to 180 nm and satisfies the relationship of nx>nz>ny in the refractive indices thereof.

Description

  The present invention relates to a VA liquid crystal panel and a liquid crystal display device.

  A liquid crystal display (LCD) is a device that displays characters and images using the electro-optical characteristics of liquid crystal molecules, and is widely used in mobile phones, notebook computers, liquid crystal televisions, and the like. In general, a liquid crystal panel in which polarizing plates are arranged on both sides of a liquid crystal cell is used for the LCD. The liquid crystal cell has a configuration in which, for example, a spacer is disposed between a pair of substrates, and a liquid crystal layer is sandwiched in a space between the pair of substrates. One substrate is provided with a switching element (for example, TFT) for controlling the electro-optical characteristics of liquid crystal molecules, and a scanning line for supplying a gate signal to the switching element and a signal line for supplying a source signal.

  The liquid crystal display device utilizes the fact that the polarization state of light transmitted through the liquid crystal cell changes variously by applying a voltage to the liquid crystal cell (liquid crystal layer) and controlling the alignment direction of the liquid crystal molecules in the liquid crystal layer. Thus, bright display (white display) and dark display (black display) are possible. In general, the “normally black mode” is for displaying black in a non-driving state where no voltage is applied to the liquid crystal cell, and the “normally white mode” is for displaying black when the voltage is applied to the liquid crystal cell. ".

  A vertical alignment (VA) mode is known as a driving mode of a liquid crystal cell used in an LCD. In the VA liquid crystal cell, since liquid crystal molecules have an alignment substantially perpendicular to the substrate surface in a non-driven state, light incident on the liquid crystal cell passes through the liquid crystal layer with almost no change in the plane of polarization. Therefore, when a polarizing plate is disposed above and below the VA liquid crystal cell so that the absorption axis directions are orthogonal to each other, black display can be obtained in a non-driven state (normally black mode). On the other hand, when the polarizing plates are arranged above and below the VA liquid crystal cell so that the absorption axis directions are parallel to each other, white display can be obtained in a non-driven state (normally white mode).

  Since the polarization plane of the light transmitted through the VA liquid crystal cell in the non-driven state is hardly changed, the normally black VA liquid crystal panel can obtain almost perfect black display and has high contrast. . On the other hand, normally white liquid crystal panels have high transmittance, and are expected to reduce power consumption by improving white luminance.

  In order to realize a wide viewing angle of a VA liquid crystal display device, a multi-domain VA liquid crystal cell that tilts liquid crystal molecules in different directions when a voltage is applied is widely used. A multi-domain VA type liquid crystal cell, for example, tilts liquid crystal molecules in four directions of 45 degrees, 135 degrees, 225 degrees, and 315 degrees counterclockwise with respect to the longitudinal direction of the liquid crystal cell for each pixel. The pixel is divided into a plurality of domains. In this way, by allowing the liquid crystal cells to have liquid crystal molecules arranged in different directions, the field of view is not limited to a specific direction, and a wide viewing angle is realized.

  In addition, in a normally black mode VA liquid crystal panel, it has been proposed to increase the viewing angle by using various optical compensation films in addition to multi-domain liquid crystal cells (for example, Patent Document 1). reference). However, since normally white mode VA liquid crystal panels have hardly been put to practical use, little consideration has been given to widening the viewing angle.

JP 2004-46065 A

  In view of the above situation, an object of the present invention is to provide a normally white mode VA liquid crystal panel and a liquid crystal display device having high contrast and a wide viewing angle.

  As a result of the study by the present inventors, the multi-domain VA liquid crystal cell has circular polarizing plates composed of a quarter-wave plate and a polarizer above and below the multi-domain VA liquid crystal cell, and the quarter-wave plate has predetermined three-dimensional refractive index characteristics It was found that a liquid crystal panel having a high contrast and a wide viewing angle are possible.

  The present invention provides a liquid crystal cell, a first polarizer disposed on one side of the liquid crystal cell, a second polarizer disposed on the other side of the liquid crystal cell, the first polarizer and the liquid crystal A normally white mode VA comprising a first quarter-wave plate disposed between the cell and a second quarter-wave plate disposed between the second polarizer and the liquid crystal cell. The present invention relates to a liquid crystal panel. Furthermore, this invention relates to a liquid crystal display device provided with the said liquid crystal panel. The liquid crystal cell is a multi-domain VA liquid crystal cell.

  The angle formed between the absorption axis direction of the first polarizer and the slow axis direction of the first quarter-wave plate is preferably about 45 °. It is preferable that the slow axis direction of the first quarter wave plate and the slow axis direction of the second quarter wave plate are orthogonal to each other. The first quarter wavelength plate and the second quarter wavelength plate preferably have a front retardation of 90 to 180 nm and a refractive index of nx> nz> ny. Here, nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the plane of the quarter wavelength plate, respectively, and nz is the refractive index in the thickness direction of the quarter wavelength plate. .

  In one embodiment, the absorption axis direction of the first polarizer and the absorption axis direction of the second polarizer are parallel. The liquid crystal cell preferably has an average front retardation of 190 nm to 350 nm when not driven, that is, when displaying black.

  Since the liquid crystal panel of the present invention is configured so that circularly polarized light is incident on the liquid crystal cell, even in a multi-domain VA liquid crystal cell, even when the direction in which the liquid crystal molecules are tilted is shifted from the desired direction when a voltage is applied The light leakage in black display can be suppressed and the contrast in the front direction can be improved. Furthermore, because the quarter-wave plates constituting the circularly polarizing plates disposed above and below the liquid crystal cell have predetermined three-dimensional refractive index characteristics, light leakage during black display is also possible for oblique light. It is suppressed. Therefore, the liquid crystal panel of the present invention can achieve high contrast and a wide viewing angle when adopting the normally white mode.

It is a typical sectional view of a liquid crystal panel by one embodiment of the present invention. It is a perspective view showing typically the arrangement relation of a polarizer and a quarter wave plate in a liquid crystal panel by one embodiment of the present invention. It is typical sectional drawing which shows an example of a structure of the liquid crystal display device of this invention. FIG. 6 is a cone diagram illustrating a measurement result of contrast in the liquid crystal display device of Example 1. FIG. 10 is a cone diagram illustrating a measurement result of contrast in the liquid crystal display device of Example 2. FIG. 11 is a cone diagram illustrating a measurement result of contrast in the liquid crystal display device of Example 3. FIG. 10 is a cone diagram illustrating a measurement result of contrast in the liquid crystal display device of Comparative Example 1. FIG. 10 is a cone diagram illustrating a measurement result of contrast in the liquid crystal display device of Comparative Example 2. 10 is a cone diagram illustrating a measurement result of contrast in the liquid crystal display device of Comparative Example 3. FIG.

[Outline of LCD panel configuration]
FIG. 1 is a schematic sectional view of a liquid crystal panel according to an embodiment of the present invention. The liquid crystal panel 50 of the present invention includes a first polarizer 31 on one side of the liquid crystal cell 10 and a second polarizer 32 on the other side of the liquid crystal cell. A first quarter-wave plate 41 is disposed between the first polarizer 31 and the liquid crystal cell 10, and a second 1/1 is disposed between the second polarizer 32 and the liquid crystal cell 10. A four-wave plate 42 is arranged. In the liquid crystal display device using the liquid crystal panel of the present invention, either the first quarter wavelength plate 41 side or the second quarter wavelength plate 42 side is the viewing side, and the other is the light source side.

  Note that in this specification, the terms “viewing side” and “light source side” are used for convenience, but a liquid crystal display device including the liquid crystal panel of the present invention does not necessarily have a light source. For example, as long as it is a liquid crystal display device that can be viewed from both the front and back surfaces of the liquid crystal panel, the light source may not be provided, and a configuration in which light is incident from the side surface of the liquid crystal panel may be used.

  FIG. 2 is a schematic perspective view of a liquid crystal panel according to an embodiment of the present invention. As shown in FIG. 2, the angle formed by the absorption axis direction 31a of the first polarizer 31 and the slow axis direction 41s of the first quarter-wave plate 41 is preferably about 45 °. The angle formed by the absorption axis direction 32a of the second polarizer 32 and the slow axis direction 42s of the second quarter-wave plate 42 is preferably about 45 °. Thus, a circularly polarizing plate is formed by setting the angle formed by the absorption axis direction of the polarizer and the slow axis direction of the quarter-wave plate to about 45 °. It is preferable that the slow axis direction 41s of the first quarter-wave plate and the slow axis direction 42s of the second quarter-wave plate are orthogonal to each other.

  Here, the term “orthogonal” in the present specification is not limited to the case where the angle is strictly 90 °, and the angle between the two is generally in the range of 85 ° to 95 °, preferably 88 to 92 °, More preferably, it is 89 ° to 91 °. “Parallel” is not limited to the case where the angle is strictly 0 °, and the angle formed by both is generally in the range of 0 ± 5 °, preferably 0 ± 2 °, more preferably 0 ± 1 °. is there. About 45 ° refers to a range of approximately 40 ° to 50 °, preferably 43 ° to 47 °, and more preferably 44 ° to 46 °. Further, in this specification, unless otherwise specified, the sign (positive / negative) of the angle is not limited, and may be counterclockwise (+) or clockwise (−).

  In one embodiment, the absorption axis direction 31a of the first polarizer 31 and the absorption axis direction 32a of the second polarizer 32 are parallel. The liquid crystal display panel of the present invention according to this embodiment is a normally white mode liquid crystal panel.

[Liquid Crystal Cell]
The liquid crystal cell is a multi-domain VA liquid crystal cell and has a configuration in which a liquid crystal layer is sandwiched between a pair of substrates. As shown in FIG. 1, the liquid crystal cell 10 has a space formed by arranging a spacer (not shown) between a pair of substrates 11 and 12, and a liquid crystal layer 13 is sandwiched in the space. ing. One of the pair of substrates 11 and 12 (active matrix substrate) includes, for example, a switching element (for example, TFT) that controls the electro-optical characteristics of liquid crystal, a scanning line that supplies a gate signal to the active element, and And a signal line for transmitting a source signal. For example, a color filter is provided on the other of the pair of substrates 11 and 12.

  The color filter may be provided on the active matrix substrate side. Or, for example, when RGB three-color light sources (which may include multi-color light sources) are used as illumination means of the liquid crystal display device as in the field sequential method, the color filter may be omitted. Good. The distance (cell gap) between the pair of substrates is controlled by a spacer, for example. The cell gap is, for example, in the range of 1.0 to 7.0 μm. For example, an alignment film made of polyimide is provided on the side of each of the substrates 11 and 12 in contact with the liquid crystal layer 13. Alternatively, for example, when the alignment of liquid crystal molecules is controlled using a fringe electric field formed by a patterned transparent substrate, the alignment film may be omitted.

  The liquid crystal molecules in the liquid crystal cell are aligned in the normal direction of the substrate surface when no voltage is applied to the liquid crystal layer, and are aligned in a direction parallel to the substrate when a voltage is applied to the liquid crystal layer. To do. In the multi-domain liquid crystal cell used in the present invention, each pixel is divided into a plurality of domains, and the arrangement direction at the time of voltage application is different for each domain. For example, when each pixel is divided into four domains, the liquid crystal molecules are tilted in four directions of 45 degrees, 135 degrees, 225 degrees, and 315 degrees counterclockwise with respect to the longitudinal direction of the liquid crystal cell. Each domain is configured. In this way, by allowing the liquid crystal cells to have liquid crystal molecules arranged in different directions, the field of view is not limited to a specific direction, and a wide viewing angle is realized.

  The liquid crystal cell preferably has an average front retardation of 190 nm to 350 nm at a wavelength of 590 nm when a voltage is applied, that is, when the liquid crystal panel displays black. If the average front retardation in the driving state of the liquid crystal cell is within the above range, the polarization plane of linearly polarized light that has passed through the polarizer on the light source side and entered the liquid crystal cell is rotated by about 90 ° by the birefringence of the liquid crystal layer. Black display is possible when a voltage is applied. The average front retardation of the liquid crystal cell is an average value of retardation in each domain. The retardation of the liquid crystal cell can be appropriately set by adjusting, for example, the birefringence of the liquid crystal molecules and the distance between the pair of substrates of the liquid crystal cell (cell gap).

[Polarizer]
The first polarizer 31 and the second polarizer 32 are not particularly limited as long as they emit incident light having an arbitrary polarization state as linearly polarized light, and various types can be used. Examples of such polarizers include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene / vinyl acetate copolymer partially saponified films, and iodine and dichroic dyes. Examples thereof include a polyene-based oriented film such as a film obtained by adsorbing a color substance and uniaxially stretched, a polyvinyl alcohol dehydrated product or a polyvinyl chloride dehydrochlorinated product.

[¼ wave plate]
The first quarter wavelength plate 41 and the second quarter wavelength plate 42 have a front retardation of ¼ of the wavelength λ. The front retardation Re is the difference (nx−ny) between the refractive index nx in the slow axis direction and the refractive index ny in the fast axis direction in the plane of the quarter wavelength plate, and the thickness d of the quarter wavelength plate. Product (nx−ny) × d. In addition, it is not necessary that the retardation is “1/4 wavelength” or “λ / 4”, and the retardation is strictly ¼ times the wavelength λ, and linearly polarized light is converted into substantially circularly polarized light. Any range is acceptable. “Substantially circularly polarized light” may include not only completely circularly polarized light but also elliptically polarized light that is close to perfect circularly polarized light, that is, whose ellipticity is close to 1. For example, those having a retardation Re in the range of 90 to 180 nm at the wavelength λ = 590 nm are included in the “¼ wavelength”. The first quarter wavelength plate and the second quarter wavelength plate preferably have a retardation Re at a wavelength λ = 590 nm of 90 nm to 180 nm, and more preferably 110 nm to 160 nm.

Is preferably a plane retardation Re ₁ of the first quarter-wave plate and the front retardation Re ₂ of the second quarter-wave plate is substantially the same value. The difference between Re ₁ and Re ₂ is most preferably 0, but practically, the difference between Re ₁ and Re ₂ may be within a range of ± 20 nm, preferably ± 10 nm. When the slow axis direction of the first quarter-wave plate and the slow axis direction of the second quarter-wave plate are orthogonal to each other, and the difference between the front retardations is small, the letter in the front direction Acts so that the foundations cancel each other. Therefore, the panel transmittance when no voltage is applied (when white is displayed) is increased, and a liquid crystal display device with high white luminance can be obtained.

It is preferable that the first quarter wavelength plate and the second quarter wavelength plate satisfy the relationship of refractive index nx>nz> ny. In other words, in the first quarter wavelength plate and the second quarter wavelength plate, the Nz coefficient represented by (nz−nz) / (nx−ny) may be greater than 0 and less than 1. preferable. When Nz ₁ and Nz ₂ are within the above ranges, light leakage in an oblique direction is reduced in the driving state of the liquid crystal cell (during black display). That is, since the black luminance in the oblique direction is small, a high contrast, normally white mode liquid crystal panel can be obtained with a wide viewing angle. Note that nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the film plane, respectively, and nz is the refractive index in the film normal direction.

When Nz coefficient Nz ₂ of the first and Nz coefficient Nz ₁ quarter wave plate of the second quarter-wave plate is large, there is a tendency that the brightness is increased in the oblique direction in black display. On the other hand, when Nz ₁ and Nz ₂ are small, the luminance during white display tends to be small. Therefore, Nz ₁ and Nz ₂ are each more preferably 0.1 to 0.9, and further preferably 0.2 to 0.8.

  A quarter-wave plate satisfying the relationship of nx> nz> ny is in the thickness direction due to the stress of the shrink film as disclosed in, for example, JP-A-5-157911 and JP-A-2007-93936. It is obtained by a stretching method for orienting molecules. The stretching temperature and stretching ratio at the time of stretching can be appropriately determined according to the composition of the film. Moreover, the quarter wave plate does not need to be composed of a single film, and may be a laminate of two or more films. In addition, an alignment layer of a liquid crystal compound or the like can be used as the quarter wavelength plate. Examples of the quarter-wave plate in which two or more films are laminated include those in which a uniaxially stretched film (typically a positive A plate having an Nz coefficient of 1) and a positive C plate are laminated. Further, in addition to adjusting Nz, a quarter wavelength plate in which two or more films are laminated can be used from the viewpoint of adjusting retardation wavelength dispersion and the like.

  The material of the first quarter-wave plate and the second quarter-wave plate is not particularly limited. For example, polycarbonate resin, polyvinyl alcohol resin, triacetyl cellulose, diacetyl cellulose, tripropionyl cellulose, dipropionyl cellulose. Cellulose fatty acid esters such as cellulose ethers, cellulose resins such as cellulose ether, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyarylate resins, polyimide resins, cyclic polyolefin (polynorbornene) resins, polysulfone resins , Polyethersulfone resins, polyamide resins, polyolefin resins such as polyethylene and polypropylene, and the like.

[LCD panel]
As described above, the liquid crystal panel of the present invention includes the first polarizer 31, the first quarter-wave plate 41, the liquid crystal cell 10, the second quarter-wave plate 42, and the second polarizer. It is obtained by arranging 31 at a predetermined angle. In the manufacturing process, the members can be formed by sequentially laminating the members separately, or a member obtained by laminating several members in advance can be used. Further, the stacking order is not particularly limited.

  In particular, a first circularly polarizing plate in which a first polarizer and a first quarter-wave plate are laminated, and a second in which a second polarizer and a second quarter-wave plate are laminated. By preparing these circularly polarizing plates in advance and laminating them with the liquid crystal cell 10, it is possible to achieve excellent quality stability and assembly workability. The first polarizer and the first quarter-wave plate, and the second polarizer and the second quarter-wave plate may be directly laminated via an adhesive layer or the like. Further, a transparent protective layer as a polarizer protective film may be interposed. When the polarizer and the quarter-wave plate are bonded together without using another film, the quarter-wave plate can also serve as a transparent protective layer for the polarizer.

  The liquid crystal panel of the present invention can also include optical layers other than those described above and other members. As an example thereof, a transparent protective layer provided on the surface opposite to the side bonded to the quarter wave plate of the polarizer can be mentioned. Further, such a transparent protective layer may be further provided with a surface treatment layer such as an antireflection layer, an antisticking layer, a diffusion layer or an antiglare layer, and the like. In addition, it is also preferable to provide a brightness enhancement film on the viewing side further than the light source side polarizer. The brightness enhancement film is not particularly limited. For example, it transmits linearly polarized light having a predetermined polarization axis, such as a dielectric multilayer thin film or a multilayer laminate of thin film films having different refractive index anisotropy, and the like. For example, the light having the characteristic of reflecting can be used.

  Each optical member may be laminated as it is, but it is preferable that the optical members are bonded together via an adhesive layer or a pressure-sensitive adhesive layer. Any appropriate adhesive or pressure-sensitive adhesive can be adopted as the adhesive or pressure-sensitive adhesive forming the adhesive or pressure-sensitive adhesive layer. For example, acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate / vinyl chloride copolymers, modified polyolefins, epoxy-based, fluorine-based, natural rubber-based, rubber-based polymers such as synthetic rubber, etc. A base polymer can be appropriately selected and used.

  In the liquid crystal display device using the liquid crystal panel of the present invention, it is presumed that light leakage during driving of the liquid crystal cell (during black display) is suppressed by the following principle. Light from a light source such as a backlight is converted into linearly polarized light by entering the light source side polarizer 32. If the angle formed by the absorption axis direction of the polarizer 32 and the slow axis direction of the quarter-wave plate 42 is set to about 45, both constitute a circularly polarizing plate 92. Therefore, the linearly polarized light that has passed through the light source side polarizer 32 is converted into circularly polarized light when it enters the light source side ¼ wavelength plate 42. Circularly polarized light emitted from the quarter-wave plate 42 enters the liquid crystal cell 10. As described above, in the liquid crystal panel of the present invention, the liquid crystal cell 10 is set so that the front retardation during driving is approximately ½ wavelength. Therefore, even if the direction in which the liquid crystal molecules are tilted when a voltage is applied is deviated from the desired direction, the circularly polarized light incident on the liquid crystal cell 10 from the quarter-wave plate 42 side has a different polarity (reverse direction) from that at the time of incidence. It is emitted to the viewing side of the liquid crystal cell as circularly polarized light. Next, the circularly polarized light emitted from the liquid crystal cell 10 to the viewing side enters the quarter-wave plate 41 on the viewing side. When the slow axis direction 41s of the quarter-wave plate 41 on the viewing side and the slow axis direction 42s of the quarter-wave plate 42 on the light source side are orthogonal to each other, 1 / on the viewing side from the liquid crystal cell side. The light that has entered the four-wavelength plate 41 is converted into linearly polarized light that is orthogonal to the linearly polarized light that has passed through the light source side polarizer 32 when emitted to the viewing side polarizer 31 side.

  When the absorption axis direction 31 a of the viewing side polarizer 31 is parallel to the absorption axis direction 32 a of the light source side polarizer 32, the light emitted from the quarter wavelength plate 41 to the viewing side is transmitted by the viewing side polarizer 31. Absorbed. In this way, by causing the circularly polarized light to enter the liquid crystal cell, light leakage in black display of the normally white VA liquid crystal display device is suppressed even when the direction in which the liquid crystal molecules are tilted deviates from the desired direction when a voltage is applied. The contrast in the front direction can be improved. Furthermore, in the present invention, since the two quarter-wave plates have a predetermined refractive index characteristic as described above, light leakage in an oblique direction is also suppressed. Conventionally, in a normally black mode VA mode liquid crystal panel, nx ≧ ny> in order to cancel birefringence of liquid crystal molecules with respect to light propagating obliquely in the liquid crystal cell during black display (when not driven). It has been proposed to use a biaxial plate satisfying the three-dimensional refractive index of nz or a negative C plate having a large retardation in the thickness direction. On the other hand, when the normally white mode is adopted in the VA mode liquid crystal panel of the present invention, contrary to the case of the conventional normally black mode, it satisfies the three-dimensional refractive index of nx> nz> ny 1 By using the / 4 wavelength plate, light leakage in an oblique direction during black display is suppressed.

  Furthermore, when the viewing-side polarizer 31 and the quarter-wave plate 41 constitute the circularly polarizing plate 91, re-emission of external light reflected on the surface of the liquid crystal cell 10 or inside to the viewing side can be suppressed. That is, the angle between the absorption axis direction of the polarizer 31 and the slow axis direction of the quarter wave plate 41 of the external light (natural light) incident on the panel from the viewing side polarizer 31 side is set to about 45. Therefore, it reaches the liquid crystal cell 10 as circularly polarized light. When the light that reaches the liquid crystal cell is reflected to the viewing side on or inside the liquid crystal cell, the phase of the light is inverted, so the reflected light is circularly polarized in the reverse direction to that when it reaches the liquid crystal cell . Therefore, the reflected light is absorbed by the viewing side polarizer 31 and re-emission to the viewing side is suppressed. In particular, in the present invention, since the quarter-wave plate has a three-dimensional refractive index of nx> nz> ny, an apparent retardation angle change with respect to light propagating in an oblique direction is small. Therefore, the circularly polarizing plate 91 composed of the viewing-side polarizer and the quarter-wave plate acts as a circularly polarizing plate for light from an oblique direction, and the reflected light in the oblique direction is absorbed by the viewing-side polarizer. As a result, re-emission is suppressed.

[Liquid Crystal Display]
FIG. 3 is a schematic cross-sectional view of a liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device 100 includes a liquid crystal panel 50 and a direct-type backlight unit as the light source 80 disposed on the light source side of the liquid crystal panel 50. The direct type backlight unit includes a light emitting unit 81, a diffusion plate 82, and a prism sheet 83. Although FIG. 3 shows a case where the direct type is adopted as the backlight unit, the light source may be a sidelight type backlight unit or the like. The sidelight type backlight unit further includes a light guide plate, a light reflector, and the like in addition to the configuration of the direct type.

  The liquid crystal display device of the present invention is not necessarily a transmissive liquid crystal display device having a light source, but a reflective liquid crystal display device and a transflective liquid crystal display device having both transmissive and reflective properties. It may be. Further, the liquid crystal display device of the present invention can realize high panel transmittance because the liquid crystal panel employs a normally white mode.

  Examples of the present invention will be described together with comparative examples, but the present invention is not limited to the following examples. Measurement and evaluation of various properties and physical properties in each Example and each Comparative Example were performed by the following methods.

[Evaluation method]
(Brightness and contrast)
Using a low-intensity spectroradiometer (trade name “SR-UL2” manufactured by Topcon Corporation), the luminance during white display and black display was measured, and the contrast was calculated from the white luminance / black luminance. The measurement was performed at a distance of 1 m from the surface of the liquid crystal panel in a dark room.

(Retardation Re and Nz coefficient)
The retardation and Nz coefficient at a wavelength of 590 nm were obtained by tilting the film by 40 ° with the retardation value in the front direction and the slow axis direction as the center using the trade name “KOBRA21-ADH” manufactured by Oji Scientific Instruments. It calculated from the retardation value using the program attached to the apparatus. In addition, the value measured using the Abbe refractometer (The product made from Atago Co., Ltd. product name "DR-M4") was used for the average refractive index. The thickness was measured using an Anritsu digital micrometer “KC-351C type”.

[Example 1]
(Production of polarizer)
A polymer film (made by Kuraray Co., Ltd., trade name “VF-PS # 7500”) containing a 75 μm-thick polyvinyl alcohol resin as a main component is placed in 5 baths under the conditions [1] to [5] below, The film was immersed while applying tension in the direction, and stretched so that the final stretching ratio was 6.2 times the original film length. This stretched film was dried in an air circulation oven at 40 ° C. for 1 minute to produce a polarizer.

<Conditions>
[1] Swelling bath: 30 ° C. pure water [2] Dyeing bath: 30 ° C. aqueous solution containing 0.032 parts by weight of iodine and 0.2 parts by weight of potassium iodide with respect to 100 parts by weight of water .
[3] First cross-linking bath: 40 ° C. aqueous solution containing 3% by weight of potassium iodide and 3% by weight of boric acid.
[4] Second crosslinking bath: 60 ° C. aqueous solution containing 5% by weight of potassium iodide and 4% by weight of boric acid.
[5] Washing bath: A 25 ° C. aqueous solution containing 3% by weight of potassium iodide.

(Preparation of quarter wave plate)
A polymer film containing a resin (norbornene-based resin) obtained by hydrogenating a ring-opening polymer of norbornene-based monomer having a thickness of 100 μm (product name “ZEONOR FILM ZF-14-100” manufactured by Nippon Zeon Co., Ltd.) A 60 μm biaxially stretched polypropylene film (trade name “Torphan BO2873” manufactured by Toray Industries, Inc.) was bonded via an acrylic pressure-sensitive adhesive layer (thickness: 15 μm), and then the longitudinal direction of the film was maintained with a roll stretching machine. Then, the film was stretched under heating in an air circulation oven, and the biaxially stretched polypropylene film was peeled off together with the acrylic pressure-sensitive adhesive layer to prepare a retardation film, which had a front retardation at a wavelength of 590 nm. The retardation film was 147 nm and the Nz coefficient was 0.5. .

(Production of circularly polarizing plate)
A triacetyl cellulose film having a thickness of 80 μm (manufactured by Fuji Film, trade name “Fujitac 80UL”) was bonded to one surface of the polarizer via a polyvinyl alcohol adhesive. Next, polyvinyl alcohol is placed on the other surface of the polarizer such that the angle between the absorption axis direction of the polarizer and the slow axis direction of the quarter wavelength plate A is 45 °. A circularly polarizing plate was obtained by laminating with a system adhesive.

(Production of liquid crystal display device)
A multi-domain VA liquid crystal cell was prepared. The average front retardation when the liquid crystal cell was driven (white display) was measured with a micro-area birefringence meter (KOBRA-CCD manufactured by Oji Scientific Instruments, measurement wavelength: 590 nm) to be 270 nm.

  “The circular polarizing plate is placed on each of the upper and lower glass plates of the liquid crystal cell so that the quarter wavelength plate side faces the liquid crystal cell and the slow axis directions of the two quarter wavelength plates are orthogonal to each other. A liquid crystal panel was obtained by bonding together via an acrylic pressure-sensitive adhesive (thickness: 20 μm) (so that the absorption axis directions of the two polarizing plates were parallel). By bonding, a liquid crystal display device was manufactured.

[Examples 2 and 3, Comparative Example 1]
In the production of the quarter-wave plate of Example 1, the quarter-wave plates B, C having different Nz coefficients were changed by changing the temperature during stretching and adjusting the amount of heat shrinkage of the biaxially stretched polypropylene film. D was obtained. Instead of the quarter-wave plate A, a quarter-wave plate B (Example 2), a quarter-wave plate C (Example 3), and a quarter-wave plate D (Comparative Example 1) were used. A liquid crystal panel was produced in the same manner as in Example 1. By combining these liquid crystal panels with a backlight unit, a liquid crystal display device was produced.

[Comparative Example 2]
(Preparation of quarter wave plate)
A polymer film containing a resin (norbornene-based resin) obtained by hydrogenating a ring-opening polymer of norbornene-based monomer having a thickness of 100 μm (trade name “Zeonor Film ZF-14-100” manufactured by Nippon Zeon Co., Ltd.) While maintaining the film longitudinal direction, the film was stretched under heating in an air circulation oven to prepare a retardation film having a front retardation at a wavelength of 590 nm of 147 nm and an Nz coefficient of 1. This retardation film is referred to as “¼ wavelength plate E”.

  A liquid crystal panel was produced in the same manner as in Example 1 except that the quarter wavelength plate E was used instead of the quarter wavelength plate A. By combining these liquid crystal panels with a backlight unit, a liquid crystal display device was produced.

[Comparative Example 3]
A polymer film containing a resin obtained by hydrogenating a ring-opening polymer of norbornene monomer having a thickness of 100 μm (norbornene resin) (trade name “Zeonor Film ZF-14-100” manufactured by Nippon Zeon Co., Ltd.) A retardation film was produced by biaxially stretching using a stretching machine, and the retardation film had a front retardation at a wavelength of 590 nm of 141 nm and an Nz coefficient of 1.6. The quarter-wave plate F ”.

  A liquid crystal panel was produced in the same manner as in Example 1 except that the quarter wavelength plate F was used instead of the quarter wavelength plate A. By combining these liquid crystal panels with a backlight unit, a liquid crystal display device was produced.

[Reference Example 1]
In the production of the liquid crystal display device of Example 1, instead of laminating the circularly polarizing plates so that the slow axis directions of the two quarter-wave plates A are orthogonal, the two quarter-wave plates A The liquid crystal panel was obtained by pasting together via an acrylic adhesive (thickness: 20 μm) so that the slow axis directions were parallel (the absorption axis directions of the two polarizing plates were orthogonal). This liquid crystal panel was combined with a backlight unit to produce a normally black mode liquid crystal display device.

[Reference Example 2]
Instead of using the quarter wavelength plate A in the reference example 1, a liquid crystal panel was obtained using the same quarter wavelength plate E as used in the comparative example 2. This liquid crystal panel was combined with a backlight unit to produce a normally black mode liquid crystal display device.

[Evaluation results]
Table 1 shows the configurations of the liquid crystal display devices of the above Examples, Comparative Examples, and Reference Examples, white luminance in the front direction, and contrast. Moreover, the viewing angle distribution (cone diagram) of the contrast of the liquid crystal display device of an Example and a comparative example is shown to FIGS.

  As shown in Table 1, the normally black mode liquid crystal display device of the reference example has high contrast, but has low white luminance due to low panel transmittance. On the other hand, the white luminance of the normally white mode liquid crystal display device is about 15% higher than that of the liquid crystal display device of the reference example.

  Comparing Examples 1 to 3 and Comparative Examples 1 to 3 (FIGS. 4 to 9), the Nz coefficient of the quarter-wave plate disposed between the liquid crystal cell and the polarizer is set within a predetermined range, so that It can be seen that the contrast in the direction is improved, and a liquid crystal display device with a wide viewing angle can be obtained.

10 Liquid crystal cell 11, 12 Substrate 13 Liquid crystal layer 31, 32 Polarizer 31a, 32a Absorption axis direction 41, 42 1/4 wavelength plate 41s, 42s Slow axis direction 91 Circularly polarizing plate 92 Circularly polarizing plate 50 Liquid crystal panel 80 Light source 81 Light emitting unit 82 Diffuser plate 83 Prism sheet 100 Liquid crystal display device

Claims (4)

A liquid crystal cell, a first polarizer disposed on one side of the liquid crystal cell, a second polarizer disposed on the other side of the liquid crystal cell, and between the first polarizer and the liquid crystal cell A first quarter-wave plate disposed on the second polarizer and a second quarter-wave plate disposed between the second polarizer and the liquid crystal cell,
The liquid crystal cell is a multi-domain VA liquid crystal cell,
The angle formed by the absorption axis direction of the first polarizer and the slow axis direction of the first quarter wave plate is 45 ° ± 5 °,
The angle formed by the slow axis direction of the first quarter-wave plate and the slow axis direction of the second quarter-wave plate is 90 ° ± 5 °,
The first quarter-wave plate has a front retardation of 90 to 180 nm and a refractive index satisfying a relationship of nx>nz> ny,
The second quarter-wave plate has a front retardation of 90 to 180 nm and a refractive index satisfying a relationship of nx>nz> ny.
Normally white mode VA LCD panel;
However, nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the plane of the quarter wavelength plate, respectively, and nz is the refractive index in the thickness direction of the quarter wavelength plate.   The liquid crystal panel according to claim 1, wherein an angle formed between an absorption axis direction of the first polarizer and an absorption axis direction of the second polarizer is 0 ± 5 °.   The liquid crystal panel according to claim 1, wherein the liquid crystal cell has an average front retardation of 190 nm to 350 nm when the liquid crystal panel displays black.   A liquid crystal display device provided with the liquid crystal panel of any one of Claims 1-3.