JP4675597B2 - Optical compensation film, liquid crystal display device and polarizing plate - Google Patents

Description

The present invention relates to a VA mode liquid crystal display device using a polarizing plate having a polarizing film and a pair of protective films sandwiching the polarizing film.

  A liquid crystal display device usually has a liquid crystal cell and a polarizing plate. The polarizing plate comprises a protective film and a polarizing film, and is obtained by dyeing a polarizing film comprising a polyvinyl alcohol film with iodine, stretching, and laminating both surfaces with a protective film. In the transmissive liquid crystal display device, the polarizing plate is attached to both sides of the liquid crystal cell, and one or more optical compensation films may be disposed. In a reflective liquid crystal display device, a reflector, a liquid crystal cell, one or more optical compensation films, and a polarizing plate are arranged in this order. The liquid crystal cell includes a liquid crystal molecule, two substrates for encapsulating the liquid crystal molecule, and an electrode layer for applying a voltage to the liquid crystal molecule. The liquid crystal cell performs ON / OFF display depending on the alignment state of liquid crystal molecules, and can be applied to both transmission and reflection types. TN (Twisted Nematic), IPS (In-Plane Switching), OCB (Optically Compensatory Bend) ), VA (Vertically Aligned), and ECB (Electrically Controlled Birefringence) have been proposed.

  Optical compensation films are used in various liquid crystal display devices in order to eliminate image coloring and to expand the viewing angle. As the optical compensation film, a stretched birefringent polymer film has been conventionally used. Further, it has been proposed to use an optical compensation film having an optically anisotropic layer formed from low-molecular or high-molecular liquid crystalline molecules on a transparent support, instead of an optical compensation film made of a stretched birefringent film. Yes. Since liquid crystalline molecules have various alignment forms, the use of liquid crystalline molecules can realize optical properties that cannot be obtained with conventional stretched birefringent polymer films. Furthermore, the structure which doubles as a protective film and an optical compensation film by adding birefringence to the protective film of a polarizing plate is also proposed.

The optical properties of the optical compensation film are determined according to the optical properties of the liquid crystal cell, specifically, the difference in the display mode as described above. When liquid crystalline molecules are used, optical compensation films having various optical properties corresponding to various display modes of the liquid crystal cell can be produced. Optical compensation films using liquid crystal molecules have already been proposed for various display modes. For example, in a TN mode liquid crystal cell, the twisted structure of liquid crystal molecules is eliminated by applying a voltage, and optical compensation is performed with an optical compensation film formed by fixing the tilted alignment state on the substrate surface. The contrast viewing angle characteristic is improved by preventing leakage (see Patent Document 1). In addition, the optical compensation film for the parallel alignment liquid crystal cell also serves to improve the viewing angle characteristics of the optical compensation of the liquid crystal molecules aligned in parallel to the substrate surface and the orthogonal transmittance of the polarizing plate during black display in a voltage-free state. (See Patent Document 2). In the IPS mode liquid crystal cell, during black display in a voltage-free state, optical compensation is performed by an optical compensation film made of liquid crystal molecules aligned in parallel with the substrate surface, and the sheet improves the viewing angle characteristics of the orthogonal transmittance of the polarizing plate. It also serves (see Patent Document 3). Furthermore, in the OCB mode liquid crystal cell, the liquid crystal molecules in the center of the liquid crystal layer are vertically aligned when voltage is applied, and the tilted and aligned liquid crystal layer is optically compensated with an optical compensation film near the substrate interface to improve the viewing angle characteristics of black display. (See Patent Document 4). In the VA mode liquid crystal cell, the viewing angle characteristics of black display in a state where liquid crystal molecules are vertically aligned with respect to the substrate surface in the absence of applied voltage are improved by an optical compensation film (see Patent Document 5).
JP-A-6-214116 Japanese Patent Laid-Open No. 9-292522 Japanese Patent Laid-Open No. 10-54982 US Pat. No. 5,805,253 Japanese Patent No. 2866372

  The conventional optical compensation film for a TN mode liquid crystal cell can compensate the liquid crystal cell optically more accurately than before by using a film made of liquid crystal molecules instead of the stretched birefringent polymer film. However, even if liquid crystal molecules are used, it is very difficult to completely optically compensate the liquid crystal cell without any problem. For example, in the optical compensation film that has been proposed in the past, light leakage from the oblique direction of the polarizing plate during black display is recognized, and the viewing angle is not sufficiently expanded (to the extent that can be expected theoretically). It is. Similarly, light leakage is also observed in conventional IPS, OCB, and VA mode liquid crystal cell optical compensation films. Furthermore, since the optical compensation film for IPS and VA mode liquid crystal cells performs optical compensation only with the stretched birefringent polymer film, it is necessary to use a plurality of films. As a result, the thickness of the optical compensation film increases, It is disadvantageous for thinning. Moreover, since an adhesive layer is used for lamination | stacking of a stretched film, the adhesive layer contracted by the temperature / humidity change, and defects, such as peeling and a curvature between films, may generate | occur | produce.

The present invention has been made in view of the above problems, a simple structure, not only the display quality, it is an object to viewing angle to provide a V A mode liquid crystal display equipment, which is significantly improved.

According to the present invention, there is more accomplished VA mode liquid crystal display equipment of the following (1) to (5).
(1) VA having a pair of opposed substrates having electrodes on at least one of them, a liquid crystal layer sandwiched between the substrates, and first and second polarizing plates arranged outside the liquid crystal layer A mode liquid crystal display device,
The product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn is 0.1 to 1.0 μm,
Each of the first and second polarizing plates has a polarizing film and a pair of protective films sandwiching the polarizing film,
At least one of the pair of protective films has a slow axis substantially coinciding with the direction in which the average refractive index of the film surface is maximized, and the slow axis of the protective film on the side close to the liquid crystal layer and the The absorption axis of the polarizing film intersects at 20 ° to 70 °,
The protective film disposed on the side close to the liquid crystal layer of the pair of protective films has a thickness d ₁ (nm), and has three average refractive indexes nx, ny in the x, y, and z axis directions orthogonal to each other. And nz, the main average refraction in a plane parallel to the surface of the liquid crystal layer is nx and ny (where ny <nx), and the main average refractive index in the thickness direction of the liquid crystal layer is nz. At an arbitrary wavelength λ in the optical region,
−5 nm ≦ {(nx−ny) × d ₁ } ≦ 50 nm, and
50 nm ≦ [{(nx + ny) / 2−nz} × d ₁ ] ≦ 300 nm
VA mode liquid crystal display device that satisfies the above relationship.
(2) The VA mode liquid crystal display device according to (1), wherein the liquid crystal layer includes a nematic liquid crystal material, and liquid crystal molecules of the nematic liquid crystal material are aligned perpendicularly to ± 5 ° with respect to the surfaces of the pair of substrates during black display.
(3) The value of {(nx−ny) × d ₁ } of the protective film disposed on the side closer to the liquid crystal layer of the first and second polarizing plates is 2 to 30 nm (1) or (2) VA mode liquid crystal display device.
(4) The VA mode liquid crystal display according to any one of (1) to (3), wherein the slow axis of the protective film near the liquid crystal layer and the absorption axis of the polarizing film intersect at 40 ° to 50 °. apparatus.
(5) A retardation plate satisfying ny = nz and nx> ny is provided between the protective film on the side close to the liquid crystal layer of at least one of the first and second polarizing plates and the liquid crystal layer (1) The VA mode liquid crystal display device of any one of (4).

In the liquid crystal display device of (1 ), a polarizing plate in which the slow axis in at least one surface of the pair of protective films intersects the absorption axis of the polarizing film is used as the polarizing plate. Polarizing plate not only polarizing function, so contributing to the expansion of the viewing angle of the display device, a simple configuration, not only the display quality, V A (Vertical Alignment) viewing angle is greatly improved mode liquid crystal A display device can be provided. The polarizing plate is easily manufactured by laminating a total of three polymer films of a pair of protective films and the polarizing film by roll-to-roll by using a polarizing film prepared by using an oblique stretching method. This contributes to the improvement of the productivity of the liquid crystal display device. In addition, since the protective film of the said polarizing plate can also be functioned as an optical compensation layer, in this aspect, it becomes a liquid crystal display device excellent in display quality with a simpler configuration.
Further, in the VA mode liquid crystal display device of (1) , since the absorption axes of the polarizing films of the polarizing plates arranged with the liquid crystal layer sandwiched therebetween are orthogonal, the polarizing plate transmittance is low and the liquid crystals belonging to the normally black type are used. High contrast can be obtained in the aspect of the display device

  In the present specification, “45 °”, “parallel” or “orthogonal” means that the angle is within a range of strictly less than ± 5 °. The error from the exact angle is preferably less than 4 °, more preferably less than 3 °. Regarding the angle, “+” means the clockwise direction, and “−” means the counterclockwise direction. Further, the “slow axis” means a direction in which the refractive index is maximized. The “visible light region” means 380 nm to 780 nm. Further, the measurement wavelength of the refractive index is a value at λ = 550 nm in the visible light region unless otherwise specified.

  In this specification, unless otherwise specified, the term “polarizing plate” is cut into a size to be incorporated into a long polarizing plate and a liquid crystal device (in this specification, “cutting” includes “punching” and “cutting out”. It is used in the meaning including both of the polarizing plates. In this specification, “polarizing film” and “polarizing plate” are distinguished from each other, and “polarizing plate” is a laminate having a transparent protective film for protecting the polarizing film on at least one side of the “polarizing film”. Means.

As a result of research, the present inventor has a function of optically compensating a liquid crystal cell with the same configuration as a conventional liquid crystal display device by adjusting a material and a manufacturing method of the polarizing film, the protective film, and the liquid crystal cell. Succeeded in manufacturing an elliptical polarizing plate that has both. Furthermore, when using the polarizing plate to the liquid crystal display device is attached to a VA type liquid crystal cell, not only the display quality, viewing angle was significantly improved. Further, the conventional step of laminating while strictly adjusting the angle of one or a plurality of retardation films and the polarizing plate is not required, and it is possible to produce a polarizing plate in a roll-to-roll manner. That is, according to the present invention, a simple structure, it is possible to provide a display not quality only, VA-mode liquid crystal display equipment in which the viewing angle is greatly improved.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, constituent members of one embodiment of the liquid crystal display device of the present invention will be described in order.
FIG. 1 is a schematic view of an embodiment of a liquid crystal display device of the present invention. FIG. 2 is a schematic diagram of an embodiment of an IPS mode liquid crystal display device, and is shown as a reference example.

[Liquid Crystal Display]
First, the liquid crystal display device shown in FIG. 1 includes a liquid crystal cell (5 to 8), and an upper polarizing film 1 and a lower polarizing film 14 that are disposed with the liquid crystal cell interposed therebetween. The polarizing films 1 and 14 are sandwiched between a pair of transparent protective films 3 and 3a and 12 and 12a, respectively. The liquid crystal cells 5 to 8 are composed of a liquid crystal cell upper substrate 5, a liquid crystal cell lower substrate 8, and liquid crystal molecules 7 sandwiched between them, and the liquid crystal molecules 7 are rubbed on the opposing surfaces of the substrates 5 and 8. The orientation direction is controlled by the processing direction and the alignment film material.

  The upper polarizing plate is composed of a pair of transparent protective films 3a and 3 and a polarizing film 1 sandwiched between them (the transparent protective film 3 is disposed on the side close to the liquid crystal cell (5 to 8 in FIG. 1)). To do). The absorption axis 2 of the polarizing film 1 intersects with the slow axis 4 of the transparent protective film 3. Specifically, the angle α between the absorption axis 2 of the polarizing film 1 and the slow axis 4 of the transparent protective film 3 is preferably 10 ° to 90 °, more preferably 20 ° to 70 °, still more preferably 40 °. -50 °, particularly preferably 43-47 °. The angle formed by the slow axis of the other transparent protective film 3a (disposed on the side far from the liquid crystal cells 5 to 8) and the absorption axis 2 of the polarizing film 1 is not particularly limited, but α is preferable. Similar to range. The relationship between the absorption axis 15 of the lower polarizing film 14 and the slow axis 13 of the protective film 12 disposed on the side close to the liquid crystal cell is preferably the same.

  The slow axes of the pair of transparent protective films 3a and 3 are preferably substantially parallel to each other. It is preferable that the slow axis of one transparent protective film is parallel, since the effects of improving the mechanical stability of the polarizing plate and uniforming the optical performance can be obtained. In addition, when the slow axis of the transparent protective film disposed on the side far from the liquid crystal cell and the absorption axis of the polarizing film are substantially parallel, mechanical reliability such as dimensional change of the polarizing plate and curling prevention is improved. To do. The same effect can be obtained even if the slow axis of the transparent protective film disposed on the side far from the liquid crystal cell is orthogonal to the absorption axis of the polarizing film, and the transparent protective film has sufficient thickness and rigidity. For example, the same effect can be obtained even if the absorption axis of the polarizing film and the slow axis of the pair of protective films intersect at different angles. Alternatively, two protective films disposed on the side close to the liquid crystal layer may be used, and the slow axis of one protective film may intersect the polarizing plate absorption axis.

  In FIG. 1, the slow axes 4 and 13 of the protective films 3 and 12 near the liquid crystal cell of the polarizing film 1 and the polarizing film 14 of the upper polarizing plate and the lower polarizing plate are substantially parallel or orthogonal to each other. It is preferable. If the slow axes 4 and 13 of the transparent protective films 3 and 12 are orthogonal to each other, the optical characteristics of light perpendicularly incident on the liquid crystal display device are degraded by canceling out the birefringence of the respective protective films. Can be reduced. Further, in a mode in which the slow axes 4 and 13 are parallel to each other, when the liquid crystal layer has a residual phase difference, this phase difference can be compensated by birefringence of the protective film.

The protective film 3 disposed on the liquid crystal cell side of the upper polarizing film 1 or the protective film 12 disposed on the liquid crystal cell side of the lower polarizing film 14 satisfies the following optical characteristics at an arbitrary wavelength λ in the visible light region. To do.
−30 (nm) ≦ {(nx−ny) × d ₂ } ≦ 50 (nm), and −50 (nm) ≦ [{(nx + ny) / 2−nz} × d ₂ ] ≦ 300 (nm)
In the formula, d ₂ (nm) is the thickness of the protective film, nx and ny (where ny <nx) is the in-plane main average refractive index, and nx is the main average refractive index in the thickness direction. Nx, ny and nz are orthogonal to each other. In the present invention, the protective film exhibiting such optical characteristics is disposed so that the slow axis thereof intersects with the polarizing axis of the polarizing film as described above, so that the protective film has an optical compensation function of the liquid crystal cell. Yes. Details of the manufacturing method and materials of the protective film will be described later.

  The liquid crystal cell includes a liquid crystal layer formed of an upper substrate 5 and a lower substrate 8 and liquid crystal molecules 7 sandwiched between them. An alignment film (not shown) is formed on the surfaces of the substrates 5 and 8 that are in contact with the liquid crystal molecules 7 (hereinafter sometimes referred to as “inner surface”), and a rubbing treatment or alignment film applied on the alignment film is formed. The orientation of the liquid crystal molecules 7 in a state where no voltage is applied or a state where a voltage is applied is controlled by the material or the like. Further, on the inner surfaces of the substrates 5 and 8, a transparent electrode (not shown) capable of applying a voltage to the liquid crystal layer made of the liquid crystal molecules 7 is formed.

  The display mode of the liquid crystal layer is not particularly limited, and may be a liquid crystal layer in any display mode such as VA mode, IPS mode, ECB mode, TN mode, and OCB mode. In the present invention, the product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn is 0.1 to 1.0 μm. The optimum value of Δn · d varies depending on the display mode. In the transmission mode, the VA type, IPS type, and ECB type that do not have a twisted structure range from 0.2 to 0.4 μm, and the TN type ranges from 0.2 to 0.5 μm depending on the size of the twist angle. Further, in the OCB type, the optimum value is in the range of 0.6 to 1.0 μm. In these ranges, since the white display luminance is high and the black display luminance is small, a bright and high-contrast display device can be obtained. In addition, although the aspect of the display apparatus of the transmission mode provided with the upper side polarizing plate and the lower side polarizing plate was shown in FIG. 1, this invention may be the aspect of the reflection mode provided with only one polarizing plate, In such a case, since the optical path in the liquid crystal cell is doubled, the optimum value of Δn · d is about the above half value.

  Regarding the absorption axes 2 and 15 of the polarizing films 1 and 14, the slow axis directions 4 and 13 of the protective films 3 and 12, and the orientation direction of the liquid crystal molecules 7, the materials used for each member, the display mode, and the laminated structure of the members It can be adjusted to an optimum range according to the above. For example, in an aspect of a liquid crystal display device belonging to the VA type or IPS type normally black type, in order to obtain high contrast, the absorption axes 2 and 15 of the polarizing films 1 and 14 are substantially orthogonal to each other. Arrange to be. However, the liquid crystal display device of the present invention is not limited to this configuration.

Next, the driving principle of the embodiment of the VA mode liquid crystal display device will be described with reference to FIG.
In this embodiment, an example in which active driving is performed using a nematic liquid crystal having negative dielectric anisotropy as a field effect liquid crystal will be described. The liquid crystal display device shown in FIG. 1 has liquid crystal molecules 7 in the liquid crystal layer on the surfaces of the substrates 5 and 8 in a non-driving state in which a driving voltage is not applied to the transparent electrodes (not shown) of the liquid crystal cell substrates 5 and 8, respectively. With the result that the polarization state of the light passing therethrough hardly changes. Since the absorption axes 2 and 15 are orthogonal to each other, the light incident from the lower side (for example, the back electrode) is polarized by the polarizing film 14 and passes through the liquid crystal cells 5 to 8 while maintaining the polarization state. Is blocked by. That is, the liquid crystal display device of FIG. 1 realizes an ideal black display in the non-driven state. On the other hand, in a driving state in which a driving voltage is applied to a transparent electrode (not shown), the liquid crystal molecules 7 are tilted in a direction parallel to the surfaces of the substrates 5 and 8, and the light passing therethrough is polarized by the tilted liquid crystal molecules 7. Change state. Therefore, the light incident from the lower side (for example, the back electrode) is polarized by the polarizing film 14 and further passes through the liquid crystal cells 5 to 8 to change the polarization state and pass through the polarizing film 1. That is, in the liquid crystal display device shown in FIG. 1, white display is obtained in the driving state.

  Here, since an electric field is applied between the upper and lower substrates 5 and 8, a liquid crystal material having a negative dielectric anisotropy is used so that the liquid crystal molecules 7 respond in a direction perpendicular to the electric field direction. When an electrode is formed only on one of the substrates 5 and 8 and an electric field is applied in a lateral direction parallel to the substrate surface, a liquid crystal material having positive dielectric anisotropy may be used. it can.

  The features of the VA mode are high-speed response and high contrast. However, the conventional VA mode liquid crystal display device has a problem that the contrast is high in the front but deteriorates in an oblique direction. Since the liquid crystal molecules 7 are aligned perpendicular to the surfaces of the substrates 5 and 8 during black display, the liquid crystal molecules 7 have almost no birefringence when viewed from the front, so that the transmittance is low and high contrast is obtained. However, birefringence occurs in the liquid crystal molecules 7 when observed from an oblique direction. Furthermore, the crossing angle of the absorption axes 2 and 15 of the upper and lower polarizing films 1 and 14 is 90 ° orthogonal at the front, but is larger than 90 ° when viewed from an oblique direction. Because of these two factors, leakage light occurs in the oblique direction, and the contrast is lowered. In the liquid crystal display device of FIG. 1, a transparent protective film 3 exhibiting predetermined optical characteristics is arranged on the side close to the liquid crystal cell of the polarizing film 1 so that its slow axis 4 intersects the absorption axis 2 of the polarizing film 1. By arranging the transparent protective film 12 exhibiting predetermined optical characteristics on the side close to the liquid crystal cell of the polarizing film 14 so that its slow axis 13 intersects the absorption axis 15 of the polarizing film 14. The viewing angle characteristics of transmittance in black display are improved, and a wide viewing angle is achieved.

  In addition, since the liquid crystal molecules 7 are tilted during white display, the magnitude of birefringence of the liquid crystal molecules 7 when viewed from an oblique direction differs between the tilt direction and the opposite direction, resulting in differences in brightness and color tone. A structure called multi-domain in which one pixel of a liquid crystal display device is divided into a plurality of regions is preferable because the viewing angle characteristics of luminance and color tone are improved. Specifically, each pixel is composed of two or more (preferably 4 or 8) regions in which the initial alignment state of the liquid crystal molecules is different from each other, and averaging is performed. Can be reduced. Further, the same effect can be obtained even if each pixel is constituted by two or more different regions where the alignment direction of liquid crystal molecules continuously changes in a voltage application state.

  In order to form a plurality of regions having different alignment directions of the liquid crystal molecules 7 in one pixel, for example, a method of providing a slit in the electrode, providing a protrusion, changing the electric field direction, or imparting bias to the electric field density is used. Can be used. In order to obtain a uniform viewing angle in all directions, the number of divisions may be increased. However, a substantially uniform viewing angle can be obtained by using four or more divisions. In particular, it is preferable that the polarizing plate absorption axis is set at an arbitrary angle when dividing into eight.

  At the region boundary of each domain, the liquid crystal molecules 7 tend to hardly respond. In the normally black mode such as the VA mode, since black display is maintained, a decrease in luminance becomes a problem. Therefore, it is possible to reduce the boundary region between domains by adding a chiral agent to the liquid crystal material. On the other hand, since the white display state is maintained in the normally white mode, the front contrast is lowered. Therefore, a light shielding layer such as a black matrix covering the region may be provided.

  There are two types of drive systems, active matrix and passive matrix, for liquid crystal display devices, and liquid crystal display devices used in notebook personal computers, flat TVs, etc. generally use active matrix thin film transistors. It is preferable that the absorption axes 2 and 15 of the polarizing films 1 and 14 substantially cross at 45 ° with respect to the wiring for sending an electric signal to the active matrix thin film transistor because the viewing angle characteristic becomes a symmetrical structure. . The same applies not only to the VA mode but also to the TN and OCB modes. If the absorption axis of the polarizing plate is parallel or perpendicular to the long side of the liquid crystal cell substrate, wiring is necessary in consideration of the crossing angle between the signal line and the absorption axis. As shown in FIG. If the signal line is originally designed to be parallel or perpendicular to the long side of the liquid crystal cell substrate, the absorption axis of the liquid crystal cell substrate crosses at 45 ° with respect to the long side of the liquid crystal cell substrate. A corner is obtained. From this point of view, it is ideal that the absorption axes 2 and 15 of the polarizing films 1 and 14 in FIG. 1 intersect the long sides of the liquid crystal cell substrates 5 and 8 at + 45 ° or −45 °. is there. However, considering the case where the signal lines are not straight, it is preferable that the signal lines intersect at 45 ° ± 10 ° or −45 ° ± 10 °.

  A VA mode liquid crystal cell is formed by rubbing a nematic liquid crystal material having a negative dielectric anisotropy between Δn = 0.0813 and Δε = −4.6 between the upper and lower substrates 5 and 8, for example. A director indicating the orientation direction of molecules, that is, a so-called tilt angle of about 89 ° can be produced. The thickness d of the liquid crystal layer is not particularly limited, but can be set to about 3.5 μm when the liquid crystal having the characteristics in the above range is used. Since the brightness at the time of white display changes depending on the magnitude of the product Δn · d of the thickness d and the refractive index anisotropy Δn, Δn · d is 0.2 to 0.0 in order to obtain the maximum brightness. It is preferable to set it in the range of 5 μm. In addition, in the VA mode liquid crystal display device, the addition of a chiral material generally used in the TN mode liquid crystal display device is rarely used to degrade the dynamic response characteristics, but in order to reduce alignment defects. May be added. As described above, the multi-domain structure is advantageous for adjusting the alignment of the liquid crystal molecules in the boundary region between the domains.

In the above-described various liquid crystal display modes, the VA mode has been described in the so-called normally black mode in which black display is performed when no voltage is applied or low voltage is applied and white display is applied when a high voltage is applied. The invention is not limited to this, and may be an embodiment using the IPS mode, which is another normally black mode. Further, a mode using a normally white mode in which white display is performed when no voltage is applied or a low voltage is applied and black display is performed when a high voltage is applied, and an OCB mode, ECB mode, or TN mode liquid crystal cell is used. You can also. In addition, a liquid crystal cell in which the liquid crystal molecules of the nematic liquid crystal material are aligned substantially parallel to the surface of the substrate during black display can be used. Specifically, the liquid crystal molecules are parallel to the substrate surface when no voltage is applied. It is also possible to use an IPS mode or ECB mode liquid crystal cell that is aligned and displays black. In this embodiment, in order to obtain the effect of improving the viewing angle, the value of (nx−ny) × d ₁ of the protective film of the polarizing plate is set to around the value of Δn · d of the liquid crystal layer. preferable.

  The liquid crystal display device of the present invention is not limited to the configuration shown in FIG. 1, and may include other members. For example, a color filter may be disposed between the liquid crystal cell and the polarizing film. Further, as will be described later, an optical compensation film can be separately disposed between the liquid crystal cell and the polarizing plate. In the case of use as a transmission type, a cold cathode or a hot cathode fluorescent tube, or a backlight having a light emitting diode, a field emission element, or an electroluminescent element as a light source can be disposed on the back surface. In addition, the liquid crystal display device of the present invention may be of a reflective type. In such a case, only one polarizing plate may be disposed on the observation side, and reflected on the back surface of the liquid crystal cell or the inner surface of the lower substrate of the liquid crystal cell. Install the membrane. Of course, it is also possible to provide a front light using the light source on the liquid crystal cell observation side.

  The liquid crystal display device of the present invention includes an image direct view type, an image projection type, and a light modulation type. The present invention is particularly effective when applied to an active matrix liquid crystal display device using three-terminal or two-terminal semiconductor elements such as TFT and MIM. Of course, an embodiment applied to a passive matrix liquid crystal display device represented by STN type called time-division driving is also effective.

  The present invention is intended to improve the viewing angle of a liquid crystal display device by having a predetermined relationship between the slow axis of the transparent protective film of the polarizing plate and the absorption axis of the polarizing film. It is preferable to dispose an optical compensation film between the liquid crystal cell and the liquid crystal cell because the viewing angle is further improved. The optical compensation film is not particularly limited and may have any configuration as long as it has optical compensation capability. Examples thereof include a birefringent polymer film, and a laminate of an optically anisotropic layer composed of a transparent support and liquid crystal molecules formed on the transparent support. In the latter embodiment, the transparent protective films 3 and 12 on the side close to the liquid crystal layer of the polarizing plate may also serve as the support for the optically anisotropic layer.

  In order to improve the viewing angle of the VA mode, a method using a phase difference plate having a positive refractive index anisotropy and a phase difference plate having a negative refractive index anisotropy is described in JP-A-10-153802. Therefore, the method can be applied to the present invention. The retardation plate has three average refractive indexes nx, ny and nz in the x, y and z axis directions orthogonal to each other, the in-plane average refractive index is nx and ny, and the thickness direction average refractive index is nz. Where nx, ny = nz, nx> ny (hereinafter referred to as “optically anisotropic layer A”) and nx = ny, nz, nx> nz (wherein, And “optically anisotropic layer B”). When the laminated body of the optically anisotropic layer A and the optically anisotropic layer B is used as an optical compensation film, it is possible to prevent light leakage when viewed from an oblique direction of VA mode black display. Further, as described above, when the absorption axes 2 and 15 of the upper polarizing film 1 and the lower polarizing film 14 are arranged orthogonally, there is a problem that the crossing angle is deviated from a right angle and leakage light increases when observed obliquely. . It is known that this leakage light can be reduced by using a laminate in which the optically anisotropic layer A and the optically anisotropic layer B are laminated (see JP-A-2001-350022). The optically anisotropic layer B is effective for compensating the viewing angle of the liquid crystal molecules vertically aligned in the VA mode, but the optically anisotropic layer is effective for improving the polarizing plate viewing angle. A is also required. Therefore, when the laminate of the optically anisotropic layer A and the optically anisotropic layer B is used as an optical compensation film, the optical compensation of the viewing angle of the liquid crystal molecules vertically aligned in the VA mode, and the polarizing plate viewing angle It is advantageous for improvement.

Furthermore, the liquid crystal display device of the present invention may have an optical compensation film in which the optically anisotropic layer A and the optically anisotropic layer B described above are combined. There are various modes depending on the size of Δnd of the liquid crystal layer, the arrangement position of the layers, and the optical performance of the protective film of the polarizing plate.
For example, when the Re value ((nx−ny) × d ₁ ; d ₁ is the thickness of the protective film (nm)) of the protective film (3 or 12 in FIG. Using the isotropic layer A and the optically anisotropic layer B as an optical compensation film, between the liquid crystal cell and the polarizing plate (in FIG. 1, between the substrate 8 and the protective film 12, or between the protective film 3 and the substrate 5). (Between). At this time, it is preferable that the optically anisotropic layer A is disposed closest to the light source to reduce leakage light.

When the Re value of the protective film (3 or 12 in FIG. 1) of the polarizing plate is 0 nm and the Rth value ({(nx + ny) / 2−nz} × d ₁ ) is about 50 to 200 nm, the protective film is optical. Since the optical compensation ability similar to that of the anisotropic layer B is exhibited, only the optical anisotropic layer A is used as the optical compensation layer, and between the liquid crystal cell and the polarizing plate (between the substrate 8 and the protective film 12 in FIG. 1). Or between the protective film 3 and the substrate 5). At this time, it is effective to dispose the optically anisotropic layer A most below the liquid crystal cell from the light source, that is, on the light source side. Further, in order to compensate for the Rth deficiency of the protective film, an optically anisotropic layer B may be separately arranged.

  When both the Re value and the Rth value of the protective film (3 or 12 in FIG. 1) of the polarizing plate are not 0 nm, the protective film exhibits an optical compensation capability. Therefore, even if an optical compensation layer is not separately provided, the optical compensation effect is obtained. can get. In order for the transparent protective film to have a function as an optical compensation layer, it is preferable that the Re value of at least one protective film is 5 to 50 nm and the Rth value is 50 to 300 nm. Even when the transparent protective film has an optical compensation capability, an optically anisotropic layer A and an optically anisotropic layer B are separately provided to compensate for the shortage of the Re value and Rth value of the protective film. May be.

  In an embodiment in which an optical compensation film having an optically anisotropic layer is separately incorporated, the transparent protective film disposed on the side close to the liquid crystal cell of the polarizing plate can also serve as a support for the optically anisotropic layer. Therefore, you may incorporate in a liquid crystal display device as an integrated polarizing plate laminated | stacked in order of the transparent protective film, the polarizing film, the transparent protective film (it also serves as a transparent support body), and the optically anisotropic layer. Alternatively, a liquid crystal display device may be manufactured while sequentially stacking. In the liquid crystal display device, the order of the transparent protective film, the polarizing film, the transparent protective film (also serving as the transparent support of the optically anisotropic layer) and the optically anisotropic layer from the outside of the device (the side far from the liquid crystal cell) Is preferably laminated.

Next, the outline substantially schematic view of a liquid crystal display device is a reference example in FIG. The liquid crystal display device of the present embodiment has a configuration in which an optical compensation layer 10 is further incorporated into the liquid crystal display device shown in FIG. In FIG. 2, the same members as those in FIG. In FIG. 2, the protective film disposed outside the pair of protective films of the upper polarizing film 1 and the lower polarizing film 14 is omitted.

In the liquid crystal display device shown in FIG. 2, the optical characteristics of the protective film 12 satisfy the following relationship at an arbitrary wavelength λ in the visible light region.
−30 (nm) ≦ {(nx−ny) × d ₂ } ≦ 50 (nm), and −50 (nm) ≦ [{(nx + ny) / 2−nz} × d ₂ ] ≦ 300 (nm)
The definitions in the formula are as described above. Further, the liquid crystal display device of FIG. 2 includes an optical compensation layer 10 disposed adjacent to the protective film 12 in addition to the components of the liquid crystal display device of FIG. The optical compensation layer 10 is a film made of a compound having a discotic structural unit, and the discotic surface is oriented substantially perpendicular to the substrate surface. Furthermore, the alignment control direction of the optical compensation layer (for example, the rubbing axis when the alignment is controlled by a rubbing alignment film) and the slow axis 13 of the protective film 12 are on the absorption axis of the polarizing film. It arrange | positions substantially parallel with respect to. In this mode, light leakage when viewed from an oblique direction is prevented by making the retardation value of the layer (including the protective film of the polarizing film) through which light passes from the upper and lower polarizing films to the liquid crystal cell asymmetric. Has improved. In particular, this embodiment is effective in reducing oblique leakage light in an embodiment in which the absorption axes of the upper polarizing plate 1A and the lower polarizing plate 14A are orthogonal to each other.

  The lower polarizing plate 14A is obtained by integrally manufacturing the polarizing film 14, the protective film 12, and the optical compensation layer 10. By adopting such a configuration, the protective film 12 can also serve as a support for the optical compensation layer 10, which contributes to a reduction in the weight and thickness of the liquid crystal display device. In the present embodiment, the alignment control direction 11 of the optical compensation layer 10 and the slow axis 13 of the protective film 12 are arranged substantially parallel to the absorption axis 15 of the polarizing film 14, so that the integrated polarization When producing a plate, it is also advantageous in that the axis can be easily aligned.

The driving mode of the liquid crystal cell (5 to 8) of the present embodiment is not particularly limited, but is preferably an IPS mode liquid crystal cell.
FIG. 3 shows a schematic side sectional view of an IPS mode liquid crystal cell. An IPS mode liquid crystal cell usually has a plurality of pixels by matrix electrodes, but a part of one pixel is shown. A linear electrode 16 is formed inside a pair of transparent substrates 5 and 8, and an alignment control film (not shown) is formed thereon. The rod-like liquid crystal molecules 7 sandwiched between the substrates 5 and 8 are oriented so as to have a slight angle with respect to the longitudinal direction of the linear electrode 16 when no electric field is applied. In this case, the dielectric anisotropy of the liquid crystal is assumed to be positive. When an electric field is applied, the liquid crystal molecules 7 change their direction in the direction of the electric field.

  The light transmittance can be changed by sandwiching the IPS mode liquid crystal cell and arranging the polarizing plates 1A and 14A at a predetermined angle. The angle formed by the electric field direction with respect to the surface of the substrate 8 is preferably 20 degrees or less, more preferably 10 degrees or less, that is, substantially parallel. Hereinafter, in the present invention, those below 20 degrees are generically expressed as a parallel electric field. In addition, the effect does not change even if the electrode 16 is formed separately on the upper and lower substrates or only on one substrate.

As the liquid crystal material LC, nematic liquid crystal having a positive dielectric anisotropy Δε is used. The thickness (gap) of the liquid crystal layer was more than 2.8 μm and less than 4.5 μm. Thus, when the retardation value (Δn · d) is more than 0.25 μm and less than 0.32 μm, a transmittance characteristic having almost no wavelength dependency within the visible light range can be obtained more easily. By the combination of the alignment film and the polarizing plate described later, the maximum transmittance can be obtained when the liquid crystalline molecules are rotated 45 degrees from the rubbing direction to the electric field direction. The thickness (gap) of the liquid crystal layer is controlled by polymer beads. Of course, the same gap can be obtained with glass bead fiber or resin columnar spacers. The liquid crystal material LC is not particularly limited as long as it is a nematic liquid crystal. As the value of the dielectric anisotropy Δε is larger, the driving voltage can be reduced, and as the refractive index anisotropy Δn is smaller, the thickness (gap) of the liquid crystal layer can be increased, and the liquid crystal sealing time is shortened. In addition, gap variation can be reduced.
The nematic liquid crystal material contained in the liquid crystal layer may be composed of two or more domain regions having different alignment states.

  As described above, the display mode of the liquid crystal display device of this embodiment is not particularly limited, but the ECB mode and the IPS mode are preferably used. In the present embodiment, the product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn is preferably 0.2 to 1.2 μm. The optimum value of Δn · d is 0.2 to 0.5 μm. In these ranges, since the white display luminance is high and the black display luminance is small, a bright and high-contrast display device can be obtained. Note that these optimum values are values in the transmission mode, and in the reflection mode, the optical path in the liquid crystal cell is doubled. Therefore, the optimum Δnd value is about a half of the above value. The liquid crystal display device used in this embodiment is effective not only in the display mode but also in a mode applied to the VA mode, OCB mode, TN mode, HAN mode, and STN mode.

Hereinafter, materials used for various members usable in the liquid crystal display device of the present invention, manufacturing methods thereof, and the like will be described in detail.
[Polarizer]
A polarizing plate generally comprises a polarizing film and a pair of protective films that sandwich the polarizing film. In the polarizing plate according to the present invention, of the pair of protective films of the polarizing film, at least a protective film formed on a surface disposed closer to the liquid crystal cell exhibits specific optical characteristics described later. One embodiment of the polarizing plate of the present invention is a polarizing plate having an optical compensation capability, in which an optical compensation layer (also referred to as an “optically anisotropic layer”) formed from a liquid crystal compound is pasted. In addition, a polarizing plate having an optical compensation layer formed of a polymer film or liquid crystal compound having predetermined optical characteristics as a protective film may also have an optical compensation function, and a polarizing plate having such a configuration can also be used. . The optical compensation layer is preferably formed directly from liquid crystal molecules on the surface of the polarizing film or the protective film of the polarizing film, or from liquid crystal molecules via an alignment film. Specifically, the optically anisotropic layer can be formed by applying the coating liquid for the optically anisotropic layer to the surface of the polarizing film or the surface of the protective film of the polarizing film. In the former mode, a thin polarized light having a small stress (strain × cross-sectional area × elastic modulus) associated with a change in the size of the polarizing film without using a polymer film between the protective film of the polarizing film and the optically anisotropic layer. A plate can be made. When the polarizing plate according to the present invention is attached to a large liquid crystal display device, an image with high display quality is displayed without causing problems such as light leakage.

The polarizing film is preferably a coating type polarizing film represented by Optiva Inc., or a polarizing film made of a binder and iodine or a dichroic dye. Iodine and dichroic dye in the polarizing film exhibit deflection performance by being oriented in the binder. It is preferable that the iodine and the dichroic dye are aligned along the binder molecule, or the dichroic dye is aligned in one direction by self-assembly such as liquid crystal.
Currently, commercially available polarizers are made by immersing a stretched polymer in a solution of iodine or dichroic dye in a bath and allowing the iodine or dichroic dye to penetrate into the binder. Is common.
The commercially available polarizing film has iodine or dichroic dye distributed about 4 μm (about 8 μm on both sides) from the polymer surface, and a thickness of at least 10 μm is necessary to obtain sufficient polarizing performance. The penetrability can be controlled by the solution concentration of iodine or dichroic dye, the temperature of the bath, and the immersion time.
As described above, the lower limit of the binder thickness is preferably 10 μm. The upper limit of the thickness is preferably as thin as possible from the viewpoint of light leakage of the liquid crystal display device. It is preferably not more than a commercially available polarizing plate (about 30 μm), preferably 25 μm or less, and more preferably 20 μm or less. When the thickness is 20 μm or less, the light leakage phenomenon is not observed on a 17-inch liquid crystal display device.

The binder of the polarizing film may be cross-linked.
As the crosslinked binder, a polymer that can be crosslinked per se can be used. A polarizing film can be formed by reacting a polymer having a functional group or a binder obtained by introducing a functional group into a polymer between the binders by light, heat, or pH change. Moreover, you may introduce | transduce a crosslinked structure into a polymer with a crosslinking agent. Crosslinking is generally carried out by applying a coating liquid containing a polymer or a mixture of a polymer and a crosslinking agent on a transparent support and then heating. Since it is only necessary to ensure durability at the stage of the final product, the crosslinking treatment may be performed at any stage until the final polarizing plate is obtained.

  As the binder for the polarizing film, either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent can be used. As an example of a polymer, the thing similar to the polymer which can be utilized for preparation of the orientation film mentioned later is mentioned. Most preferred are polyvinyl alcohol and modified polyvinyl alcohol. The modified polyvinyl alcohol is described in JP-A-8-338913, JP-A-9-152509 and JP-A-9-316127. Two or more kinds of polyvinyl alcohol and modified polyvinyl alcohol may be used in combination.

  The addition amount of the crosslinking agent in the binder is preferably 0.1 to 20% by mass with respect to the binder. The orientation of the polarizing element and the wet heat resistance of the polarizing film are improved.

The polarizing film contains some crosslinking agent that has not reacted even after the crosslinking reaction has been completed. However, the amount of the remaining crosslinking agent is preferably 1.0% by mass or less and more preferably 0.5% by mass or less in the alignment film. In this way, even if the polarizing film is incorporated in a liquid crystal display device and used for a long time or left in a high temperature and high humidity atmosphere for a long time, the degree of polarization does not decrease.
The crosslinking agent is described in US Reissue Patent 23297. Boron compounds (eg, boric acid, borax) can also be used as a crosslinking agent.

  As the dichroic dye, an azo dye, stilbene dye, pyrazolone dye, triphenylmethane dye, quinoline dye, oxazine dye, thiazine dye or anthraquinone dye is used. The dichroic dye is preferably water-soluble. The dichroic dye preferably has a hydrophilic substituent (eg, sulfo, amino, hydroxyl). Examples of the dichroic dye include compounds described in, for example, the Japan Society for Invention and Innovation, Japanese Patent No. 2001-1745, page 58 (issued on March 15, 2001).

  In order to increase the contrast ratio of the liquid crystal display device, the transmittance of the polarizing plate is preferably higher and the degree of polarization is preferably higher. The transmittance of the polarizing plate is preferably in the range of 30 to 50%, more preferably in the range of 35 to 50%, and most preferably in the range of 40 to 50% in light having a wavelength of 550 nm. . The degree of polarization is preferably in the range of 90 to 100%, more preferably in the range of 95 to 100%, and most preferably in the range of 99 to 100% in light having a wavelength of 550 nm.

  The polarizing film and the optical compensation layer, the protective film of the polarizing film and the optically anisotropic layer, or the polarizing film and the alignment film used to form the optically anisotropic layer may be bonded via an adhesive. As the adhesive, a polyvinyl alcohol resin (including a modified polyvinyl alcohol with an acetoacetyl group, a sulfonic acid group, a carboxyl group, or an oxyalkylene group) or an aqueous boron compound solution can be used. A polyvinyl alcohol resin is preferred. The thickness of the adhesive layer is preferably in the range of 0.01 to 10 μm after drying, and particularly preferably in the range of 0.05 to 5 μm.

[Production of polarizing plate]
From the viewpoint of yield, the polarizing film is stretched at an angle of 10 to 80 degrees with respect to the longitudinal direction (MD direction) of the polarizing film (stretching method) or rubbed (rubbing method). It is preferable to dye with a dichroic dye. The tilt angle is preferably stretched so as to match the angle formed between the transmission axis of the two polarizing plates bonded to both sides of the liquid crystal cell constituting the LCD and the vertical or horizontal direction of the liquid crystal cell. A normal inclination angle is 45 °. Recently, however, devices that are not necessarily 45 ° have been developed for transmissive, reflective, and transflective LCDs, and it is preferable that the stretching direction can be arbitrarily adjusted in accordance with the design of the LCD.

In the stretching method, the stretching ratio is preferably 2.5 to 30.0 times, and more preferably 3.0 to 10.0 times. Stretching can be performed by dry stretching in air. Moreover, you may implement wet extending | stretching in the state immersed in water. The stretch ratio of dry stretching is preferably 2.5 to 5.0 times, and the stretch ratio of wet stretching is preferably 3.0 to 10.0 times. The stretching step may be performed in several steps including oblique stretching. By dividing into several times, it is possible to stretch more uniformly even at high magnification. Before the diagonal stretching, a slight stretching may be performed horizontally or vertically (to the extent that shrinkage in the width direction is prevented). Stretching can be performed by performing tenter stretching in biaxial stretching in different steps. The biaxial stretching is the same as the stretching method performed in normal film formation. In biaxial stretching, stretching is performed at different speeds on the left and right, so that the thickness of the binder film before stretching needs to be different on the left and right. In casting film formation, the flow rate of the binder solution can be differentiated between the left and right sides by tapering the die.
As described above, a binder film that is obliquely stretched by 10 to 80 degrees with respect to the MD direction of the polarizing film is produced.

In the rubbing method, a rubbing treatment method widely adopted as a liquid crystal alignment treatment process of LCD can be applied. That is, the orientation is obtained by rubbing the surface of the film in a certain direction using paper, gauze, felt, rubber, nylon, or polyester fiber. Generally, it is carried out by rubbing several times using a cloth in which fibers having a uniform length and thickness are planted on average.
The roll itself is preferably carried out using a rubbing roll whose roundness, cylindricity, and deflection (eccentricity) are all 30 μm or less. The film wrap angle on the rubbing roll is preferably 0.1 to 90 °. However, as described in JP-A-8-160430, a stable rubbing treatment can be obtained by winding 360 ° or more.
When rubbing a long film, the film is preferably transported at a speed of 1 to 100 m / min in a constant tension state by a transport device. The rubbing roll is preferably rotatable in the horizontal direction with respect to the film traveling direction for setting an arbitrary rubbing angle. It is preferable to select an appropriate rubbing angle in the range of 0 to 60 °. When used in a liquid crystal display device, the angle is preferably 40 to 50 °. 45 ° is particularly preferred.

  A polymer film that protects the polarizing film is preferably disposed on the surface of the polarizing film opposite to the optically anisotropic layer (arrangement of optically anisotropic layer / polarizing film / polymer film). The polymer film may have an antireflection film whose outermost surface has antifouling properties and scratch resistance.

[Protective film]
The polarizing plate according to the present invention is obtained by laminating a pair of protective films on both surfaces of a polarizing film. The kind of protective film is not particularly limited, and cellulose esters such as cellulose acetate, cellulose acetate butyrate, and cellulose propionate, polycarbonate, polyolefin, polystyrene, polyester, and the like can be used.

  The protective film is usually supplied in a roll form, and it is preferable that the protective film is continuously bonded to the long polarizing film so that the longitudinal directions thereof coincide. Here, the orientation axis (slow axis) of the protective film may be any direction, and the orientation axis of the protective film is preferably parallel to the longitudinal direction for ease of operation.

In the present invention, at least one of the pair of protective films sandwiching the polarizing film is one having a slow axis that substantially coincides with the direction in which the average refractive index of the film surface is maximized. That is, at least one protective film has three average refractive indexes nx, ny and nz in the x, y and z axis directions orthogonal to each other, and the in-plane average refractive index is nx and ny, and the thickness direction average When the refractive index is nz, a film satisfying the relationship of nx, ny = nz, nx>ny; a film satisfying nx = ny, nz, nx> nz, or the like. Examples thereof include a film having optical characteristics as the optically anisotropic layer A or the optically anisotropic layer B. As described above, in order to impart an optical compensation capability to the protective film, −5 nm ≦ {(nx−ny) × d ₁ } ≦ 50 nm and 50 nm ≦ [{(nx + ny) at an arbitrary wavelength λ in the visible light region. ) / 2-nz} × 2] ≦ 300 nm is preferably satisfied.

  On the other hand, in an embodiment where the protective film does not function as an optical compensation layer, the retardation of the transparent protective film is preferably low. In an embodiment where the absorption axis of the polarizing film and the orientation axis of the transparent protective film are not parallel, the letter of the transparent protective film is particularly preferable. When the retardation value is equal to or greater than a certain value, the polarization axis and the alignment axis (slow axis) of the transparent protective film are obliquely shifted, so that linearly polarized light changes to elliptically polarized light, which is not preferable. Accordingly, the retardation of the transparent protective film is, for example, preferably 10 nm or less at 632.8 nm, and more preferably 5 nm or less. As the polymer film having low retardation, polyolefins such as cellulose triacetate, ZEONEX, ZEONOR (both manufactured by Nippon Zeon Co., Ltd.) and ARTON (manufactured by JSR Co., Ltd.) are preferably used. Other examples include non-birefringent optical resin materials as described in JP-A-8-110402 or JP-A-11-293116.

  When laminating the protective film and the polarizing film, at least one protective film (protective film disposed on the side close to the liquid crystal cell when incorporated in a liquid crystal display device), the slow axis (alignment axis), The protective film and the polarizing film are laminated so that the absorption axis (stretching axis) of the polarizing film intersects. Specifically, the angle between the absorption axis of the polarizing film and the slow axis of the protective film is preferably 10 ° to 90 °, more preferably 20 ° to 70 °, still more preferably 40 ° to 50 °, particularly Preferably it is 43-47 degrees. The angle between the slow axis of the other protective film and the absorption axis of the polarizing film is not particularly limited, and can be appropriately set according to the purpose of the polarizing plate, but is preferably in the above range, and the retardation of the pair of protective films The phase axes are preferably coincident. When the slow axis of the protective film and the absorption axis of the polarizing film are parallel to each other, the mechanical stability of the polarizing plate such as dimensional change of the polarizing plate and prevention of curling can be improved. At least two axes of a total of three films of the polarizing film and the pair of protective films, the slow axis of one protective film and the absorption axis of the polarizing film, or the slow axes of the two protective films should be substantially parallel. The same effect can be obtained.

Further, when the retardation value of the protective film of the upper and lower polarizing plates is asymmetric, it greatly contributes to prevention of leakage light when viewed from an oblique direction. In particular, when the retardation value of the protective film disposed between the liquid crystal cell and the polarizing film of the upper and lower polarizing plates is made asymmetric, it is effective in reducing oblique leakage light in an aspect in which the absorption axes of the upper and lower polarizing plates are orthogonal to each other. . In order to make the retardation asymmetrical, {(nx−ny) × d ₁ } or {(nx + ny) is applied to at least one of the pair of protective films of the upper polarizing plate and at least one of the pair of protective films of the lower polarizing plate. / 2-nz} × d ₁ having different values is used. On the other hand, an embodiment in which polarizing plates having the same configuration are arranged on the upper and lower polarizing plates of the liquid crystal cell, that is, when the retardation of a pair of protective films of the upper and lower polarizing plates is the same, an optical compensation film that is incorporated by these protective films or separately Thus, the liquid crystal cell can be optically compensated.

<Adhesive>
The adhesive between the polarizing film and the protective film is not particularly limited, and examples thereof include PVA resins (including modified PVA such as acetoacetyl group, sulfonic acid group, carboxyl group, oxyalkylene group) and boron compound aqueous solution. PVA resin is preferable. The thickness of the adhesive layer is preferably 0.01 to 10 μm after drying, and particularly preferably 0.05 to 5 μm.

<Integrated manufacturing process of polarizing film and transparent protective film>
The polarizing plate according to the present invention has a drying step in which the polarizing film is stretched and then contracted to reduce the volatile content, and after heating or after the transparent protective film is bonded to at least one surface during drying, post-heating is performed. It is preferable to have a process. In the aspect in which the transparent protective film also serves as a support for the optically anisotropic layer functioning as an optical compensation layer, a transparent support having a transparent protective film on one side and an optically anisotropic layer on the opposite side is bonded. It is preferable to carry out post-heating later. As a specific attaching method, during the film drying process, the transparent protective film is attached to the polarizing film using an adhesive while holding both ends, and then both ends are cut off, or after drying, from both end holding parts There is a method of releasing the polarizing film, cutting off both ends of the film, and then attaching a transparent protective film. As a method for cutting off the ears, general techniques such as a method of cutting with a cutter such as a blade or a method of using a laser can be used. After bonding, it is preferable to heat in order to dry the adhesive and to improve the polarization performance. The heating condition varies depending on the adhesive, but in the case of an aqueous system, it is preferably 30 ° C. or higher, more preferably 40 ° C. or higher and 100 ° C. or lower, further preferably 50 ° C. or higher and 90 ° C. or lower. It is more preferable in terms of performance and production efficiency that these processes are manufactured in a consistent line.

<Performance of polarizing plate>
Optical properties and durability (short-term and long-term storage stability) of a polarizing plate comprising a transparent protective film, a polarizer and a transparent support related to the present invention are commercially available super high contrast products (for example, Sanritz Corporation). Manufactured by HLC2-5618 and the like) and preferably have equivalent or better performance. Specifically, the visible light transmittance is 42.5% or more, and the degree of polarization {(Tp−Tc) / (Tp + Tc)} ^1/2 ≧ 0.9995 (where Tp is parallel transmittance and Tc is orthogonal transmission) The rate of change in light transmittance before and after standing in an atmosphere of 60 ° C. and humidity 90% RH for 500 hours and 80 ° C. in a dry atmosphere for 500 hours is 3% or less based on the absolute value, Further, it is preferably 1% or less, and the rate of change in polarization degree is preferably 1% or less, more preferably 0.1% or less, based on the absolute value.

  The polarizing plate used in the present invention may have an optical compensation layer as described above. The optical compensation layer is preferably made of a compound having a discotic structural unit, and is an optical compensation layer in which the discotic surface is oriented substantially perpendicular to the substrate surface. Details and preferred ranges of the material and the production method of the optical compensation layer are the same as those of the optically anisotropic layer, which is a constituent layer of the optical compensation film described below.

[Optical compensation film]
The optical compensation film is used for eliminating image coloring and expanding the viewing angle in a liquid crystal display device. In the present invention, as described above, the optical compensation film is not an essential member. For example, in an aspect in which birefringence is added to one or both of the pair of protective films of the polarizing plate to function as the optical compensation film. It may not be necessary.

  The in-plane retardation (Re) of the entire optical compensation film is preferably 20 to 200 nm. The thickness direction retardation (Rth) of the entire optical compensation film is preferably 50 to 500 nm. In-plane retardation (Re) and thickness direction retardation (Rth) of the optical compensation film represent in-plane retardation and retardation in the thickness direction, respectively. Re is measured with KOBRA 21ADH (manufactured by Oji Scientific Instruments Co., Ltd.) by making light of wavelength λ nm incident in the normal direction of the film. Rth was measured by making light having a wavelength λ nm incident from a direction inclined + 40 ° with respect to the film normal direction with the Re, in-plane slow axis (determined by KOBRA 21ADH) as the tilt axis (rotation axis). The retardation value and the retardation value measured by making light of wavelength λ nm incident from a direction inclined by −40 ° with respect to the film normal direction with the in-plane slow axis as the tilt axis (rotation axis). KOBRA 21ADH is calculated based on the retardation value measured in the direction. Here, as the assumed value of the average refractive index, the values in the polymer handbook (JOHN WILEY & SONS, INC) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of the main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). KOBRA 21ADH calculates nx, ny, and nz by inputting these assumed values of average refractive index and film thickness.

  Examples of the optical compensation film include an optical compensation film made of a stretched birefringent polymer film and an optical compensation film having an optically anisotropic layer formed from a low-molecular or high-molecular liquid crystalline compound on a transparent support. Any can be used in the invention. In addition to the laminated body of the optically anisotropic layer A and the optically anisotropic layer B described above, an optical compensation film having a laminated structure can also be used. Regarding the optical compensation film having a laminated structure, in consideration of the thickness, an optical compensation film made of a coating-type laminate is preferable to an optical compensation film made of a laminate of polymer stretched films.

  The polymer film used as the optical compensation film may be a stretched polymer film or a combination of a coating type polymer layer and a polymer film. As a material for the polymer film, a synthetic polymer (eg, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, norbornene resin, triacetylcellulose) is generally used.

Next, the optical compensation film having an optically anisotropic layer made of a liquid crystalline compound will be described in detail.
[Optically anisotropic layer made of liquid crystalline compound]
Since the liquid crystalline compound has various alignment forms, the optically anisotropic layer made of the liquid crystalline compound exhibits a desired optical property by a single layer or a multilayered structure. That is, the optical compensation film may be an embodiment comprising a support and one or more optically anisotropic layers formed on the support. The retardation of the entire optical compensation film of this aspect can be adjusted by the optical anisotropy of the optical anisotropic layer. Liquid crystal compounds can be classified into rod-like liquid crystal compounds and discotic compounds based on their shapes. Furthermore, there are low molecular weight and high molecular weight types, respectively, and both can be used. The optically anisotropic layer made of the liquid crystalline compound used in the present invention preferably uses a rod-like liquid crystal compound or a discotic compound as the liquid crystalline compound, and has a discotic shape having a rod-like liquid crystal compound having a polymerizable group or a polymerizable group. More preferably, the compound is used.

(Bar-shaped liquid crystalline compound)
As rod-like liquid crystalline molecules, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.
The rod-like liquid crystalline molecule includes a metal complex. In addition, a liquid crystal polymer containing a rod-like liquid crystalline molecule in a repeating unit can also be used as the rod-like liquid crystalline molecule. In other words, the rod-like liquid crystal molecule may be bonded to a (liquid crystal) polymer.
For rod-like liquid crystalline molecules, see Chapter 4, Chapter 7 and Chapter 11 of the Chemistry of the Quarterly Chemistry Vol. 22 (1994) The Chemical Society of Japan, and the 142th Committee of the Japan Society for the Promotion of Science. Described in Chapter 3.
The birefringence of the rod-like liquid crystal molecule is preferably in the range of 0.001 to 0.7. The rod-like liquid crystalline molecule preferably has a polymerizable group in order to fix its alignment state. The polymerizable group is preferably a radically polymerizable unsaturated group or a cationically polymerizable group. Specifically, for example, the polymerizable groups described in paragraphs [0064] to [0086] of JP-A-2002-62427 are described. Group and a polymerizable liquid crystal compound.

(Discotic compound)
It is also preferable to use a discotic compound as the liquid crystalline compound forming the optically anisotropic layer. The discotic compound is preferably oriented substantially perpendicular to the polymer film surface (average inclination angle in the range of 50 to 90 degrees). The discotic compounds are described in various literatures (C. Destrade et al., Mol. Crysr. Liq. Cryst., Vol. 71, page 111 (1981); edited by The Chemical Society of Japan, Quarterly Chemical Review, No. 22, Liquid Crystals). Chemistry, Chapter 5, Chapter 10 Section 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. Comm., Page 1794 (1985); J. Zhang et al., J. Am. Chem.Soc., Vol.116, page 2655 (1994)). The polymerization of the discotic compound is described in JP-A-8-27284.

The discotic compound preferably has a polymerizable group so that it can be fixed by polymerization. For example, a structure in which a polymerizable group is bonded as a substituent to a disk-shaped core of a disk-shaped compound is conceivable. However, when a polymerizable group is directly bonded to the disk-shaped core, the orientation state can be maintained in the polymerization reaction. It becomes difficult. Therefore, a structure having a linking group between the discotic core and the polymerizable group is preferable. That is, the discotic compound having a polymerizable group is preferably a compound represented by the following formula (III).
Formula (III) D (-LP) _n
In the formula, D is a discotic core, L is a divalent linking group, P is a polymerizable group, and n is an integer of 4 to 12.

  Preferred specific examples of the discotic core (D), the divalent linking group (L), and the polymerizable group (P) in the formula (III) are (D1) described in JP-A No. 2001-4837, respectively. To (D15), (L1) to (L25), and (P1) to (P18), and the contents described in the publication can be preferably used.

(Alignment of liquid crystalline compounds)
These liquid crystalline compounds are preferably substantially uniformly oriented in the optically anisotropic layer, more preferably fixed in a substantially uniformly oriented state. It is most preferable that the liquid crystal compound is fixed by. In the case of a rod-like liquid crystal compound having a polymerizable group, it is preferably fixed in a substantially horizontal (homogeneous) orientation. Substantially horizontal means that the average angle (average inclination angle) between the major axis direction of the rod-like liquid crystal compound and the surface of the optically anisotropic layer is in the range of 0 ° to 40 °. The rod-like liquid crystalline compound may be aligned obliquely or may be gradually changed (hybrid alignment). Even in the case of oblique alignment or hybrid alignment, the average inclination angle is preferably 0 ° to 40 °. An optically anisotropic layer formed from a rod-like liquid crystal compound fixed in such an orientation may be incorporated in a VA mode or IPS mode liquid crystal display device, and contributes to improving the viewing angle characteristics of the liquid crystal display device. Can contribute as.
In the case of a discotic compound having a polymerizable group, it is preferable to substantially vertically align. Substantially perpendicular means that the average angle (average inclination angle) between the disc surface of the discotic compound and the surface of the optically anisotropic layer is in the range of 50 ° to 90 °. The discotic compound may be oriented obliquely, or the inclination angle may be gradually changed (hybrid orientation). Even in the case of oblique orientation or hybrid orientation, the average inclination angle is preferably 50 ° to 90 °. An optically anisotropic layer formed from a discotic compound fixed in such an orientation may be incorporated into a VA mode or IPS mode liquid crystal display device, and contributes to an improvement in viewing angle characteristics of the liquid crystal display device. Can contribute.

  The optically anisotropic layer is preferably formed by applying a coating liquid containing a liquid crystalline compound and the following polymerization initiator and other additives onto the alignment film. As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination. The coating liquid can be applied by a known method (eg, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).

(Fixation of alignment state of liquid crystalline compounds)
The aligned liquid crystalline compound is preferably fixed while maintaining the alignment state. The immobilization is preferably carried out by a polymerization reaction of a polymerizable group introduced into the liquid crystal compound. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator, and a photopolymerization reaction is more preferable. Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Acridine and phenazine compounds (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,212,970).

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by mass, more preferably 0.5 to 5% by mass, based on the solid content of the coating solution. Light irradiation for the polymerization of the liquid crystalline compound is preferably performed using ultraviolet rays. The irradiation energy is preferably ^{20mJ / cm 2 ~50J / cm 2} , further preferably 100 to 800 mJ / cm ^2. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions. The thickness of the optically anisotropic layer is preferably 0.1 to 10 μm, and more preferably 0.5 to 5 μm.

(Alignment film)
In order to align the liquid crystalline compound during the formation of the optically anisotropic layer, it is preferable to use an alignment film. The alignment film may be an organic compound (preferably polymer) rubbing treatment, oblique deposition of an inorganic compound, formation of a layer having a microgroup, or an organic compound (eg, ω-triconic acid) by the Langmuir-Blodgett method (LB film). , Dioctadecyldimethylammonium chloride, methyl stearylate, etc.). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field or light irradiation is also known. An alignment film formed by a polymer rubbing treatment is particularly preferable. The rubbing process is carried out by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth. The type of polymer used for the alignment film can be determined according to the alignment (particularly the average tilt angle) of the liquid crystal compound. For example, in order to align the liquid crystalline compound horizontally, a polymer (ordinary alignment polymer) that does not decrease the surface energy of the alignment film is used. Specific types of polymers are described in various documents about liquid crystal cells or optical compensation films. Any of the alignment films preferably has a polymerizable group for the purpose of improving the adhesion between the liquid crystal compound and the transparent support. The polymerizable group can be introduced by introducing a repeating unit having a polymerizable group in the side chain or as a substituent of a cyclic group. More preferably, an alignment film that forms a chemical bond with the liquid crystal compound at the interface is used, and such an alignment film is described in JP-A-9-152509.
The thickness of the alignment film is preferably 0.01 to 5 μm, and more preferably 0.05 to 1 μm.
In addition, after aligning the liquid crystalline compound using the alignment film, the liquid crystalline compound is fixed in the aligned state to form an optically anisotropic layer, and only the optically anisotropic layer is polymer film (or transparent support) It may be transferred onto the body).

[Vertical alignment film]
In order to align the liquid crystalline compound vertically on the alignment film side, it is important to reduce the surface energy of the alignment film. Specifically, the surface energy of the alignment film is lowered by the functional group of the polymer, thereby bringing the liquid crystalline compound into a standing state. As the functional group for reducing the surface energy of the alignment film, a hydrocarbon group having 10 or more fluorine atoms and carbon atoms is effective. In order for a fluorine atom or a hydrocarbon group to be present on the surface of the alignment film, it is preferable to introduce a fluorine atom or a hydrocarbon group into the side chain rather than the main chain of the polymer. The fluoropolymer preferably contains fluorine atoms in a proportion of 0.05 to 80% by weight, more preferably in a proportion of 0.1 to 70% by weight, and in a proportion of 0.5 to 65% by weight. More preferably, it is most preferably contained in a proportion of 1 to 60% by weight. The hydrocarbon group is an aliphatic group, an aromatic group, or a combination thereof. The aliphatic group may be cyclic, branched or linear. The aliphatic group is preferably an alkyl group (which may be a cycloalkyl group) or an alkenyl group (which may be a cycloalkenyl group). The hydrocarbon group may have a substituent that does not exhibit strong hydrophilicity, such as a halogen atom. The hydrocarbon group has preferably 10 to 100 carbon atoms, more preferably 10 to 60, and most preferably 10 to 40 carbon atoms. The main chain of the polymer preferably has a polyimide structure or a polyvinyl alcohol structure.

  Polyimide is generally synthesized by a condensation reaction of tetracarboxylic acid and diamine. A polyimide corresponding to a copolymer may be synthesized using two or more kinds of tetracarboxylic acids or two or more kinds of diamines. The fluorine atom or hydrocarbon group may be present in the repeating unit derived from tetracarboxylic acid, may be present in the repeating unit derived from diamine, or may be present in both repeating units. When introducing a hydrocarbon group into polyimide, it is particularly preferable to form a steroid structure in the main chain or side chain of the polyimide. The steroid structure present in the side chain corresponds to a hydrocarbon group having 10 or more carbon atoms, and has a function of vertically aligning the liquid crystalline compound. In this specification, the steroid structure is a cyclopentanohydrophenanthrene ring structure or a ring structure in which a part of the bond of the ring is an aliphatic ring (a range in which an aromatic ring is not formed) is a double bond. means.

  Furthermore, as a means for vertically aligning the liquid crystalline compound, a method of mixing an organic acid with a polymer of polyvinyl alcohol or polyimide can be suitably used. As the acid to be mixed, carboxylic acid, sulfonic acid and amino acid are preferably used. You may use what shows the acidity among the below-mentioned air interface aligning agent. The mixing amount is preferably 0.1% by weight to 20% by weight and more preferably 0.5% by weight to 10% by weight with respect to the polymer.

  For uniform alignment of the discotic liquid crystalline compound, the vertical alignment film is rubbed to control the alignment direction. The rubbing process is carried out by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth. On the other hand, it is preferable not to perform rubbing treatment for the alignment of the rod-like liquid crystalline compound. In any alignment film, the alignment film preferably has a polymerizable group for the purpose of improving the adhesion between the liquid crystal compound and the transparent support. The polymerizable group can be introduced by introducing a repeating unit having a polymerizable group in the side chain or as a substituent of a cyclic group. It is more preferable to use an alignment film that forms a chemical bond with the liquid crystal compound at the interface. Such an alignment film is described in JP-A-9-152509. The thickness of the alignment film is preferably 0.01 to 5 μm, and more preferably 0.05 to 1 μm. In addition, after aligning a liquid crystalline compound using an alignment film, the liquid crystalline compound is fixed in the alignment state to form a retardation layer, and only the retardation layer is formed on the polymer film (or transparent support). You may transcribe.

[Air interface alignment agent]
Since ordinary liquid crystalline compounds have the property of being tilted and aligned on the air interface side, it is necessary to control the alignment of the liquid crystal compound vertically also on the air interface side in order to obtain a uniformly vertically aligned state. . For this purpose, a compound that is unevenly distributed on the air interface side and has an action of vertically aligning the liquid crystalline compound by the excluded volume effect or the electrostatic effect is added to the liquid crystal coating liquid. The action of vertically aligning the liquid crystal compound corresponds to the action of reducing the tilt angle of the director, that is, the angle formed between the director and the coated liquid crystal air side surface in the discotic liquid crystal compound. Compounds that reduce the angle of inclination of the director of discotic liquid crystalline molecules include those with multiple F atoms bonded to the air interface as shown below, and those with a sulfonyl group or carboxyl group bonded. In addition, a compound in which a rigid structural unit that gives an excluded volume effect such that the liquid crystal molecules are aligned perpendicularly is bonded preferably.

  In addition to the exemplified compounds, compounds described in JP-A Nos. 2002-20363 and 2002-129162 can be used as the air interface alignment agent. Also, paragraph numbers 0072 to 0075 of Japanese Patent Application No. 2002-212100, paragraph numbers 0038 to 0040 and 0048 to 0049 of Japanese Patent Application No. 2002-243600, and paragraph numbers 0037 to 0039 of Japanese Patent Application No. 2002-262239. The matters described in Paragraph Nos. 0071 to 0078 of Japanese Patent Application No. 2003-91752 can also be appropriately applied to the present invention.

  The amount of the air interface alignment agent used in the liquid crystal coating solution is preferably 0.05% by weight to 5% by weight. Moreover, when using a fluorine saturation type | system | group air interface aligning agent, it is preferable that it is 1 weight% or less.

  The support for supporting the optically anisotropic layer is not particularly limited, and various polymer films can be used. For example, a triacetyl cellulose, norbornene resin, etc. are mentioned. Further, as described above, the protective film of the polarizing plate may also serve as the support for the optically anisotropic layer. Specific examples of the material of the support in this embodiment are the same as the specific examples of the material of the protective film of the polarizing plate, and are as described above.

  The present invention will be described more specifically with reference to the following examples. The materials, reagents, amounts and ratios of substances, operations, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples.

[Example 1]
A liquid crystal display device having the configuration shown in FIG. 1 was produced. That is, from the observation direction (top), the upper polarizing plate (protective film 3a, polarizing film 1, protective film 3), liquid crystal cell (upper substrate 5, liquid crystal layer 7, lower substrate 8), lower polarizing plate (protective film 12, polarized light) The film 14 and the protective film 12a) were laminated, and a backlight light source (not shown) was further disposed.
Below, the manufacturing method of each used member is demonstrated.
<Production of liquid crystal cell>
The liquid crystal cell has a cell gap of 3 μm between substrates, and a liquid crystal material having negative dielectric anisotropy (“MLC6680”, manufactured by Merck) is dropped between the substrates and sealed, and a liquid crystal layer is interposed between the substrates. Formed. The retardation of the liquid crystal layer (that is, the product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn) was set to 300 nm. The liquid crystal material was aligned so as to be vertically aligned.

<Preparation of upper and lower polarizing plates>
(Preparation of polarizing film)
A PVA film having an average degree of polymerization of 2400 and a film thickness of 100 μm was washed with ion exchange water at 15 to 17 ° C. for 60 seconds, and the surface moisture was scraped off with a stainless steel blade. The sample was immersed in an aqueous solution of 0.77 g / L of iodine and 60.0 g / L of potassium iodide at 40 ° C. for 55 seconds while correcting the concentration. Further, while correcting the concentration so that the concentration becomes constant, it was immersed in an aqueous solution of 42.5 g / L boric acid and 30 g / L potassium iodide at 40 ° C. for 90 seconds, and then the excess moisture on both sides of the film was removed from the stainless steel blade. The film was scraped off and introduced into a tenter stretching machine in a state where the moisture content distribution in the film was 2% or less.
Sending 100m at a transfer speed of 4m / min, stretching up to 5 times in a 95 ° C atmosphere at 60 ° C, then bending the tenter with respect to the stretching direction, and then drying in a 70 ° C atmosphere while keeping the width constant and shrinking After leaving it, it left the tenter. The moisture content of the PVA film before starting stretching was 32%, and the moisture content after drying was 1.5%. The difference in transport speed between the left and right tenter clips was less than 0.05%, and the angle between the center line of the introduced film and the center line of the film sent to the next process was 46 °. Here, | L1-L2 | is 0.7 m, W is 0.7 m, and | L1-L2 | = W. The substantial stretching direction Ax-Cx at the tenter outlet was inclined by 45 ° with respect to the center line 22 of the film sent to the next process. Wrinkles and film deformation at the tenter exit were not observed. The thickness of the film after stretching and drying was 18 μm.

(Lamination of transparent protective film)
About the polarizing film produced by the above-described oblique stretching method, after cutting out 3 cm from the width direction using a cutter, both surfaces of the polarizing film were treated with a PVA (PVA-117H manufactured by Kuraray Co., Ltd.) 3% aqueous solution as an adhesive. A cellulose triacetate film for transparent protective film (Re value = 30 nm, Rth = 130 nm) that had been saponified was bonded together, and further heated at 70 ° C. for 10 minutes to provide a cellulose triacetate protective film on both sides with an effective width of 650 mm A scale-shaped polarizing plate was obtained. This film had a slow axis that substantially coincided with the direction in which the average refractive index of the film surface was maximum.
When laminating the upper polarizing plate, the axis angles of the slow axis of the upper protective film, the absorption axis of the polarizing film, and the slow axis of the lower protective film are (0 °, 45 ° with respect to the horizontal direction of the display device). , 0 °), and the axis angle of the lower polarizing plate was (0 °, −45 °, 0 °).
The absorption axis direction of the polarizing film produced above was inclined 45 ° with respect to the longitudinal direction. Therefore, by cutting to 310 × 233 mm size, the absorption axis direction was 45 ° with respect to the side with an area efficiency of 91.5%. Was obtained. In addition, no color omission stripes were observed with the naked eye.

The obtained polarizing plate has a polarizing plate performance of visible light transmittance of 43.5 and polarization degree {(Tp−Tc) / (Tp + Tc)} ^1/2 ≧ 0.9997
(Where Tp is parallel transmittance, Tc is orthogonal transmittance), and light transmission before and after standing at a temperature of 60 ° C. and a humidity of 90% RH for 500 hours and at 80 ° C. for 500 hours in a dry atmosphere. The rate of change of the rate was 1% or less based on the absolute value, and the rate of change of the polarization degree was 0.05% or less based on the absolute value.

<Measurement of leakage light of the manufactured liquid crystal display device>
The leakage light of the liquid crystal display device thus manufactured was measured. The leakage light when observed from the left direction of 60 ° was 0.7%. In the viewing angle characteristics of the liquid crystal display device, it is desirable that the viewing angles with a contrast ratio of 5 to 1 or more are 80 ° or more in the left, right, top and bottom. In the manufactured liquid crystal display device, a transmittance of about 30% is obtained for white display. Therefore, if the leakage light of black display satisfies less than 1% at a viewing angle of 60 °, a viewing angle with a contrast ratio of 5 to 1 or more. It can be estimated that 80 ° or more are obtained in the left, right, up and down directions.

[Example 2]
<Production of liquid crystal display device>
In the liquid crystal display device produced in Example 1, when producing the upper and lower polarizing plates, the same as Example 1 except that norbornene-based films showing various Re and Rth values were used as protective films as shown in Table 1 below. Liquid crystal display device No. 1-24 were produced. Each of these norbornene-based films had a slow axis that substantially coincided with the direction in which the average refractive index of the film surface was maximized.

<Measurement of leakage light of liquid crystal display device>
The produced liquid crystal display device No. The value of leakage light when observed from 1 to 24 obliquely from 60 ° was measured. The results are shown in Table 1.

  Table 1: Black display transmittance (%) at 60 ° viewing angle

[Example 3]
Next, an example using a polarizing plate having an optical compensation layer having optical compensation capability will be described.
<Production of optical compensation film>
(Preparation of transparent protective film for polarizing film and transparent support for optical compensation layer)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.
Cellulose acetate solution composition Cellulose acetate having an acetylation degree of 60.7 to 61.1% 100 parts by mass of triphenyl phosphate (plasticizer) 7.8 parts by weight of biphenyl diphenyl phosphate (plasticizer) 3.9 parts by weight of methylene chloride (first Solvent) 336 parts by mass Methanol (second solvent) 29 parts by mass

  In another mixing tank, 16 parts by mass of the following retardation increasing agent, 92 parts by mass of methylene chloride and 8 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution. A dope was prepared by mixing 474 parts by mass of the cellulose acetate solution with 25 parts by mass of the retardation increasing agent solution and stirring sufficiently. The addition amount of the retardation increasing agent was 3.5 parts by mass with respect to 100 parts by mass of cellulose acetate.

The obtained dope was cast using a band stretching machine. After the film surface temperature on the band reached 40 ° C., the film was dried with warm air of 70 ° C. for 1 minute, and the film from the band was dried with 140 ° C. of drying air for 20 minutes. A cellulose acetate film (thickness: 146 μm) was prepared. For the produced cellulose acetate film (transparent support, transparent protective film), the Re retardation value and the Rth retardation value at a wavelength of 550 nm were measured using an ellipsometer (M-150, manufactured by JASCO Corporation). Re was 2 nm (variation ± 1 nm), and Rth was 190 nm (variation ± 3 nm). Furthermore, Re of each wavelength of 400 nm to 700 nm was in the range of 2 ± 1 nm, and Rth of each wavelength of 400 nm to 700 nm was in the range of 190 ± 2 nm.
The produced cellulose acetate film was immersed in a 2.0N potassium hydroxide solution (25 ° C.) for 2 minutes, neutralized with sulfuric acid, washed with pure water, and then dried. The surface energy of the cellulose acetate film was determined by a contact method and found to be 63 mN / m. Thus, a cellulose acetate film for a transparent support and transparent protective film was produced. The obtained film had a slow axis that substantially coincided with the direction in which the average refractive index of the film surface was maximum.

(Preparation of alignment layer)
On this cellulose acetate film, a coating solution having the following composition was applied at 28 ml / m ² with a # 16 wire bar coater. The film was dried at 25 ° C. for 60 seconds, 60 ° C. warm air for 60 seconds, and 90 ° C. hot air for 150 seconds. The alignment film thickness after drying was 1.1 μm. Further, the surface roughness of the alignment film was measured with an atomic force microscope (AFM: Atomic Force Microscope, SPI3800N, manufactured by Seiko Instruments Inc.), and found to be 1.147 nm. Next, the formed film was rubbed in the −45 ° direction with respect to the slow axis (measured at a wavelength of 632.8 nm) of the cellulose acetate film.

Alignment film coating solution composition Modified polyvinyl alcohol 20 parts by weight Water 361 parts by weight Methanol 119 parts by weight Glutaraldehyde (crosslinking agent) 0.5 parts by weight

(Preparation of optically anisotropic layer)
On the above alignment film, a coating solution having the following composition is continuously applied using a bar coater, dried, and heated (alignment aging), and further irradiated with ultraviolet rays to achieve a horizontal alignment of 1.1 μm in thickness. An isotropic layer (A) was formed to produce an optical compensation film. The optically anisotropic layer had a slow axis in the direction of −45 ° with respect to the longitudinal direction of the transparent support. The Re value at 550 nm was 130 nm.
Coating liquid composition for optically anisotropic layer (A) The following rod-like liquid crystalline compound I-2 38.1% by mass
Sensitizer A 0.38% by mass
The following photopolymerization initiator B 1.14% by mass
Orientation control agent C 0.19 mass%
Glutaraldehyde 0.04% by mass
Methyl ethyl ketone 60.1% by mass

  The prepared optical compensation film composed of the optically anisotropic layer and the transparent support is placed between the lower polarizing film 14 and the lower substrate 8 for liquid crystal cell in FIG. = 2 nm, Rth = 190 nm) was incorporated so as to be in contact with the polarizing film 14. That is, a liquid crystal display device in which the transparent protective film 12 also serves as a transparent support of an optically anisotropic layer having optical compensation ability was produced. Other configurations were the same as those in Example 1. That is, the axis angle of the slow axis of the upper protective film, the absorption axis of the polarizing film, and the slow axis of the lower protective film of the upper polarizing plate with respect to the horizontal direction of the display device (0 °, 45 °, Similarly, the axis angle of the lower polarizing plate was (0 °, −45 °, 0 °), and the slow axis (rubbing direction) of the optically anisotropic layer was −45 °.

In the production of the optical compensation film, the Re value and Rth value of the transparent support made of cellulose acetate film were adjusted as shown in Table 2, and the liquid crystal display device No. was prepared in the same manner as above except that an optical compensation film was produced. . 25-40 were produced. The cellulose acetate film used had a slow axis that substantially coincided with the direction in which the average refractive index of the film surface was maximized.
<Measurement of leakage light of the manufactured liquid crystal display device>
The liquid crystal display device no. Leakage light was observed by observation from 25 to 40 at an angle of 60 °. The results are shown in Table 2.

  Table 2: Black display transmittance (%) at 60 ° viewing angle

[Example 4]
<Production of optical compensation film>
A transparent support adjusted to Re value = 10 nm and Rth = 76 nm was prepared in the same manner as the transparent support made of the cellulose acetate film prepared in Example 3. This film had a slow axis that substantially coincided with the direction in which the average refractive index of the film surface was maximum. Further, the support was saponified, and the alignment film used in Example 3 was applied thereon. Further, a rubbing treatment was performed in the direction of 45 ° with respect to the longitudinal direction, and the coating solution composition for the optically anisotropic layer (A) used in Example 3 was continuously applied using a bar coater, dried, and Heating (orientation aging) and ultraviolet irradiation were performed to form an optically anisotropic layer having a thickness of 0.43 μm. The optically anisotropic layer had a slow axis in the direction of 45 ° with respect to the longitudinal direction of the transparent support. The retardation value at 550 nm was 53 nm.

  The prepared optical compensation film comprising the optically anisotropic layer and the transparent support is placed between the upper polarizing film 1 and the upper substrate 5 for liquid crystal cell in FIG. 10 nm, Rth = 176 nm) was incorporated so as to be in contact with the polarizing film 1. That is, a liquid crystal display device in which the transparent protective film 3 also serves as a transparent support of an optically anisotropic layer having optical compensation ability was produced. Other configurations were the same as those in Example 1. That is, the axis angle of the slow axis of the upper protective film, the absorption axis of the polarizing film, and the slow axis of the lower protective film of the upper polarizing plate with respect to the horizontal direction of the display device (0 °, 45 °, 0 °), the slow axis (rubbing direction) of the optically anisotropic layer was 45 °, and the axis angle of the lower polarizing plate was (0 °, −45 °, 0 °).

In the production of the optical compensation film, the Re value of the optically anisotropic layer was adjusted as shown in Table 3, and the liquid crystal display device no. 41-46 were produced.
<Measurement of leakage light of the manufactured liquid crystal display device>
The liquid crystal display device no. Leakage light was observed by observation from 41 to 46 at an angle of 60 °. The results are shown in Table 3.

Table 3: Black display transmittance (%) at 60 ° viewing angle

[Example 5]
A liquid crystal display device was produced in the same manner as in Example 1 except that a cellulose triacetate film having an Re value of 0 nm and an Rth value of 133 nm was used as a protective film for the upper and lower polarizing plates. That is, the axis angles of the slow axis of the upper protective film of the upper polarizing plate, the absorption axis of the polarizing film, and the slow axis of the lower protective film are (0 °, 45 °, 0) with respect to the horizontal direction of the display device. Similarly, the axis angle of the lower polarizing plate was (0 °, −45 °, 0 °). The cellulose acetate film used had a slow axis that substantially coincided with the direction in which the average refractive index of the film surface was maximized.

As shown in Table 4 below, as a protective film for the upper and lower polarizing plates, a liquid crystal display device No. 1 was used in the same manner as described above except that a cellulose triacetate film having various Re and Rth values was used. 47-70 were produced. The cellulose acetate film used had a slow axis that substantially coincided with the direction in which the average refractive index of the film surface was maximized.
<Measurement of leakage light of the manufactured liquid crystal display device>
The liquid crystal display device no. The leakage light observed from diagonally 60 to 47-70 was measured. The results are shown in Table 4.

  Table 4: Black display transmittance (%) at 60 ° viewing angle

[Example 6]
Example 6 is a comparative example.
In Example 1, the stretching direction of the polarizing film was 90 ° with respect to the film longitudinal direction. Using a so-called normal width direction uniaxial stretching type tenter stretching machine, a PVA film having an original thickness of 100 μm is dyed in a dichroic material dyeing tank, coated with a crosslinking agent solution by a coating means, and bitten into a tenter stretching machine. After being uniaxially stretched in the width direction in an atmosphere of 30 ° to 80 ° and 70 to 99% RH, it is dried while keeping the width substantially constant, and after removing volatile matter sufficiently, it is separated and polarized with a thickness of 18 μm. A membrane was obtained. The axis angles of the slow axis of the upper protective film, the absorption axis of the polarizing film, and the slow axis of the lower protective film are set to (0 °, 90 °, 0 °) with respect to the horizontal direction of the display device. The axial angle of the side polarizing plate was (90 °, 0 °, 90 °). Other configurations were the same as those in Example 1. The leakage light of the liquid crystal display device thus manufactured was measured. Leakage light in observation from the left direction of 60 ° was 0.6%.

Examples 7 to 16 below are reference examples or comparative examples thereof.
[Example 7]
<Production of liquid crystal cell>
A pair of transparent substrates 5 having a linear electrode formed inside and an orientation control film formed thereon were prepared. The rod-like liquid crystal molecules 7 sandwiched between the substrates are aligned so as to have a slight angle with respect to the longitudinal direction of the linear electrode when no electric field is applied. In this case, the dielectric anisotropy of the liquid crystal is assumed to be positive. When an electric field is applied, the liquid crystal molecules 7 change their direction in the direction of the electric field. The light transmittance can be changed by arranging the polarizing plate 1 at a predetermined angle. Note that the angle formed by the electric field direction with respect to the surface of the substrate 5 is actually 20 degrees or less, and is preferably substantially parallel. Hereinafter, in the present invention, those below 20 degrees are generically expressed as a parallel electric field. Moreover, even if the electrodes are formed separately on the upper and lower substrates or the electrodes are formed only on one substrate, the effect does not change.

  As a liquid crystal material, a nematic liquid crystal having a positive dielectric anisotropy Δε, a value of 13.2, and a refractive index anisotropy Δn of 0.081 (589 nm, 20 ° C.) was used. The thickness (gap) of the liquid crystal layer was more than 2.8 μm and less than 4.5 μm. This is because when the retardation Δn · d is more than 0.25 μm and less than 0.32 μm, a transmittance characteristic having almost no wavelength dependence within the visible light range can be obtained. By the combination of the alignment film and the polarizing plate described later, the maximum transmittance can be obtained when the liquid crystal molecules are rotated by 45 ° from the rubbing direction to the electric field direction. The thickness (gap) of the liquid crystal layer is controlled by polymer beads. Of course, similar gaps can be formed by glass beads, fibers, or resin-made columnar spacers.

  The upper and lower polarizing plate protective films are made of a cellulose acetate film, and a saponified commercially available cellulose acetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) is used for the protective film for the upper and lower polarizing plates far from the liquid crystal layer. The Re value was set to 3 nm and the Rth value was set to 50 nm. The transparent protective film on the side of the upper and lower polarizing plates near the liquid crystal cell was prepared by the following method and saponified. The transparent protective film on the side close to the liquid crystal layer of the upper polarizing plate has a Re value of 10 nm and the Rth value of 80 nm, and the transparent protective film on the side of the lower polarizing plate close to the liquid crystal layer has an Re value of 3 nm. The Rth value is 50 nm. Next, an optically anisotropic layer was formed on the transparent protective film on the side close to the liquid crystal layer of the upper polarizing plate and was disposed between the liquid crystal cell and the transparent protective film. The axis angles of the slow axis of the upper protective film, the absorption axis of the polarizing film, and the slow axis of the lower protective film are set to (0 °, 90 °, 0 °) with respect to the horizontal direction of the display device. The axial angle of the side polarizing plate was (90 °, 0 °, 90 °). The cellulose acetate film used for the transparent protective film had a slow axis that substantially coincided with the direction in which the average refractive index of the film surface was maximized.

The optically anisotropic layer disposed between the transparent protective film of the upper polarizing plate and the liquid crystal cell was formed by orienting the discotic compound vertically with the transparent protective film as a support. The retardation value was 150 nm, and the crossing angle between the orientation control direction and the polarizing film absorption axis was 90 °. The leakage light of the liquid crystal display device thus manufactured was measured. Leakage light in observation from the left direction of 60 ° was 0.1%.
Moreover, even if the arrangement of the protective film of the polarizing plate as the upper polarizing plate close to the liquid crystal layer was reversed, the same effect was obtained.

[Example 8]
In Example 7, except that the upper and lower polarizing plates have an absorption axis and a slow axis other than the upper side (0 °, 0 °, 0 °) and the lower side (90 °, 90 °, 90 °). In the case of the same configuration, the leakage light in observation from the left direction of 60 ° was 0.2%.

[Example 9]
In Example 8, the optically anisotropic layer disposed between the transparent protective film of the upper polarizing plate and the liquid crystal cell was changed from a layer formed from a discotic compound to a polyolefin-based stretched film (for example, Arton) (thickness 80 μm). In this case, the other configuration is the same. Leakage light in observation from the left direction of 60 ° was 0.3%.

[Example 10]
In Example 8, no optically anisotropic layer was placed. Leakage light in observation from the left direction of 60 ° was 0.5%.

[Example 11]
A liquid crystal display device having the structure shown in FIG. 2 was produced. That is, from the observation direction (above), a protective film (not shown), an upper polarizing plate 1A comprising an upper polarizing film 1 and a protective film 3, a liquid crystal cell (upper substrate 5, liquid crystal layer 7, lower substrate 8), In addition, a lower polarizing plate 14A composed of the optical compensation layer 10, the protective film 12, the lower polarizing film 14, and a protective film (not shown) is laminated, and the lower polarizing plate 14A is further cooled on the lower side. A backlight (not shown) using a cathode fluorescent lamp was arranged.

Below, the manufacturing method of each used member is demonstrated.
(Production of IPS mode liquid crystal cell)
FIG. 3 shows a cross-sectional view of the liquid crystal display device. One of a pair of transparent substrates 8, a linear electrode made of ITO (or metal such as chromium or aluminum) is formed inside the substrate, and an alignment control film (not shown) is formed thereon. . The rod-like liquid crystal molecules 7 sandwiched between the substrates are aligned so as to have a slight angle with respect to the longitudinal direction of the linear electrode when no electric field is applied. In this case, the dielectric anisotropy of the liquid crystal is assumed to be positive. When an electric field is applied, the liquid crystal molecules 7 change the direction in the direction of the electric field. Then, the upper polarizing plate 1A and the lower polarizing plate 14A configured as described above were arranged at a predetermined angle. The angle formed by the electric field direction with respect to the surface of the substrate 8 was a parallel electric field. Here, the parallel electric field means that the angle formed by the electric field direction with respect to the surface of the substrate is 20 degrees or less, more preferably 10 degrees or less, and still more preferably parallel. Moreover, even if the electrodes are formed separately on the upper and lower substrates or the electrodes are formed only on one substrate, the effect does not change.

  The liquid crystal material used was a nematic liquid crystal having a positive dielectric anisotropy Δε and a value of 13.2, and a refractive index anisotropy Δn of 0.085 (589 nm, 20 degrees) (Merck). , MLC 9100-100). The thickness (gap) of the liquid crystal layer was 3.5 μm.

(Preparation of polarizing plate)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution having the following composition.

Composition of cellulose acetate solution Cellulose acetate having an acetylation degree of 60.9% 100 parts by mass Triphenyl phosphate (plasticizer) 7.8 parts by mass biphenyl diphenyl phosphate (plasticizer) 3.9 parts by mass methylene chloride (first solvent) 300 Part by mass Methanol (second solvent) 54 parts by mass 1-butanol (third solvent) 11 parts by mass

  In another mixing tank, 16 parts by mass of the following retardation increasing agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution. Then, 7 parts by mass of the obtained retardation increasing agent solution was mixed with 487 parts by mass of the cellulose acetate solution and sufficiently stirred to prepare a dope.

Retardation raising agent

  The obtained dope was cast using a band casting machine. After the film surface temperature on the band reached 40 ° C., the film was dried with warm air of 60 ° C. for 1 minute, and the film was peeled off from the band. Next, the film was dried with a drying air at 140 ° C. for 10 minutes to produce a cellulose acetate film having a thickness of 100 μm.

  The optical properties of the cellulose acetate film were measured using an automatic birefringence meter (KOBRA-21ADH, manufactured by Oji Scientific Instruments). As a result, Re = 10 (nm) and Rth = 102 (nm).

(Preparation of optical compensation layer)
The surface of the cellulose acetate film was saponified, and an alignment film coating solution having the following composition was coated thereon with a wire bar coater so as to be 20 ml / m ² . Then, it dried for 60 seconds with 60 degreeC warm air, and also for 120 seconds with 100 degreeC warm air. Next, the formed film was rubbed in a direction parallel to the slow axis direction of the film.

Composition of alignment film coating solution Modified polyvinyl alcohol 15 parts by weight Water 334 parts by weight Methanol 100 parts by weight Glutaraldehyde 1 part by weight Paratoluenesulfonic acid 0.3 parts by weight

  0.9 g of the following discotic liquid crystalline compound, 0.2 g of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) 0 0.06 g, 0.02 g of sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) and 0.01 g of the air interface side vertical alignment agent described below were dissolved in 3.9 g of methyl ethyl ketone. This solution was applied onto the alignment film with a # 3.4 wire bar. Furthermore, it was affixed to a metal frame and heated in a thermostatic bath at 125 ° C. for 3 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed for 30 seconds using a 120 W / cm high-pressure mercury lamp at 100 ° C. to crosslink the discotic liquid crystalline compound. Then, it stood to cool to room temperature. In this way, an optical compensation layer was manufactured.

  Using an automatic birefringence meter (KOBRA-21ADH, manufactured by Oji Scientific Instruments Co., Ltd.), measure the light incident angle dependency of Re of the optical compensation layer, and subtract the contribution of the cellulose acetate film measured in advance. Thus, the optical characteristics of the discotic liquid crystal layer alone were calculated. As a result, Re was 50 nm, Rth was −25 nm, the average tilt angle of the liquid crystal was 89.9 degrees, and the discotic liquid crystal was aligned perpendicular to the film surface. It was confirmed that The slow axis direction was parallel to the rubbing direction (alignment control direction) of the alignment film.

  A polarizing film was produced by adsorbing iodine to a stretched polyvinyl alcohol film. Using the polyvinyl alcohol-based adhesive, the produced optical compensation layer was attached to one side of the polarizing film so that the cellulose acetate film was on the polarizing film side. The transmission axis of the polarizing film and the slow axis of the optical compensation layer were arranged in parallel. A commercially available cellulose acetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was subjected to saponification treatment and attached to the opposite side of the polarizing film using a polyvinyl alcohol adhesive. In this way, a lower polarizing plate 14A was produced. This is pasted on one of the IPS mode liquid crystal cells produced above so that the slow axis of the optical compensation layer is parallel to the rubbing direction of the liquid crystal cell and the discotic liquid crystal application surface side is the liquid crystal cell side. I attached. Subsequently, a commercially available polarizing plate (HLC2-5618, manufactured by Sanlitz Co., Ltd.) was attached to the other upper side of the IPS mode liquid crystal cell as an upper polarizing plate 1A in a crossed Nicol arrangement, to produce a liquid crystal display device. The pair of protective films of this polarizing plate had Re of 3 nm and Rth of 38 nm.

  In addition, the axis angle of the upper polarizing plate and the polarizing film absorption axis is set to 0 degree with respect to the horizontal direction of the display device, the slow axis of the upper protective film is set to 0 degree, and the alignment control direction (rubbing direction) of the substrate on the liquid crystal cell is set. Similarly, the lower polarizing plate has an axial angle of 90 degrees, the lower optical compensation layer has an orientation control direction of 90 degrees, the orientation control direction (rubbing direction) of the lower substrate of the liquid crystal cell is 270 degrees, and the lower protective film The slow axis was 90 degrees and the lower polarizing film absorption axis was 90 degrees.

(Measurement of leakage light of the manufactured liquid crystal display device)
The leakage light of the liquid crystal display device thus manufactured was measured. The measuring device (luminance meter BM-5, manufactured by Topcon Corporation) was used, and the ratio of the light source luminance to the leakage light luminance was defined as the transmittance. The leakage light when observed from the left diagonal direction of 70 degrees was 0.28%. Moreover, even if it observed from the lower side, it was the same leak light transmittance. That is, the same effect can be obtained even when the upper side and the lower side are interchanged with the liquid crystal cell as the center.

[Example 12]
In the liquid crystal display device manufactured in Example 1, the slow axis of the lower protective film was set to 0 degree as the horizontal reference of the display device. Other configurations were the same as those in Example 1. The leakage light when observed from the left diagonal direction of 70 degrees was 0.35%.

[Example 13]
A commercially available polarizing plate (HLC2-5618, manufactured by Sanritz Co., Ltd.) was attached to both sides of the produced IPS mode liquid crystal cell 1 in a crossed Nicol arrangement to produce a liquid crystal display device. An optical compensation layer was not used. In the liquid crystal display device, as in Example 1, the polarizing plate was attached so that the transmission axis of the upper polarizing plate was parallel to the rubbing direction of the liquid crystal cell. The leakage light of the liquid crystal display device thus manufactured was measured. The leakage light when observed from the left diagonal direction of 70 degrees was 0.72%.

[Example 14]
TD80 (Re is 3 nm, Rth is 38 nm) is used as the protective film and support used in Example 11 for the upper polarizing plate in the configuration of Example 13, and the optical compensation layer is further supported by the same production method as Example 11 It was formed by rubbing in a direction parallel to the axis. The produced protective film with an optical compensation layer was bonded to the liquid crystal cell-side protective film of the upper polarizing plate with an adhesive so that the slow axes of the protective films were substantially perpendicular to each other. The leakage light when observed from the left diagonal direction of 70 degrees was 0.35%.

[Example 15]
In the liquid crystal display device manufactured in Example 11, the orientation control direction of the same discotic liquid crystalline compound as in Example 11 was set to 90 degrees, and other configurations were the same as those in Example 1. The leakage light when observed from the left diagonal direction of 70 degrees was 0.75%.

[Example 16]
In the liquid crystal display device fabricated in Example 11, the protective film on the liquid crystal cell side of the upper polarizing plate was the protective film of the lower polarizing plate, the same Re value was 10 nm, and the Rth value was 102 nm. And no optical compensation layer was disposed. The leakage light when observed from the left diagonal direction of 70 degrees was 0.6%.

1 is a schematic diagram illustrating an embodiment of a liquid crystal display device of the present invention. It is a schematic diagram of the liquid crystal display device of a reference example . It is a schematic diagram which shows the structure of the liquid crystal display device of the IPS mode of a reference example .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper polarizing film 1A Upper polarizing plate 2 Absorption axis 3 of upper polarizing film, 3a Upper protective film 4 Slow axis 5 of upper protective film Liquid crystal cell upper substrate 6 Upper substrate Liquid crystal alignment rubbing direction 7 Liquid crystalline molecule 8 Liquid crystal cell lower Side substrate 9 Lower substrate Liquid crystal alignment rubbing direction 10 Optical compensation layer 11 Optical compensation layer orientation control direction 12, 12a Lower protective film 13 Slow axis 14 of lower protective film Lower polarizing film 14A Lower polarizing film 15 Absorption axis 16 of lower polarizing film Linear electrode

Claims (5)

VA mode liquid crystal display having a pair of opposed substrates having electrodes on at least one side, a liquid crystal layer sandwiched between the substrates, and first and second polarizing plates arranged outside the liquid crystal layer A device,
The product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn is 0.1 to 1.0 μm,
Each of the first and second polarizing plates has a polarizing film and a pair of protective films sandwiching the polarizing film,
At least one of the pair of protective films has a slow axis substantially coinciding with the direction in which the average refractive index of the film surface is maximized, and the slow axis of the protective film on the side close to the liquid crystal layer and the The absorption axis of the polarizing film intersects at 20 ° to 70 °,
The protective film disposed on the side close to the liquid crystal layer of the pair of protective films has a thickness d ₁ (nm), and has three average refractive indexes nx, ny in the x, y, and z axis directions orthogonal to each other. And nz, the main average refraction in a plane parallel to the surface of the liquid crystal layer is nx and ny (where ny <nx), and the main average refractive index in the thickness direction of the liquid crystal layer is nz. At an arbitrary wavelength λ in the optical region,
- 5 nm ≦ {(nx- ny) × d 1} ≦ 50nm, and 50nm ≦ [{(nx + ny ) / 2-nz} × d 1] ≦ 300nm
VA mode liquid crystal display device that satisfies the above relationship. 2. The VA mode liquid crystal display device according to claim 1, wherein the liquid crystal layer includes a nematic liquid crystal material, and liquid crystal molecules of the nematic liquid crystal material are aligned at ± 5 ° perpendicular to the surfaces of the pair of substrates during black display. 3. The VA mode according to claim 1, wherein a value of {(nx−ny) × d ₁ } of the protective film disposed on the side closer to the liquid crystal layer of the first and second polarizing plates is 2 to 30 nm. Liquid crystal display device. 4. The VA mode liquid crystal display device according to claim 1, wherein the slow axis of the protective film close to the liquid crystal layer and the absorption axis of the polarizing film intersect at 40 ° to 50 °. 5. . The phase difference plate of ny = nz and nx> ny is provided between the protective film on the side close to at least one liquid crystal layer of the first and second polarizing plates and the liquid crystal layer. The VA mode liquid crystal display device according to any one of the above.

Images