JP4726740B2 - Optical compensation film and liquid crystal display device - Google Patents

Description

  The present invention relates to a liquid crystal display device, particularly an in-plane switching mode liquid crystal display device that performs display by applying a horizontal electric field to liquid crystal molecules aligned in the horizontal direction, and to improve the viewing angle characteristics of the liquid crystal display device. The present invention relates to a contributing optical compensation film.

  As a liquid crystal display device, a liquid crystal layer formed by twisting nematic liquid crystals is sandwiched between two polarizing plates arranged with the polarization axes orthogonal to each other, and an electric field is applied in a direction perpendicular to the substrate, so-called TN. Modes are widely used. In this system, since the liquid crystal rises with respect to the substrate during black display, birefringence occurs due to liquid crystal molecules when viewed from an oblique direction, and light leakage occurs. To solve this problem, a system for optically compensating the liquid crystal cell and preventing this light leakage by using a film in which liquid crystalline molecules are hybrid-oriented has been put into practical use. However, even if liquid crystal molecules are used, it is very difficult to completely optically compensate the liquid crystal cell without any problem, resulting in a problem that gradation reversal in the lower direction of the screen cannot be suppressed.

  In order to solve such a problem, a liquid crystal display device using a so-called in-plane switching (IPS) mode in which a lateral electric field is applied to the liquid crystal, or a liquid crystal having a negative dielectric anisotropy is vertically aligned in the panel. A vertical alignment (VA) mode in which alignment is divided by protrusions and slit electrodes has been proposed and put into practical use. In recent years, these panels have been developed not only for monitor applications but also for TV applications, and screen brightness has been greatly improved accordingly. For this reason, slight light leakage in the diagonally oblique incidence direction during black display, which has not been considered as a problem in these operation modes, has become apparent as a cause of deterioration in display quality.

As one means for improving the color tone and the viewing angle of black display, the arrangement of an optical compensation material having birefringence characteristics between the liquid crystal layer and the polarizing plate is also studied in the IPS mode. For example, by arranging a birefringent medium having an optical axis orthogonal to each other to compensate for the increase / decrease in retardation of the liquid crystal layer during tilting, a white display or a halftone display is diagonally arranged between the substrate and the polarizing plate. It is disclosed that coloring can be improved when viewing directly from (see Patent Document 1).
In addition, a method using an optical compensation film made of a styrenic polymer having a negative intrinsic birefringence or a discotic liquid crystalline compound (see Patent Documents 2, 3, and 4), or an optical axis as an optical compensation film with positive birefringence. Is a method of combining a film in the plane of the film with a film having a positive birefringence and an optical axis in the normal direction of the film (see Patent Document 5), biaxial optical compensation with a retardation of 1/2 wavelength A method using a sheet (see Patent Document 6), a method using a film having a negative retardation as a protective film of a polarizing plate, and providing an optical compensation layer having a positive retardation on this surface (see Patent Document 7) Proposed.
Japanese Patent Laid-Open No. 9-80424 Japanese Patent Laid-Open No. 10-54982 JP-A-11-202323 Japanese Patent Laid-Open No. 9-292522 JP 11-133408 A JP-A-11-305217 JP-A-10-307291

  However, many of the proposed methods are methods that improve the viewing angle by canceling the birefringence anisotropy of the liquid crystal in the liquid crystal cell, so the polarization axis crossing angle when the orthogonal polarizing plate is viewed from an oblique direction. There is a problem that the light leakage based on the deviation from orthogonality cannot be solved sufficiently. Even in a system that can compensate for this light leakage, it is very difficult to completely optically compensate the liquid crystal cell without any problem. Furthermore, in the optical compensation sheet for IPS mode liquid crystal cell that performs optical compensation with the stretched birefringent polymer film, it is necessary to use a plurality of films. As a result, the thickness of the optical compensation sheet increases, and the display device becomes thinner. It is disadvantageous. 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.

  Furthermore, there is a problem that light leakage from an oblique direction during black display is not completely suppressed in the visible light region, and the viewing angle is not sufficiently expanded. More importantly, in the oblique direction during black display, it is difficult to completely compensate for light leakage at all wavelengths of visible light, so that there is a problem that the azimuth direction dependency of color misregistration occurs. It was. In particular, regarding the optical compensation used in the IPS mode, the difference between the in-plane retardation wavelength dispersion and the retardation wavelength dispersion in the thickness direction has not been sufficiently considered, and the effect of suppressing light penetration is insufficient. There was a problem that there was.

  The present invention has been made in view of the above-mentioned problems, and has an object to provide a liquid crystal display device, particularly an IPS liquid crystal display device, which has a simple structure and improved display angle characteristics as well as display quality. To do. Another object of the present invention is to provide an optical compensation film that contributes to the improvement of viewing angle characteristics of a liquid crystal display device, particularly an IPS liquid crystal display device.

Means for solving the above-mentioned problems are as follows.
[1] An optical compensation film having at least two layers of a first retardation layer exhibiting optical anisotropy and a second retardation layer exhibiting optical anisotropy,
When the in-plane retardation at the wavelength λ of the first and second retardation layers is Re (λ) and the retardation in the thickness direction is Rth (λ),
A ratio Re / Rth (450 nm) of Re and Rth at a wavelength of 450 nm of the first retardation layer is 0.4 to 0.95 times Re / Rth (550 nm) at a wavelength of 550 nm, and Re / Rth (at a wavelength of 650 nm). 650 nm) is 1.05 to 1.93 times Re / Rth (550 nm), Rth (550 nm) is 70 nm to 400 nm, Re (550 nm) is 20 nm to 150 nm, and the second phase difference An optical compensation film in which Re (550 nm) of the layer is substantially 0 and Rth (550 nm) is from −80 nm to −400 nm.
[2] A liquid crystal layer including at least a first polarizing film, a first retardation layer, a second retardation layer, and a liquid crystal cell having a liquid crystal layer and a pair of substrates sandwiching the liquid crystal layer, during black display A liquid crystal display device in which liquid crystal molecules therein are aligned substantially parallel to the surfaces of the pair of substrates,
When the in-plane retardation at the wavelength λ of the first and second retardation layers is Re (λ) and the retardation in the thickness direction is Rth (λ),
A ratio Re / Rth (450 nm) of Re and Rth at a wavelength of 450 nm of the first retardation layer is 0.4 to 0.95 times Re / Rth (550 nm) at a wavelength of 550 nm, and Re / Rth (at a wavelength of 650 nm). 650 nm) is 1.05 to 1.93 times Re / Rth (550 nm), Rth (550 nm) is 70 nm to 400 nm, and Re (550 nm) is 20 nm to 150 nm,
Re (550 nm) of the second retardation layer is substantially 0, Rth (550 nm) is −80 nm to −400 nm, and the transmission axis of the first polarizing film is the slow phase of the liquid crystal molecules in the liquid crystal layer during black display A liquid crystal display device parallel to the axial direction.
[3] The first polarizing film, the first retardation layer, the second retardation layer, and the liquid crystal cell are arranged in this order, and the slow axis of the first retardation layer is the first retardation layer. The liquid crystal display device according to [2], which is substantially parallel to the transmission axis of the polarizing film.
[4] The first polarizing film, the second retardation layer, the first retardation layer, and the liquid crystal cell are arranged in this order, and the slow axis of the first retardation layer is the first polarizing film. The liquid crystal display device according to [2], which is substantially perpendicular to a transmission axis of the liquid crystal display.
[5] A second polarizing film having a transmission axis perpendicular to the transmission axis of the first polarizing film is further provided, and the first retardation layer and the second polarizing film are interposed between the first and second polarizing films. The liquid crystal display device according to any one of [2] to [4], wherein the retardation layer and the liquid crystal cell are disposed.
[6] Retardation in the thickness direction of the protective film on the side closer to the liquid crystal layer of the pair of protective films, having a pair of protective films arranged with the first polarizing film and / or the second polarizing film interposed therebetween The liquid crystal display device according to any one of [2] to [5], wherein Rth is 40 nm or less.
[7] It has a pair of protective films arranged with the first polarizing film and / or the second polarizing film interposed therebetween, and the protective film on the side close to the liquid crystal layer of the pair of protective films is a cellulose acylate film or The liquid crystal display device according to any one of [2] to [6], which is a norbornene film.
[8] The second retardation layer includes a layer formed of a composition containing a rod-like liquid crystal compound, and the molecules of the rod-like liquid crystal compound are fixed in a substantially vertically aligned state in the layer [ The liquid crystal display device according to any one of 2] to [7].

  According to the present invention, it is possible to provide a liquid crystal display device, particularly an IPS liquid crystal display device, which has a simple configuration and improved not only display quality but also viewing angle characteristics. Moreover, according to this invention, the optical compensation film which contributes to the improvement of the viewing angle characteristic of a liquid crystal display device, especially an IPS type | mold liquid crystal display device can be provided.

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, an embodiment of the liquid crystal display device of the present invention and its constituent members will be described in order. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

  In the present specification, “parallel” and “orthogonal” mean that the angle is within a range of strictly less than ± 10 °. In this range, an error from a strict angle is preferably less than ± 5 °, and more preferably less than ± 2 °. Further, “substantially vertical” means within a range of less than ± 20 ° from a strict vertical angle. In this range, an error from a strict angle is preferably less than ± 15 °, and more preferably less than ± 10 °. Further, the “slow axis” means a direction in which the refractive index is maximized. Further, the measurement wavelength of retardation and refractive index is a value at λ = 550 nm in the visible light region unless otherwise specified.

  In this specification, “polarizing plate” is cut into a size to be incorporated into a long polarizing plate and a liquid crystal device unless otherwise specified (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. “Polarizing plate” means a laminate having a transparent protective film for protecting the polarizing film on at least one side of the “polarizing film”. It shall be.

  In this specification, Re (λ) and Rth (λ) respectively represent in-plane retardation and retardation in the thickness direction at a wavelength λ. The measurement wavelength λ nm may be any wavelength as long as it is in the visible light range, specifically 400 to 800 nm, but is preferably in the range of 400 to 750 nm, preferably in the range of 400 nm to 700 nm. More preferably it is. In this specification, unless otherwise specified, Re and Rth mean values measured at 530 to 600 nm (or values calculated based on these values). In-plane retardation (Re) is a value measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments). When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth is calculated by the following method.

Rth is defined as Re, with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis) (in the absence of the slow axis, any direction in the film plane is the rotation axis). )) At a step of 10 degrees from the normal direction to 50 degrees on one side with respect to the film normal direction, light of wavelength λ nm is incident from each inclined direction, and a total of 6 points are measured, and the measured retardation value KOBRA 21ADH or WR is calculated based on the assumed average refractive index and the input film thickness value.
In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.
In addition, the retardation value is measured from the two inclined directions, with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), Based on the value, the assumed value of the average refractive index, and the input film thickness value (d), Rth can also be calculated from the following equations (1) and (2).

上記式中のＲｅ(θ)は法線方向から角度θ傾斜した方向におけるレターデーション値を表す。
上記式中のｎｘは面内における遅相軸方向の屈折率を表し、ｎｙは面内においてｎｘに直交する方向の屈折率を表し、ｎｚはｎｘ及びｎｙに直交する方向の屈折率を表す。

Re (θ) in the above formula represents a retardation value in a direction inclined by an angle θ from the normal direction.
In the above formula, nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, and nz represents the refractive index in the direction perpendicular to nx and ny.

In the case where the film to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film having no so-called optic axis, Rth is calculated by the following method. Rth is the Re in 10 degree steps from −50 degrees to +50 degrees with respect to the normal direction of the film, with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis). 11 points of light having a wavelength of λ nm are incident from an inclined direction, and KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed average refractive index, and the input film thickness value. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny and nz. In this specification, unless otherwise specified, the measurement wavelength is 590 nm, and the measurement value is 25 ° C. and 60% RH.
Here, in this specification, as wavelengths of R, G, and B, R has a wavelength of 650 nm, G has a wavelength of 550 nm, and B has a wavelength of 450 nm. The wavelengths of R, G, and B are not necessarily represented by these wavelengths, but are considered to be suitable wavelengths for defining the optical characteristics that exhibit the effects of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 and 3 are schematic views of an embodiment of the liquid crystal display device of the present invention. FIG. 2 is a schematic diagram showing an example of a pixel region of the liquid crystal display device of the present invention.
[Liquid Crystal Display]
The liquid crystal display device shown in FIG. 1 includes polarizing films 8 and 20, a first retardation layer 10, a second retardation layer 12, substrates 13 and 17, and a liquid crystal layer 15 sandwiched between the substrates. . The polarizing films 8 and 20 are sandwiched between protective films 7a and 7b and 19a and 19b, respectively.

  In the liquid crystal display device of FIG. 1, the liquid crystal cell includes substrates 13 and 17 and a liquid crystal layer 15 sandwiched between them. The product Δn · d of the thickness d (μm) of the liquid crystal layer 15 and the refractive index anisotropy Δn is optimal in the range of 0.2 to 0.4 μm for the IPS type having no twisted structure in the transmission mode. . In this range, the white display luminance is high and the black display luminance is small, so that a bright and high-contrast display device can be obtained. An alignment film (not shown) is formed on the surfaces of the substrates 13 and 17 that are in contact with the liquid crystal layer 15, and the liquid crystal molecules are aligned substantially parallel to the surfaces of the substrates 13 and 17 and applied to the alignment films. By the rubbing treatment directions 14 and 18 and the like, the liquid crystal molecule alignment direction in the voltage non-application state or the low application state is controlled, and has a slow axis 16 in a predetermined direction. Further, an electrode (not shown) capable of applying a voltage to the liquid crystal molecules is formed on the inner surface of the substrate 13 or 17.

  FIG. 2 schematically shows the orientation of the liquid crystal molecules in one pixel region of the liquid crystal layer 15. FIG. 2 shows the alignment of liquid crystal molecules in a very small area corresponding to one pixel of the liquid crystal layer 15 in the rubbing direction 4 of the alignment film formed on the inner surfaces of the substrates 13 and 17 and the substrates 13 and 17. It is the schematic diagram shown with the electrodes 2 and 3 which can apply a voltage to the liquid crystal molecule formed in the inner surface. When active driving is performed using a nematic liquid crystal having positive dielectric anisotropy as a field effect liquid crystal, the liquid crystal molecule alignment directions in a no voltage application state or a low application state are 5a and 5b. A display is obtained. When applied between the electrodes 2 and 3, the liquid crystal molecules change their alignment direction in the directions of 6 a and 6 b in accordance with the voltage. Usually, bright display is performed in this state.

In FIG. 1 again, the polarizing film 8 and the polarizing film 20 are arranged with their transmission axes 9 and 21 orthogonal to each other. The slow axis 11 of the first retardation layer 10 is parallel to the transmission axis 9 of the polarizing film 8 and the slow axis direction 16 of the liquid crystal molecules in the liquid crystal layer 15 during black display.
In the liquid crystal display device shown in FIG. 1, the configuration in which the polarizing film 8 is sandwiched between the two protective films 7a and 7b is shown, but the protective film 7b may be omitted. Further, although the polarizing film 20 is also sandwiched between the two protective films 19a and 19b, the protective film 19a on the side close to the liquid crystal layer 15 may be omitted. In the embodiment of FIG. 1, the first retardation layer and the second retardation layer may be disposed between the liquid crystal cell and the viewing-side polarizing film with reference to the position of the liquid crystal cell. You may arrange | position between the liquid crystal cell and the polarizing film of the back side.

  The first retardation layer 10 and the second retardation layer contribute to optical compensation of the retardation of the liquid crystal cell. The ratio Re / Rth (450 nm) of Re and Rth at a wavelength of 450 nm of the first retardation layer 10 is 0.4 to 0.95 times Re / Rth (550 nm) at a wavelength of 550 nm, and Re / Rth at a wavelength of 650 nm. (650 nm) is 1.05 to 1.93 times Re / Rth (550 nm), Rth (550 nm) is 70 nm to 400 nm, and Re (550 nm) is 20 nm to 150 nm. On the other hand, Re (550 nm) of the second retardation layer 12 is substantially 0, and Rth (550 nm) is −80 nm to −400 nm. In this embodiment, the first retardation layer 10 is arranged with the slow axis 11 parallel to the transmission axis 9 of the polarizing film 8.

Here, the optical compensation effect obtained by the first and second retardation layers in the liquid crystal display device having the configuration of FIG. 1 will be described using the Poincare sphere shown in FIG. Here, the light is incident from the lower polarizing film 20 side, and the propagation direction of the light is set to a direction having an azimuth angle of 45 degrees and a polar angle of 34 degrees. In FIG. 4, the Poincare sphere is viewed from the positive direction of the S2 axis. The “polar angle” refers to the inclination in the z-axis direction when the layer plane (light incident surface) of the retardation layer is the xy plane, and the polar angle = 0 ° is parallel to the layer plane. The angle = 90 ° coincides with the normal direction of the layer plane. The “azimuth angle” is an inclination with respect to one of the orthogonal axes in the plane of the retardation layer. For example, when the horizontal direction is the right side and the horizontal direction is the x-axis + side toward the layer plane of the retardation layer. It means the angle formed with the counterclockwise x-axis.
In FIG. 4, the polarization state of the light passing through the polarizing film 20 corresponds to point A. On the other hand, the direction of the absorption axis of the polarizing film 8, that is, the polarization state completely absorbed by the polarizing film 8, corresponds to the B point. In general, the OFF AXIS loss of light in the oblique direction during black display is caused by the deviation of the points A and B. The role of the optical compensation film is to finally convert the polarization state at point A, which is the first polarization state, into the polarization state at point B, including the transition caused by passing through the liquid crystal layer. If the polarization state finally becomes the B ′ point that is not the B point, light leakage proportional to the distance from the B point to the B ′ point occurs. In this aspect, by combining the first and second retardation layers exhibiting predetermined optical characteristics and arranging them in a predetermined order, light leakage in an oblique direction during black display with the final polarization state as point B In addition, the color shift depending on the viewing angle is suppressed.

  In the liquid crystal display device having the configuration of FIG. 1, first, the polarization state of the light that has passed through the polarizing film 20 becomes point A, and even after passing through the protective film 19a having a small optical anisotropic layer, the polarization state is It remains in the vicinity of point A. For example, when the retardation of the protective film 19a is set to almost 0, the polarization state does not move from the point A at all. After that, when passing through the second retardation layer, the polarization state changes. However, since the second retardation layer 12 has a positive refractive index anisotropy and an optical axis in a substantially vertical direction, on the Poincare sphere, The transition of the polarization state by passing through the second retardation layer is a rotation represented by an arrow from top to bottom as shown in FIG. The rotation angle is proportional to the value Δn′d ′ / λ obtained by dividing the effective retardation Δn′d ′ from the oblique direction of the second retardation layer 12 by the wavelength, and this Δn′d ′ / λ value. Is not constant because the wavelengths of R light, G light, and B light are different. Therefore, the polarization state after passing through the second retardation layer 12 is different in each of R, G, and B as shown in FIG. In this aspect, the second phase difference is obtained by passing the first retardation layer 10 in which the Re / Rth value, Re (550 nm) value, and Rth (550 nm) in R, G, and B described above satisfy a predetermined relationship. R light, G light, and B light that pass through the layer 12 and are in different polarization states are transitioned to a point B that is in the same polarization state. As a result, light incident obliquely during black display is blocked by the polarizing film 8 and light leakage is reduced, and coloring dependent on the viewing angle can be eliminated.

  In this embodiment, the first retardation layer 10 and the second retardation layer 12 may be incorporated in the liquid crystal display device as an optical compensation film that is an integral member, or incorporated as individual optical compensation films. It may be. Moreover, you may incorporate in the liquid crystal display device as an elliptically polarizing plate integrated with the polarizing film 8 and its protective film 7a, 7b.

Another embodiment of the present invention is shown in FIG. In addition, the same number is attached | subjected about the member same as FIG. 1, and detailed description is abbreviate | omitted.
In the liquid crystal display device of FIG. 3, the arrangement order of the second retardation layer 12 and the first retardation layer 10 is reversed, and the second retardation layer 12 is disposed between the polarizing film 8 and the first retardation layer 10. ing. In the embodiment shown in FIG. 3, the first retardation layer 10 has a slow axis 11 perpendicular to the transmission axis 9 of the polarizing film 8 and the slow axis direction 16 of the liquid crystal molecules in the liquid crystal layer 15 during black display. Be placed. In the aspect of FIG. 3, the first retardation layer and the second retardation layer may be disposed between the liquid crystal cell and the viewing-side polarizing film with reference to the position of the liquid crystal cell. You may arrange | position between the liquid crystal cell and the polarizing film of the back side.

  As in the liquid crystal display device of FIG. 1, the protective film 7b on the side close to the liquid crystal layer 15 of the polarizing film 8 may not be provided, and the protective film 19a on the side of the polarizing film 20 close to the liquid crystal layer 15 is not provided. May be. Further, like the liquid crystal display device of FIG. 1, the first retardation layer 10 and the second retardation layer 12 may be incorporated in the liquid crystal display device as an optical compensation film that is an integral member, respectively. It may be incorporated as a single optical compensation film. Moreover, you may incorporate in the liquid crystal display device as an elliptically polarizing plate integrated with the polarizing film 8 and its protective film 7a, 7b.

  The optical compensation effect of the liquid crystal display device having the configuration shown in FIG. 3 can also be described using the Poincare sphere in the same manner as the liquid crystal display device having the configuration shown in FIG.

  1 and 3 show a mode of a transmissive mode display device including an upper polarizing plate and a lower polarizing plate, the present invention is a mode of a reflective mode including only one polarizing plate. In such a case, since the optical path in the liquid crystal cell is doubled, the optimum value Δn · d of the liquid crystal layer is about ½ of the above value. The liquid crystal cell used in the present invention is not limited to the IPS mode, and any liquid crystal display device in which liquid crystal molecules are aligned substantially parallel to the surfaces of the pair of substrates during black display can be used. It can be used suitably. Examples thereof include a ferroelectric liquid crystal display device, an antiferroelectric liquid crystal display device, and an ECB type liquid crystal display device.

  Moreover, the liquid crystal display device of this invention is not limited to the structure shown in FIGS. 1-3, The other member may be included. For example, a color filter may be disposed between the liquid crystal layer and the polarizing film. Further, an antireflection treatment or a hard coat may be applied to the surface of the protective film of the polarizing film. Moreover, you may use what gave electroconductivity to the structural member. 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 this case, the arrangement of the backlight may be on the upper side or the lower side in FIGS. In addition, a reflective polarizing plate, a diffusion plate, a prism sheet, or a light guide plate can be disposed between the liquid crystal layer and the backlight. In addition, as described above, 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 the back side of the liquid crystal cell or the lower side of the liquid crystal cell. A reflective film is disposed on the inner surface of the substrate. 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 a three-terminal or two-terminal semiconductor element such as TFT or MIM. Of course, a mode applied to a passive matrix liquid crystal display device called time-division driving is also effective.

  Hereinafter, preferred optical characteristics of various members usable in the liquid crystal display device of the present invention, materials used for the production thereof, manufacturing methods, and the like will be described in detail.

First, the first and second retardation layers will be described. The first and second retardation layers may be composed of only one optical anisotropic layer that satisfies the above optical characteristics alone, or a plurality of optical elements that satisfy the above optical characteristics by combining a plurality of layers. It may be a laminate of anisotropic layers. Moreover, the laminated body of one or more optically anisotropic layers and one or more optically isotropic layers may be sufficient.
[First retardation layer]
The first retardation layer used in the present invention has Rth (550 nm) of 70 to 400 nm and Re (550 nm) of 20 to 150 nm. In order to further reduce light leakage in an oblique direction, Re (550 nm) of the first retardation layer is more preferably 40 nm to 115 nm, further preferably 60 nm to 95 nm, and Rth (550 nm) is 100 to 400 nm is preferable, and 200 to 300 nm is more preferable. Further, in the first retardation layer, the Re / Rth ratio Re / Rth (450 nm) at a wavelength of 450 nm is 0.4 to 0.95 times Rep / Rth (550 nm) at a wavelength of 550 nm. 5 to 0.8 times), and Re / Rth (650 nm) at a wavelength of 650 nm is 1.05 to 1.93 times (preferably 1.2 to 1.6 times) Re / Rth (550 nm). . Re / Rth (550 nm) is preferably from 0.1 to 0.6, more preferably from 0.15 to 0.4, and even more preferably from 0.18 to 0.3.
Further, Nz defined by Nz = (nx−nz) / (nx−ny) of the first retardation layer is preferably 1.5 to 7, and preferably 2.0 to 5.5. More preferably, it is 2.5 to 4.5.

  As long as the first retardation layer has the optical characteristics, the material and form thereof are not particularly limited. For example, a retardation film made of a birefringent polymer film may be used. Further, as described above, the first retardation layer may be a laminate, for example, a support formed of a polymer film or the like, and a film formed by applying a polymer compound solution or melt on the support. And a laminated film having a support made of a polymer film and the like, and an optically anisotropic layer formed thereon from a composition containing a low-molecular or high-molecular liquid crystalline compound, etc. Either can be used. Moreover, each can also be laminated | stacked and used. In the aspect in which the first retardation layer is a laminate of an optically anisotropic layer formed from a liquid crystalline composition and a support made of a polymer film or the like that supports the optically anisotropic layer, the support is It may or may not contribute to the optical characteristics.

  In particular, in the present invention, it is one feature that the first retardation layer exhibits a predetermined wavelength dispersion characteristic. The wavelength dispersion characteristics of the birefringent polymer are as follows. For Re, the side chain is oriented in the direction perpendicular to the stretching direction, and a compound that reversely disperses retardation is added. For Rth, flatness that increases Rth only on the short wave side. It can be adjusted to a desired range by adding a compound having a high value. The wavelength dispersion characteristic of the optically anisotropic layer formed from the liquid crystal composition can be adjusted to a desired range by adjusting the absorption wavelength of the liquid crystal composition to be used to the short wavelength side.

  The birefringent polymer film is preferably a film having excellent controllability of birefringence characteristics, transparency and heat resistance. In this case, the polymer material to be used is not particularly limited as long as it is a polymer capable of achieving uniform biaxial orientation, but is preferably a conventionally known material that can be formed by a solution casting method or an extrusion method, and is preferably a norbornene-based material. Polymers, polycarbonate polymers, polyarylate polymers, polyester polymers, aromatic polymers such as polysulfone, cellulose acylate, or polymers obtained by mixing two or more of these polymers It is done. Among these, norbornene polymers and cellulose acylate are preferable.

The first retardation layer is biaxially oriented. A biaxially oriented polymer film is a film made of a polymer (preferably a thermoplastic resin) produced by an appropriate method such as an extrusion molding method or a casting film forming method, such as a longitudinal stretching method using a roll or a tenter. It can be obtained by subjecting it to a stretching treatment by a transverse stretching method or a biaxial stretching method. In the longitudinal stretching method using the roll, an appropriate heating method such as a method using a heating roll, a method of heating an atmosphere, or a method of using them together can be adopted. In the biaxial stretching method using a tenter, an appropriate method such as a simultaneous biaxial stretching method using an all tenter method or a sequential biaxial stretching method using a roll tenter method can be employed.
Moreover, a thing with little orientation nonuniformity and phase difference nonuniformity is preferable. The thickness can be appropriately determined depending on the phase difference or the like, but in general, it is preferably 1 to 300 μm, more preferably 10 to 200 μm, more preferably 20 to 150 μm from the viewpoint of thinning. Is more preferable.

  As the norbornene-based polymer, norbornene and derivatives thereof, tetracyclododecene and derivatives thereof, dicyclopentadiene and derivatives thereof, methanotetrahydrofluorene and derivatives thereof monomers are polymers of monomers as a main component, Ring-opening polymer of norbornene monomer, ring-opening copolymer of norbornene monomer and other monomer capable of ring-opening copolymerization, addition polymer of norbornene monomer, copolymerizable with norbornene monomer Examples include addition copolymers with other monomers and hydrogenated products thereof. Among these, from the viewpoints of heat resistance, mechanical strength, and the like, a ring-opening polymer hydride of a norbornene monomer is most preferable. The molecular weight of the norbornene polymer, the polymer of the monocyclic olefin, or the polymer of the cyclic conjugated diene is appropriately selected according to the purpose of use, but a cyclohexane solution (a toluene solution when the polymer resin does not dissolve) The weight average molecular weight in terms of polyisoprene or polystyrene measured by gel permeation chromatography is usually 5,000 to 500,000, preferably 8,000 to 200,000, more preferably 10,000 to 100,000. When it is in the range of 000, the mechanical strength of the film (A) and the moldability are highly balanced and suitable.

  The acyl group of cellulose acylate may be an aliphatic group or an allyl group, and is not particularly limited. They are, for example, cellulose alkylcarbonyl esters, alkenylcarbonyl esters or aromatic carbonyl esters, aromatic alkylcarbonyl esters, etc., each of which may further have a substituted group, and an ester having a total carbon number of 22 or less. Groups are preferred. These preferable cellulose acylates include acyl groups having a total carbon number of 22 or less in the ester portion (for example, acetyl, propionyl, butyroyl, barrel, heptanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, hexadecanoyl, octadecanoyl, etc. ), Arylcarbonyl groups (such as acryl and methacryl), allylcarbonyl groups (such as benzoyl and naphthaloyl), and cinnamoyl groups. Among these, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate stearate, cellulose acetate benzoate, and the like are not particularly limited in the case of mixed esters, but preferably acetate is the total ester. It is preferable that it is 30 mol% or more.

  Among these, cellulose acylate is preferred, and photographic grades are particularly preferred, and commercially available photographic grades can be obtained with satisfactory quality such as viscosity average degree of polymerization and substitution degree. As manufacturers of photographic grade cellulose triacetate, Daicel Chemical Industries, Ltd. (for example, LT-20, 30, 40, 50, 70, 35, 55, 105, etc.), Eastman Kodak Company (for example, CAB-551) 0.01, CAB-551-0.02, CAB-500-5, CAB-381-0.5, CAB-381-02, CAB-381-20, CAB-321-0.2, CAP-504 0.2, CAP-482-20, CA-398-3, etc.), Coatles, Hoechst, etc., any of which can use photographic grade cellulose acylate. Further, for the purpose of controlling the mechanical properties and optical properties of the film, plasticizers, surfactants, retardation modifiers, UV absorbers, and the like can be used in the future (reference material: JP-A No. 2002-277632). Gazette, JP-A-2002-182215)

As a method for forming the transparent polymer into a sheet or film, for example, either a hot melt molding method or a solution casting method can be used. The heat-melt molding method can be further classified into an extrusion molding method, a press molding method, an inflation molding method, an injection molding method, a blow molding method, a stretch molding method, etc. Among these methods, mechanical strength, surface In order to obtain a film excellent in accuracy and the like, the extrusion molding method, the inflation molding method, and the press molding method are preferable, and the extrusion molding method is most preferable. The molding conditions are appropriately selected depending on the purpose of use and the molding method. In the case of the heat-melt molding method, the cylinder temperature is preferably set in the range of preferably 100 to 400 ° C, more preferably 150 to 350 ° C. The thickness of the sheet or film is preferably 10 to 300 μm, more preferably 30 to 200 μm.
When the glass transition temperature of the transparent polymer is Tg, the stretching of the sheet or film is preferably in the temperature range of Tg-30 ° C to Tg + 60 ° C, more preferably in the temperature range of Tg-10 ° C to Tg + 50 ° C. In at least one direction, the stretching ratio is preferably 1.01 to 2 times. The stretching direction may be at least one direction, but when the sheet is obtained by extrusion, the direction is preferably the mechanical flow direction (extrusion direction) of the resin. A free shrink uniaxial stretching method, a fixed width uniaxial stretching method, a biaxial stretching method, and the like are preferable. The optical characteristics can be controlled by controlling the draw ratio and the heating temperature.

  In the present invention, it is preferable to use a cellulose acylate film as the first retardation layer. The Re (550 nm) of the cellulose acylate film is adjusted to 20 to 150 nm, and the Rth (550 nm) is adjusted to 70 to 400 nm. In the present invention, the Re / Rth ratio at 450, 550 and 650 nm satisfies the above relationship in the first retardation layer. These optical properties can be adjusted by adding a rod-shaped compound having an aromatic ring to cellulose acylate. Furthermore, a cellulose acylate film having desired optical properties can be produced by adjusting the kind of rod-shaped compound, the amount added, and the draw ratio.

[Cellulose acylate film]
As the raw material cotton of cellulose acylate, a known raw material can be used (for example, refer to the Japanese Society for Invention and Innovation 2001-1745). Cellulose acylate can also be synthesized by a known method (for example, see Mita et al., Wood Chemistry pages 180-190 (Kyoritsu Shuppan, 1968)). The viscosity average polymerization degree of cellulose acylate is preferably 200 to 700, more preferably 250 to 500, and most preferably 250 to 350. The cellulose ester used in the present invention preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a mass average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.5 to 5.0, more preferably 2.0 to 4.5, and more preferably 3.0 to 4.0. Further preferred.

The acyl group of the cellulose acylate film is not particularly limited, but an acetyl group or a propionyl group is preferably used, and an acetyl group is particularly preferable. The degree of substitution of all acyl groups is preferably 2.7 to 3.0, more preferably 2.8 to 2.95. In this specification, the substitution degree of an acyl group is a value calculated according to ASTM D817.
The acyl group is most preferably an acetyl group, and when cellulose acetate having an acyl group is an acetyl group is used, the degree of acetylation is preferably 59.0 to 62.5%, and 59.0 to 61.5%. Is more preferable. When the acetylation degree is within this range, Re does not become larger than the desired value due to the conveying tension during casting, there is little in-plane variation, and there is little change in the retardation value due to temperature and humidity.
The substitution degree of the 6-position acyl group is preferably 0.9 or more from the viewpoint of suppressing variations in Re and Rth.

[Retardation control agent]
In the present invention, it is preferable to use a rod-shaped compound having at least two aromatic rings as a retardation control agent. The rod-like compound preferably has a linear molecular structure. The linear molecular structure means that the molecular structure of the rod-like compound is linear in the most thermodynamically stable structure. The most thermodynamically stable structure can be obtained by crystal structure analysis or molecular orbital calculation. For example, molecular orbital calculation can be performed using molecular orbital calculation software (eg, WinMOPAC2000, manufactured by Fujitsu Limited) to determine the molecular structure that minimizes the heat of formation of the compound. The molecular structure being linear means that in the thermodynamically most stable structure obtained by calculation as described above, the angle formed by the main chain in the molecular structure is 140 degrees or more.

As the rod-shaped compound having at least two aromatic rings, a compound represented by the following general formula (I) is preferable.
Formula (I): Ar ¹ -L ¹ -Ar ²
In the general formula (I), Ar ¹ and Ar ² are each independently an aromatic group.
In the present specification, the aromatic group includes an aryl group (aromatic hydrocarbon group), a substituted aryl group, an aromatic heterocyclic group, and a substituted aromatic heterocyclic group.
An aryl group and a substituted aryl group are more preferable than an aromatic heterocyclic group and a substituted aromatic heterocyclic group. The heterocycle of the aromatic heterocyclic group is generally unsaturated. The aromatic heterocycle is preferably a 5-membered ring, 6-membered ring or 7-membered ring, more preferably a 5-membered ring or 6-membered ring. Aromatic heterocycles generally have the most double bonds. As a hetero atom, a nitrogen atom, an oxygen atom or a sulfur atom is preferable, and a nitrogen atom or a sulfur atom is more preferable. Examples of aromatic heterocycles include furan ring, thiophene ring, pyrrole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine Rings, pyridazine rings, pyrimidine rings, pyrazine rings, and 1,3,5-triazine rings are included.
As the aromatic ring of the aromatic group, a benzene ring, a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, a thiazole ring, an imidazole ring, a triazole ring, a pyridine ring, a pyrimidine ring and a pyrazine ring are preferable, and a benzene ring is particularly preferable. .

  Examples of substituents for substituted aryl groups and substituted aromatic heterocyclic groups include halogen atoms (F, Cl, Br, I), hydroxyl, carboxyl, cyano, amino, alkylamino groups (eg, methylamino, ethylamino) , Butylamino, dimethylamino), nitro, sulfo, carbamoyl, alkylcarbamoyl groups (eg, N-methylcarbamoyl, N-ethylcarbamoyl, N, N-dimethylcarbamoyl), sulfamoyl, alkylsulfamoyl groups (eg, N- Methylsulfamoyl, N-ethylsulfamoyl, N, N-dimethylsulfamoyl), ureido, alkylureido groups (eg, N-methylureido, N, N-dimethylureido, N, N, N′-trimethyl) Ureido), alkyl groups (eg, methyl, ethyl, propyl, butyl, pentyl, Butyl, octyl, isopropyl, s-butyl, t-amyl, cyclohexyl, cyclopentyl), alkenyl groups (eg, vinyl, allyl, hexenyl), alkynyl groups (eg, ethynyl, butynyl), acyl groups (eg, formyl, acetyl, Butyryl, hexanoyl, lauryl), acyloxy groups (eg, acetoxy, butyryloxy, hexanoyloxy, lauryloxy), alkoxy groups (eg, methoxy, ethoxy, propoxy, butoxy, pentyloxy, heptyloxy, octyloxy), aryloxy groups (Eg, phenoxy), alkoxycarbonyl group (eg, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, heptyloxycarbonyl), aryloxycarbo Group (eg, phenoxycarbonyl), alkoxycarbonylamino group (eg, butoxycarbonylamino, hexyloxycarbonylamino), alkylthio group (eg, methylthio, ethylthio, propylthio, butylthio, pentylthio, heptylthio, octylthio), arylthio group (eg, , Phenylthio), alkylsulfonyl groups (eg, methylsulfonyl, ethylsulfonyl, propylsulfonyl, butylsulfonyl, pentylsulfonyl, heptylsulfonyl, octylsulfonyl), amide groups (eg, acetamide, butylamide group, hexylamide, laurylamide) and non- Aromatic heterocyclic groups (eg, morpholyl, pyrazinyl) are included.

Substituents for substituted aryl groups and substituted aromatic heterocyclic groups include halogen atoms, cyano, carboxyl, hydroxyl, amino, alkyl-substituted amino groups, acyl groups, acyloxy groups, amide groups, alkoxycarbonyl groups, alkoxy groups, alkylthios. And groups and alkyl groups are preferred.
The alkyl moiety of the alkylamino group, alkoxycarbonyl group, alkoxy group, and alkylthio group and the alkyl group may further have a substituent. Examples of alkyl moieties and substituents of alkyl groups include halogen atoms, hydroxyl, carboxyl, cyano, amino, alkylamino groups, nitro, sulfo, carbamoyl, alkylcarbamoyl groups, sulfamoyl, alkylsulfamoyl groups, ureido, alkylureido Group, alkenyl group, alkynyl group, acyl group, acyloxy group, alkoxy group, aryloxy group, alkoxycarbonyl group, aryloxycarbonyl group, alkoxycarbonylamino group, alkylthio group, arylthio group, alkylsulfonyl group, amide group and non-aromatic An aromatic heterocyclic group is included. As the substituent for the alkyl moiety and the alkyl group, a halogen atom, hydroxyl, amino, alkylamino group, acyl group, acyloxy group, acylamino group, alkoxycarbonyl group and alkoxy group are preferable.

In the general formula (I), L ¹ is a divalent linking group selected from an alkylene group, an alkenylene group, an alkynylene group, —O—, —CO— and a combination thereof.
The alkylene group may have a cyclic structure. As the cyclic alkylene group, cyclohexylene is preferable, and 1,4-cyclohexylene is particularly preferable. As the chain alkylene group, a linear alkylene group is more preferable than a branched alkylene group.
The number of carbon atoms of the alkylene group is preferably 1-20, more preferably 1-15, still more preferably 1-10, still more preferably 1-8, and most preferably 1-6. It is.

  The alkenylene group and the alkynylene group preferably have a chain structure rather than a cyclic structure, and more preferably have a linear structure rather than a branched chain structure. The alkenylene group and the alkynylene group preferably have 2 to 10 carbon atoms, more preferably 2 to 8, more preferably 2 to 6, still more preferably 2 to 4, and most preferably 2. (Vinylene or ethynylene). The arylene group preferably has 6 to 20 carbon atoms, more preferably 6 to 16, and still more preferably 6 to 12.

The example of the bivalent coupling group which consists of a combination is shown.
L-1: —O—CO-alkylene group —CO—O—
L-2: -CO-O-alkylene group -O-CO-
L-3: —O—CO—alkenylene group —CO—O—
L-4: -CO-O-alkenylene group -O-CO-
L-5: -O-CO-alkynylene group -CO-O-
L-6: -CO-O-alkynylene group -O-CO-
L-7: -O-CO-arylene group -CO-O-
L-8: -CO-O-arylene group -O-CO-
L-9: -O-CO-arylene group -CO-O-
L-10: -CO-O-arylene group -O-CO-

In the molecular structure of the general formula (I), the angle formed by Ar ¹ and Ar ² across L ¹ is preferably 140 degrees or more. As the rod-shaped compound, a compound represented by the following formula (II) is more preferable.
Formula (II): Ar ¹ -L ² -XL ³ -Ar ²
In the general formula (II), Ar ¹ and Ar ² are each independently an aromatic group. The definition and examples of the aromatic group are the same as those of Ar ¹ and Ar ^{2 in} the general formula (I).

In the general formula (II), L ² and L ³ are each independently a divalent linking group selected from an alkylene group, —O—, —CO—, and a group consisting of a combination thereof. The alkylene group preferably has a chain structure rather than a cyclic structure, and more preferably has a linear structure rather than a branched chain structure.
The number of carbon atoms of the alkylene group is preferably 1 to 10, more preferably 1 to 8, still more preferably 1 to 6, still more preferably 1 to 4, and 1 or 2 (methylene or Most preferred is ethylene). L ² and L ³ are particularly preferably —O—CO— or CO—O—.

  In the general formula (II), X is 1,4-cyclohexylene, vinylene or ethynylene. Specific examples of the compound represented by the general formula (I) are shown below.

  Specific examples (1) to (34), (41), and (42) have two asymmetric carbon atoms at the 1-position and the 4-position of the cyclohexane ring. However, since the specific examples (1), (4) to (34), (41), and (42) have a symmetrical meso type molecular structure, there are no optical isomers (optical activity), and geometric isomers (trans Type and cis type). The trans type (1-trans) and cis type (1-cis) of specific example (1) are shown below.

As described above, the rod-like compound preferably has a linear molecular structure. Therefore, the trans type is preferable to the cis type. Specific examples (2) and (3) have optical isomers (a total of four isomers) in addition to geometric isomers. As for geometric isomers, the trans type is similarly preferable to the cis type. The optical isomer is not particularly superior or inferior, and may be D, L, or a racemate. In specific examples (43) to (45), the central vinylene bond includes a trans type and a cis type. For the same reason as above, the trans type is preferable to the cis type.
Other preferred compounds are shown below.

  As the retardation control agent, it is preferable to use a rod-shaped compound having a maximum absorption wavelength (λmax) shorter than 250 nm in the ultraviolet absorption spectrum of the solution, and it is preferable to use two or more rod-shaped compounds having such characteristics in combination. The rod-like compound can be synthesized with reference to methods described in literature. As literature, Mol. Cryst. Liq. Cryst. 53, 229 (1979), 89, 93 (1982), 145, 111 (1987), 170, 43 (1989), J. Am. Am. Chem. Soc. 113, p. 1349 (1991), p. 118, p. 5346 (1996), p. 92, p. 1582 (1970). Org. Chem. 40, 420 pages (1975), Tetrahedron, Vol. 48, No. 16, page 3437 (1992). The addition amount of the retardation control agent is preferably from 0.1 to 30% by mass, and more preferably from 0.5 to 20% by mass, based on the amount of the polymer.

  An aromatic compound is used in 0.01-20 mass parts with respect to 100 mass parts of cellulose acylates. The aromatic compound is preferably used in a range of 0.05 to 15 parts by mass, and more preferably in a range of 0.1 to 10 parts by mass with respect to 100 parts by mass of cellulose acylate. Two or more kinds of compounds may be used in combination.

[Manufacture of cellulose acylate film]
It is preferable to use a cellulose acylate film produced by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) prepared by dissolving cellulose acylate in an organic solvent. The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to contain. Ethers, ketones and esters may have a cyclic structure. A compound having two or more functional groups of ether, ketone, and ester (that is, —O—, —CO—, and COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole. Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms substituted by halogen in the halogenated hydrocarbon is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is most preferable that it is 40-60 mol%. Methylene chloride is a representative halogenated hydrocarbon. Two or more organic solvents may be mixed and used.

The cellulose acylate solution can be prepared by a general method, specifically, at a temperature of 0 ° C. or higher (normal temperature or high temperature). The solution can be prepared by using a dope preparation method and apparatus in a normal solvent cast method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent.
The amount of cellulose acylate is adjusted so as to be contained in the obtained solution in an amount of 10 to 40% by mass. The amount of cellulose acylate is more preferably 10 to 30% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent). The solution can be prepared by stirring the cellulose acylate and the organic solvent at room temperature (0 to 40 ° C.). The high concentration solution may be stirred under pressure and heating conditions. Specifically, the cellulose acylate and the organic solvent are placed in a pressure vessel and sealed, and stirred while being heated to a temperature equal to or higher than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., and more preferably 80 to 110 ° C.

  Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure. When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid. It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall. Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.

  A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, cellulose acylate can be dissolved in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a cellulose acylate with a normal melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly according to a cooling melt | dissolution method. In the cooling dissolution method, first, cellulose acylate is gradually added to an organic solvent at room temperature while stirring. The amount of cellulose acylate is preferably adjusted so as to be contained in the mixture in an amount of 10 to 40% by mass. The amount of cellulose acylate is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture.

The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this way, the mixture of cellulose acylate and organic solvent solidifies.
The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling until the final cooling temperature is reached.

Furthermore, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), cellulose acylate dissolves in the organic solvent. The temperature can be raised by simply leaving it at room temperature or in a warm bath.
The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. .
A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution with the naked eye.

In the cooling dissolution method, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container.
In addition, according to differential scanning calorimetry (DSC), a 20% by mass solution of cellulose acylate (acetylation degree: 60.9%, viscosity average polymerization degree: 299) dissolved in methyl acetate by the cooling dissolution method is There is a quasi-phase transition point between a sol state and a gel state in the vicinity of 33 ° C., and a uniform gel state is obtained below this temperature. Therefore, this solution needs to be stored at a temperature equal to or higher than the pseudo phase transition temperature, preferably about the gel phase transition temperature plus about 10 ° C. However, this pseudo phase transition temperature varies depending on the degree of acetylation of cellulose acylate, the degree of viscosity average polymerization, the solution concentration, and the organic solvent used.

Next, a cellulose acylate film is produced from the prepared cellulose acylate solution (dope) by a solvent cast method.
The dope is cast on a drum or band and the solvent is evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. For casting and drying methods in the solvent casting method, U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.
The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

A plasticizer can be added to the cellulose acylate film in order to improve mechanical properties or increase the drying rate. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethyl hexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.
The addition amount of the plasticizer is preferably 0.1 to 25% by mass of the amount of cellulose acylate, more preferably 1 to 20% by mass, and most preferably 3 to 15% by mass.

  A degradation inhibitor (eg, antioxidant, peroxide decomposer, radical inhibitor, metal deactivator, acid scavenger, amine) may be added to the cellulose acylate film. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The amount of the deterioration inhibitor added is 0.01 to 1 of the solution (dope) to be prepared from the viewpoint that the effect of addition of the deterioration inhibitor is manifested and that the deterioration inhibitor is prevented from bleeding out on the film surface. It is preferable that it is mass%, and it is further more preferable that it is 0.01-0.2 mass%. Examples of particularly preferred deterioration inhibitors include butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

[Stretching treatment of cellulose acylate film]
The retardation of the cellulose acylate film can be adjusted by stretching. The draw ratio is preferably 3 to 100%.
The stretching method is not particularly limited, and an existing method can be used, but tenter stretching is particularly preferably used from the viewpoint of in-plane uniformity. The cellulose acylate film preferably has a width of at least 100 cm, and the variation in the Re value of the entire width is preferably ± 5 nm, and more preferably ± 3 nm. Further, the variation of the Rth value is preferably ± 10 nm, and more preferably ± 5 nm. Further, it is preferable that the variation in the Re value and the Rth value in the length direction is also within the range of the variation in the width direction.
In addition, the stretching process may be performed in the middle of the film forming process, or the raw film that has been formed and wound may be stretched. In the former case, the stretching may be performed in a state including the residual solvent amount, and the stretching can be preferably performed at a residual solvent amount of 2 to 30%. At this time, it is preferable to stretch the film in the direction perpendicular to the longitudinal direction while conveying the film in the longitudinal direction so that the slow axis of the film is orthogonal to the longitudinal direction of the film.
The stretching temperature can be selected appropriately depending on the amount of residual solvent and the film thickness during stretching. When stretching in a state containing a residual solvent, it is preferable to dry after stretching. The drying method can be performed according to the method described in the film production.
The cellulose acylate film after stretching has a thickness of 110 μm or less, preferably 40 to 110 μm, more preferably 60 to 110 μm, and preferably 80 to 110 μm.

[Surface treatment of cellulose acylate film]
When the first retardation layer is made of a cellulose acylate film, the cellulose acylate film may be used as a transparent protective film for a polarizing plate. In such a case, it is preferable to surface-treat the cellulose acylate film.
As the surface treatment, corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment or ultraviolet irradiation treatment is performed. It is particularly preferable to perform acid treatment or alkali treatment, that is, saponification treatment on cellulose acylate.

In the present invention, a film comprising a cellulose acylate composition containing a rod-shaped compound having a linear structure having at least two aromatic rings described above is stretched to obtain desired retardation values Re, Rth, and Re / A cellulose acylate film satisfying the Rth ratio (preferably a cellulose acylate film having a thickness of 40 μm to 110 μm) can be used as the first retardation layer.
In addition, when using a cellulose acylate film as a 1st phase difference layer, this cellulose acylate film may serve as the support body of a 2nd phase difference layer.

[Second retardation layer]
The second retardation layer of the liquid crystal display device of the present invention has Re (550 nm) of approximately 0 and Rth (550 nm) of −80 nm to −400 nm. The more preferable range of Rth (550 nm) of the second retardation layer varies depending on the optical characteristics of other optical members, and in particular, a protective film (for example, a triacetyl cellulose film) of a polarizing film located closer to it. Fluctuates greatly depending on Rth. In order to effectively reduce light leakage in an oblique direction, Rth (550 nm) of the second retardation layer is more preferably −100 nm to −340 nm, and further preferably −120 nm to −270 nm. . On the other hand, Re (550 nm) of the second retardation layer is a value near zero. Specifically, the in-plane retardation Re (550 nm) is preferably 0 to 50 nm, and more preferably 0 to 20 nm.

  The material and form of the second retardation layer are not particularly limited as long as it has the optical characteristics. For example, a retardation film made of a birefringent polymer film may be used. Further, as described above, the second retardation layer may be a laminate, for example, from a support made of a polymer film or the like and a composition containing a low-molecular or high-molecular liquid crystalline compound thereon. Any laminated film having an optically anisotropic layer formed can be used. Moreover, each can also be laminated | stacked and used. In the aspect in which the second retardation layer is a laminate of an optically anisotropic layer formed from a liquid crystalline composition and a support made of a polymer film or the like that supports the optically anisotropic layer, the support is It may or may not contribute to the optical characteristics.

The retardation film made of a birefringent polymer film that satisfies the above optical properties is obtained by stretching a polymer film in the thickness direction of the film, or applying and drying a vinylcarbazole polymer (Japanese Patent Laid-Open No. 2001-091746). Can be easily formed.
In addition, as an optically anisotropic layer formed of a liquid crystalline composition that satisfies the above optical characteristics, a composition containing a cholesteric discotic liquid crystal compound containing a chiral structural unit is applied to the substrate surface, and the cholesteric disco is applied. A layer formed by orienting molecules of a tic liquid crystal compound so that its spiral axis is substantially perpendicular to the substrate and then fixing in the oriented state; and a composition containing a rod-like liquid crystal compound having a positive refractive index anisotropy And the like, and the like. For example, JP-A-6-331826 can be exemplified. No. gazette and Japanese Patent No. 2853064). The rod-like liquid crystal compound may be a low molecular compound or a high molecular compound. Furthermore, not only one optically anisotropic layer but also a plurality of optically anisotropic layers may be laminated to form a second retardation layer exhibiting the above optical characteristics. Further, the second retardation layer may be configured so that the entire laminated body of the support and the optically anisotropic layer satisfies the optical characteristics. As the rod-like liquid crystal compound to be used, those that take a nematic liquid crystal phase, a smectic liquid crystal phase, and a lyotropic liquid crystal phase in a temperature range in which the orientation is fixed are preferably used. A liquid crystal exhibiting a smectic A phase and a B phase capable of obtaining uniform vertical alignment without fluctuation is preferable. In particular, in the presence of an additive, a rod-like liquid crystalline compound that becomes a liquid crystal state in an appropriate orientation temperature range is formed by using a composition containing the additive and the rod-like liquid crystalline compound. Is also preferable.

《Bar-shaped liquid crystalline compound》
In the present invention, the second retardation layer may be formed from a composition containing a rod-like liquid crystalline compound. Examples of the rod-like liquid crystalline compound include 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. In addition to the above low-molecular liquid crystalline molecules, high-molecular liquid crystalline molecules can also be used. As the liquid crystal molecules, those having a partial structure capable of causing polymerization or crosslinking reaction by actinic rays, electron beams, heat, or the like are preferably used. The number of the partial structures is 1 to 6, preferably 1 to 3.

  In the case where the second retardation layer includes an optically anisotropic layer formed from a composition containing a rod-like liquid crystalline compound, the optically anisotropic layer substantially vertically aligns the molecules of the rod-like liquid crystalline compound. It is preferable that the optically anisotropic layer be fixed in that state. The term “substantially perpendicular” means that the angle formed between the layer plane and the director of the molecules of the rod-like liquid crystal compound is in the range of 70 ° to 90 °. These rod-like liquid crystal molecules may be aligned obliquely or may be aligned (hybrid alignment) so that the inclination angle gradually changes. Even in the case of oblique orientation or hybrid orientation, the average inclination angle is preferably 70 ° to 90 °, more preferably 80 ° to 90 °, and most preferably 85 ° to 90 °.

  An optically anisotropic layer formed from a composition containing a rod-shaped liquid crystalline compound is a coating liquid containing a rod-shaped liquid crystalline compound and, if desired, the following polymerizable initiator, air interface vertical alignment agent and other additives. It can be formed by applying to the surface of the vertical alignment film, vertically aligning the rod-like liquid crystalline molecules, and fixing the alignment state. When formed on the temporary support, the optically anisotropic layer may be transferred from the temporary support to the support. Furthermore, not only one optically anisotropic layer but also a plurality of retardation layers may be laminated to produce a second retardation layer that satisfies the above optical characteristics. Further, the second retardation layer may be configured so that the entire laminated body of the support and the optically anisotropic layer satisfies the optical characteristics.

  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).

  After coating the coating liquid on the surface (preferably the surface of the vertical alignment film), it is preferable that the rod-like liquid crystal molecules are vertically aligned by heating or the like if desired, and the alignment state is maintained and fixed. The immobilization is preferably performed by a polymerization reaction of the polymerizable group (P) 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. A photopolymerization reaction is preferred. 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) Description), 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. The light irradiation for polymerizing the rod-like liquid crystalline molecules preferably uses 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 first retardation layer including the optically anisotropic layer is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and even more preferably 1 to 5 μm. preferable.

<< Vertical alignment film >>
In order to align the molecules of the liquid crystal 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 to make a fluorine atom or a hydrocarbon group exist 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 mass, more preferably in a proportion of 0.1 to 70% by mass, and in a proportion of 0.5 to 65% by mass. More preferably, it is most preferable to contain in the ratio of 1-60 mass%. 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 (may be a cycloalkyl group) or an alkenyl group (may be a cycloalkenyl group). The hydrocarbon group may have a substituent that does not exhibit strong hydrophilicity, such as a halogen atom. The number of carbon atoms of the hydrocarbon group is preferably 10 to 100, more preferably 10 to 60, and most preferably 10 to 40. 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 ring bond is a double bond in the range of an aliphatic ring (a range that does not form an aromatic ring). means.

Further, as a means for vertically aligning the liquid crystalline compound, a method of mixing an organic acid with a polymer of polyvinyl alcohol, modified 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. Moreover, quaternary ammonium salts can also be used suitably. The mixing amount is preferably 0.1% by mass to 20% by mass and more preferably 0.5% by mass to 10% by mass with respect to the polymer.

  The saponification degree of the polyvinyl alcohol is preferably 70 to 100%, more preferably 80 to 100%. The polymerization degree of polyvinyl alcohol is preferably 100 to 5000.

  When aligning the molecules of the rod-like liquid crystalline compound, the alignment film is preferably made of a polymer having a hydrophobic group as a functional group in the side chain. The specific type of functional group is determined according to the type of liquid crystal molecule and the required alignment state. For example, the modifying group of the modified polyvinyl alcohol can be introduced by copolymerization modification, chain transfer modification or block polymerization modification. Examples of modifying groups include hydrophilic groups (carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, amino groups, ammonium groups, amide groups, thiol groups, etc.), hydrocarbon groups having 10 to 100 carbon atoms, fluorine atoms Substituted hydrocarbon groups, thioether groups, polymerizable groups (unsaturated polymerizable groups, epoxy groups, azirinidyl groups, etc.), alkoxysilyl groups (trialkoxy, dialkoxy, monoalkoxy) and the like can be mentioned. Specific examples of these modified polyvinyl alcohol compounds include, for example, paragraph numbers [0022] to [0145] in JP-A No. 2000-155216 and paragraph numbers [0018] to [0018] in JP-A No. 2002-62426. And the like described in [0022].

  The alignment film is formed by using a polymer having a side chain having a crosslinkable functional group bonded to the main chain or a polymer having a crosslinkable functional group on a side chain having a function of aligning liquid crystal molecules. When the retardation film is formed using a composition containing a polyfunctional monomer, the polymer in the alignment film and the polyfunctional monomer in the retardation film formed thereon can be copolymerized. As a result, a covalent bond is formed not only between the polyfunctional monomers but also between the alignment film polymers and between the polyfunctional monomer and the alignment film polymer, and the alignment film and the retardation film are firmly bonded. Therefore, the strength of the optical compensation sheet can be remarkably improved by forming the alignment film using a polymer having a crosslinkable functional group. The crosslinkable functional group of the alignment film polymer preferably contains a polymerizable group in the same manner as the polyfunctional monomer. Specific examples include those described in paragraphs [0080] to [0100] in JP-A-2000-155216.

  Apart from the crosslinkable functional group, the alignment film polymer can also be crosslinked using a crosslinking agent. Examples of the crosslinking agent include aldehydes, N-methylol compounds, dioxane derivatives, compounds that act by activating carboxyl groups, active vinyl compounds, active halogen compounds, isoxazole and dialdehyde starch. Two or more kinds of crosslinking agents may be used in combination. Specific examples include compounds described in paragraphs [0023] to [024] in JP-A-2002-62426. Aldehydes having high reaction activity, particularly glutaraldehyde are preferred.

  0.1-20 mass% is preferable with respect to a polymer, and, as for the addition amount of a crosslinking agent, 0.5-15 mass% is more preferable. The amount of the unreacted crosslinking agent remaining in the alignment film is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less. By adjusting in this way, even if the alignment film is used for a long time in a liquid crystal display device or left in a high-temperature and high-humidity atmosphere for a long time, sufficient durability without occurrence of reticulation can be obtained.

  The alignment film can be basically formed by applying a composition containing the polymer and the crosslinking agent, which are alignment film forming materials, onto a transparent support, followed by drying by heating (crosslinking) and rubbing treatment. it can. As described above, the crosslinking reaction may be performed at an arbitrary time after coating on the transparent support. When a water-soluble polymer such as polyvinyl alcohol is used as the alignment film forming material, the coating solution is preferably a mixed solvent of an organic solvent (eg, methanol) having a defoaming action and water. The ratio of water: methanol is preferably 0: 100 to 99: 1, and more preferably 0: 100 to 91: 9. Thereby, generation | occurrence | production of a bubble is suppressed and the defect of the alignment film and also the phase difference layer surface reduces remarkably.

  As a coating method used for producing the alignment film, a spin coating method, a dip coating method, a curtain coating method, an extrusion coating method, a rod coating method or a roll coating method is preferable. A rod coating method is particularly preferable. The film thickness after drying is preferably 0.1 to 10 μm. Heating and drying can be performed at 20 ° C to 110 ° C. In order to form sufficient cross-linking, 60 ° C to 100 ° C is preferable, and 80 ° C to 100 ° C is particularly preferable. The drying time can be 1 minute to 36 hours, preferably 1 minute to 30 minutes. The pH is preferably set to an optimum value for the crosslinking agent to be used. When glutaraldehyde is used, the pH is 4.5 to 5.5, and 5 is particularly preferable.

  The alignment film is preferably provided on the transparent support. The alignment film is used by crosslinking the polymer layer as described above. The rubbing treatment is preferably not performed for the vertical alignment of the rod-like liquid crystalline compound. In addition, the liquid crystalline molecules are aligned on the alignment film, the liquid crystalline molecules are fixed in the alignment state to form an optically anisotropic layer, and only the optically anisotropic layer is formed on the polymer film (support). You may transcribe.

《Air interface vertical alignment agent》
Usually, since the liquid crystalline compound has a property of being inclined and aligned on the air interface side, it is necessary to control the alignment of the liquid crystalline compound vertically on the air interface side in order to obtain a uniformly vertically aligned state. . For this purpose, the composition contains a compound that is unevenly distributed on the air interface side and acts to vertically align the liquid crystalline compound by its excluded volume effect or electrostatic effect. Preferably formed.

  As the air interface vertical alignment agent, compounds described in JP-A Nos. 2002-20363 and 2002-129162 can be used. In addition, paragraph numbers [0072] to [0075] in the specification of Japanese Patent Application Laid-Open No. 2004-53981 (Japanese Patent Application No. 2002-212100), and paragraph numbers [0037] to [0039] in the specification of Japanese Patent Application No. 2002-262239. , Paragraph numbers [0071] to [0078] in the specification of Japanese Patent Application Laid-Open No. 2004-4688 (Japanese Patent Application No. 2003-91752), paragraphs in the specification of Japanese Patent Application Laid-Open No. 2004-139015 (Japanese Patent Application No. 2003-119959) Nos. [0052] to [0054], [0065] to [0066], [0092] to [0094], paragraph Nos. [0028] to [0028] in JP-A-2005-97357 (Japanese Patent Application No. 2003-330303) [0030] The matters described in paragraphs [0087] to [0090] in Japanese Patent Application No. 2004-003804 are also applicable to the present invention. It is possible to apply. Moreover, by mix | blending these compounds, applicability | paintability is improved and generation | occurrence | production of a nonuniformity or repellency is suppressed.

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

<Other materials in retardation layer>
Along with the liquid crystal compound, a plasticizer, a surfactant, a polymerizable monomer, and the like can be used together to improve the uniformity of the coating film, the strength of the film, the orientation of the liquid crystal compound, and the like. These materials are preferably compatible with the liquid crystal compound and do not inhibit the alignment.

  Examples of the polymerizable monomer include radically polymerizable or cationically polymerizable compounds. Preferably, it is a polyfunctional radically polymerizable monomer and is preferably copolymerizable with the above-described polymerizable group-containing liquid crystal compound. Examples thereof include those described in paragraph numbers [0018] to [0020] in JP-A No. 2002-296423. The amount of the compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the discotic liquid crystalline molecules.

  Examples of the surfactant include conventionally known compounds, and fluorine compounds are particularly preferable. Specifically, for example, compounds described in paragraphs [0028] to [0056] in JP-A-2001-330725, JP-A-2005-62673 (Japanese Patent Application No. 2003-295212), And compounds described in paragraphs [0069] to [0126].

  The polymer used together with the liquid crystal compound is preferably capable of thickening the coating solution. A cellulose ester can be mentioned as an example of a polymer. Preferable examples of the cellulose ester include those described in paragraph [0178] of JP-A No. 2000-155216. The addition amount of the polymer is preferably in the range of 0.1 to 10% by mass, and in the range of 0.1 to 8% by mass with respect to the liquid crystal molecules so as not to inhibit the alignment of the liquid crystal compound. It is more preferable.

[Support]
In the present invention, an optically anisotropic layer formed from a composition containing a liquid crystalline compound is formed on a support, and a laminate of the support and the optically anisotropic layer is formed as a second retardation layer or a second retardation layer. One retardation layer may be used.
The support is preferably transparent, and specifically, the light transmittance is preferably 80% or more. The support preferably has a small wavelength dispersion. Specifically, the Re400 / Re700 ratio is preferably less than 1.2. Among these, a polymer film is preferable. The transparent support can also serve as the first retardation layer, the second retardation layer, or the polarizing plate protective film. Further, the entire optically anisotropic layer formed from the transparent support and the liquid crystal composition may constitute the first retardation layer or the second retardation layer. The optical anisotropy of the support is preferably small, and the in-plane retardation (Re) is preferably 20 nm or less, more preferably 10 nm or less, and most preferably 5 nm or less.

  Examples of the polymer film as the support include cellulose ester, polycarbonate, polysulfone, polyethersulfone, polyacrylate and polymethacrylate films. A cellulose ester film is preferred, an acetyl cellulose film is more preferred, and a triacetyl cellulose film is most preferred. The polymer film is preferably formed by a solvent cast method. The thickness of the transparent support is preferably 20 to 500 μm, and more preferably 40 to 200 μm. In order to improve adhesion between the transparent support and the layer (adhesive layer, vertical alignment film or retardation layer) provided thereon, surface treatment (eg, glow discharge treatment, corona discharge treatment, ultraviolet light (UV) ) Treatment, flame treatment). An adhesive layer (undercoat layer) may be provided on the transparent support. Moreover, the average particle diameter is 10 to 100 nm in order to provide the transparent support or the long transparent support with slipperiness in the conveying process or to prevent the back surface and the surface from sticking after winding. It is preferable to use what formed the polymer layer which mixed the inorganic particle of about 5%-40% by solid content weight ratio by the application | coating or co-casting with the support body on the one side of the support body.

[Protective film for polarizing film]
In the liquid crystal display device of the present invention, the first and second polarizing film protective films have no absorption in the visible light region, light transmittance of 80% or more, and small retardation based on birefringence. preferable. Specifically, the in-plane Re is preferably 0 to 30 nm, more preferably 0 to 15 nm, and even more preferably 0 to 5 nm. Furthermore, the thickness direction retardation Rth is preferably 0 to 40 nm, more preferably 0 to 20 nm, and even more preferably 0 to 10 nm. Any film having this property can be preferably used, but from the viewpoint of durability of the polarizing film, a cellulose acylate or norbornene film is more preferable. Examples of a method for reducing Rth of the cellulose acylate film include methods described in JP-A Nos. 11-246704, 2001-247717, and Japanese Patent Application No. 2003-379975. Rth can also be reduced by reducing the thickness of the cellulose acylate film. The thickness of the cellulose sylate film as the protective film for the first and second polarizing films is preferably 10 to 100 μm, more preferably 10 to 60 μm, and still more preferably 20 to 45 μm.

  In addition, members used in the liquid crystal display device of the present invention are known liquid crystal display devices, in particular, known IPS liquid crystal display devices, ferroelectric liquid crystal display devices, antiferroelectric liquid crystal display devices, and ECB type liquid crystal display devices. Various members used in the present invention can be used as long as the effects of the present invention are not impaired.

[Optical compensation film]
The present invention also relates to an optical compensation film having the first retardation layer and the second retardation layer. For example, in one embodiment of the optical compensation film of the present invention, a polymer film (preferably a cellulose acylate film) that satisfies the optical characteristics of the first retardation layer, and the optical characteristics of the second retardation layer on the film are provided. A satisfactory optical compensation film having an optically anisotropic layer formed from a liquid crystal composition. The liquid crystal composition preferably contains a rod-like liquid crystal compound, and the molecules of the rod-like liquid crystal compound are preferably fixed in a vertically aligned state in the layer.

The present invention will be described more specifically with reference to the following examples. These examples show specific examples of the contents of the present invention, and the present invention is not limited to these examples.
[Example 1]
An optical simulation was performed on the liquid crystal display device having the configuration shown in FIG. 1 to confirm the effect. For the optical calculation, LCD Master Ver 6.08 manufactured by Shintech Co., Ltd. was used. As the liquid crystal cell, electrode, substrate, polarizing plate, etc., those conventionally used for liquid crystal displays can be used as they are. As the liquid crystal material, ZLI-4792 attached to the LCD Master was used. The orientation of the liquid crystal cell is a parallel orientation with a pretilt angle of 0 degree, the cell gap of the substrate is 3.04 microns, and the liquid crystal is made of a liquid crystal material having a positive dielectric anisotropy (ie, the liquid crystal layer). The product of the thickness d (micron) and the refractive index anisotropy Δn was set to 300 nm. G1220DU attached to LCD Master was used for the polarizing film.
Re and Rth of the first retardation layer were set to have optical characteristics shown in Table 1 below. Rth of the second retardation layer was set to 300 nm, and Re was set to 0 nm. Further, Rth and Re of the protective film 19a of the lower polarizing plate were set to 0 nm. A Backlight light source attached to the LCD Master was used as the light source.
In this way, the liquid crystal display device No. 1 having the same configuration as in FIG. 1-6 were configured.

<Leakage and chromaticity of liquid crystal display devices>
Liquid crystal display device no. For each of 1 to 6, the black display transmittance (%) and the azimuth in the viewing angle direction with an azimuth angle of 0 ° and a polar angle of 60 ° when a voltage at which the transmittance at the front is the smallest, that is, a black voltage is applied. A color shift Δx between an angle of 0 ° and a polar angle of 60 ° and an azimuth angle of 180 ° and a polar angle of 60 ° was determined. The results are shown in Table 1.

From the results shown in Table 1, Re / Rth, which is the ratio of Re to Rth at the wavelength λ = 450 nm, is 0.58 times the value of Re / Rth at the wavelength λ = 550 nm, and Re / Rth at the wavelength λ = 650 nm. However, when the Re / Rth value at the wavelength λ = 550 nm is 1.5 times, it can be understood that both the transmittance and the color shift from the front are minimized.
Liquid crystal display device no. No. 1 shows that the wavelength dispersion of the first retardation layer is outside the range of the present invention. Compared with this, Re / Rth which is the ratio of Re to Rth at λ = 450 nm of the first retardation layer is λ = Liquid crystal having a Re / Rth value of 0.5 to 0.9 times at 550 nm and Re / Rth at λ = 650 nm being 1.1 to 1.6 times the Re / Rth value at λ = 550 nm Display device no. In Nos. 2 to 6, it can be understood that light leakage at the time of black display and color shift depending on the viewing angle are reduced.

It is the schematic which shows an example of the liquid crystal display device of this invention. It is the schematic which shows the pixel area example of the liquid crystal display device of this invention. It is the schematic which shows the other example of the liquid crystal display device of this invention. It is a figure for demonstrating the optical compensation effect | action of 1 aspect of the liquid crystal display device of this invention using a Poincare sphere.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal element pixel area 2 Pixel electrode 3 Display electrode 4 Rubbing direction 5a, 5b Director of liquid crystal compound at the time of black display 6a, 6b Director of liquid crystal compound at the time of white display 7a, 7b, 19a, 19b Protective film for polarizing film 8, 20 Polarizing film 9, 21 Polarization transmission axis 10 of polarizing film First retardation layer 11 Slow axis 12 of first retardation layer Second retardation layer 13, 17 Cell substrate 14, 18 Cell substrate rubbing direction 15 Liquid crystal Layer 16 Slow axis direction of liquid crystal layer

Claims (7)

A liquid crystal cell including at least a first polarizing film, a first retardation layer, a second retardation layer, a liquid crystal layer and a pair of substrates sandwiching the liquid crystal layer, and a liquid crystal in the liquid crystal layer during black display A liquid crystal display device in which molecules are aligned substantially parallel to the surfaces of the pair of substrates,
When the in-plane retardation at the wavelength λ of the first and second retardation layers is Re (λ) and the retardation in the thickness direction is Rth (λ),
A ratio Re / Rth (450 nm) of Re and Rth at a wavelength of 450 nm of the first retardation layer is 0.4 to 0.95 times Re / Rth (550 nm) at a wavelength of 550 nm, and Re / Rth (at a wavelength of 650 nm). 650 nm) is 1.05 to 1.93 times Re / Rth (550 nm), Rth (550 nm) is 70 nm to 400 nm, and Re (550 nm) is 20 nm to 150 nm,
The Re (550 nm) of the second retardation layer is approximately 0, the Rth (550 nm) is −80 nm to −400 nm, and the transmission axis of the first polarizing film is the retardation of the liquid crystal molecules in the liquid crystal layer during black display. Ri parallel der in the axis direction,
The first retardation layer is made of a cellulose acylate film,
An IPS mode liquid crystal display device in which a first retardation layer and a second retardation layer are laminated . The first polarizing film, the first retardation layer, the second retardation layer, and the liquid crystal cell are arranged in this order, and the slow axis of the first retardation layer is the same as that of the first polarizing film. The liquid crystal display device according to claim 1 , wherein the liquid crystal display device is substantially parallel to the transmission axis. The first polarizing film, the second retardation layer, the first retardation layer, and the liquid crystal cell are arranged in this order, and the slow axis of the first retardation layer is the transmission axis of the first polarizing film. The liquid crystal display device according to claim 1 , which is substantially orthogonal to. And a second polarizing film having a transmission axis perpendicular to the transmission axis of the first polarizing film, the first retardation layer and the second retardation layer being interposed between the first and second polarizing films. and a liquid crystal display device according to claim 1, wherein the liquid crystal cell is disposed. It has a pair of protective films arranged with the first polarizing film and / or the second polarizing film in between, and the thickness direction retardation Rth of the protective film on the side close to the liquid crystal layer of the pair of protective films is 40 nm. The liquid crystal display device according to claim 1 , which is: A pair of protective films disposed between the first polarizing film and / or the second polarizing film, wherein the protective film on the side close to the liquid crystal layer is a cellulose acylate film or a norbornene-based film The liquid crystal display device according to any one of claims 1 to 5 . The first retardation layer includes a layer formed of a composition containing a rod-like liquid crystal compound, and the molecules of the rod-like liquid crystal compound are fixed in a substantially vertically aligned state in the layer . The liquid crystal display device according to any one of 6 .

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