JP2006259211A - Optical compensation film, elliptically polarizing plate, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display wherein improvement of a gradation inversion phenomenon in a display lower direction and suppression of variation of a tint in a vertical visual field direction are made compatible with each other. <P>SOLUTION: In the liquid crystal display, an ON voltage by which equivalent front luminance can be obtained in the state that at least one optical anisotropic layer is inserted between a liquid crystal cell and a pair of polarizing films is lower by 10 to 35% than an ON voltage exhibiting black or white luminance in the state that all optical anisotropic layers to be disposed therebetween are removed. When the all optical anisotropic layers driven by the voltage lower by 10 to 35% and disposed are viewed from a normal direction of the layer while a relative angle is maintained, a retardation value in a composited surface is 5 to 35 nm, the lagging axis of a composited refractive index elliptical body is orthogonal to a bisector of crossed angle of alignment axes of upper and lower substrates regulating the alignment direction of the liquid crystal cell and phase difference in the surface of at least the one optical anisotropic layer and phase difference in the thickness direction thereof simultaneously satisfy desired relations. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and an optical compensation film and an elliptically polarizing plate used in the liquid crystal display device.

  A liquid crystal display device generally includes a liquid crystal cell, a polarizing element, an optical compensation film (retardation plate), and a drive circuit. In the transmissive liquid crystal display device, two polarizing elements are arranged on both sides of the liquid crystal cell, and one or two optical compensation films are arranged between the liquid crystal cell and the polarizing element. In a reflective liquid crystal display device, a reflector, a liquid crystal cell, a single optical compensation film, and a single polarizing element are usually arranged in this order. The liquid crystal cell is composed of a rod-like liquid crystal molecule, two substrates for enclosing it, and an electrode layer for applying a voltage to the rod-like liquid crystal molecule. The liquid crystal cell is different in the alignment state of rod-like liquid crystal molecules. As for the transmissive type, TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), OCB (Optically Compensatory N) (OCB). Super Twisted Nematic), VA (Vertically Aligned), ECB (Electrically Controlled Birefringence), and reflection types are TN, HAN (Hybrid Aligned NeH), .

  Optical compensation films are used in various liquid crystal display devices in order to eliminate image coloring and expand the viewing angle. As the optical compensation film, an optical compensation film having an optically anisotropic layer formed from a discotic compound or a liquid crystalline molecule on a transparent support, such as a stretched birefringent polymer film, is generally used. The optical properties of the optical compensation film are determined according to the optical properties of the liquid crystal cell, specifically, the display mode differences as described above. Various optical compensation films corresponding to various display modes have been proposed.

  Here, with respect to an example of the alignment state at the time of voltage application of the rod-like liquid crystal molecules in the TN mode liquid crystal cell, the relationship between the inclination in the polar angle direction of the rod-like liquid crystal molecules and the position in the thickness direction of the liquid crystal layer is shown in FIG. FIG. 10 shows the relationship between the tilt in the azimuth direction of the rod-like liquid crystal molecules and the position in the thickness direction of the liquid crystal layer. The curve in the figure corresponds to the applied voltage of several tens of points to the liquid crystal layer. Note that the θ polar angle direction in FIG. 9 refers to the inclination in the z-axis direction when the layer plane of the liquid crystal layer is the xy plane, and polar angle = 0 ° is parallel to the liquid crystal layer plane and polar angle = 90 ° coincides with the normal direction of the liquid crystal layer. Further, the φ azimuth direction in FIG. 10 is an inclination with respect to one of the orthogonal axes in the layer plane, for example, counterclockwise when the right side is directed to the liquid crystal cell and the horizontal direction is the x axis + side. Means the angle formed with the x-axis. FIG. 9 and FIG. 10 are examples of a general alignment state of the TN liquid crystal display mode by the design simulation software for the liquid crystal display.

  As an optical compensation film for expanding the viewing angle of such a TN mode liquid crystal layer liquid crystal display cell, a compensation film in which a discotic compound is fixed in a hybrid alignment state has been put into practical use (for example, Patent Document 1). In this method, since the nematic liquid crystal cell composed of rod-shaped liquid crystals is compensated by the discotic compound, it is possible to compensate for incident light from an oblique direction, and the display viewing angle can be greatly expanded. is there. In this case, as shown in FIG. 11, with respect to the TN liquid crystal cell 51 in which the rod-like molecules 52 are twisted nematically oriented, the compensation films 54a and 54b made of the discotic compound 53 are arranged on the display surface side and the backlight 55. Place on the back side. The azimuth direction in which the discotic compound is oriented is the vertical and horizontal directions in the normally white mode TN liquid crystal display device by effectively compensating for the black display applied with voltage. It is designed to reduce the black transmittance and enlarge the viewing angle.

  Enlarging the viewing angle was achieved by a discotic compound, but the gradation inversion phenomenon that occurred in the downward direction of the display was not eliminated. In order to explain this, FIG. 12 shows a schematic diagram of the twisted orientation of the nematic liquid crystal 52 in the cross section of the liquid crystal layer 51 of the liquid crystal cell in the TN liquid crystal mode in the driving state. The left side is the display downward direction and the right side is the upward direction toward the page. The arrows A, B, and C indicate examples of the observation direction of the observer. When the viewpoint from the B direction is moved in the direction of the arrow 2, the retardation decreases, and then when the viewpoint is moved in the direction of the arrow 1, the retardation increases. When the liquid crystal layer is observed from the C direction, the retardation is minimized, and the retardation is the same value from the A direction and the B direction. Therefore, the transmittance is the same in these two directions, and the transmittance tends to be the lowest in the C direction. Since the lowest angle of the transmittance in the polar angle direction is generated at an angle different depending on the gradation level, an intersection of gradation levels (transmission of the transmittance) occurs. This phenomenon was not eliminated even by the means according to Patent Document 1 using the above-mentioned discotic compound. FIG. 13 shows a case where an optical compensation film for expanding the viewing angle by the above-mentioned discotic compound is used in a commercially available TN type liquid crystal TV. When the luminance level at the front is divided into seven and the luminance change in the vertical direction is plotted, it can be seen that L1 and L2 intersect at the lower 33 ° and the gradation is inverted. The normal display device design is such that the direction in which the gradation inversion occurs is directed downward, which is a less noticeable direction in a TN mode liquid crystal display.

  As a method for improving the display characteristics of the TN mode liquid crystal display, a liquid crystalline optical compensation film in which a twisted structure is also introduced on the optical compensation film side has been proposed (Patent Document 2). A twisted structure is introduced and fixed in a state in which the angle formed by the disc surface of the discotic liquid crystal and the normal to the film plane changes in the film thickness direction, that is, a so-called hybrid alignment state.

Japanese Patent No. 2587398 Japanese Patent No. 3456891

  By the methods disclosed in Patent Document 1 and Patent Document 2 described above, the viewing angle region (contrast viewing angle) capable of maintaining a high contrast of the TN liquid crystal display has been expanded. However, the phenomenon that the color changes depending on the viewing angle direction (color variation) and the gradation inversion phenomenon that occurs in the downward direction have not been solved. Today, as TN mode liquid crystal display devices are used more widely than notebook personal computers, monitors, TVs, and the like, there is a need to resolve this color variation and downward gradation inversion. In view of such a situation, the present invention industrially realizes the improvement of the color variation and the downward gradation inversion in order to further expand the use range of the TN liquid crystal mode. Here, as an indicator of gradation inversion, the angle at which L1 and L2 intersect is defined as the gradation inversion angle. When the liquid crystal display device was evaluated based on the gradation inversion angle, it was found that the inversion angle is desirably 37 ° or more. Further, it has been found that, as the hue variation, in the CIE 1976 UCS chromaticity diagram, the variation (Δu′v ′) on the chromaticity diagram with respect to the front surface is preferably within 0.15.

  As shown in FIG. 9, the present inventor has a very low angle when the voltage applied to the liquid crystal layer is low, so that the direction of C shown in FIG. Focusing on the fact that it is not conspicuous, intensive studies were conducted on a method for obtaining a sufficient contrast as a display device with a small applied voltage. As a result, when the applied voltage is reduced, the phase contrast (retardation) in the direction of the alignment axis bisector of the upper and lower substrates that defines the alignment direction of the liquid crystal molecules in the liquid crystal cell increases, thereby increasing the front contrast. It was found that a decrease in Assuming an optically equivalent refractive index ellipsoid, it was found that the in-plane component of the slow axis was formed in the vertical direction of the display surface. Furthermore, as a result of diligent investigation based on this knowledge, it has been found that this adverse effect can be eliminated by laminating optically equivalent refractive index ellipsoids with the slow axis in the horizontal direction of the display surface. . In other words, if a refractive index ellipsoid is assumed to be the same size as the retardation generated by reducing the applied voltage, the adverse effect can be eliminated by forming a structure in which the slow axis is in the horizontal direction of the display surface. Can do. However, based on this idea, it has also been found that when tone reversal is improved while avoiding a decrease in front contrast, the change in color depending on the viewing angle direction of the display device is significant. This change in color is a fatal obstacle for the display device to keep its display quality high, and it has been strongly desired to solve it.

  It is an object of the present invention to provide a TN mode liquid crystal display device that realizes good color reproduction by reducing a gradation inversion phenomenon generated in the downward direction. Another object of the present invention is to provide an optical compensation film and an elliptically polarizing plate that contribute to the reduction of the gradation reversal phenomenon produced in the downward direction and contribute to the achievement of good color reproduction.

Means for solving the above-mentioned problems are as follows.
[1] A liquid crystal cell, a pair of polarizing films sandwiching the liquid crystal cell, and at least one optically anisotropic layer disposed between at least one of the pair of polarizing films and the liquid crystal cell. A liquid crystal display device,
The at least one layer of optical anisotropy with respect to an ON voltage that exhibits black or white luminance in a state excluding all optically anisotropic layers disposed between the liquid crystal cell and the pair of polarizing films. The ON voltage at which equal front brightness is obtained with the layers inserted is 10% to 35% lower, and the 10% to 35% lower voltage is driven.
When all the optically anisotropic layers arranged between the liquid crystal cell and the pair of polarizing films are viewed from the normal direction of the layers while maintaining the relative angle, the in-plane retarder is synthesized. The retardation is 5 nm to 35 nm, and the slow axis of the synthesized refractive index ellipsoid is perpendicular to the bisector of the intersection angle of the alignment axes of the upper and lower substrates that define the alignment direction of the liquid crystal cell. A liquid crystal display device in which an in-plane retardation and a thickness direction retardation of the at least one optically anisotropic layer simultaneously satisfy the relational expressions (1) to (4);
0.48 ≦ Re (450) / Re (550) ≦ 0.50 (1)
1.26 ≦ Re (610) / Re (550) ≦ 1.27 (2)
0.88 ≦ Rth (450) / Rth (550) ≦ 0.89 (3)
1.06 ≦ Rth (610) / Rth (550) ≦ 1.07 (4)
In the formula, Re (λ) is a phase difference in the plane of the optical anisotropic layer at the wavelength (λ), and Rth (λ) is a phase difference in the thickness direction of the optical anisotropic layer at the wavelength (λ).
[2] A disc comprising a composition containing a discotic compound, the average tilt angle β value of the molecules of the discotic compound in the layer is 30 ° to 45 °, and when observed from the liquid crystal cell side, the disc The projection onto the polarizing film located closer to the average orientation direction of the molecular compound molecules has at least one optically anisotropic layer that is rotated clockwise by 1 ° or more and 10 ° or less from the polarizing film absorption axis. [1] The liquid crystal display device.
[3] When the disk is composed of a composition containing a discotic compound, the average tilt angle β value of molecules of the discotic compound in the layer is 30 ° to 45 °, and the disc is observed from the liquid crystal cell side. An optically anisotropic layer in which the projection onto the polarizing film positioned closer to the average orientation direction of the molecule-like compound molecules is rotated clockwise by 1 ° or more and 10 ° or less from the absorption axis of the polarizing film, The liquid crystal display device according to [1], wherein at least one layer is provided between the polarizing film and the liquid crystal cell.
[4] An optical compensation film for use in the liquid crystal display device of [1], comprising an optically anisotropic layer comprising a discotic compound and a transparent support, wherein the discotic compound in the optically anisotropic layer When the average inclination angle β value is 30 ° to 45 ° and the liquid crystal cell is arranged and observed from the side, the projection onto the polarizing film located closer to the orientation direction of the discotic compound is An optical compensation film rotated clockwise by 1 ° or more and 10 ° or less from the film absorption axis.
[5] An elliptically polarizing plate having the optically anisotropic layer according to [1], a transparent protective film, and a polarizing film.
[6] An elliptically polarizing plate having a transparent protective film, a polarizing film, and at least one optical compensation film of [4].

In the present specification, Re (λ) and Rth (λ) respectively represent in-plane retardation and retardation in the thickness direction at a wavelength λ. Re (λ) is measured, for example, in an ellipsometer M-150 (manufactured by JASCO Corporation) with light having a wavelength of λ nm incident in the normal direction of the film. Rth (λ) is the wavelength of λ nm from the direction inclined by + 40 ° with respect to the normal direction of the film, with Re (λ) and the in-plane slow axis (determined by M-150) as the tilt axis (rotation axis). Retardation measured by making light incident, and retarded by making light of wavelength λ nm incident from a direction inclined −40 ° with respect to the film normal direction with the in-plane slow axis as the tilt axis (rotation axis) M-150 is calculated based on the retardation measured in a total of three directions.
In addition to the ellipsometer, Re (λ) and Rth (λ) are also measured by, for example, an automatic birefringence meter (manufactured by KOBRA 21ADH Oji Scientific Instruments). An in-plane slow axis is automatically detected, Re (λ) and Rth (λ) of the film are measured at five wavelengths, and a desired wavelength value is interpolated and calculated based on an approximate expression of chromatic dispersion. Here, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured by an Abbe refractometer. Examples of the average refractive index values of main optical films are given below:
Cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), and polystyrene (1.59).
The KOBRA 21ADH calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness.

  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 the present invention, the gradation inversion phenomenon that occurs in the downward direction of the display is improved by using an optically anisotropic layer exhibiting predetermined optical characteristics as a whole and driven at a low driving voltage, and the direction seen from the front ( When the viewing angle is changed, the basic performance as a display device is maintained such that the color of the same display object is constant.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.
FIG. 1 shows an in-plane component of a slow axis of birefringence generated in a liquid crystal layer even when it is in an ON state due to a low drive voltage, and a TN type liquid crystal display device according to an embodiment of the present invention. An example of the relationship between the rubbing axis of the opposing surface of the viewer side substrate that controls the twist orientation and the twist angle by the rubbing axis of the backlight side substrate surface is schematically shown.
In FIG. 1, the slow axis of birefringence generated in the liquid crystal layer by lowering the drive voltage is indicated by a white arrow, and the rubbing of the upper and lower substrates defining the central axis direction of the twist angle, that is, the alignment direction of the liquid crystal layer. This is the direction of the bisector of the axis crossing angle (display vertical direction in FIG. 1). The generated birefringence in the ON state causes a harmful effect of lowering the front contrast. Therefore, in the present invention, in order to solve this problem, one or two or more optically anisotropic layers are incorporated so that the in-plane retardation of the composite is in the range of 5 to 35 nm to cancel the generated retardation. The slow axis of the refractive index ellipsoid formed by the optically anisotropic layer is represented by the crossing angle 2 of the rubbing axis of the upper and lower substrates defining the direction indicated by the black arrow in FIG. It cancels out in the direction perpendicular to the direction of the equipartition line (the display left-right direction in FIG. 1). At the same time, the wavelength dispersions of Re and Rth of the optically anisotropic layer are set to the following (1) to (4), so that the change in the tint that occurs at the same time is suppressed and the deterioration of the display quality is avoided.
0.48 ≦ Re (450) / Re (550) ≦ 0.50 (1)
1.26 ≦ Re (610) / Re (550) ≦ 1.27 (2)
0.88 ≦ Rth (450) / Rth (550) ≦ 0.89 (3)
1.06 ≦ Rth (610) / Rth (550) ≦ 1.07 (4)
In the formula, Re (λ) means the in-plane retardation of the optically anisotropic layer at the wavelength (λ), and Rth (λ) is the thickness direction of the optically anisotropic layer at the wavelength (λ). It means phase difference.
In the present specification, the term “optically anisotropic layer” is used for any layer exhibiting optical anisotropy regardless of the material. For example, a layer showing optical anisotropy expressed by alignment of liquid crystal molecules, a polymer layer expressed by aligning a polymer by stretching treatment, and the like are used.

Next, the operation of the liquid crystal display device of the present invention will be described in more detail with reference to the drawings.
1) First, the relationship between lowering the driving voltage of a liquid crystal display device and the effect of improving gradation inversion will be described.
Remove the optical compensation film and the polarizing film sandwiching the liquid crystal cell from the TN type liquid crystal display device to make only the liquid crystal cell, while gradually decreasing the ON voltage that exhibits the black or white transmittance of the liquid crystal cell. The result of measuring the retardation inside is shown in FIG. FIG. 2 shows a general liquid crystal cell Δnd (Δn: difference in refractive index of liquid crystal molecules, d: liquid crystal cell gap size) 360 nm, 390 nm, 410 nm measured with a general-purpose ellipsometer (manufactured by OPTIPRO H33 Syntech Co., Ltd.). It is a graph which shows the relationship between the drive voltage in the case of 460 nm, and the retardation which generate | occur | produces in a liquid crystal cell surface. As the ON voltage decreases, the liquid crystal molecules in the cell fall from the normal to the substrate more than usual. Therefore, the retardation in the liquid crystal cell surface increases as the ON voltage decreases. Here, an optically anisotropic layer is inserted between the polarizing film and the liquid crystal cell, assuming that a refractive index ellipsoid is equivalent to the retardation generated in the liquid crystal cell, and whose slow axis is orthogonal. Then, the retardation generated in the liquid crystal layer can be canceled, and normal luminance can be obtained even if the ON voltage is reduced. In a state where the ON voltage is lowered, the C direction shown in FIG. 12 is a low angle, and the gradation inversion is not conspicuous.

  FIG. 3 shows the relationship between the amount of retardation generated in the liquid crystal layer when Δnd = 410 nm and the retardation in the downward direction when the retardation at the driving voltage is canceled when the driving voltage is lowered. Indicates. In the state where the driving voltage is reduced by about 35%, the retardation generated in the liquid crystal cell reaches 33 nm. When the retardation in this state is canceled, the downward inversion angle is 51 °. This result was obtained by preparing a film having half the retardation of the liquid crystal layer obtained by measurement in advance, and inserting two sheets between the liquid crystal layer and the upper and lower polarizing films to obtain the gradation inversion angle. It is. The two optical compensation films used are for synthesizing the in-plane retardation equivalent to the in-plane retardation generated in the liquid crystal layer by laminating two sheets, and the synthesized refractive index ellipsoid The gradation inversion angle is obtained by arranging the slow axis so as to be orthogonal to the in-plane component of the slow axis of birefringence generated in the liquid crystal layer in the ON state.

  As described above, by reducing the applied voltage to the liquid crystal cell to 35% and canceling the retardation 35 nm generated thereby, the gradation inversion angle can be expanded to a normal 33 ° to 51 °. By reducing the driving voltage by 10% to 35%, the retardation of 5 nm to 35 nm is generated in the liquid crystal layer even if the difference in the liquid crystal cell Δnd is taken into account, and this is canceled. It was confirmed that improvement of gradation inversion can be realized by applying a foundation to the optically anisotropic layer.

2) The retardation generated in the liquid crystal layer of the liquid crystal cell described above and the substantially equivalent retardation form an optically anisotropic layer from the composition containing the discotic compound, and the average of the discotic compound molecules Can be easily generated by arranging the optically anisotropic layer by slightly rotating the orientation direction of the liquid crystal display device from the absorption axis direction (or transmission axis) of the upper and lower polarizing films constituting the liquid crystal display device. it can.
When an optically anisotropic layer containing discotic compound molecules is used in the TN type liquid crystal display device of the present invention, for example, an optical anisotropy output by an ellipsometer (M-150 manufactured by JASCO Corporation) or the like is used. In order to obtain sufficient front contrast, it is preferable that the range of the average inclination angle β of the layer is 30 ° to 45 °. FIG. 5 shows the relationship between the β value measured by the automatic birefringence measuring instrument and the front contrast. Therefore, even when the retardation generated in the liquid crystal layer is canceled by reducing the driving voltage by 10% to 35%, it is preferable that the β value range by such measurement is 30 ° to 45 °.

  An in-plane measured by the relative angle of the upper and lower two sheets disposed in the liquid crystal display device, actually producing an optical compensation film having an optically anisotropic layer with upper and lower limits of β value of 30 ° and 45 °. FIG. 4 shows the relationship between the retardation, the polarizing film absorption axis, and the angle formed by the orientation direction of the discotic compound. From the results shown in FIG. 4, in order to generate the retardation of 5 to 35 nm, the optical anisotropic layer having a β value in the range of 30 ° to 45 ° may be rotated from 1 ° to 10 ° from the polarizing film absorption axis. I understand that.

  The angle formed between the absorption axis of the polarizing film and the orientation direction of the optically anisotropic layer is preferably rotated clockwise as viewed from the liquid crystal layer. In this way, while maintaining the relative angle between the two compensation films, they are inserted between the liquid crystal cell and the upper and lower polarizing films, and the drive voltage is reduced by 10% to 35%, thereby generating in the liquid crystal layer. The retardation can be canceled out, and a front contrast that is not different from the conventional one can be exhibited, and at the same time, an improvement in gradation inversion can be realized.

3) In order to generate a retardation substantially equal to the retardation generated in the liquid crystal layer, the orientation direction of the optically anisotropic layer is rotated from the absorption axis of the nearby polarizing film. Can be realized. Bisector of the alignment axis angle of the upper and lower substrates defining the alignment axis of the liquid crystal cell when the optically anisotropic layer is viewed from the normal direction while maintaining the relative angle when placed in the liquid crystal display device It is preferable to determine the size of the retardation so that a slow axis is formed in an angular direction perpendicular to the angle, and a synthetic retardation composed of one or more of them is 5 nm to 35 nm.

4) Next, the change in the hue with respect to the viewing angle and its importance will be described.
FIG. 8 is a UCS chromaticity diagram determined in 1976 by CIE (Commission Internationale de l'Eclairage). On this chromaticity diagram, a conventional optical compensation film (for example, manufactured by Fuji Photo Film Co., Ltd.) using a wide viewing angle polarizing plate (LPT-HL56-12, manufactured by Sanlitz Co., Ltd.) is commercially available. The white variation in the vertical direction of the liquid crystal display device (upward 80 ° to lower 80 ° from the display normal) is 0. 0 for both u ′ and v ′ from white (u ′ = 0.20, v ′ = 0.46). A fluctuation of about 1 was generated. In contrast, the driving voltage of the liquid crystal cell is reduced by 30%, and the downward gradation inversion is improved by using a conventional optical compensation film having an optically anisotropic layer expressed by the orientation of the molecules of the discotic compound. In particular, the variation of v ′ was so large that Δv ′ = 0.34. In the case of improving the lower gradation inversion by reducing the drive voltage, the color change with respect to the viewing angle tends to increase.

  When downgradation inversion is attempted by reducing the driving voltage, the color variation tends to increase as described above. However, the in-plane retardation Re and the thickness direction retardation Rth of the optically anisotropic layer tend to increase. When the chromatic dispersion is in the range of the present invention (formulas (1) to (4)), the variation in color is suppressed, and the quality of the display device is not deteriorated. It is possible to improve gradation reversal and reduce color variation.

  Since the optical compensation film is used together with the polarizing film, it is efficient and useful to use it by previously laminating the transparent protective film and the polarizing film to form an elliptically polarizing plate.

  FIG. 6 shows an embodiment in which the present invention is applied to a transmissive liquid crystal display device. The liquid crystal display device of FIG. 6 has a transparent protective film 1a on the surface on the backlight (BL) side and the display surface side, centering on a liquid crystal cell comprising a pair of substrates 5a and 5b and a liquid crystal layer 6 sandwiched between the substrates 5a and 5b. And 1b are respectively provided with polarizing films 2a and 2b. Between the polarizing films 2a and 2b and the liquid crystal cell, there are optical compensation films each having optically anisotropic layers 4a and 4b formed from a composition containing a discotic compound, and transparent supports 3a and 3b, respectively. Two are arranged in total, one each. In each of the optically anisotropic layers 4a and 4b, the discotic compound molecules are oriented at an average inclination angle of 30 ° to 45 °, and the optically anisotropic layers 4a and 4b as a whole have an in-plane retardation of 5 to 35 nm. Indicates. In addition, when the transparent supports 3a and 3b also show optical anisotropy, the in-plane retardation as a whole including the transparent supports 3a and 3b is set to 5 to 35 nm. Furthermore, the slow axis in-plane component of the birefringence is in a direction perpendicular to the bisector of the crossing angle of the rubbing axis formed on the opposing surfaces of the substrates 5a and 5b. Thus, it is orthogonal to the slow axis in-plane component of birefringence generated in the liquid crystal layer 6 in the ON state.

  Usually, an optically anisotropic layer having optical anisotropy expressed by the orientation of a discotic compound is obtained by applying a composition containing a discotic compound on the surface of a rubbing-treated alcohol-based orientation film. It can be produced by orienting molecules in a desired direction and fixing them in the oriented state. In the present embodiment, by adjusting the rubbing axis of the alignment film used when forming the optically anisotropic layers 4a and 4b, the slow axis of the synthetic retardation can be set in the desired direction as described above. . FIG. 7 shows the rubbing axes of the alignment film used when forming the optically anisotropic layers 4a and 4b, and the rubbing axes of the opposing surfaces of the substrate 5a of the backlight side liquid crystal layer and the substrate 5b of the viewer side liquid crystal layer. An example of the relationship is schematically shown. In the conventional optical compensation film for liquid crystal display devices, the alignment direction of the alignment film for the optically anisotropic layer made of a discotic compound is substantially the same as the rubbing axis direction of the liquid crystal to be driven. It was arranged as shown in. In the present embodiment, as shown in FIG. 7, it is preferable not to coincide with the absorption axis of the polarizing film, but to be shifted from 1 ° to 10 ° inward from the absorption axis. For example, when the pair of upper and lower polarizing films is 90 °, that is, when the absorption axes of the substrates 2a and 2b intersect at 90 °, the respective rubbing axes of the alignment films used for forming the optically anisotropic layers 4a and 4b Are preferably shifted inwardly by 1 ° to 10 °, and the crossing angle of the rubbing axes of the alignment films used for forming the optically anisotropic layers 4a and 4b is preferably about 88 to 70 °. . In the case of a discotic compound, since it has a slow axis in the disc plane of the compound, the birefringence synthesized by the two upper and lower optically anisotropic layers 4a and 4b by shifting the rubbing axis inward in this way. The slow axis in-plane component is generated in the left-right direction of the display device. The direction of the slow axis and the magnitude of the generated retardation can be determined by the above-described ellipsometer.

  Concerning the color variations caused by reducing the drive voltage, the above-described equations (1) to (4) are simultaneously satisfied with respect to the conventional wavelength dispersion, thereby suppressing the significant color variations and improving the display quality. Decrease can be improved.

Hereinafter, the material and production method of the optical compensation film used in the liquid crystal display device of the present invention will be described in detail. Examples of the optical compensation film used in the liquid crystal display device of the present invention include a transparent support made of a stretched polymer film and the like, and an optical anisotropic layer having optical anisotropy expressed by the orientation of the discotic compound. The aspect which has is included.
[Support]
The support constituting the optical compensation film of the present invention is preferably transparent, and specifically, the light transmittance is preferably 80% or more. There is no restriction | limiting in particular about the material, A glass plate, a polymer film, etc. can be used. Among these, a polymer film is preferable. Examples of the polymer constituting the polymer film include cellulose esters (eg, mono-, di- and triacylates of cellulose), norbornene-based polymers and polymethyl methacrylate. A commercially available polymer (for norbornene polymers, both Arton and Zeonex are trade names)) may be used. In addition, even the conventionally known polymers such as polycarbonate and polysulfone, which easily develop birefringence, can control birefringence by modifying the molecule as described in WO00 / 26705. Then, it can be used as a transparent support.

Among these, cellulose esters are preferable, and lower fatty acid esters of cellulose are more preferable. Lower fatty acid means a fatty acid having 6 or less carbon atoms. In particular, cellulose acylate having 2 to 4 carbon atoms is preferable. Cellulose acetate is particularly preferred. Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate may be used.
The viscosity average degree of polymerization (DP) of cellulose acetate is preferably 250 or more, and more preferably 290 or more. Cellulose acetate 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. A specific value of Mw / Mn is preferably 1.0 to 1.7, and more preferably 1.0 to 1.65.

  Moreover, it is preferable to use the cellulose acetate whose acetylation degree is 55.0-62.5%. The acetylation degree is more preferably 57.0 to 62.0%. The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation is determined by measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).

In general, cellulose acetate does not evenly substitute the 2-, 3-, and 6-position hydroxyl groups of cellulose, but tends to reduce the substitution degree at the 6-position. The cellulose acetate used for the transparent support preferably has the same or greater 6-position substitution degree of cellulose than the 2-position and 3-position. The ratio of the substitution degree at the 6-position to the total substitution degree at the 2-position, the 3-position, and the 6-position is preferably 30 to 40%, more preferably 31 to 40%, and more preferably 32 to 40%. Most preferred. The substitution degree at the 6-position is preferably 0.88 or more.
These specific acyl groups and a method for synthesizing cellulose acylate are described in detail on page 9 of the Japan Society of Invention and Innovation Technical Report (Technology No. 2001-1745, published on March 15, 2001). .

Furthermore, the hygroscopic expansion coefficient of the cellulose acetate film used as the transparent support is preferably 30 × 10 ⁻⁵ /% RH or less. The hygroscopic expansion coefficient is preferably 15 × 10 ⁻⁵ /% RH or less, and more preferably 10 × 10 ⁻⁵ /% RH or less. The hygroscopic expansion coefficient is preferably small, but usually it is 1.0 × 10 ⁻⁵ /% RH or more. The hygroscopic expansion coefficient indicates the amount of change in the sample length when the relative humidity is changed at a constant temperature.
By adjusting the hygroscopic expansion coefficient, it is possible to prevent a frame-like transmittance increase (light leakage due to distortion) while maintaining the optical compensation function of the optical compensation film.
The method for measuring the hygroscopic expansion coefficient is shown below. 5 mm wide from the produced polymer film. A sample having a length of 20 mm was cut out, one end was fixed, and the sample was hung in an atmosphere of 25 ° C. and 20% RH (R ⁰ ). A weight of 0.5 g was hung from the other end and left for 10 minutes to measure the length (L ⁰ ). Next, with the temperature kept at 25 ° C., the humidity was set to 80% RH (R ¹ ), and the length (L ¹ ) was measured. The hygroscopic expansion coefficient can be calculated by the following equation. The measurement is performed 10 samples for the same sample, and the average value is adopted.
Hygroscopic expansion coefficient [/% RH] = {(L ¹ −L ⁰ ) / L ⁰ } / (R ¹ −R ⁰ )

  In order to reduce the dimensional change due to moisture absorption of the polymer film, it is preferable to add a compound having a hydrophobic group or fine particles. The compound having a hydrophobic group is preferably selected from plasticizers and degradation inhibitors having a hydrophobic group such as an aliphatic group or an aromatic group in the molecule. It is preferable that the addition amount of these compounds exists in the range of 0.01-10 mass% with respect to the solution (dope) to adjust. In addition, the free volume in the polymer film may be reduced. Specifically, the smaller the amount of residual solvent during film formation by the solvent casting method described later, the smaller the free deposition. It is preferable to dry under the condition that the residual solvent amount with respect to the cellulose acetate film is in the range of 0.01 to 1.00% by mass.

  Additives added to the polymer film according to various purposes (for example, wavelength dispersion adjusting agent, ultraviolet ray inhibitor, release agent, antistatic agent, deterioration preventing agent, antioxidant, peroxide decomposition agent, radical inhibitor, The metal deactivator, acid scavenger, infrared absorber and the like may be solid or oily. Moreover, when a film is formed from a multilayer, the kind and addition amount of the additive of each layer may differ. For these details, the materials described in detail on pages 16 to 22 of the technique No. 2001-1745 described above are preferably used. The amount of each material added is not particularly limited as long as the function is expressed, but is preferably 0.001 to 25% by mass in the entire composition of the polymer film.

[Production method of polymer film]
The polymer film is preferably produced by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) in which a polymer material is dissolved in an organic solvent. In the solvent cast method, a 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.
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 with 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, the time from casting to stripping can be shortened. 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.

In the casting step, one kind of cellulose acylate solution may be cast as a single layer, or two or more kinds of cellulose acylate solutions may be cast simultaneously and / or sequentially.
As a method of co-casting a plurality of cellulose acylate solutions of two or more layers as described above, for example, a solution containing cellulose acylate from a plurality of casting openings provided at intervals in the traveling direction of the support. A method of casting and laminating each (for example, a method described in JP-A-11-198285) A method of casting a cellulose acylate solution from two casting ports (a method described in JP-A-6-134933) A method of wrapping a flow of a high-viscosity cellulose acylate solution with a low-viscosity cellulose acylate solution and simultaneously extruding the high- and low-viscosity cellulose acylate solution (method described in JP-A-56-162617), etc. Can be mentioned. The present invention is not limited to these.
The manufacturing process of these solvent casting methods is described in detail on pages 22 to 30 of the aforementioned technical number 2001-1745, and includes dissolution, casting (including co-casting), metal support, drying, peeling. Categorized as stretching, etc.

  The thickness of the film used as the support is preferably 15 to 120 μm, and more preferably 30 to 80 μm.

[Surface treatment of polymer film]
The polymer film is preferably subjected to a surface treatment. Surface treatment includes corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment and ultraviolet irradiation treatment. Details of these are described in detail on pages 30 to 32 of the aforementioned public technical number 2001-1745. Among these, an alkali saponification treatment is particularly preferable, and it is extremely effective as a surface treatment of a cellulose acylate film.

  The alkali saponification treatment may be either immersion in a saponification solution or application of a saponification solution, but a coating method is preferred. Examples of the coating method include a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method, and an E-type coating method. Examples of the alkali saponification treatment liquid include potassium hydroxide solution and sodium hydroxide solution, and the prescribed concentration of hydroxide ions is preferably in the range of 0.1 to 3.0N. Furthermore, as an alkali treatment liquid, a solvent having good wettability to a film (eg, isopropyl alcohol, n-butanol, methanol, ethanol, etc.), a surfactant, a wetting agent (eg, diols, glycerin, etc.) is contained. Thus, the wettability of the saponification solution to the transparent support, the aging stability of the saponification solution, etc. are improved. Specifically, description of the content is mentioned, for example in Unexamined-Japanese-Patent No. 2002-82226 and WO02 / 46809.

  In place of the surface treatment, in addition to the surface treatment, an undercoat layer (described in JP-A-7-333433) or a single resin layer such as gelatin containing both a hydrophobic group and a hydrophilic group is applied. A layer that adheres well to the polymer film (hereinafter abbreviated as the first undercoat layer) is provided as the first layer method, and a hydrophilic resin layer (hereinafter referred to as gelatin) that adheres well to the alignment film as the second layer thereon. And a so-called multilayer method (for example, described in JP-A No. 11-248940).

[Optically anisotropic layer]
The optical compensation film used in the present invention preferably has an optically anisotropic layer formed from a discotic compound. Hereinafter, details of preferred embodiments of the optically anisotropic layer will be described.
The optically anisotropic layer is preferably designed to compensate for the liquid crystal compound in the liquid crystal cell in the black display of the liquid crystal display device. The alignment state of the liquid crystal compound in the liquid crystal cell in black display varies depending on the mode of the liquid crystal display device. The relationship between the alignment state of the liquid crystal compound in the liquid crystal cell and the alignment of the compensation film is described in IDW'00, FMC7-2, P411 to 414.

  In the optically anisotropic layer, since the discotic compound is hybrid-oriented, the average inclination angle of the major axis (major axis of the disc surface) of the discotic compound with respect to the layer plane is the depth direction of the optically anisotropic layer. , Increasing or decreasing with increasing distance from the transparent support interface. The average angle of inclination preferably increases with increasing distance. Further, the change in the tilt angle can be continuous increase, continuous decrease, intermittent increase, intermittent decrease, change including continuous increase and continuous decrease, or intermittent change including increase and decrease. . The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. In the present invention, even if a region where the inclination angle does not change is included, it may be increased or decreased as a whole. Furthermore, it is preferable that the inclination angle changes continuously. In the case of the present invention in which the retardation of the optically anisotropic layer is used to cancel the retardation generated in the liquid crystal layer as the driving voltage is lowered, the tilt angle β of the orientation of the discotic compound is As described above, it is preferable to adjust to 30 to 45 °.

  The optically anisotropic layer can be formed by applying a composition containing a liquid crystalline discotic compound to the surface of the transparent support and heating if necessary. In order to bring the liquid crystal discotic compound into the above-described desired alignment state, it is preferable to use an alignment film or a material that controls the alignment of liquid crystal molecules such as a chiral agent, a surfactant, and a polymer. For example, when an alignment film is used, the alignment direction of the long axis of the liquid crystalline discotic compound at the interface of the alignment film is adjusted to a desired direction by selecting a material for the alignment film or by selecting a rubbing treatment method. can do. Further, the major axis (disk surface) direction of the surface-side (air-side) discotic compound can be generally adjusted by selecting the discotic compound or the type of additive used together with the discotic compound. In addition, the composition for forming an optically anisotropic layer may contain a polymerizable monomer and an initiator that are used to fix the liquid crystalline discotic compound.

[Discotic compound]
Examples of discotic compounds that can be used in the present invention include C.I. Destrade et al., Mol. Cryst. 71, 111 (1981), benzene derivatives described in C.I. Destrade et al., Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 (1990); Kohne et al., Angew. Chem. 96, page 70 (1984) and the cyclohexane derivatives described in J. Am. M.M. Lehn et al. Chem. Commun. , 1794 (1985), J. Am. Zhang et al., J. Am. Chem. Soc. 116, 2655 (1994), azacrown type and phenylacetylene type macrocycles are included.

  Examples of discotic compounds include compounds having liquid crystallinity in which a linear alkyl group, an alkoxy group, and a substituted benzoyloxy group are radially substituted as a side chain of the mother nucleus with respect to the mother nucleus at the center of the molecule. Is also included. The molecule or the assembly of molecules is preferably a compound having rotational symmetry and imparting a certain orientation. Preferred examples of the discotic compound are described in JP-A-8-50206. The discotic compound has unique Re and Rth wavelength dispersion for each molecular structure. On the basis of these unique molecular structures, it is possible to make a molecule having a wavelength dispersion range as shown in (1) to (4) of the present invention by substituting the side chain of the molecule.

[Additive for optically anisotropic layer]
In the composition for forming the optically anisotropic layer, various additives such as a chiral agent can be contained in addition to the above-mentioned discotic compound. Examples of the additive include a plasticizer, a surfactant, a polymerizable monomer, and the like. These additives contribute to improving the uniformity of the coating film, the strength of the film, the orientation of the discotic compound, and the like. Examples of the surfactant include the following fluorine-containing surfactants.

  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 compound.

  Examples of the surfactant include conventionally known compounds, and fluorine compounds are particularly preferable. Specific examples include compounds described in paragraph numbers [0028] to [0056] in JP-A-2001-330725.

The polymer used together with the discotic compound is preferably capable of changing the tilt angle of the discotic compound.
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 with respect to the liquid crystalline discotic compound so as not to inhibit the alignment of the liquid crystalline discotic compound, and 0.1 to 8% by mass. It is more preferable that it is in the range.

[Formation of optically anisotropic layer]
The optically anisotropic layer can be formed by applying a coating liquid containing a liquid crystalline discotic compound and, if necessary, an additive or the like to the surface of the alignment film.
As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane, tetrachloroethane), 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, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).

[Immobilization of discotic compounds]
The liquid crystalline discotic compound can be fixed while maintaining the alignment state. The immobilization is preferably performed by a polymerization reaction. 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) 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 in the range of 0.01 to 20% by mass, more preferably in the range of 0.5 to 5% by mass, based on the solid content of the coating solution.
The light irradiation for the polymerization of the liquid crystalline discotic compound preferably uses ultraviolet rays. The irradiation energy is preferably in the range of ^{20mJ / cm 2 ~50J / cm 2} , more preferably in the range of 20~5000mJ / cm ^2, more preferably in the range of 100 to 800 mJ / cm ² . In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions. A protective layer may be provided on the optically anisotropic layer.

[Alignment film]
The alignment film has a function of defining the alignment direction of the discotic compound. In order to bring the liquid crystalline discotic compound into the above alignment state, it is preferable to use an alignment film. However, if the alignment state is fixed after aligning the liquid crystalline discotic compound, the alignment film plays its role. Therefore, it is not always essential as a component of the present invention. That is, it is also possible to produce the optical compensation film of the present invention by transferring only the optically anisotropic layer on the alignment film in which the alignment state is fixed onto the transparent support.

  The alignment film is an organic compound (eg, ω-tricosanoic acid) formed by rubbing treatment of an organic compound (preferably a polymer), oblique deposition of an inorganic compound, formation of a layer having a microgroove, or Langmuir-Blodgett method (LB film). , Dioctadecylmethylammonium chloride, methyl stearylate). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field, or light irradiation is also known.

The alignment film is preferably formed by polymer rubbing treatment. In principle, the polymer used for the alignment film has a molecular structure having a function of aligning liquid crystal molecules. In the present invention, in addition to the function of aligning liquid crystalline molecules, a crosslink having a function of aligning a side chain having a crosslinkable functional group (eg, double bond) to the main chain or aligning liquid crystalline molecules. It is preferable to introduce a functional functional group into the side chain.
As the polymer used for the alignment film, either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent can be used, and a plurality of combinations thereof can be used.
Examples of the polymer include methacrylate copolymers, styrene copolymers, polyolefins, polyvinyl alcohol and modified polyvinyl alcohol, poly (N-methylol) described in paragraph No. [0022] of JP-A-8-338913. Acrylamide), polyester, polyimide, vinyl acetate copolymer, carboxymethylcellulose, polycarbonate and the like. Silane coupling agents can be used as the polymer. Water-soluble polymers (eg, poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol, modified polyvinyl alcohol) are preferred, gelatin, polyvinyl alcohol and modified polyvinyl alcohol are more preferred, and polyvinyl alcohol and modified polyvinyl alcohol are most preferred. . It is particularly preferable to use two types of polyvinyl alcohol or modified polyvinyl alcohol having different degrees of polymerization.

The saponification degree of polyvinyl alcohol is preferably 70 to 100%, more preferably 80 to 100%. It is preferable that the polymerization degree of polyvinyl alcohol is 100-5000.
A side chain having a function of aligning liquid crystal molecules generally has a hydrophobic group as a functional group. 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 Examples include substituted hydrocarbon groups, thioether groups, polymerizable groups (unsaturated polymerizable groups, epoxy groups, azirinidyl groups, etc.), alkoxysilyl groups (trialkoxy, dialkoxy, monoalkoxy), and the like. As specific examples of these modified polyvinyl alcohol compounds, 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 are described. [0022] and the like.

When a side chain having a crosslinkable functional group is bonded to the main chain of the alignment film polymer, or a crosslinkable functional group is introduced into a side chain having a function of aligning liquid crystalline molecules, the alignment film polymer and the optically anisotropic film The polyfunctional monomer contained in the conductive layer can be copolymerized. As a result, not only between the polyfunctional monomer and the polyfunctional monomer, but also between the alignment film polymer and the alignment film polymer and between the polyfunctional monomer and the alignment film polymer is firmly bonded by a covalent bond. Therefore, the strength of the optical compensation film can be remarkably improved by introducing the crosslinkable functional group into the alignment film polymer.
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 No. 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 reticulation can be obtained. May occur.

  The alignment film can be basically formed by applying the polymer on the transparent support containing the alignment film forming material and the crosslinking agent, followed by drying by heating (crosslinking) and rubbing treatment. 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 layer surface of an alignment film and also an optically anisotropic layer reduces remarkably.

  The alignment film is preferably applied by spin coating, dip coating, curtain coating, extrusion coating, rod coating, or roll coating. 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 can be formed on the surface of the transparent support, or if desired, if an undercoat layer is provided on the transparent support, the surface of the undercoat layer. The alignment film may be produced by rubbing the surface after crosslinking the polymer layer as described above.
For the rubbing treatment, a treatment method widely adopted as a liquid crystal alignment treatment process of LCD can be applied. That is, a method of obtaining the orientation by rubbing the surface of the orientation film in a certain direction using paper, gauze, felt, rubber, nylon, polyester fiber or the like can be used. Generally, it is carried out by rubbing several times using a cloth or the like in which fibers having a uniform length and thickness are planted on average. When the retardation of the optically anisotropic layer is used for canceling the retardation generated in the liquid crystal layer as the drive voltage is lowered, as described above, the direction of the rubbing axis is set in the vicinity of the polarizing film disposed in the vicinity. Determined in relation to absorption axis or transmission axis.

Next, the alignment film is caused to function to align the liquid crystalline discotic compound of the optically anisotropic layer provided on the alignment film. Thereafter, if necessary, the alignment film polymer and the polyfunctional monomer contained in the optically anisotropic layer may be reacted, or the alignment film polymer may be crosslinked using a crosslinking agent.
The thickness of the alignment film is preferably in the range of 0.1 to 10 μm.

[Elliptically polarizing plate]
When the optical compensation film is used to compensate the liquid crystal cell, it is used by inserting, laminating, and optically adhering between the polarizing film and the liquid crystal layer. It is more useful to use an elliptically polarizing plate bonded and bonded to a compensation film. The optical compensation film may be bonded to a polarizing plate or used as a protective film for a polarizing film. When used as a protective film for a polarizing film, it contributes to thinning of the liquid crystal display device.
In addition, the optically anisotropic layer can be directly formed on the surface of the polarizing film. Specifically, the optically anisotropic layer is formed by applying the coating liquid for the optically anisotropic layer as described above to the surface of the polarizing film. As a result, without using a polymer film between the polarizing film and the optically anisotropic layer, a thin polarizing plate having a small stress (strain × cross-sectional area × elastic modulus) associated with the dimensional change of the polarizing film is produced. . When the polarizing plate according to the present invention is attached to a large liquid crystal display device, an image with high display quality is displayed without causing problems such as light leakage.

[Polarizing film]
A polarizing film usable in the present invention is Optiva Inc. And a polarizing film comprising a binder and iodine or a dichroic dye is preferable. Iodine and dichroic dye in the polarizing film exhibit deflection performance by being oriented in the binder. It is preferable that the iodine and the dichroic dye are aligned along the binder molecule, or the dichroic dye is aligned in one direction by self-assembly such as liquid crystal. At present, a commercially available polarizing film is produced by immersing a stretched polymer in a solution of iodine or dichroic dye in a bath and allowing iodine or dichroic dye to penetrate into the binder. Is common.
In the commercially available polarizing film, iodine or dichroic dye is distributed about 4 μm (about 8 μm on both sides) from the polymer surface, and in order to obtain sufficient polarization performance, a polarizing film having a thickness of 10 μm or more is used. Is preferred. The penetrability can be controlled by the solution concentration of iodine or dichroic dye, the temperature of the bath, and the immersion time.
As described above, the lower limit of the binder thickness is preferably 10 μm. The upper limit of the thickness is preferably as thin as possible from the viewpoint of light leakage of the liquid crystal display device. It is preferably not more than a commercially available polarizing plate (about 30 μm), preferably 25 μm or less, and more preferably 20 μm or less. When the thickness is 20 μm or less, the light leakage phenomenon is not observed on a 17-inch liquid crystal display device.

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

  As the binder of the polarizing film, either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent can be used. Examples of the polymer include the same polymers as those described for the alignment film. Most preferred are polyvinyl alcohol and modified polyvinyl alcohol. The modified polyvinyl alcohol is described in JP-A-8-338913, JP-A-9-152509 and JP-A-9-316127. Two or more kinds of polyvinyl alcohol and modified polyvinyl alcohol may be used in combination.

The addition amount of the crosslinking agent in the binder is preferably 0.1 to 20% by mass with respect to the binder. The orientation of the polarizing element and the moisture and heat resistance of the polarizing film are improved.
The polarizing film contains a certain amount of a crosslinking agent that has not reacted even after the crosslinking reaction is completed. However, the amount of the remaining crosslinking agent is preferably 1.0% by mass or less and more preferably 0.5% by mass or less in the alignment film. In this way, even if the polarizing film is incorporated in a liquid crystal display device and used for a long time or left in a high temperature and high humidity atmosphere for a long time, the degree of polarization does not decrease.
The crosslinking agent is described in US Reissue Patent 23297. Boron compounds (eg, boric acid, borax) can also be used as a crosslinking agent.

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

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

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

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

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

  Next, the optical compensation film of the present invention is bonded to the surface of the polarizing film. The surface to be bonded to the polarizing film is preferably the back surface of the transparent support (the surface on which the optically anisotropic layer is not formed). An adhesive can be used at the time of bonding. As the adhesive, a polyvinyl alcohol resin (including a modified polyvinyl alcohol with an acetoacetyl group, a sulfonic acid group, a carboxyl group, or an oxyalkylene group) or an aqueous boron compound solution can be used. A polyvinyl alcohol resin is preferred. The adhesive may be applied to the bonding surface of the polarizing film and / or the optical compensation film to form an adhesive layer, and the two layers may be stacked and bonded by heating or pressing as desired. The thickness of the adhesive layer is preferably in the range of 0.01 to 10 μm after drying, and particularly preferably in the range of 0.05 to 5 μm.

  The optical compensation film may be bonded to one surface of the polarizing film, and another polymer film or the like may be bonded to the other surface. The polymer film preferably has characteristics that can function as a protective film for a polarizing film. The polymer film is preferably provided with an antireflection film having an outermost surface having antifouling properties and scratch resistance. Any conventionally known antireflection film can be used.

[Liquid Crystal Display]
The liquid crystal display device of the present invention is preferably a liquid crystal cell in which liquid crystals are twisted and aligned, for example, a TN mode liquid crystal display device.
FIG. 6 described above is a schematic diagram of a basic configuration example of a transmissive liquid crystal display device. With reference to FIG. 6 again, a basic configuration example of a transmissive liquid crystal display device according to an embodiment of the present invention will be described.
The transmissive liquid crystal display device shown in FIG. 6 includes a transparent protective film (1a), a polarizing film (2a), a transparent support (3a), an optically anisotropic layer (4a), and a liquid crystal in order from the backlight (BL) side. Cell lower substrate (5a), rod-shaped liquid crystal layer (6), liquid crystal cell upper substrate (5b), optical anisotropic layer (4b), transparent support (3b), polarizing film (2b), and transparent protective film (1b). The transparent support and the optically anisotropic layer (3a, 4a and 4b, 3b) constitute the optical compensation film of the present invention. And a transparent protective film, a polarizing film, a transparent support body, and an optically anisotropic layer (1a-4a and 4b-1b) comprise the elliptically polarizing plate of this invention.

  The TN mode liquid crystal cell is most frequently used as a color TFT liquid crystal display device, and is described in many documents.

In this embodiment, an example using a nematic liquid crystal having positive dielectric anisotropy will be described.
A liquid crystal having positive dielectric anisotropy, refractive index anisotropy Δn = 0.0854 (589 nm, 20 ° C.) and dielectric anisotropy Δε = + 8.5 is sealed between the upper and lower substrates 6a and 6b. The product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn is preferably 0.2 to 0.5 μm. The alignment control of the liquid crystal layer can be controlled by the surface properties and rubbing axes of the alignment films formed on the inner surfaces of the upper and lower substrates 6a and 6b. The director indicating the alignment direction of the liquid crystal molecules, that is, the so-called tilt angle is preferably about 3 °. The rubbing direction is applied to the upper and lower substrates 6a and 6b in directions orthogonal to each other, and the magnitude of the tilt angle can be controlled by the strength and the number of times of rubbing. The alignment film is preferably formed by applying and baking a polyimide film. The magnitude of the twist angle of the liquid crystal layer is determined by the crossing angle of the upper and lower substrates in the rubbing direction and the chiral agent added to the liquid crystal material. For example, to make the twist angle 90 °, it is preferable to add a chiral agent with a pitch of about 60 μm. The thickness d of the liquid crystal layer may be about 5 μm, for example. The liquid crystal material LC to be used is not particularly limited as long as it is a nematic liquid crystal. As the dielectric anisotropy Δε is larger, the driving voltage can be reduced. As the refractive index anisotropy Δn is smaller, the thickness (gap) of the liquid crystal layer can be increased, and gap variation can be reduced. In addition, a larger Δn can reduce the cell gap and enable high-speed response. The twist angle (twist angle) of the liquid crystal layer is generally twisted clockwise from the light source side toward the display observation side as viewed from the observation side, and the optimum value is in the vicinity of 90 ° (85 ° to 95 °). In these ranges, since the white display luminance is high and the black display luminance is low, a bright and high-contrast display device can be obtained.

The polarizing axis of the upper polarizing film 2b and the polarizing axis of the lower polarizing film 2a are stacked approximately orthogonally, and the polarizing axis of the upper polarizing film 2b of the liquid crystal cell and the rubbing direction of the upper substrate 6b are approximately orthogonally crossed, and the lower polarizing film 2a The polarizing axis and the rubbing direction of the lower substrate 6a are laminated so as to be approximately orthogonal to each other. A transparent electrode (not shown) is formed inside the alignment film of each of the upper substrate 6b and the lower substrate 6a. In a non-driving state in which no driving voltage is applied to the electrodes, the liquid crystal molecules in the liquid crystal cell are placed on the substrate surface. As a result, the polarization state of light passing through the liquid crystal panel is propagated along the twisted structure of the liquid crystal molecules, and the polarization plane is rotated by 90 ° and emitted. That is, the liquid crystal display device realizes white display in a non-driven state. In contrast, in the driving state, the liquid crystal molecules are aligned in a direction that forms an angle with respect to the substrate surface, and the light that has passed through the lower polarizing film 2a passes through the liquid crystal layer 7 while maintaining the polarization state. It is blocked by the polarizing film 2b. In other words, a black display is obtained in the driving state. Since this liquid crystal display device includes the optical compensation film of the present invention, the gradation inversion phenomenon that occurs depending on the viewing direction is reduced, and the viewing angle is improved.
Note that these optimum values are values in the transmission mode, and in the reflection mode, the optical path in the liquid crystal cell is doubled. Therefore, the optimum Δnd value is about a half of the above value. In addition, the optimum twist angle is 30 ° to 70 °.
The liquid crystal display device of the present invention is not limited to the configuration shown in FIG. 6, and may include other members. For example, a color filter may be disposed between the liquid crystal cell and the polarizing film. A backlight using a cold cathode or a hot cathode fluorescent tube, or a light emitting diode, a field emission element, or an electroluminescent element as a light source can be disposed. The liquid crystal display device of the present invention may be a transflective type in which a reflective portion and a transmissive portion are provided in one pixel of the display device in order to achieve both transmission and reflection modes.
The liquid crystal display device of the present invention includes an image direct view type, an image projection type, and a light modulation type. The present invention is particularly effective when applied to an active matrix liquid crystal display device using three-terminal or two-terminal semiconductor elements such as TFT and MIM. Of course, an embodiment applied to a passive matrix liquid crystal display device is also effective.

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

[Example 1]
Triacetylcellulose film: Fujitac TD-80U was prepared as a transparent support, and surface saponification treatment was performed in the same manner as the saponification treatment described in Example 1 of WO02 / 46809 using an alkaline solution having the following contents. The contact angle between the film surface and water was 32 degrees, and the surface energy was 61 mN / m. This was designated as a transparent support (TK-1).
Composition of alkaline solution:
Potassium hydroxide 5.6 parts by mass Isopropyl alcohol 65.5 parts by mass Ethylene glycol 12 parts by mass Fluoroaliphatic group-containing copolymer 1.0 part by mass (Megafac F780 manufactured by Dainippon Ink Co., Ltd.)
11.4 parts by weight of water

<Formation of alignment film>
On the above Fujitac, a coating solution having the following composition was coated with a # 16 wire bar coater at a coating amount of 28 ml / m ² , and then heated with 60 ° C. hot air for 60 seconds and further with 90 ° C. hot air for 150 seconds. Dried for 2 seconds. A rubbing treatment was performed in a direction rotated 4 ° clockwise from the slow axis of the transparent support to obtain an alignment film.
<Alignment film coating solution composition>
Modified polyvinyl alcohol having the following structure 10 parts by weight Water 371 parts by weight Methanol 119 parts by weight Glutaraldehyde (crosslinking agent) 0.5 parts by weight

<Formation of optically anisotropic layer>
90 parts by mass of liquid crystalline discotic compound (A), 10 parts by mass of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), melamine formaldehyde / acrylic acid copolymer (Aldrich reagent) 0.6 Part by mass, 3.0 parts by mass of a photopolymerization initiator (Irgacure 907, manufactured by Nippon Ciba Geigy Co., Ltd.) and 1.0 part by mass of a photosensitizer (Kaya Cure DETX, manufactured by Nippon Kayaku Co., Ltd.) are dissolved in methyl ethyl ketone. A solution having a solid content concentration of 38% by mass was prepared as a coating solution.

  This coating solution was continuously applied onto the alignment film with a # 5.4 wire bar and heated at 130 ° C. for 2 minutes to orient the molecules of the liquid crystalline discotic compound.

  Next, UV irradiation was performed for 1 minute using a 120 W / cm high pressure mercury lamp at 100 ° C. to polymerize the liquid crystalline discotic compound. Then, it stood to cool to room temperature. Thus, an optical compensation film with an optically anisotropic layer (KH-1) was produced. The thickness of the formed optically anisotropic layer was 2.6 μm. Only this optically anisotropic layer was peeled from the transparent support, and the β value was output with an ellipsometer (M-150 manufactured by JASCO Corporation), which was 38.5 °.

(Preparation of polarizing film)
PVA having an average polymerization degree of 4000 and a saponification degree of 99.8 mol% was dissolved in water to obtain a 4.0% aqueous solution. This solution was band-cast using a die having a taper and dried to form a film so that the width before stretching was 110 mm, the thickness was 120 μm at the left end, and 135 μm at the right end.
This film was peeled off from the band, obliquely stretched in the 45 ° direction in a dry state, and immersed in an aqueous solution of iodine 0.5 g / L and potassium iodide 50 g / L for 1 minute at 30 ° C., and then boric acid. It is immersed in an aqueous solution of 100 g / L and potassium iodide 60 g / L at 70 ° C. for 5 minutes, further washed with water in a water-washing tank at 20 ° C. for 10 seconds, and then dried at 80 ° C. for 5 minutes. HF-1) was obtained. The polarizing film had a width of 660 mm and a thickness of 20 μm on both sides.

(Preparation of polarizing plate)
Using a polyvinyl alcohol-based adhesive, KH-1 (optical compensation film) was attached to one side of the polarizing film (HF-1) on the transparent support (TK-1) surface. Again, a surface saponification treatment was performed on another triacetylcellulose film: Fujitac TD-80U in the same manner as the saponification treatment performed in Example 1 of the specification of WO02 / 46809, and a polyvinyl alcohol adhesive was used. Pasted on the opposite side of the polarizing film.
It arrange | positioned so that the absorption axis of a polarizing film and the slow axis of a transparent support body (TK-1) may become parallel. The slow axis of the triacetyl cellulose film was arranged in parallel. In this way, a polarizing plate (HB-1) was produced in which the average orientation direction of the discotic compound molecules was rotated 4 ° clockwise with respect to the absorption axis of the polarizing film. Similar to the case of inserting only two (HB-1) liquid crystal display devices, the upper and lower two layers of discotic compounds have a relative angle of 82 ° when they are arranged orthogonally. As a result, the in-plane retardation (retardation) of the discotic compound layer is not canceled. When viewed from the normal direction of the two discotic compound layers, the slow axis assuming an index ellipsoid is formed in an obtuse angle direction. When arranged in a display device, the slow axis of the refractive index ellipsoid is formed in the left-right direction of the display surface.
Two optically anisotropic layers were cut into 5 cm squares with an orientation axis relative angle of 82 °, and two layers were stacked and loaded on an ellipsometer (M-150 manufactured by JASCO Corporation), and the retardation was measured. As a result, Re (550) was 23 nm. It was confirmed that the slow axis was oriented in the desired direction.

[Example 2]
(TK-1) was produced in the same manner as in Example 1, and an alignment film was formed. The rubbing alignment treatment was also performed in the direction rotated clockwise by 4 ° from the slow axis of the transparent support in the same manner as in Example 1. Thereafter, an optically anisotropic layer was formed in the same manner as in Example 1. In Example 2, the liquid crystalline discotic compound (B) was used as the discotic compound. This was designated as an optical compensation film (KH-2).

An optical compensation film (KH-2) was attached to one side of the polarizing film (HF-1) on the transparent support (TK-1) surface using a polyvinyl alcohol-based adhesive. Again, another triacetyl cellulose film: Fujitac TD-80U was subjected to saponification treatment and surface saponification treatment in the same manner as in Example 02 of WO02 / 46809, and using a polyvinyl alcohol-based adhesive, Pasted on the other side.
It arrange | positioned so that the absorption axis of a polarizing film and the slow axis of a transparent support body (TK-1) may become parallel. The slow axis of the triacetyl cellulose film was arranged in parallel. In this way, a polarizing plate (HB-2) was produced.

[Comparative Example 1]
(TK-1) was produced in the same manner as in Example 1, and an alignment film was formed. The rubbing alignment treatment was also performed in the direction rotated clockwise by 4 ° from the slow axis of the transparent support in the same manner as in Example 1. Thereafter, an optically anisotropic layer was formed in the same manner as in Example 1. In Example 3, the liquid crystalline discotic compound (C) was used as the discotic compound. This was designated as an optical compensation film (KH-3). The optical compensation film (KH-3) was attached to one side of the polarizing film (HF-1) with the transparent support (TK-1) surface using a polyvinyl alcohol-based adhesive. Again, another triacetyl cellulose film: Fujitac TD-80U was subjected to saponification treatment and surface saponification treatment in the same manner as in Example 1 of WO02 / 46809, and polarized using a polyvinyl alcohol-based adhesive. Affixed to the other side of the membrane.

  It arrange | positioned so that the absorption axis of a polarizing film and the slow axis of a transparent support body (TK-1) may become parallel. The slow axis of the triacetyl cellulose film was arranged in parallel. In this way, a polarizing plate (HB-3) was produced.

[Comparative Example 2]
(Preparation of transparent support)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.
(Cellulose acetate solution composition)
Cellulose acetate (linter) with an acetylation degree of 60.9% 80 parts by mass Cellulose acetate (linter) with an acetylation degree of 60.8% 20 parts by mass Triphenyl phosphate (plasticizer) 7.8 parts by mass Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by mass Methylene chloride (first solvent) 300 parts by mass Methanol (second solvent) 54 parts by mass 1? 11 parts by weight of butanol (third solvent)

In another mixing tank, 16 parts by mass of the following retardation increasing agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution.
A dope was prepared by mixing 474 parts by mass of the cellulose acetate solution with 25 parts by mass of the retardation increasing agent solution and stirring sufficiently. The addition amount of the retardation increasing agent was 3.5 parts by mass with respect to 100 parts by mass of cellulose acetate.

The obtained dope was cast using a band casting machine. After the film surface temperature on the band reached 40 ° C., it was dried for 1 minute, peeled off, and then a transparent support (TK? 2) having a residual solvent amount of 0.3 mass% with a drying air of 140 ° C. Manufactured.
The width of the obtained transparent support (TK? 2) was 1500 mm, and the thickness was 65 μm.
Moreover, it was 4 nm when the retardation value (Re) in wavelength 550nm was measured using the ellipsometer (M? 150, JASCO Corporation make). Moreover, it was 78 nm when the retardation value (Rth) of the thickness direction was measured.

An alignment film similar to that in Example 1 was formed on (TK-2), and a rubbing alignment treatment was performed in parallel with the slow axis of (TK-2).
(Formation of liquid crystalline discotic compound layer)
On the alignment film, the above liquid crystalline discotic compound (C) 46.65 kg, ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) 4.06 kg, cellulose acetate butyrate (CAB551) 0.2, manufactured by Eastman Chemical Co., Ltd.) 0.90 kg, cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co., Ltd.) 0.23 kg, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Co.) 1.35 kg A solution obtained by dissolving 0.45 kg of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 102 kg of methyl ethyl ketone was used as a coating solution, and this was coated with a # 3.6 wire bar. This was heated in a constant temperature zone of 130 ° C. for 2 minutes to align the liquid crystal compound (C). Next, UV irradiation was performed for 1 minute using a 120 W / cm high-pressure mercury lamp in an atmosphere of 60 ° C. to polymerize the discotic liquid crystalline compound. Then, it stood to cool to room temperature. In this way, a liquid crystal compound layer having a thickness of 1.4 μm was formed, and an optical compensation film (KH? 4) was produced.

  The retardation value Rth in the thickness direction of the liquid crystal compound layer measured at a wavelength of 550 nm was 103 nm. The angle (tilt angle) between the disk surface and the transparent support surface was 39 ° on average.

(Preparation of polarizing plate)
Using polyvinyl alcohol adhesive, KH? 4 (optical compensation film) was attached to one side of the polarizing film (HF? 1). Also, triacetyl cellulose film: Fujitac TD? A saponification treatment was performed on 80 U in the same manner as in Example 1, and affixed to the opposite side of the polarizing film using a polyvinyl alcohol-based adhesive.
The transmission axis of the polarizing film and TK? It arrange | positioned so that 2 slow axis might become orthogonal. It arrange | positioned so that the transmission axis of a polarizing film and the slow axis of said TD-80U may orthogonally cross. In this way, a polarizing plate (HB? 4) was produced.

[Comparative Example 3]
A conventional wide viewing angle polarizing plate (LPT-HL56-12, manufactured by Sanritz Corporation) in which a conventional optical compensation film (Fuji Photo Film Co., Ltd.), an iodine polarizing film, and a protective TAC film are integrated in advance. Was manufactured and evaluated together with Examples 1 and 2 and Comparative Examples 1 and 2.

  The produced polarizing plates are arranged in Table 1.

(Evaluation with TN mode liquid crystal display)
Remove the pair of polarizing plates provided in the liquid crystal display device (SyncMaster 172x, Nippon Samsung Co., Ltd.) using a twisted nematic alignment mode liquid crystal cell, and the retardation of the liquid crystal layer and the twist direction of the liquid crystal The measurement was performed using a general-purpose deflection analyzer H33 manufactured by KK. It was confirmed that Δnd was about 0.4 μm and the liquid crystal cell was twisted about 90 ° clockwise from the light source side toward the display observation side as viewed from the observation side.
Five sets of liquid crystal display devices were prepared, and the pair of front and back polarizing plates bonded to the liquid crystal cell was peeled off. Cut out HB-1 to 5 cm each to 20 cm ² and paste HB-1 to 5 on the front and back instead of the peeled polarizing plate with an adhesive so that the optical compensation film is on the liquid crystal cell side. It was. The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were arranged so as to be orthogonal to the liquid crystal rubbing direction on each substrate.
Of the liquid crystal display devices, those in which HB-1, HB-2, and HB-3 were attached to the front and back surfaces of the cell were modified to reduce the drive voltage by 30%. As a result, it is expected from FIG. 2 that retardation of about 23 nm occurs in the liquid crystal layer. The display device with HB-4 and HB-5 attached thereto was not modified in the drive circuit.

About the produced 5 types of liquid crystal display devices, the gradation level equally divided into 8 steps from black display (L0) to white display (L7) was measured using the measuring machine (EZ-Contrast160D, ELDIM company make). Table 2 shows the angle at which L1 and L2 intersect in the downward direction (the gradation inversion angle) obtained as a result.
Using the same measuring device (EZ-Contrast 160D, manufactured by ELDIM), the color fluctuation was also measured. In CIE 1976 and UCS coordinates, the maximum hue variation width (distance from end to end on coordinates) Δu′v ′ in the vertical direction (upward 80 ° to down 80 ° from the display normal) was compared. The results are also shown in Table 2.

  In the case of Examples 1 and 2 in which the wavelength dispersion ratio of the optically anisotropic layer satisfies (1) to (4) of the present invention at the same time, the lower gradation inversion angle is increased and the color changes by reducing the drive voltage. Can be achieved. On the other hand, when the chromatic dispersion ratio deviates from the four formulas (Comparative Example 1), it can be understood that the tone reversal can be improved, but the color change exceeds the allowable range. On the other hand, in both Comparative Examples 2 and 3, the downward gradation inversion angle cannot reach the target of 37 °.

  From the results of the above examples and comparative examples, by using an optically anisotropic layer in which Re and Rth satisfy the expressions (1) to (4) at the same time, the driving voltage is reduced and the downward gradation inversion angle is obtained. It was found that the color variation can be suppressed.

In the TN-type liquid crystal display device, the rubbing axes of the upper and lower substrates and the direction of the biaxial refraction slow axis in-plane component generated in the ON state and the birefringence slow axis in-plane component of the optically anisotropic layer to be canceled It is a figure which shows the relationship of a direction typically. It is a graph which shows the example of the relationship between the drive voltage of a liquid crystal cell, and the in-plane retardation which generate | occur | produces in a liquid crystal cell. It is a graph which shows an example of the relationship between the drive voltage of a liquid crystal cell, the in-plane retardation which generate | occur | produces in a liquid crystal cell, and a gradation inversion angle. It is a graph which shows the example of the relationship of the rotation angle of the orientation direction of the discotic compound from the polarizing film absorption axis in an optical compensation film, and the retardation to generate | occur | produce, and the relationship of (beta). It is a graph which shows the example of the relationship of the average (beta) of the angle a which the disk surface of a discotic compound, a transparent support body interface, and an air interface form, and b, and front contrast. It is a schematic diagram of a structural example of a transmissive display device using an optical compensation film composed of a discotic compound and a transparent support. It is a figure which shows typically the direction of the rubbing axis | shaft of the rod-shaped liquid crystal of the liquid crystal display device of FIG. 6, the rubbing axis | shaft of a discotic compound layer, and the slow axis of a refractive index ellipsoid by it. It is a CIE1976 USC chromaticity diagram (2 ° field of view). It is a graph which shows the relationship between the polar angle inclination angle of the nematic rod-shaped liquid crystal in a general TN mode liquid crystal cell, and the thickness direction. It is a graph which shows the relationship between the twist angle of the nematic rod-shaped liquid crystal in a general TN mode liquid crystal cell, and the thickness direction. It is a schematic diagram which shows the direction of twist of the nematic rod-like liquid crystal in a general TN mode liquid crystal cell and the orientation of the discotic compound of the optical compensation film. It is a schematic diagram explaining generation | occurrence | production of the gradation inversion in a TN mode liquid crystal cell. It is a graph which shows the relationship between the up-and-down viewing angle and the brightness | luminance in the liquid crystal display device using an example of the conventional optical compensation film, and the viewing angle which shows a gradation inversion angle was shown by the arrow in the graph.

Explanation of symbols

1a, 1b Transparent protective film 2a, 2b Polarizing film 3a, 3b Transparent support 4a, 4b Optically anisotropic layer 5a, 5b Upper and lower substrates 6 of liquid crystal cell L. Backlight 51 Liquid crystal cell 52 Schematic diagram of rod-like liquid crystalline molecules 53 Schematic diagrams showing the orientation of discotic compounds 54a and 54b Diagrams showing arrangement examples of optical compensation films

Claims (6)

A liquid crystal display device comprising a liquid crystal cell, a pair of polarizing films sandwiching the liquid crystal cell, and at least one optically anisotropic layer disposed between at least one of the pair of polarizing films and the liquid crystal cell Because
The at least one layer of optical anisotropy with respect to an ON voltage that exhibits black or white luminance in a state excluding all optically anisotropic layers disposed between the liquid crystal cell and the pair of polarizing films. The ON voltage at which equal front brightness is obtained with the layers inserted is 10% to 35% lower, and the 10% to 35% lower voltage is driven.
When all the optically anisotropic layers arranged between the liquid crystal cell and the pair of polarizing films are viewed from the normal direction of the layers while maintaining the relative angle, the in-plane retarder is synthesized. The retardation is 5 nm to 35 nm, and the slow axis of the synthesized refractive index ellipsoid is perpendicular to the bisector of the intersection angle of the alignment axes of the upper and lower substrates that define the alignment direction of the liquid crystal cell. A liquid crystal display device in which an in-plane retardation and a thickness direction retardation of the at least one optically anisotropic layer simultaneously satisfy the relational expressions (1) to (4);
0.48 ≦ Re (450) / Re (550) ≦ 0.50 (1)
1.26 ≦ Re (610) / Re (550) ≦ 1.27 (2)
0.88 ≦ Rth (450) / Rth (550) ≦ 0.89 (3)
1.06 ≦ Rth (610) / Rth (550) ≦ 1.07 (4)
In the formula, Re (λ) is the in-plane retardation of the optically anisotropic layer at the wavelength (λ), and Rth (λ) is the retardation in the thickness direction of the optically anisotropic layer at the wavelength (λ). is there. A disk-like compound molecule comprising a disk-like compound, the average inclination angle β value of the molecules of the disk-like compound in the layer is 30 ° to 45 °, and observed from the liquid crystal cell side. 2. The projection onto the polarizing film located closer to the average orientation direction of at least one optically anisotropic layer rotated clockwise by 1 ° or more and 10 ° or less from the polarizing film absorption axis. A liquid crystal display device according to 1. A disk-like compound molecule comprising a disk-like compound, the average inclination angle β value of the molecules of the disk-like compound in the layer is 30 ° to 45 °, and observed from the liquid crystal cell side. An optically anisotropic layer in which the projection onto the polarizing film positioned closer to the average orientation direction of the optical film is rotated by 1 ° or more and 10 ° or less clockwise from the absorption axis of the polarizing film. The liquid crystal display device according to claim 1, wherein at least one layer is provided between the liquid crystal cell and the liquid crystal cell. An optical compensation film for use in the liquid crystal display device according to claim 1, comprising an optically anisotropic layer and a transparent support composed of a composition containing a discotic compound, When the average tilt angle β value of the molecules of the discotic compound is 30 ° to 45 ° and when observed from the liquid crystal cell side, the polarizing film is positioned closer to the orientation direction of the discotic compound. The optical compensation film is rotated by 1 ° or more and 10 ° or less clockwise from the polarizing film absorption axis. An elliptically polarizing plate comprising the optically anisotropic layer according to claim 1, a transparent protective film, and a polarizing film. An elliptically polarizing plate having a transparent protective film, a polarizing film, and at least one optical compensation film according to claim 4.

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