JP2006276849A - Liquid crystal cell and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display apparatus in which a liquid crystal cell is precisely compensated optically to provide a high contrast. <P>SOLUTION: The liquid crystal display apparatus comprises a liquid crystal cell comprising a pair of substrates 17 and 19 disposed facing each other one of which has an electrode, and a liquid crystal material 18 supported between the pair of substrates; a first polarizing film 13 disposed outside the liquid crystal cell; and at least one in-cell optical compensating film 15' (or 20') disposed in between the pair of substrates. The optical compensation film 15' (or 20') has a plurality of mean alignment directions inside a pixel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal cell and a liquid crystal display device with improved viewing angle characteristics.

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

  Among such LCDs, for applications that require high display quality, a 90 degree twisted nematic liquid crystal display device (hereinafter referred to as a TN mode) that uses nematic liquid crystal molecules having positive dielectric anisotropy and is driven by a thin film transistor. Is mainly used. However, although the TN mode has excellent display characteristics when viewed from the front, the contrast is reduced when viewed from an oblique direction, or gradation inversion that reverses the brightness in gradation display occurs. There is a viewing angle characteristic that the display characteristic is deteriorated, and this improvement is strongly demanded.

  Recently, nematic liquid crystal molecules having negative dielectric anisotropy as shown in FIG. 8 are used as an LCD method for improving the viewing angle characteristics, and the major axis of the liquid crystal molecules is substantially perpendicular to the substrate without applying voltage. A vertical alignment nematic liquid crystal display device (hereinafter referred to as a VA mode) in which the liquid crystal is aligned in a direction and driven by a thin film transistor has been proposed (see Patent Document 1). This VA mode has not only excellent display characteristics when viewed from the front, but also the luminance change during black display when viewed from any direction by applying a viewing angle compensation phase difference film. There is little change, and the viewing angle dependency is small. Further, a multi-domain liquid crystal cell structure in which one pixel is divided into four orientation regions exhibits a wide viewing angle characteristic during white display. In the VA mode, a wide viewing angle characteristic can be obtained by using two negative uniaxial retardation films having an optical axis in a direction perpendicular to the film surface, above and below the liquid crystal cell. It is also known that a wider viewing angle characteristic can be realized by using a uniaxially oriented retardation film having a positive refractive index anisotropy with a retardation value of 50 nm (see Non-Patent Document 1). .

  However, the use of two retardation films (see Non-Patent Document 1) not only causes an increase in production cost, but also causes a decrease in yield due to the bonding of a large number of films, and further uses a plurality of films. For this reason, there is a problem that the thickness is increased, which is disadvantageous for thinning the display device. In addition, since the adhesive layer is used for laminating stretched films, the adhesive layer shrinks due to temperature and humidity changes, causing defects such as peeling and warping between films, and display unevenness especially in the periphery of the panel. There is. As a method for improving these, a method of reducing the number of retardation films (see Patent Document 2) is disclosed. However, these methods are effective for viewing angle characteristics during black display, but the problem is that the color reproducibility when viewed from an oblique direction during white display is deteriorated (colors with reduced color purity of the display color). Washout) has not been completely solved, and there has been a problem that the viewing angle has not been sufficiently expanded.

Japanese Patent Laid-Open No. 2002-221622 JP-A-11-95208 SID 97 DIGEST Pages 845-848

  An object of the present invention is to provide a liquid crystal display device in which a liquid crystal cell is accurately optically compensated and has a high contrast, particularly a VA mode liquid crystal display device. In particular, it is an object of the present invention to provide a VA mode liquid crystal display device and a liquid crystal cell in which the color reproducibility in an oblique direction at the time of white display is improved, the viewing angle contrast is improved, and the display unevenness in the periphery of the screen is reduced. To do.

Means for solving the problems of the present invention are as follows.
[1] A pair of oppositely disposed substrates having electrodes on at least one side, a liquid crystal cell having a liquid crystal material sandwiched between the pair of substrates, a first polarizing film disposed outside the liquid crystal cell, and A liquid crystal display device having at least one in-cell optical compensation film between the pair of substrates, wherein the in-cell optical compensation film has a plurality of average alignment directions in one pixel.
[2] The liquid crystal display device according to [1], further including a second polarizing film sandwiching the liquid crystal cell together with the first polarizing film.
[3] The liquid crystal display device according to [1] or [2], wherein the in-cell optical compensation film is made of a composition containing a liquid crystal compound.
[4] The liquid crystal display device according to any one of [1] to [3], wherein the in-cell optical compensation film is made of a composition containing a discotic compound.
[5] The liquid crystal display device according to any one of [1] to [4], wherein the molecular structure of the in-cell optical compensation film is hybrid-aligned with the substrate surface.
[6] At least one outer optical compensation film is disposed between the first or second polarizing film and the liquid crystal cell, and the sum of all retardation values of the intra-cell optical compensation film and the outer optical compensation film The liquid crystal display device according to any one of [1] to [5], wherein Re is 20 to 70 nm and a total retardation Rth value is 70 to 200 nm.
[7] The thickness of the liquid crystal layer is d (unit: nm), the refractive index anisotropy at wavelength λ (unit: nm) is Δn (λ), and the in-cell optical compensation film and the outer optical compensation film are When the in-plane average retardation total value at wavelength λ is Re (λ) and the average retardation value in the thickness direction at wavelength λ is Rth (λ), at least two different wavelengths between wavelengths 380 nm and 780 nm [1] to [7] satisfying the following formulas (V) to (VIII):
(V) 100 ≦ Δn (λ) × d ≦ 1000,
(VI) Rth (λ) / λ = E × Δn (λ) × d / λ,
(VII) Re (λ) / λ = F × λ / {Δn (λ) × d} + G,
(VIII) 0.726 ≦ E ≦ 0.958,
And 0.0207 ≦ F ≦ 0.0716,
And G = 0.032.
[8] The liquid crystal display device according to any one of [1] to [7], wherein the in-cell optical compensation film is formed from a plurality of regions having different retardation values in one pixel.
[9] The liquid crystal display device according to any one of [1] to [8], wherein the retardation value or average orientation direction of the in-cell optical compensation film changes discontinuously in the thickness direction within one pixel.
[10] The liquid crystal display device according to any one of [1] to [9], wherein a dye is contained in the intra-cell optical compensation film.
[11] A pair of oppositely disposed substrates having electrodes on at least one side, a liquid crystal material sandwiched between the pair of substrates, and at least one in-cell optical compensation film disposed between the pair of substrates. And the optical compensation film in the cell has a plurality of average alignment directions in one pixel.

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

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

  In this specification, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at the wavelength λ, respectively. In the present invention, Re (λ) is measured in KOBRA 21ADH (manufactured by Oji Scientific Instruments) by making light having a wavelength of λ nm incident in the normal direction of the film. Rth (λ) is 10 ° from −50 ° to + 50 ° with respect to the normal direction of the film, with Re (λ) being the in-plane slow axis (determined by KOBRA 21ADH) and the tilt axis (rotating axis). In step, light of wavelength λ nm is incident from each inclined direction and measured at 11 points, and KOBRA 21ADH calculates based on the measured retardation value, the assumed average refractive index, and the input film thickness value. 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 with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), 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. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

  According to the present invention, a multi-domain optical compensation film formed by appropriately selecting a material and a manufacturing method is disposed between substrates, thereby eliminating transmittance loss due to multiple reflections and improving luminance, that is, improving contrast ratio. can do. In addition, the retardation of the liquid crystal layer is optically controlled by a multi-domain optical compensation film in which the orientation direction in each domain is different in the in-plane and thickness directions, or the retardation value of each domain is different in the in-plane and thickness directions. Compensation can improve the color reproducibility during white display and the viewing angle dependency of luminance.

BEST MODE FOR CARRYING OUT THE INVENTION

The operation of the present invention will be described below with reference to the drawings.
[Liquid Crystal Display]
The liquid crystal display device shown in FIG. 1 includes liquid crystal cells 17 to 19, and an upper polarizing film 13 and a lower polarizing film 22 that are disposed with the liquid crystal cells 17 to 19 interposed therebetween. The polarizing films 13 and 22 are each sandwiched by a pair of transparent protective films. In FIG. 1, the transparent protective film disposed on the side close to the liquid crystal cell is disposed outside the substrate of the liquid crystal cell. The optical compensation layers 15 and 20 are also used. That is, the upper polarizing film 13 is sandwiched between the transparent protective film 11 and the outer optical compensation layer 15, and the lower polarizing film 22 is sandwiched between the transparent protective film 24 and the outer optical compensation layer 20. The liquid crystal cell includes a liquid crystal cell upper substrate 17, a liquid crystal cell lower substrate 19, and liquid crystal molecules 18 sandwiched between them, and the liquid crystal molecules 18 are formed by alignment films or rubbing applied to opposing surfaces of the substrates 17 and 19. The orientation direction is controlled by the processing direction. One pixel is divided into four, and the liquid crystal molecules 18 are tilted in four directions by voltage application. In-cell optical compensation layers 15 ′ and 20 ′ are arranged between the upper substrate 17 and the liquid crystal layer and between the liquid crystal layer and the lower substrate 19.

  The liquid crystal cell includes an upper substrate 17 and a lower substrate 19, a liquid crystal layer formed by liquid crystal molecules 18 sandwiched therebetween, and an in-cell optical compensation layer 15 formed on the inner surfaces of the upper substrate 17 and the lower substrate 19. 'And 20'. An alignment film (not shown) is formed on the surface of the substrates 17 and 19 in contact with the liquid crystal molecules 18 (hereinafter, also referred to as “inner surface”), and by a rubbing process or the like applied on the alignment film, The alignment of the liquid crystal molecules 18 in a state where no voltage is applied or a state where a voltage is not applied is controlled. Further, on the inner surfaces of the substrates 17 and 19, a transparent electrode (not shown) capable of applying a voltage to the liquid crystal layer made of the liquid crystal molecules 18 is formed.

The display mode of the liquid crystal layer is not particularly limited, and may be a liquid crystal layer in any display mode such as VA mode, IPS mode, ECB mode, TN mode, and OCB mode.
In the present invention, the product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn is preferably 0.1 to 1.0 μm, but the optimum value of Δn · d is displayed. It depends on the mode. In the transmission mode, the VA type, IPS type, and ECB type that do not have a twisted structure range from 0.2 to 0.4 μm, and the TN type ranges from 0.2 to 0.5 μm depending on the size of the twist angle. Further, in the OCB type, the optimum value is in the range of 0.6 to 1.0 μm. In these ranges, since the white display luminance is high and the black display luminance is small, a bright and high-contrast display device can be obtained.
In addition, although the aspect of the display apparatus of the transmission mode provided with the upper side polarizing plate and the lower side polarizing plate was shown in FIG. 1, this invention may be the aspect of the reflection mode provided with only one polarizing plate, In such a case, since the optical path in the liquid crystal cell is doubled, the optimum value of Δn · d is about the above half value. In a reflective liquid crystal display device, one polarizing plate is arranged on the upper side (observer side), an optical compensation film having a phase difference of λ / 4 is arranged, and display is performed by rotating polarized light (for example, Patent Gazette). JP-A-7-218906). The reason why display is performed with a single polarizing plate is to avoid attenuation of transmittance, but by arranging an optical compensation film between the substrates of the liquid crystal cell, the multiple reflection loss of transmitted light is reduced. Display using two plates is also possible. Furthermore, it is also possible to add a dye to an optical compensation film (intra-cell optical compensation film) disposed between the substrates to add a function as a polarizing film.

  Regarding the absorption axes 14 and 23 of the polarizing films 13 and 22, the slow axis directions 16 and 21 of the outer optical compensation layers (transparent protective films) 15 and 20, and the orientation direction of the liquid crystal molecules 18, It can be adjusted to an optimum range according to the display mode, the laminated structure of the members, and the like. For example, in an aspect of a liquid crystal display device belonging to the VA type or IPS type normally black type, in order to obtain high contrast, the absorption axes 14 and 23 of the polarizing films 13 and 22 are substantially orthogonal to each other. Arrange to be. However, the liquid crystal display device of the present invention is not limited to this configuration.

In the liquid crystal display device of FIG. 1, the thickness of the liquid crystal layer is d (unit: nm), the refractive index anisotropy at a wavelength λ (unit: nm) is Δn (λ), and the in-cell optical compensation film 15 ′ and In the case where 20 ′ and the outer optical compensation films 15 and 20 have an in-plane average retardation total value at a wavelength λ as Re (λ) and an average retardation total value in the thickness direction at a wavelength λ as Rth (λ), It is preferable that the following formulas (V) to (VIII) are satisfied at at least two different wavelengths between wavelengths of 380 nm and 780 nm.
(V) 100 ≦ Δn (λ) × d ≦ 1000,
(VI) Rth (λ) / λ = E × Δn (λ) × d / λ,
(VII) Re (λ) / λ = F × λ / {Δn (λ) × d} + G,
(VIII) 0.726 ≦ E ≦ 0.958,
And 0.0207 ≦ F ≦ 0.0716,
And G = 0.032.
When the member satisfies the above formulas (V) to (VIII), the contrast at the time of black display when observed from an oblique direction can be improved, and the coloring at the time of black display can be improved.

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

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

The operation of the liquid crystal display device shown in FIG. 1 will be described using the VA mode as an example. In this embodiment, an example in which active driving is performed using a nematic liquid crystal having positive dielectric anisotropy as a field effect liquid crystal will be described.
In the liquid crystal display device shown in FIG. 1, in a non-driving state in which a driving voltage is not applied to the transparent electrodes (not shown) of the liquid crystal cell substrates 17 and 19, the liquid crystal molecules 18 in the liquid crystal layer With the result that the polarization state of the light passing therethrough hardly changes. Since the absorption axes 14 and 23 are orthogonal to each other, the light incident from the lower side (for example, the back electrode) is polarized by the polarizing film 22, passes through the liquid crystal cell while maintaining the polarization state, and is blocked by the polarizing film 13. The That is, the liquid crystal display device of FIG. 1 realizes an ideal black display in the non-driven state. On the other hand, in a driving state in which a driving voltage is applied to a transparent electrode (not shown), the liquid crystal molecules 18 are tilted in a direction parallel to the surfaces of the substrates 17 and 19, and the light passing therethrough is polarized by the tilted liquid crystal molecules 18. Change state. Therefore, the light incident from the lower side (for example, the back electrode) is polarized by the polarizing film 22, further changes its polarization state by passing through the liquid crystal cell, and passes through the polarizing film 13. That is, in the liquid crystal display device shown in FIG. 1, white display is obtained in the driving state.

  Here, since an electric field is applied between the upper and lower substrates 17 and 19, a liquid crystal material having negative dielectric anisotropy is used so that the liquid crystal molecules 18 respond in a direction perpendicular to the electric field direction. Further, when an electrode is formed only on one of the substrates 17 and 19 and an electric field is applied in a lateral direction parallel to the substrate surface, a liquid crystal material having a positive dielectric anisotropy may be used. it can.

[Black display]
FIG. 2 is a schematic diagram showing a configuration of a general VA mode liquid crystal display device. The VA mode liquid crystal display device includes a liquid crystal layer 3 having a liquid crystal layer in which liquid crystal is vertically aligned with respect to a substrate surface when no voltage is applied, that is, black display, and the transmission axis of the liquid crystal layer 3. The polarizing plate 1 and the polarizing plate 2 are disposed so that the directions (shown by stripes in FIG. 2) are orthogonal to each other. In FIG. 2, light enters from the polarizing plate 1 side. When light traveling in the normal direction, that is, the z-axis direction is incident when no voltage is applied, the light passing through the polarizing plate 1 maintains the linear polarization state, and also passes through the liquid crystal layer 3 to Completely shaded. As a result, an image with high contrast can be displayed.

  However, as shown in FIG. 3, the situation is different in the case of incident light. When light is incident from an oblique direction that is not the z-axis direction, that is, an oblique direction with respect to the polarization direction of the polarizing plates 1 and 2 (so-called OFF AXIS), the incident light passes through the liquid crystal layer vertically aligned in the liquid crystal layer 3. When passing, the polarization state changes due to the influence of the oblique retardation. Furthermore, the apparent transmission axes of the polarizing plate 1 and the polarizing plate 2 deviate from the orthogonal arrangement. Due to these two factors, the incident light from the oblique direction in OFF AXIS is not completely shielded by the polarizing plate 2, and light leakage occurs during black display, resulting in a decrease in contrast.

  Here, polar angle and azimuth angle are defined. The polar angle is the normal direction of the film surface, that is, the inclination angle from the z-axis in FIGS. 2 and 3. For example, the normal direction of the film surface is the direction of polar angle = 0 degrees. The azimuth angle represents an azimuth rotated counterclockwise with respect to the positive direction of the x-axis. For example, the positive direction of the x-axis is the direction of the azimuth angle = 0 degrees, and the positive direction of the y-axis is Azimuth angle = 90 degrees. The oblique direction in the OFF AXIS described above mainly refers to the case where the polar angle is not 0 degree and the azimuth angle is 45, 135, 225, or 315 degrees.

FIG. 4 is a schematic diagram illustrating a configuration example for describing the operation of one embodiment of the present invention. In the liquid crystal display device shown in FIG. 4, the in-cell optical compensation films 4 and 5 (in FIG. 1) are formed on the inner surfaces of a pair of substrates (corresponding to the substrates 17 and 19 in FIG. 1) sandwiching the liquid crystal cell. In this case, the in-cell optical compensation films 15 'and 20' are arranged. In the liquid crystal display device of this embodiment, the refractive index anisotropy Δn at the liquid crystal layer thickness d (unit: nm, the same applies hereinafter) and the liquid crystal layer wavelength λ (unit: nm, the same applies hereinafter). (Λ), in-plane retardation Re (λ) of optical compensation films 4 and 5 at wavelength λ, and thickness direction retardation Rth (λ) at wavelength λ of at least two different wavelengths between 380 nm and 780 nm. It is preferable that the following formulas (I) to (IV) are satisfied at the wavelength.
(I) 200 ≦ Δn (λ) × d ≦ 1000,
(II) Rth (λ) / λ = A × Δn (λ) × d / λ + B,
(III) Re (λ) / λ = C × λ / {Δn (λ) × d} + D
(IV) 0.488 = <A = <0.56
And B = −0.0567
And -0.041 = <C = <0.016
And D = 0.0939

  In the embodiment shown in FIG. 4, a visible light can be obtained by combining a liquid crystal layer and an optical compensation film satisfying the above formulas (I) to (IV) (or the above formulas (V) to (VIII) in the embodiment shown in FIG. 1). Even when light of a predetermined wavelength in the region is incident in an oblique direction, optical compensation can be performed with a slow axis and retardation suitable for the wavelength. As a result, compared with the conventional liquid crystal display device, the visual contrast of the black display is remarkably improved, and the coloring in the viewing angle direction of the black display is further reduced. The liquid crystal display device of this embodiment satisfies the above formulas (I) to (IV) or the above formulas (V) to (VIII) at at least two different wavelengths. It is preferable that the two formulas (I) to (IV) or the formulas (V) to (VIII) are satisfied at two wavelengths having a difference of 50 nm or more. Which wavelength satisfies the above conditions depends on the application of the liquid crystal display device, and a wavelength and a wavelength range that most affect the display characteristics will be selected. In general, the liquid crystal display device has the above formulas (I) to (IV) or 650 nm, 550 nm, and 450 nm corresponding to the three primary colors red (R), green (G), and blue (B). It is preferable that the formulas (V) to (VIII) are satisfied. Note that the wavelengths of R, G, and B are not necessarily represented by the above wavelengths, but are considered to be wavelengths that are suitable for defining optical characteristics that exhibit the effects of the present invention.

In the prior art, the wavelength dispersion of the film for compensating for the VA mode is defined by Re, Rth, Re / Rth, or the like. In this aspect, the principle that the VA mode can be compensated for at the wavelength λ has been found by making the parameters dimensionless by paying attention to Re / λ and Rth / λ instead of values such as Re, Rth, and Re / Rth. Further, the present inventor also pays attention to the fact that there is chromatic dispersion in the birefringence Δnd of the liquid crystal layer to be compensated, and the chromatic dispersion of Re and Rth of the optical compensation film and the birefringence of the liquid crystal layer to be compensated. When the relationship between the refraction Δnd and the wavelength dispersion is intensively studied, and the above relations (I) to (IV) or the expressions (V) to (VIII) are satisfied, the viewing angle characteristics of the liquid crystal display device are remarkably improved. The knowledge that it is improved was obtained. The liquid crystal display device according to this aspect satisfies the above-mentioned relationships (I) to (IV) or the above formulas (V) to (VIII), so that light is incident from an oblique direction, and the liquid crystal layer has an oblique retardation. Even when there are two factors, that is, the apparent transmission axis of the pair of upper and lower polarizing plates is shifted, the liquid crystal layer is accurately optically compensated, and the reduction in contrast is reduced.
Further, as a method for adjusting Δnd, in addition to the above-described method for controlling the wavelength dependence of Δn of the liquid crystal material or the optical compensation film, a method for controlling the thickness d of the liquid crystal layer or the optical compensation film, both Δn and d A method of controlling is possible. In particular, regarding the thickness control, the thickness of the liquid crystal layer and the optical compensation film can be changed for each of the R, G, and B pixels to approximate the ideal wavelength dispersion characteristic of Δnd. It is also possible to change the thickness of the liquid crystal layer and the optical compensation film within one pixel. This correspondence is effective for the transflective display mode having both the reflection mode and the transmission mode.

  In the VA mode, since the liquid crystal is vertically aligned when no voltage is applied, that is, when black is displayed, the polarization state of light incident from the normal direction is not affected by the retardation of the optical compensation film during black display. In addition, the in-plane slow axis of the optical compensation film is preferably perpendicular or parallel to the polarization axis of the polarizing plate located closer.

  As described above, the present embodiment shows the relationship between the so-called birefringence Δnd / λ of the liquid crystal layer in the VA mode and the Re / λ and Rth / λ of the optical film for compensating the spectrum of the light source used. Optimized according to range or spectral distribution. The optimum range is theoretically considered, and the optimum range is clearly shown, which is different from the prior art relating to optical compensation in the VA mode. If the liquid crystal layer and the optical compensation film are combined so as to satisfy the above formulas (I) to (VI) or the above formulas (V) to (VIII), the wavelength dispersion of the liquid crystal layer is changed to the wavelength of the optical compensation film. It can be compensated by dispersion. As a result, the viewing angle contrast of the panel using the VA mode can be further reduced. In addition, since it is possible to suppress blackout in an arbitrary wavelength range, it is possible to further reduce the viewing angle color shift caused by the light passing through a specific wavelength.

  In this aspect, in order to express the optimal value of a film, it represents with the relational expression mentioned above, and the effect is confirmed in the Example. In the above formula, the range in which the effect is exhibited is defined by the parameters of A, B, C and D, or the parameters of E, F and G. However, for convenience, B and D or G are constants of values most suitable for expressing the effect range of the film, and by giving a range to A and C, or E and F, the range in which the effect of this aspect is achieved can be obtained. I decided to express it.

  In the above aspect, the present invention is applied to a VA mode liquid crystal panel exhibiting an arbitrary birefringence and wavelength dispersion, and a combination of a liquid crystal layer and one or more optical compensation films satisfying the above formula is used. Thus, the viewing angle contrast is improved and the viewing angle color shift is reduced. Furthermore, the present invention can also be applied to a display device including liquid crystal layers with different R, G, and B. For example, even when the present invention is applied to a projection-type liquid crystal layer in which R, G, and B are different liquid crystal layers, optical compensation can be performed using the conditional expression described above, and as a result, in a wide viewing angle. A high contrast can be obtained. In addition, when applied to a liquid crystal panel using a normal light source in which a large number of wavelengths are mixed, for example, the liquid crystal layer and the optical compensation film satisfy the above-described conditional expression by representing the characteristics of the liquid crystal panel using the G wavelength By using the combination, it is possible to obtain high contrast in a wide viewing angle.

  In this embodiment, the optical compensation film is not particularly limited and may have any configuration as long as it has optical compensation capability. In the present invention, at least one in-cell optical compensation film is provided between the substrates sandwiching the liquid crystal layer. One in-cell optical compensation film may be disposed on one of the upper and lower substrates. Further, as shown in FIG. 7B, which will be described later, an in-cell optical compensation film in which a region corresponding to one pixel is composed of a plurality of domains may be arranged on either the upper or lower substrate. One piece may be arranged on each of the upper and lower substrates, or two or more pieces may be arranged on one or both substrates. Further, as shown in FIG. 1, at least one outer optical compensation film may be disposed between the substrate and the polarizing film. Examples of the outer optical compensation film include a birefringent polymer film, a laminate of a transparent support and an optically anisotropic layer made of a liquid crystalline composition formed on the transparent support.

  The scope of the present invention is not limited by the display mode of the liquid crystal layer, and can be used for a liquid crystal display device having a liquid crystal layer of any display mode such as VA mode, IPS mode, ECB mode, TN mode, and OCB mode. .

[White display]
FIG. 5A shows a schematic cross-sectional view of a single domain VA mode liquid crystal cell. Since the liquid crystal molecules 18 are inclined at the time of white display, the birefringence of the liquid crystal molecules 18 when viewed from an oblique direction is different between the inclined direction 27 and the opposite direction 26, resulting in differences in luminance and color tone. On the other hand, FIG. 5B shows a schematic cross-sectional view of a structure called multi-domain in which one pixel of a liquid crystal display device is divided into two regions. Since liquid crystal molecules are tilted in the opposite direction, the average of one pixel is tilted. The angles are averaged, and the viewing angle characteristics of luminance and color tone are improved.

  In order to form a plurality of regions in which the alignment directions of the liquid crystal molecules 18 are different in one pixel, for example, a method of providing a slit in the electrode, providing a protrusion, changing the electric field direction, or imparting bias to the electric field density is used. Can be used. In order to obtain a uniform viewing angle in all directions, the number of divisions may be increased. However, a substantially uniform viewing angle can be obtained by using four or more divisions. In particular, it is preferable that the polarizing plate absorption axis can be set at an arbitrary angle when dividing into eight.

At the region boundary of each domain, the liquid crystal molecules 18 tend to hardly respond. In the normally black mode such as the VA mode, since black display is maintained, a decrease in luminance becomes a problem. Therefore, it is possible to reduce the boundary region between domains by adding a chiral agent to the liquid crystal material.
On the other hand, since the white display state is maintained in the normally white mode, the front contrast is lowered. Therefore, a light shielding layer such as a black matrix covering the region may be provided.

The VA mode liquid crystal cell is formed by, for example, nematic liquid crystal material having a negative dielectric anisotropy between upper and lower substrates 17 and 19 and having Δn = 0.0813 and Δε = −4.6 by rubbing alignment. A director indicating the orientation direction of molecules, that is, a so-called tilt angle of about 89 ° can be produced. The thickness d of the liquid crystal layer is not particularly limited, but can be set to about 3.5 μm when the liquid crystal having the characteristics in the above range is used. Since the brightness at the time of white display changes depending on the magnitude of the product Δn · d of the thickness d and the refractive index anisotropy Δn, Δn · d is 0.2 to 0.0 in order to obtain the maximum brightness. It is preferable to set it in the range of 5 μm.
In addition, in the VA mode liquid crystal display device, the addition of a chiral material generally used in the TN mode liquid crystal display device is rarely used to degrade the dynamic response characteristics, but in order to reduce alignment defects. May be added. As described above, the multi-domain structure is advantageous for adjusting the alignment of the liquid crystal molecules in the boundary region between the domains.

  In the above-described various liquid crystal display modes, the VA mode has been described in the so-called normally black mode in which black display is performed when no voltage is applied or low voltage is applied and white display is applied when a high voltage is applied. The invention is not limited to this, and may be an embodiment using the IPS mode, which is another normally black mode. Further, a mode using a normally white mode in which white display is performed when no voltage is applied or a low voltage is applied and black display is performed when a high voltage is applied, and an OCB mode, ECB mode, or TN mode liquid crystal cell is used. You can also. In addition, a liquid crystal cell in which the liquid crystal molecules of the nematic liquid crystal material are aligned substantially parallel to the surface of the substrate during black display can be used. Specifically, the liquid crystal molecules are parallel to the substrate surface when no voltage is applied. It is also possible to use an IPS mode or ECB mode liquid crystal cell that is aligned and displays black.

[Multi-domain optical compensation film]
In the present invention, at least one in-cell optical compensation film is disposed between a pair of substrates of a liquid crystal cell. The values of Re and Rth of the optical compensation film described below mean the average value of one pixel.
Here, the VA liquid crystal display device has improved the viewing angle characteristics during white display by the above-described alignment division, but the demand for higher image quality has increased as the display device has a larger screen. That is, when the VA mode liquid crystal display device is observed from an oblique direction during white display, there has been a problem that the color purity of the display color is lowered. In FIG. 5A, the cause is that the Re value of the liquid crystal layer decreases in the observation direction 27 and the observation direction 26 increases. In the direction in which Re increases, the transmittance increases and the color purity of the display color decreases. In the direction in which Re decreases, the transmittance greatly decreases. In the multi-domain of FIG. 5B, the alignment of the liquid crystal is averaged, but the average value is in the direction of increasing the Re value, and the transmittance is increased and the display color is thinned when observed from an oblique direction. In the present invention, by using an in-cell optical compensation film composed of a plurality of regions having different cell alignment directions, the liquid crystal layer is optically compensated for each region, and the viewing angle dependency of the image quality is reduced. A display device exhibiting excellent display characteristics is provided.

FIG. 6 is a schematic plan view showing the alignment direction of a VA liquid crystal cell in which one pixel is composed of multiple domains. In the figure, a gradient electric field is applied to the liquid crystal molecules by a slit electrode or the like, and the liquid crystal molecules are inclined in four directions for each of A, B, C, and D regions. In regions A and C, the observation direction 28 is the direction in which Re of the liquid crystal layer decreases, and the observation direction 29 is the direction in which Re increases. Therefore, by arranging an optically anisotropic layer that compensates for an increase in the Re value from the observation direction 29 in common with the regions A and C, the viewing angle dependency of the change in the Re value is improved.
For example, an optical compensation film (20 ′ in FIG. 1) in which discotic compounds are hybrid-aligned in regions A and C is disposed between a pair of substrates (17 and 19 in FIG. 1) that sandwich the liquid crystal layer. The alignment control direction of the regions corresponding to the regions A and C (for example, the rubbing direction for controlling the alignment of the discotic molecules) is parallel to the absorption axis 23 of the polarizing film 22, and the Re value of the liquid crystal layer in the observation direction 29 due to the hybrid alignment. To reduce the change in Re value from the front. Similarly, a compensation layer in which a discotic compound is hybrid-aligned in regions B and D in FIG. 6 is formed so that the hybrid direction differs from regions A and C by 180 °. Thereby, the amount of change from the front of the Re value in the observation direction 28 of the liquid crystal layers in the regions B and D is reduced, and the viewing angle characteristics of the display device are improved.
Another method is common to the regions A to D, and an optical compensation film is produced by orienting a discotic compound with the disc surface horizontally oriented on the substrate. On top of that, for example, optical compensation films containing rod-like liquid crystal compound molecules oriented in different directions in the regions A and C and the regions B and D can be arranged, respectively.

FIG. 7A shows a liquid crystal cell in which an in-cell optical compensation film having a plurality of regions in which the average orientation directions of the disk-like molecules 32 are different from each other is formed on the inner surface of the substrate 19 among the pair of substrates 17 and 19 of the liquid crystal cell. FIG. Further, as shown in FIG. 7B, the in-cell optical compensation film is disposed on both sides of the pair of substrates 17 and 19 of the liquid crystal cell, and is divided into a portion where the optical compensation film is disposed in one pixel and a portion where it is not disposed. Alternatively, the in-cell optical compensation films may be arranged so as not to overlap with each other on the upper and lower substrates. The method of forming the portion where the optical compensation film is disposed and the portion where the optical compensation film is not disposed in one pixel is effective for the transflective liquid crystal display device. In this display method, the thickness of the reflective part and the transmissive part is generally changed within one pixel, but the cell thickness of the reflective part is physically increased by arranging an optical compensation film inside the substrate in the reflective part. This is because the thickness can be reduced.
As described above, the in-cell optical compensation film used in the present invention has a so-called multi-domain structure having a plurality of regions having different average orientation directions. Here, when the multi-domain is defined for the in-cell optical compensation film, it means that the average orientation direction of each region of the optically anisotropic layer formed by being divided into regions in one pixel is different. The average orientation direction refers to the average direction of the molecular symmetry axes of the molecular groups constituting the in-cell optical compensation film. This is measured as an in-plane orientation axis direction by an automatic birefringence meter (KOBRA21DH, Oji Scientific Co., Ltd.). Even if the in-plane average orientation direction is the same, if the inclination angle of the average orientation direction with respect to the film surface is different (for example, when inclined by 45 ° with respect to the substrate surface normal and inclined by 30 °), it becomes a multi-domain. . The inclination angle of the average orientation direction with respect to the substrate surface is obtained by inclining the sample and measuring the retardation with an automatic birefringence meter (KOBRA21DH, Oji Scientific Co., Ltd.).

Here, the in-cell optical compensation film formed between the substrates 17 and 19 may be a discotic compound, a rod-shaped compound, a liquid crystalline material, a low molecular liquid crystal, or a polymer liquid crystal.
As a method of forming an optical compensation film in which a region corresponding to one pixel has a plurality of average alignment directions, alignment characteristics can be obtained by rubbing treatment performed after the alignment film is formed, photocuring with UV light, oblique irradiation of laser light, and the like. There is a method of changing. In the control method by rubbing, rubbing is performed by dividing one pixel into two or four regions using a mask, and a plurality of regions having different average orientation directions are obtained by changing the rubbing direction and the rubbing strength in each region. There is a method of forming. In the method of controlling by photocuring with UV light, after applying the coating solution for the optical compensation layer in the cell, light is irradiated from a polarized UV light or a light source capable of changing the irradiation intensity or angle of the UV light, and letter There is a method of making the foundation value and the orientation direction different for each region. In addition, in the control method by oblique irradiation of laser light, after applying the coating solution for the optical compensation layer in the cell, a laser beam is irradiated using a gas or a semiconductor laser as a light source, and the orientation direction is made different for each orientation region. Then, after applying the alignment film forming coating solution, a laser beam is applied to the coating layer to change the direction or size of the tilt angle of the alignment layer, and then the in-cell optical compensation film forming coating solution is applied. There is a way to cure. Further, by using a patterning mask when irradiating UV light and blocking the light, curing of the optical compensation film is suppressed, and an uncured portion is removed after UV irradiation, thereby forming a small region without retardation. It is also possible.

The Re and Rth values of the optical compensation layer are preferably 5 to 100 nm and Rth values of 50 to 300 nm in the VA, TN, and OCB modes. A stretched polymer film may be disposed, the polarizing film protective film may be provided with retardation, or a coating type compensation film may be formed on the protective film. That is, it is preferable that the total value of Re in the optical compensation layer of the entire liquid crystal display device is 20 to 70 nm and the total value of Rth is 70 to 200 nm. Further, when the above display mode is adopted for a transmissive IPS mode or a reflective display device, the Re value may be set to 100 to 300 nm and the Rth value may be set to −150 to 150 nm.
When the in-cell optical compensation film is disposed on the liquid crystal layer side of the substrate, it also functions as an alignment film, an electrode insulating film, a polarizing film, and a brightness enhancement film for the liquid crystal layer. Further, a transparent electrode, an electrode separation film, and an alignment film may be disposed between the in-cell optical compensation film and the liquid crystal layer.

In the present invention, at least one optical compensation film (in this specification, the optical compensation film disposed on the inner side of the liquid crystal cell substrate is referred to as “in-cell optical compensation film”) is disposed between a pair of substrates of the liquid crystal cell. To do. The in-cell optical compensation film only needs to be disposed between the pair of substrates. For example, the in-cell optical compensation film may be formed on one inner surface of the pair of substrates, or may be formed on both inner surfaces.
In the intra-cell optical compensation film, a region corresponding to one pixel of the liquid crystal cell is composed of a plurality of regions having different average orientation directions of molecules in the film. However, as shown in FIG. 7B, regions having different average orientation directions of molecules do not need to be on the same plane. The intra-cell optical compensation film preferably has at least one optically anisotropic layer formed from a composition containing a liquid crystal compound. Hereinafter, the in-cell optical compensation film having at least one optically anisotropic layer formed from a composition containing a liquid crystal compound will be described in detail.
<< Alignment film for optical compensation film >>
In the intra-cell optically anisotropic layer, the molecules of the liquid crystal compound are orientation-controlled and fixed in that state. Examples of the alignment method for controlling the alignment of the molecules of the liquid crystalline compound include a rubbing method for an alignment film formed between the optically anisotropic layer and the substrate. However, in the present invention, the alignment method is not limited to the rubbing method, and any alignment method may be used as long as the alignment of the liquid crystalline compound can be controlled similarly to the rubbing method. Also, by mask rubbing or the like, the in-cell optical compensation film can be multi-domained by changing the rubbing direction and rubbing intensity in one pixel of the liquid crystal display device.

  The alignment film has a function of defining the alignment direction of the liquid crystalline compound. Therefore, the alignment film is indispensable for realizing a preferred embodiment of the present invention. However, if the alignment state is fixed after aligning the liquid crystalline compound, the alignment film plays the role, and thus is not necessarily an essential component of the present invention. That is, it is possible to transfer only the optically anisotropic layer on the alignment film in which the alignment state is fixed to the substrate sandwiching the liquid crystal layer.

  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 cross-linking 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 in 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 Substituted hydrocarbon groups, thioether groups, polymerizable groups (unsaturated polymerizable groups, epoxy groups, azirinidyl groups, etc.), alkoxysilyl groups (trialkoxy, dialkoxy, monoalkoxy) and the like can be mentioned. 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 sheet 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-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 carried out at any 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 orientation 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. The 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 a sufficient crosslink, 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 also preferably set to an optimum value for the crosslinking agent to be used. When glutaraldehyde is used, the pH is 4.5 to 5.5, and 5 is particularly preferable.

  The alignment film is provided on the transparent support or the undercoat layer. The alignment film can be obtained 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.

Next, the alignment film functions to align the liquid crystalline molecules of the optically anisotropic layer provided on the alignment film. Thereafter, as necessary, the alignment film polymer and the polyfunctional monomer contained in the optically anisotropic layer are reacted, or the alignment film polymer is crosslinked using a crosslinking agent.
The thickness of the alignment film is preferably in the range of 0.1 to 10 μm.

<< Optically anisotropic layer >>
Next, details of preferred embodiments of the optically anisotropic layer made of a liquid crystalline compound will be described. The optically anisotropic layer contains a liquid crystal compound in which the orientation is controlled by an orientation axis such as a rubbing axis and the orientation is fixed.

  Examples of liquid crystalline molecules used for the optically anisotropic layer include rod-like liquid crystalline molecules and discotic liquid crystalline molecules. The rod-like liquid crystal molecules and the disk-like liquid crystal molecules may be high-molecular liquid crystals or low-molecular liquid crystals, and further include those in which low-molecular liquid crystals are cross-linked and no longer exhibit liquid crystallinity. The alignment state defined by the angle between the rod-like liquid crystal molecules and the disk-like liquid crystal molecules and the substrate surface may be any of horizontal (homogeneous) alignment, vertical alignment, and uniform tilt alignment, but optical anisotropy. When a rod-like liquid crystalline compound is used for the production of the layer, the rod-like liquid crystalline molecules preferably have an average direction of the axis projected on the support surface parallel to the alignment axis. Further, when a discotic liquid crystalline compound is used for the production of the optically anisotropic layer, the average direction of the axis of the discotic liquid crystalline molecule projected on the support surface is parallel to the alignment axis. Is preferred. In addition, the hybrid orientation described later and the uniformly tilted orientation in which the angle (tilt angle) formed by the liquid crystal molecules and the support plane changes in the depth direction are preferable.

《Bar-shaped liquid crystalline molecules》
As rod-like liquid crystalline molecules, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.
The rod-like liquid crystalline molecule includes a metal complex. In addition, a liquid crystal polymer containing a rod-like liquid crystalline molecule in a repeating unit can also be used as the rod-like liquid crystalline molecule. In other words, the rod-like liquid crystal molecule may be bonded to a (liquid crystal) polymer.
For rod-like liquid crystalline molecules, see Chapter 4, Chapter 7 and Chapter 11 of the Chemical Chemistry of the Quarterly Chemical Review Vol. 22, Liquid Crystal Chemistry (1994), and the 142nd Committee of the Japan Society for the Promotion of Science. Described in Chapter 3. The birefringence of the rod-like liquid crystal molecule is preferably in the range of 0.001 to 0.7.

  The rod-like liquid crystalline molecule preferably has a polymerizable group in order to fix its alignment state. The polymerizable group is preferably a radically polymerizable unsaturated group or a cationically polymerizable group. Specifically, for example, the polymerizable groups described in paragraphs [0064] to [0086] of JP-A-2002-62427 are described. Group and a polymerizable liquid crystal compound.

《Disk-like liquid crystalline molecule》
For discotic liquid crystal molecules, 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.

  As a discotic liquid crystalline molecule, a compound having liquid crystallinity having a structure 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. In the optically anisotropic layer formed from the discotic liquid crystalline molecules, the compound finally contained in the optically anisotropic layer does not need to be a discotic liquid crystalline molecule. Also included are compounds having a group that reacts with heat or light and, as a result, polymerized or cross-linked by reaction with heat or light, resulting in a high molecular weight and loss of liquid crystallinity. Preferred examples of the discotic liquid crystalline molecules are described in JP-A-8-50206. The polymerization of discotic liquid crystalline molecules is described in JP-A-8-27284.

  In order to fix the discotic liquid crystalline molecules by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline molecules. A compound in which the discotic core and the polymerizable group are bonded via a linking group is preferable, whereby the orientation state can be maintained even in the polymerization reaction. Examples thereof include compounds described in paragraphs [0151] to “0168” in JP-A No. 2000-155216.

  In the hybrid alignment, the angle between the disc plane of the liquid crystalline molecule or the molecular symmetry axis of the rod-like liquid crystalline molecule and the layer plane is the distance from the surface of the substrate (or alignment film) in the depth direction of the optically anisotropic layer. Increasing or decreasing with increasing. The angle preferably increases with increasing distance. Further, the change in angle can be a continuous increase, a continuous decrease, an intermittent increase, an intermittent decrease, a change including a continuous increase and a continuous decrease, or an intermittent change including an increase and a decrease. The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. Even if the angle includes a region where the angle does not change, the angle only needs to increase or decrease as a whole. Furthermore, it is preferable that the angle changes continuously. Of course, the orientation may be uniformly and uniformly inclined.

<< Other additives in optically anisotropic layer >>
Along with the liquid crystal molecules, a plasticizer, a surfactant, a polymerizable monomer, etc. can be used in combination to improve the uniformity of the coating film, the strength of the film, the orientation of the liquid crystal molecules, and the like. It is preferable that the liquid crystal molecules have compatibility with the liquid crystal molecules and can change the tilt angle of the liquid crystal molecules or do not inhibit the alignment.

  Examples of the polymerizable monomer include radically polymerizable or cationically polymerizable compounds. Preferably, it is a polyfunctional radically polymerizable monomer and is preferably copolymerizable with the above-described polymerizable group-containing liquid crystal compound. Examples thereof include those described in paragraph numbers [0018] to [0020] in JP-A No. 2002-296423. The amount of the compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the liquid crystal 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 liquid crystalline compound is preferably capable of changing the tilt angle of the molecules of the discotic liquid crystalline 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, and in the range of 0.1 to 8% by mass with respect to the liquid crystal compound so as not to disturb the alignment of the liquid crystal molecules. It is more preferable.
The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline molecules is preferably 70 to 300 ° C, more preferably 70 to 170 ° C.

<< Formation of optically anisotropic layer >>
The optically anisotropic layer can be formed by applying a coating liquid containing liquid crystalline molecules and, if necessary, a polymerization initiator described later and optional components on 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).

  The thickness of the optically anisotropic layer is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and still more preferably 0.7 to 10 μm.

<Fixing the alignment state of liquid crystalline molecules>
The aligned liquid crystal molecules 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.

It is preferable to use ultraviolet rays for light irradiation for polymerization of liquid crystalline molecules. 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.

<Method of orientation division>
A mask rubbing method can be used for disposing the optically anisotropic layer between the substrates of the liquid crystal layer and dividing the liquid crystal display device into a plurality of regions within one pixel of the liquid crystal display device. After the alignment film is applied, half of one pixel is covered with a metal mask such as stainless steel or chromium, and a rubbing process is performed. Next, the mask is slid to cover the portion where rubbing has been performed. Next, rubbing is performed in the reverse direction. This makes it possible to control the orientation in different directions by dividing one pixel into two. By changing the area of the mask covering one pixel, it is possible to divide into four or eight.
Furthermore, an optically anisotropic layer having a plurality of alignment regions per pixel can be produced by forming and solidifying an optically anisotropic layer by the process described above. Of course, in addition to the alignment control by rubbing, the alignment direction may be controlled by the various methods described above, and the region corresponding to one pixel may be divided into a plurality of regions having different average alignment directions.

  In the liquid crystal display device of the present invention, in addition to disposing the in-cell optical compensation film, the above optical anisotropic layer may be formed on a support made of a polymer film to form an outer optical compensation film. An optically anisotropic layer may be provided on another support to form an outer optical compensation film. These outer optical compensation films may function as a protective film for the deflection film.

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

[Optical compensation film arranged outside liquid crystal cell]
In the present invention, in addition to the in-cell optical compensation film, an optical compensation film may be disposed outside the liquid crystal cell (hereinafter, the optical compensation film disposed outside the liquid crystal cell is referred to as an “outside optical compensation film”). There is). The optical compensation film contributes to an increase in the viewing angle contrast of a liquid crystal display device, particularly a VA mode liquid crystal display device, and a reduction in color shift depending on the viewing angle. In the present invention, the outer optical compensation film may be disposed between the observer-side polarizing plate and the liquid crystal cell, or may be disposed between the rear-side polarizing plate and the liquid crystal cell. You may arrange. For example, the polarizing plate can be incorporated into the liquid crystal display device as an independent member, or can be made to function as an optical compensation film by imparting the optical characteristics to a protective film (support) that protects the polarizing film. As one member, it can also be incorporated in the liquid crystal display device.

  In the present invention, the material of the outer optical compensation film is not particularly limited. For example, it may be a stretched birefringent polymer film or an optically anisotropic layer formed by fixing a liquid crystalline compound in a specific orientation. The optical compensation film is not limited to a single layer structure, and may have a laminated structure in which a plurality of layers are laminated. In the aspect of the laminated structure, the material of each layer may not be the same, and may be a laminated body of a polymer film and an optically anisotropic layer made of a liquid crystalline compound, for example. In the aspect of the laminated structure, in consideration of the thickness, a coating type laminated body including a layer formed by coating is preferable to a laminated body of stretched polymer films.

  When a liquid crystal compound is used for the production of the outer optical compensation film, since the liquid crystal compound has various alignment forms, the optical anisotropic layer prepared by fixing the liquid crystal compound in a specific alignment state is The desired optical properties are expressed by a single layer or a laminate of a plurality of layers. That is, the optical compensation film may be an embodiment comprising a support and one or more optically anisotropic layers formed on the support. The retardation of the entire optical compensation film of this aspect can be adjusted by the optical anisotropy of the optical anisotropic layer. Liquid crystal compounds can be classified into rod-like liquid crystal compounds and discotic liquid crystal compounds based on their molecular shapes. Furthermore, there are low molecular weight and high molecular weight types, respectively, and both can be used. When a liquid crystal compound is used for producing the optical compensation film, it is preferable to use a rod-like liquid crystal compound or a discotic liquid crystal compound, and a rod-like liquid crystal compound having a polymerizable group or a discotic liquid crystal compound having a polymerizable group Is more preferable.

  The optical compensation film may be made of a polymer film. The polymer film may be a stretched polymer film or a combination of a coating-type polymer layer and a polymer film. As a material for the polymer film, a synthetic polymer (eg, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, norbornene resin, triacetylcellulose) is generally used. In addition, a cellulose acylate film using a composition in which a rod-like compound having an aromatic ring (specifically, an aromatic compound having two aromatic rings) is added to cellulose acylate is also preferable. A polymer film having desired optical properties can be produced by adjusting the type of aromatic compound, the amount added, and the stretching conditions of the film.

<Support>
The outer optical compensation film may also serve as a polarizing film protective film (support). Moreover, you may arrange | position a film as a support body other than a protective film. The support may be disposed anywhere as long as it is between the polarizing film and the liquid crystal layer. The support is preferably glass or a transparent polymer film. The support preferably has a light transmittance of 80% or more. When glass is used as the support, it may also serve as a substrate for sandwiching the liquid crystal layer.

Examples of the polymer constituting the polymer film include cellulose esters (eg, cellulose mono- to triacylate), 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, conventionally known polymers such as polycarbonate and polysulfone, which are likely to exhibit birefringence, have their birefringence controlled by modification of molecules as described in WO 00/26705. It is preferable to use one.

  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.

  As the polymer film, it is preferable to use cellulose acetate having an acetylation degree of 55.0 to 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 cellulose acetate, the hydroxyl groups at the 2-position, 3-position and 6-position of cellulose are not evenly substituted but the degree of substitution at the 6-position tends to be small. In the polymer film used in the present invention, it is preferable that the degree of substitution at the 6-position of cellulose is the same or greater than that at the 2- and 3-positions. 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 preferably it is. 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 JIII Journal of Technical Disclosure No. 2001-1745 (issued on March 15, 2001).

Although the preferred range of the polymer film retardation value varies depending on the liquid crystal layer in which the optical compensation sheet is used and the method of use thereof, the Re retardation value is preferably 0 to 200 nm, and the Rth retardation value is 70 to 400 nm. A range is preferred. When two optically anisotropic layers are used in the liquid crystal display device, the Rth retardation value of the polymer film is preferably in the range of 70 to 250 nm. When one optically anisotropic layer is used in the liquid crystal display device, the Rth retardation value of the substrate is preferably in the range of 150 to 400 nm.
In addition, it is preferable that the birefringence ((DELTA) n: nx-ny) of a base film exists in the range of 0.00028-0.020. The birefringence {(nx + ny) / 2−nz} in the thickness direction of the cellulose acetate film is preferably in the range of 0.001 to 0.04.

  In order to adjust the retardation of the polymer film, a method of applying an external force such as stretching is generally used, but a retardation increasing agent for adjusting the optical anisotropy is optionally added. In order to adjust the retardation of the cellulose acylate film, an aromatic compound having at least two aromatic rings is preferably used as a retardation increasing agent. The aromatic compound is preferably used in the range of 0.01 to 20 parts by mass with respect to 100 parts by mass of cellulose acylate. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring. Examples thereof include compounds described in European Patent Application Publication No. 91656, JP-A 2000-1111914, 2000-275434, and the like.

Further, the hygroscopic expansion coefficient of the cellulose acetate film used for the outer optical compensation film 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 length of the sample 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 sheet.
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 was calculated by the following equation. The measurement was performed 10 samples for the same sample, and the average value was 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. As the compound having a hydrophobic group, a material corresponding to a plasticizer or a degradation inhibitor having a hydrophobic group such as an aliphatic group or an aromatic group in the molecule is particularly preferably used. 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 volume. 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 described above to be added to the polymer film or additives that can be added in accordance with various purposes (for example, UV inhibitors, release agents, antistatic agents, deterioration inhibitors (eg, antioxidants, peroxide decomposers, The radical inhibitor, metal deactivator, acid scavenger, amine), 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 above-mentioned public technical number 2001-1745 are preferably used. The amount of these additives to be used is not particularly limited as long as the amount of each material exhibits its function, but it is preferably used in the range of 0.001 to 25% by mass in the entire polymer film composition.

<< Production Method of Polymer Film (Support) >>
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. The dope is cast on a drum or band and the solvent is evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state.

  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, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

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 above-mentioned public technical number 2001-1745, and includes dissolution, casting (including co-casting), metal support, drying, It is classified as peeling or stretching.
The thickness of the film (support) of the present invention is preferably 15 to 120 μm, more preferably 30 to 80 μm.

《Ellipse Polarizing Plate》
In the present invention, an elliptically polarizing plate in which the optically anisotropic layer is integrated with a linear polarizing film can be used. The elliptically polarizing plate is preferably molded into a shape substantially the same as that of the pair of substrates constituting the liquid crystal cell so that it can be incorporated into a liquid crystal display device as it is (for example, if the liquid crystal cell is rectangular, the elliptically polarizing plate). The plate is also preferably molded into the same rectangular shape).

  The elliptically polarizing plate can be produced by laminating an outer optical compensation film and a linearly polarizing film (hereinafter simply referred to as “linearly polarizing film” when referred to as “polarizing film”). The outer optical compensation film may also serve as a protective film for the linearly polarizing film. Of course, a dye may be added to the optical compensation layer between the substrates to form a linearly polarizing film.

  The linear polarizing film is manufactured by Optiva Inc. And a polarizing film comprising a binder and iodine or a dichroic dye is preferable. The iodine and the dichroic dye in the linearly polarizing film exhibit deflection performance by being oriented in the binder. It is preferable that the iodine and the dichroic dye are aligned along the binder molecule, or the dichroic dye is aligned in one direction by self-assembly such as liquid crystal. Currently, commercially available polarizers are made by immersing a stretched polymer in a solution of iodine or dichroic dye in a bath and allowing iodine or dichroic dye to penetrate into the binder. Is common.

  The commercially available polarizing film has iodine or dichroic dye distributed about 4 μm (about 8 μm on both sides) from the polymer surface, and a thickness of at least 10 μm is necessary to obtain sufficient polarization performance. The penetrability can be controlled by the solution concentration of iodine or dichroic dye, the temperature of the bath, and the immersion time. As described above, the lower limit of the binder thickness is preferably 10 μm. The upper limit of the thickness is preferably as thin as possible from the viewpoint of light leakage of the liquid crystal display device. It is preferably not more than a commercially available polarizing plate (about 30 μm), preferably 25 μm or less, and more preferably 20 μm or less. When the thickness is 20 μm or less, the light leakage phenomenon is not observed on a 17-inch liquid crystal display device.

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

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

  As the dichroic dye, an azo dye, stilbene dye, pyrazolone dye, triphenylmethane dye, quinoline dye, oxazine dye, thiazine dye or anthraquinone dye is used. The dichroic dye is preferably water-soluble. The dichroic dye preferably has a hydrophilic substituent (eg, sulfo, amino, hydroxyl). As an example of a dichroic dye, the compound as described in page 58 of the said technical number 2001-1745 is mentioned, for example.

  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 >>
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 can be stretched 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.

It is preferable to dispose a polymer film on the surface opposite to the optically anisotropic layer of the linearly polarizing film (arrangement of optically anisotropic layer / polarizing film / polymer film).
It is also preferable that the polymer film is provided with an antireflection film having an outermost surface having antifouling properties and scratch resistance. Any conventionally known antireflection film can be used.

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

[Example 1]
Two sets of test cells were made with a glass substrate with an electrode having a size of 30 × 40 mm, and optical characteristics were measured.
<Preparation of alignment film for optically anisotropic layer>
On a glass substrate, a coating solution having the following composition was applied at 28 mL / m ² with a # 16 wire bar coater. Drying was performed with warm air of 60 ° C. for 60 seconds, and further with warm air of 90 ° C. for 150 seconds. Next, the formed film was rubbed so as to be oriented in a direction parallel to the in-plane slow axis (the direction parallel to the casting direction) of the cellulose acetate film (that is, the rubbing axis is the slow axis of the cellulose acetate film). Parallel to the phase axis).
Alignment film coating solution composition Modified polyvinyl alcohol 20 parts by weight Water 360 parts by weight Methanol 120 parts by weight Glutaraldehyde (crosslinking agent) 1.0 part by weight

<Preparation of optically anisotropic layer>
On the alignment film, 91.0 g of the following discotic (liquid crystalline) compound, 9.0 g of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), cellulose acetate butyrate (CAB551-) 0.2, manufactured by Eastman Chemical Co., Ltd.) 2.0 g, cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co., Ltd.) 0.5 g, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Co., Ltd.) 3.0 g, Dissolve 1.0 g of sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) and 1.3 g of fluoroaliphatic group-containing copolymer (Megafac F780 Dainippon Ink Co., Ltd.) in 207 g of methyl ethyl ketone. The applied coating solution was applied with 6.2 ml / m ² with a # 3.6 wire bar. This was heated in a constant temperature zone of 130 ° C. for 2 minutes to orient the discotic compound. 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 compound. Then, it stood to cool to room temperature. In this way, an optically anisotropic layer was formed, and an in-cell optical compensation film (glass substrate with an optical compensation film) was produced.

<Production of liquid crystal cell>
The produced glass substrate with an optical compensation film was cut into 30 × 40 mm, immersed in a solution obtained by diluting a household neutral detergent with 50 cc of water, and allowed to dry naturally. Further, the separately cleaned glass substrate was cut into 30 × 40 mm, and an alignment film for liquid crystal material (“JALS-2021-R1”, manufactured by JSR) was applied to the substrate and subjected to rubbing treatment. The two substrates were assembled so that the compensation film and the rubbing surface were inside. That is, a cell having an in-cell optical compensation layer was prepared. The liquid crystal cell has a cell gap between substrates of 3.6 μm, and a liquid crystal material having negative dielectric anisotropy (“MLC6608”, manufactured by Merck & Co., Inc.) is dropped and sealed between the substrates. The layers were formed so as to be vertically aligned. The retardation of the liquid crystal layer (that is, the product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn) was set to 300 nm. In this way, a VA mode liquid crystal cell was produced. Further, a polarizing plate with a protective film of Re 2 and Rth 40 nm is disposed on the upper side of the liquid crystal cell, and a polarizing plate with a protective film of Re 10 and Rth 80 nm is disposed on the upper side. The total value of Re of the liquid crystal cell is 57 and the total value of Rth. Was set to 275 nm.

<Measurement of optical characteristics>
Two sets of the cells prepared above were used, and the hybrid direction of the discotic compound was reversed as shown in FIG. 7A, and a luminance meter (for example, BM-5 manufactured by TOPCON) was placed between the two cells. Then, measurement was performed in a measurement area having a diameter of 10 mm. The results are shown in Table 1. In both left and right directions, the color difference of white display at the front and 60 ° viewing angles was 0.05. Similar results were obtained with the arrangement of FIG.

[Comparative Example 1]
A liquid crystal cell in which the in-cell optical compensation film was not produced in Example 1 was prepared, and an optical compensation film made of a stretched film was disposed outside the substrate. That is, a cell having only the outer optical compensation film was prepared. The total value of Re was set to 57, the total value of Rth was set to 275 nm, and other configurations were the same as those in Example 1. Table 1 shows the results. The color difference during black display was 0.05, which was the same result as in Example 1. However, the color difference during white display was 0.1, and the display color is expected to be light.

[Comparison 2]
The same optical characteristics were measured using one liquid crystal cell produced in Example 1. Table 1 shows the results. The results were the same as in Example 1 except that the color difference in the right direction during white display was 0.1.

[Example 2]
Assuming a liquid crystal display device having a configuration similar to that shown in FIGS. 1 and 8, the upper polarizing plate (protective film 11, polarizing film 13, protective film 15 (also an outer optical compensation film)) from the observation direction (upper). , A liquid crystal cell (upper substrate 17, liquid crystal layer 18, lower substrate 19), a lower polarizing plate (a protective film (also an outer optical compensation film) 20, a polarizing film 22, a protective film 24) are stacked, and a backlight light source ( An optical simulation was performed on the liquid crystal display device having a configuration in which an unillustrated) was arranged, and the effect was confirmed. For the optical calculation, LCD Master Ver 6.08 manufactured by Shintech Co., Ltd. was used. For liquid crystal cells, electrodes, substrates, polarizing plates, etc., the values of materials conventionally used for liquid crystal displays were used as they were. A liquid crystal material having a negative dielectric anisotropy and Δε = −4.2 was used as the liquid crystal material. The alignment of the liquid crystal cell is approximately vertical with a pretilt angle of 89.9 degrees, the cell gap of the substrate is 3.6 microns, and the retardation of the liquid crystal (that is, the thickness d (micron) of the liquid crystal layer and the refractive index is anisotropic). The product Δn · d) with the property Δn was 318 nm at a wavelength of 450 nm, 300 nm at a wavelength of 550 nm, and 295 nm at a wavelength of 650 nm. Between the substrate 19 and the liquid crystal layer 18, an optical compensation film in which a discotic compound is hybrid-aligned is disposed. Using the extended function of LCD Master, the calculation was performed in a multi-domain divided into two. The average Re and Rth values of the optical compensation film were set to the values shown in Table 2, respectively. The C light source attached to the LCD Master was used as the light source. The substrates 17 and 19 are omitted in the simulation. Therefore, the arrangement position of the optical compensation layer is not specified as long as it is between the polarizing film and the liquid crystal layer.
In the liquid crystal display device having the configuration shown in FIG. 1, the same result can be obtained even when the relationship between the backlight and the observer is changed up and down.

  Using the parameters of Example 1, sample no. An optical simulation was conducted as 1. On the other hand, the simulation considering the chromatic dispersion characteristic is sample No. 2-No. 6 was performed.

From the results shown in Table 2, when Δnd / λ = 0.707 of the liquid crystal at a wavelength of 450 nm, Re / λ of the optical compensation film is 0.056 to 0.113, and Rth / λ is 0.291 to 0. 329, and when Δnd / λ = 0.454 of the liquid crystal at a wavelength of 650 nm, Re / λ of the optical compensation film is 0.089 to 0.129, and Rth / λ is 0.165 to 0.189. A liquid crystal display device No. 2-No. 6 is a liquid crystal display device No. 6; From the result of 1, it can be seen that the transmittance during black display at a polar angle of 60 ° is smaller. From the results in Table 2, Re / λ = 0.073, Rth / λ = 0.3111 at a wavelength of 450 nm, Re / λ = 0.095 at a wavelength of 550 nm, Rth / λ = 0.233, and Re / λ at a wavelength of 650 nm. = 0.108, Rth / λ = 0.177 It can be understood that the transmittance is minimized.
From the simulation results shown in Table 2, a liquid crystal display device No. 1 satisfying the above formulas (I) to (IV) was obtained. Nos. 2 to 6 are liquid crystal display devices No. It can be seen that the transmittance during black display at a polar angle of 60 ° is smaller than 1. That is, this means that No. 2 to No. 6 improve the contrast viewing angle compared to No. 1.

[Example 3]
In the production of the liquid crystal cell of Example 1, a rod-like liquid crystal is used to form an optically anisotropic layer on a glass substrate, the orientation direction is parallel to the substrate surface, and the orientation direction is 45 ° with the absorption axis 14 of the upper polarizing film 13. It was formed to make. The thickness was set to 1.8 μm, and Re was set to 140 nm at a wavelength of 550 nm. Rth was 70 nm. The half area of the substrate was shielded from light and photopolymerized by UV irradiation, and after irradiation, the unpolymerized compensation film was washed away with isopropyl alcohol.
On the lower side of the liquid crystal cell, a white aluminum reflecting film is formed on the portion where the optical compensation film is formed, and when removed, the polarizing plate is arranged so that the absorption axis is parallel to the upper polarizing plate.
As a result of visual observation of the optical characteristics when no voltage was applied, the optical compensation film forming portion was slightly purpleish black, and the removal portion was transmitted with backlight light, resulting in white display.
Further, a compensation film made of polycarbonate and having a Re of 280 nm at a wavelength of 550 nm was placed between the following plate of the removal part and the lower polarizing plate at a crossing angle of 45 ° with the polarizing plate absorption axis. At this time, black display was made in any part by visual observation. Further, when a voltage of 5 V was applied, both were white display.

[Example 4]
In Example 3, the first optical anisotropic layer was formed on the lower glass substrate so that Re was 280 nm at a wavelength of 550 nm. Thereafter, in the same manner as in Example 3, a second optical anisotropic layer is formed on the first optical anisotropic layer so that the alignment direction is orthogonal to the first optical compensation film, and the inside of the cell An optical compensation film was formed. The total retardation value of the in-cell optical compensation film was 140 nm for the portion having the two-layer structure, and 280 nm for the portion having one layer by removal. Note that no optical compensation film was disposed outside the substrate in the removal portion. Other configurations were the same as those in Example 3.
As a result of visual observation of the optical characteristics, an achromatic black color was obtained in the reflecting portion as compared with Example 3. Further, the white display transmittance of the transmissive portion of the removal portion was improved by 5% as compared with the case where the compensation film was disposed in the substrate.

[Example 5]
A liquid crystal display device was produced in the same manner as in Example 4 except that the first optically anisotropic layer was formed using a discotic compound. Specifically, the first optically anisotropic layer was formed such that the disk surface was aligned perpendicularly to the substrate surface and the alignment direction was orthogonal to the absorption axis of the upper polarizing plate. Furthermore, iodine was added to the coating solution for forming the first optically anisotropic layer, and the function of a polarizing plate was also added.
The cell gap was 3.6 μm. A white aluminum reflective film was disposed on the outside of the lower substrate in half of the area. Thereby, the reflection part and the transmission part could be formed with one cell.
In the visual observation of optical characteristics, the white display transmittance was improved by 5% compared to Example 4.

It is a schematic diagram explaining the structural example of the liquid crystal display device of this invention. It is a schematic diagram explaining the structural example of the liquid crystal display device of the conventional VA mode. It is a schematic diagram explaining the structural example of the liquid crystal display device of the conventional VA mode. It is a schematic diagram explaining the structural example of the one aspect | mode of the liquid crystal display device of this invention. It is a schematic cross-sectional schematic diagram explaining the structural example of the liquid crystal display device of this invention. FIG. 2 is a schematic plan view illustrating a configuration example of a liquid crystal display device of the present invention. 1 is a schematic cross-sectional view illustrating a configuration example of a liquid crystal display device of the present invention. It is a schematic diagram explaining the structural example of the conventional liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polarizing plate 2 Polarizing plate 3 Liquid crystal cell 4, 5, 6 Optical compensation film 13, 22 Polarizing film 14, 23 Absorption axis 11, 24 Protective film 12, 25 In-plane slow axis 15, 20 Outer optical compensation film (protective film) )
15 ', 20' In-cell optical compensation film 16, 21 In-plane slow axis 17, 19 Substrate 18 Liquid crystalline molecules 26, 27, 28, 29, 30 Observation direction 31 Measurement area 32 Discotic compound

Claims (11)

A pair of opposed substrates having electrodes on at least one, a liquid crystal cell having a liquid crystal material sandwiched between the pair of substrates, a first polarizing film disposed outside the liquid crystal cell, and the pair of substrates A liquid crystal display device having at least one in-cell optical compensation film between substrates, wherein the in-cell optical compensation film has a plurality of average alignment directions in one pixel. The liquid crystal display device according to claim 1, further comprising a second polarizing film sandwiching the liquid crystal cell together with the first polarizing film. The liquid crystal display device according to claim 1, wherein the intra-cell optical compensation film is made of a composition containing a liquid crystal compound. The liquid crystal display device according to claim 1, wherein the in-cell optical compensation film is made of a composition containing a discotic compound. The liquid crystal display device according to claim 1, wherein the molecular structure of the in-cell optical compensation film is hybrid-aligned with the substrate surface. At least one outer optical compensation film is disposed between the first or second polarizing film and the liquid crystal cell, and the total Re of all retardation values of the intra-cell optical compensation film and the outer optical compensation film is 20 The liquid crystal display device according to claim 1, which has a total retardation Rth value of 70 to 200 nm. The thickness of the liquid crystal layer is d (unit: nm), the refractive index anisotropy at wavelength λ (unit: nm) is Δn (λ), and the in-cell optical compensation film and the outer optical compensation film at wavelength λ. When the in-plane average retardation total value is Re (λ) and the average retardation total value in the thickness direction at wavelength λ is Rth (λ), at least two different wavelengths between 380 nm and 780 nm are described below. The liquid crystal display device according to any one of claims 1 to 7, which satisfies formulas (V) to (VIII):
(V) 100 ≦ Δn (λ) × d ≦ 1000,
(VI) Rth (λ) / λ = E × Δn (λ) × d / λ,
(VII) Re (λ) / λ = F × λ / {Δn (λ) × d} + G,
(VIII) 0.726 ≦ E ≦ 0.958,
And 0.0207 ≦ F ≦ 0.0716,
And G = 0.032. The liquid crystal display device according to claim 1, wherein the in-cell optical compensation film is formed from a plurality of regions having different retardation values in one pixel. The liquid crystal display device according to claim 1, wherein the retardation value or average orientation direction of the in-cell optical compensation film changes discontinuously in the thickness direction within one pixel. The liquid crystal display device according to claim 1, wherein a dye is contained in the intra-cell optical compensation film. A pair of opposed substrates having electrodes on at least one; a liquid crystal material sandwiched between the pair of substrates; and at least one in-cell optical compensation film disposed between the pair of substrates. The liquid crystal cell in which the optical compensation film in the cell has a plurality of average alignment directions in one pixel.

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