JP2007079424A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is improved in viewing angle characteristics, such as tone reversal, in a simple configuration and is suitable for animation image display as well. <P>SOLUTION: The liquid crystal display device has at least a liquid crystal cell composed of a pair of substrates 9 and 10, at least one of which has an electrode, and which are placed opposite to each other, and a liquid crystal layer 11 including a nematic liquid crystal material held between the substrates and aligned approximately parallel to the surfaces of the pair of substrates during the non-application of voltage, and a first polarizing film 3 and second polarizing film 18 placed to interpose the liquid crystal cell. The liquid crystal display device has an optical compensation film 7 (14) between at least one of the first polarizing film 3 and the second polarizing film 18, and the liquid crystal cell. The optical compensation film consists of a composition containing a disk-shaped compound. The molecules of the compound are fixed in the state of approximately perpendicularly aligning the disk face to the substrate faces and the liquid crystal cell has two or more alignment regions in one pixel. The liquid crystal display device is of black display during the non-application of the voltage or during the application of the low voltage. The average angles of inclination with the substrate faces of the nematic liquid crystal molecules, when applied with the high voltage, are different from each other in the alignment regions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a normally black liquid crystal display device having an optical compensation film, and more particularly to an ECB liquid crystal display device.

  A liquid crystal display device usually has a liquid crystal cell and a polarizing plate. The polarizing plate is usually composed of a protective film and a polarizing film, and is obtained by dyeing a polarizing film made of a polyvinyl alcohol film with iodine, stretching, and laminating protective films on both sides thereof. In a transmissive liquid crystal display device, this polarizing plate is usually attached to both sides of a 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 displays ON / OFF 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.

  The TN mode type liquid crystal display device is employed in a monitor panel for a notebook personal computer or a desktop personal computer. The optical compensation film for the TN mode liquid crystal display device performs optical compensation in the orientation state in which the liquid crystalline molecules are tilted to the substrate surface while the twisted structure is eliminated by applying a voltage, thereby preventing light leakage in an oblique direction during black display. The viewing angle characteristic of contrast is improved (see Patent Document 1). On the other hand, in recent years, large-screen liquid crystal televisions have been commercialized, and VA mode type liquid crystal display devices have been adopted. Further, a parallel alignment type ECB mode that can be manufactured by the same process as the manufacturing process of the TN mode liquid crystal display device and has a faster response than the VA mode has been developed for television use. (See Patent Document 2).

JP-A-6-214116 JP-A-2001-117099

However, in a TN mode or ECB mode liquid crystal cell, a gradation inversion phenomenon occurs in which the transmittance at each gradation is inverted when observed from an oblique direction. In the VA mode in which gradation inversion does not occur, the response speed is insufficient, and an afterimage phenomenon occurs when a moving image is displayed.
The present invention has been made in view of the above problems, and has a simple structure, a viewing angle characteristic such as gradation inversion remarkably improved, and a liquid crystal display device excellent in moving image display, particularly a twisted structure in a liquid crystal layer. It is an object of the present invention to provide a parallel alignment type liquid crystal display device that does not have, particularly an ECB type liquid crystal display device.

The object of the present invention has been achieved by the following means.
(1) From a liquid crystal layer including a pair of opposed substrates having at least one electrode and a nematic liquid crystal material sandwiched between the substrates and aligned substantially parallel to the surfaces of the pair of substrates when no voltage is applied A liquid crystal display device, and a liquid crystal display device having at least a first polarizing film and a second polarizing film disposed so as to sandwich the liquid crystal cell, wherein the first polarizing film and the second polarizing film An optical compensation film is provided between at least one and the liquid crystal cell, the optical compensation film is composed of a composition containing a discotic compound, and the molecules of the compound are aligned so as to be substantially perpendicular to the substrate surface. The liquid crystal cell has two or more alignment regions in one pixel, displays black when no voltage is applied or when a low voltage is applied, and the nematic liquid crystal material molecules with respect to the substrate surface when the high voltage is applied Mean inclination A liquid crystal display device characterized in that oblique angles differ from each other in the alignment region.
(2) At least one protective film is laminated on the polarizing film, and the optical compensation film is formed on the protective film. The slow axis of the protective film and the orientation direction of the discotic compound are approximately 45. The liquid crystal display device according to (1), which intersects at an angle.
(3) The liquid crystal display device according to (1) or (2), wherein the alignment direction of the discotic compound is substantially orthogonal to the alignment direction of the liquid crystal cell.
(4) The liquid crystal display according to any one of (1) to (3), wherein the optical compensation film is disposed between the liquid crystal cell and both the first and second polarizing films. apparatus.
(5) 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-plane retardation at the wavelength λ of the optical compensation film. Is Re (λ) and retardation in the thickness direction at wavelength λ is Rth (λ), the following formulas (I) to (II) are satisfied at at least two different wavelengths between 380 nm and 780 nm. The liquid crystal display device according to any one of (1) to (4):
(I) 50 ≦ Δn (λ) × d ≦ 400,
(II) −50 ≦ Re (λ) −Δn (λ) × d ≦ 50.
(6) The liquid crystal display device of (5) satisfying the above formulas (I) to (II) at all wavelengths of 450 nm, 550 nm and 650 nm.

In this specification, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at a wavelength λ, respectively. In the present invention, Re (λ) is a value measured using KOBRA 21ADH (manufactured by Oji Scientific Instruments) with light having a wavelength of λ nm incident in the normal direction of the film. Rth (λ) is a light having a wavelength of λ nm from the direction inclined by + 40 ° with respect to the normal direction of the film, with Re (λ) and the slow axis (determined by KOBRA 21ADH) as the tilt axis (rotation axis). And the retardation value measured by making light of wavelength λ nm incident from a direction inclined −40 ° with respect to the film normal direction with the slow axis as the tilt axis (rotation axis). A value calculated by KOBRA 21ADH based on the retardation values measured in three directions in total. Here, as the assumed value of the average refractive index, the values in the polymer handbook (JOHN WILEY & SONS, INC) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. Examples of the average refractive index values of main optical films are given below:
Cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), and polystyrene (1.59).
KOBRA 21ADH calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness.

  In this specification, “substantially 45 °”, “substantially parallel”, “substantially vertical” or “substantially orthogonal” means that the angle is within a range of strictly less than ± 5 °. The error from the exact angle is preferably less than 4 °, more preferably less than 3 °. Regarding the angle, “+” means the clockwise direction, and “−” means the counterclockwise direction. Further, the “slow axis” means a direction in which the refractive index is maximized. The “visible light region” means 380 nm to 780 nm.

  In the present specification, the “optical compensation film” is used as a term having the same meaning as the general meaning of the optically anisotropic layer or the optical compensation film. Further, in this specification, “polarizing film” and “polarizing plate” are distinguished from each other, and “polarizing plate” is a laminate having a protective film for protecting the polarizing film on at least one surface of the “polarizing film”. Shall mean.

  Conventionally, in an ECB mode liquid crystal cell made of a normally white nematic liquid crystal material aligned substantially parallel to the surface of the substrate when no voltage is applied, the liquid crystal molecules in the liquid crystal cell are uniformly vertically aligned when a voltage is applied. Instead, the liquid crystal molecules in the vicinity of the substrate interface were aligned in parallel, resulting in a residual phase difference. Conventionally, this residual phase difference of the liquid crystal cell is optically compensated by an optical compensation film having an optical axis substantially parallel to the film plane, so that a good black display is obtained when a voltage is applied, and the front contrast is improved. . However, the improvement of viewing angle characteristics such as contrast viewing angle and gradation inversion has not been sufficient. In the present invention, the refractive index anisotropy of the liquid crystal molecules of the liquid crystal layer is obtained by using an optical compensation film formed by fixing the disc-like molecules in a state in which the disc surface is oriented substantially perpendicular to the substrate surface. The wavelength dependences of these are roughly matched, and the normally black ECB mode liquid crystal display device has a high contrast. Further, even in a liquid crystal cell (for example, an ECB mode liquid crystal cell) in which liquid crystal molecules tend to be inclined with respect to the substrate normal line by applying a voltage, two or more (preferably 2) different alignment states of one pixel. Or, by adopting a multi-domain structure that is composed of four or more regions and averages, the occurrence of bias in luminance and color tone depending on the viewing angle is remarkably reduced. As a result, according to the present invention, a viewing angle characteristic such as gradation inversion is remarkably improved and a liquid crystal display device excellent in moving image display, in particular, a parallel alignment type ECB liquid crystal display device having no twisted structure in the liquid crystal layer. Can be provided.

  In the present invention, an elliptically polarizing plate in which the optical compensation film is integrally bonded can also be used. By using an elliptically polarizing plate having a function of optically compensating the liquid crystal cell, the above effect can be obtained. In addition to this, it is possible to provide a thinner liquid crystal display device with a simpler configuration. In addition, conventionally, when a liquid crystal display device was produced, a step of laminating while strictly adjusting the angle of one or a plurality of retardation films and a polarizing plate was required, but it was integrated with the optical compensation film. The elliptically polarizing plate can be manufactured by roll-to-roll, and the manufacturing process of the liquid crystal display device can be simplified.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.
The present invention relates to a normally black display liquid crystal display device in which black is displayed when no voltage is applied or a low voltage is applied, and the transmittance is increased and white is displayed when a high voltage is applied. A better black display is obtained when the Re value of the optical compensation film matches the retardation value of the liquid crystal layer in the black voltage application state. In particular, high contrast can be obtained by matching in the visible light range of 400 nm to 800 nm. With this configuration, a wide range of high contrast is obtained, and gradation inversion of halftone display does not occur. In the liquid crystal display device of the present invention, the crossing angle between the absorption axis of the polarizing film and the alignment treatment direction of the liquid crystal layer is preferably in the range of 40 to 50 °, more preferably 45 °. Further, the orientation control direction of the optical compensation film is preferably about 45 ° with respect to the absorption axis. Furthermore, it is needless to say that the crossing angle with the alignment treatment direction of the liquid crystal layer is preferably in the range of 70 to 110 ° and is not necessarily orthogonal.

The present invention uses an optical compensation film made of a composition containing a discotic compound and formed by fixing the compound molecules in a state in which the disc surface is oriented substantially perpendicular to the substrate surface. The optical compensation film can be formed on a support made of a polymer film, for example. The support may be one that optically does not affect the display characteristics of the liquid crystal display device, or may have characteristics that contribute to optical compensation, such as a stretched film. The optical compensation film is preferably formed by orienting the molecules of the discotic compound so that the disc surface is perpendicular to the film surface and fixing in that state. In the optical compensation film of this aspect, the optical axis is parallel to the film surface. Such an optical compensation film is a normally black display liquid crystal cell that displays black when no voltage is applied, and has two or more pixel regions, each of which is made of the nematic liquid crystal material. Two or more regions having different initial alignment states of molecules, or a liquid crystal cell having two or more regions in which the alignment direction of molecules of the nematic liquid crystal material continuously changes in a voltage applied state and the changes are different from each other. There is also an effect of reducing leakage light in the diagonal direction of black display.
In the liquid crystal display device of the present invention, in addition to such an optical compensation film, another optical compensation film, for example, an optically anisotropic layer formed from a rod-like liquid crystalline molecule or an optical compensation film made of a polymer film may be used. Alternatively, a combination thereof, that is, a laminate of these may be used.

  One embodiment of the liquid crystal display device of the present invention is an ECB type in which liquid crystal molecules are inclined with respect to a substrate normal line by applying a voltage. In such an embodiment, since the liquid crystalline molecules in the liquid crystal cell are tilted in one direction, the luminance and the color tone are biased depending on the viewing angle. However, in the present invention, one pixel has two or more different initial alignment states ( It is preferably reduced by constituting with 2 or 4 or more liquid crystal regions and averaging.

  Next, the configuration of one embodiment of the liquid crystal display device of the present invention will be described sequentially. FIG. 1 is a schematic view of an embodiment in which the present invention is applied to an ECB mode liquid crystal display device. In FIG. 1, the liquid crystal display device includes ECB mode liquid crystal cells 9 to 13 and a pair of polarizing plates, upper polarizing plates 1 to 6 and lower polarizing plates 16 to 21 disposed on both sides of the liquid crystal cell. An upper optical compensation film 7 and a lower optical compensation film 14 are disposed between the upper and lower polarizing plates and the liquid crystal cell.

The upper polarizing plate has an upper polarizing film 3 and a pair of protective films 1 and 5 that sandwich and protect the upper polarizing film 3, and the lower polarizing plate includes a lower polarizing film 18 and a lower polarizing film. And a pair of protective films 16 and 20 that sandwich and protect 18. The upper optical compensation film 7 and the lower optical compensation film 14 may be incorporated in a liquid crystal display device as a structure integrally laminated with the upper polarizing plate and the lower polarizing plate. For example, when the optical compensation films 7 and 14 are optical anisotropic layers formed from liquid crystal molecules, the lower protective film 5 of the upper polarizing plate is an optical anisotropic layer that is the upper optical compensation film 7. The upper protective film 16 of the lower polarizing plate may also serve as a support for the optically anisotropic layer that is the lower optical compensation film 14.
In the present invention, an optical compensation film in which discotic molecules are fixed between at least one of the upper and lower polarizing plates and the liquid crystal cell in a state in which the disc surface is oriented perpendicular to the substrate surface. The optical compensation film may not be disposed between both the polarizing plates and the liquid crystal cell as shown in FIG. Accordingly, it goes without saying that the configuration of the liquid crystal display device of the present invention is not limited to the configuration shown in FIG.

  In the liquid crystal display device of the present invention, as described above, an optical compensation film formed of a disk-like molecule is disposed on at least one of the upper and lower polarizing plates. Integrated polarization in which the support of the optical compensation film is also used as a protective film on one side of the polarizing film, and the protective film, the polarizing film, the protective film (also used as a transparent support) and the optical compensation film are laminated in this order. A plate can be used. The polarizing plate not only has a polarizing function, but also contributes to widening the viewing angle and reducing display unevenness. Furthermore, since the polarizing plate includes an optical compensation film having an optical compensation capability, the liquid crystal display device can be optically compensated accurately with a simple configuration. In the liquid crystal display device, the protective film, the polarizing film, the transparent support (protective film), and the optical compensation film are preferably laminated in this order from the outside of the device (the side far from the liquid crystal cell).

  Regarding the absorption axes 4 and 19 of the upper polarizing film 3 and the lower polarizing film 18, the alignment directions of the optical compensation films 7 and 14, and the alignment direction of the liquid crystalline molecules 11, The optimum range can be adjusted according to the laminated structure and the like. In order to obtain a high contrast, the absorption axis 4 of the upper polarizing film 3 and the absorption axis 19 of the lower polarizing film 18 are substantially orthogonal to each other, and each of the absorption axes 4 and 19 and the liquid crystal molecules 11 The orientation axes 10 and 13 preferably intersect at approximately 45 °. The alignment axes 10 and 13 of the liquid crystal molecules 11 are alignment axes for controlling the alignment of the liquid crystal molecules 11 included in the alignment films (not shown) formed on the inner surfaces of the upper substrate 9 and the lower substrate 12, for example. When the alignment film has a rubbing surface, it coincides with the rubbing axis.

The upper optical compensation film 7 and the lower optical compensation film 14 have optical axes 8 and 15 substantially parallel to the film surface. At least one of the upper optical compensation film 7 and the lower optical compensation film 14 may be formed from a composition containing a discotic compound. The discotic compound is preferably a liquid crystal compound. An optical compensation film having an optical axis substantially parallel to the film surface can be formed by fixing the disk-like molecules in a state in which the disk surface is oriented substantially perpendicular to the film plane. The optical axis is substantially orthogonal to the orientation control direction. The optical axes 8 and 15 of the upper optical compensation film 7 and the lower optical compensation film 14 are in a direction that contributes to the optical compensation of the liquid crystal cell. The optical axes 8 and 15 of the upper optical compensation film 7 and the lower optical compensation film 14 are preferably −20 to + 20 ° with respect to the alignment axes 10 and 13 of the liquid crystalline molecules 11, and −5 to + 5 °. It is more preferable that Further, it is preferable that the optical axes 8 and 15 of the upper optical compensation film 7 and the lower optical compensation film 14 and the slow axis of the protective film disposed at a position closer to the liquid crystal cell intersect at about 45 °. That is, the optical axis 8 of the upper optical compensation film 7 is preferably approximately 45 ° with the slow axis 6 of the protective film 5, and the optical axis 15 of the lower optical compensation film 14 is the slow axis of the protective film 16. 17 and approximately −45 ° are preferable. Further, it is preferable that the optical axes 8 and 15 of the upper optical compensation film 7 and the lower optical compensation film 14 intersect with the absorption axes of the polarizing films disposed closer to each other at ± 20 to 70 °, It is more preferable to cross at ± 35 to 55 °.
As described above, at least one of the upper optical compensation film and the lower optical compensation film may be the above optical compensation film made of a composition containing a discotic compound. There is no particular limitation on the material and configuration as long as it has compensation ability. Examples of the other optical compensation film include a birefringent polymer film and a laminate of a transparent support and an optically anisotropic layer made of liquid crystalline molecules formed on the transparent support. However, in the embodiment in which the upper and lower optical compensation films are arranged, it is preferable that both are optical compensation films formed from the composition containing the above-described discotic compound.

  Among the protective films of the polarizing film, the protective films 5 and 16 disposed on the liquid crystal cell side have optically refractive index anisotropy with respect to visible light (the preferable Re and Rth ranges of the protective film will be described later). The optical axis of the optical compensation film (average orientation direction of the molecular long axis) is arranged in parallel to the substrate surface and in a direction that cancels the phase difference of the liquid crystal layer. The viewing angle performance is further improved, the range of higher contrast is widened, and the area where gradation is inverted is greatly reduced.

  The upper substrate 9 and the lower substrate 12 of the liquid crystal cells (9 to 13) are respectively provided with an alignment film (not shown) having rubbing axes (alignment axes) 10 and 13 formed on the inner surface by rubbing treatment, and an electrode layer (Not shown). The rubbing directions 10 and 13 of the upper substrate 9 and the lower substrate 12 are set in parallel, and the liquid crystal layer is in a parallel alignment without a twist structure. The alignment film has a function of aligning the liquid crystalline molecules 11. The electrode layer has a function of applying a voltage to the liquid crystal molecules 11. The electrode layer is usually made of transparent indium tin oxide (ITO). In the parallel mode, a nematic liquid crystalline material having a positive dielectric anisotropy Δε is filled between the upper and lower substrates. When the thickness of the liquid crystal layer is d and the refractive index anisotropy of the nematic liquid crystalline material is Δn, the magnitude of the product Δn · d affects the brightness when displaying white. In order to obtain the maximum brightness, it is preferable to design the liquid crystal cell so that Δn · d is in the range of 0.2 to 0.4 μm. For example, when a liquid crystal having a refractive index anisotropy, Δn = 0.0854 (589 nm, 20 ° C.) and Δε = + 8.5 (for example, MLC-9100 manufactured by Merck) is used, the thickness of the liquid crystal layer The length d is preferably 3.5 μm.

Next, an operation mode of the liquid crystal display device of FIG. 1 will be described. In the figure, the upper side is the display surface and the lower side is the back surface. It is assumed that the light source is arranged on the back surface.
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 9 and 12, the liquid crystal molecules 11 in the liquid crystal layer are aligned substantially parallel to the surfaces of the substrates 9 and 12. As a result, the light passing therethrough changes its polarization state due to the birefringence effect of the liquid crystalline molecules 11 and passes through the polarizing film 1. At this time, the value of Δn · d of the liquid crystal layer is set within the above range so that the transmitted light is maximized. On the other hand, in a driving state in which a driving voltage is applied to a transparent electrode (not shown), the liquid crystalline molecules 11 tend to be aligned perpendicular to the surfaces of the substrates 9 and 12 depending on the magnitude of the applied voltage. However, near the center in the thickness direction between the substrates, the liquid crystal molecules 11 are substantially perpendicular to the substrate surface, but are aligned in a parallel direction near the substrate interface, and are continuously inclined and aligned toward the center thickness. . In such a state, it is difficult to obtain a complete black display.

  Therefore, in the present invention, in order to compensate for the residual phase difference of the liquid crystal layer in the vicinity of the substrate interface, the optical compensation film 7 or 14 whose optical axis is substantially parallel to the film plane is disposed, whereby light leakage during black display is achieved. Reduces the front contrast ratio. In addition, the average orientation of the tilted liquid crystal molecules in the vicinity of the substrate interface changes depending on the angle to be observed, and a viewing angle dependency occurs in which the transmittance and brightness change depending on the viewing angle. In addition, since the liquid crystal molecules 11 are tilted during halftone display, the magnitude of birefringence of the liquid crystal molecules 11 when viewed from an oblique direction is different between the tilt direction and the opposite direction, and there is a difference in luminance and color tone. Occurs. In the present invention, the change in transmittance depending on the viewing direction is reduced by averaging the viewing angle characteristics of luminance and color tone with a structure called multi-domain that divides one pixel into a plurality of regions. . As a result, the liquid crystal display device of the present invention has significantly improved viewing angle characteristics such as gradation inversion and has excellent display characteristics.

In the liquid crystal display device of the present invention, the thickness of the liquid crystal layer is d (unit: nm), the refractive index anisotropy at wavelength λ (unit: nm) is Δn (λ), and a discotic compound is contained. When the in-plane retardation at the wavelength λ of the optical compensation film formed from the composition is Re (λ) and the retardation in the thickness direction at the wavelength λ is Rth (λ), the wavelength is between 380 nm and 780 nm. If at least two different wavelengths satisfy the following formulas (I) to (II), it is preferable because visibility is further improved.
(I) 50 ≦ Δn (λ) × d ≦ 400,
(II) −50 ≦ Re (λ) −Δn (λ) × d ≦ 50
Furthermore, it is more preferable to satisfy the following formula (II) ′, and it is more preferable to satisfy the following formula (II) ″.
(II) ′ − 30 ≦ Re (λ) −Δn (λ) × d ≦ 30
(II) ”− 5 ≦ Re (λ) −Δn (λ) × d ≦ 5

  In a full-color liquid crystal display device, it is preferable that the formulas (I) to (II) are satisfied and the formulas (I) to (II) ′ are satisfied in all of the three primary wavelengths of 450 nm, 550 nm, and 650 nm. It is more preferable that the above formulas (I) to (II) "are satisfied.

  An optical system capable of compensating a continuously tilted liquid crystal layer described in JP-A-6-214116 (Patent Document 1) as one of the optical compensation films 7 and 14 or separately from these optical compensation films. It is preferable to dispose a film because the viewing angle characteristics are further improved.

  In the present invention, as described above, one pixel of a liquid crystal cell has a structure called multi-domain in which a pixel is divided into a plurality of regions, and the viewing angle characteristics of luminance and color tone are improved. Specifically, a liquid crystal cell usually has a plurality of pixel regions, and each pixel region is divided into two or more (preferably 4 or 8) regions in which the initial alignment state of liquid crystal molecules is different from each other when no voltage is applied. And averaging, it is possible to reduce the deviation of luminance and color tone depending on the viewing angle. Further, the same effect can be obtained even when each pixel region is composed of two or more regions in which the orientation direction of the liquid crystal molecules continuously changes in a voltage applied state and the change is different from each other. Furthermore, it is more preferable that one pixel consists of two or more regions having both characteristics.

FIG. 2 schematically shows an example of the alignment state of the liquid crystal molecules 11 in one pixel of the liquid crystal cell. 2A shows a voltage non-application state (OFF state), and FIG. 2B shows a voltage application state (ON state). Note that FIG. 2 is schematically shown for explanation, and details such as the shape of the liquid crystalline molecules, the number of molecules, the alignment state, and the like do not necessarily match those of an actual liquid crystal cell.
In the example shown in FIG. 2, the liquid crystal cell has two regions, a pixel region A and a pixel region B, in which the alignment direction of the liquid crystal molecules 11 is different in one pixel. In the pixel regions A and B, the direction and the size of the angle (pretilt angle) formed by the average alignment direction of the liquid crystal molecules 11 and the substrate surface are different. In the pixel region A, the tilt angle near the lower substrate 12 surface is 1 °, and 5 ° at the interface of the upper substrate 9. When a voltage is applied, the right end of the liquid crystalline molecules 11 rises in a direction perpendicular to the substrate surface due to the influence of orientation with a large tilt angle. On the other hand, in the pixel region B, the tilt angle in the vicinity of the lower substrate 12 surface is 5 °, and 1 ° at the interface of the upper substrate 9. When a voltage is applied, the left end of the liquid crystal molecules 11 rises in a direction perpendicular to the substrate surface, and is in an alignment state symmetrical to the pixel region A. By constituting one pixel from two different regions as described above, the orientation of liquid crystal molecules in one pixel is averaged, and a wide viewing angle is obtained. Note that the pretilt angle does not have to be 5 ° and 1 ° for the liquid crystal molecules to be in such an alignment state, but the pretilt angle is preferably 5 ° or less in any region.

<Multidomain production method>
The multi-domain is a structure having two or more regions in which the alignment state of liquid crystal molecules is different in one pixel when a voltage is applied. The method for forming the structure is not particularly limited, and various methods can be used. For example, a method of providing slits in the electrode, a method of changing the electric field direction by providing protrusions, a method of imparting bias to the electric field density, a method of selectively irradiating ultraviolet rays using a mask pattern after applying an alignment film, a mask rubbing, etc. Can be used. In order to obtain a uniform viewing angle in all directions, it is preferable to divide one pixel into a larger number of regions, but a substantially uniform viewing angle can be obtained by dividing into four or eight or more regions. In particular, it is preferable to divide into eight and form one pixel from eight regions because the polarizing plate absorption axis can be set to an arbitrary angle.

  At the boundary of each region, the liquid crystal molecules 11 tend to hardly respond. In the normally black mode, black display is maintained, and thus a decrease in luminance may be a problem. When a chiral agent is added to the liquid crystal material, the boundary region between domains can be reduced.

(Electrode slitting method)
FIG. 3 shows a schematic cross-sectional view of an embodiment of a liquid crystal cell having a multi-domain structure manufactured by using the electrode slit method. A transparent electrode 22, for example, ITO (indium phosphine oxide) is formed into a thin film on the upper and lower substrates by sputtering or the like. Next, a slit 22a having a width of 2 to 10 μm is formed by a photoresist, exposure, and etching process. The substrates are bonded so that the slits formed in the upper and lower substrates do not overlap.
An electric field for changing the orientation of the liquid crystal molecules is applied perpendicularly to the substrate surface, but the distribution of the electric field is biased by the slit 22a, and an oblique electric field component is generated on the substrate surface. By generating the oblique component electric field symmetrically within one pixel, the average tilt angle of liquid crystal molecules aligned in parallel (the average tilt angle of the liquid crystal molecules in the liquid crystal layer with respect to the substrate surface) is also symmetric. According to this method, the pretilt angle of the liquid crystal molecules (the angle formed between the substrate near the substrate interface and the liquid crystal molecules) can be reduced, which is advantageous for widening the viewing angle.

(Protrusion method)
FIG. 4 shows a schematic cross-sectional view of one embodiment of a liquid crystal cell having a multi-domain structure manufactured by using the protrusion method. For example, stripe-shaped protrusions 22b are formed on the transparent electrodes 22 of the upper and lower substrates, and the substrates are bonded so that the positions of the protrusions do not overlap with the upper and lower substrates. The pre-tilt angle of the parallel aligned liquid crystal molecules is determined along the slope of the protrusion, and a symmetric average tilt angle is generated with respect to the vertex of the protrusion. According to this method, the pretilt angle of the liquid crystal molecules is generated only by the protrusions, and the average pretilt angle can be reduced, which is advantageous for widening the viewing angle.

(UV irradiation method)
FIG. 2 shows a schematic cross-sectional view of one embodiment of a liquid crystal cell having a multi-domain structure manufactured by using a UV irradiation method. After forming an alignment film (not shown) on the upper and lower substrates, rubbing is performed in the anti-para direction on the upper and lower substrates. Next, it is covered with a metal mask such as stainless steel or chrome covering half of one substrate pixel and irradiated with ultraviolet rays. The pretilt tilt angle of the ultraviolet irradiation section is reduced. The same process is performed on the other substrate, and the upper and lower substrates are overlapped so that the irradiated portions do not overlap. After liquid crystal injection, the orientation of the liquid crystal layer is governed by the substrate interface having a large pretilt angle, and the orientation of the liquid crystal molecules is divided within one pixel as shown in FIG.

(Mask rubbing method)
FIG. 5 shows a schematic cross-sectional view of one embodiment of a liquid crystal cell having a multi-domain structure manufactured by using a mask rubbing method. After forming an alignment film (not shown) on the upper and lower substrates, half of the pixels are covered with a metal mask such as stainless steel or chromium, and the uncovered region is rubbed (the rubbing direction is indicated by 23 in FIG. 5). Next, the mask is slid to cover the region subjected to the rubbing process. Rub in the opposite 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 also possible to manufacture a liquid crystal cell having a multi-domain structure with four and eight divisions.

The display mode of the liquid crystal display device of the present invention is not particularly limited, but the ECB mode is preferable. 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 not particularly limited, but generally 0.2 to 1.2 μm. preferable. The optimum value of Δn · d varies depending on the display mode, and the optimum value of Δn · d of the liquid crystal is 0.2 to 0.5 μm in the ECB mode. In these ranges, since the white display luminance is high and the black display luminance is small, a bright and high-contrast display device can be obtained.
Note that these optimum values are values in the transmission mode, and in the reflection mode, the optical path in the liquid crystal cell is doubled, so the value of the optimum Δn · d is about the above half value.
The liquid crystal display device used in the present invention is effective not only in the display mode but also in an aspect applied to the IPS mode, OCB mode, VA mode, TN mode, HAN mode, and STN mode.

  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, an optical compensation 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 having a light emitting diode, a field emission element, or an electroluminescent element as a light source can be disposed on the back surface. In addition, the liquid crystal display device of the present invention may be of a reflective type. In such a case, only one polarizing plate may be disposed on the observation side, and reflected on the back surface of the liquid crystal cell or the inner surface of the lower substrate of the liquid crystal cell. Install the membrane. Of course, it is also possible to provide a front light using the light source on the liquid crystal cell observation side.

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

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]
In the present invention, at least one optical compensation film made of a composition containing a discotic compound is used. In the optical compensation film, the discotic molecules are fixed in a state of being oriented with the disc surface substantially perpendicular to the substrate surface. That is, the optical axis of the optical compensation film is substantially parallel to the film surface. The liquid crystal display device of the present invention may have two or more optical compensation films, and it is preferable that any of them is an optical compensation film whose optical axis is substantially parallel to the film surface. The optical compensation film is used in a liquid crystal display device to eliminate image coloring and expand a viewing angle. The in-plane retardation (Re) of the optical compensation film is preferably 0 to 200 nm. The retardation (Rth) in the thickness direction of the optical compensation film is preferably -50 to 500 nm.

  Other materials are not particularly limited as long as they are optical compensation films formed from a composition containing the discotic compound. When two or more optical compensation films are used, the material of the other optical compensation film is not particularly limited, and optical compensation films made of various materials can be used. For example, an optical compensation film made of a stretched birefringent polymer film, an optical compensation film made of an optically anisotropic layer formed from a low-molecular or high-molecular liquid crystalline compound, and a laminate thereof can be used. The optical compensation film may have a single layer structure or a laminated structure.

  In the present invention, the polymer film that can be used as the optical compensation film may be a stretched polymer film or a combination of a coating-type polymer layer and a polymer film. As a material for the polymer film, a synthetic polymer (eg, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, norbornene resin, triacetylcellulose) is generally used. At this time, the stretching direction of the polymer film and the direction of the optical axis of the discotic compound are substantially orthogonal to each other.

Next, an optical compensation film made of a composition containing a liquid crystal compound will be described in detail.
[Optical Compensation Film Consisting of Composition Containing Liquid Crystalline Compound]
Since liquid crystal compounds have various alignment forms, an optical compensation film made of a composition containing a liquid crystal compound exhibits desired optical properties by a single layer or a multilayered structure. The optical compensation film may be composed of only one layer or a laminate of two or more layers. The retardation of the entire optical compensation film of this aspect can be adjusted by the optical anisotropy of each layer. Liquid crystal compounds can be classified into rod-like liquid crystal compounds and discotic liquid crystal compounds based on their shapes. Furthermore, there are low molecular weight and high molecular weight types, respectively, and both can be used. The liquid crystalline compound used in the production of the optical compensation film that can be used in the present invention is preferably a rod-like liquid crystal compound or a discotic liquid crystalline compound, and a rod-like liquid crystal compound having a polymerizable group or a disc-like shape having a polymerizable group. More preferably, it is a liquid crystal compound.

(Bar-shaped liquid crystalline compound)
As rod-like liquid crystalline molecules, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.
The rod-like liquid crystalline molecule includes a metal complex. In addition, a liquid crystal polymer containing a rod-like liquid crystalline molecule in a repeating unit can also be used as the rod-like liquid crystalline molecule. In other words, the rod-like liquid crystal molecule may be bonded to a (liquid crystal) polymer.
For rod-like liquid crystalline molecules, see Chapter 4, Chapter 7 and Chapter 11 of the 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.

(Discotic liquid crystalline compounds)
In the present invention, at least one optical compensation film formed from a composition containing a discotic compound is used. The discotic compound is preferably a liquid crystal compound. The discotic liquid crystalline compound is preferably oriented substantially perpendicularly to the polymer film surface (average inclination angle in the range of 50 to 90 degrees). The discotic liquid crystalline compounds are disclosed in various documents (C. Destrade et al., Mol. Crysr. Liq. Cryst., Vol. 71, page 111 (1981); edited by The Chemical Society of Japan, Quarterly Chemical Review, No. 22, Liquid Crystal Chemistry, Chapter 5, Chapter 10 Section 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. Comm., Page 1794 (1985); J. Zhang et al., J Am.Chem.Soc., Vol.116, page 2655 (1994)). The polymerization of the discotic liquid crystalline compound is described in JP-A-8-27284.

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

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

(Alignment of liquid crystalline compounds)
These liquid crystalline compounds are preferably substantially uniformly oriented in the optical compensation film, more preferably fixed in a substantially uniformly oriented state, and liquid crystals are obtained by a polymerization reaction. Most preferably, the active compound is immobilized. In the case of a rod-like liquid crystal compound having a polymerizable group, it is preferably fixed in a substantially horizontal (homogeneous) orientation. Substantially horizontal means that the average angle (average tilt angle) between the major axis direction of the rod-like liquid crystal compound and the surface of the optical compensation film is in the range of 0 ° to 40 °. In the case of a discotic liquid crystalline compound having a polymerizable group, it is preferable to substantially align vertically. Substantially perpendicular means that the average angle (average tilt angle) between the disc surface of the discotic liquid crystalline compound and the surface of the optical compensation film is in the range of 50 ° to 90 °.

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

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

It is preferable that the usage-amount of a photoinitiator is 0.01-20 mass% of solid content of a coating liquid, and it is more preferable that it is 0.5-5 mass%. Light irradiation for the polymerization of the liquid crystalline compound is preferably performed using ultraviolet rays. The irradiation energy is preferably ^{20mJ / cm 2 ~50J / cm 2} , further preferably 100 to 800 mJ / cm ^2. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.
The thickness of the optical compensation film is preferably 0.1 to 10 μm, and more preferably 0.5 to 5 μm.

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

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

[Polarizer]
In the present invention, it is preferable to use a polarizing plate having an optical compensation capability obtained by bonding the optical compensation film. For example, an optical compensation film (when the optical compensation film is composed of a plurality of optically anisotropic layers, the optically anisotropic layer closest to the polarizing film) may be formed directly on the surface of the polarizing film, or An alignment film may be formed on the surface of the film and formed on the surface. Specifically, it is formed by applying a coating liquid for forming an optical compensation film as described above to the surface of the polarizing film. As a result, without using a polymer film between the polarizing film and the optical compensation film, it is possible to produce a thin polarizing plate having a small stress (strain × cross-sectional area × elastic modulus) associated with the dimensional change of the polarizing film. When the polarizing plate according to the present invention is attached to a large liquid crystal display device, an image with high display quality is displayed without causing problems such as light leakage. Further, as described above, the protective film on one surface of the polarizing film may also be used as a support for the optical compensation film.

(Polarizing film)
The polarizing film that can be used in the present invention is not particularly limited. It is preferable to use a coating type polarizing film and a polarizing film comprising a binder and iodine or a dichroic dye. The iodine and dichroic dye used for the production of the polarizing film exhibit a 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 polarizing performance. The penetrability can be controlled by the solution concentration of iodine or dichroic dye, the temperature of the bath, and the immersion time.
As described above, the lower limit of the binder thickness is preferably 10 μm. The upper limit of the thickness is preferably as thin as possible from the viewpoint of light leakage of the liquid crystal display device. It is preferably not more than a commercially available polarizing plate (about 30 μm), preferably 25 μm or less, and more preferably 20 μm or less. When the thickness is 20 μm or less, the light leakage phenomenon is not observed on a 17-inch liquid crystal display device.

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

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

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

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

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

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

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

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

In the present invention, it is preferable to use at least one of the pair of protective films sandwiching the polarizing film having a slow axis substantially coincident with the direction in which the average refractive index of the film surface is maximized. That is, at least one protective film has three average refractive indexes nx, ny and nz in the x, y and z axis directions orthogonal to each other, and the in-plane average refractive index is nx and ny, and the thickness direction average A film satisfying the relationship of nx, ny = nz, nx> ny where the refractive index is nz; preferably a film satisfying nx = ny, nz, nx> nz. The protective film may have optical characteristics that contribute to the optical compensation ability. In this embodiment, at an arbitrary wavelength λ in the visible light region, −5 nm ≦ {(nx−ny) × d ₁ } ≦ 50 nm and 50 nm ≦ [{(nx + ny) / 2−nz} × 2] ≦ 300 nm. Is preferably satisfied.

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

  When laminating the protective film and the polarizing film, at least one protective film (protective film disposed on the side close to the liquid crystal cell when incorporated in a liquid crystal display device), the slow axis (alignment axis), The protective film and the polarizing film are laminated so that the absorption axis (stretching axis) of the polarizing film is parallel or intersects. Specifically, the angle between the absorption axis of the polarizing film and the slow axis of the protective film is substantially parallel or orthogonal, but the angle of the slow axis of the other protective film and the absorption axis of the polarizing film is It is not specifically limited, It can set suitably according to the objective of a polarizing plate.

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

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

  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.

(Comparative Example 1)
A liquid crystal display device having the configuration shown in FIG. 1 (however, the lower optical compensation film 14 is not provided) was produced. That is, from the observation direction (top), the upper polarizing plates 1 to 6, the upper optical compensation film 7, the liquid crystal cell (upper substrate 9, liquid crystal molecules 11 included in the liquid crystal layer, lower substrate 12), lower polarizing plates 16 to 21. And a backlight (not shown) using a cold cathode fluorescent lamp was disposed below the lower polarizing plate.

Below, the manufacturing method of each used member is demonstrated.
(Production of ECB mode liquid crystal cell)
In the liquid crystal cell, a nematic liquid crystal material having a cell gap of 3.5 μm and a positive dielectric constant anisotropic layer was sealed between the substrates by drop injection, and Δn · d of the liquid crystal layer was 300 nm. The liquid crystal material is a nematic liquid crystal having positive dielectric anisotropy, refractive index anisotropy, Δn = 0.0854 (589 nm, 20 ° C.), Δε = + 8.5 (for example, MLC-9100 manufactured by Merck). used. Further, the crossing angles of the orientation axes (rubbing axes) 10 and 13 of the upper substrate 9 and the lower substrate 12 are 0 °, and the upper and lower substrates 9 and 12 of the liquid crystal cell are later bonded to the upper and lower polarizing plates. Rubbing directions (orientation control directions) 10 and 13 intersect at 45 ° with the slow axis 6 (parallel to the casting direction) of the support (protective film 5) of the optically anisotropic layer (optical compensation film 7). I tried to do it. Further, the absorption axes 4 and 19 of the polarizing films 3 and 18 intersect with the alignment directions (rubbing directions) 10 and 13 of the liquid crystal cell at approximately 45 °, respectively, and the absorption axes 4 and 19 of the upper and lower polarizing films 3 and 18 intersect. The angle was approximately 90 ° crossed Nicol.

(Production of cellulose acetate film)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.
(Cellulose acetate solution composition)
Cellulose acetate having an acetylation degree of 60.7 to 61.1% 100 parts by weight Triphenyl phosphate (plasticizer) 7.8 parts by weight Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by weight Methylene chloride (first solvent) 336 parts by weight Methanol (second solvent) 29 parts by mass 1-butanol (third solvent) 11 parts by mass

The obtained dope was cast using a band stretching machine. After the film surface temperature on the band reaches 40 ° C., the film is dried with warm air of 70 ° C. for 1 minute, and the film is dried from the band with 140 ° C. of drying air for 10 minutes. A cellulose acetate film (thickness: 80 μm) was prepared. About the produced cellulose acetate film (transparent support body, protective film), Re value and Rth value in wavelength 546nm were measured using the ellipsometer (M-150, JASCO Corporation make). Re was 3 nm and Rth was 8 nm.
The produced cellulose acetate film was immersed in a 2.0N potassium hydroxide solution (25 ° C.) for 2 minutes, neutralized with sulfuric acid, washed with pure water, and then dried. The surface energy of the cellulose acetate film was determined by a contact method and found to be 63 mN / m. Thus, the cellulose acetate film for protective films was produced.

(Production of elliptically polarizing plate)
A polarizing film was prepared by adsorbing iodine to a stretched polyvinyl alcohol film. The cellulose acetate film produced above was attached to one side of the polarizing film using a polyvinyl alcohol adhesive on one side of the polarizing film. The polarizing film was bonded so that the absorption axis of the polarizing film and the slow axis of the film (parallel to the casting direction) were parallel. Further, a saponified cellulose triacetate film (TD-80U, manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 80 μm was attached to the other surface of the polarizing film using a polyvinyl alcohol adhesive. This cellulose triacetate film becomes a protective film disposed on the side farther from the liquid crystal cell. In this way, a polarizing plate with an optical compensation film was produced.

  The produced polarizing plate was used as the upper polarizing plate. Moreover, as a lower polarizing plate produced by attaching a cellulose triacetate film (TD-80U, manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 80 μm to both surfaces of the polarizing film using a polyvinyl alcohol adhesive. Using. The prepared upper polarizing plate and lower polarizing plate were disposed with the ECB mode liquid crystal cell prepared above interposed therebetween, and a liquid crystal display device was manufactured. Note that the axis angle of the absorption axis 4 of the polarizing film 3 of the upper polarizing plate is 45 ° with respect to the horizontal direction of the display device, and the orientation control direction of the upper optical compensation film 7 (rubbing direction, orthogonal to the optical axis direction). Is 0 °, the alignment control direction (rubbing direction) 10 of the liquid crystal cell upper substrate 9 is 90 °, and similarly the polarization axis 19 of the lower polarizing film 18 is 135 °, and the alignment control direction 13 (rubbing of the lower substrate 12 of the liquid crystal cell) Direction) was set to 270 °.

(Comparative Example 2)
Using the cellulose acetate film produced in Comparative Example 1 as a support, an optical compensation film was produced thereon by the following method.
(Preparation of alignment film for optical compensation film)
The surface of the cellulose acetate film prepared in the same manner as in Comparative Example 1 was saponified, was coated an alignment film coating solution having the following composition thereon so that 20 ml / m ² with a wire bar coater. Then, it dried with 60 degreeC warm air for 60 seconds, and also with 100 degreeC warm air for 120 seconds, and formed the film | membrane. Next, the formed film was rubbed in a direction parallel to the slow axis direction of the film to obtain an alignment film.
(Orientation film coating solution composition)
The following modified polyvinyl alcohol 15 parts by mass Water 334 parts by mass Methanol 100 parts by mass Glutaraldehyde 1 part by mass Paratoluenesulfonic acid 0.3 parts by mass

(Preparation of optical compensation film)
On the above 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, A coating solution prepared by dissolving 1.0 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 414 g of methyl ethyl ketone was applied to 6.2 ml / m ² (6.2 cc / m) using a # 3.6 wire bar. ²⁾ was applied. This was heated in a constant temperature zone of 130 ° C. for 2 minutes to align the discotic liquid crystalline 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 liquid crystalline compound. Thereafter, it was allowed to cool to room temperature to form an optical compensation film.

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

On the protective film on the side of the upper and lower polarizing plates in contact with the liquid crystal cell, the laminated body of the optical compensation film prepared above and the support is placed on the back surface of the support (the surface on which the optically anisotropic layer is not formed). Affixed to one side of the polarizing film. The polarizing film was bonded so that the absorption axis of the polarizing film and the slow axis (parallel to the casting direction) of the support of the optical compensation film were parallel. Further, a saponified cellulose triacetate film (TD-80U, manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 80 μm was attached to the other surface of the polarizing film using a polyvinyl alcohol adhesive. This cellulose triacetate film becomes a protective film disposed on the side farther from the liquid crystal cell. In this way, a polarizing plate with an optical compensation film was produced.
An ECB mode liquid crystal display device was produced in the same manner as in Comparative Example 1 except that the produced polarizing plate with an optical compensation film was used as the upper and lower polarizing plates.

Example 1
(Production of liquid crystal display device)
In the liquid crystal display device manufactured in Comparative Example 2, the electrode of the upper substrate is divided into two, and the liquid crystal molecules 11 are applied so that the liquid crystal molecules 11 are aligned in the two pixel regions A and B shown in FIG. The value voltage was changed. In the pixel region A shown in FIG. 2, the effective voltage is 1.2 volts when white is displayed in an AC rectangle having a frequency of 30 Hz, and 3.5 volts when black is displayed. In the pixel region B, 1.4 volts and black is displayed when white is displayed. Sometimes 3.7 volts were applied. The halftone is set to a voltage that equally divides the luminance level between white display and black display in both areas.

(Optical measurement of the manufactured liquid crystal display device)
A rectangular wave voltage of 60 Hz was applied to the liquid crystal display devices of Comparative Examples 1 and 2 and Example 1 manufactured as described above. The measuring instrument (EZ-Contrast 160D, manufactured by ELDIM) is used, and the contrast ratio, which is the transmittance ratio (white display / black display), and the black display (L1) and white display (L8) transmittances are equally spaced. The transmittance viewing angle at 8 cut gradations was measured. Table 1 shows the front contrast ratio, the range in which the transmittance of gradations adjacent in the downward direction is not inverted, and the range in which the contrast ratio is 10: 1 or more.

(Example 2)
Assuming a liquid crystal display device having the same configuration as that shown in Example 1, the upper polarizing plate (protective film 1, polarizing film 3, protective film 5), optically anisotropic layer 7, liquid crystal from the observation direction (top) A cell (upper substrate 9, liquid crystal layer 11, lower substrate 12), optically anisotropic layer 14, and lower polarizing plate (protective film 16, polarizing film 18, protective film 20) are stacked, and a backlight light source (not shown) With respect to the liquid crystal display device having a configuration in which the above is arranged, an optical simulation was performed to confirm the effect. 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. As the liquid crystal material, a liquid crystal material having positive dielectric anisotropy and Δε = 4.2 was used. The orientation of the liquid crystal cell is approximately parallel with a pretilt angle of 0.5 degree, the cell gap of the substrate is 3.5 microns, and the retardation of the liquid crystal (ie, the thickness d (micron) of the liquid crystal layer and the refractive index is anisotropic). The product Δn · d) with the property Δn was 300 nm at a wavelength of 550 nm. Optical compensation films 7 and 14 in which a discotic compound has a disc surface oriented perpendicularly to the substrate are arranged. 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 12 and 9 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 if the relationship between the backlight and the observer is changed up and down.
Table 2 shows the calculation result of the front contrast ratio when Δnd of the liquid crystal cell and the wavelength dispersion of the optical compensation layer are changed.

  In the table, sample No. 1 has a value of | Re (λ) −Δn (λ) × d | exceeding 50 nm at wavelengths of 450 and 650 nm, and the front contrast ratio becomes 100, so that the visibility is lowered. . Sample No. 2 was obtained by simulating the same physical property values as in Example 1. A contrast ratio of 450 was obtained with a maximum value of | Re (λ) −Δn (λ) × d | of 30 nm. No. 3 is 0 nm at all wavelengths, and an ideal contrast ratio of 3000 is obtained. This value corresponds to the orthogonal transmittance of the polarizing plate. The No. 4 sample had a contrast ratio of 1500 at 5 nm. The samples No. 5 and 6 have a contrast ratio of 200 at 50 nm, and this range is preferable for obtaining good visibility.

It is the schematic which shows an example of the liquid crystal display device of this invention. It is the schematic which shows an example of the pixel area | region in the liquid crystal cell of the liquid crystal display device of this invention. It is the schematic which shows an example of the pixel area | region in the liquid crystal cell of the liquid crystal display device of this invention. It is the schematic which shows an example of the pixel area | region in the liquid crystal cell of the liquid crystal display device of this invention. It is the schematic which shows an example of the pixel area | region in the liquid crystal cell of the liquid crystal display device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper polarizing plate upper protective film 2 Upper protective film slow axis 3 Upper polarizing film 4 Upper polarizing film absorption axis 5 Upper polarizing plate lower protective film 6 Lower protective film slow axis 7 Upper optical compensation film 8 Upper optical compensation film Optical axis 9 of liquid crystal cell Upper substrate 10 Upper substrate Liquid crystal alignment rubbing direction 11 Liquid crystalline molecule 12 Liquid crystal cell lower substrate 13 Lower substrate Liquid crystal alignment rubbing direction 14 Lower optical compensation film 15 Optical axis of lower optical compensation film 16 Lower polarizing plate upper protective film 17 Upper protective film slow axis 18 Lower polarizing film 19 Lower polarizing film absorption axis 20 Lower polarizing plate lower protective film 21 Lower protective film slow axis 22 Transparent electrode 23 Liquid crystal Cell rubbing direction

Claims (6)

A liquid crystal cell comprising a pair of opposed substrates having at least one electrode, and a liquid crystal layer including a nematic liquid crystal material sandwiched between the substrates and aligned substantially parallel to the surfaces of the pair of substrates when no voltage is applied A liquid crystal display device having at least a first polarizing film and a second polarizing film arranged with the liquid crystal cell interposed therebetween, and at least one of the first polarizing film and the second polarizing film; And an optical compensation film between the liquid crystal cell, the optical compensation film is made of a composition containing a discotic compound, and molecules of the compound are oriented with the disc surface substantially perpendicular to the substrate surface. The liquid crystal cell has two or more alignment regions in one pixel, displays black when no voltage is applied or when a low voltage is applied, and the nematic liquid crystal material molecules with respect to the substrate surface when the high voltage is applied average LCD oblique angle are different from each other to each other in the alignment region. At least one protective film is laminated on the polarizing film, the optical compensation film is formed on the protective film, and the slow axis of the protective film and the orientation direction of the discotic compound intersect at about 45 °. The liquid crystal display device according to claim 1. The liquid crystal display device according to claim 1, wherein an alignment direction of the discotic compound is substantially orthogonal to an alignment direction of the liquid crystal cell. The liquid crystal display device according to claim 1, wherein the optical compensation film is disposed between the liquid crystal cell and both the first and second polarizing films. . 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-plane retardation of the optical compensation film at wavelength λ is Re ( When the retardation in the thickness direction at λ) and the wavelength λ is Rth (λ), the following formulas (I) to (II) are satisfied at at least two different wavelengths between 380 nm and 780 nm. The liquid crystal display device of any one of -4:
(I) 50 ≦ Δn (λ) × d ≦ 400,
(II) −50 ≦ Re (λ) −Δn (λ) × d ≦ 50. The liquid crystal display device according to claim 5, wherein the formulas (I) to (II) are satisfied at all wavelengths of 450 nm, 550 nm, and 650 nm.

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