JP2001100208A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device having improved display contrast and visual field angle characteristics of a display color without lowering a front contrast and provided with a bend alignment cell or a HAN mode cell excellent in high speed display. SOLUTION: This liquid crystal display device having a bend alignment liquid crystal cell or a HAN mode liquid crystal cell comprises an optical compensation sheet which is provided between the liquid crystal cell and at least one polarizing plate and having the minimum value of the absolute value of retardation in a direction inclined from the direction of the normal of the optical compensation sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display having a liquid crystal cell capable of forming a bend alignment or a hybrid arrangement.

[0002]

2. Description of the Related Art A CRT, which is a mainstream display device of OA equipment such as a Japanese word processor and a desktop personal computer.
Have been replaced by liquid crystal display devices having great advantages such as thin and light weight and low power consumption. Most of the liquid crystal display devices (hereinafter, referred to as LCDs) that are currently widely used use twisted nematic liquid crystals. Display methods using such a liquid crystal can be roughly classified into two methods, a birefringence mode and an optical rotation mode.

An LCD using a birefringence mode has a liquid crystal molecule arrangement exhibiting a twist exceeding a twist angle of 90 °, has a sharp electro-optical characteristic, and is simple even without an active element (thin film transistor or diode). Even with a matrix-shaped electrode structure, a large-capacity display can be obtained by time-division driving. However, it has the disadvantage that the response speed is slow (several hundred milliseconds) and it is difficult to display gradations.
It does not go beyond the display performance of FT-LCD and MIM-LCD.

[0004] For the TFT-LCD and the MIM-LCD, an optical rotation mode display method (TN type liquid crystal display device) in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method has a response speed of about several milliseconds and shows a high display contrast, and is the most effective method as compared with LCDs of other methods. However, since the twisted nematic liquid crystal is used, there is a problem in viewing angle characteristics that a display color and a display contrast change depending on a viewing direction due to a principle of a display method, and the display performance of a CRT cannot be exceeded.

FIG. 1 is an enlarged sectional view of a liquid crystal cell for a TN type liquid crystal display device. This liquid crystal cell has a coplanar and asymmetric director region (field) 12 (constituting a liquid crystal layer) formed between substrates 14a and 14b having transparent electrodes. The director in contact with the substrate (ie, the alignment vector; a unit vector indicating the alignment direction of the liquid crystal molecules (generally in the long axis direction)) is called a surface contact director 16. All other directors are referred to as bulk directors 13. The degree of birefringence and light transmission at each position of the liquid crystal cell 11 is a function of the angle between the light beam and the director near where the light beam travels. The minimum birefringence occurs when the ray travels parallel to the nearby director, while the maximum birefringence occurs when the ray travels perpendicular to the nearby director. For example,
The light beam 18 passing through the liquid crystal cell 11 at an angle 15 is a light beam 1
Since direction 8 is somewhat parallel to the majority of directors 13 and 16, it exhibits minimal effective birefringence. However, the light rays 17 passing through the liquid crystal cell 11 at the opposite angle 15 have the direction of the
And 16 have the most effective birefringence because they are almost non-parallel. Since an increase in birefringence naturally gives rise to an increase in retardation, a change in the color or contrast of a displayed image depending on the viewing angle of the liquid crystal display device occurs.

In order to improve the viewing angle characteristics (enlarge the viewing angle), a retardation film (optical compensatory sheet) is used in combination with a polarizing plate.
It is conceivable that the optical compensation sheet is provided between the liquid crystal cell and the N-liquid crystal cell, and various optical compensation sheets have been proposed so far. Although the installation of the optical compensatory sheet has led to an increase in the viewing angle to some extent, the viewing angle has not been wide enough to consider a CRT replacement.

Recently, a liquid crystal cell capable of essentially expanding the viewing angle has been proposed (eg, Japanese Patent Application Laid-Open No. 7-84254, flat panel display (150 to 154)).
P. 1995) and U.S. Patent No. 5,410,422). The liquid crystal cell has a liquid crystal capable of bend alignment,
It is a symmetric cell. FIG. 2 shows an enlarged sectional view of the liquid crystal cell. This liquid crystal cell includes a substrate 24 having a transparent electrode.
a and 24b formed between the “self-compensating” director regions (fields) 22a and 22b (constituting the liquid crystal layer). These two director regions are arranged symmetrically with respect to the center line 23 in the middle of the substrates 24a and 24b having the transparent electrodes. Director areas (places) 22a, 22b
Has surface contact directors 26a, 26b and bulk directors 28a, 28b, respectively. For example, the substrates 24a and 24b having the transparent electrodes are receiving voltages that maintain the self-compensating director regions 22a and 22b,
In this state, the light beam 2 passing through the liquid crystal cell 21 at an angle 29
7 shows the minimum effective birefringence (that is, the minimum retardation) in the director region 22a, since the direction of the light beam 27 is somewhat parallel to the majority of the directors 26a and 28a in the director region 22a; Then, the light beam 27 is reflected by the light beam 27 in the director area 22b.
Is substantially non-parallel to the majority of directors 26b and 28b, this region 22b exhibits minimal effective birefringence (ie, minimal retardation). Therefore, for the light beam 27 passing through the liquid crystal cell 21 at an angle 29, the effective birefringence is smaller in the director region 22a but larger in the director region 22b. Therefore, even if the incident angle of light changes, the change in the overall effective birefringence is small. The light ray 20 passing through the liquid crystal cell 21 at the opposite angle 29 is also the light ray 27.
The same effect can be obtained.

As described above, a liquid crystal cell using a liquid crystal capable of forming a bend alignment (hereinafter also referred to as a bend alignment cell) is a symmetric cell and has an essentially wide viewing angle. However, the birefringence must be compensated for, and the flat panel display (150 to
154, 1995) and U.S. Pat. No. 5,410,422 describe the use of negative birefringence compensators or biaxially oriented polymer films.

Further, the 42nd Spring Meeting of the Japan Society of Applied Physics (29
a-SZC-20, 1995), applying this concept to a reflective LCD, a HAN mode (Hybri
A liquid crystal cell of d-aligned-nematic mode) has been proposed. That is, the HAN mode liquid crystal cell utilizes the upper side of the bend alignment cell (that is, the director region 22a). FIG. 3 is an enlarged sectional view of the HAN mode liquid crystal cell. The director region 32 is formed between substrates 33a and 33b having a transparent electrode. The director region 32 has a surface contact director 36 and a bulk director 38. The light ray 34 passing through the liquid crystal cell 31 at an angle 35 exhibits a maximum effective birefringence since it is in a substantially non-parallel relationship with the majority of directors 36 and 38;
Light ray 35 reflected by substrate 33B exhibits lower birefringence because it is in a somewhat parallel relationship with the majority of directors 36 and 38. The effective negative refraction obtained by the light beam 34 and the reflected light beam 34 is the same as in the bend liquid crystal cell. In this HAN mode liquid crystal cell, when the biaxially stretched film is used as an optical compensation sheet,
It is described in the 42nd Spring Meeting of the Japan Society of Applied Physics.

[0010]

SUMMARY OF THE INVENTION The present inventor has proposed a field of view of the above liquid crystal display device using a bend alignment cell or a HAN mode cell, and using a negative birefringence compensator or a biaxially stretched polymer film as an optical compensation sheet. We have been studying the angular characteristics. As a result, the present inventor has clarified that the contrast of the liquid crystal display device provided with the above-described optical compensation sheet decreases when the inclination angle for viewing the display surface is increased (particularly in the vertical direction). An object of the present invention is to provide a liquid crystal display device having a bend alignment cell which has improved display contrast and viewing angle characteristics of display colors without deteriorating front contrast, and is excellent in high-speed display. Another object of the present invention is to provide a liquid crystal display device provided with a HAN mode cell which is excellent in high-speed display with improved display contrast and viewing angle characteristics of display colors without lowering front contrast.

[0011]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal cell having a layer of nematic liquid crystal sealed between a pair of substrates having a transparent electrode having an alignment film on the surfaces thereof, and a polarizing element provided on both sides of the liquid crystal cell. In a liquid crystal display device comprising a plate, and a layer of nematic liquid crystal showing bend alignment, and an angle of an alignment vector of the nematic liquid crystal with respect to the substrate is changed by a change in voltage applied to the liquid crystal cell.
An optical compensation sheet is provided between the liquid crystal cell and at least one polarizing plate, and the optical compensation sheet exhibits a minimum value of an absolute value of retardation in a direction inclined from a normal direction of the optical compensation sheet. There is provided a liquid crystal display device. The minimum value of the absolute value of the retardation is not zero.

A preferred embodiment of the liquid crystal display of the present invention.
Is as follows. 1) An optical compensation sheet is provided on a transparent support and on the transparent support
From a compound having a discotic structural unit
Optical anisotropic layer. 2) Disc surface of discotic structural unit of optically anisotropic layer
Are inclined with respect to the transparent support surface, and
Angle between the disk surface of the tick structure unit and the transparent support surface
Changes in the depth direction of the optically anisotropic layer. 3) the transparent support has optically negative uniaxiality and
It has an optical axis in the normal direction of the transparent support surface, and
Subject: 20 ≦ ｛(n_x + N_y ) / 2-n_z ｝ × d_Two ≦ 400 (however, n_x And n_y Indicates the principal refractive index in the plane of the support
Then n_z Represents the principal refractive index in the thickness direction, and d_Two Is the support
Is expressed in nm-converted thickness). 4) An alignment film is formed between the transparent support and the optically anisotropic layer.
Have been. 5) All the optical compensatory sheets
Absolute value Re of the total ₁ And the letter of the liquid crystal layer expressed below
Absolute value Re_Two Has the following relationship: 0.2 × Re_Two ≤Re₁ ≦ 2.0 × Re_Two [However, the retardation of the optical compensation sheet is
｛(N_Two + N_Three ) / 2-n₁｝ × d (where n₁ , N_Two 
And n_Three Represents the triaxial refractive index of the sheet, and
Each has a smaller refractive index in this order, and d is
(representing the thickness in nm)) and
The retardation of the liquid crystal layer is Δn_Three − (N₁+ N_Two )
/ 2｝ × d (where n₁ , N_Two And n_Three Is the above liquid crystal layer
, The refractive indices in the three axial directions.
And d is the nm-converted thickness of the liquid crystal layer.
Satisfies the above. 6) LCD device used in normally white mode
Is done.

Further, the present invention is a layer in which a nematic liquid crystal layer is sealed between a pair of substrates with a transparent electrode having an alignment film on their surfaces, and one of the alignment films is capable of homeotropically aligning the nematic liquid crystal. A liquid crystal cell, a polarizing plate provided on one side of the liquid crystal cell, and a reflector disposed on the other side of the liquid crystal cell, and the layer of the nematic liquid crystal shows a hybrid arrangement, and the nematic liquid crystal In a liquid crystal display device in which the angle of the orientation vector with respect to the substrate changes with a change in voltage applied to the liquid crystal cell, an optical compensation sheet is provided between the liquid crystal cell and the polarizing plate, and the optical compensation sheet is The liquid crystal display device is characterized in that the liquid crystal display device shows the minimum value of the absolute value of the retardation in a direction inclined from the normal direction of the optical compensation sheet. The minimum value of the absolute value of the retardation is not zero.

Preferred embodiments of the liquid crystal display device of the present invention are as follows. 1) The optical compensation sheet comprises a transparent support and an optically anisotropic layer provided on the transparent support and comprising a compound having a discotic structural unit. 2) The disc surface of the discotic structure unit of the optically anisotropic layer is inclined with respect to the transparent support surface, and the angle between the disc surface of the discotic structure unit and the transparent support surface is different from that of the optically anisotropic layer. It changes in the depth direction. 3) a transparent support, an optically has a negative uniaxial property, and has an optical axis in a normal direction of the transparent support surface, further the following _{conditions: 20 ≦ {(n x +} n y) / 2 _{-n z} × d 2 ≦ 400} ( where, n _x and n _y represent the main refractive index in the plane of the support, n _z represents the main refractive index in the thickness direction, d ₂ is nm in terms of the support Is expressed). 4) An alignment film is formed between the transparent support and the optically anisotropic layer. 5) the absolute value Re ₁ letter de Deployment represented by the following optical compensation sheet, and the absolute value Re ₂ letter de Deployment represented by the liquid crystal layer is, the following relationship: 0.2 × Re ₂ ≦ Re ₁ ≦ 2.0 × Re ₂ [where the retardation of the optical compensation sheet is {(n ₂ + n ₃ ) / 2−n ₁ } × d (where n ₁ , n ₂
And n ₃ represent the three-axis refractive index of the sheet, each having a smaller refractive index in this order, and d representing the thickness of the sheet in nm), and the retardation of the liquid crystal layer. Is Δn ₃ − (n ₁ + n ₂ )
/ 2｝ × d (where n ₁ , n ₂ and n ₃ represent the three-axis refractive index of the liquid crystal layer, each having a smaller refractive index in this order, and d is the nm of the liquid crystal layer in terms of nm. Defined as thickness). 6) The liquid crystal display is used in a normally white mode.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bend alignment cell or H
As an optical compensation sheet of a liquid crystal display (LCD) using an AN mode cell, an optical compensation sheet showing a minimum value of an absolute value of retardation in a direction inclined from a normal direction of the optical compensation sheet is used. Have. As described above, a liquid crystal cell using a liquid crystal capable of bend alignment (bend alignment cell) is a symmetric cell, and therefore, a liquid crystal display device having this liquid crystal cell exhibits an essentially wide viewing angle. . Similarly, the HAN mode reflection type liquid crystal display device shows an essentially wide viewing angle.

A liquid crystal cell generally includes a substrate having a transparent electrode having an alignment film formed on a pair of surfaces, and a layer of nematic liquid crystal sealed between the substrates. In the bend alignment cell, a liquid crystal that can bend in a liquid crystal cell to which a voltage is applied is generally used. Then, the angle of the orientation vector of the nematic liquid crystal with respect to the substrate changes due to a change in the voltage applied to the liquid crystal cell. Usually, the angle of the orientation vector of the nematic liquid crystal with respect to the substrate increases with an increase in the voltage applied to the liquid crystal cell, and the birefringence decreases. This change in birefringence gives an image. In the present invention, the bend alignment of the liquid crystal refers to the liquid crystal layer (22a in FIG. 2).
And 22b) that the alignment vector (ie, director or optical axis) of the liquid crystal molecules is symmetrical (linearly symmetric) with respect to the center line (23 in FIG. 2) of the liquid crystal layer and has a bend portion at least in a region near the substrate. Means The bend portion is a portion where a line formed by a director in a region near the substrate is bent.

That is, as shown in FIG. 2, the bend alignment of the liquid crystal generally means that when a voltage is applied to the liquid crystal cell, the director of the liquid crystal molecules in the cell is placed on the lower substrate (24 in FIG. 2).
b) Nearly parallel to the lower substrate, the angle between the director and the substrate surface increases as the distance from the substrate increases, and furthermore, the director has the same distance between the upper substrate and the lower substrate. In the region (centerline region) it is perpendicular or nearly perpendicular to the substrate surface, and the director further increases the angle between the director and the substrate surface with increasing distance from the lower substrate, and eventually the director becomes the upper substrate In the vicinity of (24a in FIG. 2), it means that the liquid crystal molecules are oriented so as to be substantially parallel to the upper substrate. Near the center line (region near the center line (23 in FIG. 2)), the director may be twisted (generally at approximately 180 degrees). Further, the directors in the regions close to the upper and lower substrates or the contact regions may be inclined from the substrate surface (that is, may have a tilt angle).

The nematic liquid crystal used in the HAN mode reflection type LCD of the present invention is generally a liquid crystal capable of forming a hybrid arrangement by applying a voltage. HA
The N mode is already well known in the field of liquid crystal display devices. As shown in FIG. 3, the HAN mode cell has a structure in which the lower substrate is arranged at the position of the center line of the bend alignment cell. The alignment film on the lower substrate is a layer capable of homeotropically aligning the nematic liquid crystal.
Examples of such an alignment film include an inorganic vapor-deposited film, a surfactant layer, and an organic silane layer.

A liquid crystal display device having a bend alignment cell or a HAN mode cell has a self-compensating director region. However, when the display device is large and viewed obliquely (particularly in the vertical direction), the light in the black display portion is not affected. The transmittance increases, leading to a decrease in contrast. By mounting the optical compensatory sheet of the present invention on the above cell, the contrast when viewed from the tilt direction can be greatly improved without lowering the contrast when viewed from the front.

As shown in FIG. 4, if the liquid crystal layer of the liquid crystal cell in which a black image is displayed (when voltage is applied) is considered to be a positive uniaxial optical anisotropic body, it has a negative uniaxial property. The optical anisotropic body 41 (eg, a negative birefringent film) can compensate for the retardation generated by the optical anisotropic body 44 having a positive uniaxial property. Reference numeral 42 denotes an optical compensation sheet, and reference numeral 43 denotes a liquid crystal layer of a liquid crystal cell.

The present inventor has found that an optically anisotropic body having negative uniaxiality cannot sufficiently compensate for the retardation (birefringence) generated by the liquid crystal layer. Thereafter, the present inventor has repeatedly studied and arrived at the present invention in which a sheet showing the minimum value of the absolute value of retardation in a direction inclined from the normal direction of the optical compensation sheet is used as the optical compensation sheet. The optical compensation sheet of the present invention generally comprises a transparent support and an optically anisotropic layer provided thereon, and the optically anisotropic layer comprises a compound having a discotic structural unit. The disc surface of the discotic structure unit of the optically anisotropic layer is inclined with respect to the transparent support surface, and the angle between the disc surface of the discotic structure unit and the transparent support surface is different from that of the optically anisotropic layer. It preferably changes in the depth direction.

The principle by which the optical compensatory sheet of the present invention compensates for the retardation of the bend alignment cell or the HAN mode cell will be described with reference to FIGS. The retardation can be compensated for by using an optically anisotropic body having the same orientation as the orientation state in the bend orientation cell or the HAN mode cell. FIG. 5 schematically shows an example of a mechanism for compensating for the retardation generated by the bend alignment cell. Liquid crystal layer 52 of bend alignment cell
Is composed of an optically anisotropic substance 54 having a positive uniaxial property (eg, a nematic liquid crystal molecule), and the optical compensation sheet 51 is composed of an optically anisotropic substance 53 having a negative uniaxial property (eg, a dicot liquid crystal compound). . In the optical compensation sheet 51, the optical axis (director) of the optically anisotropic body 53 having negative uniaxiality
Is tilted at a large angle from the normal line in the region near the liquid crystal layer 52 of the bend alignment cell, and its tilt angle is almost 0 degrees near the center in the thickness direction of the sheet. , The tilt angle further increases. The optical compensation sheet 51 is generally applied with a coating liquid of a compound having a discotic structural unit (eg, a discotic liquid crystalline compound) on an alignment film provided on a transparent support,
The compound can be obtained by heating to orient the compound, and then cooling to form an optically anisotropic layer. A cholesteric liquid crystal or a chiral nematic liquid crystal having a twisted structure may be used instead of the discotic liquid crystal compound. Further, a liquid crystalline polymer that forms a cholesteric phase or the like may be used. Optical compensation sheet 51
May be composed of one optically anisotropic layer, or may be composed of two optically anisotropic layers (for example, the following layers 61 and 63).

FIG. 6 schematically shows another example of a mechanism for compensating for the retardation generated by the bend alignment cell (that is, when two optical compensation sheets are used). The liquid crystal layer 62 of the bend alignment cell is made of a positive uniaxial optical anisotropic body 65 (for example, a nematic liquid crystal molecule), and the optical compensation sheet 61 is made of a negative uniaxial optical anisotropic body 64.
(For example, a dicot liquid crystal compound), and the optical compensation sheet 63 is also made of an optically anisotropic body 66 having negative uniaxiality. In the optical compensation sheets 61 and 63, the optical axis (director) of the optically anisotropic body 64 or 66 having negative uniaxiality is inclined at a large angle from the normal in a region near the liquid crystal layer 62 of the bend alignment cell. And the tilt angle decreases as the distance from the liquid crystal layer increases. The optical compensation sheets 61 and 63 may be arranged so as to overlap one side of the liquid crystal cell.

FIG. 7 schematically shows an example of a mechanism for compensating for the retardation generated by the HAN mode cell.
The HAN mode liquid crystal layer 72 is composed of a positive uniaxial optical anisotropic body 74 (eg, a nematic liquid crystal molecule), and the optical compensation sheet 71 is a negative uniaxial optical anisotropic body 73.
(Eg, a dicotic liquid crystal compound). In the optical compensation sheet 71, the optical axis (director) of the optically anisotropic body 73 having negative uniaxiality is inclined at a large angle from the normal in the region near the liquid crystal layer 72 of the bend alignment cell. The inclination angle decreases as the distance increases. The nematic liquid crystal used in the HAN mode reflection type LCD of the present invention is generally a liquid crystal capable of forming a hybrid arrangement by applying a voltage. Then, the angle of the orientation vector of the nematic liquid crystal with respect to the substrate changes due to a change in the voltage applied to the liquid crystal cell. Usually, the angle of the orientation vector of the nematic liquid crystal with respect to the substrate increases with an increase in the voltage applied to the liquid crystal cell, and the birefringence decreases. An image is given by this change in birefringence.

In a liquid crystal display device using a bend alignment cell, the absolute value Re ₁ of the total retardation of all the optical compensation sheets and the absolute value Re ₁ of the retardation of the liquid crystal layer are determined.
₂ and it is, following _{relationship: 0.2 × Re 2 ≦ Re 1} ≦ 2.0 × Re 2 [ however, retardation of the optical compensation sheet is _{{(n 2 + n 3)} / 2-n 1} × d (Where n ₁ , n ₂
And n ₃ represent the three-axis refractive index of the sheet, each having a smaller refractive index in this order, and d representing the thickness of the sheet in nm), and the retardation of the liquid crystal layer. Is Δn ₃ − (n ₁ + n ₂ )
/ 2｝ × d (where n ₁ , n ₂ and n ₃ represent the three-axis refractive index of the liquid crystal layer, each having a smaller refractive index in this order, and d is the nm of the liquid crystal layer in terms of nm. Defined by the following formula), preferably satisfying the following condition: 0.2 × Re ₂ ≦ Re ₁ ≦ 1.5 × Re ₂ , In particular, it is preferable to satisfy the following condition: 0.4 × Re ₂ ≦ Re ₁ ≦ 1.5 × Re ₂

In a liquid crystal display device using a HAN mode cell,
The absolute value R of the retardation of the optical compensation sheet
e₁ And the absolute value Re of the retardation of the liquid crystal layer_Two And
The following relationship: 0.2 × Re_Two ≤Re₁ ≦ 2.0 × Re_Two ｛However, the retardation of the above optical compensation sheet is
｛(N_Two + N_Three ) / 2-n₁｝ × d (where n₁ , N_Two 
And n_Three Represents the triaxial refractive index of the sheet, and
Each has a smaller refractive index in this order, and d is
(representing the thickness in nm)) and
The retardation of the liquid crystal layer is Δn_Three − (N₁+ N_Two )
/ 2｝ × d (where n₁ , N_Two And n_Three Is the above liquid crystal layer
, The refractive indices in the three axial directions.
And d is the nm-converted thickness of the liquid crystal layer.
It is common to satisfy｝ defined by
Preferably, the following conditions: 0.2 × Re_Two ≤Re₁ ≦ 1.5 × Re_Two And in particular, the following condition: 0.4 × Re_Two ≤Re₁ ≦ 1.5 × Re_Two In addition, | Δn described later_Three × d_Three Letter day represented by |
Is the above ｛(n _Two + N_Three ) / 2-n₁ で × d
Is synonymous with₁ × d
₁ The retardation represented by |_Three −
(N₁ + N_Two Synonymous with that expressed by) / 2 ／ × d
You. Further, the retardation of the transparent support ｛(n_x +
n_y ) / 2-n_z ｝ × d_TwoIs the letter day of the liquid crystal layer
｛(N_Two + N_Three ) / 2-n₁ Corresponds to｝ × d
Things.

The liquid crystal display device of the present invention can be used in a normally white mode (hereinafter, NW mode) and a normally black mode (hereinafter, NB mode). N
In B mode, as the viewing angle increases,
It is preferable to use it in the NW mode because the color change is large.

The optical compensatory sheet used in the liquid crystal display of the present invention comprises an optically anisotropic layer made of a compound having a discotic structural unit. Examples of the compound having a discotic structural unit include a low molecular weight discotic liquid crystal compound such as a monomer or a polymer obtained by polymerization of a polymerizable discotic liquid crystal compound. The optical compensation sheet is generally
It is preferable that the transparent support and an optically anisotropic layer formed of a compound having a discotic structural unit are provided thereon, and that an alignment film is further provided with the transparent support and the optically anisotropic layer.

As the material for the transparent support, any material can be used as long as it is transparent. A material having a light transmittance of 80% or more is preferable, and a material having optical isotropy when viewed from the front is particularly preferable. Therefore, the transparent support is preferably manufactured from a material having a small intrinsic birefringence. As such materials, commercially available products such as ZEONEX (manufactured by Nippon Zeon Co., Ltd.), ARTON (manufactured by Nippon Synthetic Rubber Co., Ltd.) and FUJITAC (manufactured by Fuji Photo Film Co., Ltd.) can be used. Furthermore, polycarbonate, polyarylate, polysulfone and polyether sulfone, even a material having a large intrinsic birefringence, solution casting, conditions such as melt extrusion,
Furthermore, it can be obtained by appropriately setting the stretching state in the vertical and horizontal directions.

The transparent support has an optical axis in a direction normal to the surface of the transparent support, and further has the following condition: 20 ≦ {( _nx + _ny ) / 2− _nz } × d ₂ ≦ 1000 ( However, n _x and n _y represent the main refractive index in the plane of the support, n _z represents the main refractive index in the thickness direction, d ₂ is satisfied indicating) the thickness of nm in terms of the support generally , further the following _{conditions: 20 ≦ {(n x +} n y) / 2-n z} is preferable to satisfy × d ₂ ≦ 400, and in particular the following _{conditions: 50 ≦ {(n x +} n y) / 2 it is preferable to satisfy the _{-n z} × d 2 ≦ 400} . The transparent support is preferably negative uniaxial. The above transparent support (film) | n _x -n _y | plane retardation represented by × d ₂ is preferably in the range of 0 to 200 nm, further a range of 0~150nm are preferred, 0 ~
A range of 100 nm is preferred.

In the above transparent support, the following chromatic dispersion value (α) is generally 1.0 or more, especially 1.0
It is preferably in the range of 1.3. α = Δn ₂ (450 nm) / Δn ₂ (600 nm) (where Δn ₂ (450 nm) represents the birefringence of the support with respect to light having a wavelength of 450 nm, and Δn ₂ (60 nm)
0 nm) represents the birefringence of the support for light having a wavelength of 600 nm. The support having the above wavelength dispersion can be manufactured by using a material having a large intrinsic birefringence.

It is preferable to provide an undercoat layer on the transparent support in order to increase the adhesive strength between the transparent support and the alignment film. The undercoat layer is generally formed by coating on the surface of a surface-treated transparent support. Surface treatment includes chemical treatment, mechanical treatment, corona discharge treatment, flame treatment, UV treatment,
High-frequency treatment, glow discharge treatment, active plasma treatment, and ozone oxidation treatment can be given. Glow discharge treatment is preferred. Various contrivances have been made for the structure of the undercoat layer, and a layer (hereinafter, abbreviated as the first undercoat layer) that adheres well to the polymer film is provided as a first layer, and an alignment film is formed thereon as a second layer. A so-called multi-layer method of applying a hydrophilic resin layer of gelatin or the like (hereinafter, abbreviated as an undercoating second layer) which adheres well to
There is a single-layer method in which only one resin layer such as gelatin containing both a hydrophobic group and a hydrophilic group is applied.

The alignment film is generally provided on a transparent support or on the undercoat layer. The alignment film functions to define the alignment direction of the liquid crystalline discotic compound provided thereon. And this orientation is R
The direction of the minimum value of e can be a direction inclined from the sheet. The orientation film may be any layer as long as it can impart orientation to the optically anisotropic layer. Preferred examples of the alignment film include a rubbed layer of an organic compound (preferably a polymer), an obliquely deposited layer of an inorganic compound, and a layer having microgrooves, ω-tricosanoic acid, dioctadecylmethylammonium chloride, and stearyl. Langmuir-Blodgett method (LB)
Film) or a layer in which a dielectric is oriented by applying an electric or magnetic field.

Examples of the organic compound for the alignment film include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleimide copolymer, polyvinyl alcohol, poly (N-methylolacrylamide),
Styrene / vinyl toluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, carboxymethyl cellulose, polyethylene,
Examples include polymers such as polypropylene and polycarbonate, and compounds such as silane coupling agents. Preferred examples of the polymer include polyimide, polystyrene, polymers of styrene derivatives, gelatin, polyvinyl alcohol, and alkyl-modified polyvinyl alcohol having an alkyl group (preferably having 6 or more carbon atoms). An alignment film obtained by performing an alignment treatment on these polymer layers can align a liquid crystalline discotic compound obliquely.

Among them, alkyl-modified polyvinyl alcohol is particularly preferable, and is excellent in the ability to uniformly align the liquid crystalline discotic compound. This is presumed to be due to strong interaction between the alkyl chains on the alignment film surface and the alkyl side chains of the discotic liquid crystal. Further, the alkyl group preferably has 6 to 14 carbon atoms, and further has -S- and-.
It is preferably bonded to polyvinyl alcohol via (CH ₃ ) C (CN)-or-(C ₂ H ₅ ) N-CS-S-. The alkyl-modified polyvinyl alcohol has an alkyl group at the end, and preferably has a saponification degree of 80% or more and a polymerization degree of 200 or more. Further, the polyvinyl alcohol having an alkyl group in the side chain is MP103 manufactured by Kuraray Co., Ltd.
Commercial products such as MP203 and R1130 can be used.

Also, a polyimide film (preferably, a fluorine atom-containing polyimide) widely used as an alignment film of an LCD is preferable as the organic alignment film. For this, a polyamic acid (for example, LQ / LX series manufactured by Hitachi Chemical Co., Ltd., SE series manufactured by Nissan Chemical Co., Ltd.) is applied to the surface of the support, and baked at 100 to 300 ° C. for 0.5 to 1 hour. Later, it is obtained by rubbing. Further, the alignment film of the present invention can cure these polymers by introducing a reactive group such as an acryloyl group into the above polymers, or by using the above polymers together with a crosslinking agent such as an isocyanate compound and an epoxy compound. Is preferably a cured film obtained by

For the rubbing treatment, a treatment method widely used as a liquid crystal alignment treatment step for LCD can be used. That is, a method of rubbing the surface of the alignment film in a certain direction using paper, gauze, felt, a sheet of rubber, nylon, polyester fiber, or the like can be used to obtain the alignment. Generally, rubbing is performed several times using a cloth or the like on which fibers having a uniform length and thickness are planted on average.

Further, as the material used in oblique vapor deposition, a representative of SiO, metal oxides TiO _2, ZnO ₂ and the like, fluorides of unpleasant MgF ₂ or the like with a further Au, A
1 and the like. Note that the metal oxide can be used as an oblique deposition material as long as it has a high dielectric constant, and is not limited to the above. The inorganic oblique deposition film can be formed using a deposition apparatus. An inorganic oblique deposition film can be formed by fixing a film (support) and vapor-depositing it, or by moving a long film and continuously vapor-depositing the film.

As a method of aligning the optically anisotropic layer without using an alignment film, a method of applying an electric field or a magnetic field while heating the optically anisotropic layer on the support to a temperature at which a discotic liquid crystal layer can be formed. Can be mentioned.

The optically anisotropic layer of the optically compensatory sheet of the present invention comprises:
It is formed on a transparent support or an alignment film. The optically anisotropic layer of the optical compensation sheet of the present invention is generally a compound having a discotic structural unit. That is, the optically anisotropic layer is usually a layer of a low molecular weight liquid crystalline discotic compound (monomer or the like) such as a monomer or a layer of a polymer obtained by polymerization (curing) of a polymerizable liquid crystalline discotic compound.

The above-mentioned discotic (disk-like) liquid crystal compound generally has a discotic structure as a core of a molecular center, and a linear alkyl group, an alkoxy group, a substituted benzoyloxy group or the like as a linear chain. It has a radially substituted structure, exhibits liquid crystallinity, and includes those generally called discotic liquid crystals. The discotic morphological characteristics of the mother nucleus portion excluding the side chain portion can be expressed, for example, as follows for the hydrogenated product as its original compound. First, the size of the mother nucleus molecule is determined as follows. 1) For molecules (mother nucleus molecules), design a planar molecular structure that is as flat as possible, preferably planar. In this case, it is preferable to use a standard value according to the orbital hybrid as the bond distance and bond angle. For example, the Chemical Society of Japan, Chemical Handbook Revised 4th Edition Basic Edition, Vol. II, Chapter 15 (1993)
Maruzen). 2) Structural optimization is performed by the molecular orbital method or the molecular force field method using the structure obtained in 1) as an initial value. As a method, for example, Gaussian92, MOPAC93,
CHARMm / QUANTA and MM3, preferably Gaussian92. 3) A sphere defined by a van der Waals radius is given to each atom whose structure has been optimized, and the shape of the molecule is described by this. 4) Let a, b, and c be the minimum three rectangular parallelepiped ridges into which the molecular portion obtained in the above 3) can enter. In order to reduce the arbitrariness, it is preferable to perform the above 3) and subsequent steps as follows. 3 ') The center of gravity of the structure obtained by the structure optimization is moved to the origin, and the coordinate axis is set to the principal axis of inertia (inertia tensor ellipse). Body axis). 4 ') Each atom is given a sphere defined by Van der Waals radius, which describes the shape of the molecule. 5 ′) Measure the length in the direction of each coordinate axis on the van der Waals surface, and let them be a, b, and c, respectively. Using a, b, and c determined by the above procedure, the form of the mother nucleus of the discotic compound can be defined as a structure that satisfies a ≧ b> c and a ≧ b ≧ a / 2. Preferably a ≧ b
> C and a ≧ b ≧ 0.7a. Further, it is more preferable that b / 2> c.

Examples of the discotic (disk-shaped) compounds of the present invention include C.I. Research reports by Destrade et al.
Mol. Cryst. 71, 111 pages (1981)
Benzene derivatives described in C.I. Destrad
e, et al., Mol. Cryst. 122 volumes, 14
1 (1985), Physics lett, A,
78, p. 82 (1990); Kohne et al., Angew.
Chem. Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. J. Lehn et al. Chem. Commun. , P. 1794 (19)
1985); Research report by Zhang et al. Am. C
hem. Soc. 116, 2655 (1994)
And the azacrown-based and phenylacetylene-based macrocycles. The above discotic (disk-shaped) compounds generally have these as a core of a molecular center, and have a linear alkyl group or an alkoxy group,
It has a structure in which a substituted benzoyloxy group or the like is radially substituted as its straight chain, exhibits liquid crystallinity, and includes those generally called discotic liquid crystals. However, the present invention is not limited to the above description as long as the molecule itself has negative uniaxiality and can impart a certain orientation. Also,
In the present invention, the term "formed from a discotic compound" does not mean that the final product need be the compound, for example,
The low-molecular-weight discotic liquid crystal has a group that reacts with heat, light, or the like, and as a result, includes a polymer that has been polymerized or crosslinked by reaction with heat, light, or the like, has a high molecular weight, and has lost liquid crystallinity.

Preferred examples of the discotic compound are shown below.

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[0051]

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[0052]

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As described above, the optical compensatory sheet used in the liquid crystal display device of the present invention is produced by providing an alignment film on a transparent support and then forming an optically anisotropic layer on the alignment film. Is preferred.

The optically anisotropic layer is generally a layer comprising a compound having a discotic structural unit. Then, the surface of the discotic structural unit is inclined with respect to the transparent support surface, and the angle between the surface of the discotic structural unit and the transparent support surface changes in the depth direction of the optically anisotropic layer. Is preferred.

The angle (tilt angle) of the surface of the discotic structure unit generally increases or decreases in the depth direction of the optically anisotropic layer and as the distance from the bottom surface of the optically anisotropic layer increases. Preferably, the angle of inclination increases with increasing distance. Further, the change in the inclination angle includes a continuous increase, a continuous decrease, an intermittent increase, an intermittent decrease, a change including the continuous increase and the continuous decrease, and an intermittent change including the increase and the decrease. it can. The intermittent change includes a region where the inclination angle does not change in the thickness direction. It is preferable that the tilt angle increases or decreases as a whole, even if it includes a region that does not change. Further, the inclination angle is preferably increased as a whole, and is particularly preferably changed continuously.

FIG. 8 schematically shows a typical example of the cross section of the optically anisotropic layer. The optically anisotropic layer 83 is provided on the alignment film 82 formed on the transparent support 86. A liquid crystalline discotic compound 83a constituting the optically anisotropic layer 83;
83b and 83c are discotic structural units Pa and P
b, Pc are planes 81 a, 81 parallel to the plane of the transparent support 86.
b, 81c and their inclination angles θa, θ
b and θc (the angle between the surface of the discotic structure unit and the surface of the transparent support) increase in order with the increase in the depth (thickness) direction from the bottom surface of the optically anisotropic layer. Reference numeral 84 represents a normal line of the transparent support. Reference numeral 85 denotes an arrow indicating a direction when the direction showing the minimum value of Re of the optically anisotropic layer is projected on the transparent support. The liquid crystalline discotic compound is a planar molecule, and therefore has only one plane in the molecule, ie, a disk surface (eg, 81a, 81b, 81c). However, when the liquid crystalline discotic compound is polymerized into a polymer, the polymer has a plurality of disk surfaces.

It is preferable that the inclination angle (angle) changes in a range of 5 to 85 degrees (particularly, in a range of 10 to 80 degrees). The minimum value of the inclination angle is preferably in the range of 0 to 85 degrees (particularly 5 to 40 degrees), and the maximum value is preferably in the range of 5 to 90 degrees (particularly 30 to 85 degrees). In FIG. 8, the tilt angle (eg, θa) of the discotic structure unit on the support side substantially corresponds to the minimum value, and the tilt angle (eg, θc) of the discotic structure unit substantially corresponds to the maximum value. I have. Further, the difference between the minimum value and the maximum value of the inclination angle is preferably in the range of 5 to 70 degrees (particularly, 10 to 60 degrees).

In general, the optically anisotropic layer is formed by applying a solution in which a discotic compound and another compound are dissolved in a solvent onto an orientation film, drying the solution, and then heating the solution to a discotic nematic phase formation temperature. (Discotic nematic phase) is obtained by cooling. Alternatively, the optically anisotropic layer is formed by applying a solution in which a discotic compound and other compounds (for example, a polymerizable monomer and a photopolymerization initiator) are dissolved in a solvent onto an alignment film, drying, and then discotic nematic It is obtained by heating to a phase forming temperature, polymerizing (by irradiation with UV light or the like), and further cooling. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound used in the present invention is preferably from 70 to
300 ° C is preferable, and 70 to 170 ° C is particularly preferable.

For example, the tilt angle of the discotic unit on the support side can be generally adjusted by selecting a discotic compound or a material of an alignment film, or by selecting a rubbing method. In addition, the tilt angle of the discotic unit on the surface side (air side) generally selects a discotic compound or another compound used together with the discotic compound (eg, a plasticizer, a surfactant, a polymerizable monomer and a polymer). Can be adjusted. Further, the degree of change of the inclination angle can be adjusted by the above selection.

The plasticizer, surfactant and polymerizable monomer are compatible with the discotic compound.
Any compound can be used as long as it can change the tilt angle of the liquid crystalline discotic compound or does not hinder the alignment. Among these, a polymerizable monomer (eg, a compound having a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group) is preferable.
The above compounds are generally used in an amount of 1 to 50% by weight, preferably 5 to 30% by weight, based on the discotic compound.

As the polymer, any polymer can be used as long as it has compatibility with the discotic compound and can change the tilt angle of the liquid crystalline discotic compound. Examples of the polymer include a cellulose ester. Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropylcellulose and cellulose acetate butyrate. The polymer is generally 0.1 to 10% by weight (preferably 0.1 to 8% by weight, particularly 0.1 to 5% by weight) based on the discotic compound so as not to hinder the alignment of the liquid crystalline discotic compound. ). The butyrylation degree of cellulose acetate butyrate (cellulose acetate butyrate) is preferably 30% or more, particularly preferably in the range of 30 to 80%. The degree of acetylation is 3
0% or more, especially the range of 30 to 80% is preferable. Viscosity of cellulose acetate butyrate (ASTM D-81
7-72) is from 0.01 to
A range of 20 seconds is preferred.

The liquid crystal display device having the optically anisotropic layer (optical compensatory sheet) having a changing inclination angle shown in FIG. 8 has an extremely wide viewing angle, and inverts or displays a black and white image. The image has almost no gradation or coloring.

The haze of the optically anisotropic layer is generally 5.0.
% Or less. Therefore, the optically compensatory sheet having the optically anisotropic layer also generally has 5.0% or less because the haze of the transparent support is low. The haze is ASTN-D
1003-52. When the haze of the optically anisotropic layer is high, light leakage which is considered to be caused by scattering occurs in the black display portion, and as a result, the contrast is reduced. This tendency is remarkable when the incident light is inclined in the normal direction and in the upward direction of the image. Therefore, in order to prevent this, the haze is preferably 5% or less, more preferably 3% or less, and particularly preferably 1% or less.

The solution for forming the optically anisotropic layer can be prepared by dissolving the discotic compound and the other compound described above in a solvent. Examples of the solvent include polar solvents such as N, N-dimethylformamide (DMF), dimethylsulfoxide (DMSO) and pyridine; non-polar solvents such as benzene and hexane; alkyl halides such as chloroform and dichloromethane; Esters such as methyl and butyl acetate; ketones such as acetone and methyl ethyl ketone; and ethers such as tetrahydrofuran and 1,2-dimethoxyethane. Alkyl halides and ketones are preferred. The solvents may be used alone or in combination.

The solution can be applied by curtain coating, extrusion coating, roll coating,
Examples include dip coating, spin coating, print coating, spray coating and slide coating. In the present invention, in the case of a mixture of only discotic compounds, a vapor deposition method can also be used. In the present invention, continuous coating is preferred. Therefore, curtain coating, extrusion coating, roll coating and slide coating are preferred. As described above, the optically anisotropic layer is obtained by applying the coating solution on the alignment film, drying the coating solution, and then heating it to a temperature equal to or higher than the glass transition temperature (then, if necessary, hardening) and cooling.

The optical compensatory sheet used in the present invention shows the minimum value of the absolute value of retardation in a direction inclined from the normal direction of the optical compensatory sheet. It is preferable that the optically anisotropic layer shows the minimum value of the absolute value of the retardation in a direction inclined from the normal direction. The direction showing the minimum value is generally inclined from the normal line by 5 to 80 degrees, preferably from 10 to 70 degrees, and particularly preferably from 20 to 60 degrees. | Δn ₃ × d ₃
The retardation (Re) of the optically anisotropic layer represented by | (Δn ₃ represents the birefringence of the optically anisotropic layer and d ₃ represents its thickness) is generally 50 to 1000 nm, and 1
00 to 500 nm is preferred.

FIG. 9 shows an example of a liquid crystal display device having the bend alignment cell of the present invention. A liquid crystal cell PIC comprising a pair of substrates with a transparent electrode having an alignment film on their surfaces and a layer of nematic liquid crystal sealed between them, a pair of polarizing plates A and B provided on both sides of the liquid crystal cell, a liquid crystal cell and a polarizing plate The optical compensation sheets OC1, OC2, and the backlight BL, which are arranged between the two, constitute a liquid crystal display device in combination. The optical compensatory sheet may be disposed on only one side (that is,
OC1 or OC2). Reference numerals R1 and R2 are arrows indicating the rubbing direction, respectively, and correspond to the direction of arrow 85 in FIG. Further, the optically anisotropic layers of the optical compensation sheets OC1 and OC2 are arranged so as to face the liquid crystal cell. However, the optically anisotropic layer may be arranged so as to face the polarizing plate, in which case the arrows R1, R2 are reversed. The solid line arrow RP2 of the liquid crystal cell PIC indicates the rubbing direction on the polarizing plate B side of the liquid crystal cell PIC.
Indicates the rubbing direction on the polarizing plate A side of the liquid crystal cell. PA and PB indicate the transmission axes of the polarizing plates A and B, respectively.

The optically anisotropic layers of the optical compensation sheets OC1 and OC2 are preferably arranged so as to face the liquid crystal cell as described above. In this case, the angle between the arrows R1 and PR1 is generally in the range of −45 to 45 degrees, and is −20 to 20 degrees.
The range of a degree is preferable, and especially the range of -10 to 10 degrees is preferable. The angle between the arrows R2 and PR2 is the same as above. It is preferable that the optical compensation sheets are provided on both sides of the liquid crystal cell. The transmission axes PA and PB are preferably perpendicular or parallel to each other, and the allowable range is usually within 10 degrees. The angle between the arrow PR1 and the transmission axis PA is generally 10 to
80 degrees, preferably 20 to 70 degrees,
Particularly, a range of 35 to 55 degrees is preferable.

FIG. 10 shows an example of a liquid crystal display device having the HAN mode cell of the present invention. A substrate with a transparent electrode having an alignment film on a pair of surfaces, a liquid crystal cell 103 composed of a nematic liquid crystal layer sealed therebetween, a polarizing plate 101 provided on one side of the liquid crystal cell, and a liquid crystal cell and a polarizing plate. Optical compensation sheet 102 and reflector 104 arranged between
Are combined to form a liquid crystal display device. One alignment film of the substrate needs to be a layer capable of homeotropically aligning a nematic liquid crystal. Thereby, the nematic liquid crystal layer can be made to have a hybrid orientation. That is, reference numeral 108 is a vertical alignment layer. A diffusion plate may be further provided on the cell. Reference numeral 106 denotes an arrow indicating the rubbing direction of the optical compensatory sheet.
5 direction. Solid arrow 10 of the liquid crystal cell 103
Reference numeral 7 denotes a rubbing direction on the upper side of the liquid crystal cell.

The optically anisotropic layer of the optical compensation sheet 102 is preferably arranged so as to face the liquid crystal cell as described above. In this case, the angle between the arrows 106 and 107 is generally in the range of -45 to 45 degrees, preferably in the range of -20 to 20 degrees, and particularly preferably in the range of -10 to 10 degrees.
The angle between the arrow 107 and the transmission axis 105 is generally 10 to 80.
Degree, preferably in the range of 20 to 70 degrees, particularly preferably 35 to 55 degrees.

The retardation (Re) of the liquid crystal layer of the liquid crystal cell represented by | Δn ₁ × d ₁ | (Δn ₁ represents the birefringence of the liquid crystal layer of the liquid crystal cell and d ₁ represents its thickness)
Is generally 300 to 31000 nm. In the bend alignment cell, the retardation is generally 700 to
It is 2000 nm, and preferably 800 to 1800 nm. In HAN mode cells, the retardation is generally between 350 and 1000 nm, and between 400 and 90 nm.
0 nm is preferred.

[0074]

【Example】

(1) Preparation of Bend Alignment Liquid Crystal Cell A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and a rubbing treatment was performed. Two glass substrates having such an alignment film are opposed to each other so that the rubbing directions are parallel to each other, are joined at a cell gap of 10 μm, and a liquid crystal ZLI1132 manufactured by Merck (Δn ₁ = 0.1396) is used.
Was injected to produce a bend alignment liquid crystal cell. The retardation (Re ₂ ) of the liquid crystal layer of the obtained liquid crystal cell was 13
96 nm.

(2) Preparation of HAN type liquid crystal cell A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and rubbing treatment was performed. Another glass substrate with an ITO electrode was prepared, and a SiO vapor deposition film was provided as an alignment film. The two glass substrates were arranged so that the alignment films faced each other, joined at a cell gap of 5 μm, and injected with a liquid crystal ZLI1132 (Δn = 0.1396) manufactured by Merck to produce a HAN type liquid crystal cell. The retardation (Re ₂ ) of the liquid crystal layer of the obtained liquid crystal cell is 698 nm.

(3) Preparation of Optical Compensation Sheet A Acrylate-modified terminal alkyl-containing polyvinyl was coated on a 100 μm thick triacetyl cellulose film (Fuji Photo Film Co., Ltd.) coated with a gelatin thin film (0.1 μm). A coating solution containing an alcohol (the following compound (1)) was applied, dried with hot air at 80 ° C., and then subjected to a rubbing treatment to form an alignment film.

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The in-plane principal refractive index is n_x , N_y In the thickness direction
Refractive index n_z , Thickness d_Two And triacetyl cellulose
Of source film_x -N_y | × d, ｛(n_x + N_y )
/ 2-n_z ｝ × d was determined. Thickness, micrometer
And Re from various directions is measured using
Psometer (AEP-100, manufactured by Shimadzu Corporation)
From the above | n_x -N_y | × d_Two , ｛(N_x + N
_y ) / 2-n_z ｝ × d _Two It was determined. The above triacetyl
Of cellulose film | n_x -N_y | × d_Two Is 5 nm
And ｛(n_x + N_y ) / 2-n_z ｝ × d_Two Is 40nm
there were. Therefore, the above triacetyl cellulose film
Is almost negative uniaxial, and its optical axis is almost
Was in the direction.

1.8 g of the above-mentioned liquid crystalline discotic compound TE-8 (8, m = 4) (the above compound example number) and ethylene glycol-modified trimethylolpropane triacrylate (V # 360; Osaka) Organic Chemical Industry Co., Ltd.) 0.2 g, cellulose acetate butyrate (CAB551-0.2; manufactured by Eastman Chemical Company) 0.04 g, photopolymerization initiator (Irgacure-90)
7; Ciba Geigy) and 0.02 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.)
A coating solution obtained by dissolving in 3.43 g of methyl ethyl ketone was applied with a wire bar (# 3 bar), attached to a metal frame, fixed, and heated in a high-temperature bath at 120 ° C. for 3 minutes. After aligning the tick compound, 120 ° C
1 minute using a high pressure mercury lamp (120 W / cm)
Irradiated with V and allowed to cool to room temperature to prepare an optical compensation sheet A of the present invention having a layer (optically anisotropic layer) containing a discotic compound having a thickness of 1.0 μm.

The optical compensation sheet A thus obtained
Was measured along the rubbing direction with an ellipsometer (AEP-100) manufactured by Shimadzu Corporation. The results shown in FIG. 11 (retardation and viewing angle (angle in which the viewing direction was inclined from the normal). Relationship with))
was gotten. As can be seen from FIG. 11, this optical compensatory sheet has no direction in which the retardation becomes zero. Simulation based on this value revealed that the average inclination angle in the direction of the minimum Re value was 21 °.

When the retardation value of only the optically anisotropic layer (discotic liquid crystal layer) was measured along the rubbing axis, the results shown in FIG. 12 (retardation and viewing angle (viewing direction from normal line) Relationship) was obtained. Even in the discotic liquid crystal layer alone, there was no direction in which the retardation was 0. As a result of simulation, the direction of the minimum value of Re shows a hybrid orientation in which the direction of the Re changes continuously from 4 ° to 68 ° in the thickness direction with respect to the normal direction of the sheet, and the retardation of | Δn ₃ · d ₃ | I found it. The retardation (Re ₁ ) of the optical compensation sheet A was 314 nm ((40 nm + 117 nm) ××) in the bend alignment cell.
2), and 157 nm (40 n) in the HAN mode cell.
m + 117 nm).

(4) Production of Optical Compensation Sheet B In the production of the optical compensation sheet A, a transparent support was used.
The following polycarbonate film is used instead of the TAC film.
Using a film, the thickness of the optically anisotropic layer is from 1 μm to 5 μm.
Was changed in the same manner as in the production of the optical compensation sheet A, except that
An optical compensation sheet B was produced. (Polycarbonate film) phosgene and bisphenol
Polycarbonate having a molecular weight of 120,000 obtained by condensation of
The solution was dissolved in methylene dichloride to give an 18% solution. This
It is cast on a steel drum and continuously stripped off.
Dry while axially stretching to obtain a film with a thickness of 60 μm
Was. This film was converted to an ellipsometer AEP-100
Therefore, the retardation value was measured and converted to a refractive index.
Where n_x = 1.540, n_y = 1.540, n_z =
1.536. n_x , N_y Is in the plane and n_z Is
It was the normal direction. | N_x -N_y | × d_Two Is 0 nm,
｛(N_x + N_y ) / 2-n_z ｝ × d _Two Is 240 nm
Was. Δn_Two (450 nm) / Δn_Two (600nm)
Was 1.1.

The optical compensation sheet B thus obtained
The retardation value of the optically anisotropic layer was adjusted along the rubbing direction by an ellipsometer (AEP-10, manufactured by Shimadzu Corporation).
0), it was found that there was no direction in which the retardation was zero. A simulation based on these data revealed that the average inclination angle in the direction of the minimum Re value was 36 ° and the retardation of | Δn ₃ · d ₃ | was 160 nm. The retardation (Re ₁ ) of the optical compensation sheet B is 800 nm in the bend alignment cell.
((240 nm + 160 nm) × 2).

The obtained optical compensatory sheet (B) of the present invention was cut along the depth in the rubbing direction using a microtome to produce an extremely thin film (sample). The sample was left to stand in an OsO ₄ atmosphere for 48 hours and stained. The obtained dyed film was observed with a transmission electron microscope (TEM), and a micrograph was obtained. In the dyed film, discotic compound TE-8
The acryloyl group of (8, m = 4) was stained and recognized as a photographic image. From this photograph, the discotic compound of the optically anisotropic layer is inclined from the surface of the transparent support,
Further, it was recognized that the inclination angle continuously increased with an increase in the distance in the depth direction from the bottom of the optically anisotropic layer.

(5) Preparation of Optical Compensation Sheet C Polycarbonate having a molecular weight of 120,000 obtained by condensation of phosgene and bisphenol A was dissolved in methylene dichloride to obtain an 18% solution. This was cast on a steel drum, continuously peeled off, and dried while being unbalanced biaxially stretched to obtain a film having a thickness of 60 μm. When this film by ellipsometer AEP-100 to measure the retardation value, in terms of refractive index, n _x =
1.546, n _y = 1.540, was n _z = 1.533. _nx and _ny were in the plane and _nz was the normal direction.

(6) Preparation of Optical Compensation Sheet D As in the preparation of the optical compensation sheet C, polycarbonate was unbalanced biaxially stretched to have a thickness of 50%.
A μm film was obtained. The stretching ratio was changed from that of the optical compensation sheet C. This film is used for ellipsometer AEP
-100 by measuring the retardation value and converting to the refractive _{index, n x = 1.544, n y} = 1.54
0, _nz = 1.536. _nx and _ny were in the plane and _nz was the normal direction.

Example 1 In the bend alignment liquid crystal cell prepared in the above (1), two optical compensation sheets A were arranged so as to sandwich the cell, and the discotic liquid crystal layer side was opposed to the cell. The rubbing direction of the bend alignment liquid crystal cell and the rubbing direction of the optical compensation sheet A were arranged so as to be antiparallel. Outside, on the optical compensation sheet, a polarizing plate was arranged in crossed Nicols. Thus, a liquid crystal display device was manufactured. The obtained liquid crystal display device has a structure shown in FIG.

A voltage was applied to this liquid crystal display device with a 55 Hz rectangular wave. N of white display 2.5V, black display 6V
In the W mode, the ratio of transmittance (white display) / (black display) was defined as the contrast ratio, and the measurement of the contrast ratio from the top, bottom, left, and right was performed on an LCD-5000 manufactured by Otsuka Electronics Co., Ltd. Upper / lower and left / right viewing angles with a contrast of 10 or more were determined. Table 1 shows the obtained results.

Example 2 A liquid crystal display device was manufactured in the same manner as in Example 1 except that the optical compensation sheet B was used instead of the optical compensation sheet A. The evaluation of the liquid crystal display was performed in the same manner as in the example. Table 1 shows the obtained results.

[Comparative Example 1] The optical compensation sheet C was placed on the near side (viewing side) of the bend alignment liquid crystal cell prepared in the above (1).
One, the direction of n _y in the rubbing direction and the optical compensation sheet C of the bend-aligned liquid crystal cell is arranged to match the. Polarizing plates were arranged in crossed Nicols so as to sandwich the whole outside. Thus, a liquid crystal display device was manufactured. A voltage was applied to this liquid crystal display device with a 55 Hz rectangular wave. An NB mode with a white display of 6 V and a black display of 2.5 V is used, and the transmittance ratio (white display) / (black display) is defined as the contrast ratio, and the contrast ratio measurement from the top, bottom, left and right is made by Otsuka Electronics Co., Ltd. LCD- 5000. Upper / lower and left / right viewing angles with a contrast of 10 or more were determined.
Table 1 shows the obtained results.

[0092]

[Table 1] Table 1 ──────────────────────────────────── Sheet Front contrast viewing angle (degree ) No. Up, down, left, right ──────────────────────────────────── Example 1 (A) 100 or more 120 or more 120 or more Example 2 (B) 100 or more 120 or more 120──────────────────────────────────── Comparative Example 1 (C) 100 or more 68 76 実 施 Examples 1 to 5 of the present invention It can be seen that the liquid crystal display device obtained in No. 2 has significantly improved viewing angle characteristics as compared with the liquid crystal display device of Comparative Example 1.

Example 3 In the HAN type liquid crystal cell prepared in (2), one optical compensatory sheet A was arranged on the near side (viewing side), and the discotic liquid crystal layer side was arranged close to the cell. The rubbing direction of the HAN type liquid crystal cell and the rubbing direction of the optical compensation sheet A were arranged to be antiparallel. A polarizing plate was arranged on the near side so that the angle between the transmission axis and the rubbing direction of the liquid crystal cell was 45 °, and a diffusing plate was further arranged on the near side of the polarizing plate. On the opposite surface, a mirror was arranged outside the glass substrate, and a reflective liquid crystal display device was manufactured. The obtained liquid crystal display device has a structure provided with a diffusion plate in addition to the structure shown in FIG.

The reflection type liquid crystal display device has two pixels from the normal direction.
The light source was placed in a direction inclined by 0 °, and light was irradiated. A voltage was applied to the liquid crystal cell with a 55 Hz rectangular wave. White display 2.5
V, black display 6V, in NW mode, the contrast ratio (white display) / (black display) is defined as the contrast ratio, and the contrast ratio measurement from the top, bottom, left and right is made by TOPCON Co., Ltd. b
m-7. Upper / lower and left / right viewing angles with a contrast of 10 or more were determined. Table 2 shows the obtained results.

[Comparative Example 2] In the HAN type liquid crystal cell prepared in (2), one optical compensation sheet D was placed on the near side (viewing side), the rubbing direction of the HAN type liquid crystal cell and n _{y of the} optical compensation sheet D were compared. Were arranged so as to match the direction. On the near side, a polarizing plate is arranged so that the angle between the transmission axis and the rubbing direction of the liquid crystal cell is 45 °, and a white plate diffusion plate containing TiO2 powder is placed on the polarizing plate, A reflection plate was provided on the opposite side (rear side) of the liquid crystal cell to produce a reflection type liquid crystal display device. The contrast ratio was measured in the same manner as in Example 2 except that a voltage of 55 Hz square wave was applied to the liquid crystal cell to set the NB mode to 6 V for white display and 2.5 V for black display. Upper / lower and left / right viewing angles with a contrast of 10 or more were determined. Table 2 shows the obtained results.

[0096]

[Table 2] Table 2 シ ー ト Sheet Front contrast viewing angle (degree ) No. Up, down, left, right {Example 3 (A) 30 64 73} ───────────────────────────────── Comparative Example 2 (D) 25 45 52 ────────液晶 The liquid crystal display device obtained in Example 3 of the present invention was
It can be seen that the viewing angle characteristics are greatly improved as compared with the liquid crystal display device of the above.

[0097]

The bend alignment liquid crystal cell or HAN of the present invention.
A liquid crystal display device using a mode liquid crystal cell includes a specific optical compensation sheet. This optical compensatory sheet shows the minimum value of the absolute value of retardation in a direction inclined from the normal direction. Such a liquid crystal display device,
The viewing angle is greatly enlarged, and the occurrence of inversion of the black display portion, inversion of gradation, coloring of an image, and the like accompanying the increase in the viewing angle is greatly reduced, and excellent viewing angle characteristics are exhibited. Further, the optical compensation sheet of the present invention may be a three-terminal element such as MIM, TFD
It goes without saying that excellent effects can be obtained even when the present invention is applied to an active matrix liquid crystal display element using a two-terminal element.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a liquid crystal cell for a TN type liquid crystal display device.

FIG. 2 is an enlarged sectional view of a bend alignment liquid crystal cell.

FIG. 3 is an enlarged sectional view of a HAN mode liquid crystal cell.

FIG. 4 is a schematic diagram showing the principle that the viewing angle characteristic of a liquid crystal cell assuming positive uniaxiality is improved by a negative uniaxial optically anisotropic body.

FIG. 5 is an example for explaining the principle of retardation compensation in a liquid crystal display device having a bend alignment cell of the present invention.

FIG. 6 is a diagram of another example for explaining the principle of retardation compensation in a liquid crystal display device having a bend alignment cell of the present invention.

FIG. 7 is an example for explaining the principle of retardation compensation in a liquid crystal display device having a HAN mode cell of the present invention.

FIG. 8 is a view showing a typical structure of an optically anisotropic layer of an optical compensation sheet used in the liquid crystal display device of the present invention.

FIG. 9 is a diagram showing a typical structure of a liquid crystal display device using the bend liquid crystal cell of the present invention.

FIG. 10 is a diagram showing a typical structure of a liquid crystal display device using a HAN mode liquid crystal cell of the present invention.

FIG. 11 is a diagram showing the angle dependence of the retardation value of the optical compensation sheet used in Example 1.

FIG. 12 is a diagram showing the angle dependence of the retardation value of the optically anisotropic layer of the optical compensation sheet used in Example 1.

[Explanation of symbols]

11, 21 Liquid crystal cell 14a, 14b, 24a, 24b, 33a, 33b Substrate with transparent electrode 12, 22a, 22b, 32 Director region (field) 16, 26a, 26b, 36 Surface contact director 13, 28a, 28b, 38 Bulk director 15, 29 Angle 17, 18, 20, 27, 34 Light ray 23 Center line 41, 53, 64, 66, 73 Negative uniaxial optically anisotropic body 42, 51, 61, 63, 71 Optical compensation sheet 43 Liquid crystal layer of liquid crystal cell 44, 54, 65, 74 Positive uniaxial optically anisotropic material 52, 62 Liquid crystal layer of bend alignment cell 72 HAN mode liquid crystal layer 86 Transparent support 82 Alignment film 83 Optically anisotropic layer 83a, 83b, 83c Liquid crystal discotic compound Pa, Pb, Pc Surface of discotic structural unit 81a, 81 , 81c Surface parallel to the surface of the transparent support 81 θa, θb, θc Tilt angle 84 Normal line of the transparent support 85 The direction when the direction showing the minimum value of Re of the optically anisotropic layer is projected onto the transparent support Arrows shown PIC Liquid crystal cells A, B Polarizer OC1, OC2 Optical compensation sheet BL Backlight R1, R2 Rubbing direction of optical compensation sheet RP1 Rubbing direction of polarizer A side of liquid crystal cell RP2 Rubbing direction of polarizer B side of liquid crystal cell 3 shows the transmission axis of PA polarizing plate A. PB Transmission axis of polarizing plate B 103 Liquid crystal cell 101 Polarizing plate 102 Optical compensation sheet 103 Reflecting plate 106 Rubbing direction of optical compensation sheet 107 Upper rubbing direction of liquid crystal cell 108 Vertical alignment layer

Claims (14)

[Claims] 1. A liquid crystal cell in which a layer of nematic liquid crystal is sealed between a pair of substrates with a transparent electrode having an alignment film on a pair of surfaces, and polarizing plates provided on both sides of the liquid crystal cell. In a liquid crystal display device in which the layer exhibits bend alignment, and the angle of the alignment vector of the nematic liquid crystal with respect to the substrate is changed by a change in voltage applied to the liquid crystal cell, the liquid crystal display device has a structure in which A liquid crystal display device, further comprising an optical compensation sheet, wherein the optical compensation sheet exhibits a minimum absolute value of retardation in a direction inclined from a normal direction of the optical compensation sheet. 2. The liquid crystal display device according to claim 1, wherein the optical compensatory sheet comprises a transparent support and an optically anisotropic layer provided on the transparent support and comprising a compound having a discotic structural unit. 3. The disk surface of the discotic structural unit of the optically anisotropic layer is inclined with respect to the transparent support surface, and the angle formed between the disk surface of the discotic structural unit and the transparent support surface is an optically anisotropic layer. The liquid crystal display device according to claim 2, wherein the liquid crystal display device changes in a depth direction of the layer. Wherein the transparent support has an optical axis in a normal direction of the transparent support surface, further the following _{conditions: 20 ≦ {(n x +} n y) / 2-n z} × d 2 ≦ 400 (However, n _x and n _y represent the main refractive index in the plane of the support, n _z represents the main refractive index in the thickness direction, d ₂ represents the thickness of nm in terms of the support) satisfies The liquid crystal display device according to claim 2. 5. The liquid crystal display device according to claim 2, wherein an alignment film is formed between the transparent support and the optically anisotropic layer. 6. A absolute value of the letter de Deployment represented by the following absolute values Re ₁ and the liquid crystal layer of the total letter de Deployment represented by optical compensation sheet all of the following Re ₂ is the following relationship: 0.2 × Re ₂ ≦ Re ₁ ≦ 2.0 × Re ₂ [where the retardation of the optical compensation sheet is {(n ₂ + n ₃ ) / 2−n ₁ } × d (where n ₁ , n ₂
And n ₃ represent the three-axis refractive index of the sheet, each having a smaller refractive index in this order, and d representing the thickness of the sheet in nm), and the retardation of the liquid crystal layer. Is Δn ₃ − (n ₁ + n ₂ )
/ 2｝ × d (where n ₁ , n ₂ and n ₃ represent the three-axis refractive index of the liquid crystal layer, each having a smaller refractive index in this order, and d is the nm of the liquid crystal layer in terms of nm. The liquid crystal display device according to claim 1, wherein 7. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is used in a normally white mode. 8. A liquid crystal cell in which a nematic liquid crystal layer is sealed between a pair of substrates with a transparent electrode having an alignment film on their surfaces and one of the alignment films is a layer capable of homeotropically aligning the nematic liquid crystal. A polarizing plate provided on one side of the cell, and a reflector provided on the other side of the liquid crystal cell, and the layer of nematic liquid crystal shows a hybrid alignment, and a substrate of an alignment vector of nematic liquid crystal. The liquid crystal display device in which the angle with respect to changes with the change in the voltage applied to the liquid crystal cell, is provided with an optical compensation sheet between the liquid crystal cell and the polarizing plate, and the optical compensation sheet is formed of the optical compensation sheet. A liquid crystal display device which shows a minimum value of an absolute value of retardation in a direction inclined from a normal direction. 9. The liquid crystal display device according to claim 8, wherein the optical compensation sheet comprises a transparent support and an optically anisotropic layer provided on the transparent support and comprising a compound having a discotic structural unit. 10. The disk surface of the discotic structural unit of the optically anisotropic layer is inclined with respect to the surface of the transparent support, and the angle formed between the disk surface of the discotic structural unit and the surface of the transparent support is an optically anisotropic layer. The liquid crystal display device according to claim 9, wherein the liquid crystal display device changes in a depth direction of the layer. 11. transparent support has an optical axis in a normal direction of the transparent support surface, further the following _{conditions: 20 ≦ {(n x +} n y) / 2-n z} × d 2 ≦ 400 (However, n _x and n _y represent the main refractive index in the plane of the support, n _z represents the main refractive index in the thickness direction, d ₂ represents the thickness of nm in terms of the support) satisfies The liquid crystal display device according to claim 9. 12. The liquid crystal display device according to claim 9, wherein an alignment film is formed between the transparent support and the optically anisotropic layer. 13. the absolute value Re ₁ letter de Deployment represented by the following optical compensation sheet, and the absolute value Re ₂ letter de Deployment represented by the liquid crystal layer is, the following relationship: 0.2 × Re ₂ ≦ Re ₁ ≦ 2.0 × Re ₂ [where the retardation of the optical compensation sheet is {(n ₂ + n ₃ ) / 2−n ₁ } × d (where n ₁ , n ₂
And n ₃ represent the three-axis refractive index of the sheet, each having a smaller refractive index in this order, and d representing the thickness of the sheet in nm), and the retardation of the liquid crystal layer. Is Δn ₃ − (n ₁ + n ₂ )
/ 2｝ × d (where n ₁ , n ₂ and n ₃ represent the three-axis refractive index of the liquid crystal layer, each having a smaller refractive index in this order, and d is the nm of the liquid crystal layer in terms of nm. The liquid crystal display device according to claim 8, which satisfies the formula: 14. The liquid crystal display device according to claim 8, which is used in a normally white mode.