JP2005099329A - Retardation plate and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display, particularly, a retardation plate for contributing to the improvement of the field angle of the liquid crystal display of an IPS mode and STN mode. <P>SOLUTION: The retardation plate includes a transparent support, an alignment film formed of a composition having an acid effectively acting polyvinyl alcohol-based polymer, a multifunctional aldehyde compound crosslinking and hard-coating the polymer and a crosslinking hard coating thereon, and an optical anisotropic layer aligned and controlled on a rubbing processing face of the alignment film, and formed of a discotheque liquid crystal compound fixed in the alignment state. The optically anisotropic layer contains an additive enlarging an angle making a vertical line of a director and a layer plane in an air interface of molecules of the discotic-type liquid crystal compound more than a non-addition state. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a retardation plate having an optically anisotropic layer containing a discotic liquid crystalline compound that is controlled in alignment by a specific alignment film and fixed in the alignment state, and a liquid crystal display using the retardation plate Relates to the device.

  A liquid crystal display device usually has a liquid crystal cell and a polarizing plate. The polarizing plate is 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 both surfaces with a protective film. In the transmissive liquid crystal display device, the polarizing plate is attached to both sides of the liquid crystal cell, and one or more optical compensation sheets may be disposed. In a reflective liquid crystal display device, a reflector, a liquid crystal cell, one or more optical compensation sheets, and a polarizing plate are arranged in this order. The liquid crystal cell includes a liquid crystal molecule, two substrates for encapsulating the liquid crystal molecule, and an electrode layer for applying a voltage to the liquid crystal molecule. The liquid crystal cell performs ON / OFF display depending on the alignment state of liquid crystal molecules, and can be applied to both transmission and reflection types. TN (Twisted Nematic), IPS (In-Plane Switching), OCB (Optically Compensatory Bend) ), VA (Vertical Aligned), ECB (Electrically Controlled Birefringence), and STN (Super Twisted Nematic).

  Optical compensation sheets are used in various liquid crystal display devices in order to eliminate image coloring and expand the viewing angle. For example, an STN type liquid crystal display device includes an STN type liquid crystal cell, two polarizing plates, and one or two optical compensation sheets (retardation plates) provided between the STN type liquid crystal cell and the polarizing plate. The liquid crystal cell is composed of a rod-like liquid crystal molecule, two substrates for enclosing it, and an electrode layer for applying a voltage to the rod-like liquid crystal molecule. In the STN type liquid crystal cell, an alignment film for aligning rod-like liquid crystalline molecules is provided on two substrates. Further, the rod-like liquid crystalline molecules are twisted and aligned at 180 to 360 degrees using a chiral agent. In an STN type liquid crystal display device without an optical compensation sheet, the display image is colored blue or yellow due to the birefringence of rod-like liquid crystal molecules. The coloring of the display image is inconvenient for both monochrome display and color display. The optical compensation sheet is used for eliminating such coloring and obtaining a bright and clear image. The optical compensation sheet may also be given a function of expanding the viewing angle of the liquid crystal cell. As the optical compensation sheet, a stretched birefringent polymer film has been conventionally used (see Patent Documents 1 and 2). Further, it has been proposed to use an optical compensation sheet having an optically anisotropic layer formed from low-molecular or high-molecular liquid crystalline molecules on a transparent support, instead of an optical compensation sheet comprising a stretched birefringent film. Yes. Since liquid crystalline molecules have various alignment forms, the use of liquid crystalline molecules can realize optical properties that cannot be obtained with conventional stretched birefringent polymer films (see Patent Document 3).

  The optical properties of the optical compensation sheet are determined according to the optical properties of the liquid crystal cell, specifically, the display mode differences as described above. When liquid crystalline molecules are used, optical compensation sheets having various optical properties corresponding to various display modes of the liquid crystal cell can be produced. Optical compensation sheets using liquid crystal molecules have already been proposed for various display modes. For example, in order to optically compensate an STN type liquid crystal cell using discotic liquid crystalline molecules, it is necessary to align the discotic liquid crystalline molecules substantially vertically (homogeneous alignment). It is preferable that the discotic liquid crystalline molecules are further twisted and aligned (see Patent Document 4).

  The optical compensation sheet for a TN mode liquid crystal cell performs optical compensation by an optical anisotropic layer made of liquid crystal tilted with respect to the substrate surface while eliminating the twisted structure of the liquid crystal molecules in the liquid crystal cell when a voltage is applied. The contrast viewing angle characteristic is improved by preventing light leakage in an oblique direction during black display (see Patent Document 5). In recent years, an IPS liquid crystal panel in which the longitudinal direction of rod-like liquid crystal molecules is always aligned in parallel with and close to the plane direction of a glass substrate sandwiching the rod-like liquid crystal molecules has been manufactured and put on the market. In the IPS mode, the viewing angle characteristic is considerably wider than that of the TN liquid crystal panel due to the characteristics of the liquid crystal mode, and a retardation film for optical compensation is not so required. However, in a conventional liquid crystal device including such an IPS mode liquid crystal panel, there is a direction with a slightly narrower viewing angle in consideration of the alignment direction of liquid crystal molecules, and leakage light is generated in this direction. As an optical compensation sheet for an IPS mode liquid crystal cell, a function of optical compensation of liquid crystal molecules aligned in parallel to the substrate surface is required during black display in a voltage-free state (see Patent Document 6). In addition, as a retardation film for improving the viewing angle of an IPS mode liquid crystal panel, it is a retardation film having negative uniaxial anisotropy, and a disc surface of discotic liquid crystal molecules is transparent on a transparent sheet. A retardation plate having an optically anisotropic layer that is oriented and fixed so as to be perpendicular or substantially perpendicular to the surface direction of the support is disclosed (see Patent Document 7).

That is, as a retardation film for optical compensation of an STN mode liquid crystal panel or an IPS mode liquid crystal panel, discotic liquid crystal molecules are aligned with the disk surface perpendicular or substantially perpendicular to the surface direction of the support. It is required to be fixed, and an alignment film used for this purpose is required. As an alignment film for standing a discotic liquid crystalline compound vertically or substantially vertically, an alignment film having a low surface energy (see Patent Documents 8 and 9) and an excluded volume effect alignment film (see Patent Document 10) are disclosed. ing. However, as a result of studies by the present inventors, problems such as orientation defects or repelling during orientation occurred in these orientation films. In addition, since it has high functionality, it is necessary to modify the polymer or synthesize the polymer using a special monomer. As a result, the alignment film becomes expensive and industrially cheaper. An alignment film has been desired.
JP-A-7-104284, JP-A-7-13021 JP 2000-104073 A JP-A-9-26572 JP-A-6-214116 Japanese Patent Laid-Open No. 10-54982 Japanese Patent Laid-Open No. 9-292522 JP 2000-56310 A JP 2000-104073 A JP 2000-105316 A

  The present invention has been made in view of the above-mentioned problems, and is formed by fixing molecules of a discotic liquid crystalline compound in a state in which the disc surface is oriented with (substantially) perpendicular to the layer plane. It is an object to provide a retardation plate having an optically anisotropic layer. It is another object of the present invention to provide a retardation plate that contributes to the improvement of the viewing angle of liquid crystal display devices, particularly STN liquid crystal display devices and IPS liquid crystal display devices. It is another object of the present invention to provide not only display quality but also a liquid crystal display device in which a viewing angle is remarkably improved, particularly an STN type liquid crystal display device and an IPS type liquid crystal display device.

  As a result of intensive studies by the present inventors, the molecules of the discotic liquid crystalline compound are aligned on the air interface on an alignment film formed from a composition obtained by adding a polyfunctional aldehyde compound and an inorganic or organic acid to a polyvinyl alcohol polymer. It has been found that by aligning in the presence of a control agent, the discotic liquid crystal compound molecules can be aligned with the disk surface (substantially) perpendicular to the layer plane. Further studies were made based on this finding, and the present invention was completed. JP-A-10-2188938 discloses a technique for forming an alignment film by applying a composition obtained by adding a bifunctional aldehyde compound and an inorganic or organic acid to a polyvinyl alcohol polymer on a substrate. A state in which the discotic liquid crystalline compound is (substantially) vertically aligned has not been obtained.

The above problems have been solved by the following means.
[1] An alignment film formed from a transparent support, a polyvinyl alcohol polymer thereon, a polyfunctional aldehyde compound capable of crosslinking and hardening the polymer, and an acid that effectively acts on the crosslinking film A retardation plate comprising an optically anisotropic layer formed of a discotic liquid crystalline compound, the orientation of which is controlled on the rubbing surface of the alignment film and fixed in the alignment state. A phase difference plate, wherein the isotropic layer contains an additive capable of making an angle formed by a director at the air interface of molecules of the discotic liquid crystalline compound and a perpendicular of a layer plane larger than that in a non-added state.
[2] The retardation plate according to [1], wherein the acid has an acid dissociation constant of 10 ⁻⁵ or more.
[3] The retardation plate according to [1] or [2], wherein the additive is a compound represented by the following general formula (V).
General formula (V)
(Hb−L ² −) _n B ¹
(In the formula, Hb represents an aliphatic group having 6 to 40 carbon atoms or an aliphatic substituted oligosiloxanoxy group having 6 to 40 carbon atoms, and L ² represents —O—, —S—, —CO—, —NR ⁵ —, —SO ₂ —, a divalent linking group selected from the group consisting of an alkylene group, an alkenylene group, an arylene group and a combination thereof, R ⁵ represents a hydrogen atom or an alkyl having 1 to 6 carbon atoms. Represents a group, n represents an integer of 2 to 12, and B ¹ represents an n-valent group containing at least three ring structures.)

[4] A pair of polarizing plates, a pair of glass substrates disposed between the pair of polarizing plates, and a liquid crystal cell composed of rod-like liquid crystal molecules having positive uniaxial anisotropy sandwiched between the glass substrates. The liquid crystal cell is a liquid crystal display device driven in a mode in which the long axis of the rod-like liquid crystal molecules is always aligned in parallel or substantially parallel to the surface direction of the glass substrate, and at least one of the pair of polarizing plates A liquid crystal display device having the retardation plate according to any one of [1] to [3] between one side and the liquid crystal cell.
[5] Two disc polarizing plates, an STN liquid crystal cell disposed therebetween, and a discotic liquid crystalline compound disposed between the STN liquid crystal cell and one or both of the two polarizing plates A STN-type liquid crystal display device having at least one optically anisotropic layer formed from a composition containing the same, wherein the optically anisotropic layer is a polyvinyl alcohol polymer, and a polyfunctional film capable of crosslinking and hardening the polymer. On an alignment film formed from a composition containing an acid that effectively acts on an aldehyde compound and a cross-linked dura, the discotic liquid crystalline compound molecules are arranged such that the disk surface is perpendicular or substantially perpendicular to the layer plane. A layer formed by being controlled in a substantially monodomain and in a twisted orientation state with a twist angle in the range of 90 to 360 degrees, and fixed in that orientation state. STN liquid crystal display device.

  According to the present invention, a retardation having an optically anisotropic layer formed by fixing molecules of a discotic liquid crystalline compound in a state in which the disc surface is oriented with (substantially) perpendicular to the layer plane. A board can be provided stably. The retardation plate of the present invention contributes to the improvement of the viewing angle of liquid crystal display devices, particularly STN type liquid crystal display devices and IPS type liquid crystal display devices.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.
The retardation plate of the present invention comprises an optically anisotropic layer containing a transparent support, a specific alignment film, and a discotic liquid crystalline compound in which the alignment is controlled on the alignment film and fixed in the alignment state. Have.
[Optical properties of retardation plate]
The retardation plate of the present invention preferably has a total in-plane retardation (Re) of 20 to 200 nm. Moreover, it is preferable that the retardation (Rth) of the thickness direction of the whole phase difference plate is 50-500 nm. In-plane retardation (Re) and retardation in the thickness direction (Rth) of the retardation film are respectively defined by the following equations. Here, d ₂ is the thickness (μm) of the optical compensation sheet.
Re = (nx−ny) × d ₂
Rth = ((nx + ny) / 2−nz) × d ₂

[Alignment film]
In the present invention, the alignment film is formed from a composition containing a polyvinyl alcohol-based polymer, a polyfunctional aldehyde compound capable of crosslinking and hardening the polymer, and an acid that effectively acts on the crosslinking and hardening film. As a usable polyvinyl alcohol-based polymer, a polyvinyl alcohol-based polymer disclosed in JP-A-10-2188938 can be preferably used. That is,
1) Unmodified polyvinyl alcohol,
2) modified polyvinyl alcohol,
3) A polyvinyl alcohol derivative represented by the following general formula (I):
4) A polyvinyl alcohol derivative in which at least one hydroxyl group is substituted with a group represented by the following general formula (II):
5) A polyvinyl alcohol derivative represented by the following general formula (III):
It is.

In the general formula (I), L ¹¹ represents an ether bond, a urethane bond, an acetal bond or an ester bond. When L ¹¹ represents an acetal bond, the acetal bond is bonded to the main chain with two Os, and one side chain is bonded to L (-CH ₂ —CH—CH ₂ —CH) — via L ^11. and those that are (hereinafter, also applies to the formula (III).) R ¹¹ represents an alkylene group, L ¹² represents a linking group connecting the R ¹¹ and Q ^11, Q ¹¹ is, Represents a vinyl group, an oxiranyl group or an aziridinyl group, and under the condition of x1 + y1 + z1 = 100, x1 is 10 to 99.9 mol%, y1 is 0.01 to 80 mol%, and z1 is 0 to 70 mol%, K and h are 0 or 1, respectively.

In the general formula (II), R ²¹ represents an unsubstituted alkyl group, an unsubstituted alkoxy group, or an alkyl group, an alkoxy group, an aryl group, a halogen, a vinyl group, a vinyloxy group, an oxiranyl group, an acryloyloxy group, or a methacryloyl group. It represents an alkyl group substituted with at least one substituent selected from the group consisting of oxy and crotonoyloxy groups. W ²¹ represents an unsubstituted alkyl group, an unsubstituted alkoxy group, or an alkyl group, an alkoxy group, an aryl group, a halogen, a vinyl group, a vinyloxy group, an oxiranyl group, an acryloyloxy group, a methacryloyloxy group, and a crotonoyloxy group. It represents an alkyl group or an alkoxy group substituted with at least one selected. The alkyl chain of the unsubstituted or substituted alkyl group and the substituted or unsubstituted alkoxy group may be linear, branched or cyclic, or a combination thereof. q is 0 or 1, and n is an integer of 0-4.

In the general formula (III), L ³¹ represents an ether bond, a urethane bond, an acetal bond or an ester bond. A ³¹ represents an arylene group, R ³¹ represents an alkylene group, L ³² represents a linking group connecting the R ³¹ and Q ^31, Q ³¹ represents a vinyl group, an oxiranyl group or aziridinyl group. Under the condition of x2 + y2 + z2 = 100, x2 is 10 to 99.9 mol%, y2 is 0.01 to 80 mol%, and z2 is 0 to 70 mol%, and k1, h1, and f are each 0 or 1 It is.

  Details, preferred ranges, and specific examples of the compounds represented by the general formulas (I) to (III) are described in columns 0018 to 0073 of JP-A-10-2188938, and the present invention also includes Can be applied.

Specific examples of the polyfunctional aldehyde used for preparing the alignment film include the following. Moreover, you may add polyfunctional aldehyde as equivalents, such as an acetal body.
1) Aliphatic bifunctional aldehydes such as glyoxal, malonaldehyde, succinaldehyde, glutaraldehyde, adipaldehyde,
2) Aromatic bifunctional aldehydes such as phthalaldehyde, isophthalaldehyde, terephthalaldehyde,
3) Polymer bifunctional aldehydes such as terminally aldehyded poval and dialdehyde starch.
Of these, aliphatic bifunctional aldehydes with high reaction activity are preferred.

Moreover, the following can be mentioned as a specific example of the acid which coexists with the polyfunctional aldehyde of the present invention and effectively acts on the crosslinked dura.
1) Inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, sulfurous acid, carbonic acid,
2) Organic carboxylic acids such as acetic acid, propionic acid, oxalic acid, monochloroacetic acid, dichloroacetic acid, trifluoroacetic acid, benzoic acid, salicylic acid,
3) Organic sulfonic acids such as methanesulfonic acid, benzenesulfonic acid and p-toluenesulfonic acid.

The acid dissociation constant of the acid used is preferably 10 ⁻⁵ or more, more preferably 10 ⁻⁴ or more, and even more preferably 10 ⁻³ or more. Nonvolatile sulfuric acid or p-toluenesulfonic acid is particularly preferable. The addition amount of these acids may be as small as 10 μmol to 10 mmol, preferably 100 μmol to 10 mmol, per 1 g of the polyvinyl alcohol polymer. The addition amount of the bifunctional aldehyde is preferably 0.1 to 20% by mass, particularly preferably 0.5 to 15% by mass. The alignment film contains a certain amount of cross-linking agent that has not reacted even after the cross-linking reaction is completed. The amount of the cross-linking agent is preferably 1.0% by mass or less in the alignment film. In particular, it is preferably 0.5% by mass or less.

  In the present invention, the alignment film is formed, for example, by applying a composition (coating liquid) containing the polyvinyl alcohol polymer, polyfunctional aldehyde and acid to the surface of the transparent support, followed by drying by heating and rubbing. Can be formed. When drying the coating solution coated on the support, the crosslinking reaction of the material may be allowed to proceed, or may be allowed to proceed at any time after being coated on the transparent support. In order to promote the crosslinking reaction, it is preferable to advance the crosslinking reaction under heating. For the preparation of the coating solution, it is preferable to use a mixed solvent of water and an organic solvent such as methanol having an antifoaming effect, and the ratio is generally from 0: 100 to 99: 1 in water: methanol. Yes, preferably 0: 100 to 91: 9. Thereby, generation | occurrence | production of a bubble is suppressed and the defect of the layer surface of an orientation film and also an optically anisotropic layer reduces remarkably. Examples of the coating solution coating method include spin coating, dip coating, curtain coating, extrusion coating, bar coating, and E-type coating. The E-type coating method is particularly preferable. The film thickness is preferably 0.1 to 10 μm. Heating and drying can be performed at 20 ° C to 150 ° C. If it is the said temperature range, the crosslinking reaction of the material in a composition can be advanced simultaneously with drying. In order to form sufficient cross-linking, 60 ° C to 140 ° C is preferable, and 80 ° C to 130 ° C is particularly preferable. The drying time can be 0.5 minutes to 36 hours. Preferably, it is 1 minute to 30 minutes.

[Optically anisotropic layer]
In the present invention, the optically anisotropic layer is formed by controlling the orientation of the molecules of the discotic liquid crystalline compound on the rubbing-treated surface of the orientation film and fixing it in the orientation state. There are low molecular weight and high molecular weight types of discotic liquid crystalline compounds, and any of them can be used. As the discotic liquid crystalline compound used in the present invention, a discotic liquid crystalline compound having a polymerizable group is preferably used. In the present invention, the optically anisotropic layer is a layer exhibiting optical anisotropy expressed by the orientation of the liquid crystalline molecules, and the layer controls not only the liquid crystalline compounds but also the orientation of the liquid crystalline molecules. It may contain a material that contributes to the above, a material necessary for fixing the liquid crystal molecules in the aligned state, and the like. Further, the liquid crystalline molecules may lose liquid crystallinity after being fixed in the alignment state.

  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.

  The molecules of the discotic liquid crystalline compound are preferably substantially uniformly oriented in the optically anisotropic layer, more preferably fixed in a substantially uniformly oriented state. Most preferably, it is fixed by a polymerization reaction. 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 crystal compound molecule and the layer plane is in the range of 50 ° to 90 °. The discotic liquid crystalline compound may be oriented obliquely or may be changed so that the inclination angle gradually changes (hybrid orientation). Even in the case of oblique orientation or hybrid orientation, the average inclination angle is preferably 50 ° to 90 °.

  The optically anisotropic layer is preferably formed by applying a discotic liquid crystalline compound and a composition (coating liquid) containing the following polymerization initiator and other additives onto 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, toluene, hexane), alkyl halides (eg, , Chloroform, dichloromethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, 2-butanone, cyclohexanone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane) and the like. 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).

  The liquid crystalline molecules aligned on the alignment film are fixed while maintaining the alignment state. The immobilization is preferably performed by a polymerization reaction of the polymerizable group (P) introduced into the liquid crystal molecule. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator, a photopolymerization reaction using a photopolymerization initiator, and EB curing using an electron beam. Of these, photopolymerization (photocuring) and EB curing are preferred. Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Description) Acridine and phenazine compounds (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,212,970) are included.

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by mass, more preferably 0.05 to 5% by mass, based on the solid content of the coating solution. It is preferable to use ultraviolet rays for light irradiation for polymerization of liquid crystalline molecules. The irradiation energy is more preferably it is 20mJ / cm ² ~50J / cm ² is preferably ^{50mJ / cm 2 ~800mJ / cm 2} . In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions. The thickness of the optically anisotropic layer is preferably 0.1 μm to 15 μm, and the thickness varies depending on the liquid crystal display device used as the retardation film.

[Air interface orientation control agent]
In the present invention, the optically anisotropic layer contains an additive capable of making the angle formed by the director at the air interface of the molecules of the discotic liquid crystalline compound and the perpendicular of the layer plane larger than the additive-free state. In the present specification, the additive having the above action is referred to as “air interface orientation control agent”. Any compound (low molecular compound or high molecular compound) can be added as the air interface alignment control agent as long as it is a compound that can exhibit a desired function, and is represented by the following general formula (V). It is preferable to use a compound.
General formula (V)
(Hb-L ^1- ) _n B ¹
In the formula (V), Hb represents an aliphatic group having 6 to 40 carbon atoms or an aliphatic substituted oligosiloxanoxy group having 6 to 40 carbon atoms, and L ¹ represents —O—, —S—, — CO—, —NR ⁵ —, —SO ₂ —, a divalent linking group selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, and combinations thereof, R ⁵ represents a hydrogen atom or a carbon number of 1 to 6 represents an alkyl group, n represents an integer of 2 to 12, and B ¹ represents an n-valent group containing at least three ring structures.

Details of Hb, L ¹ , B ¹ and n in the general formula (V) are described in JP-A-2002-129162, columns 0018 to 0148, and the contents thereof can also be applied to the present invention. .

In addition to the discotic liquid crystalline compound and the air interface alignment controller, other additives may be contained in the coating liquid for forming the optically anisotropic layer.
[Chiral agent]
When producing a retardation plate to be incorporated into an STN mode liquid crystal display device, it is necessary to twist and align the discotic liquid crystalline compound in a spiral manner. For this purpose, a composition for forming an optically anisotropic layer It is preferable to add a chiral agent. An asymmetric carbon atom may be introduced into the discotic liquid crystalline compound to function as a chiral agent, or a compound containing an asymmetric carbon atom that is not in a disk shape may be added as a chiral agent. Various natural or synthetic compounds can be used as the compound containing an asymmetric carbon atom.

[Transparent support]
In the present invention, a transparent support is used. Specifically, a support having a light transmittance of 80% or more is used. The transparent support is preferably a polymer film having small wavelength dispersion, and specifically, the ratio of Re400 / Re700 is preferably less than 1.2. The transparent support also preferably has a small optical anisotropy. Specifically, the in-plane retardation (Re) is preferably 20 nm or less, and more preferably 10 nm or less. An alignment film and an optically anisotropic layer can also be formed continuously on a long transparent support. The long transparent support has a roll-like or rectangular sheet-like shape. It is preferable to laminate the optically anisotropic layer using a roll-shaped transparent support and then cut it into a required size. Examples of the polymer include cellulose ester, polycarbonate, polysulfone, polyethersulfone, polyacrylate and polymethacrylate. Cellulose esters are preferred, acetyl cellulose is more preferred, and triacetyl cellulose is most preferred. The polymer film is preferably formed by a solvent cast method. The thickness of the transparent support is preferably 20 to 500 μm, and more preferably 50 to 200 μm. In order to improve adhesion between the transparent support and the layer (adhesive layer, vertical alignment film or optically anisotropic layer) provided on the transparent support, surface treatment (eg, glow discharge treatment, corona discharge treatment, ultraviolet ray) is applied to the transparent support. (UV) treatment, flame treatment) may be performed. An adhesive layer (undercoat layer) may be provided on the transparent support.

The retardation plate of the present invention can be used for various applications, for example, as an optical compensation sheet for a liquid crystal display device.
[Liquid Crystal Display]
One embodiment of a liquid crystal display device of the present invention includes a pair of polarizing plates, a pair of glass substrates disposed between the pair of polarizing plates, and a rod-like liquid crystal having positive uniaxial anisotropy sandwiched between the glass substrates. A liquid crystal cell made of molecules, and the retardation plate of the present invention is provided between at least one of the pair of polarizing plates and the liquid crystal cell. The retardation plate may be disposed so as to reduce leakage light during black display of the liquid crystal display device. It is preferable to arrange the optically anisotropic layer of the retardation plate so as to be closer to the liquid crystal cell. The driving mode of the liquid crystal cell is preferably an IPS mode liquid crystal cell that is driven in a mode in which the long axis of the rod-like liquid crystal molecules is always aligned in parallel or substantially parallel to the surface direction of the glass substrate. In addition, there is no restriction | limiting in particular about other members including the polarizing plate used for the liquid crystal display device of this aspect, and its positional relationship, It can produce with reference to various conventionally well-known liquid crystal display devices.

  In another aspect of the liquid crystal display device of the present invention, two polarizing plates, an STN type liquid crystal cell arranged therebetween, and an arrangement between the STN type liquid crystal cell and one or both of the two polarizing plates are provided. An STN liquid crystal display device having at least one optically anisotropic layer formed from a composition containing a discotic liquid crystalline compound, wherein the discotic liquid crystal property is contained in the optically anisotropic layer. In an STN liquid crystal display device in which the molecules of the compound are fixed in a twisted orientation state substantially in the monodomain and in a twist angle range of 90 to 360 degrees with the disk surface perpendicular or substantially perpendicular to the layer plane is there. A composition containing a discotic liquid crystalline compound, an air interface alignment controller and a chiral agent is applied on the alignment film of the present invention, and the discotic liquid crystal molecules are present in the presence of the air interface alignment controller and the chiral agent. By orienting, the twisted orientation state can be stably formed. Thereafter, the optically anisotropic layer used in this embodiment can be produced by fixing the discotic liquid crystalline molecules in the alignment state. When incorporated in a liquid crystal display device in the form of a retardation plate having a support, the optically anisotropic layer is disposed closer to the STN liquid crystal cell. In addition, other members including the polarizing plate used in the liquid crystal display device of this embodiment and the positional relationship thereof are not particularly limited, and can be manufactured with reference to a conventionally known STN liquid crystal display device.

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

[Example 1]
(Preparation of alignment film)
A triacetyl cellulose film (TD80U, manufactured by Fuji Photo Film Co., Ltd., Fujitac) was coated with a coating solution containing polyvinyl alcohol having the composition shown below with a bar coater, and heated and dried at 120 ° C. for 2 minutes to obtain 0.8 μm. A polymer layer having a film thickness was formed (hereinafter, “part” means “part by mass”). The surface of the obtained polymer layer was rubbed to form an alignment film.
Composition of coating liquid for alignment film formation The following polyvinyl alcohol polymer 1.00 parts Water 18.00 parts Methanol 6.00 parts Glutaraldehyde (50 mass% aqueous solution) 0.1 part p-Toluenesulfonic acid 0.01 part

(Formation of discotic liquid crystalline compound layer (optically anisotropic layer))
A coating solution having the following composition was applied to the rubbing treated surface of the alignment film with a bar coater. The film having this coating layer is passed through a heating zone at 125 ° C. for 2 minutes, and then the coating layer is irradiated with UV light and cured to fix the alignment state of the aligned discotic liquid crystal compound (optical) An anisotropic layer having a layer thickness of 2 μm was formed to produce a retardation plate.
Composition of coating liquid for forming optically anisotropic layer 100 parts of the following discotic liquid crystalline compound 10 parts of the following polyfunctional monomer 10 parts of the following additives 1 part of the following photopolymerization initiator 3 parts of the following sensitizer 1 part of methyl ethyl ketone 400 parts

[Comparative Example 1: When no acid was added during alignment film formation]
An alignment film was formed in the same manner as in Example 1 except that p-toluenesulfonic acid was not added to the alignment film coating solution used in Example 1, and a retardation plate was prepared in the same manner as in Example 1. .
[Comparative Example 2: When no additive was added]
A retardation film was prepared in the same manner as in Example 1 except that the alignment film was formed in the same manner as in Example 1 and then the additive was not included in the coating liquid when forming the optically anisotropic layer.

(Optical measurement of retardation plate)
As optical characteristics of the obtained retardation plate, the retardation axis was inclined with the slow axis as the rotation axis, and the retardation (retardation: Re) at the front (0 °) and ± 40 ° was measured at a wavelength of 569 nm. . The thickness of the layer in which the orientation of the discotic liquid crystalline compound was fixed was also measured. The results are shown in Table 1. Table 1 also shows the results of calculating the average tilt angle of the discotic liquid crystalline molecules by simulation. The retardation plate obtained by the present invention has the highest front retardation, and the retardation is smaller when the sample is tilted. The retardation at + 40 ° and −40 ° is almost the same. It was. From the simulation results, it can be seen that the disc surface of the discotic liquid crystalline compound is aligned substantially perpendicular to the support. On the other hand, in Comparative Example 1 (in the case where no acid was added at the time of forming the alignment film), the retardation value increased as -40 °, front, and + 40 °. In Comparative Example 2 (in the case where no additive was added), the retardation value also increased as -40 °, front, and + 40 ° as in Comparative Example 1, but the retardation value was comparative. Less than 1. It was found that the average tilt angle of the disc surface of each discotic liquid crystalline compound was smaller than 50 °.

[Comparative Example 3: Phase difference plate using vertical alignment film with low surface energy]
A retardation plate having a thickness (thickness of the optically anisotropic layer) of 2 μm and a front retardation of 125 nm was prepared by the method disclosed in Japanese Patent Application Laid-Open No. 2000-104073. When a retardation value of ± 40 ° was measured by the above method and then a simulation was performed, the average inclination angle was 88 °.
Comparative Example 4: Retardation Plate Using Excluded Volume Effect Type Vertical Alignment Film
A retardation plate having a thickness (the thickness of the optically anisotropic layer) of 2 μm and a front retardation of 128 nm was prepared by the method disclosed in Japanese Patent Application Laid-Open No. 2000-105316. When a retardation value of ± 40 ° was measured by the above method and then a simulation was performed, the average inclination angle was 89 °.

[Example 2]
(Observation of retardation film by polarizing microscope)
The optically anisotropic layer of the retardation plate produced in Example 1 and the optically anisotropic layer of the retardation plate produced in Comparative Examples 3 and 4 were observed under a polarizing microscope (quenching position). The optically anisotropic layer produced in Example 1 had no cissing or no alignment defect at the time of coating, and the liquid crystalline molecules were fixed in a uniform monodomain alignment state. In Comparative Example 3, although there were few alignment defects, there were many cissings. In Comparative Example 4, there were few cissings but many alignment defects.

[Example 3]
(Production of IPS mode liquid crystal device)
In accordance with the first embodiment described in JP-A-9-292522, a retardation plate produced in the same manner as in Example 1 was mounted on a liquid crystal panel, and the viewing angle dependency in black display was examined. Leaked light decreased at any viewing angle, which was good. Moreover, the transmittance and color shift in white display were also improved.

[Example 4]
(Production of STN type display device)
According to Example 1 of Japanese Patent Laid-Open No. 2000-104073, a retardation plate for an STN type display device was produced. That is, a coating solution having the following composition was applied on the alignment film produced in the same manner as in Example 1, and the film having the coating layer was passed through a heating zone at 125 ° C. for 2 minutes, and then the UV was applied to the coating layer. By irradiating and curing light, a thin film in which the orientation of the oriented discotic liquid crystalline compound was fixed was formed, and a retardation plate was produced. When the emitted light was analyzed using an optical instrument (Multi Channel Photo Analyser, manufactured by Otsuka Electronics Co., Ltd.) at an angle of 45 degrees with respect to the rubbing axis, the discotic liquid crystalline compound stands upright on the support surface. It was found that the disk surface was twisted 240 degrees.
────────────────────────────────────
Composition of coating solution for optically anisotropic layer ────────────────────────────────────
The following discotic liquid crystalline compound (1) 80 parts by mass The following discotic liquid crystalline compound (2) 20 parts by mass The following fluorine-containing surfactant 0.1 part by mass Photopolymerization initiator 0.2 part by mass (Irgacure 907 , Made by Nippon Ciba-Geigy Corporation)
185 parts by weight of methyl ethyl ketone ────────────────────────────────────

In accordance with Example 5 of Japanese Patent Laid-Open No. 2000-104073, an STN type display device was produced using the retardation plate produced in Example 4 above. When visual characteristics were evaluated with the obtained STN type liquid crystal display device, an angle range with a contrast ratio of 5 or more was obtained 130 ° or more on the left and right, and 160 ° or more on the top and bottom.

Claims (5)

An alignment film formed of a transparent support, a polyvinyl alcohol polymer thereon, a polyfunctional aldehyde compound capable of crosslinking and curing the polymer, and an acid that effectively acts on the crosslinking film; and An optically anisotropic layer formed of a discotic liquid crystalline compound, the orientation of which is controlled on the rubbing-treated surface of the alignment film and fixed in the aligned state, and the optically anisotropic layer However, the retardation plate contains an additive that can make the angle formed by the director at the air interface of the molecules of the discotic liquid crystalline compound and the perpendicular of the layer plane larger than the additive-free state. The phase difference plate according to claim 1, wherein the acid has an acid dissociation constant of 10 ⁻⁵ or more. The retardation plate according to claim 1, wherein the additive is a compound represented by the following general formula (V).
General formula (V)
(Hb−L ² −) _n B ¹
(In the formula, Hb represents an aliphatic group having 6 to 40 carbon atoms or an aliphatic substituted oligosiloxanoxy group having 6 to 40 carbon atoms, and L ² represents —O—, —S—, —CO—, —NR ⁵ —, —SO ₂ —, a divalent linking group selected from the group consisting of an alkylene group, an alkenylene group, an arylene group and a combination thereof, R ⁵ represents a hydrogen atom or an alkyl having 1 to 6 carbon atoms. Represents a group, n represents an integer of 2 to 12, and B ¹ represents an n-valent group containing at least three ring structures.) A pair of polarizing plates, a pair of glass substrates disposed between the pair of polarizing plates, and a liquid crystal cell composed of rod-like liquid crystal molecules having positive uniaxial anisotropy sandwiched between the glass substrates, and The liquid crystal cell is a liquid crystal display device driven in a mode in which the major axis of the rod-like liquid crystal molecules is always aligned in parallel or substantially parallel to the surface direction of the glass substrate, and the liquid crystal cell is at least one of the pair of polarizing plates and the The liquid crystal display device which has a phase difference plate of any 1 paragraph of Claims 1-3 between liquid crystal cells. Two polarizing plates, an STN liquid crystal cell disposed therebetween, and a composition containing a discotic liquid crystalline compound disposed between the STN liquid crystal cell and one or both of the two polarizing plates STN liquid crystal display device having at least one optically anisotropic layer formed from a product, wherein the optically anisotropic layer is a polyvinyl alcohol polymer, a polyfunctional aldehyde compound capable of crosslinking and hardening the polymer, and On an alignment film formed from a composition containing an acid that effectively acts on the cross-linked dura, the molecules of the discotic liquid crystalline compound are substantially aligned so that the disk surface is perpendicular or substantially perpendicular to the layer plane. It is a layer formed by being controlled in a mono-domain and in a twisted orientation state in the range of a twist angle of 90 to 360 degrees and being fixed in that orientation state. TN liquid crystal display device.