JP2007249108A - Optical compensation sheet, polarizing plate using the same, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical compensation sheet which contributes to reduction of leak light from an oblique direction of, for example, 60° and tint variation of a liquid crystal display device, especially, an IPS mode or FFS mode liquid crystal display device. <P>SOLUTION: The optical compensation sheet has, on a base, an optical anisotropic layer formed of a cylindrical liquid crystalline compound and a liquid crystalline compound containing a photopolymerization initiator, and the reaction rate of polymerizable groups present in the liquid crystalline composition is ≥70% on a base-side interface of the optical anisotropic layer and ≥70% on an interface on the opposite side from the base. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel optical compensation sheet, and a polarizing plate and a liquid crystal display device using the same. The present invention relates to an optical compensation sheet having an optically anisotropic layer containing a liquid crystalline compound with a controlled degree of alignment order, and further a liquid crystal display device using the optical compensation sheet, particularly an in-plane switching (IPS) mode or FFS. The present invention relates to a mode liquid crystal display device and the like.

  As a liquid crystal display device, a so-called TN mode, in which a liquid crystal layer in which nematic liquid crystal is twisted and arranged between two orthogonal polarizing plates, and an electric field is applied in a direction perpendicular to the substrate is widely used. In this method, since the liquid crystal rises with respect to the substrate during black display, birefringence due to the liquid crystalline compound occurs when viewed from an oblique direction, and light leakage occurs. In order to solve this problem, a system in which a liquid crystal cell is optically compensated and a light leakage is prevented by using a film in which liquid crystal compounds are hybrid-aligned has been put into practical use. However, even if a liquid crystal compound is used, it is very difficult to completely optically compensate the liquid crystal cell without any problem, resulting in a problem that gradation reversal in the lower direction of the screen cannot be suppressed.

  In order to solve such a problem, a liquid crystal display device using a so-called IPS mode or FFS mode in which a lateral electric field is applied to the liquid crystal, a protrusion formed in the panel by vertically aligning a liquid crystal having a negative dielectric anisotropy, A vertical alignment (VA) mode in which alignment is divided by a slit electrode has been proposed and put into practical use. In recent years, these panels have been developed not only for monitor applications but also for TV applications, and screen brightness has been greatly improved accordingly. For this reason, a slight light leakage in the diagonally oblique incident direction during black display, which has not been considered as a problem in these operation modes, has become apparent as a cause of a decrease in display quality.

  As one means for improving the color tone and the viewing angle of black display, disposing an optical compensation material having birefringence characteristics between the liquid crystal layer and the polarizing plate is also studied in the IPS and FFS modes. For example, by arranging a birefringent medium with optical axes orthogonal to each other to compensate for increase / decrease in retardation of the liquid crystal layer during tilting, the white display or halftone display is obliquely arranged between the substrate and the polarizing plate. It is disclosed that coloring can be improved when viewing directly from (see Patent Document 1). Further, as an optical compensation film, a method of combining a film having a positive birefringence and an optical axis in the plane of the film with a film having a positive birefringence and an optical axis in the normal direction of the film (see Patent Document 2), letter A method using a biaxial optical compensation sheet with a half wavelength of the retardation (see Patent Document 3), a film having a negative retardation as a polarizing plate protective film, and an optical having a positive retardation on this surface A method of providing a compensation layer (see Patent Document 4) has been proposed.

Japanese Patent Laid-Open No. 9-80424 JP 11-133408 A JP-A-11-305217 JP-A-10-307291

However, when optically compensating an IPS mode or FFS mode liquid crystal cell using an optical compensation sheet made of a stretched birefringent polymer film, it is necessary to use a plurality of films. Optical compensation sheets using an optically anisotropic layer formed from a rod-like liquid crystalline compound or the like have been developed.
An optical compensation sheet comprising an optically anisotropic layer made of a liquid crystalline composition can be usually produced by providing an optically illegal layer containing an alignment film and a liquid crystalline compound on a transparent support, The optically anisotropic layer is cured by polymerizing the liquid crystalline compound with UV light (ultraviolet light). If this polymerization / curing reaction is insufficient, the adhesion between the alignment film and the optical anisotropic layer will be insufficient, causing delamination or bonding in the bonding process with the polarizing film or the bonding process with the liquid crystal cell. In order to cause a problem of white turbidity in the surface treatment step with an alkali of the optically anisotropic layer, which is the previous step, improvement has been desired.

  An object of the present invention is to provide an optical compensation sheet that contributes to reduction of leakage light and color change from an oblique direction, for example, 60 °, of a liquid crystal display device, in particular, an IPS mode or FFS mode liquid crystal display device. Another object of the present invention is to provide an optical compensation sheet that can facilitate the bonding process with the polarizing film and the bonding process with the liquid crystal cell, and can improve the yield.

In order to solve the above problems, as a result of investigating the relationship between the bonding property with the polarizing film and the panel and the reactivity of the polymerizable compound in the composition for forming the optically anisotropic layer, the range in which the problem occurs is optical. It was discovered that the reaction rate of the polymerizable compound on both surfaces of the anisotropic layer was closely related, and the present invention was reached. That is, the present invention provides the following.
[1] An optical compensation sheet having an optically anisotropic layer formed from a liquid crystalline composition containing a rod-like liquid crystalline compound and a photopolymerization initiator on a support, and present in the liquid crystalline composition An optical compensation sheet in which the reaction rate of the polymerizable group is 70% or more at the support-side interface of the optically anisotropic layer and 20% or more at the interface on the side opposite to the support.
[2] The optical compensation sheet according to [1], wherein the liquid crystalline composition includes a compound having 3 or more polymerizable groups in one molecule and having a molecular weight of 250 to 650.
[3] The optical compensation according to [1] or [2], wherein the optically anisotropic layer is formed by irradiating the liquid crystalline composition with active light in an atmosphere having an oxygen content of 5% by volume or less. Sheet.

[4] The optical compensation sheet according to any one of [1] to [3], further including an alignment film between the support and the optically anisotropic layer.
[5] A polarizing plate having the optical compensation sheet according to any one of [1] to [5].
[6] A liquid crystal display device having the polarizing plate according to [5].
[7] A liquid crystal display device comprising the optical compensation sheet according to any one of [1] to [5], a polarizing plate having a polarizing film, and a liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates, The liquid crystal compound in the liquid crystal cell during black display is aligned substantially parallel to the surfaces of a pair of substrates, and the Re of the support measured from the normal direction of the support is 20 nm to 150 nm, The Nz value of the support is 1.5 to 7, the Re of the optically anisotropic layer is 5 nm or less, the Rth is −80 nm to −400 nm, and the liquid crystalline compound in the optically anisotropic layer is homeotropic A liquid crystal display device which is oriented and has a transmission axis of the polarizing film parallel to a slow axis direction of a liquid crystal compound in a liquid crystal cell during black display.

  In the optical compensation sheet of the present invention, the problem of the bonding process with the polarizing film or the liquid crystal panel is solved, and the yield of the bonding process can be greatly improved.

  Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

In the present specification, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at the wavelength λ, respectively. Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments).
When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is the Re (λ), and the in-plane slow axis (determined by KOBRA 21ADH or WR) is the tilt axis (rotation axis). The light is incident at a wavelength of λnm in 10 degree steps from the normal direction to 50 degrees on one side with respect to the film normal direction (with the direction of the rotation axis as the rotation axis). KOBRA 21ADH or WR is calculated based on the measured retardation value, average refractive index assumption, and input film thickness value.
In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, the retardation at a tilt angle larger than the tilt angle is used. The value is calculated by KOBRA 21ADH or WR after changing the sign to negative.
In addition, the retardation value is measured from two inclined directions, with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), Based on the value, the assumed value of the average refractive index, and the input film thickness value, Rth can also be calculated from the following formulas (1) and (2).

Note:
The above Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction.
In formula (1), nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, and nz represents the refractive index in the direction perpendicular to nx and ny. .

Rth = ((nx + ny) / 2-nz) xd --- Formula (2)

In the case where the film to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film having no so-called optic axis, Rth (λ) is calculated by the following method.

Rth (λ) is from −50 degrees to +50 degrees with respect to the normal direction of the film, with Re (λ) as the slow axis (indicated by KOBRA 21ADH or WR) in the plane and the tilt axis (rotation axis). Measured at 11 points with light of wavelength λ nm from each inclined direction in 10 degree steps, and KOBRA 21ADH or based on the measured retardation value, average refractive index assumption and input film thickness value Calculated by WR.
In the above measurement, the assumed value of the average refractive index may be the value in the polymer handbook (JOHN WILEY & SONS, INC) and various optical film catalogs. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of the main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). By inputting these assumed values of average refractive index and film thickness, KOBRA 21ADH or WR calculates nx, ny, and nz.

  In the present specification, the “slow axis” means a direction in which the refractive index is maximized. In this specification, the term “polarizing plate” is used to include both a long polarizing plate and a polarizing plate cut into a size incorporated in a liquid crystal device unless otherwise specified. In this specification, “polarizing film” and “polarizing plate” are distinguished from each other, and “polarizing plate” is a laminate having a transparent protective film for protecting the polarizing film on at least one surface of the “polarizing film”. Means.

Hereinafter, embodiments of the optical compensation sheet of the present invention will be described in detail.
The optical compensation sheet of the present invention is an optical compensation sheet having an optically anisotropic layer formed from a liquid crystalline composition containing a rod-like liquid crystalline compound and a photopolymerization initiator on a support. The alignment state of the rod-like liquid crystal compound is fixed when a compound having a polymerizable group present in the liquid crystal composition undergoes a polymerization reaction upon irradiation with active light. The alignment form is more preferably homeotropic alignment.
In the optical compensation sheet of the present invention, the reaction rate of the polymerizable group present in the liquid crystalline composition is 70% or more at the support-side interface of the optically anisotropic layer, and at the interface opposite to the support. It is characterized by being 20% or more. The reaction rate is a ratio of the number of reacted polymerizable groups to the sum of the number of reacted polymerizable groups and the number of unreacted polymerizable groups. The reaction rate at the layer interface was determined by observing signals derived from unreacted polymerizable groups and signals derived from reacted polymerizable groups using a spectroscopic method capable of irradiating only the surface layer of the layer with measurement light. The signal intensity or signal area can be determined by analyzing the signal intensity or signal area as is normally done in the field and determining the relative number of each group. Examples of the measuring method that can irradiate only the surface layer of the layer with measuring light include infrared spectroscopy (IR).

[Bar-shaped liquid crystalline compound]
Examples of the rod-like liquid crystalline compound in the present invention include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted compounds. Phenylpyrimidines, phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used. The rod-like liquid crystalline compound includes a metal complex. Moreover, the liquid crystal polymer which contains a rod-shaped liquid crystalline compound in a repeating unit can also be used as a rod-shaped liquid crystalline compound in this invention. In other words, the rod-like liquid crystalline compound may be bonded to a (liquid crystal) polymer. Regarding rod-like liquid crystalline compounds, for example, Quarterly Chemistry Review Volume 22 Liquid Crystal Chemistry (1994) Chapter 4, Chapter 7 and Chapter 11 of the Chemical Society of Japan, and Liquid Crystal Device Handbook, Japan Society for the Promotion of Science, 142nd member Those described in Chapter 3 of the meeting can be adopted.
The birefringence of the rod-like liquid crystalline compound is preferably in the range of 0.001 to 0.7.

[Polymerizable liquid crystalline compound]
As the rod-like liquid crystalline compound, those having a polymerizable group are preferably used.
The polymerizable liquid crystalline compound is not particularly limited as long as it is fixed by a polymerization reaction. For example, a liquid crystalline compound having a polymerizable group of [Chemical Formula 11] and [Chemical Formula 12] in paragraph numbers [0049] to [0050] of JP-A-2004-339193 is preferable. Among them, a liquid crystal compound having an acrylate group and / or a methacrylate group is particularly preferable. Specific examples of the rod-like liquid crystal compound having one or two acrylate groups and / or methacrylate groups are disclosed in paragraphs [0082] to [0105] of JP-A-8-3111 and JP-A-9-281331. Paragraph numbers [0022] to [0040], Paragraph numbers [0115] to [0128] of JP-A No. 2000-281628, Paragraph numbers [0250] to [0400] of JP-A No. 2002-220421, JP-A 2003-2003 And compounds described in paragraph Nos. [0056] to [0075] of Japanese Patent No. 48903. However, the rod-like liquid crystalline compound having one or two acrylate groups and / or methacrylate groups used in the present invention is not limited to these.
The polymerizable liquid crystalline compound may be in the range of 50 to 99.9% by mass, and preferably in the range of 70 to 99% by mass with respect to the total amount of the liquid crystalline composition (excluding the solvent for coating and the like).

[Orientation order]
The degree of orientation order in the present invention (hereinafter sometimes referred to as S) is defined as a range of 0 ≦ S ≦ 1, which is used as a representation of the degree of orientation of a polymer film and the degree of liquid crystal orientation. If S = 0, a completely random state such as a liquid state is indicated. If S = 1, there is no molecular fluctuation like a crystal, and the film is perfectly oriented in one direction. In general, the orientation degree of the crystalline polymer film is measured by an X-ray diffraction pattern. However, when a film having nematic liquid crystallinity is measured, this method is not preferable as a measuring method because the sensitivity is low. The degree of orientation in this specification is measured by “Nanofinder” manufactured by Tokyo Instruments Co., Ltd. with an excitation laser wavelength of 532 nm, an excitation laser output of about 400 uW at the sample portion, and a depolarizer attached in front of the spectrometer. went. The measuring method cut | disconnected the film diagonally at about 1-2 degree | times, and performed the polarization Raman measurement of the surface or interface vicinity among the liquid-crystal material layers in a film. Rotate the film, change the angle between the orientation of the film surface and the electric field direction of the incident laser polarization, and measure at several angles. Of the scattered light components, the polarization component I parallel to the incident laser polarization electric field I parallel and perpendicular Each polarized component I perpendicular was detected spectroscopically using an analyzer. Furthermore, a fitting analysis based on the least square method was performed on the band having a peak derived from the skeleton of the liquid crystalline compound by using a theoretically derived equation with the alignment order parameters P2 and P4 as parameters, and the degree of alignment order was obtained.

The degree of alignment order of the present invention is preferably 0.3 ≦ S ≦ 0.7, preferably 0.45 ≦ S ≦ 0.65 when the optically anisotropic layer exhibits nematic liquid crystallinity. Is more preferable. If the degree of orientation order is in this range, it contributes to improvement of the front contrast when the optically anisotropic layer is bonded to a liquid crystal display device. When the optically anisotropic layer exhibits smectic liquid crystallinity, 0.5 ≦ S ≦ 0.90 is preferable, and 0.65 ≦ S ≦ 0.90 is more preferable.

[Alignment film]
As for the specific type of polymer used for the alignment film in the optical compensation sheet of the present invention, any of a polymer that can be crosslinked by itself and a polymer that is crosslinked by a crosslinking agent can be used. A combination of these can also be used. Examples of the polymer used for the alignment film in the present invention include, for example, compounds described in paragraph No. [0022] of JP-A-8-338913. Preferred are water-soluble polymers (for example, poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol, and modified polyvinyl alcohol), among which gelatin, polyvinyl alcohol, and modified polyvinyl alcohol are more preferable, and polyvinyl alcohol and modified polyvinyl alcohol. More preferred is polyvinyl alcohol.

  The saponification degree of polyvinyl alcohol is preferably 70 to 100%, more preferably 80 to 100%, and still more preferably 85 to 95%. The polymerization degree of polyvinyl alcohol is preferably 100 to 3000.

  The modifying group of the modified polyvinyl alcohol can be introduced by copolymerization modification, chain transfer modification or block polymerization modification. Examples of modifying groups include hydrophilic groups (carboxylic acid groups, sulfonic acid groups, phosphonic acid groups, amino groups, ammonium groups, amide groups, thiol groups, etc.), hydrocarbon groups having 10 to 100 carbon atoms, fluorine atoms Substituted hydrocarbon groups, thioether groups, polymerizable groups (unsaturated polymerizable groups, epoxy groups, azirinidyl groups, etc.), alkoxysilyl groups (trialkoxy, dialkoxy, monoalkoxy) and the like can be mentioned. Specific examples of these modified polyvinyl alcohol compounds include, for example, paragraph No. [0074] of JP-A No. 2000-56310, paragraph Nos. [0022] to [0145] of JP-A No. 2000-155216, and No. 2002-62426. And those described in paragraph numbers [0018] to [0022].

[Alignment accelerator]
In the present invention, the alignment accelerator is used for the purpose of enhancing the alignment of the rod-like liquid crystal. For example, a polymer compound having a fluoroalkyl group and a carboxylic acid in the side chain contributes to vertically aligning the rod-like liquid crystal molecules at the air interface of the optically anisotropic layer. Specifically, the polymer compound described as the polymer A in [0023] to [0053] of Japanese Patent Application No. 2005-282893 can be mentioned.

The preferred range of the content of the polymer A varies depending on the use, but is preferably 0.005 to 8% by mass with respect to the total amount of the liquid crystalline composition (excluding the solvent for coating and the like) More preferably, it is 0.01-5 mass%, and it is still more preferable that it is 0.05-1 mass%. Moreover, it is preferable that the addition amount of the repeating unit induced | guided | derived from the said fluoroalkyl group containing monomer is 0.004 mass% or more and 6.5 mass% or less.
By setting it as such a range, it can prevent that the coating film becomes difficult to dry sufficiently. Further, the performance as an optical film (for example, uniformity of retardation) tends to be further improved.

  The onium salt contributes to the vertical alignment of the molecules of the rod-like liquid crystalline compound on the alignment film interface side. Examples of onium salts that can be added to the liquid crystal composition include ammonium salts containing nitrogen atoms, sulfonium salts containing sulfur atoms, phosphonium salts containing phosphorus atoms, and the like. Specifically, Japanese Patent Application No. 2005-282893 Examples thereof include the onium salts described in [0055] to [0086].

  The preferred content of the onium salt in the optically anisotropic layer varies depending on the type of the onium salt. Usually, the content of the liquid crystal compound contained in the liquid crystal composition in the liquid crystal composition. The content is preferably 0.01 to 10% by mass, and more preferably 0.05 to 7% by mass. Two or more types of onium salts may be used, but it is preferable that the total amount of all types used be within the above range.

  The liquid crystalline composition for forming the optically anisotropic layer of the optical compensation sheet of the present invention may further contain other additives. Examples of other additives include plasticizers, surfactants, polymerizable monomers and polymers. These additives are preferably compatible with essential components such as a liquid crystal compound and contribute to control of the tilt angle of the liquid crystal compound or do not inhibit alignment.

[Method for producing optically anisotropic layer]
In the optical compensation sheet of the present invention, a liquid crystal composition (usually a coating solution) is applied to, for example, the support surface, preferably the alignment film surface, to align the molecules of the liquid crystal compound and fix the alignment state. It is possible to make it.
As a solvent used for preparation of a coating liquid, an organic solvent is preferable. Examples of organic solvents include amides (eg N, N-dimethylformamide), sulfoxides (eg dimethyl sulfoxide), heterocyclic compounds (eg pyridine), hydrocarbons (eg benzene, hexane), alkyl halides (eg , Chloroform, dichloromethane, tetrachloroethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane), alkyl halides and ketones Is preferred. Further, two or more kinds of organic solvents may be used in combination. When producing a highly uniform optical film, the surface tension of the coating solution is preferably 25 mN / m or less, and more preferably 22 mN / m or less.

  The coating solution can be applied by a known method (for example, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method). preferable.

The immobilization is preferably performed by a photopolymerization reaction. In addition to the photopolymerization initiator that initiates photopolymerization, the liquid crystalline composition preferably contains a polymerizable monomer that works effectively for fixing the liquid crystalline compound. As a polymerizable monomer, the compound which has a vinyl group, an acryloyl group, and a methacryloyl group is preferable, for example, 1-50 mass% is preferable with respect to a liquid crystalline compound, and it should be 3-30 mass%. Is more preferable.
Preferable polymerizable monomers include polymerizable compounds having 3 or more polymerizable groups in the molecule and a molecular weight of 250 to 650. When the rod-like liquid crystal having a polymerizable group is homeotropic alignment (vertical alignment), the polymerizable group is biased toward the air interface side, and the surface layer is difficult to polymerize due to the effect of inhibiting the polymerization of oxygen. Thus, polymerization on the air interface side can be promoted. In addition, these monomers have a function of increasing the polymerizability on the alignment film side, and therefore the polymerizability and film properties of the layer are improved by being unevenly distributed up and down in the process of applying and drying the photoanisotropic layer. It is thought to let you. Specific examples include trifunctional and polyfunctional acrylic esters, methacrylic esters, styrenic monomers, allylic monomers described in, for example, Photographic Materials Handbook, Photopolymer Social Association, pages 38 to 54 of Bunshin Publishing (1995). Mention may be made of monomers. More effective and specific compounds include, but are not limited to, monomers having the following structure.

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. 4,221,970). In addition, photopolymerization initiators described in Japanese Patent Application Nos. 2005-273162 and 2005-31276 are also effectively used.
The amount of the photopolymerization initiator used is preferably 0.01 to 20% by mass, and 0.5 to 5% by mass with respect to the total amount of the liquid crystalline composition (excluding the solvent for coating and the like). More preferably.

Ultraviolet rays are preferably used for light irradiation for polymerization of a liquid crystal compound (liquid crystal molecule). The irradiation energy is preferably in the range of ^{20mJ / cm 2 ~50J / cm 2} , more preferably in the range of ^{20mJ / cm 2 ~5000mJ / cm 2} , a range of 100mJ / cm ² ~800mJ / cm ² More preferably. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.
In addition, it is possible to improve the polymerizability by performing atmospheric light irradiation of air with a reduced amount of oxygen by nitrogen substitution or the like. In particular, in order to increase the polymerizability of the surface layer of the optically anisotropic layer that is in direct contact with the air layer, which has a large effect of inhibiting polymerization by oxygen, the oxygen content is preferably 5% by volume or less.

  The thickness of the optically anisotropic layer in the optical compensation sheet of the present invention is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and still more preferably 1 to 10 μm. A protective layer may be provided on the optically anisotropic layer.

[Support]
In the optical compensation sheet of the present invention, the optically anisotropic layer may be directly formed on the alignment film or may be directly formed on the support. The support is preferably transparent, and specifically, the light transmittance is preferably 80% or more. The support preferably has a small wavelength dispersion, and specifically, the ratio of Re ₄₀₀ / Re ₇₀₀ is preferably less than 1.2. Among these, a polymer film is preferable. The support for the optically anisotropic layer may be a part of the retardation film or the entire retardation film. Moreover, the support body of the said optically anisotropic layer may function as a protective film (polarizing plate protective film) of the polarizing plate in this invention.

  The optical anisotropy of the support is preferably small, and the in-plane retardation (Re) is preferably 20 nm or less, more preferably 10 nm or less, and most preferably 5 nm or less. Moreover, when it serves also as a phase difference film, Re is preferably 20 nm to 150 nm, more preferably 40 nm to 115 nm, and further preferably 60 nm to 95 nm. Moreover, Nz is 1.5-7, it is more preferable that it is 2.0-5.5, and it is further more preferable that it is 2.5-5.0.

  Examples of the polymer film as the support include cellulose ester, polycarbonate, polysulfone, polyethersulfone, polyacrylate, and polymethacrylate films. A cellulose ester film is preferred, and cellulose acetate is more preferred. The polymer film is preferably formed by a solvent cast method. The thickness of the support is preferably 20 to 500 μm, and more preferably 40 to 200 μm. In order to improve the adhesion between the support and the layer (adhesive layer, vertical alignment film or optically anisotropic layer) provided thereon, the support is subjected to surface treatment (for example, glow discharge treatment, corona discharge treatment, ultraviolet light (UV ) Treatment, flame treatment). An adhesive layer (undercoat layer) may be provided on the support. Further, the case where the support is a film of a polymer having a polymerizable group is also preferable because the adhesion to the optically anisotropic layer is improved. The average particle size is 10 to 100 nm in order to give the support or the long support a slippery property in the transporting process or to prevent the back surface and the surface from sticking after winding. It is preferable to use a polymer layer in which 5% to 40% of the solid particles are mixed by coating or co-casting with a support on one side of the support.

  The optical compensation sheet of the present invention can be used alone for a member of a liquid crystal display device or the like, but can also be integrated with a polarizing plate and incorporated into a liquid crystal display device as one member in the polarizing plate. The polarizing plate in which the optical compensation sheet of the present invention is integrated not only has a polarizing function but also contributes to an increase in the viewing angle of the liquid crystal display device. Further, the optical compensation sheet of the present invention may be used as a protective film for the polarizing film, and such a configuration contributes to thinning of the liquid crystal display device.

Hereinafter, the polarizing plate using the optical compensation sheet of the present invention will be described in detail.
[Polarizer]
A polarizing plate generally has a polarizing film produced by adsorbing and orienting a dichroic substance on a base film and a protective film bonded to at least one surface of the polarizing film. As the polymer used for the base film of the polarizing film, a polyvinyl alcohol (hereinafter referred to as PVA) polymer is generally used. As the dichroic substance, iodine or a dichroic dye is used alone or in combination.

  Here, the PVA used for the polarizing film is usually saponified polyvinyl acetate, but can be copolymerized with vinyl acetate such as unsaturated carboxylic acid, unsaturated sulfonic acid, olefins, and vinyl ethers. You may contain a component. In addition, modified PVA containing an acetoacetyl group, a sulfonic acid group, a carboxyl group, an oxyalkylene group, or the like can also be used. The degree of saponification of PVA is not particularly limited, but is preferably 80 to 100 mol%, particularly preferably 90 to 100 mol% from the viewpoints of solubility, polarization, heat resistance, moisture resistance and the like. Moreover, although the polymerization degree of PVA is not specifically limited, 1000-10000 are preferable and 1500-5000 are more preferable from film strength, heat resistance, moisture resistance, stretchability, etc. Moreover, it does not specifically limit about the syndiotacticity of PVA, It can also take arbitrary values according to the objective.

  In order to prepare a polarizing film by dyeing and stretching PVA, a method in which a PVA film as a raw fabric is stretched by dry or wet and then immersed in a solution of iodine or dichroic dye, iodine or dichroic dye There are a method of stretching and orienting a PVA film in the above solution, a method of stretching and orienting a PVA film in iodine or a dichroic dye and then wet or dry. Moreover, when film-forming a PVA original fabric by a solution film-forming method, the method of previously containing a dichroic substance in a PVA solution is also employable.

  A manufacturing method by wet stretching of a typical polarizing plate will be described below. First, the raw fabric PVA film is pre-swelled with an aqueous solution. Subsequently, it is immersed in the solution of a dichroic substance, and a dichroic substance is adsorbed. Further, it is uniaxially stretched in the traveling direction in an aqueous solution of a boron compound such as boric acid. If necessary, a color adjustment bath, a curing bath or the like may be provided after this. When it is dried to some extent, a protective film is bonded using an adhesive such as PVA. Further, it is dried to obtain a polarizing plate.

  Various organic solvents, inorganic salts, plasticizers, boric acids and the like may be added to the pre-swelled solution in the aqueous solution.

  When iodine is used as the dichroic substance, for example, an iodine-potassium iodide aqueous solution can be used as the staining liquid. It is preferable that iodine-potassium iodide aqueous solution is 0.1-20 g / liter of iodine, 1-100 g / liter of potassium iodide, and the weight ratio of iodine and potassium iodide is 1-100. The dyeing time is preferably 30 to 5000 seconds, and the liquid temperature is preferably 5 to 50 ° C. It is also preferable to include a compound that crosslinks PVA such as a boron compound in the dyeing solution. The boron compound in the stretching bath is particularly preferably boric acid. The boric acid concentration is preferably 1 to 200 g / liter, more preferably 10 to 120 g / liter. In addition to the boron compound, the stretching bath may contain an inorganic salt such as potassium iodide, various organic solvents, or a dichroic dye. In addition to the dichroic dye, an inorganic salt such as potassium iodide, a boron compound, and the like are contained in the color adjustment bath and the curing bath as necessary.

  As the PVA stretching step, as exemplified above, tension is applied in the traveling direction of the continuous film, and the film is stretched and oriented in the traveling direction, as well as in the width direction of the film by stretching means such as a so-called tenter method. A method of applying tension and orienting in the width direction is also applicable. The stretching is preferably performed 3 times or more in a uniaxial direction, and more preferably 4.5 times or more. Biaxial stretching may be performed depending on the purpose of use of the polarizing film. Although the film thickness after extending | stretching is not specifically limited, 5-100 micrometers is preferable from a viewpoint of a handleability, durability, and economical efficiency, and 10-40 micrometers is more preferable. Although the temperature at the time of stretching varies depending on the stretching conditions, it is preferably 10 to 250 ° C. When dry stretching at a temperature of 100 ° C. or higher, it is preferably performed in an inert gas atmosphere such as nitrogen. Moreover, it is preferable to perform a crystallization treatment at a temperature of 100 ° C. or higher before dyeing a previously stretched film.

  As the dyeing method, not only the immersion method exemplified above, but also any means such as application or spraying of iodine or a dye solution is possible. In addition to the liquid layer adsorption described above, adsorption by donation can be performed as necessary. It is also preferable to dye with a dichroic dye. Specific examples of the dichroic dye include dye compounds such as azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes and anthraquinone dyes. I can give you. A water-soluble one is preferred, but not limited thereto. Further, it is preferable that a hydrophilic substituent such as a sulfonic acid group, an amino group, or a hydroxyl group is introduced into these dichroic molecules.

  Typical examples of dichroic molecules include C.I. Eye. direct. Yellow 12, sea. Eye. direct. Orange 39, sea. Eye. direct. Orange 72, sea. Eye. direct. Red 28, Sea. Eye. direct. Red 39, Sea. Eye. direct. Red 79, Sea. Eye. direct. Red 81, Sea. Eye. direct. Red 83, Sea. Eye. direct. Red 89, Sea. Eye. direct. Violet 48, C.I. Eye. direct. Blue 67, Sea. Eye. direct. Blue 90, Sea. Eye. direct. Green 59, Sea. Eye. Acid. Red 37 etc. are mentioned. Further, JP-A-1-161202, JP-A-1-172906, JP-A-1-172907, JP-A-1-183602, JP-A-2000-48105, JP-A-2000-65205, JP-A-7-261024. And the like described in each of the above publications. In particular, Sea. Eye. direct. Red 28 (Congo Red) has long been known as preferred for this application. These dichroic molecules are used as free acids or alkali metal salts, ammonium salts, and salts of amines.

  By blending two or more of these dichroic molecules, it is possible to produce polarizers having various hues. As a polarizing element or polarizing plate, a compound (pigment) that exhibits black when the polarization axes are orthogonal to each other, or a compound in which various dichroic molecules are blended so as to exhibit black is excellent in terms of both the single plate transmittance and the polarization.

  From the viewpoint of increasing the heat resistance and moisture resistance of the polarizing film, it is preferable to include an additive that crosslinks PVA in the manufacturing process of the polarizing film. As the crosslinking agent, those described in US Reissue Patent No. 232897 can be used, but boric acid and borax are preferably used practically. In addition, it is known that the polarizing film contains a metal salt such as zinc, cobalt, zirconium, iron, nickel, manganese, etc., because it is known to improve durability. These crosslinking agents and metal salts may be contained in any of the above-described pre-swelling bath, dichroic material dyeing bath, stretching bath, curing bath, color adjusting bath, etc., and the order of the steps is particularly limited. Not. There are no particular limitations on the adhesive that bonds the protective film and the polarizing film, and any known adhesive such as PVA-based, modified PVA-based, urethane-based, or acrylic-based can be used. The thickness of the adhesive layer is preferably from 0.01 to 20 μm, more preferably from 0.1 to 10 μm.

  As the polarizing plate of the present invention, preferably, the optical compensation sheet of the present invention (more preferably, the support surface of the optical compensation sheet having a support is in contact with the polarizing film) is applied to one surface of the polarizing film. In addition, it is preferable to dispose a polymer film made of cellulose acylate or the like on the opposite surface (arrangement of optically anisotropic layer / polarizing film / polymer film).

  The optical compensation sheet of the present invention can be used in various liquid crystal display devices. In particular, it is preferably used for an IPS mode liquid crystal display device. When the optical compensation sheet of the present invention is disposed in a liquid crystal display device having a liquid crystal cell and a pair of polarizing films sandwiching the liquid crystal cell, the optical compensation sheet is interposed between at least one of the pair of polarizing films and the liquid crystal cell. It is preferable to arrange. The optical compensation sheet of the present invention preferably determines the optical characteristics of the optically anisotropic layer so as to compensate for the liquid crystalline compound in the liquid crystal cell in the black display of the liquid crystal display device. Since the alignment state of the liquid crystalline compound in the liquid crystal cell in black display varies depending on the mode of the liquid crystal display device, the preferred range of the optical characteristics of the optically anisotropic layer also varies depending on the application. The alignment state of the liquid crystal compound in the liquid crystal cell is described in IDW'00, FMC7-2, P411 to 414, and the like.

  As described above, the preferred range of the optical characteristics of the optical compensation sheet of the present invention varies depending on its use, for example, which mode is used for optical compensation of a liquid crystal cell. In the IPS mode liquid crystal display device, Re of the optically anisotropic layer is preferably −5 to 5 nm, more preferably −3 to 3 nm, and Rth is preferably −80 to −400 nm. More preferably, it is −150 to −350 nm. In order to form an optically anisotropic layer exhibiting such optical characteristics, for example, a rod-like liquid crystalline compound is used, and vertical alignment (the long axis direction of the rod-like molecule is substantially perpendicular to the surface of the optically anisotropic layer). To be fixed in a vertical alignment state. The Re of the support is preferably 20 to 150 nm, more preferably 20 to 100 nm. Nz is preferably 1.5 to 7.0, and more preferably 2.0 to 6.0.

  Details of the IPS mode liquid crystal display device are described in Japanese Patent Application Laid-Open Nos. 2003-207797 and 2005-128498, and the contents thereof can be applied to the present invention.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[Example 1]

(Production of polymer substrate (support))
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution. The solution was filtered using a filter paper (Advantech, No. 63) having a retention particle size of 4 μm and a drainage time of 35 seconds at 0.5 MPa (5 kg / cm ² ) or less.

──────────────────────────────────
Cellulose acetate solution composition ───────────────────────────────────
Cellulose acetate having an acetylation degree of 60.9% (degree of polymerization: 300, Mn / Mw = 1.5) 100 parts by weight Triphenyl phosphate (plasticizer) 7.8 parts by weight Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by weight Methylene chloride (first solvent) 300 parts by weight Methanol (second solvent) 54 parts by weight 1-butanol (third solvent) 11 parts by weight ──────────────────── ──────────────

  In another mixing tank, 16 parts by mass of the following retardation increasing agent A, 8 parts by mass of retardation increasing agent B, 0.28 parts by mass of silicon dioxide fine particles (average particle size: 100 nm), 80 parts by mass of methylene chloride and A solution A was prepared by adding 20 parts by mass of methanol and stirring while heating. 40 parts by mass of the solution A was mixed with 474 parts by mass of the cellulose acetate solution, and stirred well to prepare a dope.

  The obtained dope was cast using a band casting machine. A film having a residual solvent amount of 15% by mass was stretched transversely at a stretch ratio of 20% using a tenter under the conditions of 130 ° C., held at 50 ° C. for 30 seconds with the stretched width, and then clipped to remove cellulose. An acetate film was prepared. The residual solvent amount at the end of stretching was 5% by mass, and further dried to prepare a film with the residual solvent amount being less than 0.1% by mass.

  The polymer substrate thus obtained had a thickness of 80 μm. About the produced polymer base material, the light incident angle dependence of Re was measured using the automatic birefringence meter (KOBRA-21ADH, Oji Scientific Instruments Co., Ltd. product). It was found that Re was 60 nm, Rth was 200 nm, and that Nz was 3.8.

(Production of optical compensation sheet)
The surface of the produced polymer substrate was subjected to saponification treatment, and an alignment film forming coating solution having the following composition was adjusted on this film with potassium hydroxide so as to have a pH of 6.0. The alignment film coating solution was applied at 20 ml / m ² with a wire bar coater. The alignment film was obtained by drying with warm air of 60 ° C. for 60 seconds and further with warm air of 100 ° C. for 120 seconds.

(Composition of alignment film forming coating solution)
The following modified polyvinyl alcohol 20 parts by mass Potassium hydroxide 0.05 parts by mass Glutaraldehyde 0.5 parts by mass Water 360 parts by mass Methanol 120 parts by mass

(Formation of optically anisotropic layer)
First, an optically anisotropic layer forming solution was prepared by dissolving the following composition in 102 g of methyl ethyl ketone.
(Composition of optically anisotropic layer)
Rod-like liquid crystalline compound having the following two acrylate groups (Ac-2) 45.07 parts by mass The following onium salt (1) 0.45 parts by mass The following polymer A 0.18 parts by mass Photopolymerization initiator (Irgacure 907, Ciba-Geigy 1.35 parts by mass sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.45 parts by mass dipentaerythritol hexaacrylate (M-8 in the text) 4.50 parts by weight

  This coating solution was applied to the surface of the alignment film with a wire bar. This was attached to a metal frame and heated in a constant temperature bath at 100 ° C. for 2 minutes to align the rod-like liquid crystalline compound. Next, UV irradiation was performed at 60 ° C. with a 120 W / cm high-pressure mercury lamp for 20 seconds to crosslink the rod-like liquid crystalline compound, and then allowed to cool to room temperature to prepare an optically anisotropic layer. About the produced optically anisotropic layer, when the optical incident angle dependence of Re was measured using the automatic birefringence meter (KOBRA-21ADH, Oji Scientific Instruments Co., Ltd. product), Re was 0 nm and Rth was -260 nm. Further, the optically anisotropic layer exhibited homeotropic alignment.

(Evaluation of orientation order of optically anisotropic layer)
The degree of orientation order was calculated using “Nanofinder” manufactured by Tokyo Instruments Co., Ltd. with reference to the method described on pages 651 to 654 of Proceedings of IDW'04, 651 (2004). The degree of orientation order was 0.54.

(Measurement of reaction rate of polymerizable group at air side interface and alignment film side interface of optically anisotropic layer)
The reaction rate of the polymerizable group in the surface layer of the air-side interface (interface opposite to the support) of the optically anisotropic layer was measured using a 710 FT-IR SPECTROMETER manufactured by Nicolet, with an attached cell capable of measuring only the surface layer. Calculated from the results. From the peak area ratio of around 1600 cm ^-1 derived from the peak and ester groups 810 cm ^-1 derived from acrylate groups, to calculate the composition of the residual acrylate groups, and further calculates the degree of polymerization of the optically anisotropic layer.
The reaction rate of the polymerizable group at the alignment film side interface (support side interface) was measured by the same method as described above after peeling the optically anisotropic layer from the alignment film. The results are shown in Table 1.

(Evaluation of adhesion of optical compensation sheet)
The adhesion of the optical compensation sheet was evaluated by preparing a test piece in accordance with the JIS K 5400 8.5.2 base tape method. However, polyester adhesive tape NO31RH manufactured by Nitto Denko was used for evaluation. The results are shown in Table 1. 10 points are those with good adhesion and no peeling, and 0 points when the entire surface is peeled off due to insufficient adhesion. The higher the score, the better the adhesion.
(Evaluation of suitability for optical compensation sheet pre-treatment process)
The optical compensation sheet is immersed in 1.5 N potassium hydroxide at 55 ° C. for 2 minutes, washed with water, then immersed in 0.1 N hydrochloric acid at 30 ° C. for 20 seconds, washed with water, and dried in this order to make the film surface turbid. It was examined visually. The results are shown in Table 1. In the table, ○ is transparent with no change, Δ is slightly cloudy, and X is markedly cloudy.

[Examples 2 to 10, Comparative Examples 1 to 3]
Except that the components of the optically anisotropic layer of Example 1 and the atmosphere during light irradiation were changed as shown in Table 1,
Optical compensation sheets of Examples 2 to 10 and Comparative Examples 1 to 3 were prepared by the same procedure as Example 1.
Table 1 shows the results of the reaction rate measurement of the polymerizable group on the air-side interface surface layer and the alignment film-side interface surface layer of the optically anisotropic layer, the evaluation of the adhesion of the optical compensation sheet, and the suitability evaluation of the pre-bonding process of the optical compensation sheet. Show.
From Examples 1 to 10 and Comparative Examples 1 to 3, it can be seen that the optical compensation sheet of the present invention has good adhesion and no problem in the pre-bonding process, and therefore the yield of the bonding process is increased.

Claims (7)

An optical compensation sheet having an optically anisotropic layer formed from a liquid crystalline composition containing a rod-like liquid crystalline compound and a photopolymerization initiator on a support, the polymerizable group present in the liquid crystalline composition The optical compensation sheet has a reaction rate of 70% or more at the support-side interface of the optically anisotropic layer and 20% or more at the interface opposite to the support. The optical compensation sheet according to claim 1, wherein the liquid crystalline composition contains a compound having 3 or more polymerizable groups in one molecule and having a molecular weight of 250 to 650. The optical compensation sheet according to claim 1 or 2, wherein the optically anisotropic layer is formed by irradiating the liquid crystalline composition with active light in an atmosphere having an oxygen content of 5% by volume or less. The optical compensation sheet according to any one of claims 1 to 3, further comprising an alignment film between the support and the optically anisotropic layer. The polarizing plate which has an optical compensation sheet as described in any one of Claims 1-5. A liquid crystal display device comprising the polarizing plate according to claim 5. A liquid crystal display device comprising: a polarizing plate having the optical compensation sheet according to any one of claims 1 to 5; a polarizing film; and a liquid crystal cell having a liquid crystal layer sandwiched between a pair of substrates, wherein the liquid crystal is displayed during black display. The liquid crystalline compound in the cell is aligned substantially parallel to the surfaces of a pair of substrates, the Re of the support measured from the normal direction of the support is 20 nm to 150 nm, and the Nz value of the support Is 1.5 to 7, Re is 5 nm or less and Rth is −80 nm to −400 nm, and the liquid crystalline compound in the optical anisotropic layer is homeotropically aligned, A liquid crystal display device in which the transmission axis of the polarizing film is parallel to the slow axis direction of the liquid crystal compound in the liquid crystal cell during black display.