JP2007264449A - Optical compensation sheet, method of manufacturing optical compensation sheet, polarizing plate, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical compensation sheet controlling an inclined angle on an air interface side and an alignment layer side, containing a discotic liquid crystalline compound with hybrid alignment in an optically anisotropic layer and contributing to improvement in a visual field angle of a liquid crystal display device of a TN mode, an OCB mode, a VA mode, an IPS mode, and the like, to provide a polarizing plate using the same and to provide the liquid crystal display device of the TN mode, the OCB mode, the VA mode, the IPS mode, and the like. <P>SOLUTION: The optical compensation sheet comprising a supporting body and an optically anisotropic layer, is characterized in that the inclined angle of liquid crystalline molecules forming the optically anisotropic layer is changed depending on the distance from the surface of the supporting body, the inclined angle on the air interface side is made larger than the inclined angle on the supporting body side, inclined angle difference therebetween is 40 to 90° and the inclined angle on the supporting body side is 0 to 10°. The polarizing plate and the liquid crystal display device are also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a novel optical compensation sheet. In particular, the present invention relates to an optical compensation sheet in which the tilt angle of liquid crystal on the alignment film side and the air interface side of an optically anisotropic layer made of a discotic liquid crystal composition is controlled.

  Optical compensation sheets are used in various liquid crystal display devices in order to eliminate image coloring and expand the viewing angle. Conventionally, stretched birefringent films have been used as optical compensation sheets, but in recent years, instead of stretched birefringent films, optical compensation sheets having an optically anisotropic layer made of a liquid crystalline compound on a transparent support have been used. It has been proposed to do. In this optically anisotropic layer, a composition containing a discotic liquid crystalline compound is usually applied on an alignment film, and heated to a temperature higher than the alignment temperature to align the discotic liquid crystalline compound, and the alignment state is changed. It is formed by fixing. In general, the discotic liquid crystalline compound has a large birefringence and various alignment forms. And by using a liquid crystalline compound, it has become possible to realize optical properties that cannot be obtained with conventional stretched birefringent films.

  As described above, since various orientation forms exist in the discotic liquid crystalline compound, it is necessary to control the orientation of the discotic liquid crystalline compound in the optically anisotropic layer in order to develop desired optical characteristics. In particular, in order to develop optical compensation performance, it is important to realize a so-called “hybrid alignment” state in which the tilt angle of the discotic liquid crystalline compound is aligned so as to change with the distance from the support surface. It is the most important factor that determines the performance of the compensation sheet, that is, the viewing angle expansion, the contrast reduction due to the viewing angle change, the gradation inversion, the black-and-white inversion, and the hue change. This hybrid alignment is the difference between the inclination angle of the alignment film surface provided on the support and the inclination angle of the air-side interface, which is the outermost surface of the optical compensation sheet, for the purpose of regulating the orientation angle of the discotic liquid crystalline compound. It is realized by using. After applying and drying an optical compensation sheet using a discotic liquid crystalline compound, the discotic liquid crystalline compound is monodomain aligned at a stable tilt angle at both the air interface and the alignment film interface. As a result, an alignment state in which the inclination angle continuously changes in the thickness direction of the film is formed. The discotic liquid crystalline compound has a property of having a high tilt angle of 50 ° or more at the air interface. Therefore, in order to realize hybrid alignment, the tilt angle of the alignment film interface must be significantly smaller than the tilt angle of the air interface. An alignment film using polyvinyl alcohol is suitably used for realizing the target hybrid alignment (Patent Document 1).

  On the other hand, in order to obtain a desired optical compensation function, it is necessary to control the inclination angle on the air interface side and the inclination angle on the alignment film side. As a method of obtaining an angle exceeding 50 ° which is an inclination angle obtained at a normal air interface, a method of adding an esterified product of a cellulose portion or a method of adding a polymer compound having a specific structure has been proposed (Patent Document 2). However, when the present inventor actually used these optical compensation sheets, it was found that light leakage from the oblique direction of the polarizing plate was observed and that the viewing angle was not sufficiently expanded. As one of the reasons why the optical compensation function becomes insufficient, it has been found that the tilt angle of the discotic liquid crystalline compound is not sufficient, that is, does not expand to the extent that can be theoretically expected. One reason for the insufficient optical compensation function is that the tilt angle of the discotic liquid crystalline compound is not sufficiently controlled.

In the prior art, an optical compensation sheet has been developed mainly assuming a small or medium-sized liquid crystal display device of 15 inches or less. However, recently, it is also necessary to assume a liquid crystal display device having a large size of 17 inches or more and high brightness. When a conventional optical compensation sheet was attached as a protective film to a polarizing plate of a large liquid crystal display device, it was found that unevenness occurred on the panel. This unevenness was not so conspicuous in a small-sized or medium-sized liquid crystal display device, but it is necessary to further develop an optical film that copes with the light leakage unevenness in response to an increase in size and brightness. As a technique for improving unevenness, a method of incorporating a leveling agent into a polymerizable liquid crystal has been disclosed (for example, see Patent Document 3). However, it has been found that this method is effective only when the polymerizable liquid crystal is homogeneously aligned, and cannot be applied to complicated alignment such as hybrid alignment as in the present invention. In the present invention, as a method for applying the optical compensation sheet, a method using a wire bar has been mainly used so far. In the method using the wire bar, stepped unevenness is likely to occur due to the vibration of the coating liquid in the liquid receiving tank and the eccentricity or deflection of the roll related to the coating. In order to solve these problems, there is an increasing demand for a method for continuous precision thin film coating on a web using a slot die coater, particularly a thin film coating method having a wet film thickness of 20 μm or less. Such an optical compensation sheet has a strict requirement for coating film thickness accuracy and coating film properties, and a highly accurate thin layer coating technique has been proposed (Patent Document 4).
JP-A-8-50206 JP-A-8-95030 JP-A-11-148080 Japanese National Publication No. 9-511682

  The present invention controls the tilt angle of a liquid crystal compound that is hybrid-aligned in an optically anisotropic layer, has an excellent optical compensation function, and has a display quality that hardly causes gradation inversion when applied to an image display device. It is an object to provide an optical compensation sheet capable of displaying a high image. In particular, a liquid crystal display device such as a TN mode, an OCB mode, a VA mode, and an IPS mode, in which the tilt angle on the air interface side and the alignment film side is controlled, and the optically anisotropic layer contains a hybrid-aligned discotic liquid crystalline compound It is an object of the present invention to provide an optical compensation sheet that contributes to improving the viewing angle.

  The object of the present invention has been achieved by the following.

(1) In an optical compensation sheet comprising a support and an optically anisotropic layer, the tilt angle of the liquid crystalline molecules forming the optically anisotropic layer varies with the distance from the support surface, and the tilt angle on the air interface side An optical compensation sheet characterized in that the inclination angle is larger than the inclination angle on the support side, the difference between these inclination angles is 40 degrees or more and 90 degrees or less, and the inclination angle on the support side is 0 degrees or more and 10 degrees or less.
(2) The optical compensation sheet according to (1), wherein the inclination angle difference is 50 degrees or more and 90 degrees or less.
(3) The optical compensation sheet according to (1) or (2), wherein an inclination angle on the support side is from 0 degree to 5 degrees.
(4) After applying a liquid containing a nematic liquid crystal compound in an organic solvent on the support, evaporating and drying the organic solvent, and then heating to a temperature higher than the liquid crystal transition temperature to form an optically anisotropic layer A method for producing an optical compensation sheet, which is produced by cooling to a temperature of 40 ° C. or lower and then polymerizing and / or curing by UV irradiation.
(5) The method for producing an optical compensation sheet according to (4), wherein the cooling is performed at an average speed in the range of 0.5 ° C./second or more and 50 ° C./second or less to a temperature of 40 ° C. or less.
(6) The method for producing an optical compensation sheet according to (5), wherein the cooling temperature is 20 ° C. or lower.
(7) The optical compensation sheet according to any one of (1) to (3), wherein the liquid crystal compound is a discotic liquid crystal compound.
(8) The optical compensation sheet according to any one of (4) to (6), wherein an optically anisotropic layer or an alignment layer is applied to the surface of the transparent support by a slide coater or a slot die coater. Manufacturing method.
(9) The optical compensation sheet according to any one of (1) to (3) and (7), and the optical compensation sheet according to any one of (4) to (6) and (8). A polarizing plate having an optical compensation sheet.
(10) A liquid crystal display device having the polarizing plate according to (9).

  According to the present invention, the tilt angle (the tilt angle on the air interface side and the alignment film side) of the liquid crystal compound that is hybrid-aligned is controlled, the viewing angle characteristics of the liquid crystal display device of various modes are improved, and the gradation inversion occurs. It is possible to provide a novel optical compensation sheet that is difficult to display and excellent in display quality.

  Hereinafter, the contents of the present invention will be described in detail. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value. The term “polymerization” as used in the present invention is intended to include copolymerization. Furthermore, the term “on the support” or “alignment film” as used in the present invention refers to a direct surface of the support or the like, and a surface provided with any layer (film) on the support or the like. This is intended to include both cases.

Further, in the present specification, “substantially parallel” and “substantially orthogonal” mean that the angle is within a range of strictly less than ± 10 °. In this range, an error from a strict angle is preferably less than ± 5 °, and more preferably less than ± 2 °.
Further, the “slow axis” means a direction in which the refractive index is maximized. Further, the measurement wavelength of the refractive index is a value at λ = 550 nm in the visible light region unless otherwise specified.

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

[Optically anisotropic layer]
The optically anisotropic layer is preferably designed so as to compensate for the liquid crystal compound in the liquid crystal cell in the black display of the liquid crystal display device. The alignment state of the liquid crystal compound in the liquid crystal cell in black display varies depending on the mode of the liquid crystal display device. The alignment state of the liquid crystal compound in this liquid crystal cell is described in IDW'00, FMC 7-2, pages 411 to 414.
The optically anisotropic layer is formed directly from liquid crystalline molecules on the support, or is formed from liquid crystalline molecules via an alignment film. The alignment film preferably has a thickness of 10 μm or less.
Liquid crystalline molecules used for the optically anisotropic layer include rod-like liquid crystalline molecules and discotic liquid crystalline compounds. The rod-like liquid crystal molecule and the discotic liquid crystal compound may be a high-molecular liquid crystal or a low-molecular liquid crystal, and further include those in which the low-molecular liquid crystal is cross-linked and no longer exhibits liquid crystallinity.
The optically anisotropic layer can be formed by applying a liquid crystal molecule and, if necessary, a coating liquid containing a polymerizable initiator and optional components on the alignment film.
A preferred example of the alignment film of the present invention is described in JP-A-8-338913.

As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane, tetrachloroethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.
When producing an optical film with very high uniformity as in the present invention, the surface tension is preferably 25 mN / m or less, and more preferably 22 mN / m or less.
The thickness of the optically anisotropic layer is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and most preferably 1 to 10 μm.
The coating liquid can be applied by a known method (eg, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).
A preferred die coating method application of the optical compensation sheet of the present invention will be described.
FIG. 1 is a schematic view of a coater using a slot die embodying the present invention. The coater 10 applies a coating solution 14 from the slot die 13 to the web 12 that is continuously supported by the backup roll 11 to form a coating film 14 b on the web 12.

  The slot die 13 has a pocket 15 and a slot 16 formed therein. The pocket 15 has a curved cross section and a straight line. For example, a substantially circular shape as shown in FIG. 1 or a semicircular shape may be used. The pocket 15 is a liquid storage space for the coating liquid extended in the width direction of the slot die 13 with its cross-sectional shape, and the length of the effective extension is generally equal to or slightly longer than the coating width. The coating liquid 14 is supplied to the pocket 15 from the side of the slot die 13 or from the center of the surface opposite to the slot, and the pocket 15 is provided with a stopper for preventing the coating liquid 14 from leaking out. Yes.

  The slot 16 is a flow path of the coating liquid 14 from the pocket 15 to the web 12, and has a cross-sectional shape in the width direction of the slot die 13 like the pocket 15, and the opening 16a located on the web side is generally Using a width regulating plate (not shown), the width is adjusted to be approximately the same as the coating width. The angle between the slot 16 and the tangent in the web traveling direction of the backup roll 11 at the slot tip is generally 30 ° or more and 90 ° or less, and the effect of the present invention is limited to the slot die having the above shape. is not.

  The tip lip 17 of the slot die 13 where the opening 16a of the slot 16 is located is tapered, and the tip is a flat portion 17a called a land. In this flat portion 17 a, the upstream side of the web 12 in the traveling direction of the web 12 with respect to the slot 16 is hereinafter referred to as an upstream lip land 18 and the downstream side is referred to as a downstream lip land 19.

The length I _LO in the web running direction of the downstream lip land 19 is preferably 30 μm to 500 μm, more preferably 30 μm to 100 μm, and still more preferably 30 μm to 60 μm. Further, the length I _UP of the upstream lip land 18 in the web traveling direction is not particularly limited, but is preferably used in the range of 500 μm to 1 mm.

FIG. 2 shows a cross-sectional shape of the slot die 13 in comparison with the conventional one, (A) shows the slot die 13 of the present invention, and (B) shows the conventional slot die 30. In the conventional slot die 30, the land length I _LO of the downstream lip land 31 is not taken into consideration, and the length is substantially the same as the length I _UP of the upstream lip land. Reference numeral 32 denotes a pocket, and 33 denotes a slot. On the other hand, in the slot die 13 of the present invention, the downstream side lip land length I _LO is shortened, whereby the wet film thickness of 20 μm or less can be applied with high accuracy. In addition, by setting the land length I _LO of the downstream lip land 19 in the range of 30 μm to 100 μm, a lip land with good dimensional accuracy can be formed.

Further, in order to make the film thickness of the coating film uniform with high accuracy, the fluctuation width in the width direction of the slot die 13 of the land length I _LO of the downstream side lip land 19 is set within 20 μm. This is because the bead formation becomes unstable when the land length I _LO of the downstream lip land 19 is increased. Moreover, the bead becomes unstable due to a slight disturbance, and the suitability for production is lost. For this reason, the slot die 13 is manufactured so that the fluctuation width in the width direction of the slot die 13 is within 20 μm.

  As a measure for improving the strength and surface state of the tip lip 17 including the opening a of the slot 16, the material of the slot die including at least this portion is made of a super hard material mainly composed of WC. By using a super hard material, in addition to the homogeneity of the surface shape, it also serves as a measure against the abrasion of the tip lip caused by the coating liquid that is always discharged. This is particularly effective when applying a magnetic liquid containing an abrasive as the coating liquid. As the super hard material, a material obtained by bonding a WC carbide crystal having an average particle diameter of 5 μm with a bonding metal such as Co is used, but the bonding metal is not limited to this, and includes Ti, Ta, Nb and the like. Various metals can be used. In addition, as long as the average particle diameter of a WC crystal is within 5 micrometers, you may use the thing of arbitrary average particle diameters.

Further, in order to maintain the coating thickness of the thin layer uniformly with high accuracy, in addition to maintaining the dimensional accuracy of the land length I _LO of the downstream lip land 19 in the coating width direction, the tip lip of the slot die 13 is also maintained. The straightness of both 17 and the backup roll 11 is also important. Since this is achieved by two combinations of the straight end of the slot die 10 and the backup roll 13, it is meaningless to improve only one of them. The required straightness can be obtained with practically sufficient accuracy although it is an approximation using the following formula (1), but is not limited thereto. Here, the pressure outside the bead meniscus in the traveling direction of the P ₀ web 12 as shown in FIG. 3, Pp is the pressure of the pocket 15, although not shown below, sigma is the surface tension of the coating liquid 14, mu is The viscosity of the coating liquid 14a, U is the coating speed, h is the film thickness, d is the length of the gap between the downstream lip land 19 and the web 12, L is the length of the slot 16 of the slot die 13, and D is the slot die 13. Slot spacing. The differential pressure P ₀ -Pp between the internal pressure Pp of the pocket 15 of the slot die 13 and the pressure PO outside the bead meniscus on the web traveling direction side is made constant in the width direction of the slot die 13 and the following equation (1) is used: Find the required straightness. This is because the differential pressure between the pocket 15 of the slot die 13 and the outside of the bead meniscus is constant even if the length d of the gap between the tip of the slot die 13 and the backup roll 11 changes. This is because the flow in the width direction of the die 13 is generated in the pocket 15 and becomes a flow distribution.
P ₀ −Pp = 1.34σ / h (μU / σ) ^2/3 +12 μUI _LO (d / 2−h) / d ³
-12μhUL / D ³ (1)

  Although strictly different depending on conditions by using the above formula (1), in a coating system used for general industrial production, the coating film thickness distribution is 2% with a straightness in the die block width direction of about 5 μm. Will occur. Therefore, it can be considered that this limit is the limit when high-precision thin film coating is performed. Thereby, when the slot die 13 is set at the coating position, the straightness between the tip lip and the backup roll is such that the fluctuation width in the slot die width direction of the gap between the tip lip and the web is within 5 μm. Put out.

(Rod-like liquid crystalline molecules)
Examples of rod-like liquid crystalline molecules include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines. , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used.
The rod-like liquid crystalline molecule includes a metal complex. In addition, a liquid crystal polymer containing a rod-like liquid crystalline molecule in a repeating unit can also be used as the rod-like liquid crystalline molecule. In other words, the rod-like liquid crystal molecule may be bonded to a (liquid crystal) polymer.
For rod-like liquid crystalline molecules, see Chapter 4, Chapter 7 and Chapter 11 of the Chemistry of the Quarterly Chemistry Vol. 22 (1994) The Chemical Society of Japan, and the 142th Committee of the Japan Society for the Promotion of Science. Described in Chapter 3.
The birefringence of the rod-like liquid crystal molecule is preferably in the range of 0.001 to 0.7. The rod-like liquid crystalline molecule preferably has a polymerizable group in order to fix its alignment state. The polymerizable group is preferably an unsaturated polymerizable group or an epoxy group, more preferably an unsaturated polymerizable group, and most preferably an ethylenically unsaturated polymerizable group.

(Discotic liquid crystalline compounds)
Examples of discotic liquid crystalline compounds include C.I. Benzene derivatives described in a research report of Destrade et al. (Mol. Cryst. 71, 111 (1981)), C.I. Destrode et al. (Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 (1990)) described in The cyclohexane derivatives described in the research report of Kohne et al. (Angew. Chem. 96, 70 (1984)) and M.M. Lehn et al. (J. Chem. Commun., 1794 (1985)), J. Chem. Azacrown-type and phenylacetylene-type macrocycles described in the research report of Zhang et al. (J. Am. Chem. Soc. 116, 2655 (1994)) are included.
As a discotic liquid crystalline compound, a compound having liquid crystallinity in which a linear alkyl group, an alkoxy group, and a substituted benzoyloxy group are radially substituted as a side chain of the mother nucleus with respect to the mother nucleus at the center of the molecule Is also included. The molecule or the assembly of molecules is preferably a compound having rotational symmetry and imparting a certain orientation. In the optically anisotropic layer formed from the discotic liquid crystalline compound, the compound finally contained in the optically anisotropic layer does not have to be a discotic liquid crystalline compound. Also included are compounds having a group that reacts with heat or light and, as a result, polymerized or cross-linked by reaction with heat or light, resulting in a high molecular weight and loss of liquid crystallinity. Preferred examples of the discotic liquid crystalline compound are described in JP-A-8-50206. The polymerization of discotic liquid crystalline compounds is described in JP-A-8-27284.

  In order to fix the discotic liquid crystalline compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline compound. However, when the polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain the orientation state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystalline compound having a polymerizable group is preferably a compound represented by the following formula (III).

Formula (III) D (-LQ) _n1
In formula (III), D is a discotic core; L is a divalent linking group, Q is a polymerizable group, and n is an integer of 4-12.
An example of the disk-shaped core (D) is shown below. In each of the following examples, LQ (or QL) means a combination of a divalent linking group (L) and a polymerizable group (Q).

  In the orientation of the present invention, the tilt angle increases in the depth direction of the optically anisotropic layer and with the distance from the transparent support surface. Further, as the change of the inclination angle, a change including a continuous increase, an intermittent increase, a continuous increase and a continuous decrease is possible. The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. Even if a region where the angle does not change is included, it may be increased or decreased as a whole. However, it is preferred that the tilt angle changes continuously. In the discotic liquid crystal, the tilt angle is an angle between the major axis (disk surface) of the discotic liquid crystalline compound and the surface of the support.

  The average direction of the major axis (disk surface) of the discotic liquid crystalline compound (average angle with the substrate surface in the major axis direction of each molecule) is generally selected from the material of the discotic liquid crystalline compound or the alignment film, or the rubbing treatment method And selection of a quenching method from a temperature higher than the nematic liquid crystal phase-solid phase transition temperature to a temperature of 40 ° C. or lower. The temperature for rapid cooling from the temperature above the nematic liquid crystal phase-solid phase transition temperature is preferably 40 ° C. or less, and particularly preferably 20 ° C. or less. Moreover, when quenching, it is preferable to cool at an average speed in the range of 0.5 ° C./second or more and 50 ° C./second or less, and further, at an average speed in the range of 5 ° C./second or more and 50 ° C./second or less. It is preferable to do.

  The plasticizer, surfactant and polymerizable monomer used together with the discotic liquid crystalline compound are preferably compatible with the discotic liquid crystalline compound and do not inhibit the alignment. Among the additive components, addition of a polymerizable monomer (eg, a compound having a vinyl group, a vinyloxy group, an acryloyl group and a methacryloyl group) is preferable. The amount of the compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the discotic liquid crystalline compound. In addition, when a monomer having 4 or more polymerizable reactive functional groups is mixed and used, the adhesion between the alignment film and the optically anisotropic layer can be improved.

  The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound is preferably 70 to 300 ° C, more preferably 70 to 170 ° C.

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

The amount of the photopolymerization initiator used is preferably in the range of 0.01 to 20% by mass, more preferably in the range of 0.5 to 5% by mass, based on the solid content of the coating solution.
It is preferable to use ultraviolet rays for light irradiation for polymerization of liquid crystalline molecules.
The irradiation energy is preferably in the range of ^{20mJ / cm 2 ~50J / cm 2} , more preferably in the range of 20~5000mJ / cm ^2, more preferably in the range of 100 to 800 mJ / m ² .
The ultraviolet rays are preferably irradiated after cooling to a desired temperature, preferably cooled to a temperature of 40 ° C. or lower, more preferably 20 ° C. or lower after cooling.
A protective layer may be provided on the optically anisotropic layer.

The tilt angle of the liquid crystal compound on the alignment film side is preferably 10 degrees or less, more preferably 5 degrees or less, and the tilt angle on the air interface side is preferably 60 degrees or more, and more preferably 65 degrees or more.
In an optically anisotropic layer in which a discotic compound or rod-shaped compound is oriented, the tilt angle on one surface of the optically anisotropic layer (the physical target axis of the discotic compound or rod-shaped compound is the interface of the optically anisotropic layer) It is difficult to directly and accurately measure θ1 and the tilt angle θ2 of the other surface. Therefore, in this specification, θ1 and θ2 are calculated by the following method. Although this method does not accurately represent the actual orientation state of the present invention, it is effective as a means for expressing the relative relationship of some optical properties of the optical film.
In this method, in order to facilitate calculation, the following two points are assumed and the tilt angle at the two interfaces of the optically anisotropic layer is used.
1. The optically anisotropic layer is assumed to be a multilayer body composed of layers containing a discotic compound or a rod-like compound. Further, it is assumed that the minimum unit layer (assuming that the tilt angle of the discotic compound or rod-shaped compound is uniform in the layer) is optically uniaxial.
2. It is assumed that the tilt angle of each layer changes monotonically with a linear function along the thickness direction of the optically anisotropic layer.
The specific calculation method is as follows.
(1) In a plane in which the tilt angle of each layer changes monotonically with a linear function along the thickness direction of the optically anisotropic layer, the incident angle of the measurement light to the optically anisotropic layer is changed, and three or more The retardation value is measured at the measurement angle. In order to simplify measurement and calculation, it is preferable to measure the retardation value at three measurement angles of −40 °, 0 °, and + 40 °, with the normal direction to the optically anisotropic layer being 0 °. Such measurements include KOBRA-21ADH and KOBRA-WR (manufactured by Oji Scientific Instruments), transmission ellipsometer AEP-100 (manufactured by Shimadzu Corporation), M150 and M520 (manufactured by JASCO Corporation) ), ABR10A (manufactured by UNIOPT Co., Ltd.).
(2) In the above model, the refractive index of ordinary light of each layer is no, the refractive index of extraordinary light is ne (ne is the same value in all layers, and no is the same), and the thickness of the entire multilayer body is d And Further, based on the assumption that the tilt direction of each layer and the uniaxial optical axis direction of the layer coincide with each other, the calculation of the angular dependence of the retardation value of the optically anisotropic layer agrees with the measured value. Fitting is performed using the tilt angle θ1 on one surface of the isotropic layer and the tilt angle θ2 on the other surface as variables, and θ1 and θ2 are calculated. Here, for no and ne, known values such as literature values and catalog values can be used. If the value is unknown, it can also be measured using an Abbe refractometer. The thickness of the optically anisotropic layer can be measured by an optical interference film thickness meter, a cross-sectional photograph of a scanning electron microscope, or the like.

(Other additives for optically anisotropic layers)
Along with the liquid crystal compound, a plasticizer, a polymerizable monomer, and the like can be used in combination to improve the uniformity of the coating film, the strength of the film, the orientation of the liquid crystal compound, and the like. These materials are preferably compatible with the liquid crystal compound and do not inhibit the alignment.
Examples of the polymerizable monomer include radically polymerizable or cationically polymerizable compounds. Preferably, it is a polyfunctional radically polymerizable monomer and is preferably copolymerizable with the above-described polymerizable group-containing liquid crystal compound. Examples thereof include those described in paragraph numbers [0018] to [0020] in JP-A No. 2002-296423. The amount of the compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the discotic liquid crystalline molecules.

[Alignment film]
The alignment film is an organic compound (eg, ω-tricosanoic acid) formed by rubbing treatment of an organic compound (preferably polymer), oblique deposition of an inorganic compound, formation of a layer having a microgroove, or Langmuir-Blodgett method (LB film). , Dioctadecylmethylammonium chloride, methyl stearylate). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field, or light irradiation is also known.
As long as the liquid crystal molecules of the optically anisotropic layer provided on the alignment film can be provided with a desired alignment, any layer may be used as the alignment film. From the viewpoint of easy control, an alignment film formed by a rubbing treatment of a polymer is particularly preferable. The rubbing treatment can be generally carried out by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth. In particular, as described later in the present invention, it is described in the liquid crystal manual (Maruzen Co., Ltd.). It is preferable to carry out by the method.
The thickness of the alignment film is preferably 0.01 to 10 μm, and more preferably 0.05 to 1 μm.
The polymer used for the alignment film is described in many documents, and many commercially available products can be obtained. In the alignment film for an optical compensation film of the present invention, polyvinyl alcohol and derivatives thereof are preferably used. Particularly preferably, modified polyvinyl alcohol to which a hydrophobic group is bonded is particularly preferable, and the tilt angle on the alignment film side can be controlled by the content of the hydrophobic group. Regarding the alignment film, reference can be made to the description of page 43, line 24 to page 49, line 8 of WO01 / 88574A1.

[Rubbing density of alignment film]
As a method for changing the rubbing density of the alignment film, a method described in Liquid Crystal Handbook (Maruzen Co., Ltd.) can be used. The rubbing density (L) is quantified by the formula (A).
Formula (A) L = Nl (1 + 2πrn / 60v)
In the formula (A), N is the number of rubbing, l is the contact length of the rubbing roller, r is the radius of the roller, n is the number of rotations (rpm) of the roller, and v is the stage moving speed (second speed).
In order to increase the rubbing density, the rubbing frequency should be increased, the contact length of the rubbing roller should be increased, the radius of the roller should be increased, the rotation speed of the roller should be increased, and the stage moving speed should be decreased, while the rubbing density should be decreased. To do this, you can reverse this.

[Transparent support]
The in-plane retardation (Re) of the transparent support of the present invention is preferably 5 to 1000 nm, and more preferably 10 to 300 nm. The retardation (Rth) in the thickness direction of the transparent support having optical biaxiality is preferably 10 to 1000 nm, more preferably 15 to 300 nm, and still more preferably 20 to 200 nm.

As the transparent support having optical anisotropy, a synthetic polymer (eg, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, norbornene resin) is generally used. However, as described in European Patent 0911656A2, (1) use of a retardation increasing agent, (2) reduction of acetylation degree of cellulose acetate, or (3) production of a film by a cooling dissolution method, optical A cellulose ester film having anisotropy can also be produced. The transparent support made of a polymer film is preferably formed by a solvent cast method.

Even in the case of polymers that are easily known to exhibit birefringence, such as polycarbonate and polysulfone, which are conventionally known, the birefringence can be developed by modifying the molecule as described in WO '00 / 26705. Can be used for the optical film of the present invention.
When using the optical film of the present invention for a polarizing plate protective film or a retardation film, it is preferable to use cellulose acetate having an acetylation degree of 55.0 to 62.5% as the polymer film. The acetylation degree is more preferably 57.0 to 62.0%.

The degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation is determined by measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like).
The viscosity average degree of polymerization (DP) of cellulose acetate is preferably 250 or more, and more preferably 290 or more. Cellulose acetate preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a mass average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 1.7, more preferably 1.0 to 1.65, and most preferably 1.0 to 1.6. preferable.

In cellulose acetate, the hydroxyl groups at the 2-position, 3-position and 6-position of cellulose are not evenly substituted, but the substitution degree at the 6-position tends to be small. In the polymer film used in the present invention, it is preferable that the degree of substitution at the 6-position of cellulose is the same or greater than that at the 2- and 3-positions.
The ratio of the substitution degree at the 6-position to the total substitution degree at the 2-position, the 3-position, and the 6-position is preferably 30 to 40%, more preferably 31 to 40%, and more preferably 32 to 40%. Most preferably it is. The substitution degree at the 6-position is preferably 0.88 or more.
The degree of substitution at each position can be measured by NMR.
Cellulose acetate having a high degree of substitution at the 6-position is described in Synthesis Example 1 described in Paragraph Nos. 0043 to 0044, Synthesis Example 2 described in Paragraph Nos. 0048 to 0049, and Paragraph Nos. 0051 to 0052. It can be synthesized with reference to the method of Synthesis Example 3.

  In order to obtain the transparent support of the present invention, it is preferable to carry out a stretching treatment on the polymer film. When manufacturing the transparent support body of this invention, it is preferable to implement an unbalance biaxial stretching process. In unbalanced biaxial stretching, the polymer film is stretched in a certain direction (for example, 3 to 100%, preferably 5 to 30%) in a certain direction, and further in the direction perpendicular thereto (for example, 6 to 200%, preferably 10 to 90%). The bi-directional stretching process may be performed simultaneously. The stretching direction (the direction in which the stretching ratio is high in unbalanced biaxial stretching) and the in-plane slow axis of the film after stretching are preferably substantially the same direction. The angle between the stretching direction and the slow axis is preferably less than 10 °, more preferably less than 5 °, and most preferably less than 3 °.

You may laminate | stack the transparent support body of this invention, and the transparent support body (for example, cellulose acetate film) which has optical isotropy. The thickness of the transparent support is preferably 10 to 500 μm, and more preferably 50 to 200 μm. In order to improve the adhesion between the transparent support and the layer (adhesive layer, alignment film or optically anisotropic layer) provided on the transparent support, surface treatment (eg, glow discharge treatment, corona discharge treatment, ultraviolet light ( UV) treatment, flame treatment). An ultraviolet absorber may be added to the transparent support. An adhesive layer (undercoat layer) may be provided on the transparent support. The adhesive layer is described in JP-A-7-333433. The thickness of the adhesive layer is preferably 0.1 to 2 μm, and more preferably 0.2 to 1 μm.

[Polarizing film]
The optical compensation film of the present invention exhibits its functions remarkably by being bonded to a polarizing plate or used as a protective film for a polarizing plate.
The polarizing film of the present invention is preferably a coating type polarizing film typified by Optiva, or a polarizing film comprising a binder and iodine or a dichroic dye.
Iodine and dichroic dye in the polarizing film exhibit deflection performance by being oriented in the binder. It is preferable that the iodine and the dichroic dye are aligned along the binder molecule, or the dichroic dye is aligned in one direction by self-assembly such as liquid crystal.
Currently, general-purpose polarizers are produced by immersing a stretched polymer in a solution of iodine or dichroic dye in a bath and allowing the iodine or dichroic dye to penetrate into the binder. Is common.
In general-purpose polarizing films, iodine or dichroic dye is distributed about 4 μm (about 8 μm on both sides) from the polymer surface, and a thickness of at least 10 μm is necessary to obtain sufficient polarization performance. The penetrability can be controlled by the solution concentration of iodine or dichroic dye, the temperature of the bath, and the immersion time.
As described above, the lower limit of the binder thickness is preferably 10 μm. On the other hand, the upper limit of the thickness is not particularly limited, but the thinner the better, from the viewpoint of the light leakage phenomenon that occurs when the polarizing plate is used in a liquid crystal display device. Currently, it is preferably a general-purpose polarizing plate (about 30 μm) or less, preferably 25 μm or less, and more preferably 20 μm or less. When the thickness is 20 μm or less, the light leakage phenomenon is not observed on a 17-inch liquid crystal display device.

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

  As the binder for the polarizing film, either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent can be used. Examples of polymers include polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, polystyrene, gelatin, polyvinyl alcohol, modified polyvinyl alcohol, poly (N-methylolacrylamide), polyvinyltoluene, chlorosulfonated polyethylene, nitrocellulose, chlorinated Polyolefin (eg, polyvinyl chloride), polyester, polyimide, polyvinyl acetate, polyethylene, carboxymethyl cellulose, polypropylene, polycarbonate and copolymers thereof (eg, acrylic acid / methacrylic acid polymer, styrene / maleimide polymer, styrene / vinyl) Toluene polymer, vinyl acetate / vinyl chloride polymer, ethylene / vinyl acetate polymer). Water-soluble polymers (eg, poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol and modified polyvinyl alcohol) are preferred, gelatin, polyvinyl alcohol and modified polyvinyl alcohol are more preferred, and polyvinyl alcohol and modified polyvinyl alcohol are most preferred. .

The saponification degree of polyvinyl alcohol and modified polyvinyl alcohol is preferably 70 to 100%, more preferably 80 to 100%, and most preferably 95 to 100%. As for the polymerization degree of polyvinyl alcohol, 100-5000 are preferable.
Modified polyvinyl alcohol is obtained by introducing a modifying group into polyvinyl alcohol by polymerization modification, chain transfer modification or block polymerization modification. In the polymerization modification, COONa, Si (OH) ₃ , N (CH ₃ ) ₃ .Cl, C ₉ H ₁₉ COO, SO ₃ Na, C ₁₂ H ₂₅ can be introduced as modifying groups. In chain transfer modification, COONa, SH, or SC ₁₂ H ₂₅ can be introduced as a modifying group. The degree of polymerization of the modified polyvinyl alcohol is preferably 100 to 3000. The modified polyvinyl alcohol is described in JP-A-8-338913, JP-A-9-152509 and JP-A-9-316127.
Unmodified polyvinyl alcohol and alkylthio-modified polyvinyl alcohol having a saponification degree of 85 to 95% are particularly preferable. Two or more kinds of polyvinyl alcohol and modified polyvinyl alcohol may be used in combination.

When a large amount of the crosslinking agent for the binder is added, the heat and humidity resistance of the polarizing film can be improved. However, when 50 mass% or more of a crosslinking agent is added to the binder, the orientation of iodine or the dichroic dye is lowered. 0.1-20 mass% is preferable with respect to a binder, and, as for the addition amount of a crosslinking agent, 0.5-15 mass% is more preferable. The binder contains some crosslinking agent that has not reacted even after the crosslinking reaction has been completed. However, the amount of the remaining crosslinking agent is preferably 1.0% by mass or less in the binder, and more preferably 0.5% by mass or less. When the crosslinking agent is contained in the binder layer in an amount exceeding 1.0% by mass, there may be a problem in durability. That is, when a polarizing film having a large amount of residual crosslinking agent is incorporated in a liquid crystal display device and used for a long time or left in a high-temperature and high-humidity atmosphere for a long time, the degree of polarization may decrease.
The crosslinking agent is described in US Reissue Patent 23297. Boron compounds (eg, boric acid, borax) can also be used as a crosslinking agent.

As the dichroic dye, an azo dye, stilbene dye, pyrazolone dye, triphenylmethane dye, quinoline dye, oxazine dye, thiazine dye or anthraquinone dye is used. The dichroic dye is preferably water-soluble. The dichroic dye preferably has a hydrophilic substituent (eg, sulfo, amino, hydroxyl).
Examples of dichroic dyes include C.I. I. Direct Yellow 12, C.I. I. Direct Orange 39, C.I. I. Direct Orange 72, C.I. I. Direct Red 39, C.I. I. Direct Red 79, C.I. I. Direct Red 81, C.I. I. Direct Red 83, C.I. I. Direct Red 89, C.I. I. Direct Violet 48, C.I. I. Direct Blue 67, C.I. I. Direct Blue 90, C.I. I. Direct Green 59, C.I. I. Acid Red 37 is included. As for the dichroic dyes, those described in JP-A-1-161202, 1-172906, 1-172907, 1-183602, 1-248105, 1-265205, 7-261024 are used. There are descriptions in each publication. The dichroic dye is used as a free acid or an alkali metal salt, ammonium salt or amine salt. By blending two or more kinds of dichroic dyes, polarizing films having various hues can be produced. A polarizing film using a compound (pigment) that exhibits a black color when the polarization axes are orthogonal to each other, or a polarizing film or a polarizing plate in which various dichroic molecules are blended so as to exhibit a black color, have both a single-plate transmittance and a polarizability. It is excellent and preferable.

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

  It is also possible to dispose the polarizing film and the optically anisotropic layer, or the polarizing film and the alignment film via an adhesive. As the adhesive, a polyvinyl alcohol resin (including a modified polyvinyl alcohol with an acetoacetyl group, a sulfonic acid group, a carboxyl group, or an oxyalkylene group) or an aqueous boron compound solution can be used. Of these, polyvinyl alcohol resins are preferred. The thickness of the adhesive layer is preferably in the range of 0.01 to 10 μm after drying, and particularly preferably in the range of 0.05 to 5 μm.

(Manufacture of polarizing plates)
From the viewpoint of yield, the polarizing film is stretched at an angle of 10 to 80 degrees with respect to the longitudinal direction (MD direction) of the polarizing film (stretching method) or rubbed (rubbing method). It is preferable to dye with a dichroic dye. The tilt angle is preferably stretched so as to match the angle formed between the transmission axis of the two polarizing plates bonded to both sides of the liquid crystal cell constituting the LCD and the vertical or horizontal direction of the liquid crystal cell.
A normal inclination angle is 45 °. Recently, however, devices that are not necessarily 45 ° have been developed for transmissive, reflective, and transflective LCDs, and it is preferable that the stretching direction can be arbitrarily adjusted in accordance with the design of the LCD.

In the stretching method, the stretching ratio is preferably 2.5 to 30.0 times, and more preferably 3.0 to 10.0 times. Stretching can be performed by dry stretching in air. Moreover, you may implement wet extending | stretching in the state immersed in water. The stretch ratio of dry stretching is preferably 2.5 to 5.0 times, and the stretch ratio of wet stretching is preferably 3.0 to 10.0 times. The stretching step may be performed in several steps including oblique stretching. By dividing into several times, it is possible to stretch more uniformly even at high magnification. Before the oblique stretching, a slight stretching (a degree to prevent shrinkage in the width direction) may be performed horizontally or vertically.
Stretching can be performed by performing tenter stretching in biaxial stretching in different steps. The biaxial stretching is the same as the stretching method performed in normal film formation.
In biaxial stretching, stretching is performed at different speeds on the left and right, so that the thickness of the binder film before stretching needs to be different on the left and right. In casting film formation, the flow rate of the binder solution can be differentiated between the left and right sides by tapering the die.
As described above, a binder film that is obliquely stretched by 10 to 80 degrees with respect to the MD direction of the polarizing film is produced.

In the rubbing method, a rubbing treatment method widely adopted as a liquid crystal alignment treatment process of LCD can be applied. That is, orientation is obtained by rubbing the surface of the film in a certain direction using paper, gauze, felt, rubber, nylon, or polyester fiber. In general, it is carried out by rubbing several times using a cloth in which fibers having a uniform length and thickness are planted on average. It is preferable to carry out using a rubbing roll in which the roundness, cylindricity, and deflection (eccentricity) of the roll itself are all 30 μm or less. The film wrap angle on the rubbing roll is preferably 0.1 to 90 °. However, as described in JP-A-8-160430, a stable rubbing treatment can be obtained by winding 360 ° or more.
When rubbing a long film, the film is preferably transported at a speed of 1 to 100 m / min in a constant tension state by a transport device. The rubbing roll is preferably rotatable in the horizontal direction with respect to the film traveling direction for setting an arbitrary rubbing angle. It is preferable to select an appropriate rubbing angle in the range of 0 to 60 °. When used for a liquid crystal display device, 40 to 50 ° is preferable. 45 ° is particularly preferred.
It is preferable to dispose a polymer film (arrangement of optically anisotropic layer / polarizing film / polymer film) on the surface of the polarizing film opposite to the optically anisotropic layer.

[Optical compensation sheet, stacking order and stacking angle of layers constituting polarizing plate]
The optical compensation sheet of the present invention is laminated between a polarizing film and a liquid crystal cell in the order of a transparent film and an optically anisotropic layer from the polarizing film side. The polarizing film and the optically anisotropic layer are laminated so that the absorption axis of the polarizing film and the slow axis of the optically anisotropic layer are substantially perpendicular to each other. When the polarizing plate is used, it is preferable that the optical compensation sheet also serves as a protective film on one side of the polarizing plate.
An alignment film, an adhesive layer, a further optically anisotropic layer, and the like can be appropriately added between the above layers as necessary.

[Hard coat film, antiglare film, antireflection film]
Any or all of a hard coat layer, an antiglare layer, and an antireflection layer can be applied to the optical compensation sheet and polarizing plate of the present invention and the liquid crystal display device described below. Preferred embodiments of such an antiglare film and antireflection film are described in detail in pages 54 to 57 of the Japan Institute of Invention and Technology (Publication No. 2001-1745, published on March 15, 2001, Japan Society of Invention). Are listed.

<Liquid crystal display device>
[Configuration of general liquid crystal display device]
In the optical compensation sheet of the present invention, the transmission axis of the polarizing film and the slow axis of the optical compensation sheet may be arranged at any angle. The liquid crystal display device includes a liquid crystal cell in which liquid crystal is supported between two electrode substrates, two polarizing plates disposed on both sides thereof, and at least between the liquid crystal cell and the polarizing film of the polarizing plate. It has a configuration in which one optical compensation sheet is arranged.

  The liquid crystal layer of the liquid crystal cell is usually formed by sealing liquid crystal in a space formed by sandwiching a spacer between two substrates. The transparent electrode layer is formed on the substrate as a transparent film containing a conductive substance. The liquid crystal cell may further be provided with a gas barrier layer, a hard coat layer, or an undercoat layer (undercoat layer) (used for adhesion of the transparent electrode layer). These layers are usually provided on the substrate. The substrate of the liquid crystal cell generally has a thickness of 50 μm to 2 mm.

[Types of liquid crystal display devices]
The optical compensation sheet of the present invention can be used for liquid crystal cells in various display modes. TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-Ferroly Liquid Liquid Crystal), OCB (Optically Charged STP). Various display modes such as ECB (Electrically Controlled Birefringence) and HAN (Hybrid Aligned Nematic) have been proposed. In addition, a display mode in which the above display mode is oriented and divided has been proposed. The cellulose acylate film of the present invention is effective in any display mode liquid crystal display device. Further, it is effective in any of a transmissive type, a reflective type, and a transflective liquid crystal display device.

[TN type liquid crystal display]
The optical compensation sheet of the present invention may be used as an optical compensation sheet for a TN liquid crystal display device having a TN mode liquid crystal cell. TN mode liquid crystal cells and TN type liquid crystal display devices have been well known for a long time. The optical compensation sheet used in the TN type liquid crystal display device is described in JP-A-3-9325, JP-A-6-148429, JP-A-8-50206, and JP-A-9-26572. Moreover, it is described in Mori et al. (Jpn. J. Appl. Phys. Vol. 36 (1997) p. 143 and Jpn. J. Appl. Phys. Vol. 36 (1997) p. 1068). is there.

  The present invention will be described more specifically with reference to the following 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 is not limited to the specific examples shown below.

[Example 1]
(Production of polymer substrate)
The following composition was put into a mixing tank and stirred while heating to 30 ° C. to dissolve each component to prepare a cellulose acetate solution.
────────────────────────────────────
Cellulose acetate solution composition (parts by mass) Inner layer Outer layer ────────────────────────────────────
Cellulose acetate having an acetylation degree of 60.9% 100 parts by weight 100 parts by weight Triphenyl phosphate (plasticizer) 7.8 parts by weight 7.8 parts by weight Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by weight 3.9 parts by weight Methylene chloride (first solvent) 293 parts by mass 314 parts by mass Methanol (second solvent) 71 parts by mass 76 parts by mass 1-butanol (third solvent) 1.5 parts by mass 1.6 parts by mass Silica fine particles (AEROSIL R972, Japan) Aerosil Co., Ltd.)
0 parts by weight 0.8 parts by weight Retardation raising agent 0.5 parts by weight 0 parts by weight ────────────────────────────── ───────

The obtained inner layer dope and outer layer dope were cast on a drum cooled to 0 ° C. using a three-layer co-casting die. The film having a residual solvent amount of 70% by mass was peeled off from the drum, both ends were fixed with a pin tenter, and the film was dried at 80 ° C. while transporting at a draw ratio of 115% in the transport direction, resulting in a residual solvent amount of 10%. By the way, it was dried at 110 ° C. Thereafter, it was dried at a temperature of 155 ° C. for 20 minutes to produce a cellulose acetate film (outer layer: 3 μm, inner layer: 74 μm, outer layer: 3 μm) having a residual solvent of 0.3% by mass. Optical properties were measured using the produced cellulose acetate film as a polymer substrate.
The width of the polymer substrate (PK-1) was 1340 mm and the thickness was 75 μm. When the retardation value (Re) at a wavelength of 630 nm was measured using an ellipsometer (M-150, manufactured by JASCO Corporation), the slow axis was 8 nm, which was in a direction perpendicular to the transport direction. Moreover, it was 35 nm when the retardation value (Rth) in wavelength 630nm was measured.
The polymer substrate (PK-1) was immersed in a 2.0N potassium hydroxide solution (25 ° C.) for 2 minutes, neutralized with sulfuric acid, washed with pure water and dried. The surface energy of this PK-1 was determined by the contact angle method and found to be 63 mN / m.
On this PK-1, an alignment film coating solution having the following composition was coated at a coating amount of 28 ml / m @ 2 with a # 16 wire bar coater. Drying was performed with warm air of 60 ° C. for 60 seconds and further with warm air of 90 ° C. for 150 seconds.

(Orientation film coating solution composition)
The following modified polyvinyl alcohol 10 parts by weight Water 371 parts by weight Methanol 119 parts by weight Glutaraldehyde (crosslinking agent) 0.5 parts by weight

  The alignment film was rubbed in a direction parallel to the slow axis (measured at a wavelength of 632.8 nm) of the polymer substrate (PK-1).

(Formation of optically anisotropic layer)
Optically anisotropic layer composition A
The following discotic liquid crystalline compound 41.01 parts by mass Ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) 4.06 parts by mass Photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) 1.35 parts by mass Sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) 0.45 parts by mass

  The optically anisotropic layer composition A was dissolved in methyl ethyl ketone to obtain a coating solution 14 having a specific gravity of 0.920.

The coating liquid 14 was applied to the web 12 at 7.5 ml / m @ 2 using the slot die 13 having an upstream lip land length _IUP of 1 mm and a downstream lip land length _ILO of 50 .mu.m. The coating speed was 60 m / min. A polymer base material (PK-1) on which an alignment film was applied was used for the web 12, and the length of the gap with the downstream lip land 19 was set to 40 μm. In the rubbing treatment, the alignment film was rubbed in a direction orthogonal to the slow axis (measured at a wavelength of 632.8 nm) of the polymer substrate (PK-1). The coating liquid 14 was continuously applied and heated at 125 ° C. for 2 minutes to align the discotic liquid crystalline compound. Next, the mixture was cooled to 40 ° C. at a rate of 0.5 ° C./second, and irradiated with UV for 2 minutes using a 120 W / cm high-pressure mercury lamp at 40 ° C. to polymerize the discotic liquid crystalline compound. Then, it stood to cool to room temperature. In this manner, an optical compensation sheet (KH-1) with an optically anisotropic layer was produced.
The Re retardation value of the optically anisotropic layer measured at a wavelength of 546 nm is 55 nm, and is substantially orthogonal to the parallel direction of the line obtained by projecting the direction of the director of the liquid crystal molecules onto the surface of the transparent support. Were arranged to be.
Discotic liquid crystalline compounds

(Production of polarizer)
PVA having an average polymerization degree of 4000 and a saponification degree of 99.8 mol% was dissolved in water to obtain a 4.0% aqueous solution. This solution was band-cast using a die having a taper and dried to form a film so that the width before stretching was 110 mm, the thickness was 120 μm at the left end, and 135 μm at the right end.
The film was peeled off from the band, obliquely stretched in the 45 ° direction in a dry state, and immersed in an aqueous solution of iodine 0.5 g / L and potassium iodide 50 g / L for 1 minute at 30 ° C., and then boric acid 100 g / L. L, immersed in an aqueous solution of 60 g / L of potassium iodide at 70 ° C. for 5 minutes, further washed with water at 20 ° C. for 10 seconds and then dried at 80 ° C. for 5 minutes to give an iodine-based polarizer (HF-01) Obtained. The polarizer had a width of 660 mm and a thickness of 20 μm on both the left and right sides.

(Preparation of polarizing plate)
Using a polyvinyl alcohol-based adhesive, KH-1 (optical compensation sheet) was attached to one side of the polarizer (HF-01) on the polymer substrate (PK-1) surface. Moreover, the saponification process was performed to the 80-micrometer-thick triacetylcellulose film (TD-80U: Fuji Photo Film Co., Ltd. product), and it affixed on the other side of the polarizer using the polyvinyl alcohol-type adhesive agent.
The transmission axis of the polarizer and the slow axis of the polymer substrate (PK-1) were arranged in parallel.
The transmission axis of the polarizer and the slow axis of the triacetyl cellulose film were arranged so as to be orthogonal to each other. In this way, a polarizing plate (HB-1) was produced.

[Examples 2 to 5, Comparative Examples 1 and 2]
An optical compensation sheet was prepared in the same manner as in Example 1 except that the amount of the compound used in Example 1 and the added layer were changed and the characteristics were changed as shown in Table 1.

(Evaluation with TN liquid crystal cell)
A pair of polarizing plates provided in a liquid crystal display device (LL-191A, manufactured by Sharp Corporation) using a TN type liquid crystal cell is peeled off, and the polarizing plate (HB-1) prepared in Example 1 is used instead. The optical compensation sheet (KH-1) was attached to the viewer side and the backlight side one by one through an adhesive so that the liquid crystal cell side would be on the liquid crystal cell side. The transmission axis of the polarizing plate on the viewer side and the transmission axis of the polarizing plate on the backlight side were arranged to be in the O mode.
About the produced liquid crystal display device, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using the measuring machine (EZ-Contrast160D, ELDIM company make). For Example 2 and Comparative Examples 1 and 2, a liquid crystal display device was produced in the same manner, and the viewing angle contrast was measured. The viewing angle results with a contrast ratio of 10 or more are shown in Table 1.
The black-side gradation inversion is determined by the inversion between L1 / 3 and L2 / 3, and the results of the downward gradation inversion angle are shown in Table 2.

(Evaluation of tilt angle of liquid crystal compounds)
The tilt angle in the vicinity of the alignment film of the liquid crystalline compound and the tilt angle in the vicinity of the air interface in the optically anisotropic layer of the optical compensation sheet are changed by using an ellipsometer (APE-100, manufactured by Shimadzu Corporation). The retardation was measured and estimated by the method described above. The measurement wavelength is 632.8 nm, and the results are shown in Table 1.

  As can be seen from the results of Examples 1 to 5 and Comparative Examples 1 and 2 shown in Table 1 above, after heating to the liquid crystal transition temperature or higher according to the present invention to form the optically anisotropic layer, 40 ° C. or lower. In the optical compensation sheet, which is manufactured by polymerizing and / or curing by UV irradiation after cooling to the temperature of the LCD, the lower gradation inversion angle of the liquid crystal display device is sufficiently expanded, greatly contributing to the expansion of the viewing angle In addition, there is no occurrence of unevenness (Examples 1 to 5). On the other hand, in the optical compensation sheet (Comparative Examples 1 and 2) which is a manufacturing method that is not within the scope of the present invention, the lower gradation inversion angle and the viewing angle are not sufficiently enlarged.

(Example 6)
An optical compensation sheet and further an optical compensation were obtained in the same manner as in Example 1 except that the addition amount of the retardation increasing agent used in Example 1 was changed to prepare a polymer substrate having Rth of 60 and 80 nm. A polarizing plate with a sheet was prepared. Even when the Rth of the polymer substrate was changed to 60 and 80 nm, the same vertical and horizontal viewing angles as those obtained in Example 1 were obtained.

(Example 7)
1.35 parts by weight of the photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) and 0.45 parts by weight of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) used in Example 1 were added to the following compound U 1. An optical compensation sheet and a polarizing plate with an optical compensation sheet were produced in the same manner as in Example 1 except that the amount was 35 parts by mass. Even when the photopolymerization initiator was changed, the same vertical and horizontal viewing angles as those obtained in Example 1 were obtained.
Compound U

It is the schematic of the slot coater which can be utilized for this invention. FIG. 2 is a schematic diagram (A) of a cross-sectional shape of a slot die 13 in FIG. 1 and a schematic diagram (B) of a cross-sectional shape of another slot die 30. It is the schematic of the slot coater which can be utilized for this invention.

Explanation of symbols

10 Coater
DESCRIPTION OF SYMBOLS 11 Backup roll 12 Web 13, 30 Slot die 14 Coating liquid 15, 32 Pocket 16, 33 Slot 17 Tip lip part 18 Upstream lip land 19 Downstream lip land

Claims (10)

  In an optical compensation sheet comprising a support and an optically anisotropic layer, the tilt angle of the liquid crystalline molecules forming the optically anisotropic layer varies with the distance from the support surface, and the tilt angle on the air interface side is on the support side. An optical compensation sheet characterized in that the inclination angle difference is greater than or equal to 40 degrees and the inclination angle difference is not less than 40 degrees and not more than 90 degrees, and the inclination angle on the support side is not less than 0 degrees and not more than 10 degrees.   The optical compensation sheet according to claim 1, wherein the tilt angle difference is 50 degrees or greater and 90 degrees or less.   3. The optical compensation sheet according to claim 1, wherein an inclination angle on the support side is not less than 0 degrees and not more than 5 degrees.   After applying a liquid containing a nematic liquid crystal compound in an organic solvent on the support, evaporating and drying the organic solvent, and heating to a temperature higher than the liquid crystal transition temperature to form an optically anisotropic layer, 40 ° C A method for producing an optical compensation sheet, which is produced by being polymerized and / or cured by UV irradiation after cooling to the following temperature.   The method for producing an optical compensation sheet according to claim 4, wherein the cooling is performed at an average speed in the range of 0.5 ° C / second or more and 50 ° C / second or less to a temperature of 40 ° C or less.   The method for producing an optical compensation sheet according to claim 5, wherein the cooling temperature is 20 ° C. or less.   4. The optical compensation sheet according to claim 1, wherein the liquid crystal compound is a discotic liquid crystal compound.   The method for producing an optical compensation sheet according to any one of claims 4 to 6, wherein an optically anisotropic layer or an alignment layer is applied to the surface of the transparent support by a slide coater or a slot die coater.   A polarizing plate comprising the optical compensation sheet according to any one of claims 1 to 3 and 7, and the optical compensation sheet produced by the method for producing an optical compensation sheet according to any one of claims 4 to 6 and 8.   A liquid crystal display device comprising the polarizing plate according to claim 9.

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