JP2000147260A - Phase difference plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase difference plate which can produce λ/4 or λ/2 difference for the whole wavelength region to be used. SOLUTION: The phase difference plate has laminated layers of an optically anisotropic layer containing liquid crystal molecules and a polymer film. The retardation Re400A, Re550A and Re700A of the optically anisotropic layer measured at 400 nm, 550 nm and 700 nm wavelengths, respectively, and retardation Re400F, Re550F and Re700F of the polymer film measured at 400 nm, 550 nm and 700 nm wavelengths, respectively, satisfy the relation represented by Re550A<Re550F and Re400F/Re700F<Re400A/Re700A. Further, the direction where the refractive index in the plane of the optically anisotropic layer is the max., and the direction where the refractive index in the plane of the polymer film is the max. are substantially perpendicular to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate in which an optically anisotropic layer containing liquid crystal molecules and a polymer film are laminated. In particular, the present invention relates to a λ / 4 plate or a λ / 2 plate used in a reflection type liquid crystal display device, a λ / 4 plate used for a pickup for writing on an optical disk, or a λ / 4 plate used as an antireflection film. The present invention relates to a retardation plate effective as a plate.

[0002]

2. Description of the Related Art The λ / 4 plate and the λ / 2 plate have a very large number of uses and have already been actually used. However, even if it is called a λ / 4 plate or a λ / 2 plate, it only achieves λ / 4 or λ / 2 at a certain specific wavelength,
None achieved λ / 4 or λ / 2 over the entire wavelength range used. It is known that λ / 4 and λ / 2 can be achieved in a narrow range by laminating retardation films having different wavelength dispersions. However, in the laminated body of the retardation film, chips obtained by cutting the retardation film are laminated so as to be orthogonal to each other. Therefore, complicated processing is required for laminating the film, and the cost is increased, so that the film has not been put to practical use. In a reflection type LCD (liquid crystal display), a λ / 4 plate or a λ / 2 plate made of a norbornene polymer film having small wavelength dispersion is used as a retardation plate. However, such a retardation plate is designed to have a wavelength of λ / 4 or λ / 2 at a specific wavelength (often around 550 nm). Is not satisfied. For this reason, light leakage occurs, which causes a problem in the quality of the display image of the device. The λ / 4 plate used as an anti-reflection film for anti-glare also has the same problem as the reflection type LCD. Optical disk (eg, C
D, DVD), there is a problem with the λ / 4 plate used for the pickup for writing, that the writing wavelength of the optical disk varies from one company to another. Therefore, a quartz plate cut out according to the specifications of each company is used as a λ / 4 plate. Quartz plates manufactured in such a manner are very expensive.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a retardation plate capable of achieving λ / 4 or λ / 2 over the entire wavelength range to be used.

[0004]

Means for Solving the Problems The object of the present invention has been attained by the following retardation plates [1] to [6]. [1] A retardation plate in which an optically anisotropic layer containing liquid crystal molecules and a polymer film are laminated, and a wavelength of 400 n
m, Re400A and Re55, which are the retardation values of the optically anisotropic layer measured at 550 nm and 700 nm, respectively.
0A and Re700A, wavelength 400nm, 550n
Re400F, Re550F and Re700F, which are the retardation values of the polymer film measured at m and 700 nm, satisfy the following expressions (1) and (2), and further, the in-plane refractive index of the optically anisotropic layer is maximized. A phase difference plate, wherein the direction and the direction in which the in-plane refractive index of the polymer film is maximized are substantially orthogonal. (1) Re550A <Re550F (2) Re400F / Re700F <Re400A / R
e700A [2] The retardation plate according to [1], wherein the liquid crystalline molecules of the optically anisotropic layer are substantially uniformly oriented. [3] The retardation plate according to [2], wherein the liquid crystal molecules of the optically anisotropic layer are fixed in a substantially uniformly oriented state. [4] The retardation plate according to [3], wherein the liquid crystalline molecules are fixed by a polymerization reaction. [5] The liquid crystal molecule according to [1], wherein the liquid crystal molecules of the optically anisotropic layer are discotic liquid crystal molecules, and the discotic liquid crystal molecules are oriented substantially perpendicular to the polymer film surface. Phase difference plate. [6] The retardation plate according to [1], wherein Re400F, Re700F, Re400A and Re700A satisfy the following formulas (2a) and (2b). (2a) Re400F / Re700F <1.2 (2b) 1.3 <Re400A / Re700A

[0005]

As a result of the research by the present inventors, the laminate of an optically anisotropic layer containing liquid crystal molecules and a polymer film was used as a retardation plate, and the optical properties of the optically anisotropic layer and the polymer film were determined. It has been found that λ / 4 or λ / 2 can be achieved over the entire wavelength range used by a simple means of adjusting. The adjustment of the optical properties refers to the above equations (1) and (2).
And adjusting the direction in which the in-plane refractive indices of the optically anisotropic layer and the polymer film are maximized. The optically anisotropic layer containing liquid crystal molecules is easier to adjust the optical specification than the polymer film. Since the optical properties required by the present invention are all relative regulations between the optically anisotropic layer and the polymer film, it is easy to adjust the optical properties on the optically anisotropic layer side. Can be achieved. For example,
Orientation of the liquid crystalline molecules contained in the optically anisotropic layer so that the direction in which the in-plane refractive index of the polymer film becomes maximum is orthogonal to the direction in which the in-plane refractive index of the optically anisotropic layer becomes maximum. Is adjusted, the desired λ / 4 plate or λ / 2 plate can be obtained at low cost by roll-to-roll processing without chipping the film.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Optical Properties of Retardation Plate]
Next, the retardation value (Re550F) of the polymer film measured at a wavelength of 550 nm was measured, and the retardation value of the optically anisotropic layer measured at a wavelength of 550 nm (Re550).
Adjust to a larger value than A). That is, Re550
A and Re550F are set so as to satisfy the following expression (1). (1) Re550A <Re550F For the use of a λ / 4 plate, the difference between Re550A and Re550F is preferably 100 to 180 nm, and 1
It is more preferably 20 to 160 nm, and 13
Most preferably, it is 0 to 150 nm. In the application of λ / 2 plate, the difference between Re550A and Re550F is 2
The thickness is preferably from 00 to 360 nm, more preferably from 240 to 320 nm, and from 260 to 3 nm.
Most preferably, it is 00 nm.

Second, the ratio (Re400F / Re400F / Re) between the retardation value (Re400F) of the polymer film measured at a wavelength of 400 nm and the retardation value (Re700F) of the polymer film measured at a wavelength of 700 nm.
700F) and the retardation value (Re400A) of the optically anisotropic layer measured at a wavelength of 400 nm and a wavelength of 70 nm.
The ratio (Re400A / Re700) to the retardation value (Re700A) of the optically anisotropic layer measured at 0 nm.
Adjust so that A) has a larger value. That is,
Re400F, Re700F, Re400A and Re
700A satisfies the following equation (2). (2) Re400F / Re700F <Re400A / R
e700A Re400F, Re700F, Re400A and Re
700A preferably satisfies the following formulas (2a) and (2b), more preferably satisfies the following formulas (2c) and (2d), and more preferably the following formulas (2e) and (2d).
Most preferably, f) is satisfied. (2a) Re400F / Re700F <1.2 (2b) 1.3 <Re400A / Re700A (2c) Re400F / Re700F <1.15 (2d) 1.45 <Re400A / Re700A (2e) Re400F / Re700F <1.1 (2f) 1.6 <Re400A / Re700A

Third, the direction in which the in-plane refractive index of the optically anisotropic layer is maximized is substantially orthogonal to the direction in which the in-plane refractive index of the polymer film is maximized. Substantially orthogonal means that the angle between the two directions is between 75 and 105 °. The angle between the two directions is between 80 and 10
It is preferably 0 °, more preferably 85 to 95 °, and most preferably 87 to 93 °.

The retardation value in the formulas (1) and (2) means an in-plane retardation value with respect to light incident from the normal direction of the optically anisotropic layer or the polymer film. Specifically, it is a value defined by the following equation (3). (3) Retardation value (Re) = (nx−ny) ×
d In the formula, nx and ny are the in-plane principal refractive indices of the optically anisotropic layer or the polymer film, and d is the thickness (nm) of the optically anisotropic layer or the polymer film.

Since the retardation plate has the above optical properties, λ / 4 or λ can be obtained over the entire required wavelength range.
/ 2 can be achieved. The required wavelength range is generally selected from the visible range, i.e., in the range of 300 to 900 nm. It is desirable that λ / 4 or λ / 2 can be achieved even in a range of 100 nm or more from the visible region. If necessary, λ / 4 or λ / 2 can be achieved even in the entire rental area of 200 nm or more or 300 nm or more. To be able to achieve λ / 4 or λ / 2 means that the phase difference in a specific region is within a range of ± 15%. The phase difference is preferably within a range of ± 10%, and more preferably within a range of ± 5%. There is no particular limitation on the arbitrary wavelength range (for example, 30
0-400 nm or 450-550 nm).

[Structure of Retardation Plate] FIG. 1 is a schematic sectional view showing a typical constitution of the retardation plate of the present invention. As shown in FIG. 1, a typical retardation plate has a configuration in which a polymer film (1), a transparent support (2), an alignment film (3), and an optically anisotropic layer (4) are laminated in this order. Have. The direction (4) in which the in-plane refractive index of the optically anisotropic layer (4) is maximized
1) and the direction (11) in which the in-plane refractive index of the polymer film (1) becomes maximum are orthogonal to each other. The optically anisotropic layer (4) contains discotic liquid crystal molecules (42).
The discotic liquid crystal molecules (42) are vertically oriented. The direction of the disc surface of the discotic liquid crystal molecules (42) corresponds to the direction (41) in which the in-plane refractive index of the optically anisotropic layer (4) is maximized. Polymer film (1)
Is a uniaxially stretched film. When the intrinsic birefringence of the polymer used is positive, the stretching direction of the film corresponds to the direction (11) in which the in-plane refractive index of the polymer film becomes maximum. When the intrinsic birefringence of the polymer used is negative, the stretching direction of the film corresponds to the direction perpendicular to the direction (11) in which the in-plane refractive index of the polymer film becomes maximum (the same direction as 41).

[Polymer film] The polymer film is formed from a polymer capable of imparting optical anisotropy to the film. Examples of such polymers include polyolefins (eg, polyethylene, polypropylene, norbornene-based polymers), polyvinyl alcohol, polymethacrylates, polyacrylates and cellulose esters. Further, a copolymer or a polymer mixture of these polymers may be used. The optical anisotropy of the film is preferably obtained by stretching. The stretching is preferably uniaxial stretching. The uniaxial stretching is preferably longitudinal uniaxial stretching utilizing a peripheral speed difference between two or more rolls or tenter stretching in which both sides of the polymer film are gripped and stretched in the width direction. In addition, the optical properties of the entire two or more films may satisfy the above-mentioned condition by using two or more polymer films. When the intrinsic birefringence of the polymer used is positive, the direction in which the in-plane refractive index of the polymer film becomes the maximum corresponds to the stretching direction of the film. When the intrinsic birefringence of the polymer used is negative, the direction in which the in-plane refractive index of the polymer film becomes maximum corresponds to the direction perpendicular to the stretching direction of the film. Polymer films are
In order to reduce birefringence unevenness, it is preferable to manufacture by a solvent casting method. The thickness of the polymer film is preferably from 20 to 500 nm,
The thickness is more preferably from 200 to 200 nm, and most preferably from 50 to 100 nm.

[Optically Anisotropic Layer] The optically anisotropic layer contains liquid crystalline molecules. As the liquid crystal molecules, rod-shaped liquid crystal molecules or discotic liquid crystal molecules are preferable, and discotic liquid crystal molecules are particularly preferable. The liquid crystal molecules are preferably aligned substantially uniformly, more preferably fixed in a state where they are substantially uniformly aligned, and the liquid crystal molecules are fixed by a polymerization reaction. Is most preferred. The orientation of the liquid crystal molecules is adjusted so that the direction in which the in-plane refractive index of the optically anisotropic layer is maximum is substantially orthogonal to the direction in which the in-plane refractive index of the polymer film is maximum. When a discotic liquid crystal is used, the liquid crystal is oriented homogeneously such that the director of the liquid crystal is oriented in a direction in which the in-plane refractive index of the polymer film is maximized. When a rod-shaped liquid crystal is used, the liquid crystal is homogeneously oriented so that the director is oriented in a direction orthogonal to the direction in which the in-plane refractive index of the polymer film is maximized. As the rod-like liquid crystal molecules, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters,
Cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines,
Phenyldioxane, tolan and alkenylcyclohexylbenzonitrile are preferably used. Not only low molecular liquid crystal molecules as described above but also high molecular liquid crystal molecules can be used.

Particularly preferred discotic liquid crystalline molecules will be further described. Discotic liquid crystal molecules are substantially perpendicular (50) to the polymer film plane.
(An average inclination angle in the range of 90 to 90 degrees). Discotic liquid crystalline molecules are described in various literatures (C. Destrade et al., Mol. Crysr. Liq. Cryst., Vo.
l. 71, page 111 (1981); edited by The Chemical Society of Japan, quarterly chemistry review, No. 22, Liquid Crystal Chemistry, Chapter 5, Chapter 10, Section 2
(1994); B. Kohne et al., Angew. Chem. Soc. Chem. C
omm., page 1794 (1985); J. Zhang et al., J. Am. Che
m. Soc., vol. 116, page 2655 (1994)). Regarding the polymerization of discotic liquid crystalline molecules,
It is described in JP-A-8-27284. In order to fix the discotic liquid crystal molecules by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystal molecules. However, when a polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain an oriented state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystalline molecule having a polymerizable group is preferably a compound represented by the following formula (I).

(I) D (-LP) _{n wherein} D is a discotic core; L is a divalent linking group; P is a polymerizable group; and n is 4 to 12 Is an integer. An example of the discotic core (D) of the formula (I) is shown below. In each of the following examples, LP (or PL) means a combination of a divalent linking group (L) and a polymerizable group (P).

[0016]

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[0017]

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[0018]

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[0019]

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[0020]

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[0021]

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[0022]

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In the formula (I), the divalent linking group (L)
Is an alkylene group, alkenylene group, arylene group,-
It is preferably a divalent linking group selected from the group consisting of CO-, -NH-, -O-, -S- and a combination thereof. The divalent linking group (L) includes an alkylene group, an alkenylene group, an arylene group, -CO-, -NH-,-
More preferably, the group is a group obtained by combining at least two divalent groups selected from the group consisting of O- and -S-. The divalent linking group (L) is most preferably a group obtained by combining at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, -CO- and -O-. The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbon atoms. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group, a halogen atom, a cyano, an alkoxy group, an acyloxy group).

Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is a polymerizable group (P).
To join. AL represents an alkylene group or an alkenylene group, and AR represents an arylene group. L1: -AL-CO-O-AL- L2: -AL-CO-O-AL-O- L3: -AL-CO-O-AL-O-AL- L4: -AL-CO-O-AL- O-CO-L5: -CO-AR-O-AL-L6: -CO-AR-O-AL-O-L7: -CO-AR-O-AL-O-CO-L8: -CO-NH- AL-L9: -NH-AL-O-L10: -NH-AL-O-CO-

L11: -O-AL- L12: -O-AL-O- L13: -O-AL-O-CO- L14: -O-AL-O-CO-NH-AL- L15: -O- AL-S-AL-L16: -O-CO-AR-O-AL-CO-L17: -O-CO-AR-O-AL-O-CO-L18: -O-CO-AR-O-AL -O-AL-OC
O-L19: -O-CO-AR-O-AL-O-AL-OA
L-O-CO-L20: -S-AL-L21: -S-AL-O-L22: -S-AL-O-CO-L23: -S-AL-S-AL-L24: -S-AR -AL-

The polymerizable group (P) in the formula (I) is determined according to the type of the polymerization reaction. Examples of the polymerizable group (P) are shown below.

[0027]

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[0028]

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[0029]

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[0030]

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[0031]

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[0032]

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The polymerizable group (P) is an unsaturated polymerizable group (P
1, P2, P3, P7, P8, P14, P15, P1
6) or an epoxy group (P6),
More preferably, it is an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group (P1, P7, P8, P14, P1
5, P16). In the formula (I), n is an integer of 4 to 12. The specific numbers are
It is determined according to the type of discotic core (D). The combination of a plurality of L and P may be different, but is preferably the same. Two or more discotic liquid crystalline molecules (for example, a molecule having an asymmetric carbon atom in a divalent linking group and a molecule having no asymmetric carbon atom) may be used together.

The optically anisotropic layer is formed by applying a coating liquid containing discotic liquid crystal molecules or the following polymerizable initiator or other additives on the vertical alignment film. 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), a sulfoxide (eg, dimethylsulfoxide), a heterocyclic compound (eg, pyridine),
Hydrocarbon (eg, benzene, hexane), alkyl halide (eg, chloroform, dichloromethane), ester (eg, methyl acetate, butyl acetate), ketone (eg, acetone, methyl ethyl ketone), ether (eg, tetrahydrofuran, 1,2- Dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination. The application of the coating solution can be performed by a known method (eg, an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a die coating method).

The vertically aligned discotic liquid crystalline molecules are fixed while maintaining the aligned state. The immobilization is preferably performed by a polymerization reaction of the polymerizable group (P) introduced into the discotic liquid crystalline molecule. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. Photopolymerization reactions are preferred. Examples of photopolymerization initiators include α-carbonyl compounds (US Pat.
Nos. 3,766,661 and 2,367,670), acyloin ethers (described in U.S. Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Pat. Patents 3046127 and 295175
No. 8), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in U.S. Pat. No. 3,549,367), an acridine and phenazine compound (JP-A-60-105667,
U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,221,970).

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight based on the solid content of the coating solution.
More preferably, it is 5 to 5% by weight. Light irradiation for the polymerization of discotic liquid crystalline molecules preferably uses ultraviolet light. The irradiation energy is 20 mJ /
cm ^{2 to} 50 J / cm ² , preferably 10
More preferably, it is 0 to 800 mJ / cm ² . Light irradiation may be performed under heating conditions to promote the photopolymerization reaction. The thickness of the optically anisotropic layer is 0.1 to 1
It is preferably 0 μm, more preferably 0.5 to 5 μm, and most preferably 1 to 5 μm.

[Vertical Alignment Film] In order to vertically align discotic liquid crystal molecules, it is important to lower the surface energy of the alignment film. Specifically, the surface energy of the alignment film is reduced by the functional group of the polymer,
As a result, the discotic liquid crystal molecules are set up. As the functional group that lowers the surface energy of the alignment film, a fluorine atom and a hydrocarbon group having 10 or more carbon atoms are effective. In order to make a fluorine atom or a hydrocarbon group exist on the surface of the alignment film, it is preferable to introduce a fluorine atom or a hydrocarbon group into a side chain rather than a main chain of the polymer. The fluorine-containing polymer preferably contains fluorine atoms at a ratio of 0.05 to 80% by weight, and 0.1 to 7% by weight.
The content is more preferably 0% by weight, more preferably 0.5 to 65% by weight, and most preferably 1 to 60% by weight. The hydrocarbon group is an aliphatic group, an aromatic group, or a combination thereof. The aliphatic group may be cyclic, branched, or linear. The aliphatic group is preferably an alkyl group (may be a cycloalkyl group) or an alkenyl group (may be a cycloalkenyl group). The hydrocarbon group may have a substituent that does not show strong hydrophilicity, such as a halogen atom. The number of carbon atoms in the hydrocarbon group is
It is preferably 10 to 100, more preferably 10 to 60, and most preferably 10 to 40. The main chain of the polymer preferably has a polyimide structure or a polyvinyl alcohol structure.

Polyimide is generally synthesized by a condensation reaction between a tetracarboxylic acid and a diamine. A polyimide corresponding to a copolymer may be synthesized using two or more kinds of tetracarboxylic acids or two or more kinds of diamines. The fluorine atom or the hydrocarbon group may be present in a repeating unit derived from a tetracarboxylic acid, in a repeating unit derived from a diamine, or in both repeating units. When a hydrocarbon group is introduced into a polyimide, it is particularly preferable to form a steroid structure in the main chain or side chain of the polyimide. The steroid structure present in the side chain corresponds to a hydrocarbon group having 10 or more carbon atoms, and has a function of vertically aligning discotic liquid crystalline molecules. In the present specification, a steroid structure refers to a cyclopentanohydrophenanthrene ring structure or a ring structure in which a part of the bond of the ring is a double bond in the range of an aliphatic ring (range in which an aromatic ring is not formed). means.

Fluorine-modified polyvinyl alcohol can also be preferably used for the vertical alignment film. Fluorine-modified polyvinyl alcohol has 5 repeating units containing a fluorine atom.
In the range of 7 to 80 mol%, preferably 7 to 7 mol%.
More preferably, it is contained in the range of 0 mol%. Preferred fluorine-modified polyvinyl alcohol is represented by the following formula (PV). (PV)-(VAl) x- (FRU) y- (VAc) z- wherein VAl is a repeating unit of vinyl alcohol; FRU is a repeating unit containing a fluorine atom;
VAc is a vinyl acetate repeating unit; x is 20 to 95 mol% (preferably 24 to 90 mol%); y is 5 to 80 mol% (preferably 7 to 70 mol%); , Z are 0 to 30 mol% (preferably 2 to 20 mol%). A preferred repeating unit containing a fluorine atom (FRU) is represented by the following formula (FRU-I)
And (FRU-II).

[0040]

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In the formula, L ¹ represents —O—, —CO—, —SO
₂ -, - NH-, an alkylene group, an arylene group and a divalent linking group selected from their combinations; L
² is a single bond or -O -, - CO -, - SO 2 -,
-NH-, a divalent linking group selected from an alkylene group, an arylene group and a combination thereof;
f ¹ and Rf ² are each a fluorine-substituted hydrocarbon group. The alkylene group and the arylene group may be substituted by a fluorine atom. Examples of the divalent linking group formed by the above combination are shown below.

[0042] L1: -O-CO- L2: -O -CO- alkylene group -O- L3: -O-CO- alkylene group -CO-NH- L4: -O-CO- alkylene group -NH-SO ₂ -Arylene group -O-L5: -arylene group -NH-CO-L6: -arylene group -CO-O-L7: -arylene group -CO-NH-L8: -arylene group -O-L9: -O-CO -NH-arylene group -NH-CO-

The hydrocarbon group of the fluorine-substituted hydrocarbon group is an aliphatic group, an aromatic group or a combination thereof. The aliphatic group may be cyclic, branched or linear. The aliphatic group is preferably an alkyl group (may be a cycloalkyl group) or an alkenyl group (may be a cycloalkenyl group). The aliphatic group may have a substituent that does not show strong hydrophilicity, such as another halogen atom, in addition to the fluorine atom. The hydrocarbon group preferably has 1 to 100 carbon atoms,
It is more preferably from 60 to 60, and most preferably from 3 to 40. The proportion of the hydrogen atom of the hydrocarbon group substituted by a fluorine atom is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, and further preferably 80 to 100 mol%. It is most preferably 90 to 100 mol%.

A modified polyvinyl alcohol having a hydrocarbon group having 10 or more carbon atoms can also be preferably used for the vertical alignment film. The hydrocarbon group is an aliphatic group, an aromatic group, or a combination thereof. Aliphatic groups are cyclic,
It may be either branched or linear. Aliphatic groups are
It is preferably an alkyl group (may be a cycloalkyl group) or an alkenyl group (may be a cycloalkenyl group). The hydrocarbon group may have a substituent that does not show strong hydrophilicity, such as a halogen atom.
The number of carbon atoms in the hydrocarbon group is preferably from 10 to 100, more preferably from 10 to 60, and most preferably from 10 to 40. The modified polyvinyl alcohol having a hydrocarbon group contains 2 to 8 repeating units having a hydrocarbon group having 10 or more carbon atoms.
It is preferably contained in the range of 0 mol%, more preferably 3 to 70 mol%. Preferred number of carbon atoms is 1
The modified polyvinyl alcohol having 0 or more hydrocarbon groups is represented by the following formula (PV). (PV)-(VAl) x- (HyC) y- (VAc) z- wherein VA1 is a vinyl alcohol repeating unit; HyC is a repeating unit having a hydrocarbon group having 10 or more carbon atoms. VAc is a vinyl acetate repeating unit; x is 20 to 95 mol% (preferably 2 to 95 mol%)
Y is from 2 to 80 mol%)
(Preferably 3 to 70 mol%); and z is 0 to 30 mol% (preferably 2 to 20 mol%). Preferred repeating units (HyC) having a hydrocarbon group having 10 or more carbon atoms are represented by the following formulas (HyC-I) and (HyC-II).

[0045]

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In the formula, L ¹ represents —O—, —CO—, —SO
₂ -, - NH-, an alkylene group, an arylene group and a divalent linking group selected from their combinations; L
² is a single bond or -O -, - CO -, - SO 2 -,
-NH-, a divalent linking group selected from an alkylene group, an arylene group and a combination thereof;
¹ and R ² are each a hydrocarbon group having 10 or more carbon atoms. Examples of the divalent linking group formed by the above-mentioned combination include the above-mentioned formulas (FRU-I) and (FRU-I).
-II).

The polymerization degree of the polymer used for the vertical alignment film is as follows:
It is preferably from 200 to 5,000, more preferably from 300 to 3,000. The molecular weight of the polymer is
It is preferably from 9000 to 200,000, and 13
More preferably, it is 000 to 130,000.
Two or more polymers may be used in combination. In forming the vertical alignment film, it is preferable to perform a rubbing treatment. The rubbing treatment is performed by rubbing the surface of the film containing the polymer several times with paper or cloth in a certain direction. After the discotic liquid crystalline molecules are vertically aligned using a vertical alignment film, the discotic liquid crystalline molecules are fixed in the aligned state to form an optically anisotropic layer, and only the optically anisotropic layer is formed. May be transferred onto a polymer film (or a transparent support). Discotic liquid crystal molecules fixed in the vertical alignment state can maintain the alignment state without the vertical alignment film. Therefore, in the retardation plate of the present invention, the vertical alignment film is not an essential element (although it is essential in the production of the retardation plate).

[Transparent Support] A transparent support may be used. It is preferable to use a polymer film having a small wavelength dispersion as the transparent support. The transparent support also preferably has a small optical anisotropy. Transparent support means that the light transmittance is 80% or more. The term “small chromatic dispersion” means, specifically, Re400 / Re70
Preferably, the ratio of 0 is less than 1.2. The fact that the optical anisotropy is small means that the in-plane retardation (R
e) is preferably 20 nm or less, more preferably 10 nm or less. When the transparent support has a certain optical anisotropy, the laminate of the transparent support and the above-mentioned polymer film needs to satisfy the above-mentioned optical properties of the polymer film as a whole. Examples of polymers include cellulose esters, polycarbonates, polysulfones, polyethersulfones, polyacrylates and polymethacrylates. Cellulose esters are preferred, acetyl cellulose is more preferred, and triacetyl cellulose is most preferred. The polymer film is preferably formed by a solvent casting method. The thickness of the transparent support is from 20 to 500
μm, more preferably 50 to 200 μm. To improve the adhesion between the transparent support and the layer provided thereon (adhesive layer, vertical alignment film or optically anisotropic layer), the transparent support is subjected to a surface treatment (eg, glow discharge treatment, corona discharge treatment, ultraviolet light). (UV) treatment, flame treatment). An adhesive layer (undercoat layer) may be provided on the transparent support.

[Use of Retardation Plate] The retardation plate of the present invention comprises:
Particularly advantageous as a λ / 4 plate or λ / 2 plate used in a reflection type liquid crystal display device, a λ / 4 plate used for a pickup for writing on an optical disk, or a λ / 4 plate used as an antireflection film. Used for Note that λ /
Four plates or λ / 2 plates are generally used in combination with a polarizing plate. Therefore, if the retardation plate of the present invention is configured as a laminate in which a retardation plate is combined with a polarizing plate, the retardation plate can be easily incorporated in a device such as a reflective liquid crystal display device.

[0050]

[Example 1] A triacetylcellulose film having zero retardation at 632.8 nm was used as a transparent support. A mixed solvent of the following modified polyvinyl alcohol and methanol and acetone (volume ratio = 50 /
50) to prepare a 5% by weight solution. This solution was applied to a thickness of 1 μm on a transparent support using a bar coater. The coating layer was dried with hot air at 60 ° C. for 2 minutes, and its surface was rubbed to form a vertical alignment film.

[0051]

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A coating solution having the following composition was applied on the vertical alignment film, and the discotic liquid crystal molecules were homogeneously vertically aligned. Next, ultraviolet rays were irradiated for 1 second with a mercury lamp having an illuminance of 500 w / cm ² to polymerize the discotic liquid crystal molecules. Thus, an optically anisotropic layer was formed. The discotic liquid crystal molecules were homogeneously aligned so as to have an optical axis (director) in the longitudinal direction of the transparent support. It had a slow axis in the width direction of the transparent support.

<< Composition of Optically Anisotropic Layer Coating Solution >>デ ィ ス The following discotic liquid crystalline molecules: 32.6% by weight cellulose acetate butyrate 0 0.7% by weight Modified trimethylolpropane triacrylate below 3.2% by weight Sensitizer below 0.4% by weight Photopolymerization initiator below 1.1% by weight 62.0% by weight methyl ethyl ketone ──────────────────────────────

[0054]

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[0055]

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[0056]

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Wavelengths of 400 nm, 550 nm and 700
The retardation value of the optically anisotropic layer was measured in nm.
The results are shown below. Re400A: 286 nm Re550A: 200 nm Re700A: 176 nm Re400A / Re700A: 1.625 Further, the wavelength dependence of the retardation value of the optically anisotropic layer was measured. The results are shown in FIG.

Next, a 100 μm thick polyvinyl alcohol film was subjected to uniaxial longitudinal stretching using a difference in peripheral speed between two rolls to obtain a polymer film. The polymer film had a slow axis in the longitudinal direction. 400n wavelength
The retardation values of the polymer films were measured at m, 550 nm and 700 nm. The results are shown below. Re400F: 348.8 nm Re550F: 342.0 nm Re700F: 338.6 nm Re400F / Re700F: 1.030 Further, the wavelength dependence of the retardation value of the optically anisotropic layer was measured. The results are shown in FIG.

A transparent support on which an optically anisotropic layer was formed and a polymer film were laminated so that their longitudinal directions coincided with each other to obtain a retardation plate according to the present invention. The wavelength dependence of the obtained retardation plate was measured. The results are shown in FIG.
FIG. 2 is a graph showing the wavelength dependence of an optically anisotropic layer, a polymer film and a retardation plate, and the ideal wavelength dependence of a λ / 4 plate. As shown in FIG. 2, the wavelength dependency of the retardation plate and the wavelength dependency of the ideal λ / 4 plate showed approximate values in a wide range of wavelengths from 450 nm to 700 nm.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a typical configuration of a retardation plate of the present invention.

FIG. 2 is a graph showing the wavelength dependence of an optically anisotropic layer, a polymer film, and a retardation plate, and the ideal wavelength dependence of a λ / 4 plate.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 polymer film 2 transparent support 3 alignment film 4 optically anisotropic layer 11 direction in which in-plane refractive index of polymer film becomes maximum 41 direction in which in-plane refractive index of optically anisotropic layer becomes maximum 42 discotic Liquid crystalline molecules

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA06 BA07 BA25 BA42 BB03 BB43 BC03 BC04 BC05 BC22 2H088 GA01 HA17 HA18 KA07 MA20 2H091 FA08X FA08Z FA11X FA11Z FB02 FC23 KA02 LA30

Claims (6)

[Claims] 1. A retardation plate in which an optically anisotropic layer containing liquid crystal molecules and a polymer film are laminated, and the retardation value of the optically anisotropic layer measured at wavelengths of 400 nm, 550 nm, and 700 nm. A certain Re400A,
Re550A and Re700A, wavelength 400 nm,
Re400F and Re55, which are the retardation values of the polymer films measured at 550 nm and 700 nm, respectively.
0F and Re700F are represented by the following formulas (1) and (2)
Wherein the direction in which the in-plane refractive index of the optically anisotropic layer is maximized is substantially orthogonal to the direction in which the in-plane refractive index of the polymer film is maximized. Retarder. (1) Re550A <Re550F (2) Re400F / Re700F <Re400A / R
e700A 2. The retardation plate according to claim 1, wherein the liquid crystal molecules of the optically anisotropic layer are substantially uniformly oriented. 3. The retardation plate according to claim 2, wherein the liquid crystal molecules of the optically anisotropic layer are fixed in a state of being substantially uniformly oriented. 4. The retardation plate according to claim 3, wherein the liquid crystal molecules are fixed by a polymerization reaction. 5. The liquid crystal display device according to claim 1, wherein the liquid crystal molecules of the optically anisotropic layer are discotic liquid crystal molecules, and the discotic liquid crystal molecules are oriented substantially perpendicular to the polymer film surface. The retardation plate as described. 6. Re400F, Re700F, Re40
0A and Re700A are represented by the following formulas (2a) and (2)
The retardation plate according to claim 1, which satisfies b). (2a) Re400F / Re700F <1.2 (2b) 1.3 <Re400A / Re700A