JP2001021720A - Phase difference plate and circular polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase difference plate capable of achieving satisfactory circular polarization by putting a product of orientation birefringence by a thickness of an optical anisotropic layer in a specific scope, providing the optical anisotropic layer with a twist structure whose twist angle is within a specific scope, and putting a phase difference of another optical anisotropic layer in a specific scope. SOLUTION: An optical anisotropic layer A and an optical anisotropic layer B are provided, a product of orientation birefringence by a thickness of the optical anisotropic layer A which are measured with a wavelength of 550 nm is 150 to 350 nm, and the optical anisotropic layer A has a twist structure whose twist angle is 3 to 45 deg.. A phase difference of the optical anisotropic layer B is 60 to 170 nm. It is good if the optical anisotropic layer B achieves a phase difference of 60 to 170 nm at a specific wavelength. It is preferable that the specific wavelength achieves a phase difference of 60 to 170 nm at 550 nm which is substantially intermediate wavelength in a visible region. It is possible to improve wide band characteristic greatly by introducing the twist structure into the optical anisotropic layer A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a retardation plate having two optically anisotropic layers and a circularly polarizing plate using the same. In particular, the present invention relates to a reflection type liquid crystal display device, an optical disk writing pickup, a PS conversion element, and a GH-LC.
D, a retardation plate effective as a λ / 4 plate used for an organic EL display or an antireflection film.

[0002]

2. Description of the Related Art A λ / 4 plate has a great number of uses and has already been actually used. However, even if it is called a λ / 4 plate, most achieve λ / 4 at a specific wavelength. Japanese Patent Application Laid-Open Nos. 10-68816 and 10-90521 disclose a retardation plate obtained by laminating two polymer films having optical anisotropy. The retardation plate described in Japanese Patent Application Laid-Open No. 10-68816 has a 波長 wavelength plate in which the phase difference of birefringent light is １ ／ wavelength and a あ る wavelength plate in which the phase difference of birefringent light is 波長 wavelength. The wave plate and the wave plate are bonded together with their optical axes crossing each other. The retardation plate described in JP-A-10-10-90521 has a retardation value of 160 to 320.
At least two retardation plates each having a thickness of nm are laminated such that their slow axes are not parallel or orthogonal to each other. Each of the retardation plates described in any of the publications is specifically composed of a laminate of two polymer films. Both publications explain that this makes it possible to achieve λ / 4 in a wide wavelength range.

[0003]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. H10-6881
No. 6, No. 10-90521, the production of the retardation plate requires a complicated production process in order to adjust the optical direction (optical axis or slow axis) of the two polymer films. . The optical orientation of the polymer film generally corresponds to the longitudinal or transverse direction of the sheet or roll film. A polymer film having an optical axis or a slow axis in a diagonal direction of a sheet or a roll can theoretically be manufactured but has extremely low productivity. And Japanese Patent Laid-Open No. 10-
In the inventions described in Japanese Patent Nos. 68816 and 10-90521, the optical directions of the two polymer films are set to angles that are neither parallel nor orthogonal. Therefore, Japanese Patent Application Laid-Open
In order to manufacture the retardation plates described in JP-A-68816 and JP-A-10-90521, it is necessary to cut two types of polymer films at a predetermined angle and bond the obtained chips. If a phase difference plate is to be manufactured by bonding chips, the processing is complicated, the quality is likely to be reduced due to misalignment, the yield is reduced, the cost is increased, and deterioration due to contamination is liable to occur. Further, it is difficult to strictly control the retardation value of a polymer film. The optical properties of the optically anisotropic layer composed of liquid crystal molecules are easier to adjust than the birefringence film composed of a polymer. However, when a material having a large wavelength dispersion is used for the λ / 2 phase shifter, the azimuth of the polarized light is R (650n) and G (55
0 nm) and a B (450) nm ring. As a result, when combined with a λ / 4 retarder, the reflectance is slightly increased. Liquid crystal molecules generally have large wavelength dispersion. Discotic liquid crystal molecules that are particularly effective in improving the viewing angle have particularly large wavelength dispersion. SUMMARY OF THE INVENTION An object of the present invention is to provide a retardation plate capable of uniforming the polarization azimuth after passing through a λ / 2 retarder and achieving good circularly polarized light with a λ / 4 retarder, even if an optical material having large wavelength dispersion is used. That is.

[0004]

The object of the present invention has been attained by the following retardation plates (1) to (7) and the following circularly polarizing plate (8). (1) The product of the orientation birefringence and the thickness of the optically anisotropic layer A measured at a wavelength of 550 nm having an optically anisotropic layer A and an optically anisotropic layer B is 150 to 350 nm; A retardation plate, wherein the anisotropic layer A further has a twisted structure with a twist angle of 3 to 45 °, and the optically anisotropic layer B has a retardation of 60 to 170 nm. (2) The retardation plate according to (1), wherein the optically anisotropic layer A is a layer formed from liquid crystalline molecules. (3) The retardation plate according to (1) or (2), wherein the optically anisotropic layer B is a layer formed from liquid crystalline molecules. (4) The retardation plate according to (2), wherein the liquid crystal molecules are discotic liquid crystal molecules. (5) The retardation plate according to (3), wherein the liquid crystal molecules are discotic liquid crystal molecules. (6) The retardation plate according to (2), wherein the liquid crystal molecules are fixed in a substantially uniformly oriented state. (7) The retardation plate according to (3), wherein the liquid crystal molecules are fixed while being substantially uniformly aligned. (8) The product of orientation birefringence and thickness of the optically anisotropic layer A measured at a wavelength of 550 nm having a polarizing film, an optically anisotropic layer A, and an optically anisotropic layer B is 150 to 350 nm. The optically anisotropic layer A further has a twisted structure with a twist angle of 3 to 45 °, and the optically anisotropic layer B has a phase difference of 60 to 17 °.
A circularly polarizing plate having a thickness of 0 nm. Note that the phase difference of the optically anisotropic layer B is defined to be 60 to 170 nm because of the specific wavelength (for example, 550 nm).
nm), and it is not necessary to achieve a phase difference of 60 to 170 nm in a wide wavelength region.

[0005]

As a result of the research by the present inventors, it has been found that the introduction of a twist structure into one of the two optically anisotropic layers (A in the above definition) can greatly improve the broadband characteristics. In the present invention, one (preferably, both) of the two optically anisotropic layers can be formed from liquid crystal molecules. The optical properties of the optically anisotropic layer composed of liquid crystal molecules are easier to adjust than the birefringence film composed of a polymer. The optical orientation of the optically anisotropic layer containing liquid crystal molecules is
It can be easily adjusted by the rubbing direction of the liquid crystalline molecules.
Therefore, there is no need to cut the film into chips as in the prior art. Further, the polarizing plate and the roll-to-roll bonding can be performed. Further, the required retardation value can be strictly adjusted by adjusting the type and amount of the liquid crystal molecules. As described above, according to the present invention, a broadband λ / 4 plate that can be easily manufactured is obtained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Optical Properties of Retardation Plate] The optically anisotropic layer A has a product of orientation birefringence and thickness of 150 to 35.
0 nm. The optically anisotropic layer A further has a twist structure with a twist angle of 3 to 45 °. The product of the orientation birefringence and the thickness corresponds to the in-plane retardation value when no twist structure exists. The in-plane retardation value of the optically anisotropic layer B will be described later.

The optically anisotropic layer B has a retardation of 60 to 17
0 nm. As described above, the optically anisotropic layer B only needs to achieve a phase difference of 60 to 170 nm at a specific wavelength. It is preferable that the specific wavelength achieves a phase difference of 60 to 170 nm at 550 nm, which is a wavelength approximately in the middle of the visible region. Specific wavelength (λ)
In order to achieve a phase difference of π at a specific wavelength (λ)
The retardation value of the optically anisotropic layer B measured in the above may be adjusted to 60 to 170 nm. The retardation value means an in-plane retardation value with respect to light incident from the normal direction of the optically anisotropic layer. Specifically, it is a value defined by the following equation. Retardation value (Re) = (nx−ny) × d In the formula, nx and ny are the in-plane principal refractive index of the optically anisotropic layer, and d is the thickness (nm) of the optically anisotropic layer. is there. The optically anisotropic layers A and B are preferably layers composed of birefringent films or liquid crystalline molecules, more preferably at least one of them is a layer composed of liquid crystalline molecules, and both are composed of liquid crystalline molecules. Most preferably, it is a layer.

[Birefringence film] The birefringence film is preferably made of a polymer film. The polymer film is formed from a polymer that can impart optical anisotropy to the film. Examples of such polymers include polyolefins (eg, polyethylene, polypropylene, norbornene-based polymers), polyvinyl chloride, polystyrene, polyacrylonitrile, polysulfone, polyarylate, polyvinyl alcohol, polymethacrylate, polyacrylate, and cellulose. Esters are included. 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, using two or more polymer films,
The optical properties of the entire two or more films may satisfy the above conditions. The polymer film is preferably manufactured by a solvent casting method in order to reduce birefringence unevenness. The thickness of the polymer film is 20 to 5
The thickness is preferably 00 nm, more preferably 50 to 200 nm, and most preferably 50 to 100 nm.

[Layer formed from liquid crystal 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 substantially uniformly oriented, more preferably fixed in a substantially uniform orientation state, and the liquid crystal molecules are fixed by a polymerization reaction. Is most preferred. The alignment of the liquid crystal molecules is adjusted according to the optical properties (described above) required for the optically anisotropic layers A and B. Examples of rod-like liquid crystal molecules include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, and 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.

Discotic liquid crystalline molecules are described in various literatures (C. Destrade et al., Mol. Crysr. Liq. Cryst., V
ol. 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)). Discotic liquid crystal molecules and their polymerization reactions are described in JP-A-8-5837 and JP-A-8-2728.
4, No. 8-334621, and No. 9-104656. 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.

D (-LQ) _{n wherein} D is a discotic core; L is a divalent linking group; Q is a polymerizable group; and n is an integer from 4 to 12. is there. An example of the discotic core (D) of the above formula 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).

[0012]

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[0013]

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[0014]

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[0015]

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[0016]

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[0017]

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[0018]

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In the above formula, the divalent linking group (L) is
Alkylene group, alkenylene group, arylene group, -CO
It is preferably a divalent linking group selected from the group consisting of-, -NH-, -O-, -S- and a combination thereof. The divalent linking group (L) is an alkylene group, an alkenylene group, an arylene group, -CO-, -NH-, -O-
And a group obtained by combining at least two divalent groups selected from the group consisting of 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 bonded to the polymerizable group (Q). 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-AL-AR-O-AL-O-CO-L17: -O-CO-AR-O-AL-CO-L18: -O-CO-AR-O-AL-O-CO-L19: -O-CO-AR-O-AL-O-AL-OC
O-L20: -O-CO-AR-O-AL-O-AL-OA
L-O-CO-L21: -S-AL-L22: -S-AL-O-L23: -S-AL-O-CO-L24: -S-AL-S-AL-L25: -S-AR -AL-

In the optically anisotropic layer A, since a twist structure is introduced, an asymmetric carbon atom is introduced into AL (alkylene group or alkenylene group), and the discotic liquid crystal molecules can be twisted in a helical manner. Examples of AL * containing an asymmetric carbon atom are given below. The left side is the disc-shaped core (D) side, and the right side is the polymerizable group (Q) side. The carbon atom (C) marked with * is an asymmetric carbon atom. The optical activity may be either S or R.

AL * 1: -CH ₂ CH ₂ -C * HCH _{3
-CH 2 CH 2 CH 2 - AL} * 2: -CH 2 CH 2 CH 2 -C * HCH 3 -CH
_{2 CH 2 - AL * 3:} -CH 2 -C * HCH 3 -CH 2 CH 2 CH
_{2 CH 2 - AL * 4:} -C * HCH 3 -CH 2 CH 2 CH 2 CH 2
_{CH 2 - AL * 5: -CH} 2 CH 2 CH 2 CH 2 -C * HCH 3
_{-CH 2 - AL * 6: -CH} 2 CH 2 CH 2 CH 2 CH 2 -C * H
_{CH 3 - AL * 7: -C} * HCH 3 -CH 2 CH 2 CH 2 CH 2
_{- AL * 8: -CH 2 -C} * HCH 3 -CH 2 CH 2 CH
_{2 - AL * 9: -CH 2} CH 2 -C * HCH 3 -CH 2 CH
_{2 - AL * 10: -CH 2} CH 2 CH 2 -C * HCH 3 -CH
_{2 - AL * 11: -CH 2} CH 2 CH 2 CH 2 -C * HCH 3
- AL * 12: -C * HCH 3 -CH 2 CH 2 CH 2 - AL * 13: -CH 2 -C * HCH 3 -CH 2 CH 2 - AL * 14: -CH 2 CH 2 -C * HCH 3 _{-CH 2 - AL * 15: -CH} 2 CH 2 CH 2 -C * HCH 3 -

[0024] _{AL * 16: -CH 2 -C *} HCH 3 - AL * 17: -C * HCH 3 -CH 2 - AL * 18: -C * HCH 3 -CH 2 CH 2 CH 2 CH 2
_{CH 2 CH 2 - AL * 19} : -CH 2 -C * HCH 3 -CH 2 CH 2 CH
_{2 CH 2 CH 2 - AL *} 20: -CH 2 CH 2 -C * HCH 3 -CH 2 CH
_{2 CH 2 CH 2 - AL *} 21: -CH 2 CH 2 CH 2 -C * HCH 3 -CH
_{2 CH 2 CH 2 - AL *} 22: -C * HCH 3 -CH 2 CH 2 CH 2 CH 2
_{CH 2 CH 2 CH 2 - AL} * 23: -CH 2 -C * HCH 3 -CH 2 CH 2 CH
₂ CH ₂ CH ₂ CH ₂ -AL * 24: -CH ₂ CH ₂ -C * HCH ₃ -CH ₂ CH
_{2 CH 2 CH 2 CH 2 -} AL * 25: -CH 2 CH 2 CH 2 -C * HCH 3 -CH
_{2 CH 2 CH 2 CH 2 -} AL * 26: -C * HCH 3 - (CH 2) 8 - AL * 27: -CH 2 -C * HCH 3 - (CH 2) 8 - AL * 28: -CH 2 _{-C * HCH 2 CH 3 - AL} * 29: -CH 2 -C * HCH 2 CH 3 -CH 2 - AL * 30: -CH 2 -C * HCH 2 CH 3 -CH 2 CH
₂ −

AL * 31: -CH ₂ -C * HCH ₂ CH _{3
-CH 2 CH 2 CH 2 CH 2} - AL * 32: -CH 2 -C * H (n-C 3 H 7) -CH 2
_{CH 2 - AL * 33: -CH} 2 -C * H (n-C 3 H 7) -CH 2
_{CH 2 CH 2 CH 2 - AL} * 34: -CH 2 -C * H (OCOCH 3) -CH 2
_{CH 2 - AL * 35: -CH} 2 -C * H (OCOCH 3) -CH 2
_{CH 2 CH 2 CH 2 - AL} * 36: -CH 2 -C * HF-CH 2 CH 2 - AL * 37: -CH 2 -C * HF-CH 2 CH 2 CH 2 C
_{H 2 - AL * 38: -CH} 2 -C * HCl-CH 2 CH 2 - AL * 39: -CH 2 -C * HCl-CH 2 CH 2 CH 2
_{CH 2 - AL * 40: -CH} 2 -C * HOCH 3 -CH 2 CH 2 - AL * 41: -CH 2 -C * HOCH 3 -CH 2 CH 2 C
_{H 2 CH 2 - AL * 42} : -CH 2 -C * HCN-CH 2 CH 2 - AL * 43: -CH 2 -C * HCN-CH 2 CH 2 CH 2
_{CH 2 - AL * 44: -CH} 2 -C * HCF 3 -CH 2 CH 2 - AL * 45: -CH 2 -C * HCF 3 -CH 2 CH 2 CH
₂ CH ₂ −

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

[0027]

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The polymerizable group (Q) is an unsaturated polymerizable group (Q1
To Q7), an epoxy group (Q8) or an aziridinyl group (Q9), more preferably an unsaturated polymerizable group, and more preferably an ethylenically unsaturated polymerizable group (Q
1 to Q6) are most preferred. In the above formula, n is an integer of 4 to 12. Specific numbers are determined according to the type of discotic core (D).
The combination of a plurality of L and Q may be different, but is preferably the same. Two or more discotic liquid crystal molecules may be used in combination. For example, a molecule having an asymmetric carbon atom in the divalent linking group and a molecule having no asymmetric carbon atom can be used in combination. Further, a molecule having a polymerizable group (Q) and a molecule having no polymerizable group (Q) may be used in combination.

The non-polymerizable discotic liquid crystal molecules are
It is preferable that the compound is obtained by changing the polymerizable group (Q) of the polymerizable discotic liquid crystal molecule to a hydrogen atom or an alkyl group. That is, the non-polymerizable discotic liquid crystal molecule is preferably a compound represented by the following formula. D (-LR) _{n wherein} D is a discotic core; L is a divalent linking group; R is a hydrogen atom or an alkyl group;
Is an integer of 4 to 12. Disc-shaped core of the above formula (D)
Is the same as the above-mentioned example of the polymerizable discotic liquid crystal molecule except that LQ (or QL) is changed to LR (or RL). Examples of the divalent linking group (L) also include
This is the same as the example of the polymerizable discotic liquid crystal molecules described above. The alkyl group for R preferably has 1 to 40 carbon atoms, and more preferably 1 to 30 carbon atoms. A chain alkyl group is more preferable than a cyclic alkyl group, and a straight-chain alkyl group is more preferable than a branched chain alkyl group. R is particularly preferably a hydrogen atom or a linear alkyl group having 1 to 30 carbon atoms.

Instead of introducing an asymmetric carbon atom into the divalent linking group (L) of the discotic liquid crystalline molecule, a compound having an asymmetric carbon atom and exhibiting optical activity (chiral agent) is added to the optically anisotropic layer. Even if added, the discotic liquid crystalline molecules can be twisted and aligned in a helical manner. As the compound containing an asymmetric carbon atom, various natural or synthetic compounds can be used. The same or similar polymerizable group as the discotic liquid crystalline molecule may be introduced into the compound containing an asymmetric carbon atom. When a polymerizable group is introduced, the discotic liquid crystal molecules are aligned substantially vertically (homogeneously) and then fixed, and at the same time, the compound containing an asymmetric carbon atom is also optically anisotropic by the same or similar polymerization reaction. It can be fixed in layers. The following are examples of chiral agents.
C-1, C-3 and C-4 are left-handed chiral agents, and C-2 and C-5 are right-handed chiral agents.

[0031]

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[0032]

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[0033]

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It is preferable to add a cellulose ester to the optically anisotropic layer in order to align the discotic liquid crystal molecules substantially uniformly even on the air interface side.
As the cellulose ester, it is preferable to use a lower fatty acid ester of cellulose. The “lower fatty acid” in the lower fatty acid ester of cellulose means a fatty acid having 6 or less carbon atoms. 2 to 5 carbon atoms
And more preferably 2 to 4. A substituent (eg, hydroxy) may be bonded to the fatty acid. Two or more fatty acids may form an ester with cellulose. Examples of lower fatty acid esters of cellulose include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose hydroxypropionate, cellulose acetate propionate, and cellulose acetate butyrate. Cellulose acetate butyrate is particularly preferred.
The butyrylation degree of cellulose acetate butyrate is 3
It is preferably at least 0%, more preferably from 30 to 80%. The acetylation degree of cellulose acetate butyrate is preferably 30% or less, more preferably 1 to 30%. The cellulose ester is preferably used in an amount in the range of 0.005 to 0.5 g / m ² , and 0.01 to 0.45 g / m ^2.
g / m ² , more preferably 0.02 to 0.4 / m ² ,
Most preferably, it is in the range of 0.03 to 0.35 / m ² . Further, the amount of the discotic liquid crystalline molecule is set to 0.
It is also preferred to use from 1 to 5% by weight.

The optically anisotropic layer is formed by coating a liquid crystal molecule and, if necessary, a compound containing an asymmetric carbon atom, a cellulose ester, or a coating solution containing the following polymerization initiator or other additives with a vertical alignment film. It is formed by applying on top of 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), sulfoxide (eg, dimethylsulfoxide), heterocyclic compound (eg, pyridine), hydrocarbon (eg, benzene, hexane), alkyl halide (eg, chloroform, dichloromethane), ester (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.

The coating solution can be applied by a known method (eg, extrusion coating, direct gravure coating, reverse gravure coating, die coating, bar coating). The aligned liquid crystal molecules are fixed while maintaining the alignment state. The immobilization is preferably performed by a polymerization reaction of the polymerizable group (Q) introduced into the liquid crystal molecules. 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 (U.S. Pat.
No. 7661, No. 2367670), 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. Patents 3046127 and 2951758), triarylimidazole dimer and p
-Combination with aminophenyl ketone (US Patent 35
No. 49367), acridine and phenazine compounds (described in JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (described in U.S. Pat. No. 4,221,970).

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight of the solid content of the coating solution.
More preferably, it is 5 to 5% by weight. Light irradiation for the polymerization of liquid crystalline molecules is preferably performed using ultraviolet light. The irradiation energy is 20 mJ / cm ^{2 to} 50 J
/ Cm ² , preferably 100 to 800 mJ
/ Cm ² is more preferable. Light irradiation may be performed under heating conditions to promote the photopolymerization reaction. The thickness of the optically anisotropic layer is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and most preferably 1 to 5 μm.

[Alignment Film] It is preferable that the liquid crystal molecules are aligned substantially vertically. To be substantially vertically aligned means that the average tilt angle of the liquid crystal molecules is 60 to 90 °. The tilt angle of the liquid crystal molecules corresponds to the angle between the disc surface and the alignment film surface in the case of discotic liquid crystal molecules, and corresponds to the angle between the alignment film surface and the rod-shaped liquid crystal molecules.
In order to vertically align 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 groups of the polymer, and thereby the discotic liquid crystal molecules are in a standing state. As the functional group that lowers the surface energy of the alignment film, a hydrocarbon group having 10 or more carbon atoms is effective. In order to make the hydrocarbon group exist on the surface of the alignment film, it is preferable to introduce the hydrocarbon group into a side chain rather than the main chain of the polymer. 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 main chain of the polymer preferably has a polyimide structure or a polyvinyl alcohol structure.

Polyimide is generally synthesized by a condensation reaction between tetracarboxylic acid and 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 hydrocarbon group may be present in the repeating unit derived from a tetracarboxylic acid, may be present in the repeating unit derived from a diamine, or may be present 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.

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 modified polyvinyl alcohol having a hydrocarbon group having 10 or more carbon atoms is represented by the following formula (P
V). (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).

[0042]

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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 combination are shown below.

[0044] 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 degree of polymerization 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 essential (although it is essential in the production of the retardation plate).

[Transparent Support] As the transparent support, it is preferable to use a polymer film having a small wavelength dispersion. The transparent support also preferably has a small optical anisotropy. Transparent support means that the light transmittance is 80% or more. Specifically, it is preferable that the ratio of Re400 / Re700 is less than 1.2 when the wavelength dispersion is small. The optical anisotropy is small, specifically,
The in-plane retardation (Re) is preferably at most 20 nm, more preferably at most 10 nm. The long transparent support has a roll shape or a rectangular sheet shape. It is preferable that an optically anisotropic layer is laminated using a roll-shaped transparent support, and then cut into a required size. 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 preferably 20 to 500 μm,
More preferably, it is 0 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 (UV) treatment, flame treatment) may be performed. An adhesive layer (undercoat layer) may be provided on the transparent support.

[Circularly Polarizing Plate] The retardation plate of the present invention is a combination of a λ / 4 plate used in a reflection type liquid crystal display device, a λ / 4 plate used in a pickup for writing on an optical disk, and a cholesteric liquid crystal. Can be particularly advantageously used as a λ / 4 plate used in the above or a λ / 4 plate used as an antireflection film. The λ / 4 plate is generally used as a circularly polarizing plate combined with a polarizing film. Therefore,
If a circularly polarizing plate is formed by combining a retardation plate and a polarizing film, it can be easily incorporated into a device such as a reflection type liquid crystal display device. The polarizing film includes an iodine-based polarizing film, a dye-based polarizing film using a dichroic dye, and a polyene-based polarizing film. The iodine-based polarizing film and the dye-based polarizing film are generally manufactured using a polyvinyl alcohol-based film. The transmission axis of the polarizing film corresponds to a direction perpendicular to the stretching direction of the film. The polarizing film generally has protective films on both sides. However, in the present invention, the transparent support can function as a protective film on one side of the polarizing film. When a protective film is used separately from the transparent support, it is preferable to use a cellulose ester film having high optical isotropy, particularly a triacetyl cellulose film, as the protective film.

The wide band λ / 4 is, specifically, a wavelength 45
The retardation value / wavelength value measured at 0 nm, 550 nm and 650 nm is 0.2 to 0.3.
Within the range. Retardation value /
The value of the wavelength is preferably in the range of 0.21 to 0.29, more preferably in the range of 0.22 to 0.28, and in the range of 0.23 to 0.27. More preferably, it is most preferably in the range of 0.24 to 0.26.

[0049]

[Example 1] Thickness 100 μm, width 500 mm
The optically isotropic triacetyl cellulose film was used as a transparent support. The following coating solution was applied on one surface of the transparent support with a bar coater and dried at 130 ° C. for 3 minutes to form a 0.5 μm thick vertical alignment film.

組成 Composition of vertical alignment film coating solution ───── ─────────────────────────────── Steroid-modified polyamic acid 5.0% by weight N-methyl-2-pyrrolidone 25.0 Weight% ethylene glycol monobutyl ether 25.0 weight% methyl ethyl ketone 45.0 weight% ───

After performing the rubbing treatment on the vertical alignment film,
A coating solution having the following composition is applied, dried, and further 500 W /
Irradiate ultraviolet light for 1 second with a mercury lamp of illuminance of cm ² ,
An optically anisotropic layer A was formed. The thickness of the optically anisotropic layer A is
The retardation was adjusted so as to be 250 nm.

<< Composition of Optically Anisotropic Layer A Coating Solution >>デ ィ ス The following discotic liquid crystalline molecules (1) 32.6% by weight cellulose Acetate butyrate 0.2% by weight Modified trimethylolpropane triacrylate below 3.2% by weight Following sensitizer 0.4% by weight Photopolymerization initiator below 1.1% by weight Chiral agent C-2 0.35 Wt% Methyl ethyl ketone 62.5 wt% ────────────────────────────────────

[0053]

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[0054]

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[0055]

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A total reflection prism was attached to an ellipsometer (M-1500, manufactured by JASCO Corporation), and while the optically anisotropic layer A was rotated, the liquid crystal alignment direction was measured from the change in phase difference near the air interface. The twist angle was determined from the difference from the rubbing axis. The results are shown in the graph of FIG. Further, the polarizing plate and the transparent support are bonded together so that the polarizing transmission axis of the polarizing plate and the rubbing axis of the optically anisotropic layer A are 15 °, and the ellipsometric analysis (KOBUURA-21DH, Oji Scientific Instruments Co., Ltd.)
Made). Wavelength 480 nm, 550 nm and 63
The relationship between the largest difference in the polarization azimuth angle at 0 nm and the twist angle is shown in the graph of FIG.

A polarizing plate, an optically anisotropic layer A and an optically anisotropic layer B were laminated in this order to produce a circularly polarizing plate. As the optically anisotropic layer B, a polycarbonate film having a retardation of 137 nm at a wavelength of 550 nm was used. The transparent support of the optically anisotropic layer A was disposed on the polarizing plate side. The angle between the transmission axis of the polarizing plate and the rubbing direction of the optically anisotropic layer A is 15 °; the angle between the transmission axis of the polarizing plate and the slow axis of the optically anisotropic layer B is 70 °; The angle between the rubbing direction of A and the slow axis of the optically anisotropic layer B was set at 55 °. Wavelength dispersion analysis (KOBUURA-31PR, manufactured by Oji Scientific Instruments) was performed on the retardation of the circularly polarizing plate. The results are shown in FIG. Further, a circularly polarizing plate was attached to a total reflection mirror, and the reflection characteristics were examined. FIG. 4 shows the results.

Comparative Example 1 A circularly polarizing plate was prepared and evaluated in the same manner as in Example 1 except that the chiral agent C-2 was not added. FIG. 1 shows the twist angle, FIG. 2 shows the relationship between the largest difference in polarization azimuth angle and the twist angle, FIG. 3 shows the result of chromatic dispersion analysis, and FIG. 4 shows the reflection characteristics.

Example 2 A circularly polarizing plate was prepared and evaluated in the same manner as in Example 1 except that the amount of the chiral agent C-2 was changed to 0.02% by weight. Figure 1 twist angle
FIG. 2 shows the relationship between the largest difference in polarization azimuth and the twist angle.

Example 3 A circularly polarizing plate was prepared and evaluated in the same manner as in Example 1 except that the amount of the chiral agent C-2 was changed to 0.05% by weight. Figure 1 twist angle
FIG. 2 shows the relationship between the largest difference in polarization azimuth and the twist angle.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of a chiral agent added and the twist angle.

FIG. 2 is a graph showing the relationship between the largest difference in polarization azimuth and the twist angle.

FIG. 3 is a graph showing the results of wavelength dispersion analysis of the circularly polarizing plates of Example 1 and Comparative Example 1.

FIG. 4 is a graph showing reflection characteristics of the circularly polarizing plates of Example 1 and Comparative Example 1.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Ken Kawata 210 Nakanakanuma, Minamiashigara-shi, Kanagawa Prefecture Fuji Photo Film Co., Ltd. F-term (reference) 2H049 BA02 BA03 BA07 BA42 BB03 BC02 BC04 BC22 2H091 FA11X FA11Z HA07 JA01 KA02 LA19

Claims (8)

[Claims] 1. An optically anisotropic layer A having an optically anisotropic layer A and an optically anisotropic layer B, wherein the product of orientation birefringence and thickness of the optically anisotropic layer A measured at a wavelength of 550 nm is 150 to 350 nm, The optically anisotropic layer A further has a twisted structure having a twist angle of 3 to 45 °, and the optically anisotropic layer B has a retardation of 60 to 17 °.
A retardation plate having a thickness of 0 nm. 2. The retardation plate according to claim 1, wherein the optically anisotropic layer A is a layer formed from liquid crystalline molecules. 3. The retardation plate according to claim 1, wherein the optically anisotropic layer B is a layer formed from liquid crystalline molecules. 4. The retardation plate according to claim 2, wherein the liquid crystal molecules are discotic liquid crystal molecules. 5. The retardation plate according to claim 3, wherein the liquid crystal molecules are discotic liquid crystal molecules. 6. The retardation plate according to claim 2, wherein the liquid crystal molecules are fixed in a state of being substantially uniformly aligned. 7. The retardation plate according to claim 3, wherein the liquid crystal molecules are fixed in a state of being substantially uniformly aligned. 8. An optically anisotropic layer A having a polarizing film, an optically anisotropic layer A, and an optically anisotropic layer B, and measured at a wavelength of 550 nm.
The product of the orientation birefringence and the thickness of the optically anisotropic layer A is 150 to 350 nm, the optically anisotropic layer A further has a twisted structure with a twist angle of 3 to 45 °, and the optically anisotropic layer B has a
A circularly polarizing plate having a thickness of from about 170 nm to about 170 nm.