JP2009234104A - Optical film, polarizing plate and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film or the like in which the change of in-plane retardation is suppressed as a whole even if the in-plane retardation of each optical anisotropic layer changes due to shrinkage or the like.
An optical film of the present invention includes a first optical anisotropic layer containing a liquid crystalline compound, a second optical anisotropic layer containing a thermoplastic resin having a positive photoelastic coefficient, and negative photoelasticity. A third optical anisotropic layer containing a thermoplastic resin having a coefficient, and an in-plane retardation Re (550) at a wavelength of 550 nm of the third optical anisotropic layer is 10 nm or less.
[Selection figure] None

Description

  The present invention relates to an optical film, a polarizing plate using the optical film, and a liquid crystal display device having the polarizing plate.

  In recent years, an increase in the size of a liquid crystal display device has been desired. Accordingly, an increase in the size of an optical compensation film for compensating for a phase difference generated in light transmitted through a liquid crystal cell, which is used in a liquid crystal display device, is desired.

When the liquid crystal display device is enlarged and the optical compensation film is also enlarged, light leakage (frame unevenness) may occur around the liquid crystal display portion (monitor) of the liquid crystal display device, which has been a problem.
The cause of this light leakage is that the in-plane retardation of the optical compensation film changes. This change in the in-plane retardation significantly occurs in the peripheral portion of the optical compensation film. The change in the in-plane retardation is due to stress generated by contraction of the optical compensation film under high temperature or low humidity conditions.

  As an optical film applied to an increase in the size of a liquid crystal display device, for example, a retardation layer in which a polymer exhibiting positive intrinsic birefringence (for example, a norbornene polymer) is aligned, and a negative intrinsic birefringence are provided. There has been proposed an optical film having a retardation layer in which a polymer (for example, an acrylic polymer) to be oriented is aligned and a retardation layer containing a liquid crystal compound (see Patent Document 1). The optical film of Patent Document 1 is said to improve contrast, uniformity of screen display, and the like even in the case of a large-screen liquid crystal display device.

However, the norbornene-based polymer, acrylic polymer, etc. used for the retardation layer of the optical film of Patent Document 1 have a photoelastic coefficient (absolute value) of less than 10 × 10 ⁻¹³ cm ² / dyn, and are stretched. For example, it is difficult to express optical characteristics greatly. Therefore, there has been a problem that it is difficult to uniformly control the in-plane retardation in each retardation layer.

JP 2002-90530 A

An object of the present invention is to solve the conventional problems and achieve the following objects.
That is, the present invention relates to an optical film in which the change in the in-plane retardation is suppressed as a whole even if the in-plane retardation of each optical anisotropic layer changes due to shrinkage or the like, and a polarizing plate using the optical film And a liquid crystal display device including the polarizing plate.

Means for solving the problems are as follows. That is,
<1> a first optically anisotropic layer containing a liquid crystalline compound;
A second optically anisotropic layer comprising a thermoplastic resin having a positive photoelastic coefficient;
A third optically anisotropic layer comprising a thermoplastic resin having a negative photoelastic coefficient,
An in-plane retardation Re (550) at a wavelength of 550 nm of the third optically anisotropic layer is 10 nm or less.
The optical film of <1> has a first optical anisotropic layer containing a liquid crystalline compound, a second optical anisotropic layer containing a thermoplastic resin having a positive photoelastic coefficient, and a negative photoelastic coefficient. A third optically anisotropic layer containing a thermoplastic resin, and an in-plane retardation Re (550) at a wavelength of 550 nm of the third optically anisotropic layer is 10 nm or less. Even if the in-plane retardation of the anisotropic layer changes, the change in the in-plane retardation is suppressed as a whole.
<2> The optical film according to <1>, wherein the second optical anisotropic layer has a photoelastic coefficient of 10 × 10 ⁻¹³ cm ² / dyn or more.
<3> The optical film according to <1> or <2>, wherein the first optical anisotropic layer, the second optical anisotropic layer, and the third optical anisotropic layer are laminated in this order.
<4> The optical film according to any one of <1> to <3>, wherein the liquid crystalline compound of the first optically anisotropic layer includes a discotic liquid crystalline compound.
<5> The optical film according to any one of <1> to <4>, wherein the thermoplastic resin having a positive photoelastic coefficient of the second optically anisotropic layer is a cellulose acylate film.
<6> A polarizing plate having at least the optical film according to any one of <1> to <5> and a polarizing film.
<7> A liquid crystal display device having at least a liquid crystal cell and the polarizing plate according to <6>.
<8> The liquid crystal display device according to <7>, wherein the liquid crystal cell has a size of 26 inches or more.
<9> The liquid crystal display device according to <7> or <8>, wherein the liquid crystal cell is a TN method.

  According to the present invention, even if the in-plane retardation of each optical anisotropic layer changes due to shrinkage or the like, as a whole, an optical film in which the change in in-plane retardation is suppressed, a polarizing plate using the optical film, And a liquid crystal display device provided with the polarizing plate.

  In this specification, Re (λ) represents an in-plane retardation value (unit: nm) at a wavelength λ (nm) of a film-like measurement object such as an optically anisotropic layer, a film, or a laminate, and Rth (Λ) represents a retardation value (unit: nm) in the thickness direction at a wavelength λ (nm).

In this specification, Re (λ) represents an in-plane retardation value at a wavelength λ, and Rth (λ) represents a thickness direction retardation value at a wavelength λ.
Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of a film-like measurement object in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments).
As a method of changing the measurement wavelength λnm, there are a method of manually exchanging the wavelength selection filter, and a method of measuring the measured value by converting it with a program or the like.
When the film-like measurement object to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis) (in the absence of a slow axis, film-like From the normal direction to the normal direction of the film-like measurement object (in any plane in the plane of the measurement object) from the normal direction to 50 ° on one side in 10 ° steps. A total of 6 points are measured by making light of wavelength λ nm incident, and KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed value of the average refractive index, and the input film thickness value.
In the above, in the case of a film-like measurement object having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis as the rotation axis from the normal direction, the tilt angle is larger than the tilt angle. The retardation value is calculated by KOBRA 21ADH or WR after changing the sign to negative.
Retardation from two inclined directions with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, any direction in the plane of the film-like object to be measured is the rotation axis) Rth can also be calculated from the following formula (A) and formula (B) based on the measured value, the assumed value of the average refractive index, and the input film thickness value.

... Formula (A)

Note that Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction.
In the formula (A), nx represents a refractive index in the slow axis direction in the plane, ny represents a refractive index in a direction perpendicular to nx in the plane, and nz is a direction orthogonal to nx and ny. Represents the refractive index. d represents a film thickness.

  Rth = ((nx + ny) / 2−nz) × d (B)

In the case where the film-like measurement object to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a measurement object without a so-called optical axis, Rth (λ ) Is calculated.
Rth (λ) is from −50 ° to +50 with respect to the film normal direction, with Re (λ) being the in-plane slow axis (determined by KOBRA 21ADH or WR) and the tilt axis (rotation axis). Measured at 11 points by injecting light of wavelength λnm from each inclined direction in 10 ° steps up to °°, and KOBRA based on the measured retardation value, assumed value of average refractive index, and input film thickness value. 21ADH or WR is calculated.
In the above measurement, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. Examples of the average refractive index of main optical films are cellulose acylate (1.48), cycloolefin polymer (1.52), and polycarbonate (1.59). Polymethyl methacrylate (1.49) and polystyrene (1.59). The KOBRA 21ADH or WR calculates nx, ny, and nz by inputting the assumed average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

  In the present specification, the “slow axis” of a film-like measurement object such as an optically anisotropic layer, a film, or a laminate represents a direction in which the refractive index is maximized. For example, KOBRA 21DH (manufactured by Oji Scientific Instruments) can be used to measure the slow axis of the measurement object.

  Further, in this specification, an angle such as “45 °”, “orthogonal” or “parallel” means that the angle is within a range of strictly less than ± 5 °. The error from the exact angle is preferably less than 4 °, more preferably less than 3 °.

  Further, the “photoelastic coefficient” in the present specification is a value measured using an ellipsometer (M-150, manufactured by JASCO Corporation) at 25 ° C. and 60% RH.

[Optical film]
The optical film of the present invention includes a first optical anisotropic layer, a second optical anisotropic layer, and a third optical anisotropic layer.

(First optical anisotropic layer)
The first optical anisotropic layer includes a liquid crystal compound. The first optically anisotropic layer is formed from a composition containing a liquid crystal compound.

  The first optically anisotropic layer is preferably designed to compensate for a liquid crystalline compound in a liquid crystal cell in black display of a 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. Regarding the alignment state of the liquid crystal compound in this liquid crystal cell, IDW'00, FMC7-2 p. 411-414 and the like.

The first optical anisotropic layer may be formed directly on the support using the second optical anisotropic layer or the third optical anisotropic layer as a support, or via an alignment film. You may form on this support body.
The first optically anisotropic layer is produced from a composition containing a liquid crystal compound or the like.
There is no restriction | limiting in particular as this alignment film, According to the objective, it selects suitably. Note that when the rubbing treatment is performed on the alignment film, the orientation direction of the liquid crystalline compound in the first optical anisotropic layer can be determined by appropriately setting the rubbing treatment direction.
When the alignment film is formed, a saponification treatment may be appropriately performed on the second optical anisotropic layer or the third optical anisotropic layer serving as a support.
There is no restriction | limiting in particular in the thickness of this alignment film, Although it sets suitably according to the objective, 10 micrometers or less are preferable.

  The liquid crystalline compound in the first optically anisotropic layer is not particularly limited and may be appropriately selected depending on the intended purpose. For example, a rod-like liquid crystalline compound and a discotic liquid crystalline compound are preferable, and a discotic liquid crystalline property is preferable. Compounds are particularly preferred.

(Bar-shaped liquid crystalline compound)
Examples of the rod-like liquid crystalline compound 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 crystal compound includes a metal complex. Moreover, the liquid crystal polymer which contains this rod-shaped liquid crystalline compound in a repeating unit can also be used as the rod-shaped liquid crystalline compound of the present invention. In other words, the rod-like liquid crystalline compound may be bonded to a (liquid crystal) polymer.
As for the rod-like liquid crystalline compound, for example, the quarterly review of chemical review, Vol. 22, Chemistry of Liquid Crystal (1994), Chapter 4, Chapter 7 and Chapter 11 of the Chemical Society of Japan, and the 142nd Committee of the Japan Society for the Promotion of Science Those described in Chapter 3 of the meeting can be adopted.
The birefringence of the rod-like liquid crystal compound is preferably in the range of 0.001 to 0.7.

  The rod-like liquid crystalline compound preferably has a polymerizable group in order to fix the alignment state. The polymerizable group is preferably an unsaturated polymerizable group or an epoxy group, more preferably an unsaturated polymerizable group, and particularly preferably an ethylenically unsaturated polymerizable group.

(Discotic liquid crystalline compounds)
Examples of the discotic liquid crystalline compound 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. (JCS, Chem. Commun., 1794 (1985)), J.C. Azacrown-type and phenylacetylene-type macrocycles described in the research report of Zhang et al. (J. Am. Chem. Soc. 116, 2655 (1994)) are included.

The discotic liquid crystalline compound also includes a compound having a structure 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. The molecule or the assembly of molecules is preferably a compound having rotational symmetry and imparting a certain orientation.
In the first optical anisotropic layer formed from the discotic liquid crystalline compound, the compound finally contained in the first optical anisotropic layer does not need to be a discotic liquid crystalline compound. The tick liquid crystalline molecule has a group that reacts with heat or light, and as a result, a compound that is polymerized or cross-linked by reaction with heat or light to have a high molecular weight and lose liquid crystallinity is also included. Preferred examples of the discotic liquid crystalline compound are described in JP-A-8-50206. Moreover, about superposition | polymerization of a discotic liquid crystalline compound, Unexamined-Japanese-Patent No. 8-27284 has description.

  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. Accordingly, the discotic liquid crystalline compound having a polymerizable group is preferably a compound represented by the following general formula (1).

(In General Formula (1), D is a discotic core, L is a divalent linking group, Q is a polymerizable group, and n is an integer of 4 to 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 general formula (1), the divalent linking group (L) is a group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. It is preferably a divalent linking group selected more.
The divalent linking group (L) is a divalent linking in which at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO-, -NH-, -O-, and S- are combined. More preferably, it is a group.
The divalent linking group (L) is particularly preferably a divalent linking group obtained by combining at least two divalent groups selected from the group consisting of an alkylene 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, and the arylene group preferably has 6 to 10 carbon atoms. .

As examples of the divalent linking group (L), (L1 to L25) 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. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl 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-O-CO-
L20: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-
L21: -S-AL-
L22: -S-AL-O-
L23: -S-AL-O-CO-
L24: -S-AL-S-AL-
L25: -S-AR-AL-

  The polymerizable group (Q) of the general formula (1) is determined according to the type of polymerization reaction. Examples of the polymerizable group (Q) are shown below.

The polymerizable group (Q) is preferably an unsaturated polymerizable group (Q1, Q2, Q3, Q7, Q8, Q15, Q16, Q17) or an epoxy group (Q6, Q18). More preferably, it is particularly preferably an ethylenically unsaturated polymerizable group (Q1, Q7, Q8, Q15, Q16, Q17).
Moreover, in the said General formula (1), n is an integer of 4-12. A specific value of n is determined according to the type of the disk-shaped core (D). In addition, although the combination of several L and Q may differ, it is preferable that it is the same.

In the hybrid alignment, the angle between the major axis (disc surface) of the discotic liquid crystalline compound and the surface of the support (optical film), that is, the tilt angle is determined by the depth of the optically anisotropic layer (that is, the support (optical film)). And increases or decreases with increasing distance from the plane of the polarizing film. The angle preferably decreases with increasing distance.
In addition, as the change in inclination angle, continuous increase, continuous decrease, intermittent increase, intermittent decrease, change including continuous increase and continuous decrease, or intermittent change including increase and decrease are possible. . The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction.
Even if the inclination angle includes a region where the angle does not change, the inclination angle may be increased or decreased as a whole. Furthermore, it is preferable that the inclination angle changes continuously.

The average direction of the major axis (disk surface) of the discotic liquid crystalline compound (average of the major axis direction of each molecule) is generally selected by selecting the discotic liquid crystalline compound or the material of the alignment film, or selecting the rubbing treatment method. This can be adjusted.
The major axis (disk surface) direction of the discotic liquid crystalline compound on the surface side (air side) is generally adjusted by selecting the type of additive used together with the discotic liquid crystalline compound or the discotic liquid crystalline compound. be able to.
Examples of the additive used together with the discotic liquid crystalline compound include a plasticizer, a surfactant, a polymerizable monomer and a polymer. The degree of change in the orientation direction of the major axis can also be adjusted by selecting liquid crystalline molecules and additives as described above.

The plasticizer, surfactant and polymerizable monomer used together with the discotic liquid crystalline compound are compatible with the discotic liquid crystalline compound, and can change the tilt angle of the discotic liquid crystalline compound or change the orientation. It is preferable not to inhibit. 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, adhesion between the alignment film and the first optically anisotropic layer can be improved.

The first optically anisotropic layer may contain a polymer together with the discotic liquid crystalline compound. The polymer preferably has a certain degree of compatibility with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound.
Examples of the polymer include cellulose ester.
Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose, and cellulose acetate butyrate.
As described above, cellulose esters, particularly cellulose acetate butyrate, promotes the formation of domains as the amount added increases. Therefore, the amount of the polymer added is disco so as not to inhibit the orientation of the discotic liquid crystalline compound. It is preferably in the range of 0.1 to 2.0% by weight, more preferably in the range of 0.1 to 1.5% by weight, based on the tick liquid crystalline compound, and 0.1 to 1.0% by weight. % Is more preferable.
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.
Moreover, you may add a fluorine-type polymer etc. suitably as said polymer.

(Fixing the alignment state of liquid crystal 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. Among them, the photopolymerization reaction is preferable.
Examples of photopolymerization initiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin compounds ( US Pat. No. 2,722,512), polynuclear quinone compounds (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), acridine, and Phenazine compounds (described in JP-A-60-105667 and US Pat. No. 4,239,850) and oxadiazole compounds (described in US Pat. No. 4,221,970) are included.

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 20~5,000mJ / cm ^2, in a range of 100 to 800 mJ / cm ² Further preferred. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.

(Second optically anisotropic layer)
The second optical anisotropic layer includes a thermoplastic resin having a positive photoelastic coefficient. “Having a positive photoelastic coefficient” means that when the resin is stretched, the refractive index in the stretching direction becomes larger than the direction perpendicular thereto, and the stretching direction becomes the slow axis.

The photoelastic coefficient of the second optical anisotropic layer is 10 × 10 ⁻¹³ cm ² / dyn or more.

There is no restriction | limiting in particular as a thermoplastic resin which has a positive photoelastic coefficient, According to the objective, it selects suitably.
Examples of the thermoplastic resin include cellulosic polymers, polycarbonate, polyarylate, polysulfone, polyolefin, polyethylene terephthalate, and polyethylene naphthalate. Moreover, the polymer etc. which mixed 2 or more types of these polymers are mentioned.

There is no restriction | limiting in particular as thickness of this 2nd optically anisotropic layer, Although it selects suitably according to the objective, 5 micrometers-200 micrometers are preferable, 10 micrometers-150 micrometers are more preferable, 20 micrometers-100 micrometers are still more preferable.
If the thickness of the second optically anisotropic layer is less than 5 μm, there may be a problem in conveyance in the manufacturing process, and if it exceeds 200 μm, the effect of thinning is lost and a failure such as a crack is likely to occur. It may be disadvantageous in terms of cost.

There is no restriction | limiting in particular as Re (550) of this 2nd optically anisotropic layer, Although it selects suitably according to the objective, 5 nm-200 nm are preferable, 10 nm-150 nm are more preferable, 20 nm-100 nm are still more preferable .
When Re (550) of the second optically anisotropic layer is less than 5 nm, the viewing angle expansion effect of the liquid crystal display device may be reduced. When the Re (550) exceeds 200 nm, the viewing angle expansion effect of the liquid crystal display device is similarly reduced. May become smaller.

The Rth (550) of the second optically anisotropic layer is not particularly limited and is appropriately selected depending on the intended purpose, but is preferably 5 nm to 400 nm, more preferably 10 nm to 350 nm, and even more preferably 20 nm to 300 nm. .
When Rth (550) of the second optically anisotropic layer is less than 5 nm, the viewing angle expansion effect of the liquid crystal display device may be reduced. When the Rth (550) exceeds 400 nm, the viewing angle expansion effect of the liquid crystal display device is similarly reduced. May become smaller.

There is no restriction | limiting in particular as a manufacturing method of this 2nd optically anisotropic layer, According to the objective, it selects suitably. For example, the second optically anisotropic layer can be produced from a film made of the thermoplastic resin.
There is no restriction | limiting in particular as a manufacturing method of this film, According to the objective, it selects suitably.

  In order to adjust the retardation value of the film to the above preferable range, it is common to use a method of applying an external force such as stretching. Further, a retardation increasing agent may be added to the film to adjust the retardation value.

There is no restriction | limiting in particular as said retardation increasing agent, Although it selects suitably according to the objective, The aromatic compound which has at least two aromatic rings is preferable. The aromatic compound is preferably used in an addition amount of 0.01 to 20 parts by mass with respect to 100 parts by mass of the polymer. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.
The retardation increasing agent is described in, for example, European Patent Application No. 0911656, Japanese Patent Application Laid-Open Nos. 2000-1111914, and 2000-275434.

  In order to adjust the photoelastic coefficient of the film to the above preferable range, a material (polymer) to be used may be appropriately selected. For example, a material having a desired photoelastic coefficient can be obtained by mixing two or more polymers at an appropriate blending ratio.

(Third optical anisotropic layer)
The third optically anisotropic layer includes a thermoplastic resin having a “negative photoelastic coefficient”. “Having a negative photoelastic coefficient” means that when the resin is stretched, the refractive index in the stretching direction is smaller than the direction perpendicular thereto, and the direction perpendicular to the stretching direction is the slow axis direction. .

The photoelastic coefficient of the third optical anisotropic layer is −5 × 10 ⁻¹³ cm ² / dyn or less.

There is no restriction | limiting in particular as a thermoplastic resin which has a negative photoelastic coefficient, According to the objective, it selects suitably.
Examples of the thermoplastic resin include acrylic polymers such as polymethyl methacrylate, and styrene polymers such as polystyrene and modified polystyrene. Moreover, the polymer etc. which mixed 2 or more types of these polymers are mentioned.

There is no restriction | limiting in particular as thickness of this 3rd optically anisotropic layer, Although it selects suitably according to the objective, 5 micrometers-200 micrometers are preferable, 10 micrometers-150 micrometers are more preferable, 20 micrometers-100 micrometers are still more preferable.
If the thickness of the third optically anisotropic layer is less than 5 μm, there may be a problem in conveyance in the manufacturing process, and if it exceeds 200 μm, the effect of thinning is lost and failure such as cracking is likely to occur. Therefore, it may be disadvantageous in terms of cost.

The Re (550) of the third optical anisotropic layer is preferably 10 nm or less, preferably 5 nm or less, and more preferably 3 nm or less.
If Re (550) of the third optical anisotropic layer exceeds 10 nm, unevenness may occur in the surface.

The Rth (550) of the third optically anisotropic layer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 10 nm or less, more preferably 5n or less, and still more preferably 3 nm or less.
If Rth (550) of the third optically anisotropic layer exceeds 10 nm, unevenness may occur in the plane.

There is no restriction | limiting in particular as a manufacturing method of this 3rd optically anisotropic layer, According to the objective, it selects suitably. For example, the third optically anisotropic layer can be produced from a film made of the thermoplastic resin.
There is no restriction | limiting in particular as a manufacturing method of this film, According to the objective, it selects suitably.

  In order to adjust the retardation value of the film to the above preferable range, it is common to use a method of applying an external force such as stretching. Further, a retardation increasing agent may be added to the film to adjust the retardation value.

There is no restriction | limiting in particular as said retardation increasing agent, Although it selects suitably according to the objective, The aromatic compound which has at least two aromatic rings is preferable. The aromatic compound is preferably used in an addition amount of 0.01 to 20 parts by mass with respect to 100 parts by mass of the polymer. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.
The retardation increasing agent is described in, for example, European Patent Application No. 0911656, Japanese Patent Application Laid-Open Nos. 2000-1111914, and 2000-275434.

  In order to adjust the photoelastic coefficient of the film to the above preferable range, a material (polymer) to be used may be appropriately selected. For example, a material having a desired photoelastic coefficient can be obtained by mixing two or more kinds of polymers at an appropriate blending ratio.

(Other layers)
In the optical film, other than the first optical anisotropic layer, the second optical anisotropic layer, and the second optical anisotropic layer, other optical anisotropies may be used as long as the function of the present invention is not impaired. A layer, a protective layer, or the like may be laminated.

[Lamination method of optical film]
The stacking order of the first optical anisotropic layer, the second optical anisotropic layer, and the third optical anisotropic layer in the optical film is not particularly limited and may be appropriately selected depending on the purpose. The optically anisotropic layer, the second optically anisotropic layer, and the third optically anisotropic layer are preferably laminated in this order.

  Moreover, when laminating | stacking a 1st optically anisotropic layer, a 2nd optically anisotropic layer, and a 3rd optically anisotropic layer, you may laminate | stack through a well-known adhesive agent (adhesive) suitably.

〔Polarizer〕
The polarizing plate of the present invention includes at least the optical film and a polarizer. The polarizing plate may further include a protective film (protective film) as appropriate.

(Polarizer)
The polarizer includes a polarizing film. The polarizer is preferably a coating type polarizing film represented by Optiva, or a polarizing film made of 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.

A general-purpose polarizer can be prepared, for example, 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. it can.
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 not more than a general-purpose polarizing plate (about 30 μm), preferably not more than 25 μm, and more preferably not more than 20 μm. When it is 20 μm or less, the light leakage phenomenon is not observed in 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 liquid 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 cross-linking 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 particularly preferred. .

The saponification degree of polyvinyl alcohol and modified polyvinyl alcohol is preferably 70 to 100%, more preferably 80 to 100%, and particularly preferably 95 to 100%. The polymerization degree of polyvinyl alcohol is preferably 100 to 5,000.
The modified polyvinyl alcohol is obtained by introducing a modifying group into polyvinyl alcohol by copolymerization modification, chain transfer modification or block polymerization modification.
In the copolymerization modification, —COONa, —Si (OH) ₃ , N (CH ₃ ) ₃ .Cl, C ₉ H ₁₉ COO—, —SO ₃ Na, —C ₁₂ H ₂₅ may be introduced as a modifying group. it can.
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 3,000. 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 preferred.
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 still 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, and more preferably 0.5% by mass or less in the binder. If the binder layer contains a crosslinking agent 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, both with a single plate transmittance and a polarization rate 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). It is particularly preferable that 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 particularly 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 more preferably in the range of 0.05 to 5 μm.

(Manufacture of polarizers)
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 degrees. Recently, however, devices that are not necessarily 45 degrees 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.
Generally, it is carried out by rubbing several times using a cloth in which fibers having a uniform length and thickness are planted on average. At this time, it is preferable to carry out using a rubbing roll whose roundness, cylindricity, and runout (eccentricity) are all 30 μm or less. The film wrap angle on the rubbing roll is preferably 0.1 to 90 degrees. However, as described in JP-A-8-160430, a stable rubbing treatment can be obtained by winding 360 degrees 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 degrees. When used in a liquid crystal display device, 40 to 50 degrees is preferable. 45 degrees is particularly preferable.
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.

[Liquid Crystal Display]
The optical film and polarizing plate of the present invention can be used for liquid crystal display devices in various modes. The liquid crystal display device includes at least a liquid crystal cell and two polarizing plates disposed on both sides thereof. The liquid crystal cell carries a liquid crystal between two electrode substrates.
Examples of the liquid crystal mode to which the optical film and the polarizing plate of the present invention can be applied include a TN mode, an OCB mode, a VA mode, an ECB mode, an STN mode, and an IPS mode. In particular, the TN mode is preferable.

  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 cellulose acetate film (second optically anisotropic layer))
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.

(Cellulose acetate solution composition)
――――――――――――――――――――――――――――――――――――――――
-Cellulose acetate with an acetylation degree of 60.7-61.1% 100 parts by mass-Triphenyl phosphate (plasticizer) 7.8 parts by mass-Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by mass-Methylene chloride (first Solvent) 336 parts by mass • Methanol (second solvent) 29 parts by mass • 1-butanol (third solvent) 11 parts by mass ――――――――――――――――――――――― ―――――――――――――――――

  In another mixing tank, 16 parts by mass of a retardation increasing agent having the following structural formula, 92 parts by mass of methylene chloride and 8 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution. A dope was prepared by mixing 147.7 parts by mass of the retardation increasing agent solution with 487.7 parts by mass of the cellulose acetate solution and stirring sufficiently.

Retardation raising agent

The obtained dope was cast using a band stretching machine. After the film surface temperature on the band reaches 40 ° C., dry with 70 ° C. warm air for 1 minute, peel off the film from the band, dry with 140 ° C. dry air for 10 minutes, and sandwich with a tenter clip. Then, lateral stretching was performed to prepare a cellulose acetate film (thickness: 40 μm) having a residual solvent amount of 0.3 mass%.
When the retardation values Re (550) and Rth (550) at a wavelength of 550 nm were measured for the produced cellulose acetate film using KOBRA 21ADH (manufactured by Oji Scientific Instruments), Re (550) = 80 nm, Rth ( 550) = 60 nm.

Moreover, the photoelastic coefficient of the produced cellulose acetate film was measured with an ellipsometer (M-150, manufactured by JASCO Corporation) in an environment of 25 ° C. and 60% RH. As a result, the photoelastic coefficient showed a positive photoelastic coefficient, and the value was 15 × 10 ⁻¹³ cm ² / dyn.

(Preparation of polymethyl methacrylate film (third optically anisotropic layer))
A polymethyl methacrylate (PMMA) resin was supplied to a T-die melt extruder to obtain a polymethyl methacrylate film having a thickness of 80 μm, Re (550) = 2 nm, and Rth (550) = 3 nm.

When the photoelastic coefficient of the produced polymethylmethacrylate film was measured, it showed a negative photoelastic coefficient and was −7 × 10 ⁻¹³ cm ² / dyn. Note that the measurement apparatus and measurement conditions are the same as those for the cellulose acetate film.

(Saponification treatment)
The produced cellulose acetate film was immersed in a 2.0 N potassium hydroxide solution (25 ° C.) for 2 minutes, neutralized with sulfuric acid, washed with pure water, and dried. The surface energy of this film was determined by a contact angle method and found to be 62 mN / m.

(Preparation of alignment film)
On this cellulose acetate film, a coating liquid (alignment film coating liquid) having the following composition was coated at 24 mL / m ² with a # 14 wire bar coater, and then the coating liquid on the cellulose acetate film was heated with 100 ° C. hot air. It was dried for 120 seconds to form a film. Next, the longitudinal direction of the cellulose acetate film was set to 0 degree, and the formed film was rubbed in the 0 degree direction to produce an alignment film.

(Orientation film coating solution composition)
――――――――――――――――――――――――――――――――――――――――
-40 parts by weight of modified polyvinyl alcohol having the following structural formula-728 parts by weight of water-228 parts by weight of methanol-2 parts by weight of glutaraldehyde (crosslinking agent)-0.69 parts by weight of citric acid ester (AS3, Sankyo Chemical Co., Ltd.) ―――――――――――――――――――――――――――――――――――――――

(Preparation of liquid crystalline compound layer (first optically anisotropic layer))
On the alignment film, a coating solution (liquid crystal compound layer coating solution) having the following composition is conveyed at 28 m / min by rotating a # 3.0 wire bar at 1093 rpm in the same direction as the film conveying direction. The film was continuously applied to the alignment film surface of the film. Next, in the step of continuously heating from room temperature to 100 ° C., the solvent was dried, and then heated in a drying zone at 125 ° C. for about 120 seconds to align the liquid crystalline compound. Next, it is transported to a drying zone at 95 ° C., and irradiated with ultraviolet rays having an illuminance of 600 mW for 4 seconds by an ultraviolet irradiation device (ultraviolet lamp: output 160 W / cm, emission length 1.6 m) to advance the cross-linking reaction, thereby liquid crystal The active compound was fixed in the orientation. Thereafter, the film was allowed to cool to room temperature, wound into a cylindrical shape, and a roll-shaped film including a cellulose acetate film (second optical anisotropic layer) and a liquid crystal compound layer (first optical anisotropic layer) was obtained. .

(Liquid crystal compound layer coating solution composition)
―――――――――――――――――――――――――――――――――――――――
-41.01 parts by mass of a discotic liquid crystalline compound having the following structural formula-ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) 4.06 parts by mass-Cellulose acetate butyrate (CAB531- 1. Eastman Chemical Co., Ltd.) 0.35 parts by mass Photopolymerization initiator (Irgacure 907, Ciba Geigy Co.) 1.35 parts by mass Sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) 0. 45 parts by mass ・ Fluoroaliphatic group-containing copolymer (Megafac F780 manufactured by Dainippon Ink Co., Ltd.) 0.10 parts by mass ・ Methyl ethyl ketone 102.00 parts by mass ―――――――――――――― ―――――――――――――――――――――――――

(Production of optical film)
The cellulose acetate film side of the film formed by forming a liquid crystalline compound layer on the cellulose acetate film and the polymethyl methacrylate film are laminated via an adhesive SK-1478 (manufactured by Soken Chemical Co., Ltd.), and the liquid crystalline compound An optical film in which a layer, a cellulose acetate film, and a polymethyl methacrylate film were laminated in this order was produced.

The photoelastic coefficient was measured about the obtained optical film. As a result, the optical film exhibited a positive photoelastic coefficient and was 2 × 10 ⁻¹³ cm ² / dyn. Note that the measurement apparatus and measurement conditions are the same as those for the cellulose acetate film.

(Preparation of polarizing plate)
A polyvinyl alcohol (PVA) film having a thickness of 80 μm is dyed by immersing it in an aqueous iodine solution having an iodine concentration of 0.05% by mass at 30 ° C. for 60 seconds, and then in an aqueous boric acid solution having a boric acid concentration of 4% by mass. The film was vertically stretched to 5 times the original length while being immersed for 2 seconds, and then dried at 50 ° C. for 4 minutes to obtain a polarizing film having a thickness of 20 μm.
A commercially available cellulose acetate film was immersed in an aqueous sodium hydroxide solution at 55 ° C. at 1.5 mol / L, and then the sodium hydroxide was sufficiently washed away with water. Then, after being immersed in a diluted sulfuric acid aqueous solution at 35 ° C. for 1 minute at 0.005 mol / L, the diluted sulfuric acid aqueous solution was sufficiently washed away by immersion in water. Finally, the cellulose acetate film was sufficiently dried at 120 ° C. to obtain a protective film.

The polarizing film is obtained by bonding the optical film produced as described above and a protective film made of a commercially available cellulose acetate film subjected to saponification treatment using a polyvinyl alcohol adhesive so as to sandwich the polarizing film. It was. Here, the liquid crystalline compound layer of the optical film was disposed so as to be on the outside. As a commercially available cellulose acetate film, Fujitac TF80UL (manufactured by FUJIFILM Corporation) was used.
At this time, since the polarizing film, the protective film outside the polarizing film, and the optical film are produced in a roll form, the longitudinal directions of the roll films are parallel to each other and are continuously bonded. Therefore, the roll longitudinal direction of the optical film (the casting direction of the cellulose acetate film) and the polarizer absorption axis were parallel to each other.

(Production of TN mode liquid crystal display device)
A liquid crystal display device (LC-26HU25, manufactured by Xoseco) using a 26-inch TN liquid crystal cell was prepared, and a pair of polarizing plates provided in the liquid crystal display device was peeled off. In place of the peeled polarizing plate, the above-prepared polarizing plate is attached to the viewer side and the backlight side one by one through an adhesive so that the optical film is on the liquid crystal cell side, and the example 1 A liquid crystal display device was obtained. At this time, the transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side were set to be orthogonal to each other.

FIG. 1 is an explanatory diagram showing an outline of the liquid crystal display device. Reference numeral 3 in FIG. 1 represents a liquid crystal display device, reference numeral 1 represents an optical film, and reference numeral 2 represents a polarizing plate.
Reference numeral 10 represents a first optically anisotropic layer, reference numeral 20 represents a second optically anisotropic layer, reference numeral 30 represents a third optically anisotropic layer, and reference numeral 40 represents a polarizer (polarized light). The reference numeral 50 represents a protective film. In FIG. 1, only one polarizing plate is shown for convenience of explanation.

(Luminance evaluation)
About the produced liquid crystal display device, the center of each side of the upper, lower, left and right sides of the rectangular liquid crystal display portion is within 1 cm from the end within 5 minutes after the power is turned on after being left for 2 hours or more with the power off. The luminance at the close position was measured using a luminance meter (Topcon BM-5). The average value of the luminance at the four measured positions was obtained. As a result, the luminance (average value) was 0.5 cd / cm ² . The temperature (average value) measured at the same position was 26 ° C.
Furthermore, the same measurement was performed when 1 hour passed after lighting. As a result, the luminance (average value) was 0.7 cd / cm ² . Moreover, the temperature of the said position when 1 hour passed after lighting was 49 degreeC. Thereby, the luminance change due to the temperature change was 0.2 cd / cm ² .

In addition, the manufactured liquid crystal display device under 25 ° C. and 60% RH conditions (reference conditions) is allowed to stand for 24 hours at 25 ° C. and 10% RH with the power off, and the same measurement is performed immediately after lighting. went. As a result, the luminance (average) was 0.7 cd / cm ² . Thereby, the luminance change due to the humidity change was 0.2 cd / cm ² . The results are shown in Table 1.

[Example 2]
In the same manner as in Example 1, the polymethyl methacrylate film (third optically anisotropic layer) produced in Example 1 was saponified, and then an alignment film was formed and rubbed, so that a liquid crystal was formed on the polymethyl methacrylate film. An organic compound layer (first optically anisotropic layer) was formed.

(Production of optical film)
The cellulose acetate film (second optically anisotropic layer) produced in Example 1 was laminated on the polymethyl methacrylate film side of the polymethyl methacrylate film on which the liquid crystal compound layer was formed via the adhesive SK-1478. Thus, an optical film in the order of a liquid crystalline compound layer, a polymethyl methacrylate film, and a cellulose acetate film was obtained.

  A polarizing plate and a liquid crystal display device were produced in the same manner as in Example 1. Further, the luminance of the liquid crystal display device was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
An optical film was produced in the same manner as in Example 1 except that “Z-TAC” (a low retardation cellulose acetate film manufactured by FUJIFILM Corporation) was laminated instead of the polymethyl methacrylate film of Example 1. did.
When Z-TAC was measured with KOBRA 21ADH, Re (550) = 1 nm and Rth (550) = 1 nm. Moreover, when measured with an ellipsometer, the photoelastic coefficient under conditions of 25 ° C. and 60% RH was 16 × 10 ⁻¹³ cm ² / dyn.

In the same manner as in Example 1, a polarizing plate and a liquid crystal display device were produced. Further, the luminance of the liquid crystal display device was evaluated in the same manner as in Example 1. The results are shown in Table 2.
In Table 3, “first layer” represents one of the two types of cellulose acylate films close to the first optically anisotropic layer, and “second layer” represents the other film. To express.

[Comparative Example 2]
In order to obtain optical properties equivalent to those of the cellulose acetate film (second optically anisotropic layer) of Example 1 using the polymethyl methacrylate film produced in Example 1, the temperature and stretching conditions were examined. The results are shown in Table 3.
However, as can be seen from the fact that the photoelastic coefficient of the polymethylmethacrylate film is small, it is difficult to develop a phase difference, and the target optical characteristics cannot be obtained in the first place before the luminance evaluation.
In Table 3, “first layer” represents one of the two types of polymethyl methacrylate films close to the first optically anisotropic layer, and “second layer” represents the other film. To express.

FIG. 1 is an explanatory diagram showing an outline of a liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical film 2 Polarizing plate 3 Liquid crystal display device 10 1st optical anisotropic layer 20 2nd optical anisotropic layer 30 3rd optical anisotropic layer 40 Polarizer 50 Protective film

Claims (9)

A first optically anisotropic layer containing a liquid crystalline compound;
A second optically anisotropic layer comprising a thermoplastic resin having a positive photoelastic coefficient;
A third optically anisotropic layer comprising a thermoplastic resin having a negative photoelastic coefficient,
An in-plane retardation Re (550) at a wavelength of 550 nm of the third optically anisotropic layer is 10 nm or less. The optical film according to claim 1, wherein the photoelastic coefficient of the second optical anisotropic layer is 10 × 10 ⁻¹³ cm ² / dyn or more.   The optical film of Claim 1 or 2 laminated | stacked in order of the 1st optically anisotropic layer, the 2nd optically anisotropic layer, and the 3rd optically anisotropic layer.   The optical film according to claim 1, wherein the liquid crystalline compound of the first optical anisotropic layer contains a discotic liquid crystalline compound.   The optical film according to any one of claims 1 to 4, wherein the thermoplastic resin having a positive photoelastic coefficient of the second optically anisotropic layer is a cellulose acylate film.   A polarizing plate comprising at least the optical film according to claim 1 and a polarizing film.   A liquid crystal display device having at least a liquid crystal cell and the polarizing plate according to claim 6.   The liquid crystal display device according to claim 7, wherein the liquid crystal cell has a size of 26 inches or more. The liquid crystal display device according to claim 7 or 8, wherein the liquid crystal cell is a TN system.