JP4931837B2 - Optical compensation film and liquid crystal display device - Google Patents

Description

  The present invention relates to a novel optical compensation film that contributes to an improvement in viewing angle characteristics of a liquid crystal display device, particularly a vertical alignment (VA) mode liquid crystal display device, and a liquid crystal display device having the optical compensation film.

The VA mode liquid crystal display device is characterized by high contrast and fast response speed. In addition, it is known that the multi-domain structure can reduce the viewing angle dependence of the contrast of white display / black display. On the other hand, halftone display other than black display has a problem that the display state has a viewing angle dependency, and a solution is desired.
For example, in Patent Document 1, a layer having negative birefringence is inclined and laminated to form a laminated group, and two such laminated groups are laminated so that the directions of inclination are opposite to each other. A viewing angle compensation film characterized in that the viewing angle compensation film contributes to the improvement of the viewing angle characteristics of the VA mode liquid crystal display device is described.
Patent Document 2 further includes at least a pair of first and second optical films each including a group of refractive index ellipsoids made of a disk-shaped polymer, and the refractive index ellipsoid in the first optical film is thick. The refractive index ellipsoid in the second optical film is in a state where it is gradually inclined with respect to a plane perpendicular to the vertical direction, and the refractive index ellipsoid in the second optical film is an index ellipsoid in the first optical film. An optical phase difference plate is proposed, characterized in that it is in a state where it is gradually inclined so as to be anti-parallel to the inclination direction and is in a hybrid arrangement in the thickness direction. It is described that it contributes to improving the viewing angle-luminance characteristics.
JP 2002-182036 A JP 2005-62724 A

However, as a result of examination by the present inventor, when the viewing angle compensation film proposed in Patent Documents 1 and 2 is used, light leakage occurs in an oblique direction depending on the orientation during black display, and the contrast is lowered. It has been found.
Therefore, the present invention contributes to improving the viewing angle characteristics of a halftone display of a liquid crystal display device, particularly a VA mode liquid crystal display device, and to reducing light leakage during black display in an oblique direction in all directions. It is an object of the present invention to provide an optical compensation film.
It is another object of the present invention to provide a liquid crystal display device, particularly a VA mode liquid crystal display device, in which the viewing angle characteristics of halftone display are improved and high contrast can be achieved in oblique directions in all directions.

Means for solving the above problems are as follows.
[1] An optical compensation film having at least a first and a second optically anisotropic layer, wherein the normal line extends from the normal line to the film surface direction within a plane including the in-plane fast axis and the normal line of the film surface. Of the in-plane retardation Re (+ 40 °) measured from the direction of 40 ° clockwise and Re (−40 °) measured from the direction of 40 ° counterclockwise from the normal, the larger one is ReL and small. When the direction is ReS, the optical compensation film satisfies the following formula (I):
(I) 14 ≦ ReL / ReS ≦ 27.
[2] The optical compensation film according to [1], wherein the in-plane retardation Re (550) at a wavelength of 550 nm of each of the first and second optically anisotropic layers is 20 to 30 nm.
[3] Each of the first and second optically anisotropic layers is an optically anisotropic layer containing molecules of a liquid crystal compound fixed in an alignment state that is parallel to each other and controlled by an opposite alignment treatment direction. The optical compensation film according to [1] or [2], wherein
[4] The first and second optically anisotropic layers each contain molecules of a discotic liquid crystal compound that are fixed in a hybrid alignment state that is parallel to each other and controlled by opposite alignment processing directions. The optical compensation film according to [3].
[5] It further has a polymer film having an in-plane retardation Re (550) at a wavelength of 550 nm of 0 to 3 nm and a thickness direction retardation Rth (550) at the same wavelength of 0 to 40 nm. The optical compensation film according to any one of 1] to [4].
[6] A liquid crystal display device having a pair of polarizers arranged so that their polarization axes are orthogonal to each other, and a liquid crystal cell in a vertical alignment mode between the pair of polarizers, the liquid crystal cell and the pair A liquid crystal display device comprising the optical compensation film of any one of [1] to [5] between each of the polarizers.
[7] The liquid crystal display device according to [6], wherein the vertical alignment mode liquid crystal cell is a liquid crystal cell having a multi-domain structure.

According to the present invention, it contributes to improving the viewing angle characteristics of a halftone display of a liquid crystal display device, particularly a VA mode liquid crystal display device, and to reducing light leakage during black display in an oblique direction of all directions. An optical compensation film can be provided.
In addition, according to the present invention, it is possible to provide a liquid crystal display device, particularly a VA mode liquid crystal display device, in which the viewing angle characteristics of halftone display are improved and high contrast can be achieved in oblique directions in all directions.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail. In the present specification, “to” indicates a range including the numerical values described before and after the minimum and maximum values, respectively.
(Retardation, Re, Rth)
In the present specification, Re (λ) and Rth (λ) represent in-plane retardation (nm) and retardation in the thickness direction (nm) at wavelength λ, respectively. Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments).
When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis) (if there is no slow axis, any in-plane film The light is incident at a wavelength of λ nm from the inclined direction in steps of 10 degrees from the normal direction to 50 degrees on one side with respect to the film normal direction of the rotation axis of 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 case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.
In addition, the retardation value is measured from the two inclined directions, with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), Based on the value, the assumed value of the average refractive index, and the input film thickness value, Rth can also be calculated from the following equations (10) and (11).

注記：
上記のＲｅ（θ）は法線方向から角度θ傾斜した方向におけるレターデーション値をあらわす。また、式中、ｎｘは面内における遅相軸方向の屈折率を表し、ｎｙは面内においてｎｘに直交する方向の屈折率を表し、ｎｚはｎｘ及びｎｙに直交する方向の屈折率を表す。ｄは膜厚を表す。

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

When the film to be measured is a film that cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film without a so-called optical axis, Rth (λ) is calculated by the following method.
Rth (λ) is from −50 degrees to +50 degrees with respect to the normal direction of the film, with Re (λ) being the in-plane slow axis (determined by KOBRA 21ADH or WR) and the tilt axis (rotating axis). In each of the 10 degree steps, light of wavelength λ nm is incident from the inclined direction and measured at 11 points. Based on the measured retardation value, the assumed average refractive index, and the input film thickness value, KOBRA 21ADH or WR is calculated.
In the above measurement, the assumed value of the average refractive index may be a value in a polymer handbook (John Wiley & Sons, Inc.) or a catalog of various optical films. Those whose average refractive index is not known can be measured with an Abbe refractometer. Examples of the average refractive index values of main optical films are given below:
Cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), and polystyrene (1.59).
By inputting the assumed value of the average refractive index and the film thickness, KOBRA 210 ADH or WR calculates nx, ny, and nz. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.
In this specification, the measurement wavelength such as retardation is a value at λ = 550 nm in the visible light region unless otherwise specified. The “in-plane slow axis” is the direction in which the refractive index is maximized in the plane, and the “in-plane fast axis” is the direction orthogonal to the in-plane slow axis in the plane.

The present invention relates to an optical compensation film having first and second optically anisotropic layers. FIG. 1 is a schematic diagram for explaining the properties of the optical compensation film of the present invention. The optical compensation film 10 of the present invention has an in-plane slow axis s where the first and second in-plane refractive indices are maximum, and an in-plane fast axis F where the in-plane refractive index is minimum, In-plane retardation Re (+ 40 °) measured from a direction D + of 40 ° clockwise from the normal F in the plane of the film P in the plane P including the in-plane fast axis F and the normal N of the film surface Of Re (−40 °) measured from a direction D− of 40 ° counterclockwise from the normal line, the following formula (I) is satisfied when the larger one is ReL and the smaller one is ReS: Features.
(I) 14 ≦ ReL / ReS ≦ 27

  In the optical compensation film having the first and second optically anisotropic layers disclosed in Patent Documents 1 and 2, etc., the slow axes of the first and second optically anisotropic layers are matched with each other. When the layers are stacked, the first and second optical anisotropic directions can be obtained even if the viewing angle is rotated by a predetermined angle from the normal direction to either the clockwise direction or the counterclockwise direction (for example, a polar angle of 60 °). Since the phase-advancing directions of the conductive layers coincide with each other, light leakage does not occur in the black state where the polarization axes of the polarizing plates are orthogonal. On the other hand, in a direction different from the in-plane slow axis (for example, the fast axis direction orthogonal to the in-plane slow axis), the viewing angle is set to a predetermined angle, either clockwise or counterclockwise from the normal direction. When rotated (for example, at a polar angle of 60 °), the first and second optically anisotropic layers act as different polarizing media, and therefore light even in the black state where the polarizing axes of the polarizing plates are orthogonal to each other. Leakage occurs and an ideal black state cannot be obtained. As a result of intensive studies by the inventor, by satisfying the above formula (I), the two optically anisotropic layers cancel each other's polarization characteristics, and there is no light leakage in the oblique direction of any direction. We have found that an ideal black state can be achieved. As a result, by using the optical compensation film of the present invention for a liquid crystal display device, the viewing angle characteristics of halftone display can be improved by combining the first and second optically anisotropic layers, and at the time of black display. Light leakage does not occur in any orientation, and high contrast can be achieved in oblique directions in all orientations.

  In an aspect used for optical compensation of the VA mode liquid crystal display device, Re (550) of the first and second optical anisotropic layers is preferably 20 to 30 nm. It is preferable that Re (550) of the first and second optically anisotropic layers is in the above range because the viewing angle characteristics of halftone display of the VA mode liquid crystal display device can be further improved.

  FIG. 2 shows a schematic cross-sectional view of an example of the optical compensation film of the present invention. The optical compensation film 10 includes molecules of a liquid crystal compound fixed in alignment states controlled by alignment processing directions a and b which are parallel to each other and in a reverse relationship (hereinafter referred to as “anti-parallel”). It has the 1st optically anisotropic layer 12a and the 2nd optically anisotropic layer 12b which contain. The alignment treatment directions a and b are, for example, rubbing treatment directions applied to the surface of the alignment film used for producing each optically anisotropic layer. In the embodiment used for optical compensation of the VA mode liquid crystal display device, the optically anisotropic layers 12a and 12b are made of discotic liquid crystal compounds fixed in alignment states controlled by alignment processing directions a and b, which are antiparallel to each other. It preferably contains molecules. Furthermore, it is preferable that the discotic liquid crystal molecules are fixed in a hybrid alignment state in each optically anisotropic layer. In an optically anisotropic layer containing discotic liquid crystal molecules fixed in a hybrid alignment state in which alignment is controlled by a predetermined alignment processing direction (for example, rubbing processing direction), in general, the alignment processing direction is The in-plane average refractive index is in the maximum direction. Therefore, the first and second optically anisotropic layers 12a and 12b containing the discotic liquid crystal molecules fixed in the hybrid alignment state have the in-plane refractive index maximized in the directions of the alignment treatment directions a and b, respectively. The optical compensation film 10 has an in-plane slow axis s in that direction. On the other hand, since the orientation processing directions a and b are opposite, the tilt orientations of the hybrid array are not the same, and the orientation is determined by the orientation processing directions a and b and is antiparallel. Therefore, the first and second optically anisotropic layers 12a and 12b act as different polarizing media for obliquely incident light in directions other than the in-plane slow axis s. Since the above formula (I) is satisfied, the polarization characteristics of each other can be canceled. As a result, light leakage can be reduced at the time of black display with respect to obliquely incident light in any direction. it can.

  In the optical compensation film of FIG. 2, the first and second optically anisotropic layers 12a and 12b show the optical characteristics achieved by the alignment of liquid crystal molecules, and Re (550) is adjusted to 20 to 30 nm. Is preferred.

  In FIG. 3, the cross-sectional schematic diagram of the other example of the optical compensation film of this invention is shown. The same members as those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. The optical compensation film 10 ′ shown in FIG. 3 further includes a support 14 that supports the first and second optical anisotropic layers 12 a and 12 b. The support 14 is preferably a polymer film. When the polymer film has an in-plane slow axis c, the in-plane slow axis c should be parallel to the alignment treatment directions a and b of the first and second optical anisotropic layers 12a and 12b. Preferably, as a result, the optical compensation film 10 'has an in-plane slow axis s parallel to the alignment processing directions a and b. It is preferable that the support 14 does not impair the optical characteristics of the first and second optical anisotropic layers 12a and 12b. From this viewpoint, Re (550) of the support 14 is preferably approximately 0 nm, and the tolerance is 3 nm. On the other hand, Rth (550) is preferably 0 to 40 nm.

  In FIG. 3, the support 14 is shown adjacent to the second optical anisotropic layer 12b. Of course, the support may be adjacent to the first optical anisotropic layer 12a. .

  When the support 14 is a polymer film, it can also be used as a protective film for a polarizing film. Therefore, when the support 14 is incorporated in a liquid crystal display device, the optical compensation film 10 ′ and the polarizing film can be incorporated in an integrated state. it can. In the embodiment in which the first and second optically anisotropic layers 12a and 12b are non-self-supporting films formed by coating or transfer, the first and second optically anisotropic layers 12a and 12b are supported by a support 14 made of a polymer film. Thus, a member having self-supporting property is obtained, and the handling property is improved, which is preferable.

  FIG. 4 shows a schematic cross-sectional view of an example of a VA mode liquid crystal display device provided with the optical compensation film 10 ′ shown in FIG. The liquid crystal display device shown in FIG. 3 includes polarizing plates PL1 and PL2 and a VA mode liquid crystal cell LC therebetween. Each of the polarizing plates PL1 and PL2 includes a polarizer 16, a protective film 18 on the outer surface thereof, and an optical compensation film 10 'on the liquid crystal cell side surface thereof. In the drawing, the layer structure of the optical compensation film 10 ′ is omitted, but the optical compensation film 10 ′ has the first optical anisotropic layer 12a on the liquid crystal cell LC side and a support 14 made of a polymer film. It is bonded to the polarizer 16 side. The polarizers 16 are arranged with their absorption axes c orthogonal to each other, and the optical compensation films 10 ′ are arranged with their slow axes s orthogonal to the absorption axis c of the adjacent polarizer 16. That is, the optical compensation film 10 ′ is arranged with the slow axes s orthogonal to each other. The surface-side protective film 18 of the polarizer 16 is made of a low moisture-permeable polymer film and has a function of protecting the polarizer 16 from the external environment.

  In the VA mode liquid crystal cell LC, liquid crystal molecules are almost perpendicular to the substrate (not shown) when there is no electric field. can do. Furthermore, it is preferable to use a liquid crystal cell LC having a multi-domain structure because the viewing angle dependence of the contrast of white display / black display can be reduced. The multi-domain structure can be manufactured by a protrusion disposed on the inner surface of the substrate or an electric field gradient. The liquid crystal display device of FIG. 3 has the optical compensation film of the present invention (the optical compensation film 10 ′ in FIG. 4), so that the viewing angle dependency in halftone display is improved and the omnidirectional oblique direction. High contrast can be achieved.

Hereinafter, various materials and production methods that can be used for producing the optical compensation film of the present invention will be described.
[First and second optically anisotropic layers]
The optical compensation film of the present invention has first and second optically anisotropic layers. The first and second optically anisotropic layers are preferably formed from a liquid crystal composition containing a liquid crystal compound.
The optically anisotropic layer may be formed directly on the surface of the support, or may be formed on the alignment film by forming an alignment film on the support. Moreover, it is also possible to produce the optical compensation film of the present invention by transferring a liquid crystal compound layer formed on another substrate onto a support using an adhesive or the like.
Examples of the liquid crystal compound used for forming the optically anisotropic layer include a rod-like liquid crystal compound and a discotic liquid crystal compound. The rod-like liquid crystal compound and the discotic liquid crystal compound may be a polymer liquid crystal or a low molecular liquid crystal, and further include those in which the low molecular liquid crystal is cross-linked and no longer exhibits liquid crystallinity. Of these, discotic liquid crystal compounds are preferred.

[Bar-shaped liquid crystal compound]
Examples of the rod-shaped liquid crystal compound that can be used in the present invention 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. A liquid crystal polymer containing a rod-like liquid crystal compound in a repeating unit can also be used. In other words, the rod-like liquid crystal compound may be bonded to a (liquid crystal) polymer. For rod-shaped liquid crystal compounds, Chapters 4, 7, and 11 of the Quarterly Review of Chemical Review Vol. 22, “Chemicals of Liquid Crystal (1994), Chemical Society of Japan”, and the 142nd Committee of the Japan Society for the Promotion of Science It is described in Chapter 3 of the volume.

  The birefringence of the rod-like liquid crystal compound used in the present invention is preferably in the range of 0.001 to 0.7. The rod-like liquid crystal compound preferably has a polymerizable group in order to fix its alignment state. The polymerizable group is preferably an unsaturated polymerizable group or an epoxy group, more preferably an unsaturated polymerizable group, and particularly preferably an ethylenically unsaturated polymerizable group.

[Discotic liquid crystal compound]
Examples of discotic liquid crystal compounds include C.I. Destrade et al., Mol. Cryst. 71, 111 (1981), benzene derivatives described in C.I. Destrade et al., Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 (1990); Kohne et al., Angew. Chem. 96, page 70 (1984) and the cyclohexane derivatives described in J. Am. M.M. Lehn et al. Chem. Commun. , 1794 (1985), J. Am. Zhang et al., J. Am. Chem. Soc. 116, 2655 (1994), azacrown type and phenylacetylene type macrocycles are included. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystal compound is preferably 70 to 300 ° C, more preferably 70 to 170 ° C.

  The discotic liquid crystal compound exhibits liquid crystallinity with a structure in which a linear alkyl group, an alkoxy group, or a substituted benzoyloxy group is radially substituted as a side chain of the mother nucleus with respect to the mother nucleus at the center of the molecule. Also included are compounds. The molecule or the assembly of molecules is preferably a compound having rotational symmetry and imparting a certain orientation. When an optically anisotropic layer is formed from a discotic liquid crystal compound, the compound finally contained in the optically anisotropic layer no longer needs to exhibit liquid crystallinity. For example, a low-molecular discotic liquid crystal compound has a group that reacts with heat or light, and the group reacts with heat or light to polymerize or crosslink to increase the molecular weight. When a layer is formed, the compound contained in the optically anisotropic layer may no longer have liquid crystallinity. Preferred examples of the discotic liquid crystal compound are described in JP-A-8-50206. The polymerization of discotic liquid crystal compounds is described in JP-A-8-27284.

  In order to fix the discotic liquid crystal compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystal 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 crystal compound having a polymerizable group is preferably a compound represented by the following general formula (I).

  In the above general formula (I), 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.

  As examples of the disk-shaped core (D), (D1) to (D15) are 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 (I), the divalent linking group (L) is composed of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. A divalent linking group selected from the group is preferred. The divalent linking group (L) is a combination of at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, —CO—, —NH—, —O—, and —S—. More preferably, it is a valent linking group. The divalent linking group (L) is particularly preferably a divalent linking group in which at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO- and -O- are combined. . 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.

As examples of the divalent linking group (L), (L1 to L24) 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, 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-AR-O-AL-CO-
L17: -O-CO-AR-O-AL-O-CO-
L18: -O-CO-AR-O-AL-O-AL-O-CO-
L19: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-
L20: -S-AL-
L21: -S-AL-O-
L22: -S-AL-O-CO-
L23: -S-AL-S-AL-
L24: -S-AR-AL-

  The polymerizable group (Q) of the general formula (I) is determined according to the type of polymerization reaction. The polymerizable group (Q) is preferably an unsaturated polymerizable group or an epoxy group, more preferably an unsaturated polymerizable group, and particularly preferably an ethylenically unsaturated polymerizable group. Moreover, in the said general formula (I), n is an integer of 4-12. A specific number 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.

  Regarding the orientation of the liquid crystal compound in the optically anisotropic layer, the average direction of the molecular symmetry axis of the optically anisotropic layer is preferably 43 ° to 47 ° with respect to the longitudinal direction. In the aspect used for optical compensation of the VA mode liquid crystal display device, it is preferable that Re (550) is adjusted to 20 to 30 nm in each of the first and second optical anisotropic layers. Such optical properties can be achieved by an optically anisotropic layer containing discotic liquid crystal molecules fixed in a hybrid alignment state. In the hybrid arrangement, the angle between the molecular symmetry axis of the liquid crystal compound and the surface of the support increases or decreases in the depth direction of the optically anisotropic layer and with an increase in the distance from the surface of the support. The angle preferably increases with increasing distance. Further, the change in angle can be continuous increase, continuous decrease, intermittent increase, intermittent decrease, change including continuous increase and continuous decrease, or intermittent change including increase and decrease. The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. Even if the angle includes a region where the angle does not change, the angle only needs to increase or decrease as a whole. Furthermore, it is preferred that the angle changes continuously. In one example of the present invention, the molecules of the discotic liquid crystal compound in the first and second optically anisotropic layers are fixed in a hybrid alignment state determined by the alignment treatment direction. When the alignment treatment directions of the first and second optically anisotropic layers are antiparallel, the tilt directions are also antiparallel.

The average direction of the molecular symmetry axis of the liquid crystal compound can be generally adjusted by selecting a material for the liquid crystal compound or the alignment film or by selecting a rubbing treatment method. Moreover, the molecular symmetry axis direction of the liquid crystal compound on the surface side (air side) can be generally adjusted by selecting the type of the liquid crystal compound or the additive used together with the liquid crystal compound.
Examples of the additive used together with the liquid crystal compound include a plasticizer, a surfactant, a polymerizable monomer and a polymer. Similar to the above, the degree of change in the orientation direction of the molecular symmetry axis can be adjusted by selecting the liquid crystal compound and the additive. In particular, regarding the surfactant, it is preferable that the surface tension control of the coating solution is compatible.

The plasticizer, surfactant, and polymerizable monomer used together with the liquid crystal compound are preferably compatible with the discotic liquid crystal compound and can change the tilt angle of the liquid crystal compound or do not inhibit the alignment. As the polymerizable monomer, a compound having a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group is preferable.
Moreover, the addition amount of the said compound exists in the range of 1-50 mass% generally with respect to a liquid crystal compound, and it is preferable to exist in the range of 5-30 mass%. In addition, when a monomer having 4 or more polymerizable reactive functional groups is mixed and used, adhesion between the alignment film and the optically anisotropic layer can be improved.

  When a discotic liquid crystal compound is used as the liquid crystal compound, it is preferable to use a polymer that has a certain degree of compatibility with the discotic liquid crystal compound and can change the tilt angle of the discotic liquid crystal compound. A cellulose ester can be mentioned as an example of a polymer. Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropylcellulose, and cellulose acetate butyrate. The addition amount of the polymer is preferably in the range of 0.1 to 10% by mass, and in the range of 0.1 to 8% by mass with respect to the discotic liquid crystal compound so as not to inhibit the orientation of the discotic liquid crystal compound. It is more preferable that it is in the range of 0.1 to 5% by mass.

  In the present invention, the thickness of the first and second optically anisotropic layers is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and 1 to 10 μm. Particularly preferred.

<< Support >>
The optical compensation film of the present invention may have a support that supports the first and second optical anisotropic layers. The support is preferably transparent, and specifically, a transparent polymer film having a light transmittance of 80% or more is preferable. Examples of the polymer film that can be used as a support include polymer films made of cellulose ester (eg, cellulose acetate, cellulose diacetate), norbornene-based polymer, polymethyl methacrylate, and the like. Commercially available polymers (Arton (registered trademark) and Zeonex (registered trademark) may be used for norbornene-based polymers. Among them, a film composed of cellulose ester is preferable, and a film composed of a lower fatty acid ester of cellulose is more preferable. The lower fatty acid means a fatty acid having 6 or less carbon atoms, particularly preferably 2 (cellulose acetate), 3 (cellulose propionate) or 4 (cellulose butyrate), among these. Films made of cellulose acetate are particularly preferred, and mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate can also be used.

  Even in the case of a conventionally known polymer such as polycarbonate or polysulfone that easily develops birefringence, the birefringence can be expressed by modifying the molecule as described in the pamphlet of International Publication WO00 / 26705. If controlled, it can also be used as a support in the present invention.

  When using the optical compensation film of this invention as a protective film of a polarizing plate, it is preferable to use the cellulose acetate whose acetylation degree is 55.0-62.5% as a polymer film. The acetylation degree is more preferably 57.0 to 62.0%. Here, the degree of acetylation means the amount of bound acetic acid per unit mass of cellulose. The degree of acetylation is determined by measurement and calculation of the degree of acetylation in ASTM: D-817-91 (testing method for cellulose acetate, etc.). The viscosity average degree of polymerization (DP) of cellulose acetate is preferably 250 or more, and more preferably 290 or more. Cellulose acetate preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a mass average molecular weight, Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably 1.0 to 40, more preferably 1.0 to 1.65, and particularly preferably 1.0 to 1.6.

  In cellulose acetate, the hydroxyl groups at the 2-position, 3-position and 6-position of cellulose are not evenly substituted but the degree of substitution at the 6-position tends to be small. In the polymer film used as the support, it is preferable that the degree of substitution at the 6-position of cellulose is the same or greater than that at the 2- and 3-positions. The ratio of the substitution degree at the 6-position to the total substitution degree at the 2-position, the 3-position and the 6-position is preferably 30 to 40%, more preferably 31 to 40%, and more preferably 32 to 40%. It is particularly preferred. Further, the substitution degree at the 6-position is preferably 0.88 or more. The degree of substitution at each position can be measured by NMR. Cellulose acetate having a high 6-position substitution degree is described in Synthesis Example 1 described in Paragraph Nos. [0043] to “0044” of JP-A No. 11-5851, Synthetic Example 2 described in Paragraph Nos. [0048] to [0049], And by referring to the method of Synthesis Example 3 described in Paragraph Nos. [0051] to [0052].

  The Re (550) and Rth (550) of the support are preferably in a range that does not impair the optical properties of the first and second optically anisotropic layers. From this point of view, the Re (550) of the support is preferably about 0 nm, and the tolerance is 3 nm. On the other hand, Rth (550) is preferably 0 to 40 nm. However, the aspect in which the optical characteristics of the support are positively used for optical compensation is not limited to this range.

<< Alignment film >>
For the production of the first and second optically anisotropic layers, an alignment film is preferably used.
The alignment film is preferably a layer made of a crosslinked polymer. The polymer used for the alignment film may be either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent. The alignment film is formed by reacting a polymer having a functional group or a polymer having a functional group introduced therein with light, heat, pH change, or the like, or is a highly reactive compound. It can be formed by introducing a bonding group derived from a cross-linking agent between polymers using an agent and cross-linking the polymers.

  The alignment film composed of a crosslinked polymer can be usually formed by applying a coating solution containing the polymer or a mixture of a polymer and a crosslinking agent on a support, followed by heating. In the rubbing process described later, it is preferable to increase the degree of crosslinking in order to suppress the dust generation of the alignment film. A value (1- (Ma / Mb)) obtained by subtracting 1 from the ratio (Ma / Mb) of the amount (Ma) of the crosslinking agent remaining after crosslinking to the amount (Mb) of the crosslinking agent added to the coating solution. When Mb)) is defined as the degree of crosslinking, the degree of crosslinking is preferably from 50 to 100%, more preferably from 65 to 100%, particularly preferably from 75 to 100%.

  Examples of the polymer include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleimide copolymer, polyvinyl alcohol, and modified polyvinyl alcohol, poly (N-methylolacrylamide), styrene / vinyltoluene copolymer. Polymers such as coalescence, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, carboxymethyl cellulose, polyethylene, polypropylene and polycarbonate And compounds such as silane coupling agents. Examples of preferred polymers are water-soluble polymers such as poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol, and modified polyvinyl alcohol, and gelatin, polyvinyl alcohol, and modified polyvinyl alcohol are preferred. Mention may be made of bil alcohol and modified polyvinyl alcohol.

Among the above polymers, polyvinyl alcohol or modified polyvinyl alcohol is preferable. The polyvinyl alcohol has, for example, a saponification degree of 70 to 100%, generally a saponification degree of 80 to 100%, and more preferably a saponification degree of 85 to 95%. The degree of polymerization is preferably in the range of 100 to 3,000. Examples of the modified polyvinyl alcohol include those modified by copolymerization (for example, COONa, Si (OX) ₃ , N (CH ₃ ) ₃ .Cl, C ₉ H ₁₉ COO, SO ₃ , Na, C ₁₂ H ₂₅ Etc.), modified by chain transfer (for example, COONa, SH, C ₁₂ H ₂₅ etc. are introduced as modifying groups), modified by block polymerization (modified groups, for example, COOH, CONH ₂ , COOR, C ₆ H _5, etc. are introduced). The degree of polymerization is preferably in the range of 100 to 3,000. Among these, unmodified or modified polyvinyl alcohol having a saponification degree of 80 to 100% is preferable, and unmodified or alkylthio-modified polyvinyl alcohol having a saponification degree of 85 to 95% is more preferable.

As the modified polyvinyl alcohol used for the alignment film, a reaction product of a compound represented by the following general formula (2) and polyvinyl alcohol is preferable. In the following general formula (2), R ¹ represents an unsubstituted alkyl group, or an alkyl group substituted with an acrylolyl group, a methacryloyl group, or an epoxy group, and W represents a halogen atom, an alkyl group, or an alkoxy group. , X represents an atomic group necessary for forming an active ester, acid anhydride or acid halide, l represents 0 or 1, and n represents an integer of 0-4.

Moreover, as the modified polyvinyl alcohol used for the alignment film, a reaction product of a compound represented by the following general formula (3) and polyvinyl alcohol is also preferable. In the following general formula (3), X ¹ represents an atomic group necessary for forming an active ester, acid anhydride or acid halide, and m represents an integer of 2 to 24.

As the polyvinyl alcohol used for reacting with the compound represented by the general formula (2) and the general formula (3), the unmodified polyvinyl alcohol and the copolymer modified one, that is, by chain transfer. Examples thereof include modified products of polyvinyl alcohol such as modified products and modified products by block polymerization.
Preferred examples of the specific modified polyvinyl alcohol are described in detail in JP-A-8-338913. When using a hydrophilic polymer such as polyvinyl alcohol for the alignment film, it is preferable to control the moisture content from the viewpoint of the degree of hardening, and the controlled moisture content is 0.4 to 2.5%. Is preferable, and it is more preferable that it is 0.6 to 1.6%. The water content can be measured with a commercially available Karl Fischer moisture content measuring device.
The alignment film preferably has a thickness of 10 μm or less.

An example of the manufacturing method of the roll-shaped optical compensation film of this invention includes the following process.
Step (1): A step of rubbing the surface of the long support conveyed in the longitudinal direction or the surface of the alignment film formed on the support in the a direction with a rubbing roller.
Process (2): The process of apply | coating the coating liquid containing a liquid crystalline compound to the said rubbing process surface.
Step (3): Simultaneously or after drying the applied coating solution, the liquid crystal compound is aligned at a temperature equal to or higher than the liquid crystal transition temperature, and the alignment is fixed to form the first optical anisotropic layer. Manufacturing step.
Step (4): The surface of the first optical anisotropic layer or the surface of the alignment film formed on the first optical anisotropic layer is b direction (provided that the b direction is the a direction) by a rubbing roller. A step of rubbing in a parallel and opposite direction).
Process (5): The process of apply | coating the coating liquid containing a liquid crystalline compound to the said rubbing process surface.
Step (6): Simultaneously or after drying the applied coating solution, the liquid crystal compound is oriented at a temperature equal to or higher than the liquid crystal transition temperature, and the orientation is fixed to form the second optical anisotropic layer. Manufacturing step.
Step (7): A step of winding the long laminate on which the first and second optically anisotropic layers are formed.
By this method, a long optical compensation film can be continuously manufactured, and further, a polarizing plate can be continuously manufactured by laminating with a long polarizing film with a roll-to-roll. .

Furthermore, in the manufacturing method of the optical compensation film of the present invention, it is desirable to include any of the following requirements (a) to (d). Details of each of these steps are described in JP-A-9-73081.
(A) In the steps (2) and (5), a polymerizable liquid crystal compound having a crosslinkable functional group is used as the liquid crystal compound, and in the steps (3) and (6), the coating layer is continuously irradiated with light. The polymerizable liquid crystal compound is cured by polymerization and fixed in an aligned state.
(B) In the above steps (1) and (4), rubbing with a rubbing roller while removing the surface of the support or alignment film.
(C) Before the steps (2) and (5), the surface of the support or the alignment film subjected to the rubbing treatment, and the first optically anisotropic layer subjected to the rubbing treatment or the alignment film formed thereon. To remove dust.
(D) An inspection step of inspecting the first and second optical anisotropic layers formed by continuously measuring the optical properties before the step (7).

Here, the detail of the said process is demonstrated below.
[Steps (1) and (4)]
In the steps (1) and (4), a rubbing treatment is applied to the surface of the long support conveyed in the longitudinal direction or the surface of the alignment film formed on the support by a rubbing roller.

The diameter of the rubbing roller used in the steps (1) and (4) is preferably 100 to 500 mm, and more preferably 200 to 400 mm, from the viewpoints of handling suitability and fabric life. The width of the rubbing roller needs to be wider than the width of the film to be conveyed, and is preferably not less than the film width × ^2½ . Further, the number of rotations of the rubbing roller is preferably set low from the viewpoint of dust generation, and depending on the orientation of the liquid crystal compound, it is preferably 100 to 1,000 rpm, and more preferably 250 to 850 rpm. preferable.

In order to maintain the orientation of the liquid crystal compound even when the number of rotations of the rubbing roll is lowered, it is preferable to heat the support or the alignment film during rubbing. The heating temperature is the film surface temperature of the support or the alignment film, and is preferably (material Tg−50 ° C.) to (material Tg + 50 ° C.). In the case of using an alignment film made of polyvinyl alcohol, it is preferable to control the environmental humidity of rubbing, preferably 25 to 70% RH as a relative humidity at 25 ° C., and more preferably 30 to 60% RH. It is preferably 35 to 55% RH, and particularly preferably.

The conveyance speed of the support is preferably 10 to 100 m / min, and more preferably 15 to 80 m / min, from the viewpoints of productivity and liquid crystal orientation. The conveyance can be performed using various apparatuses conventionally used for film conveyance, and the conveyance method is not particularly limited.

The alignment film can be produced by applying a coating solution prepared by dissolving the above-described material such as polyvinyl alcohol in water and / or an organic solvent to the surface of the support and drying it. The alignment film can be prepared before the series of steps described above, and the alignment film may be continuously formed on the surface of the long support to be conveyed.

[Steps (2) and (5)]
In the steps (2) and (5), a coating liquid containing a liquid crystal compound is applied to the rubbing surface. As the solvent used for preparing the coating liquid for forming the optically anisotropic layer, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane, tetrachloroethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.

In order to produce an optically anisotropic layer with high uniformity, the surface tension of the coating solution is preferably 25 mN / m or less, and more preferably 22 mN / m or less. In order to realize this low surface tension, the coating liquid for forming the optically anisotropic layer is used in a surfactant or a fluorine compound, particularly a repeating unit corresponding to the monomer (i) below and the following (ii) It is preferable to contain a fluorine-based polymer such as a fluoroaliphatic group-containing copolymer containing a repeating unit corresponding to a monomer.
(I) Fluoroaliphatic group-containing monomer represented by the following general formula (4) (ii) Poly (oxyalkylene) acrylate and / or poly (oxyalkylene) methacrylate

In the general formula (4), R ¹ represents a hydrogen atom or a methyl group, X represents an oxygen atom, a sulfur atom, or —N (R ² ) —, m is an integer of 1 to 6, and n is , Represents an integer of 2 to 4. R ² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

The weight average molecular weight of the fluoropolymer added to the coating solution for forming an optically anisotropic layer is preferably 3,000 to 100,000, more preferably 6,000 to 80,000.
Furthermore, the addition amount of the fluorine-based polymer is preferably 0.005 to 8% by mass, more preferably 0.01 to 1% by mass with respect to the coating composition (coating component excluding the solvent) mainly composed of a liquid crystal compound. Preferably, 0.05 to 0.5% by mass is more preferable. When the addition amount of the fluorine-based polymer is less than 0.005% by mass, the effect is insufficient, and when it exceeds 8% by mass, the coating film cannot be sufficiently dried, or the performance as an optical compensation film ( For example, the retardation uniformity is adversely affected.

Application | coating to the rubbing process surface of the said coating liquid can be implemented by a well-known method (For example, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method). The coating amount can be appropriately determined based on the desired thickness of the optically anisotropic layer.

[Steps (3) and (6)]
In the above steps (3) and (6), the liquid crystal compound is aligned at a temperature equal to or higher than the liquid crystal transition temperature at the same time as or after drying the applied coating solution, and the alignment is fixed to obtain an optical difference. An isotropic layer is produced. The liquid crystal compound has a desired orientation by heating during drying or by heating after drying. The drying temperature can be determined in consideration of the boiling point of the solvent used in the coating solution and the materials of the support and the alignment film. The alignment temperature of the liquid crystal compound can be determined according to the liquid crystal phase-solid phase transition temperature of the liquid crystal compound used.
When a discotic liquid crystal compound is used as the liquid crystal compound, the alignment temperature is preferably 70 to 300 ° C, and more preferably 70 to 170 ° C.
Further, the viscosity in the liquid crystal state is preferably 10 to 10,000 cp, and more preferably 100 to 1,000 cp.
If the viscosity is too low, it is easily affected by wind during orientation, and very accurate wind speed / wind direction control is required for continuous production. On the other hand, if the viscosity is high, it is difficult to be affected by the wind, but the alignment of the liquid crystal becomes slow and the productivity is very deteriorated.
The viscosity of the liquid crystal layer can be appropriately controlled by the molecular structure of the liquid crystal compound. Moreover, the method of adjusting to a desired viscosity by using an appropriate amount of the above-mentioned additive (especially cellulose polymer etc.), a gelling agent, etc. is used preferably.
Heating can be carried out by blowing hot air at a predetermined temperature or by conveying in a heating chamber maintained at a predetermined temperature.
As for the warm air at this time, as shown in the following formula (3), it is preferable that the wind speed other than the rubbing direction hitting the liquid crystal compound layer is controlled. In the following formula (3), V is the film surface wind speed (m / sec) on the surface of the liquid crystal compound, and η is the viscosity (cp) of the liquid crystal compound layer at the alignment temperature of the liquid crystal compound.
0 <V <5.0 × 10 ⁻³ × η ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Formula (3)

Furthermore, the aligned liquid crystal compound is fixed while maintaining the alignment state, and an optically anisotropic layer is formed. The liquid crystal compound can be fixed by cooling to a solid phase transition temperature or by a polymerization reaction, but preferably 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. A photopolymerization reaction is preferred.
Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. No. 2,367,661 and US Pat. No. 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbons. A substituted aromatic acyloin compound (described in US Pat. No. 2,722,512), a polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a triarylimidazole dimer, 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 (US Pat. No. 4,212,970) Is 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 proceeding and fixing the polymerization of the liquid crystal compound. The irradiation energy is preferably in the range of 20~50J / cm ^2, more preferably in the range of 20~5,000mJ / cm ^2, and still more preferably in the range of 100 to 800 mJ / cm ^2.
In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions. The light irradiation can be carried out by passing the support on which the coating liquid for forming the optically anisotropic layer is passed through a conveyance path in which one or more light sources are arranged at any one of the vertical and horizontal positions.

Before moving to the step (7), a protective layer can be provided on the second optically anisotropic layer produced in the step (6). For example, a protective layer film prepared in advance may be continuously laminated on the surface of the optically anisotropic layer prepared in a long shape.

In the step (7), the long laminate on which the optically anisotropic layer is formed is wound up. The winding may be performed, for example, by winding a support having an optically anisotropic layer that is continuously conveyed around a cylindrical core.
Since the optical compensation film obtained by the step (7) is in the form of a roll, it can be easily handled even when manufactured in large quantities. It can be stored and transported as it is.

  The above example includes two coating steps. For example, one optical anisotropic layer is formed by one coating step, and is cut into a predetermined size, so that the alignment treatment direction is antiparallel. Thus, a laminated body of the first and second optically anisotropic layers can be produced by laminating the respective optically anisotropic layers.

(Polarizer)
As described above, the optical compensation film of the present invention can be bonded to a polarizing film and incorporated into a liquid crystal display device as an elliptically polarizing plate. Examples of the polarizing film include Optiva Inc. And a polarizing film comprising a binder and iodine, or a dichroic dye is preferable. The iodine and the dichroic dye 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 commercially available polarizing film is produced by immersing a stretched polymer in a solution of iodine or dichroic dye in a bath and allowing iodine or dichroic dye to penetrate into the binder. It is common.

  A protective film is preferably bonded to the surface of the polarizing film on the side where the optical compensation film of the present invention is not bonded. The protective film is the same as the polymer film used as the support.

  The optical compensation film of the present invention is useful for a VA mode, particularly a multi-domain VA mode liquid crystal display device. In the conventional VA mode liquid crystal display device, the halftone display has a viewing angle dependency. However, according to the liquid crystal display device of the present invention, the γ characteristic of 25/255 gradation is expected to be greatly improved compared to the prior art. It is. Furthermore, the liquid crystal display device of the present invention can achieve high contrast in the omnidirectional oblique direction. Specifically, when the left-right direction of the screen is set to an azimuth angle of 0 degrees, the contrast measured from an oblique direction with a polar angle of 60 degrees in the azimuths of 0 degrees and 90 degrees can achieve about 50 degrees, and 45 A contrast measured from an oblique direction with a polar angle of 60 ° in an azimuth of 25 ° can be achieved at 25 or more.

The present invention will be described more specifically with reference to the following examples. The materials, reagents, amounts and ratios of substances, operations, and the like shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples.
(Production of optical compensation film)
<Creation of support>
As a support for the optical compensation film, a Z-tack manufactured by Fujifilm was prepared. When the values of Re and Rth of this support were measured, both Re and Rth were almost 0 nm.

A 1.0N potassium hydroxide solution (solvent: water / isopropyl alcohol / propylene glycol = 69.2 parts by mass / 15 parts by mass / 15.8 parts by mass) is applied to the band surface side of the prepared support at 10 mL / m ^2. After coating and holding at about 40 ° C. for 30 seconds, the alkaline solution was scraped off, washed with pure water, and water droplets were removed with an air knife.
Then, it dried at 100 degreeC for 15 second. The contact angle of this support with pure water was determined to be 42 °.

<< Preparation of alignment film >>
On this support (alkali-treated surface), an alignment film coating solution having the following composition was coated at 28 mL / m ² with a # 16 wire bar coater. The film was dried with warm air of 60 ° C. for 60 seconds and further with warm air of 90 ° C. for 150 seconds to produce an alignment film.

[Alignment film coating solution composition]
・ Modified polyvinyl alcohol represented by the following general formula (6): 10 parts by mass, water: ...・ ・ ・ ・ ・ ・ 371 parts by mass ・ Methanol ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 119 parts by mass ・ Glutaraldehyde (crosslinking agent)・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 0.5 parts by mass ・ Citrate ester (AS3 manufactured by Sankyo Chemical Co., Ltd.) ・ ・ ・ ・ ・ ・ ・ ・ 0.35 parts by mass

<< rubbing process >>
The support was conveyed at a speed of 20 m / min, a rubbing roll (300 mm diameter) was set so as to be rubbed in the longitudinal direction, and rotated at 650 rpm, and the alignment film installation surface of the support was rubbed. The contact length between the rubbing roll and the support was set to be 18 mm.

<Formation of optically anisotropic layer>
On the alignment film, 41.01 kg of a discotic liquid crystalline compound represented by the following general formula (7), 4.06 kg of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), cellulose acetate Butyrate (CAB531-1, Eastman Chemical) 0.45 kg, Photopolymerization initiator (Irgacure 907, Ciba Geigy) 1.35 kg, Sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) 0 0.1 kg of fluoroaliphatic group-containing copolymer (Megafac F780 Dainippon Ink Co., Ltd.) is added to a coating solution in which 45 kg is dissolved in 102 kg of methyl ethyl ketone, and a # 3.4 wire bar is rotated at 391 revolutions. Rotate in the same direction as the film transport direction and arrange the support transported at 20 m / min. An optically anisotropic layer (discotic liquid crystal compound layer) was formed by continuously coating on the facing surface.

In the step of continuously heating from room temperature to 100 ° C., the solvent is dried, and then the film surface wind speed of the discotic liquid crystal compound layer is 2.5 m / sec with a dry zone of 130 ° C. The discotic liquid crystal compound was aligned by heating for about 90 seconds. Next, the film is conveyed to a dry zone at 80 ° C., and the surface temperature of the film is about 100 ° C. with an ultraviolet irradiation device (ultraviolet lamp: output 160 W / cm, emission length 1.6 m) with an illuminance of 600 mW. Ultraviolet rays were irradiated for 4 seconds to advance the crosslinking reaction, and the discotic liquid crystal compound was fixed to the alignment. Thereafter, the mixture was allowed to cool to room temperature to form an optically anisotropic layer (first optically anisotropic layer).
Next, the alignment film coating solution was applied onto the first optically anisotropic layer to form a film, and the film surface was rubbed in the longitudinal direction. However, the treatment direction was reversed. The same optically anisotropic layer forming coating solution as described above is applied to this rubbing surface in the same manner, dried and cured, and allowed to cool to room temperature, and then optically anisotropic layer (second optically anisotropic layer) ) Was formed.
Thereafter, it was wound into a cylindrical shape to form a roll. Thus, the roll-shaped optical compensation film 1 was produced. A part of the produced roll-shaped optical compensation film 1 was cut out and used as a sample to measure optical characteristics. Re (550) of the optical compensation film 1 was measured. The results are shown in Table 1. Also, Re (+ 40 °) from the D + direction and Re (−40 °) from the D− direction in FIG. 1 were measured, and the larger one was ReL and the smaller one was ReS. The results are shown in Table 1.

  The in-plane slow axis of the optical compensation film 1 coincides with the longitudinal direction, that is, the in-plane slow axis of the cellulose acylate film as the support, and the rubbing of the first and second optical anisotropic layers. It was consistent with the processing direction.

In the production of the optical compensation film 1, during the method of forming the first and second optical anisotropic layers,
Optical compensation films 2 and 3 shown in Table 1 below were produced in the same manner except that the thickness of the optically anisotropic layer and the rubbing conditions (contact length) were changed.
Further, in the production of the optical compensation film 1, the cellulose acylate film used as the support was replaced with “Fujitac” cellulose acylate film manufactured by Fuji Film (Re (550) and Rth (550) are shown in Table 1 below.) In the same manner except that the film thickness of the optically anisotropic layer and the rubbing conditions (contact length) were changed during the formation methods of the first and second optically anisotropic layers. The optical compensation film 4 shown was produced.
Re (550), ReL and ReS of the optical compensation films 2 to 4 were also measured in the same manner as the optical compensation film 1. The results are shown in Table 1.

[Production of optical compensation film for comparative example]
A polymer film (Re (550) is 55 nm and Rth (550) is 125 nm) prepared by biaxially stretching a cellulose acylate film was used as the optical compensation film 1c for comparative example.
In the production of the optical compensation film 1, during the method of forming the first and second optical anisotropic layers,
An optical compensation film 2c for Comparative Example was produced in the same manner except that the film thickness of the optically anisotropic layer and the rubbing conditions (contact length) were changed.
In the production of the optical compensation film 1, during the method of forming the first and second optical anisotropic layers,
An optical compensation film 3c for comparative example was produced in the same manner except that the film thickness of the optically anisotropic layer and the rubbing conditions (contact length) were changed.
The Re (550), ReL and ReS of the optical compensation films 2c and 3c were also measured in the same manner as the optical compensation film 1. The results are shown in Table 1.

[Preparation of polarizing plate]
A polarizing film was prepared by adsorbing iodine to a polyvinyl alcohol film.
Each of the optical compensation films 1 to 4 and the optical compensation films 1c to 3c for comparative examples was bonded to the surface of the polarizing film to prepare polarizing plates. In addition, the commercially available cellulose acylate film (the Fujifilm make, Fujitac) was affixed on the surface which did not bond the optical compensation film of each polarizing plate.
In addition, as a polarizing plate for Comparative Example 4 shown in Table 1 below, a polarizing plate in which a commercially available cellulose acylate film (manufactured by Fuji Film, Fujitac) was attached to both surfaces of the polarizing film was also produced.

[Production and evaluation of liquid crystal display devices]
A liquid crystal display device having the same configuration as that of the VA mode liquid crystal display device shown in FIG. 4 was produced using each of the polarizing plates produced above. Specifically, two polarizing plates prepared as described above were prepared and used as the polarizing plates PL1 and PL2 in FIG. A vertical alignment cell was prepared as the liquid crystal cell LC. This liquid crystal cell includes liquid crystal (ZLI-2806, manufactured by Merck & Co., Inc.), and in the cell, a vertical alignment material (LQ-1800, Hitachi Chemical Co., Ltd.) is preliminarily placed on the substrate so that the liquid crystal is vertically aligned with respect to the substrate surface. What applied and dried (made by DuPont Microsystems) was used. The cell gap was formed using silica spheres. Δn × d = 300 nm, which is the birefringence of the cell. The axial relationship of each layer was also as shown in FIG.
The following evaluation was performed about each produced liquid crystal display device.
-Contrast evaluation When the horizontal direction of the screen is set to 0 degrees, (1) azimuth angle 0 degrees and polar angle 60 degrees, (2) azimuth angle 90 degrees and polar angle 60 degrees, and (3) azimuth angle 45 degrees and polar angle. The transmittance of white display and black display in three oblique directions of 60 was measured, and the contrast was calculated. The results are shown in Table 1 below.
-Gamma characteristic (25/255 gradation) evaluation (Evaluation of viewing angle dependence of luminance of halftone display)
The γ characteristic in the halftone of the azimuth angle of 45 degrees and the polar angle of 60 degrees was measured with the horizontal direction of the screen as 0 degree. 25 gradations were used as gradations representing halftones. The γ characteristic at 25 gradations is given by the following equation, where the 25 gradation luminance value is L25 and the 255 gradation luminance value (white state) is L255.
γ = log (L25 / L255) / log (25/255)
Table 1 shows the results of the γ characteristics.

＊１ Ｒｅ（５５０）が５５ｎｍ及びＲｔｈ（５５０）が１２５ｎｍのポリマーフィルムを使用。

* 1 Use polymer film with Re (550) of 55 nm and Rth (550) of 125 nm.

  From the results shown in the above table, by using the optical compensation film having the first and second optically anisotropic layers satisfying the formula (I), the viewing angle characteristics of the halftone display are improved. It can be understood that a high contrast can be achieved in an oblique direction (polar angle 60 °) in any orientation of 0 °, 90 °, and 45 ° (γ characteristic is 0.9 or more).

It is a perspective view of an optical compensation film used for explanation of the present invention. It is a cross-sectional schematic diagram of an example of the optical compensation film of this invention. It is a cross-sectional schematic diagram of the other example of the optical compensation film of this invention. It is a cross-sectional schematic diagram of an example of the liquid crystal display device of this invention.

Explanation of symbols

10, 10 'Optical compensation film 12a First optical anisotropic layer 12b Second optical anisotropic layer 14 Support 16 Polarizer 18 Protective film a, b Orientation processing direction c Absorption axis S, s of optical compensation film In-plane slow axis F In-plane fast axis N of optical compensation film Normal direction P of optical compensation film surface Normal plane within plane D + plane P including fast axis S and normal N of optical compensation film Direction D1 rotated clockwise by 40 ° (+ 40 °) in the surface direction D− Direction PL1 and PL2 in which the normal line is rotated by 40 ° (−40 °) counterclockwise in the film surface direction in the plane P Liquid crystal cell

Claims (6)

An optical compensation film having at least first and second optically anisotropic layers, wherein the first and second optically anisotropic layers are controlled by orientation processing directions that are parallel to each other and opposite to each other. A disk-like liquid crystal compound molecule fixed in a hybrid alignment state, and a direction of 40 ° clockwise from the normal to the film surface direction in a plane including the in-film phase advance axis and the normal of the film surface Of the in-plane retardation Re (+ 40 °) measured from the above and Re (−40 °) measured from the direction of 40 ° counterclockwise from the normal, the larger one is ReL and the smaller one is ReS. An optical compensation film satisfying the following formula (I):
(I) 14 ≦ ReL / ReS ≦ 27. 2. The optical compensation film according to claim 1, wherein the in-plane retardation Re (550) at a wavelength of 550 nm of each of the first and second optically anisotropic layers is 20 to 30 nm. Each of the first and second optically anisotropic layers is an optically anisotropic layer containing molecules of a liquid crystal compound that are fixed in an alignment state that is parallel to each other and controlled by an opposite alignment treatment direction. The optical compensation film according to claim 1, wherein the optical compensation film is a film. The in-plane retardation Re (550) at a wavelength of 550 nm is 0 to 3 nm, and the polymer film further has a thickness direction retardation Rth (550) at the same wavelength of 0 to 40 nm. the optical compensation film described in any one of the three. A liquid crystal display device comprising a pair of polarizers arranged with their polarization axes orthogonal to each other and a liquid crystal cell in a vertical alignment mode between the pair of polarizers, wherein the liquid crystal cell and the pair of polarizers between each, the liquid crystal display device characterized by having an optical compensation film of any one of claims 1-4. The liquid crystal display device according to claim 5 , wherein the vertical alignment mode liquid crystal cell is a liquid crystal cell having a multi-domain structure.

Images