JP2001100039A - Cellulose ester film, optical compensation sheet and elliptically polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the relation between the retardation (Rth) in a thickness direction and the retardation (Re) in a plane direction of a cellulose ester film. SOLUTION: The tensile elastic modulus of the cellulose ester film in the machine direction is controlled to 360 to 480 kgf/mm2, and the tensile elastic modulus in the direction perpendicular to the machine direction is controlled to 260 to 440 kgf/mm2. Moreover, the ratio of the tensile elastic modulus in the machine direction to the modulus in the direction perpendicular to the machine direction is controlled to 0.80 to 1.36.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cellulose ester film, an optical compensatory sheet and an elliptically polarizing plate.

[0002]

2. Description of the Related Art A liquid crystal display device comprises a liquid crystal cell, a polarizing element, and an optical compensation sheet (retardation plate). In a transmission type liquid crystal display device, two polarizing elements are attached to both sides of a liquid crystal cell, and one or two optical compensation sheets are arranged between the liquid crystal cell and the polarizing element. In a reflection type liquid crystal display device, a reflection plate, a liquid crystal cell, one optical compensation sheet, and one polarization element are arranged in this order. The liquid crystal cell is composed of rod-like liquid crystal molecules, two substrates for enclosing the same, and an electrode layer for applying a voltage to the rod-like liquid crystal molecules. In the liquid crystal cell, the alignment state of the rod-like liquid crystal molecules is different. For the transmission type, TN (Twisted Nematic) and IPS (In-Plane Sw) are used.
itching), FLC (Ferroelectric Liquid Crysta)
l), OCB (Optically Compensatory Bend), STN
(Supper Twisted Nematic), VA (Vertically Align)
ed) and reflection type HAN (Hybrid Aligned Nem).
atic). A polarizing element generally has a configuration in which two transparent protective films are attached to both sides of a polarizing film.

[0003] Optical compensatory sheets are used in various liquid crystal display devices in order to eliminate coloring of images and to increase the viewing angle. As the optical compensation sheet, a stretched birefringent film has been conventionally used. It has been proposed to use an optical compensatory sheet having an optically anisotropic layer formed of liquid crystalline molecules (particularly discotic liquid crystalline molecules) on a transparent support, instead of an optical compensatory sheet composed of a stretched birefringent film. ing. The optically anisotropic layer is formed by aligning liquid crystalline molecules and fixing the alignment state.
In general, an alignment state is fixed by a polymerization reaction using liquid crystal molecules having a polymerizable group. Liquid crystalline molecules have a large birefringence. The liquid crystal molecules have various alignment forms. By using liquid crystal molecules, it has become possible to realize optical properties that cannot be obtained with a conventional stretched birefringent film.

[0004] The optical properties of the optical compensatory sheet are determined according to the optical properties of the liquid crystal cell, specifically, the above-mentioned difference in display mode. When liquid crystal molecules, particularly discotic liquid crystal molecules, are used, an optical compensatory sheet having various optical properties corresponding to various display modes of a liquid crystal cell can be manufactured. As optical compensation sheets using discotic liquid crystal molecules, ones corresponding to various display modes have already been proposed. For example, optical compensation sheets for TN mode liquid crystal cells are disclosed in JP-A-6-214116, US Pat. Nos. 5,583,679 and 5,646,703.
And German Patent Publication No. 391620A1. Further, an optical compensation sheet for a liquid crystal cell of IPS mode or FLC mode is disclosed in
There is a description in the publication. In addition, OCB mode or HA
An optical compensation sheet for an N-mode liquid crystal cell is disclosed in US Pat.
05253 and International Patent Application WO 96/37804
No. is described in each specification. Furthermore, an optical compensatory sheet for a liquid crystal cell of the STN mode is disclosed in JP-A-9-26572.
There is a description in the publication. An optical compensation sheet for a VA mode liquid crystal cell is described in Japanese Patent No. 2866372.

[0005] Liquid crystal molecules have various alignment forms.
In some cases, the liquid crystal cell cannot be sufficiently optically compensated only by the optical anisotropy of the liquid crystal molecules. In such a case,
A method has been proposed in which the transparent support of the optical compensation sheet is made optically anisotropic and the liquid crystal cell is optically compensated together with the optical anisotropy of the liquid crystal molecules (US Pat. No. 5,646,703). As the optically anisotropic transparent support, specifically, a stretched film of a synthetic polymer is used. A stretched synthetic polymer film conventionally used as an optically anisotropic support has a problem in its function as a support. When a stretched synthetic polymer film is used as a transparent support, it is also difficult to manufacture an elliptically polarizing plate in which an optical compensation sheet and a polarizing plate are integrated.

[0006]

The problem to be solved by the invention is disclosed in European Patent No. 091165.
No. 6 discloses an optical compensatory sheet using a cellulose ester film having a high retardation value in the thickness direction (70 to 400 nm) as a transparent support. The cellulose ester film has an excellent function as a support. When a cellulose ester film is used as a transparent support, it is easy to manufacture an elliptically polarizing plate in which an optical compensation sheet and a polarizing plate are integrated.
However, the conventional cellulose ester film was characterized by having high optical isotropy (low retardation value). The invention described in the above-mentioned European Patent No. 0911656 discloses a means for increasing the retardation value of the cellulose ester film, thereby enabling the use of the cellulose ester film as an optically anisotropic transparent support. The specification discloses the use of a compound having at least two aromatic rings and having a molecular structure that does not sterically hinder the conformation of two aromatic rings (a retardation increasing agent) as means for increasing the retardation value. Is disclosed.

By using a retardation increasing agent, it has become possible to produce a cellulose ester film having a high retardation. However, the retardation increasing agent increases the in-plane retardation value (Re) in addition to the retardation value (Rth) in the thickness direction. Therefore, it was difficult to arbitrarily adjust the relationship between the retardation value (Rth) in the thickness direction and the in-plane retardation value (Re) using only the retardation increasing agent. An object of the present invention is to provide a cellulose ester film in which the relationship between the retardation value in the thickness direction (Rth) and the in-plane retardation value (Re) is adjusted. Another object of the present invention is to provide an optical compensation sheet using an optically anisotropic transparent support having an excellent function as a support. Still another object of the present invention is to provide an integrated elliptically polarizing plate using an optically anisotropic transparent support having an excellent protective function for a polarizing film.

[0008]

The object of the present invention is to provide the following cellulose ester films (1) to (8), optical compensation sheets (9) to (10) and (11)
This was achieved by the elliptically polarizing plate of (12). (1) The tensile modulus in the machine direction is 360 to 480 kgf
/ Mm ² , the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² , and the ratio of the tensile modulus in the machine direction / tensile modulus in the direction perpendicular to the machine direction is 0. A cellulose ester film having a molecular weight of 80 to 1.36. (2) The cellulose ester film according to (1), produced by a solvent casting method. (3) The cellulose according to (1), which is produced by stretching in a drying step of a solvent casting method by 0.1 to 20% in a direction perpendicular to the machine direction with a residual solvent amount of 5 to 3% by weight. Ester film. (4) The cellulose ester film according to (1), which is produced by stretching such that the ratio of the stretching ratio in the direction perpendicular to the machine direction / the stretching ratio in the machine direction is 0.70 to 8.0. (5) The cellulose ester film according to (1), comprising a compound having at least two aromatic rings and having a molecular structure that does not hinder the conformation of the two aromatic rings by steric hindrance. (6) In-plane retardation value is -50 to 50 nm
(1) The cellulose ester film according to (1). (7) The retardation value in the thickness direction is 60 to 100
The cellulose ester film according to (1), which has a thickness of 0 nm. (8) The cellulose ester film according to (1), which is optically negative uniaxial and has an optical axis substantially parallel to a normal to the film surface.

(9) The tensile modulus in the machine direction is 360 to 480 kgf / mm ² , the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² ,
An optical compensatory sheet comprising a cellulose ester film having a ratio of tensile elastic modulus in the machine direction / tensile elastic modulus in a direction perpendicular to the machine direction of 0.80 to 1.36. (10) An optical compensation sheet having a transparent support and an optically anisotropic layer formed from liquid crystalline molecules, wherein the transparent support has a tensile modulus in the machine direction of 360 to 480 kgf.
/ Mm ² , the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² , and the ratio of the tensile modulus in the machine direction / tensile modulus in the direction perpendicular to the machine direction is 0. An optical compensation sheet comprising a cellulose ester film having a thickness of from 80 to 1.36. (11) An elliptically polarizing plate in which a transparent protective film, a polarizing film and an optically anisotropic transparent support are laminated in this order, wherein the optically anisotropic transparent support has a tensile modulus in the machine direction of 360 to 480 kgf. / Mm ² , the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² , and the ratio of the tensile modulus in the machine direction / tensile modulus in the direction perpendicular to the machine direction is 0. An elliptically polarizing plate, which is a cellulose ester film having a thickness of 80 to 1.36. (12) An elliptically polarizing plate in which a transparent protective film, a polarizing film, a transparent support, and an optically anisotropic layer formed of liquid crystal molecules are laminated in this order, wherein the transparent support has tensile elasticity in the machine direction. The modulus is 360 to 480 kgf / mm ² , and the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 k
gf / mm ² and the tensile modulus in the machine direction /
An elliptically polarizing plate comprising a cellulose ester film having a tensile modulus in a direction perpendicular to the machine direction of 0.80 to 1.36.

[0010]

According to the study of the present inventor, by adjusting the tensile modulus in the machine direction and the tensile modulus in the direction perpendicular to the machine direction (transverse direction) of the cellulose ester film, the in-plane of the cellulose ester film can be adjusted. It has been found that the retardation value (Re) can be controlled. Specifically, if the tensile modulus in the transverse direction is set to a value larger than usual, or the tensile modulus in the machine direction is set to a smaller value than usual (in other words, the tensile modulus in the transverse direction and the tensile modulus in the machine direction). When the ratio is set to a value close to that, a cellulose ester film having a relatively high retardation value (Rth) in the thickness direction but a relatively low in-plane retardation value (Re) can be obtained. The tensile modulus can be easily adjusted by a stretching treatment at the time of producing the cellulose ester film. By carrying out the stretching in the transverse direction (not carried out by the usual method), the tensile modulus in the transverse direction can be made larger than usual. In addition, when the stretching in the longitudinal direction is suppressed (in a normal method, the stretching is performed for the production process such as the film winding process without performing the stretching process in particular), the tensile modulus in the longitudinal direction is reduced. It can be smaller than usual. When a stretching treatment and a retardation increasing agent are used in combination, it is possible to obtain a cellulose ester film in which the retardation value (Rth) in the thickness direction and the in-plane retardation value (Re) are arbitrarily adjusted. The cellulose ester film of the present invention has high retardation and excellent function as a support, and can be advantageously used as an optically anisotropic transparent support for an optical compensation sheet. Further, this cellulose ester film has an excellent function of protecting the polarizing film, and can be advantageously used as an optically anisotropic transparent support for an integrated elliptically polarizing plate.

[0011]

FIG. 1 is a schematic diagram showing the basic structure of a transmission type liquid crystal display device. The transmission type liquid crystal display device shown in FIG. 1A includes, in order from the backlight (BL) side, a transparent protective film (1a), a polarizing film (2a), a transparent support (3a), and an optically anisotropic layer ( 4a), lower substrate (5a) of liquid crystal cell, liquid crystal layer (6) composed of rod-like liquid crystal molecules, upper substrate (5b) of liquid crystal cell, optically anisotropic layer (4b), transparent support (3b), polarized light Film (2b) and a transparent protective film (1
b). Transparent support (3a) to optically anisotropic layer (4
a) and optically anisotropic layer (4b) to transparent support (3b)
Constitute two optical compensation sheets. The transparent protective film (1a) to the optically anisotropic layer (4a) and the optically anisotropic layer (4b) to the transparent protective film (1b) constitute two elliptically polarizing plates. The cellulose ester film of the present invention can be used as a transparent support (3a, 3b). Incidentally, the cellulose ester film of the present invention,
Because of high retardation and optical anisotropy,
The optically anisotropic layer (4
The liquid crystal cell can be optically compensated only by the optical anisotropy of the transparent support (3a, 3b) by eliminating a, 4b).

The transmission type liquid crystal display device shown in FIG. 1B has a transparent protective film (1) in order from the backlight (BL) side.
a), a polarizing film (2a), a transparent support (3a), an optically anisotropic layer (4a), a lower substrate (5a) of a liquid crystal cell, a liquid crystal layer (6) composed of rod-like liquid crystal molecules, and a liquid crystal cell. Substrate (5
b), a transparent protective film (1b), a polarizing film (2b), and a transparent protective film (1c). The transparent support (3a) to the optically anisotropic layer (4a) constitute an optical compensation sheet.
Further, the transparent protective film (1a) to the optically anisotropic layer (4a)
It constitutes an elliptically polarizing plate. The cellulose ester film of the present invention can be used as a transparent support (3a). Since the cellulose ester film of the present invention has high retardation and optical anisotropy, the optically anisotropic layer (4a) is removed from the optical compensation sheet or the elliptically polarizing plate, and the transparent support ( It is also possible to optically compensate the liquid crystal cell only by the optical anisotropy of 3a).

The transmission type liquid crystal display device shown in FIG. 1C has a transparent protective film (1) in order from the backlight (BL) side.
a), polarizing film (2a), transparent protective film (1b), lower substrate (5a) of liquid crystal cell, liquid crystal layer (6) composed of rod-like liquid crystal molecules, upper substrate (5b) of liquid crystal cell, optical anisotropy Layer (4
b), a transparent support (3b), a polarizing film (2b), and a transparent protective film (1c). The optically anisotropic layer (4b) to the transparent support (3b) constitute an optical compensation sheet.
Further, the optically anisotropic layer (4b) to the transparent protective film (1c) are
It constitutes an elliptically polarizing plate. The cellulose ester film of the present invention can be used as a transparent support (3b). Since the cellulose ester film of the present invention has high retardation and high optical anisotropy, the optically anisotropic layer (4b) is removed from the optical compensation sheet or the elliptically polarizing plate, and the transparent support ( It is also possible to optically compensate the liquid crystal cell only by the optical anisotropy of 3b).

FIG. 2 is a schematic diagram showing a basic configuration of a reflection type liquid crystal display device. In the reflection type liquid crystal display device shown in FIG. 2, the lower substrate (5)
a), a liquid crystal layer (6) composed of rod-like liquid crystal molecules, an upper substrate (5b) of a liquid crystal cell, an optically anisotropic layer (4b), a transparent support (3b), a polarizing film (2b), and a transparent protective film. (1b)
Consists of Optically anisotropic layer (4b) to transparent support (3b)
Constitute an optical compensation sheet. The optically anisotropic layer (4b) to the transparent protective film (1b) constitute an elliptically polarizing plate. The cellulose ester film of the present invention can be used as a transparent support (3b). Since the cellulose ester film of the present invention has high retardation and high optical anisotropy, the optically anisotropic layer (4b) is removed from the optical compensation sheet or the elliptically polarizing plate, and the transparent support ( It is also possible to optically compensate the liquid crystal cell only by the optical anisotropy of 3b).

[Cellulose Ester Film] In the present invention, the tensile elastic modulus in the machine direction of the cellulose ester film is set to 360 to 480 kgf / mm ² . The tensile modulus in the machine direction is preferably 380 to 460 kgf / mm ² , and more preferably 400 to 440 kgf / mm ² . In the present invention, the tensile modulus of the cellulose ester film in the direction perpendicular to the machine direction (lateral direction) is set to 260 to 440 kgf / mm ² . The tensile modulus in the transverse direction is preferably from 280 to 420, and more preferably from 300 to 400 kgf / mm ² . Further, in the present invention, the ratio of the tensile modulus in the machine direction of the cellulose ester film to the tensile modulus in the direction perpendicular to the machine direction (transverse direction) is 0.80.
To 1.36. The ratio of the tensile modulus in the machine direction / tensile modulus in the transverse direction is preferably from 0.84 to 1.32, and more preferably from 0.88 to 1.28.

The thickness of the cellulose ester film is 2
0 to 500 μm, preferably 50 to 20 μm.
More preferably, it is 0 μm. It is preferable that the cellulose ester film is optically negative uniaxial and the optical axis is substantially parallel to the normal to the film surface.
The retardation value (Rth) in the thickness direction of the cellulose ester film is preferably from 60 to 1000 nm. Further, the in-plane retardation value (Re) of the cellulose ester film is preferably from -50 to 50 nm, more preferably from -20 to 20 nm. The retardation value in the thickness direction is a value obtained by multiplying the birefringence in the thickness direction by the thickness of the film.
The in-plane retardation value is a value obtained by multiplying the in-plane birefringence by the film thickness. The specific value is obtained by measuring the in-plane retardation based on the slow axis with the incident direction of the measurement light as the direction perpendicular to the film surface and the incident direction relative to the direction perpendicular to the film surface. Extrapolated from the tilted measurement result. The measurement can be performed using an ellipsometer (for example, M-150: manufactured by JASCO Corporation). As a measurement wavelength, 550 nm is adopted. The retardation value (Rth) in the thickness direction and the in-plane retardation value (Re) are calculated according to the following. Retardation value in the thickness direction (Rth) = ｛(nx + n
y) / 2−nz｝ × d In-plane retardation value (Re) = (nx−ny) ×
In the formula, nx is the refractive index in the machine direction in the film plane, ny is the refractive index in the direction (transverse direction) perpendicular to the machine direction in the film plane, and nz is the refraction in the direction perpendicular to the film plane. And d is the film thickness (nm).

The birefringence in the thickness direction ｛(nx + n
y) / 2-nz} is 7 × 10^-Four~ 4 × 10^-3Is
Preferably 1 × 10^-3~ 4 × 10^-3Being
Is more preferable, and 1.5 × 10^-3~ 4 × 10^-3Is
More preferably, 2 × 10^-3~ 4 × 10^-3In
More preferably, 2 × 10^-3~ 3 × 10
^-3Is most preferably 2 × 10^-3~ 2.5 ×
10^-3Is particularly preferred. Above tensile modulus and
And optical properties of cellulose ester film
Can be manufactured as follows.

As the cellulose ester, a lower fatty acid ester of cellulose is preferably used. The lower fatty acid means a fatty acid having 6 or less carbon atoms. The number of carbon atoms is preferably 2 (cellulose acetate), 3 (cellulose propionate) or 4 (cellulose butyrate). Cellulose acetate is particularly preferred. Mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate may be used. The average acetylation degree (acetylation degree) of cellulose acetate is preferably 55.0% or more and less than 62.5%. From the viewpoint of physical properties of the film, the average acetylation degree is more preferably 58.0% or more and less than 62.5%. However, the average degree of acetylation is from 55.0% to less than 58.0% (preferably from 57.0% to 58.0%).
%), A film having a high retardation in the thickness direction can be produced.

Preferably, the cellulose ester film is produced by a solvent casting method. In the solvent casting method, a film is produced using a solution (dope) in which a cellulose ester is dissolved in an organic solvent. The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to include ether,
Ketones and esters may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, -O-, -CO- and -COO-) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any one of the functional groups.

Examples of the ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole and phenetole. Examples of the ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone. Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of the organic solvent having two or more types of functional groups include
Includes 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms substituted by halogen atoms in halogenated hydrocarbons is preferably 25 to 75 mol%, and preferably 3 to 75 mol%.
The content is more preferably 0 to 70 mol%, still more preferably 35 to 65 mol%, and 40 to 60 mol%.
Most preferably, it is mol%. Methylene chloride is a typical halogenated hydrocarbon. Two or more organic solvents may be used as a mixture.

The cellulose ester solution can be prepared by a general method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (normal temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a usual solvent casting method. In addition,
In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly, methylene chloride) as the organic solvent. The amount of cellulose ester is 10
It is adjusted to be contained in an amount of about 40% by weight. More preferably, the amount of cellulose ester is from 10 to 30% by weight. In the organic solvent (main solvent), any additives described below may be added. The solution can be prepared by stirring the cellulose ester and the organic solvent at room temperature (0 to 40 ° C.). The highly concentrated solution may be stirred under pressure and heating conditions. Specifically, the cellulose ester and the organic solvent are put in a pressurized container, sealed, and stirred while being heated under pressure to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 2
It is 00 ° C, more preferably 80 to 110 ° C.

The components may be roughly mixed in advance and then placed in a container. Moreover, you may put in a container sequentially. The container must be configured to be able to stir. The container can be pressurized by injecting an inert gas such as nitrogen gas. Further, an increase in the vapor pressure of the solvent due to heating may be used.
Alternatively, each component may be added under pressure after the container is sealed. When heating, it is preferable to heat from outside the container. For example, a jacket-type heating device can be used. Alternatively, a plate heater may be provided outside the container, and the entire container may be heated by circulating the liquid through piping. It is preferable to provide a stirring blade inside the container and stir using the stirring blade. The stirring blade preferably has a length reaching the vicinity of the container wall. At the end of the stirring blade, a scraping blade is preferably provided to renew the liquid film on the container wall. Instruments such as a pressure gauge and a thermometer may be installed in the container. Dissolve each component in the solvent in the container.
The prepared dope is taken out of the vessel after cooling, or is taken out and then cooled using a heat exchanger or the like.

The solution can be prepared by a cooling dissolution method. In the cooling dissolution method, the cellulose ester can be dissolved in an organic solvent (an organic solvent other than a halogenated hydrocarbon) which is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent (for example, halogenated hydrocarbon) which can dissolve the cellulose ester by the usual dissolution method, the cooling dissolution method has an effect that a uniform solution can be obtained quickly. When the cooling dissolution method is used, the retardation of the produced cellulose ester film becomes a high value. In the cooling dissolution method, first, a cellulose ester is gradually added to an organic solvent at room temperature while stirring. It is preferable to adjust the amount of the cellulose ester so that the mixture contains 10 to 40% by weight of the mixture.
More preferably, the amount of cellulose ester is from 10 to 30% by weight. Further, an optional additive described below may be added to the mixture.

Next, the mixture is heated to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to
To -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). Upon such cooling, the mixture of the cellulose ester and the organic solvent solidifies. The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and 12 ° C./min.
/ Min or more is most preferable. A higher cooling rate is preferred, but 10,000 ° C./sec is a theoretical upper limit, 1000 ° C./sec is a technical upper limit, and
0 ° C./sec is a practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at which the cooling is started and the final cooling temperature by the time from when the cooling is started to when the temperature reaches the final cooling temperature.

Further, the temperature is raised to 0 to 200 ° C (preferably 0 to 150 ° C, more preferably 0 to 120 ° C,
When heated to the temperature of 0 to 50 ° C., the cellulose ester dissolves in the organic solvent. The temperature may be raised only by leaving it at room temperature or may be heated in a warm bath. The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The heating rate is preferably as high as possible, but the theoretical upper limit is 10,000 ° C./sec.
C / sec is a technical upper limit, and 100 C / sec is a practical upper limit. Note that the heating rate is a value obtained by dividing the difference between the temperature at which heating is started and the final heating temperature by the time from when the heating is started until the final heating temperature is reached. . As described above, a uniform solution is obtained. In addition,
If the dissolution is insufficient, the operation of cooling and heating may be repeated. Whether or not the dissolution is sufficient can be determined only by visually observing the appearance of the solution.

In the cooling dissolution method, it is desirable to use a closed container in order to avoid water contamination due to dew condensation during cooling. Also, in the cooling and heating operation, pressurization during cooling,
By reducing the pressure during the heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container. According to the differential scanning calorimetry (DSC), a 20% by weight solution of cellulose acetate (acetylation degree: 60.9%, viscosity average polymerization degree: 299) dissolved in methyl acetate by a cooling dissolution method was 3%.
A pseudo phase transition point between the sol state and the gel state exists near 3 ° C., and below this temperature, the gel state becomes uniform. Therefore,
This solution must be stored at a temperature equal to or higher than the quasi phase transition temperature, preferably at a temperature of about 10 ° C. plus the gel phase transition temperature. However, the pseudo phase transition temperature varies depending on the average acetylation degree of cellulose acetate, the average degree of viscosity polymerization, the solution concentration, and the organic solvent used.

From the prepared cellulose ester solution (dope), a cellulose ester film is produced by a solvent casting method. The dope is cast on a drum or band and the solvent is evaporated to form a film.
The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35%. It is preferable that the surface of the drum or the band is finished in a mirror state.
The casting and drying methods in the solvent casting method are described in U.S. Pat. Nos. 2,336,310 and 2,367,603.
Nos. 2492078, 2492977, 24
No. 92978, No. 2607704, No. 2739069
Nos. 2739070, British Patent Nos. 640731 and 736892, Japanese Patent Publication No. 45-4554,
JP-A-49-5614, JP-A-60-176834, JP-A-60-203430 and JP-A-62-115035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. It is preferable to dry the film by blowing it for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried with high-temperature air whose temperature is gradually changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in JP-B-5-17844. According to this method, the time from casting to stripping can be reduced. In order to carry out this method, it is necessary that the dope gels at the surface temperature of the drum or band during casting. The solution (dope) prepared according to the present invention satisfies this condition. Note that a stretching process described later can be performed simultaneously with the drying step.

A plasticizer can be added to the cellulose ester film in order to improve the mechanical properties or to increase the drying speed. As a plasticizer,
Phosphate or carboxylate esters are used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCC).
P) is included. Representative carboxylic esters include phthalic esters and citric esters. Examples of phthalate esters include dimethyl phthalate (DM
P), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP). Examples of citrate esters include O-acetyl triethyl citrate (OACT
E) and tributyl O-acetylcitrate (OACT
B) is included. Examples of other carboxylic esters include butyl oleate, methylacetyl ricinoleate,
It includes dibutyl sebacate and various trimellitate esters. Phthalate ester plasticizers (DMP, DE
P, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred. The amount of the plasticizer added is 0.1 to 25 times the amount of the cellulose ester.
%, More preferably 1 to 20% by weight, most preferably 3 to 15% by weight.

The cellulose ester film includes a retardation increasing agent, a deterioration inhibitor (eg, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, an amine) and an ultraviolet ray, which will be described later. Inhibitors may be added. Regarding the deterioration inhibitor, see JP-A-3-199201.
No., 5-1907073, 5-194789,
These are described in JP-A-5-271471 and JP-A-6-107854. The amount of the deterioration inhibitor added is preferably 0.01 to 1% by weight, more preferably 0.01 to 0.2% by weight of the solution (dope) to be prepared. If the amount is less than 0.01% by weight, the effect of the deterioration inhibitor is hardly recognized. If the amount exceeds 1% by weight, bleeding out (bleeding out) of the deterioration inhibitor on the film surface may be observed. A particularly preferred example of the deterioration inhibitor is butylated hydroxytoluene (BHT). The UV inhibitors are described in JP-A-7-11056. The cellulose acetate having an average degree of acetylation of 55.0 to 58.0% is more stable than the cellulose triacetate having an average degree of acetylation of 58.0% or more. Has the drawback that its physical properties are inferior. However, this disadvantage can be substantially eliminated by using an antioxidant such as the above-mentioned deterioration inhibitor, particularly butylated hydroxytoluene (BHT).

[Stretching of Cellulose Ester Film] In the drying step of the solvent casting method described above, the amount of the residual solvent of the cellulose ester film is 5 to 3% by weight, and 0.1 to 20% in the direction perpendicular to the machine direction. % Stretching is preferred. However, in the film drying step, when the film temperature is equal to or higher than the glass transition temperature of the cellulose ester, it is preferable that the film is not substantially stretched in the machine direction (stretching ratio is 0 to 0.1%). . In other words, it is preferable that the stretching treatment of 0.1 to 20% stretching is performed at a temperature of the film lower than the glass transition temperature of the cellulose ester. For this purpose, when the residual solvent content of the cellulose ester film is 5 to 3% by weight, the temperature of the film is lowered to a temperature lower than the glass transition temperature of the cellulose ester. The ratio of the stretching ratio in the direction perpendicular to the machine direction (lateral direction) / the stretching ratio in the machine direction is preferably from 0.70 to 8.0, and more preferably from 0.7 to 6.0. In order to obtain the above-mentioned stretching ratio, it is preferable to perform a stretching process in the transverse direction on the cellulose ester film. The stretching in the transverse direction can be performed by drying the film while regulating the width of the roll film using a pin tenter. Regarding the stretching process in the transverse direction using a pin tenter, see JP-A-61-1.
Nos. 58413 and 61-158414 and JP-A-Hei.
It is described in each publication of No. -1009.

[Retardation Raising Agent] It is preferable to add a retardation raising agent to the cellulose ester film. As a retardation enhancer,
A compound having at least two aromatic rings and having a molecular structure in which the configuration of the two aromatic rings is not sterically hindered can be used. The retardation increasing agent is preferably used in an amount of 0.01 to 20 parts by weight based on 100 parts by weight of the cellulose ester. The compound having at least two aromatic rings has a π-bonding plane having 7 or more carbon atoms. Unless the configuration of the two aromatic rings is sterically hindered, the two aromatic rings form the same plane. According to the study of the present inventors, it is important to form the same plane with a plurality of aromatic rings in order to increase the retardation of a cellulose ester film. In the present specification, the “aromatic ring” includes an aromatic hetero ring in addition to an aromatic hydrocarbon ring. The aromatic hydrocarbon ring is 6
Particularly preferred is a member ring (that is, a benzene ring).

The aromatic hetero ring is generally an unsaturated hetero ring. The aromatic hetero ring is preferably a 5-, 6-, or 7-membered ring, more preferably a 5- or 6-membered ring. Aromatic heterocycles are generally
It has the most double bonds. As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of the aromatic hetero ring, furan ring, thiophene ring, pyrrole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring,
Pyran ring, pyridine ring, pyridazine ring, pyrimidine ring,
It includes a pyrazine ring and a 1,3,5-triazine ring. As the aromatic ring, a benzene ring, a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, a thiazole ring,
Preferred are an imidazole ring, a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring and a 1,3,5-triazine ring.

The number of aromatic rings contained in the retardation increasing agent is preferably from 2 to 20, and preferably from 2 to 12
Is more preferably, 2 to 8 is more preferable, and 2 to 6 is most preferable. When the compound has three or more aromatic rings, the configuration of at least two aromatic rings need not be sterically hindered. The bonding relationship between two aromatic rings can be classified into (a) a case where a condensed ring is formed, (b) a case where they are directly connected by a single bond, and (c) a case where they are bonded via a linking group. , A spiro bond cannot be formed). In terms of the retardation increase function,
Any of (a) to (c) may be used. However, in the case of (b) or (c), it is necessary that the conformation of the two aromatic rings is not sterically hindered.

Examples of the condensed ring of (a) (condensed ring of two or more aromatic rings) include an indene ring, a naphthalene ring, an azulene ring, a fluorene ring, a phenanthrene ring, an anthracene ring, an acenaphthylene ring, a biphenylene ring, Naphthacene ring, pyrene ring, indole ring, isoindole ring, benzofuran ring, benzothiophene ring, indolizine ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring, purine ring, indazole ring, chromene ring, quinoline Ring, isoquinoline ring,
A quinolidine ring, a quinazoline ring, a cinnoline ring, a quinoxaline ring, a phthalazine ring, a pteridine ring, a carbazole ring, an acridine ring, a phenanthridine ring, a xanthene ring, a phenazine ring, a phenothiazine ring, a phenoxatiin ring, a phenoxazine ring and a thianthrene ring; included. Preferred are a naphthalene ring, an azulene ring, an indole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, a benzotriazole ring and a quinoline ring. The single bond in (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be linked by two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.

The connecting group (c) is also preferably bonded to carbon atoms of two aromatic rings. The linking group is an alkylene group, alkenylene group, alkynylene group, -CO-, -O
-, -NH-, -S- or a combination thereof is preferred. Examples of the linking group consisting of a combination are shown below. Note that the left and right relationships in the following examples of the linking group may be reversed. c1: -CO-O-c2: -CO-NH-c3: -alkylene-O-c4: -NH-CO-NH-c5: -NH-CO-O-c6: -O-CO-O-c7: -O-alkylene-O-c8: -CO-alkenylene-c9: -CO-alkenylene-NH-c10: -CO-alkenylene-O-c11: -alkylene-CO-O-alkylene-O-CO
-Alkylene-c12: -O-alkylene-CO-O-alkylene-O-
CO-alkylene-O-c13: -O-CO-alkylene-CO-O-c14: -NH-CO-alkenylene- c15: -O-CO-alkenylene-

The aromatic ring and the linking group may have a substituent. However, it is necessary that the substituent does not hinder the conformation of the two aromatic rings. For steric hindrance, the type and position of the substituents become a problem. As the type of the substituent, a sterically bulky substituent (for example, a tertiary alkyl group) is likely to cause steric hindrance. As the position of the substituent, steric hindrance is likely to occur when a position adjacent to the bond of the aromatic ring (ortho position in the case of a benzene ring) is substituted. Examples of the substituent include a halogen atom (F, Cl, B
r, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl, sulfamoyl,
Ureido, alkyl group, alkenyl group, alkynyl group,
Aliphatic acyl group, aliphatic acyloxy group, alkoxy group, alkoxycarbonyl group, alkoxycarbonylamino group, alkylthio group, alkylsulfonyl group, aliphatic amide group, aliphatic sulfonamide group, aliphatic substituted amino group, aliphatic substituted carbamoyl Groups, aliphatic substituted sulfamoyl groups, aliphatic substituted ureido groups and non-aromatic heterocyclic groups.

The alkyl group preferably has 1 to 8 carbon atoms. A chain alkyl group is preferable to a cyclic alkyl group, and a linear alkyl group is particularly preferable.
The alkyl group may further have a substituent (eg, hydroxy, carboxy, alkoxy group, alkyl-substituted amino group). Examples of alkyl groups (including substituted alkyl groups) include methyl, ethyl, n-butyl, n-hexyl,
-Hydroxyethyl, 4-carboxybutyl, 2-methoxyethyl and 2-diethylaminoethyl. The alkenyl group preferably has 2 to 8 carbon atoms. A chain alkenyl group is preferable to a cyclic alkenyl group, and a linear alkenyl group is particularly preferable.
The alkenyl group may further have a substituent. Examples of the alkenyl group include vinyl, allyl and 1-hexenyl. The alkynyl group preferably has 2 to 8 carbon atoms. A chain alkynyl group is preferable to a cyclic alkynyl group, and a linear alkynyl group is particularly preferable. The alkynyl group may further have a substituent. Examples of the alkynyl group include ethynyl, 1-butynyl and 1-hexynyl.

The number of carbon atoms of the aliphatic acyl group is 1 to 1
It is preferably 0. Examples of the aliphatic acyl group include acetyl, propanoyl and butanoyl. The aliphatic acyloxy group preferably has 1 to 10 carbon atoms. Examples of the aliphatic acyloxy group include acetoxy. The alkoxy group preferably has 1 to 8 carbon atoms. The alkoxy group may further have a substituent (eg, an alkoxy group). Examples of alkoxy groups (including substituted alkoxy groups) include methoxy, ethoxy, butoxy and methoxyethoxy. The alkoxycarbonyl group preferably has 2 to 10 carbon atoms. Examples of the alkoxycarbonyl group include methoxycarbonyl and ethoxycarbonyl. The alkoxycarbonylamino group preferably has 2 to 10 carbon atoms. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino.

The number of carbon atoms of the alkylthio group is 1 to 1
It is preferably 2. Examples of the alkylthio group include methylthio, ethylthio and octylthio.
The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl. The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide. The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamide group include methanesulfonamide, butanesulfonamide and n-octanesulfonamide. The aliphatic substituted amino group preferably has 1 to 10 carbon atoms. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino. The aliphatic substituted carbamoyl group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl. The aliphatic substituted sulfamoyl group preferably has 1 to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl. The aliphatic substituted ureido group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted ureido group include methyl ureide. Examples of the non-aromatic heterocyclic group include piperidino and morpholino. The molecular weight of the retardation increasing agent is preferably from 300 to 800. The boiling point of the retardation increasing agent is preferably 260 ° C. or higher.

[Surface Treatment of Cellulose Ester Film] When a cellulose ester film is used as a transparent support, the surface treatment of the cellulose ester film can be performed. Corona discharge treatment,
Glow discharge treatment, flame treatment, acid treatment, alkali treatment or ultraviolet irradiation treatment is performed. In order to improve the adhesion between the transparent support and the alignment film or the optically anisotropic layer, it is preferable to provide a gelatin undercoat layer. The thickness of the gelatin undercoat layer is preferably from 0.01 to 1 μm, more preferably from 0.02 to 0.5 μm, and most preferably from 0.05 to 0.2 μm.

[Alignment Film] The alignment film is formed by rubbing an organic compound (preferably a polymer), obliquely depositing an inorganic compound, forming a layer having microgrooves, or using an organic compound by the Langmuir-Blodgett method (LB film). (Eg, ω-tricosanoic acid, dioctadecylmethylammonium chloride, methyl stearylate). In addition, the application of an electric field,
There is also known an alignment film in which an alignment function is generated by applying a magnetic field or irradiating light. An alignment film formed by rubbing a polymer is particularly preferable. The rubbing treatment is performed by rubbing the surface of the polymer layer several times with paper or cloth in a certain direction. The type of polymer used for the alignment film is determined according to the type of display mode of the liquid crystal cell. In a display mode (eg, VA, OCB, HAN) in which most of the rod-like liquid crystal molecules in the liquid crystal cell are substantially vertically aligned, the liquid crystal molecules in the optically anisotropic layer are substantially horizontally aligned. An alignment film having a function is used. A display mode in which many of the rod-like liquid crystal molecules in the liquid crystal cell are substantially horizontally aligned (eg,
In STN), an alignment film having a function of substantially vertically aligning liquid crystal molecules of the optically anisotropic layer is used. In a display mode (eg, TN) in which most of the rod-like liquid crystal molecules in the liquid crystal cell are substantially obliquely aligned, an alignment having a function of substantially obliquely aligning the liquid crystal molecules of the optically anisotropic layer. Use a membrane.

With respect to specific types of polymers, there are descriptions in the literature on optical compensatory sheets using discotic liquid crystalline molecules corresponding to the various display modes described above. The strength of the alignment film may be enhanced by crosslinking the polymer used for the alignment film. By introducing a crosslinkable group into the polymer used for the alignment film and reacting the crosslinkable group,
The polymer can be crosslinked. The crosslinking of the polymer used for the alignment film is described in JP-A-8-3389.
No. 13 has a description. The thickness of the alignment film is preferably 0.01 to 5 μm, and more preferably 0.05 to 1 μm. After aligning the liquid crystal molecules using an alignment film, the liquid crystal molecules are fixed in the alignment state to form an optically anisotropic layer, and only the optically anisotropic layer is transferred onto a support. You may. Discotic liquid crystalline molecules fixed in an aligned state can maintain the aligned state without an alignment film. Therefore, in the optical compensation sheet, the alignment film is not an essential element (although it is essential in the production of the optical compensation sheet containing discotic liquid crystalline molecules).

[Optical Anisotropic Layer] The optically anisotropic layer is formed from liquid crystalline molecules. As the liquid crystal molecules, rod-shaped liquid crystal molecules or discotic liquid crystal molecules are preferable, and discotic liquid crystal molecules are particularly preferable. Examples of rod-like liquid crystal molecules include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, and alkoxy-substituted phenylpyrimidines. , Phenyldioxane, tolan and alkenylcyclohexylbenzonitrile are preferably used. Not only low molecular liquid crystal molecules as described above but also high molecular liquid crystal molecules can be used. The high-molecular liquid crystal molecules are polymers having side chains corresponding to the low-molecular liquid crystal molecules described above. An optical compensatory sheet using high-molecular liquid crystalline molecules is described in JP-A-5-53016.

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

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

[0046]

Embedded image

[0047]

Embedded image

[0048]

Embedded image

[0049]

Embedded image

[0050]

Embedded image

[0051]

Embedded image

[0052]

Embedded image

[0053]

Embedded image

[0054]

Embedded image

In the formula (I), the divalent linking group (L)
Is an alkylene group, alkenylene group, arylene group,-
It is preferably a divalent linking group selected from the group consisting of CO-, -NH-, -O-, -S- and a combination thereof. The divalent linking group (L) includes an alkylene group, an alkenylene group, an arylene group, -CO-, -NH-,-
More preferably, the group is a group obtained by combining at least two divalent groups selected from the group consisting of O- and -S-. The divalent linking group (L) is most preferably a group obtained by combining at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, -CO- and -O-. The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbon atoms. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group, a halogen atom, a cyano, an alkoxy group, an acyloxy group). Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is bonded to the polymerizable group (P). AL represents an alkylene group or an alkenylene group, and AR represents an arylene group.

L1: -AL-CO-O-AL- L2: -AL-CO-O-AL-O- L3: -AL-CO-O-AL-O-AL- L4: -AL-CO-O -AL-O-CO-L5: -CO-AR-O-AL-L6: -CO-AR-O-AL-O-L7: -CO-AR-O-AL-O-CO-L8: -CO -NH-AL-L9: -NH-AL-O-L10: -NH-AL-O-CO-L11: -O-AL-L12: -O-AL-O-

L13: -O-AL-O-CO-L14: -O-AL-O-CO-NH-AL-L15: -O-AL-S-AL-L16: -O-CO-AL-AR -O-AL-O-CO-L17: -O-CO-AR-O-AL-CO-L18: -O-CO-AR-O-AL-O-CO-L19: -O-CO-AR- O-AL-O-AL-OC
O-L20: -O-CO-AR-O-AL-O-AL-OA
L-O-CO-L21: -S-AL-L22: -S-AL-O-L23: -S-AL-O-CO-L24: -S-AL-S-AL-L25: -S-AR -AL-

In order to optically compensate for a liquid crystal cell in which rod-like liquid crystal molecules are twisted in the STN mode, it is preferable that the discotic liquid crystal molecules are also twisted. When an asymmetric carbon atom is introduced into the AL (alkylene group or alkenylene group), the discotic liquid crystal molecule can be twisted and aligned in a helical manner. Further, even when a compound having an optical activity (chiral agent) containing an asymmetric carbon atom is added to the optically anisotropic layer, the discotic liquid crystal molecules can be twisted in a helical manner.

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

[0060]

Embedded image

[0061]

Embedded image

[0062]

Embedded image

[0063]

Embedded image

[0064]

Embedded image

[0065]

Embedded image

The polymerizable group (P) is an unsaturated polymerizable group (P
1, P2, P3, P7, P8, P15, P16, P1
7) or an epoxy group (P6, P18), more preferably an unsaturated polymerizable group,
Ethylenically unsaturated polymerizable groups (P1, P7, P8, P1
5, P16, P17). In the formula (I), n is an integer of 4 to 12. Specific numbers are determined according to the type of discotic core (D). The combination of a plurality of L and P may be different, but is preferably the same.

Two or more discotic liquid crystal molecules may be used in combination. For example, the polymerizable discotic liquid crystal molecules and the non-polymerizable discotic liquid crystal molecules described above can be used in combination. The non-polymerizable discotic liquid crystal molecule is preferably a compound in which the polymerizable group (P) of the polymerizable discotic liquid crystal molecule is changed to a hydrogen atom or an alkyl group. That is, the non-polymerizable discotic liquid crystalline molecule is preferably a compound represented by the following formula (II). (II) D (-LR) _{n wherein} D is a discotic core; L is a divalent linking group; R is a hydrogen atom or an alkyl group;
Is an integer of 4 to 12. An example of the discotic core (D) of formula (II) is that LP (or PL) is replaced by LR (or R
Except for changing to L), it is the same as the example of the polymerizable discotic liquid crystal molecule described above. Further, a divalent linking group (L)
Is the same as the example of the polymerizable discotic liquid crystal molecule described above. The alkyl group represented by R has 1 to 4 carbon atoms.
It is preferably 0, more preferably 1 to 30. A chain alkyl group is more preferable than a cyclic alkyl group, and a straight-chain alkyl group is more preferable than a branched chain alkyl group. R is particularly preferably a hydrogen atom or a linear alkyl group having 1 to 30 carbon atoms.

The optically anisotropic layer is composed of liquid crystal molecules or the following polymerizable initiators and optional additives (eg, plasticizer, monomer, surfactant, cellulose ester, 1,3,5-triazine compound, It is formed by applying a coating solution containing a chiral agent) on the alignment film. As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethylsulfoxide),
Heterocyclic compound (eg, pyridine), hydrocarbon (eg, benzene, hexane), alkyl halide (eg, chloroform, dichloromethane), ester (eg, methyl acetate, butyl acetate), ketone (eg, acetone, methyl ethyl ketone), ether (Eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination. The application of the coating solution can be performed by a known method (eg, an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a die coating method).

The liquid crystal molecules are preferably oriented substantially uniformly, more preferably fixed in a state of being substantially uniformly oriented, and the liquid crystal molecules are fixed by a polymerization reaction. Is most preferred. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. Photopolymerization reactions are preferred. Examples of the photopolymerization initiator include α-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661 and 2,367,670) and acyloin ethers (U.S. Pat.
828), α-hydrocarbon-substituted aromatic acyloin compounds (described in US Pat. No. 2,722,512),
Polynuclear quinone compounds (U.S. Pat.
51758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), an acridine and phenazine compound (Japanese Unexamined Patent Publication No. Sho 60-105667).
No. 4,239,850) and oxadiazole compounds (described in US Pat. No. 4,221,970). The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight, more preferably 0.5 to 5% by weight of the solid content of the coating solution. Light irradiation for the polymerization of discotic liquid crystalline molecules preferably uses ultraviolet light. The irradiation energy is preferably from 20 mJ / cm ^{2 to} 50 J / cm ² , more preferably from 100 to 800 mJ / cm ² . Light irradiation may be performed under heating conditions to promote the photopolymerization reaction.

The thickness of the optically anisotropic layer is generally 0.1
To 10 μm. The thickness of the optically anisotropic layer is preferably 0.5 to 5 μm, more preferably 1 to 5 μm. However, depending on the mode of the liquid crystal cell, the optically anisotropic layer may be thick (3 to 10 μm) in order to obtain high optical anisotropy. According to the study of the present inventor, it is preferable that the thickness be 0.5 to 5 μm, more preferably 1 to 5 μm. As described above, the alignment state of liquid crystal molecules in the optically anisotropic layer is determined according to the type of display mode of the liquid crystal cell. Specifically, the alignment state of liquid crystal molecules is determined by the types of liquid crystal molecules, types of alignment films, and additives in the optically anisotropic layer (eg, plasticizer, binder, surfactant).
Controlled by the use of

[Liquid Crystal Display Device] An optical compensatory sheet or an integrated elliptically polarizing plate using the cellulose ester film of the present invention can be made of TN (Twisted Nematic), IPS (In-Plan).
e Switching), FLC (Ferroelectric Liquid Crysta)
l), OCB (Optically Compensatory Bend), STN
(Supper Twisted Nematic), VA (Vertically Align)
ed) and HAN (Hybrid Aligned Nematic). The cellulose ester film of the present invention is particularly effective in a liquid crystal display device (for example, TN or VA) requiring high retardation for optical compensation. The liquid crystal display device includes a liquid crystal cell, a polarizing element, and an optical compensation sheet (retardation plate). A polarizing element generally includes a polarizing film and a protective film. The polarizing film includes an iodine-based polarizing film, a dye-based polarizing film using a dichroic dye, and a polyene-based polarizing film.
The iodine-based polarizing film and the dye-based polarizing film are generally manufactured using a polyvinyl alcohol-based film. The polarization axis of the polarizing film corresponds to a direction perpendicular to the stretching direction of the film.
The protective films are provided on both surfaces of the polarizing film. The optical compensation sheet or its transparent support can also function as a protective film on one side of the polarizing film (forming an integrated elliptically polarizing plate). It is preferable to use a (normal) cellulose ester film as the protective film on the other side.

[0072]

EXAMPLES Example 1 (Preparation of Cellulose Ester Film) The following composition was charged into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose ester solution.

組成 Cellulose ester solution composition───────セ ル ロ ー ス 100% by weight of cellulose acetate having a degree of acetylation of 60.9% triphenyl phosphate (plasticizer) 7 0.8 parts by weight Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by weight Methylene chloride (first solvent) 300 parts by weight Methanol (second solvent) 54 parts by weight 1-butanol 11 parts by weight ───────────────────────────

The following composition was charged into another mixing tank, and the mixture was stirred while heating to dissolve each component to prepare a retardation increasing solution.

組成 Composition of Retardation Elevator Solution ───── ─────────────────────────────── 2-hydroxy-4-benzyloxybenzophenone (a retardation increasing agent) 12 parts by weight 2 4,4-benzyloxybenzophenone (retardation increasing agent) 4 parts by weight Methylene chloride 80 parts by weight Methanol 20 parts by weight ──────────

To 474 parts by weight of the cellulose ester solution,
A dope was prepared by adding 22 parts by weight of a retardation increasing agent solution and sufficiently stirring. The total added amount of the two kinds of retardation increasing agents is cellulose acetate 10
It is 3 parts by weight with respect to 0 parts by weight. The dope was cast from a casting port onto a drum cooled to 0 ° C. Solvent content 70
Wt% of the film, and the film was fixed at both ends in the width direction with a pin tenter (FIG. 3 of JP-A-4-1009). 3% stretch ratio (in the direction perpendicular to the machine direction)
Drying while maintaining the interval. Thereafter, the film is further dried by being conveyed between the rolls of a heat treatment apparatus, and in the region where the glass transition temperature exceeds 120 °, the stretching ratio in the machine direction is substantially 0%. The thickness of the cellulose acetate film having a thickness of 107 μm was prepared by adjusting the ratio of the stretching ratio in the transverse direction to the stretching ratio in the machine direction to 0.75 (considering). The tensile elastic modulus in the machine direction of the produced film is 430 kgf / mm ² , and the tensile elastic modulus in the direction perpendicular to the machine direction is 360 kg.
f / mm ² and the ratio of tensile modulus in the machine direction / tensile modulus in the direction perpendicular to the machine direction was 1.19. The retardation (Rth) in the thickness direction is 80.
The in-plane retardation (Re) was 17 nm. The precipitation of the retardation increasing agent was not recognized at all immediately after the production, but also in the treatment after the production of the film described later.

(Formation of First Undercoat Layer) The prepared cellulose ester film was used as a transparent support. On the transparent support, a coating solution having the following composition was applied at 28 ml / m ² and dried to form a first undercoat layer.

<< Composition of First Undercoat Layer Coating Solution >> ──────────────────────────────── Gelatin 5.42 parts by weight Formaldehyde 1.36 parts by weight Salicylic acid 1.6 parts by weight Acetone 391 parts by weight Methanol 158 parts by weight Methylene chloride 406 parts by weight Water 12 parts by weight ───────────────────────────────── ───

(Formation of Second Undercoat Layer) On the first undercoat layer, a coating solution having the following composition was applied at 7 ml / m ² and dried to form a second undercoat layer.

<< Composition of Coating Solution for Second Undercoat Layer >> ──────────────────────────────── The following anionic polymer 0.79 parts by weight citric acid half ethyl ester 10.1 Parts by weight Acetone 200 parts by weight Methanol 877 parts by weight Water 40.5 parts by weight ────────────────────────────────── ──

[0081]

Embedded image

(Formation of Back Layer) A coating solution having the following composition was applied on the opposite surface of the transparent support at 25 ml / m ² and dried to form a back layer.

<< Composition of Back Layer Coating Solution >>セ ル ロ ー ス Cellulose diacetate with 55% acetylation degree 6.56 parts by weight Silica-based matting agent (average Particle size: 1 μm) 0.65 parts by weight Acetone 679 parts by weight Methanol 104 parts by weight ────

(Formation of Alignment Film) On the second undercoat layer, the following aqueous solution of modified polyvinyl alcohol was applied.
After drying with hot air at ℃, rubbing treatment was performed to form an alignment film.

[0085]

Embedded image

(Formation of Optically Anisotropic Layer) 1.8 g of the following discotic liquid crystal compound, ethylene oxide-modified trimethylolpropane triacrylate (V # 36)
0, manufactured by Osaka Organic Chemical Co., Ltd.) 0.2 g, cellulose acetate butyrate (CAB531-1.0, manufactured by Eastman Chemical Company) 0.04 g, photopolymerization initiator (Irgacure 907, manufactured by Nippon Ciba Geigy Co., Ltd.) 0.06 g and a sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.)
Was dissolved in 8.43 g of methyl ethyl ketone to prepare a coating solution. The coating solution was applied on the alignment film using a # 2.5 wire bar. This was adhered to a metal frame and heated in a thermostat at 130 ° C. for 2 minutes to align the discotic liquid crystalline compound. While maintaining the temperature of 130 ° C., ultraviolet rays were irradiated for 1 minute using a high-pressure mercury lamp of 120 W / cm to polymerize the vinyl group of the discotic liquid crystal compound and fix the alignment state. Then, it was left to cool to room temperature. Thus, an optical compensation sheet was produced. The thickness of the optically anisotropic layer was 1.0 μm.

[0087]

Embedded image

(Preparation of Transparent Protective Film) A triacetyl cellulose film having a thickness of 80 μm was prepared in the same manner as in the preparation of the transparent support, except that the discotic compound (retardation increasing agent) was not added. This was used as a transparent protective film. On one surface of the transparent protective film, a first undercoat layer and a second undercoat layer were provided in the same manner as the transparent support.

(Preparation of Elliptical Polarizing Plate) Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare a polarizing film. An optical compensation sheet was attached to one side of the polarizing film using a polyvinyl alcohol-based adhesive so that the optically anisotropic layer was on the outside. On the opposite side, a transparent protective film was attached using a polyvinyl alcohol-based adhesive. The absorption axis of the polarizing film and the rubbing direction of the optically anisotropic layer were arranged so as to be parallel. Thus, an elliptically polarizing plate was produced.

(Production of Liquid Crystal Display) A polyimide alignment film was provided on a glass substrate provided with an ITO transparent electrode, and a rubbing treatment was performed. Two substrates were stacked via a 5 μm spacer so that the alignment films faced each other. The orientation of the substrate was adjusted so that the rubbing directions of the alignment films were orthogonal. In the gap between the substrates, rod-like liquid crystal molecules (ZL479
2, manufactured by Merck) to form a liquid crystal layer. Δn of the liquid crystal molecule was 0.0969. An elliptically polarizing plate was attached to both sides of the TN liquid crystal cell manufactured as described above so that the optically anisotropic layer faced the substrate, thereby manufacturing a liquid crystal display device. The slow axis of the laminate of the optically anisotropic layer and the transparent support was arranged to be orthogonal to the rubbing direction of the liquid crystal cell. When a display image was examined by applying a voltage to the liquid crystal cell of the liquid crystal display device, a wide viewing angle was obtained.

Comparative Example 1 The dope prepared in Example 1 was cast from a casting port onto a drum cooled to 0 ° C. It is peeled off at a solvent content of 70% by weight, and the stretching rate in the machine direction is 6%, and the stretching rate in the transverse direction (direction perpendicular to the machine direction) is 0%
Drying was performed under the following conditions to prepare a cellulose acetate film having a thickness of 107 μm. The tensile elasticity of the produced film in the machine direction was 410 kgf / mm ² , and the tensile elasticity in the direction perpendicular to the machine direction was 300 kgf / mm ^2.
And the ratio of the tensile modulus in the machine direction / tensile modulus in the direction perpendicular to the machine direction was 1.37. Also,
The retardation (Rth) in the thickness direction was 85 nm, and the in-plane retardation (Re) was 25 nm. An optical compensatory sheet, an elliptically polarizing plate, and a liquid crystal display were sequentially manufactured in the same manner as in Example 1 except that the manufactured cellulose ester film was used. When a display image was examined by applying a voltage to the liquid crystal cell of the liquid crystal display device, the viewing angle was narrower than that of the liquid crystal display device manufactured in Example 1.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a basic configuration of a transmission type liquid crystal display device.

FIG. 2 is a schematic diagram showing a basic configuration of a reflection type liquid crystal display device.

[Explanation of symbols]

 BL backlight RP reflector 1a, 1b, 1c Transparent protective film 2a, 2b Polarizing film 3a, 3b Transparent support 4a, 4b Optically anisotropic layer 5a Liquid crystal cell lower substrate 5b Liquid crystal cell upper substrate 6 Rod-like liquid crystal molecules Liquid crystal layer consisting of

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 1/10 C08L 1/10 // B29K 1:00 B29K 1:00 B29L 7:00 B29L 7:00 11 : 00 11:00 F-term (reference) 2H049 BA02 BA04 BA06 BA42 BB03 BB33 BB49 BC03 BC09 4F071 AA09 AH19 BA02 BB02 BB07 BC01 BC17 4F100 AJ06A AR00C AS00B BA03 BA07 EJ37A GB90 JA11B JK07A JL01C01B01Q01 J02A01 4J002 AB021 EA036 ED056 EE036 EH006 EP016 FD206

Claims (12)

[Claims] 1. The tensile modulus in the machine direction is from 360 to 48.
0 kgf / mm ² , the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² , and the ratio of the tensile modulus in the machine direction / tensile modulus in the direction perpendicular to the machine direction is 0. .80 to 1.36. 2. The cellulose ester film according to claim 1, which is produced by a solvent casting method. 3. The method according to claim 2, wherein in the drying step of the solvent casting method, the resin is stretched by 0.1 to 20% in a direction perpendicular to the machine direction with a residual solvent amount of 5 to 3% by weight. Cellulose ester film. 4. The cellulose ester film according to claim 1, wherein the cellulose ester film is produced by stretching such that the ratio of the stretching ratio in the direction perpendicular to the machine direction / the stretching ratio in the machine direction is 0.70 to 8.0. . 5. The cellulose ester according to claim 1, comprising 0.01 to 20% by weight of a compound having a molecular structure that has at least two aromatic rings and does not hinder the conformation of the two aromatic rings. Film. 6. The cellulose ester film according to claim 1, wherein the in-plane retardation value is -50 to 50 nm. 7. The cellulose ester film according to claim 1, wherein the retardation value in the thickness direction is from 60 to 1,000 nm. 8. The cellulose ester film according to claim 1, wherein the film is optically negative uniaxial and the optical axis is substantially parallel to the normal to the film surface. 9. The tensile modulus in the machine direction is from 360 to 48.
0 kgf / mm ² , the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² , and the ratio of the tensile modulus in the machine direction / tensile modulus in the direction perpendicular to the machine direction is 0. An optical compensation sheet comprising a cellulose ester film having a thickness of from 80 to 1.36. 10. An optical compensation sheet having an optically anisotropic layer formed from a transparent support and liquid crystal molecules,
The transparent support has a tensile modulus in the machine direction of 360 to 48.
0 kgf / mm ² , the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² , and the ratio of the tensile modulus in the machine direction / tensile modulus in the direction perpendicular to the machine direction is 0. An optical compensatory sheet characterized by being a cellulose ester film having a thickness of from 80 to 1.36. 11. An elliptically polarizing plate in which a transparent protective film, a polarizing film and an optically anisotropic transparent support are laminated in this order, wherein the optically anisotropic transparent support has a tensile modulus in the machine direction of 360. 480 kgf / mm ² , and the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm 2.
^2. An elliptically polarizing plate, which is a cellulose ester film having a ratio of tensile elastic modulus in a machine direction / tensile elastic modulus in a direction perpendicular to the machine direction of 0.80 to 1.36. 12. An elliptically polarizing plate in which a transparent protective film, a polarizing film, a transparent support and an optically anisotropic layer formed of liquid crystal molecules are laminated in this order, wherein the transparent support has a machine direction. The tensile modulus is 360 to 480 kgf / mm ² , the tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² , and the tensile modulus in the machine direction / tensile in the direction perpendicular to the machine direction. The elastic modulus ratio is 0.
An elliptically polarizing plate, which is a cellulose ester film having a thickness of 80 to 1.36.