JP2010284972A - Tn liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To regulate the relation between perpendicular retardation (Rth) and in-plane retardation (Re) of a cellulose ester film. <P>SOLUTION: The cellulose ester film is produced by stretching it 0.1 to 20% in the direction perpendicular to machine direction, in a drying process of a solvent cast method; provided that the stretch substantially does not take place in the machine direction when film temperature hits or exceeds a glass transition temperature of the cellulose ester, and that the amount of residual solvent is kept 5 to 3 wt.% when the film temperature is lower than the glass transition temperature of the cellulose ester. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a cellulose ester film.

The liquid crystal display device includes a liquid crystal cell, a polarizing element, and an optical compensation sheet (retardation plate). In a transmissive 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 disposed between the liquid crystal cell and the polarizing element. In a reflective liquid crystal display device, a reflector, a liquid crystal cell, a single optical compensation sheet, and a single polarizing element are arranged in this order.
The liquid crystal cell is composed of a rod-like liquid crystal molecule, two substrates for enclosing it, and an electrode layer for applying a voltage to the rod-like liquid crystal molecule. The liquid crystal cell is different in the alignment state of rod-like liquid crystal molecules. As for the transmission type, TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), OCB (Optically Compensatory Bend), STN (STN) Various display modes such as HAN (Hybrid Aligned Nematic) have been proposed for Supper Twisted Nematic (VA), VA (Vertically Aligned), and reflection type.
A polarizing element generally has a configuration in which two transparent protective films are attached to both sides of a polarizing film.

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

The optical properties of the optical compensation sheet are determined according to the optical properties of the liquid crystal cell, specifically, the display mode differences as described above. When liquid crystal molecules, particularly discotic liquid crystal molecules are used, optical compensation sheets having various optical properties corresponding to various display modes of the liquid crystal cell can be produced.
Optical compensation sheets using discotic liquid crystalline molecules have already been proposed for various display modes. For example, Patent Documents 1 to 4 describe optical compensation sheets for TN mode liquid crystal cells. Patent Document 5 describes an optical compensation sheet for liquid crystal cells in IPS mode or FLC mode. Further, Patent Documents 6 and 7 describe optical compensation sheets for liquid crystal cells in OCB mode or HAN mode. Furthermore, an optical compensation sheet for liquid crystal cells in STN mode is described in Patent Document 8. A VA mode liquid crystal cell optical compensation sheet is described in Patent Document 9.

Although liquid crystal molecules have various alignment forms, the liquid crystal cell may not 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 crystalline molecules (see Patent Document 3). ). Specifically, a synthetic polymer stretched film is used as the optically anisotropic transparent support.
A synthetic polymer stretched film conventionally used as an optically anisotropic support has a problem in function as a support. In addition, when a synthetic polymer stretched film is used as a transparent support, it is difficult to produce an elliptically polarizing plate in which an optical compensation sheet and a polarizing plate are integrated.

JP-A-6-214116 US Pat. No. 5,583,679 US Pat. No. 5,646,703 German Patent Invention No. 3911620A1 Japanese Patent Laid-Open No. 10-54982 US Pat. No. 5,805,253 International Publication No. 96/37804 Pamphlet JP-A-9-26572 Japanese Patent No. 2866372

European Patent No. 0911656 discloses an optical compensation 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. In addition, when a cellulose ester film is used as a transparent support, it is easy to produce an elliptically polarizing plate in which an optical compensation sheet and a polarizing plate are integrated. However, the conventional cellulose ester film is characterized by having high optical isotropy (low retardation value).
The invention described in the above-mentioned European Patent 0911656 discloses means for increasing the retardation value of a cellulose ester film, and enables the cellulose ester film to be used as an optically anisotropic transparent support. This specification uses a compound (retardation increasing agent) having a molecular structure that has at least two aromatic rings and does not sterically hinder the conformation of the two aromatic rings as a means for increasing the retardation value. Is disclosed.

The use of a retardation increasing agent makes it possible to produce a cellulose ester film having a high retardation. However, the retardation increasing agent also increases the in-plane retardation value (Re) in addition to the retardation value (Rth) in the thickness direction. Therefore, it is difficult to arbitrarily adjust the relationship between the retardation value (Rth) in the thickness direction and the in-plane retardation value (Re) with 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 (Rth) in the thickness direction and the in-plane retardation value (Re) is adjusted.

The object of the present invention has been achieved by the following methods (1) to (8) for producing a cellulose ester film.
(1) A method for producing a cellulose ester film by a solvent cast method, and in the drying step of the solvent cast method, when the film temperature is equal to or higher than the glass transition temperature of the cellulose ester, it is substantially in the machine direction. If the film temperature is lower than the glass transition temperature of the cellulose ester, provided that the residual solvent amount is 5 to 3% by weight, the film is perpendicular to the machine direction. A method for producing a cellulose ester film, which is produced by stretching 0.1 to 20% in any direction.
(2) The cellulose ester film to be produced has a tensile modulus in the machine direction of 360 to 480 kgf / mm ² , a tensile modulus in the direction perpendicular to the machine direction is 260 to 440 kgf / mm ² , and the machine direction The method according to (1), wherein the ratio of tensile modulus of elasticity / tensile modulus of elasticity in the direction perpendicular to the machine direction is 0.80 to 1.36.
(3) The in-plane retardation value of the produced cellulose ester film is −50 to 50 nm, the retardation value in the thickness direction is 60 to 1000 nm, and the thickness is 50 to 200 μm. The manufacturing method as described in.
(4) Stretch ratio so that the ratio of the stretch ratio in the direction perpendicular to the machine direction / the stretch ratio in the machine direction including stretching in the machine direction at the time of peeling is 0.70 to 8.0 (1 ) Manufacturing method.

(5) The cellulose ester film comprises 0.01 to 20% by weight of a compound having a molecular structure having at least two aromatic rings and not sterically hindering the conformation of the two aromatic rings. Manufacturing method.
(6) The production method according to (1), wherein the produced cellulose ester film is optically negative uniaxial, and the optical axis is substantially parallel to the normal of the film surface.
(7) The production method according to (1), wherein the cellulose ester is cellulose acetate.
(8) The solvent of the cellulose ester solution used in the solvent cast method is an ether having 3 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms, and 1 carbon atom. The production method according to (1), which is selected from the group consisting of 6 to 6 halogenated hydrocarbons.

By inventor's research, by adjusting the tensile modulus in the machine direction of the cellulose ester film and the tensile modulus in the direction perpendicular to the machine direction (transverse direction), the in-plane retardation value of the cellulose ester film ( It has been found that Re) can be controlled. Specifically, if the tensile modulus in the transverse direction is set to a larger value 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 elasticity in the machine direction are When the ratio is close), 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.
A tensile elasticity modulus can be easily adjusted with the extending | stretching process at the time of manufacture of a cellulose-ester film. When the stretching process in the transverse direction (not carried out by a normal method) is carried out, the tensile modulus in the transverse direction can be made larger than usual. In addition, if the stretching in the machine direction is suppressed (the film is stretched for the convenience of the manufacturing process such as the film winding process even if the film is not subjected to a particular stretching process in the usual method), the tensile modulus in the machine direction is reduced. The value 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 a high retardation and an excellent function as a support, and can be advantageously used as an optically anisotropic transparent support for optical compensation sheets. Furthermore, the cellulose ester film has an excellent protective function for the polarizing film, and can be advantageously used as an optically anisotropic transparent support for an integral elliptically polarizing plate.

It is a schematic diagram which shows the basic composition of a transmissive liquid crystal display device. It is a schematic diagram which shows the basic composition of a reflection type liquid crystal display device.

FIG. 1 is a schematic diagram showing a basic configuration of a transmissive liquid crystal display device.
The transmissive 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), an optically anisotropic layer ( 4a), lower substrate (5a) of the liquid crystal cell, liquid crystal layer (6) composed of rod-like liquid crystalline molecules, upper substrate (5b) of the liquid crystal cell, optically anisotropic layer (4b), transparent support (3b), polarized light It consists of a film (2b) and a transparent protective film (1b).
The transparent support (3a) to the optically anisotropic layer (4a) and the optically anisotropic layer (4b) to the 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 elliptical polarizing plates.
The cellulose ester film of the present invention can be used as a transparent support (3a, 3b). In addition, since the cellulose ester film of the present invention has high retardation and optical anisotropy, the optically anisotropic layer (4a, 4b) is deleted from the optical compensation sheet or the elliptically polarizing plate to provide a transparent support. It is also possible to optically compensate the liquid crystal cell only by the optical anisotropy of the bodies (3a, 3b).

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

The transmissive liquid crystal display device shown in FIG. 1C has a transparent protective film (1a), a polarizing film (2a), a transparent protective film (1b), and a lower substrate of a liquid crystal cell (from the backlight (BL) side). 5a), liquid crystal layer (6) composed of rod-like liquid crystalline molecules, upper substrate (5b) of liquid crystal cell, optical anisotropic layer (4b), transparent support (3b), polarizing film (2b), and transparent protective film (1c).
The optically anisotropic layer (4b) to the transparent support (3b) constitute an optical compensation sheet.
Moreover, the optically anisotropic layer (4b) to the transparent protective film (1c) 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 optical anisotropy, the optically anisotropic layer (4b) is deleted from the optical compensation sheet or the elliptically polarizing plate, and a 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 reflective liquid crystal display device.
The reflective liquid crystal display device shown in FIG. 2 includes, in order from the reflective plate (RP) side, a lower substrate (5a) of a liquid crystal cell, a liquid crystal layer (6) made of rod-like liquid crystalline molecules, an upper substrate (5b) of a liquid crystal cell, It consists of an optically anisotropic layer (4b), a transparent support (3b), a polarizing film (2b), and a transparent protective film (1b).
The optically anisotropic layer (4b) to the 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 optical anisotropy, the optically anisotropic layer (4b) is deleted from the optical compensation sheet or the elliptically polarizing plate, and a 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 modulus in the machine direction of the cellulose ester film is 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 elastic modulus in the direction perpendicular to the machine direction (lateral direction) of the cellulose ester film is 260 to 440 kgf / mm ² . The tensile modulus in the transverse direction is preferably 280 to 420, and more preferably 300 to 400 kgf / mm ² .
Furthermore, in the present invention, the ratio of the tensile modulus in the machine direction of the cellulose ester film / the tensile modulus in the direction perpendicular to the machine direction (lateral direction) is 0.80 to 1.36. The ratio of the tensile modulus in the machine direction / the tensile modulus in the transverse direction is preferably 0.84 to 1.32, and more preferably 0.88 to 1.28.

The thickness of the cellulose ester film is preferably 20 to 500 μm, and more preferably 50 to 200 μm.
The cellulose ester film is optically negative uniaxial, and the optical axis is preferably substantially parallel to the normal of the film surface.
The retardation value (Rth) in the thickness direction of the cellulose ester film is preferably 60 to 1000 nm.
The in-plane retardation value (Re) of the cellulose ester film is preferably -50 to 50 nm, and more preferably -20 to 20 nm.
The retardation value in the thickness direction is a value obtained by multiplying the birefringence index 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 values are the measurement results of the in-plane retardation with respect to the slow axis as the incident direction of the measurement light perpendicular to the film film surface, and the incident direction relative to the vertical direction relative to the film film surface. Obtained by extrapolating from the tilted measurement results. The measurement can be performed using an ellipsometer (for example, M-150: manufactured by JASCO Corporation). As the measurement wavelength, 550 nm is adopted.
The retardation value (Rth) in the thickness direction and the in-plane retardation value (Re) are calculated as follows.
Retardation value in the thickness direction (Rth) = {(nx + ny) / 2−nz} × d
In-plane retardation value (Re) = (nx−ny) × d
In the equation, nx is the refractive index in the machine direction in the film plane, ny is the refractive index in the direction (lateral direction) perpendicular to the machine direction in the film plane, and nz is the refractive index in the direction perpendicular to the film surface. And d is the film thickness (nm).

The birefringence {(nx + ny) / 2−nz} in the thickness direction is preferably 7 × 10 ^{−4 to} 4 × 10 ⁻³ , and preferably 1 × 10 ^{−3 to} 4 × 10 ^−3. , still more preferably it is 1.5 × 10 ^-3 to 4 × 10 ^-3, yet still more preferably from 2 × 10 ^-3 to 4 × 10 ^-3, 2 × 10 ^-3 to 3 X10 ⁻³ is most preferable, and 2 × 10 ^{−3 to} 2.5 × 10 ⁻³ is particularly preferable.
The cellulose ester film having the above tensile modulus and optical properties can be produced as follows.

As the cellulose ester, it is preferable to use a lower fatty acid ester of cellulose. 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 the physical properties of the film, the average degree of acetylation is more preferably 58.0% or more and less than 62.5%. However, when cellulose acetate having an average acetylation degree of 55.0% or more and less than 58.0% (preferably 57.0% or more and less than 58.0%) is used, a film having a high retardation in the thickness direction is produced. be able to.

It is preferable to produce a cellulose ester film by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) in which 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 contain.
The ether, ketone and ester 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 functional group.

Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.
Examples of 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 kinds of functional groups include 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 halogenated hydrocarbon hydrogen atoms substituted with halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is 40 to 60 mol%, and most preferably. Methylene chloride is a representative halogenated hydrocarbon.
Two or more organic solvents may be mixed and used.

A 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 (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solvent cast method. 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 the cellulose ester is adjusted so as to be contained in the obtained solution by 10 to 40% by weight. The amount of cellulose ester is more preferably 10 to 30% by weight. Arbitrary additives described later may be added to the organic solvent (main solvent).
The solution can be prepared by stirring the cellulose ester and the organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, the cellulose ester and the organic solvent are placed in a pressure vessel and sealed, and stirred while heating 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 200 ° C., more preferably 80 to 110 ° C.

Each component may be coarsely mixed in advance and then placed in a container. Moreover, you may put into a container sequentially. The container needs to be configured so that it can be stirred. The container can be pressurized by injecting an inert gas such as nitrogen gas. Moreover, you may utilize the raise of the vapor pressure of the solvent by heating. Or after sealing a container, you may add each component under pressure.
When heating, it is preferable to heat from the outside of the container. For example, a jacket type heating device can be used. The entire container can also be heated by providing a plate heater outside the container and piping to circulate the liquid.
It is preferable to provide a stirring blade inside the container and stir using this. The stirring blade preferably has a length that reaches the vicinity of the wall of the container. A scraping blade is preferably provided at the end of the stirring blade in order to renew the liquid film on the vessel wall.
Instruments such as a pressure gauge and a thermometer may be installed in the container. Each component is dissolved in a solvent in the container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.

A solution can also 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 the halogenated hydrocarbon) that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent (for example, halogenated hydrocarbon) which can melt | dissolve a cellulose ester with a normal melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly according to a cooling melt method. Further, when the cooling dissolution method is used, the retardation of the cellulose ester film to be produced becomes high.
In the cooling dissolution method, first, a cellulose ester is gradually added to an organic solvent with stirring at room temperature.
The amount of the cellulose ester is preferably adjusted so as to be contained in the mixture by 10 to 40% by weight. The amount of cellulose ester is more preferably 10 to 30% by weight. Furthermore, you may add the arbitrary additive mentioned later in a mixture.

The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 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.). When cooled in this manner, the mixture of cellulose ester and organic solvent solidifies.
The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling until the final cooling temperature is reached.

Further, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), the cellulose ester is dissolved in the organic solvent. The temperature may be increased by simply leaving it at room temperature or 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 higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. .
A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether or not the dissolution is sufficient can be determined by merely observing the appearance of the solution with the naked eye.

In the cooling dissolution method, it is desirable to use a sealed container in order to avoid moisture mixing due to condensation during cooling. In the cooling and heating operation, when the pressure is applied during cooling and the pressure is reduced during heating, the dissolution time can be shortened. In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container.
A 20 wt% solution of cellulose acetate (degree of acetylation: 60.9%, viscosity average degree of polymerization: 299) dissolved in methyl acetate by the cooling dissolution method was measured by differential scanning calorimetry (D
According to SC), there exists a quasi-phase transition point between a sol state and a gel state in the vicinity of 33 ° C., and a uniform gel state is obtained below this temperature. Therefore, this solution needs to be stored at a temperature equal to or higher than the pseudo phase transition temperature, preferably about the gel phase transition temperature plus about 10 ° C. However, this pseudo phase transition temperature varies depending on the average degree of acetylation, the degree of viscosity average polymerization, the concentration of the solution, and the organic solvent used.

From the prepared cellulose ester solution (dope), a cellulose ester film is produced by a solvent cast method.
The dope is cast on a drum or band, and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. As for casting and drying methods in the solvent casting method, U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.
The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferably dried by being exposed to wind for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting. The solution (dope) prepared according to the present invention satisfies this condition.
In addition, the extending | stretching process mentioned later can also be implemented simultaneously with this drying process.

A plasticizer can be added to the cellulose ester film in order to improve mechanical properties or increase the drying rate. As the plasticizer, phosphoric acid ester or carboxylic acid ester is used. Examples of phosphate esters include triphenyl phosphate (TPP) and tricresyl phosphate (TCP). Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of phthalic acid esters include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethyl hexyl phthalate (DEHP). Examples of citrate esters include triethyl O-acetylcitrate (OACTE) and tributyl O-acetylcitrate (OACTB). Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Phthalate plasticizers (DMP, DEP, DBP, DOP, DPP, DEHP) are preferably used. DEP and DPP are particularly preferred.
The addition amount of the plasticizer is preferably 0.1 to 25% by weight, more preferably 1 to 20% by weight, and most preferably 3 to 15% by weight of the amount of the cellulose ester.

Cellulose ester film contains retardation increasing agents, deterioration inhibitors (eg, antioxidants, peroxide decomposing agents, radical inhibitors, metal deactivators, acid scavengers, amines) and UV inhibitors as described below. It may be added. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The addition amount of the deterioration preventing agent is preferably 0.01 to 1% by weight of the solution (dope) to be prepared, and more preferably 0.01 to 0.2% by weight. When the addition amount is less than 0.01% by weight, the effect of the deterioration preventing agent is hardly recognized. When the added amount exceeds 1% by weight, bleed-out (bleeding) of the deterioration preventing agent to the film surface may be observed. As a particularly preferred example of the deterioration preventing agent, butylated hydroxytoluene (BHT) can be mentioned. The ultraviolet ray preventing agent is 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, and the produced film. There is a disadvantage that the physical properties are inferior. However, this drawback can be substantially eliminated by using the above-described deterioration preventing agent, particularly an antioxidant such as butylated hydroxytoluene (BHT).

[Stretching treatment of cellulose ester film]
In the above-described drying process of the solvent cast method, the cellulose ester film is preferably stretched by 0.1 to 20% in a direction perpendicular to the machine direction when the residual solvent amount of the cellulose ester film is 5 to 3% by weight.
However, in the film drying step, it is preferable that the film is not substantially stretched in the machine direction (stretching rate is 0 to 0.1%) in a state where the film temperature is equal to or higher than the glass transition temperature of the cellulose ester. . In other words, the stretching treatment of the above 0.1 to 20% stretching is preferably performed at a temperature where the film temperature is lower than the glass transition temperature of the cellulose ester. For this purpose, when the residual solvent amount of the cellulose ester film is 5 to 3% by weight, the film temperature 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 (transverse direction) / the stretching ratio in the machine direction is preferably 0.70 to 8.0, and more preferably 0.7 to 6.0. In order to obtain the above stretching ratio, it is preferable to perform a stretching process in the transverse direction on the cellulose ester film.
The stretching process in the transverse direction can be performed by drying the film while regulating the width of the roll film using a pin tenter. About the extending | stretching process of the horizontal direction using a pin tenter, Unexamined-Japanese-Patent No. 61-158413, 61-158414, and Unexamined-Japanese-Patent No. 4-1009 have description.

[Retardation raising agent]
It is preferable to add a retardation increasing agent to the cellulose ester film. As the retardation increasing agent, a compound having at least two aromatic rings and a molecular structure that does not sterically hinder the conformation of the two aromatic rings can be used. The retardation increasing agent is preferably used in the range of 0.01 to 20 parts by weight with respect to 100 parts by weight of the cellulose ester.
A compound having at least two aromatic rings has a π-bonding plane of 7 or more carbon atoms. Unless the steric hindrance of the conformation of the two aromatic rings, the two aromatic rings form the same plane. According to the study of the present inventor, in order to increase the retardation of the cellulose ester film, it is important to form the same plane by a plurality of aromatic rings.
In the present specification, the “aromatic ring” includes an aromatic heterocycle in addition to an aromatic hydrocarbon ring. The aromatic hydrocarbon ring is particularly preferably a 6-membered ring (that is, a benzene ring).

The aromatic heterocycle is generally an unsaturated heterocycle. The aromatic heterocycle is preferably a 5-membered ring, 6-membered ring or 7-membered ring, more preferably a 5-membered ring or 6-membered ring. Aromatic heterocycles generally have 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 aromatic heterocycles include 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, pyrazine ring and 1,3,5-triazine ring.
As the aromatic ring, benzene ring, furan ring, thiophene ring, pyrrole ring, oxazole ring, thiazole ring, imidazole ring, triazole ring, pyridine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring are preferable.

The number of aromatic rings contained in the retardation increasing agent is preferably 2 to 20, more preferably 2 to 12, still more preferably 2 to 8, and most preferably 2 to 6. preferable. In the case of having three or more aromatic rings, the conformation of at least two aromatic rings should not be sterically hindered.
The bond relationship between two aromatic rings can be classified into (a) a condensed ring, (b) a direct bond with a single bond, and (c) a bond through a linking group (for aromatic rings). , Spiro bonds cannot be formed). From the viewpoint of the retardation increasing function, any of (a) to (c) may be used. However, in the case of (b) or (c), it is necessary not to sterically hinder the conformation of the two aromatic rings.

Examples of the condensed ring (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, a 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, quinolidine ring, quinazoline ring, cinnoline ring, quinoxaline ring, phthalazine ring, pteridine ring, carbazole ring, acridine ring, phenanthridine ring, xanthene ring, phenazine ring, phenothiazine ring, phenoxathiin ring, phenoxazine ring and thiant It includes emissions ring. Naphthalene ring, azulene ring, indole ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring and quinoline ring are preferred.
The single bond (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be bonded with two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.

The linking group in (c) is also preferably bonded to carbon atoms of two aromatic rings. The linking group is preferably an alkylene group, an alkenylene group, an alkynylene group, —CO—, —O—, —NH—, —S—, or a combination thereof. Examples of linking groups composed of combinations are shown below. In addition, the relationship between the left and right 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, the substituent is required not to sterically hinder the conformation of the two aromatic rings. In steric hindrance, the type and position of substituents are problematic. As the type of the substituent, a sterically bulky substituent (for example, a tertiary alkyl group) tends 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 halogen atom (F, Cl, Br, 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 sulfonamido group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic Substituted sulfamoyl groups, aliphatic substituted ureido groups and non-aromatic heterocyclic groups are included.

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, 2-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 alkenyl groups 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 alkenyl group, and a linear alkynyl group is particularly preferable. The alkynyl group may further have a substituent. Examples of alkynyl groups include ethynyl, 1-butynyl and 1-hexynyl.

The aliphatic acyl group preferably has 1 to 10 carbon atoms. 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 number of carbon atoms of the alkoxy group is preferably 1 to 8. The alkoxy group may further have a substituent (eg, 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 number of carbon atoms of the alkoxycarbonylamino group is preferably 2 to 10. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino.

The alkylthio group preferably has 1 to 12 carbon atoms. 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 sulfonamido group include methanesulfonamido, butanesulfonamido and n-octanesulfonamido.
The number of carbon atoms of the aliphatic substituted amino group is preferably 1 to 10. 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 number of carbon atoms in the aliphatic substituted ureido group is preferably 2 to 10. Examples of the aliphatic substituted ureido group include methylureido.
Examples of non-aromatic heterocyclic groups include piperidino and morpholino.
The molecular weight of the retardation increasing agent is preferably 300 to 800. The boiling point of the retardation increasing agent is preferably 260 ° C. or higher.

[Surface treatment of cellulose ester film]
When the cellulose ester film is used as a transparent support, the cellulose ester film can be surface-treated. As the surface treatment, 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 0.01 to 1 μm, more preferably 0.02 to 0.5 μm, and most preferably 0.05 to 0.2 μm.

[Alignment film]
The alignment film is an organic compound (eg, ω-tricosanoic acid) formed by rubbing treatment of an organic compound (preferably polymer), oblique deposition of an inorganic compound, formation of a layer having a microgroove, or Langmuir-Blodgett method (LB film). , Dioctadecylmethylammonium chloride, methyl stearylate). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field, or light irradiation is also known. An alignment film formed by a polymer rubbing treatment is particularly preferable. The rubbing treatment is carried out by rubbing the surface of the polymer layer several times in a certain direction with paper or cloth.
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 many rod-like liquid crystal molecules in the liquid crystal cell are aligned substantially vertically, the liquid crystal molecules in the optically anisotropic layer are aligned substantially horizontally. An alignment film having a function is used. In a display mode in which many rod-like liquid crystal molecules in the liquid crystal cell are aligned substantially horizontally (eg, STN), the alignment has a function of aligning the liquid crystal molecules of the optically anisotropic layer substantially vertically. Use a membrane. In a display mode (eg, TN) in which many rod-like liquid crystalline molecules in the liquid crystal cell are substantially obliquely aligned, the alignment has a function of substantially obliquely aligning the liquid crystalline molecules of the optically anisotropic layer. Use a membrane.

Specific polymer types are described in the literature on optical compensation sheets using discotic liquid crystalline molecules corresponding to the various display modes described above.
The polymer used for the alignment film may be cross-linked to enhance the strength of 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. In addition, about bridge | crosslinking of the polymer used for an alignment film, Unexamined-Japanese-Patent No. 8-338913 has description.
The thickness of the alignment film is preferably 0.01 to 5 μm, and more preferably 0.05 to 1 μm.
In addition, after aligning the liquid crystalline molecules using the alignment film, the liquid crystalline molecules are fixed in the aligned state to form an optically anisotropic layer, and only the optically anisotropic layer is transferred onto the support. May be. The discotic liquid crystalline molecules fixed in the alignment state can maintain the alignment state even without the 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).

[Optically anisotropic layer]
The optically anisotropic layer is formed from liquid crystal molecules.
As the liquid crystal molecule, a rod-like liquid crystal molecule or a discotic liquid crystal molecule is preferable, and a discotic liquid crystal molecule is particularly preferable.
Examples of rod-like liquid crystalline molecules 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. In addition to the above low-molecular liquid crystalline molecules, high-molecular liquid crystalline molecules can also be used. The high-molecular liquid crystalline molecule is a polymer having a side chain corresponding to the above low-molecular liquid crystalline molecule. An optical compensation sheet using polymer liquid crystalline molecules is described in JP-A-5-53016.

Discotic liquid crystalline molecules are described in various literature (C. Destrade et al., Mol. Crysr. Liq.
Cryst., Vol. 71, page 111 (1981); 22, Liquid Crystal Chemistry, Chapter 5, Chapter 10 Section 2 (1994); B. Kohne et al., Angew. Chem. Soc. Chem. Comm., Page 1794 (1985); J. Zhang et al. , J. Am. Chem. Soc., Vol. 116, page 2655 (1994)). The polymerization of discotic liquid crystalline molecules is described in JP-A-8-27284.
In order to fix the discotic liquid crystalline molecules by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline molecules. However, when the polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain the orientation state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Accordingly, the discotic liquid crystalline molecule is preferably a compound represented by the following formula (I).

(I)
D (-LP) n
Where D is a discotic core; L is a divalent linking group; P is a polymerizable group; and n is an integer from 4 to 12.
Examples of the disk-shaped core (D) of the formula (I) are 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).

In the formula (I), the divalent linking group (L) is selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. A divalent linking 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 alkenylene group, an arylene group, —CO—, —NH—, —O—, and —S—. More preferably, it is a group. 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 number of carbon atoms in the arylene group is preferably 6 to 10. The alkylene group, alkenylene group and arylene group may have a substituent (eg, alkyl group, halogen atom, cyano, alkoxy group, 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-O-CO-
L20: -O-CO-AR-O-AL-O-AL-O-AL-O-CO-
L21: -S-AL-
L22: -S-AL-O-
L23: -S-AL-O-CO-
L24: -S-AL-S-AL-
L25: -S-AR-AL-

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

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

The polymerizable group (P) is preferably an unsaturated polymerizable group (P1, P2, P3, P7, P8, P15, P16, P17) or an epoxy group (P6, P18). More preferably, it is most preferably an ethylenically unsaturated polymerizable group (P1, P7, P8, P15, P16, P17).
In the formula (I), n is an integer of 4 to 12. A specific number is determined according to the type of discotic core (D). In addition, although the combination of several L and P may differ, it is preferable that it is the same.

Two or more kinds of discotic liquid crystal molecules may be used in combination. For example, a polymerizable discotic liquid crystalline molecule and a non-polymerizable discotic liquid crystalline molecule as described above can be used in combination.
The non-polymerizable discotic liquid crystalline molecule is preferably a compound in which the polymerizable group (P) of the polymerizable discotic liquid crystalline 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
Where D is a discotic core; L is a divalent linking group; R is a hydrogen atom or an alkyl group; and n is an integer from 4 to 12.
The example of the discotic core (D) of the formula (II) is the same as the example of the polymerizable discotic liquid crystal molecule except that LP (or PL) is changed to LR (or RL).
Examples of the divalent linking group (L) are the same as the examples of the polymerizable discotic liquid crystal molecules.
The alkyl group for R preferably has 1 to 40 carbon atoms, and more preferably 1 to 30 carbon atoms. A chain alkyl group is preferred to a cyclic alkyl group, and a linear alkyl group is preferred to 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 a liquid crystalline molecule, or the following polymerizable initiator or any additive (eg, plasticizer, monomer, surfactant, cellulose ester, 1,3,5-triazine compound, chiral agent). It is formed by applying a coating solution containing, onto 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, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane), 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.
The coating liquid can be applied by a known method (eg, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).

The liquid crystalline molecules are preferably substantially uniformly aligned, more preferably fixed in a substantially uniformly aligned state, and the liquid crystalline 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. A photopolymerization reaction is preferred.
Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Acridine and phenazine compounds (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,212,970).
The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight, more preferably 0.5 to 5% by weight, based on the solid content of the coating solution.
Light irradiation for polymerization of discotic liquid crystalline molecules is preferably performed using ultraviolet rays.
The irradiation energy is preferably 20 mJ / cm ^{2 to} 50 J / cm ² , and more preferably 100 to 800 mJ / cm ² . In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.

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, and more preferably 1 to 5 μm. However, depending on the mode of the liquid crystal cell, the optically anisotropic layer may be thickened (3 to 10 μm) in order to obtain high optical anisotropy. According to the inventor's research, the thickness is more preferably 0.5 to 5 μm, and most preferably 1 to 5 μm.
As described above, the alignment state of the liquid crystalline 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 controlled by the type of liquid crystal molecules, the type of alignment film, and the use of additives (eg, plasticizers, binders, surfactants) in the optically anisotropic layer. The

[Liquid Crystal Display]
The optical compensation sheet or the integral elliptical polarizing plate using the cellulose ester film of the present invention includes TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), OCB (Optically Compensatory Bend), STN ( It can be used for liquid crystal display devices of various display modes such as Supper Twisted Nematic (VA), VA (Vertically Aligned), 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) that requires 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 comprises a polarizing film and a protective film.
Examples of the polarizing film include an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film. The iodine polarizing film and the dye polarizing film are generally manufactured using a polyvinyl alcohol film. The polarization axis of the polarizing film corresponds to a direction perpendicular to the film stretching direction.
The protective film is 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 (form an integral elliptically polarizing plate). As the protective film on the other side, it is preferable to use a (normal) cellulose ester film.

[Example 1]
(Preparation of cellulose ester film)
The following composition was put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose ester solution.

────────────────────────────────────────
Cellulose ester solution composition ────────────────────────────────────────
Cellulose acetate having an acetylation degree of 60.9% 100 parts by weight Triphenyl phosphate (plasticizer) 7.8 parts by weight Biphenyl diphenyl phosphate (plasticizer) 3.9 parts by weight Methylene chloride (first solvent) 300 parts by weight Methanol (No. 1) 2 solvents) 54 parts by weight 1-butanol 11 parts by weight ────────────────────────────────────── ──

  The following composition was put into another mixing tank and stirred while heating to dissolve each component to prepare a retardation increasing agent solution.

────────────────────────────────────────
Retardation raising agent solution composition ─────────────────────────────────────────
2-hydroxy-4-benzyloxybenzophenone (retardation increasing agent)
12 parts by weight 2,4-benzyloxybenzophenone (retardation increasing agent) 4 parts by weight Methylene chloride 80 parts by weight Methanol 20 parts by weight ────────────────────── ──────────────────

A dope was prepared by adding 22 parts by weight of the retardation increasing agent solution to 474 parts by weight of the cellulose ester solution and stirring sufficiently. The total amount of the two types of retardation increasing agents is 3 parts by weight with respect to 100 parts by weight of cellulose acetate.
The dope was cast from a casting port onto a drum cooled to 0 ° C. The film is peeled off at a solvent content of 70% by weight, and both ends in the width direction of the film are fixed with a pin tenter (a pin tenter described in FIG. 3 of JP-A-4-1009), and the solvent content is 3 to 5% by weight. Then, it was dried while maintaining an interval at which the stretching ratio in the transverse direction (direction perpendicular to the machine direction) was 3%. After that, it is further dried by transporting between the rolls of the heat treatment apparatus, and in the region where the glass transition temperature exceeds 120 °, the stretching rate in the machine direction is substantially 0% (4% stretching in the machine direction when stripping. A cellulose acetate film having a thickness of 107 μm was prepared by adjusting the ratio of the stretching ratio in the transverse direction and the stretching ratio in the machine direction to 0.75.
The produced film has a tensile modulus in the machine direction of 430 kgf / mm ² , a tensile modulus in the direction perpendicular to the machine direction is 360 kgf / mm ² , and a tensile modulus in the machine direction / perpendicular to the machine direction. The ratio of tensile modulus in the direction was 1.19. The thickness direction retardation (Rth) was 80 nm, and the in-plane retardation (Re) was 17 nm. In addition, precipitation of the retardation increasing agent was not recognized at all in the processing after film production described later as well as immediately after production.

(Formation of first undercoat layer)
The produced 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 the first undercoat 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 undercoating layer, the coating solution having the following composition 7 ml / m ² was applied to form a second undercoating layer and dried.

────────────────────────────────────────
Composition of the second undercoat coating solution ────────────────────────────────────────
The following anionic polymers 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 ──────────────── ────────────────────────

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

────────────────────────────────────────
Back layer coating composition ────────────────────────────────────────
Cellulose diacetate with 55% acetylation 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 modified polyvinyl alcohol aqueous solution was applied, dried with warm air at 80 ° C., and then rubbed to form an alignment film.

(Formation of optically anisotropic layer)
1.8 g of the following discotic liquid crystalline compound, 0.2 g of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), cellulose acetate butyrate (CAB531-1.0, Eastman Chemical) 0.04 g of photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Japan) and 0.02 g of sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.), 8.43 g of methyl ethyl ketone. A coating solution was prepared by dissolving in The coating solution was applied onto the alignment film with a # 2.5 wire bar. In a state where this was affixed to a metal frame, it was heated in a thermostatic bath at 130 ° C. for 2 minutes to align the discotic liquid crystalline compound. While maintaining a temperature of 130 ° C., ultraviolet rays were irradiated for 1 minute using a 120 W / cm high-pressure mercury lamp to polymerize the vinyl group of the discotic liquid crystalline compound, and the alignment state was fixed. Then, it stood to cool to room temperature.
In this way, an optical compensation sheet was produced. The thickness of the optically anisotropic layer was 1.0 μm.

(Preparation of transparent protective film)
A triacetylcellulose film having a thickness of 80 μm was produced in the same manner as the production of the transparent support, except that the discotic compound (retardation increasing agent) was not added. This was used as a transparent protective film. Similar to the transparent support, a first undercoat layer and a second undercoat layer were provided on one surface of the transparent protective film.

(Production of elliptically polarizing plate)
Iodine was adsorbed on the 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 in parallel. In this manner, an elliptically polarizing plate was produced.

(Production of liquid crystal display device)
A polyimide alignment film was provided on a glass substrate on which an ITO transparent electrode was provided, and a rubbing treatment was performed. The two substrates were stacked with a 5 μm spacer so that the alignment films face each other. The orientation of the substrate was adjusted so that the rubbing directions of the alignment film were orthogonal. A rod-like liquid crystal molecule (ZL4792, manufactured by Merck & Co., Inc.) was injected into the gap between the substrates to form a liquid crystal layer. The Δn of the liquid crystal molecule was 0.0969.
An elliptically polarizing plate was attached to both sides of the TN liquid crystal cell produced as described above so that the optically anisotropic layer faced the substrate to produce a liquid crystal display device. The slow axis of the laminate of the optically anisotropic layer and the transparent support and the rubbing direction of the liquid crystal cell were arranged to be orthogonal to each other.
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. Cellulose with a solvent content of 70% by weight is dried off and dried under the conditions that the stretching ratio in the machine direction is 6% and the stretching ratio in the lateral direction (direction perpendicular to the machine direction) is 0%. An acetate film was prepared.
The produced film has a tensile modulus in the machine direction of 410 kgf / mm ² , a tensile modulus in the direction perpendicular to the machine direction is 300 kgf / mm ² , and a tensile modulus in the machine direction / perpendicular to the machine direction. The ratio of the tensile modulus in the direction was 1.37. The thickness direction retardation (Rth) was 85 nm, and the in-plane retardation (Re) was 25 nm.
An optical compensation sheet, an elliptically polarizing plate and a liquid crystal display device were sequentially produced in the same manner as in Example 1 except that the produced 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 produced in Example 1.

BL Backlight RP Reflector 1a, 1b, 1c Transparent protective film 2a, 2b Polarizing film 3a, 3b Transparent support 4a, 4b Optical anisotropic layer 5a Lower substrate of liquid crystal cell 5b Upper substrate of liquid crystal cell 6 Rod-like liquid crystalline molecule Liquid crystal layer consisting of

Claims (8)

  This is a method for producing a cellulose ester film by the solvent cast method, and in the drying step of the solvent cast method, when the film temperature is higher than the glass transition temperature of the cellulose ester, it is not substantially stretched in the machine direction. If the temperature of the film is lower than the glass transition temperature of the cellulose ester, the amount of residual solvent is 5 to 3% by weight, and the direction perpendicular to the machine direction. A method for producing a cellulose ester film, which is produced by stretching 0.1 to 20%. The produced cellulose ester film has a tensile modulus in the machine direction of 360 to 480 kgf / mm ² , a tensile modulus in the direction perpendicular to the machine direction of 260 to 440 kgf / mm ² , and a tensile elasticity in the machine direction. The method according to claim 1, wherein the ratio of the tensile modulus in the direction perpendicular to the modulus / machine direction is 0.80 to 1.36.   The in-plane retardation value of the produced cellulose ester film is -50 to 50 nm, the retardation value in the thickness direction is 60 to 1000 nm, and the thickness is 50 to 200 µm. Production method.   The stretch ratio in the direction perpendicular to the machine direction / stretch ratio in the machine direction including the stretch in the machine direction at the time of stripping is stretched so as to be 0.70 to 8.0. Manufacturing method.   The production method according to claim 1, wherein the cellulose ester film contains 0.01 to 20% by weight of a compound having a molecular structure which has at least two aromatic rings and does not sterically hinder the conformation of the two aromatic rings. .   The production method according to claim 1, wherein the produced cellulose ester film is optically negative uniaxial, and the optical axis is substantially parallel to the normal of the film surface.   The production method according to claim 1, wherein the cellulose ester is cellulose acetate.   The solvent of the cellulose ester solution used in the solvent casting method is an ether having 3 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms, an ester having 3 to 12 carbon atoms, and an ester having 1 to 6 carbon atoms. The production method according to claim 1, which is selected from the group consisting of halogenated hydrocarbons.

Images