JP4485301B2 - Cellulose ester film and laminated retardation plate - Google Patents

Description

  The present invention relates to a cellulose ester film having a negative retardation in a film thickness direction, an optical compensation sheet using the same, a polarizing plate, and a liquid crystal display device.

The cellulose ester film is used in a support for a silver halide photographic material, a retardation plate (optical compensation sheet), a support for a retardation plate, a protective film for a polarizing plate, and a liquid crystal display device.
The cellulose ester film is generally produced by a solvent cast method or a melt cast method. In the solvent cast method, a film having a surface shape superior to that of the melt cast method having a problem such as die streaking can be produced. Therefore, the solvent cast method is mainly employed in the cellulose ester film. The retardation (Rth) in the film thickness direction of the cellulose ester film usually shows a positive value, and the Rth can be lowered by significantly increasing the substitution degree of the cellulose ester, but at the same time, the solubility in an organic solvent is very high. To drop.

  The solvent of the cellulose ester used for the solvent casting method is generally an organic solvent, and a chlorinated hydrocarbon such as dichloromethane is mainly used. However, since a cellulose ester having a very high degree of substitution (for example, a degree of substitution of 2.87 or more) is poor in solubility, the cellulose ester is swollen in a halogen-based organic solvent, which is a conventional dissolution method, and then room temperature. Even if you try to dissolve it in the process of stirring at a temperature close to, it is very difficult to dissolve, and not only a solution with a practically sufficient concentration can be obtained, but also a film for optical use with excellent surface shape It was not possible to form a film.

On the other hand, instead of the conventional dissolution method, a method of dissolving a cellulose ester at a low temperature, that is, a cooling dissolution method has been proposed (for example, see Non-Patent Document 1). According to the report, cellulose acetate (degree of acetylation 60.1% to 61.3%) is cooled to −80 ° C. to −70 ° C. in acetone and then heated to 0.5 to 5% by mass. A dilute solution of is obtained. As an application of the obtained solution, a spinning technique has been proposed (see, for example, Non-Patent Document 1).
Furthermore, it has also been proposed to produce a cellulose ester film using a solution obtained by a cooling dissolution method (see, for example, Patent Documents 1 to 3).
Therefore, by applying a cooling dissolution method to an organic solvent containing a halogenated hydrocarbon that is superior in solubility to cellulose ester than acetone, it is possible to sufficiently dissolve a highly substituted cellulose ester having poor solubility, It is expected that a cellulose ester film having a negative Rth can be obtained.

  On the other hand, there is disclosed a method for continuously producing a film having negative Rth by adhering a heat-shrinkable film to a light-transmitting film and subjecting the film to heat stretching (for example, see Patent Document 4). In this method, the production rate cannot be sufficiently increased, and a large amount of heat-shrinkable film is generated during production, so that the productivity is not sufficient. Furthermore, there is a problem of variation depending on the location of retardation of the obtained film, and this problem is particularly remarkable in a polymer having a high elastic modulus such as cellulose ester.

Makromol. chem. 143, 105, 1971 Journal of the Textile Machinery Society, 34, 57-61, 1981 JP-A-9-95538 JP-A-9-95544 JP-A-9-95557 Japanese Patent Laid-Open No. 2000-23310

  When the cellulose ester film is used for optical applications such as a retardation plate (optical compensation sheet), a polarizing plate and a liquid crystal display device, its optical anisotropy is very important. In general, cellulose ester film is easy to control in-plane retardation (Re) within the range of (intrinsic birefringence × film thickness), but is difficult to control retardation in the thickness direction (Rth). Yes. In particular, it was very difficult to produce a cellulose ester film such that the retardation in the thickness direction was a negative value.

  In a display device using a cellulose ester film as an optical material, the retardation value of the cellulose ester film is a very important parameter that determines the performance (for example, visibility) of the display device. There are many types of panel display modes and configurations for members of liquid crystal display devices (for example, optical compensation sheets and polarizing plates). The optimum retardation value varies depending on the display mode and configuration. Therefore, when a cellulose ester film is used as a retardation film (optical compensation sheet), a support for the retardation film or a protective film for the polarizing plate, it is necessary to prepare a large number of cellulose ester films having various retardations.

  An object of the present invention is to provide a cellulose ester film that can be used for adjusting a retardation value by bonding with a cellulose ester film having a positive Rth as conventionally known. By using the film thus obtained, it is also possible to provide a retardation plate and a polarizing plate in which the retardation value is adjusted, and to provide a liquid crystal display device excellent in visibility. In addition, like the conventional triacetyl cellulose (TAC) film, the film of the present invention having an appropriate water vapor transmission rate is provided as a protective film for a polarizing plate having the function of a retardation plate. It is also to provide a plate and provide an excellent liquid crystal display device.

The present invention provides the cellulose ester film of the following (1) to (3) and the laminated retardation plate of the following (4) .

(1) A cellulose ester film comprising an ester of cellulose and a lower fatty acid having 2 to 4 carbon atoms and having a thickness direction retardation value of −600 nm to −1 nm measured at a wavelength of 589 nm .
(2) The cellulose ester film according to (1), wherein the retardation value in the thickness direction is −400 nm to −5 nm .
(3) The cellulose ester film according to (1) or (2), comprising a cellulose ester having a substitution degree with an acetyl group of 2.87 or more .

(4) Cellulose ester film having a negative retardation value in the thickness direction and a cellulose ester film having a positive retardation value in the thickness direction, and having a negative retardation value in the thickness direction A laminated phase difference plate , wherein the ester film is the cellulose ester film described in (1) .

[Retardation]
In the following description, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at a wavelength λ, respectively. A value in the range of 450 to 750 nm is usually used for the wavelength λ. In this specification, a value of 589 nm is used.
Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA · 21ADH (manufactured by Oji Scientific Instruments). Rth (λ) is a wavelength λnm from a direction inclined by + 40 ° with respect to the normal direction of the film, with Re (λ) and an in-plane slow axis (determined by KOBRA · 21ADH) as an inclination axis (rotation axis). The retardation value measured with the incident light and the in-plane slow axis as the tilt angle (rotation axis), measured with the light of wavelength λ nm incident from a direction inclined by -40 ° with respect to the film normal direction KOBRA · 21ADH is calculated based on the retardation values measured in a total of three directions. Here, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. Examples of the average refractive index values of main optical films are given below.

Cellulose acylate: 1.48
Cycloolefin polymer: 1.52
Polycarbonate: 1.59
Polymethyl methacrylate: 1.49
Polystyrene: 1.59
By inputting these assumed values of average refractive index and film thickness, KOBRA · 21ADH calculates nx, ny, and nz. Nz = (nx−nz) / (nx−ny) can also be calculated based on the calculated values of ny, ny, and nz.

[Retardation variation]
The dispersion of the retardation value is 100 m in the longitudinal direction at 5 points in the width direction of the film (center, end (5% of the total width from both ends) and 2 points in the middle and end). sampled every, removed sample of 2 cm ² size, which is the difference between the maximum value and the minimum value of the retardation value of each point was determined according to the method described above. In addition, in the case of {(sample winding length) / 100} <10, sampling was performed for each one-tenth of the total length.

[Moisture permeability]
Moisture permeability is measured by changing the mass change (g / g) before and after conditioning the cup with calcium chloride covered with each film sample and sealed for 24 hours under conditions of 40 ° C. and 90% RH. (M ² · day)) is a value obtained by evaluating the moisture permeability of the film.

[Tensile modulus]
A sample having a length of 150 mm and a width of 10 mm was measured at an initial sample length of 100 mm and a tensile speed of 10 mm / min in accordance with the standard of ISO1184-1983, and the tensile elastic modulus was determined.

The present inventor has succeeded in continuously obtaining a high-quality cellulose ester film having a negative Rth value by devising the primary structure of the cellulose ester and devising a film forming method.
It is difficult to control the retardation (Rth) in the thickness direction of the cellulose ester film by adjusting the conditions in the production process, and it is particularly difficult to reduce Rth. However, if there is a cellulose ester film in which Rth has a negative value, it can be used as it is as an optical film for improving the visibility of an IPS mode liquid crystal display device, and the conventionally known Rth is positive. Rth can be easily controlled by laminating with a cellulose ester film having a value. For example, a film having an Rth of zero can be provided by bonding two films having the same absolute value of Rth but different signs.

These films with adjusted retardation values can be used as they are as retardation plates. Furthermore, since the cellulose ester film of the present invention has an appropriate water vapor transmission rate as in the case of the conventional TAC film, even when the film is used singly or when a plurality of films are laminated, the retardation film is used. It can be provided as a protective film of a polarizing plate having the functions of, more preferably as a protective film disposed between the polarizer and the liquid crystal layer, and as a result, a high-functional polarizing plate can be provided, An excellent liquid crystal display device can be provided.
A biaxially stretched polystyrene film is well known as a polymer film having a negative Rth value. However, a polystyrene film and a cellulose ester film have different physical properties such as an expansion coefficient and optical properties such as a refractive index. Therefore, when a polystyrene film and a cellulose ester film are bonded together, a problem due to a difference in physical properties (for example, curl) or a problem due to a difference in optical properties (for example, a decrease in transmittance) occurs. When a polystyrene film is used alone, the brittleness of the film is also a problem.

Also known as a polymer film having negative Rth is a polycarbonate film produced by bonding a heat-shrinkable polypropylene film on both sides and subjecting it to a heat stretching treatment. However, problems due to the low moisture permeability of polycarbonate films (for example, if this is used as a protective film for polarizing plates, polarizers containing water will not dry properly, so a polarizing plate with sufficient degree of polarization will be produced. ) And problems due to low elastic modulus and high photoelasticity (for example, partial blanking when formed into a panel) are not preferable.
By using the cellulose ester film having a negative Rth value obtained by the present invention, it is used as a retardation film, an optical compensation sheet or a support thereof, and a protective film for a polarizing plate without causing the above-mentioned problems. It has become possible to freely control the Rth of the film to be produced. By using these retardation plates, optical compensation sheets, or polarizing plates, a highly reliable image display device can be obtained.

[Cellulose ester]
The cellulose ester film of the present invention is a film containing a cellulose ester compound and a compound having an ester-substituted cellulose skeleton obtained by introducing a functional group biologically or chemically using cellulose as a raw material. Among these, a cellulose acylate film is more preferable.
Cellulose ester is an ester of cellulose and acid. The acid constituting the ester is preferably an organic acid, more preferably a carboxylic acid, more preferably a fatty acid having 2 to 22 carbon atoms, still more preferably a lower fatty acid having 2 to 4 carbon atoms, and most preferably acetic acid. .

Cellulose acylate is an ester of cellulose and carboxylic acid. In the cellulose acylate, all or a part of the hydrogen atoms of the hydroxyl group present at the 2-position, 3-position and 6-position of the glucose unit constituting the cellulose are substituted with an acyl group. Examples of acyl groups include acetyl, propionyl, butanoyl, isobutanoyl, t-butanoyl, heptanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl, cyclohexanecarbonyl, oleoyl, benzoyl , Naphthylcarbonyl, and cinnamoyl. Acetyl, propionyl, butanoyl, dodecanoyl, octadecanoyl, t-butanoyl, oleoyl, benzoyl, naphthylcarbonyl and cinnamoyl are preferred, acetyl, propionyl and butanoyl are more preferred, and acetyl is most preferred.
The cellulose ester may be an ester of cellulose and a plurality of acids. The cellulose acylate may be substituted with a plurality of acyl groups.

  The substitution degree of the cellulose ester is preferably 2.87 or more, more preferably 2.87 to 2.96, further preferably 2.88 to 2.95, and 2.90 to 2.95. Most preferred.

  The basic principle of the cellulose ester synthesis method is described in Nobuhiko Umeda et al., Wood Chemistry pages 180-190 (Kyoritsu Shuppan, 1968). A typical synthesis method of cellulose acylate is a liquid phase acetylation method using a carboxylic acid anhydride-acetic acid-sulfuric acid catalyst. Specifically, cellulose raw materials such as cotton linter and wood pulp are pretreated with an appropriate amount of acetic acid, and then put into a pre-cooled carboxylic acid mixture to be esterified to complete cellulose acylate (2nd, 3rd and 6th). The total degree of acyl substitution at the position is approximately 3.00). The carboxylated mixed solution generally contains acetic acid as a solvent, carboxylic anhydride as an esterifying agent, and sulfuric acid as a catalyst. The carboxylic anhydride is usually used in a stoichiometric excess over the sum of the cellulose that reacts with it and the water present in the system.

  After the acylation reaction is completed, a neutralizing agent (for example, calcium, magnesium, iron, aluminum or zinc carbonate) is used to partially neutralize the hydrolysis and esterification catalyst of excess carboxylic anhydride remaining in the system. Salt, acetate or oxide) in water. Next, the obtained complete cellulose acylate is saponified and aged by maintaining it at 50 to 90 ° C. in the presence of a small amount of an acetylation reaction catalyst (generally, remaining sulfuric acid) to obtain a desired acyl substitution degree and polymerization. The cellulose acylate having a degree is changed. When the desired cellulose acylate is obtained, the catalyst remaining in the system is completely neutralized with a neutralizing agent as described above, or in water or dilute sulfuric acid without neutralization. The cellulose acylate solution is added (or water or dilute sulfuric acid is added into the cellulose acylate solution) to separate the cellulose acylate, and the cellulose acylate is obtained by washing and stabilizing treatment.

  The degree of polymerization of the cellulose ester is preferably 200 to 700, more preferably 250 to 550, still more preferably 250 to 400, and most preferably 250 to 350 in terms of viscosity average degree of polymerization. The viscosity average degree of polymerization can be measured according to Uda et al.'S limiting viscosity method (Kazuo Uda, Hideo Saito, Journal of Textile Science, Vol. 18, No. 1, pages 105-120, 1962). A method for measuring the viscosity average degree of polymerization is also described in JP-A-9-95538.

A cellulose ester having a small amount of low molecular components has a high average molecular weight (degree of polymerization), but its viscosity is lower than that of a normal cellulose ester. A cellulose ester having a small amount of low molecular components can be obtained by removing low molecular components from a cellulose ester synthesized by an ordinary method. The removal of the low molecular component can be performed by washing the cellulose ester with an appropriate organic solvent. In addition, a cellulose ester having a small amount of low molecular components can be synthesized. When producing a cellulose ester having a small amount of low molecular components, the amount of sulfuric acid catalyst in the acetylation reaction is preferably adjusted to 0.5 to 25 parts by mass with respect to 100 parts by mass of cellulose. When the amount of the sulfuric acid catalyst is in the above range, a cellulose ester that is preferable also in terms of molecular weight distribution (uniform molecular weight distribution) can be synthesized.
The raw material cotton and the synthesis method of cellulose ester are also described in pages 7 to 12 of published technical bulletin 2001-1745 (issued on March 15, 2001, Invention Association).

[Cellulose ester film]
In the cellulose ester film, the polymer component constituting the film is preferably substantially composed of a cellulose ester. “Substantially” means 55% by mass or more (preferably 70% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more) of the polymer component. Two or more types of cellulose esters may be used in combination with the cellulose ester film.
The cellulose ester film is preferably produced by a solvent cast method using a cellulose ester solution.

[State of cellulose ester]
As a raw material of the cellulose ester solution, it is preferable to use cellulose ester particles. 90% by mass or more of the particles to be used preferably have a particle diameter of 0.5 to 5 mm. Further, it is preferable that 50% by mass or more of the particles to be used have a particle diameter of 1 to 4 mm. The cellulose ester particles preferably have a shape as close to a sphere as possible.
The cellulose ester used for the preparation of the cellulose ester solution preferably has a moisture content of 2% by mass or less, more preferably 1% by mass or less, and most preferably 0.7% by mass or less. Cellulose esters generally have a water content of 2.5-5% by weight. Therefore, it is preferable to use the cellulose ester after drying it.

[solvent]
The main solvent of the cellulose ester solution is preferably an organic solvent, more preferably a halogenated hydrocarbon, still more preferably a chlorinated hydrocarbon, still more preferably dichloromethane and chloroform, and most preferably dichloromethane. In addition, the main solvent of a cellulose ester solution indicates that solvent when it is composed of a single solvent, and when it is composed of a plurality of solvents, it is the solvent having the highest mass fraction among the constituent solvents. It shows that.
Examples of the organic solvent used in combination with these main solvents include esters, ketones, ethers, alcohols and hydrocarbons. The organic solvent preferably has 1 to 12 carbon atoms. The ester, ketone, ether, alcohol and hydrocarbon may have a branched structure or a cyclic structure. A compound having any two or more of ester, ketone, ether, and alcohol functional groups (that is, —O—, —CO—, —COO—, —OH) can also be used as the solvent. The hydrogen atom in the hydrocarbon moiety of the ester, ketone, ether and alcohol may be substituted with a halogen atom (particularly a fluorine atom).

Examples of the ester having 2 to 12 carbon atoms include methyl formate, ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate, and pentyl acetate.
Examples of the ketone having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone.
Examples of ethers having 3 to 12 carbon atoms are diethyl ether, methyl-t-butyl ether, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, 4-methyldioxolane, tetrahydrofuran, Contains anisole and phenetole.

Examples of alcohols having 1 to 12 carbon atoms are methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-methyl-2-butanol, Includes cyclohexanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, 2,2,3,3-tetrafluoro-1-propanol.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol, 2-butoxyethanol, and methyl acetoacetate.
Examples of the hydrocarbon having 6 to 12 carbon atoms include n-pentane, cyclohexane, hexane, benzene, toluene and xylene.

Particularly preferred organic solvents are dichloromethane, methyl formate, ethyl formate, methyl acetate, acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, cyclohexane. Hexanol, methyl acetoacetate, hexane and cyclohexane.
Among these, it is preferable from a viewpoint of the solubility improvement of a cellulose ester to contain at least 10-30 mass% in all the solvents, More preferably, 11-30 mass%, More preferably, 12-25 mass% alcohol is contained.
Further, from the viewpoint of reducing Rth, an organic solvent which is a poor solvent for cellulose ester having a small volatilization ratio with the halogenated hydrocarbon at the initial stage of the drying process and having a boiling point of 95 ° C. or higher is gradually added to all the solvents. -10% by mass, more preferably 1.5-8% by mass, still more preferably 2-6% by mass.
The organic solvent having a boiling point of 95 ° C. or higher is preferably an alcohol from the viewpoint of reducing the peeling load from the band and reducing Rth, and the alcohol is composed of two or more alcohols from the viewpoint of improving productivity by reducing the drying load. The mixture preferably comprises an alcohol having a boiling point of 95 ° C. or higher and an alcohol having a boiling point of less than 95 ° C.
Although the example of the combination of the organic solvent preferably used in this invention is given below, it is not limited to these. The numerical value of a ratio is a mass part.

(1) Dichloromethane / methanol / ethanol / butanol = 80/10/5/5
(2) Dichloromethane / acetone / methanol / propanol = 80/10/5/5
(3) Dichloromethane / methanol / butanol / cyclohexane = 75/10/5/5/5
(4) Dichloromethane / methyl ethyl ketone / methanol / butanol = 80/10/5/5

(5) Dichloromethane / acetone / methyl ethyl ketone / ethanol / isopropanol = 68/10/10/5/7
(6) Dichloromethane / cyclopentanone / methanol / isopropanol = 77/10/5/8
(7) Dichloromethane / methyl acetate / butanol = 80/10/10
(8) Dichloromethane / cyclohexanone / methanol / hexane = 70/20/5/5

(9) Dichloromethane / methyl ethyl ketone / acetone / methanol / ethanol = 50/20/20/5/5
(10) Dichloromethane / 1,3-dioxolane / methanol / ethanol = 70/20/5/5
(11) Dichloromethane / dioxane / acetone / methanol / ethanol = 60/20/10/5/5
(12) Dichloromethane / acetone / cyclopentanone / ethanol / isobutanol / cyclohexane = 65/10/10/5/5/5

(13) Dichloromethane / methyl ethyl ketone / acetone / methanol / ethanol = 70/10/10/5/5
(14) Dichloromethane / acetone / ethyl acetate / ethanol / butanol / hexane = 65/10/10/5/5/5
(15) Dichloromethane / methyl acetoacetate / methanol / ethanol = 65/20/10/5
(16) Dichloromethane / cyclopentanone / ethanol / butanol = 65/20/10/5
(17) Dichloromethane / methanol / butanol / cyclohexane = 80/10/5/5
(18) Dichloromethane / acetone / methyl ethyl ketone / ethanol / butanol = 68/10/10/7/5

(19) Dichloromethane / cyclopentanone / methanol / pentanol = 80/2/15/3
(20) Dichloromethane / methyl acetate / ethanol / butanol = 70/12/15/3
(21) Dichloromethane / cyclohexanone / methanol / pentanol = 80/2/15/3
(22) Dichloromethane / methyl ethyl ketone / acetone / methanol / pentanol = 50/20/20/5/5
(23) Dichloromethane / 1,3-dioxolane / methanol / butanol = 70/20/5/5
(24) Dichloromethane / dioxane / acetone / methanol / butanol = 80/2/10/5/3

(25) Dichloromethane / acetone / cyclopentanone / ethanol / isobutanol / cyclohexane = 60/18/3/15/2/2
(26) Dichloromethane / methyl ethyl ketone / acetone / methanol / isobutanol = 70/10/10/5/5
(27) Dichloromethane / acetone / ethyl acetate / ethanol / butanol / hexane = 69/10/10/5/5/1
(28) Dichloromethane / methyl acetoacetate / methanol / isobutanol = 65/20/10/5
(29) Dichloromethane / cyclopentanone / ethanol / butanol = 86/2/10/2

[Solution concentration]
The concentration of the cellulose ester solution to be prepared is preferably 10 to 30% by mass, more preferably 13 to 27% by mass, and most preferably 15 to 25% by mass.
The cellulose ester can be adjusted to a predetermined concentration at the stage of dissolution in a solvent. Alternatively, a low concentration (for example, 9 to 14% by mass) solution may be prepared in advance and then concentrated. Furthermore, you may dilute after preparing a high concentration solution beforehand. By adding an additive, the concentration of the cellulose ester can be reduced.

[Additive]
The cellulose ester solution can contain various liquid or solid additives depending on the application in each preparation step. Examples of the additive include a plasticizer (preferably added amount is 0.1 to 20% by mass based on the cellulose ester, the same applies hereinafter), a modifier (0.1 to 20% by mass), an ultraviolet absorber (0. 001 to 5% by mass), fine particle powder (0.001 to 5% by mass) having an average particle diameter of 5 to 3000 nm, fluorine-based surfactant (0.001 to 2% by mass), release agent (0.0001 To 2% by mass), an anti-degradation agent (0.0001 to 2% by mass), an optical anisotropy control agent (0.1 to 15% by mass), and an infrared absorber (0.1 to 5% by mass). .

About a plasticizer, Unexamined-Japanese-Patent No. 2001-151901 has description. About an infrared absorber, Unexamined-Japanese-Patent No. 2001-194522 has description. The timing for adding the additive is determined according to the type of the additive.
When the cellulose ester film has a multilayer structure, the types and amounts of additives in each layer may be different (for example, described in JP-A No. 2001-151902).
Additives for cellulose ester film are also described in pages 16 to 22 of published technical bulletin 2001-1745 (issued March 15, 2001, Invention Association).

Among these, the plasticizer and / or modifier preferably used in the present invention is preferably contained in an amount of 0.1 to 30% by mass, and preferably 1 to 25% by mass, based on the cellulose ester. It is preferable to contain 5 to 20% by mass.
The plasticizer and / or modifier preferably used in the present invention is preferably a compound that lowers Rth. The Rth of the cellulose ester film appears as the sum of Rth derived from the cellulose ester and Rth derived from the additive. Therefore, an additive that disturbs the orientation of the cellulose ester and is difficult to orient itself and / or has a small polarizability anisotropy. It is a compound that effectively lowers Rth. Therefore, in order to disturb the orientation of the cellulose ester, a compound having both a polar group and a nonpolar group is preferable. Further, in order to hinder the orientation of the compound itself or to reduce the polarizability anisotropy, a compound having a rigid structure such as liquid crystallinity is preferable, and when having a plurality of aromatic rings, they are in the same plane. It is preferable that it does not exist.

[Preparation of solution]
The preparation of the cellulose ester solution (dope) is preferably performed by a cooling dissolution method, and can also be performed in combination with a high temperature dissolution method. Regarding the method for preparing the cellulose ester solution, JP-A-58-127737, JP-A-61-106628, JP-A-2-276830, JP-A-4-259511, JP-A-5-163301, JP-A-9-95544, JP-A-10 45950, 10-95854, 11-71463, 11-302388, 11-322946, 11-322947, 11-323017, JP 2000-53784, 2000- 273184 and 2000-273239.
The method for preparing the cellulose ester solution is also described in the published technical report 2001-1745 (issued on March 15, 2001, Invention Association), page 25.
In addition, when the heating temperature in the high temperature dissolution method is equal to or higher than the boiling point of the organic solvent to be used, heating is performed while applying pressure.
The cooling temperature of the step of cooling the mixture of cellulose ester and solvent is not particularly limited, but is preferably −100 ° C. to −10 ° C., more preferably −100 ° C. to −30 ° C., and −100 ° C. to −50 ° C. Is particularly preferred.

[Solution properties]
The cellulose ester solution preferably has a viscosity at 30 ° C. of 1 to 400 Pa · s, more preferably 10 to 200 Pa · s.
The cellulose ester solution preferably has a dynamic storage elastic modulus at 15 ° C. of 100 Pa or more, and more preferably 500 to 1,000,000 Pa. Moreover, the dynamic storage elastic modulus at low temperature is so preferable that it is large. For example, when the temperature of the support on which the dope is cast is −5 ° C., the dynamic storage elastic modulus at −5 ° C. is preferably 10,000 to 1,000,000 Pa. When the temperature of the support is −50 ° C., the dynamic storage elastic modulus at −50 ° C. is preferably 10,000 to 5 million Pa.
Viscosity and dynamic storage elastic modulus are measured using a rheometer (CLS500, manufactured by TA Instruments) by placing 1 mL of the sample solution in a container (Steel Cone, manufactured by TA Instruments) having a diameter of 4 cm and a cone angle of 2 °. The measurement conditions were measured by using the conditions (Oscillation Step / Temperature Ramp) attached to the apparatus and varying the range from 40 ° C. to −10 ° C. at 2 ° C./min. Thereby, the static non-Newtonian viscosity (n * (Pa · s)) at 40 ° C. and the storage elastic modulus (G ′ (Pa)) at −5 ° C. are obtained. Measurement is started after the sample solution is kept warm at the measurement start temperature until the liquid temperature becomes constant.

[Casting]
The cellulose ester film can be produced using a conventional solution casting film forming apparatus according to a conventional solution casting film forming method. The dope (cellulose ester solution) prepared in the dissolving machine (kettle) is temporarily stored in a storage kettle, and the foam contained in the dope is defoamed for final preparation. The dope is kept at 30 ° C., and is sent from the dope discharge port to the pressure die through a pressure metering gear pump capable of delivering a constant amount of liquid with high accuracy, for example, by the number of rotations. The cast film is uniformly cast on the metal support of the cast portion, and the dough film (also referred to as web) is peeled off from the metal support at the peeling point where the metal support has almost gone around.

In the casting step, two or more cellulose ester solutions may be cast simultaneously or sequentially.
Two or more cellulose ester solutions may have exactly the same composition. If the composition is different, the type of solvent or additive can be changed from solution to solution. Two or more solutions may have different concentrations. Two or more solutions may have different aggregate molecular weights of cellulose esters. Two or more solutions may have different temperatures. Two or more solutions or layers to be formed may have different coating amounts, viscosities, film thicknesses after drying, constituent component distributions, physical properties, or physical property distributions. Physical properties of cellulose ester film (haze, transmittance, spectral characteristics, Re retardation, Rth retardation, molecular orientation axis, axial deviation, tear strength, folding strength, tensile strength, roll-in / out-Rth difference, creaking, dynamic friction, alkaline hydrolysis Decomposition, curl value, moisture content, residual solvent amount, heat shrinkage rate, high humidity dimensional evaluation, moisture permeability, base flatness, dimensional stability, heat shrinkage starting temperature, elastic modulus, bright spot foreign matter, impedance, surface shape , Yellow Index, Transparency, Tg, Heat of Crystallization), published technical bulletin 2001-1745 (issued March 15, 2001, Invention Association), pages 6-7 and 2001-1745 (March 2001). (Issued on the 15th, Japan Institute of Invention), page 11.

  In general, an undercoat layer, an antistatic layer, an antihalation layer and a protective layer are provided on a cellulose ester film used as a support for a silver halide photographic light-sensitive material and as a functional protective film for an image display device. In order to provide each layer, a coating apparatus is often used in addition to a solution casting film forming apparatus in solution casting film forming. Regarding the metal casting used in each production process (casting (including co-casting), drying, peeling, stretching) of solution casting film formation, published technical report 2001-1745 (issued on March 15, 2001) , Invention Association), pages 25-30.

The space temperature in casting the solution is preferably -50 ° C to 50 ° C, more preferably -30 ° C to 40 ° C, and most preferably -20 ° C to 30 ° C. The cellulose ester solution cast at a low space temperature is instantaneously cooled on the support and the gel strength is improved. Thereby, a film in which a large amount of the organic solvent remains can be obtained. Therefore, the film can be peeled off from the support in a short time without evaporating the organic solvent from the cellulose ester. Ordinary air, nitrogen, argon or helium can be used as the gas for cooling the space. The relative humidity is preferably 0 to 70%, more preferably 0 to 50%.
The temperature of the support (casting part) for casting the cellulose ester solution is preferably -50 ° C to 130 ° C, more preferably -30 ° C to 25 ° C, and most preferably -20 ° C to 15 ° C. In order to cool the casting part, a cooled gas can be introduced into the casting part. You may cool a space by arrange | positioning a cooling device in a casting part. In cooling, it is important to pay attention so that water does not adhere to the casting part. When cooling with gas, it is desirable to dry the gas.

[Dry]
The both ends of the web obtained by peeling from the metal support are sandwiched between clips, transported by a tenter while holding the width, dried, then transported by a roll group of a drying apparatus, dried and finished with a winder. Wind up to length. The combination of the tenter and the roll group dryer varies depending on the purpose.
The residual solvent in the film thus dried is preferably 0 to 5% by mass, more preferably 0 to 2% by mass, and still more preferably 0 to 1% by mass. After drying, trim both ends and wind up. A preferable width is 0.5 to 5 m, more preferably 0.7 to 3 m, and still more preferably 1 to 2 m. A preferable winding length is 300 to 30000 m, more preferably 500 to 10000 m, and still more preferably 1000 to 7000 m.

[Stretching]
Unlike the conventionally known plastic film, the cellulose ester film of the present invention can obtain a film having a desired Rth without undergoing an active drawing step. However, the film can be stretched in order to further adjust Re and Rth. Stretching may be performed in an undried state during film formation (for example, after peeling from the support after casting and after completion of drying), or may be performed after completion of drying. These stretching operations may be performed on-line during the film-forming process, or may be performed off-line after winding up once after film-forming is completed.
The stretching is preferably performed at Tg or more and Tg + 50 ° C or less, more preferably Tg + 1 ° C or more and Tg + 30 ° C or less, and further preferably Tg + 2 ° C or more and Tg + 20 ° C or less. A preferred draw ratio is 1% to 500%, more preferably 3% to 400%, and still more preferably 5% to 300%. These stretching operations may be performed in one stage or in multiple stages. The draw ratio here is determined using the following equation.
Stretch ratio (%) = 100 × {(Length after stretching) − (Length before stretching)} / Length before stretching Such stretching is performed by using two or more pairs of nip rolls having a higher peripheral speed on the outlet side. The film may be stretched in the longitudinal direction (longitudinal stretching), or both ends of the film may be held by a chuck and spread in the orthogonal direction (perpendicular to the longitudinal direction) (lateral stretching). Generally, in any case, Rth can be increased by increasing the draw ratio. Further, Re can be increased by increasing the difference between the ratios of longitudinal stretching and lateral stretching.

Further, the ratio of Re and Rth can be freely controlled by controlling the value (aspect ratio) obtained by dividing the space between nip rolls by the film width in the case of longitudinal stretching. That is, the Rth / Re ratio can be increased by reducing the aspect ratio. In the case of lateral stretching, it can be controlled by stretching in the orthogonal direction and simultaneously stretching in the longitudinal direction, or conversely relaxing. That is, the Rth / Re ratio can be increased by stretching in the vertical direction, and the Rth / Re ratio can be decreased by relaxing in the vertical direction.
Such stretching speed is preferably 10 to 10000% / min, more preferably 20 to 1000% / min, and further preferably 30 to 800% / min.
The angle θ formed by the film forming direction (longitudinal direction) and the slow axis of Re of the film is preferably 0 ± 10 ° or 90 ± 10 °, and preferably 0 ± 5 ° or 90 ± 5 °. Is more preferably 0 ± 3 ° or 90 ± 3 °, and in some cases, 0 ± 1 ° is preferred.

[Film thickness]
The film thickness of the cellulose ester film of the present invention is preferably 20 to 200 μm or less, more preferably 40 to 150 μm, still more preferably 60 to 120 μm. When the film thickness is thinner than 20 μm, handling properties and curling of the polarizing plate when processing into a polarizing plate or the like are not preferable. Therefore, it is not preferable from the viewpoint of productivity. The film thickness unevenness is preferably 0 to 2% in both the film thickness direction and the width direction, both unstretched and after stretching, more preferably 0 to 1.5%, and still more preferably 0 to 1%.

[Physical properties of film (retardation)]
Rth of the cellulose ester film of the present invention can be appropriately adjusted according to the purpose of use, but is preferably -600 nm to -1 nm, more preferably -400 nm to -5 nm, still more preferably -200 nm to -10 nm,- Most preferred is 100 nm to -15 nm. Re can be appropriately adjusted according to the purpose of use.
The variation in these retardation values is preferably 10 nm or less, more preferably 8 nm or less, and most preferably 6 nm or less.

[Physical properties of film (moisture permeability)]
The moisture permeability of the film of the present invention is such that when the film is used as a protective film for a polarizing plate, drying of the polarizer proceeds at an appropriate speed to provide sufficient polarization degree and adhesion. It is preferably 100 g / (m ² · day) or more, and is 200 to 1000 g / (m ² · day) in order to efficiently improve the durability of the polarizing plate without significantly increasing the film thickness. More preferably, it is 250 to 500 g / (m ² · day).
The moisture permeability increases as the temperature rises and rises as the humidity rises, but the magnitude relationship between the moisture permeability due to the film remains unchanged regardless of the conditions. Therefore, a value at 40 ° C. and 90% RH is used as a representative example. Further, the moisture permeability decreases as the film thickness increases, and increases as the film thickness decreases. Therefore, the measured moisture permeability is multiplied by the actually measured film thickness, and the value divided by 80 is converted to a moisture permeability of 80 μm film thickness. It was.

[Physical properties of film (tensile modulus)]
The tensile modulus of elasticity in at least one direction of the cellulose ester film of the present invention is preferably 3000 to 6000 MPa, more preferably 3300 to 5000 MPa, and most preferably 3500 to 4800 MPa.

[surface treatment]
It is possible to improve the adhesion between the cellulose ester film and each functional layer (for example, the undercoat layer and the back layer) by appropriately performing a surface treatment on the unstretched and stretched cellulose ester film of the present invention. It becomes. The surface treatment includes glow discharge treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, saponification treatment (acid saponification treatment, alkali saponification treatment), and glow discharge treatment and alkali saponification treatment are particularly preferable.
The glow discharge treatment includes a low-temperature plasma treatment performed under a low pressure gas of 10 ^{−3 to} 20 Torr. Plasma treatment under atmospheric pressure is also a preferable glow discharge treatment. As the plasma exciting gas, argon, helium, neon, krypton, xenon, nitrogen, carbon dioxide, chlorofluorocarbon (eg, tetrafluoromethane) and a mixture thereof are used. The plasma treatment at atmospheric pressure is preferably performed at 10 to 1000 Kev, more preferably 30 to 500 Kev. The irradiation energy is preferably 20 to 500 kGy, more preferably 20 to 300 kGy. The glow discharge treatment is described in published technical bulletin 2001-1745 (issued March 15, 2001, Invention Association), pages 30-32.

The alkali saponification treatment is carried out by applying a saponification solution to the film or immersing the film in the saponification solution.
As a coating method, a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method or an E-type coating method can be adopted. The solvent of the coating solution has good wettability with respect to the film, and it is desirable to keep the surface shape good without forming irregularities on the film surface. Specifically, the solvent is preferably alcohol, and isopropyl alcohol is particularly preferable. Further, water (preferably an aqueous solution of a surfactant) can be used as a solvent. The alkali is preferably an alkali metal hydroxide, and more preferably KOH and NaOH. The pH of the saponification coating solution is preferably 10 or more, and more preferably 12 or more. The reaction conditions during alkali saponification are preferably 1 second to 5 minutes at room temperature, more preferably 5 seconds to 5 minutes, and most preferably 20 seconds to 3 minutes. After the alkali saponification reaction, it is preferable to wash the surface to which the saponification solution is applied, or after washing with an acid. Further, the coating-type saponification treatment and the alignment film uncoating described later can be performed continuously, and the number of steps can be reduced. Specific examples of these saponification methods are described in JP-A-2002-82226 and WO02 / 46809.

In order to improve the adhesion between the film and the functional layer, an undercoat layer (adhesive layer) can be provided in addition to or in place of the surface treatment. The undercoat layer is described in published technical bulletin No. 2001-1745 (issued on March 15, 2001, Invention Association), page 32, and these can be used as appropriate.
The functional layer provided in the cellulose ester film is described in Published Technical Bulletin No. 2001-1745 (issued March 15, 2001, Invention Association), pages 32 to 45, and these can be used as appropriate.

[Application (retardation plate)]
The cellulose ester film of the present invention having a negative retardation value in the thickness direction can be freely laminated with a cellulose ester film having a positive retardation value in the thickness direction. It can be used as a controlled retardation plate. Lamination of the film can be performed using an adhesive or an adhesive.
Cellulose ester film with a negative retardation value in the thickness direction, or a retardation film in which a plurality of the retardation films are laminated, or a film in which a cellulose ester film with a positive retardation value in the thickness direction is laminated. Can be used as a retardation plate (including its support), a polarizing plate protective film, or a polarizing plate protective film having the functions of a retardation plate.
The cellulose ester film can be used as a retardation plate as it is. In addition, the cellulose ester film and the retardation plate can be used as a support, and an optically anisotropic layer (for example, a layer formed from liquid crystalline molecules) can be provided thereon to produce a retardation plate.

[Application (Polarizing plate)]
A polarizing plate consists of a polarizing film and two polarizing plate protective films which protect both surfaces. The cellulose ester film or retardation plate of the present invention can be used as at least one polarizing plate protective film.
When used as a polarizing plate protective film, the cellulose ester film is preferably subjected to alkali saponification treatment. When using a polarizing film obtained by immersing and stretching a polyvinyl alcohol film in an iodine solution, the alkali saponification surface of the cellulose ester film can be bonded to both surfaces of the polarizing film using an adhesive. As the adhesive, an aqueous solution of polyvinyl alcohol or polyvinyl acetal (eg, polyvinyl butyral) or a latex of a vinyl polymer (eg, polybutyl acrylate) can be used. A particularly preferred adhesive is an aqueous solution of fully saponified polyvinyl alcohol.
Surface treatment other than the alkali saponification treatment (described in JP-A-6-94915 and JP-A-6-118232) may be performed.
After the production of the polarizing plate, before use, an external protective film is bonded to one surface of the polarizing plate and a separate film is bonded to the opposite surface. The external protective film and the separate film are used for the purpose of protecting the polarizing plate in shipment of the polarizing plate and product inspection. The external protective film is used on the side opposite to the side where the polarizing plate is bonded to the liquid crystal cell. The separate film is used for the purpose of covering an adhesive layer for bonding the polarizing plate to the liquid crystal cell.

[Usage (Liquid Crystal Display)]
The cellulose ester film according to the present invention, and the retardation plate, optical compensation sheet, and polarizing plate using the same can be used for liquid crystal display devices in various display modes. Display modes include TN (Twisted Nematic), IPS (In-Plane Switching), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-ferroelectric Liquid Crystal), OCB (Optically Compensatory Bend), STN (Supper Twisted Nematic), VA. (Vertically Aligned), ECB (Electrically Controlled Birefringence), HAN (Hybrid Aligned Nematic), and ASM (Axially Symmetric Aligned Microcell) are included, and the cellulose ester film of the present invention is effective in any display mode liquid crystal display device. . As the liquid crystal display device, any of a transmissive type, a reflective type and a transflective type liquid crystal display device is effective.
In general, a liquid crystal display device is provided with a liquid crystal cell between two polarizing plates. In general, a liquid crystal cell is injected between two substrates. Therefore, a normal liquid crystal display device has four polarizing plate protective films. The cellulose ester film according to the present invention may be used for any of the four polarizing plate protective films. However, it can be used particularly advantageously as a film disposed between a polarizer and a liquid crystal layer in a liquid crystal display device.

(TN type liquid crystal display device)
The cellulose ester film of the present invention may be used as a support for a retardation plate of a TN liquid crystal display device having a TN mode liquid crystal cell. TN mode liquid crystal cells and TN type liquid crystal display devices have been well known for a long time. The optical compensation sheet used in the TN type liquid crystal display device is described in JP-A-3-9325, JP-A-6-148429, JP-A-8-50206, and JP-A-9-26572. Moreover, it is described in Mori et al. (Jpn. J. Appl. Phys. Vol. 36 (1997) p. 143 and Jpn. J. Appl. Phys. Vol. 36 (1997) p. 1068). is there.

(STN type liquid crystal display device)
The cellulose ester film of the present invention may be used as a support for a retardation plate of an STN type liquid crystal display device having an STN mode liquid crystal cell. In general, in a STN type liquid crystal display device, rod-like liquid crystalline molecules in a liquid crystal cell are twisted in the range of 90 to 360 degrees, and the refractive index anisotropy (Δn) and cell gap (d) of the rod-like liquid crystalline molecules. Product (Δnd) is in the range of 300 to 1500 nm. The optical compensation sheet used in the STN type liquid crystal display device is described in JP-A-2000-105316.

(VA type liquid crystal display device)
The cellulose ester film of the present invention may be used as a retardation plate or a support for a retardation plate in a VA liquid crystal display device having a VA mode liquid crystal cell. The VA-type liquid crystal display device may be an alignment-divided system as described in, for example, JP-A-10-123576.

(IPS liquid crystal display device and ECB liquid crystal display device)
The cellulose ester film of the present invention is particularly advantageous as a retardation plate for a IPS liquid crystal display device and an ECB liquid crystal display device having IPS mode and ECB mode liquid crystal cells, a support for the retardation plate, or a protective film for a polarizing plate. Used for. In these modes, the liquid crystal material is aligned substantially in parallel during black display, and black is displayed by aligning liquid crystal molecules parallel to the substrate surface in the absence of voltage. In these embodiments, the polarizing plate using the cellulose ester film of the present invention contributes to widening the viewing angle and improving the contrast.

(OCB type liquid crystal display device and HAN type liquid crystal display device)
The cellulose ester film of the present invention is also advantageously used as a support for a retardation plate of an OCB type liquid crystal display device having an OCB mode liquid crystal cell or a HAN type liquid crystal display device having a HAN mode liquid crystal cell. In the retardation plate used for the OCB type liquid crystal display device or the HAN type liquid crystal display device, it is preferable that the direction in which the absolute value of retardation is minimum does not exist in the plane of the retardation plate or in the normal direction. The optical properties of the retardation plate used in the OCB type liquid crystal display device or the HAN type liquid crystal display device are also the optical properties of the optical anisotropic layer, the optical properties of the support, and the optical anisotropic layer and the support. Is determined by the arrangement of Japanese Patent Application Laid-Open No. 9-197397 discloses a retardation plate used in an OCB type liquid crystal display device or a HAN type liquid crystal display device. Further, it is described in a paper by Mori et al. (Jpn. J. Appl. Phys. Vol. 38 (1999) p. 2837).

(Reflective liquid crystal display)
The cellulose ester film of the present invention is also advantageously used as a retardation plate of a TN type, STN type, HAN type, GH (Guest-Host) type reflective liquid crystal display device. These display modes have been well known since ancient times. The TN type reflection type liquid crystal display device is described in JP-A-10-123478, WO98848320, and Japanese Patent No. 3022477. The optical compensation sheet used for the reflection type liquid crystal display device is described in WO00-65384.

(Other liquid crystal display devices)
The cellulose ester film of the present invention is also advantageously used as a support for an optical compensation sheet of an ASM type liquid crystal display device having a liquid crystal cell in an ASM (axially aligned microcell) mode. The ASM mode liquid crystal cell is characterized in that the thickness of the cell is maintained by a resin spacer whose position can be adjusted. Other properties are the same as those of the TN mode liquid crystal cell. The ASM mode liquid crystal cell and the ASM type liquid crystal display device are described in Kume et al. (Kume et al., SID 98 Digest 1089 (1998)).

(Hard coat film, anti-glare film, anti-reflection film)
In some cases, the cellulose ester film of the present invention can be preferably applied to a hard coat film, an antiglare film, and an antireflection film. For the purpose of improving the visibility of flat panel displays such as LCD, PDP, CRT, EL, etc., any or all of a hard coat layer, an antiglare layer and an antireflection layer are provided on one or both sides of the cellulose ester film of the present invention. can do. Preferred embodiments of such an antiglare film and antireflection film are described in detail in pages 54 to 57 of the Japan Society for Invention and Technology (Publication No. 2001-1745, published on March 15, 2001, Japan Society for Invention). The cellulose ester film of the present invention can be preferably used.

  The use of the cellulose ester film is also described in the published technical bulletin 2001-1745 (issued on March 15, 2001, Invention Association), pages 45-59.

[Example 1]
(Preparation of cellulose ester solution)
Cellulose acetate powder having a substitution degree of 2.91 was used as the cellulose ester. The viscosity average polymerization degree of cellulose ester is 270, the substitution degree of acetyl group at the 6-position is 0.93, the acetone extract is 7% by mass, the mass average molecular weight / number average molecular weight ratio is 2.3, and the glass transition temperature (Tg) is 160 ° C., moisture content is 0.2 mass%, viscosity in dichloromethane solution is 305 mPa · s, residual acetic acid content is 0.1 mass% or less, Ca content is 65 ppm, Mg content is 26 ppm, iron content The amount was 0.8 ppm, the sulfate ion content was 18 ppm, the yellow index was 1.9, and the amount of free acetic acid was 47 ppm. The average particle diameter of the powder was 1.5 mm, and the standard deviation was 0.5 mm.

  In a 400 liter stainless steel dissolution tank having stirring blades and circulating cooling water around the periphery, 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent), butanol (third solvent) 5.0 parts by mass, 2.4 parts by mass of trimethylolpropane triacetate (plasticizer), 2,6-di-t-butyl-4-methylphenol (deterioration inhibitor), 2,4-bis (octylthio) -6 -(4-hydroxy-3,5-di-t-butylanilino) -1,3,5-triazine (ultraviolet absorber A) 0.2 parts by mass, 2- (2'-hydroxy-3 ', 5'- Di-t-butylphenyl) -5-chlorobenzotriazole (UV absorber B) 0.2 parts by mass, 2- (2′-hydroxy-3 ′, 5′-di-t-amylphenyl) -5-chloro Benzotriazole ( External absorbent C) 0.2 parts by mass, silicon dioxide fine particles having an average particle diameter of 20 nm (Mohs hardness: about 7) 0.05 parts by mass, citric acid ethyl ester (a 1: 1 mixture of monoester and diester) 04 parts by mass were added. The water contents of dichloromethane (main solvent), methanol (second solvent) and butanol (third solvent) were all 0.2% by mass or less.

While stirring and dispersing each component, 20 parts by mass of cellulose acetate powder (flakes) was gradually added to prepare a total of 200 kg. After the cellulose acetate powder was put into the dispersion tank, the pressure inside the tank was reduced to 1300 Pa. Stirring is performed using a dissolver type eccentric stirring shaft that stirs at a peripheral speed of 15 m / sec (shear stress 5 × 104 kgf / m / sec ² ) and an anchor blade on the central axis, and a peripheral speed of 1 m / sec (shear stress 1 The test was carried out for 30 minutes using a stirring shaft stirred at × 104 kgf / m / sec ² ). The starting temperature of stirring was 25 ° C., stirring was performed while flowing cooling water, and the final temperature reached 35 ° C. Thereafter, the high-speed stirring shaft was stopped, the peripheral speed of the stirring shaft having an anchor blade was set to 0.5 m / sec, and stirring was further performed for 100 minutes to swell the cellulose acetate powder (flakes). Until the end of swelling, the inside of the tank was pressurized to 0.12 MPa with nitrogen gas. For explosion prevention, the oxygen concentration in the tank was set to less than 2 vol%. It was confirmed that the amount of water in the dope was 0.2% by mass or less.

  The obtained non-uniform gel-like substance is fed with a screw pump whose center is heated to 30 ° C., cooled from the outer periphery of the screw, and the cooling portion is set at −75 ° C. for 3 minutes. I let it pass. Cooling was performed using a -80 ° C refrigerant cooled by a refrigerator. The solution obtained by cooling was heated to 35 ° C. during liquid feeding by a screw pump and transferred to a stainless steel container. After stirring at 50 ° C. for 2 hours to obtain a homogeneous solution, the solution is filtered with a filter paper having absolute filtration accuracy of 0.01 mm (# 63, manufactured by Toyo Filter Paper Co., Ltd.), and further filtered with an absolute filtration accuracy of 2.5 μm (FH025, Pall) Manufactured). The obtained cellulose ester solution is heated and pressurized at 110 ° C. and 1 MPa at the heating and pressurizing part of the liquid feeding pipe, and released to normal pressure (about 0.1 Mpa) to volatilize and cool the organic solvent. A solution having a temperature of 40 ° C. and a cellulose acetate concentration of 24.0% by mass was obtained. The viscosity (40 ° C.) of the solution is 120 Pa · s, the dynamic storage elastic modulus (15 ° C.) is 3800 Pa, the dynamic storage elastic modulus (−5 ° C.) is 35,000 Pa, and the dynamic storage elastic modulus (−50 ° C. ) Was 240,000 Pa. Further, the degree of polymerization of the aggregates was 2.8 to 3.2 million.

(Preparation of cellulose ester film)
The filtered cellulose ester solution at 50 ° C. was cast on a mirror surface stainless steel support, which is a drum having a diameter of 3 m, through a casting Giesser (described in JP-A-11-314233). The temperature of the support was set to -5 ° C. The casting speed was 75 m / min and the coating width was 200 cm. The space temperature of the entire casting part was set to 15 ° C. Then, the cellulose ester film that had been cast and rotated 50 cm before the cast part was peeled off from the drum, and both ends were clipped with a pin tenter. The cellulose ester film held by the pin tenter was conveyed to the drying zone. In the initial drying, a drying air of 45 ° C. was blown. Next, it was dried at 110 ° C. for 5 minutes and further at 145 ° C. for 10 minutes (film temperature was about 140 ° C.) to obtain a cellulose acetate film having a film thickness of 80 μm.
The obtained sample was cut at 3 cm at both ends, further knurled at a height of 100 μm at a portion 2 to 10 mm from the end, and wound into a roll.
The retardation (Rth) value in the thickness direction of the cellulose ester film was measured by the method described above.
The film surface state was visually confirmed and evaluated in the following three stages.
A: Transverse unevenness and irregularities were not recognized in the film.
B: Slight horizontal unevenness and irregularities were observed in the film.
C: Unevenness on the film surface was remarkable, and it was not applicable as an optical film.
The results are shown in Table 1.

[Example 2]
A cellulose ester film was prepared and evaluated in the same manner as in Example 1 except that 2.4 parts by mass of trimethylolpropane triacetate (plasticizer) was changed to 2.4 parts by mass of trimethylolpropane diacetate octanoate.
The results are shown in Table 1.

[Example 3]
A cellulose ester film was prepared and evaluated in the same manner as in Example 1 except that 2.4 parts by mass of trimethylolpropane triacetate (plasticizer) was changed to 2.4 parts by mass of benzenesulfonanilide.
The results are shown in Table 1.

[Example 4]
A cellulose ester film was prepared and evaluated in the same manner as in Example 1 except that 2.4 parts by mass of trimethylolpropane triacetate (plasticizer) was changed to 2.4 parts by mass of trityl alcohol.
The results are shown in Table 1.

[Example 5]
A solvent composition comprising 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent), and 5.0 parts by mass of butanol (third solvent) is 80.4 parts by mass of dichloromethane (main solvent). A cellulose ester film was prepared and evaluated in the same manner as in Example 1 except that the solvent composition was changed to 14.6 parts by mass of butanol (second solvent).
The results are shown in Table 1.

[Example 6]
A solvent composition comprising 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent) and 5.0 parts by mass of butanol (third solvent) is 80.4 parts by mass of dichloromethane (main solvent). A cellulose ester film was prepared and evaluated in the same manner as in Example 2 except that the solvent composition was changed to 14.6 parts by mass of butanol (second solvent).
The results are shown in Table 1.

[Example 7]
A solvent composition comprising 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent), and 5.0 parts by mass of butanol (third solvent) is 80.4 parts by mass of dichloromethane (main solvent). A cellulose ester film was prepared and evaluated in the same manner as in Example 3 except that the solvent composition was changed to 14.6 parts by mass of butanol (second solvent).
The results are shown in Table 1.

[Example 8]
A solvent composition comprising 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent), and 5.0 parts by mass of butanol (third solvent) is 80.4 parts by mass of dichloromethane (main solvent). A cellulose ester film was prepared and evaluated in the same manner as in Example 4 except that the solvent composition was changed to 14.6 parts by mass of butanol (second solvent).
The results are shown in Table 1.

[Example 9]
Cellulose acetate having a degree of substitution of 2.91, a viscosity average degree of polymerization of 270, and a 6-position acetyl group substitution degree of 0.93, a substitution degree of 2.92, a viscosity average degree of polymerization of 300, and a 6-position acetyl group substitution A cellulose ester film was prepared and evaluated in the same manner as in Example 1 except that the degree of cellulose acetate was changed to 0.94.
The results are shown in Table 1.

[Example 10]
Cellulose acetate having a substitution degree of 2.91, a viscosity average polymerization degree of 270, and a 6th-position acetyl group substitution degree of 0.93, a substitution degree of 2.92, a viscosity-average polymerization degree of 300, and a 6th-position acetyl group substitution A cellulose ester film was prepared and evaluated in the same manner as in Example 2 except that the degree of cellulose acetate was changed to 0.94.
The results are shown in Table 1.

[Example 11]
Cellulose acetate having a substitution degree of 2.91, a viscosity average polymerization degree of 270, and a 6th-position acetyl group substitution degree of 0.93, a substitution degree of 2.92, a viscosity-average polymerization degree of 300, and a 6th-position acetyl group substitution A cellulose ester film was prepared and evaluated in the same manner as in Example 3 except that the degree of cellulose acetate was changed to 0.94.
The results are shown in Table 1.

[Example 12]
Cellulose acetate having a degree of substitution of 2.91, a viscosity average degree of polymerization of 270, and a 6-position acetyl group substitution degree of 0.93, a substitution degree of 2.92, a viscosity average degree of polymerization of 300, and a 6-position acetyl group substitution A cellulose ester film was prepared and evaluated in the same manner as in Example 4 except that the degree of cellulose acetate was changed to 0.94.
The results are shown in Table 1.

[Example 13]
The cellulose ester film prepared in Example 1 and the triacetyl cellulose ester film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) were bonded together using an adhesive, and the thickness direction retardation ( Rth) value was measured.
The results are shown in Table 1.

[Example 14]
The two cellulose ester films prepared in Example 2 and the triacetyl cellulose ester film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) were bonded together using an adhesive, and the thickness direction letter of the film was formed by the method described above. The foundation (Rth) value was measured.
The results are shown in Table 1.

[Comparative Example 1]
A cellulose ester film was prepared and evaluated in the same manner as in Example 1 except that the step of cooling to -75 ° C in the preparation of the cellulose ester solution was omitted.
The results are shown in Table 1.

[Comparative Example 2]
A cellulose ester film was prepared and evaluated in the same manner as in Example 2 except that the step of cooling to −75 ° C. was omitted in the preparation of the cellulose ester solution.
The results are shown in Table 1.
In addition, since the film surface shape was very poor, the retardation (Rth) value in the thickness direction was not measurable.

[Comparative Example 3]
A cellulose ester film was prepared and evaluated in the same manner as in Example 3 except that the step of cooling to −75 ° C. was omitted in the preparation of the cellulose ester solution.
The results are shown in Table 1.
In addition, since the film surface shape was very poor, the retardation (Rth) value in the thickness direction was not measurable.

[Comparative Example 4]
A cellulose ester film was prepared and evaluated in the same manner as in Example 4 except that the step of cooling to −75 ° C. was omitted in the preparation of the cellulose ester solution.
The results are shown in Table 1.
In addition, since the film surface shape was very poor, the retardation (Rth) value in the thickness direction was not measurable.

[Comparative Example 5]
Cellulose acetate having a degree of substitution of 2.91, a viscosity average degree of polymerization of 270, and a 6-position acetyl group substitution degree of 0.93, a substitution degree of 2.76, a viscosity average degree of polymerization of 300, and a 6-position acetyl group substitution A cellulose ester film was prepared and evaluated in the same manner as in Example 1 except that the degree of cellulose acetate was changed to 0.90.
The results are shown in Table 1.

[Comparative Example 6]
Cellulose acetate having a degree of substitution of 2.91, a viscosity average degree of polymerization of 270, and a 6-position acetyl group substitution degree of 0.93, a substitution degree of 2.76, a viscosity average degree of polymerization of 300, and a 6-position acetyl group substitution A cellulose ester film was prepared and evaluated in the same manner as in Example 2 except that the degree of cellulose acetate was changed to 0.90.
The results are shown in Table 1.

[Comparative Example 7]
Cellulose acetate having a degree of substitution of 2.91, a viscosity average degree of polymerization of 270, and a 6-position acetyl group substitution degree of 0.93, a substitution degree of 2.76, a viscosity average degree of polymerization of 300, and a 6-position acetyl group substitution A cellulose ester film was prepared and evaluated in the same manner as in Example 3 except that the degree of cellulose acetate was changed to 0.90.
The results are shown in Table 1.

[Comparative Example 8]
Cellulose acetate having a degree of substitution of 2.91, a viscosity average degree of polymerization of 270, and a 6-position acetyl group substitution degree of 0.93, a substitution degree of 2.76, a viscosity average degree of polymerization of 300, and a 6-position acetyl group substitution A cellulose ester film was prepared and evaluated in the same manner as in Example 4 except that the degree of cellulose acetate was changed to 0.90.
The results are shown in Table 1.

[Comparative Example 9]
A solvent composition comprising 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent), and 5.0 parts by mass of butanol (third solvent) is 70.4 parts by mass of methyl acetate (main solvent). A cellulose ester film was prepared and evaluated in the same manner as in Example 1 except that the solvent composition was made up of 6.5 parts by weight of acetone (second solvent) and 4.1 parts by weight of ethanol (third solvent). .
The results are shown in Table 1.

[Comparative Example 10]
A solvent composition composed of 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent) and 5.0 parts by mass of butanol (third solvent) was converted to 70.4 masses of methyl acetate (main solvent). A cellulose ester film was prepared and evaluated in the same manner as in Example 2 except that the solvent composition was changed to 6.5 parts by weight, acetone (second solvent), and 4.1 parts by weight ethanol (third solvent). .
The results are shown in Table 1.

[Comparative Example 11]
A solvent composition composed of 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent) and 5.0 parts by mass of butanol (third solvent) was converted to 70.4 masses of methyl acetate (main solvent). A cellulose ester film was prepared and evaluated in the same manner as in Example 3 except that the solvent composition was changed to 6.5 parts by mass, acetone (second solvent), and 4.1 parts by mass ethanol (third solvent). .
The results are shown in Table 1.

[Comparative Example 12]
A solvent composition composed of 80.0 parts by mass of dichloromethane (main solvent), 10.0 parts by mass of methanol (second solvent) and 5.0 parts by mass of butanol (third solvent) was converted to 70.4 masses of methyl acetate (main solvent). A cellulose ester film was prepared and evaluated in the same manner as in Example 4 except that the solvent composition was changed to 6.5 parts by weight of acetone (second solvent) and 4.1 parts by weight of ethanol (third solvent). .
The results are shown in Table 1.

Table 1 (Part 1)
────────────────────────────────────────
Film Degree of substitution Main solvent Dissolution method Rth Film surface ──────────────────────────────────────── ─
Example 1 2.91 Dichloromethane Cooling -43 nm A
Example 2 2.91 Dichloromethane Cooling -24nm A
Example 3 2.91 Dichloromethane Cooling −40 nm A
Example 4 2.91 Dichloromethane Cooling -39 nm A
Example 5 2.91 Dichloromethane Cooling −40 nm A
Example 6 2.91 Dichloromethane Cooling -20 nm A
Example 7 2.91 Dichloromethane Cooling -38 nm A
Example 8 2.91 Dichloromethane Cooling -38 nm A
Example 9 2.92 Dichloromethane Cooling -46nm A
Example 10 2.92 Dichloromethane Cooling -28 nm A
Example 11 2.92 Dichloromethane Cooling -43 nm A
Example 12 2.92 dichloromethane cooled -40 nm A
────────────────────────────────────────

Table 1 (Part 2)
────────────────────────────────────────
Film Degree of substitution Main solvent Dissolution method Rth Film surface ──────────────────────────────────────── ─
Comparative Example 1 2.91 Dichloromethane Normal temperature +3 nm B
Comparative Example 2 2.91 Dichloromethane Normal temperature Unmeasurable C
Comparative Example 3 2.91 Dichloromethane Normal temperature Unmeasurable C
Comparative Example 4 2.91 Dichloromethane Normal temperature Unmeasurable C
Comparative Example 5 2.76 Dichloromethane Cooling +45 nm A
Comparative Example 6 2.76 Dichloromethane Cooling +62 nm A
Comparative Example 7 2.76 Dichloromethane Cooling +53 nm A
Comparative Example 8 2.76 Dichloromethane Cooling +53 nm A
Comparative Example 9 2.91 Methyl acetate Cooling Unmeasurable C
Comparative Example 10 2.91 Methyl acetate Cooling Unmeasurable C
Comparative Example 11 2.91 Methyl acetate Cooling Unmeasurable C
Comparative Example 12 2.91 Methyl acetate Cooling Unmeasurable C
────────────────────────────────────────
Example 13 2.91 Dichloromethane Cooling -3nm A
Example 14 2.91 Dichloromethane Cooling -3nm A
────────────────────────────────────────

<Measurement method>
The measurement methods and evaluation methods of characteristics used in the following examples are shown below.

[Moisture permeability]
Moisture permeability is measured by changing the mass change (g / g) before and after conditioning the cup with calcium chloride covered with each film sample and sealed for 24 hours under conditions of 40 ° C. and 90% RH. (M ² · day)) is a value obtained by evaluating the moisture permeability of the film.

[Tensile modulus]
A sample cut out with a length of 150 mm and a width of 10 mm was measured at an initial sample length of 100 mm and a tensile speed of 10 mm / min in accordance with the standard of ISO 1184-1983 to determine the tensile modulus.

[Substitution degree of cellulose ester]
The acyl substitution degree of the cellulose ester is determined by Carbohydr. Res. Was determined by ¹³ C-NMR according to the method described in 273 (1995) 83-91 (Tezuka et al.).

[Viscosity average polymerization degree]
About 0.2 g of completely dried cellulose acylate was precisely weighed and dissolved in 100 mL of a mixed solvent of dichloromethane: ethanol = 9: 1 (mass ratio). This was measured with an Ostwald viscometer at 25 ° C. for the number of falling seconds, and the degree of polymerization DP was determined by the following equation.
ηrel = T / T0 T: Seconds of measurement sample falling [η] = 1n (ηrel) / C T0: Seconds of fall of solvent alone
DP = [η] / Km C: concentration (g / L)
Km: 6 × 10 ⁻⁴

[Degree of polarization]
The transmittance (Tp) when the produced two polarizing plates are superposed in parallel with the absorption axis and the transmittance (Tc) when the absorption axes are superposed with each other perpendicular to each other are measured and expressed by the following formula: The degree of polarization (P) was calculated.
Polarization degree P = ((Tp−Tc) / (Tp + Tc)) ^ 0.5

<Production of film>
Although the specific embodiment about the cellulose ester film of this invention is described below, it is not limited to these.
[Examples 101 to 119, Comparative Examples 105 to 110]
(Preparation of cellulose ester solution)
1) Cellulose ester The following cellulose ester was selected and listed in Table 2.
Cellulose ester A:
Cellulose acetate powder (15 parts by mass) with a substitution degree of 2.91 was used as the cellulose ester. The viscosity average polymerization degree of cellulose acetate is 270, the substitution degree of acetyl group at the 6-position is 0.93, the acetone extract is 7% by mass, the mass average molecular weight / number average molecular weight ratio is 2.3, and the glass transition temperature (Tg) is 160 ° C., moisture content is 0.2 mass%, viscosity in dichloromethane solution is 305 mPa · s, residual acetic acid content is 0.1 mass% or less, Ca content is 65 ppm, Mg content is 26 ppm, iron content The amount was 0.8 ppm, the sulfate ion content was 18 ppm, the yellow index was 1.9, and the amount of free acetic acid was 47 ppm. The average particle diameter of the powder was 1.5 mm, and the standard deviation was 0.5 mm.
Cellulose ester B:
Cellulose acetate powder (15 parts by mass) having a substitution degree of 2.93, a viscosity average polymerization degree of 300, and a 6-position acetyl group substitution degree of 0.94 was used as the cellulose ester.
Cellulose ester C:
Daicel Chemical Industries, Ltd. LT-35 was purchased and used. This cellulose ester had a degree of substitution of 2.92, a viscosity average degree of polymerization of 300, and an acetyl group substitution degree at the 6-position of 0.94.
Cellulose ester D:
Cellulose acetate powder (15 parts by mass) having a substitution degree of 2.76, a viscosity-average polymerization degree of 300, and a 6-position acetyl group substitution degree of 0.90 was used as the cellulose ester.
Cellulose ester E:
CAP482-20 manufactured by Eastman Chemical Japan Co., Ltd. was purchased and used.
Cellulose ester F:
CAB381-20 manufactured by Eastman Chemical Japan Co., Ltd. was purchased and used.

2) Solvents Selected from the following solvents and listed in Table 2.
Solvent A: dichloromethane / methanol / butanol (79.0 / 14.0 / 2.0 parts by mass)
Solvent B: dichloromethane / methanol / 1-propanol (80.0 / 10.0 / 5.0 parts by mass)
Solvent C: Methyl acetate / acetone / ethanol (70.4 / 6.5 / 4.1 parts by mass)
Solvent D: Dichloromethane / methanol (82.7 / 12.4 parts by mass)
Solvent E: dichloromethane / methanol / butanol (57.0 / 30.0 / 8.0 parts by mass)
The water content of these solvents was 0.2% by mass or less.

3) Additives Selected from the following additives and listed in Table 2 together with the amount added. In addition, in preparing all solutions, 0.1 part by mass of 2,6-di-t-butyl-4-methylphenol (deterioration inhibitor), 2,4-bis (octylthio) -6- (4-hydroxy-3) , 5-Di-t-butylanilino) -1,3,5-triazine (UV absorber A) 0.2 parts by mass, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) -5-Chlorobenzotriazole (UV absorber B) 0.2 parts by mass, 2- (2'-hydroxy-3 ', 5'-di-t-amylphenyl) -5-chlorobenzotriazole (UV absorber C) ) 0.2 parts by mass, silicon dioxide fine particles (average particle size 20 nm, Mohs hardness of about 7) 0.05% by mass, citric acid ethyl ester (1: 1 mixture of monoester and diester) 0.04 part by mass did.
Additive A: Trimethylolpropane triacetate Additive B: Trimethylolpropane diacetate octanoate Additive C: Benzenesulfonanilide Additive D: Trityl alcohol

4) Swelling and dissolution A solvent and an additive were put into a 400 liter stainless steel dissolution tank having stirring blades and circulating cooling water around the outer periphery.

While stirring and dispersing each component, the cellulose ester was gradually added to prepare a total of 300 kg. After the cellulose acetate powder was put into the dispersion tank, the pressure inside the tank was reduced to 1300 Pa. Stirring is performed at a peripheral speed of 1 m / sec (shearing) with an eccentric stirring shaft of a dissolver type stirring at a peripheral speed of 15 m / sec (shear stress 5 × 10 ⁴ kgf / m / sec ² ) and an anchor blade on the central axis. This was carried out for 30 minutes using a stirring shaft that was stirred at a stress of 1 × 10 ⁴ kgf / m / sec ² ). The starting temperature of stirring was 25 ° C., stirring was performed while flowing cooling water, and the final temperature reached 30 ° C. Thereafter, the high-speed stirring shaft was stopped, the peripheral speed of the stirring shaft having an anchor blade was set to 0.5 m / sec, and stirring was further performed for 100 minutes to swell the cellulose acetate powder (flakes). Until the end of swelling, the inside of the tank was pressurized to 0.12 MPa with nitrogen gas. It was confirmed that the amount of water in the dope was 0.2% by mass or less.

  The obtained non-uniform gel-like substance is fed with a screw pump whose center is heated to 30 ° C., cooled from the outer periphery of the screw, and the cooling portion is set at −75 ° C. for 3 minutes. I let it pass. Cooling was performed using a -80 ° C refrigerant cooled by a refrigerator. The solution obtained by cooling was heated to 30 ° C. during liquid feeding by a screw pump and transferred to a stainless steel container. And it stirred at 30 degreeC for 2 hours, and was set as the uniform solution.

5) Filtration and concentration The cellulose ester solution obtained above was filtered with a filter paper with absolute filtration accuracy of 0.01 mm (# 63, manufactured by Toyo Filter Paper Co., Ltd.), and further with filter paper with absolute filtration accuracy of 2.5 μm (FH025, (Manufactured by Paul Corporation). The obtained cellulose ester solution is heated and pressurized at 110 ° C. and 1 MPa at the heating and pressurizing part of the liquid feeding pipe, and released to normal pressure (about 0.1 Mpa) to volatilize and cool the organic solvent. A solution having a temperature of 40 ° C. and a cellulose acetate concentration of 18.0% by mass was obtained.

(Preparation of cellulose ester film)
The filtered cellulose ester solution at 30 ° C. was cast on a mirror surface stainless steel support having a band length of 60 m set at 15 ° C. through a casting Giesser (described in JP-A-11-314233). The casting speed was 35 m / min and the coating width was 200 cm. The space temperature of the entire casting part was set to 15 ° C. Then, the cellulose ester film that had been cast and rotated 50 cm before the cast part was peeled off from the drum, and both ends were clipped with a pin tenter. The cellulose ester film held by the pin tenter was conveyed to the drying zone. In the initial drying, a drying air of 45 ° C. was blown. Next, it was dried at 110 ° C. for 5 minutes and further at 145 ° C. for 10 minutes (film temperature was about 140 ° C.) to obtain a cellulose acetate film.
The obtained sample was cut at 3 cm at both ends, and further knurled at a height of 1.25 times the film thickness at a portion 2 to 10 mm from the end, and wound into a 1000 m roll.

(Evaluation of cellulose ester film)
The film surface state was visually confirmed and evaluated in the following three stages.
A: Transverse unevenness and irregularities were not recognized in the film.
B: Slight horizontal unevenness and irregularities were observed in the film.
C: Unevenness on the film surface was remarkable, and it was not applicable as an optical film.

[Retardation]
Re and Rth of the cellulose ester film were measured by the method described above.

[Moisture permeability]
The moisture permeability of the cellulose ester film was measured by the method described above.

[Tensile modulus]
The tensile elastic modulus of the cellulose ester film was measured by the method described above using a sample cut out with a length of 150 mm in the film forming direction and a width of 10 mm in the width direction.
The results are shown in Table 2.

[Comparative Examples 101-104]
A cellulose ester film was prepared and evaluated in the same manner as in Example 101 except that the steps of “4) swelling and dissolution” and “5) filtration and concentration” in Example 101 were changed to the following methods.
4) Swelling and dissolution A solvent and an additive were put into a 400 liter stainless steel dissolution tank having stirring blades and circulating cooling water around the outer periphery.
While stirring and dispersing each component, the cellulose ester was gradually added to prepare a total of 300 kg. After the cellulose acetate powder was put into the dispersion tank, the pressure inside the tank was reduced to 1300 Pa. Stirring is performed at a peripheral speed of 1 m / sec (shearing) with an eccentric stirring shaft of a dissolver type stirring at a peripheral speed of 15 m / sec (shear stress 5 × 10 ⁴ kgf / m / sec ² ) and an anchor blade on the central axis. This was carried out for 30 minutes using a stirring shaft that was stirred at a stress of 1 × 10 ⁴ kgf / m / sec ² ). The starting temperature of stirring was 25 ° C., stirring was performed while flowing cooling water, and the final temperature reached 30 ° C. Thereafter, the high-speed stirring shaft was stopped, the peripheral speed of the stirring shaft having an anchor blade was set to 0.5 m / sec, and stirring was further performed for 100 minutes to swell the cellulose acetate powder (flakes). Until the end of swelling, the inside of the tank was pressurized to 0.12 MPa with nitrogen gas. It was confirmed that the amount of water in the dope was 0.2% by mass or less.
The swollen solution was heated from the tank to 50 ° C. with a jacketed pipe, further heated to 90 ° C. under a pressure of 2 MPa to dissolve, and the temperature was lowered to 30 ° C.

5) Filtration and concentration The cellulose ester solution obtained above was filtered with a filter paper with absolute filtration accuracy of 0.01 mm (# 63, manufactured by Toyo Filter Paper Co., Ltd.), and further with filter paper with absolute filtration accuracy of 2.5 μm (FH025, (Manufactured by Paul Corporation). The obtained cellulose ester solution is heated and pressurized at 110 ° C. and 1 MPa at the heating and pressurizing part of the liquid feeding pipe, and released to normal pressure (about 0.1 Mpa) to volatilize and cool the organic solvent. A solution having a temperature of 40 ° C. and a cellulose acetate concentration of 18.0% by mass was obtained.

The angle θ between the film forming direction (longitudinal direction) and the Re slow axis of the film is within 90 ± 10 ° in Examples 101 to 119, and within 0 ± 12 ° in Comparative Examples 101 and 105. In Comparative Examples 106 and 108 to 110, it was within 0 ± 10 °.
Further, the elastic modulus in the width direction was lower than the elastic modulus in the film forming direction.

<Production of retardation plate>
The cellulose ester film of the present invention can be used as it is as a retardation plate having a small Re and a negative Rth. Here, a retardation plate having a Re / Rth ratio controlled by stretching the film was produced. .

[Example 201]
A cellulose ester film was prepared and evaluated in the same manner as in Example 101 except that the process of “(Production of cellulose ester film)” in Example 101 was changed to the following method.
(Preparation of cellulose ester film)
The filtered cellulose ester solution at 30 ° C. was cast on a mirror surface stainless steel support having a band length of 60 m set at 15 ° C. through a casting Giesser (described in JP-A-11-314233). The casting speed was 20 m / min and the coating width was 200 cm. The space temperature of the entire casting part was set to 15 ° C. Then, the cellulose ester film that has been cast and rotated 50 cm before the casting part is peeled off from the drum, transported in the drying zone of the tenter while fixing both ends with a tenter having a clip, and dried with drying air. Stretching was performed. The inside of the tenter was divided into three zones, and the drying air temperature of each zone was set to 90 ° C., 100 ° C., and 110 ° C. from the upstream side.
The cellulose ester film held by the tenter was conveyed to the drying zone. First, it was dried at 110 ° C. for 5 minutes and further at 145 ° C. for 10 minutes (film temperature was about 140 ° C.) to obtain a cellulose acetate film having a film thickness of 80 μm.
The obtained sample was cut at 3 cm at both ends, further knurled at a height of 100 μm in a portion 2 to 10 mm from the end, and wound up into a 1000 m roll.

[Example 202]
A cellulose ester film was prepared and evaluated in the same manner as in Example 101 except that the process of “(Production of cellulose ester film)” in Example 101 was changed to the following method.
(Preparation of cellulose ester film)
The filtered cellulose ester solution at 30 ° C. was cast on a mirror surface stainless steel support having a band length of 60 m set at 15 ° C. through a casting Giesser (described in JP-A-11-314233). The casting speed was 20 m / min and the coating width was 100 cm. The space temperature of the entire casting part was set to 15 ° C. Then, the cellulose ester film which has been cast and rotated 50 cm before the casting part is peeled off from the drum, and the aspect ratio L / W between the width (W) of the cellulose ester film and the distance between stretches (L) is 3 Stretching was performed by increasing the peripheral speed on the outlet side between the two pairs of nip rolls. The temperature between the nip rolls was 100 ° C.
The retained cellulose ester film was conveyed to a drying zone. First, it was dried at 110 ° C. for 5 minutes and further at 145 ° C. for 10 minutes (film temperature was about 140 ° C.) to obtain a cellulose acetate film having a film thickness of 80 μm.
The obtained sample was cut at 3 cm at both ends, further knurled at a height of 100 μm in a portion 2 to 10 mm from the end, and wound up into a 1000 m roll.

Table 3 ─────────────────────────────────────────
Laminated retardation plate Stretch direction Stretch ratio Re [nm] Rth [nm]
────────────────────────────────────────
Example 201 Width direction 1.1 11 -29
Example 202 Film-forming direction 1.1 14 -31
────────────────────────────────────────

  The angle θ formed by the film forming direction (longitudinal direction) and the slow axis of Re of the film was within 0 ± 3 ° in Example 201 and within 90 ± 3 ° in Example 202.

<Production of laminated retardation plate>
[Examples 301 to 304]
The cellulose ester film of the present invention and the triacetyl cellulose ester film having a positive Rth (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) are bonded together by roll-to-roll using an adhesive, and the film is prepared by the method described above. Re and Rth were measured.
The results are shown in Table 4.

[Examples 305 to 307]
The cellulose ester film of the present invention was bonded by roll-to-roll using an adhesive, and Re and Rth of the film were measured by the method described above.
The results are shown in Table 4.

Table 4 ─────────────────────────────────────────
Laminated retardation plate Layer structure Re [nm] Rth [nm]
────────────────────────────────────────
Example 301 Example 101 / TD80UF 1-2
Example 302. Example 102 / TD80UF3 15
Example 303 Example 102 / Example 102 / TD80UF 7-7
Example 304. Example 113 / TD80UF 1-5
Example 305 Example 101 / Example 101 8-84
Example 306 Example 109 / Example 109 6-99
Example 307 Example 202 / Example 202 28-62
────────────────────────────────────────

<Production of polarizing plate>
[Examples 401 to 405]
The cellulose ester film of the present invention and / or the retardation film (herein abbreviated as film) were saponified to produce a polarizing plate.

The cellulose acylate film was immersed in a 1.5 N NaOH aqueous solution (saponification solution) adjusted to 60 ° C. for 2 minutes, then immersed in a 0.1 N sulfuric acid aqueous solution for 30 seconds, and further saponified through a washing bath.
According to Example 1 of Japanese Patent Laid-Open No. 2001-141926, a Fujitac (TD-80UF) is formed on one surface of a polarizing layer having a thickness of 20 μm that is produced by giving a peripheral speed difference between two pairs of nip rolls and extending in the longitudinal direction. ) Was saponified on the other side, and a 3% aqueous solution of polyvinyl alcohol (PVA-117H manufactured by Kuraray Co., Ltd.) 3% aqueous solution was bonded to produce a polarizing plate.

[curl]
The curling of the polarizing plate was visually confirmed and evaluated in the following three stages.
Yu: Almost no curling was observed.
Good: Some curling was confirmed, but it was acceptable for use in optical applications.
Inferior: Curling or waviness on the surface was remarkable, and it was not applicable for optical use.

[Degree of polarization]
The degree of polarization of the polarizing plate was calculated by the method described above.

Table 5─────────────────────────────────────────
Polarizing film Film A Film B Curl Polarization degree [%]
────────────────────────────────────────
Example 401 Example 101 Example 101 Excellent 99.9
Example 402 Example 101 TD80UF Good 99.9
Example 403 Example 202 Example 202 Excellent 99.9
Example 404 Example 301 Example 301 Good 99.8
Example 405 Example 305 Example 305 Good 99.8
────────────────────────────────────────

<Production of liquid crystal display device>
As shown in FIG. The present invention was applied to the described IPS liquid crystal display device. This liquid crystal display device was compared with a liquid crystal display device incorporating a polarizing plate of TD80UF which is widely known from both sides, and the light leakage rate during black display when observed from an oblique direction was evaluated. It was confirmed that the contrast of the display device was improved when any of the polarizing plates of the invention was used as compared with the case where a conventional polarizing plate was used.

Claims (4)

A cellulose ester film comprising an ester of cellulose and a lower fatty acid having 2 to 4 carbon atoms, and having a retardation value in the thickness direction measured at a wavelength of 589 nm of -600 nm to -1 nm . The cellulose ester film according to claim 1, wherein the retardation value in the thickness direction is -400 nm to -5 nm .   The cellulose ester film according to claim 1 or 2, comprising a cellulose ester having a degree of substitution with an acetyl group of 2.87 or more. A cellulose ester film comprising a cellulose ester film having a negative retardation value in the thickness direction and a cellulose ester film having a positive retardation value in the thickness direction, and a cellulose ester film having a negative retardation value in the thickness direction. A laminated phase difference plate, which is the cellulose ester film according to claim 1 .