JP2000154261A - Cellulose acetate film, production thereof, optical compensation sheet, and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cellulose acetate film which can be suitably used as an optical compensation sheet for a liquid crystal display by specifying the average degree of acetylation and the retardation value at a specified wavelength in the thickness direction. SOLUTION: This cellulose acetate film has an average degree of acetylation of 55.0-58.0% and a retardation value (Rth550) of 200-400 nm at a wavelength of 550 nm in the thickness direction. Preferably, the retardation value at a wavelength of 400 nm (Rth400) in the thickness direction, that at a wavelength of 550 nm (Rth550) in the thickness direction, and that at a wavelength of 700 nm (Rth700) in the thickness direction satisfy the formula: |Rth700-Rth400|/300 Rth550<0.0012. This film is obtained by causing cellulose acetate to swell in an organic solvent, cooling the swollen mixture to -100<= to -10 deg.C, heating the mixture to 200 deg.C to give a cellulose acetate solution, and casting the solution on a substrate to evaporate the solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cellulose acetate film, a method for producing the same, and an optical compensation sheet and a liquid crystal display using the same.

[0002]

2. Description of the Related Art Cellulose acetate films are used for various photographic materials and optical materials because of their toughness and flame retardancy. Cellulose acetate film is a typical support for photographic light-sensitive materials. Cellulose acetate films are also used in liquid crystal display devices. Cellulose acetate film is characterized by having higher optical isotropy (lower retardation value) than other polymer films. Therefore, it is common to use a cellulose acetate film for an element of a liquid crystal display device requiring optical isotropy, for example, a protective film or a color filter of a polarizing element. Conversely, an optical compensation sheet (retardation film), which is an element of another liquid crystal display device
Requires a high retardation value. Therefore, it is common to use a synthetic polymer film having a high retardation value, such as a polycarbonate film or a polysulfone film, as the optical compensation sheet. In addition to an optical compensation sheet made of a polymer film, an optical compensation sheet in which an optically anisotropic layer containing a discotic liquid crystal is provided on a transparent support has also been proposed (Japanese Patent Laid-Open No. 3-9).
No. 325, No. 6-148429, No. 8-50206
No. 9-26572). The high retardation value required for an optical compensation sheet is achieved by an optically anisotropic layer containing a discotic liquid crystal. On the other hand, since a transparent support is required to have high optical isotropy (low retardation value), a cellulose acetate film is generally used.

[0003] Photographic materials and optical materials have an average acetylation degree of 5%.
Cellulose acetate films of 8.0 to 62.5% are commonly used. Cellulose acetate having an average acetylation degree of 58% or more is classified as cellulose triacetate. Cellulose acetate film is
Generally, it is manufactured by a solvent casting method. In the solvent casting method, a solution (dope) in which cellulose acetate is dissolved in a solvent is cast on a support, and the solvent is evaporated to form a film. Many improvements have been proposed for cellulose acetate films and methods for producing the same. Recently, a method has been proposed in which a mixture of cellulose acetate and an organic solvent is cooled and further heated to dissolve the cellulose acetate in an organic solvent to prepare a cellulose acetate solution (Japanese Patent Laid-Open No. 9-95544). 9-95557
Nos. 9-95538 and U.S. Pat.
Nos. 3310 and 5705632). According to a method having a cooling step and a heating step (hereinafter, referred to as a cooling dissolution method), a solution is prepared even with a combination of cellulose acetate and an organic solvent, which cannot be dissolved by a conventional method. be able to. The cooling dissolution method is used when producing a film from cellulose triacetate having low solubility (average acetylation degree is 58% or more).
It is an effective means.

[0004]

According to the study of the present inventors, the cellulose acetate film produced by the cooling dissolution method has a problem that the retardation value in the thickness direction is high. As described above, in the use of a conventional cellulose acetate film such as a protective film of a polarizing plate,
It is necessary to lower the retardation value in the thickness direction. The present inventor has studied using a cellulose acetate film for applications requiring a high retardation value in the thickness direction, such as an optical compensation sheet of a liquid crystal display device, by utilizing the above problem in reverse. did. However, the cellulose acetate film produced by the cooling dissolution method has a high retardation value in the thickness direction,
The value was lower than that of the synthetic polymer film, and was unsuitable for use as an optical compensation sheet for a liquid crystal display device. An object of the present invention is to provide a cellulose acetate film that can be preferably used as an optical compensation sheet for a liquid crystal display.

[0005]

According to the research of the present inventors,
It was found that a film produced using cellulose acetate having an average acetylation degree of 55.0 to 58.0% had a high retardation value in the thickness direction. Further, if the cooling dissolution method is used, a higher retardation value can be obtained. As described above, in the cooling dissolution method, cellulose triacetate having low solubility (average acetylation degree is 58% or more)
This is a method developed for manufacturing films from.
Therefore, with respect to cellulose acetate having a high solubility and an average acetylation degree of less than 58.0%, the cooling dissolution method has hardly been studied. An object of the present invention is to provide a cellulose acetate film of the following (1) to (6), a method for producing a cellulose acetate film of the following (7) to (8), an optical compensation sheet of the following (9) to (10), and This was achieved by the liquid crystal display devices of 11) to (13).

(1) A cellulose acetate film having an average acetylation degree of 55.0 to 58.0%, wherein a retardation value (Rth ⁵⁵⁰ ) in a thickness direction at a wavelength of 550 nm is 200 to 400 nm. Cellulose acetate film. (2) Thickness direction retardation value (Rth ⁴⁰⁰ ) at a wavelength of ⁴⁰⁰ nm, thickness direction retardation value (Rth ⁵⁵⁰ ) at a wavelength of ⁵⁵⁰ nm, and a wavelength of 700 n
Retardation value in the thickness direction at m (Rth ⁷⁰⁰ )
Satisfies the following formula (11): The cellulose acetate film according to (1). Equation (11) | Rth ⁷⁰⁰ -Rth ⁴⁰⁰ | / 300 Rth ⁵⁵⁰ <0.001
2 (3) The cellulose acetate film according to (1), wherein the in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of 550 nm is from 20 to 300 nm. (4) The in-plane retardation value (Re ⁴⁰⁰ ) at a wavelength of ⁴⁰⁰ nm, the in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of ⁵⁵⁰ nm, and the in-plane retardation value (Re ⁷⁰⁰ ) at a wavelength of 700 nm satisfy the following formula (12). The cellulose acetate film according to (1). Formula (12) | Re ⁷⁰⁰ −Re ⁴⁰⁰ | / 300Re ⁵⁵⁰ <0.002 (5) The cellulose acetate film according to (1), having a thickness of 40 to 120 μm. (6) The cellulose acetate according to (1), which is formed by a solvent casting method using an ether having 3 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms or an ester having 3 to 12 carbon atoms as a solvent. Film.

(7) mixing cellulose acetate having an average acetylation degree of 55.0 to 58.0% with an organic solvent to swell the cellulose acetate in the organic solvent; Cooling the mixture to −10 ° C .; heating the cooled mixture to 0 to 200 ° C. to prepare a cellulose acetate solution in which cellulose acetate is dissolved in an organic solvent; placing the prepared cellulose acetate solution on a support A method for producing a cellulose acetate film, comprising a step of casting; and a step of evaporating an organic solvent to form a cellulose acetate film. (8) The cellulose according to (7), wherein the organic solvent is selected from the group consisting of ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, and esters having 3 to 12 carbon atoms. A method for producing an acetate film. (9) An optical compensatory sheet comprising a cellulose acetate film containing cellulose acetate having an average degree of acetylation of 55.0 to 58.0%. (10) An optical compensation sheet in which an optically anisotropic layer containing discotic liquid crystal molecules is provided on a cellulose acetate film containing cellulose acetate having an average degree of acetylation of 55.0 to 58.0%. (11) A liquid crystal cell carrying a liquid crystal between two electrode substrates, two polarizing elements disposed on both sides thereof, and at least one optical compensation between the liquid crystal cell and the polarizing element. A liquid crystal display device having a sheet disposed thereon, wherein the optical compensation sheet is made of a cellulose acetate film containing cellulose acetate having an average acetylation degree of 55.0 to 58.0%. (12) The liquid crystal display device according to (11), wherein an optically anisotropic layer containing discotic liquid crystal molecules is provided on the liquid crystal cell side of the cellulose acetate film. (13) The liquid crystal display device according to (11), wherein the liquid crystal cell is a VA mode, OCB mode, or HAN mode liquid crystal cell.

[0008]

As a result of the study by the present inventors, a high retardation value (wavelength 550) usable as an optical compensation sheet was obtained.
The retardation value in the thickness direction at nm (Rth
⁵⁵⁰ ) having a thickness of 200 to 400 nm). This cellulose acetate film is, for example, 55.0 to 5
It can be easily produced by a cooling dissolution method using cellulose acetate having an average acetylation degree of 8.0%.
The cellulose acetate film having a high retardation value of the present invention can be used as it is as an optical compensation sheet in a liquid crystal display. In an optical compensatory sheet in which an optically anisotropic layer containing discotic liquid crystalline molecules is provided on a support, the cellulose acetate film having a high retardation value of the present invention may be used as the support.

A conventional optical compensation sheet using discotic liquid crystal molecules is mainly composed of a TN (Twisted Nematic) for a TFT.
matic) mode liquid crystal cell was designed to optically compensate. Such an optical compensation sheet is provided by VA (Vertic
ally aligned mode, OCB (Optically Compensato)
ry Bend mode or HAN (Hybrid Aligned Nem)
A problem that cannot be dealt with (optical compensation cannot be achieved) even when used in a liquid crystal cell of the (atic) mode. Therefore, the support of the optical compensation sheet is also made optically anisotropic, and in cooperation with the optical anisotropy of the optically anisotropic layer containing discotic liquid crystal molecules, the VA mode, OCB mode or HAN mode is used. It is conceivable to correspond to the liquid crystal cell (optical compensation). As the optically anisotropic support, the cellulose acetate film having a high retardation value of the present invention can be particularly advantageously used. A synthetic polymer film having a high retardation value, such as a polycarbonate film or a polysulfone film, can be used as an optically anisotropic support. However, such a synthetic polymer film has poor function as a support (physical properties and affinity with a coating layer). Therefore, a laminate obtained by laminating a cellulose acetate film having an excellent function as a support (but generally having a low retardation value) and a synthetic polymer film having a high retardation value is used as an optically anisotropic support. It is desirable to use it as. According to the present invention, a cellulose acetate film having a high retardation value is obtained, so that a single cellulose acetate film having an excellent function as a support can be used as an optically anisotropic support. became.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Cellulose Acetate] The cellulose acetate used in the present invention has an average degree of acetylation (degree of acetylation) of 55.0% or more and less than 58.0%, preferably 57.0% or more and 58% or less. Less than 0.0%. The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like). The viscosity average degree of polymerization (DP) of cellulose acetate is preferably 250 or more,
More preferably, it is 90 or more. Further, the cellulose acetate used in the present invention preferably has a narrow molecular weight distribution of Mw / Mn (Mw is a weight average molecular weight, Mn is a number average molecular weight) determined by gel permeation chromatography. Specific values of Mw / Mn include:
It is preferably 0 to 1.7, and 1.3 to 1.6.
More preferably, it is 5 and most preferably 1.4 to 1.6.

[Retardation Value of Film] The cellulose acetate film of the present invention is characterized by an optical property indicated by a retardation value. The retardation value in the thickness direction of the film is a value obtained by multiplying the birefringence in the thickness direction by the thickness of the film. Specifically, the incident direction of the measurement light is set to the direction perpendicular to the film surface, and the in-plane retardation measurement result with respect to the slow axis, and the incident direction is inclined with respect to the direction perpendicular to the film surface. Extrapolated from the measured results. The measurement can be performed using an ellipsometer (for example, M-150: manufactured by JASCO Corporation). The retardation value in the thickness direction (Rt
h) and the in-plane retardation value (Re) are calculated according to the following equations (1) and (2), respectively. Formula (1) Retardation value in the thickness direction (Rth) = ｛(nx + n
y) / 2−nz｝ × d Equation (2) In-plane retardation value (Re) = (nx−ny) × d where nx is the refractive index in the x direction in the film plane;
ny is the refractive index in the y direction in the film plane, nz is the refractive index in the direction perpendicular to the film plane, and d is the film thickness (nm). Retardation value in the thickness direction at a wavelength of 550 nm (Rth ⁵⁵⁰⁾ is 200
To 400 nm, preferably 200 to 30 nm.
0 nm, more preferably 200 to 250 nm.
Most preferably, it is nm. The in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of 550 nm is 20 to 3
The thickness is preferably 00 nm, more preferably 30 to 300 nm.

Further, the absolute value of the retardation value in the thickness direction (Rth ⁵⁵⁰⁾ the reference value (= 1) to the slope of the distribution of Rth (a) at a wavelength of 550 nm, preferably less than 0.0012. The slope (a) of the distribution of Rth is
From the measured data of three points of the retardation value in the thickness direction at a wavelength of 400 nm (Rth ⁴⁰⁰ ), the retardation value in the thickness direction at a wavelength of 550 nm (Rth ⁵⁵⁰ ), and the retardation value in the thickness direction at a wavelength of 700 nm (Rth ⁷⁰⁰ ), It is calculated according to equation (3). Equation (3) Rth distribution slope (a) = | Rth ⁷⁰⁰ −Rth ⁴⁰⁰ | / 3
00Rth ⁵⁵⁰ Thus, Rth ^400, Rth ⁵⁵⁰ and Rth ⁷⁰⁰ preferably satisfies the following formula (11). Equation (11) | Rth ⁷⁰⁰ -Rth ⁴⁰⁰ | / 300 Rth ⁵⁵⁰ <0.001
2 Rth ⁴⁰⁰ , Rth ⁵⁵⁰ and Rth ⁷⁰⁰ are represented by the following formula (13)
Is more preferably satisfied. Formula (13) -0.0012 <(Rth ⁷⁰⁰ -Rth ⁴⁰⁰ ) / 300Rth
⁵⁵⁰ <0.0006

[0013] Further, an in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of 550 nm is a reference value (= 1).
The absolute value of the gradient (b) of the distribution of e is preferably less than 0.002. The slope (b) of the distribution of Re is wavelength 4
In-plane retardation value (Re at 00 nm)
⁴⁰⁰ ), an in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of ⁵⁵⁰ nm and an in-plane retardation value (Re ⁷⁰⁰ ) at a wavelength of 700 nm.
It is calculated according to the following equation (4). Equation (4): slope of distribution of Re (b) = | Re ⁷⁰⁰ −Re ⁴⁰⁰ | / 3
00Re ⁵⁵⁰ Therefore, Re ^400, Re ⁵⁵⁰ and Re ^700, it is preferable to satisfy the following equation (12). Formula (12) | Re ⁷⁰⁰ -Re ⁴⁰⁰ | / 300Re ⁵⁵⁰ <0.002 Re ⁴⁰⁰ , Re ⁵⁵⁰ and Re ⁷⁰⁰ are represented by the following formula (13)
Is more preferably satisfied. Formula (13) -0.002 <(Rth ⁷⁰⁰ -Rth ⁴⁰⁰ ) / 300Rth
⁵⁵⁰ <0.001

[Production of Film] In the present invention, it is preferable to produce a cellulose acetate film by a solvent casting method. In the solvent casting method, a film is manufactured using a solution (dope) in which cellulose acetate is dissolved in an organic solvent. Organic solvents include ethers having 3 to 12 carbon atoms, and 3 to 12 carbon atoms.
And a solvent selected from a ketone, an ester having 3 to 12 carbon atoms and a halogenated hydrocarbon having 1 to 6 carbon atoms. Ethers, ketones and esters may have a cyclic structure. Functional groups of ether, ketone and ester (ie, -O-, -C
A compound having two or more of any of O- and -COO-) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any one of the functional groups.

Examples of the ethers having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, anisole and phenetole. Examples of the ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone. Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate. Examples of the organic solvent having two or more types of functional groups include
Includes 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol. As the halogenated hydrocarbon having 1 to 6 carbon atoms, methylene chloride is representative. Technically, halogenated hydrocarbons such as methylene chloride can be used without any problem, but from the viewpoint of the global environment and work environment, it is preferable that the organic solvent contains substantially no halogenated hydrocarbons.
“Substantially free” means that the proportion of halogenated hydrocarbon in the organic solvent is less than 5% by weight (preferably less than 2% by weight). Further, it is preferable that no halogenated hydrocarbon such as methylene chloride is detected at all from the produced cellulose acetate film.

Two or more organic solvents may be used as a mixture. Particularly preferred organic solvents are mixed solvents of three different solvents, wherein the first solvent has 3 carbon atoms.
To 12 ketones and esters having 3 to 12 carbon atoms, the second solvent is selected from linear monohydric alcohols having 1 to 5 carbon atoms, and the third solvent has a boiling point of 30 carbon atoms. Alcohol at ~ 170 ° C and boiling point 30
Selected from hydrocarbons at 乃至 170 ° C. The ketone and ester of the first solvent are as described above.
The second solvent is selected from linear monohydric alcohols having 1 to 5 carbon atoms. The hydroxyl group of the alcohol may be bonded to the terminal of the hydrocarbon straight chain (primary alcohol),
It may be attached in the middle (secondary alcohol). The second solvent is specifically selected from methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol and 3-pentanol. The number of carbon atoms of the linear monohydric alcohol is preferably 1 to 4, more preferably 1 to 3, and most preferably 1 or 2. Ethanol is particularly preferably used.

The third solvent is selected from alcohols having a boiling point of 30 to 170 ° C. and hydrocarbons having a boiling point of 30 to 170 ° C. Preferably, the alcohol is monovalent.
The hydrocarbon portion of the alcohol may be linear, branched, or cyclic. The hydrocarbon portion is
Preferably, it is a saturated aliphatic hydrocarbon. The hydroxyl group of the alcohol may be any of primary to tertiary.
Examples of alcohol include methanol (boiling point: 64.65
C), ethanol (78.325C), 1-propanol (97.15C), 2-propanol (82.4).
C), 1-butanol (117.9C), 2-butanol (99.5C), t-butanol (82.45C),
1-pentanol (137.5 ° C), 2-methyl-2-
Butanol (101.9 ° C) and cyclohexanol (161 ° C).

Although the alcohol is the same as the definition of the second solvent, any alcohol of a different kind from the alcohol used as the second solvent can be used as the third solvent. For example, when ethanol is used as the second solvent, other alcohols (methanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol) included in the definition of the second solvent are used. , 2-pentanol or 3-pentanol)
May be used as the third solvent. The hydrocarbon may be linear, branched, or cyclic. Both aromatic hydrocarbons and aliphatic hydrocarbons can be used. Aliphatic hydrocarbons may be saturated or unsaturated. Examples of hydrocarbons include cyclohexane (boiling point: 80.7 ° C), hexane (69 ° C), benzene (80.1 ° C), toluene (110.6 ° C) and xylene (138.4 to 144.4 ° C). Is included.

The first solvent is preferably contained in the mixed solvent of 50 to 95% by weight, more preferably 60 to 92% by weight, and more preferably 65 to 90% by weight.
More preferably, the content is most preferably 70 to 88% by weight. The second solvent is preferably contained in an amount of 1 to 30% by weight, more preferably 2 to 27% by weight, even more preferably 3 to 24% by weight, and more preferably 4 to 22% by weight. Most preferred. The third solvent is preferably contained in an amount of 1 to 30% by weight, more preferably 2 to 27% by weight, even more preferably 3 to 24% by weight, and more preferably 4 to 22% by weight. Most preferred.
Further, another organic solvent may be used in combination to form a mixed solvent of four or more kinds. When four or more kinds of mixed solvents are used, the fourth and subsequent solvents are preferably selected from the three kinds of solvents described above. Nitromethane can also be used as the fourth solvent other than the three types of solvents described above.

The solution (dope) is preferably prepared according to a cooling dissolution method. Hereinafter, the cooling dissolution method will be described. First, cellulose acetate is gradually added to an organic solvent at room temperature with stirring. In addition, even if it is a solvent which can dissolve cellulose acetate at room temperature, according to the cooling dissolution method, there is an effect that a uniform solution can be obtained quickly. The amount of cellulose acetate is 1 in this mixture.
It is preferable to adjust so as to contain 0 to 40% by weight. The amount of cellulose acetate is 10 to 30% by weight
Is more preferable. Further, an optional additive described below may be added to the mixture.

Next, the mixture is heated to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -10 ° C).
To -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). Upon such cooling, the mixture of cellulose acetate and the organic solvent solidifies. The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more.
Most preferably, the temperature is at least ° C / min. The cooling rate is preferably as fast as possible, but 10,000 ° C./sec is the theoretical upper limit, 1000 ° C./sec is the technical upper limit, and
00 ° C / sec is a practical upper limit. The cooling rate is
This is a value obtained by dividing the difference between the temperature at which cooling is started and the final cooling temperature by the time from when cooling is started to when the temperature reaches the final cooling temperature. Further, the temperature is raised to 0 to 200 ° C (preferably 0 to 150 ° C, more preferably 0 to 12 ° C).
When heated to 0 ° C., most preferably 0 to 50 ° C.), the cellulose acetate dissolves in the organic solvent. The temperature rise is
It may be left alone at room temperature or heated in a warm bath. The heating rate is preferably 4 ° C./min or more,
It is more preferably at least 8 ° C./min, most preferably at least 12 ° C./min. The heating rate is preferably as fast as possible, but 10,000 ° C./sec is the theoretical upper limit,
1000 ° C / sec is a technical upper limit, and 100 ° C
/ Sec is a practical upper limit. Note that the heating rate is a value obtained by dividing the difference between the temperature at which heating is started and the final heating temperature by the time from when the heating is started until the final heating temperature is reached. .

As described above, a uniform solution is obtained. If the dissolution is insufficient, the operation of cooling and heating may be repeated. Whether or not the dissolution is sufficient can be determined only by visually observing the appearance of the solution. In the cooling dissolution method, it is preferable to use a closed container in order to avoid water contamination due to condensation during cooling. In addition, in the cooling and heating operation, if the pressure is increased during cooling and the pressure is reduced during heating, the dissolution time can be shortened.
In order to perform pressurization and decompression, it is desirable to use a pressure-resistant container. A 20% by weight solution of cellulose acetate (degree of acetylation: 60.9%, viscosity average polymerization degree: 299) dissolved in methyl acetate by a cooling dissolution method was subjected to viscoelasticity measurement by an oscillation method (for example, T
According to an oscillation measurement using a CSL2 rheometer of A Instruments Inc.), a pseudo phase transition point between a sol state and a gel state exists around 33 ° C., and below this temperature, a uniform gel state is obtained. Therefore, this solution must be stored at a temperature equal to or higher than the quasi-phase transition temperature, preferably at a temperature of about 10 ° C. plus the gel phase transition temperature. However, the pseudo phase transition temperature varies depending on the average acetylation degree of cellulose acetate, the average degree of viscosity polymerization, the solution concentration, and the organic solvent used.

From the prepared cellulose ester solution (dope), a cellulose acetate film is produced by a solvent casting method. The dope is cast on a drum or band and the solvent is evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35%. It is preferable that the surface of the drum or the band is finished in a mirror state. The casting and drying methods in the solvent casting method are described in U.S. Pat. Nos. 2,336,310 and 23,676.
No. 03, No. 2492078, No. 2492977, No. 2492978, No. 2607704, No. 27390
Nos. 69 and 2739070, British Patent 640731
Nos. 736892 and JP-B-45-455.
No. 4, No. 49-5614, JP-A-60-176834.
And JP-A-60-203430 and JP-A-62-115035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less.
It is preferable to dry the film by blowing it for 2 seconds or more.
Strip the obtained film from the drum or band,
Further, the residual solvent can be evaporated by drying with high-temperature air having a temperature sequentially changed from 100 to 160 ° C. The above method is described in JP-B-5-17844. According to this method, the time from casting to stripping can be reduced. In order to carry out this method, it is necessary that the dope gels at the surface temperature of the drum or band during casting. The solution (dope) prepared according to the present invention satisfies this condition. The thickness of the film to be produced is preferably 40 to 120 μm, more preferably 70 to 100 μm.

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

The cellulose acetate film may be added with a deterioration inhibitor (eg, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, an amine) or an ultraviolet inhibitor. Good. As for the deterioration inhibitor, JP-A-3-199201, JP-A-5-1907073, and JP-A-5-1907073.
194789, 5-271471, 6-107
It is described in each publication of No. 854. The amount of the deterioration inhibitor added is preferably 0.01 to 1% by weight, more preferably 0.01 to 0.2% by weight, of the solution (dope) to be prepared. If the amount is less than 0.01% by weight, the effect of the deterioration inhibitor is hardly recognized. If the amount exceeds 1% by weight, bleeding out (bleeding out) of the deterioration inhibitor on the film surface may be observed. A particularly preferred example of the deterioration inhibitor is butylated hydroxytoluene (BHT). The UV inhibitors are described in JP-A-7-11056. The average degree of acetylation is 55.0 to 58.0.
% Cellulose acetate has an average degree of acetylation of 58.
Compared to cellulose triacetate which is 0% or more,
There is a drawback that the stability of the prepared solution and the physical properties of the produced film are inferior. However, this disadvantage can be substantially eliminated by using an antioxidant such as the above-mentioned deterioration inhibitor, particularly butylated hydroxytoluene (BHT).

[Stretching of Film] In order to increase the in-plane retardation value of the cellulose acetate film, it is preferable to stretch the produced film. The stretching of the film is performed at normal temperature or under heating conditions. The heating temperature is preferably equal to or lower than the glass transition temperature of the film. The stretching of the film is preferably uniaxial stretching. The film can be stretched by a process during drying. For example, if the speed of the film transport roller is adjusted so that the film winding speed is faster than the film peeling speed, the film is stretched. The film can also be stretched by conveying while holding the width of the film with a tenter and gradually widening the width of the tenter.
After drying the film, the film can be stretched using a stretching machine (preferably, uniaxial stretching using a long stretching machine). The stretching ratio of the film (the ratio of the increase by stretching to the original length) is preferably 10 to 30%.

[Construction of General Liquid Crystal Display Device] The cellulose acetate film can be used for various purposes. The cellulose acetate film of the present invention is particularly effective when used as an optical compensation sheet for a liquid crystal display. Since the cellulose acetate film of the present invention has a feature that the retardation value in the thickness direction is high,
The film itself can be used as an optical compensation sheet. When the film itself is used as the optical compensation sheet, the transmission axis of the polarizing element (described later) and the slow axis of the optical compensation sheet made of cellulose acetate film are arranged so as to be substantially parallel or perpendicular. Is preferred. The arrangement of such a polarizing element and an optical compensation sheet is described in JP-A-10-48420. A liquid crystal display device has a liquid crystal cell holding liquid crystal between two electrode substrates, two polarizing elements disposed on both sides thereof, and at least one sheet between the liquid crystal cell and the polarizing element. It has a configuration in which an optical compensation sheet is arranged. The configuration of a general liquid crystal display device will be described with reference to FIG.

FIG. 1 is a schematic sectional view of a general liquid crystal display device. The liquid crystal layer (7) is provided between the resin substrates (5a, 5b). A transparent electrode layer (6a, 6b) is provided on the liquid crystal side of the resin substrate (5a, 5b). The above liquid crystal layer,
The resin substrate and the transparent electrodes (5 to 7) constitute a liquid crystal cell. Optical compensation sheets (4a, 4b) above and below the liquid crystal cell
Is glued. The cellulose acetate film of the present invention can be used as the optical compensation sheet (4a, 4b). In addition, the optical compensation sheet (4a, 4b)
Also has a function of protecting the side of the polarizing film (3a, 3b) on which the protective film (2a, 2b) is not provided. Above and below the optical compensation sheets (4a and 4b), polarizing elements (2a,
2b, 3a, 3b) are provided. The polarizing element includes a protective film (2a, 2b) and a polarizing film (3a, 3b). In the liquid crystal display device shown in FIG. 1, a surface treatment film (1) is further provided on one side of the polarizing element. The surface treatment film (1) is provided on the side where a person views from the outside.
The backlight of the liquid crystal display device is provided on the opposite side (2b side). Hereinafter, the liquid crystal cell, the optical compensation sheet, and the polarizing element will be further described.

The liquid crystal layer of the liquid crystal cell is usually formed by enclosing a liquid crystal in a space formed by sandwiching a spacer between two substrates. The transparent electrode layer is formed on a substrate as a transparent film containing a conductive substance. The liquid crystal cell may further be provided with a gas barrier layer, a hard coat layer or an undercoat layer (used for bonding the transparent electrode layer). These layers are usually provided on a substrate. The substrate of the liquid crystal cell generally has a thickness of 80 to 500 μm.

The optical compensatory sheet is a birefringent film for removing coloring of the liquid crystal screen. The cellulose acetate film of the present invention itself can be used as an optical compensation sheet. Further, in order to improve the viewing angle of the liquid crystal display device, the cellulose acetate film of the present invention may be used as an optical compensatory sheet by superimposing a film exhibiting the opposite birefringence (in a positive / negative relationship). The thickness range of the optical compensation sheet is the same as the preferred thickness of the film of the present invention described above.

As the polarizing film of the polarizing element, an iodine-based polarizing film,
There are a dye-based polarizing film using a dichroic dye and a polyene-based polarizing film. All polarizing films are generally manufactured using a polyvinyl alcohol-based film. The protective film of the polarizing plate is 25
It preferably has a thickness of from 350 to 350 μm, more preferably from 50 to 200 μm. As in the liquid crystal display device shown in FIG. 1, a surface treatment film may be provided. The functions of the surface treatment film include a hard coat, an anti-fog treatment, an anti-glare treatment and an anti-reflection treatment.

As described above, an optical compensatory sheet in which an optically anisotropic layer containing a liquid crystal (particularly discotic liquid crystal molecules) is provided on a support has been proposed (Japanese Patent Laid-Open No. 3-9).
No. 325, No. 6-148429, No. 8-50206
No. 9-26572). The cellulose acetate film of the present invention can also be used as a support for such an optical compensation sheet.

[Optically Anisotropic Layer Containing Discotic Liquid Crystalline Molecules] The optically anisotropic layer is preferably a layer containing discotic liquid crystal molecules having negative uniaxiality and being obliquely aligned. It is preferable that the angle between the discotic surface of the discotic liquid crystalline molecules and the support surface changes in the depth direction of the optically anisotropic layer (hybrid alignment). The optical axis of the discotic liquid crystal molecule exists in the direction normal to the disk surface. Discotic liquid crystal molecules have a birefringence in which the refractive index in the disc surface direction is larger than the refractive index in the optical axis direction. Discotic liquid crystalline molecules are
It may be oriented substantially horizontally with respect to the support surface.
In that case, the average tilt angle of the discotic liquid crystalline molecules (the angle between the disk surface of the molecules and the surface of the support) is preferably less than 5 °. Further, the angle between the line obtained by orthogonally projecting the normal line of the discotic liquid crystal molecules on the surface of the support and the slow axis of the support may be adjusted to about 45 ° (error less than 5 °). The optically anisotropic layer is preferably formed by aligning the discotic liquid crystal molecules by an alignment film described later and fixing the discotic liquid crystal molecules in the aligned state. The discotic liquid crystal molecules are preferably fixed by a polymerization reaction. The optically anisotropic layer has no direction in which the retardation value becomes zero. In other words, the minimum value of the retardation of the optically anisotropic layer is a value exceeding 0.

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

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

[0036]

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[0037]

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[0038]

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[0039]

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[0040]

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[0041]

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[0042]

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In the formula (I), the divalent linking group (L)
Is an alkylene group, alkenylene group, arylene group,-
It is preferably a divalent linking group selected from the group consisting of CO-, -NH-, -O-, -S- and a combination thereof. The divalent linking group (L) includes an alkylene group, an alkenylene group, an arylene group, -CO-, -NH-,-
More preferably, the group is a group obtained by combining at least two divalent groups selected from the group consisting of O- and -S-. The divalent linking group (L) is most preferably a group obtained by combining at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, -CO- and -O-. The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbon atoms. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group, a halogen atom, a cyano, an alkoxy group, an acyloxy group).

Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is a polymerizable group (P).
To join. AL represents an alkylene group or an alkenylene group, and AR represents an arylene group. L1: -AL-CO-O-AL- L2: -AL-CO-O-AL-O- L3: -AL-CO-O-AL-O-AL- L4: -AL-CO-O-AL- O-CO-L5: -CO-AR-O-AL-L6: -CO-AR-O-AL-O-L7: -CO-AR-O-AL-O-CO-L8: -CO-NH- AL-L9: -NH-AL-O-L10: -NH-AL-O-CO-

L11: -O-AL- L12: -O-AL-O- L13: -O-AL-O-CO- L14: -O-AL-O-CO-NH-AL- L15: -O- AL-S-AL-L16: -O-CO-AR-O-AL-CO-L17: -O-CO-AR-O-AL-O-CO-L18: -O-CO-AR-O-AL -O-AL-OC
O-L19: -O-CO-AR-O-AL-O-AL-OA
L-O-CO-L20: -S-AL-L21: -S-AL-O-L22: -S-AL-O-CO-L23: -S-AL-S-AL-L24: -S-AR -AL-

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

[0047]

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[0048]

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[0049]

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[0050]

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[0051]

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[0052]

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The polymerizable group (P) is an unsaturated polymerizable group (P
1, P2, P3, P7, P8, P15, P16, P1
7) or an epoxy group (P6),
More preferably, it is an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group (P1, P7, P8, P15, P1
6, P17). In the formula (I), n is an integer of 4 to 12. The specific numbers are
It is determined according to the type of discotic core (D). The combination of a plurality of L and P may be different, but is preferably the same. Two or more discotic liquid crystalline molecules (for example, a molecule having an asymmetric carbon atom in a divalent linking group and a molecule having no asymmetric carbon atom) may be used together.

The optically anisotropic layer is formed by applying a coating solution containing discotic liquid crystal molecules, the following polymerizable initiator and other additives on the alignment film. As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, dimethylformamide), sulfoxides (eg, dimethylsulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg,
Chloroform, dichloromethane), ester (eg, methyl acetate, butyl acetate), ketone (eg, acetone, methyl ethyl ketone), ether (eg, tetrahydrofuran,
1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.

The coating solution can be applied by a known method (eg, extrusion coating, direct gravure coating, reverse gravure coating, die coating). The aligned discotic liquid crystalline molecules are fixed while maintaining the aligned state. The immobilization is preferably performed by a polymerization reaction of the polymerizable group (P) introduced into the discotic liquid crystalline molecule. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. Photopolymerization reactions are preferred. Examples of the photopolymerization initiator include α-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661 and 2,367,670) and acyloin ethers (U.S. Pat.
828), α-hydrocarbon-substituted aromatic acyloin compounds (described in US Pat. No. 2,722,512),
Polynuclear quinone compounds (U.S. Pat.
51758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), an acridine and phenazine compound (Japanese Unexamined Patent Publication No. Sho 60-105667).
No. 4,239,850) and oxadiazole compounds (described in US Pat. No. 4,221,970).

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight of the solid content of the coating solution.
More preferably, it is 5 to 5% by weight. Light irradiation for the polymerization of discotic liquid crystalline molecules preferably uses ultraviolet light. The irradiation energy is 20 mJ /
cm ^{2 to} 50 J / cm ² , preferably 10
More preferably, it is 0 to 800 mJ / cm ² . Light irradiation may be performed under heating conditions to promote the photopolymerization reaction. The thickness of the optically anisotropic layer is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and most preferably 1 to 5 μm.

[Alignment Film] The alignment film has a function of defining the alignment direction of the discotic liquid crystal molecules of the optically anisotropic layer. The alignment film is an organic compound (preferably a polymer)
Rubbing treatment, oblique deposition of inorganic compounds, formation of a layer having microgrooves, or organic compounds by Langmuir-Blodgett method (LB film) (eg, ω-tricosanoic acid, dioctadecylmethylammonium chloride, methyl stearylate) Can be provided by means such as accumulation of Further, an alignment film in which an alignment function is generated by application of an electric field, a magnetic field, or light irradiation is also known. The alignment film is preferably formed by rubbing a polymer. Polyvinyl alcohol is a preferred polymer. Modified polyvinyl alcohol to which a hydrophobic group is bonded is particularly preferred. Since the hydrophobic group has an affinity for the discotic liquid crystalline molecules of the optically anisotropic layer,
By introducing a hydrophobic group into polyvinyl alcohol, discotic liquid crystal molecules can be uniformly aligned. The hydrophobic group is bonded to the main chain terminal or side chain of polyvinyl alcohol. The hydrophobic group is preferably an aliphatic group having 6 or more carbon atoms (preferably an alkyl group or an alkenyl group) or an aromatic group. When a hydrophobic group is bonded to the main chain terminal of polyvinyl alcohol, it is preferable to introduce a linking group between the hydrophobic group and the main chain terminal. Examples of the linking group include —S—, —C (CN) R ¹ —, and —NR ²
-, -CS- and combinations thereof. R ¹ and R ² are each a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (preferably, an alkyl group having 1 to 6 carbon atoms). When a hydrophobic group is introduced into the side chain of polyvinyl alcohol, the acetyl group (-CO-CH
₃ ) is partially converted to an acyl group having 7 or more carbon atoms (-CO
-R ³ ). R ³ has 6 carbon atoms
The above is an aliphatic group or an aromatic group.

A commercially available modified polyvinyl alcohol (eg, M
P103, MP203, R1130, Kuraray Co., Ltd.)
May be used. The saponification degree of (modified) polyvinyl alcohol used for the alignment film is preferably 80% or more. (Modification) The polymerization degree of polyvinyl alcohol is 200
It is preferable that it is above. The rubbing treatment is performed by rubbing the surface of the alignment film several times with paper or cloth in a certain direction. It is preferable to use a cloth in which fibers having uniform length and thickness are uniformly planted. When the discotic liquid crystalline molecules are oriented substantially horizontally with respect to the support surface (especially at an inclination angle of less than 5 °), the lower fatty acid ester of cellulose, fluorine-containing surfactant or melamine compound is oriented. Preferably, it is added to the membrane. The amount of the lower fatty acid ester of cellulose used is preferably 0.01 to 1% by weight based on the amount of the discotic liquid crystal molecules. The use amount of the fluorine-containing surfactant is preferably 2 to 30% by weight based on the amount of the discotic liquid crystal molecules. The amount of the melamine compound used is preferably 0.1 to 20% by weight of the discotic liquid crystal molecules. After aligning the discotic liquid crystal molecules using the alignment film, the discotic liquid crystal molecules are fixed in the aligned state to form an optically anisotropic layer, and only the optically anisotropic layer is used as a support. It may be transferred on top. Discotic liquid crystalline molecules fixed in an aligned state can maintain the aligned state without an alignment film. Therefore, in the optical compensation sheet, the alignment film is not an essential element (although it is essential in the production of the optical compensation sheet containing discotic liquid crystalline molecules).

[VA Liquid Crystal Display Device] The cellulose acetate film of the present invention is particularly advantageously used as a support for an optical compensation sheet of a VA liquid crystal display device having a VA mode liquid crystal cell. Regarding the VA type liquid crystal display device,
This will be described with reference to FIGS. FIG. 2 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in a VA mode liquid crystal cell when no voltage is applied. As shown in FIG. 2, the liquid crystal cell has a structure in which a liquid crystal compound (12) is sealed between an upper substrate (11) and a lower substrate (13). The liquid crystal compound (12) used for a VA mode liquid crystal cell generally has a negative dielectric anisotropy. When the applied voltage of the VA mode liquid crystal cell is 0 (when no voltage is applied), the molecules of the liquid crystalline compound (12) are vertically aligned as shown in FIG. When a pair of polarizing elements (not shown) are arranged in crossed Nicols on both sides of the upper and lower substrates (11, 13), no retardation occurs in the normal direction (14) of the substrate surface. As a result, light cannot be transmitted in the normal direction (14) of the substrate surface, and black display is performed. When the line of sight is shifted from the normal direction (14) of the substrate to the direction (15) inclined, light is transmitted due to the occurrence of retardation, and the contrast is reduced. This oblique retardation can be compensated by the optical anisotropy of the optical compensation sheet. Details will be described later (with reference to FIG. 5). In FIG. 2, all of the liquid crystal compound (12) is completely oriented in the vertical direction, but is actually slightly tilted (pretilted) in a certain direction. This is because all the liquid crystal compounds are tilted in a fixed direction (pretilt direction) when a voltage is applied (described with reference to FIG. 3 below).

FIG. 3 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in a VA mode liquid crystal cell when a voltage is applied. The upper substrate (21) and the lower substrate (23) each have an electrode layer (not shown), and can apply a voltage to the liquid crystal compound (22). As shown in FIG. 3, when a voltage is applied, the molecules of the liquid crystal compound at the center of the liquid crystal cell are horizontally aligned. As a result, retardation occurs in the normal direction (24) of the substrate surface, and light is transmitted. As described above, the liquid crystal molecules in the central portion of the liquid crystal cell are in a horizontal alignment state, but the liquid crystal molecules in the vicinity of the alignment film are not in the horizontal alignment state but are inclinedly aligned in the pretilt direction. Moving the line of sight in the direction (25) inclined from the normal direction (24) of the substrate surface causes a small change in retardation angle, whereas moving the line of sight in another direction (26) changes the angle of retardation. Is big. Accordingly, when the pretilt direction of the liquid crystalline compound is the downward direction of the image (the same direction as 26), the viewing angle in the left-right direction is symmetric and wide, and the viewing angle in the downward direction is wide, but the viewing angle in the upward direction is narrow and vertically asymmetric. Viewing angle characteristics. In order to improve the viewing angle characteristics, it is necessary to compensate for the retardation caused by the liquid crystal molecules that are not horizontally aligned but tilted when a voltage is applied. The optical compensatory sheet has a function of compensating for the above-mentioned retardation and improving visual characteristics (removing asymmetry in the visual direction of transmittance when a voltage is applied).

FIG. 4 is a schematic view of a refractive index ellipse obtained from a VA mode liquid crystal cell in which polarizing elements are arranged in crossed Nicols when viewed from the normal direction of the cell substrate. FIG. 4 (a)
Is a refractive index ellipse when no voltage is applied, and (b) is a refractive index ellipse when voltage is applied. In the crossed Nicols arrangement, the transmission axis (31a, 31b) of the polarization element on the incident side and the transmission axis (32a, 32b) of the polarization element on the emission side are arranged perpendicularly. When no voltage is applied, the liquid crystal molecules in the cell are oriented perpendicular to the cell substrate surface. Accordingly, the refractive index ellipse (33a) obtained from the normal direction of the cell substrate is circular. In this case, since the retardation of the liquid crystal cell is 0, no light is transmitted. On the other hand, when a voltage is applied, the liquid crystal molecules in the cell are oriented substantially horizontally with respect to the cell substrate surface. Therefore, the refractive index ellipse (33b) obtained from the normal direction of the cell substrate is elliptical. In this case, since the retardation of the liquid crystal cell has a value other than 0, light is transmitted. FIG. 4B also shows an orthogonal projection (34) of the optical axis of the liquid crystal molecules in the cell onto the surface of the liquid crystal cell substrate.

FIG. 5 is a schematic diagram showing the refractive index ellipse of a positive uniaxial liquid crystal cell and the refractive index ellipse of a negative uniaxial optical compensation sheet. When positive uniaxial optical anisotropy occurs in the liquid crystal cell (43), the refractive index (44x, 44y) in the plane parallel to the liquid crystal cell substrate and the refractive index (44x) in the thickness direction of the liquid crystal cell. The refractive index ellipse (44) formed by the above has a rugby ball standing shape as shown in FIG. When the liquid crystal cell having such a rugby ball-shaped (not spherical) refractive index ellipse is viewed from an oblique direction (15 in FIG. 2) as described with reference to FIG. 2, retardation occurs. This retardation is canceled by the negative uniaxial optical compensation sheet (42), and light leakage can be suppressed. Optical compensation sheet having negative uniaxiality (42)
Then, the main refractive index in the plane of the optical compensation sheet (41x, 41x)
y) and the main refractive index (41z) in the thickness direction of the optical compensation sheet
(41) of the refractive index of the optical compensation sheet formed by
Has an unpan shape as shown in FIG. So 4
The sum of 1x and 44x, the sum of 41y and 44y, and the sum of 41z and 44z have almost the same value. As a result, retardation generated in the liquid crystal cell is canceled. The optical compensation sheet of the present invention has a function of preventing light leakage at oblique incidence when no voltage is applied as described above, in addition to the function of improving the visual characteristics described above.

FIG. 6 is a schematic sectional view showing a combination of a VA mode liquid crystal cell and two optical compensation sheets.
As shown in FIG. 6, two optical compensation sheets (53, 5
4) is any of the four variations (a) to (d) and can be combined with the VA mode liquid crystal cell (50). In the variations (a) and (c), the side of the optically anisotropic layer (51) containing discotic liquid crystal molecules of the optical compensation sheet (53, 54) is
It is used by being attached to an A-mode liquid crystal cell (50).
In the variation of (a), the optically anisotropic layer (51)
An alignment film is provided on the transparent support (52) side to align discotic liquid crystal molecules. In the variation (c), an alignment film is provided on the VA-mode liquid crystal cell (50) side of the optically anisotropic layer (51) to align discotic liquid crystal molecules. In the variations (b) and (d), the side of the transparent support (52) of the optical compensation sheet (53, 54) is connected to the VA mode liquid crystal cell (5).
0). In the variation (b), an alignment film is provided on the transparent support (52) side of the optically anisotropic layer (51) to align discotic liquid crystal molecules. In the variation (d), an alignment film is provided outside the optically anisotropic layer (51) to align the discotic liquid crystal molecules.

FIG. 7 is a schematic sectional view showing a combination of a VA mode liquid crystal cell and one optical compensation sheet.
As shown in FIG. 7, one optical compensation sheet (63)
Any of the four variations (e) to (h) can be combined with the VA mode liquid crystal cell (60). In variations of (e) and (g),
The optical compensatory sheet (63) is used by bonding the optically anisotropic layer (61) containing discotic liquid crystalline molecules to a VA mode liquid crystal cell (60). In the variation (e), an alignment film is provided on the transparent support (62) side of the optically anisotropic layer (61) to align discotic liquid crystal molecules. In the variation of (g),
VA mode liquid crystal cell (6) of optically anisotropic layer (61)
An alignment film is provided on the 0) side to align the discotic liquid crystalline molecules. In the variations (f) and (h), the transparent support (62) of the optical compensation sheet (63) is used.
Side is attached to a VA mode liquid crystal cell (60). In the variation (f), an alignment film is provided on the transparent support (62) side of the optically anisotropic layer (61) to align discotic liquid crystal molecules. In the variation (h), an alignment film is provided outside the optically anisotropic layer (61) to align discotic liquid crystal molecules.

FIG. 8 is a schematic sectional view of an optical compensatory sheet used in a VA liquid crystal display device. The optical compensation sheet shown in FIG. 8 has a layer structure in the order of a support (71), an alignment film (72), and an optically anisotropic layer (73). This layer configuration is
This corresponds to the optical compensation sheet of FIGS. 6A and 6B or FIGS. 7E and 7F. The alignment film (72) is provided with an alignment function by rubbing in a certain direction (75). The discotic liquid crystal molecules (73a, 73b, 73c) contained in the optically anisotropic layer (73) are planar molecules. Discotic liquid crystal molecules (73a, 7
3b and 73c) have only one plane in the molecule, that is, a disk surface (Pa, Pb, Pc). Disk surface (Pa,
Pb, Pc) are parallel to the plane of the support (71) (71).
a, 71b, 71c). Disk surface (P
a, Pb, Pc) and the planes (71a, 71) parallel to the support surface.
b, 71c) are the inclination angles (θa, θb, θ
c). As the distance from the alignment film (62) increases along the normal line (74) of the support, the inclination angle also increases (θa <θb <θc). Tilt angle (θa, θb, θc)
Preferably changes within a range of 0 to 60 °. The minimum value of the tilt angle is preferably in the range of 0 to 55 °, and more preferably in the range of 5 to 40 °. The maximum value of the tilt angle is preferably in the range of 5 to 60 °, and more preferably in the range of 20 to 60 °. The difference between the minimum value and the maximum value of the inclination angle is preferably in the range of 5 to 55 °, and preferably 10 to 40 °
More preferably, it is within the range. When the inclination angle is changed as shown in FIG. 8, the viewing angle expanding function of the optical compensation sheet is significantly improved. Further, the optical compensation sheet having the changed inclination angle has a function of preventing inversion, gradation change, or coloring of the displayed image.

FIG. 9 is a schematic sectional view of a typical VA liquid crystal display device. The liquid crystal display device shown in FIG. 9 includes a VA mode liquid crystal cell (VAC), a pair of polarizing elements (A, B) provided on both sides of the liquid crystal cell, and a pair of polarizing elements disposed between the liquid crystal cell and the polarizing element. Optical compensation sheet (OC1, OC2)
And a backlight (BL). Only one of the optical compensation sheets (OC1, OC2) may be arranged. Arrows (R1, R2) of optical compensation sheets (OC1, OC2)
Is the rubbing direction of the alignment film provided on the optical compensation sheet (corresponding to arrow 75 in FIG. 8). In the liquid crystal display device shown in FIG. 9, the optically anisotropic layers of the optical compensation sheets (OC1, OC2) are arranged on the liquid crystal cell side. The optically anisotropic layer of the optical compensation sheet (OC1, OC2) may be disposed on the polarizing element (A, B) side. When the optically anisotropic layer is arranged on the polarizing element (A, B) side, the rubbing directions (R1, R2) of the alignment film are opposite to those in FIG. Arrows (RP1, RP2) of the liquid crystal cell (VAC) indicate the rubbing direction of the alignment film provided on the liquid crystal cell substrate. Arrows (PA, PB) of the polarizing elements (A, B) are transmission axes of polarized light of the polarizing elements, respectively.

The rubbing directions (R1, R2) of the alignment film provided on the optical compensation sheet and the rubbing directions (RP1, RP2) of the alignment film provided on the liquid crystal cell substrate are substantially parallel or antiparallel, respectively. Is preferred. It is preferable that the transmission axes (PA, PB) of the polarized light of the polarizing element are arranged to be substantially orthogonal or parallel. Substantially orthogonal,
Parallel or anti-parallel means that the angle shift is 20 °
Less than (preferably less than 15 °, more preferably less than 10 °
, And most preferably less than 5 °). Rubbing direction (RP) of alignment film provided on liquid crystal cell substrate
1, RP2) and the transmission axis (PA, P
The angle with B) is preferably from 10 to 80 °, more preferably from 20 to 70 °, and most preferably from 35 to 55 °.

In the optical compensatory sheet used for the VA liquid crystal display device, it is preferable that the direction in which the absolute value of the retardation is minimum does not exist in the plane of the optical compensatory sheet nor in the normal direction. The optical properties of the optical compensatory sheet used in the VA liquid crystal display device are determined by the optical properties of the optically anisotropic layer, the optical properties of the support, and the arrangement of the optically anisotropic layer and the support. . Details of their optical properties are described below. Regarding the optical properties, (1) the optically anisotropic layer, (2) the support, and (3) the entire optical compensation sheet, the in-plane retardation (Re), the retardation in the thickness direction (Rth) and The angle (β) between the direction in which the absolute value of the retardation is minimum and the normal line of the sheet is important. The in-plane retardation and the retardation in the thickness direction are the same as the definition of the cellulose acetate film described above. However, in the optically anisotropic layer and the optical compensatory sheet as a whole, nx, ny, and nz in the above-mentioned definitions mean an in-plane principal refractive index satisfying nx ≧ ny ≧ nz.

When two optical compensation sheets are used in a VA liquid crystal display device, the in-plane retardation of the optical compensation sheet is preferably in the range of -5 nm to 5 nm. Therefore, the absolute value of the in-plane retardation (Re ³¹ ) of each of the two optical compensation sheets is 0 ≦ | Re ³¹
It is preferable that | ≦ 5. In order to adjust Re ³¹ to the above range, the difference between the absolute value of the in-plane retardation (Re ¹ ) of the optically anisotropic layer and the absolute value of the in-plane retardation (Re ² ) of the support (|| Re ¹ | − | Re ² |
|) Is set to 5 nm or less, and the optically anisotropic layer and the support are preferably arranged such that the in-plane slow axes are substantially perpendicular to each other. When one optical compensatory sheet is used for a VA liquid crystal display device, the in-plane retardation of the optical compensatory sheet is set to -10 nm to 10 nm.
Is preferably within the range. Therefore, the absolute value of the in-plane retardation (R ³² ) of one optical compensation sheet is
It is preferable that 0 ≦ | Re ³² | ≦ 10. To adjust Re ³² to the above range, the difference between the absolute value of the in-plane retardation (Re ¹ ) of the optically anisotropic layer and the absolute value of the in-plane retardation (Re ² ) of the support. (|| R
e ¹ | − | Re ² ||) is set to 10 nm or less, and the optically anisotropic layer and the support are arranged so that the slow axes in their planes are substantially perpendicular to each other. preferable.

Regarding the optical compensatory sheet used in the VA type liquid crystal display device, preferred ranges of the optical properties of (1) the optically anisotropic layer, (2) the support and (3) the entire optical compensatory sheet are summarized below. Show. The unit of Re and Rth is n
m. The superscript number 1 means the value of the optically anisotropic layer, the superscript number 2 means the value of the support, and the superscript number 3 means the value of the optical compensatory sheet. The meanings of Re ³¹ and Re ³² are as described above. The preferred ranges of the retardation in the thickness direction of the support (Rth ² ) and the in-plane retardation (Re ² ) are as defined above as the optical properties of the cellulose acetate film.

──────────────────────────────────── Preferred range Further preferred range Most preferred range ─── ───────────────────────────────── 0 <| Re ¹ | ≦ 200 5 ≦ | Re ¹ | ≦ 150 10 ≦ | Re ¹ | ≦ 100 0 ≦ | Re ³¹ | ≦ 4.5 0 ≦ | Re ³¹ | ≦ 40 ≦ | Re ³¹ | ≦ 3.5 0 ≦ | Re ³² | ≦ 90 0 ≦ | Re ³² | ≦ 80 ≦ | Re ³² | ≦ 7────────────────────────────────────10 ≦ | Rth ¹ Rth ¹ | ≦ 300 30 ≦ | Rth ¹ | ≦ 200 10 ≦ | Rth ³ | ≦ 600 60 ≦ | Rth ³ | ≦ 500 100 ≦ | Rth ³ | ≦ 400 ───────────────────────── ^{─── 0 ° <β 1 ≦ 60} ° 0 ° <β 1 ≦ 50 ° 0 ° <β 1 ≦ 40 ° 0 ° ≦ β 2 ≦ 10 ° 0 ° ≦ β 2 ≦ 5 ° 0 ° ≦ β 2 ≦ 3 ° 0 ° <β ³ ≦ 50 ° 0 ° <β ³ ≦ 45 ° 0 ° <β ³ ≦ 40 ° ───────────────────────── ───────────

[OCB Liquid Crystal Display Device and HAN Liquid Crystal Display Device] The cellulose acetate film of the present invention is an OCB 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. It is also advantageously used as a support for an optical compensation sheet. The OCB type liquid crystal display device and the HAN type liquid crystal display device will be described with reference to FIGS. FIG. 10 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in an OCB mode liquid crystal cell. FIG. 10 shows a state of black display, which corresponds to a case where a voltage is applied in the normally white mode or a case where no voltage is applied in the normally black mode. As shown in FIG. 10, the OCB mode liquid crystal cell has a structure in which a liquid crystal compound (12) is sealed between an upper substrate (11) and a lower substrate (13). O
In the liquid crystal cell of the CB mode, a certain light travel direction (16
With respect to a), the liquid crystal compound (1) was observed near the lower substrate (13).
The birefringence of 2) is small, and the birefringence of the liquid crystal compound (12) near the upper substrate (11) is large. This direction (16a)
With respect to the direction (16
b) In the vicinity of the lower substrate (13), the liquid crystal compound (12)
Of the liquid crystal compound (12) near the upper substrate (11) is small. As described above, the OCB mode liquid crystal cell has an optical self-compensation function because the retardation is symmetric about the normal line of the substrate. Therefore, the OCB mode liquid crystal cell has a wide viewing angle in principle.

FIG. 11 is a sectional view schematically showing the orientation of a liquid crystal compound in a HAN mode liquid crystal cell. FIG.
Is a state of black display, which corresponds to a voltage application in the normally white mode or a voltage non-application in the normally black mode. As shown in FIG.
The HAN mode liquid crystal cell also has a structure in which a liquid crystal compound (22) is sealed between an upper substrate (21) and a lower substrate (23). The HAN mode is a liquid crystal cell in which the concept of the OCB mode (transmission type) liquid crystal cell is applied to a reflection type liquid crystal cell. In the HAN mode liquid crystal cell, the incident light (27)
With respect to the liquid crystal compound (2) near the upper substrate (21).
2) Large birefringence. The birefringence of the liquid crystal compound (22) is small near the lower substrate (23). On the other hand, outgoing light (28)
As for the liquid crystal compound (2) near the lower substrate (23),
The birefringence of 2) is large, and the birefringence of the liquid crystal compound (22) near the upper substrate (21) is small. Thus, HAN
The mode liquid crystal cell has an optical self-compensation function because the retardation of incident light and reflected light is symmetric. Therefore, the HAN mode liquid crystal cell also has a wide viewing angle in principle.

In a liquid crystal cell of the OCB mode or the HAN mode, when the viewing angle is increased, the transmittance of light from the black display portion is significantly increased, and the contrast is reduced. The optical compensatory sheet is used to prevent a decrease in contrast when light is incident in an oblique direction, improve viewing angle characteristics, and further improve frontal contrast. When the liquid crystal cell has positive uniaxiality in black display, optical compensation is performed using a negative uniaxial optical compensation sheet as described with reference to FIG.

FIG. 12 is a schematic sectional view showing a combination of an OCB mode liquid crystal cell and optically anisotropic layers of two optical compensation sheets. As shown in FIG. 12, the two optical compensation sheets have optically anisotropic layers (51, 52) of OCB.
It is preferable to combine and use the liquid crystal cells (50) in the mode. Optically anisotropic layer (51, 52)
Have an alignment state (optically compensated) corresponding to the alignment state of the liquid crystal molecules of the OCB mode liquid crystal cell (50).

FIG. 13 is a schematic sectional view showing a combination of a HAN mode liquid crystal cell and an optically anisotropic layer of one optical compensation sheet. As shown in FIG. 13, one optical compensation sheet is preferably used in combination so that the optically anisotropic layer (61) is on the display surface side of the HAN mode liquid crystal cell (60). The discotic liquid crystal molecules of the optically anisotropic layer (61) have an alignment state (optically compensated) corresponding to the alignment state of the liquid crystal molecules of the HAN mode liquid crystal cell (60). As shown in FIGS. 12 and 13, the alignment state of the liquid crystal cell in the OCB mode and the HAN mode can be optically compensated by the optically anisotropic layer containing discotic liquid crystal molecules. However, with the optically anisotropic layer alone, the correction of the retardation of the liquid crystal cell and the correction of the retardation generated in the optically anisotropic layer itself are insufficient. Therefore, as described above, the retardation is corrected by setting the support to optical anisotropy. The combination of the optically anisotropic layer and the optically anisotropic support, that is, the basic configuration (cross-sectional schematic view) of the optical compensatory sheet is the optical compensatory sheet used for the VA liquid crystal display device described with reference to FIG. Is the same as

FIG. 14 is a schematic sectional view of a typical OCB type liquid crystal display device. The liquid crystal display device shown in FIG.
CB mode liquid crystal cell (OCBC), a pair of polarizing elements (A, B) provided on both sides of the liquid crystal cell, a pair of optical compensation sheets (OC) disposed between the liquid crystal cell and the polarizing element.
1, OC2) and a backlight (BL). Only one of the optical compensation sheets (OC1, OC2) may be arranged. Arrows (R) of the optical compensation sheets (OC1, OC2)
1, R2) is the rubbing direction of the alignment film provided on the optical compensation sheet. In the liquid crystal display device shown in FIG. 14, the optically anisotropic layers of the optical compensation sheets (OC1, OC2) are arranged on the liquid crystal cell side. Optical compensation sheet (OC1, OC
The optically anisotropic layer 2) may be arranged on the polarizing element (A, B) side. When the optically anisotropic layer is disposed on the polarizing element (A, B) side, the rubbing direction of the alignment film (R1, R2)
Is in the opposite direction to FIG. Liquid crystal cell (OCBC)
Arrows (RP1, RP2) indicate the rubbing direction of the alignment film provided on the liquid crystal cell substrate. Arrows (PA, PB) of the polarizing elements (A, B) are transmission axes of polarized light of the polarizing elements, respectively.

The rubbing directions (R1, R2) of the alignment film provided on the optical compensation sheet and the rubbing directions (RP1, RP2) of the alignment film provided on the liquid crystal cell substrate are substantially parallel or antiparallel, respectively. Is preferred. It is preferable that the transmission axes (PA, PB) of the polarized light of the polarizing element are arranged to be substantially orthogonal or parallel. Substantially orthogonal,
Parallel or anti-parallel means that the angle shift is 20 °
Less than (preferably less than 15 °, more preferably less than 10 °
, And most preferably less than 5 °). Rubbing direction (RP) of alignment film provided on liquid crystal cell substrate
1, RP2) and the transmission axis (PA, P
The angle with B) is preferably from 10 to 80 °, more preferably from 20 to 70 °, and most preferably from 35 to 55 °. Also,
The transmission axis (PA, PB) of the polarized light of the polarizing element and the slow axis of the support of the optical compensation sheet may be adjusted substantially in parallel (with an error of less than 5 °). In this case, as described above, the angle between the line obtained by orthogonally projecting the normal line of the discotic liquid crystal molecules onto the support surface and the slow axis of the support of the optical compensation sheet is set to about 45 ° (error 5 ° or less). ) Is preferably adjusted.

FIG. 15 is a schematic sectional view of a typical HAN type liquid crystal display device. The liquid crystal display device shown in FIG.
From an AN mode liquid crystal cell (HANC), a polarizing element (A) provided on the display surface side of the liquid crystal cell, an optical compensation sheet (OC) and a reflector (RB) disposed between the liquid crystal cell and the polarizing element. Become. The arrow (R) of the optical compensation sheet (OC) indicates the rubbing direction of the alignment film provided on the optical compensation sheet. The arrow (RP) of the liquid crystal cell (HANC) indicates the rubbing direction of the alignment film provided on the liquid crystal cell substrate. An arrow (PA) of the polarizing element (A) is a transmission axis of polarized light of the polarizing element. The rubbing direction (R) of the alignment film provided on the optical compensation sheet and the rubbing direction (RP) of the alignment film provided on the liquid crystal cell substrate are preferably substantially parallel or antiparallel, respectively. Substantially parallel or antiparallel means that the angle shift is less than 20 ° (preferably less than 15 °, more preferably less than 10 °, most preferably 5 °).
Less). The angle between the rubbing direction (RP) of the alignment film provided on the liquid crystal cell substrate and the polarization transmission axis (PA) of the polarizing element is preferably 10 to 80 °, and more preferably 20 to 70 °. Preferably
Most preferably, it is 35 to 55 °.

In the optical compensatory sheet used for the OCB type liquid crystal display device or the HAN type liquid crystal display device, the direction in which the absolute value of the retardation is minimum does not exist in the plane of the optical compensatory sheet nor in the normal direction. preferable. The optical properties of the optical compensatory sheet used in the OCB type liquid crystal display device or the HAN type liquid crystal display device also include the optical properties of the optically anisotropic layer, the optical properties of the support, and the optically anisotropic layer and the support. Is determined by the arrangement. Details of their optical properties are described below. As for the optical properties, the in-plane retardation (R) of each of (1) the optically anisotropic layer, (2) the support, and (3) the entire optical compensatory sheet.
e) and the retardation (Rth) in the thickness direction are important. In the OCB type liquid crystal display device or the HAN type liquid crystal display device, (4) the optical properties of the liquid crystal cell (in-plane retardation and retardation in the thickness direction)
The relative relationship with is also important. The in-plane retardation and the retardation in the thickness direction are the same as the definition of the cellulose acetate film described above. However, in the optically anisotropic layer and the optical compensatory sheet as a whole, nx, ny, and nz in the above-mentioned definitions mean an in-plane principal refractive index satisfying nx ≧ ny ≧ nz.

In the embodiment using two optical compensation sheets,
The relationship between the in-plane retardation of the optical compensation sheet and (Re ³⁾ and the in-plane retardation of the liquid crystal cell (Re ^4),
It is preferable to adjust so as to satisfy the following expression. Re ⁴ −20 ≦ | Re ³ | × 2 ≦ Re ⁴ +20 In the embodiment in which one optical compensation sheet is used, the in-plane retardation (Re ³ ) of the optical compensation sheet and the in-plane retardation (Re ⁴ ) of the liquid crystal cell are used. Is preferably adjusted so as to satisfy the following expression. Re ⁴ −20 ≦ | Re ³ | ≦ Re ⁴ +20 The preferred ranges of the optical properties of (1) the optically anisotropic layer and (3) the optical compensatory sheet are summarized below. In addition,
The unit of Re and Rth is nm. The superscript number 1 means the value of the optically anisotropic layer, the superscript number 2 means the value of the support, and the superscript number 3 means the value of the optical compensatory sheet. In addition, (2) the retardation in the thickness direction of the support (Rth
The preferred ranges of ² ) and the in-plane retardation (Re ² ) are as defined above for the optical properties of the cellulose acetate film. Further, the in-plane retardation (Re ³ ) of the optical compensation sheet is adjusted in relation to the above-mentioned in-plane retardation (Re ⁴ ) of the liquid crystal cell.

────────────────────────────────────Preferable range Further preferred range Most preferred range─── ───────────────────────────────── 0 <| Re ¹ | ≦ 200 5 ≦ | Re ¹ | ≦ 150 10 ≦ | Re ¹ | ≦ 100 0 ≦ | Re ³ | ≦ 4.5 0 ≦ | Re ³ | ≦ 40 ≦ | Re ³ | ≦ 3.5 ^{３ ───────────────────── 50 ≦ | Rth 1 | ≦} 1000 50 ≦ | Rth 1 | ≦ 800 100 ≦ | Rth 1 | ≦ 500 50 ≦ | Rth 3 | ≦ 1000 60 ≦ | Rth ³ | ≦ 500 100 ≦ | Rth ³ | ≦ 400 ─────────────────────────────── ─────

[Other Liquid Crystal Display Devices] The cellulose acetate film of the present invention is manufactured by ASM (Axially Symmetri
AS with liquid crystal cell of c Aligned Microcell) mode
It is also advantageously used as a support for an optical compensation sheet of an M-type liquid crystal display device. 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. As for the ASM mode liquid crystal cell and the ASM type liquid crystal display device, a paper by Kume et al.
et al., SID 98 Digest 1089 (1998)).
The cellulose acetate film of the present invention may be used as a support for an optical compensation sheet of a TN type liquid crystal display device having a TN mode liquid crystal cell. The TN mode liquid crystal cell and the TN type liquid crystal display device have been well known for a long time. The optical compensatory sheet used for the TN type liquid crystal display device is disclosed in JP-A-3-9325 and JP-A-6-148429.
Nos. 8-50206 and 9-26572.

[0084]

[Example 1] At room temperature, average acetylation degree 5
17 parts by weight of 7.0% cellulose acetate, a mixed solvent of methyl acetate / methanol / n-butanol (mixing ratio = 8
(0/15/5% by weight) 80.28 parts by weight and 2.72 parts by weight of triphenyl phosphate (plasticizer) were mixed. At room temperature, the cellulose acetate did not dissolve and swelled in the mixed solvent. The resulting swollen mixture did not dissolve and formed a slurry. Next, the swelling mixture was placed in a double-layered container. The water / ethylene glycol mixture was poured as a coolant into the outer jacket while stirring the mixture slowly. This allows the mixture in the inner container to be
C. (Cooling rate: 8 ° C./min). Cooling with the refrigerant was continued until the mixture was uniformly cooled and solidified (30 minutes).

The refrigerant in the jacket outside the vessel was removed and warm water was instead poured into the jacket. At a stage where the sol formation of the content has progressed to some extent, stirring of the content was started. In this way, the mixture was heated to room temperature (heating rate: 8).
° C / min). Further, the above cooling and heating operations were repeated once. The solution (dope) obtained by the cooling dissolution method was cast using a band casting machine having an effective length of 6 m so that the dry film thickness became 100 μm. Band temperature is 0
° C. The film was exposed to the wind for 2 seconds for drying, and when the volatile content in the film became 50% by weight, the film was peeled off from the band, and further 3 minutes at 100 ° C, 5 minutes at 130 ° C,
Then, the film was shrunk freely without fixing at 160 ° C. for 5 minutes and dried stepwise to evaporate the remaining solvent. The film thus obtained (volatile content: 10% by weight)
Was further heat-treated at 150 ° C. for 1 hour.

[Examples 2 and 3 and Comparative Examples 1 and 2] The average acetylation degree of cellulose acetate was 55% (Example 2).
57.9% (Example 3), 59% (Comparative Example 1) or 6
A cellulose acetate solution was prepared in the same manner as in Example 1 except that the content was changed to 1% (Comparative Example 2), and a cellulose acetate film was produced.

(Measurement of Retardation Value) Using an ellipsometer (M-150, manufactured by JASCO Corporation), the wavelength of the produced cellulose acetate film was measured.
The retardation value in the thickness direction at 00 nm (Rth
⁴⁰⁰ ), a retardation value in the thickness direction at a wavelength of 550 nm (Rth ⁵⁵⁰ ), a retardation value in a thickness direction at a wavelength of 700 nm (Rth ⁷⁰⁰ ), a wavelength of 400 nm.
In-plane retardation value (Re ⁴⁰⁰ ), wavelength 5
In-plane retardation value at 50 nm (Re ⁵⁵⁰ )
And an in-plane retardation value (Re ⁷⁰⁰ ) at a wavelength of 700 nm were measured. Further, the slope (a) of the distribution of Rth and the slope (b) of the distribution of Re were calculated according to the above-described equations. Table 1 shows the measurement results of Rth ⁵⁵⁰ , a and b.

[0088]

[Table 1] Table 1 度 Film acetylation degree Rth ⁵⁵⁰ Re ⁵⁵⁰ ab ──────────────────────────────────── Example 1 57% 250 nm 5 nm-0.0010 -0.0019 Example 2 55% 300 nm 8 nm -0.0020 -0.0030 Example 3 57.9% 200 nm 4 nm -0.0003 -0.0015 Comparative Example 1 59% 150 nm 3 nm 0.0004 -0.0013 Comparative Example 261% 80 nm 2 nm 0.0012 0.0013 ────────────────────────────────────

[Examples 4 to 6] Cellulose acetate films were prepared and evaluated in the same manner as in Examples 1 to 3, except that the same amount of diphenyl phosphate was used in place of triphenyl phosphate as a plasticizer. The results are shown in Table 2.

[0090]

[Table 2] Table II Film Acetylation Rth ⁵⁵⁰ Re ⁵⁵⁰ ab ──────────────────────────────────── Example 4 57% 320 nm 5 nm-0.0020 −0.0019 Example 5 55% 400 nm 8 nm −0.0030 −0.0030 Example 6 57.9% 300 nm 4 nm −0.0006 −0.0015 ──────────────── ────────────────────

Example 7 A cellulose acetate solution was prepared in the same manner as in Example 1, except that 1 part by weight of butylated hydroxytoluene (BHT) was added as an antioxidant (per 1000 parts by weight of dope). The dopes obtained in Example 1 and Example 7 were left at 80 ° C. for 200 hours. Dope of Example 1 before heating and Example 1 after heating
The viscosities of the dopes 7 and 7 were measured. The measurement was performed using a high viscosity viscometer (Rotovisco, manufactured by Haake) at a shear rate of 0.1 (1 / s) and a temperature of 0 ° C. The results are shown in Table 3. The values shown in Table 3 are relative values where the viscosity of the dope of Example 1 before heating was 100. Further, a cellulose acetate film was produced in the same manner as in Example 1 using the dope treated as described above. 90 films
It was left for 200 hours under conditions of 100 ° C. and 100% relative humidity.
Then, the film was dissolved in methylene chloride, and the intrinsic viscosity (η) was measured. The intrinsic viscosity (η) was measured using a viscosity tube in which the flow time of water at 30 ° C. was 150 seconds.
First, the flow time of the solvent methylene chloride (t)
0) and then 0.3, 0.6 and 1.0 g /
The flow time (t) of the dl concentration solution was measured. And
For the concentration c (g / dl), ln (t at c = 0
/ T0) / c) was determined and defined as the intrinsic viscosity (η).
The results are shown in Table 3.

[0092]

[Table 3] Table 3 イ ル Dope and film dope viscosity (relative Value) (η) of film solution ──────────────────────────────────── Example 1 (not Heating) 100 1.2 Example 1 (after heating) 80 0.8 Example 7 (after heating) 100 1.2────────────────────── ──────────────

Example 8 (Preparation of Liquid Crystal Cell) A polyimide film was provided as an alignment film on a glass substrate provided with electrodes (ITO), and a rubbing treatment was performed. The two glass substrates thus obtained were faced to face each other, the cell gap was set to 10 μm, and a liquid crystal (ZLI1132, manufactured by Merck) was injected to form an OCB mode liquid crystal cell.

(Preparation of Liquid Crystal Display) Two cellulose acetate films prepared in Example 1 were arranged as optical compensation sheets so as to sandwich a liquid crystal cell. A polarizing element was arranged outside the outside so as to sandwich the whole. When a voltage of 55 Hz was applied to the liquid crystal display device, a clear image without coloring was obtained.

Example 9 (Support for Optical Compensation Sheet) The cellulose acetate film prepared in Example 4 was used as a support for the optical compensation sheet.

(Formation of Alignment Film) A coating solution having the following composition was applied on a support by a slide coater at 25 ml / m ² . 60 seconds with 60 ° C hot air, and 15 seconds with 90 ° C hot air
Dry for 0 seconds. Next, a rubbing treatment was performed on the formed film in a direction parallel to the slow axis direction of the support.

<< Composition of Alignment Layer Coating Solution >>変 性 The following modified polyvinyl alcohol 10 parts by weight Water 371 parts by weight Methanol 119 parts by weight Glutaraldehyde (crosslinked Agent) 0.5 parts by weight ────────────────────────────────────

[0098]

Embedded image

(Formation of Optically Anisotropic Layer) 1.8 g of the following discotic liquid crystalline compound and ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.) were placed on the alignment film. 0.2 g, cellulose acetate butyrate (CAB551-0.
2, Eastman Chemical Co., Ltd.) 0.04 g, photopolymerization initiator (Irgacure 907, Ciba Geigy Co., Ltd.)
A coating solution prepared by dissolving 0.62 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 8.43 g of methyl ethyl ketone was applied using a # 2.5 wire bar. This was attached to a metal frame and heated in a thermostat at 130 ° C. for 2 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed at 130 ° C. for 1 minute using a 120 W / cm high-pressure mercury lamp to crosslink the discotic liquid crystalline compound. Then, it was left to cool to room temperature. Thus, an optical compensation sheet (1) was produced.

[0100]

Embedded image

(Evaluation of Optical Compensation Sheet) The thickness of the optically anisotropic layer was about 1.0 μm. When the retardation value of only the optically anisotropic layer was measured along the rubbing axis, there was no direction in which the retardation was 0. The average inclination angle of the optical axis of the optically anisotropic layer, that is, the angle (β ¹ ) between the direction in which the retardation was minimized and the normal line of the sheet was 28 °. The in-plane retardation was 15 nm (Re ¹ = 15), and the retardation in the thickness direction was 35 nm (Rth ¹ = 35). The optical compensatory sheet (1) was cut vertically using a microtome along the rubbing direction to obtain an extremely thin vertical fragment (sample). The samples were left in the OsO ₄ atmosphere for 48 hours to stain. The stained sample was observed with a transmission electron microscope (TEM), and a micrograph was obtained. In the stained sample, the acryloyl group of the discotic liquid crystalline compound was stained and observed as a photograph image. As a result of examining this photograph, it was confirmed that the discotic structural units of the discotic liquid crystalline compound were inclined from the surface of the support. Furthermore, the tilt angle continuously increased as the distance from the support surface increased.

(Preparation of VA Mode Liquid Crystal Cell) Octadecyldimethylammonium chloride (coupling agent) was added at 1% by weight to a 3% by weight aqueous solution of polyvinyl alcohol. This was spin-coated on a glass substrate with an ITO electrode, heat-treated at 160 ° C., and rubbed to form a vertical alignment film. The rubbing treatment was performed so that the two glass substrates face in opposite directions.
Two glass substrates faced each other so that the cell gap (d) became 5.5 μm. In the cell gap, a liquid crystalline compound (Δn: 0.
05) was injected to form a VA mode liquid crystal cell. Δn
And d was 275 nm.

(Preparation of VA Type Liquid Crystal Display Device) In a VA mode liquid crystal cell, two optical compensatory sheets (1) were sandwiched between the optical compensatory sheets (1). Were arranged to face each other. The rubbing direction of the alignment film of the VA mode liquid crystal cell and the rubbing direction of the alignment film of the optical compensation sheet were arranged to be antiparallel. Polarizing elements were arranged in crossed Nicols on both sides of these. VA
A voltage was applied to the mode liquid crystal cell with a 55 Hz rectangular wave. The NB mode of black display 2V and white display 6V was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right can be measured using an instrument (EZ-Contra
st160D, manufactured by ELDIM). as a result,
A favorable result was obtained in which the front contrast ratio was 300, and the viewing angle (viewing angle at which a contrast ratio of 10 was obtained) was 70 degrees in both the upper, lower, left and right directions.

Example 10 (Support of Optical Compensation Sheet) The cellulose acetate film prepared in Example 4 was used as a support of the optical compensation sheet.

(Formation of Alignment Film) A coating solution having the following composition was applied on a support by a slide coater at 25 ml / m ² . Dry at 60 ° C. for 2 minutes. Next, rubbing treatment was performed on the formed film in a direction parallel to the direction in which the main refractive index was large in the plane of the support. The rubbing conditions were as follows: the rubbing roll diameter was 150 mm, the transport speed was 10 m / min, the lapping angle was 6 °, and the rubbing roll rotation speed was 1200 rpm.

<< Composition of Alignment Film Coating Solution >> １０ 10% by weight aqueous solution of the modified polyvinyl alcohol used in Example 9 24 g Water 73 g Methanol 23 g Glutar 0.2 g of 50% by weight aqueous solution of aldehyde (crosslinking agent)

(Formation of Optically Anisotropic Layer) On the alignment film, the discotic liquid crystal compound 1.8 used in Example 9 was used.
g, ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.)
0.2 g, cellulose acetate butyrate (CAB5
51-0.2, manufactured by Eastman Chemical Company) 0.04
g, cellulose acetate butyrate (CAB531-
1.0, manufactured by Eastman Chemical Co., Ltd.) 0.01 g, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy)
A coating solution prepared by dissolving 0.06 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 3.4 g of methyl ethyl ketone was applied using a # 6 wire bar. This was affixed to a metal frame and heated in a thermostat at 140 ° C. for 3 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed at 140 ° C. for 1 minute using a 120 W / cm high-pressure mercury lamp to crosslink the discotic liquid crystal compound. Then, it was left to cool to room temperature. Thus, an optical compensation sheet (2) was produced.

(Evaluation of Optical Compensation Sheet) The thickness of the optically anisotropic layer was 2.0 μm. When the retardation value of only the optically anisotropic layer was measured along the rubbing axis, there was no direction in which the retardation was 0. When the retardation value was fitted by simulation, a hybrid orientation state in which the negative uniaxiality continuously changed from 4 ° to 68 ° in the thickness direction could be confirmed. The in-plane retardation of the optically anisotropic layer was 43 nm (Re ¹ = 43), and the retardation in the thickness direction was 135 nm (Rth ¹ = 135). The optical compensatory sheet (2) was cut vertically using a microtome along the rubbing direction to obtain an extremely thin vertical fragment (sample). The samples were left in the OsO ₄ atmosphere for 48 hours to stain. The stained sample was observed with a transmission electron microscope (TEM), and a micrograph was obtained.
In the stained sample, the acryloyl group of the discotic liquid crystalline compound was stained and observed as a photograph image. As a result of examining this photograph, it was confirmed that the discotic structural units of the discotic liquid crystalline compound were inclined from the surface of the support. Furthermore, the tilt angle continuously increased as the distance from the support surface increased.

(Preparation of OCB Mode Liquid Crystal Cell) A polyimide film was provided as an alignment film on a glass substrate provided with an ITO electrode, and a rubbing treatment was performed. The rubbing treatment was performed so that the two glass substrates face in opposite directions. Two glass substrates faced each other so that the cell gap (d) became 8 μm. In the cell gap, Δn is 0.139
The liquid crystal compound No. 6 (ZLI1132, manufactured by Merck) was injected to prepare an OCB mode liquid crystal cell. The product of Δn and d is 1117 nm, and the in-plane retardation is 92 nm
(Re ⁴ = 92).

(Preparation of OCB Type Liquid Crystal Display Device) In an OCB mode liquid crystal cell, two optical compensatory sheets (2) are sandwiched between the optical compensatory sheets (2). Were arranged to face each other. The rubbing direction of the alignment film of the OCB mode liquid crystal cell and the rubbing direction of the alignment film of the optical compensation sheet were arranged to be antiparallel. Polarizing elements were arranged in crossed Nicols on both sides of these. A voltage was applied to the OCB mode liquid crystal cell with a 55 Hz rectangular wave. The NW mode of 2 V for white display and 6 V for black display was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right
CD-5000, manufactured by Otsuka Electronics Co., Ltd.). As a result, favorable results were obtained in which the upper viewing angle (viewing angle at which a contrast ratio of 10 was obtained) was 80 degrees or more, the lower viewing angle was 58 degrees, and both the left and right viewing angles were 66 degrees. .

[Example 11] (Preparation of HAN mode liquid crystal cell) A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and rubbing treatment was performed. Another glass substrate with an ITO electrode was prepared, and silicon oxide was deposited to form an alignment film. Two glass substrates faced each other so that the cell gap (d) became 4 μm. In the cell gap, Δn is 0.13
96 liquid crystal compounds (ZLI1132, manufactured by Merck) were injected to prepare HAN mode liquid crystal cells. The product of Δn and d is 558 nm, and the in-plane retardation is 46 nm
(Re ⁴ = 46).

(Preparation of HAN Type Liquid Crystal Display Device) One optical compensation sheet (2) prepared in Example 10 was placed on the display surface side of the HAN mode liquid crystal cell so that the optically anisotropic layer was on the cell side. Placed. The rubbing direction of the alignment film of the HAN mode liquid crystal cell and the rubbing direction of the alignment film of the optical compensation sheet are:
They were arranged to be antiparallel. The polarizing element was arranged on the optical compensation sheet such that the angle between the transmission axis of the polarizing element and the rubbing direction of the liquid crystal cell was 45 °. A diffusion plate was disposed on the polarizing element. A mirror (reflector) was arranged on the opposite side of the HAN mode liquid crystal cell. The light source was placed in a direction inclined by 20 ° from the normal direction of the display surface of the prepared HAN type liquid crystal display device, and irradiated with light. A voltage was applied to the HAN mode liquid crystal cell with a 55 Hz rectangular wave. White display 2
V, black display 6V NW mode, and the transmittance ratio (white display / black display) was taken as the contrast ratio. The contrast ratio from the top, bottom, left and right was measured with a meter (bm-7, manufactured by TOPCON). As a result, favorable results were obtained in which the upper viewing angle (viewing angle at which a contrast ratio of 10 was obtained) was 44 degrees, the lower viewing angle was 26 degrees, and both the left and right viewing angles were 39 degrees.

[Example 12] (Stretching of film) In the production of the film of Example 4, stretching was performed in the same manner as in Example 4 except that the winding speed was adjusted to 1.1 times the peeling speed. A film was manufactured. Retardation value in the thickness direction at a wavelength of 550nm of the stretched film (Rth ⁵⁵⁰⁾ is 240 nm, the in-plane retardation value at a wavelength of 550nm (Re ^55
0 ) was 30 nm.

(Preparation of Optical Compensation Sheet) Using the above stretched film as a support, the coating amount of the optically anisotropic layer was adjusted to 2
An optical compensatory sheet was prepared in the same manner as in Example 9 except that the magnification was changed to twice.

(Preparation of VA Type Liquid Crystal Display Device) VA was prepared in the same manner as in Example 9 except that the above-mentioned optical compensation sheet was used.
Type liquid crystal display device was created. A voltage was applied to the VA mode liquid crystal cell with a 55 Hz rectangular wave. The NB mode of black display 2V and white display 6V was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right can be measured using an instrument (EZ-Contrast 160D, ELDI
M). As a result, favorable results were obtained in which the front contrast ratio was 290, and the viewing angle (viewing angle at which a contrast ratio of 10 was obtained) was 68 degrees or more in all of the upper, lower, left, and right directions.

Example 13 (Stretching of Film) The film produced in Example 4 was stretched at 140 ° C. using a long stretching machine. The film was stretched 10% in the machine direction. The width direction of the film was fixed and was not stretched. Thus, a stretched film was manufactured. The retardation value (Rth ⁵⁵⁰ ) in the thickness direction at a wavelength of 550 nm of the stretched film is 240 nm,
The in-plane retardation value at a wavelength of 550 nm (Re
^{55 0} ) was 30 nm.

(Preparation of Optical Compensation Sheet) Using the above stretched film as a support, the coating amount of the optically anisotropic layer was adjusted to 2
An optical compensatory sheet was prepared in the same manner as in Example 9 except that the magnification was changed to twice.

(Preparation of VA-Type Liquid Crystal Display Device) VA
Type liquid crystal display device was created. A voltage was applied to the VA mode liquid crystal cell with a 55 Hz rectangular wave. The NB mode of black display 2V and white display 6V was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right can be measured using an instrument (EZ-Contrast 160D, ELDI
M). As a result, favorable results were obtained in which the front contrast ratio was 290, and the viewing angle (viewing angle at which a contrast ratio of 10 was obtained) was 68 degrees or more in all of the upper, lower, left, and right directions.

[Example 14] (Preparation of optical compensation sheet) Example 10 was repeated except that the stretched film prepared in Example 12 was used as a support and the coating amount of the optically anisotropic layer was changed to twice. In the same manner as in the above, an optical compensation sheet was prepared.

(Preparation of OCB Liquid Crystal Display Device) An OCB liquid crystal display device was prepared in the same manner as in Example 10 except that the above-mentioned optical compensation sheet was used. A voltage was applied to the OCB mode liquid crystal cell with a 55 Hz rectangular wave. The NW mode of 2 V for white display and 6 V for black display was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right was measured with an instrument (LCD-5000, manufactured by Otsuka Electronics Co., Ltd.). As a result, the upper viewing angle (viewing angle at which a contrast ratio of 10 is obtained) is 80 degrees or more, the lower viewing angle is 60 degrees, and the left and right viewing angles are all 6 degrees.
A good result of 8 degrees was obtained.

Example 15 (Preparation of Optical Compensation Sheet) Example 10 was repeated except that the stretched film prepared in Example 13 was used as a support and the coating amount of the optically anisotropic layer was changed to twice. In the same manner as in the above, an optical compensation sheet was prepared.

(Preparation of OCB-Type Liquid Crystal Display Device) An OCB-type liquid crystal display device was prepared in the same manner as in Example 10 except that the above-mentioned optical compensation sheet was used. A voltage was applied to the OCB mode liquid crystal cell with a 55 Hz rectangular wave. The NW mode of 2 V for white display and 6 V for black display was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right was measured with an instrument (LCD-5000, manufactured by Otsuka Electronics Co., Ltd.). As a result, the upper viewing angle (viewing angle at which a contrast ratio of 10 is obtained) is 80 degrees or more, the lower viewing angle is 60 degrees, and the left and right viewing angles are all 6 degrees.
A good result of 8 degrees was obtained.

[Example 16] (Preparation of HAN type liquid crystal display device) A HAN type liquid crystal display device was prepared in the same manner as in Example 11 except that the optical compensation sheet prepared in Example 14 was used. The light source was placed in a direction inclined by 20 ° from the normal direction of the display surface of the prepared HAN type liquid crystal display device, and irradiated with light. A voltage was applied to the HAN mode liquid crystal cell with a 55 Hz rectangular wave. The NW mode of 2 V for white display and 6 V for black display was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right was measured with a meter (bm-7, manufactured by TOPCON). As a result, favorable results were obtained in which the upper viewing angle (angle of the viewing field at which a contrast ratio of 10 was obtained) was 48 degrees, the lower viewing angle was 28 degrees, and both the left and right viewing angles were 41 degrees.

[Example 17] (Preparation of HAN type liquid crystal display device) A HAN type liquid crystal display device was prepared in the same manner as in Example 11 except that the optical compensation sheet prepared in Example 15 was used. The light source was placed in a direction inclined by 20 ° from the normal direction of the display surface of the prepared HAN type liquid crystal display device, and irradiated with light. A voltage was applied to the HAN mode liquid crystal cell with a 55 Hz rectangular wave. The NW mode of 2 V for white display and 6 V for black display was used, and the ratio of transmittance (white display / black display) was defined as the contrast ratio. The contrast ratio from the top, bottom, left and right was measured with a meter (bm-7, manufactured by TOPCON). As a result, favorable results were obtained in which the upper viewing angle (angle of the viewing field at which a contrast ratio of 10 was obtained) was 48 degrees, the lower viewing angle was 28 degrees, and both the left and right viewing angles were 41 degrees.

Example 18 (Preparation of OCB Type Liquid Crystal Display Device) The average direction of a line obtained by orthogonally projecting the normal of the disk surface of the optically anisotropic layer onto the surface of the support, the slow axis of the support and An OCB-type liquid crystal display device was produced in the same manner as in Example 12, except that the angle was adjusted to 45 °.
Observation of an image displayed on the OCB mode liquid crystal cell showed that light leakage from a diagonal direction of black display was smaller than that of the liquid crystal display device of Example 12.

[Example 19] (Preparation of OCB type liquid crystal display device) The average direction of a line obtained by orthogonally projecting the normal of the disk surface of the optically anisotropic layer onto the support surface, the slow axis of the support, An OCB type liquid crystal display device was produced in the same manner as in Example 13 except that the angle was adjusted to 45 °.
Observation of an image displayed on the OCB mode liquid crystal cell showed that light leakage from a diagonal direction of black display was smaller than that of the liquid crystal display device of Example 13.

Example 20 (Preparation of VA-Type Liquid Crystal Display Device) The support side of the optical compensation sheet prepared in Example 12 was attached to one surface of a polarizing film obtained by doping iodine into stretched polyvinyl alcohol. On the other surface of the polarizing film, a commercially available protective film (TD
80U, manufactured by Fuji Photo Film Co., Ltd.) to form a polarizing element. A VA liquid crystal display device was prepared in the same manner as in Example 9 except that the above-mentioned polarizing element was used as a polarizing element on one side without using an optical compensation sheet (the polarizing element on the other side was not changed). Created. The image quality of the image displayed on the VA mode liquid crystal cell was equivalent to the image displayed in Example 9.

[Example 21] (Preparation of OCB type liquid crystal display device) The support side of the optical compensation sheet prepared in Example 13 was attached to one surface of a polarizing film obtained by doping iodine into stretched polyvinyl alcohol. On the other surface of the polarizing film, a commercially available protective film (T
D80U, Fuji Photo Film Co., Ltd.)
A polarizing element was made. An OCB type liquid crystal display device was prepared in the same manner as in Example 10 except that the above-mentioned polarizing element was used as a polarizing element on one side without using an optical compensation sheet (the polarizing element on the other side was not changed). Created. The image quality of the image displayed in the OCB mode liquid crystal cell was equivalent to the image displayed in Example 10.

[Example 22] (Preparation of HAN type liquid crystal display device) The HAN type liquid crystal display was manufactured in the same manner as in Example 11 except that the polarizing element prepared in Example 21 was used without using the optical compensation sheet. A display device was created. The image quality of the image displayed on the HAN mode liquid crystal cell was equivalent to the image displayed in Example 11.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a general liquid crystal display device.

FIG. 2 is a cross-sectional view schematically showing the orientation of a liquid crystalline compound in a VA mode liquid crystal cell when no voltage is applied.

FIG. 3 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in a VA mode liquid crystal cell when a voltage is applied.

FIG. 4 is a schematic diagram of a refractive index ellipsoid obtained when a VA mode liquid crystal cell in which polarizing elements are arranged in crossed Nicols is viewed from the normal direction of the cell substrate.

FIG. 5 is a schematic diagram showing a refractive index ellipse of a positive uniaxial liquid crystal cell and a refractive index ellipse of a negative uniaxial optical compensation sheet.

FIG. 6 is a schematic cross-sectional view showing a combination of a VA mode liquid crystal cell and two optical compensation sheets.

FIG. 7 is a schematic cross-sectional view showing a combination of a VA mode liquid crystal cell and one optical compensation sheet.

FIG. 8 is a schematic cross-sectional view of an optical compensation sheet used for a VA liquid crystal display device.

FIG. 9 is a schematic cross-sectional view of a typical VA liquid crystal display device.

FIG. 10 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in an OCB mode liquid crystal cell.

FIG. 11 is a cross-sectional view schematically showing the orientation of a liquid crystal compound in a HAN mode liquid crystal cell.

FIG. 12 is a schematic sectional view showing a combination of an OCB mode liquid crystal cell and optically anisotropic layers of two optical compensation sheets.

FIG. 13 is a schematic cross-sectional view showing a combination of a HAN mode liquid crystal cell and an optically anisotropic layer of one optical compensation sheet.

FIG. 14 is a schematic sectional view of a representative OCB type liquid crystal display device.

FIG. 15 is a schematic sectional view of a typical HAN type liquid crystal display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Surface treatment film 2a, 2b Protective film of polarizing element 3a, 3b Polarizing film 4a, 4b Optical compensation sheet 5a, 5b Resin substrate of liquid crystal cell 6a, 6b Transparent electrode layer 7 Liquid crystal layer 11, 21 Upper substrate of liquid crystal cell 12, Reference Signs List 22 liquid crystal compound 13, 23 lower substrate of liquid crystal cell 14, 24 normal direction of substrate 15, 25, 26 direction tilted from substrate normal 16a, 16b light traveling direction 27 incident light 28 emitted light 31a, 31b incident Transmission axes 32a, 32b of the polarizing elements on the output side Transmission axes 33a of the polarization elements on the emission side 33a Refractive index ellipse of VA mode liquid crystal cell when no voltage is applied 33b Refractive index ellipse of VA mode liquid crystal cell when voltage is applied 34 VA mode Projection of the optical axis of the liquid crystal molecules in the liquid crystal cell on the liquid crystal cell substrate surface 41 Refractive index ellipsoid of the negative uniaxial optical compensation sheet 41x, 41y In the optical compensation sheet In-plane main refractive index 41z Main refractive index in the thickness direction of optical compensation sheet 42 Negative uniaxial optical compensation sheet 43 Positive uniaxial liquid crystal cell 44 Refractive index ellipsoid 44x of positive uniaxial liquid crystal cell 44y Refractive index in a plane parallel to the liquid crystal cell substrate 44z Refractive index in the thickness direction of the liquid crystal cell 50, 60 Liquid crystal cell 51, 61, 73 Optically anisotropic layer 52, 62, 71 Support 53, 54, 63 OC1, OC2, OC Optical compensation sheet 72 Alignment film 73a, 73b, 73c Discotic liquid crystalline molecules Pa, Pb, Pc Disc surfaces 71a, 71b, 71c of discotic liquid crystalline molecules Surfaces parallel to the surface of support θa, θb , Θc Tilt angle 74 Normal line of support 75, R1, R2, R Rubbing direction of alignment film of optical compensation sheet VAC VA mode liquid crystal cell OCBC OCB mode liquid Cell HANC HAN-mode liquid crystal cell A of, B polarizing element BL backlight RP1, RP2, RP transmission axis RB reflector polarization transmission axis PB polarizing element B of polarization of the rubbing direction PA polarizing element A of the alignment layer of the liquid crystal cell

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // B29K 1:00 B29L 7:00 F term (reference) 2H049 BA02 BA06 BA42 BB03 BB49 BC03 BC22 2H091 FA11X FA11Z FB02 FC01 FC22 HA18 KA02 LA12 4F071 AA09 AC10 AE19 AF31Y AG35 AG36 AH12 AH16 BA02 BB02 BB07 BC01 BC02 BC12 4F205 AA01 AC05 AC07 AE10 AG01 AH33 AH73 GA07 GB02 GC06 GE02 GE06 GE09 GE22 GF24 GN22 4J002 AB021 GP00

Claims (13)

[Claims] 1. A cellulose acetate film having an average acetylation degree of 55.0 to 58.0%, wherein the cellulose acetate film has a wavelength of 5
The retardation value in the thickness direction at 50 nm (Rth
⁵⁵⁰ ) is from 200 to 400 nm. 2. A thickness direction retardation value (Rth ⁴⁰⁰ ) at a wavelength of ⁴⁰⁰ nm, a thickness direction retardation value (Rth ⁵⁵⁰ ) at a wavelength of 550 nm, and a thickness direction retardation value (Rth ⁵⁵⁰ ) at a wavelength of 700 nm.
The cellulose acetate film according to claim 1, wherein (th ⁷⁰⁰ ) satisfies the following formula (11). Equation (11) | Rth ⁷⁰⁰ -Rth ⁴⁰⁰ | / 300 Rth ⁵⁵⁰ <0.001
2 3. The cellulose acetate film according to claim 1, wherein the in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of 550 nm is from 20 to 300 nm. 4. An in-plane retardation value (Re ⁴⁰⁰ ) at a wavelength of ⁴⁰⁰ nm, an in-plane retardation value (Re ⁵⁵⁰ ) at a wavelength of ⁵⁵⁰ nm, and an in-plane retardation value (Re ⁷⁰⁰ ) at a wavelength of 700 nm satisfy the following formula (12). The cellulose acetate film according to claim 1, which satisfies. Formula (12) | Re ⁷⁰⁰ −Re ⁴⁰⁰ | / 300Re ⁵⁵⁰ <0.002 5. The cellulose acetate film according to claim 1, having a thickness of 40 to 120 μm. 6. The method according to claim 1, which is formed by a solvent casting method using an ether having 3 to 12 carbon atoms, a ketone having 3 to 12 carbon atoms or an ester having 3 to 12 carbon atoms as a solvent. Cellulose acetate film. 7. A method of mixing cellulose acetate having an average acetylation degree of 55.0 to 58.0% with an organic solvent,
Swelling cellulose acetate in an organic solvent;
Cooling the swollen mixture to −100 to −10 ° C .; heating the cooled mixture to 0 to 200 ° C. to prepare a cellulose acetate solution in which cellulose acetate is dissolved in an organic solvent; A method for producing a cellulose acetate film, comprising: casting an acetate solution on a support; and evaporating an organic solvent to form a cellulose acetate film. 8. The organic solvent, wherein the organic solvent has 3 to 1 carbon atoms.
The method for producing a cellulose acetate film according to claim 7, wherein the ether is selected from the group consisting of ethers having 2 carbon atoms, ketones having 3 to 12 carbon atoms, and esters having 3 to 12 carbon atoms. 9. An optical compensatory sheet comprising a cellulose acetate film containing cellulose acetate having an average acetylation degree of 55.0 to 58.0%. 10. An optical compensation wherein an optically anisotropic layer containing discotic liquid crystal molecules is provided on a cellulose acetate film containing cellulose acetate having an average acetylation degree of 55.0 to 58.0%. Sheet. 11. A liquid crystal cell carrying a liquid crystal between two electrode substrates, two polarizing elements disposed on both sides of the liquid crystal cell,
And a liquid crystal display device having at least one optical compensation sheet disposed between the liquid crystal cell and the polarizing element, wherein the optical compensation sheet has an average acetylation degree of 55.0 to 58.0%. A liquid crystal display device comprising a cellulose acetate film containing: 12. The liquid crystal display device according to claim 11, wherein an optically anisotropic layer containing discotic liquid crystal molecules is provided on the liquid crystal cell side of the cellulose acetate film. 13. The liquid crystal display device according to claim 11, wherein the liquid crystal cell is a VA mode, OCB mode, or HAN mode liquid crystal cell.