JP2000284124A - Elliptic polarizing plate and tn type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an integrated elliptic polarizing plate suitable to the TN type liquid crystal display device by allowing an optical anisotropic protection film to have a wavelength dispersed value of specific refractive index anisotropy. SOLUTION: The TN type liquid crystal display device has layer structure of a lower elliptic polarizing plate, a TN liquid crystal cell, and an upper elliptic polarizing plate laminated in order from a back light side. The integrated elliptic polarizing plate is formed by laminating a transparent protection film 11, a polarizing film 12, and an optical anisotropic protection film 13 in this order. Th optical anisotropic protection film 13 is adjusted in the dispersed value of refractive index anisotropy, defined by α=Δn(450)/Δn(600), to 0.7 to 1.3. Here, α is the wavelength dispersed value of the refractive index anisotropy of the optical anisotropic protection film 13, Δn(450) is the refractive index anisotropy of the protection film 13 which is measured with light of 450 nm in wavelength, and Δn(600) is the refractive index anisotropy of the protection film 13 measured with light of 600 nm in wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an elliptically polarizing plate comprising a transparent protective film, a polarizing film and an optically anisotropic protective film, and a TN type liquid crystal display.

[0002]

2. Description of the Related Art A TN (Twisted Nematic) type liquid crystal display device includes a TFT (Thin Film Transistor) and an MIM (Meta
l is the most widely used liquid crystal display device in combination with an active element such as an Insulator Metal.

A TN type liquid crystal display device comprises a TN type liquid crystal cell and two polarizing elements. The liquid crystal cell is composed of rod-like liquid crystal molecules, two substrates for enclosing the same, and an electrode layer for applying a voltage to the rod-like liquid crystal molecules. In a TN-type liquid crystal cell, an alignment film for aligning rod-like liquid crystal molecules at a twist angle of 90 ° is provided on two substrates. TN
In order to improve the viewing angle of a liquid crystal display device, an optical compensation sheet (retardation plate) is generally provided between the liquid crystal cell and the polarizing element. The laminate of the polarizing element (polarizing film) and the optical compensation sheet functions as an elliptically polarizing plate. As the optical compensation sheet, a stretched birefringent film has been conventionally used.

[0004]

When a laminate of an optical compensatory sheet comprising a stretched birefringent film and a polarizing element (polarizing film) is used as an elliptically polarizing plate, the stretched birefringent film is used as one protective film of the polarizing element. Can function as Such an elliptically polarizing plate has a layer structure in the order of a transparent protective film, a polarizing film, and an optically anisotropic protective film (stretched birefringent film). The liquid crystal display device is characterized in that it is thin and lightweight, and if one of the constituent elements is reduced by dual use, the device can be made thinner and lighter. Further, if one component of the liquid crystal display device is reduced, one component bonding step is also reduced, and the possibility of occurrence of a failure when manufacturing the device is reduced.

However, in many cases, the optical properties required for the optical compensation sheet and the optical properties required for the protective film of the polarizing element are different. Therefore, an integrated elliptically polarizing plate in which an optical compensatory sheet made of a stretched birefringent film and one protective film of a polarizing element are used in common has been conventionally proposed, but few examples have been actually used.

In order to put into practical use an integrated elliptically polarizing plate having a common protective film for the optical compensatory sheet and one of the polarizing elements,
The optical properties required for the optical compensation sheet and the optical properties required for the protective film of the polarizing element must be satisfied without contradiction. The object of the present invention is in particular for TN
To provide an integrated elliptically polarizing plate suitable for a liquid crystal display device. Another object of the present invention is to provide a TN type liquid crystal display device which is easy to manufacture and is lighter and thinner than the conventional one.

[0007]

An object of the present invention is to provide an optical compensatory sheet of the following (1) to (5) and a T (6) of the following (6).
This was achieved by an N-type liquid crystal display device. (1) An elliptically polarizing plate in which a transparent protective film, a polarizing film, and an optically anisotropic protective film are laminated in this order, wherein the optically anisotropic protective film is in the range of 0.7 to less than 1.3. An elliptically polarizing plate having a wavelength dispersion value of refractive index anisotropy defined by a formula. α = Δn (450) / Δn (600) where α is the wavelength dispersion value of the refractive index anisotropy of the optically anisotropic protective film; Δn (450) is the optical anisotropy measured with light having a wavelength of 450 nm. The refractive index anisotropy of the conductive protective film; and
Δn (600) is the refractive index anisotropy of the optically anisotropic protective film measured at a wavelength of 600 nm. (2) The optically anisotropic protective film has a Re retardation value defined by the following formula in the range of 0 to 100 nm, and an Rth retardation value defined by the following formula in the range of 20 to 400 nm. The elliptically polarizing plate according to (1), which has a value. Re = │nx-ny│ × d Rth = {(n1 + n2) / 2−n3} × d where nx and ny are the in-plane principal refractive indexes of the laminate; d is the thickness of the laminate (nm) ); And n1,
n2 and n3 are the triaxial refractive indexes of the laminate satisfying n1 ≧ n2 ≧ n3. (3) The elliptically polarizing plate according to (1), wherein the slow axis of the optically anisotropic protective film and the transmission axis of the polarizing film are substantially parallel. (4) The elliptically polarizing plate according to (1), wherein the slow axis of the optically anisotropic protective film and the transmission axis of the polarizing film are substantially perpendicular. (5) The elliptically polarizing plate according to (1), wherein the optically anisotropic protective film is a cellulose ester film.

(6) It comprises a TN type liquid crystal cell and two polarizing elements arranged on both sides of the TN type liquid crystal cell. At least one of the polarizing elements has a transparent protective film, a polarizing film and an optically anisotropic protective film in order from the outside. TN which is a laminated elliptically polarizing plate
TN type liquid crystal display device, wherein the optically anisotropic protective film has a wavelength dispersion value of refractive index anisotropy defined by the following formula within a range of 0.7 or more and less than 1.3. Liquid crystal display device. α = Δn (450) / Δn (600) where α is the wavelength dispersion value of the refractive index anisotropy of the optically anisotropic protective film; Δn (450) is the optical anisotropy measured with light having a wavelength of 450 nm. The refractive index anisotropy of the conductive protective film; and
Δn (600) is the refractive index anisotropy of the optically anisotropic protective film measured at a wavelength of 600 nm. In the present specification, the slow axis means a direction in which the refractive index becomes maximum in the plane. Further, the transmission axis means a direction in which the transmittance becomes maximum in the plane. Further, as used herein, "substantially parallel"
Or, “substantially perpendicular” means that the error from exact parallel or perpendicular is less than ± 10 °. The error is
It is preferably less than ± 8 °, more preferably less than ± 4 °, even more preferably less than ± 2 °, and most preferably less than ± 1 °.

[0009]

As a result of the research, the present inventors have found that the wavelength dispersion of the refractive index anisotropy of the optically anisotropic protective film is adjusted within the range of 0.7 or more and less than 1.3, thereby achieving optical compensation. It has been found that the optical properties required for the sheet and the optical properties required for the protective film of the polarizing element can be satisfied without contradiction. By using the optically anisotropic protective film having the above wavelength dispersion value, an integrated elliptically polarizing plate having excellent optical properties can be obtained. This integrated elliptically polarizing plate is particularly effective when used in a TN liquid crystal display device. By using the integrated elliptically polarizing plate, a TN-type liquid crystal display device which is easy to manufacture, lighter and thinner than the conventional one can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram of a TN type liquid crystal display using an integrated elliptically polarizing plate. The TN type liquid crystal display device has a layer configuration in which a lower elliptically polarizing plate (1), a TN liquid crystal cell (2), and an upper elliptically polarizing plate (3) are stacked in this order from the backlight (BL) side. Solid arrows (TA1, TA) written on the lower elliptically polarizing plate (1) and the upper elliptically polarizing plate (3)
3) is the transmission axis of the polarizing film in the elliptically polarizing plate. The wavy arrows (SA1, SA3) drawn on the lower elliptically polarizing plate (1) and the upper elliptically polarizing plate (3) are the slow axes of the laminate of the elliptically polarizing plate and the optically anisotropic protective film. Arrows (RD1, RD2) written in the TN liquid crystal cell (2) indicate the rubbing directions of the two alignment films provided in the liquid crystal cell. FIG.
As shown in (a), the slow axis of the optically anisotropic protective film and the transmission axis of the polarizing film are substantially parallel, or
As shown in FIG. 1B, the slow axis of the optically anisotropic protective film is preferably substantially perpendicular to the transmission axis of the polarizing film.

FIG. 2 is a schematic view of an integrated elliptically polarizing plate. As shown in FIG. 2, the integrated elliptically polarizing plate has a configuration in which a transparent protective film (11), a polarizing film (12), and an optically anisotropic protective film (13) are laminated in this order. Hereinafter, each component of the integrated elliptically polarizing plate will be described in this order.

[Transparent Protective Film] As the transparent protective film, an optically isotropic transparent polymer film is preferably used. Being transparent means that the light transmittance is 80% or more. Specifically, the optical isotropy has an in-plane retardation (Re) of preferably 10 nm or less, more preferably 5 nm or less. Also,
The retardation (Rth) in the thickness direction is preferably 40 nm or less, more preferably 20 nm or less. The definition of the in-plane retardation (Re) and the retardation in the thickness direction (Rth) will be described later for the optically anisotropic protective film. As the transparent protective film, a cellulose ester film, preferably a triacetyl cellulose film, is generally used. The cellulose ester film is preferably formed by a solvent casting method. The thickness of the transparent protective film is 20 to 500.
μm, more preferably 50 to 200 μm.

[Polarizing Film] Iodine-based polarizing films,
There are a dye-based polarizing film using a dichroic dye and a polyene-based polarizing film. The iodine-based polarizing film and the dye-based polarizing film are generally manufactured using a polyvinyl alcohol-based film. The transmission axis (polarization axis) of the polarizing film corresponds to a direction perpendicular to the stretching direction of the film.

[Optical Anisotropic Protective Film] The thickness of the optically anisotropic protective film is preferably from 20 to 500 μm, and preferably 5 to 500 μm.
More preferably, it is 0 to 200 μm. In the present invention, for the optically anisotropic protective film, the wavelength dispersion value of the refractive index anisotropy defined by the following formula is adjusted within the range of 0.7 or more and less than 1.3. α = Δn (450) / Δn (600) where α is the wavelength dispersion value of the refractive index anisotropy of the optically anisotropic protective film; Δn (450) is the optical anisotropy measured with light having a wavelength of 450 nm. The refractive index anisotropy of the conductive protective film; and
Δn (600) is the refractive index anisotropy of the optically anisotropic protective film measured at a wavelength of 600 nm.

[0015] The optically anisotropic protective film has a thickness of 0 to 100.
It is preferable to have a Re retardation value defined by the following formula in the range of nm and an Rth retardation value defined by the following formula in the range of 20 to 400 nm. Re = │nx-ny│ × d Rth = {(n1 + n2) / 2−n3} × d where nx and ny are the in-plane principal refractive indexes of the laminate; d is the thickness of the laminate (nm) ); And n1,
n2 and n3 are the triaxial refractive indexes of the laminate satisfying n1 ≧ n2 ≧ n3.

Further, the wavelength of the optically anisotropic protective film is 600n.
The retardation value in the thickness direction at m is from 20 to
400 nm, preferably 50 to 300 nm
More preferably, it is 60 to 200 nm.
Is most preferred. The birefringence in the thickness direction
{(Nx + ny) / 2-nz} is 7 × 10^-FourOr 4x
10^-3Is preferably 1 × 10^-3~ 4 × 10
^-3More preferably 1.5 × 10^-3Or 4x
10^-3More preferably, 2 × 10^-3To 4
× 10^-3More preferably, 2 × 10^-3
~ 3 × 10 ^-3Is most preferably 2 × 10^-3
~ 2.5 × 10^-3Is particularly preferred.

For the optically anisotropic protective film, it is preferable to use a cellulose ester film having a high retardation. The in-plane retardation (Re) of the cellulose ester film can be adjusted (increased) by stretching the cellulose ester film. Retardation in the thickness direction of cellulose ester film (Rth)
Can be adjusted (to a high value) by (1) using a retardation increasing agent, (2) adjusting the average acetylation degree (acetylation degree), or (3) manufacturing a film by a cooling dissolution method. As a result, a cellulose ester film conventionally considered to be optically isotropic can be used as an optically anisotropic protective film having an optical compensation function. Hereinafter, a method for producing a cellulose ester film having a high retardation will be described.

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

The retardation in the thickness direction can be increased by using a retardation increasing agent. As the retardation increasing agent, a compound having at least two aromatic rings and having a molecular structure that does not sterically hinder the conformation of the two aromatic rings can be used. The retardation increasing agent is preferably used in an amount of 0.3 to 20 parts by weight based on 100 parts by weight of the cellulose ester. The compound having at least two aromatic rings has a π-bonding plane having 7 or more carbon atoms. Unless the configuration of the two aromatic rings is sterically hindered, the two aromatic rings form the same plane. According to the inventor's research,
In order to increase the retardation of the cellulose ester film, it is important that a plurality of aromatic rings form the same plane. In the present specification, the “aromatic ring” includes an aromatic hetero ring in addition to an aromatic hydrocarbon ring. The aromatic hydrocarbon ring is particularly preferably a 6-membered ring (that is, a benzene ring).

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

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

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

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

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

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

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

The number of carbon atoms of the alkylthio group is 1 to 1
It is preferably 2. Examples of the alkylthio group include methylthio, ethylthio and octylthio.
The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl. The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide. The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamide group include methanesulfonamide, butanesulfonamide and n-octanesulfonamide. The aliphatic substituted amino group preferably has 1 to 10 carbon atoms. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino. The aliphatic substituted carbamoyl group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl. The aliphatic substituted sulfamoyl group preferably has 1 to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl. The aliphatic substituted ureido group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted ureido group include methyl ureide. Examples of the non-aromatic heterocyclic group include piperidino and morpholino.

The molecular weight of the retardation enhancer is 30.
It is preferably from 0 to 800. The boiling point of the retardation increasing agent is preferably 260 ° C. or higher.
The boiling point can be measured using a commercially available measuring device (for example, TG / DTA10).
0, manufactured by Seiko Denshi Kogyo KK).

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

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

The solution may be prepared by a general method without employing the cooling dissolution method. The general method means that the treatment is performed at a temperature of 0 ° C. or higher (normal temperature or high temperature).
The solution can be prepared using a dope preparation method and apparatus in a usual solvent casting method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly, methylene chloride) as the organic solvent. The amount of the cellulose ester is adjusted so that the obtained solution contains 10 to 40% by weight. More preferably, the amount of cellulose ester is from 10 to 30% by weight. In the organic solvent (main solvent), any additives described below may be added. The solution can be prepared by stirring the cellulose ester and the organic solvent at room temperature (0 to 40 ° C.). The highly concentrated solution may be stirred under pressure and heating conditions. Specifically, the cellulose ester and the organic solvent are put in a pressurized container, sealed, and stirred while being heated under pressure to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., and more preferably 80 to 1 ° C.
10 ° C.

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

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

Next, the mixture is heated to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -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 the cellulose ester and the organic solvent solidifies. The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and 12 ° C./min.
/ Min or more is most preferable. A higher cooling rate is preferred, but 10,000 ° C./sec is a theoretical upper limit, 1000 ° C./sec is a technical upper limit, and
0 ° C./sec is a practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at which the cooling is started and the final cooling temperature by the time from when the cooling is started to when the temperature reaches the final cooling temperature.

Further, the temperature is raised to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C.,
When heated to the temperature of 0 to 50 ° C., the cellulose ester dissolves in the organic solvent. The temperature may be raised only by leaving it at room temperature or may be heated in a warm bath. The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The heating rate is preferably as high as possible, but the theoretical upper limit is 10,000 ° C./sec.
C / sec is a technical upper limit, and 100 C / sec is a practical upper limit. Note that the heating rate is a value obtained by dividing the difference between the temperature at which heating is started and the final heating temperature by the time from when the heating is started until the final heating temperature is reached. .

As described above, a uniform solution is obtained. If the dissolution is insufficient, the operation of cooling and heating may be repeated. Whether or not the dissolution is sufficient can be determined only by visually observing the appearance of the solution.

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

From the prepared cellulose ester solution (dope), a cellulose ester film is produced by a solvent casting method. The dope is cast on a drum or band and the solvent is evaporated to form a film.
The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35%. It is preferable that the surface of the drum or the band is finished in a mirror state.
The casting and drying methods in the solvent casting method are described in U.S. Pat. Nos. 2,336,310 and 2,367,603.
Nos. 2492078, 2492977, 24
No. 92978, No. 2607704, No. 2739069
Nos. 2739070, British Patent Nos. 640731 and 736892, Japanese Patent Publication No. 45-4554,
JP-A-49-5614, JP-A-60-176834, JP-A-60-203430, and JP-A-62-115035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. It is preferable to dry the film by blowing it for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried with high-temperature air whose temperature is gradually changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in JP-B-5-17844. According to this method, the time from casting to stripping can be reduced. In order to carry out this method, it is necessary that the dope gels at the surface temperature of the drum or band during casting. The solution (dope) prepared as described above satisfies this condition. The thickness of the film to be produced is preferably 40 to 120 μm,
More preferably, it is 70 to 100 μm.

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

The cellulose ester film may contain an antioxidant (eg, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, an amine) or an ultraviolet inhibitor. Good. Regarding the deterioration inhibitor, see JP-A-Hei 3
-199201, 5-1907073, 5-1
No. 94789, No. 5-271471, No. 6-1078
No. 54 describes each of them. The addition amount of the deterioration inhibitor
It 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. Note that cellulose acetate having an average acetylation degree of 55.0 to 58.0% has an average acetylation degree of 58.0%.
As compared with the above-mentioned cellulose triacetate, there is a defect 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).

[Liquid crystal display device] The elliptically polarizing plate of the present invention comprises:
It can be applied to liquid crystal cells of various display modes. Already TN
(Twisted Nematic), IPS (In-Plane Switchin)
g), FLC (Ferroelectric Liquid Crystal), OC
B (Optically Compensatory Bend), STN (Supper
Various display modes such as Twisted Nematic, VA (Vertically Aligned) or HAN (Hybrid Aligned Nematic) have been proposed. The elliptically polarizing plate of the present invention,
This is particularly effective in a TN mode liquid crystal display device.
If the optical anisotropy of the optically anisotropic protective film alone is insufficient for optical compensation of the liquid crystal cell, an optical compensation sheet may be inserted between the elliptically polarizing plate and the liquid crystal cell. Good.

[0042]

[Example 1] (Preparation of optically anisotropic protective film) At room temperature, 45 parts by weight of cellulose acetate having an average acetylation degree of 60.9%, and 1.35 parts by weight of the following retardation increasing agent (1) 2.75 parts by weight of triphenyl phosphate (plasticizer), 2.20 parts by weight of biphenyldiphenyl phosphate (plasticizer), 232.72 parts by weight of methylene chloride, 42.57 parts by weight of methanol and 8.37 parts by weight of n-butanol. A solution (dope) was prepared by mixing 50 parts by weight.

[0043]

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The obtained dope was cast and dried using a band casting machine having an effective length of 6 m so that the dry film thickness became 100 μm. About the obtained cellulose acetate film (optically anisotropic protective film), an ellipsometer (M
-150, manufactured by JASCO Corporation, using a wavelength of 600 n.
The measured retardation (Rth) in the thickness direction at m was 80 nm. The in-plane retardation (Re) was 10 nm. Further, as the wavelength dispersion value of the refractive index anisotropy of the optically anisotropic protective film, Δn (450), which is the refractive index anisotropy of the optically anisotropic protective film measured with light having a wavelength of 450 nm, and at the wavelength of 600 nm. Δn (60), which is the measured refractive index anisotropy of the optically anisotropic protective film.
0), Δn (450) / Δn (600) was 0.86.

(Preparation of Transparent Protective Film) A cellulose acetate film (transparent protective film) was prepared in the same manner as in the preparation of the optically anisotropic protective film except that the retardation increasing agent was not added. The obtained transparent protective film was measured for retardation (Rth) in the thickness direction at a wavelength of 600 nm using an ellipsometer (M-150, manufactured by JASCO Corporation), and was found to be 40 nm. The in-plane retardation (Re) was 10 nm. Further, as the wavelength dispersion value of the refractive index anisotropy of the transparent protective film, Δn (450), which is the refractive index anisotropy of the transparent protective film measured at a wavelength of 450 nm, and the value of the transparent protective film measured at a wavelength of 600 nm. The refractive index anisotropy Δn (60
0) and Δn (450) / Δn (600) were measured and found to be −5.80.

(Preparation of Elliptical Polarizing Plate) Iodine was adsorbed to a stretched polyvinyl alcohol film to prepare a polarizing film. An optically anisotropic protective film was attached to one side of the polarizing film using a polyvinyl alcohol-based adhesive. On the opposite side, a transparent protective film was attached using a polyvinyl alcohol-based adhesive. The transmission axis of the polarizing film and the slow axis of the optically anisotropic protective film were arranged to be perpendicular. Thus, an elliptically polarizing plate was produced. The elliptically polarizing plate was attached to a glass plate using an acrylic adhesive, aged under high temperature and pressure, and then placed in a thermostat at 90 ° C. and left for 500 hours. Examination of the elliptically polarizing plate revealed no problems such as peeling, generation of bubbles, or generation of wrinkles. Further examination after 500 hours (total 1000 hours) in a thermostat at 90 ° C. revealed no problems such as peeling, foaming or wrinkling.

(Preparation of Liquid Crystal Display) A polyimide alignment film was provided on a glass substrate provided with an ITO transparent electrode, and rubbing treatment was performed. Two substrates were stacked via a 5 μm spacer so that the alignment films faced each other. The orientation of the substrate was adjusted so that the rubbing directions of the alignment films were orthogonal. In the gap between the substrates, rod-like liquid crystal molecules (ZL479
2, manufactured by Merck) to form a liquid crystal layer. Δn of the liquid crystal molecule was 0.0969. An elliptically polarizing plate was attached to both sides of the TN liquid crystal cell manufactured as described above so that the optically anisotropic protective film faced the substrate, thereby manufacturing a liquid crystal display device. The slow axis of the optically anisotropic protective film and the rubbing direction of the liquid crystal cell were arranged in parallel. A voltage is applied to the liquid crystal cell of the liquid crystal display device, and the ratio of the transmittance between white display and black display at 2 V for white display and 5 V for black display is defined as the contrast ratio. The viewing angle was measured with the region not present as the viewing angle.
As a result, the vertical viewing angle is 55 ° and the horizontal viewing angle is 85 °.
Was ゜. The front contrast was 110.

Example 2 (Preparation of Optically Anisotropic Protective Film) Instead of 1.35 parts by weight of the retardation increasing agent (1), 1.01 parts by weight of the retardation increasing agent (1) and the following letter An optically anisotropic protective film was produced in the same manner as in Example 1, except that a mixture with 0.34 parts by weight of the deion raising agent (2) was used.

[0049]

Embedded image

With respect to the obtained cellulose acetate film (optically anisotropic protective film), an ellipsometer (M
-150, manufactured by JASCO Corporation, using a wavelength of 600 n.
The measured retardation (Rth) in the thickness direction at m was 80 nm. The in-plane retardation (Re) was 10 nm. Further, as the wavelength dispersion value of the refractive index anisotropy of the optically anisotropic protective film, Δn (450), which is the refractive index anisotropy of the optically anisotropic protective film measured with light having a wavelength of 450 nm, and at the wavelength of 600 nm. Δn (60), which is the measured refractive index anisotropy of the optically anisotropic protective film.
0), Δn (450) / Δn (600) was 0.86.

(Preparation of Elliptically Polarizing Plate) An elliptically polarizing plate was prepared in the same manner as in Example 1 except that the optically anisotropic protective film prepared as described above was used. The elliptically polarizing plate was attached to a glass plate using an acrylic adhesive, aged under high temperature and pressure, and then placed in a thermostat at 90 ° C. and left for 500 hours. Examination of the elliptically polarizing plate revealed no problems such as peeling, generation of bubbles, or generation of wrinkles. Further examination after 500 hours (total 1000 hours) in a thermostat at 90 ° C. revealed no problems such as peeling, foaming or wrinkling.

(Preparation of Liquid Crystal Display) A liquid crystal display was prepared in the same manner as in Example 1 except that the above-mentioned elliptically polarizing plate was used. A voltage is applied to the liquid crystal cell of the liquid crystal display device, and the ratio of the transmittance between white display and black display at 2 V for white display and 5 V for black display is defined as the contrast ratio. The viewing angle was measured with the region not present as the viewing angle. As a result, the upper and lower viewing angles are 60
゜, left and right viewing angles were 90 °. The front contrast was 110.

[Example 3] (Preparation of elliptically polarizing plate) Except that the transmission axis of the polarizing film and the slow axis of the optically anisotropic protective film were arranged in parallel, the same as in Example 1 was used. Thus, an elliptically polarizing plate was produced. Attach the elliptically polarizing plate to the glass plate using an acrylic adhesive,
After aging under high temperature and pressure, it was placed in a thermostat at 90 ° C. and left for 500 hours. When I examined the elliptically polarizing plate,
No problems such as peeling, generation of bubbles or generation of wrinkles were observed. Further examination after 500 hours (total 1000 hours) in a thermostat at 90 ° C. revealed no problems such as peeling, foaming or wrinkling.

(Production of Liquid Crystal Display) A liquid crystal display was produced in the same manner as in Example 1 except that the above-mentioned elliptically polarizing plate was used. A voltage is applied to the liquid crystal cell of the liquid crystal display device, and the ratio of the transmittance between white display and black display at 2 V for white display and 5 V for black display is defined as the contrast ratio. The viewing angle was measured with the region not present as the viewing angle. As a result, the vertical viewing angle is 50
゜, left and right viewing angles were 90 °. The front contrast was 110.

Comparative Example 1 (Preparation of Polarizing Plate) Iodine was adsorbed on a stretched polyvinyl alcohol film to prepare a polarizing film. Two transparent protective films prepared in Example 1 were attached to both sides of the polarizing film using a polyvinyl alcohol-based adhesive. Thus, a polarizing plate was produced.

(Production of Liquid Crystal Display) A liquid crystal display was produced in the same manner as in Example 1 except that the above-mentioned polarizing plate was used in place of an elliptically polarizing plate. A voltage is applied to the liquid crystal cell of the liquid crystal display device, and the ratio of the transmittance between white display and black display at 2 V for white display and 5 V for black display is defined as a contrast ratio.
The viewing angle was measured using a region having a contrast ratio of 10 at the top, bottom, left and right and no gradation inversion as a viewing angle. As a result, the vertical viewing angle was 50 ° and the horizontal viewing angle was 70 °. The front contrast was 120.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a TN liquid crystal display device using an integrated elliptically polarizing plate.

FIG. 2 is a schematic view of an integrated elliptically polarizing plate.

[Explanation of symbols]

BL backlight 1 lower elliptically polarizing plate 2 TN liquid crystal cell 3 upper elliptically polarizing plate TA1, TA3 Transmission axis of polarizing film SA1, SA3 Slow axis of optically anisotropic protective film RD1, RD2 of alignment film provided in liquid crystal cell Rubbing direction 11 Transparent protective film 12 Polarizing film 13 Optically anisotropic protective film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA02 BA04 BA06 BA42 BB03 BB33 BB49 BC09 BC22 2H091 FA08X FA08Z FA11X FA11Z FD06 GA16 HA07 LA11 LA12

Claims (6)

[Claims] 1. An elliptically polarizing plate in which a transparent protective film, a polarizing film and an optically anisotropic protective film are laminated in this order, wherein the optically anisotropic protective film is in a range of 0.7 or more and less than 1.3. Characterized by having a wavelength dispersion value of refractive index anisotropy defined by the following formula: α = Δn (450) / Δn (600) where α is the wavelength dispersion value of the refractive index anisotropy of the optically anisotropic protective film; Δn (450) is the optical anisotropy measured with light having a wavelength of 450 nm. The refractive index anisotropy of the conductive protective film; and
Δn (600) is the refractive index anisotropy of the optically anisotropic protective film measured at a wavelength of 600 nm. 2. The method according to claim 1, wherein the optically anisotropic protective film has a thickness of 0 to 100.
2. A film having a Re retardation value defined by the following formula in the range of nm and an Rth retardation value defined by the following formula in the range of 20 to 400 nm.
The elliptically polarizing plate according to 1. Re = │nx-ny│ × d Rth = {(n1 + n2) / 2−n3} × d where nx and ny are the in-plane principal refractive indexes of the laminate; d is the thickness of the laminate (nm) ); And n1,
n2 and n3 are the triaxial refractive indexes of the laminate satisfying n1 ≧ n2 ≧ n3. 3. The elliptically polarizing plate according to claim 1, wherein the slow axis of the optically anisotropic protective film and the transmission axis of the polarizing film are substantially parallel. 4. The elliptically polarizing plate according to claim 1, wherein the slow axis of the optically anisotropic protective film and the transmission axis of the polarizing film are substantially perpendicular. 5. The elliptically polarizing plate according to claim 1, wherein the optically anisotropic protective film is a cellulose ester film. 6. A TN type liquid crystal cell and two polarizing elements disposed on both sides of the TN type liquid crystal cell. At least one of the polarizing elements has a transparent protective film, a polarizing film, and an optically anisotropic protective film laminated in order from the outside. TN liquid crystal display device, which is an elliptically polarizing plate, wherein the optically anisotropic protective film has a wavelength dispersion of refractive index anisotropy defined by the following formula within a range of 0.7 or more and less than 1.3. A TN-type liquid crystal display device having a value. α = Δn (450) / Δn (600) where α is the wavelength dispersion value of the refractive index anisotropy of the optically anisotropic protective film; Δn (450) is the optical anisotropy measured with light having a wavelength of 450 nm. The refractive index anisotropy of the conductive protective film; and
Δn (600) is the refractive index anisotropy of the optically anisotropic protective film measured at a wavelength of 600 nm.