JP2006208465A - Polarizing plate and liquid crystal display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate which hardly causes light leakage into a frame shape on a liquid crystal panel due to distortion by heat or else, and to provide a liquid crystal display device which is provided with the polarizing plate and has high display quality. <P>SOLUTION: The polarizing plate has a layer constitution made by laminating an adhesive layer 1, an optical compensation sheet 2, a polarizing film 3 and a protective layer 4 in this order. The plate is punched out in such a manner that the absorption axis of the polarizing plate is in a direction at an angle of 0° or 90° with respect to the end line of the polarizing plate. The absolute value of the photoelastic coefficient of the adhesive layer is specified to ≤500×10<SP>-12</SP>(1/Pa). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polarizing plate and a liquid crystal display device using the same, and more specifically, a polarizing plate provided with an adhesive layer and an optical compensation sheet that does not cause problems such as light leakage due to distortion such as heat, And a liquid crystal display device having high image display quality using the polarizing plate.

The liquid crystal display device is composed of a polarizing plate and a liquid crystal cell. In a TN mode TFT liquid crystal display device which is currently mainstream, an optical compensation sheet is inserted between a polarizing plate and a liquid crystal cell as described in Patent Document 1 to realize a liquid crystal display device with high display quality.
However, this method has a problem that the liquid crystal display device itself becomes thick.
Therefore, in Patent Document 2, the front contrast can be increased without increasing the thickness of the liquid crystal display device by using an elliptically polarizing plate having a retardation film on one side of the polarizing film and a protective film on the other side. Liquid crystal display devices have been proposed. However, in this proposal, it has been found that the retardation film (optical compensation sheet) is likely to cause an unexpected retardation at the end of the liquid crystal display device due to heat distortion or the like, and has a problem in durability. In other words, this phase difference causes a frame-like light leakage (an increase in transmittance at the end of the liquid crystal display device) during black display on the liquid crystal display device, resulting in a deterioration in display quality of the liquid crystal display device. It was.
With respect to the problem of phase difference generation due to distortion, in Patent Document 3 and Patent Document 4, an optical compensation sheet in which an optically anisotropic layer made of a discotic compound is coated on a transparent support is directly used as a polarizing plate. As a protective film, it has been proposed to solve the above-mentioned problem regarding durability without increasing the thickness of the liquid crystal display device.

In Patent Document 5, the product of the photoelastic coefficient of the optical compensation sheet and the elastic modulus of the adhesive layer is 1.2 × 10 ⁻⁵ or less. In Patent Document 6, the elastic modulus of the adhesive layer is According to Patent Document 7, the product of the linear expansion coefficient of the polarizing plate protective layer and the elastic modulus of the pressure-sensitive adhesive layer is 1.0 × 10 ⁻⁵ (° C.− ¹ · MPa) or less. However, Patent Document 8 proposes that the product of the photoelastic coefficient of the polarizing plate protective layer and the elastic modulus of the pressure-sensitive adhesive layer be 8.0 × 10 ⁻¹² (m ² / N · MPa) or less. Therefore, it is said that the above-mentioned problems relating to durability can be solved.

JP-A-8-50206 JP-A-2-247602 Japanese Patent Laid-Open No. 7-191217 European Patent Application No. 91656 JP 2001-264538 A JP 2001-272542 A JP 2002-122739 A JP 2002-122740 A

However, recently, there are many requests for large-sized liquid crystal display devices of 17 inches or more, and a polarizing plate using the optical compensation sheet according to each of the above proposals as a protective film is mounted on a large panel for such large-sized liquid crystal display devices. However, it has been found that light leakage such as a frame shape due to thermal distortion does not completely disappear. The optical compensation sheet needs not only to have a function of optically compensating the liquid crystal cell but also to be excellent in durability due to a change in use environment.
An object of the present invention is to provide a polarizing plate that reduces light leakage due to distortion such as heat, and a liquid crystal display device having high image display quality using the polarizing plate.

As a result of intensive studies, the present inventors have found that when the liquid crystal panel is heated (when taken into a high-temperature dry dryer, where light leakage due to thermal strain is observed remarkably), polarized light is applied. In a liquid crystal display device using a polarizing plate punched so that the absorption axis direction of the polarizing plate is substantially 0 degree or 90 degrees with respect to the end line of the plate, the absorption axis direction of the polarizing plate is conventionally Compared with a liquid crystal display device using a polarizing plate punched so as to be −45 degrees and 45 degrees, light leakage due to the above-described thermal distortion occurring in the liquid crystal panel peripheral part and the liquid crystal panel corner part is remarkably reduced. I found
The cause is that most of the slow axis of the phase difference generated in each part of the optical compensation sheet of the polarizing plate occurs almost parallel or perpendicular to the end line of the polarizing plate. Compared to the leakage light due to the phase difference generated in each part of the optical compensation sheet when using the polarizing plate punched so that the absorption axis direction of the plate is −45 degrees and 45 degrees, On the other hand, when the polarizing plate punched so that the absorption axis direction of the polarizing plate is substantially 0 degree and 90 degrees is used, the leakage light due to the phase difference generated in each part of the optical compensation sheet is reduced. I found out.
As a result of further intensive studies, the present inventors have found that when the liquid crystal panel is heated, a phase difference due to photoelasticity does not occur only in the optical compensation sheet of the polarizing plate, but the pressure-sensitive adhesive of the polarizing plate. A phase difference was also generated in the agent layer, and it was discovered that light leakage due to the thermal distortion occurred in the liquid crystal panel peripheral part and the liquid crystal panel corner part.
Most acrylic pressure-sensitive adhesives currently in use have a negative photoelastic coefficient, the absolute value of which is as large as about 800 × 10 ^-12 (1 / Pa), and the amount of light leakage due to the thermal strain. Depends on the photoelastic coefficient of the pressure-sensitive adhesive layer of the polarizing plate. If the absolute value of the photoelastic coefficient of the pressure-sensitive adhesive layer is 500 × 10 ⁻¹² (1 / Pa) or less, light leakage due to the thermal strain is caused. I discovered that it can be controlled.
Further, when the polarizing plate is incorporated in a general liquid crystal display device currently on the market, the light leakage amount increases at the light leakage portion at the backlight brightness of about 6000 cd / m ² of the device. That is, it was found that if the increase in transmittance due to heat treatment of the light leakage portion is 0.06% or less, the light leakage due to the thermal strain can hardly be observed with the naked eye and the above object can be achieved.
Further, the above was confirmed not only when the polarizing plate was stretched on the liquid crystal cell but also when it was stretched on the glass plate.
As a result of intensive studies based on the above, it has been found that the above object can be achieved by a polarizing plate having the following constitution, and the present invention has been completed.

In other words, the above discovery has revealed that the above object of the present invention can be achieved by a liquid crystal display device having the following configuration.
(1) A polarizing plate having a layer structure in which an adhesive layer, an optical compensation sheet, a polarizing film, and a protective layer are sequentially laminated, and the absorption axis direction of the polarizing plate is substantially 0 with respect to the end line of the polarizing plate. A polarizing plate that has been punched to an angle of 90 ° or 90 ° and has an absolute value of the photoelastic coefficient of the pressure-sensitive adhesive layer of 500 × 10 ⁻¹² (1 / Pa) or less.
(2) A liquid crystal display device having the polarizing plate according to (1).
(3) A liquid crystal display device in which the liquid crystal display device in (2) is in the TN mode.
(4) A polarizing plate having a layer structure in which an adhesive layer, an optical compensation sheet, a polarizing film, and a protective layer are sequentially laminated, and the absorption axis direction of the polarizing plate is substantially 0 with respect to the end line of the polarizing plate. A TN mode liquid crystal display device having a polarizing plate punched out at an angle of 90 degrees or 90 degrees.

It is possible to provide a liquid crystal display device with high display quality without causing light leakage that occurs when heat or the like is applied to the liquid crystal display device.
In addition, the method of the present invention is excellent in image display quality, and can be advantageously used for OCB (Optically Compensatory Bend), VA (Vertically Aligned), IPS (In Plane Switching), etc. in addition to a TN mode liquid crystal display device. .

  Below, the polarizing plate of this invention is demonstrated. The polarizing plate of the present invention can be used for a liquid crystal display device.

[Polarizer]
A polarizing plate consists of a polarizing film and two transparent protective films arrange | positioned at the both sides. And in this invention, the optical compensation sheet mentioned later is used as one protective film. As the other protective film, a normal polymer film having a light transmittance of 80% or more can be used. It is preferable to use a cellulose acetate film as the polymer film. About a cellulose acetate film, the same thing as what is described as a support body used for an optical compensation sheet can be used.
The polarizing plate of the present invention preferably has a layer structure in which an adhesive layer 1, an optical compensation sheet 2, a polarizing film 3, and a protective layer 4 are sequentially laminated (see FIG. 1). The polarizing plate is attached to the liquid crystal display device through the pressure-sensitive adhesive layer.
The polarizing plate of the present invention is a polarizing plate punched out so that the absorption axis direction of the polarizing plate is substantially 0 degree or 90 degrees with respect to the end line of the polarizing plate. Here, substantially 0 degrees and 90 degrees are preferably 0 degrees ± 10 degrees or 90 degrees ± 10 degrees, more preferably 0 degrees ± 5 degrees or 90 degrees ± 5 degrees.

  Examples of the polarizing film include an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film. The iodine polarizing film and the dye polarizing film are generally produced using a polyvinyl alcohol film. As the production method, a conventionally known method can be applied, and for example, the method described in Patent Document 5 can be mentioned.

[Adhesive]
Examples of the material of the pressure-sensitive adhesive used for the pressure-sensitive adhesive layer constituting the polarizing plate of the present invention (which may be referred to as an adhesive) include a rubber-based pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, and a urethane-based pressure-sensitive adhesive. A pressure sensitive adhesive such as a polyether adhesive and a polyester adhesive is preferred.

In the case of an acrylic pressure-sensitive adhesive, monomers used in the base polymer acrylic polymer include various (meth) acrylic acid esters [(meth) acrylic acid esters include acrylic acid esters and methacrylic acid esters. This is a generic expression, and the following compound names with (meth) have the same meaning. ] Can be used. Specific examples of such (meth) acrylic acid esters include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like. Can be used alone or in combination. Further, in order to impart polarity to the resulting acrylic polymer, a small amount of (meth) acrylic acid can be used instead of a part of the (meth) acrylic acid ester. Furthermore, glycidyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide and the like may be used in combination as the crosslinkable monomer. Furthermore, if desired, other copolymerizable monomers such as vinyl acetate and styrene may be used in combination as long as the adhesive properties of the (meth) acrylic acid ester polymer are not impaired.
Examples of the base polymer of the rubber adhesive include natural rubber, isoprene rubber, styrene-butadiene rubber, recycled rubber, polyisobutylene rubber, styrene-isoprene-styrene rubber, and styrene-butadiene-styrene rubber. Etc.
Examples of the base polymer of the silicone pressure-sensitive adhesive include dimethylpolysiloxane and diphenylpolysiloxane.
Examples of the base polymer of the polyether-based pressure-sensitive adhesive include polyvinyl ethyl ether, polyvinyl butyl ether, polyvinyl isobutyl ether and the like.

The photoelastic coefficient Cn of the pressure-sensitive adhesive layer (PET-W (S) manufactured by Sanlitz Co., Ltd.) currently used for the optical compensation sheet of the WV film manufactured by Fuji Photo Film is -750 × 10 ⁻¹² (1 / Pa) and negative, but the absolute value of the photoelastic coefficient of the pressure-sensitive adhesive layer is preferably smaller, and the absolute value of the photoelastic coefficient is more preferably 500 × 10 ⁻¹² (1 / Pa) or less. .
In order to adjust the photoelastic coefficient of the pressure-sensitive adhesive layer to a desired value, there is a method of selecting a polymer as a main agent used in the pressure-sensitive adhesive. Other than this, the following method is conceivable, but is not limited to this method. One of them is a method of adjusting the optical anisotropy, that is, the intrinsic birefringence of the resin molecule itself, which is an effective means. As a method for adjusting the intrinsic birefringence, “Optical Transparent Resin”, Technical Information Association, (2001), page 20, (1) Modification of molecular structure, (2) Random copolymerization method, (3) Alloying Methods are described and these methods can also be applied in the present invention.
Further, an anisotropic low-molecular doping method as described in Molding, (2003), Vol. 15, No. 3, page 196 can be preferably used.
Further, the anisotropic inorganic particle doping method disclosed in SCIENCE, (2003), VOL301, P812 can be particularly preferably used.
In order to adjust the elastic modulus of the pressure-sensitive adhesive layer to a desired value, the molecular weight of the polymer used for the pressure-sensitive adhesive may be adjusted, or the mixing ratio of the materials may be adjusted.

The pressure-sensitive adhesive can contain a crosslinking agent.
Examples of the crosslinking agent include polyisocyanate compounds, polyamine compounds, melamine resins, urea resins, and epoxy resins.
Furthermore, the pressure-sensitive adhesive may be appropriately selected from conventionally known tackifiers, plasticizers, fillers, antioxidants, ultraviolet absorbers, and the like, as necessary, without departing from the object of the present invention. It can also be used.
The method for forming the pressure-sensitive adhesive layer on the polarizing plate is not particularly limited. Conventional methods such as a method of applying a pressure-sensitive adhesive solution to the polarizing plate and drying, a method of transferring with a release sheet provided with a pressure-sensitive adhesive layer, and the like. Known methods are listed.
Although the thickness of an adhesive layer is not specifically limited, It is preferable to set it as about 10-40 micrometers with a dry film thickness.
As described above, the pressure-sensitive adhesive layer is provided on the upper surface (the surface having the optically anisotropic layer) of the optical compensation sheet of the polarizing plate to obtain the polarizing plate with the pressure-sensitive adhesive layer.

[Optical compensation sheet]
The optical compensation sheet in the present invention is an optical compensation sheet disposed on the liquid crystal cell side of the polarizing plate of the liquid crystal display device.
As the optical compensation sheet used in the present invention, for example, a polymer optical compensation film such as a polymer of triacetylcellulose or norbornene, or an optically anisotropic layer made of a liquid crystal compound is provided on a transparent support. Can be used.

(Polymer optical compensation sheet, transparent support, protective layer for polarizing plate)
The polymer optical compensation sheet and the transparent support of the optical compensation sheet can be used without particular limitation, but it is preferable to use a polymer film having a light transmittance of 80% or more.
As the protective layer of the polarizing plate, the same polymer optical compensation sheet or the same transparent support as the optical compensation sheet can be used.
Examples of the polymer constituting the polymer film include cellulose ester (eg, cellulose acetate, cellulose diacetate, cellulose triacetate (triacetyl cellulose)), polyolefin (eg, norbornene polymer), polycarbonate, and polysulfone. Commercially available polymers (for norbornene polymers, Arton (manufactured by JSR), Zeonore (manufactured by Nippon Zeon), etc.) may be used.

As the support, it is preferable to use a support mainly composed of triacetylcellulose or norbornene. In this specification, “mainly” means that the polymer is 50% or more in the polymer film as the support.
Of these, a cellulose ester is particularly preferable, and a lower fatty acid ester of cellulose is more preferable. 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. Most preferably, the lower fatty acid ester of cellulose is cellulose acetate.
The acetylation degree of cellulose acetate is preferably 55.0 to 62.5%, and more preferably 59.0 to 61.5%. The degree of acetylation means the amount of bound acetic acid per unit mass 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 (also referred to as acetyl cellulose) is preferably 250 or more, and more preferably 290 or more.
The cellulose ester (cellulose acetate) used in the present invention preferably has a narrow molecular weight distribution of Mw / Mn (Mw is mass average molecular weight, Mn is number average molecular weight) by gel permeation chromatography. The specific value of Mw / Mn is preferably in the range of 1.0 to 1.7, more preferably in the range of 1.3 to 1.65, and in the range of 1.4 to 1.6. Most preferably.

  In general, the 2, 3, and 6 hydroxyl groups of cellulose acetate are not evenly distributed by 1/3 of the total substitution degree, and the substitution degree of the 6-position hydroxyl group tends to be small. In the present invention, it is preferable that the substitution degree of the 6-position hydroxyl group of cellulose acetate is larger than that of the 2- and 3-positions. The hydroxyl group at the 6-position with respect to the total substitution degree is preferably substituted with 30% or more, more preferably 31% or more, particularly preferably 32% or more. Furthermore, the substitution degree of the 6-position acetyl group of cellulose acetate is preferably 0.88 or more. In addition to the acetyl group, the hydroxyl group at the 6-position is substituted with a propionyl group, butyroyl group, valeroyl group, benzoyl group, acryloyl group or the like, which is an acyl group having 3 or more carbon atoms. I can do it. The degree of substitution at each position can be determined by NMR. As the cellulose acetate of the present invention, Synthesis Example 1 described in paragraph Nos. 0043 to 0044 of JP-A No. 11-5851, Synthesis Example 2 described in paragraph Nos. 0048 to 0049, and Synthesis examples described in paragraph Nos. 0051 to 0052 The cellulose acetate obtained by the method 3 can be used.

(Retardation raising agent)
When a cellulose acetate film is used as a support for an optical compensation sheet, an aromatic compound having at least two aromatic rings is preferably used as a retardation increasing agent in order to adjust the retardation of the support. The aromatic compound is preferably used in the range of 0.01 to 20 parts by mass, more preferably in the range of 0.05 to 15 parts by mass, with respect to 100 parts by mass of cellulose acetate. It is more preferable to use in the range of 10 to 10 parts by mass. Two or more aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic hetero ring in addition to the aromatic hydrocarbon ring.

  The aromatic hydrocarbon ring is particularly preferably a 6-membered ring (that is, a benzene ring). The aromatic heterocycle is generally an unsaturated heterocycle. The aromatic heterocycle is preferably a 5-membered ring, 6-membered ring or 7-membered ring, more preferably a 5-membered ring or 6-membered ring. Aromatic heterocycles generally have the most double bonds. As the hetero atom, a nitrogen atom, an oxygen atom and a sulfur atom are preferable, and a nitrogen atom is particularly preferable. Examples of aromatic heterocycles include furan ring, thiophene ring, pyrrole ring, oxazole ring, isoxazole ring, thiazole ring, isothiazole ring, imidazole ring, pyrazole ring, furazane ring, triazole ring, pyran ring, pyridine ring , Pyridazine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring. As the aromatic ring, benzene ring, furan ring, thiophene ring, pyrrole ring, oxazole ring, thiazole ring, imidazole ring, triazole ring, pyridine ring, pyrimidine ring, pyrazine ring and 1,3,5-triazine ring are preferable, More preferred are a benzene ring and a 1,3,5-triazine ring. It is particularly preferred that the aromatic compound has at least one 1,3,5-triazine ring.

  The number of aromatic rings contained in the aromatic compound is preferably 2 to 20, more preferably 2 to 12, still more preferably 2 to 8, and most preferably 2 to 6. . The bonding relationship between two aromatic rings can be classified into (a) when a condensed ring is formed, (b) when directly linked by a single bond, and (c) when linked via a linking group (for aromatic rings). , Spiro bonds cannot be formed). The connection relationship may be any of (a) to (c).

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 naphthacene ring, a pyrene ring, Indole ring, isoindole ring, benzofuran ring, benzothiophene ring, indolizine ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring, purine ring, indazole ring, chromene ring, quinoline ring, isoquinoline ring, quinolidine Ring, quinazoline ring, cinnoline ring, quinoxaline ring, phthalazine ring, pteridine ring, carbazole ring, acridine ring, phenanthridine ring, xanthene ring, phenazine ring, phenothiazine ring, phenoxathiin ring, phenoxazine ring and thianthrene ring Be Naphthalene ring, azulene ring, indole ring, benzoxazole ring, benzothiazole ring, benzimidazole ring, benzotriazole ring and quinoline ring are preferred.
The single bond (b) is preferably a bond between carbon atoms of two aromatic rings. Two aromatic rings may be bonded with two or more single bonds to form an aliphatic ring or a non-aromatic heterocyclic ring between the two aromatic rings.

The linking group in (c) is preferably bonded to carbon atoms of two aromatic rings. The linking group is preferably an alkylene group, an alkenylene group, an alkynylene group, —CO—, —O—, —NH—, —S—, or a combination thereof. Examples of linking groups composed of combinations are shown below. In addition, the relationship between the left and right in the following examples of the linking group may be reversed.
c1: -CO-O-
c2: —CO—NH—
c3: -alkylene-O-
c4: —NH—CO—NH—
c5: —NH—CO—O—
c6: —O—CO—O—
c7: -O-alkylene-O-
c8: -CO-alkenylene-
c9: -CO-alkenylene-NH-
c10: -CO-alkenylene-O-
c11: -alkylene-CO-O-alkylene-O-CO-alkylene-
c12: -O-alkylene-CO-O-alkylene-O-CO-alkylene-O-
c13: -O-CO-alkylene-CO-O-
c14: -NH-CO-alkenylene-
c15: -O-CO-alkenylene-

The aromatic ring and the linking group may have a substituent. Examples of the substituent include halogen atom (F, Cl, Br, I), hydroxyl, carboxyl, cyano, amino, nitro, sulfo, carbamoyl, sulfamoyl, ureido, alkyl group, alkenyl group, alkynyl group, aliphatic acyl group , Aliphatic acyloxy group, alkoxy group, alkoxycarbonyl group, alkoxycarbonylamino group, alkylthio group, alkylsulfonyl group, aliphatic amide group, aliphatic sulfonamido group, aliphatic substituted amino group, aliphatic substituted carbamoyl group, aliphatic Substituted sulfamoyl groups, aliphatic substituted ureido groups and non-aromatic heterocyclic groups are included.
In the present specification, when a hydrogen atom is substituted with an atom other than a hydrogen atom, an atom other than the hydrogen atom is also treated as a substituent for convenience.

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

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

The alkylthio group preferably has 1 to 12 carbon atoms. Examples of the alkylthio group include methylthio, ethylthio and octylthio.
The alkylsulfonyl group preferably has 1 to 8 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl and ethanesulfonyl.
The aliphatic amide group preferably has 1 to 10 carbon atoms. Examples of the aliphatic amide group include acetamide.
The aliphatic sulfonamide group preferably has 1 to 8 carbon atoms. Examples of the aliphatic sulfonamido group include methanesulfonamido, butanesulfonamido and n-octanesulfonamido.
The number of carbon atoms of the aliphatic substituted amino group is preferably 1 to 10. Examples of the aliphatic substituted amino group include dimethylamino, diethylamino and 2-carboxyethylamino.
The aliphatic substituted carbamoyl group preferably has 2 to 10 carbon atoms. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl.
The aliphatic substituted sulfamoyl group preferably has 1 to 8 carbon atoms. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl.
The number of carbon atoms in the aliphatic substituted ureido group is preferably 2 to 10. Examples of the aliphatic substituted ureido group include methylureido.
Examples of non-aromatic heterocyclic groups include piperidino and morpholino.

  The molecular weight of the retardation increasing agent is preferably 300 to 800. Specific examples of the retardation increasing agent include compounds described in JP-A Nos. 2000-1111914, 2000-275434, and WO 00/065384.

(Manufacture of cellulose acetate film)
Next, the manufacturing method of a cellulose acetate film is described. As the method and equipment for producing the cellulose acetate film, a conventionally known solution casting film forming method and solution casting film forming apparatus for use in producing a cellulose acetate film are used.
Especially, it is preferable to manufacture a cellulose acetate film by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) in which cellulose acetate is dissolved in an organic solvent. The organic solvent is a solvent selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to contain. The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of ether, ketone and ester (that is, —O—, —CO— and —COO—) can also be used as the organic solvent. The organic solvent may have another functional group such as an alcoholic hydroxyl group. In the case of an organic solvent having two or more types of functional groups, the number of carbon atoms may be within the specified range of the compound having any functional group.

Examples of the ether having 3 to 12 carbon atoms include diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole and phenetole.
Examples of ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.
The number of carbon atoms of the halogenated hydrocarbon is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogenated hydrocarbon hydrogen atoms substituted with halogen is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is 40 to 60 mol%, and most preferably. Methylene chloride is a representative halogenated hydrocarbon.
Two or more organic solvents may be mixed and used.

  A cellulose acetate solution can be prepared by a general method. The general method here means that the treatment is performed at a temperature of 0 ° C. or higher (room temperature or high temperature). The solution can be prepared using a dope preparation method and apparatus in a normal solvent cast method. In the case of a general method, it is preferable to use a halogenated hydrocarbon (particularly methylene chloride) as the organic solvent. The amount of cellulose acetate is preferably adjusted so as to be 10 to 40% by mass in the obtained cellulose acetate solution, and more preferably 10 to 30% by mass. Arbitrary additives described later may be added to the organic solvent (main solvent). The solution can be prepared by stirring cellulose acetate and an organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, cellulose acetate and an organic solvent are placed in a pressure vessel and sealed, and stirred while heating to a temperature not lower than the boiling point of the solvent at normal temperature and in a range where the solvent does not boil. The heating temperature is usually 40 ° C. or higher, preferably 60 to 200 ° C., more preferably 80 to 110 ° C.

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

  A solution can also be prepared by a cooling dissolution method. In the cooling dissolution method, cellulose acetate can be dissolved in an organic solvent that is difficult to dissolve by a normal dissolution method. In addition, even if it is a solvent which can melt | dissolve a cellulose acetate with a normal melt | dissolution method, according to the cooling melt | dissolution method, there exists an effect that a uniform solution can be obtained rapidly, and it is preferable. In the cooling dissolution method, usually, cellulose acetate is first gradually added to an organic solvent with stirring at room temperature. The amount of cellulose acetate is preferably adjusted so as to be contained in the mixture at 10 to 40% by mass. The amount of cellulose acetate is more preferably 10 to 30% by mass. Furthermore, you may add the arbitrary additive mentioned later in a mixture.

  The mixture is then cooled to -100 to -10 ° C (preferably -80 to -10 ° C, more preferably -50 to -20 ° C, most preferably -50 to -30 ° C). The cooling can be performed, for example, in a dry ice / methanol bath (−75 ° C.) or a cooled diethylene glycol solution (−30 to −20 ° C.). When cooled in this way, the mixture of cellulose acetate and organic solvent solidifies. The cooling rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The faster the cooling rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The cooling rate is a value obtained by dividing the difference between the temperature at the start of cooling and the final cooling temperature by the time from the start of cooling until the final cooling temperature is reached.

  Furthermore, when this is heated to 0 to 200 ° C. (preferably 0 to 150 ° C., more preferably 0 to 120 ° C., most preferably 0 to 50 ° C.), cellulose acetate is dissolved in the organic solvent. The temperature can be raised by simply leaving it at room temperature or in a warm bath. The heating rate is preferably 4 ° C./min or more, more preferably 8 ° C./min or more, and most preferably 12 ° C./min or more. The higher the heating rate, the better. However, 10,000 ° C./second is the theoretical upper limit, 1000 ° C./second is the technical upper limit, and 100 ° C./second is the practical upper limit. The heating rate is a value obtained by dividing the difference between the temperature at the start of heating and the final heating temperature by the time from the start of heating until the final heating temperature is reached. . A uniform solution is obtained as described above. If the dissolution is insufficient, the cooling and heating operations may be repeated. Whether the dissolution is sufficient or not can be judged by observing the appearance of the solution by visual observation.

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

  As described above, it is preferable to produce a cellulose acetate film from the prepared cellulose acetate solution (dope) by a solvent cast method. In the case of producing cellulose acetate used as a support for the optical compensation sheet, it is preferable to add the above-mentioned retardation increasing agent to the dope. The dope is cast on a drum or band and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. The casting and drying methods in the solvent casting method are described in U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-115035. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less. After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum or band, and further dried by high-temperature air whose temperature is successively changed from 100 to 160 ° C. to evaporate the residual solvent. The above method is described in JP-B-5-17844, and this method is preferable because it can shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum or band during casting.

  It is also possible to form a film by casting two or more layers using the adjusted cellulose acetate solution (dope). In this case, it is preferable to produce a cellulose acetate film by a solvent cast method. The dope is cast on a drum or band and the solvent is evaporated to form a film. It is preferable to adjust the concentration of the dope before casting so that the solid content is in the range of 10 to 40%. The surface of the drum or band is preferably finished in a mirror state.

  When casting a plurality of cellulose acetate liquids of two or more layers, it is possible to cast a plurality of cellulose acetate solutions, and cellulose acetate from a plurality of casting openings provided at intervals in the traveling direction of the support. A film may be produced while casting and laminating solutions each containing. For example, the methods described in JP-A-61-158414, JP-A-1-122419, and JP-A-11-198285 can be used. It can also be formed into a film by casting a cellulose acetate solution from two casting ports. For example, JP-B-60-27562, JP-A-61-94724, JP-A-61-947245, JP-A-61-104413, JP-A-61-158413, and JP-A-6-134933. The method described in each publication can be used. Further, a cellulose acetate film casting method is disclosed in which a flow of a high-viscosity cellulose acetate solution described in JP-A-56-162617 is wrapped with a low-viscosity cellulose acetate solution, and the high- and low-viscosity cellulose acetate solution is simultaneously extruded. It can also be used.

  Also, using two casting ports, the film formed on the support by the first casting port is peeled off, and the second casting is performed on the side that was in contact with the support surface to produce a film. You can also For example, the method described in Japanese Patent Publication No. 44-20235 can be mentioned. As the cellulose acetate solution to be cast, the same solution may be used, or different cellulose acetate solutions may be used. In order to give a function to a plurality of cellulose acetate layers, a cellulose acetate solution corresponding to the function may be pushed out from each casting port. Furthermore, the cellulose acetate solution can be cast simultaneously with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, an ultraviolet absorbing layer, a polarizing layer).

  In the conventional single-layer liquid, it is necessary to extrude a cellulose acetate solution having a high concentration and a high viscosity in order to obtain a necessary film thickness. In such a case, the stability of the cellulose acetate solution is poor and solid matter is generated, which often causes problems such as defects in the surface and poor flatness. As a solution to this problem, by casting a plurality of cellulose acetate solutions from the casting port, it is possible to extrude a highly viscous solution onto the support at the same time. Not only can it be produced, but also the use of a concentrated cellulose acetate solution can achieve a reduction in drying load and increase the production speed of the film.

(Additive)
Polyester urethane is preferably added to the cellulose acetate film in order to improve mechanical properties. The polyester urethane is preferably a reaction product of a polyester diol represented by the following general formula (1) and a diisocyanate, and is preferably soluble in dichloromethane.
General formula (1):

_{H - (- O- (CH 2} ) p -OOC- (CH 2) m -CO) n -O- (CH 2) p -OH

In general formula (1), p represents an integer of 2 to 4; m represents an integer of 2 to 4; and n represents an integer of 1 to 100.
More specifically, in the constituent polyester, the glycol component is ethylene glycol, 1,3-propanediol, or 1,4-butanediol, and the dibasic acid component is succinic acid, glutaric acid, or adipine. It is a polyester having hydroxyl groups at both ends made of an acid, and the degree of polymerization n is in the range of 1-100. The optimum degree of polymerization varies slightly depending on the type of glycol and dibasic acid used, and the molecular weight of the polyester is particularly preferably in the range of 1000 to 4500.
The dichloromethane-soluble polyester urethane resin is a compound having a repeating unit represented by the following general formula (2), which is obtained by the reaction of the polyester of the general formula (1) and diisocyanate.

General formula (2):

-CONH-R-NHCO- (O- ( CH 2) p -OOC- (CH 2) m -CO) n -O- (CH 2) p -O) -

In general formula (2), p represents an integer of 2 to 4; m represents an integer of 2 to 4; n represents an integer of 1 to 100; R represents a divalent atomic group residue Represents. Examples of the divalent atomic group residue include those represented by the following formula, for example.

Examples of the diisocyanate component used in the polyurethane compound include polymethylene diisocyanate represented by ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (general formula: OCN (CH ₂ ) _p NCO (p represents an integer of 2 to 8)), p-phenylene diisocyanate, tolylene diisocyanate, p, p′-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate Aromatic diisocyanates such as narate, m-xylylene diisocyanate and the like can be mentioned, but are not limited thereto. Among these, tolylene diisocyanate, m-xylylene diisocyanate, and tetramethylene diisocyanate are readily available, relatively stable and easy to handle, and cellulose acetate when polyurethaneized. This is preferable because of its excellent compatibility.

The molecular weight of the polyester urethane resin is preferably in the range of 2,000 to 50,000, and can be appropriately selected depending on the type or molecular weight of the component polyesters or the diisocyanate component that is a linked group thereof. The molecular weight of the polyester urethane resin is more preferably in the range of 5,000 to 15,000 in terms of improving the mechanical properties of the cellulose acetate film and compatibility with the cellulose acetate. The synthesis of the dichloromethane-soluble polyester urethane can be easily obtained by mixing the polyester diol represented by the general formula (1) and diisocyanate and heating with stirring. The polyester diol represented by the general formula (1) is a hot melt condensation method by a polyesterification reaction or transesterification reaction between a corresponding dibasic acid or an alkyl ester thereof and a glycol, or an acid of these acids. It can be easily synthesized by appropriately adjusting the terminal group to be a hydroxyl group by any of the interfacial condensation methods of chloride and glycols.
The dichloromethane-soluble polyester urethane resin used in the present invention is extremely compatible with cellulose acetate having an acetylation degree of 58% or more. Although a slight difference is recognized depending on the structure of the resin, when the molecular weight of the polyester urethane is 10,000 or less, even 200 parts by mass of the polyester urethane is compatible with 100 parts by mass of the cellulose acetate.

  Therefore, when polyester urethane resin is mixed with cellulose acetate to improve the mechanical properties of the film, the content of polyester urethane resin is appropriately determined according to the type of urethane resin, molecular weight, and desired mechanical properties. That's fine. In order to improve mechanical properties while maintaining the properties of cellulose acetate, it is preferable to contain 10 to 50% by mass of polyester urethane resin with respect to cellulose acetate. This polyester urethane resin is stable and does not thermally decompose up to at least 180 ° C. This dichloromethane-soluble polyester urethane is extremely compatible with cellulose acetate having a degree of acetylation of 58% or more. Therefore, when both are mixed and formed into a film, a film with extremely high transparency can be obtained. Moreover, since these polyester urethanes have a high average molecular weight, they are hardly volatile even at high temperatures, unlike conventional low-molecular plasticizers. Therefore, the film obtained by forming a film from these mixtures has less inconvenience due to the volatilization and migration of the plasticizer found in the conventional plasticizer in the subsequent processing.

Addition of polyester urethane to the cellulose acetate film is preferable because the folding strength and tear strength at high and low temperatures are increased, and the film is difficult to tear.
Conventionally, low molecular plasticizers have been used to improve the bending strength and tear strength of a film. This method is effective to some extent at room temperature and high humidity, but the film is not flexible at low temperature and high humidity, and satisfactory results are not always obtained. Furthermore, when an attempt was made to improve mechanical properties with a low molecular plasticizer, it was common that the mechanical properties such as tensile strength significantly decreased with the amount of plasticizer added. When dichloromethane-soluble polyester urethane resin is added to cellulose acetate, a slight decrease in tensile strength is observed with the amount of resin added, but there is clearly little decrease in strength compared to the addition of low molecular plasticizer, A tough film having a high bending strength almost equal to the case of no addition can be obtained.
Furthermore, the migration of the plasticizer at low temperature and high humidity can be prevented by mixing polyester urethane. Therefore, a transparent and glossy film that does not adhere to each other, is very flexible, and does not cause wrinkles can be obtained.

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

  Degradation inhibitors (eg, antioxidants, peroxide decomposers, radical inhibitors, metal deactivators, acid scavengers, amines) may be added to the cellulose acetate film. The deterioration preventing agents are described in JP-A-3-199201, JP-A-51907073, JP-A-5-194789, JP-A-5-271471, and JP-A-6-107854. The addition amount of the deterioration preventing agent is preferably 0.01 to 1% by mass of the solution (dope) to be prepared, and more preferably 0.01 to 0.2% by mass. When the addition amount is less than 0.01% by mass, the effect of the deterioration preventing agent is hardly recognized. When the addition amount exceeds 1% by mass, bleed-out (bleeding) of the deterioration preventing agent to the film surface may be observed. Examples of particularly preferred deterioration inhibitors include butylated hydroxytoluene (BHT) and tribenzylamine (TBA).

(Biaxial stretching)
The cellulose acetate film is preferably stretched in order to reduce virtual strain. Since the virtual strain in the stretching direction can be reduced by stretching, biaxial stretching is more preferable in order to reduce the strain in all directions in the plane. Biaxial stretching includes simultaneous biaxial stretching and sequential biaxial stretching, but sequential biaxial stretching is preferred from the viewpoint of continuous production, and after casting the dope, the film is peeled off from the band or drum, After stretching in the width direction (longitudinal method), the film is stretched in the longitudinal direction (width direction). Methods for stretching in the width direction are described in, for example, JP-A-62-115035, JP-A-4-152125, JP-A-2842211, JP-A-298310, and JP-A-11-48271. Yes.
The film is stretched at room temperature or under heating conditions. The heating temperature is preferably not higher than the glass transition temperature of the film. The film can be stretched by a treatment during drying, and is particularly effective when the solvent remains. In the case of stretching in the longitudinal direction, for example, the film is stretched by adjusting the speed of the film transport roller so that the film winding speed is higher than the film peeling speed. In the case of stretching in the width direction, 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 the film is dried, it can be stretched using a stretching machine (preferably uniaxial stretching using a long stretching machine). The stretch ratio of the film (the ratio of the increase due to stretching relative to the original length) is preferably in the range of 5 to 50%, more preferably in the range of 10 to 40%, and in the range of 15 to 35%. Most preferably.

  These steps from casting to post-drying may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas. The winder used for producing the cellulose acetate film used in the present invention may be a commonly used winder such as a constant tension method, a constant torque method, a taper tension method, a program tension control method with a constant internal stress, or the like. It can be wound up by the method.

(Surface treatment of cellulose acetate film)
The cellulose acetate film is preferably subjected to a surface treatment. Specific examples include corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment, and ultraviolet irradiation treatment. It is also preferable to provide an undercoat layer as described in JP-A-7-333433. From the viewpoint of maintaining the flatness of the film, the temperature of the cellulose acetate film in these treatments is preferably Tg (glass transition temperature) or less, specifically 150 ° C. or less.
When using a cellulose acetate film as a transparent protective film of a polarizing plate, it is particularly preferable to carry out an acid treatment or an alkali treatment, that is, a saponification treatment on cellulose acetate, from the viewpoint of adhesiveness with a polarizing film. The surface energy is preferably 55 mN / m or more, and more preferably 60 mN / m or more and 75 mN / m or less.

  Hereinafter, the alkali saponification treatment will be specifically described as an example. The alkali saponification treatment of the cellulose acetate film is preferably performed in a cycle in which the film surface is immersed in an alkaline solution, neutralized with an acidic solution, washed with water and dried. Examples of the alkaline solution include a potassium hydroxide solution and a sodium hydroxide solution, and the prescribed concentration of hydroxide ions is preferably in the range of 0.1 to 3.0 mol / L, and preferably 0.5 to 2.0. More preferably, it is in the range of mol / L. The alkaline solution temperature is preferably in the range of room temperature to 90 ° C, and more preferably in the range of 40 to 70 ° C.

The surface energy of a solid can be determined by a contact angle method, a wet heat method, and an adsorption method as described in “Basics and Applications of Wetting” (issued by Realize 1989.12.10). In the case of the cellulose acetate film of the present invention, it is preferable to use a contact angle method. Specifically, two types of solutions having known surface energies are dropped on a cellulose acetate film, and at the intersection between the surface of the droplet and the surface of the film, the angle formed by the tangent line drawn on the droplet and the film surface The surface angle of the film can be calculated by defining the angle containing the droplet as the contact angle.
The thickness of the support is preferably 10 to 200 μm, and more preferably 20 to 150 μm.

(Alignment film)
The optical compensation sheet is provided with an optically anisotropic layer formed from a liquid crystalline compound on a support (which will be described below using a cellulose acetate film which is a preferred example of the support as a representative of the support). Although it is produced by this, an orientation film can be provided between the optically anisotropic layers provided on a cellulose acetate film. Thus, in this specification, “on the support” means not only directly on the support but also includes a case where the support is provided via another layer such as an alignment film.
The alignment film functions to align the liquid crystalline compound used for the optically anisotropic layer in a certain direction. Therefore, an alignment film is essential for producing an optical compensation sheet. However, if the alignment state is fixed after aligning the liquid crystalline compound, the alignment film plays its role and is not particularly necessary for the optical compensation sheet itself. It is not an essential component. Therefore, once the optical anisotropic layer is aligned on the alignment film, the formed alignment state is fixed, and only the optical anisotropic layer on the alignment film in which the alignment state is fixed is transferred onto the cellulose acetate film. Thus, it is possible to produce an optical compensation sheet comprising a support having no alignment film and an optically anisotropic layer.

  The alignment film has a function of defining the alignment direction of the liquid crystalline compound. The alignment film is an organic compound (eg, ω-tricosanoic acid) formed by rubbing treatment of an organic compound (preferably polymer), oblique deposition of an inorganic compound, formation of a layer having a microgroove, or Langmuir-Blodgett method (LB film). , Dioctadecylmethylammonium chloride, methyl stearylate). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field, or light irradiation is also known.

  The alignment film is preferably formed by polymer rubbing treatment. Polyvinyl alcohol is a preferred polymer. Particularly preferred is a modified polyvinyl alcohol to which a hydrophobic group is bonded. The alignment film can be formed from one type of polymer, but is more preferably formed by rubbing a layer composed of two types of crosslinked polymers. As the at least one polymer, it is preferable to use either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent. The alignment film is formed by reacting a polymer having a functional group or a polymer into which a functional group is introduced by polymerizing the polymer by light, heat, pH change, or the like; or a cross-linking agent that is a compound having high reaction activity Can be formed by introducing a linking group derived from a cross-linking agent between polymers to cross-link between the polymers.

  Such crosslinking is carried out by applying an alignment film coating solution containing the polymer or a mixture of a polymer and a crosslinking agent on a cellulose acetate film and then heating the coating film. As long as the durability of the optical compensation sheet can be ensured, the cross-linking process may be performed at any stage after the alignment film is coated on the cellulose acetate film until the optical compensation sheet is obtained. Considering the orientation of the liquid crystal compound layer (optically anisotropic layer) formed on the alignment film, it is also preferable to sufficiently crosslink after aligning the liquid crystal compound. In general, the alignment film is crosslinked by applying an alignment film coating solution on a cellulose acetate film and drying by heating. It is preferable that the heating temperature of the coating solution is set low so that the alignment film is sufficiently cross-linked at the stage of the heat treatment when forming the optically anisotropic layer described later.

  As the polymer used for the alignment film, either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent can be used. Of course, some polymers are possible. Examples of polymers include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleimide copolymer, polyvinyl alcohol and modified polyvinyl alcohol, poly (N-methylol acrylamide), styrene / vinyl toluene copolymer, Polymers such as chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, carboxymethyl cellulose, polyethylene, polypropylene, and polycarbonate, Mention may be made of compounds such as gelatin and silane coupling agents. Examples of preferable polymers include water-soluble polymers such as poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol, and modified polyvinyl alcohol. Gelatin, polyvinyl alcohol and modified polyvinyl alcohol are preferably used, and polyvinyl alcohol and modified polyvinyl alcohol are more preferably used. It is most preferable to use two types of polyvinyl alcohol or modified polyvinyl alcohol having different degrees of polymerization.

Examples of polyvinyl alcohol include polyvinyl alcohol having a saponification degree in the range of 70 to 100%. Generally, the degree of saponification is in the range of 80 to 100%, and more preferably in the range of 85 to 95%. The polymerization degree of polyvinyl alcohol is preferably in the range of 100 to 3000. Examples of the modified polyvinyl alcohol include polyvinyl alcohol modified by copolymerization, modification by chain transfer, or modification by block polymerization. Examples of the modifying group in the case of copolymerization modification include COONa, Si (OH) ₃ , N (CH ₃ ) ₃ .Cl, C ₉ H ₁₉ COO, SO ₃ , Na, C ₁₂ H _{25 and the} like. Examples of the modifying group in the case of modification by chain transfer include COONa, SH, C ₁₂ H _{25 and the} like. Examples of the modifying group in the case of modification by block polymerization include COOH, CONH ₂ , C ₆ H _{5 and the} like. Among these, unmodified or modified polyvinyl alcohol having a saponification degree in the range of 80 to 100% is preferable. Further, unmodified polyvinyl alcohol and modified polyvinyl alcohol having a saponification degree in the range of 85 to 95% are more preferable.

  As the modified polyvinyl alcohol, it is particularly preferable to use a modified product of polyvinyl alcohol modified with a compound represented by the following general formula. Hereinafter, this modified polyvinyl alcohol is referred to as a specific modified polyvinyl alcohol.

In the formula, R ¹ represents an alkyl group, an acryloylalkyl group, a methacryloylalkyl group, or an epoxyalkyl group; W represents a halogen atom, an alkyl group, or an alkoxy group; X represents an active ester, an acid anhydride, Or represents a group of atoms necessary to form an acid halide; p represents 0 or 1; and n represents an integer of 0 to 4. The specific modified polyvinyl alcohol is preferably a modified product of polyvinyl alcohol by a compound represented by the following general formula.

In the formula, X ¹ represents an atomic group necessary for forming an active ester, an acid anhydride, or an acid halide, and m represents an integer of 2 to 24.

  Examples of the polyvinyl alcohol used for reacting with the compounds represented by these general formulas include the above-mentioned unmodified polyvinyl alcohol and those modified by copolymerization, that is, modified by chain transfer, modified by block polymerization. A modified product of polyvinyl alcohol, such as those obtained. Preferred examples of the specific modified polyvinyl alcohol are described in detail in JP-A-9-152509. A method for synthesizing these polymers, a method for measuring a visible absorption spectrum, a method for determining a modification group introduction rate, and the like are described in detail in JP-A-8-338913.

  Examples of crosslinking agents include aldehydes, N-methylol compounds, dioxane derivatives, compounds that act by activating carboxyl groups, active vinyl compounds, active halogen compounds, isoxazoles, and dialdehyde starch. Can do. Examples of aldehydes include formaldehyde, glyoxal, and glutaraldehyde. Examples of N-methylol compounds include dimethylol urea and methylol dimethyl hydantoin. Examples of dioxane derivatives include 2,3-dihydroxydioxane. Examples of compounds that act by activating the carboxyl group include carbenium, 2-naphthalenesulfonate, 1,1-bispyrrolidino-1-chloropyridinium, and 1-morpholinocarbonyl-3- (sulfonatoaminomethyl). Can be mentioned. Examples of active vinyl compounds include 1,3,5-triacroyl-hexahydro-s-triazine, bis (vinylsulfone) methane, and N, N′-methylenebis- [β- (vinylsulfonyl) propionamide]. . An example of the active halogen compound is 2,4-dichloro-6-hydroxy-s-triazine. These can be used alone or in combination. These are preferable when used in combination with the above water-soluble polymer, particularly polyvinyl alcohol and modified polyvinyl alcohol (including the above-mentioned specific modified products). In view of productivity, it is preferable to use an aldehyde having a high reaction activity, particularly glutaraldehyde.

  There is no particular limitation on the amount of crosslinking agent added to the polymer. The moisture resistance tends to be improved by adding more crosslinking agent. However, when the crosslinking agent is added in an amount of 50% by mass or more based on the polymer, the alignment ability as the alignment film is lowered. Accordingly, the amount of the crosslinking agent added to the polymer is preferably in the range of 0.1 to 20% by mass, and more preferably in the range of 0.5 to 15% by mass. The alignment film contains a certain amount of the crosslinking agent that has not reacted even after the crosslinking reaction is completed. The amount of the crosslinking agent is preferably 1.0% by mass or less in the alignment film. More preferably, it is 5 mass% or less. When the amount of the unreacted crosslinking agent in the alignment film is within the above range, reticulation occurs when used in a liquid crystal display device, when used for a long time, or when left in a high temperature and high humidity atmosphere for a long time. However, sufficient durability is obtained, which is preferable.

The alignment film can be formed by applying a solution containing the polymer or a solution containing the polymer and a crosslinking agent on the cellulose acetate film, followed by drying by heating (crosslinking) and rubbing treatment. The cross-linking reaction may be performed at any time after the coating solution is coated on the cellulose acetate film. When a water-soluble polymer such as polyvinyl alcohol is used as the alignment film forming material, the solvent for preparing the coating solution is an organic solvent such as methanol having a defoaming action, or a mixture of an organic solvent and water. It is preferable to use a solvent. When methanol is used as the organic solvent, the mass ratio of water: methanol is generally 0: 100 to 99: 1, and more preferably 0: 100 to 91: 9. Thereby, generation | occurrence | production of a bubble is suppressed and the defect of the surface of an alignment film and also an optical anisotropic layer reduces remarkably.
Examples of the coating method include a spin coating method, a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method, and an E type coating method. Among these, the E type coating method is particularly preferable.

  The thickness of the alignment film is preferably in the range of 0.1 to 10 μm. The heat drying can be performed at a heating temperature in the range of 20 to 110 ° C. In order to form sufficient crosslinking, the heating temperature is preferably in the range of 60 to 100 ° C, and preferably in the range of 80 to 100 ° C. The drying time can be 1 minute to 36 hours. Preferably it is 5 to 30 minutes. The pH is also preferably set to an optimum value for the crosslinking agent to be used. When glutaraldehyde is used, it is preferably in the range of pH 4.5 to 5.5, particularly preferably pH 5.

  For the rubbing treatment, a treatment method widely adopted as a liquid crystal alignment treatment step of the liquid crystal display device can be used. That is, a method of obtaining alignment by rubbing the surface of the alignment film in a certain direction using paper, gauze, felt, rubber, nylon, polyester fiber or the like can be used. In general, it is carried out by rubbing several times using a cloth in which fibers having a uniform length and thickness are flocked on average.

[Optically anisotropic layer]
In the present invention, the optically anisotropic layer formed from the liquid crystalline compound is formed on the cellulose acetate film directly or via another layer such as an alignment film. As the liquid crystalline compound having a polymerizable group used in the optically anisotropic layer, a rod-like liquid crystalline compound and a discotic liquid crystalline compound are used. The optically anisotropic layer is formed by applying a liquid crystal compound and, if necessary, a coating liquid containing a polymerizable initiator and optional components on the alignment film, and fixing the alignment of the liquid crystal compound by a polymerization reaction. Can be formed.

As a solvent used for adjusting the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane, tetrachloroethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination. The coating liquid can be applied by a known method (eg, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method).
The thickness of the optically anisotropic layer is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and most preferably 1 to 10 μm. Examples of the liquid crystalline compound used in the present invention include rod-shaped liquid crystalline compounds and discotic liquid crystalline compounds, and it is particularly preferable to use discotic liquid crystalline compounds.

(Bar-shaped liquid crystalline compound)
Examples of rod-like liquid crystalline compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines. , Phenyldioxanes, tolanes and alkenylcyclohexylbenzonitriles are preferably used. The rod-like liquid crystalline compound includes a metal complex.
As for the rod-like liquid crystalline compounds, Chapter 4, Chapter 7 and Chapter 11 of the “Chemical Review of Vol. 22” published by the Chemical Society of Japan (1994), and “Liquid Crystal” of the 142th Committee of the Japan Society for the Promotion of Science. It is described in Chapter 3 of “Device Handbook”. The birefringence of the rod-like liquid crystalline compound is preferably in the range of 0.001 to 0.7. The rod-like liquid crystalline compound needs to have a polymerizable group in order to fix its alignment state. Examples of the polymerizable group (Q) are shown below.

  The polymerizable group (Q) is preferably an unsaturated polymerizable group (Q1 to Q7), an epoxy group (Q8) or an aziridinyl group (Q9), more preferably an unsaturated polymerizable group, and an ethylenic group. Most preferably, it is an unsaturated polymerizable group (Q1 to Q6). The rod-like liquid crystalline compound preferably has a molecular structure that is substantially symmetrical with respect to the minor axis direction. For that purpose, it is preferable to have a polymerizable group at both ends of the rod-like molecular structure. Below, the example of a rod-shaped liquid crystalline compound is shown.

  The optically anisotropic layer is composed of a rod-like liquid crystalline compound or a polymerizable initiator described later, or any conventionally known additive (eg, plasticizer, monomer, surfactant, cellulose ester, 1,3,5-triazine compound). And a liquid crystal composition (coating solution) containing a chiral agent) is applied on the alignment film, and the alignment of the liquid crystalline compound is fixed by a polymerization reaction.

(Discotic liquid crystalline compounds)
Examples of discotic liquid crystalline compounds include C.I. Destrade et al., Mol. Cryst. 71, 111 (1981), benzene derivatives described in C.I. Destrade et al., Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 (1990); Kohne et al., Angew. Chem. 96, page 70 (1984) and the cyclohexane derivatives described in J. Am. M.M. Lehn et al. Chem. Commun. , 1794 (1985), J. Am. Zhang et al., J. Am. Chem. Soc. 116, 2655 (1994), and azacrown and phenylacetylene macrocycles. In addition, the discotic liquid crystalline compounds generally have a structure in which these are used as the mother nucleus at the center of the molecule, and linear alkyl groups, alkoxy groups, substituted benzoyloxy groups, etc. are radially substituted as the linear chains. Is also included and exhibits liquid crystallinity. However, the molecule itself is not limited to these as long as it has negative uniaxiality and can give a certain orientation.

  In order to fix the discotic liquid crystalline compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline compound. However, when the polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain the orientation state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystalline compound having a polymerizable group is preferably a compound represented by the following general formula (3).

General formula (3): D (-LP) _n

In the general formula (3), D is a discotic core; L is a divalent linking group, P is a polymerizable group, and n is an integer of 4 to 12. An example of the general formula (3) 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).

  In the general formula (3), the divalent linking group (L) is selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, —CO—, —NH—, —O—, —S—, and combinations thereof. It is preferable that it is a bivalent coupling group. The divalent linking group (L) is a divalent combination of at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO-, -NH-, -O-, and -S-. More preferably, it is a linking group. The divalent linking group (L) is most preferably a divalent linking group in which at least two divalent groups selected from the group consisting of an alkylene group, an arylene group, -CO- and -O- are combined. . The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The number of carbon atoms in the arylene group is preferably 6 to 10.

Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is bonded to the polymerizable group (P). AL represents an alkylene group or an alkenylene group, and AR represents an arylene group. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl 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-O-CO-
L19: -O-CO-AR-O-AL-O-AL-O-AL-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) of the general formula (3) can be determined according to the type of polymerization reaction. Examples of the polymerizable group (P) are shown below.

The polymerizable group (P) is preferably an unsaturated polymerizable group (P1, P2, P3, P7, P8, P15, P16, P17) or an epoxy group (P6, P18). More preferably, it is most preferably an ethylenically unsaturated polymerizable group (P1, P7, P8, P15, P16, P17).
In the general formula (3), as described above, n is an integer of 4 to 12. Specific numbers can be determined according to the type of the disk-shaped core (D). In addition, although the combination of several L and P may differ, it is preferable that it is the same.

  When the discotic liquid crystalline compound is used, the optically anisotropic layer is a layer having negative birefringence, and the surface of the discotic structural unit is inclined with respect to the surface of the cellulose acetate film and the discotic structural unit. The angle formed between the surface and the surface of the cellulose acetate film is preferably changed in the depth direction of the optically anisotropic layer.

  The surface angle (tilt angle) of the disk-like structural unit generally increases or decreases in the depth direction of the optically anisotropic layer and with an increase in the distance from the bottom surface of the optically anisotropic layer. The tilt angle preferably increases with increasing distance. In addition, changes in the inclination angle include continuous increase, continuous decrease, intermittent increase, intermittent decrease, change including continuous increase and continuous decrease, and intermittent change including increase and decrease. it can. The intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. Even if the tilt angle includes a region where the tilt angle does not change, the tilt angle preferably increases or decreases as a whole. Further, the inclination angle is preferably increased as a whole, and particularly preferably continuously changed.

  The tilt angle of the disk-shaped unit on the support side can be generally adjusted by selecting a disk-like liquid crystalline compound or a material for the alignment film, or by selecting a rubbing treatment method. Further, the inclination angle of the disk-like unit on the surface side (opposite to the support) can generally be adjusted by selecting a discotic liquid crystalline compound or another compound used together with the discotic liquid crystalline compound. Examples of the compound used together with the discotic liquid crystalline compound include conventionally known compounds such as a plasticizer, a surfactant, a polymerizable monomer and a polymer. Further, the degree of change in the tilt angle can be adjusted by the same selection as described above.

  The plasticizer, surfactant, and polymerizable monomer used together with the discotic liquid crystalline compound are compatible with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound or can be aligned. Any compound can be used as long as it does not inhibit Among these, polymerizable monomers (eg, compounds having a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group) are preferable. The amount of the compound added is generally in the range of 1 to 50% by mass and preferably in the range of 5 to 30% by mass with respect to the discotic liquid crystalline compound.

  As the polymer used together with the discotic liquid crystalline compound, any polymer can be used as long as it is compatible with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound. A cellulose ester can be mentioned as an example of a polymer. Preferred examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose, and cellulose acetate butyrate. In order not to inhibit the orientation of the discotic liquid crystalline compound, the amount of the polymer added is generally in the range of 0.1 to 10% by mass with respect to the discotic liquid crystalline compound, and in the range of 0.1 to 8% by mass. It is more preferable that it is in the range of 0.1 to 5% by mass.

  The optically anisotropic layer is generally formed by applying a solution obtained by dissolving a discotic liquid crystalline compound and other compounds in a solvent onto an alignment film, drying it, and then heating it to a discotic nematic phase formation temperature, and then aligning it (disco It can be obtained by cooling while maintaining the (tick nematic phase). Alternatively, the optically anisotropic layer is formed by applying a solution obtained by dissolving a discotic liquid crystalline compound and another compound (for example, a polymerizable monomer, a photopolymerization initiator) in a solvent onto the alignment film, and then drying, It is obtained by heating to a discotic nematic phase formation temperature, polymerizing (by irradiation with UV light or the like), and further cooling. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound used in the present invention is preferably 70 to 300 ° C, particularly preferably 70 to 170 ° C.

(Fixing the alignment state of liquid crystalline compounds)
In the present invention, since the liquid crystalline compound has a polymerizable group, the alignment state of the aligned liquid crystalline compound can be maintained and fixed, and thereby the alignment of the optically anisotropic layer is fixed. The The immobilization is preferably performed by a polymerization reaction. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. A photopolymerization reaction is preferred.
Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatics. Group acyloin compounds (described in US Pat. No. 2,722,512), polynuclear quinone compounds (described in US Pat. Nos. 3,046,127 and 2,951,758), combinations of triarylimidazole dimers and p-aminophenyl ketone (US patents) No. 3549367), acridine and phenazine compounds (JP-A-60-105667, US Pat. No. 4,239,850) and oxadiazole compounds (US Pat. No. 4,221,970).
The amount of the photopolymerization initiator used is preferably in the range of 0.01 to 20% by mass, more preferably in the range of 0.5 to 5% by mass, based on the solid content of the coating solution.
Light irradiation for the polymerization of the liquid crystalline compound is preferably performed using ultraviolet rays. The irradiation energy is preferably in the range of 20 mJ / cm ² to 50 J / cm ^2, more preferably in the range of 20 to 5000 mJ / cm ^2, and still more preferably in the range of 100 to 800 mJ / cm ² .
In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions. A protective layer may be provided on the optically anisotropic layer. As described above, an optical compensation sheet can be produced by providing an optically anisotropic layer on a cellulose acetate film.

[Liquid Crystal Display]
The polarizing plate of the present invention is advantageously used for a liquid crystal display device, particularly a TN mode transmissive liquid crystal display device.
In a TN mode liquid crystal cell, rod-like liquid crystalline molecules are substantially horizontally aligned when no voltage is applied, and are twisted and aligned at 60 to 120 °. The TN mode liquid crystal cell is most frequently used as a color TFT liquid crystal display device, and is described in many documents.
When the polarizing plate of the present invention is used in a TN mode transmissive liquid crystal display device, the absorption axis TN2 and the backlight side of the polarizing plate on the viewer side are the same as in the TN mode transmissive liquid crystal display device that is normally used. The polarizers are laminated so that the absorption axis TN13 of the polarizing plate is substantially orthogonal, and the absorption axis TN2 of the polarizing plate on the viewer side is parallel to the rubbing direction (alignment control direction) TN6 of the electrode substrate on the viewer side of the liquid crystal cell. Further, the absorption axis TN13 of the polarizing plate on the backlight side and the rubbing direction (alignment control direction) TN9 of the substrate on the backlight side of the liquid crystal cell are laminated in parallel (FIG. 2). Since the absorption axis directions TN2 and TN13 of the polarizing plate are substantially 0 degrees or 90 degrees with respect to the end line of the polarizing plate, in the normal TN mode transmissive liquid crystal display device, the absorption axis direction of the polarizing plate Unlike the liquid crystal cell rubbing directions of −45 degrees and 45 degrees, in the TN mode transmission type liquid crystal display device of the present invention, not only the absorption axis directions TN2 and TN13 of the polarizing plate but also the rubbing direction of the liquid crystal cell. TN6 and TN9 are substantially 0 degrees or 90 degrees with respect to the end line of the polarizing plate or the liquid crystal cell.
In addition to the TN mode liquid crystal cell, the polarizing plate of the present invention can be advantageously used for liquid crystal display devices such as OCB (Optically Compensatory Bend), VA (Vertically Aligned), and IPS (In Plane Switching).
That is, the liquid crystal display device of the present invention can be applied to TN mode, OCB, VA, IPS, and the like.

  Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

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

<Cellulose acetate solution composition>
Cellulose acetate having an acetylation degree of 60.9% 100 parts by weight Triphenyl phosphate (plasticizer) 8.0 parts by weight Biphenyl diphenyl phosphate (plasticizer) 4.0 parts by weight Methylene chloride (first solvent) 250 parts by weight Methanol (No. 1) 2 solvents) 20 parts by mass

  In another mixing tank, 16 parts by mass of the following retardation increasing agent, 80 parts by mass of methylene chloride and 20 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution. A dope was prepared by mixing 22 parts by mass of the retardation increasing agent solution with 477 parts by mass of the cellulose acetate solution and stirring sufficiently. The addition amount of the retardation increasing agent was 3.0 parts by mass with respect to 100 parts by mass of cellulose acetate.

The obtained dope was cast using a band casting machine. The film having a residual solvent amount of 40% by mass was peeled off from the band, and dried while blowing hot air at 120 ° C. while applying 101% draw in the conveying direction, and spreading by 3% in the width direction with a tenter. . Next, after removing the tenter clip, the film was dried with hot air at 140 ° C. for 20 minutes to produce a cellulose acetate film (thickness: 107 μm) having a residual solvent amount of 0.3 mass%.
The produced cellulose acetate film was immersed in a 2.0N potassium hydroxide solution (25 ° C.) for 2 minutes, neutralized with sulfuric acid, washed with pure water, dried and saponified.

(Formation of alignment film)
On the produced cellulose acetate film, a coating solution having the following composition was applied at 24 ml / m ² with a # 14 wire bar coater. Drying was performed with warm air of 60 ° C. for 60 seconds, and further with warm air of 90 ° C. for 150 seconds. Next, the formed film was rubbed in a direction parallel to the longitudinal direction of the cellulose acetate film.

<Alignment film coating solution composition>
The following modified polyvinyl alcohol 20 parts by mass Water 360 parts by mass Methanol 120 parts by mass Glutaraldehyde (crosslinking agent) 1.0 part by mass

(Formation of optically anisotropic layer and production of optical compensation sheet)
On the alignment film, 91.0 g of the following discotic (liquid crystalline) compound, 9.0 g of ethylene oxide-modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), cellulose acetate butyrate (CAB551-) 0.2, manufactured by Eastman Chemical Co., Ltd.) 2.0 g, cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co., Ltd.) 0.5 g, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Co., Ltd.) 3.0 g, A coating solution in which 1.0 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) was dissolved in 207 g of methyl ethyl ketone was applied with 6.2 cc / m ² with a # 3.6 wire bar. This was heated in a constant temperature zone of 130 ° C. for 2 minutes to orient the discotic compound. Next, UV irradiation was performed for 1 minute using a 120 W / cm high pressure mercury lamp in an atmosphere of 60 ° C. to polymerize the discotic compound. Then, it stood to cool to room temperature. Thus, an optically anisotropic layer was formed and an optical compensation sheet was produced.

  A polarizing film is prepared by adsorbing iodine to a stretched polyvinyl alcohol film, and the optical compensation sheet prepared as described above is subjected to the saponification treatment described above using a polyvinyl alcohol adhesive, and then the cellulose acetate film. Is attached to one side of the polarizing film so that is on the polarizing film side. The transmission axis of the polarizing film and the slow axis of the cellulose acetate film were arranged in parallel. A commercially available cellulose triacetate film (thickness 80 μm, Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) was saponified and pasted as a transparent protective film on the opposite side of the polarizing film using a polyvinyl alcohol adhesive. . In this way, a polarizing plate was produced.

(Punching of polarizing plate)
Two polarizing plates were punched out from the polarizing plate produced as described above so that the absorption axis directions of the polarizing plate were 0 ° and 90 ° with respect to the end line of the polarizing plate.

[Preparation of Polarizing Plate 2]
Two polarizing plates were punched out so that the polarizing plates produced in the same manner as in Production 1 of the polarizing plates were −45 degrees and 45 degrees in the absorption axis direction of the polarizing plates with respect to the end line of the polarizing plates.

[Preparation of pressure-sensitive adhesive 1]
Production of copolymer In a 1000 cc reactor equipped with a cooling device so that nitrogen gas is refluxed and temperature control is facilitated, 94.5 parts by mass of n-butyl acrylate (BA), 5 parts by mass of acrylic acid (AA), A monomer mixture composed of 0.5 part by mass of 2-hydroxyethyl (meth) acrylate (2-HEMA) was added. And 100 mass parts of ethyl acetate (EA) was thrown in as a solvent. Next, in order to remove oxygen out of the system, it was purged with nitrogen gas for 20 minutes and maintained at 65 ° C. to make it uniform, and then 0.03 parts by mass of azobisisobutyronitrile (AIBN) as a reaction initiator Was diluted with 50% concentration in ethyl acetate and allowed to react for 10 hours to obtain the final acrylic polymer.

The acrylic polymer solution (about 50% solid content) obtained by the copolymerization process was mixed well. Next, 1.2 parts by mass of tolylene diisocyanate adduct (TDI-1) of trimethylolpropane, which is an isocyanate-based crosslinking agent, is diluted to 10% by mass in an ethyl acetate solution, and coating properties are taken into consideration. After diluting to an appropriate concentration and mixing uniformly, it was coated on a release paper and dried to obtain a uniform pressure-sensitive adhesive layer of 30 microns.
It was -750 * 10 < ^-12 > (1 / Pa) when the photoelastic coefficient of the above adhesive layer was measured with the JASCO Corporation ellipsometer M-150.

[Preparation of pressure-sensitive adhesive 2]
Production of Copolymer In a 1000 cc reactor equipped with a cooling device so that nitrogen gas is refluxed and temperature control is facilitated, 49.5 parts by mass of n-butyl acrylate (BA), 10 parts by mass of acrylic acid (AA), A monomer mixture composed of 0.5 parts by mass of 2-hydroxyethyl (meth) acrylate (2-HEMA) and 40 parts by mass of benzyl methacrylate (BZMA) was added. And 100 mass parts of ethyl acetate (EA) was thrown in as a solvent. Next, in order to remove oxygen out of the system, it was purged with nitrogen gas for 20 minutes and maintained at 65 ° C. to make it uniform, and then 0.03 parts by mass of azobisisobutyronitrile (AIBN) as a reaction initiator Was diluted with 50% concentration in ethyl acetate and allowed to react for 10 hours to obtain the final acrylic polymer.

The acrylic polymer solution (about 50% solid content) obtained by the copolymerization process was mixed well. Next, 1.2 parts by mass of tolylene diisocyanate adduct (TDI-1) of trimethylolpropane, which is an isocyanate-based crosslinking agent, is diluted to 10% by mass in an ethyl acetate solution, and coating properties are taken into consideration. After diluting to an appropriate concentration and mixing uniformly, it was coated on a release paper and dried to obtain a uniform pressure-sensitive adhesive layer of 30 microns.
It was -500 * 10 < ^-12 > (1 / Pa) when the photoelastic coefficient of the above adhesive layer was measured with the JASCO Corporation ellipsometer M-150.

[Preparation of pressure-sensitive adhesive 3]
NR (pale crepe) 60 parts by mass, SBR (B / S = 71/29) 40 parts by mass, polyisobutylene 10 parts by mass, polyterpene resin (softening point 115 ° C.) 60 parts by mass, hydrogenated rosin glycerol ester 10 parts by mass, 2 parts by mass of an antioxidant (2,6-di-t-butyl-4-cruzol) was dissolved in n-hexane so as to have a solid content of 20% to obtain an adhesive syrup.

The pressure-sensitive adhesive syrup was coated on a release paper and dried to obtain a uniform pressure-sensitive adhesive layer of 30 microns.
It was 500 * 10 < ^-12 > (1 / Pa) when the photoelastic coefficient of the above adhesive layer was measured with the ellipsometer M-150 by JASCO Corporation.

[Preparation of pressure-sensitive adhesive 4]
NR (pale crepe) 60 parts by mass, SBR (B / S = 71/29) 30 parts by mass, polyisobutylene 10 parts by mass, polyterpene resin (softening point 115 ° C.) 60 parts by mass, hydrogenated rosin glycerol ester 10 parts by mass, 2 parts by mass of an antioxidant (2,6-di-t-butyl-4-cruzol) was dissolved in n-hexane so as to have a solid content of 20% to obtain an adhesive syrup.

The pressure-sensitive adhesive syrup was coated on a release paper and dried to obtain a uniform pressure-sensitive adhesive layer of 30 microns.
It was 800 * 10 < ^-12 > (1 / Pa) when the photoelastic coefficient of the above adhesive layer was measured with the ellipsometer M-150 by JASCO Corporation.

(Evaluation of polarizing plate)
[Comparative Example 1]
The adhesive obtained in [Preparation of adhesive 1] was transferred to the polarizing plate obtained in [Preparation of polarizing plate 2] to obtain a polarizing plate with an adhesive.
The polarizing plates produced as described above were attached to both sides of the quartz glass plate one by one. At this time, the two polarizing plates were pasted so that the absorption axes were orthogonal to each other. (Figure 3 (b))
The glass plate on which the above polarizing plate was attached was placed in a 70 ° C. dry dryer for 170 hours and heat-treated, and then the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, light leakage was observed around the polarizing plate. In addition, the luminance distribution was measured with a luminance meter to measure the amount of leakage light.
As a result, the increase in the transmittance of the maximum light leakage portion due to the thermo treatment was 0.12%.

[Comparative Example 2]
The adhesive obtained in [Preparation of adhesive 2] was transferred to the polarizing plate obtained in [Preparation of polarizing plate 2] to obtain a polarizing plate with an adhesive.
The polarizing plates produced as described above were attached to both sides of the quartz glass plate one by one. At this time, the two polarizing plates were pasted so that the absorption axes were orthogonal to each other. (Figure 3 (b))
The glass plate on which the above polarizing plate was attached was placed in a 70 ° C. dry dryer for 170 hours and heat-treated, and then the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, light leakage was observed around the polarizing plate. In addition, the luminance distribution was measured with a luminance meter to measure the amount of leakage light.
As a result, the increase in the transmittance of the maximum light leakage portion due to the thermo treatment was 0.08%.

[Comparative Example 3]
The adhesive obtained in [Preparation 3 of adhesive] was transferred to the polarizing plate obtained in [Preparation 2 of polarizing plate] to obtain a polarizing plate with an adhesive.
The polarizing plates produced as described above were attached to both sides of the quartz glass plate one by one. At this time, the two polarizing plates were pasted so that the absorption axes were orthogonal to each other. (Figure 3 (b))
The glass plate on which the above polarizing plate was attached was placed in a 70 ° C. dry dryer for 170 hours and heat-treated, and then the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, light leakage was observed around the polarizing plate. In addition, the luminance distribution was measured with a luminance meter to measure the amount of leakage light.
As a result, the increase in the transmittance of the maximum light leakage portion due to the thermo treatment was 0.08%.

[Comparative Example 4]
The pressure-sensitive adhesive obtained in [Preparation of pressure-sensitive adhesive 4] was transferred to the polarizing plate obtained in [Preparation of polarizing plate 2] to obtain a polarizing plate with pressure-sensitive adhesive.
The polarizing plates produced as described above were attached to both sides of the quartz glass plate one by one. At this time, the two polarizing plates were pasted so that the absorption axes were orthogonal to each other. (Figure 3 (b))
The glass plate on which the above polarizing plate was attached was placed in a 70 ° C. dry dryer for 170 hours and heat-treated, and then the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, light leakage was observed around the polarizing plate. In addition, the luminance distribution was measured with a luminance meter to measure the amount of leakage light.
As a result, the increase in the transmittance of the maximum light leakage portion due to the thermo treatment was 0.12%.

[Example 1] The pressure-sensitive adhesive obtained in [Preparation of pressure-sensitive adhesive 1] was transferred to the polarizing plate obtained in [Preparation of polarizing plate 1] to obtain a polarizing plate with pressure-sensitive adhesive.
The polarizing plates produced as described above were attached to both sides of the quartz glass plate one by one. At this time, the two polarizing plates were pasted so that the absorption axes were orthogonal to each other. (Fig. 3 (a))
The glass plate on which the above polarizing plate was attached was placed in a 70 ° C. dry dryer for 170 hours and heat-treated, and then the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, almost no light leakage was observed around the polarizing plate. In addition, the luminance distribution was measured with a luminance meter to measure the amount of leakage light.
As a result, the increase in the transmittance of the maximum light leakage portion due to the thermo treatment was 0.06%.

[Example 2]
The adhesive obtained in [Preparation of pressure-sensitive adhesive 2] was transferred to the polarizing plate obtained in [Preparation of polarizing plate 1] to obtain a polarizing plate with adhesive.
The polarizing plates produced as described above were attached to both sides of the quartz glass plate one by one. At this time, the two polarizing plates were pasted so that the absorption axes were orthogonal to each other. (Fig. 3 (a))
The glass plate on which the above polarizing plate was attached was placed in a 70 ° C. dry dryer for 170 hours and heat-treated, and then the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, almost no light leakage was observed around the polarizing plate. In addition, the luminance distribution was measured with a luminance meter to measure the amount of leakage light.
As a result, the increase in the transmittance of the maximum light leakage portion due to the thermo treatment was 0.03%.

[Example 3]
The adhesive obtained in [Preparation of adhesive 3] was transferred to the polarizing plate obtained in [Preparation of polarizing plate 1] to obtain a polarizing plate with adhesive.
The polarizing plates produced as described above were attached to both sides of the quartz glass plate one by one. At this time, the two polarizing plates were pasted so that the absorption axes were orthogonal to each other. (Fig. 3 (a))
The glass plate on which the above polarizing plate was attached was placed in a 70 ° C. dry dryer for 170 hours and heat-treated, and then the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, almost no light leakage was observed around the polarizing plate. In addition, the luminance distribution was measured with a luminance meter to measure the amount of leakage light.
As a result, the increase in the transmittance of the maximum light leakage portion due to the thermo treatment was 0.03%.

[Example 4]
The adhesive obtained in [Preparation of pressure-sensitive adhesive 4] was transferred to the polarizing plate obtained in [Preparation of polarizing plate 1] to obtain a polarizing plate with adhesive.
The polarizing plates produced as described above were attached to both sides of the quartz glass plate one by one. At this time, the two polarizing plates were pasted so that the absorption axes were orthogonal to each other. (Fig. 3 (a))
The glass plate on which the above polarizing plate was attached was placed in a 70 ° C. dry dryer for 170 hours and heat-treated, and then the entire black display state was visually observed in a dark room to evaluate light leakage. As a result, almost no light leakage was observed around the polarizing plate. In addition, the luminance distribution was measured with a luminance meter to measure the amount of leakage light.
As a result, the increase in the transmittance of the maximum light leakage portion due to the thermo treatment was 0.06%.

From the results of the above examples and comparative examples, the polarizing plate punched so that the absorption axis direction of the polarizing plate is substantially 0 ° or 90 ° with respect to the end line of the polarizing plate is It can be seen that the leakage is reduced. Therefore, it is obvious that light leakage due to thermal distortion of the liquid crystal display device can be reduced by using this polarizing plate in a TN mode liquid crystal display device in which such a polarizing plate has not been used conventionally.
In addition, it can be seen that light leakage due to thermal strain is further reduced in the polarizing plate in which the absolute value of the photoelastic coefficient of the pressure-sensitive adhesive layer is 500 × 10 ⁻¹² (1 / Pa) or less. Therefore, it is clear that light leakage due to thermal distortion of the liquid crystal display device can be further reduced when such a polarizing plate is used in the liquid crystal display device as well as the TN mode.

The typical structural example of the polarizing plate of this invention is shown. The schematic diagram of the TN mode liquid crystal display device of this invention is shown. The relationship of the absorption axis of an upper and lower polarizing plate is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Adhesive layer 2 Optical compensation sheet 3 Polarizing film 4 Protective layer
TN 1 upper polarizer
TN 2 upper polarizing plate absorption axis
Optically anisotropic layer on TN 3
TN 4 upper optical anisotropic layer orientation control direction
TN 5 LCD cell electrode substrate
TN 6 upper substrate orientation control direction
TN 7 liquid crystal layer
TN 8 LCD cell lower electrode substrate
TN 9 Lower substrate orientation control direction
TN 10 Lower optical anisotropic layer
TN 11 Lower optical anisotropic layer orientation control direction
TN 12 Lower polarizing plate
TN 13 Lower polarizing plate absorption axis

Claims (4)

A polarizing plate having a layer structure in which an adhesive layer, an optical compensation sheet, a polarizing film, and a protective layer are sequentially laminated, and the absorption axis direction of the polarizing plate is substantially 0 degree or 90 degrees with respect to the end line of the polarizing plate. A polarizing plate, which is punched so as to have a degree, and has an absolute value of a photoelastic coefficient of the pressure-sensitive adhesive layer of 500 × 10 ⁻¹² (1 / Pa) or less.   A liquid crystal display device comprising the polarizing plate according to claim 1.   3. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is in a TN mode.   A polarizing plate having a layer structure in which an adhesive layer, an optical compensation sheet, a polarizing film, and a protective layer are sequentially laminated, and the absorption axis direction of the polarizing plate is substantially 0 degree or 90 degrees with respect to the end line of the polarizing plate. A TN mode liquid crystal display device having a polarizing plate punched to a certain degree.

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