JP6211118B2 - Optical film, polarizing plate, and liquid crystal display device - Google Patents

Description

  The present invention relates to an optical film useful for a liquid crystal display device, and a polarizing plate and a liquid crystal display device having the optical film.

  A cellulose ester film typified by a cellulose acetate film has high transparency, and is conventionally used as an optical film in various applications for liquid crystal display devices. For example, it is used as a polarizing plate protective film in a liquid crystal display device because it can easily ensure adhesion with polyvinyl alcohol used in a polarizer.

  In recent years, thinning of liquid crystal display devices, particularly liquid crystal display devices for small and medium-sized applications, has been progressing rapidly. There is a demand for thinning a protective film, a protective film that also serves as a retardation film, a normal protective film having a small retardation, and the like.

  As a film used for a liquid crystal display device, for example, Patent Document 1 discloses a polyester polymer containing a polyester component derived from a diol containing an alicyclic skeleton and a dicarboxylic acid derivative containing an alicyclic skeleton, and Cellulose acylate films containing cellulose acylate are described as having improved tear strength.

  Patent Document 2 discloses that a cellulose ester film having an ester plasticizer having an aliphatic cyclic glycol and an aliphatic cyclic dibasic acid having a benzenecarboxylic acid or a phenol residue at both ends is a change in humidity of optical performance. It is described that durability is improved.

JP 2004-292696 A JP 2007-84692 A

By the way, when the present inventors made a thin film of an optical film used for an IPS type liquid crystal display device, a film in which some aliphatic ester oligomers described in Patent Documents 1 and 2 were contained in a cellulose ester was produced. As a result, it was found that due to the low rigidity, there was a problem in manufacturing and handling suitability, and there was a problem that the roll surface was deformed into an uneven shape when wound up and stored in a roll shape (hereinafter also referred to as a depressed beco). It was.
In addition, a film in which some aliphatic ester oligomers described in Patent Documents 1 and 2 are contained in a cellulose ester can be used for a polarizing plate even when a depressed bevel does not occur depending on the type of the aliphatic ester oligomer. It was also found that when the polarizer durability was poor or the addition amount of the aliphatic ester oligomer was small, the retardation would be high.
Patent Documents 1 and 2 do not describe anything about rigidity, and each film described in the Examples exhibits high retardation, and when used in an IPS liquid crystal display device, the display performance is remarkably high. It turns out that it falls.

  The present invention provides an optical film, a polarizing plate, and a liquid crystal display device that can achieve both a high rigidity and a low retardation while achieving a thin film, and improve polarizer durability when used in a polarizing plate. It is an invention to do.

  When the present inventors diligently studied for the purpose of solving the above-mentioned problems, by adding a polyester containing an alicyclic skeleton and having a hydroxyl group-terminated hydrogen atom substituted with a monocarboxylic acid-derived acyl group, It has been found that the above problems can be solved.

（一般式（１）中、Ｘは炭素数２〜１０の非環状の２価の連結基を表す。Ｙは３〜６員環の脂環構造を含む炭素数３〜１２の連結基を表す。）
［５］ ［１］〜［４］のいずれかに記載の光学フィルムは、モノカルボン酸が、炭素数２〜１０の脂肪族モノカルボン酸であることが好ましい。
［６］ ［１］〜［５］のいずれかに記載の光学フィルムは、前記ポリエステルの水酸基価が１０ｍｇＫＯＨ／ｇ以下であることが好ましい。
［７］ ［１］〜［６］のいずれかに記載の光学フィルムは、ポリエステルの含有量が、セルロースエステルに対して５〜２０質量％であることが好ましい。
［８］ ［１］〜［７］のいずれかに記載の光学フィルムを少なくとも１枚有する偏光板。
［９］ 液晶セルおよび該液晶セルの両側に配置された２枚の偏光板を有する液晶表示装置であって、偏光板の少なくとも１つが、［８］に記載の偏光板を有する液晶表示装置。
［１０］ ［９］に記載の液晶表示装置は、液晶セルが、横電界スイッチングモード（ＩＰＳ）型の液晶セルであることが好ましい。
［１１］ ［９］または［１０］に記載の液晶表示装置は、［１］〜［７］のいずれかに記載の光学フィルムが、偏光子と液晶セルとの間に配置されることが好ましい。 The present invention which is means for solving the above problems is as follows.
[1] Cellulose ester and at least one polyester including a cycloaliphatic skeleton in which a hydrogen atom at a hydroxyl group is substituted with an acyl group derived from a monocarboxylic acid, a thickness of 10 to 45 μm, and a relative humidity of 25 ° C. In-plane retardation (Re) at a wavelength of 590 nm in an environment of 60% is −5 to 5 nm, retardation in a thickness direction at a wavelength of 590 nm (Rth) in an environment of 60% relative humidity at 60 ° C. is −5 to 5 nm, and an elastic modulus is An optical film characterized by being 4.2 GPa or more.
[2] In the optical film according to [1], the number average molecular weight Mn of the polyester is preferably 500 to 3000.
[3] In the optical film according to [1] or [2], the polyester is a polymer of a dicarboxylic acid containing an acyclic aliphatic diol and an alicyclic structure, or an aliphatic diol containing an alicyclic structure and an acyclic structure. Preferably, it is derived from a polymer of an aliphatic dicarboxylic acid.
[4] In the optical film according to any one of [1] to [3], the polyester preferably includes a repeating unit represented by the following general formula (1).

(In General Formula (1), X represents an acyclic divalent linking group having 2 to 10 carbon atoms. Y represents a linking group having 3 to 12 carbon atoms including a 3 to 6-membered alicyclic structure. .)
[5] In the optical film according to any one of [1] to [4], the monocarboxylic acid is preferably an aliphatic monocarboxylic acid having 2 to 10 carbon atoms.
[6] In the optical film according to any one of [1] to [5], the hydroxyl value of the polyester is preferably 10 mgKOH / g or less.
[7] In the optical film according to any one of [1] to [6], the polyester content is preferably 5 to 20% by mass with respect to the cellulose ester.
[8] A polarizing plate having at least one optical film according to any one of [1] to [7].
[9] A liquid crystal display device having a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell, wherein at least one of the polarizing plates has the polarizing plate according to [8].
[10] In the liquid crystal display device according to [9], the liquid crystal cell is preferably a transverse electric field switching mode (IPS) type liquid crystal cell.
[11] In the liquid crystal display device according to [9] or [10], the optical film according to any one of [1] to [7] is preferably disposed between the polarizer and the liquid crystal cell. .

  ADVANTAGE OF THE INVENTION According to this invention, the optical film which can achieve high rigidity and a low retardation optical characteristic, achieving a thin film, and improves polarizer durability when used for a polarizing plate can be provided.

  Hereinafter, the contents of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

[Optical film]
The optical film of the present invention includes an alicyclic skeleton, includes at least one polyester in which a hydroxyl group-terminated hydrogen atom is substituted with an acyl group derived from a monocarboxylic acid, has a thickness of 10 to 45 μm, and has a relative humidity of 25 ° C. In-plane retardation (Re) at a wavelength of 590 nm in an environment of 60% is −5 to 5 nm, retardation in a thickness direction at a wavelength of 590 nm (Rth) in an environment of 60% relative humidity at 60 ° C. is −5 to 5 nm, and an elastic modulus is It is characterized by being 4.2 GPa or more.

The optical film of the present invention uses an polyester having a cycloaliphatic skeleton and having a hydroxyl group-terminated hydrogen atom substituted with an acyl group derived from a monocarboxylic acid, so that an ester oligomer is embedded so as to fill a free volume portion of a cellulose ester. Even if it is a thin film, an optical film having high rigidity and low retardation and improved polarizer durability when used in a polarizing plate can be obtained.
Hereinafter, preferred embodiments of the optical film of the present invention will be described.

(Cellulose ester)
The optical film of the present invention contains one or more cellulose esters as a main component. Examples of the cellulose ester include a cellulose ester compound and a compound having an ester-substituted cellulose skeleton obtained by introducing a functional group biologically or chemically using cellulose as a raw material. Here, “main component” means a polymer when a single polymer is included as a raw material, and a polymer with the highest mass fraction when two or more polymers are included as a raw material. Means that.

  The cellulose ester is an ester of cellulose and acid. As the acid constituting the ester, an organic acid is preferable, a carboxylic acid is more preferable, a fatty acid having 2 to 22 carbon atoms is more preferable, and a cellulose acylate which is a lower fatty acid having 2 to 4 carbon atoms is the most. preferable.

  Examples of the cellulose acylate raw material cellulose include cotton linter and wood pulp (hardwood pulp, softwood pulp) and the like, and any cellulose acylate obtained from any raw material cellulose may be used, and may be used in some cases. . Detailed descriptions of these raw material celluloses can be found in, for example, “Plastic Materials Course (17) Fibrous Resin” (Marusawa, Uda, Nikkan Kogyo Shimbun, published in 1970) and Invention Association Publication Technical Report 2001-1745 ( The cellulose described in pages 7 to 8) can be used.

  In the cellulose acylate used in the present invention, a hydrogen atom of a hydroxyl group of cellulose is substituted with an acyl group. The number of carbon atoms in the acyl group is preferably 2-22. The acyl group may be an aliphatic acyl group or an aromatic acyl group, and may be single or substituted with two or more types of acyl groups. Specifically, examples of the cellulose acylate include cellulose alkylcarbonyl ester, alkenylcarbonyl ester, aromatic carbonyl ester, and aromatic alkylcarbonyl ester. Each of the alkyl moiety, the alkenyl moiety, the aromatic moiety, and the aromatic alkyl moiety may further have a substituent. Examples of preferred acyl groups include acetyl, propionyl, butanoyl, heptanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, hexadecanoyl, octadecanoyl, i-butanoyl, t-butanoyl, cyclohexanecarbonyl, Oleoyl, benzoyl, naphthylcarbonyl, cinnamoyl groups and the like are included. Among these, acetyl, propionyl, butanoyl, dodecanoyl, octadecanoyl, t-butanoyl, oleoyl, benzoyl, naphthylcarbonyl, and cinnamoyl are preferable, acetyl, propionyl, and butanoyl are more preferable, and acetyl is most preferable.

  The acyl substitution degree of the cellulose acylate to be used is not particularly limited, but when cellulose acylate having an acyl substitution degree of 2.00 to 2.95 is used, film forming properties and various characteristics of the produced film are considered. Is preferable. The acyl substitution degree can be obtained by measuring the degree of binding of fatty acid such as acetic acid and calculating it. As a measuring method, it can carry out according to ASTM D-817-91.

In the embodiment of the cellulose acylate having at least two kinds of acyl groups of acetyl group / propionyl group / butanoyl group, the total substitution degree is preferably 2.50 to 2.95, and more preferably the acyl substitution degree is 2. It is 60-2.95, More preferably, it is 2.65-2.95.
In the cellulose acylate having only an acetyl group, ie, cellulose acetate, the total substitution degree is preferably 2.00 to 2.95. Furthermore, the substitution degree is more preferably 2.40 to 2.95, and further preferably 2.85 to 2.95.

  The degree of polymerization of cellulose acylate preferably used in the present invention is 180 to 700 in terms of viscosity average polymerization degree, and in cellulose acetate, 180 to 550 is more preferable, 180 to 400 is more preferable, and 180 to 350 is particularly preferable. . If the degree of polymerization is not more than the upper limit, the viscosity of the cellulose acylate dope solution does not become too high, and a film can be easily produced by casting. If the degree of polymerization is equal to or greater than the lower limit, it is preferable because there is no inconvenience such as a decrease in strength of the produced film. The viscosity average degree of polymerization can be measured by Uda et al.'S intrinsic viscosity method {Kazuo Uda, Hideo Saito, "Journal of the Textile Society," Vol. 18, No. 1, pages 105-120 (1962)}. This method is also described in detail in JP-A-9-95538.

  The molecular weight distribution of cellulose acylate preferably used in the present invention is evaluated by gel permeation chromatography, and its polydispersity index Mw / Mn (Mw is a mass average molecular weight, Mn is a number average molecular weight) is small, and the molecular weight A narrow distribution is preferred. The specific value of Mw / Mn is preferably 1.0 to 4.0, more preferably 2.0 to 4.0, and more preferably 2.3 to 3.4. Further preferred.

(polyester)
The polyester used in the present invention will be described.
The polyester is a polyester having an alicyclic skeleton and having a hydroxyl group-terminated hydrogen atom substituted with an acyl group derived from a monocarboxylic acid. It is presumed that ester oligomers exist so as to fill the free volume portion of the cellulose ester, and that both high rigidity and low retardation of the film can be achieved by increasing the ratio of the rigid alicyclic structure.

The polyester is not particularly limited as long as the polyester includes an alicyclic skeleton and a hydrogen atom at a hydroxyl group is substituted with an acyl group derived from a monocarboxylic acid, but a dicarboxylic acid including an acyclic aliphatic diol and an alicyclic structure. It is preferably a derivative derived from a polymer of an acid, or a derivative derived from a polymer of an aliphatic diol containing an alicyclic structure and an acyclic aliphatic dicarboxylic acid, and among them, an acyclic aliphatic diol and More preferred is a derivative derived from a polymer of a dicarboxylic acid containing an alicyclic structure.
The polyester includes an alicyclic skeleton in the main chain, and is a polyester in which a hydroxyl group-terminated hydrogen atom is substituted with an acyl group derived from a monocarboxylic acid, so that a linear aliphatic structural unit is substituted with a cyclic structure. It is particularly preferable from the viewpoint that the film hardness can be improved by itself, and the main chain is a derivative derived from a polymer of an acyclic aliphatic diol and a dicarboxylic acid containing an alicyclic structure, or an aliphatic diol containing an alicyclic structure and a non-cyclic diol. More preferably, the derivative is derived from a polymer of a cyclic aliphatic dicarboxylic acid, and in particular, a derivative derived from a polymer of a dicarboxylic acid whose main chain includes an acyclic aliphatic diol and an alicyclic structure. It is even more particularly preferable, and specifically includes a repeating unit represented by the following general formula (1).

（一般式（１）中、Ｘは炭素数２〜１０の非環状の２価の連結基を表す。Ｙは３〜６員環の脂環構造を含む炭素数３〜１２の連結基を表す。）

(In General Formula (1), X represents an acyclic divalent linking group having 2 to 10 carbon atoms. Y represents a linking group having 3 to 12 carbon atoms including a 3 to 6-membered alicyclic structure. .)

X represents a non-cyclic divalent linking group having 2 to 10 carbon atoms. X is preferably a non-cyclic divalent linking group having 2 to 8 carbon atoms, and more preferably a non-cyclic divalent linking group having 2 to 6 carbon atoms. As the linking group, an alkylene group (preferably 2 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, particularly preferably 2 to 6 carbon atoms), an alkynylene group (preferably 3 to 12 carbon atoms, more preferably carbon atoms). 3 to 10 and particularly preferably 3 to 6 carbon atoms, and the like, and the linking group may contain a molecule other than carbon such as an oxygen atom and a nitrogen atom. The divalent linking group may have a substituent, and examples of the substituent include an alkyl group, an alkoxy group, a hydroxyl group, an alkoxy-substituted alkyl group, and a carboxyl group.
In the present specification, non-cyclic means that a cyclic structure is not included. Examples of the group that does not include a cyclic structure include a linear or branched group.

  Y represents a C3-C12 linking group containing a 3-6 membered alicyclic structure. Y has preferably 3 to 10 carbon atoms, preferably 3 to 8 carbon atoms, and more preferably 3 to 6 carbon atoms. The linking group represented by Y is an alkylene group having an alicyclic structure (preferably having 3 to 12 carbon atoms, more preferably 3 to 10 carbon atoms, particularly preferably 3 to 6 carbon atoms), and an alkynylene group having an alicyclic structure. (Preferably 3 to 12 carbon atoms, more preferably 3 to 10 carbon atoms, and particularly preferably 3 to 6 carbon atoms). The alicyclic structure contained in Y may be either monocyclic or polycyclic as long as it is a 3- to 6-membered ring, but is preferably a single ring. The alicyclic structure is a 3- to 6-membered ring, and a 5- to 6-membered ring is preferable. Specifically, a cyclopropylene group, 1,2-cyclobutylene group, 1,3-cyclobutylene group, 1,2- Examples include a cyclopentylene group, 1,3-cyclopentylene group, 1,2-cyclohexylene group, 1,3-cyclohexylene group, 1,4-cyclohexylene group and the like. The linking group may have a substituent, and examples of the substituent include an alkyl group, an alkoxy group, a hydroxyl group, an alkoxy-substituted alkyl group, and a carboxyl group. The alicyclic structure may have a substituent, and examples of the substituent having the alicyclic structure include an alkyl group, an alkoxy group, a hydroxyl group, an alkoxy-substituted alkyl group, a carboxyl group, and the like. It is a group.

The number average molecular weight (Mn) of the polyester in the present invention is preferably 500 to 3000, more preferably 600 to 1500, and still more preferably 800 to 1200. If the number average molecular weight of the polyester is 500 or more, the volatility is low, and film failure and process contamination due to volatilization under high temperature conditions during stretching of the optical film are less likely to occur. Moreover, if it is 3000 or less, compatibility with a cellulose ester will become high and it will become difficult to produce the bleed-out at the time of film forming and the heat-stretching.
The number average molecular weight of the polyester in the present invention can be measured and evaluated by gel permeation chromatography. Specifically, the value measured by the following method is adopted. The polyester was dissolved in THF, and a high speed GPC manufactured by Tosoh Corporation was used. The number average molecular weight Mn was calculated in terms of polystyrene.

  The polyester used in the present invention is a dicarboxylic acid containing an acyclic aliphatic diol having 2 to 10 carbon atoms and an alicyclic structure having 3 to 12 carbon atoms, or an aliphatic containing an alicyclic structure having 2 to 10 carbon atoms. It is preferable to synthesize from a diol and an acyclic aliphatic dicarboxylic acid having 3 to 12 carbon atoms. As the synthesis method, a known method such as a dehydration condensation reaction of a dicarboxylic acid and a diol, or addition of a dicarboxylic anhydride to glycol and a dehydration condensation reaction can be used.

Here, the polyester is preferably a polyester oligomer obtained by synthesis of an aliphatic dicarboxylic acid, which is a dicarboxylic acid, and a diol.
Hereinafter, dicarboxylic acids and diols that can be preferably used in the synthesis of the polyester in the present invention will be described.

-Dicarboxylic acid-
As the dicarboxylic acid, an aliphatic dicarboxylic acid is used.
Examples of the aliphatic dicarboxylic acid having a 3-6 membered alicyclic structure include 1,4-cyclohexyl dicarboxylic acid, 3-methyl-1,4-cyclohexyl dicarboxylic acid, cyclopropane dicarboxylic acid, 1,2-cyclohexane. Butyl dicarboxylic acid, 1,3-cyclobutyl dicarboxylic acid, 1,2-cyclopentyl dicarboxylic acid, 1,3-cyclopentyl dicarboxylic acid, 1,2-cyclohexyl dicarboxylic acid, 1,3-cyclohexyl dicarboxylic acid, 1 , 4-cyclohexyldicarboxylic acid, and the like. Of these, 1,4-cyclohexyl dicarboxylic acid and 3-methyl-1,4-cyclohexyl dicarboxylic acid are preferable.
Examples of the acyclic aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, suberic acid, azelaic acid, cyclohexanedicarboxylic acid, and sebacic acid. Of these, succinic acid and adipic acid are preferable, and adipic acid is particularly preferable.
The carbon number of the dicarboxylic acid used in the present invention is preferably 3-12, and more preferably 4-8. In the present invention, a mixture of two or more kinds of dicarboxylic acids may be used. In this case, the average carbon number of the two or more kinds of dicarboxylic acids is preferably within the above range. If the carbon number of the dicarboxylic acid is in the above range, it is preferable because it is excellent in compatibility with cellulose acylate and bleed-out hardly occurs even when the optical film is formed and heated.
An acyclic aliphatic dicarboxylic acid and an aliphatic dicarboxylic acid having an alicyclic structure may be used in combination. Specifically, a combination of adipic acid and 1,4-cyclohexyl dicarboxylic acid and a combination of adipic acid and 3-methyl-1,4-cyclohexyl dicarboxylic acid can be mentioned.
When an acyclic aliphatic dicarboxylic acid and an aliphatic dicarboxylic acid having an alicyclic structure are used in combination, the ratio (molar ratio) between them is the molar ratio of the repeating unit derived from the acyclic aliphatic dicarboxylic acid, m, and the alicyclic When the molar ratio of the repeating unit derived from the aliphatic dicarboxylic acid having a structure is n, m: n is 0:10 to 3: 7, and more preferably 0:10 to 1: 9.

-Diol-
An aliphatic diol is used as the diol.
Examples of the aliphatic diol having an alicyclic structure include 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol.
Examples of the acyclic aliphatic diol include alkyl diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl-1 , 3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentane Diol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, diethylene glycol, and the like.
Preferred aliphatic diols are at least one of ethylene glycol, 1,2-propanediol, and 1,3-propanediol, and particularly preferably at least one of ethylene glycol and 1,2-propanediol. Of these, ethylene glycol is particularly preferred from the viewpoint of compatibility with cellulose. When two types are used, it is preferable to use ethylene glycol and 1,2-propanediol.
The number of carbon atoms of the glycol is preferably 2 to 10, more preferably 2 to 6, and particularly preferably 2 to 4. When using 2 or more types of glycols, it is preferable that the average number of carbons of 2 or more types falls in the above range. If the number of carbon atoms of the glycol is in the above range, it is preferable because the compatibility with cellulose acylate is excellent and bleed-out is unlikely to occur at the time of film formation and heat stretching of the optical film.

-Replacement-
The hydrogen atom at the hydroxyl terminal of the polyester used in the present invention is substituted with an acyl group derived from a monocarboxylic acid (hereinafter also referred to as a monocarboxylic acid residue) (hereinafter, the hydrogen atom at the hydroxyl terminal is sealed). Also say). At this time, both ends of the polyester are monocarboxylic acid residues. This is due to the fact that protecting the terminal with a hydrophobic functional group is effective in improving the polarizer durability of the polarizing plate and shows a role of delaying hydrolysis of the ester group.
Here, the residue is a partial structure of the polyester and represents a partial structure having the characteristics of the monomer forming the polyester. For example, the monocarboxylic acid residue formed from monocarboxylic acid R—COOH is R—CO—. An aliphatic monocarboxylic acid residue is preferred, the monocarboxylic acid residue is more preferably an aliphatic monocarboxylic acid residue having 2 to 10 carbon atoms, and an aliphatic monocarboxylic acid residue having 2 to 3 carbon atoms is more preferred. It is more preferably a group, and particularly preferably an aliphatic monocarboxylic acid residue having 2 carbon atoms.
When the number of carbon atoms of the monocarboxylic acid residues at both ends of the polyester is 3 or less, the volatility decreases, the weight loss due to heating of the polyester does not increase, and process contamination and surface failure occur. Can be reduced. That is, as the monocarboxylic acid used for sealing, an aliphatic monocarboxylic acid is preferable to an aromatic monocarboxylic acid from the viewpoint of production suitability and surface quality. More preferably, the monocarboxylic acid is an aliphatic monocarboxylic acid having 2 to 22 carbon atoms, more preferably an aliphatic monocarboxylic acid having 2 to 3 carbon atoms, and an aliphatic monocarboxylic acid residue having 2 carbon atoms. Particularly preferred is a group. For example, acetic acid, propionic acid, butanoic acid and derivatives thereof are preferable, acetic acid or propionic acid is more preferable, and acetic acid (terminal is an acetyl group) is most preferable. Two or more monocarboxylic acids used for sealing may be mixed.
When the hydrogen atom at the end of the hydroxyl group is replaced with an acyl group derived from a monocarboxylic acid, the state at room temperature is unlikely to become a solid form, handling becomes good, and humidity stability and polarizer durability are excellent. A film can be obtained.
From the viewpoint of improving polarizer durability, the hydroxyl value of the polyester is preferably 10 mgKOH / g or less, more preferably 5 mgKOH / g, and particularly preferably 0 mgKOH / g.

-Synthesis method-
The polyester may be synthesized by a conventional method, a hot melt condensation method using a polyesterification reaction or a transesterification reaction between the dicarboxylic acid, the diol, and a monocarboxylic acid for end-capping, or an acid chloride and glycol of these acids. It can be easily synthesized by any of the interfacial condensation methods.

-Addition (content)-
In the optical film of the present invention, the content of the polyester is preferably 5 to 20% by mass, more preferably 5 to 18% by mass, and 5 to 15% by mass with respect to the cellulose ester. It is particularly preferred. Polyester may contain only 1 type and may contain 2 or more types. When two or more types are included, the total amount falls within the above range.

(UV absorber)
The optical film of the present invention preferably contains an ultraviolet (UV) absorber together with the main component cellulose ester. The UV absorber contributes to improvement of polarizer durability. In particular, in an embodiment in which the optical film of the present invention is used as a surface protective film for a liquid crystal display device, the addition of a UV absorber is effective.

  There is no restriction | limiting in particular about UV absorber which can be used for this invention. Any of the UV absorbers conventionally used in cellulose acylate films can be used. Examples of the ultraviolet absorber include compounds described in JP-A No. 2006-184874. Polymer ultraviolet absorbers can also be preferably used. In particular, polymer type ultraviolet absorbers described in JP-A-6-148430 are preferably used.

The amount of the UV absorber used is not uniform depending on the type of UV absorber, usage conditions, etc., but the UV absorber is contained in a proportion of 1 to 3% by mass with respect to the cellulose acylate as the main component. More preferably.
Examples include ultraviolet absorbers having the following structure, but the ultraviolet absorbers to be added are not limited to these.

(Other additives)
The optical film may further contain at least one other additive as long as the effects of the present invention are not impaired. Examples of other additives include other high-molecular plasticizers other than polyester in which the terminal containing the repeating unit represented by the general formula (1) is sealed with a monocarboxylic acid (for example, phosphate ester type) Plasticizers, carboxylic acid ester plasticizers, polycondensation oligomer plasticizers, etc.), ultraviolet absorbers, antioxidants and matting agents described below.
As content of the said other additive contained in the optical film of this invention, 3 mass% or less is preferable with respect to a cellulose ester, 1 mass% or less is more preferable, and it is still more preferable that it does not contain substantially.
Further, the content of the retardation developing agent (including the retardation reducing agent) contained in the optical film of the present invention is preferably 3% by mass or less, more preferably 1% by mass or less, and substantially the cellulose ester. More preferably, it is not contained.

-Other polymer plasticizers-
In the optical film of the present invention, other polymer plasticizers can be added as long as the effects of the present invention are not impaired. Examples of the polymer plasticizer include polyester polyurethane plasticizers, aliphatic hydrocarbon polymers, alicyclic hydrocarbon polymers, acrylic polymers such as polyacrylic acid esters and polymethacrylic acid esters (as ester groups, Methyl, ethyl, propyl, butyl, isobutyl, pentyl, hexyl, cyclohexyl, octyl, 2-ethylhexyl, nonyl, isononyl, tert-nonyl, dodecyl, tridecyl, stearyl Group, oleyl group, benzyl group, phenyl group, etc.), polyvinyl isobutyl ether, vinyl polymers such as poly N-vinyl pyrrolidone, styrene polymers such as polystyrene and poly 4-hydroxystyrene, polyethers such as polyethylene oxide and polypropylene oxide The Amides, polyurethanes, polyureas, phenol - formaldehyde condensates, urea - formaldehyde condensate, vinyl acetate, and the like.

Among these, it is particularly preferable to use an acrylic polymer in combination. In the present invention, the acrylic polymer is preferably a homopolymer or copolymer synthesized from monomers such as acrylic acid or alkyl methacrylate.
Examples of the acrylate monomer having no aromatic ring include, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i, s-, t-), acrylic Pentyl acid (n-, i-, s-), hexyl acrylate (n, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n -, I-), myristyl acrylate (n-, i-), acrylic acid (2-ethyl hesyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl) Acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid (2-methoxyethyl), Acrylic acid (2-ethoxyethyl), etc., or the acrylic acid ester may include those obtained by changing the methacrylic acid ester. Examples of the acrylic monomer used for the acrylic polymer having an aromatic ring include styrene, methylstyrene, and hydroxystyrene.

  When the acrylic polymer is a copolymer, it is composed of X (monomer component having a hydrophilic group) and Y (monomer component having no hydrophilic group), and X: Y (molar ratio) is 1: 1 to 1:99. Is preferred. It is preferable that content of an acrylic polymer is 1-20 mass% with respect to a cellulose ester. These acrylic polymers can be synthesized with reference to the method described in JP-A-2003-12859.

-Antioxidant-
In the present invention, known antioxidants for cellulose acylate solutions such as 2,6-di-tert-butyl-4-methylphenol, 4,4′-thiobis- (6-tert-butyl-3-methylphenol) ), 1,1′-bis (4-hydroxyphenyl) cyclohexane, 2,2′-methylenebis (4-ethyl-6-tert-butylphenol), 2,5-di-tert-butylhydroquinone, pentaerythrityl-tetrakis A phenolic or hydroquinone antioxidant such as [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] can be added. Further, tris (4-methoxy-3,5-diphenyl) phosphite, tris (nonylphenyl) phosphite, tris (2,4-di-tert-butylphenyl) phosphite, bis (2,6-di-tert) It is preferable to add a phosphorus-based antioxidant such as -butyl-4-methylphenyl) pentaerythritol diphosphite and bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite. The addition amount of the antioxidant is preferably 0.05 to 5.0 parts by mass with respect to 100 parts by mass of the cellulose resin.

[Method for producing optical film]
There is no restriction | limiting in particular in the method of manufacturing the said optical film, It can form into a film using a well-known method. For example, the film may be formed using either a solution casting film forming method or a melt film forming method. From the viewpoint of improving the surface shape of the film, the optical film is preferably produced using a solution casting film forming method. Hereinafter, although the case where the solution casting film forming method is used will be described as an example, the present invention is not limited to the solution casting film forming method. In addition, about the case where a melt film forming method is used, a well-known method can be used.

-Polymer solution-
In the solution casting film forming method, a web is formed using the above-mentioned cellulose ester, polyester, and a polymer solution (cellulose ester solution) containing various additives as required. Hereinafter, a polymer solution (hereinafter also referred to as a cellulose acylate solution as appropriate) that can be used in the solution casting film forming method will be described.

-Solvent-
The cellulose ester used in the present invention is dissolved in a solvent to form a dope, which is cast on a substrate to form a film. At this time, since it is necessary to evaporate the solvent after extrusion or casting, it is preferable to use a volatile solvent.
Furthermore, it does not react with a reactive metal compound or a catalyst, and does not dissolve the casting base material. Two or more solvents may be mixed and used.
Alternatively, the cellulose ester and the reactive metal compound capable of hydrolytic polycondensation may be dissolved in different solvents and then mixed.
Here, an organic solvent having good solubility with respect to the cellulose ester is referred to as a good solvent, and has a main effect on dissolution, and an organic solvent used in a large amount among them is a main (organic) solvent or a main (organic) ) Solvent.

  Examples of the good solvent include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, and the like. In addition to esters such as methyl acid, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide, sulfolane, nitroethane, Examples include methylene chloride and methyl acetoacetate, and 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferred.

The dope preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent.
After casting the dope on the metal support, the solvent starts to evaporate and the ratio of alcohol increases so that the web (the name of the dope film after casting the cellulose acylate dope on the support is called It is used as a gelling solvent that makes it easy to peel off from the metal support, and when these ratios are small, it promotes dissolution of cellulose acylate of non-chlorine organic solvent There is also a role to suppress gelation, precipitation, and viscosity increase of the reactive metal compound.

Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, and propylene glycol monomethyl ether.
Of these, methanol and ethanol are preferred because they are excellent in dope stability, have a relatively low boiling point, good drying properties, and no toxicity. Ethanol is most preferred. These organic solvents alone are not soluble in cellulose esters and are referred to as poor solvents.

In the present invention, the cellulose ester that is a raw material of the cellulose ester contains hydrogen bonding functional groups such as hydroxyl groups, esters, and ketones, and therefore 5 to 30% by mass, more preferably 7 to 25% by mass, It is preferable to contain 10-20 mass% alcohol from a viewpoint of the peeling load reduction from a casting support body preferably.
Further, in the present invention, it is effective to contain a small amount of water to increase the solution viscosity and the film strength in the wet film state at the time of drying, or to increase the dope strength at the time of casting the drum method. It may be contained in an amount of 0.1 to 5% by mass, more preferably 0.1 to 3% by mass, and particularly 0.2 to 2% by mass.

  Examples of combinations of organic solvents preferably used as the solvent for the polymer solution in the present invention are described in JP-A-2009-262551.

  In addition, if necessary, a non-halogen organic solvent can be used as a main solvent, and detailed description can be found in the Japan Institute of Invention Publication (Publication No. 2001-1745, published on March 15, 2001, Invention Association). There is a description.

The cellulose ester concentration in the polymer solution in the present invention is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, and most preferably 15 to 30% by mass.
The cellulose ester concentration can be adjusted to a predetermined concentration at the stage of dissolving the cellulose ester in the solvent. Further, after preparing a solution with a low concentration (for example, 4 to 14% by mass) in advance, the solution may be concentrated by evaporating the solvent or the like. Furthermore, after preparing a high concentration solution in advance, it may be diluted. Moreover, the density | concentration of a cellulose ester can also be reduced by adding an additive.

  The timing of adding the additive can be appropriately determined according to the type of the additive. For example, aromatic ester oligomers and UV absorbers can be doped after dissolving UV absorbers in alcohols such as methanol, ethanol, butanol, organic solvents such as methylene chloride, methyl acetate, acetone, dioxolane, or mixed solvents thereof. It may be added or added directly during the dope composition. For an inorganic powder that does not dissolve in an organic solvent, a dissolver or a sand mill is used in the organic solvent and cellulose ester to disperse and then added to the dope.

  The most preferable solvent that satisfies such conditions and dissolves cellulose ester, which is a preferred polymer compound, at a high concentration is a mixed solvent having a ratio of methylene chloride: ethyl alcohol of 95: 5 to 80:20. Alternatively, a mixed solvent of methyl acetate: ethyl alcohol 60:40 to 95: 5 is also preferably used.

(1) Dissolution step In a dissolution vessel, the cellulose ester and additives are dissolved in an organic solvent mainly containing a good solvent for the cellulose ester while stirring to form a dope, or the additive solution is mixed with the cellulose ester solution. And forming a dope.
For dissolution of the cellulose ester, a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, JP-A-9-95544, JP-A-9-95557, Alternatively, various dissolution methods such as a cooling method as described in JP-A-9-95538 and a high-pressure method as described in JP-A-11-21379 can be used. A method in which pressure is applied at a boiling point or higher is preferred.
The concentration of the cellulose ester in the dope is preferably 10 to 35% by mass. It is preferable that an additive is added to the dope during or after dissolution to dissolve and disperse, then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

(2) Casting process An endless metal belt, such as a stainless steel belt or a rotating metal drum, that feeds the dope to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it indefinitely. This is a step of casting the dope from the pressure die slit to the casting position on the support.
A pressure die that can adjust the slit shape of the die base and facilitates uniform film thickness is preferred. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

(3) Solvent evaporation process A web (which is a state before it is a finished product of an optical film and still containing a lot of solvent) is heated on a metal support so that the web can be peeled from the metal support. This is the process of evaporating the solvent until
To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the metal support by a liquid, a method of transferring heat from the front and back by radiant heat, etc. However, drying efficiency is preferable. A method of combining them is also preferable. In the case of backside liquid heat transfer, it is preferable to heat at or below the boiling point of the main solvent of the organic solvent used in the dope or the organic solvent having the lowest boiling point.

(4) Peeling process It is the process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process. In addition, if the residual solvent amount (the following formula) of the web at the time of peeling is too large, peeling is difficult, or conversely, if the film is peeled off after being sufficiently dried on the metal support, a part of the web is in the middle. It may come off.
Here, there is a gel casting method (gel casting) as a method for increasing the film forming speed (the film forming speed can be increased by peeling while the residual solvent amount is as large as possible). For example, there are a method in which a poor solvent for cellulose ester is added to the dope and the gel is formed after casting the dope, a method in which the temperature of the metal support is lowered and gelled. By gelling on the metal support and increasing the strength of the film at the time of peeling, the speed of film formation can be increased by speeding up the peeling.
The amount of residual solvent during peeling of the web on the metal support is preferably within a range of 5 to 150% by mass depending on the strength of drying conditions, the length of the metal support, etc., but the amount of residual solvent is larger. In the case of peeling at the time, the amount of residual solvent at the time of peeling is determined in consideration of economic speed and quality. In the present invention, the temperature at the peeling position on the metal support is preferably -50 to 40 ° C, more preferably 10 to 40 ° C, and most preferably 15 to 30 ° C.

The residual solvent amount of the web at the peeling position is preferably 10 to 150% by mass, and more preferably 10 to 120% by mass.
The amount of residual solvent can be represented by the following formula.
Residual solvent amount (% by mass) = [(MN) / N] × 100
Here, M is the mass of the web at an arbitrary point in time, and N is the mass when the mass M is dried at 110 ° C. for 3 hours.

(5) Drying or heat treatment step, stretching step After the peeling step, a drying device that alternately conveys the web through a plurality of rolls arranged in the drying device, and / or a tenter that clips and conveys both ends of the web with clips. It is preferred to dry the web using an apparatus.

When heat treatment is performed in the present invention, the heat treatment temperature is less than Tg-5 ° C, preferably Tg-20 ° C or more and less than Tg-5 ° C, and preferably Tg-15 ° C or more and less than Tg-5 ° C. More preferred.
The heat treatment temperature is preferably 30 minutes or less, more preferably 20 minutes or less, and particularly preferably about 10 minutes.

  As a means for drying and heat treatment, hot air is generally blown on both sides of the web, but there is also a means for heating by applying a microwave instead of the wind. The temperature, air volume, and time vary depending on the solvent used, and the conditions may be appropriately selected according to the type and combination of the solvents used.

  The stretching process may be performed in one direction of MD and TD, or may be biaxially stretched in both directions. Biaxial stretching is preferred. Stretching may be performed in one stage or in multiple stages. The tensile elastic modulus is adjusted to the above range by adjusting the type of cellulose acylate to be used and the acyl substitution degree, selecting the type of additive, or adjusting the ratio thereof. Can do.

The stretching ratio in stretching in the film transport direction MD is preferably 0 to 20%, more preferably 0 to 15%, and particularly preferably 0 to 10%. The stretch ratio (elongation) of the web during the stretching can be achieved by the peripheral speed difference between the metal support speed and the stripping speed (stripping roll draw). For example, when an apparatus having two nip rolls is used, the film can be preferably stretched in the conveying direction (longitudinal direction) by increasing the rotational speed of the nip roll on the outlet side rather than the rotational speed of the nip roll on the inlet side. it can. By performing such stretching, the tensile modulus of MD can be adjusted.
Here, the “stretch ratio (%)” means that obtained by the following formula.
Stretch ratio (%) = 100 × {(Length after stretching) − (Length before stretching)} / Length before stretching

The stretching ratio in stretching in the direction TD perpendicular to the film conveying direction is preferably 0 to 30%, more preferably 1 to 20%, and particularly preferably 20 to 15%.
In addition, in this invention, it is preferable to extend | stretch using a tenter apparatus as a method of extending | stretching to the direction TD orthogonal to a film conveyance direction.

  In the biaxial stretching, a desired retardation value can be obtained by relaxing in the longitudinal direction, for example, 0.8 to 1.0 times. The draw ratio is set according to various purposes. When manufacturing the said optical film, it can also uniaxially stretch in a elongate direction.

  It is preferable for the temperature during stretching to be Tg or less because the tensile elastic modulus in the stretching direction increases. The stretching temperature is preferably Tg-50 ° C to Tg, and more preferably Tg-30 ° C to Tg-5 ° C. On the other hand, when stretched under the above temperature conditions, the tensile elastic modulus in the stretching direction increases, while the tensile elastic modulus in the direction orthogonal thereto tends to decrease. Therefore, in order to increase the tensile elastic modulus in both the MD and TD directions by stretching, it is preferable to perform stretching in both directions, that is, biaxial stretching in the above temperature range.

  In addition, you may dry after an extending process. When drying after the stretching step, the drying temperature, the amount of drying air and the drying time differ depending on the solvent used, and the drying conditions may be appropriately selected according to the type and combination of the solvents used. In the present invention, the drying temperature after the stretching step is preferably lower than the stretching temperature in the stretching step from the viewpoint of increasing the front contrast when the film is incorporated into a liquid crystal display device.

(6) Winding The length of the film obtained as described above is preferably wound at 100 to 10000 m per roll, more preferably 500 to 7000 m, and further preferably 1000 to 6000 m. . The width of the film is preferably 0.5 to 5.0 m, more preferably 1.0 to 3.0 m, and still more preferably 1.0 to 2.5 m. When winding, it is preferable to give knurling to at least one end, the knurling width is preferably 3 mm to 50 mm, more preferably 5 mm to 30 mm, and the height is preferably 0.5 to 500 μm, more preferably 1 to 200 μm. is there. This may be a single push or a double push.

  The web thus obtained can be wound up to obtain an optical film.

(Layer structure)
In the present specification, a film having a functional layer, which will be described later, may be referred to as an optical film including the functional layer. In particular, an optical film other than the functional layer is referred to as a “film containing a cellulose ester”. The optical film (film containing cellulose ester) used in the present invention may be a single layer film or may have a laminated structure of two or more layers. For example, a laminated structure composed of two layers of a core layer and an outer layer (sometimes referred to as a surface layer or a skin layer) or a laminated structure composed of three layers of an outer layer, a core layer, and an outer layer are also preferable. It is also preferable that the laminated structure be formed by co-casting.
When the optical film used in the present invention has a laminated structure of two or more layers, it is preferable to add a matting agent to the outer layer. As the matting agent, for example, those described in JP-A-2011-127045 can be used, and for example, silica particles having an average particle size of 20 nm can be used.

(Thickness of optical film)
The optical film has a thickness of 10 to 45 μm, preferably 15 to 35 μm, and more preferably 15 to 32 μm.

(Elastic modulus of optical film)
The elastic modulus (tensile modulus) of the optical film is 4.2 GPa or more, preferably 4.3 GPa or more, and more preferably 4.5 GPa or more. Although there is no restriction | limiting in particular about an upper limit, It is 10 GPa or less. By setting the elastic modulus to 4.2 GPa or more, the rigidity can be improved.
The elastic modulus is measured, for example, by using a universal tensile tester “STM T50BP” manufactured by Toyo Baldwin Co., Ltd. and measuring the stress at 0.5% elongation at 23 ° C. and a relative humidity of 60% at a tensile rate of 10% / min. The average value of the tensile elastic modulus of MD and TD can be measured as the elastic modulus.

(Optical characteristics of optical film)
The in-plane retardation (Re) at a wavelength of 590 nm in an environment of 25% relative humidity 60% of the optical film is preferably −5 to 5 nm, more preferably 0 to 5 nm, and 0 to 3 nm. More preferably it is.
The retardation (Rth) in the thickness direction at a wavelength of 590 nm in an environment of 25% relative humidity 60% of the optical film is preferably −5 to 5 nm, more preferably −3 to 5 nm, More preferably, it is in the range of 5 nm.

  In this specification, Re (λ) and Rth (λ) represent in-plane retardation and retardation in the thickness direction at the wavelength λ, respectively. In the present specification, the wavelength λ is 590 nm unless otherwise specified. Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH (manufactured by Oji Scientific Instruments). Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH) as the tilt axis (rotary axis) (in the absence of the slow axis, any direction in the film plane) Is measured in 6 points from the inclined direction in 10 degree steps from the normal direction to 50 degrees on one side with respect to the normal direction of the film. KOBRA 21ADH calculates based on the retardation value, the assumed average refractive index, and the input film thickness value. The retardation value is measured from any two directions with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), and the value Rth can also be calculated from the following formula (A) and formula (B) based on the assumed average refractive index and the input film thickness value. Here, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). The KOBRA 21ADH calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

Here, Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction, nx, ny, and nz represent refractive indexes in respective principal axis directions of the refractive index ellipsoid, and d represents a film. Represents thickness.
Rth = ((nx + ny) / 2−nz) × d Formula (B)

<Use of optical film>
The optical film of the present invention is useful for various applications such as a polarizing plate protective film and a surface protective film disposed on an image display surface. In order to show a function suitable for each application, the optical film may have, for example, a hard coat layer, an antiglare layer, a clear hard coat layer, an antireflection layer, an antistatic layer, an antifouling layer, and the like. Good.

  Since the optical film of the present invention includes a film film containing the above-described cellulose ester, the optical film of the present invention has good bonding properties with a polarizer and is suitable for use in a liquid crystal display device having a polarizing plate as an essential member.

In addition to the antiglare layer or the clear hard coat layer, the polarizing plate protective film used on the surface side of the display device preferably has an antireflection layer, an antistatic layer, and an antifouling layer.
Further, at the time of producing the polarizing plate, when the optical film of the present invention has an in-plane slow axis, it is preferable to bond the in-plane slow axis and the polarizer so that the transmission axes are parallel or orthogonal to each other. .

[Polarizer]
The present invention also relates to a polarizing plate having at least one optical film of the present invention. The polarizing plate of the present invention preferably has the optical film of the present invention and a polarizer.
The polarizing plate of the present invention can be produced by a general method. For example, it can be produced by bonding one surface of the optical film of the present invention and a polarizer. The bonding surface of the optical film is preferably subjected to an alkali saponification treatment. Moreover, complete saponification type polyvinyl alcohol aqueous solution can be used for bonding.

  A conventionally well-known thing can be used as said polarizer. For example, a film made of a hydrophilic polymer such as polyvinyl alcohol or ethylene-modified polyvinyl alcohol having an ethylene unit content of 1 to 4 mol%, a polymerization degree of 2000 to 4000, and a saponification degree of 99.0 to 99.99 mol%, A film stretched by treatment with a dichroic dye such as the above, or a film oriented by treating a plastic film such as vinyl chloride is used.

  The film thickness of the polarizer is preferably 5 to 30 μm. The polarizer thus obtained is bonded to the optical film of the present invention.

The optical film of the present invention may be further bonded to the surface opposite to the surface where the optical film of the present invention is bonded to the polarizer, or a conventionally known optical film may be bonded.
As for the above-described conventionally known optical film, there is no particular limitation on any of the optical properties and materials, but an optical film made of an acrylic resin or a cyclic olefin resin can be preferably used, and is optically isotropic. Even if a film is used, an optically anisotropic retardation film may be used.
As for the above-mentioned conventionally known optical film, as an acrylic film, an optical film made of a (meth) acrylic resin containing a styrene resin described in Japanese Patent No. 4570042, described in Japanese Patent No. 5041532 An optical film made of a (meth) acrylic resin having a glutarimide ring structure in the main chain, an optical film made of a (meth) acrylic resin having a lactone ring structure described in JP2009-122664A, and JP2009- An optical film made of a (meth) acrylic resin having a glutaric anhydride unit described in JP-A-139754 can be used.
In addition, as for the above-mentioned conventionally known optical film, as the one made of a cyclic olefin resin, the cyclic olefin-based resin film described in paragraph [0029] and subsequent paragraphs of JP-A-2009-237376, Japanese Patent No. 4881827, A cyclic olefin resin film containing an additive for reducing Rth described in JP-A-2008-063536 can be used.
In an embodiment in which the polarizing plate of the present invention is used in a liquid crystal display device, the optical film of the present invention is disposed on the inner side of the polarizer (that is, between the polarizer and the liquid crystal cell) and on the outer side (that is, the surface opposite to the surface on the liquid crystal cell side). Any of these arrangements can be preferably used, but it is preferably arranged between the polarizer and the liquid crystal cell.

[Liquid Crystal Display]
The liquid crystal display device of the present invention has the optical film of the present invention or the polarizing plate of the present invention. There is no restriction | limiting in particular about the function in the liquid crystal display device of the optical film of this invention. An example of the arrangement method of the optical film of the present invention is between the polarizer and the liquid crystal cell (that is, the surface of the polarizing plate on the liquid crystal cell side) in the backlight side polarizing plate without the hard coat layer. It is the surface protective film of the arrange | positioned polarizing plate. Another example of the arrangement method of the optical film of the present invention is that between the polarizer and the liquid crystal cell in the polarizing plate on the display surface side without the hard coat layer (that is, the surface on the liquid crystal cell side of the polarizing plate). ) Is a surface protective film.
As for other configurations, any configuration of a known liquid crystal display device can be adopted. There is no particular limitation on the mode, and TN (Twisted Nematic), IPS (In-Plane Switching (transverse electric field switching mode)), FLC (Ferroelectric Liquid Crystal), AFLC (Anti-ferroelectric Liquid Crystal), Bumper Olyptic Crystal ), Super Twisted Nematic (STN), Vertically Aligned (VA), and Hybrid Aligned Nematic (HAN), but an IPS mode liquid crystal display is preferable.

  The features of the present invention will be described more specifically with reference to examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[Example 1]
(Preparation of core layer cellulose acylate dope)
The following composition was put into a mixing tank and stirred to dissolve each component to prepare a cellulose acetate solution.
-------------------------------------------------- -----------
Cellulose acetate with an acetyl substitution degree of 2.88 100 parts by mass Ester oligomer A 13 parts by mass Methylene chloride (first solvent) 430 parts by mass Methanol (second solvent) 64 parts by mass
-------------------------------------------------- -----------

表１中、１，４−ＣＨＡ；１，４−シクロヘキシルジカルボン酸、３Ｍｅ−１，４−ＣＨＡ；３−メチル−１，４−シクロヘキシルジカルボン酸、ＡＡ；アジピン酸、ＥＧ；エチレングリコール、ＰＧ；プロピレングリコールをそれぞれ示す。
また、末端構造において、ＡｃＯはアセチル基で封止されたものであり、ＯＨは、水酸基を示す。Ｍｎは数平均分子量を表す。

In Table 1, 1,4-CHA; 1,4-cyclohexyldicarboxylic acid, 3Me-1,4-CHA; 3-methyl-1,4-cyclohexyldicarboxylic acid, AA; adipic acid, EG; ethylene glycol, PG; Propylene glycol is shown respectively.
In the terminal structure, AcO is sealed with an acetyl group, and OH represents a hydroxyl group. Mn represents a number average molecular weight.

(Preparation of outer layer cellulose acylate dope)
10 parts by mass of the following matting agent solution was added to 90 parts by mass of the core layer cellulose acylate dope to prepare an outer layer cellulose acetate solution.
-------------------------------------------------- --------------
Silica particles having an average particle size of 20 nm (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd.)
2 parts by mass Methylene chloride (first solvent) 76 parts by mass Methanol (second solvent) 11 parts by mass Core layer Cellulose acylate dope 1 part by mass
-------------------------------------------------- --------------

(Production of optical film)
The polymer solution is filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm, and then the core layer cellulose acylate dope and the outer layer cellulose acylate dope on both sides thereof are simultaneously cast from the casting port at 20 ° C. Cast on a drum (band casting machine). The film was peeled off at a solvent content of about 20% by mass, both ends in the width direction of the film were fixed with tenter clips, and dried while being stretched 1.1 times in the lateral direction. Then, it dried further by conveying between the rolls of a heat processing apparatus, and produced the 25-micrometer-thick optical film, and let this be the optical film of Example 1.

[Examples 2 to 11, Reference Example and Comparative Examples 1 to 4]
In the production of the optical film of Example 1, the types and amounts of polyester used in the optical film, and the film thickness were changed as described in the following table, in the same manner as in Example 1, Examples 2 to 11, Optical films of Reference Examples and Comparative Examples 1 to 4 were produced.
The optical film of the reference example is excellent in terms of optical performance, elastic modulus, depressed shape, and polarizer durability, but since the film thickness is 50 μm, it is difficult to reduce the thickness, and the problem to be solved by the present invention is It cannot be solved.

[Evaluation]
The following evaluation was performed using the optical films of the obtained Examples, Reference Examples and Comparative Examples. The results of each evaluation are shown in Table 2 below.

(Measurement of optical performance)
The retardation at a wavelength of 590 nm was measured using KOBRA 21ADH (manufactured by Oji Scientific Instruments) in an environment of 25 ° C. and a relative humidity of 60%.

(Measurement of elastic modulus)
Using a universal tensile tester “STM T50BP” manufactured by Toyo Baldwin Co., Ltd., the stress at 0.5% elongation was measured at 23%, 60% relative humidity at a tensile rate of 10% / min. The average value of the elastic modulus was measured as the elastic modulus.

(Evaluation of collapsed beco)
About the optical film of each Example, a reference example, and a comparative example, after making a roll-shaped optical film of 3900 m, making it age for 1 week, visually observing an external appearance, and implemented the following determination. The results are shown in the table.
A: The roll does not deform.
B: The roll surface is deformed into irregularities.

(Preparation of polarizing plate)
1) Saponification of film The optical films of Examples, Reference Examples and Comparative Examples prepared in Examples, Reference Examples and Comparative Examples, and Fujitac TD40UC (manufactured by Fuji Film Co., Ltd.) were adjusted to 37 ° C. at 4.5 mol / After immersing in L sodium hydroxide aqueous solution (saponification solution) for 1 minute, the film was washed with water, then immersed in 0.05 mol / L sulfuric acid aqueous solution for 30 seconds, and then passed through a water washing bath. Then, draining with an air knife was repeated three times, and after dropping the water, the film was retained in a drying zone at 70 ° C. for 15 seconds and dried to produce a saponified film.

2) Production of Polarizer According to Example 1 of Japanese Patent Application Laid-Open No. 2001-141926, a circumferential speed difference was given between two pairs of nip rolls, and the film was stretched in the longitudinal direction to prepare a polarizing film having a thickness of 20 μm.

3) Bonding After selecting two sheets from the polarizing film thus obtained and the saponified film and sandwiching the polarizing film between them, PVA (manufactured by Kuraray Co., Ltd., PVA-117H) 3% Using an aqueous solution as an adhesive, a polarizing plate was prepared by laminating with a roll-to-roll so that the polarizing axis and the longitudinal direction of the film were orthogonal to each other. Here, one film of the polarizing film was a saponified film selected from the film group shown in Table 2 below, and the other film was a saponified film of Fujitac TD40UC.

(Polarizer durability evaluation)
About the polarizing plate produced above, 2 sets of samples (about 5 cm x 5 cm) which bonded one side of the optical film of each Example, a reference example, and each comparative example to the glass plate with the adhesive were produced. This was arranged in a crossed Nicol state, and the orthogonal transmittance was measured at 410 nm using an automatic polarizing film measuring device VAP-7070 manufactured by JASCO Corporation. Thereafter, the orthogonal transmittance after storage for 400 hours in an environment of 60 ° C. and 95% relative humidity was measured by the above method. The evaluation value of the polarizer durability of the polarizing plate is defined as follows.
Evaluation value of polarizer durability of polarizing plate = [orthogonal transmittance after time (%) − orthogonal transmittance before time (%)] / orthogonal transmittance before time (%)
There is no problem in practical use when the polarizer durability evaluation value of the polarizing plate is 40 or less, the polarizer durability evaluation value is preferably 30 or less, and the polarizer durability evaluation value is More preferably, it is 27 or less.
The obtained results are shown in Table 2 below.

Since the optical films of Examples 1 to 11, Comparative Examples 1 and 4 and Reference Example have a high elastic modulus of the film, no sag occurs on the depression, but the optical films of Comparative Examples 2 to 3 have a low elastic modulus. In the roll state, the dents on the sink occurred after 1 week.
In the optical films of Comparative Example 4 and Reference Example, the change in orthogonal transmittance after the passage of time was large, and the contrast was lowered. On the other hand, in the optical films of Examples 1 to 11 of the present invention, the durability of the polarizer was high, and a decrease in contrast could be suppressed compared to the optical films of Comparative Example 4 and Reference Example.

(IPS liquid crystal display device mounting evaluation)
From the commercially available liquid crystal television (IPS mode slim type 42-inch liquid crystal television), the polarizing plate sandwiching the liquid crystal cell is peeled off, and the produced polarizing plate is used in the Examples, Reference Examples and Comparative Examples shown in Table 2. The optical film side was re-bonded to the liquid crystal cell via an adhesive so that the optical film side was placed on the liquid crystal cell side. When confirming the display characteristics of the reassembled liquid crystal television and confirming the brightness and color from the front and diagonal, the polarizing plate produced using Comparative Example 1 has a large color change when observed from the diagonal, It was confirmed that the display characteristics were inferior. The polarizing plates of Examples 1 to 11, Comparative Examples 2 to 4, and Reference Example all exhibited the same characteristics as before the polarizing plate was peeled off.

Claims (9)

Cellulose ester,
Including at least one polyester comprising an alicyclic skeleton, wherein a hydrogen atom at a hydroxyl terminal is substituted with an acyl group derived from a monocarboxylic acid,
The cellulose ester has an acyl substitution degree of 2.00 to 2.95,
The polyester is a polymer of an acyclic aliphatic diol and an aliphatic dicarboxylic acid, and the ratio m of the aliphatic dicarboxylic acid of the aliphatic dicarboxylic acid to the aliphatic dicarboxylic acid having an alicyclic structure: n is 0:10 to 3: 7,
The monocarboxylic acid is an aliphatic monocarboxylic acid having 2 to 10 carbon atoms;
The thickness is 10 to 45 μm,
In-plane retardation (Re) at a wavelength of 590 nm in an environment of 25 ° C. and a relative humidity of 60% is −5 to 5 nm,
The thickness direction retardation (Rth) at a wavelength of 590 nm in an environment at 25 ° C. and a relative humidity of 60% is −5 to 5 nm,
The elastic modulus Ri Der more 4.2GPa,
An optical film comprising silica particles ;
Here you the molar ratio of repeating units derived from non-cyclic aliphatic dicarboxylic acids m, the molar ratio of repeating units derived from an aliphatic dicarboxylic acid having an alicyclic structure and n.   The optical film of Claim 1 whose number average molecular weight Mn of the said polyester is 500-3000. The optical film of Claim 1 or 2 in which the said polyester contains the repeating unit represented by following General formula (1).

(In General Formula (1), X represents an acyclic divalent linking group having 2 to 10 carbon atoms. Y represents a linking group having 3 to 12 carbon atoms including a 3 to 6-membered alicyclic structure. .)   The optical film of any one of Claims 1-3 whose content of the said polyester is 5-20 mass% with respect to the said cellulose ester.   The optical film of any one of Claims 1-4 whose thickness of the said optical film is 10-32 micrometers.   A polarizing plate comprising at least one optical film according to claim 1. A liquid crystal display device having a liquid crystal cell and two polarizing plates disposed on both sides of the liquid crystal cell,
A liquid crystal display device, wherein at least one of the polarizing plates is the polarizing plate according to claim 6.   The liquid crystal display device according to claim 7, wherein the liquid crystal cell is a transverse electric field switching mode (IPS) type liquid crystal cell.   The liquid crystal display device according to claim 7 or 8, wherein the optical film according to any one of claims 1 to 5 is disposed between a polarizer and the liquid crystal cell.