JP2012007015A - Optical film, polarizing plate, display element and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film suppressed in a variation of Rth with respect to a change of a temperature of a use environment.SOLUTION: The optical film contains: cellulose ester; and 1.0×10mol of a compound expressed by at least one kind of a general formula (1) with respect to 1g of the cellulose ester. (In the general formula (1), Rindependently denotes a halogen atom or a hydroxy group, respectively, and n denotes an integer of 0 to 4.).

Description

  The present invention relates to an optical film, and a polarizing plate, a display element, and a liquid crystal display device using the optical film. Moreover, this invention relates also to the optical performance humidity dependence improving agent for cellulose ester films used for the optical film of this invention.

  Liquid crystal display devices are increasingly used year by year as space-saving image display devices with low power consumption. Conventionally, a liquid crystal display device has a major drawback that the viewing angle dependency of a display image is large. However, a wide viewing angle liquid crystal mode such as a VA mode has been put into practical use, and thereby, a high-quality image such as a television can be obtained. In demanded markets, the demand for liquid crystal display devices is expanding rapidly.

  The basic configuration of a liquid crystal display device is one in which polarizing plates are provided on both sides of a liquid crystal cell. The polarizing plate plays a role of allowing only light having a polarization plane in a certain direction to pass through, and the performance of the liquid crystal display device is greatly influenced by the performance of the polarizing plate. The polarizing plate generally has a configuration in which transparent protective films are bonded to both front and back sides of a polarizer made of a polyvinyl alcohol film or the like on which iodine or dye is adsorbed and oriented. A cellulose ester film typified by cellulose acetate has been widely used as a polarizing plate protective film because it has high transparency and can easily ensure adhesion with polyvinyl alcohol used in a polarizer.

  In addition, by arranging an optically biaxial retardation film (optical film) between the polarizing plate and the liquid crystal cell of the liquid crystal display device, a wider viewing angle can be realized, that is, display characteristics can be improved. It has been known. As such an optical film, a cellulose ester film capable of exhibiting excellent optical performance has attracted attention, and the cellulose ester film is used as an optical film in a liquid crystal display device.

  On the other hand, the cellulose ester film has a problem in that it easily absorbs water as compared with other synthetic polymers, and therefore the film performance is likely to change with changes in environmental humidity. In recent years, as the application of liquid crystal display devices has been expanded, large-size and high-quality applications such as televisions have been expanded, and demands for the quality of polarizing plates, retardation films and polarizing plate protective films have further increased. In particular, a large-size and high-quality liquid crystal display device is required to be used in various harsh environments as compared with the conventional liquid crystal display device. From such a viewpoint, an improvement in resistance to humidity has been strongly desired for cellulose ester films used in liquid crystal display devices.

  In contrast, by adding various compounds to the cellulose ester film as an optical performance humidity dependency improver for cellulose ester films, a method for suppressing changes in the optical compensation ability due to heat and humidity of the optical film has been studied. It has been. As such an additive, for example, a compound in which a substituent is linked to an aromatic ring such as a triazine ring or a benzene ring via an —NH— linking group is used (see Patent Documents 1 to 3).

On the other hand, for a compound having a structure in which the —NH— linking group or —NH ₂ group, and the —COO— linking group or —COOH group are both directly linked to a benzene ring or the like, the variation in optical properties with respect to humidity is reduced. From the viewpoint, addition to the cellulose ester film has been hardly studied.

Here, Patent Document 4 discloses a method for producing a cellulose acylate film by adding a trace amount of aromatic monocarboxylic acid such as aminobenzoic acid as a release agent to a cellulose acylate solution. This document describes that these release agents are added to the cellulose acylate film within a range that does not impair the releasability and transparency, and specifically, from 1 × 10 ⁻⁹ to 1 g of cellulose acylate. There is a description that an addition amount of 3 × 10 ⁻⁵ mol is preferable, and in the example of the document, an embodiment in which 200 ppm of citric acid as a release agent is added to cellulose acylate is disclosed. However, the example which examined the effect about the humidity dependence of an optical characteristic is not indicated by the same literature about the obtained film, Increasing the addition amount of a release agent, or aromatic mono-acids, such as aminobenzoic acid. None of the use of carboxylic acid as a release agent has been studied. Therefore, an optical film containing a cellulose ester as a main component, a compound having a structure in which —NH— linking group or —NH ₂ group, and —COO— linking group or —COOH group are both directly connected to a benzene ring or the like. In fact, there is no disclosure or suggestion of the effect on humidity fluctuations when added to.

JP 2005-99191 A JP 2005-154664 A JP 2006-317922 A JP 2002-212338 A

  When this inventor examined the humidity dependency improvement effect of the optical characteristic about the optical film using the additive of patent documents 1-3, it turns out that the effect is still small and needs further improvement. all right.

  The objective of this invention is providing the optical film by which the fluctuation | variation of Rth with respect to the change of the humidity of a use environment was suppressed.

In order to solve the above problems, the present inventor has a structure in which a wide variety of —NH— linking group or —NH ₂ group and —COO— linking group or —COOH group are directly linked to a benzene ring or the like. As a result of diligent research on the effect of improving the humidity dependence on optical performance of the above compound, a compound having a structure in which both —NH ₂ group and —COOH group are directly linked to a benzene ring is used as an optical film containing cellulose ester as a main component. By adding, it came to discover that the optical performance humidity dependence of the obtained optical film can be improved remarkably remarkably.
As a result of intensive studies, it has been found that a compound having the above-mentioned specific structure, which has received little attention as a release agent in the field of optical films, can improve the optical performance and humidity dependency of the optical film. On the other hand, the compound having the above specific structure is described in Patent Document 4 or the like so as to be added to the cellulose acylate film within a range that does not impair the peelability and transparency. In addition, from the viewpoint of film strength and light resistance, it was considered that such a compound is preferably used in a small amount when added to a film mainly composed of cellulose ester. However, by adding more than a specific amount of the compound having the above specific structure that exceeds the range of preferable addition amounts described in Patent Document 4 and the like, surprisingly, the optical performance humidity dependency of the optical film is greatly improved. I came to find out what I could do. That is, the said subject is solved by this invention of the following structures.

（一般式（Ｉ）中、Ｒ^１はそれぞれ独立にハロゲン原子または水酸基を表し、ｎは０〜４の整数を表す。）
［２］ 前記一般式（Ｉ）中、前記Ｒ^１がそれぞれ独立にフッ素原子または水酸基を表し、ｎは０〜４の整数を表すことを特徴とする［１］に記載の光学フィルム。
［３］ 前記セルロースエステルが、総アシル置換度２．０〜３．０のセルロースアシレートであることを特徴とする［１］または［２］に記載の光学フィルム。
［４］ 前記セルロースエステルが、総アシル置換度２．０〜２．５５のセルロースアシレートであることを特徴とする［１］〜［３］のいずれか一項に記載の光学フィルム。
［５］ 膜厚方向のレターデーションＲｔｈが７０〜１４０ｎｍであることを特徴とする［１］〜［４］のいずれか一項に記載の光学フィルム。
［６］ 膜厚方向のレターデーションＲｔｈが１２０〜１４０ｎｍであることを特徴とする［１］〜［５］のいずれか一項に記載の光学フィルム。
［７］ 下記条件（Ａ）での膜厚方向のレターデーションＲｔｈの変化量が、セルロースエステルのみから成るフィルムを下記条件（Ａ）での膜厚方向のレターデーションＲｔｈの変化量の７０％以下であることを特徴する［１］〜［６］のいずれか一項に記載の光学フィルム。
条件（Ａ）：２５℃相対湿度１０％で２時間以上調湿後の膜厚方向のレターデーションＲｔｈを測定し、その後２５℃相対湿度８０％に湿度変化させて２時間以上調湿後の膜厚方向のレターデーションＲｔｈを測定する。
［８］ 偏光子と、［１］〜［７］のいずれか一項に記載の光学フィルムを少なくとも１枚含むことを特徴とする偏光板。
［９］ ［８］に記載の偏光板を少なくとも１枚含むことを特徴とする表示素子。
［１０］ ［８］に記載の偏光板を少なくとも１枚含むことを特徴とする液晶表示装置。
［１１］ 下記一般式（Ｉ）で表されるセルロースエステルフィルム用光学性能湿度依存性改良剤。
一般式（Ｉ）

（一般式（Ｉ）中、Ｒ^１はそれぞれ独立にハロゲン原子または水酸基を表し、ｎは０〜４の整数を表す。）
［１２］ 前記一般式（Ｉ）中、前記Ｒ^１がそれぞれ独立にフッ素原子または水酸基を表し、ｎは０〜４の整数を表すことを特徴とする［１１］に記載のセルロースエステルフィルム用光学性能湿度依存性改良剤。
［１３］ 膜厚方向のレターデーションＲｔｈを増加させることができることを特徴とする［１１］または［１２］に記載のセルロースエステルフィルム用光学性能湿度依存性改良剤。 [1] An optical film comprising a cellulose ester and at least one compound represented by the following general formula (I) in an amount of 1.0 × 10 ⁻⁴ mol or more with respect to 1 g of the cellulose ester.
Formula (I)

(In general formula (I), R ¹ each independently represents a halogen atom or a hydroxyl group, and n represents an integer of 0 to 4.)
[2] The optical film as described in [1], wherein in the general formula (I), each R ¹ independently represents a fluorine atom or a hydroxyl group, and n represents an integer of 0 to 4.
[3] The optical film as described in [1] or [2], wherein the cellulose ester is cellulose acylate having a total acyl substitution degree of 2.0 to 3.0.
[4] The optical film as described in any one of [1] to [3], wherein the cellulose ester is cellulose acylate having a total acyl substitution degree of 2.0 to 2.55.
[5] The optical film according to any one of [1] to [4], wherein retardation Rth in the film thickness direction is 70 to 140 nm.
[6] The optical film according to any one of [1] to [5], wherein retardation Rth in the film thickness direction is 120 to 140 nm.
[7] The change amount of retardation Rth in the film thickness direction under the following condition (A) is 70% or less of the change amount of retardation Rth in the film thickness direction under the following condition (A). The optical film according to any one of [1] to [6], wherein
Condition (A): Film thickness direction retardation Rth after conditioning for 2 hours or more at 25 ° C. and 10% relative humidity, and then changing humidity to 25 ° C. and 80% relative humidity for 2 hours or more The retardation Rth in the thickness direction is measured.
[8] A polarizing plate comprising a polarizer and at least one optical film according to any one of [1] to [7].
[9] A display element comprising at least one polarizing plate according to [8].
[10] A liquid crystal display device comprising at least one polarizing plate according to [8].
[11] An optical performance humidity dependency improving agent for cellulose ester films represented by the following general formula (I):
Formula (I)

(In general formula (I), R ¹ each independently represents a halogen atom or a hydroxyl group, and n represents an integer of 0 to 4.)
[12] In the general formula (I), the R ¹ independently represents a fluorine atom or a hydroxyl group, and n represents an integer of 0 to 4, wherein the cellulose ester film optical element according to [11] Performance humidity dependency improver.
[13] The optical performance humidity dependency improving agent for cellulose ester films according to [11] or [12], wherein retardation Rth in the film thickness direction can be increased.

  ADVANTAGE OF THE INVENTION According to this invention, the optical film by which the fluctuation | variation of Rth with respect to the change of the humidity of a use environment was suppressed can be provided. The optical film of the present invention can be suitably used for a polarizing plate, a display element, a liquid crystal display device and the like in a liquid crystal display device, and can suppress fluctuations in Rth with respect to changes in humidity in each use environment. According to the optical performance humidity dependence improving agent for cellulose ester films of the present invention, it is possible to provide the optical film of the present invention in which fluctuations in Rth with respect to changes in humidity in the use environment are suppressed.

It is the schematic which shows the example of the liquid crystal display device of this invention.

  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. In addition, in the present specification, the term “Rth” refers to retardation in the film thickness direction when converted to a film thickness of 50 μm, unless otherwise specified.

（一般式（Ｉ）中、Ｒ^１はそれぞれ独立にハロゲン原子または水酸基を表し、ｎは０〜４の整数を表す。）
ここで、いかなる理論に拘泥するものでもないが、セルロースエステルを主成分とする光学フィルムの使用環境の湿度の変化に対するＲｔｈの変動は、セルロースエステル中の残存ヒドロキシル基やセルロースアシレートの置換基に存在するカルボニル基に水分子が配位することにより、セルロースエステルの複屈折性が変化することで生じていると推測される。前記一般式（Ｉ）で表される化合物は、水素結合性基を適当な位置に有するため、添加剤として用いるとセルロースエステルのカルボニル基または水酸基に効果的に相互作用し、光学フィルムの使用環境の湿度の変化に対するＲｔｈの変動を抑制することができる。すなわち、前記一般式（Ｉ）で表される化合物は、セルロースエステルフィルム用光学性能湿度依存性改良剤として好ましく用いることができる。
さらに、本発明のセルロースエステルフィルム用光学性能湿度依存性改良剤は、膜厚方向のレターデーションＲｔｈを増加させることができることがより好ましい。セルロースエステルフィルム用光学性能湿度依存性改良剤は一般的に光学フィルムのＲｔｈを減少させつつ、Ｒｔｈの湿度変動に対する変動幅を低減させていた。これに対し、本発明のより好ましい態様では、光学フィルムのＲｔｈを増加させ、かつ、湿度依存性をも改善することができる。
以下、本発明のフィルムについて説明する。 [Optical film]
The optical film of the present invention (hereinafter also referred to as the film of the present invention) comprises 1.0 × 10 ^{−4 of} cellulose ester and at least one compound represented by the following general formula (I) with respect to 1 g of the cellulose ester. It is characterized by containing more than mol.
Formula (I)

(In general formula (I), R ¹ each independently represents a halogen atom or a hydroxyl group, and n represents an integer of 0 to 4.)
Here, without being bound by any theory, the fluctuation of Rth with respect to the change of humidity in the environment of use of the optical film mainly composed of cellulose ester is caused by residual hydroxyl groups in cellulose ester and substituents of cellulose acylate. It is presumed that this is caused by the change in the birefringence of the cellulose ester due to the coordination of water molecules to the existing carbonyl group. Since the compound represented by the general formula (I) has a hydrogen bonding group at an appropriate position, when it is used as an additive, it effectively interacts with a carbonyl group or a hydroxyl group of a cellulose ester, and the use environment of the optical film Variation in Rth with respect to changes in humidity can be suppressed. That is, the compound represented by the general formula (I) can be preferably used as an optical performance humidity dependency improving agent for cellulose ester films.
Furthermore, it is more preferable that the optical performance humidity dependency improving agent for cellulose ester films of the present invention can increase the retardation Rth in the film thickness direction. Optical performance humidity dependency improvers for cellulose ester films generally reduce the Rth of the optical film while reducing the fluctuation range of the Rth with respect to humidity fluctuations. On the other hand, in a more preferred embodiment of the present invention, the Rth of the optical film can be increased and the humidity dependency can be improved.
Hereinafter, the film of the present invention will be described.

<Cellulose acylate>
The film of the present invention contains a cellulose ester, and among them, a cellulose acylate is preferably contained. Moreover, it is preferable that the film of this invention has a cellulose ester as a main component. Here, having cellulose ester as a main component means that 50% by mass or more of cellulose ester is contained in the optical film of the present invention.

The cellulose acylate that can be used in the present invention will be described in detail.
The degree of substitution of cellulose acylate means the ratio of acylation of three hydroxyl groups present in the structural unit of cellulose (glucose having a (β) 1,4-glycoside bond). The degree of substitution (acylation degree) can be calculated by measuring the amount of bound fatty acid per unit mass of cellulose. In the present invention, the degree of substitution of the cellulose body is determined from the peak intensity ratio of carbonyl carbon in the acyl group by dissolving the cellulose body in a solvent such as dimethyl sulfoxide substituted with deuterium and measuring the ¹³ C-NMR spectrum. This can be calculated. This can be determined by ¹³ C-NMR measurement after substituting the remaining hydroxyl group of cellulose acylate with another acyl group different from the acyl group of cellulose acylate itself. Details of the measurement method are described in Tezuka et al. (Carbohydrate. Res., 273 (1995) 83-91).

The cellulose acylate in the present invention preferably has a total acyl substitution degree of 2.0 to 3.0, more preferably 2.0 to 2.55 from the viewpoint of Rth expression. 4 to 2.5 is particularly preferable. However, the optical film of the present invention can sufficiently improve the humidity dependency of optical properties even when a cellulose ester having a total acyl substitution degree exceeding 2.55 is used. Among the cellulose esters having a total acyl substitution degree exceeding 2.55, the total acyl substitution degree is preferably 2.6 to 3.0, and more preferably 2.8 to 3.0.
As the acyl group of the cellulose acylate of the present invention, an acetyl group, a propionyl group, and a butyryl group are particularly preferable, and an acetyl group is more preferable.

A mixed fatty acid ester composed of two or more kinds of acyl groups can also be preferably used as the cellulose acylate in the present invention. Also in this case, the acyl group is preferably an acetyl group and an acyl group having 3 to 4 carbon atoms.
In the present invention, two types of cellulose acylates having different substituents and / or degree of substitution may be used in combination, mixed, or from a plurality of layers composed of different cellulose acylates by the co-casting method described later. A film may be formed.

  Furthermore, mixed acid esters having fatty acid acyl groups and substituted or unsubstituted aromatic acyl groups described in JP-A-2008-20896, [0023] to [0038] can also be preferably used in the present invention.

  The cellulose acylate used in the present invention preferably has a mass average degree of polymerization of 250 to 800, more preferably 300 to 600. The cellulose acylate used in the present invention preferably has a number average molecular weight of 70000 to 230,000, more preferably 75000 to 230,000, and most preferably 78,000 to 120,000. preferable.

  The cellulose acylate used in the present invention can be synthesized using an acid anhydride or acid chloride as an acylating agent. When the acylating agent is an acid anhydride, an organic acid (for example, acetic acid) or methylene chloride is used as a reaction solvent. Further, a protic catalyst such as sulfuric acid can be used as the catalyst. When the acylating agent is an acid chloride, a basic compound can be used as a catalyst. In the most common synthetic method in the industry, cellulose is an organic acid corresponding to acetyl group and other acyl groups (acetic acid, propionic acid, butyric acid) or their acid anhydrides (acetic anhydride, propionic anhydride, butyric anhydride). A cellulose ester is synthesized by esterification with a mixed organic acid component containing.

  In the above method, cellulose such as cotton linter or wood pulp is activated with an organic acid such as acetic acid and then esterified using a mixture of organic acid components as described above in the presence of a sulfuric acid catalyst. In many cases. The organic acid anhydride component is generally used in an excess amount relative to the amount of hydroxyl groups present in the cellulose. In this esterification treatment, in addition to the esterification reaction, a hydrolysis reaction (depolymerization reaction) of the cellulose main chain (β) 1,4-glycoside bond) proceeds. When the hydrolysis reaction of the main chain proceeds, the degree of polymerization of the cellulose ester is lowered, and the physical properties of the cellulose ester film to be produced are lowered. Therefore, the reaction conditions such as the reaction temperature are preferably determined in consideration of the degree of polymerization and molecular weight of the resulting cellulose ester.

<Additives>
(Compound represented by formula (I))
The film of the present invention is prepared by adding 1.0 × 10 ⁻⁴ mol of the compound represented by the general formula (I), that is, the optical performance humidity dependency improving agent for cellulose ester film of the present invention to 1 g of the cellulose ester. Including above.
Hereinafter, the compound represented by the general formula (I) will be described.

Details of the structure of the compound represented by formula (I) used in the present invention will be described. In addition, deriving a compound having such a structure by improving the structure of the humidity dependency improving agent of the optical performance of the known structure in Patent Documents 1 to 3 and the like is required for the humidity dependency improving agent of the optical performance. Since the structure of amide and sulfonamide was considered essential as a structure to be obtained, it was difficult. In the compound having a structure in which three —NH— linking groups are directly linked to the triazine ring, all the substituents containing the —NH— linking group on the triazine ring are the same or at least two are the same. Was mainly considered. Therefore, for the structure having only one —NH ₂ group on the aromatic ring, such as the compound represented by the general formula (I) used in the present invention, the effect of improving the humidity dependency of the optical performance has not been studied. There wasn't.
General formula (1)

In the general formula (I), R ¹ represents a halogen atom or a hydroxyl group independently, n represents an integer of 0-4.
The halogen atom is not particularly limited, but among them, a fluorine atom is preferable. That is, in the general formula (I), the said R ¹ represents a fluorine atom or a hydroxyl group independently, n represents preferably an integer of 0-4.

Said n represents the integer of 0-4, and it is preferable that it is 3-4.
When n is less than 4, the benzene ring in the compound represented by the general formula (I) represents a hydrogen atom. That is, when n is less than 4, the benzene ring in the compound represented by the general formula (I) has no substituents other than R ¹ , —NH ₂ group and —COOH group, and the general formula The compound represented by (I) does not have a plurality of —NH ₂ groups or —COOH groups.

The compound represented by the general formula (I) is a compound in which both —NH ₂ group and —COOH group are directly linked to a benzene ring. Here, the -NH ₂ group and -COOH group, no particular limitation is imposed on the arrangement on the benzene ring ortho, meta, or at any positional relationship para. Among them, the ortho or para positional relationship is preferable, and the para positional relationship is more preferable.

In the compound represented by the general formula (I), the —NH ₂ group and the —COOH group further have no substituent. That is, in the compound represented by the general formula (I), neither the —NH ₂ group nor the —COOH group forms an amide bond or an ester bond.

On the other hand, the compound represented by the general formula (I) may be ionized in a solvent such as an aqueous solution as long as the —NH ₂ group and the —COOH group are reversible. May be formed.

  Specific examples of the compound represented by the general formula (I) include the following. However, the compound represented by the general formula (I) that can be used as the humidity dependency improving agent of the present invention is not limited to these.

From the viewpoint of obtaining a sufficient effect of improving humidity dependency, the film of the present invention contains 1.0 × 10 ⁻⁴ mol or more of the compound represented by the following general formula (I) with respect to 1 g of the cellulose ester. × preferably contains ¹⁰ -4 ^mol~1.0 × ¹⁰ -3 mol, and more preferably contains ^{1.5 × 10 -4 mol~3.0 × 10 -3} mol. In addition, such an addition amount is an addition amount that greatly exceeds the use mode as a release agent that has been added at an addition amount of about 1 × 10 ^{−9 to} 3 × 10 ⁻⁵ mol per gram of cellulose ester. It has not been known or implemented that the humidity dependency improving effect can be obtained by using the compound represented by the general formula (I).
Moreover, it is preferable that the addition amount of the compound represented by the said general formula (I) is 1-20 mass% with respect to a cellulose ester. If it is 1% by mass or more, the effect of improving humidity dependency is easily obtained, and if it is 20% by mass or less, bleeding out and bleeding are less likely to occur when a cellulose ester film is formed. The more preferable addition amount of the compound represented by the general formula (I) is 2 to 15% by mass, and particularly preferably 4 to 12% by mass with respect to the cellulose ester. In addition, such an addition amount is an addition amount that greatly exceeds the use mode as a release agent added at an addition amount of about 200 ppm with respect to the cellulose ester, and is a compound represented by the general formula (I). It has not been known or implemented that the effect of improving humidity dependency can be obtained by using.
Moreover, although the compound represented by the said general formula (I) may be added 1 type or multiple types in a cellulose-ester film, it is preferable that the total addition amount is the range of the said addition amount. .

  In the compound represented by the general formula (I), the molecular weight of the compound represented by the general formula (I) is preferably 130 to 2000, particularly preferably 130 to 250, and 130 to 210. More particularly preferred. By using a compound having a molecular weight in the above range, volatilization of the additive in the film production process can be suppressed, and compatibility with the cellulose ester can be easily secured, which is preferable.

(Method for producing compound represented by general formula (I))
The method for producing the compound represented by the general formula (I), that is, the optical performance humidity dependency improving agent for cellulose ester film of the present invention is not particularly limited, and a known method can be used.
The compound represented by the general formula (I) may be obtained commercially and used in the present invention. For example, the compound represented by the general formula (I) can be purchased from Tokyo Chemical Industry Co., Ltd. or Wako Pure Chemical Industries, Ltd.

(Other additives)
The film of the present invention may contain other additives in addition to the compound represented by the general formula (I). Other additives that can be added to the film of the present invention include known plasticizers, matting agents, deterioration inhibitors and the like.
Hereinafter, other additives that may be contained in the film of the present invention will be described.

(1) Plasticizer A known plasticizer for cellulose acylate film may be added to the optical film of the present invention. Known plasticizers include, for example, phosphate ester plasticizers, phthalate ester plasticizers, trimellitic ester plasticizers, pyromellitic acid plasticizers described in JP-A-2007-298916. Examples thereof include polyhydric alcohol plasticizers, glycolate plasticizers, citrate plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, and polyester plasticizers.

It is preferable that the addition amount of a plasticizer is 0-50 mass% with respect to a cellulose ester. Furthermore, the preferable addition amount is 0-40 mass% with respect to a cellulose ester, Most preferably, it is 0-30 mass%.
Moreover, although 1 type may be added in a cellulose-ester film, or multiple types may be added, it is preferable that the total addition amount is the range of the said addition amount.

(2) Matting Agent It is preferable to add fine particles as a matting agent to the optical film of the present invention. The fine particles used in the present invention include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate and Mention may be made of calcium phosphate. Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  These fine particles usually form secondary particles having an average particle diameter of 0.1 to 3.0 μm, and these fine particles are present as aggregates of primary particles in the film, and 0.1 to 0.1 μm on the film surface. It is preferable to form irregularities of 3.0 μm. The primary and secondary particle sizes were determined by observing the particles in the film with a scanning electron microscope and determining the diameter of a circle circumscribing the particles as the particle size. In addition, 200 particles were observed at different locations, and the average value was taken as the average particle size.

  As the fine particles of silicon dioxide, for example, commercially available products such as Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (above Nippon Aerosil Co., Ltd.) can be used. Zirconium oxide fine particles are commercially available, for example, under the trade names Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Among these, Aerosil 200V and Aerosil R972V are fine particles of silicon dioxide having a primary average particle diameter of 20 nm or less and an apparent specific gravity of 70 g / liter or more, and while maintaining low turbidity of the optical film, friction This is particularly preferable because the effect of reducing the coefficient is great.

  In order to obtain a cellulose ester film having particles having a small secondary average particle size in the present invention, several methods are conceivable when preparing a fine particle dispersion. For example, a fine particle dispersion prepared by stirring and mixing a solvent and fine particles is prepared in advance, and the fine particle dispersion is added to a small amount of a separately prepared cellulose ester solution, dissolved by stirring, and further mixed with the main cellulose ester solution (dope solution). There is a way. This method is a preferred preparation method in that the dispersibility of the silicon dioxide fine particles is good and the silicon dioxide fine particles are more difficult to reaggregate. In addition, after adding a small amount of cellulose ester to the solvent and dissolving with stirring, add the fine particles to this and disperse with a disperser, and use this as a fine particle additive solution. There is also a method of mixing.

(3) Deterioration preventive agent A deterioration inhibitor (for example, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, an amine, etc.) is added to the optical film of the present invention. May be. 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. Moreover, it is preferable that the addition amount of the said deterioration inhibitor is 0.01-1 mass% of the solution (dope) to prepare, and it is further more preferable that it is 0.01-0.2 mass%. If the addition amount is 0.01% by mass or more, the effect of the deterioration inhibitor is sufficiently exhibited, and if the addition amount is 1% by mass or less, the deterioration inhibitor bleeds out to the film surface (bleeding). And the like are less likely to occur.

<Method for producing optical film>
The optical film of the present invention can be produced by forming a solution containing a cellulose ester and the compound represented by the general formula (I), and can be produced, for example, by a solvent cast method. In the solvent cast method, a film is produced using a solution (dope) in which cellulose ester is dissolved in an organic solvent.

The organic solvent is selected from ethers having 3 to 12 carbon atoms, ketones having 3 to 12 carbon atoms, esters having 3 to 12 carbon atoms, and halogenated hydrocarbons having 1 to 6 carbon atoms. It is preferable to include a solvent.
The ether, ketone and ester may have a cyclic structure. A compound having two or more functional groups of the 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 kinds of functional groups, the number of carbon atoms is preferably within the above-described preferable range of carbon atoms of the solvent 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 the ketones having 3 to 12 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, diisobutyl ketone, cyclohexanone and methylcyclohexanone.
Examples of the esters having 3 to 12 carbon atoms include ethyl formate, propyl formate, pentyl formate, methyl acetate, ethyl acetate and pentyl acetate.
Examples of the organic solvent having two or more kinds of functional groups include 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.

The number of carbon atoms of the halogenated hydrocarbon having 1 to 6 carbon atoms is preferably 1 or 2, and most preferably 1. The halogen of the halogenated hydrocarbon is preferably chlorine. The proportion of halogen atoms substituted by halogen in the halogenated hydrocarbon is preferably 25 to 75 mol%, more preferably 30 to 70 mol%, and more preferably 35 to 65 mol%. More preferably, it is most preferable that it is 40-60 mol%. Methylene chloride is a representative halogenated hydrocarbon.
Two or more kinds of organic solvents may be mixed and used.

  The cellulose ester solution (dope) can be prepared by a general method comprising processing at a temperature of 0 ° C. or higher (normal temperature or high temperature). The cellulose ester solution can be prepared by 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 the cellulose ester in the cellulose ester solution is adjusted so as to be contained in an amount of 10 to 40% by mass in the obtained solution. The amount of the cellulose ester is more preferably 10 to 30% by mass. Arbitrary additives may be added to the organic solvent (main solvent).

  The cellulose ester solution can be prepared by stirring the cellulose ester and the organic solvent at room temperature (0 to 40 ° C.). High concentration solutions may be stirred under pressure and heating conditions. Specifically, the cellulose ester and the organic solvent are put 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., and 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 must be configured to allow stirring. 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.

  Stirring is preferably performed using a stirring blade provided inside the container. 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 is dissolved in a solvent in a container. The prepared dope is taken out of the container after cooling, or taken out and then cooled using a heat exchanger or the like.

  A cellulose ester solution can also be prepared by a cooling dissolution method. As for the details of the cooling dissolution method, the techniques described in [0115] to [0122] of JP-A-2007-86748 can be used.

  It is preferable to produce a cellulose ester film from the prepared cellulose ester solution (dope) by a solvent cast method. To the dope, a compound represented by the general formula (I) is added. Other additives such as a retardation enhancer may be further added to the dope. The dope is cast on a drum or band and the solvent is evaporated to form a film. The concentration of the dope before casting is preferably adjusted so that the solid content is 18 to 35%. The surface of the drum or band is preferably finished in a mirror state. The dope is preferably cast on a drum or band having a surface temperature of 10 ° C. or less.

  Regarding the drying method in the solvent cast method, U.S. Pat. Nos. 2,336,310, 2,367,603, 2,492,078, 2,492,977, 2,492,978 Nos. 2,607,704, 2,739,069 and 2,739,070, British Patent Nos. 640731 and 736892, and Japanese Examined Patent Publication No. 45-4554. 49-5614, JP-A-60-176834, JP-A-60-203430 and JP-A-62-115035. Drying on the band or drum can be performed by blowing an inert gas such as air or nitrogen.

  Further, the obtained film can be peeled off from the drum or band and further dried with high-temperature air whose temperature is successively changed from 100 ° C. to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to 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.

  Two or more layers can be cast using the prepared cellulose ester solution (dope) to form a film. In this case, it is preferable to produce a cellulose ester 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% by mass. The surface of the drum or band is preferably finished in a mirror state.

  When casting a plurality of cellulose ester solutions of two or more layers, it is possible to cast a plurality of cellulose ester solutions, and cellulose from a plurality of casting openings provided at intervals in the traveling direction of the support. You may produce a film, casting and laminating | stacking the solution containing ester, respectively. 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 ester 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-6-158413. The method described in each publication of No. 134933 can be used. Further, a method of casting a cellulose ester film is used, in which a flow of a high-viscosity cellulose ester solution described in JP-A-56-162617 is wrapped with a low-viscosity cellulose ester solution, and the high-low viscosity cellulose ester solution is simultaneously extruded You can also.

  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 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 ester solution to be cast, the same solution may be used, or two or more different cellulose ester solutions may be used. In order to give a function to a plurality of cellulose ester layers, a cellulose ester solution corresponding to the function may be extruded from each casting port. Furthermore, the cellulose ester solution in the present invention can be cast simultaneously with other functional layers (for example, an adhesive layer, a dye layer, an antistatic layer, an antihalation layer, an ultraviolet absorption layer, a polarizing layer, etc.).

  In the conventional single-layer liquid, it is necessary to extrude a cellulose ester solution having a high concentration and a high viscosity in order to obtain a necessary film thickness. In that case, the stability of the cellulose ester solution is poor and solid matter is generated, which often causes problems such as defects and poor flatness. As a solution to this problem, by casting a plurality of cellulose ester 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 a concentrated cellulose ester solution can be used to reduce the drying load and increase the film production speed.

(Addition of additives)
In this invention, the timing which adds the compound represented with the said general formula (I) to a cellulose-ester solution will not be specifically limited if it is added at the time of film forming. For example, you may add at the time of the synthesis | combination of a cellulose ester, and may mix with a cellulose ester at the time of dope preparation.

  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 ester film 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.

(Extension process)
The optical film of the present invention is preferably subjected to a stretching treatment. A desired retardation can be imparted to the cellulose ester film by the stretching treatment. The stretching direction of the cellulose ester film is preferably either the width direction or the longitudinal 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 stretching of the film is preferably carried out under heating conditions. 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 stretching of the optical film of the present invention is preferably performed at a temperature of (Tg−5 ° C.) to (Tg + 40 ° C.) using the glass transition temperature Tg (unit: ° C.) of the cellulose ester film, and Tg˜ (Tg + 35 ° C.). ) Is more preferable, and (Tg + 10 ° C.) to (Tg + 30 ° C.) is particularly preferable. In the case of a dry film, 130 ° C to 200 ° C is preferable.
Moreover, when extending | stretching in the state in which the dope solvent remained after casting, it becomes possible to extend | stretch at temperature lower than a dry film, In this case, 100 to 170 degreeC is preferable.

The stretch ratio of the optical film of the present invention (elongation relative to the film before stretching) is preferably 1% to 200%, more preferably 5% to 150%. In particular, stretching in the width direction is preferably 1% to 200%, more preferably 5% to 150%, and particularly preferably 30 to 45%.
The stretching speed is preferably 1% / min to 300% / min, more preferably 10% / min to 300% / min, and most preferably 30% / min to 300% / min.

  In addition, the optical film of the present invention is manufactured through a step (hereinafter sometimes referred to as “relaxation step”) of holding for a certain period of time at a draw ratio lower than the maximum draw ratio after being drawn to the maximum draw ratio. Also good. The stretching ratio in the relaxation step is preferably 50% to 99% of the maximum stretching ratio, more preferably 70% to 97%, and most preferably 90% to 95%. Moreover, the time of the relaxation process is preferably 1 second to 120 seconds, and more preferably 5 seconds to 100 seconds.

Furthermore, the optical film of the present invention can be preferably manufactured by including a shrinking step of shrinking while gripping the film in the width direction.
In the manufacturing method characterized by including a stretching process for stretching in the width direction of the film and a shrinking process for contracting in the film conveyance direction (longitudinal direction), the film width is held by a pantograph type or linear motor type tenter. The film can be shrunk by gradually narrowing the interval between the clips in the conveying direction while stretching in the direction.

  In the method described above, it can be said that at least a part of the stretching step and the shrinking step are performed simultaneously.

  In addition, Ichikin Kogyo Co., Ltd. is a stretching apparatus that specifically performs a stretching process that stretches either the longitudinal direction or the width direction of the film as described above, simultaneously shrinks the other, and simultaneously increases the film thickness of the film. A company-made FITZ machine or the like can be desirably used. This apparatus is described in (Japanese Patent Laid-Open No. 2001-38802).

The stretching ratio in the stretching step and the shrinkage rate in the shrinking step can be arbitrarily selected depending on the target in-plane retardation Re and the thickness direction retardation Rth. It is preferable that the draw ratio is 10% or more and the shrinkage rate in the shrinking step is 5% or more.
In particular, it preferably includes a stretching step of stretching 10% or more in the width direction of the film and a shrinking step of contracting the transport direction of the film by 5% or more while holding the film in the width direction of the film.
In addition, the shrinkage rate as used in the field of this invention means the ratio of the contracted length of the film after contraction with respect to the length of the film before contraction in the contraction direction.
The shrinkage rate is preferably 5 to 40%, particularly preferably 10 to 30%.

<Characteristics of cellulose ester film>
(Retardation)
Next, the characteristics of the optical film of the present invention will be described in detail.
The preferable range of the optical characteristics of the optical film of the present invention varies depending on the application.
For the VA mode, Re measured at 589 nm is preferably 30 to 200 nm, more preferably 30 to 150 nm, particularly preferably 40 to 100 nm, and further preferably 45 to 65 nm. Rth is preferably 70 to 400 nm, more preferably 70 to 140 nm, particularly preferably 100 to 140 nm, and further preferably 120 to 140 nm.
In the optical film of the present invention, the amount of change in retardation Rth in the film thickness direction under the following condition (A) is the amount of change in retardation Rth in the film thickness direction under the following condition (A). Is preferably 70% or less.
Condition (A): Film thickness direction retardation Rth after conditioning for 2 hours or more at 25 ° C. and 10% relative humidity, and then changing humidity to 25 ° C. and 80% relative humidity for 2 hours or more The retardation Rth in the thickness direction is measured.
In the optical film of the present invention, the amount of change in retardation Rth in the film thickness direction under the condition (A) is the amount of change in retardation Rth in the film thickness direction under the condition (A). Is more preferably 60% or less, and particularly preferably 55% or less.
The humidity control time in the condition (A) is not particularly limited as long as it is 2 hours or longer. However, for example, the humidity may be adjusted for 10 hours or longer. In the examples of the present invention described later, the humidity was adjusted for 12 hours. .

In this specification, Re (λ) and Rth (λ) respectively represent in-plane retardation and retardation in the thickness direction at a wavelength λ. In addition, in this specification, the terms “Re” and “Rth” refer to Re and Rth at a wavelength of 589 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 or WR (manufactured by Oji Scientific Instruments).
When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis) (in the absence of the slow axis, any in-plane value) The light is incident at a wavelength of λ nm from the inclined direction in steps of 10 degrees from the normal direction to 50 degrees on one side with respect to the film normal direction of the rotation axis of KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed average refractive index, and the input film thickness value.
In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.
In addition, the retardation value is measured from the two inclined directions, with the slow axis as the tilt axis (rotation axis) (when there is no slow axis, the arbitrary direction in the film plane is the rotation axis), Based on the value, the assumed value of the average refractive index, and the input film thickness value, Rth can also be calculated from the following equations (21) and (22).

Note:
The above Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction. In formula (21), nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, and nz represents the refractive index in the direction perpendicular to nx and ny. . d represents the thickness of the film.

Rth = ((nx + ny) / 2−nz) × d Formula (22)
In the case where the film to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film having no so-called optical axis, Rth (λ) is calculated by the following method.
Rth (λ) is the above-mentioned Re (λ), and the in-plane slow axis (determined by KOBRA 21ADH or WR) is the tilt axis (rotation axis) from −50 degrees to +50 degrees with respect to the film normal direction. The light of wavelength λ nm is incident from each inclined direction in 10 degree steps and measured at 11 points. Based on the measured retardation value, the assumed average refractive index, and the input film thickness value, KOBRA 21ADH or WR is calculated.
In the above measurement, 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). By inputting these assumed values of average refractive index and film thickness, KOBRA 21ADH or WR calculates nx, ny, and nz. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

(Thickness of cellulose ester film)
The thickness of the cellulose ester film in the present invention is preferably 30 μm to 100 μm, more preferably 30 μm to 80 μm, and most preferably 30 μm to 60 μm.

<Polarizing plate protective film>
(Saponification treatment)
The optical film of the present invention can be used as a polarizing plate protective film by imparting adhesion to a polarizer material such as polyvinyl alcohol by alkali saponification treatment. The saponification method is described in [0211] and [0212] of JP-A-2007-86748, and the method of making a polarizer of a polarizing plate, the optical characteristics of the polarizing plate, etc. are described in [0213] to [0255] of the same publication. Based on these descriptions, a polarizing plate using the film of the present invention as a protective film can be produced.

  For example, the alkali saponification treatment for the optical film of the present invention is preferably performed in a cycle in which the film surface is immersed in an alkali 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 concentration of hydroxide ions is preferably in the range of 0.1 to 5.0 mol / L, and 0.5 to 4.0 mol / L. More preferably, it is in the range of L. The alkaline solution temperature is preferably in the range of room temperature to 90 ° C, more preferably in the range of 40 to 70 ° C.

<Phase difference film>
The optical film of the present invention can be used as a retardation film. The term “retardation film” or “optical compensation film” generally refers to an optical material having optical anisotropy used in a display device such as a liquid crystal display device, and is synonymous with an optical compensation sheet. is there. In a liquid crystal display device, an optical compensation film is used for the purpose of improving the contrast of a display screen or improving viewing angle characteristics and color.
Also, a plurality of optical films of the present invention can be laminated, or an optical film of the present invention and a film outside of the present invention can be laminated to adjust Re and Rth as appropriate, and used as an optical compensation film. Lamination of the film can be performed using a pressure-sensitive adhesive or an adhesive.

[Polarizer]
The polarizing plate of the present invention comprises a polarizer and at least one optical film of the present invention.
A polarizing plate generally comprises a polarizer and two transparent protective films disposed on both sides thereof. As one protective film, the optical film of the present invention can be used. The other protective film may be a normal cellulose acetate film. Examples of the polarizer include an iodine polarizer, a dye polarizer using a dichroic dye, and a polyene polarizer. The iodine polarizer and the dye polarizer are generally produced using a polyvinyl alcohol film. When using the optical film of this invention as a polarizing plate protective film, the preparation methods of a polarizing plate are not specifically limited, It can manufacture by a general method. There is a method in which the obtained cellulose ester film is treated with an alkali and bonded to both surfaces of a polarizer prepared by immersing and stretching a polyvinyl alcohol film in an iodine solution using a completely saponified polyvinyl alcohol aqueous solution. Instead of alkali treatment, easy adhesion processing as described in JP-A-6-94915 and JP-A-6-118232 may be performed. Examples of the adhesive used to bond the protective film-treated surface and the polarizer include polyvinyl alcohol adhesives such as polyvinyl alcohol and polyvinyl butyral, vinyl latexes such as butyl acrylate, and the like. The polarizing plate is composed of a polarizer and a protective film that protects both surfaces of the polarizer, and is further constructed by laminating a protective film on one surface of the polarizing plate and a separate film on the opposite surface. The protective film and the separate film are used for the purpose of protecting the polarizing plate at the time of shipping the polarizing plate and at the time of product inspection. In this case, the protect film is bonded for the purpose of protecting the surface of the polarizing plate, and is used on the side opposite to the surface where the polarizing plate is bonded to the liquid crystal plate. Moreover, a separate film is used in order to cover the contact bonding layer bonded to a liquid crystal plate, and is used for the surface side which bonds a polarizing plate to a liquid crystal plate.

The optical film of the present invention is preferably bonded to the polarizer so that the transmission axis of the polarizer and the slow axis of the optical film of the present invention are substantially parallel.
In the liquid crystal display device of the present invention, it is preferable that the transmission axis of the polarizing plate and the slow axis of the optical film of the present invention are substantially parallel. Here, being substantially parallel means that the deviation between the direction of the main refractive index nx of the optical film of the present invention and the direction of the transmission axis of the polarizing plate is within 5 °, and within 1 °. The angle is preferably within 0.5 °. If the deviation is larger than 1 °, the polarization degree performance under the polarizing plate crossed Nicols is lowered, and light leakage occurs, which is not preferable.

<Functionalization of polarizing plate>
The polarizing plate in the present invention is a function that is combined with an optical film having functional layers such as an antireflection film, a brightness enhancement film, a hard coat layer, a forward scattering layer, and an antiglare (antiglare) layer for improving display visibility. It is also preferably used as a polarizing plate. The antireflection film, brightness enhancement film, other functional optical film, hard coat layer, forward scattering layer, and antiglare layer for functionalization are described in [0257] to [0276] of JP-A-2007-86748. Thus, a functionalized polarizing plate can be created based on these descriptions.

[Display element]
Next, the display element of the present invention will be described. The polarizing plate of the present invention can be used for various display elements, and examples thereof include a liquid crystal display device, an optical shutter and a filter. Among these, it is preferable to use the polarizing plate of this invention for a liquid crystal display device. Hereinafter, the liquid crystal display device of the present invention will be described.

[Liquid Crystal Display]
The liquid crystal display device of the present invention includes at least one polarizing plate of the present invention.

  FIG. 1 is a schematic view showing an example of the liquid crystal display device of the present invention. In FIG. 1, a liquid crystal display device 10 includes a liquid crystal cell having a liquid crystal layer 5 and a liquid crystal cell upper electrode substrate 3 and a liquid crystal cell lower electrode substrate 6 disposed above and below, and upper polarizing plates disposed on both sides of the liquid crystal cell. 1 and the lower polarizing plate 8. A color filter may be disposed between the liquid crystal cell and each polarizing plate. When the liquid crystal display device 10 is used as a transmission type, a cold cathode or hot cathode fluorescent tube, or a backlight having a light emitting diode, a field emission element, or an electroluminescent element as a light source is disposed on the back surface.

It is preferable that the upper polarizing plate 1 and the lower polarizing plate 8 each have a configuration in which a polarizer is sandwiched between two protective films. The liquid crystal display device 10 of the present invention is preferably laminated in the order of the transparent protective film, the polarizer and the optical film of the present invention from the outside of the device (the side far from the liquid crystal cell).
The liquid crystal display device 10 includes an image direct view type, an image projection type, and a light modulation type. The present invention is effective for an active matrix liquid crystal display device using a three-terminal or two-terminal semiconductor element such as TFT or MIM. Of course, it is also effective in a passive matrix liquid crystal display device typified by STN mode called time-division driving.

(VA mode)
The liquid crystal cell of the liquid crystal display device of the present invention is preferably in the VA mode.
In the VA mode, the dielectric anisotropy between the upper and lower substrates is negative, and a liquid crystal having Δn = 0.0813 and Δε = −4.6 is rubbed to provide a director indicating the alignment direction of the liquid crystal molecules, so-called tilt angle is about Fabricate at 89 °. The thickness d of the liquid crystal layer 5 in FIG. 1 is preferably set to about 3.5 μm. Here, the brightness at the time of white display changes depending on the magnitude of the product Δnd of the thickness d and the refractive index anisotropy Δn. Therefore, in order to obtain the maximum brightness, the thickness of the liquid crystal layer is set to be in the range of 0.2 μm to 0.5 μm.

  The absorption axis 2 of the upper polarizing plate 1 of the liquid crystal cell and the absorption axis 9 of the lower polarizing plate 8 are laminated substantially orthogonally. A transparent electrode (not shown) is formed inside each alignment film of the liquid crystal cell upper electrode substrate 3 and the liquid crystal cell lower electrode substrate 6, but in a non-driving state where no driving voltage is applied to the electrodes, the liquid crystal layer 5 The liquid crystal molecules therein are aligned substantially perpendicular to the substrate surface, and as a result, the polarization state of the light passing through the liquid crystal panel hardly changes. That is, the liquid crystal display device realizes an ideal black display in the non-driven state. On the other hand, in the driving state, the liquid crystal molecules are inclined in a direction parallel to the substrate surface, and the light passing through the liquid crystal panel changes the polarization state by the inclined liquid crystal molecules. In other words, in the liquid crystal display device, white display is obtained in the driving state. In FIG. 1, reference numerals 4 and 7 denote orientation control directions.

Here, since an electric field is applied between the upper and lower substrates, it is preferable to use a liquid crystal material having a negative dielectric anisotropy so that liquid crystal molecules respond perpendicularly to the electric field direction. When an electrode is disposed on one substrate and an electric field is applied in a lateral direction parallel to the substrate surface, a liquid crystal material having a positive dielectric anisotropy is used.
In addition, in a VA mode liquid crystal display device, the addition of a chiral agent generally used in a TN mode liquid crystal display device is rarely used to degrade dynamic response characteristics, but in order to reduce alignment defects. Sometimes added.

  The features of the VA mode are high-speed response and high contrast. However, the contrast is high in the front, but there is a problem that it is deteriorated in the oblique direction. During black display, the liquid crystal molecules are aligned perpendicular to the substrate surface. When observed from the front, the liquid crystal molecules have almost no birefringence, so the transmittance is low and a high contrast can be obtained. However, when observed obliquely, birefringence occurs in the liquid crystal molecules. Further, the crossing angle of the upper and lower polarizing plate absorption axes is 90 ° perpendicular to the front, but is larger than 90 ° when viewed from an oblique direction. Because of these two factors, leakage light occurs in the oblique direction, and the contrast is lowered. In order to solve this, the optical film of the present invention is disposed as an optical compensation sheet (retardation film).

  In addition, the liquid crystal molecules are tilted during white display, but the birefringence of the liquid crystal molecules when viewed from an oblique direction differs between the tilt direction and the opposite direction, resulting in differences in luminance and color tone. In order to solve this, it is also preferable to adopt a structure called multi-domain in which one pixel of a liquid crystal display device is divided into a plurality of regions.

(Multi-domain)
For example, in the VA system, the viewing angle characteristics are averaged by inclining liquid crystal molecules into a plurality of different regions within one pixel by applying an electric field. In order to divide the orientation within one pixel, the electrode is provided with slits or protrusions, and the electric field direction is changed or the electric field density is biased. In order to obtain a uniform viewing angle in all directions, the number of divisions may be increased, but a substantially uniform viewing angle can be obtained by dividing into four or eight or more. In particular, it is preferable that the polarizing plate absorption axis can be set at an arbitrary angle when dividing into eight.

  Also, the liquid crystal molecules are difficult to respond at the alignment division region boundary. For this reason, in normally black display, since black display is maintained, a reduction in luminance becomes a problem. Therefore, it is possible to reduce the boundary region by adding a chiral agent to the liquid crystal material.

(IPS mode)
The optical film of the present invention is also particularly advantageously used as a support for an optical compensation sheet of an IPS liquid crystal display device having an IPS mode liquid crystal cell, or as a protective film for a polarizing plate. In these modes, the liquid crystal material is aligned substantially in parallel during black display, and black is displayed by aligning liquid crystal molecules in parallel with the substrate surface in the absence of applied voltage. In these embodiments, the polarizing plate using the optical film of the present invention is effective in reducing changes in color and contrast depending on the viewing angle.

  The features of the present invention will be described more specifically with reference to examples and comparative 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.

[Examples 1 and 2]
[Film formation of cellulose acylate film]
1. Preparation of Film 4% by weight of Compound 1 having the structure shown in Table 1 below is added as an additive to 7 g of cellulose acetate having a degree of acetyl substitution of 2.45, and a solid content concentration of 15% by weight is added to methylene chloride / A dope was prepared by adding a mixed solution of methanol (87/13 by weight). After the solid content was completely dissolved, the dope was placed on a glass plate cooled to 20 ° C., the film thickness was made uniform with an applicator, and dried at 70 ° C. for 6 minutes. Thereafter, the film on the glass plate was peeled off, fixed to a drying frame, and dried at 100 ° C. for 10 minutes and 140 ° C. for 20 minutes to completely remove the solvent.

  In addition, in the following Table 1, the addition amount of an additive represents the addition amount (mol) with respect to 1 g of cellulose acylate resins.

2. Preparation of measurement sample About the cellulose acylate film of each Example manufactured as described above, 3 points in the width direction (center, end portion (position of 5% of the total width from both ends)) are 3 in every 10 m in the longitudinal direction. The sample film was sampled twice, and a sample film having a length and width of 5.5 cm square was cut out and stretched at 200 ° C. and 1.3 times in the width direction. Thereafter, the evaluation described later was performed. In the case of non-stretching, the evaluation described later was performed without performing stretching.

[Examples 4-6, Comparative Examples 1-13]
In Example 1, Examples 4 to 6 and Comparative Example were similarly performed except that the total acyl substitution degree of cellulose acylate, the type of additive, and the presence or absence of stretching were changed as described in Table 1 and Table 2 below. 1 to 13 cellulose acylate films were produced, and sample films were cut out.

<Evaluation>
(Rth expression)
After adjusting the sample film for 24 hours at 25 ° C. and 60% relative humidity, the film surface was measured at 25 ° C. and 60% relative humidity using an automatic birefringence meter (KOBRA-21ADH: manufactured by Oji Scientific Instruments). The retardation in the film thickness direction is measured by measuring the phase difference at a wavelength of 589 nm from the direction inclined in increments of 10 ° from + 50 ° to −50 ° from the normal to the film surface with the vertical axis and the slow axis as the rotation axis. The value (Rth) was calculated. After converting the film thickness to a value of 50 μm, the obtained results are shown in Tables 1 and 2 below.

(Rth humidity dependence (ΔRth))
Regarding the change in retardation value with humidity, Rth (Rth (10%)) measured and calculated in the same manner as above except that the film was conditioned at 25 ° C. and 10% relative humidity for 12 hours. ), And Rth (Rth (80%)) measured and calculated in the same manner as above except that the humidity was adjusted for 12 hours at 25 ° C. and 80% relative humidity. did. Specifically, a value of ΔRth = Rth (10%) − Rth (80%) was calculated, and the obtained results are shown in Tables 1 and 2 below.

(Rth humidity dependency reduction rate)
Further, the ratio of the Rth humidity dependency (ΔRth) of the cellulose acetate films of other examples and comparative examples to the Rth humidity dependency (ΔRth) of the cellulose acetate films obtained in Comparative Examples 1 and 2 was obtained and obtained. The values (%) are shown in Table 1 and Table 2 below as the Rth humidity dependency reduction rate.

[Comparative Examples 14 to 16]
Further, the case where the additive amount of each additive was reduced to 1/10 with respect to Examples 1, 3, and 6 was similarly examined. The results are shown in Table 3 below.

From the results shown in Tables 1 and 2, the optical films of Examples 1 to 6 using compounds in which both the amino group and the carboxylic acid group are substituted with a benzene ring have no additive regardless of whether they are stretched or unstretched. It was found that the humidity dependence of Rth was greatly improved as compared with the optical films of Comparative Examples 1 and 2 to which the additive was added. Furthermore, when the optical film of Comparative Examples 3-13 and the optical film of Examples 1-6 were compared, the compound 1-5 of this invention was used rather than the case where the compounds 6-13 used by the comparative example were used. It was found that the humidity dependence of Rth was greatly improved in the case. That is, it was found that the humidity dependency improving agent of the present invention has a higher humidity dependency improving effect than the additive used in each comparative example.
Further, from the comparison of the results in Table 1 and Table 3, the amount of the compound represented by the general formula (I) is 1 than the amount added when the cellulose acylate film is conventionally added as a release agent. It was found that the humidity dependence of Rth was greatly improved by adding more than an order of magnitude.

DESCRIPTION OF SYMBOLS 1 Upper polarizing plate 2 Upper polarizing plate Absorption axis direction 3 Liquid crystal cell upper electrode substrate 4 Upper substrate alignment control direction 5 Liquid crystal layer 6 Liquid crystal cell lower electrode substrate 7 Lower substrate alignment control direction 8 Lower polarizing plate 9 Lower polarization Direction of plate absorption axis 10 Liquid crystal display device

Claims (13)

Cellulose ester,
An optical film comprising 1.0 × 10 ⁻⁴ mol or more of at least one compound represented by the following general formula (I) with respect to 1 g of the cellulose ester.
Formula (I)

(In general formula (I), R ¹ each independently represents a halogen atom or a hydroxyl group, and n represents an integer of 0 to 4.) The optical film of claim 1 wherein in formula (I), wherein R ¹ each independently represents a fluorine atom or a hydroxyl group, n represents, characterized in that an integer of 0-4.   The optical film according to claim 1, wherein the cellulose ester is cellulose acylate having a total acyl substitution degree of 2.0 to 3.0.   The optical film according to claim 1, wherein the cellulose ester is cellulose acylate having a total acyl substitution degree of 2.0 to 2.55.   The optical film according to any one of claims 1 to 4, wherein retardation Rth in the film thickness direction is 70 to 140 nm.   The optical film according to any one of claims 1 to 5, wherein a retardation Rth in a film thickness direction is 120 to 140 nm. The amount of change in retardation Rth in the film thickness direction under the following conditions (A) is 70% or less of the amount of change in retardation Rth in the film thickness direction under the following conditions (A) for a film consisting only of cellulose ester. The optical film according to claim 1, wherein:
Condition (A): Film thickness direction retardation Rth after conditioning for 2 hours or more at 25 ° C. and 10% relative humidity, and then changing humidity to 25 ° C. and 80% relative humidity for 2 hours or more The retardation Rth in the thickness direction is measured.   A polarizing plate comprising at least one polarizer and an optical film according to claim 1.   A display element comprising at least one polarizing plate according to claim 8.   A liquid crystal display device comprising at least one polarizing plate according to claim 8. Optical performance humidity dependence improving agent for cellulose ester films represented by the following general formula (I).
Formula (I)

(In general formula (I), R ¹ each independently represents a halogen atom or a hydroxyl group, and n represents an integer of 0 to 4.) In formula (I), wherein R ¹ represents a fluorine atom or a hydroxyl group independently, n represents a cellulose ester film for optical performance humidity dependence of claim 11, characterized in that an integer of 0 to 4 Improver.   The optical performance humidity dependency improving agent for cellulose ester films according to claim 11 or 12, characterized in that the retardation Rth in the film thickness direction can be increased.

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