WO2014091759A1

WO2014091759A1 - Optical film and method for producing same, circularly polarizing plate, and organic el display device

Info

Publication number: WO2014091759A1
Application number: PCT/JP2013/007300
Authority: WO
Inventors: 真一郎鈴木
Original assignee: コニカミノルタ株式会社
Priority date: 2012-12-14
Filing date: 2013-12-11
Publication date: 2014-06-19
Also published as: JPWO2014091759A1

Abstract

The purpose of the present invention is to provide an optical film which seldom cracks due to diagonal stretching, and is capable of minimizing wrinkles in a diagonal direction which are produced when bending an organic EL display device. This film is an optical film to be used in an organic EL display device and containing: a substrate layer containing a plasticizer and a cellulose acetate propionate or a cellulose acetate having an acetal-group degree of substitution of 2.0-2.6, inclusive; and a surface layer positioned on both surfaces of the substrate layer and containing a plasticizer and a cellulose acetate having an acetal-group degree of substitution of more than 2.6 and not more than 3.0. Furthermore, the direction of the slow axis in the plane of the optical film is diagonal in relation to the widthwise direction of the film, the ratio (X/Y) of the modulus of elasticity in tension (X) in the slow axis direction to the modulus of elasticity in tension (Y) in a direction perpendicular to the slow axis direction is 1.5-5.0, inclusive, and the amount of the plasticizer contained in the surface layer is at least 1.2 and not more than 5.5 times the amount of the plasticizer contained in the substrate layer.

Description

Optical film and manufacturing method thereof, circularly polarizing plate and organic EL display device

The present invention relates to an optical film and a manufacturing method thereof, a circularly polarizing plate, and an organic EL display device.

An organic EL display device (for example, a top emission type organic EL display device) usually includes an organic EL element in which a metal electrode (cathode), an organic light emitting layer, a transparent electrode (anode), and a transparent substrate are laminated in this order.

In such an organic EL display device, not only light emitted from the light emitting layer but also external light incident through the transparent substrate is specularly reflected on the surface of the metal electrode and extracted as outgoing light. For this reason, there is a problem in that the outside light such as room lighting is reflected and the visibility is lowered.

In order to suppress such a decrease in visibility due to the reflection of external light, it has been studied to provide a circularly polarizing plate on the viewing side of the organic EL element. As a λ / 4 retardation film constituting the circularly polarizing plate, for example, a laminated film of cellulose triacetate (TAC) has been proposed (for example, Patent Document 1).

In addition, TAC / cellulose acetate propionate (CAP) / TAC laminated film (for example, Patent Document 2), CAP laminated film (for example, Patent Document 3), as a laminated film used for a retardation film of a liquid crystal display device, etc. And a laminated film of TAC (for example, Patent Document 4) have been proposed.

JP 2003-014933 A JP 2011-158839 A JP 2002-265638 A JP 2001-131301 A

By the way, since the λ / 4 retardation film has a relatively large retardation, the main component thereof is cellulose diacetate (DAC) having a high retardation development property, and cellulose acetate propionate which is easily stretched at a high magnification ( CAP) is considered preferable.

On the other hand, the present inventors have found that the film surface containing CAP or DAC as a main component is more easily destroyed by saponification with an aqueous alkaline solution than the film containing TAC as a main component. It was found by observation of the film surface. Specifically, the destruction of the film surface means that a film containing CAP or DAC as a main component contains a relatively larger amount of hydroxyl groups than a film containing TAC as a main component. It is thought that it is caused by excessive hydrolysis of the cellulose ester. Therefore, it has been found that the film mainly composed of CAP and DAC is inferior in adhesiveness to the polarizer of the saponified film than the film mainly composed of TAC.

On the other hand, a laminated film having a base material layer mainly composed of CAP or DAC and a surface layer mainly composed of TAC has a polarizing layer because the surface layer mainly composed of TAC is not easily damaged by saponification. It is thought that the adhesion with the child can be improved.

However, when the laminated film is stretched at a high magnification in an oblique direction, cracks may occur in the surface layer. Further, when a flexible organic EL display device including the laminated film is bent, wrinkles in an oblique direction may occur in the laminated film at the bent portion. The wrinkles in the oblique direction are likely to cause a deterioration in display performance.

The present invention has been made in view of the above circumstances, and provides an optical film that has few cracks caused by oblique stretching, has good flatness, and can suppress wrinkles in an oblique direction that occur when an organic EL display device is bent. With the goal.

[1] Substrate layer containing cellulose acetate propionate or cellulose acetate having a substitution degree of acetyl group of 2.0 or more and 2.6 or less and a plasticizer, and disposed on both sides of the substrate layer, acetyl group An optical film for an organic EL display device comprising a cellulose acetate having a degree of substitution of more than 2.6 and not more than 3.0 and a surface layer containing a plasticizer, and an in-plane slow axis direction of the optical film Is an oblique direction with respect to the width direction of the film, and the ratio X / Y of the tensile elastic modulus X in the slow axis direction to the tensile elastic modulus Y in the direction orthogonal to the slow axis direction is 1.5 or more The optical film which is 5.0 or less and the mass ratio of the amount of the plasticizer contained in the surface layer to the amount of the plasticizer contained in the base material layer is 1.2 times or more and 5.5 times or less.
[2] The optical film according to [1], wherein the in-plane slow axis direction of the optical film is in a range of 40 to 50 ° with respect to the width direction of the film.
[3] The optical film according to [1] or [2], wherein the base material layer further contains a wavelength dispersion adjusting agent.
[4] The amount of the plasticizer contained in the surface layer is 15 to 50% by mass with respect to cellulose acetate having a substitution degree of the acetyl group contained in the surface layer of more than 2.6 and 3.0 or less. ] To [3].
[5] The cellulose acetate propionate contained in the base material layer or cellulose acetate having a substitution degree of acetyl group of 2.0 or more and 2.6 or less has a weight average molecular weight Mw of 150,000 to 300,000 and a number average The optical film according to any one of [1] to [4], which has a molecular weight Mn of 50,000 to 200,000.
[6] The optical film according to any one of [1] to [5], wherein the plasticizer contained in the surface layer is a polyester compound obtained by a polycondensation reaction between a diol and a dicarboxylic acid.
[7] The optical film according to [6], wherein the polyester compound has a weight average molecular weight of 700 to 2,000.
[8] The optical film according to [6] or [7], wherein the molecular terminal of the polyester compound is a hydroxyl group or is sealed with an acetyl group.
[9] The optical film according to any one of [6] to [8], wherein the dicarboxylic acid constituting the polyester compound contains an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid.
[10] The optical film has a retardation Ro in the in-plane direction at a wavelength of 550 nm defined by the formula (I) in the range of 120 to 180 nm, defined by the formula (II), and in the thickness direction at the wavelength of 550 nm. The optical film according to any one of [1] to [9], wherein the retardation Rth is 50 to 100 nm.
Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx: refractive index in the slow axis direction x in the film plane, ny: refractive index in the direction y perpendicular to the slow axis direction x in the film plane, nz: refractive index in the thickness direction z of the film, d: Film thickness (nm))
[11] A circularly polarizing plate comprising the optical film according to any one of [1] to [10].
[12] An organic EL display device comprising the optical film according to any one of [1] to [10].

[13] The method for producing an optical film according to any one of [1] to [10], wherein cellulose acetate propionate or cellulose acetate having a substitution degree of acetyl group of 2.0 or more and 2.6 or less and plasticity A first layer containing an agent, and a second layer containing cellulose acetate having a degree of substitution of acetyl group of more than 2.6 and not more than 3.0 and a plasticizer disposed on both sides of the first layer And a step of obtaining the optical film by stretching the laminated film at a magnification of 1.5 times or more and 3.0 times or less obliquely with respect to the width direction of the laminated film. The manufacturing method of an optical film containing these.
[14] The step of obtaining the laminated film includes cellulose acetate propionate or cellulose acetate having a substitution degree of acetyl group of 2.0 or more and 2.6 or less, a first layer dope containing a plasticizer and an organic solvent. Obtaining a second layer dope containing cellulose acetate having a substitution degree of acetyl group of more than 2.6 and not more than 3.0, a plasticizer and an organic solvent; and the second layer dope and the second dope A step of casting the layer dope simultaneously or sequentially on the casting support; and the organic solvent contained in the laminated first layer dope and the second layer dope. The method for producing an optical film according to [13], including a step of removing a layer to obtain a laminated film.
[15] The method for producing an optical film according to [13] or [14], wherein the stretching of the laminated film is performed in a direction of 40 to 50 ° with respect to the width direction of the film.

According to the present invention, it is possible to provide an optical film that has few cracks caused by oblique stretching and can suppress wrinkles in an oblique direction that occurs when the organic EL display device is bent.

It is a schematic diagram which shows an example of the wrinkle of the diagonal direction which arises in an optical film when an organic EL display apparatus is bent. It is a schematic diagram which shows an example of the laminated constitution of an optical film. It is a schematic diagram which shows the measuring method of a tensile elasticity modulus. It is the schematic which shows an example of the rail pattern of a diagonal stretcher. It is a schematic diagram which shows the example of the diagonal stretcher from which a rail pattern differs. It is a schematic diagram which shows an example of a fundamental structure of an organic electroluminescence display. It is a schematic diagram explaining the reflection preventing function by a circularly-polarizing plate.

1. Optical film The optical film of the present invention comprises a substrate layer and at least one surface thereof; preferably a surface layer disposed on both surfaces. The optical film of the present invention is preferably used as an optical film constituting a circularly polarizing plate of an organic EL display device.

About Base Material Layer The base material layer contains cellulose acetate propionate A1 or cellulose acetate A2 having a substitution degree of acetyl group of 2.0 or more and 2.6 or less, and a plasticizer.

The cellulose acetate propionate A1 contained in the base material layer is a cellulose ester in which an acyl group is composed of a propionyl group and an acetyl group.

The total substitution degree of the acyl group of cellulose acetate propionate A1 is preferably 2.0 or more and 3.0 or less, more preferably 2.2 or more and 2.9 or less, and 2.4 or more and 2. It is more preferably 8 or less, and particularly preferably 2.4 or more and 2.5 or less. When the total substitution degree of the acyl group is low, the expression of retardation Ro in the in-plane direction is high, but the wavelength dispersion characteristic of Ro tends to be flat. On the other hand, when the total substitution degree of the acyl group is high, the expression of retardation Ro in the in-plane direction is low, but the wavelength dispersion characteristic of Ro tends to be reverse dispersion.

The degree of substitution of the propionyl group of cellulose acetate propionate A1 is preferably 0.5 or more, and more preferably 0.8 or more in order to make the stretchability of the film constant or more. On the other hand, in order to ensure the strength of the film, the substitution degree of the propionyl group is preferably 1.5 or less, and more preferably 1.0 or less.

The method for measuring the total degree of acyl group substitution (acetyl group substitution degree) can be measured according to ASTM-D817-96.

The cellulose acetate A2 contained in the base material layer is a cellulose ester in which all of the acyl groups are acetyl groups, and the total substitution degree of the acyl groups (acetyl substitution degree) is 2.0 or more and 2.6 or less.

The total substitution degree (acyl group substitution degree) of the acyl group of cellulose acetate A2 is more preferably 2.2 or more and 2.5 or less in order to obtain a certain retardation or more.

The weight average molecular weight Mw of cellulose acetate propionate A1 and cellulose acetate A2 is preferably 120,000 to 350,000, and preferably 150,000 to 300,000 in order to easily form a film and obtain the mechanical strength of the film. It is preferable that the average particle diameter is 18 to 250,000. Further, the number average molecular weight Mn of cellulose acetate propionate A1 and cellulose acetate A2 is preferably 40,000 to 210,000, preferably 50,000 to 200,000, and preferably 60,000 to 100,000. More preferred.

The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of cellulose acetate propionate A1 and cellulose acetate A2 is preferably 1.0 to 3.0. More preferably, it is 2.2 or more and 2.9 or less.

The weight average molecular weights of cellulose acetate propionate A1 and cellulose acetate A2 can be measured by gel permeation chromatography (GPC). The measurement conditions are as follows.
Solvent: Methylene chloride Column: Three Shodex K806, K805, K803G (manufactured by Showa Denko KK) are connected and used.
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) Mw = 1.0 × 10 ⁶ to 5.0 × 10 ² 13 calibration curves are used. The 13 samples are preferably selected at approximately equal intervals.

Since cellulose acetate propionate A1 contains a propionyl group, the stretchability is relatively high. In addition, since all of the acyl groups of the cellulose acetate A2 are acetyl groups and have a low degree of substitution, the phase difference developability due to stretching is high. Therefore, cellulose acetate propionate A1 and cellulose acetate A2 are both suitable as optical films for organic EL display devices having a certain retardation or more.

Plasticizers contained in the base material layer include polyester compounds, sugar ester compounds, ester compounds (including fatty acid ester compounds and phosphate ester compounds), polyhydric alcohol ester compounds, polycarboxylic acid ester compounds (phthalate ester compounds) And a glycolate compound. Among these, a polyester compound is preferable from the viewpoint of high compatibility with the cellulose ester and improvement in mechanical strength.

The polyester compound contains a repeating unit derived from a condensate of dicarboxylic acid and diol. The dicarboxylic acid constituting the polyester compound can be an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid, or an aromatic dicarboxylic acid. The carbon number of the aliphatic dicarboxylic acid is preferably 4 to 20, and more preferably 4 to 12. Examples of the aliphatic dicarboxylic acid include malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like.

The carbon number of the aromatic dicarboxylic acid is preferably 8 to 20, and more preferably 8 to 12. Examples of aromatic dicarboxylic acids include 1,2-benzenedicarboxylic acid (phthalic acid), 1,3-benzenedicarboxylic acid (isophthalic acid), 1,4-benzenedicarboxylic acid (terephthalic acid), 1,5-naphthalene Dicarboxylic acid, 1,4-xylidene dicarboxylic acid and the like are included, and 1,4-benzenedicarboxylic acid (terephthalic acid) is preferable.

The carbon number of the alicyclic dicarboxylic acid is preferably 6 to 20, and more preferably 6 to 12. Examples of the alicyclic dicarboxylic acid include 1,3-cyclobutane dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,4-cyclohexane diacetic acid and the like.

The dicarboxylic acid constituting the polyester compound may be one type or two or more types. The dicarboxylic acid constituting the polyester compound preferably contains an aromatic dicarboxylic acid in order to enhance the compatibility with the cellulose ester; and in order to impart flexibility, it preferably contains an aliphatic dicarboxylic acid. In order to impart sufficient flexibility to the film and to easily suppress cracks, the dicarboxylic acid constituting the polyester compound preferably contains both an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid. The molar ratio of aromatic dicarboxylic acid to aliphatic dicarboxylic acid can be in the range of 5/95 to 95/5, preferably in the range of 30/70 to 70/30.

The diol constituting the polyester compound can be an aliphatic diol, an alkyl ether diol, an alicyclic diol, or an aromatic diol. The carbon number of the aliphatic diol is preferably 2 to 20, more preferably 2 to 12, and further preferably 2 to 4. Examples of aliphatic diols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-propanediol, 2-methyl- 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2,2-diethyl-1,3-propane Diol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentanediol, 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, and 1,12 -Octadecanediol and the like are included. The carbon number of the alkyl ether diol is preferably 4 to 20, and more preferably 4 to 12. Examples of the alkyl ether diol include polytetramethylene ether glycol, polyethylene ether glycol and polypropylene ether glycol.

The carbon number of the alicyclic diol is preferably 4 to 20, and more preferably 4 to 12. Examples of the alicyclic diol include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and the like.

The carbon number of the aromatic diol is preferably 6 to 20, and more preferably 6 to 12. Examples of aromatic diols include 1,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), 1,4-dihydroxybenzene (hydroquinone), and the like.

The diol constituting the polyester compound may be one type or two or more types. The diol constituting the polyester compound preferably contains an aliphatic diol.

The molecular terminal of the polyester compound may be sealed with monocarboxylic acid or monoalcohol as necessary.

The monocarboxylic acid can be an aliphatic monocarboxylic acid, an alicyclic monocarboxylic acid or an aromatic monocarboxylic acid. The carbon number of the aliphatic monocarboxylic acid can be preferably 2 to 30, more preferably 2 to 4. Examples of the aliphatic carboxylic acid include acetic acid, propionic acid, butanoic acid, caprylic acid, caproic acid, decanoic acid, dodecanoic acid, stearic acid, oleic acid and the like. Examples of the alicyclic monocarboxylic acid include cyclohexyl monocarboxylic acid. Examples of aromatic monocarboxylic acids include benzoic acid, para-tert-butyl benzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethyl benzoic acid, ethyl benzoic acid, normal propyl benzoic acid, aminobenzoic acid, acetoxybenzoic acid, Phenylacetic acid, 3-phenylpropionic acid and the like are included.

The monoalcohol can be an aliphatic monoalcohol, an alicyclic monoalcohol or an aromatic monoalcohol. The aliphatic monoalcohol has 1 to 30 carbon atoms, preferably 1 to 3 carbon atoms. Examples of aliphatic monoalcohols are methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol, hexanol, isohexanol, octanol, isooctanol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl alcohol Tert-nonyl alcohol, decanol, dodecanol, dodecahexanol, dodecaoctanol, allyl alcohol, oleyl alcohol and the like. Examples of the alicyclic monoalcohol include cyclohexyl alcohol and the like. Examples of the aromatic monoalcohol include benzyl alcohol, 3-phenylpropanol and the like.

Among them, in order to increase the affinity with the cellulose ester, it is preferable that the molecular terminal of the polyester compound is unsealed or is sealed with an aliphatic monocarboxylic acid (preferably acetic acid); More preferably, it is sealed with a monocarboxylic acid (preferably acetic acid).

The weight average molecular weight of the polyester compound is preferably 500 to 2000, and more preferably 700 to 2000. If the weight average molecular weight is too small, bleeding out may occur. If the weight average molecular weight is too large, the compatibility with the cellulose ester may be lowered.

Specific examples of the polyester compound having a ring structure include the following. In Table 1 described later, TPA: terephthalic acid, PA: phthalic acid, SA: succinic acid, AA: adipic acid, SEA: sebacic acid are shown.

The sugar ester compound is preferably a compound represented by the following formula (FA).

R ₁ to R _{8 in} the formula (FA) each represents a substituted or unsubstituted alkylcarbonyl group or a substituted or unsubstituted arylcarbonyl group. R ₁ to R ₈ may be the same as or different from each other.

The substituted or unsubstituted alkylcarbonyl group is preferably a substituted or unsubstituted alkylcarbonyl group having 2 or more carbon atoms. Examples of the substituted or unsubstituted alkylcarbonyl group include a methylcarbonyl group (acetyl group) and an ethylcarbonyl group. Examples of the substituent that the alkyl group has include an aryl group such as a phenyl group.

The substituted or unsubstituted arylcarbonyl group is preferably a substituted or unsubstituted arylcarbonyl group having 7 or more carbon atoms. Examples of the arylcarbonyl group include a phenylcarbonyl group. Examples of the substituent that the aryl group has include an alkyl group such as a methyl group.

Specific examples of the compound represented by the formula (FA) include the following. R represents R ₁ to R ₈ in the formula (FA).

The ester compound includes a fatty acid ester compound, a citrate ester compound, a phosphate ester compound, and the like. Examples of the fatty acid ester compound include butyl oleate, methylacetyl ricinoleate, and dibutyl sebacate. Examples of the citrate ester compound include acetyltrimethyl citrate, acetyltriethyl citrate, and acetyltributyl citrate. Examples of the phosphate ester compound include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, biphenyl diphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc., preferably triphenyl phosphate .

These plasticizers may be used alone or in combination of two or more.

The content of the plasticizer in the base material layer may be a range in which the ratio of the content of the plasticizer in the surface layer / the content of the plasticizer in the base material layer falls within the range described later, and is preferably the cellulose ester It is 1 to 45% by mass, and more preferably 1.5 to 40% by mass. If the content of the plasticizer is less than 1% by mass, the effect of imparting plasticity may not be sufficient. From the viewpoint of reducing the moisture permeability of the film, the plasticizer content is preferably 20% by mass or more. On the other hand, when the content of the plasticizer is more than 45% by mass, the plasticizer may ooze out from the optical film.

The base material layer may further contain a wavelength dispersing agent, an ultraviolet absorber, a matting agent, a retardation adjusting agent, a deterioration preventing agent and the like as required.

The wavelength dispersing agent contained in the base material layer is preferably a compound represented by the following general formula (A).

In the general formula (A), L ₁ and L ₂ each independently represent a single bond or a divalent linking group. R ₁ , R ₂ and R ₃ each independently represent a substituent. n represents an integer from 0 to 2. Wa and Wb each represent a hydrogen atom or a substituent. Wa and Wb may combine with each other to form a ring; at least one of Wa and Wb may have a ring structure; at least one of Wa and Wb is an alkenyl group or an alkynyl group; Also good.

Specific examples of the substituent represented by Wa and Wb include halogen atoms (eg, fluorine atom, chlorine atom, bromine atom, iodine atom), alkyl groups (eg, methyl group, ethyl group, n-propyl group, Isopropyl group, tert-butyl group, n-octyl group, 2-ethylhexyl group, etc.), cycloalkyl group (for example, cyclohexyl group, cyclopentyl group, 4-n-dodecylcyclohexyl group, etc.), alkenyl group (for example, vinyl group, Allyl group), cycloalkenyl group (eg 2-cyclopenten-1-yl, 2-cyclohexen-1-yl group, etc.), alkynyl group (eg ethynyl group, propargyl group etc.), aryl group (eg phenyl group) , P-tolyl group, naphthyl group, etc.), heterocyclic group (for example, 2-furyl group, 2-thienyl group, 2-pi Midinyl group, 2-benzothiazolyl group, etc.), cyano group, hydroxyl group, nitro group, carboxyl group, alkoxy group (for example, methoxy group, ethoxy group, isopropoxy group, tert-butoxy group, n-octyloxy group, 2- Methoxyethoxy group), aryloxy group (for example, phenoxy group, 2-methylphenoxy group, 4-tert-butylphenoxy group, 3-nitrophenoxy group, 2-tetradecanoylaminophenoxy group, etc.), acyloxy group (for example, , Formyloxy group, acetyloxy group, pivaloyloxy group, stearoyloxy group, benzoyloxy group, p-methoxyphenylcarbonyloxy group, etc.), amino group (for example, amino group, methylamino group, dimethylamino group, anilino group, N -Methyl-anilino group, diphe ), Acylamino groups (for example, formylamino group, acetylamino group, pivaloylamino group, lauroylamino group, benzoylamino group, etc.), alkyl and arylsulfonylamino groups (for example, methylsulfonylamino group, butylsulfonylamino group, Phenylsulfonylamino group, 2,3,5-trichlorophenylsulfonylamino group, p-methylphenylsulfonylamino group, etc.), mercapto group, alkylthio group (eg, methylthio group, ethylthio group, n-hexadecylthio group, etc.), arylthio group (Eg, phenylthio group, p-chlorophenylthio group, m-methoxyphenylthio group, etc.), sulfamoyl group (eg, N-ethylsulfamoyl group, N- (3-dodecyloxypropyl) sulfamoyl group, N, N— Dimethylsulfamoyl group, N-acetylsulfamoyl group, N-benzoylsulfamoyl group, N- (N′phenylcarbamoyl) sulfamoyl group, etc.), sulfo group, acyl group (for example, acetyl group pivaloylbenzoyl group) ), Carbamoyl groups (eg, carbamoyl group, N-methylcarbamoyl group, N, N-dimethylcarbamoyl group, N, N-di-n-octylcarbamoyl group, N- (methylsulfonyl) carbamoyl group, etc.) Can do. These substituents may be further substituted with the above groups.

When Wa and Wb are bonded to each other to form a ring, the following structures are exemplified.

In the formula, R ₄ , R ₅ and R ₆ each represent a hydrogen atom or a substituent. Examples of the substituent include the same groups as the specific examples of the substituent represented by R ₁ , R ₂ and R ₃ .

In general formula (A), the ring formed by bonding of Wa and Wb to each other is preferably a nitrogen-containing 5-membered ring or a sulfur-containing 5-membered ring. In the general formula (A), the compound in which Wa and Wb are bonded to each other to form a ring is preferably a compound represented by the following general formula (1).

A ₁ and A _{2 in} the general formula (1) each independently represent O, S, NR _X (R _X represents a hydrogen atom or a substituent) or CO. Examples of the substituent represented by R _X has the same meaning as specific examples of substituents represented by the Wa and Wb. R _X is preferably a hydrogen atom, an alkyl group, an aryl group, or a heterocyclic group.

X in the general formula (1) may be a non-metal atom of Group 14 to 16 after the third period, or a substituent containing a non-metal atom of Group 14 to 16 or a conjugated system after the third period. X is preferably O, S, NRc, or C (Rd) Re. Rc, Rd and Re represent substituents, and specific examples of the substituents represented by Wa and Wb are given as examples.

_{_{_{_{L 1, L 2, R 1}}}} , R 2, R 3 and n in the general formula (1) is a _{_{_{_{L 1, L 2, R 1}}}} , R 2, R 3 and n as defined in formula (A) .

Specific examples of the compound represented by formula (A) are shown below.

The content of the wavelength dispersing agent contained in the base material layer is preferably 0.5 to 15% by mass with respect to the cellulose ester contained in the base material layer in order to impart desired wavelength dispersibility. The content is more preferably 1 to 10% by mass, and further preferably 2 to 6% by mass.

As the ultraviolet absorber contained in the base material layer, a compound that is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less and that has good liquid crystal display properties and that absorbs less visible light having a wavelength of 400 nm or more is preferably used. Examples of the ultraviolet absorber include hindered phenol compounds, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like.

Specific examples of the ultraviolet absorber include the following UV-1 to UV-3.

The content of the ultraviolet absorber is preferably 1 ppm to 1.0% by mass relative to the cellulose ester, more preferably 10 to 1000 ppm.

The optical film of the present invention may further contain a matting agent (fine particles) in order to improve the surface slipperiness.

Matting agents (fine particles) contained in the base material layer are silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, kaolin, talc, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate Inorganic fine particles such as calcium phosphate, and organic fine particles such as a crosslinked polymer. Among these, fine particles of silicon dioxide are preferable because the haze increase of the film is small.

The primary average particle diameter of the fine particles is preferably 20 nm or less, preferably 5 to 18 nm, and more preferably 5 to 16 nm. The primary particle diameter of the fine particles can be obtained as an average value of the particle diameters of 100 primary particles by observing the primary particles with a transmission electron microscope at a magnification of 500,000 to 2,000,000 times.

The content of fine particles in the base material layer can be 0.05 to 1.0% by mass, preferably 0.1 to 0.8% by mass with respect to the cellulose ester contained in the base material layer.

About the surface layer The surface layer contains cellulose acetate B having a substitution degree of acetyl group of more than 2.6 and 3.0 or less, and a plasticizer.

Cellulose acetate B contained in the surface layer is a cellulose ester in which all of the acyl groups are acetyl groups, and the total substitution degree of the acyl groups (substitution degree of acetyl groups) is more than 2.6 and not more than 3.0. Since the surface of such a film containing cellulose acetate B as a main component is not easily broken by saponification with an alkaline aqueous solution, the adhesion between the polarizer and the optical film can be improved.

The total substitution degree of the acyl group of cellulose acetate B (acetyl substitution degree) is preferably 2.65 or more and 2.95 or less, more preferably 2.7 or more and 2.95 or less.

Examples of the plasticizer contained in the surface layer include the same plasticizers contained in the base material layer. Especially, since the compatibility with cellulose acetate B is favorable, the above-mentioned polyester compound and phosphoric acid ester compound are preferable, and the above-mentioned polyester compound is more preferable.

The dicarboxylic acid constituting the polyester compound contained in the surface layer is to add flexibility and suppress cracks, and to improve compatibility with the cellulose ester, both aromatic dicarboxylic acid and aliphatic dicarboxylic acid are used. It is preferable to include.

The molecular terminal of the polyester compound contained in the surface layer may be sealed as described above. In order to increase the affinity with the cellulose ester, the molecular end of the polyester compound is preferably unsealed or preferably sealed with an aliphatic monocarboxylic acid (preferably acetic acid); an aliphatic monocarboxylic acid More preferably, it is sealed with (preferably acetic acid).

The weight average molecular weight of the polyester compound contained in the surface layer is preferably 500 to 2000, and more preferably 700 to 2000. If the weight average molecular weight is too small, bleeding out may occur. If the weight average molecular weight is too large, the compatibility with the cellulose ester may be lowered.

The optical film of the present invention functions as a λ / 4 retardation film of a circularly polarizing plate of an organic EL display device as will be described later. Therefore, the optical film of this invention is obtained through the process of extending | stretching a laminated | multilayer film diagonally at high magnification. However, when the laminated film is stretched at a high magnification in an oblique direction, cracks may occur in the surface layer of the obtained optical film. Further, when the organic EL display device having the optical film is folded, wrinkles in an oblique direction may occur in the optical film.

FIG. 1 is a schematic view showing an example of an oblique wrinkle generated in an optical film when an organic EL display device is bent. As shown in FIG. 1, wrinkles occur in an oblique direction (slow axis direction) with respect to the bending axis C of the optical film 1.

The cause of the occurrence of wrinkles in the oblique direction due to such bending is not necessarily clear, but is estimated as follows. That is, 1) the film after being stretched at a high magnification in an oblique direction due to the relatively high tensile elastic modulus of the laminated film being stretched, 2) the tensile elastic modulus of each layer of the laminated film being stretched being different, etc. It is thought that distortion tends to remain in the film. It is considered that when the film is bent, wrinkles are generated in an oblique direction in the bent portion due to the distortion remaining in the stretched film.

In order to reduce the strain remaining in the stretched film, it is preferable to 1) lower the tensile elastic modulus of the laminated film to be stretched.

In order to lower the tensile elastic modulus of the laminated film, it is preferable to add a plasticizer to the surface layer and the base material layer of the laminated film. The content of the plasticizer in the surface layer is preferably 15 to 50% by mass and more preferably 25 to 45% by mass with respect to the cellulose ester. Thereby, it is thought that the crack which is easy to arise in the surface layer of the film after extending | stretching is further suppressed easily.

However, 1) The wrinkles in the oblique direction at the time of bending as described above may not be sufficiently suppressed only by reducing the tensile elastic modulus of the laminated film to be stretched. That is, in order to sufficiently suppress wrinkles in an oblique direction during bending, not only 1) lowering the tensile elastic modulus of the laminated film to be stretched; 2) the tensile elastic modulus of each layer of the laminated film to be stretched It is important to reduce the difference.

The absolute value of the difference in tensile elastic modulus between the surface layer and the base material layer is preferably 1 GPa or less, and more preferably 0.5 GPa or less. The tensile elastic modulus of the surface layer and the base material layer can be measured using Tensilon RTC-1225A manufactured by Orientec Co. in accordance with JIS K7127. The measurement conditions may be a distance between chucks of 50 mm under 23 ° C. and 50% RH.

The difference in tensile elastic modulus between the surface layer and the base material layer can be preferably adjusted by the ratio between the amount of plasticizer contained in the surface layer and the amount of plasticizer contained in the base material layer. That is, the amount of the plasticizer contained in the surface layer is preferably larger than the amount of the plasticizer contained in the base material layer, and preferably 1.2 times or more the amount of the plasticizer contained in the base material layer. 1.4 times or more is more preferable. Even if the amount of the plasticizer contained in the surface layer is too much relative to the amount of the plasticizer contained in the base material layer, the difference in tensile modulus between the surface layer and the base material layer may not be reduced. Therefore, the amount of the plasticizer contained in the surface layer is preferably 5 times or less, more preferably 2.5 times or less of the amount of the plasticizer contained in the base material layer.

That is, in order to suppress wrinkles in an oblique direction at the time of bending, a plasticizer is contained in both the surface layer and the base material layer (preferably the amount of plasticizer contained in the surface layer is set to a certain level or more) and is contained in the surface layer It is preferable that the ratio (mass ratio) of the plasticizer amount to the plasticizer amount contained in the base material layer is a certain level or more.

The surface layer may further contain the same additive as the base material layer as necessary.

The substrate layer and the surface layer may each be a single layer or two or more layers. In particular, the optical film preferably has one base material layer and two surface layers sandwiching the base material layer (having a three-layer structure) in order to reduce the film thickness and to prevent distortion. .

The total thickness of the optical film is preferably 10 to 250 μm, more preferably 15 to 100 μm, and still more preferably 20 to 80 μm, in order to obtain a sufficient retardation as a λ / 4 retardation film. Particularly preferably, it may be 25 to 65 μm.

The ratio of the thickness of the base material layer to the total thickness of the optical film is preferably in the range of 30 to 90%, more preferably 50 to 85%. If the thickness ratio of the base material layer is too low, the retardation of the optical film may not be sufficient. If the thickness ratio of the base material layer is too high, breakage due to saponification of the optical film surface may not be sufficiently suppressed.

FIG. 2 is a schematic diagram showing an example of a preferable laminated structure of the optical film. As shown in FIG. 2, the optical film 10 includes a base material layer 11 and a pair of surface layers 13 and 13 ′ that sandwich the base material layer 11.

The compositions and thicknesses of the surface layers 13 and 13 ′ may be the same or different from each other. However, in order to suppress warping of the film, the compositions and thicknesses of the surface layers 13 and 13 ′ may be the same. preferable.

Physical properties of optical film [In-plane slow axis]
In the present invention, as described later, it is preferable to produce a circularly polarizing plate by laminating an optical film and a polarizer with a roll-to-roll. A polarizer usually has an absorption axis in the longitudinal direction. Therefore, in the film plane, the optical film has a slow axis in an oblique direction with respect to the width direction (or longitudinal direction) of the film; preferably 40 to 50 °; more preferably 45 ± 2 °.

The in-plane slow axis of the optical film is an axis in the direction in which the refractive index is maximum in the film plane; it can be measured by an automatic birefringence meter AxoScan or the like.

[Tension modulus ratio]
As will be described later, the optical film of the present invention is obtained through a step of stretching at a high magnification in an oblique direction in order to obtain a sufficient retardation as a λ / 4 retardation film. Therefore, the tensile modulus of elasticity of the optical film of the present invention; that is, the in-plane slow axis direction is high. Specifically, the ratio X / Y of the tensile elastic modulus X in the in-plane slow axis direction to the tensile elastic modulus Y in the direction orthogonal thereto is preferably 1.5 or more and 5.0 or less, more preferably It may be 1.6 or more and 3.0 or less, more preferably 1.7 or more and 2.5 or less.

The ratio of the tensile modulus can be measured by the following procedure. FIG. 3 is a schematic diagram showing a method for measuring the tensile elastic modulus. FIG. 3 illustrates an example in which the slow axis of the optical film is + 45 ° with respect to the TD direction.
1) First, the sample film S1 is cut into a size of 1 cm × 10 cm parallel to the slow axis direction of the optical film (in FIG. 3A, + 45 ° direction with respect to the TD direction). On the other hand, the sample film S2 is cut to a size of 1 cm × 10 cm parallel to the direction orthogonal to the slow axis direction of the optical film (in FIG. 3A, the direction of −45 ° to the TD direction). The sample films S1 and S2 are conditioned for 24 hours in an environment of 25 ° C. and 55% RH.
2) Next, as shown in FIG. 3 (B), the sample film S1 after humidity adjustment was set in a tensile tester 15 (Tensilon RTC-1225A manufactured by Orientec Co., Ltd.) and the distance between chucks was set to 50 mm. Based on K7127, the sample film is pulled in the longitudinal direction, and the tensile elastic modulus X is measured.
3) Similarly, the tensile modulus Y is measured by pulling the sample film S2 in the longitudinal direction. The tensile modulus can be measured at 25 ° C. and 55% RH.
4) The tensile elastic modulus X and Y obtained in the above 2) and 3) are applied to the following equation to calculate the tensile elastic modulus ratio X / Y.
Tensile modulus ratio X / Y = tensile modulus X / tensile modulus Y

[Phase difference]
In the optical film of the present invention, the retardation Ro (550) in the in-plane direction measured at a wavelength of 550 nm in an environment of 23 ° C. and 55% RH is preferably in the range of 120 to 180 nm, preferably 120 to 160 nm. More preferably, it is within the range, and further preferably within the range of 130 to 150 nm. The retardation Rth in the thickness direction is preferably 40 to 120 nm, and more preferably 50 to 100 nm. An optical film having such a retardation is suitable, for example, as a λ / 4 retardation film for a circularly polarizing plate.

Retardation Ro and Rth are defined by the following equations, respectively.
Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx: refractive index in the slow axis direction x in the film plane, ny: refractive index in the direction y perpendicular to the slow axis direction x in the film plane, nz: refractive index in the thickness direction z of the film, d: Film thickness (nm))

Retardation Ro and Rth can be measured, for example, by the following method.
1) Condition the optical film at 23 ° C. and 55% RH. The average refractive index of the optical film after humidity adjustment is measured with an Abbe refractometer or the like.
2) The Ro when the light having a measurement wavelength of 550 nm is incident on the optical film after humidity adjustment in parallel to the normal line of the film surface is measured with an AxoScan manufactured by Axometric.
3) Using an AxoScan manufactured by Axometric, the wavelength measured from the angle of θ (incident angle (θ)) with respect to the normal of the surface of the optical film, with the slow axis in the plane of the optical film as the tilt axis (rotation axis) The retardation value R (θ) when 590 nm light is incident is measured. The retardation value R (θ) can be measured at 6 points every 10 ° in the range of 0 ° to 50 °. The in-plane slow axis of the optical film can be confirmed with an AxoScan manufactured by Axometric.
4) nx, ny and nz are calculated from the measured Ro and R (θ) and the above-mentioned average refractive index and film thickness by AxoScan manufactured by Axometric, and Rth at a measurement wavelength of 590 nm is calculated. . The measurement of retardation can be performed under conditions of 23 ° C. and 55% RH.

The internal haze of the optical film measured according to JIS K-7136 is preferably 0.01 to 0.1. The visible light transmittance of the optical film is preferably 90% or more, and more preferably 93% or more.

2. Method for Producing Optical Film The optical film of the present invention is 1) a first layer (layer serving as a base material layer) containing the above-mentioned cellulose acetate propionate A1 or cellulose acetate A2 and a plasticizer, and at least one of them. A step of obtaining a laminated film comprising a second layer (layer that becomes a surface layer) containing cellulose acetate B and a plasticizer; 2) at least obliquely with respect to the width direction It can be obtained through a step of obtaining an optical film including the base material layer and the surface layer by stretching at a magnification of 1.5 times or more and 3.0 times or less.

1) The step of obtaining a laminated film is preferably performed by a co-casting method because it is relatively easy to manufacture. The co-casting method may be a solution casting method or a melt casting method, and since an optical film having a good surface shape can be easily obtained, the solution casting method may be preferable.

That is, 1) the step of obtaining a laminated film is as follows: 1-1) the first dope (the base layer dope) containing the cellulose acetate propionate A1 or cellulose acetate A2, the plasticizer and the organic solvent. A second dope (surface layer dope) containing cellulose acetate B, a plasticizer and an organic solvent; 1-2) the first and second dopes simultaneously or sequentially on the casting support It is preferable to include a step of casting while laminating; 1-3) a step of removing the organic solvent in the laminated first and second dopes to obtain a laminated film.

1-1) Step for preparing a dope A cellulose ester, a plasticizer, and, if necessary, other components are dissolved in an organic solvent, and a first dope mainly composed of cellulose ester (dope for base material layer) A second dope (surface layer dope) is obtained.

The organic solvent used for the preparation of the dope may be a conventionally known organic solvent. For example, a solubility parameter in the range of 17 to 22 is preferable. Solubility parameters are described in, for example, J. Brandrup, E.I. “Polymer Handbook (4th. Edition)” such as H, and the like described in VII / 671 to VII / 714. Lower aliphatic hydrocarbon chloride, lower aliphatic alcohol, ketone having 3 to 12 carbon atoms, ester having 3 to 12 carbon atoms, ether having 3 to 12 carbon atoms, fat having 5 to 8 carbon atoms Group hydrocarbons, aromatic hydrocarbons having 6 to 12 carbon atoms, fluoroalcohols (for example, described in paragraph No. [0020] of JP-A-8-143709, paragraph No. [0037] of JP-A-11-60807, etc.) Compound) and the like.

The organic solvent may be used alone or in combination of two or more. When combining two or more types, it is preferable to use a mixture of a good solvent and a poor solvent in order to stably obtain an optical film having a good surface shape. The mixing ratio of the good solvent and the poor solvent is preferably 60 to 99% by mass for the good solvent and 40 to 1% by mass for the poor solvent.

A good solvent is one that dissolves the resin used alone, and a poor solvent is one that swells or does not dissolve the resin used alone. Examples of good solvents include organic halogen compounds such as methylene chloride and dioxolanes. As examples of the poor solvent, methanol, ethanol, n-butanol, cyclohexane and the like are preferably used.

The poor solvent contained in the first and second dopes is preferably alcohol, and preferably methanol, in order to shorten the drying time of the dope on the casting support. The content of methanol in the organic solvent contained in the base layer dope A and the surface layer dope B can be 20 to 35% by mass, preferably 21 to 35% by mass, more preferably 25 to 30% by mass. It can be.

The solid content concentration of the first and second dopes (concentration of components that become solid after drying the dope) can be appropriately set according to the molecular weight of the resin. In order to obtain a dope having a viscosity suitable for solution casting film formation, the solid content concentration is preferably 16 to 30% by mass, and more preferably 18 to 25% by mass.

In order to obtain a good planar film by co-casting, it is preferable that the solid content concentrations of the first and second dopes are approximately the same. The difference in solid content concentration between the first and second dopes is preferably within 10% by mass, and more preferably within 5% by mass.

The dissolution of each component in an organic solvent can be performed by a room temperature dissolution method, a cooling dissolution method, or a high temperature dissolution method. A method for dissolving cellulose ester in an organic solvent is described, for example, in JP-A-5-163301. In the case of dissolving at a high temperature, it is preferably carried out at a pressure higher than the boiling point of the organic solvent to be used.

The obtained dope can be concentrated and filtered as necessary. The solution concentration and filtration method is described in detail on page 25 of Kokai No. 2001-1745.

1-2) Step of casting while laminating simultaneously or sequentially The first and second dopes are cast while being laminated simultaneously or sequentially on a casting support.

The co-casting of the first and second dopes can be performed by a known co-casting method. For example, each dope may be sequentially cast from a plurality of casting openings provided at intervals in the traveling direction of the casting support, and laminated, for example, Japanese Patent Laid-Open Nos. 61-158414 and 1- The methods described in JP-A No. 122419 and JP-A No. 11-198285 can be applied. Further, the dope may be cast from two casting ports simultaneously and laminated, for example, Japanese Patent Publication No. 60-27562, Japanese Patent Laid-Open No. 61-94724, Japanese Patent Laid-Open No. 61-947245, Japanese Patent Laid-Open No. 61- The methods described in JP-A-104813, JP-A-61-158413, and JP-A-6-134933 can be applied.

For example, when an optical film having a three-layer structure of surface layer / base material layer / surface layer is obtained, the second dope (surface layer dope) / first dope (base material dope) / The second dope (surface layer dope) can be co-cast. The composition of the plurality of second dopes in the laminate may be the same as or different from each other.

The casting support is not particularly limited, but is preferably a drum or a band. The surface of the support is preferably finished in a mirror state. The casting and drying methods in the solvent cast method are described in US Pat. No. 2,336,310.

The surface temperature of the casting support on which the first and second dopes are cast is preferably 5 ° C. or less, more preferably −30 to 5 ° C., and −10 to 2 ° C. Is more preferable.

1-3) Step of removing the organic solvent contained in the dope to obtain a laminated film The cast first and second dopes may be dried by heating with a temperature control plate; 2 seconds or more It may be dried in the wind. The obtained laminated film may be peeled off from the casting support, and dried with high-temperature air while sequentially changing the temperature from 100 ° C. to 160 ° C. to evaporate the residual solvent. This drying method is described in Japanese Patent Publication No. 5-17844.

2) Step of stretching the laminated film The aforementioned laminated film is stretched at a high magnification in an oblique direction with respect to at least the width direction (or longitudinal direction) of the film, and disposed on the base material layer and at least one surface thereof. An optical film including the surface layer is obtained. Diagonal stretching may be performed continuously without winding up the formed laminated film; it may be performed after winding up the formed laminated film.

The residual solvent amount at the start of stretching of the laminated film is preferably 1 to 50% by mass, more preferably 10 to 50% by mass, and further preferably 12 to 35% by mass. When a laminated film having a residual solvent amount of less than 1% is stretched, it is not preferable because stretching is difficult and the film may be broken. If the residual solvent amount exceeds 50%, the effect of increasing the elastic modulus is reduced, and sufficient surface hardness cannot be obtained.

The residual solvent amount is represented by the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
M is a mass at an arbitrary point of the laminate, and N is a mass when the laminate for which M is measured is dried at 110 ° C. for 3 hours.

Stretching is preferably performed in an oblique direction with respect to at least the width direction (or the long direction) of the film as described above. Thereby, a polarizer unwound from the roll body and having an absorption axis in the longitudinal direction of the film, and an optical film unwound from the roll body and having a slow axis in an oblique direction with respect to the longitudinal direction of the film; Can be easily manufactured by simply laminating them in a roll-to-roll manner so that their longitudinal directions overlap each other. Therefore, the cut loss of the film can be reduced, which is advantageous in production.

The oblique direction with respect to the width direction (or length direction) of the film is specifically a direction of 40 to 50 ° with respect to the width direction (or length direction) of the film; preferably 45 ± 2 °. The direction. If necessary, the stretching in the oblique direction and the stretching in the width direction or the longitudinal direction may be combined.

The stretching ratio in the oblique direction is preferably 1.5 times or more and 3.0 times or less, for obtaining a sufficient retardation as a λ / 4 retardation film, and is preferably 1.7 times or more and 2.3 times or less. It is more preferable that

As described above, by including a certain amount or more of the plasticizer in the stretched laminated film, the tensile elastic modulus of the laminated film can be lowered and the occurrence of cracks in the surface layer can be suppressed.

Stretching in the oblique direction can be performed with an oblique stretching machine. The oblique stretching machine usually has a pair of rails arranged on both ends in the width direction of the film and a number of gripping tools that run on the rails and grip both ends in the width direction of the film.

The pair of rails each have an endless continuous track, and the gripping tool that has released the grip of the film at the exit of the tenter travels outside and is sequentially returned to the entrance. The rail pattern of the pair of rails has an asymmetric shape on the left and right, and the rail pattern can be adjusted according to the orientation angle θ, the draw ratio, and the like given to the long stretched film to be manufactured.

FIG. 4 is a schematic view showing an example of a rail pattern of an oblique stretching machine. As shown in FIG. 4, in general, in the oblique stretching machine, the feeding direction D1 of the long original film is different from the winding direction D2 of the stretched film after stretching, and the feeding angle θi is formed. . The feeding angle θi can be arbitrarily set to a desired angle within a range of more than 0 ° and less than 90 °.

At the entrance of the oblique stretching machine (position A in the figure), the both ends of the long laminated film described above are gripped with the left and right grippers (tenters) and run. The left and right gripping tools Ci and Co facing the direction substantially orthogonal to the film transport direction (feeding direction D1) at the entrance of the oblique stretching machine (position A in the drawing) are: Each travels on asymmetrical rails Ri and Ro. The left and right gripping tools release the gripped film at the position at the end of stretching (position B in the figure).

As the left and right gripping tools facing at the entrance of the oblique stretching machine (position A in the figure) travel on the left and right asymmetric rails Ri and Ro, the gripping tool Ci traveling on the Ri side travels on the Ro side. Proceed with respect to the gripping tool Co. That is, at the entrance of the oblique stretching machine (the gripping start position by the film gripping tool) A, the straight line connecting the gripping tools Ci and Co is substantially perpendicular to the film feeding direction D1. On the other hand, in the state at the position B at the end of stretching of the film, the straight line connecting the grippers Ci and Co is inclined by an angle θL with respect to a direction substantially perpendicular to the film winding direction D2. . Thereby, the laminated film is obliquely stretched in the direction of θL. The term “substantially vertical” indicates a range of 90 ± 1 °.

In the zone formed between the pair of rails, a section that travels with a constant interval between the gripping tools gripping both ends is a “preheating zone”. Further, the interval between the gripping tools gripping both ends is opened, and a section until the predetermined interval is reached becomes an “extension zone”. Furthermore, in a period in which the interval between the gripping tools after the stretching zone becomes constant again, a section in which the gripping tools at both ends travel while being parallel to each other is a “heat fixing zone or heat fixing / cooling zone”.

The temperature of the preheating zone and the stretching zone is preferably in the range of Tg to Tg + 30 ° C. when the glass transition temperature of the cellulose ester is Tg; the temperature of the heat setting zone or heat setting / cooling zone is Tg-30 It is preferable to set within the range of ~ Tg ° C.

The length of the preheating zone, stretching zone, and heat setting zone can be selected as appropriate. The length of the preheating zone can usually be in the range of 100-150% with respect to the length of the drawing zone; the length of the heat setting zone should normally be in the range of 50-100% Can do.

FIG. 5 is a schematic diagram showing an example of an oblique stretching machine having a different rail pattern. An oblique stretching machine 20 shown in FIGS. 5A to 5C includes a film feeding device 21, a transport direction changing device 23, and a winding device 25.

The obtained long optical film is wound up in the long direction (perpendicular to the width direction) of the film using a winder. The winding method is not particularly limited, and may be a constant torque method, a constant tension method, a taper tension method, or the like. The winding tension at the time of winding the optical film can be about 50 to 170N.

3. Circularly polarizing plate The polarizing plate of this invention contains a polarizer and the optical film of this invention arrange | positioned at the one surface.

A polarizer is an element that allows only light of a polarization plane in a certain direction to pass through. A typical example of the polarizer is a polyvinyl alcohol-based polarizing film, and there are one in which a polyvinyl alcohol-based film is dyed with iodine and one in which a dichroic dye is dyed.

The polarizer can be obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing; or after dying a polyvinyl alcohol film and uniaxially stretching, and preferably by further performing a durability treatment with a boron compound. The film thickness of the polarizer is preferably in the range of 5 to 30 μm, and more preferably in the range of 5 to 20 μm.

Examples of the polyvinyl alcohol film include an ethylene unit content of 1 to 4 mol%, a degree of polymerization of 2000 to 4000, a degree of saponification of 99.0 to 99 described in JP2003-248123A, JP2003-342322A, and the like. 99 mol% ethylene-modified polyvinyl alcohol is preferably used.

The optical film of the present invention is disposed on one surface of the polarizer. The in-plane slow axis of the optical film of the present invention is preferably 40 to 50 °; more preferably 45 ± 2 ° with respect to the absorption axis of the polarizer.

It is preferable that a protective film is further disposed on the other surface of the polarizer. Examples of the protective film include commercially available cellulose ester films such as Konica Minoltak KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC6UY, KC, HA, KC2UA, KC4UA, KC6UAKC, 2UAH, KC4UAH, KC6UAH (above Konica Minolta Advanced Layer Co., Ltd.); FUJIFILM Corporation).

The circularly polarizing plate of the present invention can be obtained through a step of bonding a polarizer and the optical film of the present invention through an adhesive.

The optical film of the present invention has an in-plane slow axis in an oblique direction with respect to the width direction (or longitudinal direction) of the film. Therefore, it is possible to easily manufacture a circularly polarizing plate of a polarizer simply by laminating with a roll-to-roll so that the longitudinal direction of the polarizer having the absorption axis in the longitudinal direction of the film and the longitudinal direction of the optical film overlap. it can.

The adhesive used for bonding is an aqueous adhesive such as a fully saponified polyvinyl alcohol adhesive or an active energy ray-curable adhesive, and is preferably an aqueous adhesive.

Since the surface layer of the optical film of the present invention contains the above-mentioned cellulose acetate B as a main component, it is difficult to be destroyed by the saponification treatment that is performed before bonding with a polarizer using an aqueous adhesive. Therefore, the optical film of the present invention can be in good contact with the polarizer via the aqueous adhesive.

Further, not only the water-based adhesive but also an active energy ray-curable adhesive may be used from the viewpoint that the moisture permeability of the obtained polarizing plate can be effectively controlled. When producing a polarizing plate using an active energy ray-curable adhesive, it is preferable that the active energy ray-curable adhesive further includes an ultraviolet light sensitizer.

The curable compound contained in the active energy ray-curable adhesive is a cationic polymerizable compound or a radical polymerizable compound, and a cationic polymerizable compound (for example, an epoxy compound) is preferable from the viewpoint of improving adhesiveness. The active energy ray-curable adhesive preferably further contains a photosensitizer that exhibits maximum absorption in light having a wavelength longer than 380 nm. The composition of the active energy ray-curable adhesive is described in, for example, JP-A-2011-28234.

4). Organic EL Display Device The organic EL display device of the present invention has an organic EL element and the circularly polarizing plate of the present invention disposed on the surface on the viewing side.

FIG. 6 is a schematic diagram illustrating an example of a basic configuration of an organic EL display device. As shown in FIG. 6, the organic EL display device 30 includes an organic EL element 50 and a circularly polarizing plate 70 of the present invention disposed on the surface on the viewing side.

The organic EL element 50 may have a substrate 51, a metal electrode 53, a TFT 55, an organic light emitting layer 57, a transparent electrode (ITO or the like) 59, an insulating layer 61, a sealing layer 63, and a film 65 (optional) in this order.

The substrate 51 can be a glass substrate or a plastic film such as polyimide. In particular, when the organic EL display device 30 is a flexible type, the substrate 51 is preferably a flexible glass film or resin film.

The metal electrode 53 preferably functions as a cathode and is made of a metal material having high light reflectivity. Examples of the metal material include Mg, MgAg, MgIn, Al, LiAl, and the like.

The organic light emitting layer 57 may be a laminate of various organic thin films, for example, a hole injection layer made of a triphenylamine derivative / a light emitting layer laminate made of a fluorescent organic solid such as anthracene; A light emitting layer made of a fluorescent organic solid / a laminate of an electron injection layer made of a perylene derivative or the like; a laminate of the hole injection layer / the light emitting layer / the electron injection layer, or the like. The thickness of the organic light emitting layer 57 may be about 10 nm. For this reason, the organic light emitting layer 57 also transmits light almost completely like the transparent electrode 59.

The transparent electrode 59 is an anode and is made of a transparent conductor such as indium tin oxide (ITO) in order to extract light emitted from the organic light emitting layer 57.

The film 65 may be any material that can transmit light (transparent), and may be a glass substrate, a plastic film, a thin film, or the like. Especially, when the organic EL display apparatus 30 is a flexible type, it is preferable that the film 65 is a flexible glass film or resin film.

The organic EL element 50 injects holes and electrons into the organic light emitting layer 57 by applying a voltage between the transparent electrode 59 and the metal electrode 53, and recombines these holes and electrons. Emits light.

The circularly polarizing plate 70 includes a polarizer 71, an optical film 73 of the present invention disposed on the surface of the polarizer 71 on the organic EL element 50 side, and a protective film 75 disposed on the surface of the polarizer 71 on the viewing side. Have

The optical film 73 of the present invention has the above-described base material layer 73-1 and surface layers 73-3 and 73-3 'disposed on both surfaces thereof.

FIG. 7 is a schematic diagram for explaining the antireflection function by the circularly polarizing plate 70. In FIG. 7, the same members as those in FIG. First, when light (including a1 and b1) is incident from the outside in parallel to the normal line of the display screen of the organic EL display device, only linearly polarized light (b1) parallel to the transmission axis direction of the polarizer (LP) 71 is obtained. Passes through a polarizer (LP) 71. The other linearly polarized light (a1) that is not parallel to the transmission axis direction of the polarizer (LP) 71 is absorbed by the polarizer (LP) 71. The linearly polarized light component (b2) that has passed through the polarizer (LP) 71 is converted into circularly polarized light (c2) by passing through the optical film 73. The circularly polarized light (c2) passes through the film 65, the sealing layer 63, the insulating layer 61, the transparent electrode 59, the organic light emitting layer 57, and the TFT 55, is reflected by the metal electrode 53 (see FIG. 6), and is reversely circularly polarized light. (C3). The reversely circularly polarized light (c3) passes through the TFT 55, the organic light emitting layer 57, the transparent electrode 59, the insulating layer 61, the sealing layer 63, and the film 65, and further passes through the optical film 73, whereby the polarizer (LP). 71 is converted into linearly polarized light (b3) in a direction orthogonal to the transmission axis direction of 71. This linearly polarized light (b3) cannot be passed through the polarizer (LP) 71 and is absorbed.

Thus, since all light (including a1 and b1) incident on the organic EL display device from the outside is absorbed by the polarizer (LP) 71, even if it is reflected by the metal electrode 53 of the organic EL display device, Does not exit to the outside. Therefore, it is possible to prevent a decrease in image display characteristics due to the reflection of the background.

The optical film 73 of the present invention is stretched obliquely at a high magnification because the difference in tensile elastic modulus between the base material layer 73-1 and the surface layer 73-3 disposed on both surfaces thereof is small (see FIG. 6). Therefore, there is little residual distortion. Therefore, the generation of wrinkles in an oblique direction as shown in FIG. 1 when the organic EL display device 30 including the optical film 73 of the present invention is folded can be suppressed.

Hereinafter, the present invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

1. Optical Film Material 1) Cellulose Ester The cellulose ester shown in the table below was prepared. In the following table, Dac represents the acetyl group substitution degree, Dpr represents the propionyl group substitution degree, and Dall represents the total substitution degree.

2) Plasticizer Polyester compounds shown in the following table were prepared.

3) Wavelength dispersion regulator The following compound (24)

(Example 1)
Preparation of dope The following components were put into a sealed container and completely dissolved while heating and stirring. The obtained solution was used as Azumi filter paper No. manufactured by Azumi Filter Paper Co., Ltd. After filtration at 24, the mixture was further filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to obtain a dope solution for the base material layer.
(Composition of dope for substrate layer)
CAP1: 100 parts by weight PE-A: 10 parts by weight Wavelength dispersion adjusting agent Compound (24): 4.0 parts by weight Matting agent dispersion (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd., secondary average particle size of 1.0 μm or less) ): 0.13 parts by weight of solid content with respect to 100 parts by weight of cellulose ester Dichloromethane: 406 parts by weight Methanol: 61 parts by weight Butanol: 2 parts by weight

On the other hand, the following components were put into another sealed container and completely dissolved while heating and stirring. The obtained solution was filtered in the same manner as described above to obtain a surface layer dope solution.
(Surface layer dope composition)
TAC 1: 100 parts by mass PE-A: 20 parts by mass Matting agent dispersion (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd., secondary average particle size of 1.0 μm or less): 0.13 solids content with respect to 100 parts by mass of cellulose ester Part by mass Dichloromethane: 406 parts by mass Methanol: 61 parts by mass Butanol: 2 parts by mass

Preparation of optical film Simultaneous multi-layer casting so that the obtained base layer dope and surface layer dope are laminated in the order of surface dope / base layer dope / surface layer dope using a belt casting apparatus. I let you. The dope cast on the belt was dried until the residual solvent amount was about 30% by mass, and then peeled off from the belt to obtain a film-like material.

The obtained film was dried with hot air at 140 ° C. until the residual solvent amount was less than 1.0%, and then the film was wound up. Next, the wound film was unwound and stretched in the direction of 45 ° with respect to the width direction of the film at a stretch ratio of 2.0 times at 180 ° C. Thereby, an optical film 101 having a three-layer structure of surface layer / base material layer / surface layer was obtained. The total thickness of the obtained optical film 101 was 41 μm, and the thickness of each layer was surface layer / base material layer / surface layer = 3 μm / 35 μm / 3 μm.

(Comparative Examples 1 and 2)
Optical films 102 to 103 were obtained in the same manner as in Example 1 except that the draw ratio was changed as shown in Table 4.

(Examples 2 to 6, Comparative Examples 3 to 4)
The optical films 104 to 100 were formed in the same manner as in Example 1 except that the ratio of the amount of plasticizer contained in the surface layer to the amount of plasticizer contained in the base material layer (plasticizer content ratio) was changed as shown in Table 4. 110 was obtained.

(Example 7)
An optical film 111 was obtained in the same manner as in Example 1 except that the base material layer did not contain a wavelength dispersing agent.

(Examples 8 to 10, Comparative Examples 5 to 7)
Optical films 112 to 117 were obtained in the same manner as in Example 1 except that the type of cellulose ester contained in the base material layer or the surface layer was changed as shown in Table 4.

(Examples 11 to 14)
Optical films 118 to 121 were obtained in the same manner as in Example 1 except that the type of plasticizer contained in the base material layer or the surface layer was changed as shown in Table 4.

(Examples 15 to 16)
Optical films 122 to 123 were obtained in the same manner as in Example 1 except that the thickness ratio and total thickness of each layer were changed as shown in Table 4.

(Examples 17 to 23)
Optical films 124 to 130 were obtained in the same manner as in Example 1 except that the type of plasticizer contained in the surface layer was changed as shown in Table 5.

(Example 24, Comparative Examples 8 to 9)
Optical films 131 to 133 were obtained in the same manner as in Example 1 except that the amounts of the plasticizer contained in the surface layer and the base material layer were changed as shown in Table 5.

The in-plane elastic modulus ratio of the obtained optical film, the elastic modulus difference between the surface layer and the base material layer, cracks, flatness and retardation were evaluated by the following methods.

[In-plane elastic modulus ratio]
1) First, as shown in FIG. 3A, the sample film was cut into a size of 1 cm × 10 cm parallel to the slow axis direction (+ 45 ° direction with respect to the TD direction) of the optical film to obtain a sample film S1. On the other hand, a sample film S2 was cut out to a size of 1 cm × 10 cm parallel to a direction perpendicular to the slow axis direction of the optical film (−45 ° direction with respect to the TD direction). The sample films S1 and S2 were conditioned for 24 hours in an environment of 25 ° C. and 55% RH.
2) Next, according to JIS K7127, the sample film S1 after humidity control was set to 50 mm between the chucks using Tensilon RTC-1225A manufactured by Orientec Co., Ltd., and the longitudinal direction (slow axis direction) of the sample film The tensile elastic modulus X in the slow axis direction was measured.
3) Similarly, the sample film S2 was pulled in the longitudinal direction (direction perpendicular to the slow axis direction), and the tensile elastic modulus Y in the direction perpendicular to the slow axis direction was measured. The tensile modulus was measured at 25 ° C. and 55% RH.
4) Tensile modulus X and Y obtained in the above 2) and 3) were applied to the following equation to calculate the ratio X / Y of the tensile modulus.
Tensile modulus ratio X / Y = tensile modulus X / tensile modulus Y

[Difference in elastic modulus between surface layer and base material layer]
Tensilon RTC-1225A manufactured by Orientec Co., Ltd. was used in accordance with JIS K7127 for the tensile elastic modulus of a film having a thickness of 30 μm made of the material constituting the surface layer and a film having a thickness of 30 μm made of the material constituting the base material layer. Measured. Measurement conditions were set to a distance between chucks of 50 mm under 23 ° C. and 50% RH. From the obtained value of the tensile modulus, the difference in elastic modulus between the surface layer and the base material layer (= the tensile elastic modulus of the surface layer−the tensile elastic modulus of the base material layer) was determined.

[crack]
A black spray was sprayed on one side of the optical film. And the other surface (surface which is not spraying a spray) of the optical film was observed 100 times with an optical microscope, and observation area 100mm < ² >, and the presence or absence of the crack was evaluated.
◎: No cracks were observed in the observation region ○: Shallow cracks were observed in the observation region △: 1 to 10 deep cracks were observed in the observation region ×: Deep in the observation region 11 or more cracks were observed

[Flatness]
A black spray was sprayed on one side of the optical film. And the other surface (surface which is not spraying a spray) of the optical film was visually observed under the fluorescent lamp, and the flatness of the optical film was evaluated.
○: The surface was smooth. ×: Fine irregularities were observed on the surface.

[Retardation Ro and Rth]
Retardation Ro and Rth were measured by the following methods.
1) The optical film was conditioned at 23 ° C. and 55% RH. The average refractive index of the optical film after humidity control was measured with an Abbe refractometer.
2) Ro was measured with an AxoScan manufactured by Axometric, when light having a measurement wavelength of 550 nm was incident on the optical film after humidity control in parallel with the normal line of the film surface.
3) Using an AxoScan manufactured by Axometric, the wavelength measured from the angle of θ (incident angle (θ)) with respect to the normal of the surface of the optical film, with the slow axis in the plane of the optical film as the tilt axis (rotation axis) The retardation value R (θ) when 590 nm light was incident was measured. The retardation value R (θ) was measured at 6 points every 10 °, with θ ranging from 0 ° to 50 °. The in-plane slow axis of the optical film was confirmed by AxoScan manufactured by Axometric.
4) From the measured Ro and R (θ) and the above-mentioned average refractive index and film thickness, nx, ny and nz were calculated by AxoScan manufactured by Axometric, and Rth at a measurement wavelength of 590 nm was calculated. . The retardation was measured under the conditions of 23 ° C. and 55% RH.

The production conditions and evaluation results of the optical films of Examples 1 to 16 and Comparative Examples 1 to 7 are shown in Table 4; the production conditions and evaluation results of the optical films of Examples 17 to 24 and Comparative Examples 8 to 9 are shown in Table 5. Show. In Tables 4 and 5, DSP indicates a wavelength dispersing agent.

As shown in Tables 4 and 5, the optical films of Examples 1 to 23 do not cause cracks in the surface layer even when stretched at a high magnification in an oblique direction; the optical films of Comparative Examples 2 to 5 It turns out that a crack arises.

The reason why no cracks occurred in the optical films of Examples 1 to 24 is considered that the tensile elastic modulus of the surface layer was lowered by relatively increasing the amount of plasticizer contained in the surface layer. On the other hand, the reason why cracks occurred in the optical film of Comparative Example 2 is considered that the stretch ratio in the oblique direction was too high. It is considered that the cracks occurred in the optical films of Comparative Examples 3 and 4 because the amount of the plasticizer in the surface layer was small. The optical film of Comparative Example 5 is considered to have cracks due to the high tensile elastic modulus of the film. It is considered that the optical films of Comparative Examples 6 and 7 were slightly inferior in compatibility between the cellulose ester and the plasticizer in the surface layer than the optical film of Comparative Example 5, and thus the planarity of the film was lowered.

Further, the retardation Ro in the in-plane direction at a wavelength of 550 nm of the optical film of Example 1 was 135 nm; the retardation Rth in the thickness direction was 70 nm. Similarly, Ro of the optical films of Examples 2 to 24 was 120 to 140 nm, and Rth was 65 to 100 nm.

Further, the difference between the tensile elastic modulus of the film constituting the surface layer and the tensile elastic modulus of the film constituting the base material layer (the difference in elastic modulus between the surface layer and the base material layer) is 0.2 GPa in Example 1; −0.4 GPa; in Comparative Example 3, it was 1.3 GPa.

(Example 25)
Production of Polarizer A long polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched under conditions of a stretching temperature of 110 ° C. and a stretching ratio of 5 times. The obtained film was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. consisting of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. . The obtained film was washed with water and dried to obtain a long polarizer having a thickness of 20 μm.

Production of Circular Polarizing Plate 201 The surface of the produced optical film 101 bonded to the polarizer was subjected to alkali saponification treatment. Then, the optical film 101 was bonded to one surface of the long polarizer through a 5% aqueous solution of a completely saponified polyvinyl alcohol as an adhesive. The bonding was performed by aligning the longitudinal direction of the polarizer and the longitudinal direction of the optical film so that the transmission axis of the polarizer and the slow axis of the optical film 101 form 45 °.

On the other hand, Konica Minolta Tack Film KC4UA (manufactured by Konica Minolta Opto Co., Ltd.) was prepared, and the bonding surface with the polarizer was subjected to alkali saponification treatment. Then, KC4UA (manufactured by Konica Minolta Opto Co., Ltd.) was bonded to the other surface of the polarizer through a completely saponified polyvinyl alcohol 5% aqueous solution in the same manner as described above. Thereby, a circularly polarizing plate 201 was obtained.

Production of Organic EL Display Device 301 A metal electrode made of chromium having a thickness of 80 nm was formed on a PET film by sputtering; a thin film of ITO having a thickness of 40 nm was formed on the metal electrode as an anode. Next, a hole transport layer made of poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT: PSS) having a thickness of 80 nm is formed on the anode by sputtering; In addition, RGB light emitting layers (red light emitting layer, green light emitting layer, and blue light emitting layer) were respectively formed by patterning using a shadow mask. The thickness of the light emitting layer was 100 nm for each color. The red light-emitting layer contains tris (8-hydroxyquinolinate) aluminum (Alq ₃ ) as a host and a light-emitting compound [4- (dicyanomethylene) -2-methyl-6 (p-dimethylaminostyryl) -4H-pyran] (DCM). The green light-emitting layer is formed by co-evaporating Alq ₃ and the luminescent compound coumarin 6 (mass ratio 99: 1) as a host; The layer was formed by co-evaporating BAlq and a luminescent compound Perylene as a host (mass ratio 90:10).

On the obtained RGB light emitting layer, a thin film having a thickness of 4 nm made of calcium is formed as a first cathode having a low work function so that electrons can be efficiently injected by a vacuum deposition method; On top, a thin film made of aluminum having a thickness of 2 nm was formed as a second cathode to obtain an organic light emitting layer. The aluminum used as the second cathode has a role of preventing the first cathode calcium from being chemically altered when a transparent electrode is formed thereon by sputtering.

Next, a transparent conductive film made of ITO and having a thickness of 80 nm (the first cathode, the second cathode, and the transparent conductive film were combined to form a transparent electrode layer) was formed on the second cathode by sputtering. Furthermore, a thin film having a thickness of 200 nm made of silicon nitride was formed on the transparent conductive film by a CVD method to obtain an insulating film (transparent substrate). Thereby, an organic EL element was obtained.

A circularly polarizing plate 201 was bonded to the obtained insulating film (transparent substrate) of the organic EL element with an adhesive to obtain an organic EL display device 301. The circularly polarizing plate 201 was bonded so that the optical film 101 was on the insulating film side of the organic EL element.

(Examples 26 to 48, Comparative Examples 10 to 18)
Circularly polarizing plates 202 to 233 and organic EL display devices 302 to 333 were obtained in the same manner as in Example 25 except that the optical film 101 was changed as shown in Table 6.

The wrinkles and display performance during bending of the obtained organic EL display device were evaluated by the following methods.

[Wrinkles in the diagonal direction when bent]
As shown in FIG. 1 described above, the obtained organic EL display device 301 is bent at 90 ° with the width direction (or lengthwise direction) of the optical film as the bending axis C, and the operation for closing and opening is 10 Repeated times. Thereafter, the vicinity of the bent portion of the display device was visually observed, and the presence or absence of wrinkles generated in an oblique direction with respect to the bending axis C was evaluated according to the following criteria.
◎: Oblique wrinkles are not observable ○: Oblique wrinkles are observed △: Strong wrinkles are observed in the diagonal direction ×: Strong wrinkles in the oblique direction are observed

[Display performance]
The obtained organic EL display device 301 was visually observed in a light-emitting state, and the presence or absence of external light reflection on the screen was evaluated according to the following criteria.
◎: External light reflection is not recognized at all ○: Slight redness due to external light reflection is observed, but is not of concern △: Redness due to external light reflection is anxious ×: Redness due to external light reflection Is a very worrisome state.

Table 6 shows the evaluation results of the organic EL display devices of Examples 25 to 48 and Comparative Examples 10 to 18.

As shown in Table 6, the organic EL display devices of Examples 25 to 48 have almost no wrinkles in the oblique direction when bent, and the display performance is good; the organic EL displays of Comparative Examples 11 to 18 It can be seen that the display device is wrinkled in an oblique direction at least when bent, and the display performance is low.

In Comparative Example 10, it is considered that the display performance of the organic EL display device is low because the stretch ratio of the optical film 102 is low and the desired retardation is not obtained. In Comparative Examples 11 to 13, it can be seen that wrinkles in an oblique direction at the time of bending occur because the difference in tensile elastic modulus of each layer of the optical film is large as described above.

It can be seen that the display devices of Comparative Examples 14 to 16 have low display performance. This is because the main component of the surface layer of the optical film used in Comparative Example 15 is CAP; the main component of the surface layer of the optical film used in Comparative Example 16 is DAC. This is probably because the surface was destroyed.

Further, from the comparison between Examples 25 and 48 and Comparative Examples 17 to 18, “the ratio of the amount of plasticizer in the surface layer / the amount of plasticizer in the base material layer is not less than a certain value”, It can be seen that wrinkles and display characteristics when the display device is bent can be improved.

This application claims priority based on Japanese Patent Application No. 2012-273508 filed on Dec. 14, 2012. The contents described in the application specification and the drawings are all incorporated herein.

According to the present invention, it is possible to provide an optical film that is difficult to tear during processing even if the thickness is small.

DESCRIPTION OF

SYMBOLS

1, 10, 73 Optical film C Bending axis 11, 73-1 Base material layer 13, 13 ', 73-3, 73-3' Surface layer 15 Tensile tester 20 Diagonal stretcher 21 Film feeding device 23 Conveyance direction change device 25 Winding device 30 Organic EL display device 50 Organic EL element 51 Substrate 53 Metal electrode 55 TFT
57 Organic light-emitting layer 59 Transparent electrode (ITO etc.)
61 Insulating layer 63 Sealing layer 65 Film 70 Circularly polarizing plate 71 Polarizer 75 Protective film S1, S2 Sample film

Claims

Substrate layer containing cellulose acetate propionate or cellulose acetate having a substitution degree of acetyl group of 2.0 or more and 2.6 or less and a plasticizer, and disposed on both sides of the substrate layer, the substitution degree of acetyl group Is an optical film for an organic EL display device, comprising a surface layer containing cellulose acetate of more than 2.6 and 3.0 or less and a plasticizer,
The slow axis direction in the plane of the optical film is an oblique direction with respect to the width direction of the film,
The ratio X / Y of the tensile elastic modulus X in the slow axis direction to the tensile elastic modulus Y in the direction orthogonal to the slow axis direction is 1.5 or more and 5.0 or less,
The optical film whose mass ratio with respect to the quantity of the plasticizer contained in the said base material layer of the quantity of the plasticizer contained in the said surface layer is 1.2 times or more and 5.5 times or less.
The optical film according to claim 1, wherein an in-plane slow axis direction of the optical film is in a range of 40 to 50 ° with respect to a width direction of the film.
The optical film according to claim 1, wherein the base material layer further contains a wavelength dispersion adjusting agent.
The amount of the plasticizer contained in the surface layer is 15 to 50% by mass with respect to cellulose acetate having a substitution degree of the acetyl group contained in the surface layer of more than 2.6 and not more than 3.0. Optical film.
The cellulose acetate propionate contained in the base material layer or the cellulose acetate having a substitution degree of acetyl group of 2.0 to 2.6 has a weight average molecular weight Mw of 150,000 to 300,000 and a number average molecular weight. The optical film according to claim 1, wherein Mn is 50,000 to 200,000.
The optical film according to claim 1, wherein the plasticizer contained in the surface layer is a polyester compound obtained by a polycondensation reaction of a diol and a dicarboxylic acid.
The optical film according to claim 6, wherein the polyester compound has a weight average molecular weight of 700 to 2,000.
The optical film according to claim 6, wherein the molecular terminal of the polyester compound is a hydroxyl group or is sealed with an acetyl group.
The optical film according to claim 6, wherein the dicarboxylic acid constituting the polyester compound contains an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid.
The optical film has a retardation Ro in the in-plane direction at a wavelength of 550 nm defined by the formula (I) within a range of 120 to 180 nm, and is defined by the formula (II) and has a retardation Rth in the thickness direction at a wavelength of 550 nm. The optical film according to claim 1, wherein is from 40 to 120 nm.
Formula (I) Ro = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
(Nx: refractive index in the slow axis direction x in the film plane, ny: refractive index in the direction y perpendicular to the slow axis direction x in the film plane, nz: refractive index in the thickness direction z of the film, d: Film thickness (nm))
A circularly polarizing plate comprising the optical film according to claim 1.
An organic EL display device comprising the optical film according to claim 1.
It is a manufacturing method of the optical film according to claim 1,
A cellulose acetate propionate or a first layer containing cellulose acetate having a substitution degree of acetyl group of 2.0 or more and 2.6 or less and a plasticizer, and disposed on both sides of the first layer, Obtaining a laminated film comprising a cellulose acetate having a substitution degree of more than 2.6 and not more than 3.0 and a second layer containing a plasticizer;
Stretching the laminated film at least 1.5 times to 3.0 times in the oblique direction with respect to the width direction of the laminated film to obtain an optical film.
The step of obtaining the laminated film includes
Cellulose acetate propionate or cellulose acetate having a substitution degree of acetyl group of 2.0 or more and 2.6 or less, a first layer dope containing a plasticizer and an organic solvent, and a substitution degree of acetyl group of more than 2.6 Obtaining a second layer dope containing 3.0 or less cellulose acetate, a plasticizer and an organic solvent;
Casting the first layer dope and the second layer dope while being laminated simultaneously or sequentially on a casting support;
The manufacturing method of the optical film of Claim 13 including the process of removing the organic solvent contained in said dope for said 1st layer laminated | stacked and said 2nd dope for 2nd layers, and obtaining a laminated | multilayer film.
The method for producing an optical film according to claim 13, wherein the stretching of the laminated film is performed in a direction of 40 to 50 ° with respect to the width direction of the film.