JP2012215688A - Optical film, method for manufacturing the same, polarizing plate, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film that has a small photoelastic coefficient and a low haze, and is excellent in adhesion to a polarizer and interface adhesion between each layer when bonded by a conventional alkaline saponification method.SOLUTION: An optical film includes an "A" layer containing an acrylic resin having a weight average molecular weight exceeding a million, and a "B" layer containing a first cellulose acylate and a second cellulose acylate each having a different acyl substitution degree. A content ratio of the first cellulose acylate to the second cellulose acylate is 90/10 to 60/40 (mass ratio). The acyl substitution degree of the second cellulose acylate satisfies an expression (1) and at least one of expressions (2A) and (2B), with the expression (1): 2.55≤X+Y≤3.0; the expression (2A): 0.2≤Y≤1.2; and the expression (2B): -0.075n+0.72≤DS(n)≤-0.33n+2.88, where "X" is an acetyl substitution of the second cellulose acylate; "Y" is a substitution degree of an acyl group with carbon number 3 to 7 in the second cellulose acylate; DS(n) is a substitution degree of an acyl group with carbon number "n" in the second cellulose acylate; and "n" is an integer between 3 to 7).

Description

  The present invention relates to an optical film, a manufacturing method thereof, a polarizing plate, and a liquid crystal display device.

Liquid crystal display devices are widely used as image display devices for TVs, personal computers, and the like because they can be thinned with low power consumption. A liquid crystal display device has polarizing plates installed on both sides of a liquid crystal cell. The polarizing plate has a structure in which both sides of a polarizing film adsorbed and oriented with iodine or dye are sandwiched between transparent resin layers. Such a transparent resin layer has a purpose of protecting the polarizer, and a cellulose ester film is often used as a so-called polarizing plate protective film.
In recent years, with the spread of liquid crystal display devices, further thinner layers and higher performance have been demanded.
The cellulose ester film has a high transmittance, and by immersing it in an alkaline aqueous solution to saponify its surface and make it hydrophilic, excellent adhesion to a polarizer is realized. However, when incorporated in a liquid crystal display device, the problem that display unevenness is likely to occur particularly when other members in the liquid crystal display device deformed due to deterioration over time or the like are in contact with the cellulose ester film has been significantly reduced in recent years. It comes from the request.

  In order to solve this problem, an acrylic resin film having a small photoelastic coefficient has been proposed as a polarizing plate protective film in place of cellulose ester. However, it cannot be said that the adhesiveness with the polarizer is sufficiently high. The layer film was unsatisfactory because it was difficult to bond with the polarizer.

Therefore, the problem of each film is solved by laminating these films, and the excellent adhesion to the polarizer can be obtained by the conventional alkali saponification technique. A technology has been proposed that provides a polarizing plate protective film that is less likely to cause display unevenness even if it touches the polarizing plate protective film (see Patent Document 1).
Patent Document 1 discloses a technique for producing a laminated film of cellulose triacetate and an acrylic resin by a co-casting method. For example, an example of the same document describes a cellulose triacetate film / acrylic resin film / cellulose triacetate film configuration. Further, this document describes that a cellulose triacetate film as a surface layer can be saponified by a general method and bonded to a polarizer to produce a polarizing plate. However, there was no description that could specifically identify the acrylic resin used in the examples of the document as a substance.

As another configuration, an optical film in which bending resistance and surface hardness are improved by making each layer a mixed layer containing an acrylic resin and a cellulose ester resin in a laminated film of an acrylic resin and a cellulose ester resin is disclosed. (Patent Documents 2 and 3). In these documents, the acrylic resin and the cellulose ester resin are contained in the surface layer of the laminated film so that the ratio of the acrylic resin is 30 to 50% by mass (Patent Document 2) or 85 to 95% by mass (Patent Document 3). It is described that in layers other than the surface layer, the acrylic resin and the cellulose ester resin are contained so that the ratio of the acrylic resin is 55 to 80% by mass, so that the transparency is high and the bending resistance and the surface hardness can be increased. ing. Patent Documents 2 and 3 describe that the acrylic resin used has a weight average molecular weight of 1,000,000 or less from the viewpoint of production.
Here, as a cellulose ester resin that can be used in the inventions described in Patent Documents 2 and 3, the acyl substitution degree is 2.0 to 3.0, and the acyl substitution degree having 3 to 7 carbon atoms is 1.2 to 3. 0 and a weight average molecular weight of 75000 or more are described, and it is described that two or more kinds of cellulose ester resins can be mixed and used. However, in the examples of Patent Documents 2 and 3, only one type of cellulose ester resin having an acetyl substitution degree of 0.19 and a propionyl substitution degree of 2.56 was used to form a surface layer and other layers mixed with an acrylic resin. Only specific examples have been studied. Moreover, in the Example of patent document 2 and 3, when manufacturing the polarizing plate by bonding the obtained laminated | multilayer film with a polarizer, with respect to the surface layer which is a mixed layer of an acrylic resin and a cellulose-ester resin, it is a corona treatment. Then, it was bonded with a polarizer using an acrylic adhesive.

  On the other hand, for the purpose of improving the yield when manufacturing a polarizing plate or a liquid crystal display device, a polarizing plate protective film and a polarizer are bonded together to manufacture a polarizing plate, and then the polarizing plate is once attached to a glass substrate of a liquid crystal cell. The ability to peel and re-attach the polarizing plate after bonding, so-called reworkability, is also required for the polarizing plate protective film.

JP 2001-215331 A International Publication WO2010 / 116857 International Publication No. WO2010 / 116858

  When the present inventors manufactured a cellulose triacetate film / acrylic resin film / cellulose triacetate film by co-casting by the method described in Patent Document 1, the obtained film had a problem in co-casting interface adhesion, It has been newly found that there is a problem that delamination occurs due to delamination during rework.

On the other hand, when the present inventors made each layer a mixed layer containing an acrylic resin and a cellulose ester resin in the laminated film of an acrylic resin and a cellulose ester resin by the method described in Patent Documents 2 and 3, conventional alkali saponification was performed. It was found that when the polarizer and the (meth) acrylic resin film were bonded together by the method described above, the adhesion with the polarizer was inferior to the cellulose ester film. Therefore, the conventional alkali saponification such as easy adhesion treatment (for example, corona treatment) to improve the adhesion to the polarizer is performed on the film surface, or an adhesive layer is provided using an ultraviolet ray curable adhesive. It has been found that the number of processes increases compared to the method, which causes a decrease in yield, and that a cost problem arises as a method for producing a polarizing plate protective film.
Moreover, although the present inventors examined so that the content ratio of the acrylic resin and cellulose-ester resin of the outer layer of each laminated | multilayer film and each layer may be changed in the method of patent document 2 and 3, only the content ratio of these 2 components was used. It has been found that the change in the content ratio raises the haze of the resulting film, not only by changing the content ratio, but also by improving the adhesion with the polarizer by the conventional alkali saponification technique.

  The problem to be solved by the present invention is to provide an optical film having a small photoelastic coefficient, low haze, and excellent adhesion to a polarizer and interfacial adhesion between layers by a conventional alkali saponification technique. is there.

  When the present inventors diligently studied in order to solve the above-mentioned problems, the weight average molecular weight of the acrylic resin was co-cast to form a layer mainly composed of an acrylic resin and an outer layer mainly composed of cellulose acylate. By adding an appropriate proportion of the second cellulose acylate having a specific substitution degree to the outer layer containing cellulose acylate as a main component in an appropriate ratio, it has excellent transparency and is a conventional alkali saponification method. It has been found that an optical film having excellent adhesion to a polarizer and interfacial adhesion between layers can be obtained. That is, the above-described problems can be solved and the present invention has been completed.

  The above-described problems can be solved by the present invention having the following configuration.

[1] A layer containing an acrylic resin having a weight average molecular weight exceeding 1,000,000,
Having a B layer comprising a first cellulose acylate and a second cellulose acylate, which are laminated on at least one surface of the A layer and have different degrees of acyl substitution.
The content ratio of the first cellulose acylate to the second cellulose acylate is 90/10 to 60/40 (mass ratio), and the acyl substitution degree of the second cellulose acylate is represented by the following formula (1). And at least one of the following formulas (2A) and (2B).
Formula (1) 2.55 ≦ X + Y ≦ 3.0
Formula (2A) 0.2 ≦ Y ≦ 1.2
(In formulas (1) and (2A), X represents the acetyl substituent of the second cellulose acylate, and Y represents the degree of substitution of the acyl group having 3 to 7 carbon atoms of the second cellulose acylate.)
Formula (2B) −0.075n + 0.72 ≦ DS (n) ≦ −0.33n + 2.88
(In Formula (2B), DS (n) represents the degree of substitution of the acyl group having n carbon atoms in the second cellulose acylate, and n represents an integer of 3 to 7.)
[2] The optical film as described in [1], wherein the second cellulose acylate of the B layer satisfies the formula (2B).
[3] The optical film as described in [1] or [2], wherein the second cellulose acylate of the B layer satisfies the formula (2A).
[4] The acrylic resin used as a main component in the A layer has a weight average molecular weight of more than 1 million and 1.8 million or less, according to any one of [1] to [3]. Optical film.
[5] The optical film according to any one of [1] to [4], wherein the polymer having a weight average molecular weight of 100,000 or more contained in the B layer is only cellulose acylate.
[6] The optical film according to any one of [1] to [5], wherein the acrylic resin used as a main component in the A layer is made of polymethyl methacrylate.
[7] The layer A includes cellulose acylate satisfying at least one of the formula (1) and the formulas (2) and (3), and the content ratio of the acrylic resin to the cellulose acylate is 95/5 to 80. It is / 20 (mass ratio), The optical film as described in any one of [1]-[6] characterized by the above-mentioned.
[8] Any of [1] to [7], wherein the acyl group of the first cellulose acylate of the B layer is an acetyl group, and the degree of acetyl substitution is 2.7 to 3.0. An optical film according to claim 1.
[9] The optical film according to any one of [1] to [8], wherein the film thickness of the B layer is 1 μm to 10 μm, and the film thickness of the entire film is 20 μm to 80 μm. .
[10] The optical film according to any one of [1] to [9], wherein the haze value is 0.3% or less.
[11] The value of the photoelastic coefficient is −5.0 × 10 ⁻¹² Pa ^{−1 to} 5.0 × 10 ⁻¹² Pa ⁻¹ , any one of [1] to [10] The optical film described in 1.
[12] The retardation Re in the in-plane direction defined by the following formula (I) and the retardation Rth in the film thickness direction defined by the following formula (II) are expressed by the following formula (25 ° C. relative humidity 60% environment) The optical film according to any one of [1] to [11], wherein III) and the following formula (IV) are satisfied.
Formula (I) Re = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
Formula (III) | Re | <10 nm
Formula (IV) | Rth | <25 nm
(In the formulas (I) to (IV), nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is in the thickness direction of the film. (Refractive index, d is the film thickness (μm).)
[13] At least two types of dopes (A) and (B) containing a thermoplastic resin and a solvent are simultaneously or sequentially applied on the casting base material in the order of (B)-(A) from the casting base material side. The dope (A) contains an acrylic resin having a weight average molecular weight exceeding 1 million, and the dope (B) has a first cellulose acylate and a second cellulose having different degrees of acyl substitution. The second cellulose comprises an acylate, wherein a content ratio of the acylate of the first cellulose to the second cellulose acylate in the dope (B) is 90/10 to 60/40 (mass ratio). A method for producing an optical film, wherein the acyl substitution degree of acylate satisfies at least one of the following formula (1) and the following formulas (2A) and (2B).
Formula (1) 2.55 ≦ X + Y ≦ 3.0
Formula (2A) 0.2 ≦ Y ≦ 1.2
(In formulas (1) and (2A), X represents the acetyl substituent of the second cellulose acylate, and Y represents the degree of substitution of the acyl group having 3 to 7 carbon atoms of the second cellulose acylate.)
Formula (2B) −0.075n + 0.72 ≦ DS (n) ≦ −0.33n + 2.88
(In Formula (2B), DS (n) represents the degree of substitution of the acyl group having n carbon atoms in the second cellulose acylate, and n represents an integer of 3 to 7.)
[14] The optical film as described in [13], wherein the second cellulose acylate of the dope (B) satisfies the formula (2B).
[15] The optical film as described in [13] or [14], wherein the second cellulose acylate of the dope (B) satisfies the formula (2A).
[16] As the solvent, methylene chloride and a lower alcohol having 1 to 4 carbon atoms are used, and the content ratio of methylene chloride to the lower alcohol having 1 to 4 carbon atoms is in a range of 90/10 to 60/40 (volume ratio). The method for producing an optical film according to any one of [13] to [15], wherein:
[17] The polymer according to any one of [13] to [16], wherein the polymer contained in the dope (B) has a weight average molecular weight of 100,000 or more and is only cellulose acylate. Optical film.
[18] An optical film produced by the method for producing an optical film according to any one of [13] to [17].
[19] A polarizing plate comprising a polarizer and the optical film according to any one of [1] to [12] and [18].
[20] A liquid crystal display device comprising the optical film according to any one of [1] to [12] and [18] or the polarizing plate according to [19].

  According to the present invention, it is possible to provide an optical film having a small photoelastic coefficient, low haze, excellent adhesion to a polarizer and interfacial adhesion between layers by a conventional alkali saponification technique, and a method for producing the same. it can.

It is a schematic diagram which shows an example of a drum casting apparatus.

  Hereinafter, although the form for implementing this invention is demonstrated in detail, this invention is not limited to these. In the present specification, when a numerical value represents a physical property value, a characteristic value, etc., the description “(numerical value 1) to (numerical value 2)” means “(numerical value 1) or more and (numerical value 2) or less”. . (Meth) acryl represents methacryl or acryl, and (meth) acryloyl represents methacryloyl or acryloyl. Further, in the present specification, “main component” means 50% by mass or more. For example, the main component of cellulose acylate contained in the cellulose acylate layer means cellulose acylate occupying 50% by mass or more of the cellulose acylate contained in the cellulose acylate layer.

[Optical film]
The optical film of the present invention (hereinafter also referred to as the film of the present invention) is a layer A containing an acrylic resin having a weight average molecular weight exceeding 1,000,000,
Having a B layer comprising a first cellulose acylate and a second cellulose acylate, which are laminated on at least one surface of the A layer and have different degrees of acyl substitution.
The content ratio of the first cellulose acylate to the second cellulose acylate is 90/10 to 60/40 (mass ratio), and the acyl substitution degree of the second cellulose acylate is represented by the following formula (1). And at least one of the following formulas (2A) and (2B) is satisfied.
Formula (1) 2.55 ≦ X + Y ≦ 3.0
Formula (2A) 0.2 ≦ Y ≦ 1.2
(In formulas (1) and (2A), X represents the acetyl substituent of the second cellulose acylate, and Y represents the degree of substitution of the acyl group having 3 to 7 carbon atoms of the second cellulose acylate.)
Formula (2B) −0.075n + 0.72 ≦ DS (n) ≦ −0.33n + 2.88
(In Formula (2B), DS (n) represents the degree of substitution of the acyl group having n carbon atoms in the second cellulose acylate, and n represents an integer of 3 to 7.)
In the following, the A layer of the film of the present invention is also referred to as an acrylic resin layer, and the B layer is also referred to as a cellulose acylate layer.

  In the film of the present invention, the second cellulose acylate of the B layer satisfies the formula (1) and the formula (2A), and the formula (1) and the formula (2B). There is a second mode that satisfies the above and a third mode that satisfies the above formula (1), the above formula (2A), and the above formula (2B), both of which are preferable. The second embodiment and the third embodiment are more preferable, and the third embodiment is particularly preferable.

In the film of the present invention, an acrylic resin having such a weight average molecular weight much larger than the acrylic resin conventionally used in the field of optical films is used, and the outer layer mainly composed of cellulose acylate has the above formula ( 1) and a second cellulose acylate having a substitution degree satisfying at least one of the following formulas (2A) and (2B) at an appropriate ratio, a low photoelastic coefficient, a low haze, and a conventional alkali An optical film excellent in adhesiveness to a polarizer and interfacial adhesion between layers by a saponification method can be obtained.
Although not bound by any theory, the substitution degree of the second cellulose acylate of the outer layer B is controlled to a range satisfying at least one of the above formula (1) and the following formulas (2A) and (2B). Thus, the acyl group having 3 to 7 carbon atoms of the second cellulose acylate is appropriately formed on both surfaces of the outer layer B (the interface on the A layer side and the polarizer side interface of the polarizing plate). It is presumed that the hydrophobic properties on both surfaces of the outer layer B layer could be moderately suppressed by reducing the degree of substitution. As a result, it is possible to improve the interlayer adhesion between the B layer and the A layer, and to improve the alkali saponification suitability of the B layer and improve the adhesion to the polarizer by the conventional alkali saponification technique. It is estimated that it was made.
Furthermore, although not limited to any theory, an acrylic resin having a weight average molecular weight much higher than that of an acrylic resin conventionally used in the field of optical films is used in addition to the above-described configuration, and cellulose acylate is used. By adding a second cellulose acylate having a substitution degree satisfying the above formula (1) to the outer layer as a main component at an appropriate ratio, the compatibility of the interface between the A layer and the B layer can be increased, and It is estimated that the haze of the whole film was reduced and the optical film with high transparency was obtained.

In the film of the present invention, the B layer can be provided only on one surface of the A layer, that is, the B layer is at least one outer layer (also referred to as a surface layer) of the A layer. Furthermore, in order to make the physical properties of the film and the behavior with respect to environmental changes uniform, it is preferable that the B layer is provided on both sides of the A layer to be B layer / A layer / B layer. That is, it is more preferable that the B layer is an outer layer of both of the A layers, and the A layer is a core layer.
Hereinafter, preferred embodiments of the film of the present invention will be described.

<Film structure and properties>
(Ratio of cellulose acylate (B) layer and acrylic resin (A) layer)
In the film of the present invention, the acrylic resin (A) layer preferably has a film thickness of 20 to 60 μm, and the cellulose acylate (B) layer has a film thickness of any B The layer is also preferably 1-10 μm.
The film thickness of the cellulose acylate (B) layer is preferably 1 to 10 μm, more preferably 1 to 8 μm, and particularly preferably 1 to 5 μm per layer. The thickness of the acrylic resin (A) layer is preferably 20 to 60 μm, more preferably 25 to 50 μm, and particularly preferably 25 to 40 μm.
Further, the film thickness of the entire optical film as the laminate is preferably 11 to 240 μm, more preferably 15 to 150 μm, particularly preferably 20 to 80 μm, and particularly preferably 20 to 50 μm.
In the film of the present invention, the film thickness of the B layer is preferably 1 μm to 10 μm, and the film thickness of the entire film is preferably 20 μm to 80 μm.

Furthermore, the ratio of the total film thickness of the cellulose acylate layer in the total film thickness is preferably 40% or less, more preferably 1 to 30%, and particularly preferably 5 to 20%. preferable. However, the total film thickness of the cellulose acylate layer here means the total film thickness of two layers when there are two cellulose acylate layers.
By satisfying these relationships, the surface condition during casting tends to be better. Furthermore, the interfacial adhesion, curling properties, reduction in water absorption, and the like of the obtained optical film can be preferably adjusted.

(Retardation)
In this specification, Re (λ) and Rth (λ) respectively represent in-plane retardation and retardation in the thickness direction at a wavelength λ. In the present specification, the wavelength λ is 550 nm unless otherwise specified. Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments). In selecting the measurement wavelength λnm, the wavelength selection filter can be exchanged manually, or the measurement value can be converted by a program or the like.
When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis) (in the absence of the slow axis, any in-plane value) The light is incident at a wavelength of λ nm from the inclined direction in steps of 10 degrees from the normal direction to 50 degrees on one side with respect to the film normal direction of the rotation axis of KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed value of the average refractive index, and the input film thickness value.
In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.
In addition, the retardation value is measured from the two inclined directions, with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), Based on the value, the assumed value of the average refractive index, and the input film thickness value, Rth can also be calculated from the following equations (11) and (12).

上記のＲｅ(θ)は法線方向から角度θ傾斜した方向におけるレターデーション値を表す。
式（１１）におけるｎｘは面内における遅相軸方向の屈折率を表し、ｎｙは面内においてｎｘに直交する方向の屈折率を表し、ｎｚはｎｘ及びｎｙに直交する方向の屈折率を表す。ｄは膜厚である。
式（１２）
Ｒｔｈ＝｛（ｎｘ＋ｎｙ）／２−ｎｚ｝ｘｄ
測定されるフィルムが１軸や２軸の屈折率楕円体で表現できないもの、いわゆる光学軸（ｏｐｔｉｃ ａｘｉｓ）がないフィルムの場合には、以下の方法によりＲｔｈ（λ）は算出される。
Ｒｔｈ（λ）は前記Ｒｅ（λ）を、面内の遅相軸（ＫＯＢＲＡ ２１ＡＤＨまたはＷＲにより判断される）を傾斜軸（回転軸）としてフィルム法線方向に対して−５０度から＋５０度まで１０度ステップで各々その傾斜した方向から波長λｎｍの光を入射させて１１点測定し、その測定されたレターデーション値と平均屈折率の仮定値及び入力された膜厚値を基にＫＯＢＲＡ ２１ＡＤＨまたはＷＲが算出する。
上記の測定において、平均屈折率の仮定値は ポリマーハンドブック（JOHN WILEY＆SONS，INC）、各種光学フィルムのカタログの値を使用することができる。平均屈折率の値が既知でないものについてはアッベ屈折計で測定することができる。主な光学フィルムの平均屈折率の値を以下に例示する：セルロースアシレート（１．４８）、シクロオレフィンポリマー（１．５２）、ポリカーボネート（１．５９）、ポリメチルメタクリレート（１．４９）、ポリスチレン（１．５９）である。これら平均屈折率の仮定値と膜厚を入力することで、ＫＯＢＲＡ ２１ＡＤＨまたはＷＲはｎｘ、ｎｙ、ｎｚを算出する。この算出されたｎｘ、ｎｙ、ｎｚよりＮｚ＝（ｎｘ−ｎｚ）／（ｎｘ−ｎｙ）が更に算出される。

The above Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction.
In formula (11), nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction orthogonal to nx in the plane, and nz represents the refractive index in the direction orthogonal to nx and ny. . d is the film thickness.
Formula (12)
Rth = {(nx + ny) / 2−nz} xd
In the case where the film to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film having no so-called optical axis, Rth (λ) is calculated by the following method.
Rth (λ) is the above-mentioned Re (λ), and the in-plane slow axis (determined by KOBRA 21ADH or WR) is the tilt axis (rotation axis) from −50 degrees to +50 degrees with respect to the film normal direction. The light of wavelength λ nm is incident from each inclined direction in 10 degree steps and measured at 11 points. Based on the measured retardation value, the assumed average refractive index, and the input film thickness value, KOBRA 21ADH or WR is calculated.
In the above measurement, the assumed value of the average refractive index may be the value in the polymer handbook (JOHN WILEY & SONS, INC) and various optical film catalogs. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). By inputting these assumed values of average refractive index and film thickness, KOBRA 21ADH or WR calculates nx, ny, and nz. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

The film of the present invention has an in-plane retardation Re defined by the following formula (I) and a retardation Rth in the film thickness direction defined by the following formula (II) at 25 ° C. and a relative humidity of 60%. The difference between the Rth that satisfies the following formula (III) and the following formula (IV) and that is measured in an environment of 25 ° C. and a relative humidity of 10% and the Rth that is measured in an environment of a relative humidity of 25 ° C. and 80%. The absolute value is preferably 10 nm or less.
Formula (I) Re = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
Formula (III) | Re | <10 nm
Formula (IV) | Rth | <25 nm
(Where nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, nz is the refractive index in the thickness direction of the film, and d is (The thickness of the film (μm).)

The film of the present invention preferably satisfies | Re | <10 nm, more preferably | Re | ≦ 5 nm, and particularly preferably | Re | ≦ 2 nm.
The film of the present invention preferably satisfies | Rth | <25 nm, more preferably | Rth | ≦ 15 nm, and particularly preferably | Rth | ≦ 10 nm.

(Haze)
The film of the present invention preferably has a haze of 0.7% or less, more preferably 0.5% or less, and particularly preferably 0.3% or less. By setting the haze to 0.7% or less, the transparency of the film becomes higher and it becomes easier to use as an optical film.

(Photoelastic coefficient)
In the film of the present invention, the absolute value of the photoelastic coefficient is preferably 5 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 3 × 10 ⁻¹² Pa ⁻¹ or less, and more preferably 1 × 10 ⁻¹² Pa. Particularly preferably, it is ⁻¹ or less. The photoelastic coefficient is an intrinsic property of a substance, and a substance that hardly expresses the photoelastic coefficient is rather rare. For example, many polymer resins exhibit birefringence due to external stress or thermal stress. The photoelastic coefficient can define a sign in relation to the direction of applied stress. That is, when tensile stress is applied to the medium (polymer resin), the refractive index n _para for the polarized light having the polarization plane in the direction parallel to the tensile stress and the refractive index for the polarized light having the polarization plane in the direction orthogonal to the polarization stress. Thus, the sign of the photoelastic coefficient is expressed by the sign of the photoelastic coefficient c expressed by the following equation (21).
c = Δn / σ = (n _para −n _perp ) / σ (21)
That is, the photoelastic coefficient is positive when n _para is larger than n _perp and negative when it is smaller. If the photoelastic coefficient of the film of the present invention is in the range of −5 × 10 ^{−12 to} 5 × 10 ⁻¹² Pa ⁻¹ , display unevenness when the film of the present invention is incorporated in a liquid crystal display device can be suppressed, which is preferable. . In particular, the above range is preferable when the film of the present invention is incorporated into a liquid crystal display device after stretching.

(Film width)
The film of the present invention preferably has a film width of 400 to 2500 mm, more preferably 1000 mm or more, particularly preferably 1500 mm or more, and particularly preferably 1800 mm or more.

<Acrylic resin (A) layer>
The film of this invention has the said acrylic resin layer (A) layer containing an acrylic resin, The weight average molecular weight of the said acrylic resin used as a main component in the said acrylic resin layer exceeds 1 million.

(acrylic resin)
Acrylic resins used in the present invention include methacrylic resins, and acrylate / methacrylate derivatives, particularly acrylate ester / methacrylate ester (co) polymers are well known. Although it does not restrict | limit especially as said acrylic resin used as a main component in the said A layer, 50-100 mass% of methyl methacrylate units, and 0-50 mass% of other monomer units copolymerizable with this It is preferable to obtain a film having a small photoelastic coefficient, and more preferable is polymethyl methacrylate composed of 100% by mass of methyl methacrylate units.

  In the acrylic resin, the other copolymerizable monomer includes alkyl methacrylate having 2 to 18 carbon atoms in the alkyl group, alkyl acrylate having 1 to 18 carbon atoms in the alkyl number, acrylic acid, methacrylic acid, and the like. α, β-unsaturated acids, maleic acids, fumaric acids, dicarboxylic acids containing unsaturated groups such as itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α, β such as acrylonitrile and methacrylonitrile -Unsaturated nitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride and the like can be mentioned, and these can be used alone or in combination of two or more monomers as a copolymerization component. .

  Among these, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, s-butyl (from the viewpoint of thermal decomposition resistance and fluidity of the acrylic resin (Meth) acrylate, 2-ethylhexyl (meth) acrylate and the like are preferable, methyl (meth) acrylate and n-butyl (meth) acrylate are more preferable, and methyl (meth) acrylate is particularly preferably used.

  In addition, when forming a highly transparent optical film with little performance change even in a high temperature and high humidity environment, the acrylic resin contains an alicyclic alkyl group as a copolymerization component, or by intramolecular cyclization. An acrylic resin in which a cyclic structure is formed in the molecular main chain can also be used. As an example of the acrylic resin in which a cyclic structure is formed in the molecular main chain, an acrylic thermoplastic resin containing a lactone ring-containing polymer can be cited as one preferred embodiment. No. 171464. Another preferred embodiment is a resin containing glutaric anhydride as a copolymerization component, and the copolymerization component and a specific synthesis method are described in JP-A-2004-070296.

(Weight average molecular weight of acrylic resin)
Here, an acrylic resin having a molecular weight of about 100,000 is generally used for film formation. Specifically, it is impossible in the first place to form a high molecular weight acrylic resin film by melt film formation. An acrylic resin film can also be formed by solution casting, but in that case, it is necessary to prepare a dope having a viscosity that facilitates solution casting. Conventionally, if the acrylic resin has a molecular weight of about 300,000, it is easy to prepare a dope having high casting suitability, and such an acrylic resin has been conventionally used for film formation.
On the other hand, in the film of this invention, the weight average molecular weight of the said acrylic resin used as a main component for the said A layer exceeds 1 million. The weight average molecular weight of the acrylic resin used as the main component in the layer A is preferably more than 1 million and 3 million or less, more preferably more than 1 million and 1.8 million or less, more than 1.1 million and 1.8 million. It is particularly preferred that
The weight average molecular weight of the acrylic resin can be measured by gel permeation chromatography.

There is no restriction | limiting in particular as a manufacturing method of an acrylic resin, Well-known methods, such as suspension polymerization, emulsion polymerization, block polymerization, or solution polymerization, can be used.
Two or more acrylic resins can be used in combination.

(Other thermoplastic resins that can be used in combination with acrylic resins)
The acrylic resin can further contain another thermoplastic resin. Other thermoplastic resins that can be used in combination with the acrylic resin in the present invention are those having a glass transition temperature of 100 ° C. or higher and a total light transmittance of 85% or higher mixed with the acrylic resin to form a film. At this time, it is preferable in terms of improving heat resistance and mechanical strength.

  The content ratio of the acrylic resin and other thermoplastic resin components in the A layer (acrylic resin) layer is a mass ratio of [acrylic resin / (total thermoplastic resin)] × 100, preferably 30 to 99% by mass, More preferably, it is 50-97 mass%, Most preferably, it is 60-95 mass%, More preferably, it is 80-95 mass%. A content ratio of the acrylic resin in the acrylic resin layer of 30% by mass or more is preferable because heat resistance can be sufficiently exhibited.

  Examples of the other thermoplastic resins include cellulose acylate; olefin polymers such as polyethylene, polypropylene, ethylene-propylene copolymer, and poly (4-methyl-1-pentene); vinyl chloride, chlorinated vinyl resin, and the like. Halogen-containing polymers of: styrene polymers such as polystyrene, styrene-methyl methacrylate copolymer, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymer; polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc. Polyester such as nylon 6, nylon 66, nylon 610 and the like; polyacetal; polycarbonate; polyphenylene oxide; polyphenylene sulfide; Polysulfone; polyether sulfone; polyoxyethylene benzylidene alkylene; polyamideimide; polybutadiene rubber, rubber-like polymer such as acrylic rubber ABS resin or ASA resin blended with; and the like. The rubbery polymer preferably has a graft portion having a composition compatible with the ring polymer in the present invention on the surface, and the average particle size of the rubbery polymer is improved in transparency when formed into a film. In view of the above, it is preferably 100 nm or less, and more preferably 70 nm or less.

  As the other thermoplastic resin, a resin that is thermodynamically compatible with an acrylic resin is preferably used. Examples of such other thermoplastic resins include cellulose acylate, an acrylonitrile-styrene copolymer having a vinyl cyanide monomer unit and an aromatic vinyl monomer unit, and a polyvinyl chloride resin. Preferably mentioned. Among them, cellulose acylate and acrylonitrile-styrene copolymer are optical films having a glass transition temperature of 120 ° C. or more, a phase difference per 100 μm in the plane direction of 20 nm or less, and a total light transmittance of 85% or more. It is preferable because it can be easily obtained.

There is no restriction | limiting in particular as said cellulose acylate. Among them, the cellulose acylate satisfying at least one of the above formula (1) and the above formulas (2A) and (2B), which is included as the second cellulose acylate in the B layer described later, adheres to the B layer at the interface. From the viewpoint of enhancing the properties, it is preferable.
The film of the present invention contains cellulose acylate in which the A layer satisfies at least one of the formula (1) and the formulas (2A) and (2B), and the content ratio of the acrylic resin to the cellulose acylate is 95. / 5 to 80/20 (mass ratio) is more preferable, and 93/7 to 80/20 (mass ratio) is particularly preferable.
In addition, the detail of the preferable aspect of the cellulose acylate which satisfy | fills at least one of said Formula (1) and said Formula (2A) and (2B) is mentioned later.

  Specifically, as the acrylonitrile-styrene copolymer, those having a copolymerization ratio in a molar unit of 1:10 to 10: 1 are usefully used.

<Cellulose acylate (B) layer>
The film of the present invention has a B layer containing a first cellulose acylate and a second cellulose acylate having different acyl substitution levels, laminated on at least one side of the surface of the A layer. Furthermore, the film of the present invention has a content ratio of the first cellulose acylate to the second cellulose acylate of 90/10 to 60/40 (mass ratio), and acyl substitution of the second cellulose acylate. The degree satisfies at least one of the following formula (1) and the following formulas (2A) and (2B).
Formula (1) 2.55 ≦ X + Y ≦ 3.0
Formula (2A) 0.2 ≦ Y ≦ 1.2
(In formulas (1) and (2A), X represents the acetyl substituent of the second cellulose acylate, and Y represents the degree of substitution of the acyl group having 3 to 7 carbon atoms of the second cellulose acylate.)
Formula (2B) −0.075n + 0.72 ≦ DS (n) ≦ −0.33n + 2.88
(In Formula (2B), DS (n) represents the degree of substitution of the acyl group having n carbon atoms in the second cellulose acylate, and n represents an integer of 3 to 7.)

(Types of cellulose acylate)
The cellulose acylate used in the present invention is not particularly defined as the first cellulose acylate of the B layer, and the second cellulose acylate is represented by the formula (1) and the formulas (2A) and (2B). ) As long as at least one of the above is satisfied. Examples of the raw material cellulose include cotton linter and wood pulp (hardwood pulp, conifer pulp). Cellulose acylate obtained from any raw material cellulose can be used, and in some cases, it may be mixed and used. Detailed descriptions of these raw material celluloses can be found, for example, by Marusawa and Uda, “Plastic Materials Course (17) Fibrous Resin”, published by Nikkan Kogyo Shimbun (published in 1970), and the Japan Institute of Invention and Technology Publication No. 2001 The cellulose described in No.-1745 (pages 7 to 8) can be used.

(Degree of acyl substitution of cellulose acylate)
In the optical film of the present invention, the B layer contains a first cellulose acylate and a second cellulose acylate having different acyl substitution degrees.

(1) First cellulose acylate The cellulose acylate used as the first cellulose acylate of the B layer preferably has a total substitution degree of acyl groups of 1.2 or more and 3.0 or less.
Furthermore, the cellulose acylate used in the present invention has a total substitution degree of acyl groups of TA, a substitution degree of acyl groups having 2 carbon atoms, TA2, and a substitution degree of acyl groups of 3 to 7 carbon atoms. When TA3 is satisfied, the following conditions are preferably satisfied. By setting it as the following range, an optical film excellent in terms of adhesion to an adjacent layer, drum peelability, and curl reduction of the film can be obtained.
2.2 ≦ TA total ≦ 3.0
1.5 ≦ TA2 ≦ 3.0
0.0 ≦ TA3 ≦ 0.7

The first cellulose acylate is more preferably a cellulose acylate that satisfies the following conditions.
2.5 ≦ TA total ≦ 3.0
2.4 ≦ TA2 ≦ 3.0
0.0 ≦ TA3 ≦ 0.1
More preferably, TA2, that is, the degree of acetyl substitution is 2.8 to 2.94. The cellulose acylate particularly preferably has a total TA of 2.8 to 2.94, and TA3 is particularly preferably 0. The cellulose acylate is more particularly preferably cellulose acetate having an acetyl substitution degree of 2.8 to 2.94.

  In particular, at least one selected from cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate is preferable. Among these, more preferred cellulose acylates are cellulose acetate and cellulose acetate propionate, and more preferred is cellulose acetate.

  In the film of the present invention, it is particularly preferable that the acyl group of the first cellulose acylate of the B layer is an acetyl group, and the degree of acetyl substitution is 2.7 to 3.0.

  In addition, the substitution degree of an acetyl group and the substitution degree of other acyl groups can be obtained by a method prescribed in ASTM-D817-96.

(2) Second cellulose acylate In the optical film of the present invention, the cellulose acylate used as the second cellulose acylate of the B layer has an acyl substitution degree of the second cellulose acylate represented by the following formula ( 1) and at least one of the following formulas (2A) and (2B) is satisfied.
Formula (1) 2.55 ≦ X + Y ≦ 3.0
Formula (2A) 0.2 ≦ Y ≦ 1.2
(In formulas (1) and (2A), X represents the acetyl substituent of the second cellulose acylate, and Y represents the degree of substitution of the acyl group having 3 to 7 carbon atoms of the second cellulose acylate.)
Formula (2B) −0.075n + 0.72 ≦ DS (n) ≦ −0.33n + 2.88
(In Formula (2B), DS (n) represents the degree of substitution of the acyl group having n carbon atoms in the second cellulose acylate, and n represents an integer of 3 to 7.)

The second cellulose acylate preferably satisfies 2.55 ≦ X + Y ≦ 2.85 in the formula (1), more preferably satisfies 2.60 ≦ X + Y ≦ 2.95,
It is particularly preferable that 2.65 ≦ X + Y ≦ 2.90 is satisfied.

  In the formula (2A), the second cellulose acylate preferably satisfies 0.2 ≦ Y <1.2, more preferably satisfies 0.4 ≦ Y <1.0, and 0.6 It is particularly preferable that ≦ Y <0.9 is satisfied.

The second cellulose acylate preferably satisfies the following formula (2B ′) and more preferably satisfies the following formula (2B ″) with respect to the formula (2B). In addition, DS (n) and n in Formula (2B ′) and Formula (2B ″) are synonymous with Formula (2B).
Formula (2B ′) −0.075n + 0.72 ≦ DS (n) ≦ −0.25n + 2.35
Formula (2B ″) −0.15n + 1.25 ≦ DS (n) ≦ −0.22n + 2.1

  In the optical film of the present invention, the content ratio of the first cellulose acylate in the B layer to the second cellulose acylate is 90/10 to 60/40 (mass ratio). The content ratio of the first cellulose acylate to the second cellulose acylate is preferably 90/10 to 70/30 (mass ratio), more preferably 90/10 to 80/20 (mass ratio). It is more preferable.

(Weight average molecular weight of cellulose acylate)
The weight average molecular weight (Mw) of the cellulose acylate used in the present invention is such that the weight average molecular weight of the cellulose acylate used as a main component in the cellulose acylate layer is 50,000 to 500,000. From the viewpoint of improvement, it is preferably 80,000 to 400,000, more preferably 100,000 to 300,000.

  The weight average molecular weight of the cellulose acylate used in the present invention is more preferably in the range of 75000 to 300000, and more preferably in the range of 100000 to 2400, particularly from the viewpoint of adhesion to the acrylic resin. 160000-240000 are particularly preferred. If the weight average molecular weight (Mw) of a cellulose acylate is 75000 or more, the self-film-forming property and adhesion improving effect of the cellulose acylate layer itself are exhibited, which is preferable. In the present invention, in addition to the first cellulose acylate and the second cellulose acylate, other cellulose acylates may be further mixed and used.

(Other polymers included in layer B)
As long as the optical film of the present invention is not contrary to the gist of the present invention, the cellulose acylate (B) layer contains other polymer components in addition to the first cellulose acylate and the second cellulose acylate. You may go out. The other polymer component is not particularly limited, and examples thereof include an acrylic resin and the acrylic resin used as a main component of the A layer.
In the optical film of the present invention, the polymer having a weight average molecular weight of 100,000 or more contained in the B layer is preferably only cellulose acylate.

<Additives>
The optical film of the present invention may contain an additive in each of the acrylic resin layer and the cellulose ester layer together with one or two or more thermoplastic resins serving as main raw materials.

(Plasticizer)
In the film of the present invention, it is preferable to use a plasticizer to impart flexibility to the optical film, improve dimensional stability, and improve moisture resistance.

In the present invention, a plasticizer having a resin component having a molecular weight of 500 to 100,000 can be preferably used. For example, the above-mentioned acrylic resin, polyester and / or polyether described in JP-A No. 2002-22956, polyester ether, polyester urethane or polyester described in JP-A No. 5-97073, and described in JP-A No. 2-292342 And an epoxy resin or a novolak resin described in JP-A No. 2002-146044.
Moreover, as a plasticizer which is excellent in terms of volatility resistance, bleed out, low haze, and the like, it is preferable to use, for example, a polyester diol described in JP 2009-98674 A, in which both ends are hydroxyl groups. Moreover, as a plasticizer which is excellent in terms of flatness and low haze of the optical film, a sugar ester derivative described in WO2009 / 031464 is also preferable.

《Polycondensed ester》
In the present invention, it is preferable to use a polycondensed ester as the polymer plasticizer.
The polycondensation ester used in the present invention is at least one dicarboxylic acid selected from aliphatic dicarboxylic acids having 2 to 20 carbon atoms and aromatic dicarboxylic acids having 8 to 20 carbon atoms, and 2 to 12 carbon atoms. The diol is synthesized from at least one diol selected from aromatic ring-containing diols having 6 to 20 carbon atoms, and aliphatic diols having 4 to 20 carbon atoms. As a synthesis method, a known method such as a dehydration condensation reaction of a dicarboxylic acid and a diol, or addition of a dicarboxylic anhydride to a diol and a dehydration condensation reaction can be used.

  The dicarboxylic acid and diol that can be preferably used for the synthesis of the polycondensed ester in the present invention will be described below.

As the dicarboxylic acid, either an aliphatic dicarboxylic acid or an aromatic dicarboxylic acid can be used.
Examples of the aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, azelaic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and Examples include 1,4-cyclohexanedicarboxylic acid. Of these, malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, azelaic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid are preferred. .
As aromatic dicarboxylic acids, phthalic acid, isophthalic acid, terephthalic acid, 1,4-xylidene dicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, Examples include 2,8-naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid.
Among these, more preferred aliphatic dicarboxylic acids are malonic acid, succinic acid, maleic acid, fumaric acid, glutaric acid, adipic acid, azelaic acid, 1,4-cyclohexanedicarboxylic acid, and aromatic dicarboxylic acids include Phthalic acid, terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid and 1,4-naphthalenedicarboxylic acid are preferred. Particularly preferably, the aliphatic dicarboxylic acid is succinic acid, glutaric acid, or adipic acid, and the aromatic dicarboxylic acid is phthalic acid, terephthalic acid, or isophthalic acid. More particularly preferred is succinic acid or adipic acid.

The aliphatic dicarboxylic acid used in the present invention preferably has 3 to 12 carbon atoms, and more preferably 3 to 8 carbon atoms. The aromatic dicarboxylic acid preferably has 8 to 14 carbon atoms, and more preferably 8 carbon atoms.
In this invention, you may use the mixture of 2 or more types of dicarboxylic acid, In this case, it is preferable that the average carbon number of 2 or more types of dicarboxylic acid is 3-14, and it is more preferable that it is 3-8.
If the carbon number of the dicarboxylic acid is within the above range, it is preferable because in addition to improving light unevenness, it has excellent compatibility with a thermoplastic polymer, and bleed-out is unlikely to occur during film formation and heat stretching.
It is also preferable to use an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid in combination. Specifically, a combination of adipic acid and phthalic acid, a combination of adipic acid and terephthalic acid, a combined use of succinic acid and phthalic acid, and a combined use of succinic acid and terephthalic acid are preferred. The combined use of succinic acid and terephthalic acid is more preferable. When aliphatic dicarboxylic acid and aromatic dicarboxylic acid are used in combination, the ratio (molar ratio) between them is preferably 95: 5 to 40:60, and more preferably 55:45 to 45:55.

The diol (glycol) is preferably selected from aliphatic diols having 2 to 12 carbon atoms, alkyl ether diols having 4 to 20 carbon atoms, and aromatic ring-containing diols having 6 to 20 carbon atoms.
Examples of the aliphatic diol include alkyl diols and alicyclic diols. For example, ethane diol (ethylene glycol), 3-oxapentane-1,5-diol (diethylene glycol), 1,2-propanediol, 1, 3-propanediol, 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl- 1,3-propanediol (neopentyl glycol), 2,2-diethyl-1,3-propanediol (3,3-dimethylolpentane), 2-n-butyl-2-ethyl-1,3-propanediol (3,3-dimethylolheptane), 3-methyl-1,5-pentanediol, 1,4-hexanedio 1,5-hexanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8- There are octanediol, 1,9-nonanediol, 1,10-decanediol, 1,4-cyclohexanediol, or 1,4-cyclohexanedimethanol, and these glycols are used as one kind or a mixture of two or more kinds. used.
Preferred aliphatic diols include ethanediol (hereinafter also referred to as ethylene glycol), 3-oxapentane-1,5-diol, 1,2-propanediol (hereinafter also referred to as propylene glycol), 1,3-propanediol, 1 , 2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2-methyl-1,8-octanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, Particularly preferred are ethanediol, 1,2-propanediol, 1,3-propanediol, 1 2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol. More particularly preferred are ethanediol and 1,2-propanediol.

  Preferred examples of the alkyl ether diol having 4 to 20 carbon atoms include polytetramethylene ether glycol, polyethylene ether glycol, polypropylene ether glycol, and combinations thereof. Although the average degree of polymerization is not particularly limited, it is preferably 2 to 20, more preferably 2 to 10, further 2 to 5, and particularly preferably 2 to 4. As examples of these, commercially useful polyether glycols typically include Carbowax resin, Pluronics resin, and Niax resin.

  Examples of the aromatic diol having 6 to 20 carbon atoms include, but are not limited to, bisphenol A, 1,2-hydroxybenzene, 1,3-hydroxybenzene, 1,4-hydroxybenzene, and benzene-1,4-methanol. Of these, bisphenol A, 1,4-hydroxybenzene, and benzene-1,4-dimethanol are preferred.

The aromatic diol preferably has 6 to 12 carbon atoms.
When using 2 or more types of diol, it is preferable that the average carbon number of 2 or more types becomes 2-12.
If the carbon number of the diol is in the above range, in addition to improving the light unevenness, it is excellent in compatibility with the thermoplastic polymer, and it is preferable that bleeding out hardly occurs at the time of film formation and heat stretching of the polymer film.
In the present invention, a mixture of two or more diols may be used, and in this case, the average carbon number of the two or more diols is preferably 2 to 12, and more preferably 2 to 7.
Specifically, the combined use of ethylene glycol and propylene glycol is preferable. When a mixture of two or more diols is used, the ratio (molar ratio) between the two is preferably 95: 5 to 95: 5, and more preferably 55:45 to 45:55.

Both ends of the polycondensation ester used in the optical film of the present invention may be sealed or unsealed.
When both ends of the polycondensed ester are unsealed, the oligomer is preferably a polyester polyol.
In addition, at least one terminal is sealed, and the terminal is an aliphatic group having 1 to 22 carbon atoms, an aromatic ring-containing group having 6 to 20 carbon atoms, an aliphatic carbonyl group having 1 to 22 carbon atoms, and a carbon number. It is also preferable that it is at least one selected from 6 to 20 aromatic carbonyl groups.
Furthermore, when both ends of the polycondensed ester are sealed, it is more preferable to seal by reacting with a monoalcohol or monocarboxylic acid. At this time, both ends of the oligomer are monoalcohol residues or monocarboxylic acid residues. Here, the residue is a partial structure of the oligomer and represents a partial structure having the characteristics of the monomer forming the oligomer. For example, the monocarboxylic acid residue formed from monocarboxylic acid R—COOH is R—CO—.

As the monoalcohol residue, a substituted or unsubstituted monoalcohol residue having 1 to 30 carbon atoms is preferable. Methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol, hexanol, isohexanol, cyclohexyl Alcohol, octanol, isooctanol, 2-ethylhexyl alcohol, nonyl alcohol, isononyl alcohol, tert-nonyl alcohol, decanol, dodecanol, dodecahexanol, aliphatic alcohol such as dodecaoctanol, allyl alcohol, oleyl alcohol, benzyl alcohol, 3- Examples include substituted alcohols such as phenylpropanol.
The end-capping alcohol residues that can be preferably used are methanol, ethanol, propanol, isopropanol, butanol, isobutanol, isopentanol, hexanol, isohexanol, cyclohexyl alcohol, isooctanol, 2-ethylhexyl alcohol, isononyl alcohol, Oleyl alcohol and benzyl alcohol, especially methanol, ethanol, propanol, isobutanol, cyclohexyl alcohol, 2-ethylhexyl alcohol, isononyl alcohol and benzyl alcohol.

The monocarboxylic acid residue is preferably an aliphatic monocarboxylic acid residue having 2 to 22 carbon atoms, more preferably an aliphatic monocarboxylic acid residue having 2 to 3 carbon atoms, and 2 carbon atoms. Particularly preferred are aliphatic monocarboxylic acid residues.
If the number of carbon atoms of the monocarboxylic acid residues at both ends of the polyester-based oligomer is 3 or less, the volatility decreases, the weight loss due to heating of the oligomer does not increase, and process contamination and surface failure occur. Can be reduced. That is, aliphatic monocarboxylic acids are preferable as monocarboxylic acids used for sealing. The monocarboxylic acid is more preferably an aliphatic monocarboxylic acid having 2 to 22 carbon atoms, more preferably an aliphatic monocarboxylic acid having 2 to 3 carbon atoms, and an aliphatic monocarboxylic acid residue having 2 carbon atoms. Particularly preferred is a group.
Preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butanoic acid, caprylic acid, caproic acid, decanoic acid, dodecanoic acid, stearic acid, and oleic acid. Examples of the aromatic ring-containing monocarboxylic acid include benzoic acid, p-tert-butylbenzoic acid, p-tert-amylbenzoic acid, orthotoluic acid, metatoluic acid, p-toluic acid, dimethylbenzoic acid, ethylbenzoic acid, and normalpropyl benzoic acid. Acid, aminobenzoic acid, acetoxybenzoic acid, etc. are mentioned.
Among these, acetic acid, propionic acid, butanoic acid, benzoic acid and derivatives thereof are preferable, acetic acid or propionic acid is more preferable, and acetic acid (terminal is an acetyl group) is most preferable. Two or more monocarboxylic acids used for sealing may be mixed.

  When both ends are sealed, the state at normal temperature is unlikely to be in a solid form, the handling becomes good, and a polymer film excellent in humidity stability and polarizing plate durability can be obtained.

  The number average molecular weight of the polycondensed ester is preferably 500 to 2000, more preferably 600 to 1500, and still more preferably 700 to 1200. If the number average molecular weight of the polycondensed ester is 600 or more, the volatility is low, and film failure or process contamination due to volatilization under high temperature conditions during stretching of the cellulose ester film is less likely to occur. Moreover, if it is 2000 or less, compatibility with a cellulose ester will become high, and it will become difficult to produce the bleed-out at the time of film forming and the heat-stretching.

  Although the specific example of the polycondensation ester used for this invention is described in the following Table 1 and Table 2, it is not limited to these. In Tables 1 and 2 below, PA represents phthalic acid, TPA represents terephthalic acid, IPA represents isophthalic acid, AA represents adipic acid, SA represents succinic acid, and 2,6-NPA represents 2,6-naphthalenedicarboxylic acid.

  The polycondensation ester used in the present invention can be synthesized by a conventional method such as a hot melt condensation method by a polyesterification reaction or transesterification reaction between a diol and a dicarboxylic acid, or an interfacial condensation method between an acid chloride of these acids and a glycol. It can be easily synthesized by either method. In addition, the polycondensed ester according to the present invention is described in detail in Koichi Murai, “Plasticizer Theory and Application” (Kokai Shobo Co., Ltd., first edition issued on March 1, 1973). In addition, Japanese Patent Laid-Open Nos. 05-155809, 05-155810, Japanese Patent Laid-Open Nos. 05-97073, 2006-259494, 07-330670, 2006-342227, 2007-003679. The materials described in each publication can also be used.

  The content of the polycondensed ester in the layer B (cellulose ester layer) of the film of the present invention is preferably 5 to 40% by mass, more preferably 8 to 30% by mass with respect to the amount of cellulose ester. Most preferably, it is 10 to 25% by mass. The content of the polycondensed ester in the A layer of the film of the present invention is also the same as that of the B layer.

The content of the raw material aliphatic diol, dicarboxylic acid ester, or diol ester contained in the polycondensate used in the present invention in the cellulose ester layer is preferably less than 1% by mass, more preferably less than 0.5% by mass. . Examples of the dicarboxylic acid ester include dimethyl phthalate, di (hydroxyethyl) phthalate, dimethyl terephthalate, di (hydroxyethyl) terephthalate, di (hydroxyethyl) adipate, and di (hydroxyethyl) succinate. Examples of the diol ester include ethylene diacetate and propylene diacetate.
The kind and ratio of each of the dicarboxylic acid residue, diol residue, and monocarboxylic acid residue contained in the polycondensation ester used in the present invention can be measured by a usual method using H-NMR. . Usually, deuterated chloroform can be used as a solvent.
The number average molecular weight of the polycondensed ester can be measured by a usual method using GPC (Gel Permeation Chromatography), and polystyrene can be usually used as a standard material.

<< Acrylic oligomer or acrylic resin >>
In the present invention, an acrylic oligomer or an acrylic resin can be added to the A layer (acrylic resin layer) or the B layer (cellulose acylate layer) as long as it does not contradict the gist of the present invention. The ratio of the acrylic oligomer or acrylic resin to the acrylic resin used as the main component in the A layer is preferably 2 to 140% by mass based on the acrylic resin used as the main component in the acrylic resin layer. More preferably, it is 4-100 mass%, Most preferably, it is 6-60 mass%. The ratio of the acrylic oligomer or acrylic resin to the first cellulose acylate used as the main component in the B layer is 0 to 0 when the first cellulose acylate used as the main component in the B layer is used as a reference. 140 mass% is preferable, More preferably, it is 0-100 mass%, Most preferably, it is 0-60 mass%. The molecular weight of the acrylic oligomer or acrylic resin is preferably 500 to 200,000, more preferably 1000 to 100,000, still more preferably 1200 to 50,000, and particularly preferably 1200 to 10,000. By setting this molecular weight range, the acrylic resin or cellulose acylate layer used as the main component in the acrylic resin layer is excellent in transparency.

The composition of the acrylic oligomer or acrylic resin that can be used for this purpose is an aliphatic (meth) acrylic acid ester monomer, a (meth) acrylic acid ester monomer having an aromatic ring, or a (meth) acrylic acid ester having a cyclohexyl group. It is preferable to contain a monomer as a main component. The main component means that the constituent mass ratio is higher in the (co) polymer than other copolymerizable components.
Preferably, the constituent mass ratio of these components is 40 to 100% by mass, more preferably 60 to 100% by mass, and most preferably 70 to 100% by mass.

  Examples of aliphatic (meth) acrylic acid ester monomers include methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), Pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (N-, i-), myristyl acrylate (n-, i-), acrylic acid (2-ethylhexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxy Propyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid (2-methoxyethyl) Acrylic acid (2-ethoxyethyl), or the acrylic acid ester can be exemplified those obtained by changing the methacrylic acid ester. Among them, methyl methacrylate, ethyl methacrylate, propyl methacrylate (i-, n-), butyl methacrylate (n-, i-, s-, t-), methyl acrylate, ethyl acrylate Is preferred.

  Examples of the (meth) acrylic acid ester monomer having an aromatic ring include phenyl acrylate, phenyl methacrylate, acrylic acid (2 or 4-chlorophenyl), methacrylic acid (2 or 4-chlorophenyl), and acrylic acid (2 or 3). Or 4-ethoxycarbonylphenyl), methacrylic acid (2 or 3 or 4-ethoxycarbonylphenyl), acrylic acid (o or m or p-tolyl), methacrylic acid (o or m or p-tolyl), benzyl acrylate, Examples thereof include benzyl methacrylate, phenethyl acrylate, phenethyl methacrylate, and acrylic acid (2-naphthyl), and benzyl acrylate, benzyl methacrylate, phenethyl acrylate, and phenethyl methacrylate can be preferably used.

  Examples of the (meth) acrylic acid ester monomer having a cyclohexyl group include cyclohexyl acrylate, cyclohexyl methacrylate, acrylic acid (4-methylcyclohexyl), methacrylic acid (4-methylcyclohexyl), and acrylic acid (4-ethyl). Cyclohexyl), methacrylic acid (4-ethylcyclohexyl) and the like, and cyclohexyl acrylate and cyclohexyl methacrylate can be preferably used.

  In addition to the above monomers, further copolymerizable components include α, β-unsaturated acids such as acrylic acid and methacrylic acid, divalent carboxylic acids containing unsaturated groups such as maleic acid, fumaric acid and itaconic acid, and styrene. , Aromatic vinyl compounds such as α-methylstyrene, α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, and the like. Alternatively, two or more monomers can be used in combination as a copolymerization component.

  In order to synthesize an acrylic oligomer or acrylic resin having a weight average molecular weight of 10,000 or less, it is difficult to control the molecular weight in normal polymerization. As a polymerization method of such a low molecular weight polymer, a method using a peroxide polymerization initiator such as cumene peroxide or t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, polymerization A method using a chain transfer agent such as a mercapto compound or carbon tetrachloride in addition to the initiator, a method using a polymerization terminator such as benzoquinone or dinitrobenzene in addition to the polymerization initiator, and further JP-A-2000-128911 or Examples include a method of bulk polymerization using a compound having one thiol group and a secondary hydroxyl group as described in JP-A-2000-344823, or a polymerization catalyst in which the compound and an organometallic compound are used in combination. These are preferably used in the present invention, and the method described in the publication is particularly preferable.

  Examples of the low-molecular-weight oligomer compound include phosphoric acid ester, carboxylic acid ester, and polyol ester.

  Examples of phosphate esters include triphenyl phosphate (TPP), tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, biphenyl diphenyl phosphate, trioctyl phosphate, tributyl phosphate, and the like. Triphenyl phosphate and biphenyl diphenyl phosphate are preferable.

Representative examples of the carboxylic acid ester include phthalic acid esters and citric acid esters. Examples of the phthalic acid ester include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diphenyl phthalate, diethyl hexyl phthalate and the like. Examples of the citrate ester include O-acetyl triethyl citrate, O-acetyl tributyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate.
These preferred plasticizers are liquid except for TPP (melting point: about 50 ° C.) at 25 ° C., and the boiling point is 250 ° C. or higher.

  Examples of other carboxylic acid esters include butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, and various trimellitic acid esters. Examples of glycolic acid esters include triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, methyl phthalyl methyl glycolate, propyl phthalyl Examples include propyl glycolate, butyl phthalyl butyl glycolate, and octyl phthalyl octyl glycolate.

  JP-A-5-194788, JP-A-60-250053, JP-A-4-227941, JP-A-6-16869, JP-A-5-271471, JP-A-7-286068, JP-A-5-5047. No. 11, JP-A-11-80381, JP-A-7-20317, JP-A-8-57879, JP-A-10-152568, JP-A-10-120824, etc. are also preferably used. It is done. According to these publications, there are many preferable descriptions regarding not only examples of plasticizers but also their usage or characteristics, and they are preferably used in the present invention.

  Other plasticizers include (di) pentaerythritol esters described in JP-A No. 11-124445, glycerol esters described in JP-A No. 11-246704, diglycerol esters described in JP-A No. 2000-63560, Citric acid esters described in JP-A No. 11-92574, substituted phenyl phosphate esters described in JP-A No. 11-90946, ester compounds containing an aromatic ring and a cyclohexane ring described in JP-A No. 2003-165868 are preferably used. .

  These plasticizers may be used alone or in admixture of two or more. The amount of the plasticizer added can generally be 2 to 120 parts by weight, preferably 2 to 70 parts by weight, and more preferably 2 to 30 parts by weight with respect to 100 parts by weight of the thermoplastic resin contained in each dope. In particular, 5 to 20 parts by mass is preferable. In addition, when a common plasticizer is used in adjacent layers among the dopes (A) and (B) used in the production method of the present invention described later, the occurrence of disturbance of the interface of the dope during casting is reduced, From the viewpoint of improving adhesion and reducing curling, it is preferable. In particular, the dopes (A) and (B) preferably contain a common plasticizer.

(Other additives)
In addition to the plasticizer, other additives may be used for the optical film of the present invention.
Examples of additives include ultraviolet absorbers, fluorine-based surfactants (preferably added amounts are 0.001 to 1% by mass with respect to the thermoplastic resin), release agents (0.0001 to 1% by mass), and deterioration prevention. Agents (0.0001 to 1% by mass), optical anisotropy control agents (0.01 to 10% by mass), infrared absorbers (0.001 to 1% by mass), and the like.

  As the ultraviolet absorber, one having an excellent ability to absorb ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of the liquid crystal and having as little absorption of visible light having a wavelength of 400 nm or more as possible from the viewpoint of good image display properties is used. It is preferable. In particular, the transmittance at a wavelength of 370 nm is desirably 20% or less, preferably 10% or less, and more preferably 5% or less. Examples of such ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and ultraviolet absorbing groups as described above. Examples thereof include, but are not limited to, polymer ultraviolet absorbing compounds. Two or more kinds of ultraviolet absorbers may be used.

Moreover, the particle | grains which consist of a trace amount organic material, an inorganic material, and mixtures thereof may be dispersedly included in the range which does not impair the effect of this invention. When these particles are added for the purpose of improving the transportability of the film during film formation (as a matting agent), the particle size of the particles is preferably 5 to 3000 nm, and the addition amount is 1% by mass or less. Is preferred.
Particles can be added to give irregularities on the surface of the film or to impart light scattering properties to the inside of the film. In that case, the particle diameter of the particles is preferably 1 to 20 μm, and added The amount is preferably 2 to 30% by mass. The difference between the refractive index of these particles and the refractive index of the polymer film of the present invention is preferably 0 to 0.5. Examples of inorganic material particles include particles of silicon oxide, aluminum oxide, barium sulfate, etc. Is included. Examples of organic material particles include acrylic resin, divinylbenzene resin, benzoguanamine resin, styrene resin, melamine resin, acrylic-styrene resin, polycarbonate resin, polyethylene resin, polyvinyl chloride resin, etc. included. When light diffusibility is imparted to the optical film by the particles, the haze value is not limited, but it is preferably set in a range in which the backscattering property is high and the decrease in the total light transmittance is not excessively large. Specifically, the haze is preferably 1 to 60%, more preferably 3 to 50%.

<Lamination of additional layers on optical film>
In the optical film of the present invention, for example, a curable resin layer having a thickness of 0.1 μm or more and 15 μm or less may be further provided thereon. In the optical film of the present invention, an optical functional layer such as an antistatic layer, a high refractive index layer, or a low refractive index layer can be provided on the curable resin layer. The curable resin layer can also serve as an antistatic layer or a high refractive index layer.
The curable resin layer is preferably formed by a crosslinking reaction or a polymerization reaction of an ionizing radiation curable compound. For example, it is formed by applying a coating composition containing an ionizing radiation-curable polyfunctional monomer or polyfunctional oligomer on a light-transmitting substrate and causing the polyfunctional monomer or polyfunctional oligomer to undergo a crosslinking reaction or a polymerization reaction. be able to.
The functional group of the ionizing radiation curable polyfunctional monomer or polyfunctional oligomer is preferably a light, electron beam, or radiation polymerizable group, and among them, a photopolymerizable functional group is preferable.
Examples of the photopolymerizable functional group include unsaturated polymerizable functional groups such as a (meth) acryloyl group, a vinyl group, a styryl group, and an allyl group. Among them, a (meth) acryloyl group is preferable.
In addition, additives such as a known leveling agent, antifouling agent, antistatic agent, refractive index adjusting inorganic filler, scattering particles, and thixotropic agent can be used for the curable resin layer.

The strength of the optical film provided with the curable resin layer is preferably H or higher, more preferably 2H or higher, in a pencil hardness test.

[Method for producing optical film]
The method for producing an optical film of the present invention (hereinafter also referred to as the production method of the present invention) comprises at least two dopes (A) and (B) containing a thermoplastic resin and a solvent from the casting substrate side (B )-(A) in the order of simultaneous or sequential casting on the casting substrate, the dope (A) contains an acrylic resin having a weight average molecular weight exceeding 1 million, and the dope (B) Contains the first cellulose acylate and the second cellulose acylate having different degrees of acyl substitution, and the content ratio of the acylate of the first cellulose to the second cellulose acylate in the dope (B) is 90. / 10 to 60/40 (mass ratio), and the acyl substitution degree of the second cellulose acylate satisfies at least one of the following formula (1) and the following formulas (2A) and (2B). And features.
Formula (1) 2.55 ≦ X + Y ≦ 3.0
Formula (2A) 0.2 ≦ Y ≦ 1.2
(In formulas (1) and (2A), X represents the acetyl substituent of the second cellulose acylate, and Y represents the degree of substitution of the acyl group having 3 to 7 carbon atoms of the second cellulose acylate.)
Formula (2B) −0.075n + 0.72 ≦ DS (n) ≦ −0.33n + 2.88
(In Formula (2B), DS (n) represents the degree of substitution of the acyl group having n carbon atoms in the second cellulose acylate, and n represents an integer of 3 to 7.)

In the production method of the present invention, the second cellulose acylate of the dope (B) satisfies the formula (1) and the formula (2A), and the formula (1) and the formula ( There is a second mode that satisfies 2B) and a third mode that satisfies Formula (1), Formula (2A), and Formula (2B), both of which are preferred.
Corresponding to the production method of the first aspect to the third aspect of the present invention, the films of the first aspect to the third aspect of the present invention can be respectively produced.

<Preparation of dope>
Regarding the preparation of the thermoplastic resin solution (dope) used in the optical film of the present invention, the dissolution method is carried out by a room temperature dissolution method, a cooling dissolution method or a high temperature dissolution method, and further a combination thereof. Regarding these, for example, JP-A-5-163301, JP-A-61-106628, JP-A-58-127737, JP-A-9-95544, JP-A-10-95854, JP-A-10-45950, JP 2000-53784, JP 11-322946, JP 11-322947, JP 2-276830, JP 2000-273239, JP 11-71463, JP 04-259511, JP JP-A-2000-273184, JP-A-11-323017, JP-A-11-302388, etc. describe methods for preparing cellulose acylate solutions. These techniques for dissolving cellulose acylate in an organic solvent can appropriately apply these techniques to the thermoplastic resin of the present invention. About these details, especially a non-chlorine type | system | group solvent system, it implements by the method described in detail on the 22-25th pages of the above-mentioned technical numbers 2001-1745. Further, the dope solution of the thermoplastic resin is usually subjected to solution concentration and filtration, and is also described in detail on page 25 of the above-mentioned technical number 2001-1745. In addition, when it melt | dissolves at high temperature, it is the case where it is more than the boiling point of the organic solvent to be used, and in that case, it uses in a pressurized state.

(Organic solvent)
An organic solvent (also referred to as a solvent) that dissolves the thermoplastic resin of the present invention and forms a dope will be described. Examples of the organic solvent to be used include conventionally known organic solvents. For example, those having a solubility parameter in the range of 17 to 22 are preferable. Solubility parameters are described, for example, in J. Org. 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) Compound) and the like.

The solvent used in the present invention may be used alone or in combination, but it is preferable to use a mixture of a good solvent and a poor solvent in order to impart planar stability, more preferably a mixture of a good solvent and a poor solvent. The ratio of the good solvent is 60 to 99% by mass, and the poor solvent is 40 to 1% by mass. In the present invention, the good solvent means a resin that dissolves the resin used alone, and the poor solvent means a resin that swells or does not dissolve the resin used alone. Examples of the good solvent used in the present invention include organic halogen compounds such as methylene chloride and dioxolanes. Moreover, as a poor solvent used for this invention, methanol, ethanol, n-butanol, a cyclohexane etc. are used preferably, for example.
Drying on the support (casting substrate) after film formation that the proportion of alcohol in the organic solvent contained in the dopes (A) and (B) is 10 to 50% by mass of the whole organic solvent. It is preferable because the time can be shortened and the film can be quickly peeled off and dried.

In the production method of the present invention, the acrylic resin having the weight average molecular weight of more than 1,000,000 and the first and second cellulose acylates having a specific substitution range are dissolved well and obtained. From the viewpoint of reducing the haze of the film, methylene chloride and a lower alcohol having 1 to 4 carbon atoms are used as the solvent, and the content ratio of methylene chloride to the lower alcohol having 1 to 4 carbon atoms is 90/10 to 60/40. A range of (volume ratio) is preferable.
The content ratio of methylene chloride to the lower alcohol having 1 to 4 carbon atoms is more preferably in the range of 80/20 to 60/40 (volume ratio), and particularly preferably 80/20 to 70/30.
As said C1-C4 lower alcohol, methanol, ethanol, and n-butanol are preferable, methanol or ethanol is more preferable, and methanol is especially preferable.

  The material forming the optical film is preferably dissolved in the organic solvent at a concentration of 10 to 60% by mass, more preferably 10 to 50% by mass. When the cellulose acylate resin is a main component, it is preferably dissolved by 10 to 30% by mass, more preferably 13 to 27% by mass, and particularly preferably 15 to 25% by mass. The method for preparing these concentrations may be prepared so as to have a predetermined concentration at the stage of dissolution, or prepared in advance as a low concentration solution (for example, 9 to 14% by mass) and then a predetermined high concentration in the concentration step. You may adjust to a solution. Furthermore, it is good also as a solution of the predetermined | prescribed low concentration by adding various additives later as a solution of the material which forms a high concentration light transmissive base material beforehand.

(Dope solid content concentration)
In the production method of the present invention, the solid content concentration of the dope (B) (concentration of the component that becomes solid after the dope drying) is appropriately selected according to the molecular weight, but the solution casting film formation is performed. In order to obtain a dope having an appropriate viscosity, the solid content concentration is preferably 16 to 30% by mass. Conventionally, it has been considered that the solid content concentration is preferably 30 to 50% because the content of the organic solvent can be reduced and the drying time can be shortened. From the viewpoint of obtaining the effects of the present invention, it was found that the solid content concentration is more preferably adjusted. The solid content concentration of the dope (B) is more preferably 16 to 30% by mass, and particularly preferably 18 to 25% by mass.

  In the production method of the present invention, it is preferable that the solid concentrations of the dope (A) and the dope (B) are both 16 to 30% by mass.

On the other hand, in the production method of the present invention, in order to obtain a good planar film by co-casting, the solid content concentration of the dope (B) is approximately the same as the solid content concentration of the dope (A). It is preferable that The difference in solid content between the dope (B) and the dope (A) is preferably within 10% by mass, and more preferably within 5% by mass.
In particular, in the dope (B), the concentration of the sum of the components that become solid after drying is 16 to 30% by mass, and the difference in concentration between the dope (B) and the dope (A) is within 10% by mass. Is preferred.

(Complex viscosity of dope)
In the production method of the present invention, it is preferable that the complex viscosity of the dope (A) and the dope (B) is 10 to 80 Pa · s or less. By setting the complex viscosity in such a range, the solution casting suitability tends to be further improved, which is preferable. Here, the complex viscosity of the dope in the present invention refers to a viscosity measured by solution shear rheometer measurement.
More preferably, it is 20-80 Pa * s, Most preferably, it is 25-70 Pa * s. The viscosity was measured as follows. 1 mL of the sample solution was measured with a rheometer (CLS 500) using Steel Cone (both manufactured by TA Instruments) with a diameter of 4 cm / 2 °.
Measurement was started after the sample solution was kept warm at the measurement start temperature until the liquid temperature became constant. Although the temperature at this time will not be specifically limited if it is the temperature at the time of the casting, Preferably it is -5-70 degreeC, More preferably, it is -5-35 degreeC.

  In the production method of the present invention, the viscosity of the dope during casting may be different between the surface layer and the core layer, and the viscosity of the surface layer is preferably smaller than the viscosity of the core layer. It may be smaller than the viscosity. In the production method of the present invention, among them, the complex viscosity of the dope (A) and the dope (B) is 10 to 80 Pa · s or less, and the complex viscosity of the dope (B) is the dope ( It is preferable that it is larger than the complex viscosity of A) from the viewpoint of improving the film surface shape after film formation.

(Composition of dope thermoplastic resin)
Furthermore, from the viewpoint of achieving support releasability, interfacial adhesion, low curl, etc., the composition of the thermoplastic resin in the dopes (A) and (B) preferably satisfies the following conditions. The proportion of the cellulose acylate resin in the thermoplastic resin in the dope (A) is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, and most preferably 80 to 100% by mass. The proportion of the acrylic resin in the thermoplastic resin in the dope (B) is preferably 30 to 100% by mass, more preferably 50 to 100% by mass, and most preferably 70 to 100% by mass.

(Simultaneous or sequential casting process)
Casting at least two types of dopes (A) and (B) containing a thermoplastic resin and an organic solvent simultaneously or sequentially from the casting substrate side in the order of (A)-(B). The process of carrying out is included.
In the method for producing an optical film of the present invention, it is preferable that the at least two types of dopes (A) and (B) are simultaneously cast on the casting base material in this order from the casting base material side.

  The dope is cast on a drum and the solvent is evaporated to form a film. The surface of the drum is preferably finished in a mirror state. For casting and drying methods in the solvent casting method, U.S. Pat. No. 736892, JP-B Nos. 45-4554, 49-5614, JP-A-60-176834, No. 60-203430, and No. 62-1115035.

  FIG. 1 is a view showing a casting facility including a drum. FIG. 1 is a schematic view showing the main part of the casting equipment 101 and is a plan view from the side. In FIG. 1, a drum 102 is used. The casting dope 12 from the casting die 14 is cast slightly below the uppermost part of the drum 102 so that the casting film formed on the drum 102 is directed downward from the casting start position PS. Also in this case, it is preferable to determine the casting start position PS so that the tangent line at the casting start position PS on the drum 102 matches the tangent line of the casting curve from the casting die 14 as much as possible.

  The drum 102 has a temperature adjustment function. A plurality of condensing plates 105 are installed outside the casting film. The condensing plates 105 enter the external liquid receiver 53 through the inclination of the gap between the condensing plates 105 and are collected in the collecting tank 56. The cast film traveling on the drum 102 is peeled off as a film 36 by a peeling roller 37 and sent to a drying facility which is the next process. Thereby, while preventing dripping, the cast film can be dried uniformly and the solvent can be recovered in a high yield. However, even when the rotation direction of the drum 102 is reversed and the running direction of the casting film is upward from the casting start position PS, the effect of uniform drying of the casting film and the uniformization of the thickness of the film 36 are obtained. It is done.

The dope is preferably cast on a drum having a surface temperature of 5 ° C. or less. The surface temperature of the casting base material (drum) is preferably -30 to 5 ° C, more preferably -10 to 2 ° C.
After casting, it is preferable to dry it by applying air for 2 seconds or more. The obtained film can be peeled off from the drum and further dried with high-temperature air whose temperature is successively changed from 100 ° C. to 160 ° C. to evaporate the residual solvent. The above method is described in Japanese Patent Publication No. 5-17844. According to this method, it is possible to shorten the time from casting to stripping. In order to carry out this method, it is necessary for the dope to gel at the surface temperature of the drum during casting.

  In the present invention, the two or more types of dopes are cast on a casting substrate to form a film. There is no restriction | limiting in particular as a manufacturing method of the film of this invention other than the above, A well-known co-casting method can be used. For example, a film may be produced while casting and laminating a dope solution from a plurality of casting openings provided at intervals in the traveling direction of the metal support. For example, Japanese Patent Application Laid-Open No. 61-158414, The methods described in Japanese Laid-Open Patent Publication Nos. 1-122419 and 11-198285 can be applied. Further, the dope solution may be cast from two casting ports or formed into a film. For example, Japanese Patent Publication Nos. 60-27562, 61-94724, 61-947245, 61-947245, It can be carried out by the methods described in JP-A-61-104813, JP-A-61-158413, and JP-A-6-134933.

  In the production method of the present invention, it is preferable to co-cast at least two types of dopes (A) and (B) simultaneously from the casting base material side. Furthermore, in the production method of the present invention, it is preferable that the co-casting is performed in the order of the dopes (A), (B), and (A) in order from the base material side and from the support side. Here, a plurality of (A) in one laminated film may have the same composition or different compositions.

  In the case of co-casting, it is possible to produce a laminated film by co-casting dope solutions having different additive concentrations such as the above-mentioned plasticizer, ultraviolet absorber and matting agent. For example, the matting agent can be contained in the surface layer on the support surface side or in the surface layer on the support surface side only. The plasticizer and the ultraviolet absorber can be contained in the core layer more than the surface layer, and may be contained only in the core layer. Also, the type of plasticizer and ultraviolet absorber can be changed between the core layer and the surface layer. For example, the surface layer contains a low-volatile plasticizer and / or an ultraviolet absorber, and the core layer is a plasticizer with excellent plasticity. Alternatively, an ultraviolet absorber excellent in ultraviolet absorption can be added.

<Drying process>
The production method of the present invention includes a step of removing the organic solvent.
A method for drying a web that has been dried on a drum and peeled is described. The web peeled at the peeling position just before the drum makes one turn is conveyed by alternately passing through a group of rolls arranged in a staggered manner, or the both ends of the peeled web are gripped by clips or the like and are not contacted. It is conveyed by the method of conveying it automatically. Drying is performed by a method of applying wind at a predetermined temperature to both sides of the web (film) being conveyed or a method using a heating means such as a microwave. Since rapid drying may impair the flatness of the film to be formed, it is preferable to dry at a temperature at which the solvent does not foam in the initial stage of drying, and to dry at a high temperature after the drying proceeds. In the drying process after peeling from the support, the film tends to shrink in the longitudinal direction or the width direction by evaporation of the solvent. Shrinkage increases with drying at higher temperatures. Drying while suppressing this shrinkage as much as possible is preferable for improving the flatness of the finished film. From this point, for example, as shown in Japanese Patent Laid-Open No. 62-46625, a method in which all or part of the drying process is performed while holding the width at both ends of the web with clips or pins in the width direction. (Tenter method) is preferable. It is preferable that the drying temperature in the said drying process is 100-145 degreeC. The drying temperature, the amount of drying air, and the drying time vary depending on the solvent to be used.

  It is preferable to dry the multilayer cast dope and then peel it from the support. The time for the dope to be cast and peeled on the casting substrate, that is, the time for the dope to be conveyed on the casting substrate is preferably within 60 seconds, and more preferably within 30 seconds.

<Extension process>
The manufacturing method of this invention may include the process of extending | stretching the said laminated | multilayer film formed into a film after the said film forming process.
In the production of the film of the present invention, the web (film) peeled from the support is preferably stretched when the amount of residual solvent in the web is less than 120% by mass.

The residual solvent amount can be expressed by the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
Here, M is the mass of the web at an arbitrary point in time, and N is the mass when the web of which M is measured is dried at 110 ° C. for 3 hours. If the amount of residual solvent in the web is too large, the effect of stretching cannot be obtained, and if it is too small, stretching becomes extremely difficult and the web may break. The more preferable range of the residual solvent amount in the web is most preferably 10% by mass to 50% by mass, particularly 12% by mass to 35% by mass. Further, if the stretching ratio is too small, a sufficient phase difference cannot be obtained, and if it is too large, stretching may become difficult and breakage may occur.

The draw ratio can be generally 5% to 100%, and is preferably 15% to 40%. Here, extending from 5% to 100% in one direction means that the distance between clips and pins supporting the film is in the range of 1.05 to 2.00 times the distance before stretching. Means.
Stretching may be performed in the film transport direction (longitudinal direction), in the direction orthogonal to the film transport direction (transverse direction), or in both directions.

In the present invention, the solution cast film can be stretched without being heated to a high temperature as long as the residual solvent amount is in a specific range, but it is preferable because drying and stretching can shorten the process. . In this invention, it is preferable that the extending | stretching temperature in the said extending process is 110-190 degreeC, and it is more preferable that it is 120-150 degreeC. The stretching temperature is preferably 120 ° C. or higher from the viewpoint of lowering haze, and 150 ° C. or lower is preferable from the viewpoint of enhancing optical expression (thin film forming).
On the other hand, since the plasticizer volatilizes when the temperature of the web is too high, the range of room temperature (15 ° C.) to 145 ° C. or lower is preferable when using a low molecular plasticizer that easily volatilizes as a plasticizer.

  In addition, stretching in biaxial directions perpendicular to each other is an effective method from the viewpoint of improving the optical expression of the film, particularly from the viewpoint of increasing the Rth (retardation) value of the film.

In this invention, you may extend | stretch to a biaxial direction simultaneously in a extending | stretching process, and may extend | stretch to a biaxial direction sequentially. When extending | stretching to a biaxial direction sequentially, you may change extending | stretching temperature for every extending | stretching in each direction.
In the case of simultaneous biaxial stretching, the film of the present invention can be obtained even when the stretching temperature is 110 ° C. to 190 ° C., and the stretching temperature in the case of simultaneous biaxial stretching is 120 ° C. to 150 ° C. More preferably, it is 130 to 150 degreeC. Further, by simultaneous biaxial stretching, the haze is increased to some extent, but the optical expression can be further enhanced.
On the other hand, when sequentially biaxially stretching, it is preferable to first stretch in a direction parallel to the film transport direction and then stretch in a direction orthogonal to the film transport direction. A more preferable range of the stretching temperature at which the successive stretching is performed is the same as the stretching temperature range at which the simultaneous biaxial stretching is performed.

<Heat treatment process>
The film production method of the present invention is preferably provided with a heat treatment step after the drying step. The heat treatment in the heat treatment step may be performed after completion of the drying step, and may be performed immediately after the stretching / drying step, or may be separately provided only after the winding process is performed by a method described later after the completion of the drying step. . In the present invention, it is preferable to provide the heat treatment step again after the drying step is once cooled to room temperature to 100 ° C. or less. This is because a film having better thermal dimensional stability can be obtained. For the same reason, it is preferable that the amount of residual solvent is dried to less than 2% by mass, preferably less than 0.4% by mass immediately before the heat treatment step.

The heat treatment is performed by a method of applying a wind at a predetermined temperature to the film being conveyed or a method using a heating means such as a microwave.
The heat treatment is preferably performed at a temperature of 150 to 200 ° C., more preferably 160 to 180 ° C. The heat treatment is preferably performed for 1 to 20 minutes, more preferably 5 to 10 minutes.

(Heated steam treatment)
In addition, the stretched film may be manufactured through a process of spraying steam heated to 100 ° C. or higher. By passing through this water vapor spraying step, the residual stress of the manufactured optical film is relaxed, and the dimensional change is reduced, which is preferable. The temperature of the water vapor is not particularly limited as long as it is 100 ° C. or higher, but considering the heat resistance of the film, the temperature of the water vapor is 200 ° C. or lower.

<Surface treatment process>
When the optical film of the present invention is used as a protective film for a polarizing plate and adhered to a polarizer, from the viewpoint of adhesion to the polarizer, a treatment for making the surface hydrophilic by alkali saponification treatment should be performed. Is particularly preferred.
As the optical film surface treatment, acid treatment, plasma treatment, corona treatment and the like are known, but it is required that an alkaline saponification treatment with low cost and good adhesion can be adopted. In the optical film of the present invention, since the B layer mainly comprising a specific cellulose acylate is provided as an outer layer on at least one surface of the A layer, the B layer is simply subjected to alkali treatment (alkali saponification). Adhesiveness at the time of bonding with a polyvinyl alcohol polarizer usually used as a polarizer is improved. As a result, in the polarizing plate reworking process, film peeling from the polarizer hardly occurs and reworkability can be improved.
The optical film of the present invention has a B layer containing a first cellulose acylate and a second cellulose acylate having different acyl substitution degrees from each other, and the inclusion of the first cellulose acylate in the second cellulose acylate The ratio is 90/10 to 60/40 (mass ratio), and the acyl substitution degree of the second cellulose acylate satisfies at least one of the formula (1) and the formulas (2A) and (2B). By having the B layer having such a configuration, the optical film of the present invention is an optical film in which the layer mainly composed of an acrylic resin is the outermost layer on the polarizer side, or only one type of cellulose acylate and an acrylic resin. With respect to the optical film in which the mixed layer is the outermost layer on the polarizer side, the adhesiveness to the polarizer by the conventional alkali saponification technique and the interfacial adhesion between the layers are excellent.

[Polarizer]
The optical film of the present invention can be used as a protective film in a polarizing plate having a polarizer and a protective film disposed on at least one side thereof.

  Moreover, in the form which arrange | positions a protective film on both surfaces of a polarizer as a structure of a polarizing plate, it can also be used as one protective film or retardation film.

  Examples of the polarizer include an iodine polarizer, a dye polarizer using a dichroic dye, and a polyene polarizer. In general, iodine-based polarizers and dye-based polarizers can be produced using polyvinyl alcohol-based films.

As the polarizer, a known polarizer or a polarizer cut out from a long polarizer whose absorption axis is neither parallel nor perpendicular to the longitudinal direction may be used. A long polarizer whose absorption axis is not parallel or perpendicular to the longitudinal direction is produced by the following method.
That is, it stretches by applying tension while holding both ends of a polymer film such as a polyvinyl alcohol film continuously supplied by a holding means, and stretches at least 1.1 to 20.0 times in the film width direction. The difference between the longitudinal travel speeds of the holding devices at both ends of the film is within 3%, and the angle formed between the traveling direction of the film at the exit of the step of retaining both ends of the film and the substantial stretching direction of the film is inclined by 20 to 70 °. In addition, the film traveling direction can be produced by a stretching method in which the film is bent while both ends of the film are held. In particular, those inclined by 45 ° are preferably used from the viewpoint of productivity.

[Liquid Crystal Display]
The optical film of the present invention is suitably used for an image display device such as a liquid crystal display device (LCD), a plasma display panel (PDP), an electroluminescence display (ELD), or a cathode ray tube display device (CRT).

  The optical film of the present invention and the polarizing plate of the present invention can be advantageously used for an image display device such as a liquid crystal display device, and are preferably used for the outermost layer on the backlight side.

In general, a liquid crystal display device has a liquid crystal cell and two polarizing plates arranged on both sides thereof, and the liquid crystal cell carries a liquid crystal between two electrode substrates. Furthermore, one optically anisotropic layer may be disposed between the liquid crystal cell and one polarizing plate, or two optically anisotropic layers may be disposed between the liquid crystal cell and both polarizing plates.
The liquid crystal cell is preferably in TN mode, VA mode, OCB mode, IPS mode or ECB mode.

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

[Measuring method]
<Weight average molecular weight measurement conditions>
The weight average molecular weight was measured by gel permeation chromatography. The measurement conditions are as follows.
Solvent Tetrahydrofuran apparatus name TOSOH HLC-8220GPC
Three columns TOSOH TSKgel Super HZM-H (4.6 mm × 15 cm) were connected and used.
Column temperature 25 ° C
Sample concentration 0.1% by mass
Flow rate 0.35ml / min
Calibration curve A calibration curve with 7 samples from TOSOH TSK standard polystyrene Mw = 2800000-1050 was used.

(Re, Rth)
After adjusting the sample film for 24 hours at 25 ° C. and 60% relative humidity, the film surface was measured using an automatic birefringence meter (KOBRA-21ADH: manufactured by Oji Scientific Instruments) at 25 ° C. and 60% relative humidity. The phase difference at a wavelength of 590 nm was measured from the direction inclined in increments of 10 ° from + 50 ° to −50 ° from the normal to the film surface with the vertical direction and the slow axis as the rotation axis. ) And the retardation value (Rth) in the film thickness direction.

(Haze)
The haze was measured in accordance with JIS K-6714 using a haze meter “HGM-2DP” (manufactured by Suga Test Instruments Co., Ltd.) with a film sample of 40 mm × 80 mm at 25 ° C. and a relative humidity of 60%.

(Photoelastic coefficient)
A 1 cm × 5 cm sample is cut out from the produced optical film, and the retardation value in the film plane is measured using a spectroscopic ellipsometer (M-220, manufactured by JASCO Corporation) while stressing the sample at 25 ° C. And calculated from the slope of the retardation value and the stress function.

(Brittle)
In accordance with JIS P8115, a bending test was performed with an MIT testing machine, and the number of foldings was measured. The number of folding times must be one or more for practical use.
The folding endurance number is preferably 10 times or more, and more preferably 30 times or more.

[Examples 1-7 and Comparative Examples 1-11]
<Production of dope>
A core layer dope and an outer layer dope were prepared according to the composition of Table 4 below, and 10 parts by mass of plasticizer A was added to each dope with respect to 100 parts by mass of the thermoplastic resin. The plasticizer A is a condensate of adipic acid / propylene glycol (number average molecular weight = 1000, terminal acetyl ester residue).
Here, in Example 1, a dope was prepared using a dope solvent having the composition described in Table 4 below. The core layer dope (A) had a solid content concentration of 20% by mass and a complex viscosity of 40 Pa · s. The dope (B) had a solid concentration of 18% by mass and a complex viscosity of 20 Pa · s. In other examples, the core layer dope (A) has a solid content concentration of 18 to 22% by mass and a complex viscosity of 20 to 60 Pa · s, and the outer layer dope (B) has a solid content concentration of 16 to 22% by mass and a complex viscosity. It adjusted to 10-30 Pa.s.
In Table 4 below, PMMA represents polymethyl methacrylate, number average molecular weight = 1,500,000.
As cellulose acylates CA-1 to CA-6 described in Table 4 below, those shown in Table 3 below were used. In Table 3, X, Y, and n have the same meanings as X, Y, and n in Formula (1), Formula (2A), and Formula (2B).

<Film forming conditions>
Solution casting film formation was performed using the dope described in Table 4 below, and an optical film was prepared so as to have the configuration shown in Table 4 below. Specifically, it was cast so as to have the layer configuration described in Table 4 on a metal support through a casting gicer capable of co-casting with three layers. At this time, casting was performed so as to be a B layer, an A layer, and a B layer in this order from the metal support surface side. The film thickness configuration is a converted film thickness when it is assumed that a film having a uniform thickness is formed from each dope flow rate. While on the metal support, the dope was dried with a drying air at 40 ° C. to form a film, and then peeled off. Both ends of the film were fixed with pins, and 5 ° C. with a drying air of 105 ° C. while maintaining the same interval. Dried for minutes. After removing the pin, it was further dried at 130 ° C. for 20 minutes.
In addition, about the film of the comparative example 7, the single layer PMMA film was formed using only the center part of the casting Giesser in which 3 layer co-casting is possible.
In Comparative Example 8, the same PMMA as the PMMA used for the core layer dope (A) was used as the main component of the outer layer dope (B) instead of the first cellulose acylate.
Comparative Example 9 was the same as Example 2 except that PMMA used for the core layer dope (A) was acrylic 2 (PMMA resin having a weight average molecular weight of 670000), which is an acrylic resin having a weight average molecular weight of 1,000,000 or less. As a result, the surface condition deteriorated significantly during the film formation, and the film could not be collected.

<Evaluation of optical film>
The optical films prepared in each Example and Comparative Example were used as the optical films of Examples 1 to 5 and Comparative Examples 1 to 7, respectively.
About the obtained optical film of each Example and a comparative example, according to said measuring method, Re, Rth, haze, a photoelastic coefficient, and the frequency | count of folding were evaluated. The results are shown in Table 4 below.

<Preparation of polarizing plate>
After immersing each optical film and Fujitac TD60UL (manufactured by FUJIFILM Corporation) prepared in each Example and Comparative Example for 1 minute in a 4.5 mol / L sodium hydroxide aqueous solution (saponification solution) adjusted to 37 ° C. The film was washed with water, then immersed in a 0.05 mol / L sulfuric acid aqueous solution for 30 seconds, and then passed through a washing bath. Then, draining with an air knife was repeated three times, and after dropping the water, the film was retained in a drying zone at 70 ° C. for 15 seconds and dried to produce a saponified film.
According to Example 1 of Japanese Patent Laid-Open No. 2001-141926, a peripheral speed difference was given between two pairs of nip rolls, and the film was stretched in the longitudinal direction to prepare a polarizer having a thickness of 20 μm.
Two polarizers were selected from the polarizer thus obtained and the saponified film, and the polarizer was sandwiched between them. Then, a 3% aqueous solution of PVA (manufactured by Kuraray Co., Ltd., PVA-117H) was used as an adhesive. As a polarizing plate of each example and a comparative example, it bonded together by roll-to-roll so that the polarizing axis and the longitudinal direction of a film might intersect orthogonally. Here, one film of the polarizer was a film obtained by saponifying the optical film of each Example or Comparative Example shown in Table 4, and the other film was a film obtained by saponifying Fujitac TD60UL.

<Polarizer reworkability>
The polarizing plate of each Example and Comparative Example processed in this way was cut out in a size of 4 cm square parallel to the absorption axis, and the sample surface was bonded to a glass plate using an adhesive SK-2057 manufactured by Soken Chemical Co., Ltd. This polarizing plate was peeled in the direction of 45 ° with respect to the absorption axis, and evaluated according to the following criteria from the degree of peeling between the polarizer and the sample film. Ranks 4 and 5 are practically required levels.
5: No film peeling occurs on the glass side.
4: The area of the film left unstripped on the glass side is 1/4 or less of the bonded area.
3: The area of the film left unstripped on the glass side exceeds 1/4 of the bonded area and is 1/2 or less.
2: The area of the film left unstripped on the glass side exceeds 1/2 of the bonded area and is 3/4 or less.
1: The area of the film left unstripped on the glass side exceeds 3/4 of the bonded area.
The evaluation results are shown in Table 4 below.

From the said Table 4, the optical film of each Example had a small photoelastic coefficient, and was low haze. Moreover, since the reworkability was good, it was found that the adhesiveness to the polarizer and the interfacial adhesion between the respective layers by the conventional alkali saponification technique were also excellent.
On the other hand, it was found that the optical film of Comparative Example 1 had a high ratio of cellulose acylate having a high degree of substitution of acyl groups having 3 to 7 carbon atoms in the outer layer, and the brittleness and reworkability were deteriorated.
The optical film of Comparative Example 2 was obtained by adding cellulose acetate CA-2 having a low substitution degree to the core layer and the outer layer as a cellulose acylate that does not satisfy any of the above formulas (1) to (3). The film had high haze, and the adhesion between each layer was not improved sufficiently. Without being bound by any theory, it was speculated that the main cause was that CA-2 did not mix with the acrylic resin in the core layer.
The optical film of Comparative Example 3 is obtained by adding cellulose acylate CA-3, which has a high propionyl substitution degree and does not satisfy both the above formulas (2) and (3), to the core layer and the outer layer, and has an effect of improving adhesion It was insufficient.
The optical film of Comparative Example 4 is obtained by adding cellulose acylate CA-4 not satisfying the above formula (1) to the core layer and the outer layer, and the obtained film has high haze and improves adhesion between the layers. It was insufficient. Although not bound by any theory, it was speculated that the main cause was that CA-4 did not mix with the acrylic resin in the core layer.
The optical film of Comparative Example 5 was obtained by adding cellulose acylate CA-5, which has a high butyryl substitution degree and does not satisfy both the above formulas (2) and (3), to the core layer and the outer layer, and had a high haze. . Although not bound by any theory, it was speculated that the main cause was that CA-5 was not mixed with the first cellulose acylate of the outer layer.
The optical film of Comparative Example 6 is a PMMA / CA-1 / PMMA three-layer co-cast film, and is an example in which the second cellulose acylate is not blended as the second resin component in the outer layer. The adhesion of was insufficient.
The optical film of Comparative Example 7 was a single layer film in which PMMA and cellulose acylate CA-3 were blended, and the reworkability was poor.
The optical film of Comparative Example 8 is a film using the same PMMA as the PMMA used for the core layer dope (A) instead of the first cellulose acylate as the main component of the outer layer dope (B). Reworkability was bad.

(Display performance evaluation in IPS liquid crystal display device)
The polarizing plate sandwiching the liquid crystal cell is peeled off from a commercially available liquid crystal television (IPS mode slim type 42-inch liquid crystal television), and the produced polarizing plates of the examples and comparative examples are shown in Table 4 It re-bonded to the liquid crystal cell via the adhesive so that the optical film side of an example and a comparative example may be arrange | positioned at the liquid crystal cell side. The reassembled LCD TV was held in an environment of 50 ° C. and relative humidity 80% for 3 days, then moved to an environment of 25 ° C. and relative humidity 60%, kept on in a black display state, and visually observed after 48 hours. Light unevenness was evaluated.
As a result, it was found that the liquid crystal display device of each example had less light unevenness than the liquid crystal display device of each comparative example.

101 Casting equipment 102 Drum 14 Casting die 12 Dope PS Casting start position 105 Condensing plate 53 Liquid receiver 56 Recovery tank 36 Film 37 Stripping roller

Claims (20)

A layer containing an acrylic resin having a weight average molecular weight exceeding 1,000,000,
Having a B layer comprising a first cellulose acylate and a second cellulose acylate, which are laminated on at least one surface of the A layer and have different degrees of acyl substitution.
The content ratio of the acylate of the first cellulose to the second cellulose acylate is 90/10 to 60/40 (mass ratio),
An optical film characterized in that the acyl substitution degree of the second cellulose acylate satisfies at least one of the following formula (1) and the following formulas (2A) and (2B).
Formula (1) 2.55 ≦ X + Y ≦ 3.0
Formula (2A) 0.2 ≦ Y ≦ 1.2
(In formulas (1) and (2A), X represents the acetyl substituent of the second cellulose acylate, and Y represents the degree of substitution of the acyl group having 3 to 7 carbon atoms of the second cellulose acylate.)
Formula (2B) −0.075n + 0.72 ≦ DS (n) ≦ −0.33n + 2.88
(In Formula (2B), DS (n) represents the degree of substitution of the acyl group having n carbon atoms in the second cellulose acylate, and n represents an integer of 3 to 7.)   2. The optical film according to claim 1, wherein the second cellulose acylate of the B layer satisfies the formula (2B).   The optical film according to claim 1 or 2, wherein the second cellulose acylate of the B layer satisfies the formula (2A).   The optical film according to any one of claims 1 to 3, wherein the acrylic resin used as a main component in the A layer has a weight average molecular weight of more than 1,000,000 and 1,800,000 or less.   The optical film according to any one of claims 1 to 4, wherein the polymer contained in the B layer has a weight average molecular weight of 100,000 or more and is only cellulose acylate.   The optical film according to claim 1, wherein the acrylic resin used as a main component in the A layer is made of polymethyl methacrylate. The layer A includes cellulose acylate satisfying at least one of the formula (1) and the formulas (2) and (3),
The optical film according to claim 1, wherein a content ratio of the acrylic resin to the cellulose acylate is 95/5 to 80/20 (mass ratio).   The acyl group of the first cellulose acylate of the B layer is an acetyl group, and the degree of acetyl substitution is 2.7 to 3.0. Optical film. The film thickness of the B layer is 1 μm to 10 μm,
The film thickness of the whole film is 20 micrometers-80 micrometers, The optical film as described in any one of Claims 1-8 characterized by the above-mentioned.   The optical film according to any one of claims 1 to 9, wherein a haze value is 0.3% or less. The optical film according to any one of claims 1 to 10 the value of the photoelastic coefficient is equal to or is ^{-5.0 × 10 -12 Pa -1 ~5.0 ×} 10 -12 Pa -1 . The retardation Re in the in-plane direction defined by the following formula (I) and the retardation Rth in the film thickness direction defined by the following formula (II) are represented by the following formula (III) and The optical film according to claim 1, wherein the following formula (IV) is satisfied.
Formula (I) Re = (nx−ny) × d
Formula (II) Rth = {(nx + ny) / 2−nz} × d
Formula (III) | Re | <10 nm
Formula (IV) | Rth | <25 nm
(In the formulas (I) to (IV), nx is the refractive index in the slow axis direction in the film plane, ny is the refractive index in the fast axis direction in the film plane, and nz is in the thickness direction of the film. (Refractive index, d is the film thickness (μm).) At least two types of dopes (A) and (B) containing a thermoplastic resin and a solvent are cast on the casting substrate simultaneously or sequentially in the order of (B)-(A) from the casting substrate side. Including steps,
The dope (A) contains an acrylic resin having a weight average molecular weight exceeding 1,000,000.
The dope (B) contains a first cellulose acylate and a second cellulose acylate having different acyl substitution degrees,
The content ratio of the first cellulose acylate to the second cellulose acylate in the dope (B) is 90/10 to 60/40 (mass ratio),
The method for producing an optical film, wherein the acyl substitution degree of the second cellulose acylate satisfies at least one of the following formula (1) and the following formulas (2A) and (2B).
Formula (1) 2.55 ≦ X + Y ≦ 3.0
Formula (2A) 0.2 ≦ Y ≦ 1.2
(In formulas (1) and (2A), X represents the acetyl substituent of the second cellulose acylate, and Y represents the degree of substitution of the acyl group having 3 to 7 carbon atoms of the second cellulose acylate.)
Formula (2B) −0.075n + 0.72 ≦ DS (n) ≦ −0.33n + 2.88
(In Formula (2B), DS (n) represents the degree of substitution of the acyl group having n carbon atoms in the second cellulose acylate, and n represents an integer of 3 to 7.)   The optical film according to claim 13, wherein the second cellulose acylate of the dope (B) satisfies the formula (2B).   The optical film according to claim 13 or 14, wherein the second cellulose acylate of the dope (B) satisfies the formula (2A).   As the solvent, methylene chloride and a lower alcohol having 1 to 4 carbon atoms are used, and the content ratio of methylene chloride to the lower alcohol having 1 to 4 carbon atoms is in a range of 90/10 to 60/40 (volume ratio). The method for producing an optical film according to claim 13, wherein:   The optical film according to any one of claims 13 to 16, wherein the polymer contained in the dope (B) has a weight average molecular weight of 100,000 or more and is only cellulose acylate.   The optical film manufactured by the manufacturing method of the optical film as described in any one of Claims 13-17.   A polarizing plate comprising a polarizer and the optical film according to claim 1.   A liquid crystal display device comprising the optical film according to claim 1 or the polarizing plate according to claim 19.

Images