JP2013019979A - Optical film and polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film containing a specific acrylic resin which can easily adhere to a polarizer by an alkali saponification process as in the case of conventional cellulose ester and has an excellent humidity resistance (low moisture absorption property), and to provide a polarizing plate having excellent durability.SOLUTION: An optical film contains an acrylic resin (A) which is obtained by copolymerizing an ethylenically unsaturated monomer having an acetoxy group. The percentage content of the ethylenically unsaturated monomer having an acetoxy group to the total amount of the optical film is in the range of 20-100 mass%.

Description

  The present invention relates to an optical film and a polarizing plate. More specifically, an optical film having a specific acrylic resin that can be easily bonded to a polarizer by alkali saponification treatment as in the case of a conventional cellulose ester and having excellent moisture resistance (low moisture absorption) and the optical film are provided. And a polarizing plate having excellent durability.

  Cellulose ester films are applied to various optical films because they are excellent in transparency and optical isotropy. In addition, since the film surface can be hydrophilized by alkali saponification treatment, it has good adhesion to the polarizer, is particularly suitable for a polarizing plate protective film, and is an indispensable member for liquid crystal display devices. .

  By the way, with the recent advancement of technology, the thinning of the liquid crystal display device has been accelerated, and the cellulose ester film used as a polarizing plate protective film has been required to be thin.

  However, in such an application, since the cellulose ester film has high moisture permeability, sufficient moisture resistance cannot be obtained, and there has been a problem that the performance of the polarizing plate deteriorates due to long-term use.

  On the other hand, as a low hygroscopic optical film material, polymethyl methacrylate, which is a representative of acrylic resin, has been used suitably for optical films because it exhibits excellent transparency and dimensional stability in addition to low hygroscopicity. .

  However, since an acrylic film cannot hydrophilize the film surface by alkali saponification treatment like a cellulose ester film, a polarizing plate cannot be produced by a conventional bonding method.

  On the other hand, since an acrylic resin can synthesize various copolymers, an acrylic resin having characteristics suited to the application can be used. For this reason, if an acrylic film using an acrylic resin copolymerized with a hydrophilic monomer is used, a polarizing plate can be produced by a conventional adhesion method without performing an alkali saponification treatment like a cellulose ester film. it can.

  However, an acrylic film copolymerized with a hydrophilic monomer has a high moisture permeability like the cellulose ester film because the film itself is hydrophilic, so that sufficient moisture resistance cannot be obtained. The problem that the performance of the polarizing plate deteriorated occurred. Thus, it has been very difficult to achieve both moisture resistance and polarizer adhesion at the same time.

  For this reason, for example, Patent Documents 1 and 2 propose a method of easily bonding the film surface and a method of manufacturing a polarizing plate using a new adhesive.

  However, since these methods are expensive or cannot be applied to conventional polarizing plate manufacturing factories, there has been a demand for a polarizing plate protective film capable of manufacturing a polarizing plate by the same adhesion method as the cellulose ester film.

JP 2010-204622 A JP 2011-028234 A

  The present invention has been made in view of the above problems and circumstances, and a solution to the problem is an optical film containing a specific acrylic resin, which can be easily obtained by an alkali saponification treatment in the same manner as a conventional cellulose ester. It is possible to provide an optical film that can be bonded together and is excellent in moisture resistance (low moisture absorption). Moreover, it is providing the polarizing plate excellent in durability.

  As a result of various studies on acrylic resins in order to solve the above problems, the present inventor found an acrylic structure capable of hydrophilizing the film surface by alkali saponification treatment, such as a cellulose ester film. A means capable of simultaneously improving the adhesiveness has been found and the present invention has been achieved.

  That is, the said subject which concerns on this invention is solved by the following means.

  1. An optical film containing an acrylic resin (A) obtained by copolymerizing an ethylenically unsaturated monomer having an acetoxy group, wherein the content of the ethylenically unsaturated monomer having an acetoxy group is the total amount of the optical film On the other hand, the optical film is in the range of 20 to 100% by mass.

  2. The first aspect of the invention, wherein an average water contact angle on the film surface falls within a range of 10 to 55 degrees when alkali saponification treatment is carried out for 60 seconds with a 1.5N KOH solution at 40 ° C. An optical film according to item.

3. The acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio within the range of (A) :( B) = 95: 5 to 20:80, or the acrylic resin (A) and the acrylic resin are contained. The resin (C) and the cellulose ester resin (B) are contained in a mass ratio within the range of ((A) + (C)) :( B) = 95: 5 to 20:80, and the following requirement (a) The optical film according to the first or second item, which satisfies the following (c).
(A) The weight average molecular weight Mw of the acrylic resin (A) is in the range of 1000 to 1000000.
(B) The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is in the range of 2.0 to 3.0, and the weight average molecular weight Mw is in the range of 20000 to 500,000.
(C) The weight average molecular weight Mw of the acrylic resin (C) is in the range of 80000 to 1000000.

  4). The optical film as described in any one of said 1st term | claim-3rd term | claim is comprised, The polarizing plate characterized by the above-mentioned.

  By the above means of the present invention, an optical film containing a specific acrylic resin, which can be easily bonded to a polarizer by an alkali saponification treatment in the same manner as a conventional cellulose ester, and has moisture resistance (low moisture absorption). It is possible to provide an optical film excellent in the above. In addition, a polarizing plate having excellent durability can be provided.

The figure which showed typically an example of the dope preparation process, casting process, and drying process of the solution casting film forming method used for this invention

  The optical film of the present invention is an optical film containing an acrylic resin (A) obtained by copolymerizing an ethylenically unsaturated monomer having an acetoxy group, and the content of the ethylenically unsaturated monomer having the acetoxy group However, it exists in the range of 20-100 mass% with respect to the total amount of an optical film, It is characterized by the above-mentioned. This feature is a technical feature common to the inventions according to claims 1 to 4.

  As an embodiment of the present invention, from the viewpoint of manifestation of the effect of the present invention, when an alkali saponification treatment is carried out for 60 seconds with a KOH solution at 40 ° C. and 1.5 N, the average water contact angle on the film surface is 10 to 10. It is preferable to be within the range of 55 degrees. Further, the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio within the range of (A) :( B) = 95: 5 to 20:80, or the acrylic resin (A). And the acrylic resin (C) and the cellulose ester resin (B) at a mass ratio within the range of ((A) + (C)) :( B) = 95: 5 to 20:80, and the above requirements ( It is preferable that a) to (c) are satisfied.

  The optical film of the present invention can be suitably included in a polarizing plate.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit.

[Outline of optical film]
The optical film of the present invention is an optical film containing an acrylic resin (A) obtained by copolymerizing an ethylenically unsaturated monomer having an acetoxy group, and the content of the ethylenically unsaturated monomer having the acetoxy group However, it exists in the range of 20-100 mass% with respect to the total amount of an optical film, It is characterized by the above-mentioned. In the present invention, based on this characteristic, the film surface can be easily hydrophilized by alkali saponification treatment, and the adhesiveness with the polarizer is improved. In this regard, it is preferable that the average water contact angle on the film surface falls within the range of 10 to 55 degrees when alkali saponification treatment is performed for 60 seconds with a 40 ° C., 1.5N KOH solution.

In the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio within the range of (A) :( B) = 95: 5 to 20:80, or the acrylic resin. (A), acrylic resin (C), and cellulose ester resin (B) are contained in a mass ratio within the range of ((A) + (C)) :( B) = 95: 5 to 20:80, and A polarizing plate that has excellent moisture resistance (low hygroscopicity) as an optical film satisfying the following requirements (a) to (c) and has excellent durability when used as a protective film for a polarizing plate. Is preferable because it can be provided.
(A) The weight average molecular weight Mw of the acrylic resin (A) is in the range of 1000 to 1000000.
(B) The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is in the range of 2.0 to 3.0, and the weight average molecular weight Mw is in the range of 20000 to 500,000.
(C) The weight average molecular weight Mw of the acrylic resin (C) is in the range of 80000 to 1000000.
<Acrylic resin (A)>
The acrylic resin (A) used in the present invention is an acrylic resin obtained by copolymerizing an ethylenically unsaturated monomer having an acetoxy group.

  Although it does not restrict | limit especially as resin to copolymerize, the ethylenically unsaturated monomer (monomer) unit which has an acetoxy group is 20-100 mass%, and the other monomer (monomer) copolymerizable with this Body) Those consisting of 80 to 0% by mass of units are preferred.

  When the ethylenically unsaturated monomer (monomer) unit having an acetoxy group is 20% by mass or less, the water contact angle does not become 55 ° or less even after alkali saponification treatment, and the adhesion to the polarizer is lowered. Therefore, it is not preferable.

  Examples of other copolymerizable monomers (monomers) include alkyl methacrylates having 2 to 18 carbon atoms in alkyl number, alkyl acrylates having 1 to 18 carbon atoms in 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-unsaturated compounds such as acrylonitrile and methacrylonitrile Saturated 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.

  Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, styrene, and the like are preferable from the viewpoint of thermal decomposition resistance and fluidity of the copolymer. Acrylate and n-butyl acrylate are particularly preferably used.

  The acrylic resin (A) used in the optical film of the present invention has a weight average molecular weight (Mw) of 1000 to 1000, particularly from the viewpoint of improving transparency and improving brittleness when it is compatible with other resins as an optical film. It is in the range of 1000000. In particular, from the viewpoint of compatibility with other resins, the weight average molecular weight (Mw) is preferably 1,000 to 300,000, and when the acrylic resin (A) is used alone, the weight average molecular weight (Mw) is 100,000 to 1,000,000. It is preferable. When the weight average molecular weight (Mw) is smaller than 1000, it is not preferable because the brittleness is deteriorated when used by being compatible with other resins. Moreover, when a weight average molecular weight (Mw) is larger than 1000000, since transparency at the time of compatibility with other resin deteriorates, it is not preferable.

  The weight average molecular weight of the acrylic resin according to the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G
(Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

  There is no restriction | limiting in particular as a manufacturing method of the acrylic resin (A) in this invention, You may use any well-known methods, such as suspension polymerization, emulsion polymerization, block polymerization, or solution polymerization. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used. Regarding the polymerization temperature, suspension or emulsion polymerization may be performed at 30 to 100 ° C, and bulk or solution polymerization may be performed at 80 to 160 ° C. In order to control the reduced viscosity of the obtained copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

  Although the preferable specific example of the ethylenically unsaturated monomer (monomer) which has an acetoxy group used by this invention below is illustrated, it is not limited to these.

  In the present invention, the content of the ethylenically unsaturated monomer having an acetoxy group is in the range of 20 to 100% by mass with respect to the total amount of the optical film. This is preferable because the adhesion to the polarizer is improved.

<Cellulose ester resin (B)>
The cellulose ester resin (B) according to the present invention has an acyl group total substitution degree (T) of 2.0 to 3 from the viewpoint of transparency, particularly when improved in brittleness or compatible with the acrylic resin (A). 0.0 is preferred.

  In the present invention, the acyl group may be an aliphatic acyl group or an aromatic acyl group. In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes an acyl group substituent.

  When the said cellulose ester resin (B) has an aromatic acyl group as a substituent, it is preferable that the number of the substituents X substituted to an aromatic ring is 0-5. Also in this case, it is necessary to pay attention so that the substitution degree of the acyl group having 3 to 7 carbon atoms including the substituent is 1.2 to 3.0. For example, since the benzoyl group has 7 carbon atoms, when it has a substituent containing carbon, the benzoyl group has 8 or more carbon atoms and is not included in the acyl group having 3 to 7 carbon atoms. Become.

  Further, when the number of substituents substituted on the aromatic ring is 2 or more, they may be the same or different from each other, but they may be linked together to form a condensed polycyclic compound (for example, naphthalene, indene, indane, phenanthrene, quinoline). , Isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

  In the cellulose ester resin (B) as described above, having a structure having at least one kind of an aliphatic acyl group having 2 to 7 carbon atoms is used as a structure used for the cellulose resin according to the present invention.

  As for the substitution degree of the cellulose ester resin (B) according to the present invention, the total substitution degree (T) of the acyl group is 2.0 to 3.0. The cellulose ester resin (B) is particularly preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate.

  Among these, cellulose ester resins that are particularly preferred are cellulose acetate propionate and cellulose propionate.

  The portion that is not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

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

  The weight average molecular weight (Mw) of the cellulose ester resin according to the present invention is 20000 or more, particularly in the range of 20000 to 500000, from the viewpoint of improving compatibility with the acrylic resin (A) and improving brittleness. In the present invention, two or more kinds of cellulose resins can be mixed and used.

  In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 20:80 and in a compatible state, preferably 90:10 to 50. : 50, more preferably 80:20 to 60:40.

  If the mass ratio of the acrylic resin (A) and the cellulose ester resin (B) is more than 95: 5, the effect of the cellulose ester resin (B) cannot be sufficiently obtained, and the mass ratio is When the amount of acrylic resin is less than 20:80, the moisture resistance becomes insufficient.

  In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) must be contained in a compatible state.

  Whether the acrylic resin (A) and the cellulose ester resin (B) are in a compatible state can be determined by, for example, the glass transition temperature Tg.

  For example, when the glass transition temperatures of the two resins are different, when the two resins are mixed, there are two or more glass transition temperatures of the mixture because there is a glass transition temperature of each resin. When they are compatible, the glass transition temperature specific to each resin disappears and becomes one glass transition temperature, which becomes the glass transition temperature of the compatible resin.

  In addition, the glass transition temperature here is the intermediate | middle calculated | required according to JISK7121 (1987), using the differential scanning calorimeter (DSC-7 type | mold by Perkin Elmer), measured with the temperature increase rate of 20 degree-C / min. The point glass transition temperature (Tmg).

  The acrylic resin (A) and the cellulose ester resin (B) are each preferably an amorphous resin, and either one may be a crystalline polymer or a partially crystalline polymer. In the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably compatible with each other to become an amorphous resin.

  In the optical film of the present invention, the weight average molecular weight (Mw) of the acrylic resin (A), the weight average molecular weight (Mw) of the cellulose ester resin (B), and the degree of substitution are different in solubility in the solvent of both resins. It is obtained by measuring each after use. When fractionating the resin, it is possible to extract and separate the soluble resin by adding a compatible resin in a solvent that is soluble only in either one. At this time, heating operation or reflux is performed. May be. A combination of these solvents may be combined in two or more steps to separate the resin. The dissolved resin and the resin remaining as an insoluble matter are filtered off, and the solution containing the extract can be separated by an operation of evaporating the solvent and drying. These fractionated resins can be identified by general structural analysis of polymers. When the optical film of the present invention contains a resin other than the acrylic resin (A) and the cellulose ester resin (B), it can be separated by the same method.

  If the weight average molecular weights (Mw) of the compatible resins are different, the high molecular weight substances are eluted earlier by gel permeation chromatography (GPC), and the lower molecular weight substances are eluted after a longer time. Therefore, it can be easily fractionated and the molecular weight can be measured.

  In addition, the molecular weight of the compatible resin is measured by GPC, and at the same time, the resin solution eluted every time is separated, the solvent is distilled off, and the dried resin is different by quantitatively analyzing the structure. By detecting the resin composition for each molecular weight fraction, it is possible to identify each compatible resin. By measuring the molecular weight distribution of each of the resins separated in advance based on the difference in solubility in a solvent by GPC, it is possible to detect each of the compatible resins.

  In the present invention, “containing acrylic resin (A) and cellulose ester resin (B) in a compatible state” means mixing each resin (polymer), resulting in a compatible state. This means that a state in which a precursor of acrylic resin such as monomer, dimer or oligomer is mixed with cellulose ester resin (B) and then polymerized by polymerization is not included. .

  For example, the process of obtaining a mixed resin by mixing a precursor of an acrylic resin such as a monomer, dimer or oligomer with the cellulose ester resin (B) and then polymerizing it is complicated by the polymerization reaction. The resin is difficult to control the reaction, and it is difficult to adjust the molecular weight. In addition, when a resin is synthesized by such a method, graft polymerization, cross-linking reaction or cyclization reaction often occurs. In many cases, the resin is soluble in a solvent or cannot be melted by heating. Since it is difficult to elute the resin and measure the weight average molecular weight (Mw), it is difficult to control the physical properties and it cannot be used as a resin for stably producing an optical film.

  Unless the function as an optical film is impaired, the optical film of this invention may contain resin and additives other than an acrylic resin (A) and a cellulose-ester resin (B), and may be comprised.

  When the resin other than the acrylic resin (A) and the cellulose ester resin (B) is contained, even if the added resin is in a compatible state, it may be mixed without being dissolved.

<Acrylic resin (C)>
The acrylic resin (C) used in the present invention includes a methacrylic resin. Although it does not restrict | limit especially as resin, What consists of 50-99 mass% of methyl methacrylate units and 1-50 mass% of other monomer (monomer) units copolymerizable with this is preferable.

  Examples of other copolymerizable monomers (monomers) include alkyl methacrylates having 2 to 18 carbon atoms in alkyl number, alkyl acrylates having 1 to 18 carbon atoms in 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-unsaturated compounds such as acrylonitrile and methacrylonitrile Saturated 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.

  Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable from the viewpoint of thermal decomposition resistance and fluidity of the copolymer. n-Butyl acrylate is particularly preferably used.

  The acrylic resin (C) used in the optical film of the present invention is particularly improved in brittleness as an optical film, improved in transparency when it is compatible with the acrylic resin (A) and the cellulose ester resin (B), and sufficiently brittle. From the viewpoint of improvement, the weight average molecular weight (Mw) is 80,000 to 1,000,000, more preferably 150,000 to 400,000. Since the acrylic resin (C) is not used alone, it fulfills the functions of brittle reinforcement and moisture resistance when it is compatible with other resins.

  The weight average molecular weight of the acrylic resin according to the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

  There is no restriction | limiting in particular as a manufacturing method of the acrylic resin (C) in this invention, Any of well-known methods, such as suspension polymerization, emulsion polymerization, block polymerization, or solution polymerization, may be used. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used. Regarding the polymerization temperature, suspension or emulsion polymerization may be performed at 30 to 100 ° C, and bulk or solution polymerization may be performed at 80 to 160 ° C. In order to control the reduced viscosity of the obtained copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

  A commercially available thing can also be used as an acrylic resin which concerns on this invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dialal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electric Chemical Co., Ltd.), etc. are mentioned. . Two or more acrylic resins can be used in combination.

<Acrylic particles (D)>
The optical film of the present invention can also contain acrylic particles.

  The acrylic particle (D) according to the present invention is a particle state (also referred to as an incompatible state) in an optical film containing the acrylic resin (A), (C) and the cellulose ester resin (B) in a compatible state. ) Represents an acrylic component present.

  The acrylic particles (D) are, for example, collected a predetermined amount of the produced optical film, dissolved in a solvent, stirred and sufficiently dissolved / dispersed. It is preferable that the weight of the insoluble matter filtered and collected using a PTFE membrane filter is 90% by mass or more of the acrylic particles (D) added to the optical film.

  The acrylic particles (D) used in the present invention are not particularly limited, but are preferably acrylic particles (D) having a layer structure of two or more layers, particularly the following multilayer structure acrylic granular composite. It is preferable.

  The multilayer structure acrylic granular composite is formed by laminating the innermost hard layer polymer, the cross-linked soft layer polymer exhibiting rubber elasticity, and the outermost hard layer polymer from the central portion toward the outer peripheral portion. This refers to a particulate acrylic polymer having a structure.

  That is, the multilayer structure acrylic granular composite is a multilayer structure acrylic granular composite comprising an innermost hard layer, a crosslinked soft layer, and an outermost hard layer from the central portion toward the outer peripheral portion. This three-layer core-shell multilayer acrylic granular composite is preferably used.

  Preferred embodiments of the multilayer structure acrylic granular composite used in the acrylic resin composition according to the present invention include the following. (A) a monomer comprising 80 to 98.9% by mass of methyl methacrylate, 1 to 20% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and 0.01 to 0.3% by mass of a polyfunctional grafting agent ( (B) an alkyl acrylate having 4 to 8 carbon atoms in the presence of the innermost hard layer polymer in the presence of the innermost hard layer polymer. Crosslinked soft layer polymer obtained by polymerizing a monomer (monomer) mixture comprising 5% by mass, multifunctional crosslinking agent 0.01 to 5% by mass and multifunctional grafting agent 0.5 to 5% by mass (C) In the presence of the polymer comprising the innermost hard layer and the crosslinked soft layer, from 80 to 99% by mass of methyl methacrylate and 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. Monomer (monomer) The outermost hard layer polymer obtained by polymerizing the mixture has a three-layer structure, and the obtained three-layer structure polymer is the innermost hard layer polymer (a) 5 to 40% by mass, the soft layer. It is composed of 30 to 60% by mass of the polymer (b) and 20 to 50% by mass of the outermost hard layer polymer (c), and has an insoluble part when fractionated with acetone, and the methyl ethyl ketone swelling degree of the insoluble part is 1. An acrylic granular composite that is 5 to 4.0.

  As disclosed in Japanese Patent Publication No. 60-17406 or Japanese Patent Publication No. 3-39095, not only the composition and particle size of each layer of the multilayer structure acrylic granular composite are defined, but also the multilayer structure acrylic granular composite. By setting the tensile modulus of the body and the degree of swelling of methyl ethyl ketone in the acetone-insoluble part within a specific range, it is possible to realize a further sufficient balance between impact resistance and stress whitening resistance.

  Here, the innermost hard layer polymer (a) constituting the multi-layer structure acrylic granular composite is 80 to 98.9% by mass of methyl methacrylate and 1 to 20% of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. % And a polyfunctional grafting agent obtained by polymerizing a monomer (monomer) mixture comprising 0.01 to 0.3% by mass is preferable.

  Here, examples of the alkyl acrylate having 1 to 8 carbon atoms in the alkyl group include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, and the like. And n-butyl acrylate are preferably used.

  The proportion of the alkyl acrylate unit in the innermost hard layer polymer (a) is 1 to 20% by mass. When the unit is less than 1% by mass, the thermal decomposability of the polymer is increased, while the unit is 20% by mass. If it exceeds 50%, the glass transition temperature of the innermost hard layer polymer (c) is lowered, and the impact resistance imparting effect of the three-layer structure acrylic granular composite is lowered.

  Examples of the polyfunctional grafting agent include polyfunctional monomers (monomers) having different polymerizable functional groups, such as allyl esters of acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Preferably used. The polyfunctional grafting agent is used to chemically bond the innermost hard layer polymer and the soft layer polymer, and the ratio used during the innermost hard layer polymerization is 0.01 to 0.3% by mass. .

  The crosslinked soft layer polymer (b) constituting the acrylic granular composite is an alkyl acrylate 75-98.5 having 1 to 8 carbon atoms in the presence of the innermost hard layer polymer (a). What is obtained by superposing | polymerizing the monomer (monomer) mixture which consists of a mass%, polyfunctional crosslinking agent 0.01-5 mass%, and polyfunctional grafting agent 0.5-5 mass% is preferable.

  Here, as the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group, n-butyl acrylate or 2-ethylhexyl acrylate is preferably used.

  In addition to these polymerizable monomers (monomers), it is also possible to copolymerize 25% by mass or less of other monofunctional monomers (monomers) that can be copolymerized.

  Examples of other monofunctional monomers (monomers) that can be copolymerized include styrene and substituted styrene derivatives. As for the ratio of the alkyl acrylate having 4 to 8 carbon atoms in the alkyl group and styrene, the glass transition temperature of the polymer (b) decreases as the former increases, that is, the ratio can be softened.

  On the other hand, from the viewpoint of the transparency of the resin assembly, the refractive index of the soft layer polymer (b) at room temperature is set to the innermost hard layer polymer (a), the outermost hard layer polymer (c), and the hard heat. It is more advantageous to make it closer to the plastic acrylic resin, and the ratio between them is selected in consideration of these.

  As the polyfunctional grafting agent, those mentioned in the item of the innermost layer hard polymer (a) can be used. The polyfunctional grafting agent used here is used to chemically bond the soft layer polymer (b) and the outermost hard layer polymer (c), and the proportion used during the innermost hard layer polymerization is impact resistance. 0.5-5 mass% is preferable from a viewpoint of the property provision effect.

  As the polyfunctional crosslinking agent, generally known crosslinking agents such as divinyl compounds, diallyl compounds, diacrylic compounds, and dimethacrylic compounds can be used, and polyethylene glycol diacrylate (molecular weight 200 to 600) is preferably used.

  The polyfunctional cross-linking agent used here is used to generate a cross-linked structure at the time of polymerization of the soft layer (b) and develop an effect of imparting impact resistance. However, if the above-mentioned polyfunctional grafting agent is used during the polymerization of the soft layer, the polyfunctional crosslinking agent is not an essential component because the crosslinked structure of the soft layer (b) is generated to some extent. Is preferably 0.01 to 5% by mass from the viewpoint of imparting impact resistance.

  In the presence of the innermost hard layer polymer (a) and the soft layer polymer (b), the outermost hard layer polymer (c) constituting the multilayer structure acrylic granular composite is 80 to 99 mass% of methyl methacrylate. % And a mixture obtained by polymerizing a monomer (monomer) mixture of 1 to 20% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group is preferable.

  Here, as the acrylic alkylate, those described above are used, and methyl acrylate and ethyl acrylate are preferably used. The ratio of the alkyl acrylate unit in the outermost hard layer (c) is preferably 1 to 20% by mass.

  Further, for the purpose of improving the compatibility with the acrylic resin (A) during the polymerization of the outermost hard layer (c), it is also possible to use an alkyl mercaptan or the like as a chain transfer agent in order to adjust the molecular weight.

  In particular, it is preferable to provide the outermost hard layer with a gradient such that the molecular weight gradually decreases from the inside toward the outside in order to improve the balance between elongation and impact resistance. As a specific method, by dividing the monomer mixture for forming the outermost hard layer into two or more and sequentially increasing the amount of chain transfer agent added each time, It is possible to reduce the molecular weight of the polymer forming the outermost hard layer from the inside to the outside of the multilayer structure acrylic granular composite.

  The molecular weight formed at this time can also be examined by polymerizing a mixture of monomers (monomers) used each time under the same conditions, and measuring the molecular weight of the obtained polymer.

  The particle diameter of the acrylic particles (D) preferably used in the present invention is not particularly limited, but is preferably 10 nm or more and 1000 nm or less, and more preferably 20 nm or more and 500 nm or less. In particular, the thickness is most preferably from 50 nm to 400 nm.

  In the acrylic granular composite that is a multilayer structure polymer preferably used in the present invention, the mass ratio of the core and the shell is not particularly limited, but when the entire multilayer structure polymer is 100 parts by mass, The core layer is preferably 50 parts by mass or more and 90 parts by mass or less, and more preferably 60 parts by mass or more and 80 parts by mass or less. In addition, the core layer here is an innermost hard layer.

  Examples of such commercially available multilayered acrylic granular composites include, for example, “Metablene” manufactured by Mitsubishi Rayon Co., “Kane Ace” manufactured by Kaneka Chemical Co., Ltd., “Paralloid” manufactured by Kureha Chemical Co., Ltd., Rohm and Haas "Acryloid" manufactured by KK, "Staffyroid" manufactured by Gantz Kasei Kogyo Co., Ltd., "Parapet SA" manufactured by Kuraray Co., Ltd., and the like can be used.

  Further, specific examples of the acrylic particles (d-1) which are graft copolymers preferably used as the acrylic particles (D) preferably used in the present invention include unsaturated carboxylic acids in the presence of a rubbery polymer. Acid ester monomer (monomer), unsaturated carboxylic acid monomer (monomer), aromatic vinyl monomer (monomer), and other vinyl monomers copolymerizable with these if necessary ( And a graft copolymer obtained by copolymerizing a mixture of monomers (monomers).

  Although there is no restriction | limiting in particular in the rubbery polymer used for the acrylic particle (d-1) which is a graft copolymer, Diene type rubber, acrylic type rubber, ethylene type rubber, etc. can be used. Specific examples include polybutadiene, styrene-butadiene copolymer, block copolymer of styrene-butadiene, acrylonitrile-butadiene copolymer, butyl acrylate-butadiene copolymer, polyisoprene, butadiene-methyl methacrylate copolymer, Butyl acrylate-methyl methacrylate copolymer, butadiene-ethyl acrylate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-isoprene copolymer, and ethylene-methyl acrylate copolymer A polymer etc. are mentioned. These rubbery polymers can be used alone or in a mixture of two or more.

  Moreover, when adding acrylic particle (D) to the optical film of this invention, the refractive index of the mixture of acrylic resin (A), (C) and cellulose-ester resin (B), and the refractive index of acrylic particle (D). Is close in terms of obtaining a highly transparent film. Specifically, the refractive index difference between the acrylic particles (D) and the acrylic resins (A) and (C) is preferably 0.05 or less, more preferably 0.02 or less, especially 0.01 or less. It is preferable.

  In order to satisfy such a refractive index condition, a method of adjusting each monomer (monomer) unit composition ratio of acrylic resins (A) and (C) and / or rubber used for acrylic particles (D) The refractive index difference can be reduced by a method of adjusting the composition ratio of the polymer or the monomer (monomer), and an optical film excellent in transparency can be obtained.

  Note that the difference in refractive index referred to here is a solution in which the optical film of the present invention is sufficiently dissolved in a solvent in which the acrylic resins (A) and (C) are soluble under suitable conditions, and this is centrifuged. By separating the solvent-soluble part and the insoluble part by the above operation, and purifying the soluble part (acrylic resins (A) and (C)) and the insoluble part (acrylic particles (D)), respectively, the measured refractive index was measured. The difference of (23 degreeC, measurement wavelength: 550nm) is shown.

  In the present invention, the method of blending the acrylic particles (D) with the acrylic resins (A) and (C) is not particularly limited, and after blending the acrylic resin (A) and other optional components in advance, usually 200 to At 350 ° C., a method of uniformly melt-kneading with a single-screw or twin-screw extruder while adding acrylic particles (D) is preferably used.

  Further, a method in which a solution in which acrylic particles (D) are dispersed in advance is added to and mixed with a solution (dope solution) in which acrylic resins (A), (C), and cellulose ester resin (B) are dissolved, or acrylic particles A method such as in-line addition of a solution in which (D) and other optional additives are dissolved and mixed can be used.

  A commercially available thing can also be used as an acrylic particle concerning this invention. For example, Metabrene W-341 (d-1) (manufactured by Mitsubishi Rayon Co., Ltd.), Chemisnow MR-2G (d-2), MS-300X (d-3) (manufactured by Soken Chemical Co., Ltd.), etc. be able to.

  In the optical film of the present invention, it is preferable to contain 0.5 to 30% by mass of acrylic particles (D) with respect to the total mass of the resin constituting the film, and in the range of 1.0 to 15% by mass. It is more preferable to contain.

<Peeling aid, antistatic agent>
Peeling aids and antistatic agents are present on the surface, absorb moisture in the air, increase the electrical conductivity, greatly reduce the surface resistance, and further partially agglomerate on the metal belt surface. , Improve the peelability of the dope. Examples of the compound include alkyl sulfonates and alkyl benzene sulfonates. Examples of the salt include sodium salt, potassium salt, amine salt, ammonium salt, phosphonium salt and the like.

  Specific examples include sodium decylsulfonate, sodium decylbenzenesulfonate, potassium decylbenzenesulfonate, sodium dodecylsulfonate, potassium dodecylsulfonate, sodium dodecylbenzenesulfonate, potassium dodecylbenzenesulfonate, tetrabutyl dodecylbenzenesulfonate. Ammonium, tetrabutylphosphonium dodecylbenzenesulfonate, sodium tetradecylsulfonate, sodium tetradecylbenzenesulfonate, potassium tetradecylbenzenesulfonate, sodium hexadecylsulfonate, sodium hexadecylbenzenesulfonate, potassium hexadecylbenzenesulfonate, etc. Is mentioned. Moreover, as these commercially available products, Clariant Japan Co., Ltd. Hostastat HS-1, Takemoto Yushi Co., Ltd. Elecut S-412-2, Elecut S-418, Kao Corporation Neo-Perex G65, etc. are mentioned. It is done.

  In addition, when using the resin composition which concerns on this invention for shaping | molding of the optical film of this invention, when shape | molding by the solution casting method, the content rate of a compound is preferably 0.05 with respect to 100 mass parts of resin. -5 parts by mass, particularly preferably 0.1-2 parts by mass. Moreover, when shape | molding by a melt extrusion method, Preferably it is 1-10 mass parts with respect to 100 mass parts of resin, Most preferably, it is 2-7 mass parts. This is because, in the solution casting method, the compound is likely to be unevenly distributed in the vicinity of the film surface as compared with the melt extrusion method, and sufficient antistatic performance can be exhibited even if the addition amount is small.

<Other additives>
In the optical film of the present invention, a plasticizer can be used in combination in order to improve the fluidity and flexibility of the composition. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  Of these, polyester and phthalate plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

  Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

  The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

  In particular, when adipic acid, phthalic acid or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

  The ester plasticizer may be any of ester, oligoester, and polyester types, and the molecular weight is preferably in the range of 100 to 10,000, and preferably in the range of 600 to 3000, which has a large plasticizing effect.

  The viscosity of the plasticizer has a correlation with the molecular structure and molecular weight. In the case of an adipic acid plasticizer, the viscosity is preferably in the range of 200 to 5000 MPa · s (25 ° C.) in view of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the optical film of the present invention. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use.

  The optical film of the present invention preferably contains an ultraviolet absorber, and examples of the ultraviolet absorber used include benzotriazole-based, 2-hydroxybenzophenone-based or salicylic acid phenyl ester-based ones. For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone And benzophenones.

  Here, among ultraviolet absorbers, ultraviolet absorbers having a molecular weight of 400 or more are less likely to volatilize at a high boiling point and are difficult to disperse even during high-temperature molding, so that the weather resistance is effectively improved with a relatively small amount of addition. be able to.

  Examples of the ultraviolet absorber having a molecular weight of 400 or more include 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole, 2,2-methylenebis [4- (1, 1,3,3-tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol], bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis ( Hindered amines such as 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonic acid Bis (1,2,2,6,6-pentamethyl-4-piperidyl), 1- [2- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] ethyl L] -4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy] -2,2,6,6-tetramethylpiperidine and the like, hindered phenol and hindered amine Examples include hybrid systems having both structures, and these can be used alone or in combination of two or more. Among these, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2-benzotriazole and 2,2-methylenebis [4- (1,1,3,3- Tetrabutyl) -6- (2H-benzotriazol-2-yl) phenol] is particularly preferred.

  Furthermore, various antioxidants can also be added to the optical film of the present invention in order to improve the thermal decomposability and thermal coloring during molding. It is also possible to add an antistatic agent to give the optical film antistatic performance.

  For the optical film of the present invention, a flame retardant acrylic resin composition containing a phosphorus flame retardant may be used.

  Phosphorus flame retardants used here include red phosphorus, triaryl phosphate ester, diaryl phosphate ester, monoaryl phosphate ester, aryl phosphonate compound, aryl phosphine oxide compound, condensed aryl phosphate ester, halogenated alkyl phosphorus. Examples thereof include one or a mixture of two or more selected from acid esters, halogen-containing condensed phosphate esters, halogen-containing condensed phosphonate esters, halogen-containing phosphite esters, and the like.

  Specific examples include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phenylphosphonic acid, tris (β-chloroethyl) phosphate, tris (dichloropropyl). Examples thereof include phosphate and tris (tribromoneopentyl) phosphate.

[Formation of optical film]
As a method for forming the optical film of the present invention, production methods such as an inflation method, a T-die method, a calendar method, a cutting method, a casting method, an emulsion method, and a hot press method can be used. From the standpoint of suppressing optical defects such as die lines and optical defects such as die lines, solution casting by casting is preferred.

<Organic solvent>
The organic solvent useful for forming the dope when the optical film of the present invention is produced by the solution casting method is acrylic resin (A), (C), cellulose ester resin (B), and other additives at the same time. Any material that can be dissolved can be used without limitation.

  For example, as the chlorinated organic solvent, methylene chloride, as the non-chlorinated organic solvent, methyl acetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro- Examples include 2-methyl-2-propanol, 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, and nitroethane. Methylene chloride, methyl acetate, ethyl acetate and acetone can be preferably used.

  In addition to the organic solvent, the dope preferably contains 1 to 40% by mass of a linear or branched aliphatic alcohol having 1 to 4 carbon atoms. When the proportion of alcohol in the dope increases, the web gels and peeling from the metal support becomes easy. When the proportion of alcohol is small, acrylic resins (A) and (C) in a non-chlorine organic solvent system are used. ) And also promote the dissolution of the cellulose ester resin (B).

  In particular, in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms, acrylic resin (A), (C), cellulose ester resin (B), and optionally acrylic particles It is preferable that it is a dope composition in which at least 15 to 45 mass% in total of the four types of (D) are dissolved.

  Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Ethanol is preferred because of the stability of these dopes, the relatively low boiling point, and good drying properties.

  Hereinafter, the preferable film forming method of the optical film of the present invention will be described.

1) Dissolution process In the dissolution vessel, the acrylic resin (A), (C), cellulose ester resin (A), (C), cellulose ester resin (B) are dissolved in an organic solvent mainly composed of a good solvent. B) In some cases, the acrylic particles (D) and other additives are dissolved with stirring to form a dope, or the acrylic resin (A), (C), cellulose ester resin (B) solution In this step, an acrylic particle (D) solution and other additive solutions are mixed to form a dope that is a main solution.

  For dissolving the acrylic resins (A), (C) and the cellulose ester resin (B), a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, Various methods such as a method using a cooling dissolution method as described in JP-A-9-95544, JP-A-9-95557, or JP-A-9-95538, a method using a high pressure as described in JP-A-11-21379, etc. However, a method of pressurizing at a temperature equal to or higher than the boiling point of the main solvent is preferable.

  The total amount of the acrylic resins (A) and (C) and the cellulose ester resin (B) in the dope is preferably in the range of 15 to 45% by mass. An additive is added to the dope during or after dissolution to dissolve and disperse, then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

  It is preferable to use a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

  In this method, the aggregate remaining at the time of particle dispersion and the aggregate generated when the main dope is added are aggregated by using a filter medium having a collected particle diameter of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml. Can only be removed. In the main dope, the concentration of particles is sufficiently thinner than that of the additive solution, so that aggregates do not stick together at the time of filtration and the filtration pressure does not increase suddenly.

  FIG. 1 is a diagram schematically showing an example of a dope preparation step, a casting step, and a drying step of a solution casting film forming method preferable for the present invention.

  If necessary, large agglomerates are removed from the acrylic particle charging kettle 41 by the filter 44 and fed to the stock kettle 42. Thereafter, the acrylic particle additive solution is added from the stock kettle 42 to the main dope dissolving kettle 1.

  Thereafter, the main dope solution is filtered by the main filter 3, and an ultraviolet absorbent additive solution is added in-line from 16 to this.

  In many cases, the main dope may contain about 10 to 50% by mass of the recycled material. The return material may contain acrylic particles. In that case, it is preferable to control the addition amount of the acrylic particle addition liquid in accordance with the addition amount of the return material.

  The additive solution containing acrylic particles preferably contains 0.5 to 10% by mass of acrylic particles, more preferably 1 to 10% by mass, and 1 to 5% by mass. Most preferably.

  If it is in the said range, since an addition liquid is low-viscosity, it is easy to handle and it is easy to add to the main dope, it is preferable.

  The return material is a product obtained by finely pulverizing the optical film, which is generated when the optical film is formed, and is obtained by cutting off both sides of the film, or by using an optical film original that has been speculated out due to scratches, etc. .

  In addition, an acrylic resin, a cellulose ester resin, and, in some cases, acrylic particles kneaded into pellets can be preferably used.

2) Casting process An endless metal belt 31 such as a stainless steel belt or a rotating metal drum that feeds the dope to a pressure die 30 through a liquid feed pump (for example, a pressurized metering gear pump) and transfers it indefinitely. This is a step of casting a dope from a pressure die slit to a casting position on a metal support.

  A pressure die that can adjust the slit shape of the die base and facilitates uniform film thickness is preferred. The pressure die includes a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and stacked. Or it is also preferable to obtain the film of a laminated structure by the co-casting method which casts several dope simultaneously.

3) Solvent evaporation step In this step, the web (the dope is cast on the casting support and the formed dope film is called a web) is heated on the casting support to evaporate the solvent.

  To evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back side of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. High efficiency and preferable. A method of combining them is also preferably used. The web on the support after casting is preferably dried on the support in an atmosphere of 40 to 100 ° C. In order to maintain the atmosphere at 40 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or to heat by means such as infrared rays.

  From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the web from the support within 30 to 120 seconds.

4) Peeling process It is the process of peeling the web which the solvent evaporated on the metal support body in a peeling position. The peeled web is sent to the next process.

  The temperature at the peeling position on the metal support is preferably 10 to 40 ° C, more preferably 11 to 30 ° C.

  In addition, it is preferable that the residual solvent amount at the time of peeling of the web on the metal support at the time of peeling is peeled in the range of 50 to 120% by mass depending on the strength of drying conditions, the length of the metal support, and the like. If the web is peeled off at a time when the amount of residual solvent is larger, if the web is too soft, the flatness at the time of peeling will be lost, and slippage and vertical stripes are likely to occur due to the peeling tension. The amount of solvent is determined.

  The residual solvent amount of the web is defined by the following formula.

Residual solvent amount (%) = (mass before web heat treatment−mass after web heat treatment) / (mass after web heat treatment) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

  The peeling tension at the time of peeling the metal support and the film is usually 196 to 245 N / m. However, when wrinkles easily occur at the time of peeling, it is preferable to peel with a tension of 190 N / m or less. It is preferable to peel at a minimum tension that can be peeled to 166.6 N / m, and then peel at a minimum tension to 137.2 N / m, and particularly preferably peel at a minimum tension to 100 N / m.

  In the present invention, the temperature at the peeling position on the metal support is preferably -50 to 40 ° C, more preferably 10 to 40 ° C, and most preferably 15 to 30 ° C.

5) Drying and stretching step After peeling, a drying device 35 that transports the web alternately through rolls arranged in the drying device and / or a tenter stretching device 34 that clips and transports both ends of the web with clips. And dry the web.

  Generally, the drying means blows hot air on both sides of the web, but there is also a means for heating by applying microwaves instead of the wind. Too rapid drying tends to impair the flatness of the finished film. Drying at a high temperature is preferably performed from about 8% by mass or less of the residual solvent. Throughout the drying is generally carried out at 40-250 ° C. It is particularly preferable to dry at 40 to 160 ° C.

  When using a tenter stretching apparatus, it is preferable to use an apparatus that can independently control the film gripping length (distance from the start of gripping to the end of gripping) left and right by the left and right gripping means of the tenter. In the tenter process, it is also preferable to intentionally create sections having different temperatures in order to improve planarity.

  It is also preferable to provide a neutral zone between different temperature zones so that the zones do not interfere with each other.

  In addition, extending | stretching operation may be divided | segmented and implemented in multiple steps, and it is also preferable to implement biaxial stretching in a casting direction and a width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

  In this case, stepwise means that, for example, stretching in different stretching directions can be sequentially performed, stretching in the same direction is divided into multiple stages, and stretching in different directions is added to any one of the stages. Is also possible. That is, for example, the following stretching steps are possible.

-Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction-Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension. The preferable draw ratio of simultaneous biaxial stretching can be taken in the range of x1.01 to x1.5 times in both the width direction and the longitudinal direction.

  When the tenter is used, the residual solvent amount of the web is preferably 20 to 100% by mass at the start of the tenter, and it is preferable to perform drying while applying the tenter until the residual solvent amount of the web becomes 10% by mass or less. More preferably, it is 5% by mass or less.

  The drying temperature when performing the tenter is preferably 30 to 160 ° C, more preferably 50 to 150 ° C, and most preferably 70 to 140 ° C.

  In the tenter process, it is preferable that the temperature distribution in the width direction of the atmosphere is small from the viewpoint of improving the uniformity of the film. The temperature distribution in the width direction in the tenter process is preferably within ± 5 ° C, and within ± 2 ° C. Is more preferable, and within ± 1 ° C. is most preferable.

6) Winding step This is a step of winding the optical film by the winder 37 after the residual solvent amount in the web is 2% by mass or less, and the dimensional stability is achieved by setting the residual solvent amount to 0.4% by mass or less. A film having good properties can be obtained. It is particularly preferable to wind up at 0.00 to 0.10% by mass.

  As a winding method, a generally used method may be used. There are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

  The optical film of the present invention is preferably a long film. Specifically, the optical film has a thickness of about 100 m to 5000 m and is usually provided in a roll shape. Moreover, it is preferable that the width | variety of a film is 1.3-4m, and it is more preferable that it is 1.4-2m.

  Although there is no restriction | limiting in particular in the film thickness of the optical film of this invention, When using for the polarizing plate protective film mentioned later, it is preferable that it is 20-200 micrometers, it is more preferable that it is 25-100 micrometers, and it is 30-80 micrometers. It is particularly preferred.

  As an index for judging the transparency of the optical film in the present invention, haze value (turbidity) is used. In particular, in a liquid crystal display device used outdoors, it is required that sufficient brightness and high contrast are obtained even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably.

  According to the optical film of the present invention containing the acrylic resins (A) and (C) and the cellulose ester resin (B), high transparency can be obtained, but acrylic particles are used for the purpose of improving other physical properties. When used, the increase in haze value can be prevented by reducing the refractive index difference between the resin (acrylic resins (A), (C) and cellulose ester resin (B)) and acrylic particles (D). it can.

  In addition, since the surface roughness also affects the haze value as surface haze, the particle diameter and addition amount of the acrylic particles (D) are suppressed within the above range, and the surface roughness of the film contact portion during film formation is reduced. Is also effective.

  The optical film of the present invention preferably has a total light transmittance of 90% or more, more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

  Also, reduce the surface roughness of the film surface by reducing the surface roughness of the film contact part (cooling roll, calender roll, drum, belt, coating substrate in solution casting, transport roll, etc.) during film formation. It is also effective to reduce the diffusion and reflection of light on the film surface by reducing the refractive index of the acrylic resin.

  The optical film of the present invention can be particularly preferably used as a polarizing plate protective film for a large-sized liquid crystal display device or a liquid crystal display device for outdoor use as long as the above physical properties are satisfied.

〔surface treatment〕
The optical film of the present invention can achieve improved adhesion between the film and the polarizer by performing a surface treatment. For example, glow discharge treatment, ultraviolet irradiation treatment, corona treatment, flame treatment, acid or alkali treatment can be used.

The glow discharge treatment here may be low-temperature plasma that occurs in a low pressure gas of 10 ^{−3 to} 20 Torr, and plasma treatment under atmospheric pressure is also preferable.

  Plasma-excitable gas refers to a gas that is plasma-excited under the above conditions, such as argon, helium, neon, krypton, xenon, nitrogen, carbon dioxide, chlorofluorocarbons such as tetrafluoromethane, and mixtures thereof. can give. Details of these are described in detail on pages 30 to 32 in the Japan Society for Invention and Innovation Technical Report (Public Technical Number 2001-1745, published on March 15, 2001, Japan Institute of Invention), and are preferably used in the present invention. be able to.

[Alkaline saponification treatment / water contact angle measurement]
The protective film for polarizing plate of the optical film of the present invention is preferably bonded to a polarizer after alkali saponification treatment.

  Hereinafter, the alkali saponification treatment suitably used in the present invention will be described.

  Examples of the alkali saponification method used in the present invention include a dipping method and an alkaline solution coating method. From the viewpoint of productivity, the dipping method is preferred.

  The immersion method is a method in which a film is immersed in an alkaline solution under appropriate conditions, and all surfaces having reactivity with alkali on the entire surface of the film are saponified, and no special equipment is required. From the viewpoint of

  The alkaline liquid is preferably a sodium hydroxide aqueous solution. The concentration is preferably from 0.5 to 3 mol / l, more preferably from 1 to 2 mol / l. The liquid temperature of the alkaline liquid is preferably 25 to 70 ° C, more preferably 30 to 60 ° C. The treatment time may be adjusted as appropriate as long as the average water contact angle of the film is 10 to 55 degrees and the standard deviation of the water contact angle is within the range of 0.01 to 5.

  After being immersed in the alkaline solution, it is preferable to sufficiently wash with water or neutralize the alkaline component by immersing in a dilute acid so that the alkaline component does not remain in the film.

The water contact angle is determined by the θ / 2 method using a contact angle meter. The average water contact angle was measured using a protective film subjected to alkali saponification treatment at a temperature of 23 ° C. and a humidity of 55% R.D. H. After adjusting the humidity for 24 hours under the above environment, 20 water contact angles randomly selected within the range of 100 cm ² under the same environment are measured, and the calculated average value is calculated. The standard deviation of the water contact angle is calculated from this measured value.

  The optical film of the present invention has an average water contact angle of 10 to 10 when subjected to alkali saponification treatment with a KOH solution at 40 ° C. and 1.5 N for 60 seconds from the viewpoint of adhesiveness with a polarizer. It is preferably within the range of 55 degrees, more preferably 10 to 40 degrees. If the water contact angle is lower than 10 degrees, hydrolysis of the surface of the optical film proceeds excessively, and surface haze is generated, which is not preferable. Moreover, when the water contact angle is higher than 55 degrees, the adhesiveness with the polarizer is remarkably lowered, and it is peeled off when the polarizing plate is produced.

〔Polarizer〕
When using the optical film of this invention as a protective film for polarizing plates, a polarizing plate can be produced by a general method. It is preferable that an adhesive layer is provided on the back side of the optical film of the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

  On the other surface, the optical film of the present invention may be used, or another polarizing plate protective film may be used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4R-4, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, KC4FR-3, -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

  A polarizer, which is a main component of a polarizing plate, is an element that transmits only light having a plane of polarization in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

  For the polarizer, a polyvinyl alcohol aqueous solution is formed into a film and dyed by uniaxial stretching or dyed or uniaxially stretched and then preferably subjected to a durability treatment with a boron compound.

  As the pressure-sensitive adhesive used for the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 4 Pa to 1.0 × 10 9 Pa in at least a part of the pressure-sensitive adhesive layer is preferably used. A curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after applying and bonding the pressure-sensitive adhesive is suitably used.

  Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

  The pressure-sensitive adhesive may be a one-component type or a type that is used by mixing two or more components before use.

  The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The density | concentration of the said adhesive liquid should just be suitably determined with the film thickness after adhesion, the coating method, the coating conditions, etc., and is 0.1-50 mass% normally.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Synthesis of acrylic resin (A)]
A glass flask equipped with a stirrer, two dropping funnels, a gas introduction tube and a thermometer was charged with 40 g of the monomer Xa and Xb mixed solution of the types and ratios shown in Table 1, 2 g of mercaptopropionic acid as a chain transfer agent and 30 g of toluene. The temperature was raised to 90 ° C.

  Thereafter, 60 g of a mixture of monomers Xa and Xb having the types and ratios shown in Table 1 was dropped from one dropping funnel over 3 hours, and at the same time, azobisisobutyronitrile 0 dissolved in 14 g of toluene from the other funnel. .4 g was added dropwise over 3 hours.

  Thereafter, 0.6 g of azobisisobutyronitrile dissolved in 56 g of toluene was added dropwise over 2 hours, and the reaction was further continued for 2 hours to obtain Polymer X. The obtained polymer X was solid at room temperature. Next, polymers X (A1 to A45) having different molecular weights were prepared by changing the addition amount of the chain transfer agent mercaptopropionic acid and the addition rate of azobisisobutyronitrile. The weight average molecular weight of the polymer X (A1 to A45) was measured by the following measurement method.

  The monomer composition of the acrylic resin (A) according to the present invention is shown in Table 1.

(Weight average molecular weight)
The weight average molecular weight of the polymer was determined by GPC polystyrene conversion described above.

The meanings of the abbreviations indicating each monomer (monomer) described in Table 1 are as follows.
MMA: methyl methacrylate HEMA: hydroxyethyl methyl methacrylate ACMO: acryloylmorpholine VP: vinylpyrrolidone HEA: methyl hydroxyethyl acrylate AA: acrylic acid St: styrene MAA: methacrylic acid MA: maleic anhydride

[Synthesis of Cellulose Ester Resin (B)]
Cellulose esters with different acyl groups, substitution degrees, and molecular weights described in Table 2 were synthesized. That is, sulfuric acid (7.8 parts by mass with respect to 100 parts by mass of cellulose) was added as a catalyst, carboxylic acid serving as a raw material for the acyl group substituent was added, and an acylation reaction was performed at 40 ° C. At this time, the reaction rate of the acylation reaction is changed by adjusting the type and amount of the carboxylic acid and the amount of the catalyst according to the method according to the production method described in JP-A-2009-19123, By adjusting the degree of substitution and the like, cellulose esters having the types of acyl groups, the degree of substitution, and the molecular weight shown in Table 2 were synthesized. Moreover, it age | cure | ripened at 40 degreeC after acylation.

  Furthermore, samples having different average polymerization degrees were prepared by washing and removing low molecular weight components of the cellulose ester with acetone.

  The acyl substitution degree was measured according to the method of Tezuka (Tezuka, Carbohydr. Res., 273, 83 (1995)). That is, a sample (cellulose ester) was dissolved in deuterated chloroform, and a 13C-NMR spectrum was measured. For example, the carbonyl carbon signal of the acetyl group appears in the region of 169 ppm to 171 ppm, the second, third, and sixth positions from the high magnetic field, and the carbonyl carbon signal of the propionyl group appears in the same order in the region of 172 ppm to 174 ppm. .

  Therefore, the distribution of acyl groups was determined from the abundance ratios of acetyl groups, propionyl groups, etc. at the corresponding positions.

[Synthesis of acrylic resin (C)]
A glass flask equipped with a stirrer, two dropping funnels, a gas introduction tube and a thermometer was charged with 40 g of MMA monomer, 2 g of mercaptopropionic acid as a chain transfer agent and 30 g of toluene, and the temperature was raised to 90 ° C.

  Thereafter, 60 g of MMA was dropped from one dropping funnel over 3 hours, and at the same time, 0.4 g of azobisisobutyronitrile dissolved in 14 g of toluene was dropped from the other funnel over 3 hours.

  Thereafter, 0.6 g of azobisisobutyronitrile dissolved in 56 g of toluene was further added dropwise over 2 hours, and then the reaction was further continued for 2 hours to obtain an acrylic resin (C3). The obtained acrylic resin (C3) was solid at room temperature. Next, acrylic resins (C1 to C5) having different molecular weights were prepared by changing the addition amount of the chain transfer agent mercaptopropionic acid and the addition rate of azobisisobutyronitrile. The molecular weight of the acrylic resin (C) according to the present invention is shown in Table 3.

(Preparation of dope solution for optical film production)
Cellulose ester (B9) (see Table 2) 30 parts by mass Acrylic resin (A16) (see Table 1) 70 parts by mass Silicon oxide fine particles (Aerosil R972V (produced by Nippon Aerosil Co., Ltd.))
0.1 parts by mass Acrylic particles (Metabrene W-341; manufactured by Mitsubishi Rayon Co., Ltd.) 5 parts by mass Peeling aid (Elecut S-412-2 (manufactured by Takemoto Yushi Co., Ltd.)) 0.1 parts by mass Methylene chloride 300 Part by mass Ethanol 40 parts by mass The addition amount of the silicon oxide fine particles, the acrylic particles, and the peeling aid were the addition amounts when the total addition amount of the cellulose ester and the acrylic resin was 100 parts by mass.

[Production of sample No. 1]
The dope solution was prepared with Finemet NF manufactured by Nippon Seisen Co., Ltd., then filtered, and uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the amount of residual solvent reached 100%, and peeling was performed from the stainless steel band support with a peeling tension of 162 N / m.

  The peeled web of the dope was evaporated at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while stretching 1.1 times in the width direction with a tenter. At this time, the residual solvent amount when starting stretching with a tenter was 10%.

  After stretching with a tenter, relaxation was performed at 130 ° C. for 5 minutes, and then drying was completed while transporting a drying zone at 120 ° C. and 130 ° C. with many rolls, slitting to a width of 1.5 m, and a width of 10 mm at both ends of the film. A knurling process having a height of 5 μm was performed, and the sample was wound around a core of 6 inch inner diameter with an initial tension of 220 N / m and a final tension of 110 N / m. 1 (optical film 1) was obtained.

  The draw ratio in the MD direction calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 1.01. The residual solvent amount of the cellulose ester films described in Tables 4 to 6 was 0.1%, the film thickness was 40 μm, and the winding number was 4000 m.

  Subsequently, sample No. was changed except having changed the cellulose ester kind, the kind of acrylic resin, and addition amount like Tables 4-6. In the same manner as in Sample 1, 2 to 86 (optical films 2 to 86) were produced.

  In addition, about the acrylic resin (C), the said acrylic resin (C1-C5) was used.

[Preparation of polarizing plate]
A polarizing plate was produced as follows.

  A 120 μm-thick long roll polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched in the transport direction 5 times at 50 ° C. to produce a polarizer.

  Next, a polyvinyl alcohol-based adhesive was applied to both sides of the polarizer, and one side of the polarizer was subjected to alkali saponification treatment with 40 ° C., 1.5N KOH solution for 60 seconds, to produce in Example 1. Sample No. 1 is laminated with KC6UY (manufactured by Konica Minolta Opto Co., Ltd.) which has been subjected to the same saponification treatment on the other surface and bonded together with a roll machine, and then dried at 60 ° C. for 120 seconds to obtain a polarizing plate 1 was produced.

  In the same manner as described above, polarizing plates 2 to 75 were prepared using optical films 2 to 86.

<Evaluation>
Sample No. The following evaluation was performed about 1-86 (optical films 1-86).

(Moisture permeability)
Based on the calcium chloride-cup method defined in JIS Z0208, the moisture permeability was measured when kept for 24 hours under environmental conditions of a temperature of 40 ° C. and a humidity of 90% RH.

(Water contact angle)
On the optical film (polarizing plate protective film) subjected to the alkali saponification treatment, 5 μl of pure water is dropped and measured with a measuring device (using DropMaster DM300 manufactured by Kyowa Interface Science Co., Ltd.) at a temperature of 23 ° C. within a range of 100 cm ² . Randomly selected 20 water contact angles were measured and calculated by averaging the measured values.

(Polarizer adhesion)
The produced polarizing plate is cut into a square of 5 cm × 5 cm, left in an atmosphere of 23 ° C. and 55% RH for 24 hours, and then peeled off from the corner portion at the interface between the polarizer and the film. This operation is performed with 100 polarizing plates for one type of sample, and the number of polarizing plates in which peeling is observed between the polarizer and the film is counted.
A: 0 to 2 sheets ○: 3 to 5 sheets Δ: 6 to 20 sheets ×: 21 sheets or more The polarizer adhesion is preferably at least the ○ level.

(Durability of polarizing plate)
The produced polarizing plate was cut into a square of 5 cm × 5 cm, attached to a slide glass with an acrylic pressure-sensitive adhesive, and after measuring optical properties (initial optical properties), 60 ° C./95% R.D. The optical properties (optical properties after the test) after being put in the dryer of H and put into the dryer under the above conditions for a predetermined time were measured, and the durability was evaluated by the amount of change in light transmittance of the polarizing plate. The optical characteristic measurement method and evaluation criteria are described below.

<Measurement of optical characteristics>
Light transmittance change amount: Visibility was corrected in accordance with JIS Z-8701, and light transmittance (hereinafter simply referred to as transmittance) was obtained. The transmittance change amount was determined according to the following formula (2).
(Formula 2): Transmittance change amount = transmittance after test−initial transmittance ◎: Transmittance change amount is less than 1.5% ○: Transmittance change amount is 1.5% to 3.0%
Δ: Transmittance change is more than 3.0% to 4.5%
X: The transmittance | permeability variation | change_quantity exceeds 4.5% The said measurement and evaluation result is shown to Tables 4-6.

  As is clear from the results shown in Tables 4 to 6, it can be seen that the evaluation is excellent in evaluation of moisture permeability, polarizer adhesion, moisture resistance test and the like.

  That is, by the means of the present invention, an optical film containing a specific acrylic resin, which can be easily bonded to a polarizer by alkali saponification treatment as in the case of conventional cellulose esters, and has moisture resistance (low moisture absorption). It can be seen that an optical film excellent in) can be provided. Moreover, it turns out that the polarizing plate excellent in durability can be provided.

DESCRIPTION OF SYMBOLS 1 Melting pot 3, 6, 12, 15 Filter 4, 13 Stock tank 5, 14 Liquid feed pump 8, 16 Conduit 10 Ultraviolet absorber charging pot 20 Merge pipe 21 Mixer 30 Die 31 Metal support 32 Web 33 Peeling position 34 Tenter device 35 Roll dryer 41 Particle charging vessel 42 Stock tank 43 Pump 44 Filter

Claims (4)

  An optical film containing an acrylic resin (A) obtained by copolymerizing an ethylenically unsaturated monomer having an acetoxy group, wherein the content of the ethylenically unsaturated monomer having an acetoxy group is the total amount of the optical film On the other hand, the optical film is in the range of 20 to 100% by mass.   The average water contact angle on the film surface falls within a range of 10 to 55 degrees when subjected to alkali saponification treatment with a 1.5N KOH solution at 40 ° C for 60 seconds. Optical film. The acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio within the range of (A) :( B) = 95: 5 to 20:80, or the acrylic resin (A) and the acrylic resin are contained. The resin (C) and the cellulose ester resin (B) are contained in a mass ratio within the range of ((A) + (C)) :( B) = 95: 5 to 20:80, and the following requirement (a) The optical film according to claim 1, wherein the optical film satisfies the conditions (c) to (c).
(A) The weight average molecular weight Mw of the acrylic resin (A) is in the range of 1000 to 1000000.
(B) The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is in the range of 2.0 to 3.0, and the weight average molecular weight Mw is in the range of 20000 to 500,000.
(C) The weight average molecular weight Mw of the acrylic resin (C) is in the range of 80000 to 1000000.   A polarizing plate comprising the optical film according to any one of claims 1 to 3.

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