JP2011241264A - Optical film and method for producing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film excellent in transparency and improved of heat resistance stably with time.SOLUTION: In this method for producing an optical film including an acrylic resin (A) having a weight-average molecular weight Mw of 80,000-1,000,000 and a cellulose ester resin (B) having a weight-average molecular weight Mw of 75,000-300,000, total degree of substitution (T) by acyl group of 2.0-3.0, a degree of substitution by 3-8C acyl group of 1.2-3.0, in a mass ratio of 95:5 to 30:70, a cellulose acetate resin (C) having a degree of substitution by acetyl group of 2.0-3.0 is mixed with the cellulose ester resin (B) in an amount of 1 mass% or less to the total mass of the acrylic resin (A) and the cellulose ester resin (B).

Description

  The present invention relates to an optical film, a polarizing plate, and a liquid crystal display device, and more particularly to an optical film that does not deteriorate heat resistance over time, and a method for manufacturing the optical film.

  The demand for liquid crystal display devices is expanding in applications such as liquid crystal televisions and personal computer liquid crystal displays. In general, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, etc. are sandwiched between glass plates, and two polarizing plates provided on both sides thereof. The optical element (polarizing plate protective film) is sandwiched between a child (also referred to as a polarizing film or a polarizing film). As this polarizing plate protective film, a cellulose triacetate film is usually used.

  However, due to recent technological advances, the enlargement of the liquid crystal display device has been accelerated, the amount of light of the backlight has increased, and the heat resistance of the liquid crystal display device has become a problem, and its improvement has been demanded.

  There has been proposed a method of improving heat resistance and further improving brittleness of an acrylic resin by mixing a cellulose ester resin with the acrylic resin (Patent Documents 1, 2, and 3).

  However, in this method, since cellulose, which is a raw material of the cellulose ester resin, is a natural product, lot variations are inevitably generated, and there are cases where compatibility with acrylic resins is problematic. This compatibility problem became apparent in the form of deterioration of transparency and physical properties of the optical film under high temperature and high humidity over time.

  In particular, in cellulose ester resins obtained by reacting mixed acids such as cellulose acetate propionate and cellulose acetate butyrate, the reaction of propionic anhydride, butyric anhydride, etc. with cellulose is slower than acetic anhydride, When trying to introduce the desired acetyl group and propionyl group or butyryl group at the same time, the introduction amount of acetyl group and the introduction amount of propionyl group or butyryl group varied, which increased the above problem .

International Publication No. 2009/047924 JP 2009-1744 A JP 2009-179731 A

  An object of this invention is to provide the optical film excellent in the transparency which improved heat resistance stably over time in view of said subject.

  The above object of the present invention can be achieved by the following configuration.

  1. Acrylic resin (A) having a weight average molecular weight Mw of 80000 to 1000000, a weight average molecular weight Mw of 75,000 to 300,000, an acyl group total substitution degree (T) of 2.0 to 3.0, and a carbon number of 3 In the manufacturing method of the optical film which contains cellulose ester resin (B) whose acyl group substitution degree of -8 is 1.2 or more and 3.0 or less by mass ratio of 95: 5-30: 70, this cellulose ester resin ( B) is mixed with cellulose acetate resin (C) having an acetyl group substitution degree of 2.0 to 3.0 in an amount of 1% by mass or less of the total mass of acrylic resin (A) and cellulose ester resin (B). A method for producing an optical film.

  2. 2. An optical film produced by the production method according to 1 above.

  In the present invention, an optical film that improves heat resistance over time can be provided, whereby a polarizing plate and a liquid crystal display device using the optical film can be provided.

Hereinafter, the best mode for carrying out the present invention will be described in detail.
<The manufacturing method of the optical film of this invention>
The method for producing an optical film of the present invention includes an acrylic resin (A) having a weight average molecular weight Mw of 80000 to 1000000, a weight average molecular weight Mw of 75,000 to 300,000, and a total substitution degree (T) of acyl groups of 2.0. An optical film containing cellulose ester resin (B) having a mass ratio of 95: 5 to 30:70, having a carbon number of 3 to 8 and an acyl group substitution degree of 3 to 8 and a carbon number of 1.2 to 3.0. In this manufacturing method, cellulose acetate resin (C) having an acetyl group substitution degree of 2.0 or more and 3.0 or less is added to the cellulose ester resin (B), and the total mass of the acrylic resin (A) and the cellulose ester resin (B). 1% by mass or less is mixed.

  That is, the balance between the acyl group having 3 to 8 carbon atoms such as propionyl group and acetyl group of the cellulose ester resin in the optical film, the propionyl group and the like is the cellulose ester resin (B), and the acetyl group is the cellulose acetate resin (C). The method for producing an optical film is characterized by adjusting to a desired value.

  The reaction at the time of introducing an acyl group having 3 to 8 carbon atoms such as propionyl group is slower than the reaction to introduce an acetyl group, and a cellulose ester resin having a desired substitution degree of acyl group having 3 to 8 carbon atoms is obtained. However, the introduction of the acetyl group had a large variation due to the quick reaction.

  Therefore, the optical films produced so far have been unstable in transparency and physical properties over time due to lot variation of cellulose ester resins.

  In the present invention, the cellulose ester resin (B) has an acyl group substitution degree (T) of 2.0 or more and 3.0 or less, and an acyl group substitution degree of 3 to 8 carbon atoms of 1.2 or more and 3.0. It has been found that if the cellulose acetate resin (C) is 1% by mass or less in the following range, the performance of the optical film can be adjusted equally.

When the base cellulose ester resin (B) is exactly the desired one, it is not particularly necessary to mix the cellulose acetate resin (C). However, in the range of 0.01 to 1% by mass for lot stability. It is preferable to make adjustments.
<Acrylic resin (A)>
The acrylic resin used in the present invention includes a methacrylic resin. As resin, what consists of 50-99 mass% of methyl methacrylate units and 1-50 mass% of other monomer units copolymerizable with this is preferable.

  Other monomers that can be copolymerized include alkyl methacrylates having 2 to 18 carbon atoms, alkyl acrylates having 1 to 18 carbon atoms, acrylic acid, methacrylic acid, and the like. Unsaturated group-containing divalent carboxylic acids such as saturated acid, maleic acid, fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, 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 (A) used for the optical film of the present invention has a weight average molecular weight (Mw) of 80,000 to 1,000,000 particularly from the viewpoint of improving brittleness and improving transparency when it is compatible with the cellulose ester resin (B). It is especially preferable that it is in the range of 100,000 to 600,000, and it is most preferable that it is in the range of 150,000 to 400,000.

  The weight average molecular weight of the acrylic resin of 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.

  The methyl methacrylate monomer content in the acrylic resin of the present invention can be measured with a gas chromatograph mass spectrometer. The measurement conditions are as follows.

Sample: Acrylic resin is dissolved in acetonitrile to prepare a 0.1% sample solution Sample volume: 1 μl
Equipment: HP 5890 Series II / HP 5971 MSD
Column: InertCAP for amines (0.32 mmid × 30 m) manufactured by GL Sciences
Inlet: 200 ° C
MSD: SIM m / z = 55,100
OVEN: 60 ° C. (4 min) → 15 (° C./min)→120° C.
The amount of methyl methacrylate monomer in the produced optical film can also be measured by the same method.

  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.

A commercially available thing can also be used as an acrylic resin of this invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dianal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electrochemical Industry Co., Ltd.) and the like can be mentioned. . Two or more acrylic resins can be used in combination.
<Cellulose ester resin (B)>
The cellulose ester resin (B) of the present invention has a total acyl substitution degree (T) of 2.0 to 3.0 and a carbon number from the viewpoint of transparency when it is compatible with the acrylic resin (A). The degree of substitution of the acyl group having 3 to 8 is preferably 1.2 to 3.0, and the degree of substitution of the acyl group having 3 to 8 carbon atoms is preferably 2.0 to 3.0.

  That is, the cellulose ester resin (B) of the present invention is a cellulose ester resin substituted with an acyl group having 3 to 8 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used. Preferably used.

  As for the acyl substitution degree of the cellulose ester resin (B) of the present invention, the total substitution degree (T) is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 8 carbon atoms is 1.2 to 3. If it is 0.0, there is no problem, but the total substitution degree of acyl groups other than those having 3 to 8 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms, is preferably 1.3 or less.

  The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is more preferably in the range of 2.5 to 3.0.

  The cellulose ester resin (B) of the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, that is, carbon Those having an acyl group having 3 or 4 atoms as a substituent are preferred.

  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 (B) of the present invention is 75000 or more, particularly from the viewpoint of improvement in compatibility with the acrylic resin (A) and brittleness, and is preferably in the range of 75,000 to 300,000. More preferably, it is within the range of 100,000 to 240,000, particularly preferably 160000 to 240,000.

The weight average molecular weight of the cellulose ester resin (B) of the present invention can be measured by the GPC.
<Cellulose acetate resin (C)>
The cellulose acetate resin (C) having an acetyl group substitution degree of 2.0 or more and 3.0 or less is mixed with 1% by mass or less of the total mass of the acrylic resin (A) and the cellulose ester resin (B).

As the cellulose acetate resin (C) of the present invention, cellulose diacetate and cellulose triacetate are preferably used. The weight average molecular weight is preferably 100,000 to 300,000.
<Other additive resins>
In the optical film of the present invention, when a resin other than the acrylic resin (A), the cellulose ester resin (B), and the cellulose acetate resin (C) is used, the amount added is within a range that does not impair the function of the optical film of the present invention. Is preferably adjusted.

  As a preferred resin, a low molecular acrylic resin obtained by polymerizing an ethylenically unsaturated monomer described in paragraphs (0072) to (0123) of JP 2010-32655 A (weight average molecular weight Mw of 500 or more and 30000 or less) Polymer).

  Most preferably, Mw is 2000-30000. If it is 1000 or less, a problem occurs in bleed-out, and if it exceeds 30000, the transparency deteriorates.

  Also, a vinyl polymer having an amide bond described in Japanese Patent No. 413895 can be used.

The low molecular acrylic resin of the present invention and the vinyl polymer having an amide bond are 0 to 15% by mass, preferably 0 to 10% by mass, based on the total mass of the optical film.
<Acrylic particles (D)>
The optical film of the present invention may contain acrylic particles (D) described in Patent Document 1.

  As an example of a commercial item of such a multilayer structure acrylic granular composite, for example, “Metablene W-341” manufactured by Mitsubishi Rayon Co., “Kaneace” manufactured by Kaneka Chemical Co., Ltd., “Paralloid” manufactured by Kureha Chemical Co., Ltd., Examples include “Acryloid” manufactured by Rohm and Haas, “Staffroid” manufactured by Gantz Kasei Kogyo, Chemisnow MR-2G, MS-300X (manufactured by Soken Chemical Co., Ltd.), and “Parapet SA” manufactured by Kuraray These can be used alone or in combination of two or more.

The optical film of the present invention preferably contains 0 to 30% by mass of acrylic particles (D) with respect to the total mass of the resin constituting the film, and is contained in the range of 1.0 to 15% by mass. More preferably.
<Other additives>
The optical film of the present invention includes a retardation control agent for controlling retardation, a plasticizer for imparting processability to the film, an antioxidant for preventing deterioration of the film, and an ultraviolet ray for imparting an ultraviolet absorbing function. It is preferable to contain additives such as fine particles (matting agent) that impart slipperiness to the absorbent and film.

<Polyester polyol of glycol and dibasic acid>
The polyester polyol that can be used in the present invention includes a dehydration condensation reaction between a glycol having an average carbon number of 2 to 3.5 and a dibasic acid having an average carbon number of 4 to 5.5, or the glycol. It is preferable to be produced by a conventional method by addition of a dibasic anhydride having an average carbon number of 4 to 5.5 and a dehydration condensation reaction.

<Polyester of aromatic dicarboxylic acid and alkylene glycol>
As the retardation control agent of the present invention, an aromatic terminal polyester represented by the following general formula (I) can be used.

General formula (I) B- (GA) n-GB
(In the formula, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more.)
In the general formula (I), a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic group represented by A It is composed of an acid residue and can be obtained by a reaction similar to that of ordinary polyester.

  As specific compounds of the aromatic terminal polyester of the present invention, paragraphs (0183) to (0186) of JP 2010-32655 A can be mentioned.

  The content of the aromatic terminal polyester of the present invention is preferably 0 to 20% by mass, and particularly preferably 1 to 11% by mass in the optical film.

<Polyhydric ester compound>
The optical film of the present invention can contain a polyhydric alcohol ester compound.

  Examples of the polyhydric alcohol ester compounds include paragraphs (0218) to (0170) of JP 2010-32655 A.

<Sugar ester compound>
As the sugar ester compound of the present invention, it is possible to use a sugar ester compound having at least one pyranose structure or at least one furanose structure and esterifying all or part of the OH groups of the structure. preferable.

  Examples of the sugar ester compound used in the present invention include glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, cellobiose, cellotriose, maltotriose, raffinose, etc. What has is preferable. An example is sucrose.

  The sugar ester compound used in the present invention is one in which part or all of the hydroxyl groups of the sugar compound are esterified or a mixture thereof.

  Specific examples of the sugar ester compound of the present invention include paragraphs (0060) to (0070) of JP-A 2010-32655.

<Other additives>
In the optical film of the present invention, a plasticizer, a retardation control agent, an antioxidant, an ultraviolet absorber, matte particles, and the like can be used in combination.

  Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  For phosphate ester plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate and the like can be used.

  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 10000, but preferably in the range of 600 to 3000, the plasticizing effect is large.

  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 composition containing an acrylic resin. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use. These plasticizers may be used alone or in combination of two or more.

<Other phase difference control agents>
Other than the above retardation control agent of the present invention, those containing bisphenol A in the molecule are preferred. A compound in which ethylene oxide or propylene oxide is added to both ends of bisphenol A can be used.

  For example, BP series such as New Pole BP-2P, BP-3P, BP-23P, BP-5P, BPE-20 (F), BPE-20NK, BPE-20T, BPE-40, BPE-60, BPE-100, There are BPE series (manufactured by Sanyo Chemical Co., Ltd.) such as BPE-180, and BPX series (manufactured by Adeka Co., Ltd.) such as Adeka polyether BPX-11, BPX-33, BPX-55.

  Diallyl bisphenol A, dimethallyl bisphenol A, tetrabromobisphenol A with bisphenol A substituted with bromine, oligomers and polymers obtained by polymerizing this, bisphenol A bis (diphenyl phosphate) substituted with diphenyl phosphate, etc. Can be used.

  Polycarbonate obtained by polymerizing bisphenol A, polyarylate obtained by polymerizing bisphenol A with a dibasic acid such as terephthalic acid, and an epoxy oligomer or polymer polymerized with an epoxy-containing monomer can also be used.

  Modiper CL130D or L440-G obtained by graft polymerization of bisphenol A and styrene, styrene acrylic, or the like can also be used.

  Those having a triazine structure are also preferred. The compounds described in JP 2001-166144 A can be used.

<Antioxidant>
In this invention, what is generally known can be used as an antioxidant. In particular, lactone, sulfur, phenol, double bond, hindered amine, and phosphorus compounds can be preferably used.

  For example, the thing containing what is marketed by the brand name "IrgafosXP40" and "IrgafosXP60" from Ciba Japan KK is preferable.

  The phenolic compound preferably has a 2,6-dialkylphenol structure. For example, Ciba Japan Co., Ltd., “Irganox 1076”, “Irganox 1010”, and ADEKA “ADEKA STAB AO-50” are trade names. And those commercially available.

  Examples of the phosphorous compounds are Sumitomo Chemical Co., Ltd., “Sumilizer GP”, ADEKA Co., Ltd., “ADK STAB PEP-24G”, “ADK STAB PEP-36” and “ADK STAB 3010”, Ciba Japan Co., Ltd. “IRGAFOS P-EPQ”, commercially available from Sakai Chemical Industry Co., Ltd. under the trade name “GSY-P101” is preferable.

  As the hindered amine compound, for example, those commercially available from Ciba Japan Co., Ltd. under the trade names “Tinuvin 144” and “Tinvin 770”, and from ADEKA Co., Ltd. as “ADK STAB LA-52” are preferable.

  The sulfur compound is preferably commercially available from Sumitomo Chemical Co., Ltd. under the trade names “Sumilizer TPL-R” and “Sumilizer TP-D”.

  The above-mentioned double bond type compounds are preferably those commercially available from Sumitomo Chemical Co., Ltd. under the trade names “Sumilizer GM” and “Sumilizer GS”.

  Furthermore, it is possible to contain a compound having an epoxy group as described in US Pat. No. 4,137,201 as an acid scavenger.

  The amount of these antioxidants and the like to be appropriately added is determined in accordance with the process at the time of recycling, but generally 0.05 to 20% by mass, preferably with respect to the resin as the main raw material of the film Is added in the range of 0.1 to 1% by mass.

  These antioxidants can obtain a synergistic effect by using several different types of compounds in combination rather than using only one kind. For example, the combined use of lactone, phosphorus, phenol and double bond compounds is preferred.

<Colorant>
In the present invention, it is preferable to use a colorant. The colorant means a dye or a pigment. In the present invention, the colorant refers to a colorant having an effect of making the color tone of a liquid crystal screen a blue tone, adjusting a yellow index, and reducing haze.

  Various dyes and pigments can be used as the colorant, but anthraquinone dyes, azo dyes, phthalocyanine pigments and the like are effective.

<Ultraviolet absorber>
Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body. It is good also as a polymer type ultraviolet absorber.

<Matting agent>
In the present invention, it is preferable to add a matting agent in order to impart film slipperiness.

  The matting agent used in the present invention may be either an inorganic compound or an organic compound as long as it does not impair the transparency of the obtained film and has heat resistance during melting. These matting agents can be used alone or in combination of two or more.

  By using particles having different particle sizes and shapes (for example, acicular and spherical), both transparency and slipperiness can be made highly compatible.

  Among these, silicon dioxide is particularly preferably used because it has a refractive index close to that of cellulose ester and is excellent in transparency (haze).

  Specific examples of silicon dioxide include Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (manufactured by Nippon Aerosil Co., Ltd.), Sea Hoster KEP-10, Sea Hoster KEP- 30, Seahoster KEP-50 (manufactured by Nippon Shokubai Co., Ltd.), Silo Hovic 100 (manufactured by Fuji Silysia), nip seal E220A (manufactured by Nippon Silica Industry), Admafine SO (manufactured by Admatechs), etc. Goods etc. can be preferably used.

  The shape of the particles can be used without particular limitation, such as indefinite shape, needle shape, flat shape, spherical shape, etc. However, the use of spherical particles is particularly preferable because the transparency of the resulting film can be improved.

  When the particle size is close to the wavelength of visible light, light is scattered and the transparency is deteriorated. Therefore, the particle size is preferably smaller than the wavelength of visible light, and more preferably ½ or less of the wavelength of visible light. . If the size of the particles is too small, the slipperiness may not be improved, so the range of 80 nm to 180 nm is particularly preferable.

  The particle size means the size of the aggregate when the particle is an aggregate of primary particles. Moreover, when a particle is not spherical, it means the diameter of a circle corresponding to the projected area.

<Viscosity reducing agent>
In the present invention, a hydrogen bonding solvent can be added for the purpose of reducing the melt viscosity.

  The hydrogen bonding solvent is J.I. N. As described in Israel Ativili, “Intermolecular Forces and Surface Forces” (Takeshi Kondo, Hiroyuki Oshima, Maglow Hill Publishing, 1991) and electrically negative atoms (oxygen, nitrogen, fluorine, chlorine) An organic solvent capable of producing a hydrogen atom-mediated “bond” between a hydrogen atom covalently bonded to an electronegative atom, ie, a bond having a large bond moment and containing hydrogen, such as O—H (Oxygen hydrogen bond), N—H (nitrogen hydrogen bond), and organic solvent that can arrange adjacent molecules by including F—H (fluorine hydrogen bond).

These have the ability to form stronger hydrogen bonds with cellulose than intermolecular hydrogen bonds of cellulose resin. In the melt casting method performed in the present invention, the glass transition temperature of the cellulose resin used alone is higher than that. The melting temperature of the cellulose resin composition can be lowered by the addition of a hydrogen bonding solvent, or the melt viscosity of the cellulose resin composition containing a hydrogen bonding solvent can be lowered at the same melting temperature as the cellulose resin. .
(Physical properties of optical film)
Hereinafter, the characteristics of the optical film according to the present invention will be described.

<transparency>
As an index for judging the transparency of the optical film in the present invention, haze value (turbidity) is used.

  In particular, liquid crystal display devices used outdoors are required to have sufficient brightness and high contrast even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably.

  Moreover, it is preferable that the total light transmittance is 90% or more, More preferably, it is 93% or more. Moreover, as a realistic upper limit, it is about 99%.

  In the optical film of the present invention, the number of bright spots (also referred to as defects) having a diameter of 5 μm or more in the film plane is preferably 1/10 cm square or less. More preferably, it is 0.5 piece / 10 cm square or less, more preferably 0.1 piece / 10 cm square or less.

  Here, the diameter of the defect indicates the diameter when the defect is circular, and when the defect is not circular, the range of the defect is determined by observing with a microscope by the following method, and the maximum diameter (diameter of circumscribed circle) is determined.

  The range of the defect is the size of the shadow when the defect is observed with the transmitted light of the differential interference microscope when the defect is a bubble or a foreign object. When the defect is a change in the surface shape, such as transfer of a roll flaw or an abrasion, the size is confirmed by observing the defect with the reflected light of a differential interference microscope.

  In addition, when observing with reflected light, if the size of the defect is unclear, aluminum or platinum is deposited on the surface for observation.

  In order to obtain a film having excellent quality expressed by such a defect frequency with high productivity, it is necessary to filter the polymer solution with high precision immediately before casting, to increase the cleanliness around the casting machine, It is effective to set drying conditions after rolling stepwise and to dry efficiently while suppressing foaming.

  When the number of defects is greater than 1/10 cm square, for example, when the film is tensioned during processing in a later process, the film may break with the defects as a starting point, and productivity may decrease. Moreover, when the diameter of a defect becomes 5 micrometers or more, it can confirm visually by polarizing plate observation etc., and when used as an optical member, a bright spot may arise.

<Retardation>
For the retardation, a 35 mm × 35 mm sample was cut from the produced optical film, conditioned for 2 hours at 25 ° C. and 55% RH, and measured from the vertical direction at 590 nm with an automatic birefringence meter (KOBRA WR, Oji Scientific Co., Ltd.). Ro and Rt at each wavelength were calculated from the measured values and the extrapolated values of the retardation values measured in the same manner while tilting the film surface.

The optical film of the present invention has an in-plane retardation value Ro (590) defined by the following formula (I) in the range of 0 to 100 nm, and a retarder in the thickness direction defined by the following formula (II). It is preferable to adjust so that the foundation value Rt (590) is in the range of −100 to 100 nm.
Formula (I): Ro (590) = (nx−ny) × d (nm)
Formula (II): Rt (590) = {(nx + ny) / 2−nz} × d (nm)
[In the above formula, Ro (590) represents the in-plane retardation value in the film at a measurement wavelength of 590 nm, and Rt (590) represents the retardation value in the thickness direction in the film at 590 nm.

D represents the thickness (nm) of the optical film, nx represents the maximum refractive index in the plane of the film at 590 nm, and is also referred to as the refractive index in the slow axis direction. ny represents the refractive index in the direction perpendicular to the slow axis in the film plane at 590 nm, and nz represents the refractive index of the film in the thickness direction at 590 nm. ]
The in-plane retardation value Ro (590) is preferably in the range of 0 to 250 nm.

  On the other hand, the retardation value Rt (590) in the thickness direction is preferably in the range of −50 to 50 nm.

  The desired retardation is adjusted by adjusting the ratio of each resin within the range of 95: 5 to 50:50 mass ratio of acrylic resin and cellulose ester resin. This is done by adjusting the amount to be added.

  Furthermore, by adjusting and controlling the stretching temperature (combination of the temperatures of the respective sections), the magnification, the stretching speed, the stretching order, the residual solvent amount of the film when stretching, and the like according to the composition of the film. The retardation value can be set to a desired value.

  By adjusting the retardation to such a range, the viewing angle of the liquid crystal display device using the film of the present invention can be widened and the front contrast can be improved.

Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)
The viewing angle is an angle at which a certain level of contrast can be maintained when the viewing direction of the liquid crystal display device is tilted from the normal direction.

  The uniformity in the slow axis direction is also important, and the angle is preferably −5 to + 5 ° with respect to the film width direction, more preferably in the range of −1 to + 1 °, and particularly −0. It is preferably in the range of 5 to + 0.5 °, particularly preferably in the range of −0.1 to + 0.1 °. These variations can be achieved by optimizing the stretching conditions.

  In the optical film of the present invention, it is preferable that the height from the top of the adjacent mountain to the bottom of the valley is 300 nm or more and there is no streak continuous in the longitudinal direction with an inclination of 300 nm / mm or more.

  The shape of the streak was measured using a surface roughness meter. Specifically, using a Mitutoyo SV-3100S4, a stylus (diamond needle) having a tip shape of a cone of 60 ° and a tip curvature radius of 2 μm was used. The film is scanned in the width direction of the film at a measurement speed of 1.0 mm / sec while applying a load of 0.75 mN, and a cross-sectional curve is measured with a Z-axis (thickness direction) resolution of 0.001 μm.

  From this curve, the streak height reads the vertical distance (H) from the top of the mountain to the bottom of the valley. The slope of the streak is obtained by reading the horizontal distance (L) from the top of the mountain to the bottom of the valley and dividing the vertical distance (H) by the horizontal distance (L).

  The thickness of the optical film of the present invention is preferably 20 μm or more and 150 μm or less. More preferably, it is 30 μm or more and 80 μm or less.

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.
<Method for producing optical film>
The optical film of the present invention can be produced by either a melt casting coextrusion method or a solution casting method.
<Method for producing optical film by melt casting coextrusion film forming method>
The method for producing an optical film of the present invention is an optical film in which at least an acrylic resin (A), a cellulose ester resin (B), and a cellulose acetate resin (C) are melted and coextruded from a die and cast onto a cooling roll. It is a manufacturing method.

  The entire manufacturing method will be described below.

<Melted pellet manufacturing process>
A mixture of acrylic resin (A), cellulose ester (including cellulose ester resin (B)), cellulose acetate resin (C), plasticizer and other additives used for melt extrusion is usually kneaded in advance and pelletized. It is preferable to keep it.

  Pelletization may be performed by a known method. For example, dry acrylic resin (A), dry cellulose ester, plasticizer, and other additives are fed to an extruder with a feeder and kneaded using a single or twin screw extruder. Then, it can be extruded from a die into a strand, cooled with water or air, and cut.

  It is important to dry the raw material before extruding to prevent decomposition of the raw material. In particular, since the cellulose ester easily absorbs moisture, it is preferable to dry it at 70 to 140 ° C. for 3 hours or more with a dehumidifying hot air dryer or a vacuum dryer to keep the moisture content at 200 ppm or less, and further 100 ppm or less.

  Additives may be fed into the extruder and fed into the extruder, or may be fed by individual feeders. A small amount of an additive such as an antioxidant is preferably mixed in advance in order to mix uniformly.

  Mixing of the antioxidants may be performed by mixing solids, or if necessary, the antioxidant is dissolved in a solvent, and the acrylic resin (A) and cellulose ester resin (B) are impregnated and mixed. Or may be mixed by spraying.

  A vacuum nauter mixer or the like is preferable because drying and mixing can be performed simultaneously. Moreover, when touching with air, such as an exit from a feeder part or die | dye, it is preferable to set it as atmosphere, such as dehumidified air and dehumidified N2 gas.

  The extruder is preferably processed at as low a temperature as possible so that the shearing force is suppressed and the resin can be pelletized so as not to deteriorate (molecular weight reduction, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

  A film is formed using the pellets obtained as described above. It is also possible to feed the raw material powder directly to the extruder with a feeder and form a film as it is without pelletization.

<Process for extruding molten mixture from die to cooling roll>
A line for introducing the acrylic resin (A) or the like from the molten mixture to the casting die and a line for introducing the cellulose tellur resin from the molten mixture to the casting die are provided side by side, and each molten mixture is laminated in the casting die. The

  First, using a single-screw or twin-screw type extruder, the melt temperature Tm when extruding the pellet is about 200 to 300 ° C., filtered through a leaf disk type filter or the like to remove foreign matters, The film is coextruded into a film, solidified on a cooling roll, and cast while pressing with an elastic touch roll.

  When introducing from the supply hopper to the extruder, it is preferable to prevent oxidative decomposition or the like under vacuum or reduced pressure or in an inert gas atmosphere. Tm is the temperature of the die exit portion of the extruder.

  When foreign matter such as scratches or plasticizer aggregates adheres to the die, streak-like defects may occur. Such defects are also referred to as die lines, but in order to reduce surface defects such as die lines, it is preferable to have a structure in which the resin retention portion is minimized in the piping from the extruder to the die. . It is preferable to use a die that has as few scratches as possible inside the lip.

  The inner surface that contacts the molten resin such as an extruder or a die is preferably subjected to surface treatment that makes it difficult for the molten resin to adhere to the surface by reducing the surface roughness or using a material having a low surface energy. Specifically, a hard chrome plated or ceramic sprayed material is polished so that the surface roughness is 0.2 S or less.

  The cooling roll of the present invention is not particularly limited, but is a roll having a structure in which a heat medium or a coolant that can be controlled in temperature flows through a highly rigid metal roll, and the size is not limited. The size of the cooling roll is usually about 100 mm to 1 m.

  Examples of the surface material of the cooling roll include carbon steel, stainless steel, aluminum, and titanium. Further, in order to increase the surface hardness or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, ceramic spraying, or the like.

  The surface roughness of the chill roll surface is preferably 0.1 μm or less in terms of Ra, and more preferably 0.05 μm or less. The smoother the roll surface, the smoother the surface of the resulting film. Of course, it is preferable that the surface processed is further polished to have the above-described surface roughness.

  Examples of the elastic touch roll of the present invention include JP-A-03-124425, JP-A-08-224772, JP-A-07-1000096, JP-A-10-272676, WO97-028950, JP-A-11-235747, JP-A-11-235747. A silicon rubber roll coated with a thin-film metal sleeve can be used as described in JP-A-2002-36332, JP-A-2005-172940 and JP-A-2005-280217.

  When peeling the film from the cooling roll, it is preferable to control the tension to prevent deformation of the film.

<Extension process>
In the present invention, it is preferable that the film obtained as described above is further stretched 1.01 to 3.0 times in at least one direction after passing through the step of contacting the cooling roll. The sharpness of the streaks becomes gentle by stretching and can be highly corrected.

  Preferably, the film is stretched 1.1 to 2.0 times in both the longitudinal (film transport direction) and lateral (width direction) directions.

  As a method of stretching, a known roll stretching machine or tenter can be preferably used. In particular, in the case where the optical film is a retardation film that also serves as a polarizing plate protective film, it is preferable to stack the polarizing film in a roll form by setting the stretching direction to the width direction.

  By stretching in the width direction, the slow axis of the optical film becomes the width direction.

  Usually, the draw ratio is 1.1 to 3.0 times, preferably 1.2 to 1.5 times, and the draw temperature is usually Tg to Tg + 50 ° C. of the resin constituting the film, preferably Tg to Tg + 40 ° C. Performed in the temperature range.

  The stretching is preferably performed under a uniform temperature distribution controlled in the width direction. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

  For the purpose of adjusting the retardation of the optical film produced by the above method and reducing the dimensional change rate, the film may be contracted in the longitudinal direction or the width direction.

  In order to shrink in the longitudinal direction, for example, there is a method of contracting the film by temporarily clipping out the width stretching and relaxing in the longitudinal direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine.

Since the optical film of the present invention is produced by the melt casting coextrusion film forming method, the amount of the solvent contained is 0.01% by mass or less when wound up as a roll film. The amount of the solvent can be measured by the following method.
<Solution casting film forming method>
Next, the solution casting film forming method will be described.

(Organic solvent)
The organic solvents useful for forming the dope when the optical film of the present invention is produced by the solution casting method are acrylic resin (A), cellulose ester resin (B), cellulose acetate resin (C), and optionally acrylic. Any particle and other additives can be used without limitation as long as they dissolve simultaneously.

  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 ratio of alcohol in the dope increases, the web gels and peeling from the metal support becomes easy. When the ratio of alcohol is small, acrylic resin (A) and cellulose ester in non-chlorine organic solvent system. There is also a role of promoting dissolution of the resin (B) and the cellulose acetate resin (C).

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

  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.

1) Dissolution Step In an organic solvent mainly composed of a good solvent for the acrylic resin (A), cellulose ester resin (B) and cellulose acetate resin (C), the acrylic resin (A) and cellulose ester resin (B ), Cellulose acetate resin (C), optionally acrylic particles (D), other additives are dissolved with stirring to form a dope, or the acrylic resin (A), cellulose ester resin (B), cellulose acetate In this step, the resin (C) solution is mixed with an acrylic particle (D) solution and other additive solutions as occasion demands to form a dope as a main solution.

  For dissolving the acrylic resin (A), the cellulose ester resin (B), and the cellulose acetate resin (C), a method performed at normal pressure, a method performed at a temperature lower than the boiling point of the main solvent, and a method performed at a pressure higher than the boiling point of the main solvent. , A method performed by a cooling dissolution method as described in JP-A-9-95544, JP-A-9-95557, or JP-A-9-95538, and a high pressure as described in JP-A-11-21379. Although various dissolution methods such as a method can be used, a method of pressurizing at a temperature equal to or higher than the boiling point of the main solvent is particularly preferable.

  The total amount of acrylic resin (A), cellulose ester resin (B), and cellulose acetate resin (C) in the dope is preferably in the range of 15 to 45% by mass. After the additive is added to the dope during or after dissolution, the dope is dissolved and dispersed, 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.

  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 a film, and is produced by forming a film by cutting off both sides of the film, or by using a film raw material that has been speculated out by scratches or the like.

  In addition, an acrylic resin, a cellulose ester resin, and optionally an acrylic particle kneaded into pellets can be preferably used.

2) Casting process An endless metal belt, such as a stainless steel belt or a rotating metal drum, which supports the dope is fed to a pressure die through a liquid feed pump (for example, a pressurized metering gear pump) and supported infinitely. This is a step of casting a dope from a pressure die slit to a casting position on the body.

  A pressure die that can adjust the slit shape of the die base portion and can easily make the film thickness uniform is preferable. Examples of the pressure die include 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, use a drying device that alternately passes the web through rolls arranged in the drying device, or a tenter stretching device that clips and transports both ends of the web with clips. dry.

  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.

  The stretching process is preferably the same stretching process as the melt casting film forming method. When the tenter is used, the amount of residual solvent in the web is preferably 20 to 100% by mass at the start of the tenter, and drying is preferably performed while applying the tenter until the amount of residual solvent in the web is 10% by mass or less. More preferably, it is 5% by mass or less.

  30-160 degreeC is preferable, as for the drying temperature in the case of performing a tenter, 50-150 degreeC is more preferable, and 70-140 degreeC is the most preferable.

  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 process This is a process in which the amount of residual solvent in the web becomes 2% by mass or less, and is taken up by the winder 37 as a film. 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 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.

<Contained solvent amount>
Each sample was placed in a 20 ml sealed glass container, treated under the following headspace heating conditions, and then a calibration curve was prepared and measured for the solvent used in advance by the following gas chromatography. The amount of solvent contained was expressed in parts by mass relative to the total mass of the optical film.
Equipment: HP 5890SERIES II
Column: J & W Company DB-WAX (inner diameter 0.32 mm, length 30 m)
Detection: FID
GC temperature rising condition: held at 40 ° C. for 5 minutes, then heated to 80 ° C./min to 100 ° C. Headspace heating condition: 120 ° C. for 20 min
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), a cellulose ester resin (B), a cellulose acetate resin (C), or an acrylic particle (D) optionally kneaded into pellets can be preferably used.

  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 long 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.
<Polarizing plate>
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 allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is 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 in 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 used. It is preferable to use a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded.

  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.
<Liquid crystal display device>
By incorporating the polarizing plate bonded with the optical film of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, but particularly outdoors such as large liquid crystal display devices and digital signage. It is preferably used for a liquid crystal display device for use. The polarizing plate of the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

  The polarizing plate of the present invention includes various types such as a reflective type, a transmissive type, a transflective type LCD, a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), and an IPS type (including an FFS type). It is preferably used in a drive type LCD. In particular, in a large-screen display device having a VA type screen of 30 type or more, particularly 30 type to 54 type, there is no white spot in the periphery of the screen and the effect is maintained for a long time.

  The present invention will be specifically described below with reference to examples.

<Preparation of optical film 1>
(Dope solution 1 composition)
Dianal BR85 (polymethyl methacrylate (PMMA) manufactured by Mitsubishi Rayon Co., Ltd. Mw = 2800000) 65 parts by mass Cellulose acetate propionate (acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree) 2.56, Mw = 200000) 35 parts by mass Cellulose triacetate (acyl group total substitution degree 2.87, acetyl group substitution degree 2.87, Mw = 200000)
0.1 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass The above composition was sufficiently dissolved while heating to prepare Dope Solution 1.

  The produced dope solution was 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 resin web is evaporated at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while being stretched 1.15 times (15%) in the width direction with a tenter. It was. 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 140 ° 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 film was wound around a core having an initial tension of 220 N / m and a final tension of 110 N / m, and an inner diameter of 15.24 cm.

  Hereinafter, the materials were changed as shown in Table 3 as described in Tables 1 and 2, and samples were produced in the same manner as the optical film 1. In Table 3, when the mass mixing ratio of the acrylic resin (A), the cellulose ester resin (B), and the cellulose acetate resin (C) is 65: 35: 0.1, an acetyl group, Propionyl group etc. are adjusted.

  In the table, the cellulose acetate resin (C) represents the following.

Cellulose acetate C1: Degree of acetyl group substitution 2.87 Mw = 240,000
C2: Degree of substitution with acetyl group 2.41 Mw = 14,000
In the table, ac (acetyl group), pr (propionyl group), bt (butyryl group), pen (pentyl group), hp (heptyl group), bz (benzyl group), oct (octyl group), ph (phenyl) Group).

The samples described in Tables 3 and 4 were evaluated as follows.
(Durable haze)
The optical film 1 produced as described above was conditioned for 24 hours in an air-conditioned room at 23 ° C. and 55% RH, and under the same conditions, a three-piece film sample was subjected to a haze meter (NDH2000 type, Japan) according to JIS K-7136. It was measured using Denshoku Industries Co., Ltd.).

Next, the three-piece film sample was treated for 500 hours in an environment of condition 1.90 ° C. DRY, condition 2.60 ° C. 90% RH, condition 3.80 ° C. 90%, and then 23 ° C. and 55% RH. After conditioning in the air conditioning room for 24 hours, each piece was measured with a haze meter to evaluate the difference in transmittance (ΔT%) between before and after treatment.
(After elongation, elongation at break)
The optical film 1 conditioned for 24 hours in an air-conditioned room at 23 ° C. and 55% RH is cut out at 120 mm (length) × 10 mm (width) under the same conditions, and a Tensilon tester (ORICTEC manufactured by RTC-1225A) is used. Then, a tensile test was performed 5 times at a tensile speed of 50 mm / min, and the average elongation was measured.

  Next, the optical film 1 is treated for 500 hours in the environment of the above conditions 1, 2 and 3, respectively, and then conditioned for 24 hours in an air-conditioned room at 23 ° C. and 55% RH. The average elongation of the film sample was measured under the above-mentioned tension conditions, and the difference (Δ%) in the elongation at break between after treatment and before treatment was evaluated.

  As is apparent from Tables 3 and 4, the addition of the cellulose acetate resin (C) of the present invention makes it easy to adjust and the performance is excellent.

Claims (2)

  Acrylic resin (A) having a weight average molecular weight Mw of 80000 to 1000000, a weight average molecular weight Mw of 75,000 to 300,000, an acyl group total substitution degree (T) of 2.0 to 3.0, and a carbon number of 3 In the manufacturing method of the optical film which contains cellulose ester resin (B) whose acyl group substitution degree of -8 is 1.2 or more and 3.0 or less by mass ratio of 95: 5-30: 70, this cellulose ester resin ( B) is mixed with cellulose acetate resin (C) having an acetyl group substitution degree of 2.0 to 3.0 in an amount of 1% by mass or less of the total mass of acrylic resin (A) and cellulose ester resin (B). A method for producing an optical film.   An optical film produced by the production method according to claim 1.