JPWO2010055740A1 - Optical film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

The present invention relates to an optical film that has high heat resistance and significantly improved brittleness, and that retains excellent image display properties for a long period of time even when used in a high temperature environment, and the optical film The purpose is to provide a liquid crystal display device using the acrylic resin (A) and the cellulose ester resin (B) having a repeating unit represented by the following general formula (1) or (2): It was achieved by an optical film characterized by containing A and B each represent a divalent hydrocarbon group having 1 to 12 carbon atoms or a divalent hydrocarbon group having 1 to 12 carbon atoms substituted with a hydroxyl group. However, A and B may be the same or different.

Description

  The present invention relates to an optical film, and more particularly to an optical film having high heat resistance and significantly improved brittleness by blending an acrylic resin and a specific cellulose ester resin.

  Furthermore, the present invention provides a liquid crystal display device that retains very good image display properties over the long term by using the 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 (polarizer or polarizing film) is sandwiched between two optical films (polarizing plate protective film). As this polarizing plate protective film, a cellulose triacetate film is usually used.

  On the other hand, with the recent advancement of technology, the enlargement of the liquid crystal display device is accelerated, and the use of the liquid crystal display device is diversified. For example, it can be used as a large display installed on a street or in a store, or used as an advertising display in a public place using a display device called digital signage.

  In such an application, since it is assumed to be used outdoors, degradation due to moisture absorption of the polarizing film becomes a problem, and higher moisture resistance is required for the polarizing plate protective film. However, it has been difficult to obtain sufficient moisture resistance with cellulose ester films such as cellulose triacetate films that have been used in the past, and there has been a problem that the optical effect increases when the film thickness is increased to obtain moisture resistance. . Furthermore, in recent years, there has been a demand for thinning the apparatus, so that the thickness of the polarizing plate itself has also become a problem.

  On the other hand, polymethyl methacrylate (hereinafter abbreviated as PMMA), which is a representative of acrylic resin, as an optical film material with low hygroscopicity, exhibits excellent transparency and dimensional stability in addition to low hygroscopicity. It was used suitably for.

  However, as the liquid crystal display device is enlarged as described above, and the applications to the outdoors are expanded, it is necessary to increase the amount of light of the backlight so that the image can be fully recognized even outdoors. It was used under harsh conditions, and heat resistance at high temperatures and longer-term heat resistance were required.

  However, since the PMMA film has poor heat resistance, there has been a problem that the shape of the PMMA film changes when used at high temperatures or for long-term use.

  This problem is an important issue not only as a physical property of a single film but also in a polarizing plate and a display device using such a film. That is, in the liquid crystal display device, the polarizing plate curls as the film is deformed, causing a problem that the entire panel is warped.

  The problem due to film deformation is also a problem on the backlight side, but when used at the position on the viewing side surface, the design phase difference changes due to deformation, so the viewing angle changes and the color changes. The problem arises.

  In addition, the acrylic resin film is fragile and brittle when compared with a cellulose ester film and the like, and is difficult to handle. In particular, it is difficult to stably produce an optical film for a large liquid crystal display device. It was.

  As a technique for improving moisture resistance and heat resistance, a resin in which an acrylic resin is combined with an impact-resistant acrylic rubber-methyl methacrylate copolymer or butyl-modified acetyl cellulose has been proposed (Patent Document 1).

  However, sufficient brittleness improvement cannot be obtained even by this method, and handling properties are not sufficient for producing an optical film used for a large-sized liquid crystal display device. In addition, haze due to the mixed components is also generated, and when used outdoors or the like where higher contrast is required, there is a problem that the contrast of the image is lowered.

  A technique of mixing a relatively low molecular weight acrylic resin as a plasticizer or for optical performance control with respect to a conventional cellulose ester film has also been proposed (Patent Document 2).

  However, for this purpose, the acrylic resin is not added to such an extent that the moisture resistance can be sufficiently improved, so that sufficient moisture resistance cannot be obtained. Problems such as changes in value were not solved.

  Patent Document 3 proposes an optical film obtained by melt-mixing an acrylic resin having a relatively large molecular weight and a cellulose ester resin. This technique is a technique lacking versatility because the compatibility between the acrylic resin and the cellulose ester resin may not be sufficient.

  On the other hand, a cellulose ester resin grafted with an aliphatic polyester is known to have excellent optical properties (Patent Documents 4 and 5).

Japanese Patent Laid-Open No. 5-119217 JP 2003-12859 A JP 2008-88417 A JP 2007-16137 A JP 2007-254707 A

  An object of the present invention is an optical film that is transparent, highly heat resistant, and has markedly improved brittleness by blending an acrylic resin and a specific cellulose ester resin. In particular, it is an object of the present invention to provide an optical film that retains a very excellent image display property, and a liquid crystal display device using the optical film.

  The above object of the present invention is achieved by the following configurations.

  1. An optical film comprising an acrylic resin (A) and a cellulose ester resin (B) having a repeating unit represented by the following general formula (1) or (2).

  A and B represent a C1-C12 divalent hydrocarbon group or a C1-C12 divalent hydrocarbon group substituted with a hydroxyl group. However, A and B may be the same or different.

  2. A polarizing plate comprising the optical film described in 1 above.

  3. A liquid crystal display device comprising the optical film described in 1 above.

  According to the present invention, by blending an acrylic resin and a specific cellulose ester resin, it is an optical film that is transparent, highly heat resistant, and has markedly improved brittleness. It is possible to provide an optical film having very good image display properties and a liquid crystal display device using the optical film.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

<Optical film>
In the present invention, the “optical film” is a functional film used for various display devices such as a liquid crystal display, a plasma display, and an organic EL display, and more specifically, a polarizing plate protective film and a retardation film for a liquid crystal display device. , An antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an optical compensation film for expanding the viewing angle, and the like.

  The optical film of the present invention is preferably used for a polarizing plate protective film (including a polarizing plate protective film provided with a functional layer) and a retardation film.

  The optical film of the present invention comprises an acrylic resin (A) and a cellulose ester resin (B) having a repeating unit represented by the following general formula (1) or (2).

(A and B represent a divalent hydrocarbon group having 1 to 12 carbon atoms or a divalent hydrocarbon group having 1 to 12 carbon atoms substituted with a hydroxyl group, provided that A and B may be the same or different. Good.)
In the optical film of the present invention, it is preferable to add other resins, additives, and, in some cases, acrylic particles (C).

<Acrylic resin (A)>
The acrylic resin 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 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 in the optical film of the present invention has a weight average molecular weight (Mw) particularly from the viewpoint of improving brittleness as an optical film and improving transparency when it is compatible with the cellulose ester resin (B). Is preferably 80,000 to 1,000,000.

  The weight average molecular weight (Mw) of the acrylic resin (A) is more preferably in the range of 110000 to 600000, and particularly preferably in the range of 110000 to 400000.

  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 = 2,800,000-100 calibration curves were used. Sixteen 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.

  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.), Dianal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Denki Kagaku Kogyo Co., Ltd.) and the like can be mentioned. . Two or more acrylic resins can be used in combination.

<Cellulose ester resin (B) having a repeating unit represented by formula (1) or (2)>
The cellulose ester resin (B) of the present invention is a cellulose ester resin having a repeating unit represented by the general formula (1) or (2).

(A and B represent a C1-C12 divalent hydrocarbon group or a C1-C12 divalent hydrocarbon group substituted with a hydroxyl group. A and B may be the same or different. A and B are preferably hydrocarbon groups having 2 to 6 carbon atoms.
Specific examples of A are given below.
A-1-CH ₂ CH _2-
A-2 —CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ —
A-3 -CH = CH-

A-6 —CH ₂ C (CH ₃ ) ₂ —
Specific examples of B are given below.
B-1 _{-CH 2} CH 2 -
B-2-CH ₂ CH ₂ CH ₂ CH _2-

  The cellulose ester resin having a repeating unit represented by the general formula (1) or (2) of the present invention is an cellulose ester resin having an unsubstituted hydroxyl group, or an acyl such as an acetyl group, a propionyl group, a butyryl group, or a phthalyl group. An esterification reaction of a polybasic acid or an anhydride thereof with a polyhydric alcohol, or ring-opening polymerization of L-lactide or D-lactide in the presence of a cellulose ester resin in which some of the hydroxyl groups have already been substituted with groups. It can be obtained by a known method by causing self-condensation of L-lactic acid, D-lactic acid, ring-opening polymerization of a lactone ring such as γ-butyrolactone, δ-bererolactone, and ε-caprolactone.

  These components can be reacted singly or in combination of two or more, so that a graft polymer in which a so-called repeating unit is grafted to a cellulose ester is obtained.

  Examples of the polybasic acid anhydride used in the esterification reaction include, but are not limited to, maleic anhydride, phthalic anhydride, and fumaric anhydride.

  Examples of the polyhydric alcohol that can be used for the esterification reaction include glycerin, ethylene glycol, and propylene glycol.

  As the catalyst used for the esterification reaction, the reaction can be carried out without a catalyst, but a known Lewis acid catalyst or the like can be used. Examples of catalysts that can be used include metals such as tin, zinc, titanium, bismuth, zirconium, germanium, antimony, sodium, potassium, and aluminum, and derivatives thereof. Particularly, the derivatives include metal organic compounds, carbonates, oxides, halides. Is preferred.

  Specific examples include octyl tin, tin chloride, zinc chloride, titanium chloride, alkoxy titanium, germanium oxide, zirconium oxide, antimony trioxide, and alkyl aluminum.

  Moreover, an acid catalyst typified by p-toluenesulfonic acid can also be used as the catalyst. Moreover, in order to accelerate | stimulate the dehydration reaction of carboxylic acid and alcohol, you may add well-known compounds, such as carbodiimide and dimethylaminopyridine.

  This reaction may be a reaction in an organic solvent capable of dissolving cellulose ester and other compounds to be reacted, or a reaction using a batch kneader capable of heating and stirring while adding a shearing force. It may be by reaction using a uniaxial or biaxial extruder.

  The repeating unit of this invention can be suitably contained in 0.5-190 mass% with respect to a cellulose.

  Although the sum total of the substitution degree of a cellulose-ester resin can be selected suitably, it is preferable from the point of thermoplasticity and heat workability that it is 2.2-3.

  In the cellulose ester resin of the present invention, when a part of the hydroxyl group of cellulose is substituted with an aliphatic acyl group other than the repeating unit of the present invention, the aliphatic acyl group has 2 to 20 carbon atoms, specifically Include acetyl, propionyl, butyryl, isobutyryl, valeryl, pivaloyl, hexanoyl, octanoyl, lauroyl, stearoyl, etc., preferably selected from acetyl, propionyl, butyryl, most preferably an acetyl group and a propionyl group. .

  In this case, the substitution degree is preferably 0.5 to 2.5 for the acetyl group and 0.5 to 2.8 for the propionyl group.

  The repeating unit of the present invention has a number average molecular weight of 50 to 10,000, preferably 200 to 5,000, and most preferably 300 to 2,000.

Note that the number average molecular weight of a repeating unit of cellulose ester has is, GPC data cellulose ester resin after reaction with the previous cellulose ester resin to an esterification reaction was in terms of polystyrene or, ^{1 H-NMR} (JEOL JNM- EX-270: solvent: methylene dichloride).

  When the repeating unit of the present invention is introduced into cellulose, an oligomer or polyester having the repeating unit represented by the general formula (1) or (2) may be generated as a side reaction, but these compounds are used as a plasticizer. Since it acts, it does not necessarily need to be completely removed by purification, and may be contained in the cellulose ester.

  If content is 30 mass% with respect to cellulose-ester resin, there will be little change in the property of cellulose-ester resin. From the viewpoint of plasticity, it is preferably 0.5 to 20% by mass.

  These oligomers and polyesters have a number average molecular weight of 300 to 10,000, and preferably 500 to 8,000 from the viewpoint of plasticity.

  The optical film of the present invention can be produced by the solution casting method or melt casting film forming method of the cellulose ester resin of the present invention, but it is preferable to use the melt casting film forming method in view of environmental suitability.

  The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the optical film of the present invention is preferably 55% by mass or more of the optical film, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

<Other resins>
The optical film of the present invention may contain a resin other than the acrylic resin (A) and the cellulose ester resin (B) having a repeating unit represented by the general formula (1) or (2).

  As the resin, cellulose ester resins other than the cellulose ester resin (B) having a repeating unit represented by the general formula (1) or (2), polyester, polycarbonate, polystyrene resin, etc., are usually used for optical films. It is possible to appropriately contain a material having good compatibility with the acrylic resin.

<Other additives>
The optical film of the present invention includes a plasticizer for imparting processability to the film, an antioxidant for preventing deterioration of the film, an ultraviolet absorber for imparting an ultraviolet absorbing function, and fine particles (matting agent) for imparting slipperiness to the film. It is preferable to contain additives such as

<Plasticizer>
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. A terminal aromatic polyester is also preferred.

  Furthermore, it is also preferable to contain a sugar ester compound such as Monopet SB (Daiichi Kogyo Seiyaku Co., Ltd.).

  The viscosity of the plasticizer has a correlation with the molecular structure and molecular weight, but in the case of an adipic acid type plasticizer, a range of 200 to 5000 MPa · s (25 ° C.) is preferable 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.

<Antioxidant>
In this invention, what is generally known can be used as an antioxidant.

  In particular, lactone, sulfur, hindered amine, phenol, double bond, 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 “Tinvin 144” and “Tinvin 770”, “Tinuvin 111 FDL”, and ADEKA Co., Ltd. under the name “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 means an effect of making the color tone of a liquid crystal screen blue, adjusting the 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.

  As the matting agent used in the present invention, any inorganic compound or organic compound may be used as long as it has heat resistance at the time of melting without impairing the transparency of the obtained film. For example, talc, mica, zeolite, diatomaceous earth, Calcined siliceous clay, kaolin, sericite, bentonite, smectite, clay, silica, quartz powder, glass beads, glass powder, glass flakes, milled fiber, wollastonite, boron nitride, boron carbide, titanium boride, magnesium carbonate, Heavy calcium carbonate, light calcium carbonate, calcium silicate, aluminum silicate, magnesium silicate, magnesium aluminosilicate, alumina, silica, zinc oxide, titanium dioxide, iron oxide, magnesium oxide, zirconium oxide, aluminum hydroxide, calcium hydroxide, water Magnesium oxide Beam, calcium sulfate, barium sulfate, silicon carbide, aluminum carbide, titanium carbide, aluminum nitride, silicon nitride, titanium nitride, and white carbon. 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 since 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.

  At least one or more stabilizers in the cellulose ester of the present invention can be selected, and the amount to be added is 0.001% by mass to 5% by mass with respect to the mass of the cellulose ester. More preferably, it is 0.005 mass% or more and 3 mass% or less, More preferably, it is 0.01 mass% or more and 0.8 mass% or less.

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

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

  The acrylic particles (C) are obtained, for example, by collecting a predetermined amount of the produced optical film, dissolving it in a solvent, stirring, and sufficiently dissolving / dispersing it, so that the pore diameter is less than the average particle diameter of the acrylic particles (C). It is preferable that the weight of the insoluble matter filtered and collected using the PTFE membrane filter is 90% by mass or more of the acrylic particles (C) added to the optical film.

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

  A commercially available thing can also be used as an acrylic particle of this invention. For example, Metabrene W-341 (C1) (manufactured by Mitsubishi Rayon Co., Ltd.), Chemisnow MR-2G (C2), MS-300X (manufactured by Soken Chemical Co., Ltd.), Kane Ace (manufactured by Kaneka Chemical Co., Ltd.), Paraloid (manufactured by Kureha Chemical Industry Co., Ltd.), Acryloid (manufactured by Rohm and Haas Co., Ltd.), Staphyloid (manufactured by Ganz Kasei Kogyo Co., Ltd.), Parapet SA (manufactured by Kuraray Co., Ltd.) and the like can be mentioned.

  In the optical film of the present invention, 0.5 to 30% by mass of acrylic particles (C) can be contained 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.

<Physical properties of optical film>
In the present invention, the brittleness index can be determined based on a criterion of whether or not it is “an optical film in which ductile fracture does not occur”. By obtaining an optical film with improved brittleness that does not cause ductile fracture, even when creating a polarizing plate for a large-sized liquid crystal display device, breakage and cracking during production do not occur, and handling is excellent. It can be an optical film.

  Here, the ductile fracture is a fracture caused by applying a stress larger than the strength of a certain material, and is defined as a fracture accompanied by significant elongation or drawing of the material until the final fracture.

In the present invention, whether or not it is “an optical film that does not cause ductile fracture” is evaluated based on the fact that no breakage or the like is observed even when a large stress is applied such that the film is folded in two. . (This evaluation is called folding resistance.)
Even if it is used as a polarizing plate protective film for a large-sized liquid crystal display device, if it is an optical film that does not cause ductile fracture even when such a large stress is applied, problems such as breakage during production Furthermore, even when the optical film is used after being peeled off after being pasted once, no breakage occurs and the optical film can be sufficiently reduced in thickness.

  If the folding resistance is 50 to 100 times, it is possible to sufficiently reduce problems such as breakage during production even when used as a polarizing plate protective film for a large-sized liquid crystal display device. Furthermore, even when the optical film is used after being pasted once and then peeled off again, no breakage occurs, and the optical film can be sufficiently reduced in thickness.

  In the present invention, the tension softening point is used as an index of heat resistance. In addition to the increasing size of liquid crystal display devices and the increasing brightness of backlight light sources, the use of digital signage and other outdoor applications demands higher brightness. However, if the tension softening point is 105 ° C. to 145 ° C., it can be determined that sufficient heat resistance is exhibited.

  In particular, it is more preferable to control to 110 ° C to 130 ° C. When the tension softening point is less than 105 ° C., the heat generated by the backlight light source cannot be withstood, and the film is likely to be deformed or light leakage is likely to occur. In addition, in the configuration in which the acrylic resin (A) and the cellulose ester resin (B) are contained in a compatible state, only 145 ° C. can be confirmed. For this reason, the tension softening point is suitably from 105 ° C to 145 ° C.

  As a specific measuring method of the temperature indicating the tension softening point of the optical film, for example, the optical film is cut out at 120 mm (length) × 10 mm (width) using a Tensilon tester (ORIENTEC, RTC-1225A). The temperature can be raised at a rate of 30 ° C./min while pulling with a tension of 10 N, and the temperature at the time when the pressure reaches 9 N is measured three times, and the average value can be obtained.

  From the viewpoint of heat resistance, the optical film preferably has a glass transition temperature (Tg) of 110 ° C. or higher. More preferably, it is 120 ° C. or higher. Especially preferably, it is 150 degreeC or more.

  The glass transition temperature referred to here is an intermediate point determined according to JIS K7121 (1987), measured using a differential scanning calorimeter (DSC-7 model, manufactured by Perkin Elmer) at a heating rate of 20 ° C. Glass transition temperature (Tmg).

  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.

  If the dimensional change rate (%) is less than 0.5% under the conditions normally used, it can be evaluated as an optical film exhibiting sufficiently low hygroscopicity. Furthermore, it is preferable that it is less than 0.3%.

  In the optical film of the present invention, it is preferable that the number of defects in a film plane of 5 μm or more is 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 excellent in the 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 the drying conditions after casting 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.

  Moreover, even when it cannot be visually confirmed, when a hard coat layer or the like is formed on the film, the coating agent may not be formed uniformly, resulting in a defect (missing coating). Here, the defect is a void in the film (foaming defect) generated due to the rapid evaporation of the solvent in the drying process of the solution casting, a foreign matter in the film forming stock solution, or a foreign matter mixed in the film forming. This refers to the foreign matter (foreign matter defect) in the film.

  In the measurement according to JIS-K7127-1999, the optical film of the present invention preferably has a breaking elongation in at least one direction of 10% or more, more preferably 20% or more.

  The upper limit of the elongation at break is not particularly limited, but is practically about 250%. In order to increase the elongation at break, it is effective to suppress defects in the film caused by foreign matter and foaming.

  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.

  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>
Although the example of the manufacturing method of an optical film is demonstrated, this invention is not limited to this.

  As the method for producing the optical film of the present invention, the usual inflation method, T-die method, calendar method, cutting method, casting method, emulsion method, hot press method and the like can be used. From the viewpoint of suppression of defects and suppression of optical defects such as die line, a solution casting film forming method and a melt casting film forming method by a casting method are preferable. Here, the solution casting method will be described.

(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 one that simultaneously dissolves the acrylic resin (A), the cellulose ester resin (B), and other additives. It can be used without any 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 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).

  In particular, the acrylic resin (A) and the cellulose ester resin (B) in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms are at least 15 to 45% by mass in total. A dissolved dope composition is preferred.

  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 The acrylic resin (A), cellulose ester resin (B) and other additives are stirred in an organic solvent mainly composed of a good solvent for the acrylic resin (A) and the cellulose ester resin (B). It is a step of forming a dope as a main solution by mixing the acrylic resin (A), cellulose ester resin (B), and other additive solutions.

  For dissolving the acrylic resin (A) and the cellulose ester resin (B), a method performed at normal pressure, a method performed below the boiling point of the main solvent, a method performed under pressure above the boiling point of the main solvent, JP-A-9-95544 Various dissolution methods such as a method of performing a cooling dissolution method as described in JP-A-9-95557 or JP-A-9-95538, a method of performing at a high pressure as described in JP-A-11-21379, and the like. Although it can be used, a method in which pressure is applied at a temperature equal to or higher than the boiling point of the main solvent is particularly preferable.

  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.

  Recycled material is a product obtained by finely pulverizing an optical film, which is generated when an optical film is formed, and is obtained by cutting out both sides of the film, or an optical film substrate that has been speculated out due to scratches, etc. This is also reused.

  Moreover, what knead | mixed and pelletized acrylic resin, cellulose-ester resin, and another additive beforehand can be used preferably.

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, a drying device 35 that alternately conveys the web through a plurality of rolls arranged in the drying device and / or a tenter stretching device 34 that clips and conveys both ends of the web with a clip are used. 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.

  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 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 a polarizing plate protective film, 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. 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 according to the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

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

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

Example 1
[Preparation of acrylic resin]
The following acrylic resins A1-A7 and MS1 and MS2 were prepared by a known method.

A1: Monomer mass ratio (MMA: MA = 98: 2), Mw 70000
A2: monomer mass ratio (MMA: MA = 97: 3), Mw 160000
A3: monomer mass ratio (MMA: MA = 97: 3), Mw350,000
A4: monomer mass ratio (MMA: MA = 97: 3), Mw550,000
A5: monomer mass ratio (MMA: MA = 97: 3), Mw 800000
A6: monomer mass ratio (MMA: MA = 97: 3), Mw 930,000
A7: monomer mass ratio (MMA: MA = 94: 6), Mw1100000
MS1: monomer mass ratio (MMA: ST = 60: 40), Mw100,000
MS2: monomer mass ratio (MMA: ST = 40: 60), Mw100,000
MMA: Methyl methacrylate MA: Methyl acrylate ST: Styrene (Synthesis of acrylic resin A8)
First, a methyl methacrylate / acrylamide copolymer suspension was prepared as follows.

Methyl methacrylate 20 parts by weight Acrylamide 80 parts by weight Potassium persulfate 0.3 part by weight Ion-exchanged water 1500 parts by weight The above is charged into the reactor and the reactor is replaced with nitrogen gas. The reaction was allowed to proceed at 70 ° C. until converted to. The obtained aqueous solution was used as a suspending agent. A solution in which 0.05 part by mass of the above suspending agent is dissolved in 165 parts by mass of ion-exchanged water is supplied to a stainless steel autoclave having a capacity of 5 liters and equipped with a baffle and a foudra-type stirring blade, and the system is filled with nitrogen gas. It stirred at 400 rpm, replacing.

  Next, a mixed substance having the following charge composition was added while stirring the reaction system.

Methacrylic acid 27 parts by weight Methyl methacrylate 73 parts by weight t-dodecyl mercaptan 1.2 parts by weight 2,2′-azobisisobutyronitrile 0.4 part by weight The mixture was heated to 70 ° C. and the internal temperature was 70 ° C. The time at which the polymerization was reached was set as the polymerization start time, and the polymerization was continued for 180 minutes.

  Thereafter, the reaction system was cooled, the polymer was separated, washed and dried in accordance with a normal method to obtain a bead-shaped copolymer. The polymerization rate of this copolymer was 97%, and the weight average molecular weight was 130,000.

Add 0.2% by mass of additive (NaOCH ₃ ) to this copolymer and use a twin screw extruder (TEX30 (manufactured by Nippon Steel Co., Ltd., L / D = 44.5)) to add nitrogen from the hopper. While purging at a rate of 10 L / min, an intramolecular cyclization reaction is performed at a screw rotation speed of 100 rpm, a raw material supply rate of 5 kg / hour, and a cylinder temperature of 290 ° C. Resin A8 was obtained. The weight average molecular weight (Mw) of the acrylic resin A8 was 130,000, and Tg was 140 ° C.

  In addition, the following commercially available acrylic resins were used.

Dianar BR80 (Mitsubishi Rayon Co., Ltd.) Mw95000
Dianar BR83 (Mitsubishi Rayon Co., Ltd.) Mw40000
Dianar BR85 (Mitsubishi Rayon Co., Ltd.) Mw280000
Dianar BR88 (manufactured by Mitsubishi Rayon Co., Ltd.) Mw 480000
80N (Asahi Kasei Chemicals Corporation) Mw100,000
The ratio of the MMA unit in the molecule in the commercially available acrylic resin was 90% by mass or more and 99% by mass or less.

(Preparation of cellulose ester resin CE1)
100 parts by mass of cellulose diacetate (degree of acetylation 55%, average polymerization degree 160) made dry by vacuum drying at 60 ° C. for 24 hours, and L− made dry by vacuum drying at 60 ° C. for 24 hours 200 parts by mass of lactide (manufactured by Pyrac Co., Ltd.) was charged into a four-necked flask equipped with a Dimroth condenser and a thermocouple and brought into an N ₂ atmosphere. The flask was immersed in an oil bath to 140 ° C. and stirred for 60 minutes. The system was dissolved.

  Thereafter, 0.2 part by mass of tin octoate was added as a ring-opening polymerization catalyst and reacted for 30 minutes. After completion of the reaction, the flask was removed from the oil bath and cooled, and chloroform was added to completely dissolve the system.

  The chloroform solution of the reaction product was reprecipitated in a large excess of methanol to obtain a flaky precipitate (graft), and the L-lactide homopolymer was removed. The precipitate was collected by filtration and dried at 60 ° C. for 5 hours or more, and then the mass was measured. The obtained cellulose ester resin is designated as CE1. The mass increase rate (graft rate) with respect to the mass of the charged cellulose diacetate was 49% by mass.

[Production of optical film]
<Preparation of optical film 1>
(Dope solution composition 1)
Dianal BR85 (manufactured by Mitsubishi Rayon Co., Ltd.) 70 parts by mass Cellulose ester resin CE1 30 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass The above composition was sufficiently dissolved while heating to prepare a dope solution.

(Optical film formation)
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 acrylic resin web was evaporated at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while being stretched 1.1 times in the width direction by 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 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 to obtain an optical film 1 which is an acrylic resin film.

  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 1.1 times.

  The residual solvent amount of the optical film 1 described in Table 1 was 0.1%, the film thickness was 60 μm, and the winding length was 4000 m.

<Preparation of optical films 2 to 21>
Optical films 2 to 21 were produced in the same manner as in the production of the optical film 1 except that the type and composition ratio of the acrylic resin (A) were changed as shown in Table 1.

<Preparation of Comparative Optical Film for Optical Films 22-24>
The optical film 22 is an optical film produced according to the optical film described in Example 3 of JP 2008-88417 A.

  The optical film 23 is an optical film produced according to the optical film described in Example 1 of JP2007-16137A.

  The optical film 24 is an optical film produced according to the optical film described in Example 3 of JP-A-2007-254707.

"Evaluation methods"
The following evaluation was implemented about the obtained optical films 1-24.

(Ductile fracture: brittleness evaluation)
An optical film stored for 24 hours in an atmosphere of 23 ° C. and 55% RH is cut out at 100 mm (length) × 10 mm (width), and in the same atmosphere, a mountain fold and a valley fold are respectively formed in the central portion in the vertical direction Fold each time, this evaluation was measured three times and evaluated according to the following criteria. In addition, breaking of evaluation here represents having broken into two or more pieces.

○: Cannot be folded 3 times ×: Can be folded at least 1 out of 3 times (Film deformation: heat resistance evaluation for long-term use)
Each optical film was left in an atmosphere of 90 ° C. and DRY (relative humidity 5% RH or less) for 1000 hours, and then the degree of film deformation was visually observed and evaluated according to the following criteria.

○: No deformation of the film Δ: Deformation of the film is recognized ×: Remarkable deformation of the film is recognized (Dimensional change with respect to humidity change: evaluation of moisture resistance)
In the casting direction of the produced optical film, two marks (crosses) were attached and treated at 60 ° C. and 90% RH for 1000 hours, and the distance between the mark (cross) before and after treatment was measured with an optical microscope. Evaluation was made according to the following criteria.

Dimensional change rate (%) = [(a1-a2) / a1] × 100
In the formula, a1 represents a distance before heat treatment, and a2 represents a distance after heat treatment.

○: Less than 0.3% Δ: 0.3% or more, less than 0.5% ×: 0.5% or more (Characteristic evaluation as a liquid crystal display device)
<Production of Polarizing Plate (Part 1)>
A polarizing plate using each optical film as a polarizing plate protective film was prepared 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 5 times in the transport direction at 50 ° C. to prepare a polarizer.

  Next, the optical film 1 produced in Example 1 was subjected to corona treatment using an acrylic adhesive on one side of the polarizer, and then bonded.

  Furthermore, KC8UCR-5 manufactured by Konica Minolta Opto Co., Ltd., which is a retardation film subjected to alkali saponification treatment, was bonded to the other surface of the polarizer with a polyvinyl alcohol-based adhesive, and dried to produce polarizing plate 1. Similarly, polarizing plates 2 to 24 were prepared using optical films 2 to 24.

<Production of liquid crystal display device (1)>
Each of the produced polarizing plates was used to evaluate the display characteristics of the optical film.

  Remove the polarizing plates on both sides of the 32-inch TV AQ-32AD5 previously manufactured by Sharp Corporation so that the KC8UCR-5 is on the glass surface side of the liquid crystal cell. The liquid crystal display devices were each fabricated by pasting so that the absorption axis was directed in the same direction as the polarizing plate that had been pasted in advance.

(Variation of viewing angle: Evaluation of heat and moisture resistance as a polarizing plate protective film)
The following evaluation was performed using the liquid crystal display devices 1 to 24 manufactured as described above.

  The viewing angle of the liquid crystal display device was measured using EZ-Contrast 160D manufactured by ELDIM in an environment of 23 ° C. and 55% RH. Subsequently, a sample obtained by treating the polarizing plate at 60 ° C. and 90% RH for 1000 hours was measured in the same manner, and evaluated according to the following criteria.

○: No change in viewing angle △: A little change in viewing angle is observed ×: Large viewing angle change (Color shift: Evaluation of heat and moisture resistance as a polarizing plate protective film)
Regarding the produced liquid crystal display devices 1 to 24, the display was displayed in black in an environment of 23 ° C. and 55% RH and observed from an oblique angle of 45 °. Subsequently, the polarizing plate treated at 60 ° C. and 90% RH for 1000 hours was observed in the same manner, and the color change was evaluated according to the following criteria.

○: No color change Δ: Color change is slightly recognized ×: Color change is large Table 2 shows the results of the above evaluation.

  As shown in Table 2, the optical film of the present invention exhibited high heat resistance and excellent properties for improving brittleness. Moreover, the polarizing plate and liquid crystal display device produced using the optical film of the present invention exhibited excellent properties in visibility and color shift.

Example 2
<Production of Polarizing Plate (Part 2)>
In the production of the polarizing plate (part 1), the optical films 1 and 24 of the present invention are used on one side of the polarizer, and KC4UY manufactured by Konica Minolta Opto is used on the other side. In the same manner as in (No. 1), the polarizing plates 25 and 26 were produced by bonding to both sides of the polarizer.

<Production of liquid crystal display device (2)>
Only the front-side (observer side) polarizing plate of Hitachi 32-inch display W32-L7000 was peeled off, and the prepared polarizing plates 25 and 26 were each made of the film of the present invention as a glass surface of a liquid crystal cell. The liquid crystal display devices 25 and 26 were produced by bonding so that the absorption axis was directed in the same direction as the polarizing plate that had been bonded in advance.

  With respect to this liquid crystal display device, viewing angle variation and color shift were evaluated under the same conditions as described in Example 1.

  The results of the above evaluation are shown in Table 3.

  As shown in Table 3, even a polarizing plate produced using the optical film of the present invention and a liquid crystal display device of a system different from that of Example 1 exhibited excellent properties in visibility and color shift.

Claims (3)

An optical film comprising an acrylic resin (A) and a cellulose ester resin (B) having a repeating unit represented by the following general formula (1) or (2).

A and B represent a C1-C12 divalent hydrocarbon group or a C1-C12 divalent hydrocarbon group substituted with a hydroxyl group. However, A and B may be the same or different.   A polarizing plate comprising the optical film according to claim 1.   A liquid crystal display device comprising the optical film according to claim 1.