JP2010122340A - Optical film, method for forming the same, polarizing plate using them, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film and a method for forming the film improved in all brittleness, a yellow degree and a bleed-out property, and to provide a polarizing plate and a liquid crystal display device having a favorable rework property and high contrast. <P>SOLUTION: The optical film is characterized in that: the film contains an acrylic resin (A) and cellulose ester resin (B) in a mass ratio of 95:5 to 30:70; the acrylic resin (A) has a weight average molecular weight Mw of 110,000 to 1,000,000; the cellulose ester resin (B) has a total substitution degree (T) of acyl groups of 2.0 to 3.0 and a substitution degree of acyl groups having 3 to 7 carbon atoms of 1.2 to 3.0; the cellulose ester resin (B) has a weight average molecular weight Mw of 75,000 to 300,000; and the film further contains an acrylic oligomer having a weight average molecular weight Mw of 500 to 30,000; and the film contains a solvent by not more than 0.01 mass% with respect to the whole mass of the optical film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film, a method for producing the same, a polarizing plate using the same, and a liquid crystal display device. More specifically, the present invention relates to an optical film having improved brittleness, yellowness and bleed-out simultaneously, a method for producing the same, a reworkability, and a high-contrast polarizing plate and a liquid crystal display device.

  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. In this configuration, a polarizer (also referred to as a polarizer or a 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 a cellulose ester film such as a cellulose triacetate film conventionally used.

  As a technique for improving moisture resistance, a method of combining an acrylic resin with an impact-resistant acrylic rubber-methyl methacrylate copolymer or butyl-modified acetylcellulose in a quantitative ratio of 60 to 90/40 to 10 has been proposed (patent) In this method, the acrylic resin film is prone to breakage and brittleness (brittleness), and it can stabilize optical films especially for large liquid crystal display devices during film production and during rework processes. It was difficult to manufacture.

  Patent Document 2 proposes a film produced by mixing an acrylic resin and a cellulose ester resin and manufactured by a melt casting method. In the melt casting method, the resin viscosity is important, and in order to ensure an appropriate viscosity, it is necessary to lower the molecular weight of the acrylic or raise the melting temperature.

  In Patent Document 2, melt film formation is performed by reducing the molecular weight. However, this method cannot sufficiently improve brittleness because the molecular weight of the acrylic resin is small. In addition, melt film formation has a problem that phase separation is likely to occur and brittleness becomes worse as compared with solution film formation.

  If the molecular weight is increased to improve brittleness, the brittleness is improved, but it is necessary to raise the melting temperature, the resin is likely to be decomposed, and the film is colored yellow. Therefore, until now, it has been difficult to achieve both brittleness and coloring.

Patent Document 2 also describes an example in which a plasticizer is added. This improves brittleness and coloring, but plasticizer bleedout occurs, and brittleness, coloring, and bleedout can both be achieved. It wasn't.
Japanese Patent Laid-Open No. 5-119217 JP 2008-88417 A

  The present invention has been made in view of the above-described problems and situations, and a problem to be solved is to provide an optical film having improved brittleness, yellowness, and bleed-out simultaneously, and a method for producing the same. Another object of the present invention is to provide a polarizing plate and a liquid crystal display device having good reworkability and high contrast.

  The above-mentioned problem according to the present invention is solved by the following means.

  1. The acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 30:70, the weight average molecular weight Mw of the acrylic resin (A) is 110000 to 1000000, and the cellulose ester resin ( The acyl group total substitution degree (T) of B) is 2.0 to 3.0, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0, and the cellulose ester resin (B) Contains an acrylic oligomer having a weight average molecular weight Mw of 75,000 to 300,000 and a weight average molecular weight Mw of 500 to 30,000, and the content of the solvent is 0.01% by mass or less based on the total mass of the optical film. An optical film characterized in that

  2. 2. The method for producing an optical film according to 1 above, wherein the optical film is produced by a melt casting film forming method.

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

  4). 4. A liquid crystal display device comprising the polarizing plate described in 3 above.

  By the above means of the present invention, it is possible to provide an optical film having improved brittleness, yellowness and bleed-out simultaneously and a method for producing the same. Accordingly, it is possible to provide a polarizing plate and a liquid crystal display device having good reworkability and high contrast.

  The optical film of the present invention contains the acrylic resin (A) and the cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70, and the acrylic resin (A) has a weight average molecular weight Mw of 110000 to 1000000. Yes, the acyl group total substitution degree (T) of the cellulose ester resin (B) is 2.0 to 3.0, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0, The cellulose ester resin (B) has a weight average molecular weight Mw of 75,000 to 300,000, further contains an acrylic oligomer having a weight average molecular weight Mw of 500 to 30,000, and contains a solvent amount relative to the total mass of the optical film. Is 0.01% by mass or less. This feature is a technical feature common to the inventions according to claims 1 to 4.

  As a manufacturing method of the optical film of this invention, it is preferable that it is a manufacturing method of the aspect produced with the melt casting film forming method.

  The optical film of this invention can be used suitably for a polarizing plate and a liquid crystal display device having the same.

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

<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. Saturated acids, maleic acids, fumaric acids, unsaturated group-containing divalent carboxylic acids such as 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 110000 to 1000000.

  The weight average molecular weight (Mw) of the acrylic resin (A) is most preferably in the range of 130,000 to 300,000.

  The weight average molecular weight of the acrylic resin of the present invention can be measured by gel permeation chromatography (hereinafter abbreviated as GPC). The measurement conditions are as follows.

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

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

  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 (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 group substitution degree (T) of 2.0 to 3.3 from the viewpoint of transparency, particularly when it is improved in brittleness and is compatible with the acrylic resin (A). The substitution degree of 0 and the acyl group having 3 to 7 carbon atoms is preferably 1.2 to 3.0. That is, the cellulose ester resin of the present invention is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used, but a propionyl group is particularly preferably used. .

  When the total substitution degree of the acyl group of the cellulose ester resin (B) is less than 2.0, that is, when the residual degree of the hydroxyl groups (hydroxyl groups) at the 2, 3 and 6-positions of the cellulose ester molecule is more than 1.0. In such a case, when the acrylic resin (A) and the cellulose ester resin (B) are not sufficiently compatible with each other and used as an optical film, haze becomes a problem.

  Moreover, even if the total substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, still sufficient compatibility cannot be obtained, Brittleness will decrease. For example, even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1. When it is less than 2, the compatibility is lowered and the haze is increased.

  Even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 8 or more carbon atoms is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2. In such a case, the brittleness deteriorates and desired characteristics cannot be obtained.

  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 7 carbon atoms is 1.2 to 3. If it is 0.0, there is no problem, but it is preferable that the total degree of substitution of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms is 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.

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

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

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

  In the cellulose ester resin (B) as described above, having a structure having at least one kind of an aliphatic acyl group having 3 to 7 carbon atoms is used as a structure used in the cellulose resin of the present invention.

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

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

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

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

  The weight average molecular weight (Mw) of the cellulose ester resin according to the present invention is 75000 or more, particularly from the viewpoint of improving compatibility with the acrylic resin (A) and brittleness, and requires a range of 75,000 to 300,000. Preferably, it is in the range of 100,000 to 240,000, and those of 160000 to 240,000 are particularly preferable. When the important average molecular weight (Mw) of the cellulose ester resin is less than 75,000, the effect of improving heat resistance and brittleness is not sufficient, and the effect of the present invention cannot be obtained. In the present invention, two or more kinds of cellulose resins can be mixed and used.

  In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 30:70, preferably 95: 5 to 50:50, and Preferably it is 90: 10-60: 40. In addition, it is preferable that the said resin is contained in a compatible state.

  If the mass ratio of the acrylic resin (A) and the cellulose ester resin (B) is more than 95: 5, the effect of the cellulose ester resin (B) cannot be sufficiently obtained, and the mass ratio is When the amount of acrylic resin is less than 30:70, the moisture resistance becomes insufficient.

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

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

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

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

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

  In the optical film of the present invention, the weight average molecular weight (Mw) of the acrylic resin (A), the weight average molecular weight (Mw) of the cellulose ester resin (B), and the degree of substitution are different in solubility in the solvent of both resins. It is obtained by measuring each after use.

  When fractionating the resin, it is possible to extract and separate the soluble resin by adding a compatible resin in a solvent that is soluble only in either one. At this time, heating operation or reflux is performed. May be. A combination of these solvents may be combined in two or more steps to separate the resin. The dissolved resin and the resin remaining as an insoluble matter are filtered off, and the solution containing the extract can be separated by an operation of evaporating the solvent and drying.

  These fractionated resins can be identified by general structural analysis of polymers. When the optical film of the present invention contains a resin other than the acrylic resin (A) and the cellulose ester resin (B), it can be separated by the same method.

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

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

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

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

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

  For example, a resin composition disclosed in Japanese Patent Application Laid-Open No. 2007-231050, that is, a cellulose acylate (acyl cellulose) and a graft chain formed by graft polymerization of a hydroxy acid component on the hydroxyl group of this cellulose acylate The hydroxy acid-modified cellulose acylate having an average of 0.1 to 5 mol in terms of hydroxy acid with respect to 1 mol of glucose unit constituting cellulose acylate, Use a resin composition composed of a thermoplastic resin (rubber-containing styrene resin, aromatic polycarbonate resin, aromatic polyester resin, aliphatic polyester resin, etc.) as long as the function as an optical film is not impaired. Can do.

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

  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.

  When using resins and additives other than the acrylic resin (A) and the cellulose ester resin (B), it is preferable to adjust the addition amount within a range not impairing the function of the optical film of the present invention.

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

  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.

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

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

  Preferred embodiments of the multilayer structure acrylic granular composite used in the acrylic resin composition according to the present invention include the following. (A) Monomer composed of 80 to 98.9% by mass of methyl methacrylate, 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and 0.01 to 0.3% by mass of polyfunctional grafting agent An innermost hard layer polymer obtained by polymerizing a mixture of the body, (b) in the presence of the innermost hard layer polymer, an alkyl acrylate having an alkyl group of 4 to 8 carbon atoms of 75 to 98.5% by mass. A crosslinked soft layer polymer obtained by polymerizing a mixture of monomers comprising 0.01 to 5% by mass of a polyfunctional crosslinking agent and 0.5 to 5% by mass of a multifunctional grafting agent, (c) In the presence of a polymer comprising an inner hard layer and a crosslinked soft layer, a mixture of monomers comprising 80 to 99% by mass of methyl methacrylate and 1 to 20% by mass of alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. Outermost obtained by polymerizing The layered polymer has a three-layer structure, and the obtained three-layered polymer is the innermost hard layer polymer (a) 5 to 40% by mass, the soft layer polymer (b) 30 to 60% by mass. And the outermost hard layer polymer (c) 20 to 50% by mass, having an insoluble part when fractionated with acetone, and an insoluble granular part having a methyl ethyl ketone swelling degree of 1.5 to 4.0 Complex.

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

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

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

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

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

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

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

  In addition to these polymerizable monomers, it is possible to copolymerize 25% by mass or less of other monofunctional monomers capable of copolymerization.

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

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

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

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

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

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

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

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

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

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

  The particle diameter of the acrylic particles (C) preferably used in the present invention is not particularly limited, but is preferably 10 to 1000 nm, more preferably 20 to 500 nm, particularly 50 to Most preferably, it is 400 nm.

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

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

  Further, specific examples of the acrylic particles (C) that are graft copolymers suitably used as the acrylic particles (C) preferably used in the present invention include unsaturated carboxylic acid esters in the presence of a rubbery polymer. Copolymerization of a mixture of monomers, unsaturated carboxylic acid monomers, aromatic vinyl monomers, and other vinyl monomers copolymerizable with these if necessary Examples thereof include a graft copolymer.

  The rubbery polymer used for the acrylic particles (C) that are the graft copolymer is not particularly limited, but diene rubber, acrylic rubber, ethylene rubber, and the like can be used. Specific examples include polybutadiene, styrene-butadiene copolymer, block copolymer of styrene-butadiene, acrylonitrile-butadiene copolymer, butyl acrylate-butadiene copolymer, polyisoprene, butadiene-methyl methacrylate copolymer, Butyl acrylate-methyl methacrylate copolymer, butadiene-ethyl acrylate copolymer, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, ethylene-isoprene copolymer, and ethylene-methyl acrylate copolymer A polymer etc. are mentioned. These rubbery polymers can be used alone or in a mixture of two or more.

  Moreover, when adding an acrylic particle (C) to the optical film of this invention, the refractive index of the mixture of an acrylic resin (A) and a cellulose-ester resin (B) and the refractive index of an acrylic particle (C) must be near. From the viewpoint of obtaining a film with high transparency. Specifically, the refractive index difference between the acrylic particles (C) and the acrylic resin (A) is preferably 0.05 or less, more preferably 0.02 or less, and particularly preferably 0.01 or less.

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

  The difference in refractive index referred to here is a solution in which the optical film of the present invention is sufficiently dissolved in a solvent in which the acrylic resin (A) is soluble, under appropriate conditions, and this is made into a cloudy solution, which is subjected to an operation such as centrifugation. After separating the solvent-soluble part and the insoluble part and purifying the soluble part (acrylic resin (A)) and insoluble part (acrylic particles (C)), the measured refractive index (23 ° C., measuring wavelength: 550 nm). ) Difference.

  There is no restriction | limiting in particular in the method of mix | blending an acrylic particle (C) with an acrylic resin (A) in this invention, After blending an acrylic resin (A) and another arbitrary component previously, Usually at 200-350 degreeC, A method of uniformly melt-kneading with a single-screw or twin-screw extruder while adding acrylic particles (C) is preferably used.

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

  A commercially available thing can also be used as an acrylic particle concerning this invention.

  For example, metabrene W-341 (C2) (manufactured by Mitsubishi Rayon Co., Ltd.), Chemisnow MR-2G (C3), MS-300X (C4) (manufactured by Soken Chemical Co., Ltd.) and the like can be mentioned.

  In the optical film of the present invention, it is preferable to contain 0.5 to 30% by mass of acrylic particles (C) 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.

<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>
<Acrylic oligomer>
The optical film of the present invention contains an acrylic oligomer having a weight average molecular weight Mw of 500 to 30,000.

  By combining acrylic oligomers, both brittleness and bleedout can be achieved. When the molecular weight is less than 500, there is a problem that bleedout is likely to occur. When it is greater than 30000, a remarkable effect is seen in improving brittleness. There is a problem of disappearing.

  Although the monomer as a monomer unit which comprises the acrylic oligomer useful for this invention is mentioned below, it is not limited to this.

  The ethylenically unsaturated monomer unit constituting the polymer obtained by polymerizing the ethylenically unsaturated monomer is as a vinyl ester, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl pivalate, caproic acid. Vinyl, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl benzoate, vinyl cinnamate Etc .; Examples of acrylic esters include methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n -, I-, s-), hexyl acrylate (n I-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic Cyclohexyl acid, acrylic acid (2-ethylhexyl), benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3- Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, acrylic acid (2-methoxy) Ethyl), acrylic acid (2-ethoxyethyl), etc .; What changed the luric acid ester into the methacrylic acid ester; As an unsaturated acid, acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid etc. can be mentioned, for example.

  The acrylic oligomer is a homopolymer or copolymer of the above-mentioned monomers, but the acrylic acid methyl ester monomer unit preferably has 30% by mass or more, and the methacrylic acid methyl ester monomer unit has 40% by mass or more. preferable. In particular, a homopolymer of methyl acrylate or methyl methacrylate is preferred.

  In order to synthesize an oligomer having a weight average molecular weight of 500 to 30,000, it is difficult to control the molecular weight in normal polymerization, and it is desirable to use a method that can align the molecular weight as much as possible without increasing the molecular weight. Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method of using a chain transfer agent such as carbon tetrachloride, a method of using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and further, Japanese Patent Application Laid-Open No. 2000-128911 or 2000-344823. Examples include a compound having one thiol group and a secondary hydroxyl group (hydroxyl group), or a bulk polymerization method using a polymerization catalyst in which the compound and an organometallic compound are used in combination. Although preferably used in the present invention, the method described in the publication is particularly preferable.

  In the present invention, an oligomer having a hydroxyl group (hydroxyl group) in the side chain can also be preferably used. The monomer unit having a hydroxyl group (hydroxyl group) is the same as the monomer described above, but acrylic acid or methacrylic acid ester is preferable. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), Acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or Those obtained by replacing these acrylic acids with methacrylic acid can be mentioned, and preferred are 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. The acrylic acid ester or methacrylic acid ester monomer unit having a hydroxyl group (hydroxyl group) in the polymer is preferably contained in the polymer in an amount of 2 to 20% by mass, more preferably 2 to 10% by mass.

  The method of having a hydroxyl group (hydroxyl group) at at least one terminal of the main chain of the acrylic oligomer is not particularly limited as long as it has a hydroxyl group (hydroxyl group) at the terminal of the main chain. A method using a radical polymerization initiator having a hydroxyl group (hydroxyl group) such as 2-hydroxyethyl butyrate), a method using a chain transfer agent having a hydroxyl group (hydroxyl group) such as 2-mercaptoethanol, a hydroxyl group A method of using a polymerization terminator having (hydroxyl group), a method of having a hydroxyl group (hydroxyl group) at the terminal by living ion polymerization, and one thiol as disclosed in JP-A No. 2000-128911 or 2000-344823 Having a hydroxyl group and a secondary hydroxyl group (hydroxyl group), or , Using a combination with a polymerization catalyst to the compound and an organic metal compound can be obtained by a method such as the bulk polymerization, it is a preferred method according to particular publication. The polymer produced by the method related to the description in this publication is commercially available as Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used. The polymer having a hydroxyl group (hydroxyl group) at the terminal and / or the polymer having a hydroxyl group (hydroxyl group) in the side chain has an effect of significantly improving the compatibility and transparency of the polymer in the present invention.

  The hydroxyl group (hydroxyl group) value of the acrylic oligomer of the present invention is preferably 30 to 150 [mgKOH / g].

(Measurement method of hydroxyl group (hydroxyl group) value)
This measurement conforms to JIS K 0070 (1992). The hydroxyl group (hydroxyl group) value is defined as the number of mg of potassium hydroxide required to neutralize acetic acid bonded to a hydroxyl group (hydroxyl group) when 1 g of a sample is acetylated. Specifically, sample Xg (about 1 g) is precisely weighed in a flask, and 20 ml of an acetylating reagent (a solution obtained by adding pyridine to 20 ml of acetic anhydride to 400 ml) is accurately added thereto. An air cooling tube is attached to the mouth of the flask and heated in a glycerin bath at 95-100 ° C. After 1 hour and 30 minutes, the mixture is cooled, 1 ml of purified water is added from an air condenser, and acetic anhydride is decomposed into acetic acid. Next, titration is performed with a 0.5 mol / L potassium hydroxide ethanol solution using a potentiometric titrator, and the inflection point of the obtained titration curve is set as the end point. Further, as a blank test, titration is performed without a sample, and an inflection point of the titration curve is obtained. The hydroxyl group (hydroxyl group) value is calculated by the following formula.

Hydroxyl group (hydroxyl group) value = {(BC) × f × 28.05 / X} + D
(Wherein B is the amount of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test (ml), and C is the amount of 0.5 mol / L potassium hydroxide ethanol solution used in the titration (ml). F is a factor of 0.5 mol / L potassium hydroxide ethanol solution, D is an acid value, and 28.05 is 1/2 of 1 mol amount of potassium hydroxide 56.11)
The weight average molecular weight of the acrylic oligomer of the present invention can be adjusted by a known molecular weight adjusting method. Examples of such a molecular weight adjusting method include a method of adding a chain transfer agent such as carbon tetrachloride, lauryl mercaptan, octyl thioglycolate, and the like. The polymerization temperature is usually room temperature to 130 ° C., preferably 50 ° C. to 100 ° C., and this temperature or the polymerization reaction time can be adjusted.

  The measuring method of a weight average molecular weight can be based on the following method.

(Weight average molecular weight measurement method)
The weight average molecular weight Mw was measured using 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 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000 to 500 samples were used. Thirteen samples are used at approximately equal intervals.

  The acrylic oligomer 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.

<Other plasticizers>
Examples of other plasticizers include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy. Select these plasticizers depending on the application, or By using in combination, it can be applied to a wide range of uses.

<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”, ADEKA “ADEKA STAB AO-50” 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 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) 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. .

  In the present invention, the brittleness index is determined based on the 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 manufacturing a polarizing plate for a large-sized liquid crystal display device, breakage and cracking during production do not occur, and the handling property 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.) If it is an optical film that does not cause ductile fracture even when such a large stress is applied, it is used as a polarizing plate protective film for an enlarged liquid crystal display device. Even in such a case, it becomes possible to sufficiently reduce problems such as breakage at the time of manufacture. Further, even when the optical film is used after being peeled off once, the breakage does not occur, and the optical film It can sufficiently cope with thinning.

  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. When the folding resistance is less than 50 times, breakage is likely to occur during production and the reworkability is poor. Moreover, in order to exceed 100 times, it can be achieved by increasing the film thickness, but it cannot cope with the thinning of the liquid crystal display device. Therefore, in the case of a thin film, 50 to 100 times is appropriate.

  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 value determined according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a temperature rising rate of 20 ° C./min. Point 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.

  According to the optical film of the present invention containing the acrylic resin (A) and the cellulose ester resin (B), high transparency can be obtained, but when using acrylic particles for the purpose of improving another physical property. By increasing the difference in refractive index between the resin (acrylic resin (A) and cellulose ester resin (B)) and the acrylic particles (C), an increase in haze value can be prevented.

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

  Regarding bleed-out, the film was visually observed for white turbidity and dirt generated under a fluorescent lamp and a green lamp.

  Regarding the yellowness, which represents the degree of coloration of the film, the absorption spectrum of the obtained cellulose ester film was measured using a spectrophotometer U-3310 manufactured by Hitachi High-Technologies, and tristimulus values X, Y, and Z were calculated. The yellowness YI was calculated from these tristimulus values X, Y, and Z based on JIS-K7103.

  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 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.

  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 thickness of the optical film of the present invention is preferably 20 μm or more. More preferably, it is 30 μm or more.

  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 by melt casting method>
The method for producing an optical film of the present invention comprises melting an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 30:70, extruding them from a die, and placing them on a cooling roll. It is the manufacturing method of the optical film to cast.

  The entire manufacturing method will be described below.

<Melted pellet manufacturing process>
The composition constituting the optical film comprising the acrylic resin (A), cellulose ester resin (B), and other additives used for melt extrusion is usually preferably kneaded in advance and pelletized.

  Pelletization may be performed by a known method. For example, dry acrylic resin (A), dry cellulose ester resin (B) and other additives are fed to an extruder with a feeder and mixed using a single-screw or twin-screw extruder. It can be smelted, 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 as to be able to be pelletized so that the shearing force is suppressed and the resin does not deteriorate (decrease in molecular weight, 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>
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 a defect is also called a die line, but in order to reduce surface defects such as a die line, 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.

  In the present invention, there is no particular limitation on the cooling roll, but it is a roll having a structure in which a heat medium or a refrigerant body whose temperature can be controlled flows through a high-rigidity metal roll, and its size is not limited. It is sufficient that the film is large enough to cool the film, and the diameter 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 surface of the cooling roll 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.

  In the present invention, examples of the elastic touch roll include JP-A-03-124425, JP-A-08-224772, JP-A-07-1000096, JP-A-10-272676, WO97-028950, JP-A-11-235747, A silicon rubber roll coated with a thin film metal sleeve can be used as described in Japanese Unexamined Patent Application Publication No. 2002-36332, Japanese Patent Application Laid-Open No. 2005-172940 and Japanese Patent Application Laid-Open No. 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, the film obtained as described above can be further stretched 1.01 to 3.0 times in at least one direction after passing through the step of contacting the cooling roll.

  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, when the optical film 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 + 50 ° C. In the temperature range.

  The stretching is preferably performed under a uniform temperature distribution controlled in the longitudinal direction or 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 in which the film is shrunk 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.

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

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

<Contained solvent amount>
Since the optical film of the present invention is produced by the melt casting 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.

  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 up to 100 ° C. at 80 ° C./min. Headspace heating condition: 20 minutes at 120 ° C.
<Optical film manufacturing equipment>
FIG. 1 is a schematic flow sheet showing the overall configuration of the optical film manufacturing apparatus of the present invention. In FIG. 1, an optical film is manufactured by mixing a film material such as an acrylic resin, and then melt-extruding it from a casting die 4 onto a first cooling roll 5 using an extruder 1. In addition to circumscribing, the film 10 is further circumscribed by a total of three cooling rolls, that is, the second cooling roll 7 and the third cooling roll 8, and is cooled and solidified to form a film 10. Next, the film 10 peeled off by the peeling roll 9 is then stretched in the width direction by holding both ends of the film by the stretching device 12 and then wound by the winding device 16. In addition, a touch roll 6 is provided that clamps the molten film on the surface of the first cooling roll 5 in order to correct the flatness. The touch roll 6 has an elastic surface and forms a nip with the first cooling roll 5.

  In the present invention, it is preferable to add a device for automatically cleaning the belt and the roll to the manufacturing apparatus. There is no particular limitation on the cleaning device, but for example, a method of niping a brush roll, a water absorbing roll, an adhesive roll, a wiping roll, etc., an air blowing method for spraying clean air, a laser incinerator, or a combination thereof. is there.

  In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

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

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

  A polarizer, which is a main component of a polarizing plate, is an element that 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]
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 various drive LCDs. 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.

  In addition, there was little color unevenness, glare and wavy unevenness, and the eyes were not tired even during long-time viewing.

  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 A2-A7 and MS1, 2 were prepared by a known method.

A2: monomer mass ratio (MMA: MA = 97: 3), Mw120,000
A3: monomer mass ratio (MMA: MA = 97: 3), Mw 140000
A4: monomer mass ratio (MMA: MA = 97: 3), Mw200000
A5: monomer mass ratio (MMA: MA = 97: 3), Mw 500,000
A6: monomer mass ratio (MMA: MA = 97: 3), Mw550,000
A7: monomer mass ratio (MMA: MA = 94: 6), Mw 1000000
MMA: methyl methacrylate MA: methyl acrylate In addition, the following commercially available acrylic resins were used.

A1: Acrypet V (Mitsubishi Rayon Co., Ltd.) Mw100,000
[Synthesis of acrylic oligomer]
Acrylic resins AC1 to AC6 shown in Table 1 were prepared by a known method.

  Moreover, MA, MMA, and HEMA described in Table 1 are abbreviations for the following compounds, respectively.

MA: methyl acrylate MMA: methyl methacrylate HEMA: 2-hydroxyethyl methacrylate

  The weight average molecular weights of AC1 to AC6 are shown in Table 1 by the following measurement method.

(Molecular weight measurement)
The weight average molecular weight was measured using high performance liquid 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 (GL Science Co., Ltd.)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0 ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 100000 to 500 samples were used. Thirteen samples are used at approximately equal intervals.

  70 parts by weight of A2, 30 parts by weight of cellulose acetate propionate as cellulose ester (acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, total acyl group substitution degree 2.75, Mw = 200000) 3 parts by mass of AC1, 1.5 parts by mass of Tinuvin 928 (manufactured by Ciba Japan), 0.01 parts by mass of ADK STAB PEP-36 (manufactured by Asahi Denka Kogyo Co., Ltd.), Irganox 1010 (Ciba Japan) The composition 1 which comprises the optical film 1 was mix | blended in the ratio of 0.5 mass part and Sumilizer GS (Sumitomo Chemical Co., Ltd. product) 0.2 mass part.

Each of the above compositions was further dried with mixing in a vacuum nauter mixer at 80 ° C. and 1.33 × 10 ² Pa (1 Torr) for 3 hours. The dried composition was melt-mixed at 235 ° C. using a twin-screw extruder and pelletized.

  The above pellets were laminated with a T-die using each single-screw extruder, and melted and extruded into a film at a melting temperature of 240 ° C on a first cooling roll having a surface temperature of 90 ° C. An optical film 1 having a thickness of 80 μm was obtained by extrusion molding. At this time, the film was pressed on the first cooling roll with an elastic touch roll having a 2 mm thick metal surface.

  In the production of the optical film 1, a film was formed in the same manner except that the types of acrylic resin (A) and cellulose ester resin (B), molecular weight, composition ratio, type of plasticizer, and melting temperature were changed as shown in Table 2. The present invention and comparative optical films 2 to 27 having a thickness of 80 μm were obtained.

  In addition, all of these solvent contents were 0.01 mass% or less.

  Plasticizer 1: DOA (dioctyl adipate)

  The following evaluation was performed about the obtained optical film.

"Evaluation methods"
(Folding resistance)
The optical film is cut out at 120 mm (length) × 10 mm (width), conditioned in a room conditioned at a temperature of 23 ° C. and a relative humidity of 55% RH for 4 hours, and then cut by bending according to ISO877 6 / 2-1988. The number of round trips was determined, and the folding resistance was ranked according to the following criteria.

A: 80 or more B: 70 or more and less than 80 Δ: 50 or more and less than 70 ×: less than 50 50 or more is practical.

(Yellowness)
Using a spectrophotometer U-3310 manufactured by Hitachi High-Technologies Corporation, the absorption spectrum of the obtained cellulose ester film was measured, and tristimulus values X, Y, and Z were calculated. From these tristimulus values X, Y, Z, yellowness YI was calculated based on JIS-K7103, and the yellowness was ranked according to the following criteria.

○: Less than 0.8 Δ: 0.8 or more and less than 1.0 ×: 1.0 or more and less than 2.0 Less than 1.0 is practical.

(Bleed out)
The film was cut out in the width direction, and white turbidity and dirt generated on the film were visually observed under a fluorescent lamp and a green lamp, and bleed out was ranked according to the following criteria.

  ○: No cloudiness or dirt.

  Δ: There is weak cloudiness or dirt.

  X: There are strong cloudiness and dirt.

<Production of polarizing plate and liquid crystal display device>
<Preparation of polarizing plate>
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, Konica Minolta Tack KC8UCR-5 (manufactured by Konica Minolta Opto Co., Ltd.), which is an alkali saponified retardation film, was bonded to the other surface of the polarizer and dried to prepare a polarizing plate P1. Similarly, polarizing plates P2 to P27 were produced using the optical films 2 to 27.

(Reworkability)
In an atmosphere of 23 ° C. and 55% RH, the produced polarizing plate is cut into a square having a size of 20 cm × 20 cm and bonded to a glass substrate using an acrylic adhesive. Next, the bonded polarizing plate is peeled off from the glass with a strength of 5N from the corner. This operation is performed with 100 polarizing plates for one type of sample, and the number of polarizing plates that are not peeled off completely is counted. Reworkability was ranked according to the following criteria.

◯: 0 to 5 sheets △: 6 to 10 sheets △: 11 to 15 sheets ×: 16 sheets or more There is no practical problem as long as the reworkability is △ level or more, but it is preferably ◯ level or more. A level is particularly preferred.

<Production of liquid crystal display device>
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 manufactured by Sharp Corporation in advance so that Konica Minolta Tack KC8UCR-5 is on the glass surface side of the liquid crystal cell. And it bonded so that an absorption axis might face in the same direction as the polarizing plate previously bonded, and each liquid crystal display device was produced.

[Front contrast]
The measurement was performed after the backlight of each liquid crystal display device was lit continuously for 1 hour in an environment of 23 ° C. and 55% RH. For measurement, EZ-Contrast 160D manufactured by ELDIM was used to measure the luminance from the normal direction of the display screen of white display and black display with a liquid crystal display device, and the ratio was defined as the front contrast.

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 front contrast at any five points of the liquid crystal display device was measured and evaluated according to the following criteria.

○: 1100-1200
Δ: 1000 to less than 1100 ×: less than 1000

  It is clear that the optical film of the present invention is preferable in terms of reworkability and contrast, and is improved with respect to comparison.

Example 2
<Preparation of acrylic particles (C1)>
A reactor with a reflux condenser with an internal volume of 60 liters was charged with 38.2 liters of ion-exchanged water and 111.6 g of sodium dioctylsulfosuccinate, and the temperature was raised to 75 ° C. under a nitrogen atmosphere while stirring at a rotational speed of 250 rpm. The effect of oxygen was virtually eliminated. 0.36 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of 1657 g of MMA, 21.6 g of BA, and 1.68 g of ALMA was added all at once, and after the exothermic peak was detected, the mixture was held for another 20 minutes to polymerize the innermost hard layer. Completed.

  Next, 3.48 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of BA 8105 g, PEGDA (200) 31.9 g, and ALMA 264.0 g was continuously added over 120 minutes. Hold for a minute to complete the polymerization of the soft layer.

  Next, 1.32 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of 2106 g of MMA and 201.6 g of BA was continuously added over 20 minutes. The polymerization of was completed.

  Next, 1.32 g of APS was added, and after 5 minutes, a monomer mixture consisting of 3148 g of MMA, 201.6 g of BA, and 10.1 g of n-OM was continuously added over 20 minutes, and the mixture was held for another 20 minutes after the addition was completed. Next, the temperature was raised to 95 ° C. and held for 60 minutes to complete the polymerization of the outermost hard layer 2.

  A small amount of the polymer latex thus obtained was collected, and the flat particle size was determined by the absorbance method, which was 0.10 μm. The remaining latex was put into a 3% by mass sodium sulfate warm aqueous solution, salted out and coagulated, and then dried after repeated dehydration and washing to obtain acrylic particles (C1) having a three-layer structure.

  The above abbreviations are the following materials.

MMA; methyl methacrylate MA; methyl acrylate BA; n-butyl acrylate ALMA; allyl methacrylate PEGDA; polyethylene glycol diacrylate (molecular weight 200)
n-OM; n-octyl mercaptan APS; ammonium persulfate Hereinafter, Examples except that the acrylic resin (A), the cellulose ester resin (B), the acrylic particles (C), and the composition ratio were changed as shown in Table 4. Optical films 2-1 and 2-2 were produced in the same manner as in the method for producing optical film 2 described in 1.

  The acrylic resin-containing film 2-3 was prepared in the same manner as in 2-2 by adding the following ultraviolet absorber simultaneously with other resins.

Tinuvin 109 (manufactured by Ciba Japan Co., Ltd.) 1.5 parts by mass Tinuvin 171 (manufactured by Ciba Japan Co., Ltd.) 0.7 parts by mass The solvent content of these optical films is 0.01% by mass. % Or less.

  These samples were evaluated in the same manner as in Example 1. The results are shown in Table 6.

  As described above, when acrylic fine particles were further added to the optical film of the present invention, folding resistance and reworkability could be further improved.

Schematic flow sheet showing one embodiment of an optical film manufacturing apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Extruder 2 Filter 3 Static mixer 4 Casting die 5 Rotating support body (1st cooling roll)
6 Nipping pressure rotating body (touch roll)
7 Rotating support (second cooling roll)
8 Rotating support (3rd cooling roll)
DESCRIPTION OF SYMBOLS 9 Peeling roll 10 Film 11, 13, 14 Conveyance roll 12 Stretching machine 15 Slitter 16 Winding machine F Optical film of this invention

Claims (4)

The acrylic resin (A) and the cellulose ester resin (B) are contained in a mass ratio of 95: 5 to 30:70, the weight average molecular weight Mw of the acrylic resin (A) is 110000 to 1000000, and the cellulose ester resin ( The acyl group total substitution degree (T) of B) is 2.0 to 3.0, the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3.0, and the cellulose ester resin (B) Contains an acrylic oligomer having a weight average molecular weight Mw of 75,000 to 300,000 and a weight average molecular weight Mw of 500 to 30,000, and the content of the solvent is 0.01% by mass or less based on the total mass of the optical film. An optical film characterized in that It is a manufacturing method of the optical film of Claim 1, Comprising: It produces with the melt casting film forming method, The manufacturing method of the optical film characterized by the above-mentioned. A polarizing plate comprising the optical film according to claim 1. A liquid crystal display device comprising the polarizing plate according to claim 3.

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