JP2005225990A - Additive for optical film, optical film containing the same, polarizing plate and liquid crystal display device using the optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an additive for an optical film which can be blended into the optical film such as a polarizing plate-protective film without reducing transparency and chemical resistance thereof and can give sufficient ultraviolet absorption properties to the optical film over a long period of time, and to provide an optical film containing the same, and a polarizing plate and a liquid crystal display device each of which uses the optical film. <P>SOLUTION: The additive for an optical film is a copolymer of 10-50 mass% of at least one ultraviolet absorbing monomer (A) selected from a benzophenone-based ultraviolet absorbing monomer represented by formula (1) and a benzotriazole-based ultraviolet absorbing monomer represented by formula (2), 5-50 mass% of at least one halogen-containing monomer (B) selected from halogen-containing monomers represented by formulas (3) and (4), and 20-80 mass% of a vinyl monomer (C) copolymerizable with these monomers, wherein the copolymer has a weight average molecular weight of 5,000 to 100,000. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an additive compounded in an optical film used for optical applications such as a liquid crystal display device, an organic EL display device, and a plasma display, and in particular, a protective film for a polarizing plate and a retardation film used for a liquid crystal display device and the like. Additive for optical film that imparts excellent transparency (light transmittance), heat and humidity resistance, chemical resistance, etc. to the film, optical film containing the same, polarizing plate and liquid crystal using the same The present invention relates to a display device.

  In recent years, cellulose ester films such as cellulose triacetate (hereinafter sometimes referred to as TAC) have been used for optical film applications such as polarizing plate protective films and retardation films, taking advantage of their optical properties. However, the TAC film has a problem of yellowing due to light (ultraviolet rays), and addition of an ultraviolet absorber is essential to prevent the polarizing plate from being deteriorated by ultraviolet rays. Conventionally, benzophenone-based or benzotriazole-based low molecular weight UV absorbers have been used, but low molecular weight UV absorbers are not necessarily compatible with TAC films. Therefore, it often bleeds from the film over time, aggregates to hinder the transparency of the film, or deteriorates the ultraviolet absorption characteristics.

  Further, when a TAC film such as a polarizing plate is attached, there is a case where a TAC film is immersed in an aqueous sodium hydroxide solution and partially saponified for the purpose of improving the adhesiveness of the adhesive. When this treatment is performed, many particles of low molecular weight UV absorbers are coarsened or crystallized on the surface of the film and precipitate, which often hinders transparency of the film or lowers UV absorption characteristics. . In particular, when used as a liquid crystal display panel used in an automotive instrument display panel or car navigation application, the polarizing plate must satisfy severe moisture resistance, but a film added with a low molecular weight UV absorber is particularly It is easy to cause functional deterioration.

  As a method for solving the problems of these conventional low molecular weight UV absorbers, a method of adding a polymer UV absorber to a film has been proposed in Patent Document 1, Patent Document 2, and the like. In Patent Document 1, an ultraviolet-absorbing polymer comprising a copolymer of a monomer having an ultraviolet-absorbing group and methyl methacrylate is added at the time of forming a TAC film, whereby ultraviolet absorption characteristics, spectral absorption characteristics, heat and humidity resistance are obtained. Excellent TAC film. In Patent Document 2, as an ultraviolet absorbing polymer, for example, a TAC film having a transmittance of 500% or more of 92% is obtained by incorporating a copolymer of dihydroxybenzotriazole and adipic acid into the TAC film.

JP-A-6-148430 JP 2002-47357 A

  However, although the polymer ultraviolet absorber described in the above document is improved in the bleed of the ultraviolet absorber as compared with the low molecular ultraviolet absorber, the compatibility with the TAC film is not sufficient and the film is transparent. There were many things that hurt sex.

  Therefore, the present invention is an additive for optical films that can be blended in an optical film such as a polarizing plate protective film without impairing transparency and chemical resistance, and can impart sufficient ultraviolet absorption characteristics to the optical film over a long period of time. It is an object to provide an optical film including the same, a polarizing plate using the same, and a liquid crystal display device.

  As a result of intensive studies to solve the above problems, the present inventors have obtained a weight average molecular weight of 5,000 to 100, which is obtained by polymerizing an ultraviolet absorbing monomer, a halogen-containing monomer, and a vinyl monomer copolymerizable therewith. The above-mentioned problems can be solved by adding a halogen-containing polymer ultraviolet absorber of 000 or less to the optical film, and the transmittance, heat and humidity resistance and chemical resistance of the optical film compared to conventional polymer ultraviolet absorbers. The present inventors have found that the properties are further improved and have completed the present invention.

  That is, the present invention provides at least one ultraviolet absorbing monomer (A) 10 selected from a benzophenone ultraviolet absorbing monomer represented by the following formula (1) and a benzotriazole ultraviolet absorbing monomer represented by the following formula (2). 50 mass%, at least one halogen-containing monomer (B) selected from the halogen-containing monomers represented by the following formula (3) and the following formula (4), 5 to 50 mass%, and a vinyl monomer copolymerizable therewith (C) It is a copolymer with 20 to 80% by mass, and provides an additive for an optical film characterized by being a copolymer having a weight average molecular weight of 5,000 or more and 100,000 or less. is there.

(In formula (1), R ¹¹ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxyl group having 1 to 6 carbon atoms. R ¹² represents an alkylene group having 1 to 10 carbon atoms or 1 carbon atom. 10 represents an oxyalkylene group of 10 to 10, m ¹ represents 0 or 1. R ¹³ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, X ¹ represents an ester bond, an amide bond, an ether bond, or a urethane. Indicates binding.)

(In the formula (2), R ²¹ represents a hydrogen atom, a halogen atom, or a methyl group. R ²² represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. R ²³ has 1 to 10 carbon atoms. An alkylene group or an oxyalkylene group having 1 to 10 carbon atoms, m ²¹ represents 0 or 1. R ²⁴ is an alkylene group having 1 to 8 carbon atoms, an alkylene group having 1 to 8 carbon atoms having an amino group, or an alkylene group having 1 to 8 carbon atoms having a hydroxyl group, .R ²⁵ m ²² is showing a 0 or 1 is hydrogen atom, or .X ² represents an alkyl group having 1 to 3 carbon atoms is an ester bond, an amide (A bond, an ether bond, or a urethane bond is shown.)

(In formula (3), R ³¹ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. R ³² represents an alkylene group having 1 to 6 carbon atoms. R ³³ represents a hydrogen atom or a CF ₃ group. M ³ represents an integer of 1 to 7.)

(In formula (4), R ⁴¹ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.)

  Moreover, this invention provides 5-50 mass% of said optical film additives in conversion of solid content, The optical film characterized by the above-mentioned is provided. This optical film is preferably a cellulose ester film. This cellulose ester film is suitably used as a polarizing plate protective film.

  The present invention also provides a polarizing plate using the above cellulose ester film, and further, this polarizing plate is disposed on at least one side of a liquid crystal cell. Is to provide.

  The additive for optical films of the present invention can be blended without impairing the transparency and chemical resistance of the optical film itself. The film containing the additive does not deteriorate in transparency even when left for a long time under high temperature and high humidity conditions, and has sufficient ultraviolet absorption characteristics (change in transmittance at 350 nm is 1.0%) Less than). The optical film additive of the present invention is particularly compatible with the cellulose ester film and does not impair the transparency of the film. Therefore, the polarizing plate and the liquid crystal display device produced using this film have light resistance, Excellent durability.

  Moreover, since the additive for optical films of the present invention is copolymerized with a halogen-containing monomer, it has an effect of compensating for a decrease in moisture resistance of the film accompanying the thinning of the optical film. Therefore, by using the optical film containing the additive of the present invention for the polarizing plate protective film, the polarizing plate and the liquid crystal display device can be easily reduced in weight and thickness.

  Furthermore, since the additive for optical films of the present invention can be polymerized in a solvent that is a good solvent for cellulose ester, it is not necessary to take out the polymer from the solvent by an operation such as reprecipitation after the polymerization. In the case of producing an optical film, if the polymer is added to the cellulose ester solution as it is, the film can be formed by casting or the like, so that the working efficiency during film formation is greatly improved.

  The additive for optical films of the present invention comprises at least one ultraviolet absorbing monomer (A) selected from a benzophenone ultraviolet absorbing monomer represented by the formula (1) and a benzotriazole ultraviolet absorbing monomer represented by the formula (2). 10 to 50% by mass (hereinafter abbreviated as%), 5 to 50% of at least one halogen-containing monomer (B) selected from the halogen-containing monomers represented by formula (3) and formula (4), and It is a copolymer of 20 to 80% of a vinyl monomer (C) that can be copolymerized with a copolymer having a weight average molecular weight of 5,000 or more and 100,000 or less. Hereinafter, the details of the additive for optical films of the present invention will be described.

  In the present invention, as the ultraviolet absorbing monomer (A), at least one selected from the benzophenone ultraviolet absorbing monomer represented by the formula (1) and the benzotriazole ultraviolet absorbing monomer represented by the formula (2) is used. . By copolymerizing the ultraviolet absorbing monomer, yellowing of the optical film due to light (ultraviolet rays) can be prevented, and the polarizing plate can be prevented from deterioration of the ultraviolet rays.

In the formula (1), examples of the alkyl group having 1 to 6 carbon atoms (R ¹¹ ) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a s-butyl group, a t-butyl group, and a pentyl group. A hexyl group, preferably an alkyl group having 1 to 4 carbon atoms (more preferably 1 to 2 carbon atoms). Moreover, as a C1-C6 alkoxyl group (R < ¹¹ >), a methoxy group, an ethoxy group, a propoxy group, a butoxy group etc. are mentioned, for example, Preferably it is C1-C4 (more preferably 1-2). Of the alkoxyl group.

R ¹¹ may be substituted at any position in the benzene ring substituted with a hydroxyl group, and the preferred substitution position of R ¹¹ is the 3-position or 5-position.

Further, in the equation (1) and / or formula (2), the alkylene group having 1 to 10 carbon atoms (R ^12, R ^23), for example, methylene group, ethylene group, trimethylene group, propylene group, tetramethylene group , A pentamethylene group, a hexamethylene group, an octamethylene group, a decamethylene group, and the like, preferably an alkylene group having 1 to 6 carbon atoms (more preferably an alkylene group having 1 to 4 carbon atoms). Examples of the oxyalkylene group having 1 to 10 carbon atoms (R ¹² and R ²³ ) include an oxymethylene group, an oxyethylene group, and an oxypropylene group.

R ¹² may be substituted at any position in the benzene ring substituted with a hydroxyl group, and the preferred substitution position of R ¹² is the 4-position or 5-position, and the 4-position is particularly preferred. R ²³ may be substituted at any site in the benzene ring substituted with a hydroxyl group. A preferred substitution position for R ²³ is the 5-position.

Examples of the halogen atom (R ²¹ ) include a fluorine atom, a chlorine atom, and a bromine atom, and a chlorine atom is preferable. When R ²¹ is a halogen atom or a methyl group, R ²¹ may be substituted at any position in the benzene ring. Preferable R ²¹ includes a hydrogen atom.

In the hydrocarbon group having 1 to 6 carbon atoms (R ²² ), an alkyl group is preferably used as the hydrocarbon group. Such alkyl groups include those having 1 to 6 carbon atoms among the exemplified alkyl groups. R ²² may be substituted at any position in the benzene ring substituted with a hydroxyl group, and the preferred substitution position of R ²² is the 3-position.

Examples of the alkylene group having 1 to 8 carbon atoms (R ²⁴ ) include an alkylene group having 1 to 8 carbon atoms among the above-exemplified alkylene groups, preferably 1 to 4 carbon atoms (more preferably 1 to 4 carbon atoms). The alkylene group of 2) is mentioned. Moreover, as a C1-C8 alkylene group which has a C1-C8 alkylene group which has an amino group, or a hydroxyl group, what the amino group or the hydroxyl group substituted by the said alkylene group is mentioned. It is done.

X ¹ and X ² represent an ester bond, an amide bond, an ether bond, or a urethane bond, specifically, —COO—, —OCO—, —NHCO—, —CONH—, —O—, —NHCOO. -, -COONH- and the like. m ¹ , m ²¹ and m ²² represent 0 or 1, for example, when m ¹ is 0, X ¹ is directly bonded to a benzene ring substituted with a hydroxyl group without R ^12. It means that Further, when m ²¹ is 0, it means that X ² is directly bonded to the benzene ring substituted with the hydroxyl group without R ²³ , and when m ²² is 0. , X ² is directly bonded to the carbon atom to which R ²⁵ is bonded, not via R ²⁴ . That is, when m ¹ , m ²¹ or m ²² is 0, it means that R ¹² , R ²³ or R ²⁴ is not present. On the other hand, when m ¹ , m ²¹ or m ²² is 1, it means that R ¹² , R ²³ or R ²⁴ is present, for example, X ¹ is bonded to R ^12. ing.

  More specifically, examples of the benzophenone-based ultraviolet absorbing monomer represented by the formula (1) include 2-hydroxy-4-acryloyloxybenzophenone, 2-hydroxy-4-methacryloyloxybenzophenone, and 2-hydroxy-4- (2-acryloyloxy) ethoxybenzophenone, 2-hydroxy-4- (2-methacryloyloxy) ethoxybenzophenone, 2-hydroxy-4- (2-methyl-2-acryloyloxy) ethoxybenzophenone and the like can be mentioned.

  Examples of the benzotriazole-based ultraviolet absorbing monomer represented by the formula (2) include 2- [2′-hydroxy-5 ′-(methacryloyloxy) phenyl] benzotriazole and 2- [2′-hydroxy-5]. '-(Acryloyloxy) phenyl] benzotriazole, 2- [2'-hydroxy-3'-t-butyl-5'-(methacryloyloxy) phenyl] benzotriazole, 2- [2'-hydroxy-3'-methyl -5 '-(acryloyloxy) phenyl] benzotriazole, 2- [2'-hydroxy-5'-(methacryloyloxypropyl) phenyl] -5-chlorobenzotriazole, 2- [2'-hydroxy-5 '-( Methacryloyloxyethyl) phenyl] benzotriazole, 2- [2′-hydroxy-5 ′-(a Liloyloxyethyl) phenyl] benzotriazole, 2- [2′-hydroxy-3′-t-butyl-5 ′-(methacryloyloxyethyl) phenyl] benzotriazole, 2- [2′-hydroxy-3′-methyl -5 '-(acryloyloxyethyl) phenyl] benzotriazole, 2- [2'-hydroxy-5'-(acryloyloxybutyl) phenyl] -5-methylbenzotriazole, [2-hydroxy-3-t-butyl- 5- (acryloyloxyethoxycarbonylethyl) phenyl] benzotriazole and the like.

  The ultraviolet absorbing monomer (A) includes a 2-hydroxybenzophenone skeleton or a 2-hydroxybenzotriazole skeleton, and an ultraviolet absorbing compound having a functional group (hydroxyl group, carboxyl group, amino group, etc.) and a functional group (hydroxyl group, carboxyl group). And a copolymerizable vinyl compound (acrylic acid, methacrylic acid, etc.) having a group (such as an ester group, an amide bond, an ether bond, a urethane bond). .

  The copolymerization amount of the ultraviolet absorbing monomer (A) is 10 to 50%, more preferably 20 to 45%, particularly preferably 25 to 45%, based on the total amount of the monomer components. Thus, if the amount of copolymerization is less than 10%, a large amount of the additive of the present invention must be added in order to develop the ultraviolet absorption characteristics. As a result, compatibility with optical films and transparency This is because the sex is lowered. On the other hand, when it exceeds 50%, the compatibility with the optical film is lowered, and the additive bleeds out to impair the transparency of the film.

  The said ultraviolet absorption monomer (A) can be used individually or in combination of 2 or more types.

  In the present invention, as the halogen-containing monomer (B), at least one selected from halogen-containing monomers represented by the above formula (3) or formula (4) is used. By copolymerizing these halogen-containing monomers, the transparency and chemical resistance of the film when the copolymer is added to the optical film are dramatically improved. The reason is not clear, but fluorine elements with high electronegativity break hydrogen bonds with strong intermolecular forces. In other words, it is considered that the additive containing fluorine element interrupts and coordinates the hydrogen bond between triacetyl cellulose to form a bundle structure, thereby improving the compatibility and consequently improving the transparency. In particular, by copolymerizing the fluorine-containing monomer represented by the formula (3), the heat and humidity resistance of the film is improved when the copolymer is added to the optical film. The reason is not clear, but it is thought that the film is water-repellent by hydrophobic fluorine atoms contained in the copolymer.

In the formula (3), R ³¹ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ³² is an alkylene group having 1 to 6 carbon atoms, R ³³ is a hydrogen atom or CF ₃ group, m ³ is 1 to It is an integer of 7. In the formula (4), R ⁴¹ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

In formula (3) and / or formula (4), examples of the alkyl group having 1 to 3 carbon atoms (R ³¹ and R ⁴¹ ) include a methyl group, an ethyl group, a propyl group, and an isopropyl group. In the formula (3), examples of the alkylene group having 1 to 6 carbon atoms (R ³² ) include a methylene group, an ethylene group, a trimethylene group, a propylene group, a tetramethylene group, a pentamethylene group, and a hexamethylene group. An alkylene group having 1 to 4 carbon atoms is preferable.

  More specifically, examples of the halogen-containing monomer represented by the formula (3) include trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, perfluorooctylethyl methacrylate, and perfluorooctylethyl. Examples include acrylate, heptadecafluorodecyl methacrylate, heptadecafluorodecyl acrylate, and the like.

  As the halogen-containing monomer represented by the formula (3), a commercially available fluorine-containing monomer can also be used. Examples of commercially available products include trade name “light acrylate” (manufactured by Kyoeisha Chemical Co., Ltd.), Leicester (manufactured by Tosoh F-Tech) is listed.

  Examples of the halogen-containing monomer represented by the formula (4) include 3-chloro-2-hydroxypropyl acrylate and 3-chloro-2-hydroxypropyl methacrylate.

  The copolymerization amount of the halogen-containing monomer (B) is 5 to 50%, more preferably 7 to 45%, particularly preferably 10 to 40%, based on the total amount of the monomer components. Thus, the amount of copolymerization is limited to less than 5%, in order to develop heat and humidity resistance, a large amount of the polymeric ultraviolet absorber of the present invention must be added. This is because compatibility and transparency are lowered. On the other hand, when it exceeds 50%, the solubility in various solvents decreases, and the versatility of handling and processing decreases.

  The said halogen-containing monomer (B) can be used individually or in combination of 2 or more types.

  The copolymerizable vinyl monomer (C) is not particularly limited as long as it is copolymerizable with the ultraviolet absorbing monomer (A) and the halogen-containing monomer (B), and used alone or in combination of two or more. be able to. By copolymerizing the copolymerizable vinyl monomer (C) with the above monomers (A) and (B), the compatibility with the film of the optical film additive of the present invention is improved, and without bleeding out. Since the additive (polymer ultraviolet absorber) remains in the optical film, the effect is maintained for a long time. Further, by copolymerizing the copolymerizable vinyl monomer (C), it becomes easy to adjust the molecular weight and copolymerizability of the polymer. Furthermore, when the copolymer is composed only of the ultraviolet absorbing monomer (A) or the halogen-containing monomer (B), the adjustment range such as the glass transition point of the polymer after polymerization is narrowed. By containing (C) as a structural unit, there is an advantage that the degree of freedom of the adjustment range as a polymer is increased.

  Examples of the copolymerizable vinyl monomer (C) that can be used in the present invention include styrene monomers such as styrene and α-methylstyrene; methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylic Acrylic acid ester monomers such as lauryl acid and stearyl acrylate; methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, benzyl methacrylate, isophorone methacrylate, methacrylic acid Methacrylate monomers such as isobornyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate; vinyl acetate monomers such as vinyl acetate; α, β-unsaturated polybasic acid monoalkyl ester Polybasic acid ester monomers such as ter, α, β-unsaturated polybasic acid dialkyl esters; alkyl vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; alkoxy polyethylene glycol (n = 1 to 20) (meth) acrylic acid Examples include esters and phenoxypolyethylene glycol (n = 1 to 20) (meth) acrylic acid ester-containing (meth) acrylic acid ester-based monomers such as (meth) acrylic acid esters; acrylonitrile and the like.

  Among these, acrylic acid ester monomers and methacrylic acid ester monomers are preferable, and (meth) acrylic acid alkyl esters having 1 to 4 carbon atoms and methacrylic acid esters having a hydroxyl group are particularly preferable.

  The copolymerization amount of the copolymerizable vinyl monomer (C) is 20 to 80%, more preferably 25 to 70%, particularly preferably 30 to 65%, based on the total amount of the monomer components. Thus, the amount of copolymerization is limited when the content is less than 20%, the compatibility of the additive of the present invention with the optical film is decreased. On the other hand, when the content exceeds 80%, it is added to develop the ultraviolet absorption property. This is because a large amount of the agent must be used, and as a result, compatibility with the optical film and transparency are lowered.

  The weight average molecular weight (Mw) of the additive for optical films of the present invention is from 5,000 to 100,000, more preferably from 7,000 to 100,000. When the weight average molecular weight (Mw) is less than 5,000, the moisture resistance and heat resistance of the optical film is inferior. On the other hand, when the weight average molecular weight (Mw) exceeds 100,000, the compatibility between the additive and the optical film is lowered and the transparency is lowered, so that it cannot be used as an optical film. Moreover, when a weight average molecular weight is outside said range, chemical resistance is inferior, for example, there exists a problem which yellows at the time of the alkali process at the time of using as a polarizing plate protective film.

  In addition, a weight average molecular weight (Mw) is a polystyrene conversion molecular weight by the gel permeation chromatography (GPC) mentioned later.

  The copolymer of the present invention can be produced by a conventionally known polymerization method such as a solution polymerization method, a suspension polymerization method or an emulsion polymerization method. For example, when preparing by a solution polymerization method, a monomer component (an ultraviolet absorbing monomer (A), a halogen-containing monomer (B), a copolymerizable vinyl monomer (C)) is added to an organic solvent, and polymerization is performed in the presence of a polymerization initiator. However, it is not limited to these methods.

  Further, the organic solvent and polymerization initiator used in the solution polymerization are not particularly limited, and known ones can be widely used. Examples of the polymerization solvent include known solvents such as esters such as methyl acetate and ethyl acetate, aromatic hydrocarbons such as benzene, toluene and xylene, ketones such as acetone, cyclohexane and methyl ethyl ketone, and ethers such as tetrahydrofuran. These solvents can be used alone or in admixture of two or more. In addition to the above solvent, a good TAC solvent such as N-methylpyrrolidone or dichloromethane can also be used as the polymerization solvent. A copolymer obtained by solution polymerization using such a good solvent as a polymerization solvent does not need to be taken out by a separation operation such as reprecipitation, and the copolymer is added together with a solvent to an optical film preparation solution such as a cellulose ester film. This is preferable in that it can be performed. When the polymerization solvent is not distilled off after polymerization and is contained in the optical film additive together with the produced polymer as it is, the polymer concentration in the additive is usually 40 to 60% in terms of solid content. Is appropriate.

  Examples of the polymerization initiator include peroxides such as benzoyl peroxide and azo compounds such as azobisisobutyronitrile. These polymerization initiators may be used alone or in combination of two or more. Can be used. Although the usage-amount of a polymerization initiator is not specifically limited, It is good to set it as about 0.05-2% of a monomer composition.

  In addition, when prepared by an emulsion polymerization method, it can be prepared by emulsifying the above monomer components using an emulsifier if necessary, and performing emulsion polymerization in the presence of a polymerization initiator. It is not limited to the method. Moreover, a well-known emulsifier etc. can be used suitably for the emulsifier, the polymerization initiator, etc. which are used by the said emulsion polymerization. In addition, after water is distilled off from the aqueous emulsion after polymerization, the remaining polymer component can be dissolved in a solvent and used as an additive for an optical film. In this case, the polymer concentration in the additive is the solid content. It is appropriate to make it 10 to 50% in terms of conversion.

  The additive for optical films of the present invention contains a copolymer polymerized by the above-described method or the like, but the content thereof is selected according to the purpose and may be diluted with a polymerization solvent or a diluting solvent.

  The additive for optical film of the present invention is added to the optical film as a powder or a solution (dissolved or dispersed in an organic solvent). In general, the amount added is preferably 5 to 50% in terms of solid content in the optical film, more preferably 10 to 30%. If the amount added is too small, the UV absorption properties are insufficiently imparted, while if the amount added is too large, the additive bleeds out and the transparency of the film decreases. The addition method is not particularly limited. For example, when an optical film is produced by a solution casting method, a method such as adding to a solution in which a resin is dissolved may be used.

  The resin that forms the optical film is not particularly limited as long as it is used for optical applications such as a liquid crystal display device, and is a polarizing plate protective film, a retardation film, a viewing angle compensation film, a brightness enhancement film, an antireflection film, an anti-reflection film. It is usually used as a material resin for glare films, antistatic films, conductive films and the like. Examples of such resins include cellulose ester resins such as cellulose diacetate, cellulose triacetate, cellulose propionate, and cellulose butyrate, polyester resins, polyethersulfone resins, polycarbonate resins, polyamide resins, and polyimide resins. And polyethersulfone resins, polysulfone resins, polystyrene resins, acrylic resins, polynorbornene resins, polyolefin resins, and the like. Among these resins, cellulose ester resins are particularly preferably used.

  Next, a preparation example of a cellulose ester-based optical film will be described. In the present invention, a conventional method for producing an optical film can be used as it is, except that the optical film additive of the present invention is added to a solution in which the optical film material resin is dissolved. Specifically, a cellulose ester resin, which is a material for the optical film, is dissolved in a solvent, and the additive of the present invention is added thereto. If necessary, other additives (plasticizer, matting agent, etc.) are added. As the solvent, methylene chloride, dioxolane, acetone, methyl acetate, ethyl acetate or the like may be used alone or in combination. The concentration of the cellulose ester resin is preferably 10 to 30%. The cellulose ester solution is cast from a pressure die onto an endless metal belt that is infinitely transported or a support for casting a rotating metal drum, and dried to form a film.

  The optical film of the present invention can be used as various optical films such as a polarizing plate protective film, a retardation film, a viewing angle compensation film, a brightness enhancement film, an antireflection film, an antiglare film, a conductive film, and an antistatic film. The thickness of the optical film is 500 μm or less, preferably 5 to 300 μm, particularly preferably 5 to 150 μm.

  Among the above optical films, the optical film of the present invention is extremely excellent as a polarizing plate protective film. The polarizing plate can be produced by a general method. For example, the surface of the cellulose ester film of the present invention is saponified with alkali or the like, and adsorbed with iodine or dichroic dye on a polyvinyl alcohol film and stretched, and then attached to one or both surfaces of a polarizer. There is a method of bonding using an agent. By saponifying the surface of the protective film, the wettability of the adhesive is improved and the adhesiveness is improved.

  The polarizing plate of the present invention can be used for forming various display devices such as liquid crystal display devices, organic EL display devices, and plasma displays. In particular, it can be preferably used for a reflective, transflective, or transmissive liquid crystal display device in which a polarizing plate is disposed on one or both sides of a liquid crystal cell.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only the following Examples.

(Example 1)
Into a 1 L separable flask equipped with a Dim funnel, a dropping funnel, a thermometer, a nitrogen introduction tube, and a stirrer, the monomers and other raw materials shown in Table 1 are placed, and the temperature is raised to 50 ° C. while blowing nitrogen from the nitrogen introduction tube. . Thereafter, a solution of azobisisobutyronitrile dissolved in a small amount of a polymerization solvent is added dropwise over 30 minutes. After completion of the dropwise addition, the temperature is raised to 70 ° C. and the reaction is performed for 8 hours. Prepared. When the molecular weight of the halogen-containing polymeric ultraviolet absorber was examined by gel separation chromatography, the weight average molecular weight was about 10,000.

(Method for measuring weight average molecular weight by GPC)
As a column, product name “TSKGel GMHXL (manufactured by Tosoh Corporation)” × 2 and product name “TSKGel G2000HXL (manufactured by Tosoh Corporation)” × 1, tetrahydrofuran as a mobile phase, and differential refractometer as a detector RI-8000 "was used. Measurement conditions are a sample concentration of 0.5 mg / ml, a temperature of 40 ° C., and a flow rate of 0.8 ml / min.

(Examples 2 to 4)
In the same manner as in Example 1, halogen-containing polymeric ultraviolet absorbers according to Examples 2 to 4 were prepared. For the halogen-containing polymeric ultraviolet absorbers according to Examples 2 to 4, the weight average molecular weights determined by gel separation chromatography are also shown in Table 1. In Table 1, the unit of the ratio of each component is g (gram).

(Comparative Examples 1-3)
In the same manner as in Example 1, polymer ultraviolet absorbers according to Comparative Examples 1 to 3 were prepared using the raw materials shown in Table 2. For the polymeric ultraviolet absorbers according to Comparative Examples 1 to 3, the weight average molecular weight determined by gel separation chromatography is also shown in Table 2. In Table 2, the unit of the ratio of each component is g (gram).

(Comparative Example 4)
Instead of the halogen-containing polymer UV absorber, a commercially available low molecular UV absorber Tinuvin 326 (manufactured by Ciba Fine Chemicals) was used.

(Comparative Example 5)
Instead of the halogen-containing polymer ultraviolet absorber, a commercially available low-molecular ultraviolet absorber Ubinal 3050 (manufactured by BASF) was used.

[Preparation of cellulose ester film]
100 parts by weight of cellulose triacetate (acetylation degree 61.0%), 10 parts by weight of triphenyl phosphate, 10 parts by weight of UV absorbers (shown in Tables 1 and 2) of Examples 1 to 4 and Comparative Examples 1 to 5 (solid) The composition consisting of 400 parts by mass of methylene chloride and 50 parts by mass of methanol was put into a sealed container and stirred under pressure at 80 ° C. for 2 hours to completely dissolve. Next, this solution was filtered, cooled, kept at 30 ° C., and applied to a stainless steel plate with a 300 μm applicator. Then, it dried for 1 minute at 40 degreeC using the warm air circulation type dryer, and obtained the film with a film thickness of 40 micrometers.

  In addition, as a polymerization solvent of Examples 1-4 and Comparative Examples 1-5, the following pre-processing was performed about the polymer which used ethyl acetate and methyl acetate individually or together.

(Preprocessing)
Each polymer was put into 3 volumes of methanol and dispersed with a homomixer for 10 minutes. Suction filtration was performed using the filter paper of No. 2, and the residue was dried at 60 ° C. for 24 hours with a hot air circulating dryer to obtain a polymer ultraviolet absorber. A high molecular weight UV absorber was dissolved in methylene chloride to prepare a 50% methylene chloride solution.

  The cellulose triacetate films obtained in the above examples and comparative examples were evaluated by the methods shown below. A film containing no UV absorber was used as a reference example. The results are summarized in Table 3.

(Evaluation methods)
[Test Example 1: Compatibility]
Using a turbidimeter NDH-300 (manufactured by Nippon Denshoku Industries Co., Ltd.), the turbidity (HAZE value) of the cellulose ester film blended with each of the Examples and Comparative Examples prepared in the above preparation examples was measured. did. The smaller the value, the better the transparency.

[Test Example 2: Durability]
The cellulose ester film blended with the ultraviolet absorbers of the examples and comparative examples prepared in the above preparation examples was allowed to stand in a high temperature and high humidity atmosphere of 80 ° C. × 90% RH for 100 hours, and then the spectrophotometer U-3300. (Manufactured by Hitachi, Ltd.) was used to measure the transmittance% T at a wavelength of 350 nm. The rate of change (Δ% T) was obtained before and after the test, and the one with a small rate of change was regarded as good.

[Test Example 3: Chemical resistance]
After immersing the cellulose ester film blended with the ultraviolet absorbers of the examples and comparative examples prepared in the above preparation examples in an aqueous solution of sodium hydroxide at 70 ° C. and 10 wt% for 5 minutes, the appearance change of the cellulose ester film was visually observed. Observed.

  From the results in Table 3, the cellulose ester film containing the optical film additive of the present invention has excellent transparency (turbidity of 1.5 or less) and absorbs ultraviolet rays even when left for a long time under high temperature and high humidity conditions. The light transmittance change (Δ% T) at 350 nm, which is an index of ultraviolet absorptivity, was 0.5% or less. Moreover, when the film surface was saponified with an alkaline aqueous solution, it did not yellow. Furthermore, the performance was equivalent to the film without an ultraviolet absorber, and it had sufficient performance as a polarizing plate protective film.

  On the other hand, the conventional polymer ultraviolet absorber (Comparative Example 1) which is not copolymerized with a halogen-based monomer has an ultraviolet absorption ability, but is inferior in compatibility with the cellulose ester film, and also has a film surface. It yellowed when saponified with an aqueous alkali solution. Moreover, the commercially available ultraviolet absorbers (Comparative Examples 4 and 5) have insufficient ultraviolet absorption characteristics (durability), and also yellowed when the film surface was saponified with an alkaline aqueous solution.

Claims (6)

At least one ultraviolet absorbing monomer (A) selected from the benzophenone ultraviolet absorbing monomer represented by the following formula (1) and the benzotriazole ultraviolet absorbing monomer represented by the following formula (2): 5 to 50% by mass of at least one halogen-containing monomer (B) selected from the halogen-containing monomers represented by the formula (3) and the following formula (4), and vinyl monomers (C) 20 to 80 copolymerizable therewith An additive for optical films, characterized in that the additive is a copolymer having a weight average molecular weight of 5,000 or more and 100,000 or less.

(In formula (1), R ¹¹ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxyl group having 1 to 6 carbon atoms. R ¹² represents an alkylene group having 1 to 10 carbon atoms or 1 carbon atom. 10 represents an oxyalkylene group of 10 to 10, m ¹ represents 0 or 1. R ¹³ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, X ¹ represents an ester bond, an amide bond, an ether bond, or a urethane. Indicates binding.)

(In the formula (2), R ²¹ represents a hydrogen atom, a halogen atom, or a methyl group. R ²² represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. R ²³ has 1 to 10 carbon atoms. An alkylene group or an oxyalkylene group having 1 to 10 carbon atoms, m ²¹ represents 0 or 1. R ²⁴ is an alkylene group having 1 to 8 carbon atoms, an alkylene group having 1 to 8 carbon atoms having an amino group, or an alkylene group having 1 to 8 carbon atoms having a hydroxyl group, .R ²⁵ m ²² is showing a 0 or 1 is hydrogen atom, or .X ² represents an alkyl group having 1 to 3 carbon atoms is an ester bond, an amide (A bond, an ether bond, or a urethane bond is shown.)

(In formula (3), R ³¹ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. R ³² represents an alkylene group having 1 to 6 carbon atoms. R ³³ represents a hydrogen atom or a CF ₃ group. M ³ represents an integer of 1 to 7.)

(In formula (4), R ⁴¹ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.) An optical film comprising the optical film additive according to claim 1 in an amount of 5 to 50% by mass in terms of solid content. The optical film according to claim 2, wherein the optical film is a cellulose ester film. The optical film according to claim 3, wherein the cellulose ester film is a polarizing plate protective film. A polarizing plate using the polarizing plate protective film according to claim 4. 6. A liquid crystal display device, wherein the polarizing plate according to claim 5 is disposed on at least one side of a liquid crystal cell.