JP2010197680A - Optical film, and polarizing plate and display apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film having a hard coat layer of high hardness by laminating the hard coat layer on a base material film containing a thermoplastic acrylic resin and cellulose nano fiber in more detail and to provide a polarizing plate which a surface of the optical film used is hardly flawed and a display apparatus using the polarizing plate. <P>SOLUTION: In the optical film having the hard coat layer on the base material film, the base material film contains the thermoplastic acrylic resin and the cellulose nano fiber with an average fiber diameter of 4 to 200 nm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical film, a polarizing plate using the same, and a display device.

  An optical film is usually provided on the surface of a display device such as a liquid crystal display device in order to impart antireflection characteristics, antiglare properties, and the like. Since such an optical film is usually a thin film and has a low hardness and is easily damaged, a hard coat layer is often applied to give the hardness. The optical characteristics of the optical film are required to be precise, and high hardness stability is required to stably exhibit the optical characteristics.

  As a technique of the hard coat layer, Patent Document 1 discloses that two kinds of specific acrylate compounds cause curling when the support is thinned in order to make an optical film having a hard coat layer on a transparent support thin. Although the technology which eliminates as a hard-coat layer which hardened | cured the composition containing this is disclosed, pencil hardness is about H, and still higher pencil hardness is requested | required.

  According to the inventor's study, in order to achieve high hardness of the optical film having a hard coat layer, it was found that increasing the elastic modulus of the base film to improve the hardness is also an effective means, From this point of view, attention was focused on thermoplastic acrylic resin films. However, although the thermoplastic acrylic resin film certainly improves the elastic modulus, it has a problem that it is difficult to handle when used as an optical film because it is weak in tearing when stretched.

JP 2005-109773 A

  Accordingly, an object of the present invention is to provide an optical film having high hardness stability by laminating a hard coat layer on a base film containing a thermoplastic acrylic resin and cellulose nanofibers. Another object of the present invention is to provide a polarizing plate and a display device that are less likely to be scratched on the surface using the same.

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

  1. An optical film having a hard coat layer on a base film, wherein the base film contains a thermoplastic acrylic resin and cellulose nanofibers having an average fiber diameter of 4 to 200 nm.

  2. 2. The optical film as described in 1 above, wherein the base film contains 10% by mass or more of a cellulose ester resin.

  3. 3. The optical film as described in 1 or 2 above, wherein the substrate film is stretched by 10% or more in at least one of the width direction and the longitudinal direction.

  4). 4. The optical film according to any one of 1 to 3, wherein the base film contains acrylic fine particles.

  5. A polarizing plate comprising a polarizer and two polarizing plate protective films sandwiching the polarizer, wherein one of the two polarizing plate protective films is the optical film according to any one of 1 to 4 above. There is a polarizing plate.

  6). 5. A display device using the optical film according to any one of 1 to 4 or the polarizing plate according to 5.

  According to the present invention, an optical film having high hardness stability can be provided by laminating a hard coat layer on a base film containing a thermoplastic acrylic resin and cellulose nanofibers. Further, it is possible to provide a polarizing plate and a display device that are less likely to be scratched on the surface using the same.

It is the figure which showed typically the dope preparation process, casting process, and drying process of the solution casting film forming method used for this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  The present inventors pay attention to the fact that cellulose nanofibers have a small diameter, a large elastic modulus, and a small linear expansion coefficient. By using them in a base film together with a thermoplastic acrylic resin, the transparency is not impaired. By increasing the hardness of the base film itself due to its elasticity and further improving the brittleness of the thermoplastic acrylic resin due to the amorphous region of the cellulose nanofibers, it is possible to obtain a high-hardness optical film that has excellent stretchability and does not break. Has been found to be possible, leading to the present invention.

  Hereinafter, the present invention will be described in detail.

<Cellulose nanofiber>
The cellulose nanofiber according to the present invention refers to a microfibril of cellulose constituting a basic skeleton of a plant cell wall or the like or a constituent fiber thereof, and is an aggregate of unit fibers having a fiber diameter of 4 to 200 nm. The fiber is preferably a cellulosic fiber having an average fiber diameter of 4 to 200 nm. This fiber may consist of what a single fiber exists apart without being arranged. In this case, the average fiber diameter is the average diameter of single fibers. Further, the fiber according to the present invention may be one in which a plurality of (may be many) single fibers are gathered into a bundle to form one yarn. The fiber diameter is defined as the average value of the diameter of one yarn.

  In the present invention, if the average fiber diameter of the fibers exceeds 200 nm, the wavelength of visible light approaches, the visible light is easily refracted at the interface between the base film and the upper layer, and transparency is lowered. The upper limit of the average fiber diameter of the fibers used in the present invention is preferably 200 nm. Since fibers having an average fiber diameter of less than 4 nm are difficult to produce, the lower limit of the average fiber diameter of the fibers used in the present invention is 4 nm. The average fiber diameter of the fiber used in the present invention is preferably 4 to 100 nm, more preferably 4 to 60 nm.

  In addition, as long as the fiber used by this invention has an average fiber diameter in the range of 4-200 nm, the thing of the fiber diameter outside the range of 4-200 nm may be contained in the fiber, but the ratio is the whole. It is preferable that the fiber diameter of all the fibers is 200 nm or less, particularly 100 nm or less, particularly 60 nm or less.

  The length of the fiber is not particularly limited, but the average length is preferably 100 nm or more. If the average length of the fibers is shorter than 100 nm, the reinforcing effect of the hard coat layer is low, and the hardness may be insufficient. In addition, although a fiber length less than 100 nm may be contained in the fiber, it is preferable that the ratio is 30 mass% or less.

  The measurement of the said fiber diameter and fiber length can be measured with a commercially available microscope and an electron microscope. For example, by taking a photograph of cellulose nanofibers magnified 2000 times with a scanning electron microscope, and then analyzing the photographic image using “SCANNING IMAGE ANALYZER” (manufactured by JEOL Ltd.) based on this photograph It was measured. Under the present circumstances, the average value of a fiber diameter and fiber length can be calculated | required using 100 cellulose nanofibers.

  The cellulosic fiber according to the present invention preferably contains 40% or more of a crystalline region in order to obtain high strength and a low linear expansion coefficient.

  It is said that it becomes an amorphous area | region except the said crystal | crystallization area | region, and exists about 40 to 50% in a wood pulp, and about 30% in a bacterial cellulose. The presence of the amorphous region gives the microfibril soft and hard but does not become brittle. In order to obtain the effect of the present invention, it is possible to use cellulose nanofibers that are 3 to 40% as a proportion of the amorphous region. More preferred.

  Here, the crystal region refers to a state in which the cellulosic fiber has a constant repeating structure, and the amorphous region refers to an amorphous state in which a specific periodic structure is not defined.

  The above state can be analyzed for cellulose nanofibers from X-ray diffraction, molecular chain structure analysis by high-resolution electron microscope observation, and three-dimensional structure analysis of glucose ring obtained from solid state NMR measurement. Specifically, the following methods are mentioned.

  The manufactured cellulose nanofiber was mounted on a sample holder, and the diffraction angle of X-ray diffraction was manipulated from 10 ° to 32 ° for measurement. After removing background scattering from the obtained X-ray diffraction pattern, the area obtained by connecting 10 °, 18.5 °, and 32 ° on the X-ray diffraction curve with a straight line becomes an amorphous region, and the others are crystal regions. Become. The ratio of the amorphous region was calculated by the following formula.

Ratio of amorphous region = (area of amorphous region) / (area of entire X-ray diffraction diagram) × 100 (%)
Cellulosic fibers used in the cellulose nanofiber according to the present invention can be suitably used even if they are separated from plants or bacterial cellulose produced by bacterial cellulose.

  The cellulose nanofiber according to the present invention can be obtained, for example, by the methods described in JP-A-2005-60680 and JP-A-2008-1728.

  In the cellulose nanofiber according to the present invention, the cellulosic fiber is preferably refined using a plurality of pulverizing means. Although the pulverizing means is not limited, in order to finely pulverize to a particle size suitable for the purpose of the present invention, there is a method that can obtain a strong shearing force such as a high-pressure homogenizer, a media mill, a grindstone rotary grinder, and a stone mill grinder. Preferably used. For example, Japanese Patent Laid-Open No. 4-82907 proposes a method for producing fibrillated natural cellulose by pulverizing natural cellulose fibers in a dry state. Furthermore, in Japanese Patent Application Laid-Open No. 06-10286, wet pulverization treatment is performed on a suspension of fibrous cellulose by a vibration mill pulverizer using beads or balls made of glass, alumina, zirconia, zircon, steel, titania or the like as a pulverization medium. The manufacturing method of the fine fibrous cellulose which gives is disclosed.

  As a device commercially available as a high-pressure homogenizer, a nanomizer (manufactured by Nanomizer Co., Ltd.), a microfluidizer (manufactured by Microfluidics) or the like can be used.

  The cellulose nanofibers thus obtained are added directly or as a dope liquid for forming a base film as a dispersion, or as an additive liquid. The content in the base film is 0.1 to 80 mass. % Is preferable. More preferably, it is 5-70 mass%, and especially 10-60 mass% is preferable.

  When the content of the cellulose nanofiber is less than 0.1% by mass, the effect of sufficiently improving the hardness and brittleness of the base film tends to be insufficient, and when it exceeds 60% by mass, the transparency decreases and the surface Flatness may deteriorate.

  Although there is no restriction | limiting in particular in the method to contain a cellulose nanofiber in the film containing a thermoplastic acrylic resin, It is preferable to add and mix in the dope mentioned later as a dispersion liquid which disperse | distributed the cellulose nanofiber previously.

  The method for preparing the dispersion containing cellulose nanofibers is not particularly limited, but the cellulose nanofibers are added in a solvent or binder having affinity for cellulose nanofibers, and dispersed by a known dispersing machine or method. Can do. It is also preferable to use a dispersant described later because uniform dispersion can be promoted.

  Solvents include water, methylene chloride, methyl acetate, ethyl acetate, amyl acetate, methyl acetoacetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-triate. Fluoroethanol, 2,2,3,3-tetrafluoro-1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, 1,3-dimethyl-2-imidazolidinone Organic halogen compounds such as methylene chloride, dioxolane derivatives, methyl acetate, ethyl acetate, Ton, methyl acetoacetate and the like are preferable. These solvents may be used alone or as a mixed solvent of two or more.

  As a binder, the presence of a water-soluble polymer during dispersion improves dispersibility and can reduce haze. The water-soluble polymers here include starches, mannans, seaweeds such as galactan and sodium alginate, plant mucilages such as tragacanth gum, gum arabic and dextran, proteins such as gelatin and casein, methylcellulose, hydroxycellulose and carboxymethylcellulose. Celluloses, polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyvinyl pyrrolidone, polyacrylamide, and other synthetic polymers.

  If the molecular weight of these water-soluble polymers is too small, an effect for improving dispersibility is not recognized. Therefore, the molecular weight is preferably 10,000 or more, more preferably 30,000 to 200,000. The molecular weight can be measured by a viscosity method, a diffusion method, a light scattering method, a gel filtration method, a high performance liquid chromatography method or the like, and particularly a gel filtration method or a high performance liquid chromatography method is preferably applied.

  The water-soluble polymer is preferably added in a mass ratio of 0.05 to 30 times with respect to the cellulose nanofibers to be dispersed, and the aqueous solution is preferably in the range of 1 to 20% by mass.

  It is also a useful method to use various surfactants for dispersion. As the surfactant, any of anionic, cationic, amphoteric, nonionic and the like can be used, but anionic and nonionic surfactants are preferable, and a cationic surfactant is particularly preferable. In addition, when adjusting the pH, a general acid-alkali aqueous solution such as sodium hydroxide, potassium hydroxide, acetic acid, citric acid, phosphoric acid, sulfuric acid or the like, preferably a buffer solution is used.

  Dispersers used for dispersing cellulose nanofibers include, for example, centrifugal dispersers (flow jet mixer, fine flow mill, etc.), media type dispersers (ball mill, sand mill, etc.), ultrasonic dispersers, homogenizers, high pressure homogenizers. Among them, a centrifugal disperser and a media type disperser are preferable.

<Base film>
The base film according to the present invention is a film containing a thermoplastic acrylic resin and the cellulose nanofiber. Hereinafter, such a base film is referred to as an “acrylic resin-containing film”.

<Acrylic resin (A)>
A methacrylic resin is also contained in the thermoplastic acrylic resin (henceforth an acrylic resin (A)) used for this invention. 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 divalent carboxylic acids such as itaconic acid, aromatic vinyl compounds such as styrene, α-methylstyrene, and nucleus-substituted styrene, α, β- such as acrylonitrile, methacrylonitrile, etc. Examples thereof include unsaturated nitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, and the like. These may be used alone or in combination of two or more.

  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 acrylic resin-containing film according to the present invention has a weight average molecular weight (Mw) from the viewpoint of compatibility with cellulose nanofibers, mechanical strength as a film, and fluidity when producing a film. Is preferably 50,000 to 300,000.

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

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2800000-500 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. Furthermore, in order to control the reduced viscosity of the produced copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.

  A commercially available thing can also be used as an acrylic resin which concerns on this invention. For example, Delpet 60N, 80N (Asahi Kasei Chemicals Co., Ltd.), Dialal BR52, BR80, BR83, BR85, BR88 (Mitsubishi Rayon Co., Ltd.), KT75 (Electrochemical Industry Co., Ltd.) and the like can be mentioned. .

<Cellulose ester resin (B)>
The acrylic resin-containing film according to the present invention preferably contains 10% by mass or more of a cellulose ester resin (hereinafter referred to as cellulose ester resin (B)) in addition to the cellulose nanofibers, and the acrylic resin (A) together with the cellulose nanofibers. It is possible to improve the brittleness of the film and suppress breakage during stretching.

  It is preferable to adjust the content mass ratio (%) of the acrylic resin (A) and the cellulose ester resin (B) to a mass ratio of 90:10 to 50:50, more preferably the acrylic resin (A) is 70 mass%. It is to adjust above.

  When the amount of the acrylic resin (A) component is increased, for example, dimensional change under high temperature and high humidity is suppressed, and curling of the polarizing plate and warping of the panel when used as a polarizing plate can be remarkably reduced. Furthermore, in the composition in which the acrylic resin (A) component is 70% by mass or more, the above physical properties can be maintained for a longer time.

  Examples of the cellulose ester resin (B) include cellulose acetate, cellulose propionate, and cellulose butyrate, JP-A Nos. 10-45804, 08-231761, and US Pat. No. 2,319,052. Etc., mixed fatty acid esters such as cellulose acetate propionate and cellulose acetate butyrate can be used. Particularly preferred are cellulose triacetate and cellulose acetate propionate. These cellulose esters can be used alone or in combination. The molecular weight is preferably 70000-200000 in terms of number average molecular weight (Mn), more preferably 100000-200000.

  In the case of cellulose triacetate, those having an average degree of acetylation (bound acetic acid amount) of 54.0 to 62.5% are preferably used, and more preferably an average degree of acetylation of 58.0 to 62.5%. Cellulose triacetate.

  Preferred cellulose esters other than cellulose triacetate have an acyl group having 2 to 4 carbon atoms as a substituent, and when the substitution degree of acetyl group is X and the substitution degree of propionyl group or butyryl group is Y, the following formula ( It is a cellulose ester containing the cellulose ester which satisfy | fills I) and (II) simultaneously.

Formula (I) 2.0 ≦ X + Y ≦ 2.6
Formula (II) 0.1 ≦ Y ≦ 1.2
Furthermore, a cellulose acetate propionate (total acyl group substitution degree = X + Y) resin of 2.4 ≦ X + Y ≦ 2.6 and 1.4 ≦ X ≦ 2.3 is preferable. Among them, 2.4 ≦ X + Y ≦ 2.6, 1.7 ≦ X ≦ 2.3, 0.1 ≦ Y ≦ 0.9, cellulose acetate propionate resin, cellulose acetate butyrate (total acyl group substitution degree = X + Y ) Resins are preferred. The portion not substituted with an acyl group usually exists as a hydroxyl group. These cellulose ester resins can be synthesized by a known method. The measuring method of the substitution degree of an acyl group can be measured according to the rule of ASTM-D817-96.

  As the cellulose ester, cellulose ester synthesized from cotton linter, wood pulp, kenaf or the like as a raw material can be used alone or in combination. In particular, it is preferable to use a cellulose ester synthesized from cotton linter alone or in combination.

<Acrylic fine particles (C)>
In the present invention, if the acrylic resin-containing film further contains acrylic fine particles, the elasticity of the film is improved, and cracking and the like can be suppressed even when a hard coating layer having a high hardness is laminated.

  The acrylic fine particles (C) to be used are not particularly limited, but are preferably acrylic fine particles (C) having a layer structure of two or more layers, and particularly preferably the following multilayer structure acrylic granular composite. .

  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.

  Preferred embodiments of the multilayer structure acrylic granular composite 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 the body mixture, (b) in the presence of the innermost hard layer polymer, 75 to 98.5% by mass of an alkyl acrylate having an alkyl group with 4 to 8 carbon atoms, A crosslinked soft layer polymer obtained by polymerizing a monomer mixture comprising a multifunctional crosslinking agent of 0.01 to 5% by mass and a multifunctional grafting agent of 0.5 to 5% by mass; (c) the innermost hard In the presence of a polymer comprising a layer and a crosslinked soft layer, a monomer mixture 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 is polymerized. Outermost hard layer weight And the obtained three-layer structure polymer is an innermost hard layer polymer (a) 5 to 40% by mass, a soft layer polymer (b) 30 to 60% by mass, and The outermost hard layer polymer (c) is composed of 20 to 50% by mass, has an insoluble part when fractionated with acetone, and an acrylic granular composite having a methyl ethyl ketone swelling degree of 1.5 to 4.0 at the insoluble part. .

  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.

  Moreover, as another acrylic fine particle (C), a commercially available thing can also be used, for example, metabrene W-341 (C2) (made by Mitsubishi Rayon Co., Ltd.), Chemisnow MR-2G (C3), MS -300X (C4) (manufactured by Soken Chemical Co., Ltd.).

  The particle size of the acrylic granular composite that is the multilayer structure polymer is not particularly limited, but is preferably 10 nm or more and 1000 nm or less, and more preferably 20 nm or more and 500 nm or less. In particular, it is most preferably 50 nm or more and 400 nm or less.

  Further, it is preferable that the refractive index of the acrylic resin and the acrylic fine particles (C) are close to each other because the transparency of the optical film is increased. Specifically, the refractive index difference between the acrylic fine particles (C) and the acrylic resin is preferably 0.05 or less, more preferably 0.02 or less, and particularly preferably 0.01 or less.

  The optical film according to the present invention preferably contains 0.5 to 45% by mass of acrylic fine particles (C) with respect to the total mass of the resin constituting the film.

<Other additives>
In the acrylic resin containing film which concerns on this invention, in order to improve the fluidity | liquidity and softness | flexibility of a composition, it is also possible to use a plasticizer together. Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

  The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the composition containing the acrylic resin (A).

  It is also preferable to contain an ultraviolet absorber for improving the weather resistance of the base film, and examples of the ultraviolet absorber used include those of benzotriazole, 2-hydroxybenzophenone or salicylic acid phenyl ester. . For example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2- (3 Triazoles such as 5-di-t-butyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone And benzophenones.

  Furthermore, various antioxidants can also be added to the acrylic resin-containing film according to the present invention in order to improve thermal decomposability and thermal colorability during molding. In addition, an antistatic agent can be added to impart antistatic performance to the acrylic resin-containing film.

<Formation of acrylic resin-containing film>
Although the example of the film forming method of an acrylic resin containing film is demonstrated, this invention is not limited to this.

  Production methods such as inflation method, T-die method, calendar method, cutting method, casting method, emulsion method, hot press method, etc. can be used as a method for producing an acrylic resin-containing film according to the present invention, but coloring suppression is also possible. From the viewpoints of suppressing foreign matter defects and optical defects such as die lines, solution casting by casting is preferred.

  Hereinafter, the preferable film-forming method of the acrylic resin containing film which concerns on this invention is demonstrated.

1) Dissolution Step In an organic solution mainly composed of a good solvent for the acrylic resin (A) and the cellulose ester resin (B), the acrylic resin (A), the cellulose ester resin (B), and, in some cases, acrylic fine particles ( C), a step of dissolving other additives while stirring to form a dope, or the acrylic resin (A) or cellulose ester resin (B) solution, optionally with acrylic fine particle (C) solution or other additive solution Are mixed to form a dope which is a main solution.

(Organic solvent)
The organic solvent useful for forming the dope when the acrylic resin-containing film according to the present invention is produced by the solution casting method, dissolves the acrylic resin (A), the cellulose ester resin (B), and other additives at the same time. Anything can be used without limitation.

  For example, what was illustrated as an organic solvent which disperse | distributes the above-mentioned cellulose nanofiber can be mentioned, Methylene chloride, methyl acetate, ethyl acetate, and acetone can be used preferably.

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

  In particular, in a solvent containing methylene chloride and a linear or branched aliphatic alcohol having 1 to 4 carbon atoms, acrylic resin (A), cellulose ester resin (B), and acrylic fine particles (C) 3 A dope composition in which at least 15 to 45 mass% of the seed is dissolved is preferable.

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

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

  The total amount of the acrylic resin (A) and the cellulose ester resin (B) in the dope is preferably 15 to 50% by mass.

  In this dope, it is preferable to contain cellulose nanofiber in the range of 0.1 to 50% by mass. More preferably, it is 5-50 mass%, and especially 10-40 mass% is preferable.

  An additive is added to the dope during or after dissolution to dissolve and disperse, then filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

  Filtration is preferably performed using a filter medium having a collected particle size of 0.5 to 5 μm and a drainage time of 10 to 25 sec / 100 ml.

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

  FIG. 1 is a diagram schematically showing a dope preparation step, a casting step, and a drying step of a solution casting film forming method preferable for the present invention. The present invention is not limited to this.

  The cellulose nanofiber dispersion removes large agglomerates from the cellulose nanofiber charging pot 41 with a filter 44 and feeds it to the stock tank 42. Thereafter, it is added from the stock tank 42 to the main dope melting pot 1.

  Thereafter, the main dope solution is filtered by the main filter 3, and an acrylic fine particle additive solution or an ultraviolet absorber additive solution is added in-line thereto from 16.

  In many cases, the main dope may contain about 10 to 50% by mass of the recycled material. Since the returned material may contain cellulose nanofibers, acrylic fine particles, and further an ultraviolet absorber, in that case, it is preferable to control the addition amount of each additive liquid in accordance with the added amount of the returned material.

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

  The above range is preferred because the smaller the content of acrylic fine particles, the lower the viscosity and the easier the handling, and the higher the content of acrylic fine particles, the smaller the addition amount and the easier the addition to the main dope.

  Recycled material is a finely pulverized acrylic resin-containing film that is generated when an acrylic resin-containing film is formed. The original fabric is used.

  Moreover, what knead | mixed and pelletized acrylic resin, cellulose-ester resin, and the acrylic fine particle depending on the case can be used preferably.

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

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

3) Solvent evaporation step This is a step of evaporating the solvent by heating the web (the dope is cast on the casting base film and the formed dope film is called the web) on the casting base film. .

  In order to evaporate the solvent, there are a method of blowing air from the web side and / or a method of transferring heat from the back surface of the base film by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. The drying efficiency is good and preferable. A method of combining them is also preferably used.

  It is preferable to dry the web on the base film after casting on the base film in an atmosphere of 40 to 100 ° C. In order to maintain the atmosphere at 40 to 100 ° C., it is preferable to apply hot air at this temperature to the upper surface of the web or to heat by means such as infrared rays.

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

4) Peeling process It is the process of peeling the web which the solvent evaporated on the metal base film at a peeling position. The peeled web is sent to the next process.

  Preferably the temperature in the peeling position on a metal base film is 10-40 degreeC, More preferably, it is 11-30 degreeC.

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

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

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

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

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

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

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

  Since the present invention aims to obtain an optical film, the stretching process is an important step in obtaining a high level of flatness. Stretching is usually performed by a tenter stretching apparatus.

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

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

  The stretching operation may be performed in multiple stages, and it is also preferable to perform biaxial stretching in the casting direction and the width direction. When biaxial stretching is performed, simultaneous biaxial stretching may be performed or may be performed stepwise.

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

-Stretch in the casting direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction-Stretch in the width direction-Stretch in the width direction-Stretch in the casting direction-Stretch in the casting direction Simultaneous biaxial stretching includes stretching in one direction and contracting the other while relaxing the tension.

  A preferable draw ratio is in the range of 1% to 50% in at least one of the width direction and the longitudinal direction. More preferably, it is in the range of 10% to 50%. By stretching 10% or more in any direction, the distribution of cellulose nanofibers in the base film becomes uniform, and an effect of reducing variation in elastic modulus can be expected.

  When the tenter stretching is performed, the residual solvent amount of the web is preferably 20 to 100% by mass at the start of the tenter, and drying is performed while the tenter is applied until the residual solvent amount of the web becomes 10% by mass or less. Preferably, it is 5 mass% or less more preferably.

  When performing tenter stretching, the drying temperature is preferably 30 to 150 ° C, more preferably 50 to 120 ° C, and most preferably 70 to 100 ° C.

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

6) Winding step This is a step of winding up the acrylic resin-containing film by the winder 37 after the residual solvent amount in the web is 2% by mass or less, and by setting the residual solvent amount to 0.4% by mass or less. A film having good dimensional stability can be obtained.

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

  The acrylic resin-containing film according to the present invention is preferably a long film. Specifically, the acrylic resin-containing film is about 100 m to 5000 m, and is usually in the form of a roll. Moreover, it is preferable that the width | variety of a film is 1.3-4m, and it is more preferable that it is 1.4-3m.

  Although there is no restriction | limiting in particular in the film thickness of the acrylic resin containing film which concerns on this invention, When using for the polarizing plate protective film mentioned later, it is preferable that it is 20-200 micrometers, and it is more preferable that it is 25-100 micrometers, 30- It is especially preferable that it is 80 micrometers.

  The acrylic resin-containing film according to the present invention preferably has a haze value of less than 1%, preferably less than 0.5%, and a tension softening point of 105 to 145 ° C.

  The acrylic resin-containing film according to the present invention has a low haze, a device that becomes high temperature such as a projector, and a use in a high-temperature environment such as an in-vehicle display device. It becomes 105 to 145 degreeC. It is more preferable to control to 110 ° C to 130 ° C. By controlling the tension softening point within the above range, a clear image can be continuously displayed when the liquid crystal display device using the film is used for a long time. Within this range, although depending on the use environment, there is generally no fear that the image quality, color, etc. of the display device will be impaired in long-term use, and it is not necessary to use an extremely high heat-resistant acrylic resin.

  As a specific measuring method of the tension softening point temperature of the acrylic resin-containing film, for example, using a Tensilon tester (ORITC Corporation, RTC-1225A), the acrylic resin-containing film is 120 mm (length) × 10 mm (width). The temperature is increased at a rate of temperature increase of 30 ° C./min while pulling at a tension of 10 N, and the temperature at the time of 9 N is measured three times, and the average value can be obtained.

  The acrylic resin-containing film according to the present invention 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).

  The acrylic resin-containing film according to the present invention preferably has a total light transmittance of 80% or more, more preferably 90% or more. Moreover, as a realistic upper limit, it is about 99%.

<Hard coat layer>
The optical film according to the present invention preferably has a hard coat layer on an acrylic resin-containing film, and the hard coat layer is preferably provided as a layer containing an actinic radiation curable resin or a thermosetting resin.

  In the present invention, the actinic radiation curable resin refers to a resin that cures through a crosslinking reaction or the like by irradiation with actinic radiation such as ultraviolet rays or electron beams, and preferably contains a monomer having an ethylenically unsaturated double bond. A resin that cures upon irradiation is preferred.

  Examples of the ultraviolet curable resin include an ultraviolet curable acrylic urethane resin, an ultraviolet curable polyester acrylate resin, an ultraviolet curable epoxy acrylate resin, an ultraviolet curable polyol acrylate resin, and an ultraviolet curable epoxy resin. be able to.

  As specific examples, for example, compounds described in JP-A-2006-146027, JP-A-2006-285217, JP-A-2006-293201, JP-A-301169, JP-A-2007-3767, and the like are used. Can be used.

  Moreover, it is also preferable to use a photoinitiator when using an ultraviolet curable resin, and the photoinitiator described in the said literature can be used.

As the ultraviolet light source for photopolymerizing the ultraviolet curable resin, any light source that generates ultraviolet light can be used. For example, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, or the like can be used. An ArF excimer laser, a KrF excimer laser, an excimer lamp, synchrotron radiation, or the like can also be used. Irradiation conditions vary depending on each lamp, but the amount of irradiation light is preferably 1 mJ / cm ² or more, more preferably 20 mJ / cm ^{2 to} 10000 mJ / cm ² , and particularly preferably 50 mJ / cm ^{2 to} 2000 mJ / cm ^2. It is.

  Moreover, when irradiating an ultraviolet-ray, it is preferable to carry out, applying tension | tensile_strength in the conveyance direction of a film, More preferably, it is performing applying tension | tensile_strength also in the width direction. The tension to be applied is preferably 30 to 300 N / m. The method for applying tension is not particularly limited, and tension may be applied in the transport direction on the back roll, or tension may be applied in the width direction or biaxial direction by a tenter. Thereby, an optical film having a hard coat layer with excellent flatness can be obtained.

  As a thermosetting resin used by this invention, the compound as described in Unexamined-Japanese-Patent No. 2005-164890, 2007-25040, Unexamined-Japanese-Patent No. 2007-298916 etc. can be used preferably, for example.

  The method for heating the thermosetting resin is not particularly limited, but it is preferable to use a method such as a heat plate, a heat roll, a thermal head, or hot air. Moreover, you may heat continuously as a heat roll the back roll used for film conveyance. The heating temperature cannot be generally defined by the type of thermosetting resin to be used, but is preferably in a temperature range that does not affect the heat deformation of the transparent substrate, preferably 30 to 200 ° C, Furthermore, 50-120 degreeC is preferable, Especially preferably, it is 70-100 degreeC.

  Further, the hard coat layer may contain fine particles of an inorganic compound or an organic compound in order to adjust scratch resistance and slipperiness.

  Examples of inorganic fine particles used in the hard coat layer include silicon oxide, titanium oxide, aluminum oxide, tin oxide, indium oxide, ITO, zinc oxide, zirconium oxide, magnesium oxide, calcium carbonate, calcium carbonate, talc, clay, and calcined kaolin. And calcined calcium silicate, hydrated calcium silicate, aluminum silicate, magnesium silicate and calcium phosphate. In particular, silicon oxide, titanium oxide, aluminum oxide, zirconium oxide, magnesium oxide and the like are preferably used.

  Organic particles include polymethacrylic acid methyl acrylate resin powder, acrylic styrene resin powder, polymethyl methacrylate resin powder, silicone resin powder, polystyrene resin powder, polycarbonate resin powder, benzoguanamine resin powder, and melamine resin powder. Polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, or polyfluoroethylene resin powder can be added to the ultraviolet curable resin composition. Particularly preferred are cross-linked polystyrene particles (for example, SX-130H, SX-200H, SX-350H, manufactured by Soken Chemical) and polymethyl methacrylate-based particles (for example, MX150, MX300, manufactured by Soken Chemical).

  The average particle size of these fine particle powders is preferably 0.01 to 5 μm, more preferably 0.1 to 5.0 μm, and particularly preferably 0.1 to 4.0 μm. Moreover, it is preferable to contain 2 or more types of microparticles | fine-particles from which a particle size differs. The ratio of the hard coat layer coating composition and the fine particles is desirably blended so as to be 0.1 to 30 parts by mass with respect to 100 parts by mass of the resin composition.

  These hard coat layers can be coated by a known method such as a gravure coater, a dip coater, a reverse coater, a wire bar coater, a die coater, or an ink jet method. After application, it is dried by heating and subjected to a curing treatment.

  The coating amount of the hard coat layer coating solution is suitably from 0.1 to 40 μm, preferably from 0.5 to 30 μm, as the wet film thickness. Moreover, as a dry film thickness, it is an average film thickness of 0.1-30 micrometers, Preferably it is 1-20 micrometers.

  The hard coat layer coating solution may contain a solvent, or may be appropriately contained and diluted as necessary. Examples of the organic solvent contained in the coating solution include hydrocarbons (toluene, xylene), alcohols (methanol, ethanol, isopropanol, butanol, cyclohexanol), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone), It can be appropriately selected from esters (methyl acetate, ethyl acetate, methyl lactate), glycol ethers, and other organic solvents, or a mixture thereof can be used. Propylene glycol monoalkyl ether (1 to 4 carbon atoms of the alkyl group) or propylene glycol monoalkyl ether acetate ester (1 to 4 carbon atoms of the alkyl group) is 5% by mass or more, more preferably 5 to 80%. It is preferable to use the organic solvent containing at least mass%.

  Further, the hard coat layer preferably contains a silicone surfactant or a polyoxyether compound. These improve applicability | paintability and it is preferable to add these components in 0.01-3 mass% with respect to the solid content component in a coating liquid.

  The hard coat layer may have a multilayer structure of two or more layers. One of the layers may be, for example, a so-called antistatic layer containing conductive fine particles or an ionic polymer, or a color tone adjusting agent (dye having a color tone adjusting function as a color correction filter for various display elements. Or a pigment or the like) or an electromagnetic wave blocking agent or an infrared absorbing agent or the like to have the respective functions.

  The hard coat layer is a clear hard coat layer having a center line average roughness (Ra) defined by JIS B 0601 of 0.001 to 0.1 μm, or fine particles are added to adjust Ra to 0.1 to 1 μm. The antiglare hard coat layer is preferably used. The center line average roughness (Ra) is preferably measured by an optical interference type surface roughness measuring instrument, and can be measured, for example, using a non-contact surface fine shape measuring device WYKO NT-2000 manufactured by WYKO.

  Moreover, it is preferable that the total light transmittance of the optical film which has a hard-coat layer is 80% or more. The total light transmittance is measured using a spectrophotometer U-3200 (manufactured by Hitachi, Ltd.), and the spectral transmittance in the visible light region of the optical film is measured and then averaged to obtain the total light transmittance (%).

<Functional layer>
The following functional layers can be further provided on the optical film having the hard coat layer according to the present invention. Examples thereof include an antireflection layer, an antifouling layer, a backcoat layer, an anti-curl layer, an antistatic layer, an undercoat layer, a light scattering layer, and an adhesive layer.

  Among these, a back coat layer particularly useful for curling will be described.

<Back coat layer>
In the optical film according to the present invention, it is preferable to provide a back coat layer on the surface of the base film opposite to the side on which the hard coat layer is provided. The back coat layer is provided in order to correct curling caused by providing a curable resin layer or other layers. That is, the degree of curling can be balanced by imparting the property of being rounded with the surface on which the backcoat layer is provided facing inward. The back coat layer is preferably applied also as an anti-blocking layer. In this case, it is preferable that fine particles are added to the back coat layer coating composition in order to provide an anti-blocking function.

  Examples of the fine particles added to the back coat layer include the same fine particles as those used for the hard coat layer. Those containing silicon as fine particles are preferable in terms of low haze, and silicon dioxide is particularly preferable.

  Examples of the resin used as the binder of the backcoat layer include vinyl chloride-vinyl acetate copolymer, vinyl chloride resin, vinyl acetate resin, vinyl acetate-vinyl alcohol copolymer, partially hydrolyzed vinyl chloride-vinyl acetate copolymer. Polymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, ethylene-vinyl alcohol copolymer, chlorinated polyvinyl chloride, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, etc. Vinyl polymer or copolymer, nitrocellulose, cellulose acetate propionate (preferably acetyl group substitution degree 1.8-2.3, propionyl group substitution degree 0.1-1.0), diacetyl cellulose, cellulose Cellulose derivatives such as acetate butyrate resin, maleic acid and / or Or acrylic acid copolymer, acrylic ester copolymer, acrylonitrile-styrene copolymer, chlorinated polyethylene, acrylonitrile-chlorinated polyethylene-styrene copolymer, methyl methacrylate-butadiene-styrene copolymer, acrylic resin Rubber resins such as polyvinyl acetal resin, polyvinyl butyral resin, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin, polyester resin, polyether resin, polyamide resin, amino resin, styrene-butadiene resin, butadiene-acrylonitrile resin, Examples thereof include, but are not limited to, silicone resins and fluorine resins. Particularly preferred are cellulose resin layers such as diacetylcellulose and cellulose acetate propionate.

  Furthermore, it is also preferable to contain the cellulose nanofiber which concerns on this invention, and it can be made to contain by the method similar to a base film.

<Polarizer>
A polarizing plate using the optical film according to the present invention will be described.

  The polarizing plate can be produced by a general method. When the optical film according to the present invention contains a cellulose ester resin, the back side of the film is subjected to alkali saponification treatment, and the treated optical film is immersed and drawn in an iodine solution on at least one surface of a polarizing film, Bonding is performed using a completely saponified polyvinyl alcohol aqueous solution. The optical film may be used on the other surface, or another polarizing plate protective film may be used. The polarizing plate protective film used on the other surface of the optical film according to the present invention has an in-plane retardation Ro of 590 nm, an optical compensation film having a phase difference of 20 to 70 nm, and Rt of 100 to 400 nm. Phase difference film) can be used. These can be prepared, for example, by the methods described in JP-A No. 2002-71957 and Japanese Patent Application No. 2002-155395. Alternatively, a polarizing plate protective film that also serves as an optical compensation film having an optically anisotropic layer formed by aligning a liquid crystal compound such as a discotic liquid crystal can be used. For example, the optically anisotropic layer can be formed by the method described in JP-A-2003-98348.

  Moreover, as another polarizing plate protective film used for the other surface, a non-oriented film having Ro of 590 nm to 0 to 5 nm and Rt of -20 to +20 nm is also preferably used.

  As the polarizing plate protective film used on the back side, a commercially available cellulose ester film can be used, and KC8UX2MW, KC4UX, KC5UX, KC4UY, KC8UY, KC12UR, KC4UEW, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC4FR -1, KC4FR-2 (manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

  The polarizing film, which is the main component of the polarizing plate, is an element that transmits only light having a polarization plane in a certain direction. A typical polarizing film known at present is a polyvinyl alcohol polarizing film, which is a polyvinyl alcohol film. There are ones in which iodine is dyed on a system film and ones in which a dichroic dye is dyed, but it is not limited to this. As the polarizing film, a polyvinyl alcohol aqueous solution is formed and dyed by uniaxially stretching or dyed, or uniaxially stretched after dyeing, and then preferably subjected to a durability treatment with a boron compound. A polarizing film having a thickness of 5 to 30 μm, preferably 8 to 15 μm, is preferably used. On the surface of the polarizing film, one side of the optical film according to the present invention is bonded to form a polarizing plate. It is preferably bonded with an aqueous adhesive mainly composed of completely saponified polyvinyl alcohol or the like.

<Display device>
By incorporating a polarizing plate using the optical film according to the present invention on at least one surface into a liquid crystal display, various liquid crystal displays having excellent visibility can be produced. The optical film according to the present invention is incorporated in the polarizing plate, and is a reflective type, transmissive type, transflective LCD or TN type, STN type, OCB type, HAN type, VA type (PVA type, MVA type), IPS type, It is preferably used in various drive type LCDs such as OCB type.

  When the polarizing plate according to the present invention is used in place of the polarizing plate previously bonded to Sharp's 32-inch TV AQ-32AD5 which is a VA liquid crystal display, it has excellent visibility and has scratches on the surface. High durability that is difficult to stick.

  Since the optical film containing the thermoplastic acrylic resin and cellulose nanofiber according to the present invention is excellent in mechanical strength as a polarizing plate protective film, the film thickness can be reduced. A polarizing plate using the optical film and the polarizing plate Liquid crystal displays using can also be made thinner.

  The optical film according to the present invention is excellent in flatness and is preferably used for various display devices such as a plasma display, a field emission display, an organic EL display, an inorganic EL display, and electronic paper.

  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 base film>
<Preparation of TAC film 1>
(Fine particle dispersion 1)
Fine particles (Aerosil R972V manufactured by Nippon Aerosil Co., Ltd.) 11 parts by weight Ethanol 89 parts by weight The above was stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.

<In-line additive solution>
Cellulose ester A (acetyl group substitution degree: 2.92) was added to a dissolution tank containing methylene chloride, and the mixture was heated to be completely dissolved, and then dissolved in Azumi filter paper No. 1 manufactured by Azumi Filter Paper Co., Ltd. Filtered using 244.

  The fine particle dispersion was slowly added thereto while sufficiently stirring the filtered cellulose ester solution. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare an in-line additive solution.

Methylene chloride 99 parts by weight Cellulose ester A 4 parts by weight Fine particle dispersion 1 11 parts by weight A main dope solution having the following composition was prepared. First, methylene chloride and ethanol were added to the pressure dissolution tank. Cellulose ester A was added to a pressurized dissolution tank containing a solvent while stirring. This is completely dissolved with heating and stirring. This was designated as Azumi Filter Paper No. The main dope solution was prepared by filtration using 244.

(Main dope composition)
Methylene chloride 380 parts by weight Ethanol 70 parts by weight Cellulose ester A (acetyl group substitution degree 2.92) 100 parts by weight Plasticizer (trimethylolpropane tribenzoate) 10 parts by weight UV absorber (manufactured by Tinuvin 109 (Ciba Japan Co., Ltd.) 2 parts by mass or more were put into a sealed container, heated and stirred, and completely dissolved, and filtered using Azumi filter paper No. 24 manufactured by Azumi Filter Paper Co., to prepare a dope solution.

  The dope solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. in the film production line. In the inline additive solution line, the inline additive solution was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. Add 2 parts by weight of the filtered in-line additive to 100 parts by weight of the filtered dope solution, mix thoroughly with an in-line mixer (Toray static type in-pipe mixer Hi-Mixer, SWJ), and then use a belt casting apparatus. Used at a temperature of 35 ° C. and a width of 1.8 m and uniformly cast on a stainless steel band support. With the stainless steel band support, the solvent was evaporated until the residual solvent amount became 120%, and then peeled off from the stainless steel band support. The peeled cellulose ester web was evaporated at 50 ° C., slit to 1.65 m width, and then in a TD direction (direction perpendicular to the film transport direction) with a tenter at a temperature of 130 ° C. and a draw ratio of 15%. Stretched. Drying is completed while transporting the 120 ° C drying zone with many rolls, slitting to a width of 1.5m, knurling with a width of 15mm and an average height of 10μm at both ends of the film, and an TAC film with an average film thickness of 80μm 1 was produced. The winding length was 5000 m.

<Preparation of acrylic resin-containing film 1>
(Preparation of dope solution)
BR85 (acrylic resin manufactured by Mitsubishi Rayon Co., Ltd.) 100 parts by mass Plasticizer (trimethylolpropane tribenzoate) 10 parts by mass UV absorber (Tinuvin 109 (manufactured by Ciba Japan)) 2 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts Part (film formation of acrylic resin-containing film 1)
The produced dope solution was uniformly cast on a stainless steel band support at a temperature of 22 ° C. and a width of 2 m using a belt casting apparatus. With the stainless steel band support, the solvent was evaporated until the residual solvent amount reached 100%, and the film was peeled off from the stainless steel band support with a peeling tension of 162 N / m. The peeled acrylic resin web was evaporated at 35 ° C., slit to 1.6 m width, and then dried at a drying temperature of 135 ° C. while stretching 10% in the width direction with a tenter. At this time, the residual solvent amount when starting stretching with a tenter was 10%. After stretching with a tenter and relaxing at 130 ° C for 5 minutes, drying was completed while transporting the drying zone at 120 ° C and 130 ° C with a number of rolls, slitting to a width of 1.5 m, and 10 mm wide at both ends of the film. A knurling process having a thickness of 5 μm was performed, and the film was wound around a 6-inch inner diameter core with an initial tension of 220 N / m and a final tension of 110 N / m to obtain an acrylic resin-containing film 1. The draw ratio in the MD direction calculated from the rotational speed of the stainless steel band support and the operating speed of the tenter was 10%. The residual solvent amount of the acrylic resin-containing film film 1 was 0.1%, the film thickness was 80 μm, and the winding number was 5000 m.

<Preparation of acrylic resin-containing film 2>
First, cellulose nanofibers and a dispersion thereof were prepared by the following procedure.

(Preparation of cellulose nanofiber dispersion 1)
After pulverizing the softwood kraft pulp NDP-T of Nippon Paper Chemical Co., Ltd. with a high-pressure homogenizer until the average fiber diameter is 1 μm or less, this water suspension is used with a grinder (“KM1-10” manufactured by Kurita Machinery Co., Ltd.). The disk was rotated 30 times (30 pass) from the center to the outside through the disk rotating at 1200 rpm in a substantially contacted state. The obtained suspension was once dried, cellulose on the bulk was put into methylene chloride, pulverized with a high-pressure homogenizer, and further dispersed with a bead disperser using zirconia beads having an average particle diameter of 2 μm. Zirconia beads were removed by centrifugation and filtration to obtain a methylene chloride dispersion of cellulose nanofibers. A part of this dispersion was taken out and the methylochrome was evaporated, and then 100 cellulose nanofibers were observed with an electron microscope and measured to have an average fiber diameter of 60 nm and an average fiber length of 450 nm. The obtained dispersion was concentrated and adjusted so that the solid concentration was 50% by mass.

  Moreover, when the ratio of the amorphous region was measured by the above-mentioned method by adjusting the X-ray diffraction angle of the cellulose nanofibers using an X-ray diffractometer LabX XRD-6100 (manufactured by Shimadzu Corporation), 10% Met.

(Preparation of cellulose nanofiber dispersion 2)
Sulfite bleached softwood pulp equivalent to 2 g in dry mass, 0.025 g of TEMPO and 0.25 g of sodium bromide were dispersed in 150 ml of water, and then a 13 mass% sodium hypochlorite aqueous solution was added to 1 g of pulp. Then, hypochlorous acid was added to start the reaction so that the amount of sodium hypochlorite was 2.5 mmol. During the reaction, a 0.5 M aqueous sodium hydroxide solution was added dropwise to keep the pH at 10.5. When no change in pH was observed, the reaction was considered to be completed, and the reaction product was filtered, washed with sufficient water and filtered repeatedly, and water-dispersed reaction product fibers were obtained by lyophilization. Cellulose on the bulk was put into Methylkuro, pulverized with a high-pressure homogenizer, and further dispersed with a bead disperser using zirconia beads having an average particle diameter of 2 μm. Zirconia beads were removed by centrifugation and filtration to obtain a methylo dispersion of cellulose nanofibers. A part of this dispersion was taken out and the methylochrome was evaporated, and then 100 cellulose nanofibers were observed with an electron microscope and measured to have an average fiber diameter of 60 nm and an average fiber length of 450 nm. The obtained dispersion was concentrated and adjusted so that the solid concentration was 50% by mass.

  Moreover, when the ratio of the amorphous region was measured by the above-mentioned method by adjusting the X-ray diffraction angle of the cellulose nanofibers using an X-ray diffractometer LabX XRD-6100 (manufactured by Shimadzu Corporation), 10% Met.

<Preparation of cellulose nanofiber dispersions 3-7>
In cellulose nanofiber dispersion 1 or 2, the rotation conditions of the grinder, the crushing conditions of the high-pressure homogenizer, and the dispersion conditions in the bead disperser using zirconia beads were changed, and the average fiber diameter and amorphous content shown in Table 1 were changed. Cellulose nanofiber dispersions 3 to 7 having regions were prepared.

  Next, using the produced cellulose nanofiber dispersion 1, an acrylic resin-containing film 2 having a film thickness of 80 μm and a winding number of 5000 m was prepared in the same manner as in the production of the acrylic resin-containing film 1 using the following dope liquid.

(Preparation of dope solution)
BR85 (acrylic resin manufactured by Mitsubishi Rayon Co., Ltd.) 100 parts by mass Cellulose nanofiber dispersion 1 80 parts by mass (40 parts by mass as solid content of cellulose nanofibers)
Plasticizer (trimethylolpropane tribenzoate) 10 parts by mass UV absorber (Tinuvin 109 (manufactured by Ciba Japan)) 2 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass <Preparation of acrylic resin-containing film 3>
An acrylic resin-containing film 3 having a thickness of 80 μm and a winding number of 5000 m was produced in the same manner as in the production of the acrylic resin-containing film 1 using the following dope solution.

(Dope solution)
BR85 (acrylic resin manufactured by Mitsubishi Rayon Co., Ltd.) 90 parts by mass Cellulose ester (cellulose acetate propionate acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, Mw = 200000)
10 parts by mass Cellulose nanofiber dispersion 1 80 parts by mass (40 parts by mass as the solid content of cellulose nanofibers)
Acrylic fine particles (C1) 2 parts by mass Plasticizer (trimethylolpropane tribenzoate) 10 parts by mass UV absorber (Tinuvin 109 (manufactured by Ciba Japan)) 2 parts by mass Methylene chloride 300 parts by mass Ethanol 40 parts by mass (acrylic fine particles (Preparation of (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. Add 0.36 g of APS, and after stirring for 5 minutes, add a monomer mixture consisting of 1657 g of MMA, 21.6 g of BA, and 1.68 g of ALMA, and hold for another 20 minutes after detecting the exothermic peak. Polymerization of the innermost hard layer was completed.

  Next, 3.48 g of APS was added, and after stirring for 5 minutes, a monomer mixture consisting of 8105 g of BA, 31.9 g of PEGDA (200), and 264.0 g of ALMA was continuously added over 120 minutes. After completion of the addition, the mixture was further maintained for 120 minutes 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, and held for another 20 minutes after the addition was completed. The polymerization of the outermost hard layer 1 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 addition was completed. Later held for another 20 minutes. 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 fine 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 <Preparation of acrylic resin-containing films 4 to 16>
The acrylic resin containing films 4-16 were produced by the structure of Table 2 similarly to preparation of the acrylic resin containing film 3. FIG.

  Moreover, the dispersing agents in Table 2 are the following compounds.

Emulgen 404: Kao Corporation HLB value 8.8
<Production of optical film with hard coat layer>
Next, using the prepared TAC film 1 and acrylic resin films 1 to 16, the following hard coat layer is laminated on one surface, the following back coat layer is provided on the opposite surface, and an optical film with a hard coat layer is provided. 1-17 were produced.

(Hardcoat layer coating composition 1)
Dipentaerythritol hexaacrylate monomer 60 parts by weight Dipentaerythritol hexaacrylate dimer 20 parts by weight Dipentaerythritol hexaacrylate trimer or higher component 20 parts by weight Diethoxybenzophenone photoinitiator 6 parts by weight Silicone surface activity Agent FZ2207 (Nihon Unicar) 10% by weight propylene glycol monomethyl ether solution 1 part by weight Propylene glycol monomethyl ether 75 parts by weight Methyl ethyl ketone 75 parts by weight (Backcoat layer coating composition 1)
Acetone 35 parts by weight Ethyl acetate 45 parts by weight Isopropyl alcohol 5 parts by weight Diacetylcellulose 0.5 part by weight Ultrafine silica 2% acetone dispersion (Aerosil: 200 V, manufactured by Nippon Aerosil Co., Ltd.) 0.1 part by weight The back coat layer coating composition 1 was gravure coated on one surface of the film 1 so as to have a wet film thickness of 13 μm, and dried at a drying temperature of 80 ± 5 ° C. Next, the hard coat layer coating composition 1 is applied to the other surface of the TAC film 1 so as to have a wet film thickness of 15 μm, dried at a drying temperature of 90 ° C., and then irradiated with ultraviolet rays at 150 mJ / m. ² was applied to form a hard coat layer having a dry film thickness of 7 μm, thereby producing an optical film 1 with a hard coat layer.

  Similarly, optical films 2 to 17 with a hard coat layer were prepared using acrylic resin films 1 to 16.

<Evaluation>
The following evaluation was performed using the optical films 1-17 with a hard coat layer produced as described above.

(Transmittance)
A spectral photometer U-3200 (manufactured by Hitachi, Ltd.) was used to measure the spectral transmittance of the base film in the visible light range, and then averaged to obtain the total light transmittance (%).
○: Total light transmittance (%) is 80% or more ×: Total light transmittance (%) is less than 80% (stretchability)
The breaking frequency in the actual process when the base film was stretched under the above conditions was evaluated with the following evaluation scale.

◎: Almost no breakage occurs in the actual process, which is preferable ○: Breakage occurs rarely in the actual process, but it is at a practical level △: Breakage sometimes occurs in the actual process, and it is somehow practical level ×: Actual Fracture frequently occurs in the process and is not practical (pencil hardness)
The prepared base film and the optical film with a hard coat layer are conditioned for 2 hours under the conditions of a temperature of 25 ° C. and a relative humidity of 55%, and then specified by JIS K 5400 using a test pencil specified by JIS S 6006. It measured according to the pencil hardness evaluation method.

  Table 2 shows the structure of the base film, the optical film with the hard coat layer, and the evaluation results.

  In the optical films 3 to 10 and 12 to 17 with the hard coat layer of the present invention, the transmittance, the stretchability of the base film, the pencil hardness, and the pencil hardness after applying the hard coat layer are improved with respect to the comparative example. I understand.

Example 2
<Production of polarizing plate and liquid crystal display device>
(Alkaline saponification treatment)
The optical films 1 to 17 with hard coat layers and Konica Minolta Tack KC8UCR-5 (manufactured by Konica Minolta Opto Co., Ltd.) prepared above were subjected to alkali saponification treatment as described below.

Saponification step 2.5M-NaOH 50 ° C. 90 seconds Water washing step Water 30 ° C. 45 seconds Neutralization step 10 parts HCl 30 ° C. 45 seconds Water washing step Water 30 ° C. 45 seconds Water treatment, neutralization, water washing in this order Followed by drying at 80 ° C. for 15 minutes.

<Production and bonding of polarizers>
A 120 μm-thick long roll polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched in the film forming direction 6 times at 50 ° C. to produce a polarizer.

  Next, using a polyvinyl alcohol adhesive, the optical film with a hard coat layer is bonded to one side of the polarizer so that the transmission axis of the polarizer and the in-plane slow axis of the cellulose ester film are parallel to each other. Then, Konica Minolta Tack KC8UCR-5 (manufactured by Konica Minolta Opto Co., Ltd.) was bonded to the opposite surface to obtain polarizing plates 101 to 117.

  In addition, about the optical films 2 and 3 with a hard-coat layer, it does not carry out an alkali saponification process, it pastes on the single side | surface of the polarizing plate which bonded Konica Minolta Tack KC8UCR-5 on both surfaces using an acrylic adhesive. 102 and 103.

  In the polarizing plate using the optical film with a hard coat layer of the present invention, no scratch was generated in the above operation, and the yield was clearly improved.

<Production of liquid crystal display device>
The obtained polarizing plate was carefully peeled off from the viewing side polarizing plate that had been bonded in advance to Sony's 32-inch LCD TV “BRAVIA” KDL-32J5000, and aligned with the transmission axis of the polarizing plate originally applied. A liquid crystal display device was produced by pasting on the cell side via an adhesive.

  The liquid crystal display device equipped with the polarizing plate using the optical film with a hard coat layer of the present invention was excellent in surface flatness, hardly scratched, and the eyes did not get tired even when viewed for a long time.

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

Claims (6)

  An optical film having a hard coat layer on a base film, wherein the base film contains a thermoplastic acrylic resin and cellulose nanofibers having an average fiber diameter of 4 to 200 nm.   The optical film according to claim 1, wherein the base film contains 10% by mass or more of a cellulose ester resin.   The optical film according to claim 1, wherein the base film is stretched by 10% or more in at least one of the width direction and the longitudinal direction.   The optical film according to claim 1, wherein the base film contains acrylic fine particles.   It is a polarizing plate which consists of a polarizer and two polarizing plate protective films which pinch | interpose it, Comprising: One sheet of these two polarizing plate protective films is an optical film of any one of Claims 1-4 A polarizing plate characterized by the above.   A display device comprising the optical film according to claim 1 or the polarizing plate according to claim 5.

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