JP2008152118A - Optical film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film which has no interference fringe, has high pencil hardness and excellent weather resistance and is suitable for forming a polarizing plate. <P>SOLUTION: In the optical film, a base material film has a surface where ruggedness is formed by applying pressure at least on one surface thereof and has a functional layer at least on the surface where the ruggedness is formed. The base material film is constituted by laminating k pieces (k is an integer of two or more) of thermoplastic resin layers. A refractive index n<SB>i</SB>(λ) of the i-th thermoplastic resin layer at a wavelength λ within a range between 380 nm and 780 nm and a refractive index n<SB>i+1</SB>(λ) of the i+1-th thermoplastic resin layer at the wavelength λ within a range between 380 nm and 780 nm have a relation of formula [1], ¾n<SB>i</SB>(λ)-n<SB>i+1</SB>(λ)¾≤0.05, and further at least one thermoplastic resin layer has modulus of tensile elasticity A<SB>k</SB>of ≥2.8 GPa and is formed by a co-extrusion molding method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical film suitable for a protective film for a liquid crystal display element such as a polarizing plate.

The polarizing plate used for a liquid crystal display device etc. is a laminated body which consists of a polarizer and a protective film. As the polarizer, a film in which iodine or a dichroic dye is adsorbed on a film obtained by film-forming polyvinyl alcohol by a solution casting method and stretched in a boric acid solution is usually used.
On the other hand, a triacetyl cellulose film is widely used as a protective film. However, since the triacetylcellulose film has poor moisture resistance and gas barrier properties, the durability, heat resistance, mechanical strength, etc. of the polarizing plate are insufficient.

In order to improve the durability and heat resistance of the polarizing plate, it has been proposed to use a protective film other than the triacetyl cellulose film. For example, Patent Document 1 proposes to use a laminated film including a norbornene-based resin layer and a resin layer having a small haze value as a protective film. And it is disclosed that a polarizing plate is obtained by attaching the protective film to a polarizer containing polyvinyl alcohol with the surface of the norbornene resin layer facing.
JP 2005-115085 A

In Patent Document 2, a resin layer having a smaller hygroscopic property than triacetyl cellulose and having a positive photoelastic constant and a resin layer having a smaller hygroscopic property than triacetyl cellulose and having a negative photoelastic constant are laminated. A protective film having a small photoelastic constant has been proposed. And the polarizing plate formed by sticking this protective film on the polarizer containing polyvinyl alcohol is disclosed.
JP 2000-206303 A

  Moreover, optical films, such as a protective film for polarizing plates, are manufactured by laminating | stacking a functional layer on a base film. At this time, interference fringes are generated between the base film and the functional layer, which causes a problem that the optical properties of the film are deteriorated. Patent Document 2 proposes a transparent polycarbonate resin laminate in which the generation of interference fringes is suppressed by controlling the surface roughness of the interface between the base film and the functional layer. However, the polycarbonate resin plate used as the base material of the laminate proposed here has a thickness of 1 to 10 mm formed by a melt extrusion method.

JP 2001-080013 A

  By the way, when adopting extrusion as a method for industrial production of a base film that is a protective film for optical films, interference fringes can be created by increasing the extrusion speed (winding speed of the produced film), so the extrusion speed must be controlled. There is a limit to raising the production efficiency of the base film, which must be done carefully.

  An object of the present invention is to provide an optical film suitable for forming a polarizing plate having no interference fringes, high pencil hardness, and excellent weather resistance.

As a result of studying to achieve the above-mentioned object, the inventors have applied at least one surface of the base film to the thermoplastic resin layer, so that at least the film having irregularities formed on the surface thereof. An optical film having a functional layer on the surface on which the irregularities are formed,
The base film is
A film in which k thermoplastic resin layers (k is an integer of 2 or more) are laminated,
The refractive index ni (λ) at a wavelength λ in the wavelength range of 380 nm to 780 nm of the i-th (i is an integer from 1 to k−1) and 380 nm to 780 nm of the i + 1-th thermoplastic resin layer. And a refractive index n _{i + 1} (λ) at a wavelength λ in the range of
When the tensile elastic modulus of the i-th thermoplastic resin layer is A _i and the i + 1-th tensile elastic modulus is A _{i + 1} , | A _{i + 1} −A _i | ≧ 0.5 GPa for all values of _i. Yes,
Furthermore, on at least one surface of the optical film formed by a coextrusion molding method in which the tensile elastic modulus A _j (j is an integer of 1 to k) of at least one thermoplastic resin layer is 2.8 GPa or more, If a functional layer is formed on the surface of the film having irregularities formed on the surface by applying pressure, an optical film having no interference fringes, high surface hardness, and weather resistance can be obtained. I found out.
| N _i (λ) −n _{i + 1} (λ) | ≦ 0.05 Formula [1]
In addition, when a film having irregularities formed on such a surface is employed, interference fringes do not occur even if the production speed of the base film (the same as the extrusion speed and film winding speed during extrusion molding) is increased, Furthermore, the present inventors have found that the generation of interference fringes can be suppressed even when the speed at which the functional layer is formed on the film surface having irregularities on the surface is increased, and the present invention has been completed.

The present invention includes the following.
By applying pressure to at least one surface of the base film, an optical film having a functional layer on at least the surface on which the unevenness is formed of the film on which the unevenness is formed on the surface,
The base film is
A film in which k thermoplastic resin layers (k is an integer of 2 or more) are laminated,
The refractive index ni (λ) at a wavelength λ in the wavelength range of 380 nm to 780 nm of the i-th (i is an integer from 1 to k−1) and 380 nm to 780 nm of the i + 1-th thermoplastic resin layer. And a refractive index n _{i + 1} (λ) at a wavelength λ in the range of
When the tensile elastic modulus of the i-th thermoplastic resin layer is A _i and the i + 1-th tensile elastic modulus is A _{i + 1} , | A _{i + 1} −A _i | ≧ 0.5 GPa for all values of _i. Yes,
Further, an optical film formed by a coextrusion method in which at least one thermoplastic resin layer has a tensile elastic modulus A _j (j is an integer of 1 to k) of 2.8 GPa or more.
| N _i (λ) −n _{i + 1} (λ) | ≦ 0.05 Formula [1]

It is a figure which shows the refractive index n ((lambda)) of each resin layer used in the present Example. It is a figure which shows distribution of the absolute value of the difference of the refractive index n ((lambda)) of each resin layer used in the present Example. It is a figure which shows distribution of the absolute value of the difference of the refractive index n ((lambda)) of the polyvinyl alcohol used in the present Example, and the refractive index n ((lambda)) of a polymethylmethacrylate layer.

Explanation of symbols

  COP: alicyclic olefin polymer, PC: polycarbonate resin, PMMA: polymethyl methacrylate resin, PVA: polyvinyl alcohol

Hereinafter, the present invention will be described in more detail.
The optical film of the present invention is composed of a film having irregularities formed on the surface and a functional layer by applying pressure to at least one surface of the base film.
Examples of the functional layer include a hard coat layer, an antireflection layer, and an antifouling layer.

<Base film>
The base film is formed by laminating k thermoplastic resin layers (k is an integer of 2 or more). That is, the base film is formed by laminating the first to the kth thermoplastic resin layers in this order. k is usually 2 to 7, preferably 3 to 5.
In addition, one of the k thermoplastic resin layers is preferably a layer made of an acrylic resin.

  The thermoplastic resin constituting the thermoplastic resin layer is an acrylic resin, for example, polycarbonate resin, polyethersulfone resin, polyethylene terephthalate resin, polyimide resin, polymethyl methacrylate resin, polysulfone resin, polystyrene resin, polyarylate resin, polyethylene resin, It can be selected from polyvinyl chloride resin, diacetyl cellulose, triacetyl cellulose, and alicyclic olefin polymers.

As the acrylic resin, homopolymers of (meth) acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate; the hydrogen of the alkyl group is OH group, COOH group, NH ₂ group or the like Homopolymer of (meth) acrylic acid alkyl ester substituted by a functional group; or (meth) acrylic acid alkyl ester and styrene, vinyl acetate, α, β-monoethylenically unsaturated carboxylic acid, vinyl toluene, α- Examples thereof include a copolymer with a vinyl monomer having an unsaturated bond such as methylstyrene and maleic anhydride. As a thermoplastic acrylic resin, only 1 type may be used among these and it may use it in combination of 2 or more type. More preferably, the thermoplastic acrylic resin contains polymethyl methacrylate and polybutyl methacrylate as monomer units.

Examples of the alicyclic olefin polymer include a cyclic olefin random multiple copolymer described in JP-A No. 05-310845, a hydrogenated polymer described in JP-A No. 05-97978, and JP-A No. 11-124429. And thermoplastic dicyclopentadiene-based ring-opening polymers and hydrogenated products thereof. Note that not all of the illustrated thermoplastic resins can be applied to the present invention, and some of the same kind of thermoplastic resins may or may not satisfy the following requirements. Select as appropriate.
The thermoplastic resin used in the present invention includes colorants such as pigments and dyes, fluorescent brighteners, dispersants, heat stabilizers, light stabilizers, ultraviolet absorbers, antistatic agents, antioxidants, lubricants, and solvents. These compounding agents may be appropriately blended. In particular, the addition of a lubricant or an ultraviolet ray inhibitor is preferable because flexibility and weather resistance are improved.

  Lubricants include inorganic particles such as silicon dioxide, titanium dioxide, magnesium oxide, calcium carbonate, magnesium carbonate, barium sulfate, and strontium sulfate, as well as polymethyl acrylate, polymethyl methacrylate, polyacrylonitrile, polystyrene, cellulose acetate, and cellulose Organic particles such as acetate propionate can be mentioned. As particles constituting the lubricant, organic particles are preferable, and among these, particles made of polymethyl methacrylate are particularly preferable.

  As the lubricant, elastic particles made of a rubber-like elastic body can be used. Examples of the rubber-like elastic body include an acrylate-based rubber-like polymer, a rubber-like polymer containing butadiene as a main component, and an ethylene-vinyl acetate copolymer. Examples of the acrylic ester rubbery polymer include those containing butyl acrylate, 2-ethylhexyl acrylate, or the like as a main component. Of these, acrylate polymers based on butyl acrylate and rubbery polymers based on butadiene are preferred. The elastic particles may be formed by laminating two kinds of polymers. Typical examples thereof include an alkyl acrylate such as butyl acrylate, a styrene grafted rubber elastic component, and a methyl methacrylate. Examples thereof include elastic particles in which a hard resin layer made of a copolymer of a rate and / or methyl methacrylate and an alkyl acrylate forms a layer with a core-shell structure.

The elastic particles generally have a number average particle size of 2.0 μm or less, preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0.5 μm when dispersed in a thermoplastic resin. Even if the primary particle size of the elastic particles is small, if the number average particle size of the secondary particles formed by aggregation or the like is large, the protective layer has a high haze (cloudiness), and the light transmittance is low. Not suitable for display screens. Moreover, when the number average particle size becomes too small, the flexibility tends to decrease.
In the present invention, the refractive index n _p (λ) of the elastic particles at a wavelength of 380 nm to 780 nm is between the refractive index n _r (λ) of the thermoplastic resin serving as the matrix at a wavelength of 380 nm to 780 nm. It is preferable to satisfy the relationship.
| N _p (λ) −n _r (λ) | ≦ 0.05 Formula [2]
In particular, it is more preferable that | n _p (λ) −n _r (λ) | ≦ 0.045. Note that n _p (λ) and n _r (λ) are average values of the main refractive indices at the wavelength λ. When the value of | n _p (λ) −n _r (λ) | exceeds the above value, transparency may be impaired due to interface reflection caused by a difference in refractive index at the interface.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, acrylonitrile ultraviolet absorbers, triazine compounds, nickel complex compounds. And publicly known materials such as inorganic powders. Among these, 2,2′-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol), 2- (2′-hydroxy- 3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2,4-di-tert-butyl-6- (5-chlorobenzotriazol-2-yl) phenol, 2,2'- Dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4′-tetrahydroxybenzophenone and the like are preferable. Among these, 2,2'-methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol) is particularly preferable.

  The thermoplastic resin used in the present invention preferably has a light transmittance in the visible region of 400 to 700 nm at a thickness of 1 mm of 80% or more, more preferably 85% or more, and even more preferably 90% or more. . The thermoplastic resin is preferably an amorphous resin from the viewpoint of transparency. In addition, the thermoplastic resin preferably has a glass transition temperature of 60 to 200 ° C, more preferably 100 to 180 ° C. The glass transition temperature can be measured by differential scanning calorimetry (DSC).

  The thermoplastic resin used in the present invention is preferably selected from those having a melt flow rate value in the range of 10 to 100 g / 10 min (280 ° C., load 2.16 kgf). Moreover, it is preferable that the value of the melt flow rate of the thermoplastic resin which comprises each layer is comparable. Specifically, it is preferable that the difference in the melt flow rate value of the thermoplastic resin constituting the adjacent layers is 0 to 30 g / 10 minutes (280 ° C., load 2.16 kgf).

  Moreover, it is preferable that there is little content of the volatile component contained in a base film. Means for reducing the content of volatile components include: (1) reducing the amount of volatile components in the transparent resin itself; (2) pre-drying the transparent resin used before forming the protective layer; Is mentioned. The preliminary drying is performed with a hot air dryer or the like, for example, in the form of pellets or the like. The drying temperature is preferably 100 ° C. or more, and the drying time is preferably 2 hours or more. By performing preliminary drying, the amount of volatile components in the base film can be reduced, and foaming of the transparent resin to be extruded can be prevented.

The base film has a refractive index n _i (λ) at a wavelength λ in the range of 380 nm to 780 nm of the i-th (i is an integer of 1 to k−1) thermoplastic resin layer. The refractive index n _{i + 1} (λ) at the wavelength λ in the range of 380 nm to 780 nm of the layer has the relationship of the formula [1].
| N _i (λ) −n _{i + 1} (λ) | ≦ 0.05 Formula [1]
However, i represents the integer of 1-k-1. In particular, the protective layer more preferably satisfies the relationship | n _i (λ) −n _{i + 1} (λ) | ≦ 0.045.
Note that n _i (λ) and n _{i + 1} (λ) are average values of the main refractive indices at the wavelength λ. When the value of | n _i (λ) −n _{i + 1} (λ) | exceeds the above value with respect to a part or all of i = 1 to k−1, it is caused by a difference in refractive index at the interface. Interference fringes may occur on the surface of the base film due to the interface reflection. Note that the i-th thermoplastic resin layer and the (i + 1) -th thermoplastic resin layer adjacent to each other may be in direct contact with each other or may be in contact with each other through an adhesive layer described later.

  The base film can have a water absorption rate of at least one layer of the laminated thermoplastic resin layers of 0.5% or less, and further 0.1% or less. The durability of the polarizing plate can be increased by using a low water absorption rate for the protective layer. The water absorption rate of the thermoplastic resin layer can be determined according to JIS K 7209.

  The thickness of each thermoplastic resin layer constituting the base film is not particularly limited, but the thickness of the kth thermoplastic resin layer is usually 5 to 100 μm, preferably 10 μm or more, and Preferably it is 10-50 micrometers. The thickness of the 1st thermoplastic resin layer is 5-100 micrometers normally, Preferably it is 10-50 micrometers. At this time, it is preferable that the thickness of the kth thermoplastic resin layer is substantially equal to the thickness of the first thermoplastic resin layer. Specifically, the absolute value of the difference between the thickness of the first thermoplastic resin layer and the thickness of the kth thermoplastic resin layer is preferably 20 μm or less, and more preferably 10 μm or less. .

Moreover, the thickness of the intermediate thermoplastic resin layer provided as needed between the first thermoplastic resin layer and the kth thermoplastic resin layer is usually 5 to 100 μm, preferably 10-50 μm. The ratio of the thickness of the intermediate thermoplastic resin layer to the thickness of the kth thermoplastic resin layer or the thickness of the first thermoplastic resin layer (intermediate layer thickness: first layer or first layer The thickness of the kth layer is not particularly limited, but is preferably 5: 1 to 1: 5.
The thickness of such a base film whole is 20-200 micrometers normally, Preferably it is 40-100 micrometers.

  The thermoplastic resin forming the first thermoplastic resin layer is preferably selected from the same acrylic resin, alicyclic olefin polymer, and polycarbonate resin as described above, particularly selected from acrylic resins such as polymethyl methacrylate resin. Is preferred.

  The thermoplastic resin that forms the kth thermoplastic resin layer is preferably hard. Specifically, a pencil hardness (JIS K 5600-5-4, where the test load is 500 g) and harder than H is preferable. The thermoplastic resin that forms the kth thermoplastic resin layer is preferably selected from acrylic resins and styrene resins, and most preferably selected from acrylic resins such as polymethyl methacrylate resin.

  In addition, when an optical film is used as a protective layer for a polarizer, a thermoplastic resin for forming the kth thermoplastic resin layer and the first heat are used to prevent warping, bending, rounding, etc. of the polarizing plate. The thermoplastic resin forming the plastic resin layer is preferably selected from the same kind of thermoplastic resin.

The moisture permeability of the base film is preferably 5 g · m ⁻² day ⁻¹ or more and 400 g · m ⁻² day ⁻¹ or less, more preferably 10 g · m ⁻² day ⁻¹ or more, 200 g · m ^−2. day ⁻¹ or less. The moisture permeability can be measured by the cup method described in JIS Z 0208 under the test conditions for 24 hours in an environment of 40 ° C. and 92% RH.
By setting the moisture permeability of the base film to the above range, it is possible to obtain a polarizing plate excellent in durability even in a high temperature and high humidity environment.

Further, the base film has a tensile modulus of elasticity of the i-th thermoplastic resin layer as A _i and a tensile modulus of elasticity of the i + 1-th thermoplastic resin layer as A _{i + 1} . , | A _{i + 1} −A _i | ≧ 0.5 GPa. With such a configuration, strength and flexibility can be increased while preventing a decrease in optical performance due to interference fringes or the like. The tensile modulus A _{j of} the j-th (j is an integer of 1 to k) thermoplastic resin layer may be 2.8 GPa or more. In addition, the tensile elastic modulus Ak of the _kth thermoplastic resin layer can be 3.0 GPa or more. Tensile modulus A _k of the k th thermoplastic resin layer may be a larger than the tensile modulus A _k-1 of the k-1 th thermoplastic resin layer adjacent thereto. Further, the tensile elastic modulus A1 of the _first thermoplastic resin layer can be 3.0 GPa or more.

  In addition, the total number of laminated thermoplastic resin layers is preferably 7 layers or less, and more preferably 5 layers or less. When the number is larger than the number of layers, it may be difficult to control the surface shape and thickness of each layer.

  In the base film, it is preferable that the surface of the kth thermoplastic resin layer is not formed with linear concave portions or linear convex portions, and the surface is flat. Even if linear concave portions or linear convex portions are formed, linear concave portions having a depth of less than 50 nm or a width of more than 500 nm, or lines having a height of less than 50 nm or a width of more than 500 nm. It is preferable that it is a convex part. More preferably, it is a linear concave portion having a depth of less than 30 nm or a width of 700 nm, and a linear convex portion having a height of less than 30 nm or a width of greater than 700 nm. Further, it is preferable that the above-described linear concave portions and linear convex portions are not formed on the surface of the first thermoplastic resin layer as well as the kth thermoplastic resin. By not forming the linear concave portion or the linear convex portion, it is possible to prevent light leakage or optical interference.

  The thermoplastic resin layer having no linear convex part and linear concave part having such a size is formed, for example, in a lip tip part which reduces the surface roughness of the lip part of the die in a T-die type extrusion molding method. Coating with chromium, nickel, titanium, etc., spraying ceramics on the tip of the lip, coating of TiN, TiAlN, TiC, CrN, DLC (diamond-like carbon) on the inner surface of the lip by the PVD (Physical Vapor Deposition) method, etc. The temperature distribution around the molten resin immediately after being extruded from the die, the air flow, etc. are uniformly adjusted, and the resin that forms the thermoplastic resin layer is selected to have the same melt flow rate value, etc. Cast support film having a small surface roughness in the cast molding method. Can be obtained by reducing the surface roughness of the coating machine, adjusting the temperature distribution during drying of the coating layer, the drying temperature, and the drying time.

  As another means for setting the size of the linear concave portion or the linear convex portion within the above range, in the T-die type extrusion molding method, the one attached to the die lip (for example, burns or dust) is used. Examples include removing, improving die lip releasability, making die lip wettability uniform over the entire surface, reducing resin powder, reducing the amount of dissolved oxygen in resin pellets, and installing a polymer filter in the melt extruder. It is done.

  The base film is obtained by coextrusion molding of a plurality of thermoplastic resins. According to the co-extrusion molding method, a complicated process (for example, a drying process or a coating process) is not required, so that a film with less external foreign matters such as dusts and excellent optical characteristics can be provided.

<Film with irregularities on the surface>
As a method of applying a pressure to at least one surface of the substrate film to obtain a film having irregularities formed on the surface, a nip molding method using a shaping roll having irregularities on the substrate film, And a method of applying a sandwich lamination method using a film having irregularities, a blasting method, or the like.
Among them, a nip forming method using a shaping roll having irregularities is preferable, and it is preferable to sandwich a substrate film using a mirror roll and a shaping roll having irregularities. Examples of the surface material of each roll include metal, rubber, and resin. These are selected based on the transfer state of the forming, but the hardness of the forming roll is preferably equal to or higher than the hardness of the mirror surface roll. Further, in order to satisfy the above condition, for example, another system of WEB may be introduced on the mirror roll, and the pressure may be narrowed through a resin film that is softer than the shaping roll having the same surface property as the mirror roll.

  It is preferable that the mirror-shaped roll and the shaping roll having projections and depressions can be adjusted in temperature. The temperature of the mirror roll is 40 ° C. or higher and 150 ° C. or lower, and the temperature of the shaping roll having irregularities is 100 ° C. or higher and 200 ° C. or lower. The temperature of the mirror roll is preferably 60 ° C. or higher and 110 ° C. or lower, and the temperature of the shaping roll having irregularities is preferably 110 ° C. or higher and 180 ° C. or lower.

  The surface shape of the shaping roll is preferably arranged at random, the arithmetic average roughness (Ra) of the surface is 0.01 μm or more and 2.0 μm or less, and the average period (Sm) of the irregularities is 10 μm or more. It is 100 μm or less. The arithmetic average roughness is preferably from 0.1 μm to 1.5 μm, and the average period is preferably from 30 μm to 70 μm.

The arithmetic average surface roughness (Ra) of the film on which the unevenness is formed is 0.05 μm or more and 0.5 μm or less, and the average period (Sm) of the unevenness is 10 μm or more and 100 μm or less. The arithmetic average roughness is preferably from 0.1 μm to 0.3 μm, and the average period is preferably from 30 μm to 70 μm.
In addition, in this invention, the arithmetic mean surface roughness and average period of a roll and a film are the values measured according to prescription | regulation of JISB0601: 2001.

  The base film having irregularities formed on the surface has a haze of 1% or more and less than 50%. The haze is preferably 3% or more and less than 40%.

  A functional layer can be laminated | stacked, after performing the surface modification process to the single side | surface or both surfaces in the base film in which the unevenness | corrugation was formed in the surface. By performing the surface modification treatment, adhesion to the low refractive index layer and other layers described later can be improved. Examples of the surface modification treatment include energy beam irradiation treatment and chemical treatment.

  Examples of the energy ray irradiation treatment include corona discharge treatment, plasma treatment, electron beam irradiation treatment, ultraviolet ray irradiation treatment, and the like. From the viewpoint of treatment efficiency, corona discharge treatment and plasma treatment are preferred, and corona discharge treatment is particularly preferred. Examples of the chemical treatment include a method of immersing in an aqueous oxidizing agent solution such as a potassium dichromate solution or concentrated sulfuric acid and then thoroughly washing with water. In chemical treatment, it is effective to shake in an immersed state, but there is a problem that the surface dissolves or transparency decreases when treated for a long time, depending on the reactivity, concentration, etc. of the chemical used, It is necessary to adjust the processing time.

  In this way, functional layers such as a hard coat layer, an antireflection layer, and an antifouling layer are formed on the surface of the film having unevenness on the surface where the unevenness is formed, and the optical film of the present invention is obtained.

<Functional layer>
(Hard coat layer)
The hard coat layer is a layer having a function of increasing the surface hardness of the optical film of the present invention, and has a hardness of H or higher in a pencil hardness test (test plate uses a glass plate) shown in JIS K5600-5-4. It is preferable to show. The optical film provided with such a hard coat layer preferably has a pencil hardness of 4H or higher. The material for forming the hard coat layer (hard coat material) is preferably a material that is cured by heat or light. For example, organic hard such as organic silicone, melamine, epoxy, acrylic, urethane acrylate, etc. Coating materials; inorganic hard coat materials such as silicon dioxide; and the like. Among these, urethane acrylate-based and polyfunctional acrylate-based hard coat materials are preferable from the viewpoint of good adhesive strength and excellent productivity.

  The hard coat layer contains various fillers for the purpose of adjusting the refractive index, improving the flexural modulus, stabilizing the volume shrinkage, and improving heat resistance, antistatic properties, and antiglare properties, as desired. it can. Further, the hard coat layer can contain additives such as an antioxidant, an ultraviolet absorber, a light stabilizer, an antistatic agent, a leveling agent, and an antifoaming agent.

(Antireflection layer)
The antireflection layer is a layer for preventing the transfer of external light, and is laminated on the surface of the optical film (a surface exposed to the outside) directly or via another layer such as a hard coat layer. The optical film provided with the antireflection layer preferably has an incident angle of 5 °, a reflectance at a wavelength of 430 nm to 700 nm of 2.0% or less, and a reflectance at a wavelength of 550 nm of 1.0% or less. preferable.

  The thickness of the antireflection layer is preferably 0.01 μm to 1 μm, more preferably 0.02 μm to 0.5 μm. The antireflection layer has a refractive index smaller than the refractive index of a layer (such as a protective layer or a hard coat layer) on which the antireflection layer is laminated, specifically a low refractive index of 1.30 to 1.45. Examples thereof include those composed of a refractive index layer; those obtained by alternately laminating a plurality of low refractive index layers of a thin film made of an inorganic compound and high refractive index layers of a thin film made of an inorganic compound.

  The material for forming the low refractive index layer is not particularly limited as long as it has a low refractive index. Examples thereof include a resin material such as an ultraviolet curable acrylic resin, a hybrid material in which inorganic fine particles such as colloidal silica are dispersed in the resin, and a sol-gel material using a metal alkoxide such as tetraethoxysilane. The material for forming these low refractive index layers may be a polymerized polymer, or may be a monomer or oligomer serving as a precursor. Moreover, it is preferable that each material contains the compound containing a fluorine group, in order to provide antifouling property.

As the sol-gel material, a sol-gel material containing a fluorine group is preferably used. Examples of the sol-gel material containing a fluorine group include perfluoroalkylalkoxysilane. The perfluoroalkylalkoxysilane is, for example, CF ₃ (CF ₂ ) _n CH ₂ CH ₂ Si (OR) ₃ (wherein R represents an alkyl group having 1 to 5 carbon atoms, and n is 0 to 12 A compound represented by an integer). Specifically, perfluoroalkylalkoxysilanes include trifluoropropyltrimethoxysilane, trifluoropropyltriethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxy. Examples include silane and heptadecafluorodecyltriethoxysilane. Among these, the compound whose said n is 2-6 is preferable.

  The low refractive index layer can be made of a cured product of a thermosetting fluorine-containing compound or an ionizing radiation curable fluorine-containing compound. The cured product preferably has a dynamic friction coefficient of 0.03 to 0.15, and a contact angle with water of 90 to 120 degrees. Examples of the curable fluorine-containing compound include a perfluoroalkyl group-containing silane compound (for example, (heptadecafluoro-1,1,2,2-tetradecyl) triethoxysilane) and the like, and a fluorine-containing polymer having a crosslinkable functional group. Can be mentioned.

  The fluorine-containing polymer having a crosslinkable functional group is obtained by copolymerizing a fluorine-containing monomer and a monomer having a crosslinkable functional group, or by copolymerizing a fluorine-containing monomer and a monomer having a functional group, and then in the polymer. It can be obtained by adding a compound having a crosslinkable functional group to the functional group.

  Examples of the fluorine-containing monomer include fluoroolefins such as fluoroethylene, vinylidene fluoride, tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoro-2,2-dimethyl-1,3-dioxole; “Biscoat 6FM” ( (Organic Organic Chemicals Co., Ltd.), “M-2020” (Daikin Co., Ltd.) and other (meth) acrylic acid partial or fully fluorinated alkyl ester derivatives, and fully or partially fluorinated vinyl ethers.

  Monomers having a crosslinkable functional group or compounds having a crosslinkable functional group include monomers having a glycidyl group such as glycidyl acrylate and glycidyl methacrylate; monomers having a carboxyl group such as acrylic acid and methacrylic acid; hydroxyalkyl acrylate and hydroxyalkyl Monomers having a hydroxyl group such as methacrylate; methylol acrylate, methylol methacrylate; monomers having a vinyl group such as allyl acrylate and allyl methacrylate; monomers having an amino group; monomers having a sulfonic acid group;

  As a material for forming the low refractive index layer, a material containing a sol in which fine particles such as silica, alumina, titania, zirconia, magnesium fluoride and the like are dispersed in an alcohol solvent is used because it can improve scratch resistance. Can do. From the viewpoint of antireflection properties, the fine particles preferably have a lower refractive index. Such fine particles may have voids, and silica hollow fine particles are particularly preferable. The average particle size of the hollow fine particles is preferably 5 nm to 2,000 nm, and more preferably 20 nm to 100 nm. Here, the average particle diameter is a number average particle diameter obtained by observation with a transmission electron microscope.

(Anti-fouling layer)
The antifouling layer is a layer that can impart water repellency, oil repellency, sweat resistance, antifouling properties, and the like. As a material used for forming the antifouling layer, a fluorine-containing organic compound is suitable. Examples of the fluorine-containing organic compound include fluorocarbon, perfluorosilane, and polymer compounds thereof. As a method for forming the antifouling layer, a physical vapor deposition method such as vapor deposition or sputtering, a chemical vapor deposition method, a wet coating method, or the like can be used depending on the material to be formed. The average thickness of the antifouling layer is preferably 1 nm to 50 nm, more preferably 3 nm to 35 nm.

  In addition to the above, the functional layer may be other general layers employed in optical films such as an antiglare layer, a gas barrier layer, a transparent antistatic layer, a primer layer, an electromagnetic wave shielding layer, and an undercoat layer. Good.

<Optical film>
There is no particular limitation on the method for obtaining the optical film of the present invention by forming the functional layer as described above on a film having irregularities formed on the surface. For example, the dip coating method is generally used for forming each functional layer. , Air knife coating method, curtain coating method, roller coating method, wire bar coating method, gravure coating method and the like.

  The arithmetic average surface roughness (Ra) of the film after the functional layer is laminated on the irregular surface is preferably 0.1 μm or less, and more preferably 0.06 μm or less.

  The base film after the functional layer is laminated preferably has a haze of 5% or less, more preferably 3% or less.

<Use of optical film>
The optical film of the present invention is a liquid crystal display (LCD), plasma display panel (PDP), electroluminescence display (ELD), cathode ray tube display (CRT), field emission display (FED), electronic paper, touch panel, etc. As a surface protective film of the device, it can be used by directly bonding or by replacing it with a surface member incorporated in a display device such as a polarizing plate protective film or a front plate. The optical film of the present invention is suitably used for polarizing plate protection.
When the optical film of the present invention thus obtained is used as a polarizing plate protective film, the optical film of the present invention is bonded to one surface of a polarizer through an adhesive, and then the adhesive is cured to obtain an optical A polarizing plate is obtained by fixing the film to a polarizer.

<Use of optical film>
The optical film of the present invention is a liquid crystal display (LCD), plasma display panel (PDP), electroluminescence display (ELD), cathode ray tube display (CRT), field emission display (FED), electronic paper, touch panel, etc. As a surface protective film of the device, it can be used by directly bonding or by replacing it with a surface member incorporated in a display device such as a polarizing plate protective film or a front plate. The optical film of the present invention is suitably used for polarizing plate protection.
When the optical film of the present invention thus obtained is used as a polarizing plate protective film, the optical film of the present invention is bonded to one surface of a polarizer through an adhesive, and then the adhesive is cured to obtain an optical A polarizing plate is obtained by fixing the film to a polarizer.
Prior to bonding the polarizer to the optical film, the bonding surface on the optical film side may be subjected to easy adhesion treatment such as saponification treatment, corona treatment, primer treatment, and anchor coating treatment.
Polarizers can be obtained by adsorbing iodine or dichroic dye on a polyvinyl alcohol film and then uniaxially stretching in a boric acid bath, or by adsorbing iodine or dichroic dye on a polyvinyl alcohol film. In addition, examples include those obtained by modifying a part of the polyvinyl alcohol unit in the molecular chain to a polyvinylene unit. In addition, a polarizer having a function of separating polarized light into reflected light and transmitted light, such as a grid polarizer, a multilayer polarizer, and a cholesteric liquid crystal polarizer, can also be used as the polarizer. Among these, a polarizer comprising polyvinyl alcohol is preferable. The polarization degree of the polarizer is preferably 98% or more, more preferably 99% or more. The thickness (average thickness) of the polarizer is preferably 5 μm to 80 μm.

In general, after a polarizer is bonded to one surface of the optical film, a protective layer is laminated on the polarizer that is not in contact with the optical film. The protective layer may be the optical film of the present invention, or a polycarbonate resin, polyether sulfone resin, polyethylene terephthalate resin, polyimide resin, polymethyl methacrylate resin, polysulfone resin, polyarylate conventionally used for polarizing plates. It may be a protective layer made of resin, polyethylene resin, polystyrene resin, polyvinyl chloride resin, cellulose ester, alicyclic olefin polymer, or the like.
There is no particular limitation on the method of laminating the protective layer on the polarizer, and for example, a general method of laminating a protective film serving as the protective layer with the polarizer through an adhesive or the like can be employed as necessary. As an adhesive for bonding the protective layer to the polarizer, the above-mentioned photocationic curable adhesive may be used, or a conventionally known adhesive may be used.

  A liquid crystal display device can be manufactured using this polarizing plate. In the liquid crystal display device, a light source, an incident side polarizing plate, a liquid crystal cell, and an output side polarizing plate are usually arranged in this order. The polarizing plate can be provided on the emission side (viewing side) and / or the incident side (light source side) of the device, but it is preferable to dispose the polarizing plate of the present invention at least on the emission side. The liquid crystal display device of the present invention may further include a retardation plate, a brightness enhancement film, a light guide plate, a light diffusion plate, a light diffusion sheet, a light collection sheet, a reflection plate, and the like.

The present invention will be described in more detail with reference to examples and comparative examples. Parts and% are based on mass unless otherwise specified.
The protective films obtained in Examples and Comparative Examples were evaluated by the following methods.

<Refractive index of thermoplastic resin layer>
A resin is formed into a single layer, and a prism coupler (manufactured by Metricon, model 2010) is used. From the refractive index values at wavelengths of 633 nm, 407 nm, and 532 nm under the conditions of temperature 20 ° C. ± 2 ° C. and humidity 60 ± 5%, Caucy The refractive indexes of 380 nm and 780 nm are calculated according to the dispersion formula. FIG. 1 shows the distribution of the refractive index of each resin layer with respect to wavelength. Figure 2 shows the distribution of refractive index difference between polymethyl methacrylate resin (PMMA) and alicyclic olefin polymer (COP), and the distribution of refractive index difference between polymethyl methacrylate resin (PMMA) and polycarbonate (PC). ing. FIG. 3 shows polymethyl methacrylate resin (P
The distribution of the refractive index difference between MMA) and polyvinyl alcohol (PVA) is shown.

<Melt flow rate>
In accordance with JIS K 7210, measurement was performed with a melt indexer F-B01 manufactured by Toyo Seiki Seisakusho under the conditions of 280 ° C. and 2.16 kgf (Condition S).

<Tensile modulus>
A thermoplastic resin is formed into a single layer to obtain a film having a thickness of 100 μm, a 1 cm × 25 cm test piece is cut out, and a tensile tester (manufactured by Toyo Baldwin, Tensilon UTM-10T-PL) is used based on ASTM D882. Then, the measurement was performed under the condition of a tensile speed of 25 mm / min. The same measurement is performed 5 times, and the arithmetic average value is set as the representative value of the tensile elastic modulus.

<Thickness of each resin layer>
The base film was embedded in an epoxy resin, sliced using a microtome (RUB-2100, manufactured by Yamato Kogyo Co., Ltd.), and the cross section was observed and measured using a scanning electron microscope.
<Haze>
It was measured using a turbidimeter (Nippon Denshoku Co., Ltd., product name “NDM 2000”).
<Ra, Sm>
Measurement was performed using a color 3D laser microscope (manufactured by Keyence Corporation, product name “VK-9500”) in accordance with JIS B 0601: 2001.
<Observation of interference fringes on polarizing plate>
Six three-wavelength fluorescent lamps (National FL20SS / ENW / 18, manufactured by Matsushita Electric Industrial Co., Ltd.) are placed on the ceiling of the room surrounded by black cloth that does not allow light to pass. The light from the fluorescent lamp was applied to the optical film surface from the observer side, the state of interference fringes was observed, and evaluation was performed according to the following criteria.
○: Interference fringes are not visible △: Interference fringes are slightly visible ×: Interference fringes are conspicuous <Pencil hardness>
Except for changing the load to 500 g, according to JIS K 5600-5-4, the surface of the optical film (surface of the antireflection layer) was scratched by about 5 mm with a 4H pencil, and the degree of damage was confirmed.
○: No damage was found in any part.
X: Scratched or more in one place.
<Weather resistance>
The produced optical film was exposed for 200 hours under the conditions of a sunshine carbon arc lamp and a relative humidity of 60% using a sunshine weather meter (S-80, manufactured by Suga Test Instruments Co., Ltd.). Thereafter, the change in hue of the polarizing plate (ΔYI) was measured using a color difference meter (manufactured by Suga Test Instruments Co., Ltd.) and evaluated with the following indices.

(Production of elastic particles)
Into a reactor equipped with a stirrer and a condenser, 6860 ml of distilled water and 20 g of sodium dioctylsulfosuccinate as an emulsifier were added, and the temperature was raised to 75 ° C. in a nitrogen atmosphere while stirring, so that there was no influence of oxygen. An emulsifier-containing distilled water was obtained.
To this distilled water containing an emulsifier, a mixed solution consisting of MMA 220 g, n-butyl acrylate 33 g, allyl methacrylate (hereinafter referred to as ALMA) 0.8 g and diisopropylbenzene hydroperoxide (hereinafter referred to as PBP) 0.2 g was added, The first layer was polymerized by maintaining at 80 ° C. for 15 minutes.
Next, a mixed liquid consisting of 1270 g of n-butyl acrylate, 320 g of styrene, 20 g of diethylene glycol acrylate, 13.0 g of ALMA and 1.6 g of PBP was continuously dropped over 1 hour into the reaction liquid after the completion of the first layer polymerization. After completion of the dropwise addition, the reaction was further allowed to proceed for 40 minutes to polymerize the second layer.
Next, as a polymerization for the third layer, a mixed solution consisting of MMA 340 g, n-butyl acrylate 2.0 g, PBP 0.3 g and n-octyl mercaptan 0.1 g is added to the reaction solution after the reaction of the second layer. Further, a mixed solution composed of MMA 340 g, n-butyl acrylate 2.0 g, PBP 0.3 g and n-octyl mercaptan 1.0 g was added. Thereafter, the temperature was raised to 95 ° C. and held for 30 minutes to obtain a latex of multilayer structure acrylic rubber particles. A small amount of latex was sampled and the average particle size was determined by the absorbance method and found to be 0.2 μm.
The obtained latex was put into a 0.5% aluminum chloride aqueous solution to agglomerate the polymer, washed 5 times with warm water, and dried to obtain elastic particles.

  After mixing 80 parts by weight of a polymethyl methacrylate resin and 20 parts by weight of elastic body particles, a polymethyl methacrylate resin (tensile modulus 2. 5 GPa, a melt flow rate of 20 g / 10 min (280 ° C., 2.16 kgf), a glass transition temperature of 102 ° C., a water absorption rate of 0.3%: hereinafter sometimes referred to as “R-PMMA”).

(Preparation of base film 1)
Polymethyl methacrylate resin (R-PMMA) containing elastic particles is put into a double flight type single screw extruder equipped with a leaf disk-shaped polymer filter with an opening of 10 μm, and the molten resin is die-cast at an extruder outlet temperature of 260 ° C. This was supplied to one of the multi-manifold dies having a slip surface roughness Ra of 0.1 μm.

  At the same time, 2% by weight of an ultraviolet absorber was added to polymethyl methacrylate resin (tensile modulus 3.3 GPa, melt flow rate 18 g / 10 min (280 ° C., 2.16 kgf), glass transition temperature Tg = 110 ° C.) An ultraviolet absorber-containing polymethyl methacrylate resin (hereinafter sometimes referred to as “PMMA”) is introduced into a double flight type single screw extruder having a leaf disk-shaped polymer filter having an opening of 10 μm, and the exit temperature of the extruder At 260 ° C., the molten resin was supplied to the other of the multi-manifold dies having a die slip surface roughness Ra of 0.1 μm.

Each of polymethyl methacrylate resin (R-PMMA) containing elastic particles in a molten state and polymethyl methacrylate resin (PMMA) containing an ultraviolet absorber is discharged from the multi-manifold die at 260 ° C., and the temperature is adjusted to 130 ° C. Cast to a cooling roll, and then passed through a cooling roll adjusted to a temperature of 50 ° C., consisting of a three-layer structure of R-PMMA layer (10 μm) -PMMA layer (60 μm) -R-PMMA layer (10 μm), A protective film 1 having a width of 600 mm and a thickness of 80 μm was obtained by coextrusion molding. The depth of the linear concave portion or the height of the linear convex portion of this base film is 20 nm or less, the width is in the range of 800 nm or more, and the moisture permeability is 51 g · m ⁻² · day ^−1. It was. Ra of the base film was less than 0.15 μm, and haze was 4.0%.

(Manufacture of embossed film 1)
In the above process, the base film coming out of the molding machine by coextrusion molding is made of a metal mirror surface roll with hard chromium plating 100 μm heated to 110 ° C., and ceramic Ra heated to 150 ° C. is 1.2 μm. The extruded film was narrowed at a linear pressure of 100 kN / m using a forming roll having irregularities with Sm of 50 μm. The film was wound at a roll speed of 10 m / min to obtain a film (embossed film 1) having irregularities formed on one surface.
The surface of the embossed film 1 to which embossing was applied had an Ra of 0.18 μm and a haze of 17.4%.

(Manufacture of embossed film 2)
In the production of the embossed film 1, a thermoplastic polyimide resin film manufactured by Mitsui Chemicals, Inc. is supplied from a separate WEB on a metallic mirror roll having a hard chromium plating of 100 μm heated to 110 ° C. during emboss transfer. “ARUUM film” (Part No. “PL450C”) is conveyed and heated at 180 ° C., and the extruded film is subjected to linear pressure of 200 kN using a forming roll having irregularities with Ra of 1.1 μm and Sm of 50 μm. The pressure was reduced at / m. A film (embossed film 2) having irregularities formed on the surface was obtained in the same manner as in Production Example 1, except that the roll speed was 20 m / min.
Ra of the embossed surface of the embossed film 2 was 0.23 μm, and haze was 21.7%.

(Manufacture of embossed film 3)
In the production of the embossed film 1, a thermoplastic polyimide resin film manufactured by Mitsui Chemicals, Inc., supplied from another web, on a metallic mirror roll having a hard chromium plating of 100 μm heated to 70 ° C. during emboss transfer. “ARUUM film” (product number “PL450C”) is conveyed and heated at 180 ° C., and the extruded film is subjected to a forming roll having irregularities with Ra of 1.3 μm and Sm of 50 μm. The pressure was reduced at / m. A film (embossed film 3) having irregularities formed on the surface was obtained in the same manner as in Production Example 1 except that the roll speed was 30 m / min.
The surface of the embossed film 3 to which embossing was applied had an Ra of 0.26 μm and a haze of 24.1%.

(Preparation of hard coat layer forming material)
30 parts of a hexafunctional urethane acrylate oligomer, 40 parts of butyl acrylate, 30 parts of isobornyl methacrylate, and 10 parts of 2,2-diphenylethane-1-one were mixed with a homogenizer, and antimony pentoxide fine particles (average particle diameter of 20 nm, The hydroxyl group is bonded to the antimony atoms appearing on the surface of the pyrochlore structure at a ratio of 1). A 40% methyl isobutyl ketone solution is used, and the weight of the antimony pentoxide fine particles is the total solid content of the hard coat layer forming composition. The hard coat layer forming material was prepared by mixing at a ratio of 50% by weight.

(Preparation of low refractive index layer forming material)
70 parts by weight of vinylidene fluoride and 30 parts by weight of tetrafluoroethylene, which are fluorine-containing monomers, were dissolved in methyl isobutyl ketone. Next, hollow silica isopropanol dispersion sol (manufactured by Catalytic Chemical Industry Co., Ltd., solid content: 20% by weight, average primary particle diameter: about 35 nm, outer shell thickness: about 8 nm) is hollowed into this dissolved matter with respect to the fluorine-containing monomer solid content. 30% by weight of silica solid content, 3% by weight of dipentaerythritol hexaacrylate (manufactured by Shin-Etsu Chemical Co., Ltd.) with respect to the solid content, and Irgacure 184 (produced by Ciba Specialty Chemicals) with respect to the solid content 5% by weight was added to prepare a low refractive index layer forming material.

Example 1
Both surfaces of the embossed film 1 were subjected to corona discharge treatment using a high frequency transmitter (output 0.8 kW), and the surface tension was adjusted to 0.055 N / m. Next, a hard coat layer forming material is applied to the surface of the embossed film 1 on which the unevenness is formed using a die coater at a temperature of 25 ° C. and a humidity of 60% RH at a coating speed of 20 m / min. And dried in an oven at 80 ° C. to obtain a film. Further, the film was irradiated with ultraviolet rays (accumulated dose of 300 mJ / cm ² ) to form a hard coat layer having a thickness of 6 μm.

Next, on the hard coat layer side of the embossed film 1 with a hard coat layer, a material for forming a low refractive index layer at a coating speed of 20 m / min using a wire bar coater in an environment of a temperature of 25 ° C. and a humidity of 60% RH. The film was coated and allowed to dry at room temperature. The resulting film was heat-treated at 120 ° C. in an oxygen atmosphere, and then irradiated with ultraviolet rays under the conditions of an output of 160 W / cm and an irradiation distance of 60 mm. A refractive index layer (refractive index of 1.37) was formed to obtain an optical film 1 with a hard coat layer and an antireflection layer.
The optical film 1 was evaluated for Ra (antireflection layer surface), haze, interference unevenness, pencil hardness, and weather resistance. The results are shown in Table 1.

Example 2
An optical film 2 was obtained in the same manner as in Example 1 except that the embossed film 2 was used. The optical film 2 was evaluated for Ra (antireflection layer surface), haze, interference unevenness, pencil hardness, and weather resistance. The results are shown in Table 1.

Example 3
An optical film 3 was obtained in the same manner as in Example 1 except that the embossed film 3 was used. The optical film 3 was evaluated for Ra (antireflection layer surface), haze, interference unevenness, pencil hardness, and weather resistance. The results are shown in Table 1.

Comparative Example 1
Instead of the embossed film 1, an optical film 4 was obtained in the same manner as in Example 1 except that a base film before unevenness was used. The optical film 4 was evaluated for Ra (antireflection layer surface), haze, interference unevenness, pencil hardness, and weather resistance. The results are shown in Table 1.

Comparative Example 2
An optical film 5 was obtained in the same manner as in Comparative Example 1 except that the coating speeds for forming the hard coat layer and the low refractive index layer were both 10 m / min. The optical film 5 was evaluated for Ra (antireflection layer surface), haze, interference unevenness, pencil hardness, and weather resistance. The results are shown in Table 1.

From this result, it is a film formed by laminating k thermoplastic resin layers (k is an integer of 2 or more), and the refractive index ni of the i-th thermoplastic resin layer at a wavelength λ in the range of 380 nm to 780 nm. (Λ) and the refractive index ni + 1 (λ) at a wavelength λ in the range of 380 nm to 780 nm of the (i + 1) th thermoplastic resin layer have the relationship of the above equation [1], and the i th heat When the tensile elastic modulus of the plastic resin layer is A _i and the i + 1th tensile elastic modulus is A _{i + 1} , | A _{i + 1} −A _i | ≧ 0.5 GPa for all values of _i , and kth by th tensile modulus a _k of the thermoplastic resin layer with a base film is one formed by coextrusion with the above 2.8 GPa, and applying pressure to one surface thereof, rough surface Used film formed If it is, the highly transparent optical film excellent in pencil hardness and flexibility without an interference nonuniformity can be obtained (Examples 1-3).
On the other hand, when the functional layer is formed under the same conditions as when using a film with irregularities formed on the surface, it is excellent in pencil hardness and flexibility, and interference fringes of the base film itself can be suppressed, but interference is caused by coating. It can be seen that unevenness occurs (Comparative Example 1). It can be seen that even when the formation rate of the hard coat layer is slowed as a condition for forming the functional layer, the occurrence of uneven interference cannot be sufficiently suppressed (Comparative Example 2).

Claims (2)

By applying pressure to at least one surface of the base film, an optical film having a functional layer on at least the surface on which the unevenness is formed of the film on which the unevenness is formed on the surface,
The base film is
A film in which k thermoplastic resin layers (k is an integer of 2 or more) are laminated,
The refractive index ni (λ) at a wavelength λ in the wavelength range of 380 nm to 780 nm of the i-th (i is an integer from 1 to k−1) and 380 nm to 780 nm of the i + 1-th thermoplastic resin layer. And a refractive index n _{i + 1} (λ) at a wavelength λ in the range of
When the tensile elastic modulus of the i-th thermoplastic resin layer is A _i and the i + 1-th tensile elastic modulus is A _{i + 1} , | A _{i + 1} −A _i | ≧ 0.5 GPa for all values of _i. Yes,
Further, an optical film formed by a coextrusion method in which at least one thermoplastic resin layer has a tensile elastic modulus A _j (j is an integer of 1 to k) of 2.8 GPa or more.
| N _i (λ) −n _{i + 1} (λ) | ≦ 0.05 Formula [1] The optical film according to claim 1, wherein the base film contains an ultraviolet absorber.

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