JP2016001304A - Optical polyester film and polarizing plate using the same, and transparent conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film that can suppress, when mounted in a display device such as a liquid crystal display, interference colors and white color irregularity when seen from an oblique direction and has excellent appearance.SOLUTION: There is provided an optical polyester film that is a biaxially oriented polyester film that includes a polyester A layer containing 0.0001 mass% or more of particles having a refractive index of 1.5 or more based on 100 mass% of the entire polyester A layer, in which when an arbitrary one direction in the surface of the film is a direction X, the direction perpendicular to the direction X is a direction Y, and the film thickness direction is Z, the average value of refractive indices of the directions X, Y, and Z is 1.6 or less.

Description

  The present invention relates to a polyester film that is particularly suitable for optical applications (polarizer protection, transparent conductive film, etc.).

  Thermoplastic resin films, especially biaxially oriented polyester films, have excellent properties such as mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance. It is widely used as a substrate film in the above applications. In particular, in recent years, demand for various optical films such as a polarizer protective film and a transparent conductive film has been increasing in the flat panel display and touch panel fields. Among them, the conventional TAC is used for the purpose of reducing the cost for the polarizer protective film application. Replacement of a (triacetylcellulose) film with a biaxially oriented polyester film has been studied. Since biaxially oriented polyester films cause interference color when assembled as a liquid crystal display due to the orientation of the polymer during stretching, studies to make the molecular orientation a specific range to suppress interference color (For example, patent document 1), examination (for example, patent document 2) etc. which make in-plane retardation, a plane orientation degree, etc. into a specific range are performed. Moreover, examination which improves the transparency of a film and an external appearance by using the particle | grains which have birefringence is also performed (for example, patent document 3).

  However, in both Patent Documents 1 and 2, interference color when the display is viewed from the front is suppressed, but interference color suppression when viewed from an oblique direction is insufficient. Also, in Patent Document 3, the thickness direction and the refractive index control of the particles are not sufficient, and it cannot be said that the transparency and appearance when viewed from an oblique direction are sufficient.

  In transparent conductive films and anti-scattering films used for touch panels, etc., there is an increasing demand for suppression of interference colors when assembled on touch panels, etc., due to the increase in screen size and simplification of the structure. In Patent Documents 1 and 2, the characteristics were insufficient.

JP 2010-181870 A JP 2013-210598 A JP 2014-63084 A

  Therefore, in the present invention, the above-mentioned drawbacks are eliminated, and while being a biaxially stretched polyester film, when mounted on a display device such as a liquid crystal display, interference color when viewed from an oblique direction can be suppressed, and transparency, It aims at providing the polyester film excellent also in the external appearance.

The present invention for solving the above problems has the following configuration.
(1) A biaxially oriented polyester film having a polyester A layer containing 10001% by mass of the entire polyester A layer and 0.0001% by mass or more of particles having a refractive index of 1.5 or more,
An optical whose average refractive index in the X, Y, and Z directions is 1.6 or less, where X is an arbitrary direction in the film plane, Y is a direction perpendicular to the direction X, and Z is a film thickness direction. Polyester film.
(2) The optical polyester film according to (1), wherein an average value of refractive indexes in the X direction and the Y direction is 1.6 or less.
(3) The polyester film for optics as described in (1) or (2) whose film haze is 3% or less.
(4) The optical polyester film according to any one of (1) to (3), wherein a film haze when heat-treated at 100 ° C. for 12 hours is 5% or less.
(5) At least one selected from the group consisting of hard coat properties, self-repairing properties, antiglare properties, antireflection properties, low reflection properties, and antistatic properties on at least one outermost surface of the optical polyester film The optical polyester film according to any one of (1) to (4), wherein the layers exhibiting the function of (1) to (5) are used for protecting a polarizer. The optical polyester film according to any one of the above.
(7) A polarizing plate having a polarizer protective film on both sides of the polarizer, wherein the polarizer protective film used on at least one surface is the optical polyester film according to (6) .
(8) A transparent conductive film having the polyester film according to any one of (1) to (5).

  When mounted on a display device such as a liquid crystal display, the optical polyester film of the present invention has an effect of enabling high-quality display with little interference color even when viewed from an oblique direction.

Hereinafter, the optical polyester film of the present invention will be described in detail.
The optical polyester film of the present invention is a polyester containing 10001% by mass of the entire polyester A layer and 0.0001% by mass or more of particles having a refractive index of 1.5% or more from the viewpoint of film handling, transparency and appearance. It is necessary to have an A layer. By having a polyester A layer containing 10001% by mass of particles and 0.0001% by mass of particles as a whole, it is possible to improve the suppression of scratches during film formation and improve the winding property, and to obtain a high-quality film. In addition, when processing a film after film formation, it is excellent in handleability, so that generation of scratches and wrinkles during conveyance can be suppressed, and thus a high-quality polarizing plate can be obtained. The concentration of the particles having a refractive index of 1.5 or more in the polyester A layer is more preferably 0.0005% by mass or more and 0.04% by mass or less, and 0.001% by mass or more and 0.03% by mass or less. Is most preferable. The refractive index of the particles contained in the polyester A layer is more preferably 1.51 or more, and most preferably 1.52 or more and 1.8 or less.
Although it does not specifically limit as particle | grains with a refractive index of 1.5 or more, For example, as an inorganic particle, calcium carbonate (refractive index 1.58), barium sulfate (refractive index 1.64), aluminum oxide (refractive index 1 .. 76), aluminum silicate (1.65) and the like, organic particles such as styrene, silicone, acrylic acids, methacrylic acids, polyesters, divinyl compounds, etc., and having a refractive index of 1.5 or more are controlled. Can be mentioned. Furthermore, two or more of these particles may be used in combination.
The particle size of the particles having a refractive index of 1.5 or more used in the optical polyester film of the present invention is not particularly limited, but is preferably an average particle size of 0.01 μm or more and 10 μm or less, and 0.05 μm or more and 5 μm. Or less, more preferably 0.1 μm or more and 3 μm or less. The average particle diameter in the present invention refers to the number average diameter D represented by D = ΣDi / N (Di: equivalent circle diameter of particles, N: number of particles).
In the optical polyester film of the present invention, the content of particles having a refractive index of less than 1.5 in the polyester A layer is preferably less than 0.0001% by mass from the viewpoint of appearance. More preferably, it is less than mass%, and most preferably not containing substantially. In the case of containing particles having a refractive index of less than 1.5, when the display is viewed from an oblique direction, it can be visually confirmed as white spots when the display is in a dark state.
The polyester A layer in the present invention contains 95 mol% or more of an ethylene glycol component as a diol component and 82 mol% or more of a terephthalic acid component as a dicarboxylic acid component from the viewpoints of handleability, transparency, and appearance of the film. Is preferred. More preferably, it is preferable to contain 97 mol% or more of the ethylene glycol component and 97 mol% or more of the dicarboxylic acid component as the diol component.
The optical polyester film of the present invention has an average refractive index in the X, Y, and Z directions, where direction X is an arbitrary direction in the film plane, direction Y is the direction orthogonal to direction X, and film thickness direction is Z. The value needs to be 1.6 or less. Here, the refractive index in the X, Y, and Z directions refers to the refractive index of the film in each direction measured by an Abbe refractometer or the like. When two or more types of refractive index are observed in a laminated film or the like, the most clearly observed numerical value is adopted.
When the average value of the refractive indexes in the X, Y, and Z directions is larger than 1.6, since the plane orientation of the film is high, the difference between the refractive index in the in-plane direction and the thickness direction is particularly large, and the oblique direction When viewing the display from the direction, it presents an interference color. From the viewpoint of appearance from an oblique direction, the average value of the refractive indexes in the X, Y, and Z directions is more preferably 1.595 or less, and most preferably 1.5 or more and 1.59 or less.
In the optical polyester film of the present invention, the method of setting the average value of the refractive indexes in the X, Y, and Z directions to 1.6 or less is not particularly limited, but as a polyester layer constituting the polyester film of the present invention, a diol component and / Or a structure having a polyester B layer having two or more dicarboxylic acid components, a method for reducing the biaxial orientation of the polyester film, setting the stretching ratio low, raising the stretching temperature, etc. Examples thereof include a method for adjusting to reduce the biaxial orientation of the polyester film and a method for reducing the film thickness.
The polyester B layer which is a layer other than the polyester A layer of the optical polyester film of the present invention contains 60 mol% or more of an ethylene glycol component as a diol component, and contains less than 40 mol% of another diol component, a dicarboxylic acid A structure containing 60 mol% or more of a terephthalic acid component as an acid component and less than 40 mol% of another dicarboxylic acid component is preferable.

  Here, as diol components other than ethylene glycol, for example, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5- Pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis ( 4-hydroxyethoxyphenyl) propane, isosorbate, spiroglycol and the like. Among these, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, isosorbate, and spiro glycol are preferably used. These diol components may be used alone or in combination of two or more in addition to ethylene glycol.

Examples of the dicarboxylic acid component other than terephthalic acid include, for example, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4′-diphenyl. Dicarboxylic acids, 4,4'-diphenyl ether dicarboxylic acids, aromatic dicarboxylic acids such as 4,4'-diphenylsulfone dicarboxylic acid, fats such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid An aromatic dicarboxylic acid, various aromatic dicarboxylic acids, and ester derivatives with aliphatic dicarboxylic acids. Of these, isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferably used.
The polyester B layer constituting the optical polyester film of the present invention has an average value of the refractive index in the X, Y, and Z directions of 1.6 or less, particularly 60% or more and less than 82 mol% of the dicarboxylic acid component. The terephthalic acid component, preferably 18 mol% or more and less than 40 mol%, is the other dicarboxylic acid component. More preferably, 70 to 80 mol% of the dicarboxylic acid component is a terephthalic acid component, and 20 to 30 mol% is another dicarboxylic acid component. The other dicarboxylic acid component is most preferably an isophthalic acid component or a 2,6-naphthalenedicarboxylic acid component.
Further, in the step of biaxially stretching the film of the present invention, the unstretched film is stretched in the longitudinal direction and then stretched in the width direction, or the stretched in the width direction and then stretched in the longitudinal direction. The film can be stretched by a simultaneous biaxial stretching method or the like in which the longitudinal direction and the width direction of the film are stretched almost simultaneously. At this time, a method of increasing the stretching temperature is preferably used. Specifically, the stretching temperature in the longitudinal direction is preferably 95 ° C. or higher and 110 ° C. or lower. The stretching temperature in the width direction is preferably 95 ° C. or more and 150 ° C. or less. From the viewpoint of stretchability and refractive index control, the first stage is 95 ° C. or more and less than 115 ° C., the second stage is 115 ° C. or more and 150 ° C. or less. It is more preferable to raise the stretching temperature stepwise.
In the optical polyester film of the present invention, the average value of the refractive indexes in the X direction and the Y direction is preferably 1.6 or less. When the average value of the refractive index in the X and Y directions is larger than 1.6, even if the refractive index in the thickness direction is high, the plane orientation of the film is increased, so that the refractive index in the in-plane direction and the thickness The difference from the refractive index in the direction becomes large, and an interference color may be exhibited when the display is viewed from an oblique direction. From the viewpoint of appearance from an oblique direction, the average value of the refractive indexes in the X and Y directions is more preferably 1.595 or less, and most preferably 1.55 or more and 1.59 or less.
In the optical polyester film of the present invention, the method of setting the average refractive index in the X and Y directions to 1.6 or less is not particularly limited, but the average refractive index in the X and Y directions is 1.6 or less. In addition to the method described above, it is preferable to use a roll heated to 30 ° C. or higher when shifting to the longitudinal stretching step after the casting step of discharging the sheet on the cooling drum from the T die. When shifting from the casting process to the longitudinal stretching process, the film surface orientation between the processes can be suppressed by using a roll heated to 30 ° C. or more, and the surface orientation suppression in the initial stage of the film production process can be suppressed. Therefore, it becomes easy to control the average value of the refractive indexes in the X and Y directions as low as 1.6 or less.
The optical polyester film of the present invention preferably has a film haze of 3% or less from the viewpoint of appearance. By reducing the film haze to 3% or less, since the transparency is high, a clearer appearance can be achieved. The film haze is more preferably 2.5% or less, and most preferably 0% or more and 2% or less.
As a method for adjusting the haze to 3% or less, it is preferable not to contain particles having a refractive index of less than 1.5 in the film. Further, there is a method of adding a particle only to the polyester A layer or the B layer as a laminated film having at least an A layer and a B layer. In the present invention, the entire polyester A layer is included in the polyester A layer. Since 100 mass% contains particles having a refractive index of 1.5 or more in an amount of 0.0001 mass% or more, a configuration in which particles are contained only in the polyester A layer and particles are not contained in the polyester B layer is preferably used.
In the case of a laminated film including a polyester A layer and a B layer, the number of layers and the layer structure are not particularly limited, but curling of the film is suppressed, for example, warpage reduction and interference color when bonded to a polarizer in a polarizer protection application. From the viewpoint of achieving both suppression, the film is symmetrical with respect to the thickness direction, such as A layer / B layer / A layer, A layer / B layer / A layer / B layer / A layer, and both surface layers. Is preferably a layer other than the polyester A layer. In applications where it is more important to reduce warpage when bonded to a polarizer, the number of layers to be laminated is preferably 3 to 9. Moreover, it is preferable that A layer is located in the outermost layer of a film from a viewpoint of a handleability, transparency, and an external appearance.
In the present invention, the thickness ratio of the polyester A layer is preferably (A layer thickness / film thickness) of 0.05 or more and 0.5 or less, more preferably 0.1 or more and 0.4 or less. Preferably, it is most preferably 0.1 or more and 0.3 or less. Here, A layer thickness means the thickness of the whole A layer in a polyester film, and when there are two or more A layers, it shows the total thickness.
In order to achieve the whitening resistance upon heating, the optical polyester film of the present invention preferably has a film haze of 5% or less when heat-treated at 100 ° C. for 12 hours. If the film haze when subjected to heat treatment at 100 ° C. for 12 hours is higher than 5%, long-term reliability decreases, and problems such as whitening of the film may occur when used and stored at high temperatures for a long time. . The film haze after heat treatment at 100 ° C. for 12 hours is more preferably 4% or less, and most preferably 3% or less.

The method for adjusting the film haze to 5% or less when the optical polyester film of the present invention is heat-treated at 100 ° C. for 12 hours is not particularly limited, but the heat treatment temperature during the production of the polyester film of the present invention is the highest melting point. Examples thereof include a method of setting the temperature to be equal to or lower than the melting point of the low polyester layer and leaving the oriented crystals without melting. Furthermore, a method of increasing the heat treatment temperature stepwise is also very effective. In this case, the temperature of the first stage of the heat treatment is set to the melting point of −80 ° C. to −30 ° C. of the polyester layer having the lowest melting point, and the temperature of the second stage of heat setting is set to be equal to or lower than the melting point of the polyester layer having the lowest melting point. Is preferred. By performing the heat treatment in two stages in this way, the oriented crystals can be made more difficult to melt, and even if heat treatment is performed at 100 ° C. for 12 hours, crystal growth of the film does not proceed, and appearance defects such as whitening are suppressed. It becomes possible.
In addition, in order to provide process stabilization in the manufacturing process and durability in the use environment, the polyester film for optical protection of the present invention has a hard coat property, self-repairing property, antiglare property, and antireflection property on at least one surface. It is preferable to have a surface layer exhibiting one or more functions selected from the group consisting of low reflectivity, ultraviolet shielding, and antistatic properties.

The thickness of the surface layer varies depending on its function, but is preferably in the range of 10 nm to 30 μm, and more preferably 50 nm to 20 μm. If it is thinner than this, the effect is insufficient, and if it is thicker, there is a possibility of adversely affecting optical performance and the like.
Here, the hard coat property is a function of making the surface hard to be damaged by increasing the hardness of the surface. As its function, it is preferably HB or more, more preferably 2H or more, or # 0000 steel wool in the evaluation by scratch hardness (pencil method) described in JIS K-5600-5-4-1999. In the scratch resistance test conducted under the condition of 200 g / cm ^2, a state in which no scratch is made is shown.
Here, the self-repairing property is a function that makes it difficult to be damaged by repairing the wound by elastic recovery or the like. The function is preferably when the surface is rubbed with a brass brush under a load of 500 g. Within 3 minutes, more preferably within 1 minute.
The anti-glare property is a function of improving visibility by suppressing reflection of external light by light scattering on the surface. The function is preferably 2 to 50%, more preferably 2 to 40%, and particularly preferably 2 to 30% in the evaluation based on the method for obtaining haze described in JIS K-7136-2000. It is.
Antireflection and low reflectivity are functions that improve visibility by reducing the reflectance at the surface due to the interference effect of light. Its function is preferably 2% or less, particularly preferably 1% or less, by reflectance spectroscopy measurement.
The antistatic property is a function of removing triboelectricity generated by peeling from the surface or rubbing on the surface by leaking. As a standard of the function, the surface resistivity described in JIS K-6911-2006 is preferably 10 ¹¹ Ω / □ or less, more preferably 10 ⁹ Ω / □ or less. In addition to a layer containing a known antistatic agent, the antistatic property may be imparted from a layer containing a conductive polymer such as polythiophene, polypyrrole or polyaniline. Hereinafter, the provision of hard coat properties and antiglare properties will be described in more detail.
The material used for the surface layer imparting the hard coat property (hereinafter, referred to as a hard coat layer) can be a material used for a known hard coat layer, and is not particularly limited, but is dry, heat, chemical reaction Alternatively, a resin compound that polymerizes and / or reacts by irradiation with any of electron beam, radiation, and ultraviolet light can be used. Examples of such a curable resin include melamine-based, acrylic-based, silicon-based, and polyvinyl alcohol-based curable resins, but acrylic resins that are cured by electron beams or ultraviolet rays in terms of obtaining high surface hardness or optical design. A curable resin is preferred.
An acrylic resin that is cured by an electron beam or ultraviolet ray has an acrylate-based functional group. For example, a relatively low molecular weight polyester resin, polyether resin, acrylic resin, epoxy resin, urethane resin, alkyd resin, spiro resin Acetal resins, polybutadiene resins, polythiol polyene resins, oligomers or prepolymers of polyfunctional compounds such as polyhydric alcohols (meth) acrylates and prepolymers and reactive diluents such as ethyl (meth) acrylate, ethylhexyl (meth) acrylate, styrene, methyl Monofunctional monomers such as styrene and N-vinylpyrrolidone as well as polyfunctional monomers such as trimethylolpropane tri (meth) acrylate, hexanediol (meth) acrylate, tripropylene glycol di (meth) acrylate Contains rate, diethylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, etc. Things can be used.
In the case of an electron beam or ultraviolet curable resin, as a photopolymerization initiator in the above-mentioned resin, acetophenones, benzophenones, Michler benzoylbenzoate, α-amyloxime ester, tetramethyltyramium monosulfide, thioxanthones, As a photosensitizer, n-butylamine, triethylamine, tri-n-butylphosphine and the like can be mixed and used. It is preferable that the addition amount of the said photoinitiator is 0.1-10 mass parts with respect to 100 mass parts of electron beam ultraviolet curable resins.
Although it does not specifically limit as a hardening method of the said coating film, It is preferable to carry out by ultraviolet irradiation. When curing by ultraviolet rays, it is preferable to use ultraviolet rays having a wavelength range of 190 to 380 nm. Curing with ultraviolet rays can be performed, for example, with a metal halide lamp, a high-pressure mercury lamp, a low-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a carbon arc lamp, a black light fluorescent lamp, or the like. Specific examples of the electron beam source include various electron beam accelerators such as a cockcroft-wald type, a bandegraft type, a resonant transformer type, an insulating core transformer type, a linear type, a dynamitron type, and a high frequency type.
Siloxane-based thermosetting resins are also useful as the resin for the hard coat layer, and can be produced by hydrolyzing and condensing the organosilane compound alone or in combination of two or more under an acid or base catalyst.
The film thickness of the hard coat layer is preferably 0.5 μm to 20 μm, more preferably 1 μm to 20 μm, and even more preferably 1 μm to 15 μm.
As the resin used for the surface layer imparting the antiglare property (hereinafter referred to as the antiglare layer), the same resin as the electron beam or ultraviolet curable resin described above can be used. One or two or more of the above-mentioned resins can be mixed and used. Further, in order to adjust physical properties such as plasticity and surface hardness, a resin that is not cured by an electron beam or ultraviolet rays can be mixed. Examples of resins that are not cured by electron beams or ultraviolet rays include polyurethane, cellulose derivatives, polyesters, acrylic resins, polyvinyl butyral, polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, polycarbonate, and polyamide.
Specific examples of the particles used in the antiglare layer include, for example, particles of inorganic compounds such as silica particles, alumina particles, TiO ₂ particles, or polymethyl methacrylate particles, acrylic-styrene copolymer particles, crosslinked acrylic particles, melamine particles. Preferred are resin particles such as crosslinked melamine particles, polycarbonate particles, polyvinyl chloride particles, benzoguanamine particles, crosslinked benzoguanamine particles, polystyrene particles, and crosslinked polystyrene particles. As the shape, spherical particles having a uniform surface protrusion shape are preferably used, but indefinite shapes such as layered inorganic compounds such as talc and bentonite can also be used. Two or more different kinds of particles may be used in combination. Even if there are two or more kinds of material and two or more kinds of particle sizes, there is no limitation.
The average particle diameter of the particles used in the antiglare layer is 0.5 to 10 μm, more preferably 0.5 to 5 μm, further preferably 0.5 to 3 μm, and still more preferably 0.5 to 1.5 μm. . The content of the particles is 1 to 50% by weight, more preferably 2 to 30% by weight, based on the resin. The average particle diameter in the present invention refers to a number average diameter D represented by D = ΣDi / N (Di: equivalent circle diameter of particles, N: number of particles).
The film thickness of the antiglare layer is preferably 0.5 μm to 20 μm, more preferably 1 μm to 20 μm, and further preferably 1 μm to 10 μm.
As the antiglare layer used in the present invention, JP-A-6-18706, JP-A-10-20103, JP-A-2009-227735, JP-A-2009-86361, JP-A-2009-80256 are disclosed. JP, 2011-81217, JP 2010-204479, JP 2010-181898, JP 2011-197329, JP 2011-197330, JP 2011-215393, etc. The described antiglare layer can also be suitably used.
The surface layer may contain other components in addition to those described above as long as the effects of the invention are not lost. Other components include, but are not limited to, for example, inorganic or organic pigments, polymers, polymerization initiators, polymerization inhibitors, antioxidants, dispersants, surfactants, light stabilizers, leveling agents, An antistatic agent, an ultraviolet absorber, a catalyst, an infrared absorber, a flame retardant, an antifoaming agent, conductive fine particles, a conductive resin, and the like can be added.

The optical film of the present invention enables high-quality display when mounted on a display device such as a liquid crystal display, and thus can be suitably used for various optical applications. It can be suitably used for polarizer protection applications, transparent conductive film applications, glass scattering prevention film applications, and the like.
The polarizing plate of the present invention is a polarizing plate having a polarizer protecting film on both sides of the polarizer, and the polarizer protecting film on at least one surface is preferably the optical polyester film. The other polarizer protective film may be the optical polyester film of the present invention, or a film having no birefringence such as a triacetyl cellulose film, an acrylic film, or a norbornene-based film is preferably used. .
Examples of the polarizer include a polyvinyl alcohol film containing a dichroic material such as iodine. The polarizer protective film is bonded to the polarizer directly or via an adhesive layer, but it is preferable to bond the polarizer protective film via an adhesive from the viewpoint of improving adhesiveness. As a preferable polarizer for bonding the polyester film of the present invention, for example, iodine or dichroic material is dyed and adsorbed on a polyvinyl alcohol film, uniaxially stretched in a boric acid aqueous solution, and the stretched state is maintained. The polarizer obtained by performing washing | cleaning and drying is mentioned. The draw ratio of uniaxial stretching is usually about 4 to 8 times. Polyvinyl alcohol is preferred as the polyvinyl alcohol film. “Kuraray Vinylon” (manufactured by Kuraray Co., Ltd.), “Tosero Vinylon” (manufactured by Tosero Co., Ltd.), “Nippon Synthetic Chemical Co., Ltd.” (Commercially available) can be used. Examples of the dichroic material include iodine, a disazo compound, and a polymethine dye.
The transparent conductive film of the present invention is a film in which a transparent conductive layer is laminated directly or via an easy adhesion layer on the optical polyester film of the present invention. The transparent conductive layer is not particularly limited as long as a transparent conductive film can be formed. For example, indium oxide containing tin oxide (ITO), tin oxide containing antimony (ATO), zinc oxide, zinc-aluminum composite oxide And thin films of indium-zinc composite oxide, CNT, silver, copper and the like. These compounds can achieve both transparency and conductivity by selecting appropriate production conditions.

As a method for forming a transparent conductive layer, a vacuum deposition method, a sputtering method, a CVD method, an ion plating method, a spray method, a method of coating a coating liquid containing a conductive material, and the like are known. An appropriate method can be selected and used depending on the required film thickness. For example, in the case of a sputtering method, normal sputtering using a compound target, reactive sputtering using a metal target, or the like is used. At this time, a reactive gas such as oxygen, nitrogen or water vapor can be introduced, or means such as addition of ozone or ion assist can be used in combination.
Next, the preferable manufacturing method of the optical polyester film of this invention is demonstrated below. The present invention should not be construed as being limited to such examples.
First, a polyester raw material is supplied to a vent type twin screw extruder and melt extruded. A polyester A layer containing particles having a refractive index of 1.5 or more in an amount of 0.0001% by mass or more, a composition containing 60 mol% or more of an ethylene glycol component as a diol component, and less than 40 mol% of another diol component; When the polyester B layer containing 60% by mole or more of the terephthalic acid component as the dicarboxylic acid component and less than 40% by mole of the other dicarboxylic acid component is laminated, the polyester A used for the polyester A layer and the polyester B layer are used. Polyester B is supplied to a separate bent type twin screw extruder and melt extruded. Hereinafter, a description will be given of a configuration in which a polyester A layer and a polyester B layer are laminated. At this time, it is preferable to control the resin temperature to 265 ° C. to 295 ° C. under an atmosphere of flowing nitrogen in the extruder, with an oxygen concentration of 0.7% by volume or less. Next, the foreign matter is removed and the amount of extrusion is leveled through a filter and a gear pump, the polyester A layer and the polyester B layer are merged, and then discharged from the T die onto a cooling drum in a sheet form. At that time, an electrostatic application method in which a cooling drum and the resin are brought into close contact with each other by static electricity using an electrode applied with a high voltage, a casting method in which a water film is provided between the casting drum and the extruded polymer sheet, The sheet-like polymer is brought into close contact with the casting drum, cooled and solidified by a method of sticking the extruded polymer at a glass transition point to (glass transition point−20 ° C.) or a combination of these methods, and unstretched. Get a film. Among these casting methods, when using polyester, a method of applying an electrostatic force is preferably used from the viewpoint of productivity and flatness.

  The optical polyester film of the present invention is preferably a biaxially oriented film from the viewpoints of heat resistance and dimensional stability. The biaxially oriented film is obtained by stretching an unstretched film in the longitudinal direction and then stretching in the width direction, or by stretching in the width direction and then stretching in the longitudinal direction, or by the longitudinal direction of the film. It can be obtained by stretching by a simultaneous biaxial stretching method in which the width direction is stretched almost simultaneously.

In such a stretching method, it is preferable to first pass through a roll heated to 30 ° C. or higher when shifting from the casting process to the longitudinal stretching process. Subsequently, the stretching ratio in the longitudinal direction is preferably 2.8 times to 3.5 times, more preferably 3 times to 3.3 times. The stretching speed is preferably 1,000% / min or more and 200,000% / min or less. The stretching temperature in the longitudinal direction is preferably 95 ° C. or higher and 110 ° C. or lower. Further, the stretching ratio in the width direction is preferably 2.8 times or more and 3.5 times or less, more preferably 3 times or more and 3.5 times or less, and it is preferable to match the stretching ratio in the longitudinal direction. The stretching speed in the width direction is desirably 1,000% / min or more and 200,000% / min or less. Further, as the stretching temperature in the width direction, it is preferable to increase the stretching temperature stepwise from the first stage to 95 ° C. or more and less than 115 ° C., and from the second stage to 115 ° C. or more and 150 ° C. or less.
The film is heat-treated after biaxial stretching. The heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. From the viewpoint of long-term reliability, the temperature of the first heat treatment temperature is set to the melting point of −80 ° C. to −30 ° C. of the polyester layer having the lowest melting point, and the temperature of the second heat setting is equal to or lower than the melting point of the polyester layer having the lowest melting point. It is preferable to set to. Also, if the polyester B layer has very low crystallinity and it is difficult to measure the melting point by ordinary differential scanning calorimetry, it is assumed that the temperature at which the melting point of the polyester becomes difficult to observe is around 200 ° C. Thus, the heat treatment temperature is preferably set to less than 200 ° C.
The heat treatment time can be arbitrarily set within a range not deteriorating the characteristics, and is preferably 5 seconds to 60 seconds, more preferably 10 seconds to 40 seconds, and most preferably 15 seconds to 30 seconds. Good.

Furthermore, in order to improve the adhesive force with a polarizer or a transparent conductive layer, at least one surface can be subjected to corona treatment or an easy adhesion layer can be coated. As a method of providing the coating layer in-line in the film manufacturing process, at least uniaxially stretched film with a coating layer composition dispersed in water is uniformly applied using a metalling ring bar or gravure roll. Then, a method of drying the coating while stretching is preferable, and in this case, the thickness of the easy adhesion layer is preferably 0.01 μm or more and 1 μm or less. Also, various additives such as antioxidants, heat stabilizers, ultraviolet absorbers, infrared absorbers, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc. may be added to the easy-adhesion layer. Good. The resin preferably used for the easy-adhesion layer is preferably at least one resin selected from an acrylic resin, a polyester resin, and a urethane resin from the viewpoint of adhesiveness and handleability. Furthermore, off-annealing at 90 to 200 ° C. is also preferably used.
In the optical polyester film of the present invention, a surface layer is laminated on the outermost surface in order to provide functions such as hard coat property, self-repairing property, antiglare property, antireflection property, low reflection property, and antistatic property. For this, it is preferable to use a production method in which the above-mentioned coating composition is formed by coating, drying and curing.

  The method for producing the surface layer by coating is not particularly limited, but the coating composition is supported by a dip coating method, a roller coating method, a wire bar coating method, a gravure coating method, a die coating method (US Pat. No. 2,681,294), or the like. It is preferable to form the surface layer by applying to a material or the like. Further, among these coating methods, the gravure coating method or the die coating method is more preferable as the coating method.

  Next, in order to completely remove the solvent by drying the applied liquid film, it is preferable that the liquid film is heated in the drying step. Examples of the drying method include heat transfer drying (adherence to a high-temperature object), convection heat transfer (hot air), radiant heat transfer (infrared ray), and others (microwave, induction heating). Among these, a method using convective heat transfer or radiant heat transfer is preferable because it is necessary to make the drying speed uniform even in the width direction.

  Furthermore, you may perform the further hardening operation (hardening process) by irradiating a heat | fever or an energy ray. In the curing step, when cured with heat, the temperature is preferably from room temperature to 200 ° C, more preferably from 100 ° C to 200 ° C from the viewpoint of the activation energy of the curing reaction, and from 130 ° C to 200 ° C. More preferably.

Moreover, when hardening with an active energy ray, it is preferable that it is an electron beam (EB ray) and / or an ultraviolet-ray (UV ray) from a versatility point. In the case of curing with ultraviolet rays, the oxygen concentration is preferably as low as possible because oxygen inhibition can be prevented, and curing in a nitrogen atmosphere (nitrogen purge) is more preferable. When the oxygen concentration is high, the hardening of the outermost surface is inhibited, and the surface hardening may be insufficient. Examples of the ultraviolet lamp used when irradiating ultraviolet rays include a discharge lamp method, a flash method, a laser method, and an electrodeless lamp method. Case of UV cured using a high pressure mercury lamp is a discharge lamp type, illuminance of ultraviolet rays 100~3,000mW / cm ^2, preferably 200~2,000mW / cm ^2, more preferably 300~1,500mW / cm ² conditions it is preferable to perform the UV irradiation, the integrated light quantity of ultraviolet 100~3,000mJ / cm ^2, which is a preferably 200~2,000mJ / cm ^2, more preferably 300~1,500mJ / cm ² under the condition that the More preferably, UV irradiation is performed.
Here, the illuminance of ultraviolet rays is the irradiation intensity received per unit area, and changes depending on the lamp output, the emission spectrum efficiency, the diameter of the light emission bulb, the design of the reflector, and the light source distance to the irradiated object. However, the illuminance does not change depending on the conveyance speed. Further, the UV integrated light amount is irradiation energy received per unit area, and is the total amount of photons reaching the surface. The integrated light quantity is inversely proportional to the irradiation speed passing under the light source, and is proportional to the number of irradiations and the number of lamps.
The optical polyester film of the present invention is preferably used as a polarizing plate by being bonded to a PVA sheet (polarizer) prepared by containing iodine in PVA and being oriented.

  The characteristic measuring method and the effect evaluating method in the present invention are as follows.

(1) Polyester composition The polyester resin and film were dissolved in hexafluoroisopropanol (HFIP), and the content of each monomer residue component and by-product diethylene glycol was quantified using ¹ H-NMR and ¹³ C-NMR. In the case of a laminated film, each layer of the film was scraped off in accordance with the laminated thickness to collect and evaluate the components constituting each single layer. In addition, about the film of this invention, the composition was computed by calculation from the mixing ratio at the time of film manufacture.

(2) Intrinsic viscosity of polyester The intrinsic viscosity of the polyester resin and the film was measured at 25 ° C. using an Ostwald viscometer after dissolving the polyester in orthochlorophenol. In the case of a laminated film, the intrinsic viscosity of each layer was evaluated by scraping each layer of the film according to the laminated thickness.

(3) Film thickness and layer thickness The film was embedded in an epoxy resin, and the film cross section was cut out with a microtome. The cross section was observed with a transmission electron microscope (TEM H7100, manufactured by Hitachi, Ltd.) at a magnification of 5000 times to determine the film thickness and the thickness of the polyester layer.

(4) Using a melting point differential scanning calorimeter (Seiko Denshi Kogyo Co., Ltd., RDC220), measurement and analysis were performed in accordance with JIS K7121-1987 and JIS K7122-1987. Using 5 mg of a polyester film as a sample, the temperature at the apex of the endothermic peak obtained from the DSC curve when the temperature was raised from 25 ° C. to 300 ° C. at 20 ° C./min was defined as the melting point. In the case of a laminated film, the melting point of each layer alone can be measured by scraping each layer of the film according to the laminated thickness. When the laminated structure was confirmed in the cross-sectional observation of (3), each layer was scraped off with a cutter and the melting point of each layer was measured. In addition, when melting | fusing point is not observed, it describes with ND.

(5) Particle concentration Dissolve 10 g of polyester film in 100 g of orthochlorophenol, and centrifuge the particles from polyester to contain particles in the film (for the particle concentration of each layer, scrape the corresponding layer). Can be evaluated. The particle concentration is determined from the following.
(Particle concentration) = (particle mass) / (total film mass) × 100
In addition, about the film of this invention, it computed by calculating from the particle concentration in the particle master produced by adding particle | grains at the time of superposition | polymerization, and the particle master concentration in a film.

(6) Using a refractive index sodium D line (wavelength 589 nm) of the film as a light source and using an Abbe refractometer, any one direction in the film plane is the direction X, the direction orthogonal to the direction X is the direction Y, and the film thickness direction Was Z, and the respective refractive indexes in the X, Y, and Z directions were measured. In addition, when two or more types of refractive index were observed with a laminated film or the like, the numerical value observed most clearly was adopted as the refractive index in the present invention. The average value of three measurements was taken as the refractive index in each direction.

(7) Refractive Index of Particles 100 g of film was dispersed by ashing with ethanol using a plasma low-temperature ashing device (device name: Plasma Asher, manufactured by J-Science Co., Ltd.) Vacuum-dried to obtain a measurement sample, and the refractive index is measured at room temperature by using the B method (Becke's line method) of the plastic measurement method indicated in JIS-K7142 (2008). It was. As the immersion liquid, bromonaphthalene and methylene iodide were used alone or in combination depending on the refractive index range, and “Optiphoto” (manufactured by Nikon) was used as the polarizing microscope.

(8) Based on film haze JIS K 7105 (1985), it was measured using a haze meter (HGM-2GP manufactured by Suga Test Instruments Co., Ltd.). In addition, about haze at the time of performing heat treatment for 12 hours at 100 ° C., a 100 mm × 100 mm square film sample is hung in a tree shape in a hot air oven at a temperature of 100 ° C. so as not to contact the upper, lower, left and right wall surfaces of the oven, After 12 hours of storage and heat treatment, the same measurement was performed. Each measurement was performed at arbitrary 10 locations, and the average value was adopted.

(9) Visibility evaluation A test piece was prepared by laminating a 10 cm square film on one surface of a polarizer having a polarization degree of 99.9% prepared by adsorbing and orienting iodine in PVA. In addition, the laminator roll set to 85 degreeC was used for bonding. From the angle of 50 ° with respect to the plane of the test piece when the prepared test piece and the polarizing plate not attached with the film are placed on the LED light source (Tritech A3-101) in a crossed Nicol arrangement. The visibility of was confirmed.
AA: Neither interference color nor white spots are observed.
AB: No interference color is observed and some white spots are observed, but there is no problem in practical use.
AC: No interference color is observed, but white spots are observed, which is not suitable for display applications.
BA: Some interference color is observed, but white spots are not observed, and there is no problem in practical use.
BB: Some interference colors are observed and white spots are also observed, but there is no problem in practical use.
BC: The interference color is slightly observed and white spots are observed, which is not suitable for display use.
CA: Since interference color is observed, white spots are not observed, but are not suitable for display applications.
CB: Since interference colors are observed, white spots are only slightly observed, but are not suitable for display applications.
CC: Both interference colors and white spots are observed, which is not suitable for display applications.
(10) A film sampled to a grade A4 size is visually observed by transmission under a three-wavelength fluorescent lamp, the number of scratches with a length of 0.1 mm or more is counted, and the number of scratches per A4 size is Evaluation was performed based on the criteria.
A: No scratches were counted.
B: The number of scratches was 1 or more and less than 2.
C: The number of scratches was 2 or more.
(11) About the test piece obtained by pencil hardness (9), evaluation by the scratch hardness (pencil method) as described in JIS K5600-5-4 (1999) was performed, and H or more was set as the pass.
(12) Steel wool scratch resistance test (steel wool resistance)
The test piece obtained in (9) was subjected to a rubbing test under the following conditions using a rubbing tester to obtain an index of scratch resistance.

Evaluation environmental conditions: 25 ° C., 60% RH
Rubbing material: Steel wool (manufactured by Nippon Steel Wool Co., Ltd., Grade No. 0000)
Wrap around the tip (1cm x 1cm) of the scraper of the tester that comes into contact with the sample and fix the band.

Travel distance (one way): 13cm
Rubbing speed: 13 cm / second,
Load: 500 g / cm ²
Tip contact area: 1 cm × 1 cm, rubbing frequency: 10 reciprocations.

  An oil-based black ink was applied to the back side of the rubbed sample, and scratches on the rubbed portion were visually observed with reflected light, and evaluated according to the following criteria. For the evaluation, the above test was repeated three times, and the average was evaluated in five stages.

    A: No scratches are visible.

    B: Slight scratches are visible.

    C: There is a scratch that can be seen at first glance.

(Manufacture of polyester)
The polyester resin used for film formation was prepared as follows.

(Polyester A)
Polyethylene terephthalate resin (intrinsic viscosity 0.65) in which the terephthalic acid component is 100 mol% as the dicarboxylic acid component and the ethylene glycol component is 100 mol% as the glycol component.

(Polyester B)
An isophthalic acid copolymerized polyethylene terephthalate resin (inherent viscosity 0.7) having 85 mol% of terephthalic acid component as dicarboxylic acid component, 15 mol% of isophthalic acid component, and 100 mol% of ethylene glycol component as glycol component.
(Polyester C)
An isophthalic acid copolymerized polyethylene terephthalate resin (inherent viscosity 0.7) having a terephthalic acid component of 80 mol% as a dicarboxylic acid component, an isophthalic acid component of 20 mol%, and an ethylene glycol component as a glycol component of 100 mol%.
(Polyester D)
An isophthalic acid copolymerized polyethylene terephthalate resin (inherent viscosity 0.7) having 75 mol% of terephthalic acid component as dicarboxylic acid component, 25 mol% of isophthalic acid component, and 100 mol% of ethylene glycol component as glycol component.
(Polyester E)
2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate resin in which 85% by mole of terephthalic acid component as dicarboxylic acid component, 15% by mole of 2,6-naphthalenedicarboxylic acid component, and 100% by mole of ethylene glycol component as glycol component ( Intrinsic viscosity 0.7).
(Polyester F)
2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate resin in which 85% by mole of terephthalic acid component as dicarboxylic acid component, 15% by mole of 2,6-naphthalenedicarboxylic acid component, and 100% by mole of ethylene glycol component as glycol component ( Intrinsic viscosity 0.7).
(Polyester G)
2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate resin in which terephthalic acid component is 80 mol% as dicarboxylic acid component, 2,6-naphthalenedicarboxylic acid component is 20 mol%, and ethylene glycol component is 100 mol% as glycol component ( Intrinsic viscosity 0.7).

(Particle Master H)
Polyethylene terephthalate particle master (intrinsic viscosity 0.65) containing polyester carbonate A with calcium carbonate particles (refractive index: 1.58) having a number average particle diameter of 1.2 μm at a particle concentration of 2 mass%.
(Particle Master I)
Polyethylene terephthalate particle master (intrinsic viscosity 0.65) containing polyester A with aluminum silicate particles (refractive index: 1.65) having a number average particle diameter of 1.0 μm at a particle concentration of 2 mass%.
(Particle Master J)
Polyethylene terephthalate particle master (intrinsic viscosity 0.65) containing polyester A with barium sulfate particles (refractive index: 1.64) having a number average particle diameter of 0.8 μm at a particle concentration of 2 mass%.
(Particle Master K)
Polyethylene terephthalate particle master (intrinsic viscosity 0.65) containing polyester A with crosslinked polystyrene particles having a number average particle diameter of 0.6 μm (refractive index: 1.6) at a particle concentration of 2 mass%.
(Particle Master L)
Polyethylene terephthalate particle master (inherent viscosity 0.65) containing polyester oxide A with aluminum oxide particles (1.76) having a number average particle diameter of 0.2 μm at a particle concentration of 2 mass%.
(Particle Master M)
Polyethylene terephthalate particle master (intrinsic viscosity 0.65) containing polyester A with agglomerated silica particles (1.47) having a number average particle diameter of 1.2 μm at a particle concentration of 2 mass%.
(Coating composition for forming hard coat layer)
The following materials were mixed and diluted with methyl ethyl ketone to obtain a coating composition for forming a hard coat layer having a solid concentration of 40% by mass.
Toluene 30 parts by mass Polyfunctional urethane acrylate 25 parts by mass (KRM 8655 manufactured by Daicel Ornex Co., Ltd.)
25 parts by mass of pentaerythritol triacrylate mixture (PET30 manufactured by Nippon Kayaku Co., Ltd.)
1 part by mass of polyfunctional silicone acrylate (EBECRYL1360, manufactured by Daicel Ornex Co., Ltd.)
3 parts by mass of photopolymerization initiator (Irgacure 184, manufactured by Ciba Specialty Chemicals)
(Anti-glare layer forming coating composition)
The following materials were mixed and diluted with methyl ethyl ketone to obtain a coating composition for forming an antiglare layer having a solid content of 40% by mass.
Toluene 30 parts by mass Pentaerythritol triacrylate 50 parts by mass
(Nippon Kayaku Co., Ltd. PET30)
Silica dispersion (number average particle size 1 μm) 12 parts by mass
1 part by mass of polyfunctional silicone acrylate (EBECRYL1360, manufactured by Daicel Ornex Co., Ltd.)
3 parts by mass of a photopolymerization initiator (Irgacure 184 manufactured by Ciba Specialty Chemicals).

(Example 1)
The composition is as shown in the table, and the raw materials are supplied to separate bent co-directional twin-screw extruders each having an oxygen concentration of 0.2% by volume, the A-layer extruder cylinder temperature is 280 ° C., and the B-layer extruder cylinder temperature is Melt at 270 ° C. and merge into a three-layer structure of A layer / B layer / A layer in the feed block, the short tube temperature after merging is 275 ° C., the die temperature is 280 ° C., 25 ° C. from the T-die The sheet was discharged on a cooling drum controlled in temperature. At that time, a non-stretched sheet was obtained by applying static electricity using a wire electrode having a diameter of 0.1 mm and closely contacting a casting drum cooled to 20 ° C. Subsequently, the film was stretched 3.3 times in the longitudinal direction at a stretching temperature of 100 ° C., and immediately cooled with a metal roll whose temperature was controlled at 40 ° C. Next, the first-stage stretching temperature is 100 ° C., the second-stage stretching temperature is 140 ° C., and the film is stretched 3.3 times in the width direction in the tenter-type stretching machine. Heat treatment was performed at an eye heat treatment temperature of 215 ° C. to obtain a biaxially oriented polyester film having a film thickness of 20 μm. Note that the heat treatment was performed while relaxing 5% in the width direction under the second-stage heat treatment conditions.

(Example 2)
After obtaining an unstretched sheet, the process proceeds to a stretching process in the longitudinal direction through a roll heated to 40 ° C, and the heat treatment temperature after stretching in the width direction is set to 220 ° C for the first stage and 225 ° C for the second stage. Except for the above, a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 1.

(Example 3)
The composition was changed as shown in the table, and a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 2 except that the heat treatment temperature after stretching in the width direction was changed to 170 ° C. for the first stage and 200 ° C. for the second stage. .

Example 4
The composition was changed as shown in the table, and a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 2 except that the heat treatment temperature after stretching in the width direction was changed to the first stage 170 ° C. and the second stage 190 ° C. .

(Example 5)
The composition was changed as shown in the table, and a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 1 except that the heat treatment temperature after stretching in the width direction was 205 ° C. for the first stage and 215 ° C. for the second stage. .

(Example 6)
The composition was changed as shown in the table, and a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 2 except that the heat treatment temperature after stretching in the width direction was changed to the first stage 200 ° C. and the second stage 205 ° C. .

(Example 7)
The composition was changed as shown in the table, the stretching temperature in the longitudinal direction was 110 ° C., the stretching temperature in the width direction was 110 ° C. in the first stage, the second stage was 150 ° C., and the heat treatment temperature after stretching in the width direction was 180 ° C. in the first stage. A biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 2 except that the second stage was 200 ° C.

(Example 8)
The composition was changed as shown in the table, and a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 2 except that the heat treatment temperature after stretching in the width direction was changed to 170 ° C. for the first stage and 200 ° C. for the second stage. .

Example 9
The composition was changed as shown in the table, and a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 1 except that the heat treatment temperature after stretching in the width direction was 205 ° C. for the first stage and 215 ° C. for the second stage. .

(Example 10)
The composition was changed as shown in the table, and a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 2 except that the heat treatment temperature after stretching in the width direction was changed to the first stage 170 ° C. and the second stage 190 ° C. .

(Example 3-2)
The biaxially oriented polyester film obtained in Example 3 was coated with the above-mentioned coating liquid for forming a hard coat layer using a slot die coater while controlling the flow rate so that the thickness after drying was 5 μm. Dry at 1 ° C. for 1 minute to remove the solvent. Next, the film coated with the hard coat layer was irradiated with 300 mJ / cm ² ultraviolet rays using a high-pressure mercury lamp to obtain an optical polyester film on which the hard coat layer was laminated.

(Example 3-3)
On the biaxially oriented polyester film obtained in Example 3, the above-mentioned coating solution for forming an antiglare layer was applied using a slot die coater and dried at 100 ° C. for 1 minute to remove the solvent. Next, the film coated with the antiglare layer was irradiated with 300 mJ / cm ² of ultraviolet light using a high pressure mercury lamp to obtain an optical polyester film on which an antiglare hard coat layer having a thickness of 5 μm was laminated.

(Comparative Example 1)
A biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 1 except that the composition was changed as shown in the table. Since neither the polyester A layer nor the polyester B layer contains a particle master, a film containing substantially no particles was obtained.

(Comparative Example 2)
A biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 3 except that the composition was changed as shown in the table. Since the polyester A layer contained 0.75% by mass of the particle master M, the entire polyester A was 100% by mass, and the polyester A layer contained only 0.015% by mass of aggregated silica particles.

(Comparative Example 3)
The composition was changed to a single film structure as shown in the table, the drawing temperature was 90 ° C. and the draw ratio was 3.4 times in the longitudinal direction, and immediately cooled with a metal roll whose temperature was controlled at 40 ° C. Next, the first-stage stretching temperature is 90 ° C., the second-stage stretching temperature is 90 ° C., and the film is stretched 4 times in the width direction, and the first-stage heat treatment temperature is 220 ° C. in the tenter. Heat treatment was performed at a temperature of 230 ° C. to obtain a biaxially oriented polyester film having a film thickness of 20 μm. Note that the heat treatment was performed while relaxing 5% in the width direction under the second-stage heat treatment conditions. Since the polyester A layer contained 0.75% by mass of the particle master M, the entire polyester A was 100% by mass, and the polyester A layer contained only 0.015% by mass of aggregated silica particles.

(Comparative Example 4)
A biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Comparative Example 3 except that the composition was changed as shown in the table. Since the polyester A layer contained 0.75% by mass of particle master I, the entire polyester A was 100% by mass, and the polyester A layer contained 0.015% by mass of aluminum silicate particles.
(Example 3-4, Comparative example 3-2)
On the biaxially oriented polyester film obtained in Example 3 and Comparative Example 3, an ITO film was formed as a transparent conductive layer with a thickness of 30 nm by sputtering in a 150 ° C. atmosphere to produce a transparent conductive film. Then, when the visibility was confirmed based on the same evaluation criteria as in (8) the visibility test, the transparent conductive film of Example 3-4 was evaluated by AA, whereas the transparent conductivity of Comparative Example 3-2 was used. Film was evaluated as CC.

The notation in the table is as follows.
EG: ethylene glycol, TPA: terephthalic acid, IPA: isophthalic acid, NDC: 2,6-naphthalenedicarboxylic acid

The present invention relates to a polyester film that is particularly suitable for use in optical applications (polarizer protection, transparent conductive film, etc.). When mounted on a display device such as a liquid crystal display, the interference color when viewed from an oblique direction. Since it can suppress white spots and is excellent in appearance, it is preferably used as a polarizing plate by being bonded to a PVA sheet (polarizer) prepared by containing iodine in PVA and being oriented.

Claims (8)

A biaxially oriented polyester film having a polyester A layer containing 10001% by mass of the entire polyester A layer and 0.0001% by mass or more of particles having a refractive index of 1.5 or more,
An optical whose average refractive index in the X, Y, and Z directions is 1.6 or less, where X is an arbitrary direction in the film plane, Y is a direction perpendicular to the direction X, and Z is a film thickness direction. Polyester film. The optical polyester film according to claim 1, wherein an average value of refractive indexes in the X direction and the Y direction is 1.6 or less. The optical polyester film according to claim 1 or 2, wherein the film haze is 3% or less. The optical polyester film according to any one of claims 1 to 3, wherein a film haze when heat-treated at 100 ° C for 12 hours is 5% or less. At least one selected from the group consisting of hard coat properties, self-repairing properties, antiglare properties, antireflection properties, low reflectivity properties, and antistatic properties is provided on at least one outermost surface of the polyester film for protecting the polarizer. The optical polyester film according to any one of claims 1 to 4, wherein a layer exhibiting a function is laminated. The optical polyester film according to claim 1, which is used for protecting a polarizer. It is a polarizing plate which has a polarizer protective film on both surfaces of a polarizer, Comprising: The polarizer protective film used for at least one surface is the optical polyester film in any one of Claims 1-5. Polarizer. The transparent conductive film which has a polyester film in any one of Claims 1-5.