JP2017067819A - 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 including a liquid crystal display, an interference color in visual observation of a display, and is excellent in mechanical characteristics, such as tensile strength and tensile elongation.SOLUTION: There is provided an optical polyester film comprising a polyester A layer including a dicarboxylic acid component and a diol component, wherein when the total amount of the dicarboxylic acid component and the diol component in the polyester A layer is 100 mol%, the total of a component with the largest amount in the dicarboxylic acid and a component with the largest amount in the diol component is more than 85 mol% and less than 98 mol%; the optical polyester film has an in-plane phase difference of 3000 nm or more and 30000 nm or less, and a density of 1.35 g/cmor more and 1.41 g/cmor less.SELECTED DRAWING: None

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 recent years, in particular, in the flat panel display and touch panel fields, demand for various optical films such as a polarizer protective film and a transparent conductive film has increased. Among them, for polarizer protective film applications, cost reduction and moisture absorption resistance have been achieved. For the purpose, replacement of a conventional TAC (triacetyl cellulose) film with a biaxially oriented polyester film has been studied. A biaxially oriented polyester film has an interference color when assembled as a liquid crystal display due to the orientation of the polymer during stretching. Studies using an oriented polyester film having a phase difference (for example, Patent Documents 1, 2, and 3) have been conducted. However, in both Patent Documents 1, 2, and 3, by strongly stretching the polyester film in one direction, the in-plane retardation is set to a high specific range and interference colors are suppressed, but the polyester film is strongly stretched in one direction. Therefore, since the mechanical strength in the direction orthogonal to the stretching direction is low, the transportability is insufficient, and it is difficult to suppress interference spots and mechanical properties.

International Publication No. 2013/080948 JP 2010-277028 A JP 2011-53271 A

  Therefore, in the present invention, when the above-mentioned drawbacks are eliminated, and when mounted on a display device such as a liquid crystal display, the interference color when visually observing the display can be suppressed, and the polyester has excellent mechanical properties such as tensile strength and tensile elongation. The object is to provide a film.

The present invention for solving the above problems has the following configuration.
(1) It has a polyester A layer composed of a dicarboxylic acid component and a diol component, and when the total amount of the dicarboxylic acid component and the diol component in the polyester A layer is 100 mol%, The total of the most diol components exceeds 85 mol% and less than 98 mol%, the in-plane retardation is 3000 nm or more and 30000 nm or less, and the density is 1.35 g / cm ³ or more and 1.41 g / cm ^3. The following is an optical polyester film.
(2) The polyester A layer comprises a dicarboxylic acid component and a diol component, the most dicarboxylic acid component is terephthalic acid or 2,6-naphthalenedicarboxylic acid, and the most diol component is ethylene glycol. The optical polyester film described in 1.
(3) The optical polyester film according to (1) or (2), wherein the refractive index (nx) in the fast axis direction is 1.59 or more.
(4) A polyester B layer having a melting point of Tb (° C.) is laminated on at least one surface of a polyester A layer having a melting point of Ta (° C.), and Tb> Ta, (1) to (3) The optical polyester film according to any one of the above.
(5) The optical polyester film according to any one of (1) to (4), which is for protecting a polarizer.
(6) A polarizing plate having a polarizer protective film on both sides of the polarizer, wherein at least one of the polarizer protective films is the optical polyester film according to claim 5.
(7) A transparent conductive film having the polyester film according to any one of (1) to (6).

  The optical polyester film of the present invention does not exhibit interference color when mounted on a display device such as a liquid crystal display, and is compatible with mechanical properties. When used for a conductive film and a touch panel using the same, an effect of enabling high-quality display is obtained.

  Hereinafter, the optical polyester film of the present invention will be described in detail.

The in-plane retardation of the optical polyester film of the present invention is required to be 3000 nm or more and 30000 nm or less. By setting the in-plane retardation to 3000 nm or more and 30000 nm or less, it is possible to achieve both suppression of interference colors and handling properties when mounted on a display device. If the in-plane retardation is less than 3000 nm, the effect of suppressing interference spots is insufficient, and if the in-plane retardation is attempted to be larger than 30000 nm, the film thickness becomes considerably thick and the handling property as an industrial material is lowered. End up. The in-plane retardation is more preferably 5000 nm or more and 25000 nm or less, and most preferably 6000 nm or more and 20000 nm.
Here, the in-plane retardation refers to a product of the thickness and the birefringence (refractive index difference in the in-plane biaxial direction) by using an Abbe refractometer, the refractive index of any one direction of the film (n _a ), The refractive index (n _b ) in the direction orthogonal to the direction can be measured and calculated from the following formula.
In-plane retardation = | n _a −n _b | × film thickness (nm) (I)
It is also possible to measure using a phase difference measuring device such as “KOBRA” series manufactured by Oji Scientific Instruments. The in-plane retardation of the present invention was calculated from the above formula (I).
In the present invention, the in-plane retardation can be set to 3000 nm or more and 30000 nm or less depending on a birefringence control by adjusting a stretching method, a stretching ratio, stretching and heat treatment during film formation, and a thickness setting.
The optical polyester film of the present invention is preferably 10 μm or more and 500 μm or less, more preferably 20 μm or more and 300 μm or less, and most preferably 40 μm or more and 200 μm or less from the viewpoints of in-plane retardation control and handleability.
The optical polyester film of the present invention has a polyester A layer composed of a dicarboxylic acid component and a diol component, and when the total amount of the dicarboxylic acid component and the diol component in the polyester A layer is 100 mol%, the dicarboxylic acid component The sum of the most abundant component and the most abundant component of the diol components needs to be more than 85 mol% and less than 98 mol%. The present inventors contain a specific amount of a dicarboxylic acid component and / or a diol component of 2 mol% or more and 15 mol% or less in addition to the component having the largest amount of dicarboxylic acid component and the component having the largest amount of diol component. It has been found that by being biaxially stretched, when mounted on a display device such as a liquid crystal display, the interference color when viewing the display can be suppressed and the polyester film has excellent mechanical properties. By having the polyester A layer as described above, the in-plane birefringence during stretching can be increased while the progress of the plane orientation can be suppressed, that is, the refractive index in the thickness direction can be kept high. In addition, it is considered that interference colors when viewed from an oblique direction can be suppressed. For this reason, it is possible to improve mechanical properties as compared with a uniaxially stretched polyester film that is generally used as a method for suppressing in-plane birefringence and suppressing surface orientation, and achieves both high interference color suppression and mechanical properties. It becomes possible. From the viewpoint of coexistence of interference color suppression and mechanical properties, the polyester A layer has the largest amount of the dicarboxylic acid component and the largest amount of the diol component when the total amount of the dicarboxylic acid component and the diol component is 100 mol%. More preferably, the total of the components exceeds 90 mol% and less than 97 mol%, and more preferably exceeds 92 mol% and less than 96 mol%.
In the optical polyester film of the present invention, from the viewpoint of interference color suppression and mechanical properties, the polyester A layer is composed of a dicarboxylic acid component and a diol component, and the most dicarboxylic acid component is terephthalic acid or 2,6-naphthalenedicarboxylic acid. It is preferable that the most diol component is ethylene glycol. By setting the polyester A layer to the above composition, it is possible to further enhance the interference color suppressing effect and mechanical properties.
Examples of the diol component other than ethylene glycol in the polyester A layer of the present invention include 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, Examples thereof include 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.
Among these, 1,4-cyclohexanedimethanol, neopentyl glycol, isosorbate, and spiro glycol are preferable from the viewpoint of interference color suppression and mechanical properties.
Examples of dicarboxylic acid components other than terephthalic acid and 2,6-naphthalenedicarboxylic acid components include, for example, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 4,4′- Aromatic dicarboxylic acids such as diphenyldicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 4,4′-diphenylsulfone dicarboxylic acid, adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid, etc. Examples thereof include aliphatic dicarboxylic acids, various aromatic dicarboxylic acids, and ester derivatives with aliphatic dicarboxylic acids. These diol components may be used alone or in combination of two or more in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid. Isophthalic acid is preferable from the viewpoint of interference color suppression and mechanical properties.
The optical polyester film of the present invention needs to have a density of 1.35 g / cm ³ or more and 1.41 g / cm ³ or less. If the density is 1.35 g / cm ³ or more and 1.41 g / cm ³ or less, the crystals are appropriately oriented and crystallized, while suppressing interference colors when viewed from an oblique direction due to excessive progress of plane orientation, Sufficient mechanical properties can be secured. In order to make the mechanical properties compatible while suppressing interference color when viewed from an oblique direction, the density is more preferably 1.36 g / cm ³ or more and 1.41 g / cm ³ or less, and 1.37 g / cm 3. the most preferred if ³ or more 1.4 g / cm ³ or less.
The optical polyester film of the present invention preferably has a refractive index (nx) in the fast axis direction of 1.59 or more. By setting the refractive index (nx) in the fast axis direction to 1.59 or more, the orientation sufficiently proceeds in the fast axis direction, so that the mechanical characteristics can be improved. The refractive index (nx) in the fast axis direction is more preferably 1.595 or more, and most preferably 1.6 or more. Here, the fast axis direction is the direction in which the in-plane refractive index of the film is minimized, and in the present invention, the direction perpendicular to the main orientation axis is defined as the fast axis direction.
In addition, the optical polyester film of the present invention preferably has a refractive index (nZ) in the thickness direction of 1.49 or more and 1.495 or more from the viewpoint of suppressing the interference color when viewed from an oblique direction. More preferably, it is more preferably 1.5 or more.
In the optical polyester film of the present invention, the polyester A layer has a melting point of Ta (° C.) and a polyester B layer having a melting point of Tb (° C.) is laminated on at least one surface of the polyester A layer in order to further improve mechanical properties. It is preferable that Tb> Ta. When the polyester film of the present invention has a configuration in which the polyester B layer is laminated on at least one side of the polyester A layer, the number of layers and the layer configuration are not particularly limited, but curling of the film is suppressed, warpage is reduced, and handling properties are reduced. From the viewpoint, the film is symmetrical with respect to the thickness direction such as B layer / A layer / B layer, B layer / A layer / B layer / A layer / B layer, and both surface layers are polyester B layers. The structure which is is preferable.
When the optical polyester film of the present invention has a structure in which a polyester B layer having a melting point of Tb (° C.) is laminated on at least one surface of a polyester A layer having a melting point of Ta (° C.), It consists of an acid component and a diol component, and when the total amount of the dicarboxylic acid component and the diol component is 100 mol%, the sum of the most dicarboxylic acid component and the most diol component exceeds 86 mol%. It is preferable. From the viewpoint of mechanical properties, the polyester B layer has a total of 90 mol of the most dicarboxylic acid component and the most diol component when the total amount of the dicarboxylic acid component and the diol component is 100 mol%. % Is more preferable, when it exceeds 95 mol%, it is further preferable, and when it exceeds 99 mol%, it is most preferable.
In addition, the polyester B layer is composed of a dicarboxylic acid component and a diol component from the viewpoint of the lamination properties and mechanical properties of the polyester A layer, and the most dicarboxylic acid component is terephthalic acid or 2,6-naphthalenedicarboxylic acid, the most The diol component is preferably ethylene glycol.
As the diol component other than ethylene glycol in the polyester B layer of the present invention, components preferably used in the above-described polyester A layer can be used. Similarly, when the polyester B layer contains a dicarboxylic acid component other than terephthalic acid and a 2,6-naphthalenedicarboxylic acid component, the components preferably used for the polyester A layer described above can be used.
In addition, the optical polyester film of the present invention has a hard coat property, self-healing property, antiglare property, and antireflection property on at least one outermost surface in order to provide process stabilization in the production process and durability in the use environment. 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 ultraviolet blocking property is a function of improving light resistance by selectively blocking the wavelength in the ultraviolet region (wavelength 200 to 400 nm). There is no problem in either the method of reflecting the ultraviolet ray or the method of absorbing the ultraviolet ray as a method for expressing the ultraviolet blocking property, and as its function, the transmittance at a wavelength of 380 nm is preferably 30% or less, more preferably 25. % Or less, particularly preferably 0.1% or more and 20% or less.
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 particle size 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 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, JP-A-2011-81217, JP-A-2010. -204479, Unexamined-Japanese-Patent No. 2010-181898, Unexamined-Japanese-Patent No. 2011-1973329, Unexamined-Japanese-Patent No. 2011-197330, Unexamined-Japanese-Patent No. 2011-215393 etc. can also be used conveniently.
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 polyester film of the present invention, when mounted on a display device such as a liquid crystal display, can suppress interference colors when viewing the display and is excellent in mechanical properties, and therefore is preferably used for polarizer protection. it can.
In the polarizing plate of the present invention, the optical polyester film is preferably used as a polarizer protective film on at least one surface. 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 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 is preferably bonded 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 optical polyester film of the present invention can be preferably used as a transparent conductive film substrate because it can suppress interference color when viewing the display and is excellent in mechanical properties when mounted on a display device such as a liquid crystal display. be able to. 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. When the polyester A layer having a melting point of Ta (° C.) and the polyester B layer having a melting point of Tb (° C.) are laminated, the polyester A used for the polyester A layer and the polyester B used for the polyester B layer are separately provided. Supply to a vent type twin screw extruder and melt extrude. At this time, it is preferable that Tb> Ta. Further, in the polyester A layer, when the total amount of the dicarboxylic acid component and the diol component is 100 mol%, the total of the most dicarboxylic acid component and the most diol component exceeds 85 mol%. It is less than 98 mol%. The polyester B layer is composed of a dicarboxylic acid component and a diol component, and when the total amount of the dicarboxylic acid component and the diol component is 100 mol%, the most component among the dicarboxylic acid components and the most component among the diol components. It is preferable that the total of exceeds 86 mol%.
In the extruder, it is preferable that the oxygen concentration is 0.7% by volume or less and the resin temperature is controlled at 250 ° C. to 285 ° C. in a flowing nitrogen atmosphere. 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, and the casting drum temperature is set to be equal to that of the polyester resin. 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.
As the stretching ratio in such a stretching method, in order to achieve an in-plane retardation of 3000 nm or more and 30000 nm or less, a sequential biaxial stretching method of stretching in the longitudinal direction and then stretching in the width direction is adopted in order to improve the stable film forming property. It is preferable to increase the draw ratio in the width direction more than the draw ratio in the longitudinal direction. The stretching ratio in the longitudinal direction is preferably 1.1 times or more and 3.5 times or less. The stretching ratio in the longitudinal direction is more preferably 1.2 times or more and 3 times or less, and most preferably 1.3 times or more and 2.5 times or less. Moreover, it is preferable that extending | stretching temperature is 80-120 degreeC. The stretching speed is desirably 1,000% / min or more and 200,000% / min or less.
In the present invention, as described above, it is preferable to increase the stretching ratio in the width direction over the stretching ratio in the longitudinal direction, so that the refractive index (nx) in the fast axis direction is 1.59 or more in the longitudinal direction. The draw ratio is more preferably 1.5 times or more, and most preferably 1.8 times or more.
In the optical polyester film of the present invention, when the total amount of the dicarboxylic acid component and the diol component is 100 mol%, the total of the most dicarboxylic acid component and the most diol component is 85 mol%. Since it has a polyester A layer exceeding 98 mol%, the in-plane retardation is less likely to be higher than that of ordinary polyethylene terephthalate, so the in-plane retardation is more preferably in the range of 5000 nm to 25000 nm. In order to achieve this, it is preferable that the stretching pattern in the width direction is stretched at a high magnification in the first half of the stretching, and the second half of the stretching is a special stretching that lowers the magnification. For example, if the stretching ratio in the width direction is X times and the stretching section is L (m), the stretching is usually 0.5 × X times from the start of stretching to 0.5 L (m). A method of stretching 0.6 × X times to 0.8 × X times is preferably used. Moreover, it is preferable that extending | stretching temperature is 80-160 degreeC. The stretching speed is desirably 1,000% / min or more and 200,000% / min or less.
Furthermore, 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. If the heat treatment temperature is low, the dimensional stability is lowered. Conversely, if the heat treatment temperature is too high, orientation crystallization proceeds, and if it is further increased, crystal melting starts. Therefore, the heat treatment temperature is Ta-60 ° C. or higher. It is preferable to set it at 20 ° C. or lower. Moreover, in order to make the density of the optical polyester film of the present invention 1.35 g / cm ³ or more and 1.41 g / cm ³ or less, the heat treatment temperature is preferably Ta-40 ° C. or more and Ta-30 ° C. or less. Moreover, a more preferable range density, 1.37 g / cm ³ or more 1.4 g / cm ³ the heat treatment time in order to control below is not less than 10 seconds 40 seconds or less, cooling the clip temperature of the tenter in the heat treatment section The temperature is preferably controlled to 50 ° C. or higher and 150 ° C. or lower, more preferably 50 ° C. or higher and 120 ° C. or lower, and most preferably 50 ° C. or higher and 100 ° C. or lower.

  Furthermore, in order to improve the adhesive force with the polarizer and various functional layers, 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 provided on the outermost surface in order to impart functions such as hard coat properties, self-repair properties, antiglare properties, antireflection properties, low reflection properties, ultraviolet ray blocking properties, and antistatic properties In the case of laminating, 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 or a die coating method (US Pat. No. 2,681,294). 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 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) A sample is cut out with a size of 100 mm × 100 mm at an arbitrary point of the refractive index and in-plane retardation film, and a microwave molecular orientation meter MOA-2001A (frequency 4 GHz) manufactured by KS Systems (current Oji Scientific Instruments) is used. The in-plane main orientation axis of the polyester film was determined and defined as the Y direction, and the direction orthogonal to the Y direction was defined as the X direction. In the present invention, the X direction is the fast axis. Then, using a sodium D line (wavelength 589 nm) as a light source, using methylene iodide as a mounting liquid, and using an Abbe refractometer at 25 ° C., the refractive indices in the X direction, Y direction, and Z direction (thickness direction) (each nx, ny, nz), and the in-plane retardation was calculated from the following formula (I).
In-plane retardation = | nx−ny | × film thickness (nm) (I)
(5) Using a melting point differential scanning calorimeter (Seiko Denshi Kogyo Co., Ltd., RDC220), measurement and analysis were performed in accordance with JIS K-7121-1987 and JIS K-7122-1987. The polyester film was measured using 5 mg of a film sample, and the melting point was the temperature at the top of the endothermic peak obtained from the DSC curve when the temperature was raised from 25 ° C. to 300 ° C. at 20 ° C./min. In the case of a laminated film, the melting point of each layer was 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, and the higher melting point layer was designated as the polyester A layer, and the lower layer was designated as the polyester B layer. When the melting point is not observed, “ND” is indicated in the table. In the present invention, when a plurality of endothermic peaks are observed, the melting point is the temperature at which the absolute value of the heat flow is the largest.

(6) The density film was cut into a square having a side of 5 mm, and the density (g / cm 3) was measured with a density gradient tube using an aqueous sodium bromide solution. In addition, each measurement was performed 3 times and the average value was adopted.
(7) Visibility evaluation (i)
A 30 cm square film was bonded to one surface of a polarizer having a polarization degree of 99.9% prepared by adsorbing and orienting iodine in PVA to obtain a test piece. In addition, the laminator roll set to 85 degreeC was used for bonding. Visibility from the front with respect to the test piece when the prepared test piece and the polarizing plate not attached with a film are placed on an LED light source (Tritech A3-101) in a crossed Nicol arrangement. confirmed.
A: No interference color is observed.
B: A slight interference color is observed, but is acceptable.
C: The interference color is clearly observed.
A and B are acceptable levels.

(8) Visibility evaluation (ii)
In the same manner as (7), the visibility from a 50 ° angle with respect to the test piece was confirmed.
A: No interference color is observed.
B: A slight interference color is observed, but is acceptable.
C: The interference color is clearly observed.
A and B are acceptable levels.
(9) The sample was cut into a rectangle of 150 mm × 10 mm (direction X × direction Y) as the Y direction which is the main orientation axis direction of the mechanical property film and the X direction which is a direction orthogonal to the Y direction. Using a tensile tester (Orientec Tensilon UCT-100), the initial tensile chuck distance is set to 50 mm (L0), the tensile speed is set to 300 mm / minute, the tensile test is performed, and the chuck distance when the sample breaks ( L). With respect to the value obtained by the calculation formula of (L−L0) / L0 × 100, the average value of 10 measurements was defined as the elongation at break in direction X.
A: The breaking elongation in the X direction is 30% or more.
B: The breaking elongation in the X direction is 15% or more and less than 30%.
C: The breaking elongation in the X direction is less than 15%.
A and B are acceptable levels.
(10) Scratch resistance The test piece obtained in (7) 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 (Nippon Steel Wool Co., Ltd., gelled 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: A flaw is not visually recognized.
B: A flaw is visually recognized.

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

(Polyester A)
A polyethylene terephthalate resin (inherent viscosity 0.65) in which the total amount of the dicarboxylic acid component and the diol component is 100 mol%, the terephthalic acid component is 50 mol% as the dicarboxylic acid component, and the ethylene glycol component is 50 mol% as the glycol component.

(Polyester B)
Isophthalic acid copolymer polyethylene terephthalate resin in which the total amount of dicarboxylic acid component and diol component is 100 mol%, terephthalic acid component is 44 mol%, isophthalic acid component is 6 mol%, and ethylene glycol component is 50 mol% as glycol component (Intrinsic viscosity 0.7).

(Polyester C)
The total amount of the dicarboxylic acid component and the diol component is 100 mol%, the terephthalic acid component is 45 mol%, the 2,6-naphthalenedicarboxylic acid component is 5 mol%, and the ethylene glycol component is 50 mol% as the glycol component. 6-Naphthalenedicarboxylic acid copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.72).
(Polyester D)
The total amount of the dicarboxylic acid component and the diol component is 100 mol%, the terephthalic acid component is 50 mol%, the glycol component is 46 mol% ethylene glycol component, and 1,4-cyclohexanedimethanol is 1,4 mol% -Cyclohexanedimethanol copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.8).
(Polyester E)
Spiroglycol copolymer polyethylene terephthalate resin in which the total amount of dicarboxylic acid component and diol component is 100 mol%, terephthalic acid component is 50 mol%, ethylene glycol component is 47 mol% as glycol component, and spiroglycol is 3 mol% ( Intrinsic viscosity 0.75).
(Polyester F)
Neopentyl glycol copolymer polyethylene terephthalate in which the total amount of dicarboxylic acid component and diol component is 100 mol%, terephthalic acid component is 50 mol%, ethylene glycol component is 40 mol% as glycol component, and neopentylglycol is 10 mol% Resin (intrinsic viscosity 0.73).

(Particle master)
Polyethylene terephthalate particle master (intrinsic viscosity 0.65) containing agglomerated silica particles having a number average particle size of 2.2 μm in polyester A 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 photopolymerization initiator (Irgacure 184, manufactured by Ciba Specialty Chemicals)
Example 1
The composition is as shown in the table, and the raw materials are respectively supplied to a vented co-axial twin screw extruder having an oxygen concentration of 0.2% by volume. The cylinder temperature of the A layer extruder is 270 ° C., the short tube temperature is 270 ° C., and the die temperature is The sheet was discharged in a sheet form on a cooling drum whose temperature was controlled to 25 ° C. from a T die at 275 ° C. At that time, a wire electrode having a diameter of 0.1 mm was applied electrostatically and adhered to the cooling drum to obtain an unstretched sheet. Next, the film was stretched twice in the longitudinal direction at a stretching temperature of 90 ° C. and immediately cooled with a metal roll whose temperature was controlled at 40 ° C. Next, with a tenter-type transverse stretching machine, the stretching section (L) is 6 m, and the first half 3 m, which is 0.5 × (L), is stretched 3.5 times in the width direction, and the stretching section (L) 6 m totals 5 Double stretching was performed. At this time, the stretching temperature was 90 ° C. Thereafter, heat treatment was performed at 190 ° C. for 20 seconds while applying 5% relaxation in the width direction in the tenter to obtain a biaxially oriented polyester film having a film thickness of 90 μm. The clip temperature at this time was controlled at 80 ° C.

(Example 2)
A biaxially oriented polyester film having a thickness of 90 μm was obtained in the same manner as in Example 1 except that the composition was changed as shown in the table.
(Example 3)
Biaxially oriented polyester film having a thickness of 85 μm as in Example 1, except that the composition was changed as shown in the table, the draw ratio in the longitudinal direction was 1.8 times, and the heat treatment temperature after stretching in the width direction was 200 ° C. Got.
Example 4
A biaxially oriented polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the composition was changed as shown in the table and the heat treatment temperature after stretching in the width direction was 210 ° C.
(Example 5)
A biaxially oriented polyester film having a thickness of 90 μm was obtained in the same manner as in Example 1 except that the composition was as shown in the table.
(Example 6)
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 270 ° C., the B-layer extruder cylinder temperature is 280 Melt at ℃, and merge in feed block to form A layer / B layer / A layer, short tube temperature after merging is 270 ℃, die temperature is 275 ℃, T die is 25 ℃ The sheet was discharged in a sheet form on a temperature-controlled cooling drum. At that time, a wire electrode having a diameter of 0.1 mm was applied electrostatically and adhered to the cooling drum to obtain an unstretched sheet. Thereafter, a biaxially oriented polyester film having a thickness of 90 μm was obtained in the same manner as in Example 1 except that the draw ratio in the longitudinal direction was 1.7 times.
(Example 7)
A biaxially oriented polyester film having a thickness of 90 μm was obtained in the same manner as in Example 6 except that the composition was as shown in the table and the draw ratio in the longitudinal direction was 2 times.
(Example 8)
In the stretching in the width direction, the stretching section (L) is set to 6 m, and the first half of 0.5 × (L) is stretched 2.5 times in the width direction, and the stretching section (L) is stretched 5 times in total by 5 times. A biaxially oriented polyester film having a film thickness of 90 μm was obtained in the same manner as in Example 6 except that this was performed.
Example 9
A biaxially oriented polyester film having a film thickness of 90 μm was obtained in the same manner as in Example 1 except that the clip temperature in the tenter during stretching in the width direction was controlled to 110 ° C.
(Example 10)
A biaxially oriented polyester film having a film thickness of 90 μm was obtained in the same manner as in Example 1 except that the clip temperature in the tenter during stretching in the width direction was controlled at 140 ° C.
(Example 11)
A biaxially oriented polyester film having a film thickness of 90 μm was obtained in the same manner as in Example 1 except that the heat treatment time after stretching in the width direction was 40 seconds.
(Example 2-2)
The biaxially oriented polyester film obtained in Example 2 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 a biaxially oriented polyester film on which the hard coat layer was laminated.
(Example 2-3)
On the biaxially oriented polyester film obtained in Example 2, 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 ultraviolet rays using a high pressure mercury lamp to obtain a biaxially oriented polyester film in which the antiglare layer having a thickness of 5 μm was laminated.

(Comparative Example 1)
A biaxially oriented polyester film having a thickness of 80 μm was obtained in the same manner as in Example 1 except that the draw ratio in the longitudinal direction was 2.8 times.
(Comparative Example 2)
The composition is as shown in the table, the stretching ratio in the longitudinal direction is 1 time, and in the stretching in the width direction, the stretching section (L) is 6 m, and the first 3 m of 0.5 × (L) is stretched 2 times in the width direction. A biaxially oriented polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that a total of 4 times of stretching was performed at 6 m in the stretching section (L) and the heat treatment after stretching was 225 ° C.

(Comparative Example 3)
A biaxially oriented polyester film having a thickness of 85 μm was obtained in the same manner as in Example 1 except that the composition was as shown in the table and the heat treatment temperature after stretching was 225 ° C.

(Comparative Example 4)
The composition is as shown in the table, the stretching ratio in the longitudinal direction is 2 times, and in the stretching in the width direction, the stretching section (L) is 6 m, and the first half 3 m which is 0.5 × (L) is 1.5 times in the width direction. A biaxially oriented polyester film having a thickness of 100 μm was obtained in the same manner as in Example 1 except that the film was stretched, stretched 3 times in total in the stretching section (L), and subjected to heat treatment after stretching at 180 ° C.

The notation in the table is as follows.
EG: ethylene glycol, TPA: terephthalic acid, IPA: isophthalic acid, NDC: 2,6-naphthalenedicarboxylic acid, CHDM: 1,4-cyclohexanedimethanol, SPG: spiroglycol, NPG: neopentyl glycol

The present invention relates to a polyester film that is particularly suitable for optical applications,
When mounted on a display device such as a liquid crystal display, it can suppress the interference color when viewing the display and is excellent in mechanical properties such as tensile strength and tensile elongation. Preferably used.

Claims (7)

A polyester A layer comprising a dicarboxylic acid component and a diol component, and when the total amount of the dicarboxylic acid component and the diol component in the polyester A layer is 100 mol%, the most of the dicarboxylic acid components and the diol component The sum of the most numerous components is more than 85 mol% and less than 98 mol%,
An optical polyester film having an in-plane retardation of 3000 nm to 30000 nm and a density of 1.35 g / cm ^{3 to} 1.41 g / cm ³ . The polyester A layer is composed of a dicarboxylic acid component and a diol component, the most dicarboxylic acid component is terephthalic acid or 2,6-naphthalenedicarboxylic acid, and the most diol component is ethylene glycol. Optical polyester film. The optical polyester film according to claim 1 or 2, wherein a refractive index (nx) in the fast axis direction is 1.59 or more. The polyester B layer whose melting point is Tb (° C) is laminated on at least one surface of the polyester A layer whose melting point is Ta (° C), and Tb> Ta, Optical polyester film. The optical polyester film according to claim 1, which is used for protecting a polarizer. The polarizing plate which has a polarizer protective film on both surfaces of a polarizer, Comprising: At least one polarizer protective film is a polyester film for optics of Claim 5. A transparent conductive film comprising the polyester film according to claim 1.