JP2016141058A - Biaxially oriented polyester film and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film that excels in thermal dimensional stability and suppresses the occurrence of "blackout" when a display device such as a liquid crystal display is mounted with the film as a polarizer protection film, a retardation film for a circularly polarizing plate, and a transparent electrode film.SOLUTION: There is provided a biaxially oriented polyester film that satisfies following conditions (a) and (b). (a) The biaxially oriented polyester film has a leaning angle of the main orientation axis of 30° or more and 60° or less to the longitudinal direction thereof. (b) The biaxially oriented polyester film has a thermal shrinkage of 0.0% or more and 1.0% or less in the longitudinal direction and a thermal shrinkage of 0.0% or more and 1.0% or less in the width direction after being subjected to a heat treatment for 30 minutes at 150°C.SELECTED DRAWING: None

Description

  The present invention relates to a biaxially oriented polyester film suitably used as a transparent electrode member, a polarizer protective member, and a circularly polarizing plate member.

  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. Particularly in recent years, demand for various optical films such as a polarizing plate protective film (polarizer protective member), a circularly polarizing plate retardation film (circular polarizing plate member), and a transparent conductive film (transparent conductive member) in the flat panel display and touch panel fields. Is growing. Among them, for polarizing plate protective film applications, replacement of a conventional TAC (triacetyl cellulose) film with a biaxially oriented polyester film has been actively studied for the purpose of cost reduction (for example, Patent Document 1).

  The light emitted from the liquid crystal display is linearly polarized because it is transmitted through the polarizing plate. Therefore, when viewing the liquid crystal display with polarized sunglasses, the phenomenon that the display screen becomes dark depending on the angle (hereinafter, this phenomenon is referred to as blackout) may occur. In order to solve the above problem, a method is known in which a polyester film is provided as a retardation film (circular polarizing plate retardation film) for the purpose of circularly polarized light outside the polarizing plate (Patent Documents 2 and 3).

JP 2012-032819 A JP 2013-194107 A JP 2013-200355 A

  However, the method described in Patent Document 1 cannot control the orientation of the polyester film during stretching. Therefore, when assembled as a part of the display member, there is a problem that blackout cannot be sufficiently suppressed and the quality of the screen display is lowered.

  Moreover, in the methods described in Patent Documents 2 and 3, the thermal dimensional stability is improved by imparting thermal dimensional stability, but the thermal dimensional stability in the longitudinal direction of the film is insufficient, There was a problem that curling and the like could not be sufficiently suppressed and the yield could not be improved.

  Therefore, in the present invention, the above-mentioned drawbacks are eliminated, and blackout occurs when a polyester protective film, a circularly polarizing plate retardation film, or a transparent electrode film is mounted on a display device such as a liquid crystal display including a touch panel while being a polyester film. It aims at providing biaxially oriented polyester film excellent in thermal dimensional stability.

The present invention for solving the above problems has the following configuration.
(1) A biaxially oriented polyester film satisfying the following (a) and (b).

      (A) The inclination of the main orientation axis with respect to the longitudinal direction of the biaxially oriented polyester film is 30 ° or more and 60 ° or less.

(B) When the heat treatment is performed at 150 ° C. for 30 minutes, the heat shrinkage rate in the longitudinal direction and the heat shrinkage rate in the width direction of the biaxially oriented polyester film are 0.0% or more and 1.0% or less.
(2) The biaxially oriented polyester film according to (1), wherein the in-plane retardation of the biaxially oriented polyester film is 2000 nm or less.
(3) The biaxially oriented polyester film is a laminated polyester film composed of two or more layers, and one surface layer of the laminated polyester film is a polyester layer composed of a polyester resin having a melting point of 240 ° C. or higher, The other surface layer is the biaxially oriented polyester film according to the above (1) or (2), which is a polyester layer composed of a polyester resin or an amorphous polyester resin having a melting point of less than 240 ° C.
(4) The biaxially oriented polyester film according to any one of (1) to (3), wherein the biaxially oriented polyester film has a minute heat of fusion peak of 200 ° C or higher and 240 ° C or lower.
(5) The biaxially oriented polyester film according to any one of (1) to (4), wherein the total thickness of the biaxially oriented polyester film is 35 μm or more and 150 μm or less.
(6) A laminated polyester film comprising three or more layers, wherein one surface layer is made of the same polyester resin as the other surface layer, the glass transition temperature of the polyester resin constituting the surface layer is TgA, and the polyester resin constituting the inner layer Among these, when the glass transition temperature of the polyester resin having the highest glass transition temperature is TgB, the biaxiality according to any one of the above (1) to (5), wherein TgB-TgA is 3 ° C. or more and 15 ° C. or less. Oriented polyester film.
(7) A method for producing the biaxially oriented polyester film according to any one of (1) to (6) above, wherein a heat setting temperature (hereinafter referred to as Ths) 200 to 240 after biaxial stretching of the polyester film. A method for producing a biaxially oriented polyester film, comprising: a step of cooling at 35 ° C. or lower after heat setting at ° C .; and a step of performing an annealing treatment at (Ths-80) ° C. or higher and (Ths-30) ° C. or lower. .
(8) The production of the biaxially oriented polyester film according to (7), wherein heat setting is performed while finely stretching in the width direction at a magnification of 1.02 times or more and 1.20 times or less in heat setting after biaxial stretching. Method.
(9) The biaxially oriented polyester film according to any one of (1) to (6), which is used as a polarizer protective member.
(10) The biaxially oriented polyester film according to any one of (1) to (6), which is used as a circularly polarizing plate member.
(11) The biaxially oriented polyester film according to any one of (1) to (6), which is used as a transparent electrode member.

  The biaxially oriented polyester film of the present invention suppresses blackout and stabilizes thermal dimensions when mounted on a display device such as a liquid crystal display including a touch panel as a polarizer protective film, a circularly polarizing plate retardation film, or a transparent electrode film. Has an excellent effect.

It is a schematic diagram at the time of performing a visibility test by crossed Nicol arrangement of a polarizing plate.

  Hereinafter, the present invention will be described in detail with specific examples.

  The present invention relates to a biaxially oriented polyester film.

  The polyester here is obtained from a dicarboxylic acid component and a diol component. In addition, in this invention, a structural component shows the minimum unit which can be obtained by hydrolyzing polyester.

  The dicarboxylic acid component constituting the resin constituting the biaxially oriented polyester film of the present invention includes malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandione Aliphatic dicarboxylic acids such as acid, pimelic acid, azelaic acid, methylmalonic acid, ethylmalonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid Phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′- Diphenyl ether dicarboxylic acid, 5-na Examples include dicarboxylic acids such as lithium sulfoisophthalic acid, phenylendanedicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, and 9,9′-bis (4-carboxyphenyl) fluorenic acid, or ester derivatives thereof. It is not limited to these.

  Moreover, as a diol component constituting the resin constituting the biaxially oriented polyester film of the present invention, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2 -Aliphatic diols such as butanediol and 1,3-butanediol, cycloaliphatic diols such as cyclohexanedimethanol and spiroglycol, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, Diols such as 9,9′-bis (4-hydroxyphenyl) fluorene and aromatic diols, and a series of a plurality of the above diols (for example, diethylene glycol obtained by dehydration condensation between two molecules of ethylene glycol) ) And the like, but are not limited thereto.

  The resin constituting the biaxially oriented polyester film of the present invention is preferably a polyester resin mainly composed of polyethylene terephthalate or polyethylene naphthalate.

  In the present invention, the main component is the largest mole fraction of each component when the diol component and dicarboxylic acid component contained in the entire resin constituting the polyester film are each 100 mol%. It refers to a resin obtained by polycondensation of constituent components. Thus, for example, among diol constituents, a polyester that is a diol constituent that is the most abundant at 55 mol% of ethylene glycol and a dicarboxylic acid constituent that is the abundant at 85 mol% of dicarboxylic acid constituents. In the case of a film, the main component is polyethylene terephthalate obtained by polycondensation of ethylene glycol and terephthalic acid.

  In the present invention, the content of the main component is the smaller of the mole fraction of the most frequently contained diol component and the mole fraction of the most frequently contained dicarboxylic acid component, and the same mole fraction. In that case, the molar fraction is used. Therefore, for example, in the above example, 55 mol% which is the smaller mole fraction of 55 mol% of ethylene glycol and 85 mol% of terephthalic acid is the main component content.

  When the resin constituting the polyester film of the present invention contains polyethylene terephthalate and / or polyethylene naphthalate as a main component, the content of the main component is 50 mol% or more in order to sufficiently exhibit the characteristics of the main component. Is preferable, 60 mol% or more is more preferable, and 80 mol% or more is more preferable.

  The polyester resin may be a copolymer of polyethylene terephthalate or polyethylene naphthalate, a knitted body, or a blend with other polymers. In particular, a polyester resin mainly composed of polyethylene terephthalate is preferable from the viewpoints of mechanical strength, heat resistance, chemical resistance, durability, and the like.

  The biaxially oriented polyester film of the present invention has a heat shrinkage in the longitudinal direction (MD direction) and a heat shrinkage in the width direction (TD direction) of 0.0% or more when heat-treated at 150 ° C. for 30 minutes. 0% or less. When the thermal contraction rate in the longitudinal direction of the film and the thermal contraction rate in the width direction of the film are within the above ranges, thermal deformation in the processing step is small, and when pasting as a circularly polarizing plate member and a polarizer protective member, Curling and peeling in processing steps when used as a transparent electrode substrate member can be suppressed, and yield can be improved. The lower limit of the range of the heat shrinkage rate in the longitudinal direction and the heat shrinkage rate in the width direction is 0.0%. Further, the upper limit of the range of the heat shrinkage rate in the longitudinal direction and the heat shrinkage rate in the width direction is 1.0%, preferably 0.8%, more preferably 0.5%, still more preferably. 0.3%. The range of the heat shrinkage rate in the longitudinal direction and the range of the heat shrinkage rate in the width direction may be the same or different.

  In the present invention, the longitudinal direction (MD direction) of the film is a biaxially oriented polyester film on a roll, the roll winding direction is the longitudinal direction, and the roll width direction is equivalent to the width direction (TD direction). To do. On the other hand, when the biaxially oriented polyester film has a cut sheet shape, the long side direction of the film is regarded as the longitudinal direction for calculation. When the film has a substantially square shape, calculation is performed by regarding any one of the directions parallel to each side as the longitudinal direction and the width direction.

  A biaxially oriented polyester film having a heat shrinkage ratio in the longitudinal direction in the above range can be obtained, for example, by a method of performing relaxation treatment in the longitudinal direction in the heat setting step or a method of performing annealing treatment after biaxial stretching and heat setting. However, it is not limited to these. When the relaxation treatment is performed in the longitudinal direction in the heat setting step, there is a problem that the main orientation axis described later moves in conjunction with the product roll width and the product removal width decreases.

  On the other hand, the biaxially oriented polyester film of the present invention can improve the heat resistance as a polyester resin by controlling the thermal characteristics of the resin constituting the film within a specific range. Therefore, particularly in a film obtained by a method of performing an annealing treatment, the main orientation axis can be controlled within a specific range, and the effect of improving the thermal dimensional stability while suppressing blackout is remarkably obtained.

  In the biaxially oriented polyester film of the present invention, the main orientation axis needs to be in the range of 30 ° to 60 ° with respect to the longitudinal direction of the film. When the inclination of the main orientation axis with respect to the longitudinal direction of the film is within the above range, when mounted on a liquid crystal display as a circularly polarizing plate member or a polarizer protective member, and when mounted on a touch panel as a transparent electrode substrate member, Visibility is improved because blackout can be suppressed. The main orientation axis as used herein refers to the direction in which the refractive index becomes the largest on the film surface, and is measured by an optical method. Specifically, the values measured by the phase difference measuring device KOBRA series sold by Oji Scientific Instruments Co., Ltd. are used.

The biaxially oriented polyester film in which the inclination of the main orientation axis is within the above range is, for example, 1) a method in which the main orientation axis is cut obliquely in the biaxially oriented polyester film, and 2) in the biaxially oriented polyester film, A method using a film at an end away from the central portion in the width direction during film formation,
3) A method for producing a biaxially oriented polyester film using an oblique stretching method (for example, a method described in International Publication No. 2007/111313),
Can be obtained.

  In the biaxially oriented polyester film of the present invention, the heat resistance as a polyester resin can be improved by controlling the thermal characteristics of the resin constituting the film within a specific range, so that the main orientation axis can be obtained by the method 2). When a film tilted by 30 to 60 ° is obtained, the difference in distribution of heat shrinkage can be suppressed even at a position away from the center of the film during film formation. Therefore, when the said film is bonded together and used as a circularly-polarizing plate member or a polarizer protective member, thermal dimensional stability can be improved and used suitably.

  In the biaxially oriented polyester film of the present invention, particularly in the film obtained by the method 2), the effects of suppressing blackout and improving thermal dimensional stability are remarkably obtained. In addition, the biaxially oriented polyester film of the present invention improves the heat resistance of the resin that constitutes the polyester film, and suppresses blackout and improves thermal dimensional stability by setting the film forming conditions within a specific range. The effect of making it possible can be naturally obtained also in the biaxially oriented polyester film obtained by the method of 3).

  The lower limit of the range of the inclination of the main orientation axis with respect to the longitudinal direction of the biaxially oriented polyester film is 30 °, more preferably 35 °, and further preferably 40 °. The upper limit of the range of the inclination of the main alignment axis is 60 °, preferably 55 °, and more preferably 50 °.

  When the retardation of the biaxially oriented polyester film of the present invention is measured in the longitudinal direction of 10 m, the in-plane retardation is preferably 2000 nm or less. In general, retardation is a value defined as the product of the maximum value of the refractive index difference between two orthogonal directions in the plane of the film and the film thickness, and is measured using an optical method in the same manner as the main orientation axis. The In the present invention, in-plane retardation is measured by a phase difference measuring apparatus KOBRA series in a measurement method described later. When the value of retardation becomes high, an interference color is produced when mounted on a liquid crystal display as a circularly polarizing plate member, a polarizer protective member, or a transparent electrode member for a touch panel. The upper limit of the in-plane retardation range is preferably 2000 nm, more preferably 1200 nm, and still more preferably 800 nm. The lower limit of the in-plane retardation range is preferably 100 nm.

  In the present invention, the biaxially oriented polyester film is a laminated polyester film having at least two layers, and a polyester layer composed of a polyester resin having a melting point (Tm) of 240 ° C. or higher. A polyester resin having a melting point (Tm) of the polyester resin of less than 240 ° C. on the side opposite to the surface layer of the film of the polyester A layer. Or a polyester layer composed of an amorphous polyester resin (the layer may be referred to as a polyester B layer hereinafter), and the thickness of the polyester B layer is 30% of the total thickness of the polyester film. It is preferably 90% or less.

  A laminated polyester film having at least two layers of polyester film, the polyester A layer having a melting point (Tm) of the polyester resin of 240 ° C. or higher, and the melting point on the side opposite to the surface layer of the A layer film When (Tm) is less than 240 ° C. or a polyester B layer composed of an amorphous polyester resin, the oriented crystal as a whole polyester film is enhanced while enhancing the orientation crystallinity of the polyester surface layer during stretching. Sex can be suppressed. The amorphous polyester resin referred to in the present invention is a differential scanning calorimetry chart (longitudinal) by raising the temperature from 25 ° C. to 300 ° C. at a rate of temperature rise of 20 ° C./min according to JIS K7121 (1999). A polyester resin having no endothermic peak corresponding to a melting point exceeding 10 J / g is obtained.

  Moreover, it becomes easy to raise the orientation crystallinity of the surface layer of polyester, suppressing the orientation crystallinity as the whole polyester film by making the said polyester B layer into 30% or more and 90% or less with respect to the total thickness of a polyester film. . The thickness of the polyester B layer is more preferably 50% or more and 90% or less because the film forming property and workability can be improved while suppressing the orientation crystallinity of the entire polyester film, and is preferably 60% or more and 80% or less. More preferably it is.

  As a specific method of making the polyester resin constituting the polyester B layer have a melting point of less than 240 ° C. or an amorphous polyester resin, a diol constituent constituting the polyester B layer and a dicarboxylic acid constituent constituting the B layer A method of increasing the number of other components with respect to the largest number of components among the components can be mentioned.

  For example, when the ethylene glycol is most contained as the diol component constituting the layer B and the most terephthalic acid is contained as the dicarboxylic acid component, the ratio of the diol component other than ethylene glycol and the dicarboxylic acid component other than terephthalic acid By increasing the ratio, the melting point of the polyester B layer can be lowered.

  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 can be mentioned. 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.

  Moreover, as dicarboxylic acid structural components other than terephthalic acid, for example, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-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.

  The biaxially oriented polyester film of the present invention is preferably a polyester A layer in which the melting point (Tm) of the polyester resin constituting at least one surface layer is 240 ° C. or higher. By setting the melting point of the polyester resin constituting at least one surface layer within the above range, the oriented crystal of the polyester resin constituting the vicinity of the surface of the polyester film when used as a polarizer member, a circularly polarizing member, or a transparent electrode member It tends to be high.

  Further, when the resin constituting the polyester B layer has a melting point, the melting point (TmA) of the resin constituting the polyester A layer is a resin having a melting point 20 ° C. higher than the melting point (TmB) of the resin constituting the polyester B layer. It is preferable to do. In this case, in the heat setting step described later, by performing heat setting at a temperature of TmB ° C. or higher and TmA ° C. or lower, only the polyester B layer can be relaxed, and retardation can be easily suppressed. More preferably, the difference between TmA and TmB is 30 ° C. or more. In this case, since the temperature selection range in the heat setting step is widened, the relaxation of the orientation of the polyester B layer is promoted and the orientation of the polyester A layer is controlled. It will be easy.

  In the biaxially oriented polyester film of the present invention, the resin constituting the polyester B layer is more preferably composed of an amorphous polyester resin. Compared to crystalline resin, amorphous resin is less likely to be oriented when producing a biaxially stretched film, so that it is possible to suppress an increase in the retardation of the polyester B layer, and thus the non-uniform retardation of the biaxially oriented polyester film. It becomes easy to suppress. In particular, when a heat setting step is provided when producing a biaxially stretched film, this effect becomes remarkable, and the orientation generated in the polyester B layer made of an amorphous polyester resin in the stretching step in the film longitudinal direction and width direction. Can be completely relaxed in the heat setting step, and only the retardation resulting from the polyester A layer consisting essentially of the crystalline polyester is preferable because it affects the retardation of the laminated film.

The biaxially oriented polyester film of the present invention has at least three layers, and the film has a thickness direction such as A layer / B layer / A layer, A layer / B layer / A layer / B layer / A layer, etc. Therefore, one surface layer is made of the same polyester resin as the other surface layer, and the glass transition temperature (TgA) of the polyester resin constituting the surface layer and the polyester resin constituting the inner layer are the highest. The difference (TgB-TgA) from the glass transition temperature (TgB) of the polyester resin having a glass transition temperature is preferably 3 ° C or higher and 15 ° C or lower. By making TgB-TgA into the said range, the molecular mobility by the heat | fever of the polyester B layer can be suppressed, and the thermal dimensional stability of the whole film can be improved. Moreover, since TgB-TgA is 15 degrees C or less, since the glass transition temperature difference of the polyester A layer and the polyester B layer is small, it is excellent in a drawability and the yield of a film may improve. The lower limit of the TgB-TgA range is preferably 3 ° C, more preferably 5 ° C. Further, the upper limit of the TgB-TgA range is preferably 15 ° C, more preferably 12 ° C. In addition, in this invention, the same polyester resin means the thing with the same kind of dicarboxylic acid structural component and diol structural component which comprise a polyester resin, and the content rate of each structural component is also the same.
As a method of setting the glass transition temperature of the polyester A layer and the polyester B layer constituting the biaxially oriented polyester film in the above range, the resin constituting the polyester B layer is composed of two or more kinds of diol constituent components to form glass. It is preferable to increase the transition temperature. Specifically, it is preferable to contain 75 mol% or more and 95 mol% or less of ethylene glycol and 5 mol% or more and 25 mol% or less of other diol components with respect to the diol component constituting the polyester film. .

  Examples of the other diol components include cyclohexanedimethanol, cyclohexanediethanol, decahydronaphthalene diethanol, decahydronaphthalene diethanol, norbornane dimethanol, norbornane diethanol, tricyclodecane dimethanol, tricyclodecane ethanol, tetracyclododecanedi. Saturated alicyclic primary diols such as methanol, tetracyclododecane diethanol, decalin dimethanol, decalin diethanol, 2,6-dihydroxy-9-oxabicyclo [3.3.1] nonane, 3,9-bis (2- Hydroxy-1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro [5.5] undecane (spiroglycol), 5-methylol-5-ethyl-2- (1,1-dimethyl- -Hydroxyethyl) -1,3-dioxane, saturated heterocyclic primary diols containing cyclic ethers such as isosorbide, other cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis (4-hydroxycyclohexylpropane) ), 2,2-bis (4- (2-hydroxyethoxy) cyclohexyl) propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, adamantyldiol, etc. Fragrances such as various alicyclic diols, bisphenol A, bisphenol S, styrene glycol, 9,9-bis (4- (2-hydroxyethoxy) phenyl) fluorene, 9,9'-bis (4-hydroxyphenyl) fluorene Cyclic diols can be exemplified. Among these, alicyclic diols are preferable, and cyclohexanedimethanol, spiroglycol and / or isosorbide are most preferable from the viewpoint of reactivity and suppression of interference color.

The biaxially oriented polyester film of the present invention preferably has a minute melting peak (T-meta) just below the melting point of 200 to 240 ° C. When T-meta is 200 ° C. or higher, structural fixation by heat fixation is sufficiently performed, and the thermal contraction rate is easily reduced. In addition, when T-meta is 240 ° C. or lower, orientation relaxation does not occur extremely, and the film-forming property is hardly lowered. The lower limit of the range of T-meta is preferably 200 ° C, more preferably 220 ° C. The upper limit of the range of T-meta is preferably 240 ° C, more preferably 235 ° C. T-meta can be controlled by the heat setting temperature. T-meta varies depending on the film forming machine and the film forming speed, but usually increases as the heat setting temperature increases.
The thickness of the biaxially oriented polyester film of the present invention can be appropriately adjusted in the range of 4 μm to 250 μm according to the use of the film. 10 μm to 35 μm is preferable for polarizer protection use, and for various other applications such as circularly polarizing plates, 4 μm to 10 μm is preferable, and for transparent electrode use, 35 μm to 150 μm is preferable, and more than 35 μm is more preferably 150 μm. More preferably, it is 50-125 micrometers.

  The biaxially oriented polyester film of the present invention has various additives such as antioxidants, heat stabilizers, slip agents, anti-blocking agents, weather stabilizers, UV absorbers, organic lubricants, pigments, dyes, organic or Inorganic fine particles, fillers, antistatic agents, nucleating agents and the like may be added to such an extent that their properties are not deteriorated.

  Next, the preferable aspect of the manufacturing method of the biaxially-oriented polyester film of this invention is demonstrated below. The present invention should not be construed as being limited to such examples.

  In the method for producing a biaxially oriented polyester film of the present invention, a dried raw material is heated and melted in an extruder as necessary, and is extruded from a die onto a cast drum cooled (melt cast method). Can be used. As another method, the raw material is dissolved in a solvent, and the solution is extruded from a die onto a support such as a cast drum or an endless belt to form a film, and then the solvent is dried and removed from the film layer to form a sheet. A method (solution casting method) or the like can also be used.

  When the film is produced by the melt casting method, polyester A used for the polyester A layer and polyester B used for the polyester B layer having a melting point lower than that of the polyester A layer are supplied to separate extruders and melt extruded. 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, foreign matter is removed and the amount of extrusion is leveled through a filter and a gear pump, respectively, and 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.

  In the method for producing a biaxially oriented polyester film of the present invention, an unstretched film is stretched in the longitudinal direction and then stretched in the width direction, or stretched in the width direction and then stretched in the longitudinal direction. Or by stretching by the simultaneous biaxial stretching method in which the longitudinal direction and the width direction of the film are stretched almost simultaneously.

  The stretching ratio in such a stretching method is preferably 2.5 times or more and 4.0 times or less, more preferably 2.8 times or more and 3.8 times in the longitudinal direction in order to set the main orientation axis within a specific range. Hereinafter, more preferably, 3.0 times to 3.6 times is employed. The stretching speed is preferably 1,000% / min or more and 200,000% / min or less. The stretching temperature is preferably from the glass transition temperature of the resin constituting the biaxially oriented polyester film to the glass transition temperature + 100 ° C.

  In addition, the stretching ratio in the width direction is preferably 80% or more and 120% or less, and 90% or more and 110% or less with respect to the stretching ratio in the longitudinal direction in order to control the main orientation axis within a specific range. More preferably, it is more preferable to align with the draw ratio in the longitudinal direction. The stretching speed in the width direction is preferably 1,000% / min or more and 200,000% / min or less. As the stretching temperature, the glass transition temperature of the resin constituting the biaxially oriented polyester film is preferably −10 ° C. to glass transition temperature + 100 ° C.

  Furthermore, in the method for producing a biaxially oriented polyester film of the present invention, it is preferable to provide a difference in the transverse stretching speed in order to control the main orientation axis. Specifically, when the transverse stretching section is divided into two, the stretching amount of the film at the midpoint of the transverse stretching section (film width at the measurement point−film width before stretching) is 60% of the stretching amount at the end of the transverse stretching section. The above is preferable, and 70% or more is more preferable. In the present invention, transverse stretching refers to stretching in the width direction. Thus, by changing the transverse stretching speed in the first and second half of the transverse stretching section, variation in retardation in the width direction of the film can be suppressed, and the inclination of the main orientation axis is set to 30 ° to 60 °. Can be widened. As a result, it is possible to obtain a high-quality liquid crystal display without blackout when mounted on the liquid crystal display.

  Furthermore, in the method for producing a biaxially oriented polyester film of the present invention, it is also preferable to change the temperature during transverse stretching stepwise. Specifically, when the transverse stretching section is divided into two, when the first half section is before the transverse stretching middle point and the second half section is after the transverse stretching middle point, the atmospheric temperature of the second half section is the atmospheric temperature of the first half section. It is preferable to make it 20 ° C. or higher. Here, the atmospheric temperature is sufficient if there is a portion that satisfies the above conditions at a part of the temperature in the first half section and a part of the second half section. Thus, by changing the stretching temperature in the transverse stretching section stepwise, the heat shrinkage distribution in the width direction of the film can be suppressed, and the inclination of the main orientation axis is 30 ° to 60 °. Can be widened. As a result, it becomes possible to improve the workability when mounted on a liquid crystal display and to provide a high-quality liquid crystal display without blackout.

  Furthermore, the film is heat-set after biaxial stretching. The heat setting can be performed by any conventionally known method such as heating in an oven or on a heated roll. This heat setting temperature (hereinafter sometimes abbreviated as “Ths”) is carried out at a temperature not lower than the stretching temperature and not higher than the melting point of the polyester A layer, and is preferably not lower than −10 ° C. and not higher than the melting point + 30 ° C. of the polyester B layer. More preferably, it is 200 degreeC or more and 240 degrees C or less. Here, the preferable heat setting temperature refers to the highest temperature among the heat setting temperatures performed after biaxial stretching.

  In the method for producing a biaxially stretched polyester film of the present invention, it is preferable that the film is further finely stretched in the transverse direction during heat setting. The fine stretching here refers to stretching at a stretching ratio of 1.02 times or more and 1.20 times or less. By fine stretching during heat setting, crystal growth and orientation control can be performed simultaneously, and the structure of the main orientation axis can be easily fixed. This makes it easier to prevent the main alignment axis from being distorted again by the heat applied during the annealing process described later. When the draw ratio of fine stretching is 1.20 times or less, the film is hardly broken and the yield is easily improved. When the draw ratio of fine stretching is 1.02 or more, the effect of fixing the structure of the main orientation axis is easily obtained. The lower limit of the range of the draw ratio of fine stretching is preferably 1.02 times, more preferably 1.05 times. The upper limit of the range of the draw ratio of fine stretching is preferably 1.20 times, more preferably 1.10 times.

  Further, the biaxially oriented polyester film of the present invention may be subjected to a relaxation treatment of 1 to 9% in the width direction and / or the longitudinal direction at the stage of cooling the film after heat setting and / or after heat setting after fine stretching. It is preferable in obtaining.

  Further, the heat setting time can be arbitrarily set within the range in which the characteristics are not deteriorated, and is preferably 5 seconds to 60 seconds, more preferably 10 seconds to 40 seconds, and most preferably 15 seconds to 30 seconds. Is good.

  Thereafter, after cooling at a temperature of preferably 35 ° C. or lower, more preferably 25 ° C. or lower, the film edge is removed and wound on the core. Furthermore, in order to improve thermal dimensional stability, it is preferable that the wound biaxially oriented polyester film is conveyed under tension under a certain temperature condition.

  Next, in order to remove the distortion of the molecular structure and reduce the thermal shrinkage rate, it is preferable to perform an annealing treatment. The annealing temperature (hereinafter sometimes abbreviated as Ta) is preferably (Ths-80) to (Ths-30) ° C, more preferably (Ths-60) to (Ths-40) ° C. When the temperature is (Ths-30) ° C. or less, the difference from the heat setting temperature (Ths) becomes large, and the main alignment axis controlled by the heat setting process is hardly distorted by the annealing process, and the visibility is not easily lowered. When the temperature is (Ths-80) ° C. or higher, the distortion of the molecular structure is sufficiently removed by the annealing treatment, and it is easy to suppress the thermal shrinkage remaining. The lower limit of the annealing temperature range is preferably (Ths-80) ° C, more preferably (Ths-60) ° C. The upper limit of the annealing temperature range is preferably (Ths-30) ° C, more preferably (Ths-40) ° C.

The tension in the annealing step is preferably 15 g / mm ² or more and 120 g / mm ² or less, more preferably 30 g / mm ² or more and 80 g / mm ² or less. When the tension is 120 g / mm ² or less, the strain in the molecular structure in the longitudinal direction is sufficiently removed, and the heat shrinkage remains and the main orientation axis fixed in the structure is not easily disturbed. When the tension is 15 g / mm ² or more, the relaxation does not proceed excessively at the time of conveyance, and wrinkles are hardly generated. The lower limit of the range of the tension is preferably ^{15g / mm 2, 30g / mm} 2 is more preferable. The upper limit of the range of the tension is preferably ^{120g / mm 2, 80g / mm} 2 is more preferable.

  The annealing time is preferably 1 to 120 seconds. The lower limit of the annealing time range is preferably 1 second, more preferably 5 seconds, and even more preferably 20 seconds. The upper limit of the annealing time range is preferably 120 seconds, more preferably 90 seconds, and even more preferably 60 seconds. The film transport speed during the annealing treatment is preferably 10 to 300 m / min.

  Furthermore, in order to improve the adhesive force with the polarizer, 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.

  When the biaxially oriented polyester film of the present invention is mounted on a display device such as a large-screen liquid crystal display, it does not exhibit an interference color due to deformation of the display. It is preferably used as a polarizer protective member or a circularly polarizing plate member by bonding with the prepared PVA sheet (polarizer).

Since the biaxially oriented polyester film of the present invention has low thermal deformation in the processing step and excellent visibility, the chamber is evacuated to 5 × 10 ⁻⁴ Pa before plasma discharge, and then argon and oxygen are admitted into the chamber. 2 W using an indium oxide containing 36% by mass of tin oxide (manufactured by Sumitomo Metal Mining Co., Ltd., density 6.9 g / cm ³ ) as a target with a pressure of 0.3 Pa (oxygen partial pressure is 3.7 mPa). A transparent conductive layer made of ITO having a thickness of 250 nm can be formed by DC magnetron sputtering by applying power at a power density of / cm ² and mounted on the touch panel.

[Characteristic evaluation method]
A. The total thickness of the film, each layer thickness film is embedded in an epoxy resin, and the film cross section is cut out with a microtome. The cross section is observed with a transmission electron microscope (TEM H7100 manufactured by Hitachi, Ltd.) at a magnification of 5000 times to determine the total thickness of the film and the thickness of each polyester layer.

B. Retardation, inclination of main orientation axis A phase difference measuring device (KOBRA-21ADH) manufactured by Oji Scientific Instruments Co., Ltd. is used. Four samples are cut out at 3.5 cm × 3.5 cm so that the center points of the samples are 5 cm apart in the width direction of the film, and the longitudinal direction of the film is at an angle of 0 ° defined by this measuring apparatus. And the retardation of a wavelength of 590 nm at an incident angle of 0 ° and its main orientation axis are measured. The average value of the measurement results of the retardation of the four measurement samples is defined as in-plane retardation. The main orientation axis is set as the angle of the smaller one of the angles formed between the slow axis direction obtained by measurement and the film longitudinal direction when the film longitudinal direction of the measurement sample is set to the angle 0 ° direction of this measuring apparatus. Ask. The average value of the four measurement samples is defined as the inclination of the main alignment axis. Here, the slow axis is an axis in which the phase is delayed and the traveling speed of the light is the slowest when light propagates in the crystal causing birefringence.

C. 150 degreeC heat-shrink rate A heat-shrink rate measurement is performed with the following apparatus and conditions.
-Length measuring device: Universal projector-Sample size: Test length 200mm x Width 10mm
・ Heat treatment equipment: Gear oven ・ Heat treatment conditions: 150 ° C., 30 minutes ・ Load: 3 g
-Calculation method Draw a marked line on the sample at intervals of 150 mm before heat treatment, measure the distance between the marked lines after the heat treatment, and calculate the thermal shrinkage rate by the following formula. Five samples are collected and measured so that the direction of the test length is parallel to the longitudinal direction or the width direction, and the average value is evaluated.

Thermal contraction rate (%) = {(distance between marked lines before heat treatment) − (distance between marked lines after heat treatment)} / distance between marked lines before heat treatment × 100
D. In accordance with JIS K7121 (1999), the differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. and the disk session “SSC / 5200” for data analysis were used as follows. Conduct measurements.

  5 mg of a sample is weighed in a sample pan, and the sample is heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1stRUN), held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. Immediately thereafter, the temperature was increased again from 25 ° C. to 300 ° C. at a rate of temperature increase of 20 ° C./minute, and a 2ndRUN differential scanning calorimetry chart (the vertical axis represents thermal energy and the horizontal axis represents temperature) Get. The temperature at the top of the endothermic peak obtained from the 2ndRUN DSC curve was taken 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.

E. Glass transition temperature In accordance with JIS K7121 (1999), the differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. and the disk session “SSC / 5200” for data analysis were used as follows. The measurement is carried out.

  5 mg of a sample is weighed in a sample pan, and the sample is heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1stRUN), held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. Immediately thereafter, the temperature was increased again from 25 ° C. to 300 ° C. at a rate of temperature increase of 20 ° C./minute, and a 2ndRUN differential scanning calorimetry chart (the vertical axis represents thermal energy and the horizontal axis represents temperature) Get. In the 2ndRUN differential scanning calorimetry chart, in the step change portion of the glass transition, a straight line that is equidistant from the extended straight line of each base line in the vertical axis direction and a curve of the step change portion of the glass transition are Find from the point of intersection. When two or more stepwise changes in glass transition are observed, the glass transition temperature is obtained for each, and the average of these temperatures is taken as the glass transition temperature (Tg) (° C.) of the sample.

F. Micro-melting calorie peak (T-meta)
In accordance with JIS K7121 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used, and a disk session “SSC / 5200” was used for data analysis. Perform the measurement.

  5 mg of the sample was weighed in a sample pan, and the sample was heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1stRUN). At that time, a minute endothermic peak that is in the vicinity of the peak temperature of the endothermic peak at a lower temperature than the temperature of the peak of the endothermic peak of melting observed (200 ° C. or higher and lower than the peak temperature of the endothermic peak) is expressed as a minute melting heat quantity peak (T-meta). It was. T-meta can be confirmed because it is observed in the DSC first run because it has a thermal history corresponding to the heat setting temperature, and is not observed in the second run that has been heated to the melting point once and disappeared.

F. Visibility Test FIG. 1 shows a schematic diagram when a visibility test is performed in a crossed Nicol arrangement of polarizing plates.

  A test piece d is obtained by laminating a biaxially oriented polyester film c to the polarizing plate a. The visibility when the test piece d is placed on another polarizing plate b in a crossed Nicol arrangement and placed on the LED light source e (A3-101 made by Tritech) is confirmed from the direction of the measurer f in FIG.

Visibility (i)
A: Blackout is hardly seen.

B: Although there is some blackout, there is no problem in practical use.
C: Blackout is observed, and the whole is slightly darkened, but can be used practically.
X: Since blackout is clearly seen, it is not suitable for practical use.

Visibility (ii)
AA: Interference color is hardly seen A: Although interference color is slightly seen, there is no problem in practical use.
B: Although interference color is seen, it is practical.
C: Although interference color is seen as a whole, it is practical.
X: Since the interference color is clearly seen, it is not suitable for practical use.

G. A 10 cm × 10 cm sample is cut from the thermal dimensional stability film and placed in an oven at a temperature of 150 ° C. for 30 minutes. Then, after leaving for 30 minutes under the conditions of a temperature of 23 ° C. and 65% RH, the curled state at the four corners is observed, the average value of the warping amounts (mm) at the four corners is obtained, and evaluated according to the following criteria. The curl becomes better as the thermal contraction rate is smaller. Evaluation C is unacceptable.
AA: The amount of warpage is less than 2.5 mm.
A: The amount of warpage is 2.5 mm or more and less than 5 mm.
B: The amount of warpage is 5 mm or more and less than 10 mm.
C: The amount of warpage is 10 mm or more.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

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

(Polyester A)
100 mol% of terephthalic acid as a dicarboxylic acid component and 100 mol% of ethylene glycol as a diol component were charged into a transesterification reactor, and the contents were heated and dissolved. Thereafter, while stirring the contents, magnesium acetate tetrahydrate and antimony trioxide were added to conduct a transesterification reaction. Then, an ethylene glycol solution of trimethyl phosphate was added. Addition of an ethylene glycol solution of trimethyl phosphate decreases the temperature of the reaction contents. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling excess ethylene glycol. Thus, after the temperature of the reaction contents in the transesterification reactor reached a temperature of 230 ° C., the reaction contents were transferred to the polymerization apparatus, and the polymerization reaction was started by applying pressure and temperature. Thereafter, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in the form of a strand, and immediately cut to obtain polyester A.

(Polyester B)
As an amorphous polyester resin, “ALTERSTER (registered trademark)” 20 manufactured by Mitsubishi Gas Chemical Company was used as polyester B.

(Polyester C)
Copolymerized polyester (GN001 manufactured by Eastman Chemical Co., Ltd.) copolymerized with 100 mol% terephthalic acid as a dicarboxylic acid component and 80 mol% ethylene glycol and 20 mol% 1,4-cyclohexanedimethanol as a diol component ) Was used as polyester C.

(Polyester D)
Polyester D was obtained in the same manner as for polyester A except that terephthalic acid was used as a dicarboxylic acid component and 82.5 mol% and isophthalic acid was 17.5 mol%.

(Polyester E)
Polyester A and polyester B were mixed so as to have a mass fraction of 75/25 and dried for 8 hours in a vacuum dryer at 120 ° C., and then these chips were supplied to a vent type twin-screw kneading extruder to be 280 ° C. After being extruded through a metal filter made of sintered fiber stainless steel, extruded from a die having a diameter of 3 mm and a length of 10 mm, cooled, cut with a cutter and 5% spiroglycol as a diol component A polyester E of spiroglycol copolymerized polyethylene terephthalate was obtained.

Example 1
Polyester A was supplied to the polyester A layer, and polyester B was supplied to the polyester B layer, and each was supplied to separate extruders having an oxygen concentration of 0.2% by volume. The A-layer extruder cylinder temperature was 280 ° C., the B-layer extruder cylinder temperature was 270 ° C., and the mixture was melted by a merging device so as to have a three-layer configuration of A layer / B layer / A layer. The stacking ratio was adjusted so that the layer A thickness: B layer thickness: A layer thickness was 1: 4.3: 1, the short tube temperature after merging was 280 ° C. and the die temperature was 280 ° C. The sheet was discharged in a sheet form on a cooling drum whose temperature was controlled to ° C. At that time, a wire-like electrode having a diameter of 0.1 mm was applied electrostatically and adhered to the cooling drum to obtain an unstretched sheet.

  Subsequently, the sheet was preheated with a heated roll group, and then stretched 3.3 times in the longitudinal direction (MD direction) at 90 ° C., and then cooled with a roll group at 25 ° C. to obtain a uniaxially stretched film.

  This uniaxially stretched film was guided to a tenter, preheated with hot air at 85 ° C., and then stretched 3.3 times in the width direction of the film. The stretching here is adjusted to stretch to 2.6 times, which is 70% of the maximum stretching amount at 90 ° C. in the first half of the stretching section, and the stretching amount is 3.3 ° C. at a temperature of 135 ° C. in the second half of the stretching section. Adjusted to double.

  Subsequently, the film was heat-set for 10 seconds while being slightly stretched 1.10 times at a temperature of 230 ° C. in a heat setting zone in the tenter, and further relaxed in the 4% width direction at a temperature of 230 ° C.

  Subsequently, after gradually cooling in the cooling zone uniformly, the film edge portion was cut, and after being conveyed by a conveying roll, an intermediate product 1 having a width of 1000 mm and a thickness of 50 μm was obtained.

The obtained intermediate product 1 was annealed while being conveyed at a temperature of 180 ° C., a tension of 50 g / mm ² and a film running speed of 30 m / min for 30 seconds to obtain an intermediate product 2.

  The obtained intermediate product 2 was wound around a core while being cut with a slitter so as to have a width of 300 mm × 3 pieces (both ends were cut) to obtain a biaxially oriented polyester film.

  The film located in the middle part of the intermediate product 2 is shown in Reference Example 1-0, the film located on both sides of the middle part of the intermediate product is shown in Example 1-1, and the characteristics of the obtained film are shown in the table. . In addition, the measurement of each characteristic was performed by sampling from the center part of the roll of each biaxially stretched polyester film obtained by cutting the intermediate product 2. The film of Example 1-1 had characteristics excellent in interference color suppression and thermal dimensional stability.

(Example 2)
A film was obtained in the same manner as in Example 1 except that the heat setting temperature (Ths) was 215 ° C. The film located on both sides of the central part of the intermediate product 2 was designated as Example 2-1, and the obtained film was evaluated and had excellent thermal dimensional stability.

(Example 3)
A film was obtained in the same manner as in Example 1 except that the temperature of the annealing step was 200 ° C. The film located on both sides of the central part of the intermediate product 2 was designated as Example 3-1, and when the obtained film was evaluated, it had excellent thermal dimensional stability.

Example 4
A film was obtained in the same manner as in Example 1 except that the temperature of the annealing step was 150 ° C. The film located on both sides of the middle part of the intermediate product 2 was designated as Example 4-1, and the obtained film was evaluated. The resulting film was excellent in interference color suppression and thermal dimensional stability.

(Example 5)
A film was obtained in the same manner as in Example 1 except that the fine stretching ratio in the heat setting step was 1.15 times. The film located on both sides of the central part of the intermediate product 2 was designated as Example 5-1, and the obtained film was evaluated and had excellent thermal dimensional stability.

(Example 6)
A film was obtained in the same manner as in Example 1 except that polyester C was used for the polyester B layer. The film located on both sides of the central part of the intermediate product 2 was designated as Example 6-1, and the obtained film was evaluated and had excellent blackout suppression and thermal dimensional stability.

(Example 7)
A film was obtained in the same manner as in Example 1 except that polyester D was used for the polyester B layer. The film located on both sides of the middle part of the intermediate product 2 was designated as Example 7-1, and when the obtained film was evaluated, it had excellent interference color suppression properties.

(Example 8)
A film was obtained in the same manner as in Example 1 except that the lamination ratio was adjusted to be A layer thickness: B layer thickness: A layer thickness of 1: 4: 1 and the thickness was 6 μm. The film located on both sides of the middle part of the intermediate product 2 was designated as Example 8-1, and when the obtained film was evaluated, it had excellent blackout suppression characteristics.

Example 9
A film was obtained in the same manner as in Example 1 except that the lamination ratio was adjusted so that the A layer thickness: B layer thickness: A layer thickness was 1: 2.2: 1. The film located on both sides of the central part of the intermediate product 2 was designated as Example 9-1. The obtained film was evaluated and had excellent blackout suppression and thermal dimensional stability.

(Example 10)
A film was obtained in the same manner as in Example 1 except that polyester E was used for the polyester A layer. The film located on both sides of the central part of the intermediate product 2 was designated as Example 10-1, and the obtained film was evaluated. The resulting film was excellent in blackout suppression and interference color suppression.

(Example 11)
A film was obtained in the same manner as in Example 1 except that the layers were merged with a merging apparatus so as to be two layers of A layer / B layer and adjusted so that A layer thickness: B layer thickness was 1: 4. The film located on both sides of the central part of the intermediate product 2 was designated as Example 11-1, and the obtained film was evaluated. The resulting film was excellent in blackout suppression and interference color suppression.

(Example 12)
A film was obtained in the same manner as in Example 1 except that a film was produced using only polyester A. The film located on both sides of the central part of the intermediate product 2 was designated as Example 12-1, and the obtained film was evaluated and had excellent blackout suppression and thermal dimensional stability.

(Example 13)
A film was obtained in the same manner as in Example 1 except that only a polyester A was used and a film having a thickness of 25 μm was produced. The film located on both sides of the central part of the intermediate product 2 was designated as Example 13-1, and when the obtained film was evaluated, it had excellent blackout suppression characteristics.

(Comparative Example 1)
A film was obtained in the same manner as in Example 1 except that the heat setting temperature (Ths) was 190 ° C. The film located on both sides of the central part of the intermediate product 2 was designated as Comparative Example 1-1. When the obtained film was evaluated, it had characteristics inferior in blackout suppression and thermal dimensional stability.

(Comparative Example 2)
A film was obtained in the same manner as in Example 1 except that the temperature of the annealing step was 220 ° C. The film located on both sides of the central part of the intermediate product 2 was designated as Comparative Example 2-1, and when the obtained film was evaluated, the film was inferior in blackout suppression.

(Comparative Example 3)
A film was obtained in the same manner as in Example 1 except that the temperature of the annealing step was 140 ° C. The film located on both sides of the central part of the intermediate product 2 was designated as Comparative Example 3-1, and when the obtained film was evaluated, the film had inferior thermal dimensional stability.

(Comparative Example 4)
A film was obtained in the same manner as in Example 1 except that the fine stretching ratio in the heat setting step was 1.00 times. The film located on both sides of the central part of the intermediate product 2 was designated as Comparative Example 4-1, and when the obtained film was evaluated, the film was inferior in blackout suppression.

(Comparative Example 5)
A film was obtained in the same manner as in Example 1 except that a film was produced using only polyester A and that the fine stretching ratio in the heat setting step was 1.00 times. The film located on both sides of the central part of the intermediate product 2 was designated as Comparative Example 5-1, and when the obtained film was evaluated, it had characteristics inferior in blackout suppression and interference color suppression.

  The polyester film of the present invention is suppressed in blackout and is excellent in thermal dimensional stability. Therefore, it is suitably used for applications of a polarizer protective member, a circularly polarizing plate member, and a transparent electrode substrate.

a: polarizing plate b: another polarizing plate c: biaxially oriented polyester film d: test piece e: LED light source f: measurer

Claims (11)

A biaxially oriented polyester film satisfying the following (a) and (b).
(A) The inclination of the main orientation axis with respect to the longitudinal direction of the biaxially oriented polyester film is 30 ° or more and 60 ° or less.
(B) When the heat treatment is performed at 150 ° C. for 30 minutes, the heat shrinkage rate in the longitudinal direction and the heat shrinkage rate in the width direction of the biaxially oriented polyester film are 0.0% or more and 1.0% or less.   The biaxially oriented polyester film according to claim 1, wherein an in-plane retardation of the biaxially oriented polyester film is 2000 nm or less.   The biaxially oriented polyester film is a laminated polyester film composed of two or more layers, and one surface layer of the laminated polyester film is a polyester layer composed of a polyester resin having a melting point of 240 ° C. or higher, and the other The biaxially oriented polyester film according to claim 1 or 2, wherein the surface layer is a polyester layer composed of a polyester resin or an amorphous polyester resin having a melting point of less than 240 ° C.   The biaxially oriented polyester film according to any one of claims 1 to 3, wherein the biaxially oriented polyester film has a minute heat of fusion peak of 200 ° C or higher and 240 ° C or lower.   The biaxially oriented polyester film according to any one of claims 1 to 4, wherein a total thickness of the biaxially oriented polyester film is 35 µm or more and 150 µm or less.   A laminated polyester film composed of three or more layers, wherein one surface layer is made of the same polyester resin as the other surface layer, the glass transition temperature of the polyester resin constituting the surface layer is TgA, and the polyester resin constituting the inner layer The biaxially oriented polyester film according to any one of claims 1 to 5, wherein TgB-TgA is 3 ° C or higher and 15 ° C or lower when the glass transition temperature of the polyester resin having the highest glass transition temperature is TgB.   A method for producing the biaxially oriented polyester film according to any one of claims 1 to 6, wherein the polyester film is biaxially stretched and heat-set at a heat setting temperature (hereinafter referred to as Ths) of 200 to 240 ° C. The process of cooling at the temperature of 35 degrees C or less, and the manufacturing method of a biaxially-oriented polyester film including the process of performing an annealing process at (Ths-80) degreeC or more and (Ths-30) degrees C or less.   The method for producing a biaxially oriented polyester film according to claim 7, wherein the heat setting is carried out while fine stretching at a magnification of 1.02 times or more and 1.20 times or less in the width direction in heat setting after biaxial stretching.   The biaxially oriented polyester film according to any one of claims 1 to 6, which is used as a polarizer protective member.   The biaxially oriented polyester film according to any one of claims 1 to 6, which is used as a circularly polarizing plate member. The biaxially oriented polyester film according to any one of claims 1 to 6, which is used as a transparent electrode member.

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