TW202106772A - Biaxially oriented polyester film - Google Patents

Abstract

The present disclosure provides a biaxially oriented polyester film in which the rates of expansion in the width direction at 90 DEG C and at 120 DEG C are each 0-0.15% relative to the width-direction dimension at 30 DEG C.

Description

Two-axis oriented polyester film

This disclosure relates to a biaxially aligned polyester film.

From the viewpoint of processability and the like, biaxially oriented polyester films are used for a wide range of uses.

As an example of the above-mentioned technology, Japanese Patent Application Laid-Open No. 2018-021168 discloses a biaxially oriented polyester film in which the temperature rises from 25°C to 150°C in the direction of the main alignment axis of the film and the direction at right angles to it. In the measurement of the film expansion rate during the process, the film expansion rate at 150°C was 0.5% or more and 1.5% or less, respectively.

Japanese Patent Application Laid-Open No. 2002-361736 discloses a biaxially stretched polyester film for hard coating, in which the thermal expansion rate in the width direction relative to 30°C at 50°C to 100°C is -0.5% to 0.5 %, and satisfies the following formulas 1 to 2. In the following formulas 1 to 2, R is the film thickness, and ΔR is the film thickness deviation. 10μm＜R＜500μm……Formula 1 ΔR/R＜0.05……Formula 2

Japanese Patent Application Laid-Open No. 2017-127980 discloses a polyester film which is used by being bonded to a transparent conductive substrate containing an amorphous resin. The polyester film has a temperature of 150°C in the MD and TD directions. The thermal shrinkage rate, the coefficient of linear expansion from 50°C to 150°C, and the film haze after the heat treatment for 30 minutes are within a specific range.

Japanese Patent Application Laid-Open No. 2008-265318 discloses a biaxially oriented polyester film for flexible display substrates. Among them, in a biaxially oriented polyester film containing polyethylene naphthalate as the main component, The film thickness is 12-50μm, the heat shrinkage rate at 200℃×10 minutes is -0.1% or more and 0.1% or less in the longitudinal direction and width direction of the film, and every 1m×3m, the film surface wrinkles and wrinkles The number is 0 or more and 5 or less.

A biaxially oriented polyester film (hereinafter, also simply referred to as a "film") may sometimes be used as a film base material for various functional films. For example, a functional film can be manufactured by forming a functional layer (for example, a decorative layer) corresponding to a purpose on a biaxially oriented polyester film. The functional layer is usually formed by coating a liquid composition (for example, a coating liquid) on a biaxially aligned polyester film.

However, for example, if the biaxially aligned polyester film is heated during the formation process of the functional layer (for example, heat drying), streak-shaped defect regions may sometimes be generated. "Stripe defects" are wrinkles that extend in stripes along the longitudinal direction of the film and appear as unevenness in the width direction of the film, and mean wrinkles that are inevitably generated. The streak defects are not generated during the heat treatment during the film production, but are derived from wave-shaped wrinkles generated during the heat treatment of the pre-manufactured film. The wave-shaped wrinkles are solidified by cooling after the heat treatment. In addition, the "stripe defect area" refers to a streak defect locally generated in the film surface. If a stripe-shaped defect area is generated (that is, a stripe-shaped defect is locally generated in the film surface), for example, it may affect the characteristics or appearance of the functional layer formed on the film. Furthermore, the streak-shaped defect region tends to be remarkably generated when heated in a state where a tensile load is applied in the longitudinal direction of the film.

This disclosure was completed in view of the above-mentioned circumstances. An object of one embodiment of the present disclosure is to provide a biaxially aligned polyester film capable of suppressing the generation of streak-shaped defect regions caused by heating.

The following aspects are included in the solution for solving the above-mentioned problems. <1> A biaxially oriented polyester film in which the expansion rate in the width direction at 90° C. and 120° C. is 0% to 0.15% with respect to the size in the width direction at 30° C. <2> The biaxially oriented polyester film as described in <1>, wherein the number of stripe-shaped defect regions generated when heated at at least one of 90°C and 120°C is less than 3/m ² . <3> The biaxially aligned polyester film as described in <1> or <2>, wherein at least one surface has a plurality of protrusions. <4> The biaxially oriented polyester film according to any one of <1> to <3>, which has: a polyester film substrate; and at least one surface of the polyester film substrate contains average particles A layer of particles with a diameter of 0.01 μm to 0.4 μm and a plurality of protrusions on the surface. <5> The biaxially aligned polyester film as described in <3> or <4>, wherein the average height of the plurality of protrusions is 10 nm to 300 nm. <6> The biaxially oriented polyester film according to any one of <3> to <5>, wherein the density of the plurality of protrusions is 60 pcs/mm ² to 110 pcs/mm ² . <7> The biaxially oriented polyester film as described in any one of <1> to <6>, wherein the number of stripe-shaped defect regions generated when heated at 90°C is less than 3/m ² , and the number of stripe-shaped defect areas generated under heating at 120°C is less than 7/m ² , or the number of stripe-shaped defect areas generated under heating at 90°C is less than 7 pieces/m ² , and the number of stripe-shaped defect regions produced when heated at 120°C is less than 3 pieces/m ² . <8> The biaxially oriented polyester film according to any one of <1> to <7>, wherein the number of stripe-shaped defect regions generated when heated at 90°C and 120°C is less than 3 pieces/m ² . <9> The biaxially oriented polyester film according to any one of <1> to <8>, in which the average particle diameter is contained in the region from at least one surface to 5% of the film thickness in the thickness direction 0.01μm～0.4μm particles. <10> The biaxially oriented polyester film according to any one of <1> to <9>, wherein the haze is 0.5% or less. <11> The biaxially oriented polyester film according to any one of <1> to <10>, wherein the b ^{* value in the L*} a ^* b ^* color system is 0 to 0.6. <12> The biaxially aligned polyester film according to any one of <1> to <11>, wherein the surface roughness Ra of at least one surface is 1 nm to 10 nm. [Effects of the invention]

According to an embodiment of the present disclosure, there is provided a biaxially aligned polyester film capable of suppressing the generation of streak-shaped defect regions caused by heating.

Hereinafter, an embodiment of the present disclosure will be described in detail. In addition, the present disclosure is not limited by the following embodiments at all, and can be implemented with appropriate changes within the scope of the purpose of the present disclosure.

In the present disclosure, the numerical range indicated by "-" refers to a range that includes the numerical values described before and after "-" as the lower limit and the upper limit. In the numerical range described in the present disclosure, the upper limit or the lower limit in a certain numerical range can be replaced with the upper limit or the lower limit of the numerical range described in other steps. In addition, in the numerical range described in this disclosure, the upper limit or lower limit described in a certain numerical range can be replaced with the values shown in the examples. In the present disclosure, when there are multiple substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition. In the present disclosure, the term "process" not only includes an independent process, but even under the circumstances that it cannot be clearly distinguished from other processes, the intended purpose of the process is also included in this term. In the present disclosure, "mass %" and "weight%" have the same meaning, and "mass part" and "weight part" have the same meaning. In the present disclosure, a combination of two or more preferable aspects is a more preferable aspect.

＜Biaxially oriented polyester film＞ In the biaxially oriented polyester film of the present disclosure, the expansion rate in the width direction at 90°C and 120°C is 0% to 0.15% with respect to the size in the width direction at 30°C.

The biaxially aligned polyester film of the present disclosure can suppress the occurrence of streak-shaped defect regions caused by heating by having the above-mentioned structure. The reason why the biaxially oriented polyester film of the present disclosure exerts the above effects is not clear, but it is estimated as follows. The conventional biaxially oriented polyester film cannot sufficiently suppress the expansion in the width direction during heating, and therefore it is considered that it is difficult to sufficiently suppress the occurrence of streak-shaped defect regions caused by heating. In addition, in the polyester film used by being bonded to a transparent conductive substrate containing an amorphous resin (see Japanese Patent Application Laid-Open No. 2017-127980), it is necessary to show a certain change with respect to heat for the above-mentioned use (that is, , Expansion), so it is considered difficult to sufficiently suppress the generation of streak-shaped defect regions caused by heating. On the other hand, in the biaxially oriented polyester film of the present disclosure, relative to the size in the width direction at 30°C, the expansion rate in the width direction at 90°C and 120°C is adjusted to 0% to 0.15%, respectively As a result, not only can the expansion in the width direction during heating be suppressed, but also the unevenness of the expansion rate of each part of the film surface can be reduced. Therefore, it is presumed that the biaxially aligned polyester film of the present disclosure can suppress the generation of streak-shaped defect regions caused by heating.

In the present disclosure, "two-axis alignment" refers to the property of having molecular alignment in the two-axis direction. The molecular alignment is measured using a microwave transmission type molecular alignment instrument (for example, MOA-6004, manufactured by Oji Scientific Instruments). The angle formed by the two-axis directions is preferably 90°±5°, more preferably 90°±3°, and particularly preferably 90°±1°. The biaxially aligned polyester film of the present disclosure preferably has molecular alignment in the longitudinal direction and the width direction.

In this disclosure, the "width direction" refers to a direction orthogonal to the longitudinal direction. In addition, when the width direction is not clear, the direction with the strongest degree of alignment among the degree of alignment measured with a microwave transmission molecular aligner (for example, MOA-6004, manufactured by Oji Scientific Instruments) is set as the width direction.

In the present disclosure, the term "orthogonal" is not limited to strictly orthogonal, and includes substantially orthogonal. "Approximately orthogonal" means to intersect at 90°±5°, preferably at 90°±3°, and more preferably at 90°±1°.

[Polyester] The biaxially aligned polyester film of the present disclosure is a biaxially aligned film containing polyester as the main polymer component. Here, the "main polymer component" refers to the polymer with the largest content (% by mass) among all the polymers contained in the film.

Polyester is a polymer having an ester bond in the main chain. Polyester is usually formed by polycondensing a dicarboxylic acid compound and a diol compound described later.

The polyester is not limited, and a known polyester can be used. Examples of polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN). Among the above, polyester-based polyethylene terephthalate is preferred. That is, the biaxially oriented polyester film of the present disclosure is preferably a biaxially oriented polyethylene terephthalate film.

The biaxially oriented polyester film of the present disclosure may contain one type of polyester alone, or may contain two or more types of polyester.

Relative to the total mass of the polymer in the biaxially oriented polyester film, the polyester content is preferably 85% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, and 98% by mass or more It is especially good. The upper limit of the content of the polyester is not limited, and it can be appropriately set within the range of 100% by mass or less with respect to the total mass of the polymer in the biaxially oriented polyester film, for example.

Relative to the total mass of the biaxially oriented polyester film, the content of polyester is preferably 85% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 98% by mass or more. The upper limit of the content of the polyester is not limited, and can be appropriately set within a range of 100% by mass or less with respect to the total mass of the biaxially oriented polyester film.

In the case where the biaxially oriented polyester film of the present disclosure contains polyethylene terephthalate, the content of polyethylene terephthalate is 90 mass relative to the total mass of polyester in the biaxially oriented polyester film % To 100% by mass is more preferable, 95% to 100% by mass is more preferable, 98% to 100% by mass is still more preferable, and 100% by mass is particularly preferable.

(Method of manufacturing polyester) As a manufacturing method of polyester, there is no restriction|limiting, A well-known method can be utilized. For example, polyester can be produced by polycondensing at least one dicarboxylic acid compound and at least one diol compound in the presence of a catalyst.

-catalyst- The catalyst is not limited, and a known catalyst that can be used for the synthesis of polyester can be used.

Examples of the catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, and phosphorus compounds. Among the above, from the viewpoint of catalyst activity and cost, a catalyst-based titanium compound is preferable.

As the titanium compound, an organic chelated titanium complex is preferable. Organic chelated titanium complexes are titanium compounds with organic acids as ligands.

Examples of organic acids include citric acid, lactic acid, trimellitic acid, and malic acid.

As the titanium compound, the titanium compound described in paragraphs 0049 to 0053 of Japanese Patent No. 5557671 can also be used. The records in the above-mentioned bulletin are incorporated into this specification by reference.

-Dicarboxylic acid compound- Examples of the dicarboxylic acid compound include aliphatic dicarboxylic acid compounds, alicyclic dicarboxylic acid compounds, and aromatic dicarboxylic acid compounds.

As the aliphatic dicarboxylic acid compound, for example, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosane Diacid, pimelic acid, azelaic acid, methylmalonic acid and ethylmalonic acid.

As an alicyclic dicarboxylic acid compound, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, and decahydronaphthalene dicarboxylic acid are mentioned, for example.

As the aromatic dicarboxylic acid compound, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6- Naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 4,4'-diphenyl dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, isophthalic acid 5-sodium sulfonate, phenyl Indane dicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid and 9,9'-bis(4-dicarboxyphenyl) benzoic acid.

-Diol compound- Examples of the diol compound include aliphatic diol compounds, alicyclic diol compounds, and aromatic diol compounds.

Examples of the aliphatic diol compound include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol alcohol.

As an alicyclic diol compound, cyclohexanedimethanol, spirodiol, and isosorbide are mentioned, for example.

As the aromatic diol compound, for example, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9'-bis(4-hydroxyphenyl)sulfuron may be mentioned.

-Capping agent- In the manufacture of polyester, end-capping agents can be used as needed. By using an end-capping agent, a structure derived from the end-capping agent is introduced into the end of the polyester.

The blocking agent is not limited, and a known blocking agent can be used. Examples of the blocking agent include azoline compounds, carbodiimide compounds, and epoxy compounds.

Specific examples of the blocking agent are described in paragraphs 0055 to 0064 of JP 2014-189002 A. The records in the above-mentioned bulletin are incorporated into this specification by reference.

-Manufacturing conditions- The reaction temperature is not limited and may be appropriately set according to the raw materials. The reaction temperature is preferably 260°C to 300°C, more preferably 275°C to 285°C.

The pressure is not limited, and it can be set appropriately according to the raw material. The pressure is preferably from 1.33×10 ^-3 MPa to 1.33×10 ^-5 MPa, and more preferably from 6.67×10 ^-4 MPa to 6.67×10 ^-5 MPa.

As a method for synthesizing polyester, the method described in paragraphs 0033 to 0070 of Japanese Patent No. 5557671 can also be used. The records in the above-mentioned bulletin are incorporated into this specification by reference.

[Expansion rate] In the biaxially oriented polyester film of the present disclosure, relative to the size in the width direction at 30° C., the expansion ratios in the width direction at 90° C. and 120° C. are 0% to 0.15%, respectively. The expansion ratios in the width direction at 90°C and 120°C are respectively 0% to 0.15%, which can suppress the occurrence of streak-shaped defect regions due to heating. For the same reason, relative to the dimensions in the width direction at 30°C, the expansion ratios in the width direction at 90°C and 120°C, respectively, are preferably 0% to 0.10%, and more preferably 0% to 0.08%. 0%～0.04% is particularly good. In addition, the term "dimension in the width direction relative to the 30°C condition" used in relation to the expansion rate refers to the size used as a reference in the measurement of the expansion rate in the width direction at each temperature of 90°C and 120°C, which will be described later. "Dimensions in the width direction at 30°C".

The expansion coefficient in the width direction at each temperature of 90°C and 120°C was measured by the following method using a thermomechanical analyzer. (1) Prepare to be adjusted to be at least 20mm (length) in the direction parallel to the width direction of the biaxially oriented polyester film and 4mm (width) in the direction orthogonal to the width direction of the biaxially oriented polyester film Sample size. (2) Using a thermomechanical analysis device (for example, TMA-60, manufactured by SHIMADZU CORPORATION), a tensile load (0.1 g) is applied to a sample with a width of 4 mm and a length (pitch between chucks) of 20 mm. Regarding the tensile load, it is applied in the longitudinal direction of the sample. (3) The above-mentioned sample is heated from a temperature above 20°C and less than 30°C (preferably 25°C) to 150°C at a temperature rise rate of 5°C/min, thereby obtaining the temperature of the sample at each temperature (°C) The value of the size. (4) Based on the size of the sample at 30°C (L30), the size at 90°C (L90), and the size at 120°C (L120), use the following formula to find each of 90°C and 120°C The rate of expansion in the width direction at temperature. In the present disclosure, the expansion rates in the width direction under the conditions of 90°C and 120°C are respectively set as the arithmetic averages of the expansion rates obtained using 5 samples. In addition, a positive expansion rate refers to expansion, and a negative expansion rate refers to contraction. Formula: Expansion rate (%)=[(L120 or L90)-L30]/L30×100

The ratio (E120/E90) of the expansion ratio in the width direction (E120) at 120°C to the expansion ratio (E90) in the width direction at 90°C (E120/E90) is preferably 0 to 1.5, more preferably 0 to 1.1, 0 ~1.05 is particularly good. With E120/E90 in the above range, the occurrence of streak-shaped defect regions can be further suppressed. The expansion coefficient in the width direction (E90) under the condition of 90°C and the expansion coefficient (E120) in the width direction under the condition of 120°C were respectively obtained by the method using the aforementioned thermomechanical analysis device.

In the biaxially oriented polyester film of the present disclosure, the expansion ratio in the width direction can be adjusted by appropriately setting the stretching ratio, heat treatment temperature, and rail width during cooling during the manufacturing process of the biaxially oriented polyester film, for example.

[Number of streak defect regions] In the biaxially oriented polyester film of the present disclosure, the number of streak defect regions generated when heated at at least one of 90°C and 120°C is less than 3 /m ² is preferable, less than 2 pieces/m ² is more preferable, less than 1 pieces/m ² is more preferable, and less than 0.8 pieces/m ² is particularly preferable. By heating at at least one of 90°C and 120°C, the number of stripe-shaped defect regions is less than 3/m ² , for example, it is possible to suppress the characteristics of the functional layer formed on the film The occurrence of decline or poor appearance. For example, in the case of forming a decoration layer on the film, it is possible to suppress the color unevenness of the decoration layer.

In the biaxially oriented polyester film of the present disclosure, the number of stripe-shaped defect regions generated when heated at 90°C is less than 3/m ² , and it is generated when heated at 120°C The number of stripe-shaped defect areas is less than 7/m ² , or the number of stripe-shaped defect areas generated when heated at 90°C is less than 7/m ² , and heating is performed at 120°C In this case, it is preferable that the number of stripe-shaped defect regions generated is less than 3/m ^2.

In the biaxially oriented polyester film of the present disclosure, the number of stripe-shaped defect regions generated under heating at 90°C and 120°C ^{is preferably less than 3/m 2} and less than 2/m 2 ² is better.

In the above, the number of stripe-shaped defect regions generated when heated at 90°C is less than 2/m ² , and the number of striped defect regions generated when heated at 120°C Less than 3/m ² is preferable, the number of stripe-shaped defect areas generated when heated at 90°C is less than 1/m ² , and the number of stripes generated when heated at 120°C The number of stripe-shaped defect regions is less than 2/m ² is more preferably, the number of stripe-shaped defect regions generated when heating at 90°C is less than 0.8/m ² , and heating is performed at 120°C In this case, it is particularly preferable that the number of stripe-shaped defect regions generated is less than 1.8/m ^2. When the number of stripe-shaped defect regions generated when heating is performed at each temperature of 90°C and 120°C is within the above-mentioned range, the generation of stripe-shaped defect regions due to heating can be further suppressed.

The number of stripe-shaped defect regions generated when heating is performed at each temperature of 90°C and 120°C is measured by the following method. (1) While using a heating conveyor, the biaxially oriented polyester film is conveyed at a conveying speed of 30 m/min and a tension of 100 N/m while heating treatment at 90°C or 120°C for 20 seconds. The heating temperature in the heat treatment refers to the surface temperature of the film. The heating time in the heat treatment is calculated from the point when the surface temperature of the film reaches the target temperature (90°C or 120°C). (2) Place the heat-treated biaxially oriented polyester film on a flat surface, and then change the viewpoint to make the fluorescent lamp installed on the indoor ceiling (for example, Lupica Ace manufactured by Mitsubishi Electric Corporation (color temperature: 5000K) , Average color rendering evaluation number (Ra): 84)] The biaxially oriented polyester film was observed with the naked eye from the oblique direction on the light reflection side. The area where the reflected image of the fluorescent lamp reflected on the surface of the biaxially oriented polyester film was observed by the naked eye was curved as a stripe-shaped defect area. (3) Calculate the number of striped defect areas ^{per 1m 2 (pieces/m 2} ) by counting the striped defect areas observed.

[Protrusion] In the biaxially aligned polyester film of the present disclosure, it is preferable to have a plurality of protrusions (hereinafter, also simply referred to as “protrusions”) on at least one surface. Since the film has a plurality of protrusions, the winding quality of the film can be improved. Here, "winding quality" refers to the flatness of the film surface wound into a roll. An example of a specific evaluation of the winding quality will be described in Examples described later.

The shape of the protrusion is not limited. As the shape of the protrusion observed when the film surface is viewed from the top, for example, a triangle, a quadrilateral, a polygon with more than quadrilateral, a circle, an ellipse, and an irregular shape can be given.

The average height of the protrusions is preferably 10 nm to 300 nm, more preferably 50 nm to 250 nm, and particularly preferably 100 nm to 180 nm. When the average height of the protrusions is 10 nm or more, the winding quality of the film can be improved. Since the average height of the protrusions is 300 nm or less, the occurrence of transfer failure can be suppressed. Here, "transfer failure" refers to the formation of irregularities on the surface of other members by contact with the film. An example of the specific evaluation of the transfer failure will be described in Examples described later.

The average height of the protrusions is calculated by the following method. Using an optical interferometer (for example, NewView5020 manufactured by Zygo Corporation), the range of 1.07 mm×1.42 mm of the film is measured. Then, use data analysis software (for example, NewView5020 data analysis software: MetroPro 8.1.3) to measure the average height of the protrusions within the above range. In the present disclosure, the above operation is performed within 5 ranges (1.07 mm×1.42 mm of the film), and the arithmetic average of the measured values is set as the average height of the protrusions.

60 based Density protrusions / mm ² ~ 110 pieces / mm ² is preferred, 70 / mm ² ~ 100 / mm ² or more preferably of, 80 / mm ² ~ 100 pieces / mm ² is particularly preferred. When the density of the protrusions is 60/mm ² or more, the winding quality of the film can be improved. When the density of the protrusions is 110/mm ² or less, the haze can be reduced.

The density of protrusions is measured by the following method. Using an optical interferometer (for example, NewView5020 manufactured by Zygo Corporation), the range of 1.07 mm×1.42 mm of the film is measured. Then, use data analysis software (for example, NewView5020 data analysis software: MetroPro 8.1.3) to calculate the density of protrusions (pieces/mm ² ) within the above range. In the present disclosure, the above operation is performed in 5 ranges (1.07 mm×1.42 mm of the film), and the arithmetic average of the measured values is set as the density of the protrusions.

The method of forming the protrusion is not limited, and a known method can be used. As a method of forming the protrusions, a method of processing the surface of the film (for example, embossing), and a method of arranging particles described later in the vicinity of the surface of the film can be cited.

[Haze] The haze of the biaxially aligned polyester film of the present disclosure is preferably 3% or less, more preferably 1% or less, more preferably 0.5% or less, and particularly preferably 0.4% or less. When the haze is 3% or less, the transparency of the film can be improved. The smaller the haze, the better, so the lower limit of the haze is not limited. If the lower limit of the haze is set for convenience, it is 0% or more.

For the haze, use a haze meter (for example, NDH-2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.), and measure it by a method in accordance with JIS K 7105.

[b ^* values] L ^* a ^* b ^* color system based in the b ^* value is preferably 0 to 1, is more preferably 0 to 0.8, further preferably 0 to 0.6, 0 to 0.4 is particularly preferred. With the value of b ^{* in the L*} a ^* b ^* color system from 0 to 1, the yellowness of the film can be reduced, and therefore the hue of the film can be made close to colorless. As a result, for example, in applications requiring high visibility (for example, display devices), the biaxially aligned polyester film of the present disclosure can be preferably applied.

For the b ^{* value in the L*} a ^* b ^* color system, use a spectrophotometer (for example, SE-2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.), and measure it by the transmission method.

[Surface roughness Ra] From the viewpoint of improving the winding quality of the film and suppressing the occurrence of transfer failure, the surface roughness Ra of at least one surface of the biaxially oriented polyester film of the present disclosure is preferably 1 nm to 10 nm, and more preferably 1 nm to 8 nm. Preferably, 1nm～6nm is particularly preferred.

The surface roughness Ra is measured by the following method. Using an optical interferometer (for example, NewView5020 manufactured by Zygo Corporation), the range of 1.07 mm×1.42 mm of the film is measured. Then, use data analysis software (for example, NewView5020 data analysis software: MetroPro 8.1.3) to calculate the surface roughness Ra within the above range. In the present disclosure, the above operation is performed in 5 ranges (1.07 mm×1.42 mm of the film), and the arithmetic average of the measured values is set as the surface roughness Ra.

[particle] The biaxially aligned polyester film of the present disclosure preferably contains particles in a region from at least one surface to 5% of the film thickness in the thickness direction. When the film contains particles in the above-mentioned region, the winding quality of the film can be improved.

In the present disclosure, the "film thickness" refers to the thickness of the biaxially oriented polyester film (in the case where the biaxially oriented polyester film includes a plurality of layers, it refers to the total thickness of each layer. The following is the same.).

In the present disclosure, the term "containing particles in a region" is not limited to the presence of particles in the entire designated region, but also includes the presence of particles in at least a part of the designated region. For example, when the film contains particles in a region from the surface to 5% of the film thickness in the thickness direction, particles may be present in the entire region from the surface to 5% of the film thickness in the thickness direction, or The particles may be present in a region closer to the surface (for example, the region from the surface to 1% of the film thickness in the thickness direction).

The biaxially oriented polyester film of the present disclosure preferably contains particles in a region from at least one surface to 1% of the film thickness in the thickness direction, and from at least one surface to 0.5% of the film thickness in the thickness direction. It is more preferable to contain particles in the region of, and it is particularly preferable to contain particles in the region from at least one surface to 0.2% of the film thickness in the thickness direction.

Examples of particles include organic particles and inorganic particles. Among the above, from the viewpoints of film winding quality, haze, and durability (for example, thermal stability), particle-based inorganic particles are preferable.

As the organic particles, resin particles are preferred. Examples of resin particles include acrylic resin particles, polyester resin particles, silicone resin particles, styrene resin particles, and styrene-acrylic resin particles. The resin particles preferably have a cross-linked structure.

Examples of the inorganic particles include silicon dioxide particles, titanium dioxide particles (titanium oxide particles), calcium carbonate, barium sulfate, and aluminum oxide particles. Among the above, from the viewpoint of haze and durability, inorganic particle-based silica particles are preferred.

The silica particles are not limited, and well-known silica particles can be used. Examples of silica particles include vapor-phase silica and colloidal silica.

The gas phase silicon dioxide particles can be obtained, for example, by reacting a compound containing silicon atoms with oxygen and hydrogen in the gas phase. As the silicon compound used as the raw material, for example, silicon halide (for example, silicon chloride) can be cited. The vapor-phase silica particles are usually agglomerated particles, for example, AEROSIL OX50 can be cited.

The colloidal silica particles can be synthesized by, for example, a sol-gel method in which raw material compounds are hydrolyzed and condensed. As the raw material compound of colloidal silica, for example, silicon alkoxide (for example, tetraethoxysilane) and silane halide compound (for example, diphenyldichlorosilane) can be mentioned. The colloidal silica particles are usually primary particles, and for example, the SNOWTEX series manufactured by Nissan Chemical Corporation can be cited.

The form of the silicon dioxide particles may be primary particles, or may be an agglomerate of primary particles (that is, agglomerated silicon dioxide particles). As described later, the average particle size of primary particles and aggregates can be measured using scanning electron microscope (SEM) images. In addition, the average primary particle size of the aggregate can be measured by observation using a transmission electron microscope (TEM) when the particles are too small to be measured during observation using a scanning electron microscope (SEM).

The average particle size of the particles is preferably 0.01 μm or more, more preferably 0.04 μm or more, more preferably 0.1 μm or more, and particularly preferably 0.2 μm or more. When the average particle diameter of the particles is 0.01 μm or more, the winding quality of the film can be improved. The average particle diameter of the particles is preferably 0.4 μm or less, and more preferably 0.3 μm or less. Since the average particle diameter of the particles is 0.4 μm or less, the occurrence of transfer failure can be suppressed.

The average primary particle size of the particles is preferably 0.4 μm or less, more preferably 0.2 μm or less, more preferably 0.1 μm or less, and particularly preferably 0.05 μm or less. Since the average primary particle size of the particles is 0.4 μm or less, the occurrence of transfer failure can be suppressed. The average primary particle size of the particles is preferably 0.01 μm or more, and more preferably 0.03 μm or more. When the average primary particle diameter of the particles is 0.01 μm or more, the winding quality of the film can be improved.

The average particle size of the particles is determined by arithmetically average the particle sizes of 50 particles arbitrarily selected from scanning electron microscope (SEM) images. For example, by observing the particle-containing surface of the film by SEM, the arithmetic average of 50 particle diameters arbitrarily selected from the obtained image data is calculated and set as the average particle diameter. For the measurement of the primary particle size of the particles, the "particle size" is replaced with the "primary particle size".

The biaxially oriented polyester film of the present disclosure may contain one kind of particles alone, or may contain two or more kinds of particles.

From the viewpoint of improving film winding quality and suppressing transfer failure, relative to the total mass of the biaxially aligned polyester film, the content of particles is preferably 0.0001% to 0.01% by mass, and 0.0005% to 0.005% by mass. % Is more preferable, and 0.0008 mass% to 0.004 mass% is particularly preferable.

[thickness] From the viewpoint of handling suitability (especially handling suitability when laminating films), the thickness of the biaxially oriented polyester film of the present disclosure is preferably 10 μm to 100 μm, more preferably 10 μm to 50 μm, and 12 μm to 40 μm. good. The thickness of the biaxially aligned polyester film is set as the arithmetic average of the thicknesses of 5 locations measured by a scanning electron microscope (SEM).

[Layered structure] The biaxially aligned polyester film of the present disclosure may have a single-layer structure or may have a laminated structure. The biaxially aligned polyester film of the present disclosure has a polyester film substrate and a layer containing particles on at least one surface of the polyester film substrate and having a plurality of protrusions on the surface (hereinafter, also referred to as "coating layer" ".) is better. Since the film has a coating layer, the winding quality of the film can be improved.

-Polyester film substrate- The polyester film substrate is a film substrate containing polyester. As the polyester in the polyester film base material, the polyester described in the above "polyester" item can be applied, and the preferred types are also the same.

The polyester film substrate may contain one type of polyester alone, or may contain two or more types of polyester.

Relative to the total mass of the polyester film substrate, the content of polyester is preferably 85% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 98% by mass or more. The upper limit of the content of the polyester is not limited, and can be appropriately set within the range of 100% by mass or less with respect to the total mass of the polyester film base material, for example.

In the case where the polyester film base material contains polyethylene terephthalate, the content of the polyethylene terephthalate is 90% to 100% by mass relative to the total mass of the polyester in the polyester film base material More preferably, 95% by mass to 100% by mass is more preferable, 98% by mass to 100% by mass is still more preferable, and 100% by mass is particularly preferable.

From the viewpoint of handling suitability (especially handling suitability when laminating films), the thickness of the polyester substrate is preferably from 10 μm to 100 μm, more preferably from 10 μm to 50 μm, and particularly preferably from 20 μm to 40 μm. The thickness of the polyester substrate is set as the arithmetic average of the thicknesses of 5 locations measured by a scanning electron microscope (SEM).

-Cover layer- As the particles in the coating layer, the particles described in the item of "particles" above can be applied, and the preferred types are also the same.

The average particle diameter of the particles in the coating layer is preferably 0.01 μm or more, more preferably 0.04 μm or more, more preferably 0.1 μm or more, and particularly preferably 0.2 μm or more. When the average particle diameter of the particles is 0.01 μm or more, the winding quality of the film can be improved. The average particle diameter of the particles in the coating layer is preferably 0.4 μm or less, and more preferably 0.3 μm or less. Since the average particle diameter of the particles is 0.4 μm or less, the occurrence of transfer failure can be suppressed.

The average primary particle size of the particles in the coating layer is preferably 0.4 μm or less, more preferably 0.2 μm or less, more preferably 0.1 μm or less, and particularly preferably 0.05 μm or less. Since the average primary particle size of the particles is 0.4 μm or less, the occurrence of transfer failure can be suppressed. The average primary particle size of the particles in the coating layer is preferably 0.01 μm or more, and more preferably 0.03 μm or more. When the average primary particle diameter of the particles is 0.01 μm or more, the winding quality of the film can be improved.

The average particle diameter and the average primary particle diameter of the particles in the coating layer are measured by the method in accordance with the method of measuring the average particle diameter and the average primary particle diameter described in the item "Particles" above.

The coating layer may contain one kind of particles alone, or may contain two or more kinds of particles.

From the viewpoint of improving film winding quality and suppressing transfer failure, relative to the total mass of the coating layer, the content of particles is preferably 0.01% to 15% by mass, and more preferably 0.1% to 10% by mass. Preferably, 0.5% by mass to 6% by mass is particularly good.

The coating layer preferably contains a binder. As the binder, a resin binder is preferred. Examples of the resin binder include polyacrylic acid, polyurethane, polyester, and polyolefin.

The polyacrylic acid is not limited as long as it has a structural unit derived from at least one compound selected from the group consisting of acrylate and methacrylate, and known polyacrylic acid can be used. Polyacrylic acid may have structural units derived from compounds other than acrylate and methacrylate (for example, olefin compounds and styrene compounds).

The polyurethane is not limited as long as it is a polymer having a urethane bond, and a known polyurethane can be used. Polyurethane is usually produced by reacting an isocyanate compound and a polyol compound.

As the polyester, the polyester described in the above "polyester" item can be applied, and the preferred types are also the same.

The polyolefin is not limited, and known polyolefins can be used. Examples of polyolefins include polyethylene and polypropylene.

The coating layer may contain one type of adhesive alone, or may contain two or more types of adhesives.

From the viewpoint of the durability of the coating layer and the dispersibility of particles, relative to the total mass of the coating layer, the content of the binder is preferably 30% to 80% by mass, and 40% to 70% by mass is More preferably, 45% by mass to 65% by mass is particularly preferred.

The embodiment of the plurality of protrusions in the coating layer is the same as the embodiment of the protrusions described in the item of "protrusion" above, and the preferred embodiment is also the same.

From the viewpoint of manufacturing suitability of the coating layer and imparting transparency, the thickness of the coating layer is preferably 0.01 μm to 0.3 μm, more preferably 0.02 μm to 0.1 μm, and particularly preferably 0.02 μm to 0.06 μm. The thickness of the coating layer is set as the arithmetic average of the thickness of 5 parts of the cross-sectional slice orthogonal to the surface of the coating layer measured by a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

As a method of forming a coating layer, for example, a method of using a coating liquid for forming a coating layer is exemplified. For example, the coating layer can be formed by applying a coating liquid for forming a coating layer on a polyester film base material and drying as necessary. As a method of forming the coating layer, it can also be formed by co-extrusion of different materials, but from the viewpoint of making it into a film of 0.3 μm or less, it is preferable to use a coating liquid.

The coating liquid for forming a coating layer can be prepared, for example, by mixing the above-mentioned components and a solvent. Examples of the solvent include water, hexane, acetone, ethanol, tetrahydrofuran, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether. Among the above, from the viewpoints of environment, safety, and economy, solvent-based water is preferable.

The coating liquid for forming a coating layer may contain a single type of solvent, or may contain two or more types of solvents.

Relative to the total mass of the coating liquid for forming a coating layer, the content of the solvent is preferably 80% to 99% by mass, and more preferably 90% to 98% by mass.

The coating method is not limited, and a known method can be used. As the coating method, for example, a spray coating method, a slit coating method, a roll coating method, a knife coating method, a spin coating method, a bar coating method, and a dip coating method can be cited.

In the case of forming the coating layer using the coating liquid for forming the coating layer, the polyester film substrate coated with the coating liquid for forming the coating layer may be an unstretched film or a uniaxially stretched film , Or it can be a biaxially stretched film. From the viewpoint of the adhesiveness of the polyester film substrate and the coating layer, the method of forming the coating layer is to coat the coating solution for forming the coating layer on the uniaxially stretched polyester film substrate. good. For example, after forming the coating layer by applying the coating solution for forming the coating layer on the uniaxially stretched polyester film substrate, the uniaxially stretched polyester film substrate and the coating layer are simultaneously stretched, by This can improve the adhesion of the polyester film base material and the coating layer. The specific method of stretching will be described later.

[Manufacturing method of biaxially aligned polyester film] As a manufacturing method of the biaxially oriented polyester film of this disclosure, for example, a method of biaxially stretching an unstretched polyester film obtained by an extrusion molding method can be cited.

The extrusion molding method is a method of molding the raw material resin into a desired shape by extruding the raw material resin using an extruder, for example.

The biaxial stretching may be simultaneous biaxial stretching of simultaneous longitudinal stretching and lateral stretching, or it may be sequential in which the longitudinal stretching and the lateral stretching are divided into two stages or more than two stages. Biaxial stretching. As an embodiment of the sequential biaxial stretching, for example, longitudinal stretching→lateral stretching, longitudinal stretching→lateral stretching→longitudinal stretching, longitudinal stretching→longitudinal stretching→lateral stretching, and lateral stretching can be mentioned. →Longitudinal stretch. Among the above, longitudinal stretching→lateral stretching is preferable.

The device used for biaxial stretching is not limited, and a known biaxial stretching machine can be used. Hereinafter, referring to the drawings, an example of the biaxial stretching machine will be described.

As shown in Fig. 1, the biaxial stretching machine 100 includes a pair of ring-shaped rails 60a and 60b and holding members 2a to 2l that are attached to each ring-shaped rail and can move along the rails. The ring guide rails 60a and 60b are arranged symmetrically with each other with the film 200 interposed therebetween. In the biaxial stretching machine 100, the film 200 can be stretched in the width direction by gripping the film 200 with the gripping members 2a to 2l and moving along the guide rail.

The biaxial stretching machine 100 has an area including a preheating part 10, a stretching part 20, a heat setting part 30, a heat relaxation part 40 and a cooling part 50.

The preheating part 10 is a region for preheating the film 200.

The stretched portion 20 is a region where tension is applied to the preheated film 200 and stretched in the direction of the arrow TD (the film width direction) that is orthogonal to the direction of the arrow MD (long-side direction). For example, as shown in FIG. 1, in the stretching section 20, the film 200 is stretched from the width L0 to the width L1.

The heat setting part 30 is a region for heat setting by heating in a state where the tension is applied to the film 200 to which the tension is applied.

The thermal relaxation part 40 is a region where the tension of the heat-set film 200 is thermally relaxed by heating the heat-set film 200.

The cooling part 50 is a region for cooling the thermally relaxed film 200. By cooling the film 200, the shape of the film 200 can be shaped. In FIG. 1, a film 200 having a width of L2 that has passed through the cooling part 50 is shown.

Holding members 2a, 2b, 2e, 2f, 2i, and 2j that can move along the ring rail 60a are attached to the ring rail 60a. Holding members 2c, 2d, 2g, 2h, 2k, and 21 that can move along the ring rail 60b are attached to the ring rail 60b.

The gripping members 2a, 2b, 2e, 2f, 2i, and 2j grip one end of the film 200 in the direction of the arrow TD. The gripping members 2c, 2d, 2g, 2h, 2k, and 21 grip the other end of the film 200 in the direction of the arrow TD. The gripping members 2a to 2l are generally called chucks, clips, and the like.

The gripping members 2a, 2b, 2e, 2f, 2i, and 2j move counterclockwise along the ring-shaped rail 60a. The gripping members 2c, 2d, 2g, 2h, 2k, and 21 move clockwise along the ring rail 60b.

The holding members 2a to 2d move along the ring-shaped rail 60a or 60b while holding the end of the film 200 in the preheating section 10, and advance through the stretching section 20, the heat setting section 30, and the thermal relaxation section 40 to be cooled.部50. Next, the gripping members 2a and 2b and the gripping members 2c and 2d release the film at the downstream end in the direction of the arrow MD of the cooling part 50 (for example, the grip release point P and the grip release point Q in FIG. 1) in the order in the conveying direction After the end of 200, it further moves along the ring-shaped rail 60a or 60b, and returns to the preheating part 10. In the above process, the film 200 moves in the direction of the arrow MD, thereby performing preheating in the preheating part 10, stretching in the stretching part 20, heat setting in the heat setting part 30, and heat setting in the heat relaxation part 40. The thermal relaxation and cooling in the cooling section 50 are performed, and transverse stretching is performed.

By adjusting the moving speed of the holding members 2a to 2l, the conveying speed of the film 200 can be adjusted. In addition, the gripping members 2a to 2l can each independently change the moving speed.

As described above, the biaxial stretching machine 100 is capable of stretching the film 200 in the direction of the arrow TD in the stretching section 20 in the transverse direction. On the other hand, the biaxial stretching machine 100 can also stretch the film 200 in the direction of the arrow MD by changing the moving speed of the holding members 2a to 2l. That is, the biaxial stretching machine 100 can also be used to perform simultaneous biaxial stretching.

In order to support the film 200, the biaxial stretching machine 100 may have other holding members (not shown) in addition to the holding members 2a to 2l.

Next, an example of the manufacturing method of the biaxially oriented polyester film of the present disclosure will be specifically described.

The manufacturing method of the biaxially aligned polyester film of the present disclosure preferably has the following process: a process of forming an unstretched polyester film by melt-extruding polyester (hereinafter, also referred to as "extrusion molding process"). ; A process of stretching the aforementioned unstretched polyester film along the longitudinal direction (hereinafter, also referred to as "longitudinal stretching process"); and stretching the polyester stretched along the aforementioned longitudinal direction along the width direction Film manufacturing process (hereinafter, also referred to as "transverse stretching process".).

(Extrusion molding process) In the extrusion molding process, an unstretched polyester film is formed by melt-extruding polyester.

As a method of melt extrusion, for example, a method using an extruder can be cited. For example, for melt extrusion, an extruder equipped with one or two or more screws is used to heat the polyester to a temperature above the melting point, and then rotate the screw to perform melting and kneading. The polyester is melted in the extruder by heating and screw-based mixing to become a melt (melt).

The melt is extruded from the extrusion die through a gear pump, a filter, etc. Extrusion die is also abbreviated as "die" [refer to JIS B8650: 2006, a) Extrusion molding machine, No. 134]. The melt can be extruded in a single layer, or can also be extruded in multiple layers.

In melt extrusion, from the viewpoint of suppressing pyrolysis in the extruder (for example, hydrolysis of polyester), it is preferable to replace the inside of the extruder with nitrogen. In addition, from the viewpoint of keeping the kneading temperature low, the extruder is preferably a two-screw extruder.

The melt extruded from the extrusion die is formed into a film shape by being cooled. For example, by bringing the melt into contact with a casting roll, and cooling and solidifying the melt on the casting roll, the melt can be formed into a film shape. In cooling the melt, it is preferable to further blow air (preferably cold air) to the melt.

The temperature of the casting roll exceeds (Tg-10℃) and below (Tg+30℃) is better, (Tg-7℃)～(Tg+20℃) is more preferably, (Tg-5℃)～(Tg+ 10℃) is particularly good. "Tg" is the glass transition temperature of polyester.

In the case of using a casting roll in the extrusion molding process, it is better to improve the adhesion between the casting roll and the melt. As a method of improving adhesion, for example, an electrostatic application method, an air knife method, an air chamber method, a vacuum nozzle method, and a touch roll method can be cited.

The molded body (unstretched polyester film) cooled using a casting roll or the like is peeled from a cooling member such as a casting roll using a peeling member such as a peeling roll.

(Biaxial stretching) -Longitudinal stretching process- In the longitudinal stretching process, the unstretched polyester film is stretched in the longitudinal direction (hereinafter, also referred to as "longitudinal stretching").

In the longitudinal stretching process, it is preferable to preheat the unstretched polyester film before the longitudinal stretching. By preheating the unstretched polyester film, the polyester film can be easily stretched in the longitudinal direction.

The preheating temperature range (Tg-10°C) ~ (Tg+60°C) is preferred, and (Tg°C) ~ (Tg+50°C) is more preferred. Specifically, the preheating temperature is preferably from 60°C to 100°C, and more preferably from 65°C to 80°C.

The longitudinal stretching can be performed by, for example, conveying the unstretched polyester film in the longitudinal direction while applying tension between two or more pairs of nip rollers provided in the conveying direction. For example, when a pair of nip rollers A are installed on the upstream side in the conveying direction and a pair of nip rollers B are installed on the downstream side in the conveying direction, the rotation speed of the nip roller B is higher than that when the unstretched polyester film is conveyed. The rotation speed of the roll A is fast, thereby stretching the unstretched polyester film in the longitudinal direction.

The stretching ratio in the longitudinal stretching process is preferably smaller than the stretching ratio in the lateral stretching process described later. The stretching ratio in the longitudinal stretching process is preferably 2.0 times to 5.0 times, more preferably 2.5 times to 4.0 times, and particularly preferably 2.8 times to 4.0 times.

The heating temperature in the longitudinal stretching process is (Tg-20℃)～(Tg+50℃) is better, (Tg-10℃)～(Tg+40℃) is more preferable, (Tg℃)～(Tg +30℃) is particularly good. Specifically, the heating temperature in the longitudinal stretching process is preferably 70°C to 120°C, more preferably 80°C to 110°C, and particularly preferably 85°C to 100°C.

As a method of heating the unstretched polyester film, a method of heating rolls such as nip rolls that are in contact with the unstretched polyester film can be cited. As a method of heating the roller, for example, a method of installing a heater or a pipe through which the heating solvent can flow inside the roller can be cited. In addition to the above, for example, a method of blowing hot air to an unstretched polyester film, a method of contacting a heat source such as a heater, and a method of heating the unstretched polyester film by passing the vicinity of the heat source.

The stretching speed in the longitudinal stretching process is preferably 800%/sec to 1,500%/sec, more preferably 1,000%/sec to 1,400%/sec, and particularly preferably 1,200%/sec to 1,400%/sec. Here, "stretching speed" refers to the value (Δd/d0) obtained by dividing the length Δd obtained by stretching the length d0 before stretching for 1 second by the length d0 before stretching in a percentage. .

-Horizontal stretching process- In the transverse stretching process, the polyester film is stretched in the width direction (hereinafter also referred to as "transverse stretch") along the above-mentioned longitudinal direction.

In the transverse stretching process, it is preferable to preheat the polyester film stretched along the longitudinal direction before the transverse stretching. By preheating the polyester film, the polyester film can be easily stretched in the transverse direction.

The preheating temperature range (Tg-10°C) ~ (Tg+60°C) is preferred, and (Tg°C) ~ (Tg+50°C) is more preferred. Specifically, the preheating temperature is preferably 80°C to 120°C, and more preferably 90°C to 110°C.

The stretching ratio in the transverse stretching process is better than the stretching ratio in the above-mentioned longitudinal stretching process. The stretching magnification in the transverse stretching process is preferably from 3.0 times to 6.0 times, more preferably from 3.5 times to 5.0 times, and particularly preferably from 3.5 times to 4.5 times.

The area magnification represented by the product of the stretching magnification in the longitudinal stretching process and the stretching magnification in the transverse stretching process is preferably 12.8 to 15.5 times, preferably 13.5 to 15.2 times, and 14.0 to 15.0 times It is especially good. If the area magnification is 12.8 times or more, the molecular alignment in the film width direction becomes good. In addition, if the area magnification is 15.5 times or less, it is easy to maintain a state in which the molecular alignment is not easy to relax when it is subjected to heat treatment.

The heating temperature in the transverse stretching process is (Tg-10℃)～(Tg+80℃) is better, (Tg℃)～(Tg+70℃) is more preferably, (Tg℃)～(Tg+60) ℃) is particularly good. Specifically, the heating temperature in the transverse stretching process is preferably 100°C to 140°C, more preferably 110°C to 135°C, and particularly preferably 115°C to 130°C.

The stretching speed in the transverse stretching process is preferably from 8%/sec to 45%/sec, more preferably from 10%/sec to 30%/sec, and particularly preferably from 15%/sec to 20%/sec.

In the case of manufacturing a biaxially oriented polyester film with a covering layer, it is preferable to apply the coating solution for forming the covering layer on the polyester film stretched in the longitudinal direction, and then to stretch it in the transverse direction. . The adhesion of the coating layer can be improved by the above method.

(Heat treatment process) The manufacturing method of the biaxially oriented polyester film of the present disclosure preferably has a process of heat-treating the polyester film stretched along the above-mentioned width direction (hereinafter, also referred to as "heating process"). As the heat treatment process, for example, a heat setting process and a thermal relaxation process can be cited. It is preferable that the heat treatment process has at least one of a heat setting process and a heat relaxation process, and it is more preferable to have a heat setting process and a heat relaxation process.

-Heat setting process- In the heat setting process, heat setting is performed by heating the polyester film stretched along the width direction. Since the polyester can be crystallized by heat setting, shrinkage of the polyester film can be suppressed.

The heating temperature in the heat setting process is preferably from 190°C to 240°C, more preferably from 200°C to 240°C, and particularly preferably from 210°C to 230°C.

In the heat setting process, the deviation of the maximum temperature of the film surface in the width direction of the film is preferably 0.5°C to 10.0°C, more preferably 0.5°C to 7.0°C, further preferably 0.5°C to 5.0°C, and 0.5°C to 0.5°C. 4.0°C is particularly good. By adjusting the deviation of the maximum reaching film surface temperature in the film width direction within the above range, the deviation of the crystallinity in the width direction can be suppressed.

As the heating method, for example, a method of blowing hot air to the film and a method of radiating heating the film can be cited. As the device used in the radiant heating method, for example, an infrared heater can be cited.

The heating time in the heat setting process is preferably from 5 seconds to 50 seconds, more preferably from 5 seconds to 30 seconds, and particularly preferably from 5 seconds to 10 seconds.

-Thermal relaxation process- In the thermal relaxation process, thermal relaxation is performed by heating the polyester film stretched in the above-mentioned width direction. The residual strain of the polyester film can be relaxed by thermal relaxation.

The heating temperature in the thermal relaxation process is preferably 5°C or more lower than the heating temperature in the heat setting process, a temperature lower than 15°C is more preferred, a temperature lower than 25°C is even more preferred, and a temperature lower than 30°C is more preferred. The temperature is particularly good.

The heating temperature in the thermal relaxation process is preferably 100°C or higher, more preferably 110°C or higher, and particularly preferably 120°C or higher.

As the heating method, for example, a method of blowing hot air on the film and a method of radiating heating on the film can be cited. As the device used in the radiant heating method, for example, an infrared heater can be cited.

(Cooling process) The manufacturing method of the biaxially aligned polyester film of the present disclosure preferably has a process of cooling the above-mentioned heat-treated polyester film (hereinafter, also referred to as "cooling process").

As the cooling method, for example, a method of blowing air (preferably cold air) to the film and a method of bringing the film into contact with a member capable of adjusting the temperature (for example, a temperature control roll).

The average cooling rate in the cooling process is preferably 500°C/minute to 4,000°C/minute, more preferably 1,000°C/minute to 3,500°C/minute, and particularly preferably 1,500°C/minute to 3,000°C/minute. By adjusting the average cooling rate within the above-mentioned range, the surface temperature of the film in the cooling process can be made uniform, and therefore, the unevenness of the expansion rate in the width direction can be reduced. The average cooling rate is obtained using a non-contact thermometer (for example, a radiation thermometer). For example, the cooling time (Z/S) from 150°C to 70°C is obtained based on the distance Z between the point where the surface temperature of the film becomes 150°C and the point where the surface temperature of the film becomes 70°C and the transport speed S of the film. Then, by calculating (150-70)/(Z/S), find the average cooling rate.

The biaxially aligned polyester film of the present disclosure can be applied to various applications. The biaxially oriented polyester film of the present disclosure can be used for, for example, a dry film photoresist support film, a green sheet molding support film in the manufacturing process of a multilayer ceramic capacitor, and other optical member films. [Example]

Hereinafter, the present disclosure will be described in detail through embodiments, but the present disclosure is not limited to these. In addition, unless otherwise specified, "parts" and "%" are quality standards.

<Example 1> [Extrusion molding] As a polymerization catalyst, a titanium compound (citric acid chelated titanium complex, VERTEC AC-420, manufactured by Johnson Matthey) described in Japanese Patent No. 5557671 was used as a polymerization catalyst. Drying is performed so that the moisture content of the particles is 50 ppm or less. The dried pellets were put into a hopper of a uniaxial kneading extruder with a diameter of 30 mm, and then melted and extruded at 280°C. After passing the melt (melt) through a filter (pore size: 3 μm), it was extruded from a die to a cooling roll at 25° C., thereby obtaining an unstretched film. In addition, the extruded melt (melt) is in close contact with the cooling roll using an electrostatic application method.

[Stretching and coating] The above-mentioned unstretched film was sequentially biaxially stretched by the following method. (A) Longitudinal stretching The unstretched film was stretched in the longitudinal direction (transport direction) by passing the unstretched film between two pairs of nip rolls with different peripheral speeds. In addition, longitudinal stretching was performed by setting the preheating temperature to 75°C, the stretching temperature to 90°C, the stretching ratio to 3.4 times, and the stretching speed to 1,300%/sec. (B) Coating Using a bar coater, the coating liquid for forming the coating layer described below was coated on one surface of the above-mentioned longitudinally stretched film so as to become 5.6 g/m ² . (C) Transverse stretch The film subjected to the above longitudinal stretch and the above coating was stretched in the transverse direction using a tenter under the following conditions. -Conditions- Preheating temperature: 100℃ Stretching temperature: 120℃ Stretching ratio: 4.2 times Stretching speed: 50%/sec

(Coating solution for coating layer formation) By mixing each component shown below, the coating liquid for coating layer formation was obtained. After preparing the coating liquid, filtration with a 6 μm filter (F20, manufactured by MAHLE Japan Ltd.) and membrane degassing (2x6 radial flow SuperPhobic, manufactured by Polypore International, Inc.) were performed until coating. • Polyacrylic acid (AS-563A, manufactured by DAICEL FINECHEM LTD., solid content: 27.5 mass%): 167 parts •Non-ionic surfactant (NAROACTY (registered trademark) CL95, manufactured by SANYO CHEMICAL INDUSTRIES, LTD., solid content: 100% by mass): 0.7 parts • Anionic surfactant (RAPISOL (registered trademark) A-90, manufactured by NOF CORPORATION., solid content: 1% by mass diluted with water): 55.7 parts • Carnauba wax dispersion (Cellulose (registered trademark) 524, manufactured by CHUKYO YUSHI CO., LTD., solid content: 30% by mass): 7 parts •Carbodiimide compound (CARBODILITE (registered trademark) V-02-L2, manufactured by Nisshinbo Chemical Inc., solid content: 10% by mass water dilution): 20.9 parts • Condensed silica (AEROSIL OX50, manufactured by NIPPON AEROSIL CO., LTD., solid content: 10% by mass, water dispersion, average primary particle size: 40nm, average particle size: 200nm): 2.95 parts • Water: 745.8 parts

[Heat setting and thermal relaxation] The stretched film after the longitudinal stretching and the transverse stretching was heat-set under the following conditions. Furthermore, after heat setting, the width of the tenter was reduced and thermal relaxation was performed under the following conditions, followed by cooling. (Heat setting conditions) Heat setting temperature: 227℃ Heat setting time: 6 seconds (Thermal relaxation conditions) Thermal relaxation temperature: 190℃ Thermal relaxation rate: 4% (Cooling conditions) Cooling rate: 2,500°C/min

[Reeling] After the above heat setting and thermal relaxation, both ends of the film were trimmed, and then the end of the film was extruded (knurled) with a width of 10 mm, and then the stretched film was wound with a tension of 40 kg/m . By the above method, a biaxially aligned polyester film having a polyester film substrate (PET: polyethylene terephthalate) with a thickness of 30 μm and a coating layer with a thickness of 0.04 μm was obtained. The obtained biaxially aligned polyester film had a width of 1.5 m and a roll length of 7,000 m.

<Example 2> Except that the heat setting temperature was changed to 231°C, a biaxially oriented polyester film was obtained by the same method as in Example 1.

<Example 3> Except that the heat setting temperature was changed to 229°C, a biaxially oriented polyester film was obtained by the same method as in Example 1.

<Example 4> Except that the cooling rate after thermal relaxation was changed to 3,500° C./min, a biaxially oriented polyester film was obtained by the same method as in Example 1.

<Example 5> Except that the cooling rate after thermal relaxation was changed to 3,000° C./min, a biaxially oriented polyester film was obtained by the same method as in Example 1.

<Example 6> The aggregated silica in the coating solution for forming a coating layer was changed to colloidal silica (SNOWTEX (registered trademark) MP4540M, manufactured by Nissan Chemical Corporation, average primary particle size: 450nm, average particle size: 450nm), and the coating amount of the coating solution for forming the coating layer after stretching was changed to 22.4g/m ² , except for this, a biaxially oriented polyester film was obtained by the same method as in Example 1. .

<Example 7> The agglomerated silica in the coating solution for forming a coating layer was changed to colloidal silica (SNOWTEX (registered trademark) MP2040, manufactured by Nissan Chemical Corporation, average primary particle size: 200 nm, average particle size: 200nm), and the coating amount of the coating solution for forming the coating layer after stretching was changed to 11.2g/m ² , except for this, a biaxially oriented polyester film was obtained by the same method as in Example 1. .

<Example 8> The agglomerated silica in the coating solution for coating layer formation was changed to colloidal silica (SNOWTEX (registered trademark) ZL, manufactured by Nissan Chemical Corporation, average primary particle size: 100nm, average particle size: 100nm), except Otherwise, a biaxially aligned polyester film was obtained by the same method as in Example 1.

<Example 9> The condensed silica in the coating solution for forming the coating layer was changed to colloidal silica (SNOWTEX (registered trademark) XL, manufactured by Nissan Chemical Corporation, average primary particle size: 50 nm, average particle size: 50 nm), except for this Otherwise, a biaxially aligned polyester film was obtained by the same method as in Example 1.

<Example 10> Except that the amount of aggregated silica in the coating liquid for forming a coating layer was changed to 5.9 parts, a biaxially oriented polyester film was obtained by the same method as in Example 1.

<Example 11> Except that the amount of aggregated silica in the coating liquid for forming a coating layer was changed to 11.8 parts, a biaxially aligned polyester film was obtained by the same method as in Example 1.

<Example 12> Except that the amount of aggregated silica in the coating solution for forming a coating layer was changed to 1.48 parts, a biaxially aligned polyester film was obtained by the same method as in Example 1.

<Example 13> The polyacrylic acid in the coating liquid for forming a coating layer was changed to 230 parts of polyurethane (SUPER FLEX 150HS, manufactured by DKS Co. Ltd., solid content: 38.0% by mass), except that the same method as in Example 1 was used. The method obtains a biaxially aligned polyester film.

<Example 14> The polyacrylic acid in the coating liquid for forming a coating layer was changed to 187 parts of polyester (plascoat Z592, manufactured by GOO CHEMICAL CO., LTD., solid content: 25.0% by mass). In addition, the same as in Example 1 In the same way, a biaxially aligned polyester film was obtained.

<Example 15> The agglomerated silica in the coating solution for forming the coating layer was changed to polymethylmethacrylate particles (MP-1000, manufactured by Soken Chemical & Engineering Co., Ltd., average primary particle size: 400nm, average particle size : 400nm), except for this, a biaxially oriented polyester film was obtained by the same method as in Example 1. In Table 1, the polymethyl methacrylate particles are abbreviated as "PMMA".

<Example 16> A biaxially oriented polyester film was obtained by the same method as in Example 1, except that the surface of the coating liquid for forming a coating layer after the longitudinal stretching was applied was changed to two surfaces.

<Example 17> The agglomerated silica in the coating solution for coating layer formation was changed to colloidal silica (SNOWTEX (registered trademark) XL, manufactured by Nissan Chemical Corporation, average primary particle size: 50 nm, average particle size: 50 nm), and Except for changing the amount of the colloidal silica to 0.04 parts, a biaxially aligned polyester film was obtained by the same method as in Example 1.

<Example 18> The condensed silica in the coating solution for coating layer formation was changed to condensed silica (NIPGEL (registered trademark) AZ204, manufactured by Tosoh Silica Corporation., average primary particle size: 4nm, average particle size: 1.7μm), And except that the heat setting temperature was changed to 229°C, a biaxially oriented polyester film was obtained by the same method as in Example 1.

<Comparative Example 1> The aggregated silica in the coating solution for forming a coating layer was changed to colloidal silica (SNOWTEX (registered trademark) MP4540M, manufactured by Nissan Chemical Corporation, average primary particle size: 450nm, average particle size: 450nm), the coating amount of the coating solution for forming the coating layer after stretching was changed to 22.4g/m ² and the heat setting temperature was changed to 215°C, except that the same method as in Example 1 was used. A biaxially aligned polyester film was obtained.

＜Comparative example 2＞ Change the condensed silica in the coating solution for coating layer formation to condensed silica (NIPGEL (registered trademark) AZ204, manufactured by Tosoh Silica Corporation., average primary particle size: 4nm, average particle size: 1.7μm) and Except that the heat setting temperature was changed to 240°C, a biaxially oriented polyester film was obtained by the same method as in Example 1.

＜Evaluation＞ Using each of the biaxially oriented polyester films of Example 1 to Example 18 and Comparative Example 1 to Comparative Example 2, the following evaluations were performed. The evaluation results are shown in Table 1.

[Streak-shaped defect area] While using a heating conveyor, the biaxially oriented polyester film was conveyed at a conveying speed of 30 m/min and a tension of 100 N/m, and heat treatment was performed at 90°C or 120°C for 20 seconds. The heating temperature in the heat treatment refers to the surface temperature of the film. The heating time in the heat treatment is calculated from the point when the surface temperature of the film reaches the target temperature (90°C or 120°C). Place the heat-treated biaxially oriented polyester film on a flat surface, and then change the viewpoint to make the fluorescent lamp installed on the indoor ceiling [Lupica Ace manufactured by Mitsubishi Electric Corporation (color temperature: 5000K, average color rendering evaluation) Number (Ra): 84)] The biaxially oriented polyester film was observed with the naked eye from an oblique direction on the light reflection side. The area where the reflected image of the fluorescent lamp is curved on the surface of the biaxially aligned polyester film, which is observed by the naked eye, is defined as a stripe-shaped defect area. By counting the striped defect areas observed, the number of striped defect areas per 1m ² (pieces/m ² ) is calculated.

[Uneven color] In a biaxially stretched polyester film, a slit-shaped nozzle is used to coat the base layer coating containing the following formula A on the surface of the polyester film substrate opposite to the surface on which the covering layer is arranged After the liquid, it was dried at 120°C to form a base layer. Next, a black layer was formed by applying a coating liquid for a black layer containing the following formulation B on the base layer, and then drying it at 90°C or 120°C. Place the biaxially stretched polyester film provided with a black layer on the light table, and observe the color unevenness of the black layer by naked eyes at a position separated from the above biaxially stretched polyester film by 1 m, and proceed according to the following criteria Evaluation.

(Formulation A: Coating solution for base layer) • PVA205 (polyvinyl alcohol, manufactured by KURARAY CO., LTD., saponification degree: 88%, polymerization degree: 550): 32.2 parts by mass •Polyvinylpyrrolidone (manufactured by Integrated Software Products Co., Ltd., K-30): 14.9 parts • Distilled water: 524 parts by mass •Methanol: 429 parts by mass

(Formulation B: coating liquid for black layer) • Resin-coated carbon black manufactured according to paragraphs 0036 to 0042 of Japanese Patent No. 5320652: 13.1 parts by mass • Dispersant 1 (the following structure): 0.65 parts by mass •Polymer (random copolymer of benzyl methacrylate/methacrylic acid=72/28 molar ratio, weight average molecular weight: 37,000): 6.72 parts by mass • Propylene glycol monomethyl ether acetate: 79.53 parts by mass

The structure of the dispersant 1 is shown below.

[Chemical formula 1]

(Benchmark) A: Color unevenness is not confirmed at all, and it is in a good state. B: Although some color unevenness can be confirmed, there is no problem in actual use. C: Although the color unevenness can be confirmed, there is no problem in actual use. D: Color unevenness is strong, and there is a problem in actual use.

[Winding quality] A roll was manufactured by winding a 7000 m biaxially stretched polyester film with a straight roll while pressing an air nozzle. After the manufactured roll was allowed to stand for 30 days under the conditions of 25° C. and 50% RH (relative humidity), the winding quality was evaluated based on the following criteria.

(Benchmark) A: There are no wrinkles in the film. B: Although there are some wrinkles in the film, they disappear if tension is applied by hand, so there is no problem in actual use. C: Although some wrinkles are observed in the film and the flatness is impaired, there is no problem in actual use. D: Large wrinkles are observed in the film, and the flatness is impaired.

[Transfer failure] While cutting both ends of the biaxially oriented polyester film with the black layer produced in the above evaluation of color unevenness to a length of 45 cm in width, the touch roller was pressed against the diameter with a tension of 11.5 kg/m It is a 3 inch (1 inch = 2.54cm) ABS (acrylonitrile-butadiene-styrene) resin winding core, and it is wound for 100m. The obtained test body was allowed to stand for 10 days under the conditions of 25° C. and 50% RH (relative humidity). After 10 days, under a fluorescent lamp [Lupica Ace manufactured by Mitsubishi Electric Corporation (color temperature: 5000K, average color rendering evaluation number (Ra): 84)], the biaxially oriented polyester wound on the winding core was observed. The surface of the black layer in the film. Using the reflected light of a fluorescent lamp, the unevenness of the film surface was observed with the naked eye, and the transfer failure was evaluated based on the following criteria.

(Benchmark) A: No unevenness on the surface was observed at all, and it was in a very good state. B: Although some surface irregularities can be visually recognized, they are very minute irregularities and are in a state of no problem. C: Although the surface irregularities can be visually recognized, they are minute irregularities and are in a state of no problem. D: The unevenness of the surface can be clearly recognized, and the black layer is deformed, so it is a state where there is a problem in actual use.

[Table 1] Biaxially stretched polyester film Evaluation Polyester film substrate (A) Coating layer (B) Layer structure Haze [%] b ^* value 90℃ Expansion rate 120℃ Expansion rate Average height of protrusions Density of protrusions 90℃ streak defect area 120℃ Striped defect area Uneven color Winding quality Transfer failure Adhesive particle Average primary particle size of particles thickness Example 1 PET Polyacrylic acid Condensed silica 40nm 0.04μm A/B 0.46 0.5 0.04% 0.04% 200nm 85pcs/mm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 2 PET Polyacrylic acid Condensed silica 40nm 0.04μm A/B 0.46 0.5 0.10% 0.15% 200nm 85pcs/mm ² 2.3pcs/m ² 6pcs/m ² C A A Example 3 PET Polyacrylic acid Condensed silica 40nm 0.04μm A/B 0.46 0.5 0.08% 0.10% 200nm 85pcs/mm ² 1.7pcs/m ² 4.3pcs/m ² B A A Example 4 PET Polyacrylic acid Condensed silica 40nm 0.04μm A/B 0.46 0.5 0.04% 0.04% 200nm 85pcs/mm ² 2.7pcs/m ² 6.9pcs/m ² C A A Example 5 PET Polyacrylic acid Condensed silica 40nm 0.04μm A/B 0.46 0.5 0.04% 0.04% 200nm 85pcs/mm ² 1.8pcs/m ² 4.5pcs/m ² B A A Example 6 PET Polyacrylic acid Colloidal silica 450nm 0.2μm A/B 0.49 0.7 0.04% 0.04% 250nm 1570pcs/mm ² 0.7pcs/m ² 1.7pcs/m ² A A B Example 7 PET Polyacrylic acid Colloidal silica 200nm 0.1μm A/B 0.47 0.5 0.04% 0.04% 100nm 0.029pcs/μm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 8 PET Polyacrylic acid Colloidal silica 100nm 0.04μm A/B 0.52 0.4 0.04% 0.04% 50nm 3.1pcs/μm ² 0.7pcs/m ² 1.7pcs/m ² A B A Example 9 PET Polyacrylic acid Colloidal silica 50nm 0.04μm A/B 0.4 0.4 0.04% 0.04% 10nm 8.8pcs/μm ² 0.7pcs/m ² 1.7pcs/m ² A C A Example 10 PET Polyacrylic acid Condensed silica 40nm 0.04μm A/B 0.96 0.5 0.04% 0.04% 200nm 168pcs/mm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 11 PET Polyacrylic acid Condensed silica 40nm 0.04μm A/B 2.8 0.6 0.04% 0.04% 200nm 348pcs/mm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 12 PET Polyacrylic acid Condensed silica 40nm 0.04μm A/B 0.3 0.4 0.04% 0.04% 200nm 20pcs/mm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 13 PET Polyurethane Condensed silica 40nm 0.04μm A/B 0.41 0.6 0.04% 0.04% 200nm 85pcs/mm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 14 PET Polyester Condensed silica 40nm 0.04μm A/B 0.48 0.8 0.04% 0.04% 200nm 85pcs/mm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 15 PET Polyacrylic acid PMMA 400nm 0.04μm A/B 0.49 0.51 0.04% 0.04% 170nm 0.04pcs/μm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 16 PET Polyacrylic acid Condensed silica 40nm 0.04μm B/A/B 0.82 0.51 0.04% 0.04% 200nm 85pcs/mm ² 0.7pcs/m ² 1.7pcs/m ² A A A Example 17 PET Polyacrylic acid Colloidal silica 50nm 0.05μm A/B 0.2 0.4 0.10% 0.15% 10nm 1600pcs/mm ² 1.7pcs/m ² 4.3pcs/m ² B C A Example 18 PET Polyacrylic acid Condensed silica 4nm 0.05μm A/B 1.2 0.4 0.10% 0.15% 1.4μm 70pcs/mm ² 1.7pcs/m ² 4.3pcs/m ² B A C Comparative example 1 PET Polyacrylic acid Colloidal silica 450nm 0.2μm A/B 0.49 0.7 0.04% -0.30% 250nm 1570pcs/mm ² 0.7pcs/m ² 9.0pcs/m ² D A A Comparative example 2 PET Polyacrylic acid Condensed silica 4nm 0.05μm A/B 1.2 0.4 0.20% 0.50% 1.4μm 70pcs/mm ² 3.4pcs/m ² 8.8pcs/m ² D D D

In Table 1, "A" and "B" described in the "layer structure" column refer to the polyester film base material and the coating layer, respectively. In Table 1, the "/" described in the "layer structure" column indicates the boundary of the layer. For example, "A/B" refers to the state where A and B are stacked.

In Table 1, the value described in the "Haze" column is a value measured using a haze meter (NDH-2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.) by a method in accordance with JIS K 7105.

In Table 1, the ^{value described in the "b*} value" column is a value measured by a transmission method using a spectrophotometer (for example, SE-2000, manufactured by NIPPON DENSHOKU INDUSTRIES Co., LTD.).

In Table 1, the values in the columns of "90°C Expansion Rate" and "120°C Expansion Rate" are based on the method described above (refer to the item of "Expansion Rate" above) using a thermomechanical analysis device (TMA- 60, the value measured by SHIMADZU CORPORATION).

In Table 1, the value described in the "average height of protrusions" column is used after measuring the range of 1.07mm×1.42mm on the surface of the coating layer of the film using an optical interferometer (NewView5020 manufactured by Zygo Corporation) Data analysis software (NewView5020 data analysis software: MetroPro8.1.3) measured value (arithmetic average of measured values in 5 ranges).

In Table 1, the value described in the column "Density of protrusions" is used after measuring the range of 1.07mm×1.42mm on the surface of the coating layer of the film using an optical interferometer (NewView5020 manufactured by Zygo Corporation). Analysis software (NewView5020 data analysis software: MetroPro8.1.3) measured value (arithmetic average of measured values in 5 ranges).

The A side of each biaxially oriented polyester film of Example 1 to Example 15, Example 17 to Example 18, and Comparative Example 1 to Comparative Example 2 (that is, the polyester film in the biaxially oriented polyester film The surface roughness Ra of the substrate (A) on the side opposite to the coating layer (B)) was 2 nm. The B side of the biaxially oriented polyester film of Example 16 (that is, the side of the coating layer (B) opposite to the polyester film substrate (A) in the biaxially oriented polyester film) The surface roughness Ra is 4nm. Regarding the surface roughness Ra of each biaxially aligned polyester film, after measuring the 1.07mm×1.42mm range of the film using an optical interferometer (NewView5020 manufactured by Zygo Corporation), data analysis software (NewView5020 data analysis software: MetroPro8. 1.3) Measurements were taken. Specifically, by the above-mentioned method, the measured values in the five ranges (1.07 mm×1.42 mm of the film) are arithmetic averaged to obtain the surface roughness Ra.

According to Table 1, it is found that, compared with Comparative Example 1 to Comparative Example 2, the expansion rate in the width direction at 90°C and 120°C is in the range of 0% to 0.15%, respectively. In Examples 1 to 18, the stripes Few areas of shape defects. In addition, it was found that in Examples 1 to 18, which have fewer streak defect regions, compared with Comparative Examples 1 to 2, the color unevenness of the black layer was reduced.

The entire content of the disclosure of Japanese Patent Application No. 2019-099592 filed on May 28, 2019 is incorporated into this specification by reference. All the documents, patent documents, and technical standards described in this specification are incorporated into this specification by reference to the same extent as when each document, patent document, and technical standard were specifically and separately described and incorporated by reference.

2a～2l: Holding member 10: Preheating section 10 20: Stretching part 30: Heat setting department 40: Thermal relaxation part 50: Cooling part 60a, 60b: ring rail 100: Two-axis stretching machine 200: Membrane L0, L1, L2: width MD, TD: arrow P, Q: control release point

Fig. 1 is a plan view showing an example of a biaxial stretching machine.

2a~21: Holding components

10: Preheating section 10

20: Stretching part

30: Heat setting department

40: Thermal relaxation part

50: Cooling part

60a, 60b: ring rail

100: Two-axis stretching machine

200: Membrane

L0, L1, L2: width

MD, TD: arrow

P, Q: control release point

Claims (12)

A biaxially oriented polyester film, in which With respect to the size in the width direction at 30°C, the expansion rates in the width direction at 90°C and 120°C are 0% to 0.15%, respectively. The biaxially oriented polyester film according to claim 1, wherein the number of stripe-shaped defect regions generated when heated at at least one of 90°C and 120°C is less than 3/m ² . The biaxially oriented polyester film as described in claim 1, wherein There are a plurality of protrusions on at least one surface. The two-axis oriented polyester film as described in claim 1, which has: Polyester film substrate; and A layer containing particles with an average particle diameter of 0.01 μm to 0.4 μm on at least one surface of the aforementioned polyester film substrate and having a plurality of protrusions on the surface. The two-axis oriented polyester film as described in claim 3 or claim 4, wherein The average height of the plurality of protrusions is 10 nm to 300 nm. The biaxially oriented polyester film according to claim 3 or claim 4, wherein the density of the plurality of protrusions is 60 pcs/mm ² to 110 pcs/mm ² . The biaxially oriented polyester film as described in claim 1 or claim 2, wherein the number of streak-shaped defect regions generated under heating at 90°C is less than 3/m ² and at 120°C The number of stripe-shaped defect areas generated under heating is less than 7/m ² , or the number of stripe-shaped defect areas generated under heating at 90°C is less than 7/m ² , and The number of stripe-shaped defect regions produced when heated at 120°C is less than 3/m ² . The biaxially oriented polyester film according to claim 1 or claim 2, wherein the number of stripe-shaped defect regions generated when heated at 90°C and 120°C is less than 3/m ^{2 respectively} . The two-axis oriented polyester film as described in claim 1 or claim 2, wherein Particles with an average particle diameter of 0.01 μm to 0.4 μm are contained in a region from at least one surface to 5% of the film thickness in the thickness direction. The two-axis oriented polyester film as described in claim 1 or claim 2, wherein The haze is 0.5% or less. The biaxially oriented polyester film as described in claim 1 or claim 2, wherein the b ^{* value in the L*} a ^* b ^* color system is 0 to 0.6. The two-axis oriented polyester film as described in claim 1 or claim 2, wherein The surface roughness Ra of at least one surface is 1 nm to 10 nm.

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