JP2018021168A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film suitable as a protective film of a COP film, which is used for a substrate with a transparent conductive film deposited thereon, and the like.SOLUTION: The present invention provides a biaxially oriented polyester film. In a film main orientation axis direction, and a direction perpendicular to it, film expansion rates at 150°C are 0.5% or more and 1.5% or less, respectively, in film expansion measurements in a temperature rise process from 25°C to 150°C.SELECTED DRAWING: None

Description

  The present invention relates to a biaxially oriented polyester film having excellent mechanical properties and processability.

  Polyester resins, especially polyethylene terephthalate (hereinafter sometimes abbreviated as PET) and polyethylene 2,6-naphthalene dicarboxylate (hereinafter sometimes abbreviated as PEN) are mechanical properties, thermal properties, chemical resistance, electrical properties, It has excellent moldability and is used for various purposes. A polyester film obtained by forming the polyester into a film, particularly a biaxially oriented polyester film, is used as a process film for protecting a transparent electrode substrate from being damaged during the processing process because of its excellent mechanical properties and processability.

  In recent years, a transparent conductive film-forming substrate (ITO (Indium Tin Oxide) deposition substrate, etc.) used in displays and the like has been used in a transparent conductive film-forming substrate from the viewpoint of improving display performance and reducing the thickness. A film made of (COP) is used.

  In general, a substrate curing process at a constant temperature is required to increase the conductivity of the ITO film. In this step, since the film that protects the substrate is also simultaneously heated, when a film made of cycloolefin polymer (COP) is used for the film-forming substrate of the transparent conductive film, the film that protects the COP film and It is preferable that the thermal characteristics are close. Because, if there is a difference in thermal properties between the COP film and the film that protects it, the flatness of the transparent conductive film-forming substrate deteriorates or the protective film peels off and the protective function decreases. To do.

  For this reason, if the same COP film is used as a film for protecting the COP film, there is no difference in thermal characteristics. However, since COP is an amorphous resin, its toughness is low and its flexibility is poor, so cracks occur during the processing process. There is a problem that occurs.

  On the other hand, when a biaxially oriented polyester film is used as a film for protecting the COP film, COP is generally an amorphous resin, and the value of the film dimensional change rate is about 2 to 3 times that of biaxially oriented PET. Since there is a large difference in thermal characteristics, there arises a problem that the flatness of the film-forming substrate of the transparent conductive film is deteriorated or the protective film is peeled off. Then, using the biaxially-oriented polyester film which controlled the film dimensional change rate to the value close | similar to COP is examined as a protective film. (Patent Documents 1, 2, and 3)

International Publication No. 2006/104116 Pamphlet JP 2007-168148 A JP 2013-54207 A

  The biaxially oriented polyester films described in Patent Documents 1 to 3 have a certain degree of deterioration of the flatness of the transparent conductive film-forming substrate and the peeling of the protective film by controlling the film dimensional change rate to a value close to COP. Has been achieved. In general, however, the biaxially oriented polyester film retains the stress that is received in the process of orienting the polyester film biaxially. Therefore, when heated, the residual stress received in the film forming process is released, resulting in heat shrinkage. Happens. Although the polyester film obtained by the methods described in Patent Documents 1, 2, and 3 has a film dimensional change rate close to that of COP, heat shrinkage due to residual stress occurs during heating. When used as a protective film, there still remains a problem that the protective film peels off.

  In view of the background of the prior art, the object of the present invention is a biaxially oriented polyester excellent in mechanical properties and workability, which is suitably used as a protective film for a COP film used in applications such as a transparent conductive film-forming substrate. To provide a film.

In order to solve the above problems, the present invention has the following configuration. That is,
[I] In the film expansion measurement in the temperature rising process from 25 ° C. to 150 ° C. in the direction of the main film orientation axis and in the direction perpendicular to it, the film expansion coefficient at 150 ° C. is 0.5% or more, respectively. Biaxially oriented polyester film that is 5% or less.
[II] The rate of dimensional change in the temperature-decreasing process from 150 ° C. to 50 ° C. in the direction perpendicular to the film main orientation axis and in the direction perpendicular thereto is 70 ppm / ° C. to 140 ppm / ° C., respectively. Biaxially oriented polyester film.
[III] Yave (MPa) is an average value of Young's modulus in the film main orientation axis direction and the direction perpendicular to the film main orientation axis direction, and the temperature lowering from 150 ° C. to 50 ° C. in the film main orientation axis direction and the direction perpendicular to it The biaxially oriented polyester film according to [I] or [II], which satisfies the following formula (i), where αave (ppm / ° C.) is an average value of the dimensional change rate in the process.
(I) 20 ≦ Yave / αave ≦ 50
[IV] Yave (MPa) is an average value of Young's modulus in the main film orientation axis direction and a direction perpendicular to the film main orientation axis direction, and the temperature drop is 150 ° C. to 50 ° C. in the film main orientation axis direction and the direction perpendicular thereto. The biaxially oriented polyester film according to [I] to [III], which satisfies the following formula (ii) when αave (ppm / ° C.) is an average value of the dimensional change rate in the process.
(Ii) 20 ≦ Yave / αave ≦ 40
[V] A laminated polyester film having at least three layers, wherein the intrinsic viscosity of both surface layers of the polyester film is 0.67 dl / g or more and 0.9 dl / g or less, and When the average value of the intrinsic viscosity of the surface layers on both sides is IVa (dl / g), and the average value of the intrinsic viscosity of the layers other than the surface layers on both sides of the laminated polyester film is IVb (dl / g), the following (ii) The biaxially oriented polyester film according to any one of [I] to [IV] satisfying the formula:
(Iii) 0.01 ≦ IVa−IVb ≦ 0.3
[VI] The value TmA obtained by averaging the melting points of the surface layers on both sides of the polyester film is in the range of 250 ° C. or more and 280 ° C. or less, and the value TmB obtained by averaging the melting points of the layers other than the surface layers on both sides of the polyester film is 250 ° C. or less. The biaxially oriented polyester film according to [V].
[VII] The ratio of the sum of the thicknesses of the surface layers on both sides of the polyester film and the sum of the thicknesses of the layers other than the surface layer (sum of the thicknesses of the surface layers on both sides / sum of the thicknesses of the layers other than the surface layer) is 1/9 to The biaxially oriented polyester film according to [V] or [VI], which is 1/2.
[VIII] The biaxially oriented polyester film according to any one of [I] to [VII], wherein the amount of change in haze before and after heat treatment at 140 ° C. for 90 minutes is 5.0% or less.
[IX] The amount of ester cyclic trimer on the surface of the polyester film after heat treatment at 140 ° C. for 90 minutes is 0 mg / m ² or more and 1.5 mg / m ² or less of [I] to [VIII] The biaxially oriented polyester film according to any one of the above.
[X] The biaxially oriented polyester film according to any one of [I] to [IX], wherein at least one of the surface roughness Ra is 1 nm to 200 nm and the maximum height roughness Rz is 100 nm to 2000 nm.

  According to the present invention, a biaxially oriented polyester film having a film expansion coefficient close to that of a film made of COP and excellent in laminating properties, mechanical properties, and workability can be obtained.

The polyester film of the present invention needs to be a biaxially oriented polyester film from the viewpoint of mechanical properties. The polyester here has a dicarboxylic acid component and a diol component. In addition, in this specification, a structural component shows the minimum unit which can be obtained by hydrolyzing polyester. The polyester film of the present invention is preferably made of polyethylene terephthalate or a copolymer of polyethylene terephthalate from the viewpoint of mechanical properties.

The polyester film of the present invention has a film expansion coefficient of 0.5 at 150 ° C. in the film expansion measurement in the temperature rising process from 25 ° C. to 150 ° C. in the direction perpendicular to the main film orientation axis direction. % Or more and 1.5% or less. More preferably, it is 0.7% or more and 1.4% or less. More preferably, it is 0.9% or more and 1.3% or less.
Generally, a transparent conductive film is formed on a substrate at a temperature higher than room temperature, then heated to a temperature higher than room temperature, and then gradually cooled to room temperature through a curing process. It goes through a temperature drop process. Here, since the COP film used for the transparent conductive film is an amorphous resin, the molecular chain tends to move when heated, and tends to thermally expand when the temperature is raised from room temperature (film expansion). The rate is positive). On the other hand, the biaxially oriented polyester film retains the stress received in the process of orienting the polyester film biaxially, so the residual stress received in the film forming process is released when heated from room temperature to a high temperature state. Thermal contraction occurs (the film has a negative expansion coefficient). Therefore, when the conventional biaxially oriented polyester film is used as a protective film for COP, the flatness of the transparent conductive film-forming substrate is deteriorated or the protective film is peeled off due to the difference in expansion coefficient of the film. Had occurred.
Therefore, by setting the film expansion coefficient of the PET film protecting the transparent conductive film to a value close to the expansion coefficient of the COP film, problems such as wrinkles and peeling occur in the transparent conductive film in a process performed at a temperature higher than room temperature. Can be suppressed. Based on the above points, in the film expansion measurement in the temperature rising process from 25 ° C. to 150 ° C. in the direction of the main film orientation axis of the polyester film and the direction perpendicular thereto, the film expansion coefficient at 150 ° C. is 0 respectively. When it is used as a PET film for protecting a transparent conductive film by setting it to 5% or more and 1.5% or less, wrinkles and peeling can be suppressed, it is excellent in bonding properties with COP, and a conductive film is formed. The conductivity can be kept good without losing the flatness of the transparent conductive film-forming substrate later.

  When the film expansion coefficient at 150 ° C. is less than 0.5%, when used as a transparent conductive film by bonding with COP, the film expansion coefficient when heated in the processing step is small compared to COP. There is a possibility that peeling occurs, the planarity of the transparent conductive film-forming substrate is deteriorated after the conductive film is formed, the transparent conductive film is lost, and the conductivity is impaired.

Further, when the film expansion coefficient at 150 ° C. exceeds 1.5%, when used as a transparent conductive film by bonding with COP, the film expansion coefficient when heated in the processing step is larger than that of COP. In some cases, peeling may occur, the flatness of the film-forming substrate of the transparent conductive film may be deteriorated after the conductive film is formed, and the conductive film may be lost due to loss of the transparent conductive film.
As used herein, the main orientation axis direction of the film refers to the direction having the maximum refractive index in the film as the main orientation axis. The direction of the maximum refractive index in the film may be obtained by measuring the refractive index in all directions of the film with a refractometer, and the slow axis direction may be determined by a phase difference measuring device (birefringence measuring device) or the like. It may be obtained by deciding.

The film expansion coefficient of the biaxially oriented polyester film of the present invention is determined by the method described later, and represents the dimensional change rate when the film is heated.
As a method for measuring the film expansion coefficient, a thermomechanical measuring device TMA / SS6000 (manufactured by Seiko Instruments Inc.) is used, and a load of 3 g is applied to a sample having a sample width of 4 mm and a sample length (distance between chucks) of 20 mm. The temperature is raised from room temperature to 160 ° C. at a heating rate of 10 ° C./min, and the value of the dimension of the sample at each temperature (° C.) is obtained. And it calculates from the following formula (iii) from the dimension L (25 ° C.) (mm) of the sample at 25 ° C. and the dimension L (150 ° C.) (mm) at 150 ° C. In addition, a film expansion coefficient is implemented by n = 5 about the film main orientation axis direction and each direction perpendicular thereto, and is calculated as an average value thereof.
(Iv) Film expansion rate (%) = L (150 ° C.) / L (25 ° C.) × 100
The method for setting the film expansion coefficient of the biaxially oriented polyester film of the present invention in the above range is not particularly limited, and for example, the following methods (I) and (II) can be employed.
(I) The polyester film is a laminated polyester film having at least three layers, and a value TmA obtained by averaging the melting points of the surface layers on both sides of the polyester film is in the range of 250 ° C. or more and 280 ° C. or less, and other than the surface layers on both sides of the polyester film The value TmB obtained by averaging the melting points of the layers shall be 250 ° C. or less.
(II) The polyester film after being biaxially stretched is off-annealed or returned to the longitudinal direction in the tenter of the heat setting step in film formation, and relaxed in the longitudinal direction.

  First, (I) will be described. In order to increase the expansion coefficient of the film, it is important to make the resin constituting the film amorphous or close to amorphous. By setting the biaxially oriented polyester film to the configuration of (I), a biaxially oriented polyester film having a layer having a lower melting point than a general biaxially oriented polyester film and a layer having a higher melting point than that is obtained. When heat is applied to the biaxially oriented polyester film having the constitution (I) in the heat treatment step, the crystal structure of the layers other than the surface layer on both sides of the polyester film having a low melting point is broken, resulting in an amorphous structure with irregular orientation. As a result, the amorphous nature of the film increases and the film expansion rate can be increased. In addition, since the surface layers on both sides of the polyester film maintain the crystal structure, the orientation is maintained, the mechanical properties are excellent, and the generation of oligomers can be suppressed.

  Next, (II) will be described. By passing the step (II) in the method for producing a biaxially oriented polyester film, it is possible to remove the residual stress applied when the polyester film is biaxially oriented. Details will be described later.

  As a method of setting the value TmA of the melting points of the surface layers on both sides of the polyester film described in (I) to 250 ° C. or more and 280 ° C. or less, the polyester resin constituting the surface layers on both sides is made of polyethylene terephthalate (PET) and / or Polyethylene naphthalate (PEN) is preferred. In order to make the value TmB, which is the average of the melting points of the layers other than the surface layer on both sides of the polyester film, 250 ° C. or less, when the polyester resin is PET and / or PEN, copolymerize isophthalic acid as a dicarboxylic acid component. Examples thereof include a method of copolymerizing cyclohexanedimethanol as a diol component. These may be copolymerized singly or a plurality of types may be copolymerized. As the copolymerization amount, the total of the copolymerization components is preferably 5 mol% or more and 20 mol% or less with respect to the total amount of the constituent components of the polyester.

  A value TmA obtained by averaging the melting points of the surface layers on both sides of the biaxially oriented polyester film of the present invention is preferably in the range of 250 ° C. or higher and 280 ° C. or lower from the viewpoint of mechanical properties and workability.

If the value TmA, which is the average of the melting points of the surface layers on both sides of the biaxially oriented polyester film, is less than 250 ° C., it is close to amorphous, so it is inferior in mechanical properties and tends to generate oligomers. Become.
Moreover, when TmA exceeds 280 degreeC, since crystallinity is too high, it is inferior to film forming property and a mechanical characteristic.

  A value TmB obtained by averaging the melting points of the layers other than the surface layers on both sides of the biaxially oriented polyester film of the present invention is preferably 250 ° C. or less from the viewpoint of controlling the film expansion rate, the film dimensional change rate, and the mechanical properties. More preferably, it is 220 degreeC or more and 250 degrees C or less, More preferably, it is 230 degreeC or more and 240 degrees C or less.

When the value TmB, which is the average of the melting points of the layers other than the surface layer on both sides of the biaxially oriented polyester film, is less than 220 ° C., the film is close to an amorphous state. If the film becomes too large or is heated to a temperature close to the crystallization temperature of the film, random coarse crystals are formed, which not only impairs the transparency of the film, but also the molecular chains existing around the random coarse crystals. As a result, the mechanical properties are inferior and the dimensional change rate of the film also decreases.
On the other hand, when TmB exceeds 250 ° C., it is close to crystallinity, and as a result, the molecular chain of the film cannot be freely moved by heat.

  The conditions for the off-annealing of the biaxially stretched polyester film described in (II) are as follows: the off-annealing temperature is 140 ° C. or higher and lower than 200 ° C., and the film width direction is free. It is in a state where it is not constrained in the width direction, and it is possible to remove the residual stress applied when the polyester film is biaxially oriented by winding while applying a tension of 10N to 100N in the longitudinal direction. . The tension applied in the longitudinal direction is preferably 20N or more and 60N or less.

Moreover, the method of returning a dimension to a longitudinal direction in the tenter of the heat-setting process in film-forming the polyester film after biaxial stretching as described in (II), and the method of relaxing in the longitudinal direction is the longitudinal direction after stretching in the longitudinal direction. A so-called relaxation process is performed in which the dimension is returned to 0.01 to 7%. The relaxation treatment temperature at this time is preferably in the range of the temperature equal to or lower by 30 ° C. than the longitudinal stretching temperature in the second and subsequent stages. In addition, this relaxation process is usually efficient between heating and cooling rolls having a difference in peripheral speed, but may be performed in a hot air oven in which free rolls are arranged or in an MD relaxation tenter with a clip. In the biaxially oriented polyester film of the invention, the rate of dimensional change in the temperature-decreasing process from 150 ° C. to 50 ° C. in the direction perpendicular to the main orientation axis direction of the film is 70 ppm / ° C. or more and 140 ppm / ° C. or less, respectively. It is preferable from the viewpoint of bonding properties with COP because it can suppress wrinkling and peeling when bonded with COP.

  In recent years, in a film made of COP, which is an amorphous resin used as a substrate for forming a transparent conductive film, the film dimensional change rate when the temperature is lowered from 150 ° C. to 50 ° C. depends on the molecular skeleton of COP. It is not lower than 140 ° C. and not higher than 140 ppm / ° C. By setting the film dimensional change rate when the temperature of the film of the present invention is lowered from 150 ° C. to 50 ° C. within the above range, the dimensional change behavior in the slow cooling process after heating in the processing step can be brought close to COP. Can be prevented from wrinkling and peeling, and maintain good conductivity without losing the flatness of the transparent conductive film-forming substrate after the conductive film is formed. Can do. More preferably, they are 80 ppm / degrees C or more and 120 ppm / degrees C or less, More preferably, they are 90 ppm / degrees C or more and 110 ppm / degrees C or less.

  When the dimensional change rate of the film is less than 70 ppm / ° C., when used as a transparent conductive film by being bonded to COP, the dimensional change during cooling after heating in the processing step is small compared to COP, resulting in a dimensional difference. For this reason, wrinkles and peeling occur, the flatness of the film-forming substrate of the transparent conductive film deteriorates after the conductive film is formed, and the conductive film may be lost due to loss of the transparent conductive film.

  Moreover, when the dimensional change rate of the film exceeds 140 ppm / ° C., when used as a transparent conductive film by being bonded to COP, the dimensional change at the time of temperature drop after heating in the processing step is larger than that of COP, and the dimensional difference is large. As a result, wrinkles and peeling occur, the flatness of the film-forming substrate of the transparent conductive film deteriorates after the conductive film is formed, and the conductive film may be lost due to loss of the transparent conductive film.

In the biaxially oriented polyester film of the present invention, the average value of Young's modulus in the direction perpendicular to the film main orientation axis direction is Yave (MPa), the film main orientation axis direction, and the direction perpendicular to it. When the average value of the dimensional change rate in the temperature lowering process from 150 ° C. to 50 ° C. is α ave (ppm / ° C.), satisfying the following formula (iv) is used as a transparent conductive film by bonding with COP Since curling after the curing process can be suppressed, it is preferable from the viewpoint of workability.
(Vi) 20 ≦ Yave / αave ≦ 50
The Young's modulus indicates the rigidity of the film. The higher the Young's modulus, the higher the rigidity of the film and the higher the deformation stress associated with dimensional changes. Therefore, if there is a difference in Yave / αave between COP and PET film, when it is used as a transparent conductive film by bonding with COP, the film curls due to the difference in stress due to dimensional change when it is gradually cooled to room temperature after the curing process. , Workability is impaired. By setting Yave / αave to 20 or more and 40 or less, the stress difference in dimensional change between COP and PET is reduced, so curling can be suppressed and workability is improved, which is preferable. More preferably, it is 30-40. When Yave / αave is less than 20, the rigidity of the film is significantly lower than that of COP, so the curl amount is increased on the polyester film side, and scratches are likely to occur during processing, resulting in poor processability. On the other hand, if Yave / αave exceeds 50, the rigidity of the film becomes higher than that of COP, so that the curl amount becomes extremely large on the COP side and the workability may be inferior.

  The biaxially oriented polyester film of the present invention is a laminated polyester film having at least three layers, and the intrinsic viscosity of both surface layers of the polyester film is 0.67 dl / g or more and 0.9 dl / g or less. Is preferable from the viewpoint of controlling the rigidity of the biaxially oriented polyester film. More preferably, it is 0.70 dl / g or more and 0.85 dl / g or less. More preferably, it is 0.72 dl / g or more and 0.80 dl / g or less.

  Polyester resins generally have a correlation between the degree of polymerization (molecular chain length) and the intrinsic viscosity. Therefore, the intrinsic viscosity serves as an index of the degree of polymerization (the length of the molecular chain) of the polyester resin, and the higher the degree of polymerization (the longer the molecular chain), the higher the intrinsic viscosity. By making the intrinsic viscosity of the polyester resin constituting the surface layer on both sides of the polyester film above the lower limit of the above range, the molecular chain of the polyester resin constituting the surface layer on both sides of the polyester film becomes longer and the mobility of the molecular chain decreases. Therefore, the molecular chain becomes rigid and the Young's modulus increases. Therefore, even when the amorphousness of the layers other than the surface layer on both sides of the polyester film is increased, the Young's modulus of the entire polyester film can be suppressed from being extremely lowered, and the Young's modulus can be set within a preferable range.

  When the intrinsic viscosity of the polyester resin constituting the surface layer on both sides of the polyester film is less than 0.67 dl / g, the Young's modulus of the polyester resin constituting the surface layer on both sides of the polyester film is lowered, and the transparent conductive material is bonded to COP. When used as a film, the planarity may deteriorate.

  Moreover, when the intrinsic viscosity of the polyester resin constituting the surface layer on both sides of the polyester film exceeds 0.90 dl / g, the Young's modulus becomes extremely high, so that the film may be inferior in mechanical properties and workability.

In the biaxially oriented polyester film of the present invention, the average value of the intrinsic viscosity of the surface layer on both sides of the laminated polyester film is IVa (dl / g), and the intrinsic viscosity of the layers other than the surface layer on both sides of the laminated polyester film is averaged. When the value is IVb (dl / g), it is preferable from the viewpoint of controlling the mechanical properties of the biaxially oriented polyester film that the following formula (ii) is satisfied. More preferably, it is 0.03 dl / g or more and 0.2 dl / g or less. More preferably, it is 0.05 dl / g or more and 0.15 dl / g or less.
(Ii) 0.01 ≦ IVa−IVb ≦ 0.3
By making IVa-IVb into the said range, the fall of an extreme Young's modulus can be suppressed and a mechanical characteristic and workability can be kept favorable.

  If IVa-IVb is less than 0.01, the Young's modulus of the entire laminated polyester film is lowered and the mechanical properties may be inferior. On the other hand, when IVa-IVb exceeds 0.3, Young's modulus becomes extremely high, and therefore mechanical properties and workability may be inferior.

  The biaxially oriented polyester film of the present invention has a ratio of the sum of the thicknesses of the surface layers on both sides of the polyester film and the sum of the thicknesses of the layers other than the surface layer (sum of the thicknesses of the surface layers on both sides / the sum of the thicknesses of the layers other than the surface layer). ) Is preferably 1/9 to 1/2.

  When the thickness of the outermost layer is thin and the ratio of the sum of the thicknesses of layers other than the surface layer is less than 1/9, the effect of improving the film forming property and the mechanical property by lamination may not be obtained. On the other hand, when the thickness of the outermost layer is thick and the ratio of the sum of the thicknesses of the layers other than the surface layer exceeds 1/2, it is strongly influenced by the orientation of the outermost layer, and the inner layer is forcibly stretched. May be worse.

  The biaxially oriented polyester film of the present invention preferably has a haze change amount of 5.0% or less before and after heat treatment at 140 ° C. for 90 minutes. More preferably, it is 3.0% or less. More preferably, it is 1.0% or less.

  A biaxially oriented polyester film is not preferred if the amount of change in haze before and after heat treatment at 140 ° C. for 90 minutes exceeds 5.0% because oligomers are generated on the surface of the film and cause whitening of the film.

In the biaxially oriented polyester film of the present invention, at least one surface has an ester cyclic trimer amount of 0 mg / m ² or more and 1.5 mg / m ² or less on the surface of the polyester film after heat treatment at 140 ° C. for 90 minutes. In addition to being able to suppress the precipitation of the cyclic trimer when bonded to COP and to suppress the generation of foreign matters and the whitening of the film, it is preferable because contamination of the member in the bonding step can be suppressed. More preferably not more than 0 mg / ^{m 2} or more 1.0 mg / ^{m 2,} more preferably not more than 0 mg / ^{m 2} or more 0.5 mg / ^{m 2.} If at least one surface exceeds the amount of ester cyclic trimer on the surface of the polyester film after heat treatment at 140 ° C. for 90 minutes exceeding 1.5 mg / m ² , foreign matter due to cyclic trimer precipitation when bonded to COP In addition to occurrence and whitening of the film, there is a possibility of contamination of the members in the bonding process. In addition, the biaxially oriented polyester film of the present invention has at least one surface with a change amount of the cyclic trimer on the film surface before and after heat treatment at 140 ° C. for 90 minutes (surface precipitation amount before and after heat treatment) of 1.4 mg / m 2. It is preferable that it is ² or less. More preferably, it is 1.0 mg / m ² or less. In addition, the cyclic trimer here represents a cyclic trimer of a repeating unit of polyester. When the polyester is polyethylene terephthalate, it means an ethylene terephthalate cyclic trimer. Ethylene terephthalate cyclic trimer is a kind of low molecular weight substance existing in polyethylene terephthalate resin, and is produced by intermolecular transesterification and intramolecular transesterification. The three monomers have a cyclic structure and occupy about 80% by weight of the low molecular weight material in the polyethylene terephthalate resin. The amount of cyclic trimer precipitation is determined by the measurement method described later. The method for setting the ester cyclic trimer amount on the surface of the polyester film after heat treatment at 140 ° C. for 90 minutes to the above range is not particularly limited, but for example, the crystallinity of the resin constituting the film is reduced ( A method of bringing it close to amorphous). Specifically, when the resin constituting the polyester film has a crystallization parameter ΔTcg obtained by differential scanning calorimetry in the range of 80 ° C. or more and 120 ° C. or less, the cyclic trimer deposited on the film surface by heat treatment is reduced. This makes it possible to reduce the amount of cyclic trimer deposited on the surface of the polyester film before and after heat treatment. Preferably, it is 90 degreeC or more and 115 degrees C or less. More preferably, it is 95 ° C. or higher and 110 ° C. or lower.

A general polyester film is often composed of a crystalline polyester resin. In a polyester film obtained by biaxially stretching such a crystalline polyester resin, a portion where the polyester resin is crystallized by orientation (hereinafter referred to as orientation). Crystallized part) and amorphous part. Here, the oligomer component centering on the cyclic trimer has a high affinity with the amorphous part, and a large amount exists in the amorphous part. This amorphous part is in a thermally unstable state as compared to the oriented crystallized part, and when subjected to heat, the molecular mobility is increased and the system is transferred in a direction in which the energy becomes stable. That is, the amorphous part is transferred to the crystallized part by heat. When such a system transition occurs, the oligomer component centered on the cyclic trimer that has been present inside the amorphous part is excluded to the outside. As a result, the oligomer component is deposited on the film surface, and in addition to the generation of foreign matter and whitening of the film, contamination of members in the bonding process occurs. Therefore, by providing an amorphous layer on the polyester film, precipitation of the cyclic trimer on the film surface can be suppressed,
Not only can the generation of foreign matter and whitening of the film be suppressed, but also the amount of cyclic trimer deposited on the surface of the polyester film before and after heat treatment can be reduced, and contamination of the components in the bonding process can be suppressed. Become. Specifically, a method in which an amorphous region is clearly formed on a polyester film can be mentioned. Since this amorphous region is made of an amorphous polyester resin, it hardly crystallizes even when subjected to heat treatment. Therefore, the oligomer component centering on the cyclic trimer can be sufficiently trapped in the amorphous region, and precipitation of the oligomer from the surface layer of the polyester film can be prevented.

  The biaxially oriented polyester film of the present invention has at least one surface roughness Ra of 1 nm to 200 nm and a maximum height roughness Rz of 100 nm to 2000 nm. It is preferable because charging at the time of peeling can be prevented. The surface roughness Ra is more preferably 5 nm or more and 100 nm or less. More preferably, it is 10 nm or more and 50 nm or less. When the surface roughness Ra is less than 1 nm, the surface is smooth, so that the adhesion becomes too high when it is bonded to the COP, and the bubbles cannot be formed well and bubbles may be generated or peeling electrification may occur. is there. When the surface roughness Ra exceeds 200 nm, it becomes the starting point for generation of dents and the like, and bubbles may be generated when the COP is bonded. Further, the maximum height roughness Rz is more preferably not less than 300 nm and not more than 1500 nm. More preferably, it is 400 nm or more and 1000 nm or less. If the maximum height roughness Rz is less than 100 nm, the surface is smooth, so that the adhesiveness becomes too high when bonded to COP, so that it is not possible to stick well and bubbles are generated or peeling charge is generated. There is a case. When the maximum height roughness Rz exceeds 2000 nm, it becomes the starting point for the occurrence of dents and the like, and bubbles may be generated when the COP is bonded. The method for setting the surface roughness of at least one of the above ranges is not particularly limited. For example, while the layers other than the surface layer on both sides of the polyester film are brought close to the amorphous layer, the surface layers on both sides of the polyester film are The method of making particle | grains contain in the polyester resin to comprise is mentioned. By bringing the layers other than the surface layer on both sides of the polyester film closer to the amorphous layer, a flexible amorphous structure is formed as compared to the rigid crystal structure, so when the particles are contained, the particles formed on the surface layer Since it becomes easy to embed and the particles are easily dispersed evenly, it is possible to form projections on the surface layer of the film evenly, and the surface roughness Ra and the maximum height roughness Ra can be set within a preferable range. .

  As content of the particle | grains contained in the polyester resin which comprises the surface layer of the both sides of a polyester film, it is preferable that it is 0.01 to 5 weight%. If the particle content is less than 0.01% by weight, the formation of surface protrusions may be insufficient. If the particle content is more than 5% by weight, the surface protrusions may become too large. More preferably, it is 0.01 wt% or more and 3 wt% or less.

  Although it does not specifically limit as particle | grains contained in the biaxially-oriented polyester film of this invention, Both inorganic particles and organic particles can be used. Specific examples include inorganic particles such as clay, mica, titanium oxide, calcium carbonate, wet silica, dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina silicate, kaolin, talc, montmorillonite, alumina, and zirconia. Examples thereof include organic particles having acrylic acid, styrene resin, silicone, imide and the like as constituent components, and core-shell type organic particles.

  Further, the above-mentioned particles preferably have a particle size of 0.5 μm or more and 10 μm or less from the viewpoint of controlling the surface shape, and more preferably 0.8 μm or more and 8 μm or less. In addition, when the polyester film of this invention is a laminated polyester film of 3 layers or more, it is preferable that said particle | grains contained in the polyester resin composition which comprises a surface layer are 0.5 micrometer or more and 10 micrometers or less.

  Next, although the specific example is given and demonstrated about the manufacturing method of the biaxially-oriented polyester film of this invention, this invention should not be limited and limited to this example.

First, a polyester resin is heated and melted in an extruder and then discharged from a die to obtain an unstretched sheet. When the biaxially oriented polyester film of the present invention has a laminated structure, it can be obtained by a conventionally known production method.
(1) When producing an unstretched sheet by discharging the melted polyester from the die, it is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 ° C. or more and 40 ° C. or less to produce an unstretched sheet.
(2) The area ratio of the unstretched sheet obtained in (1) in the longitudinal direction (MD) of the film and the width direction (TD) of the film at a temperature T1n (° C.) satisfying the following formula (v): Biaxial stretching to 5 times or more and 16.0 times or less.
(Vii) Tg (° C.) ≦ T1n (° C.) ≦ Tg + 40 (° C.)
Tg: Glass transition temperature (° C.) of the resin constituting the polyester film
(3) The biaxially stretched film obtained in (2) is subjected to a heat setting treatment for 1 second to 30 seconds at a temperature (Th0 (° C.)) that satisfies the following formula (vi), and gradually cooled gradually Then, a polyester film is obtained by cooling to room temperature.
(Viii) Tm-60 (° C.) ≦ Th0 (° C.) ≦ Tm-10 (° C.)
Tm: Melting point (° C.) of the resin constituting the film
A substantially amorphous polyester film can be obtained by obtaining an unstretched sheet under the conditions satisfying (1), and (2) a film having good mechanical properties that facilitates imparting orientation to the film in the subsequent steps. Can be easily obtained.
By obtaining a biaxially stretched film under the conditions satisfying (2), it is possible to impart an appropriate orientation to the film and to obtain a film with good mechanical properties.
When the crystal structure of the layer having a low melting point is broken under the condition satisfying (3) and the amorphous structure is irregularly oriented, the amorphous property of the film is increased, and the film expansion coefficient can be increased. In addition, since the surface layers on both sides of the polyester film are crystallographically oriented, the structure of the polyester molecular chain in which the orientation is formed is stable, and a film having excellent mechanical properties and heat shrinkage can be obtained.

  In addition, in (2), as a method of biaxial stretching, the sequential biaxial separation is performed by separating the film longitudinal direction (MD) and the film width direction (direction perpendicular to the film longitudinal direction, TD) separately. You may perform using any of the extending | stretching method and the simultaneous biaxial stretching method which performs extending | stretching of a longitudinal direction and the width direction simultaneously. Moreover, when extending | stretching temperature (T1n) (degreeC) is less than Tg (degreeC), it is difficult to extend | stretch. When T1n (° C.) exceeds Tg + 40 (° C.), the film is frequently broken and the film may not be obtained by stretching. More preferably, Tg + 10 (° C.) ≦ T1n (° C.) ≦ Tg + 30 (° C.).

  In the step (3), when Th0 exceeds Tm−10 ° C., the orientation of the film imparted by stretching collapses, the film has an excessively large expansion coefficient, and random coarse crystals are produced, thereby causing transparency of the film. As a result of fixing the molecular chains existing around them by random coarse crystals, the mechanical properties are inferior and the film dimensional change rate is also reduced. When Th0 is lower than Tm−60 ° C., the structure of the molecular chain is not stable, and the planarity is deteriorated or the film forming property is deteriorated.

[Characteristic measurement method and effect evaluation method]
A. Using a film expansion coefficient thermomechanical measuring device TMA / SS6000 (manufactured by Seiko Instruments Inc.) in the temperature rising process from 25 ° C. to 150 ° C., the load is applied to a sample having a sample width of 4 mm and a sample length (distance between chucks) of 20 mm. Load 3g. The temperature is raised from room temperature to 160 ° C. at a heating rate of 10 ° C./min, and the value of the dimension of the sample at each temperature (° C.) is obtained. And it calculates from the following formula (iii) from the dimension L (25 ° C.) (mm) of the sample at 25 ° C. and the dimension L (150 ° C.) (mm) at 150 ° C. In addition, a film expansion coefficient is implemented by n = 5 about the film main orientation axis direction and each direction perpendicular thereto, and is calculated as an average value thereof.
(Iii) Film expansion coefficient (%) = L (150 ° C.) / L (25 ° C.) × 100
B. Dimensional change rate (CTE) (ppm / ° C) during the cooling process from 150 ° C to 50 ° C
In accordance with JIS K7197 (1991), a thermomechanical measuring device TMA / SS6000 (manufactured by Seiko Instruments Inc.) is used and a sample width of 4 mm is applied to a sample having a sample length (distance between chucks) of 20 mm. The temperature is raised from room temperature to 160 ° C. at a rate of temperature rise of 10 ° C./min, held for 10 minutes, and then lowered to 20 ° C. at 10 ° C./min to obtain the value of the dimension of the sample at each temperature (° C.). From the sample size L (150 ° C.) (mm) at 150 ° C. and the sample size L (50 ° C.) (mm) at 50 ° C., it is calculated from the following equation (vii). In addition, a dimensional change rate is implemented by n = 5 for each of the film main orientation axis direction and the direction perpendicular thereto, and is calculated as an average value thereof.
(Ix) CTE (ppm / ° C.) = 10 ⁶ × (L (150 ° C.) − L (50 ° C.))) / {20 × (150-50)}
C. Film, melting point of resin constituting each layer (Tm, TmA, TmB) (° C.)
Using a method based on JIS K 7121 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. and a disk session “SSC / 5200” for data analysis were used. Perform the measurement in the following manner.
Weigh each 5 mg sample into the sample pan, heat the sample from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1st RUN), hold in that state for 5 minutes, and then rapidly cool to 25 ° C. or lower . Immediately thereafter, the temperature was increased again from 25 ° C. to 300 ° C. at a rate of temperature increase of 20 ° C./minute, and a 2ndRUN differential scanning calorimetry chart (the vertical axis represents thermal energy and the horizontal axis represents temperature) Get. In the 2ndRUN differential scanning calorimetry chart, the temperature at the peak top in the crystal melting peak, which is the endothermic peak, is obtained, and this is defined as the melting point (° C.). When two or more crystal melting peaks are observed, the temperature at the peak top having the largest peak area is defined as the melting point.
When measuring the melting point of the resin constituting each layer of the laminated polyester film, only the resin constituting each layer is shaved from the laminated polyester film using a microtome and used for measurement.

D. Film, glass transition temperature (Tg) of resin constituting each layer
In accordance with JIS K7121 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used, and a disk session “SSC / 5200” was used for data analysis. Perform the measurement.
5 mg of a sample is weighed in a sample pan, and the sample is heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1stRUN), held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. Immediately thereafter, the temperature was increased again from 25 ° C. to 300 ° C. at a rate of temperature increase of 20 ° C./minute, and a 2ndRUN differential scanning calorimetry chart (the vertical axis represents thermal energy and the horizontal axis represents temperature) Get. In the 2ndRUN differential scanning calorimetry chart, in the step change portion of the glass transition, a straight line that is equidistant from the extended straight line of each base line in the vertical axis direction and a curve of the step change portion of the glass transition are Find from the point of intersection. When two or more stepwise changes in glass transition are observed, the glass transition temperature is obtained for each, and the average of these temperatures is taken as the glass transition temperature (Tg) (° C.) of the sample. When measuring the glass transition temperature of the resin constituting each layer of the laminated polyester film, only the resin constituting each layer is cut out from the laminated polyester film using a microtome and used for measurement.

E. Film, crystallization temperature (Tc) of resin constituting each layer, crystallization parameter (ΔTcg)
In accordance with JIS K7121 (1999), a differential scanning calorimeter “Robot DSC-RDC220” manufactured by Seiko Denshi Kogyo Co., Ltd. was used, and a disk session “SSC / 5200” was used for data analysis. Perform the measurement.
5 mg of a sample is weighed in a sample pan, and the sample is heated from 25 ° C. to 300 ° C. at a heating rate of 20 ° C./min (1stRUN), held in that state for 5 minutes, and then rapidly cooled to 25 ° C. or lower. Immediately thereafter, the temperature is raised again from 25 ° C. to 300 ° C. at a rate of temperature increase of 20 ° C./min to obtain a 2ndRUN differential scanning calorimetry chart (vertical axis is thermal energy and horizontal axis is temperature). From the differential scanning calorimetry chart of 2ndRUN, the temperature is obtained as the peak top temperature of the crystallization peak, which is an exothermic peak at the time of temperature rise, and this is defined as the crystallization temperature (Tc) (° C.). When two or more crystallization peaks are observed, the crystallization temperature is obtained from the peak top temperature of each peak, and the average of these temperatures is taken as the crystallization temperature (Tc) (° C.) of the sample.
ΔTcg (° C.) is obtained from the following equation using Tg and Tc obtained by the above method.
ΔTcg = Tc−Tg.
When measuring the crystallization temperature of the resin constituting each layer of the laminated polyester film, only the resin constituting each layer is cut out from the laminated polyester film using a microtome and used for measurement.

F. Young's modulus (MPa)
A film cut to a width of 10 mm and a length of 150 mm was set in an apparatus having a distance between chucks of 50 mm using an automatic tensile strength measuring device “Tensilon AMF / RTA-100” manufactured by Orientec Co., Ltd., and a tensile speed of 300 mm. / Min, a temperature of 25 ° C., and a relative humidity of 65% were subjected to a tensile test, and the Young's modulus was obtained from the tangent of the rising portion of the obtained load-elongation curve. The Young's modulus is calculated as an average value obtained by performing n = 5 for each of the film main orientation axis direction and the direction perpendicular thereto.

G. Intrinsic viscosity (IV)
The polyester film is dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / dl), and the viscosity of the solution at 25 ° C. is measured using an Ostwald viscometer. Similarly, the viscosity of the solvent is measured. Using the obtained solution viscosity and solvent viscosity, [η] (dl / g) is calculated by the following formula (viii), and the obtained value is used as the intrinsic viscosity (IV).
(X) ηsp / C = [η] + K [η] 2 · C (where ηsp = (solution viscosity (dl / g) / solvent viscosity (dl / g)) − 1, K is a Huggins constant (0. 343)).
When measuring melting | fusing point of resin which comprises each layer of a laminated polyester film, only resin which comprises each layer is cut out from laminated polyester film using cutters, such as a cutter, and it uses for a measurement.

H. ΔHaze (change in haze before and after treatment at 140 ° C. for 90 minutes) (%)
The film was cut into a square shape with a side of 10 cm, and a haze meter NDH-5000 manufactured by Nippon Denshoku Co., Ltd. was used to measure the haze at three locations randomly to calculate the average value, and the haze H0 (%) before the test. And The sample was fixed in a room maintained at 23 ° C. and a relative humidity of 65% RH in an oven made by Tabai Espec Co., Ltd., and the four sides of the sample were fixed and dried at 140 ° C. and a relative humidity of 0% RH or less. Heat-treat for 90 minutes. The haze of the film after heat treatment is measured in the same manner to determine H1 (%). Δhaze (ΔH) is determined by the following formula (ix).
(Xi) Δhaze (%) = H1−H0
The value of Δhaze is determined as follows.
A; Δhaze 1.0% or less B; Δhaze 1.0% to 3.0% or less C; Δhaze 3.0% to 5.0% or less D; Δhaze 5.0% A exceeding is the best and D is the worst.

I. Evaluation of bonding with COP film (wrinkle)
The film of the present invention was cut into a size of 20 cm × 20 cm, bonded to a COP film, and then placed in an oven at 120 ° C. and allowed to stand for 1 hour. Thereafter, the oven temperature was cooled to room temperature at a rate of 20 ° C./min. Thereafter, the number of wrinkles having a length of 3 cm or more on the sheet obtained by bonding the film of the present invention and the COP film is measured and determined as follows.
Less than 4; A
4 or more and 9 or less; B
10 or more and 15 or less; C
16 or more; D
A is the best and D is the worst.
As the COP film, “ZEONOR ZF14” manufactured by Nippon Zeon Co., Ltd., a film having a thickness of 40 μm is used. For pasting, Toray Cortex Co., Ltd. “Toyo Retex” R5000 as a pressure-sensitive adhesive was adjusted to a toluene solution adjusted to a pressure-sensitive adhesive content of 15% with respect to 100 parts by mass of the toluene solution. What applied what added 3 mass parts of crosslinking agent "Coronate L" so that the coating thickness after drying might be 10 micrometers was used.

J. et al. Evaluation of bonding with COP film (number of bubbles before heat treatment)
The film of the present invention was cut into a size of 20 cm × 20 cm and bonded to a COP film. Thereafter, the number of bubbles having a size of 1 mm or more and 10 mm or less in the sheet obtained by bonding the film of the present invention and the COP film is measured and determined as follows.
Less than 5; A
6 or more and 10 or less; B
11 or more and 15 or less; C
16 or more; D
A is the best and D is the worst.
As the COP film, “ZEONOR ZF14” manufactured by Nippon Zeon Co., Ltd., a film having a thickness of 40 μm is used. For pasting, Toray Cortex Co., Ltd. “Toyo Retex” R5000 as a pressure-sensitive adhesive was adjusted to a toluene solution adjusted to a pressure-sensitive adhesive content of 15% with respect to 100 parts by mass of the toluene solution. What applied what added 3 mass parts of crosslinking agent "Coronate L" so that the coating thickness after drying might be 10 micrometers was used.

K. Evaluation of bonding with COP film (number of bubbles after heat treatment)
The film of the present invention was cut into a size of 20 cm × 20 cm, bonded to a COP film, and then placed in an oven at 120 ° C. and allowed to stand for 1 hour. Thereafter, the oven temperature was cooled to room temperature at a rate of 20 ° C./min. Thereafter, the number of bubbles having a size of 1 mm or more and 10 mm or less in the sheet obtained by bonding the film of the present invention and the COP film is measured and determined as follows.
Less than 10; A
11 or more and 20 or less; B
21 to 30; C
31 or more; D
A is the best and D is the worst.
As the COP film, “ZEONOR ZF14” manufactured by Nippon Zeon Co., Ltd., a film having a thickness of 40 μm is used. For pasting, Toray Cortex Co., Ltd. “Toyo Retex” R5000 as a pressure-sensitive adhesive was adjusted to a toluene solution adjusted to a pressure-sensitive adhesive content of 15% with respect to 100 parts by mass of the toluene solution. What applied what added 3 mass parts of crosslinking agent "Coronate L" so that the coating thickness after drying might be 10 micrometers was used.

L. Curling property of laminate with COP film The laminate produced in the section was placed in an oven at 120 ° C. and allowed to stand for 1 hour. Thereafter, the temperature of the oven was cooled to room temperature at a rate of 20 ° C./min and left for 1 hour. Then, place the film on the horizontal surface so that the COP film is on the upper side, measure the amount of floating from the horizontal surface of the four corners of the laminate, determine the average value, and as the curl amount (mm) Judgment is made as follows. When the corner of the laminate does not float from the horizontal surface by the above method, the PET film is placed on the upper side, and the curl amount is obtained as a negative value.
0 mm or more and less than 20 mm; A
20 mm or more and less than 40 mm or more than 0 mm and less than -5 mm; B
40 mm or more and less than 55 mm or -5 mm or more and less than -10 mm; C
55 mm or more or -10 mm or more; D
N. Film-forming property The number of times the film breaks during film formation is counted. A less than 1 time is evaluated as A, 1 time or more and less than 5 times is evaluated as B, and 5 times or more is evaluated as C. A is the best film-forming property, and C is the worst.

  In the above measurement, when the longitudinal direction and the width direction of the film to be measured are not known, the direction having the maximum refractive index in the film is regarded as the longitudinal direction, and the direction perpendicular to the longitudinal direction is regarded as the width direction. The direction of the maximum refractive index in the film may be obtained by measuring the refractive index in all directions of the film with a refractometer, and the slow axis direction may be determined by a phase difference measuring device (birefringence measuring device) or the like. It may be obtained by deciding.

O. Amount of cyclic trimer present on the surface of the polyester film The polyester film is heated in air at 140 ° C. for 90 minutes. Thereafter, the heat-treated film is formed into a box shape with the measurement surface (coating layer) as the inner surface so that the upper part is 10 cm in length and width and the height is 3 cm. Next, 4 ml of DMF (dimethylsulfoamide) was placed in the box prepared by the above method and allowed to stand for 3 minutes, and then DMF was recovered and subjected to liquid chromatography (manufactured by Shimadzu Corporation: LC-7A, mobile phase A: Acetonitrile, mobile phase B: 2% aqueous acetic acid, column: “MCI GEL ODS 1HU” manufactured by Mitsubishi Chemical Corporation, column temperature: 40 ° C., flow rate: 1 ml / min, detection wavelength: 254 nm) The amount of the cyclic trimer was determined, and this value was divided by the film area in contact with DMF to obtain the amount of the film surface cyclic trimer (mg / m ² ). The ester cyclic trimer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method). The standard sample was prepared by accurately weighing the pre-sorted ester cyclic trimer and dissolving it in accurately measured DMF. Further, the amount of surface cyclic trimer before heat treatment is measured in the same manner, and the initial amount of surface cyclic trimer (mg / m ² ) is obtained. The amount of surface cyclic trimer precipitation (mg / m ² ) before and after heat treatment is determined by the following formula (x).
(X) Precipitation amount of surface cyclic trimer before and after heat treatment = Amount of surface cyclic trimer after heat treatment−Amount of initial surface cyclic trimer Cyclic Trimer Content of Film A mixed solvent of hexafluoroisopropanol / chloroform is added to 0.05 g of a film to dissolve it, and then this solution is put into acetonitrile to precipitate a polymer component. Filter the precipitate and dry the supernatant. The dried product was dissolved in 2 ml of acetonitrile to obtain a sample solution for liquid chromatogram. Using a chromatogram LC20A manufactured by Shimadzu Corporation, using Develosil ODS-MG3 manufactured by Nomura Chemical Co., Ltd. as a column, using a water-acetonitrile mixed solution as a developing solution, a chromatogram is obtained with UV light having a wavelength of 254 nm, and circular The cyclic trimer was quantified by substituting a calibration curve prepared with dimethyl terephthalate.

Q. Surface roughness (Ra), maximum height roughness (Rz)
The surface morphology of the polyester film is measured under the following conditions in accordance with JIS-B0601 (1994) using a high-definition fine shape measuring instrument (three-dimensional surface roughness meter) of the stylus method.
・ Measuring device: 3D fine shape measuring instrument (model ET-4000A), manufactured by Kosaka Laboratory Ltd./Analyzing equipment: 3D surface roughness analysis system (model TDA-31)
-Stylus: Tip radius 0.5 μm R, diameter 2 μm, made of diamond • Needle pressure: 100 μN
・ Measurement direction: film longitudinal direction and film width direction average after each measurement ・ X measurement length: 1.0 mm
-X feed speed: 0.1 mm / s (measurement speed)
・ Y feed pitch: 5μm (measurement interval)
-Number of Y lines: 81 (measured number)
・ Z magnification: 2000 times (vertical magnification)
・ Low frequency cut-off: 0.20mm (swell cut-off value)
High frequency cut-off: R + Wmm (roughness cut-off value) R + W means not cut off.
-Filter method: Gaussian space type-Leveling: Available (tilt correction)
- reference area: ^1mm 2.
The surface roughness Ra of one surface was RaA and the maximum height roughness RzA, and the surface roughness Ra of the other surface was RaB and the maximum height roughness RzB.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.
[Production of PET-1] Polymerization was carried out from terephthalic acid and ethylene glycol by a conventional method using antimony trioxide as a catalyst to obtain melt-polymerized PET. The obtained melt-polymerized PET had a glass transition temperature of 80 ° C., a melting point of 255 ° C., and an intrinsic viscosity of 0.62.
[Production of PET-2] PET-1 was solid-phase polymerized by a conventional method to obtain PET-2. The obtained PET-2 had a glass transition temperature of 82 ° C., a melting point of 255 ° C., and an intrinsic viscosity of 0.85.
[Production of PET-3]
PET-1 was solid-phase polymerized by a conventional method to obtain PET-3. The obtained PET-3 had a glass transition temperature of 82 ° C., a melting point of 255 ° C., and an intrinsic viscosity of 0.96.
[Production of PET-4]
PET-1 was solid-phase polymerized by a conventional method to obtain PET-4. The obtained PET-4 had a glass transition temperature of 82 ° C., a melting point of 255 ° C., and an intrinsic viscosity of 0.80.
[Production of PET-A] From terephthalic acid, isophthalic acid and ethylene glycol, polymerization is carried out by a conventional method so that the copolymerization amount of isophthalic acid is 5 mol% with respect to the total amount of digalbonic acid component using antimony trioxide as a catalyst. Copolymerized PET was obtained. The obtained copolymerized PET had a glass transition temperature of 78 ° C., a melting point of 245 ° C., and an intrinsic viscosity of 0.74.
[Production of PET-B] From terephthalic acid, isophthalic acid and ethylene glycol, polymerization is carried out in a conventional manner so that the amount of isophthalic acid copolymerization is 10 mol% with respect to the total amount of digalbonic acid component using antimony trioxide as a catalyst. Copolymerized PET was obtained. The obtained copolymerized PET had a glass transition temperature of 76 ° C., a melting point of 235 ° C., and an intrinsic viscosity of 0.74.
[Production of PET-C] From terephthalic acid, isophthalic acid and ethylene glycol, polymerization is performed by a conventional method using antimony trioxide as a catalyst so that the copolymerization amount of isophthalic acid is 15 mol% with respect to the total amount of digalbonic acid component, Copolymerized PET was obtained. The resulting copolymerized PET had a glass transition temperature of 74 ° C., a melting point of 230 ° C., and an intrinsic viscosity of 0.74.
[Production of PET-D] From terephthalic acid, isophthalic acid and ethylene glycol, polymerization is carried out by a conventional method so that the amount of copolymerized isophthalic acid is 20 mol% with respect to the total amount of digalbonic acid component using antimony trioxide as a catalyst. Copolymerized PET was obtained. The obtained copolymerized PET had a glass transition temperature of 73 ° C., a melting point of 220 ° C., and an intrinsic viscosity of 0.74.
[Production of PET-E] From terephthalic acid, isophthalic acid and ethylene glycol, polymerization is carried out by a conventional method so that the copolymerization amount of isophthalic acid is 25 mol% with respect to the total amount of digalbonic acid component using antimony trioxide as a catalyst. Copolymerized PET was obtained. The copolymerized PET obtained had a glass transition temperature of 70 ° C. and no melting point was observed. Intrinsic viscosity was 0.74.
[Production of PET-F] From terephthalic acid, cyclohexanedimethanol (CHDM) and ethylene glycol, using antimony trioxide as a catalyst, the amount of copolymerization of cyclohexanedimethanol is 10 mol% with respect to the total amount of diol components. Polymerization was performed to obtain copolymerized PET. The copolymerized PET obtained had a glass transition temperature of 72 ° C., a melting point of 235 ° C., and an intrinsic viscosity of 0.74.
[Production of PET-G] From terephthalic acid, cyclohexanedimethanol (CHDM) and ethylene glycol, using antimony trioxide as a catalyst, the amount of cyclohexanedimethanol copolymerization is 20 mol% based on the total amount of diol components by a conventional method. Polymerization was performed to obtain copolymerized PET. The obtained copolymerized PET had a glass transition temperature of 70 ° C., a melting point of 221 ° C., and an intrinsic viscosity of 0.74.
[Production of particle master batch A] 99 parts by mass of a polyester resin and 1 part by mass of calcium carbonate particles (particle size: 1.1 μm) were put into a vented extruder and melt-kneaded in the extruder at 280 ° C. to obtain a polyester composition A particle master batch A was prepared.
[Production of particle masterbatch B] 50 parts by mass of polyester resin and 50 parts by mass of calcium carbonate particles (particle size 1.1 μm) were put into a vented extruder and melt-kneaded in the extruder at 280 ° C. to obtain a polyester composition A particle master batch B was prepared.

Example 1
The resin was composed of 3 layers of A / B / A, and 100 parts by mass of PET-2 as a resin constituting the surface layer was vacuum dried at 160 ° C. for 2 hours, and then charged into the extruder 1. Further, 100 parts by mass of PET-B as a resin constituting the inner layer was vacuum-dried at 160 ° C. for 2 hours, and then charged into the extruder 2. Each raw material is melted in the extruder, and the resin introduced into the extruder 1 is merged with a merging apparatus so as to be both surface layers of the film, extruded onto a casting drum having a surface temperature of 25 ° C., and a laminated sheet having a three-layer structure Was made. Subsequently, the sheet is preheated with a heated roll group, and then stretched 3.2 times in the longitudinal direction (MD direction) at a temperature of 90 ° C., and then cooled with a roll group at a temperature of 25 ° C. to be a uniaxially stretched film. Got. The obtained uniaxially stretched film was stretched 3.8 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 100 ° C. in the tenter while holding both ends with clips. Subsequently, heat setting was performed for 10 seconds at a temperature of 220 ° C. in a heat treatment zone in the tenter. Subsequently, the film was gradually cooled in a cooling zone and wound up to obtain a biaxially oriented polyester film. The obtained film is annealed in a hot-air oven installed between the film winding roll and the film winding roll so that the film is heat-treated for 5 minutes while applying a tension of 50 N at a temperature of 180 ° C. And a biaxially oriented polyester film having a thickness of 125 μm was obtained. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 1 has a film expansion rate of 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate is also in a suitable range. It was. Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

(Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the resin constituting the inner layer was changed to 100 parts by mass of PET-A. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 2 was a film having a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction and excellent in bonding properties with COP. Furthermore, since Yave / αave was in a suitable range, the film was excellent in workability and had a very small change in haze due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. Therefore, it was a film with less generation of bubbles after heating.

(Example 3)
A biaxially oriented polyester film was obtained by the same method as in Example 1 except that the resin constituting the inner layer was changed to 100 parts by mass of PET-C. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 3 was a film having a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction, and a film dimensional change rate in a suitable range. . Furthermore, since Yave / αave was in a suitable range, the film was considerably excellent in workability, and the film had little change in haze due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. Therefore, it was a film with less generation of bubbles after heating.

Example 4
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the resin constituting the inner layer was changed to 100 parts by mass of PET-D. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 4 was a film excellent in bonding properties with COP because the film expansion coefficient was 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate was also in a suitable range. Furthermore, since Yave / αave was in a suitable range, the film was considerably excellent in workability, and the film had little change in haze due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the film has less generation of bubbles when bonded to COP. However, since the amount of the cyclic trimer present on the surface of the film after the heat treatment is large, the film has many bubbles generated after the heating.

(Example 5)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the lamination ratio was changed. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 5 was a film having a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction, and a film dimensional change rate in a suitable range. . Furthermore, since Yave / αave was in a suitable range, the film was considerably excellent in workability, and the change in haze due to heating was very small. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

(Example 6)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the lamination ratio was changed. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 6 has a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate is also in a suitable range. It was. Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

(Example 7)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the hot air oven temperature during the annealing treatment was changed to 200 ° C. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 7 has a film expansion rate of 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate is also in a suitable range. It was. Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

(Example 8)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the hot-air oven temperature during the annealing treatment was changed to 160 ° C. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 8 has a film expansion rate of 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate is also in a suitable range. It was. Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

Example 9
The resin constituting the surface layer is changed to 100 parts by mass of PET-3, the resin constituting the inner layer is changed to 100 parts by mass of PET-A, and the lamination ratio, film forming conditions, and annealing temperature are changed as described in the table. A biaxially oriented polyester film was obtained in the same manner as in Example 1. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 9 was a film having a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction and excellent in bonding properties with COP. Furthermore, since Yave / αave was in a suitable range, the film was excellent in workability and had a very small change in haze due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. Therefore, it was a film with less generation of bubbles after heating.

(Example 10)
Biaxial orientation in the same manner as in Example 1 except that PET-4 was changed to 100 parts by mass as the resin constituting the surface layer, and the lamination ratio, film forming conditions, and annealing temperature were changed as described in the table. A polyester film was obtained. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 10 was a film excellent in the bonding property with COP because the film expansion coefficient was 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate was also in a suitable range. Further, since Yave / αave was in a suitable range, the film was excellent in workability and had little change in haze due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

(Example 11)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the resin constituting the inner layer was changed to 100 parts by mass of PET-F. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 11 had a film expansion rate of 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate was also in a suitable range. . Furthermore, since Yave / αave was in a suitable range, the film was considerably excellent in workability, and the change in haze due to heating was very small. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

(Example 12)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the resin constituting the inner layer was changed to 100 parts by mass of PET-G. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 12 was a film having a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction and excellent in bonding properties with COP. Further, since Yave / αave was in a suitable range, the film was excellent in workability and had little change in haze due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the film has less generation of bubbles when bonded to COP. However, since the amount of the cyclic trimer present on the surface of the film after the heat treatment is large, the film has many bubbles generated after the heating.

(Example 13)
PET-B was vacuum-dried at 160 ° C. for 2 hours, then charged into an extruder, melted in the extruder, extruded onto a casting drum having a surface temperature of 25 ° C., and a laminated sheet having a three-layer structure was produced. Subsequently, the sheet is preheated with a heated roll group, and then stretched 3.2 times in the longitudinal direction (MD direction) at a temperature of 90 ° C., and then cooled with a roll group at a temperature of 25 ° C. to be a uniaxially stretched film. Got. The obtained uniaxially stretched film was stretched 3.8 times in the width direction (TD direction) perpendicular to the longitudinal direction in a heating zone at a temperature of 100 ° C. in the tenter while holding both ends with clips. Subsequently, heat setting was performed for 10 seconds at a temperature of 220 ° C. in a heat treatment zone in the tenter. Subsequently, the film was gradually cooled in a cooling zone and wound up to obtain a biaxially oriented polyester film. The obtained film is annealed in a hot-air oven installed between the film winding roll and the film winding roll so that the film is heat-treated for 5 minutes while applying a tension of 50 N at a temperature of 180 ° C. And a biaxially oriented polyester film having a thickness of 125 μm was obtained. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 13 was a film excellent in bonding property with COP because the film expansion coefficient was 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate was also in a suitable range. Furthermore, since Yave / αave was in a suitable range, the film was excellent in workability. However, the film had a large change in haze due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

(Example 14)
The resin constituting the surface layer was changed to 97.5 parts by mass of PET-2 and 2.5 parts by mass of the particle master batch A, and the resin constituting the inner layer was changed to 50 parts by mass of PET-A and 50 parts by mass of PET-C. Except for this, a biaxially oriented polyester film was obtained in the same manner as in Example 1. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 14 has a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate is also in a suitable range. It was. Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is very small, and the amount of cyclic trimer present on the film surface after heat treatment is also suitable. Due to the range, the film generated very little bubbles after heating.

(Example 15)
A biaxially oriented polyester film was obtained by the same method as Example 1 except that PET-2 was changed to 97.5 parts by mass and the particle master batch A was changed to 2.5 parts by mass as the resin constituting the surface layer. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 15 has a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate is also in a suitable range. It was. Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is very small, and the amount of cyclic trimer present on the film surface after heat treatment is also suitable. Due to the range, the film was much less likely to generate bubbles after heating.

(Example 16)
As in Example 1, except that the resin constituting the surface layer was changed to 97.5 parts by mass of PET-2, 2.5 parts by mass of the particle master batch A, and 100 parts by mass of the resin constituting the inner layer. A biaxially oriented polyester film was obtained by this method. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 16 had a film expansion rate of 0.5% or more in both the MD direction and the TD direction, and the film dimensional change rate was also in a suitable range. . Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is very small, and the amount of cyclic trimer present on the film surface after heat treatment is also suitable. Due to the range, the film produced less bubbles after heating.

(Example 17)
As in Example 1, except that the resin constituting the surface layer is changed to 97.5 parts by mass of PET-2, 2.5 parts by mass of the particle master batch A, and the resin constituting the inner layer is changed to 100 parts by mass of PET-D. A biaxially oriented polyester film was obtained by this method. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 17 has a film expansion coefficient of 0.5% or more in both the MD direction and the TD direction, the film dimensional change rate is also in a suitable range, and the surface roughness, maximum height, and roughness are also in a suitable range. It was a film excellent in pasting property with COP. Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the film was generated with considerably less bubbles when bonded to the COP. However, since the amount of the cyclic trimer present on the surface of the film after the heat treatment is large, the film has many bubbles generated after the heating.

(Example 18)
In the same manner as in Example 1, except that the resin constituting the surface layer was changed to 88 parts by mass of PET-2, 12 parts by mass of the particle master batch B, and 100 parts by mass of the resin constituting the inner layer. A biaxially oriented polyester film was obtained. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 18 is inferior to the preferred range in terms of surface roughness, maximum height and roughness, but both the MD direction and the TD direction have a film expansion coefficient of 0.5% or more, and the film dimensional change rate is also in a suitable range. In addition, since the amount of the ester cyclic trimer deposited on the surface of the polyester film before and after the heat treatment at 140 ° C. for 90 minutes was within a suitable range, it was a film excellent in bonding property with COP. Furthermore, because Yave / αave is in a suitable range, the workability is excellent, and the change in haze due to heating is very small. When used as a transparent conductive film by bonding with COP, it is a film having very excellent performance. there were. However, since the surface roughness and the maximum height roughness are large, many bubbles are generated when bonded to the COP, and the amount of cyclic trimer present on the film surface after the heat treatment is large. It was a film with a lot of occurrence.

(Example 19)
A biaxially oriented polyester film was obtained in the same manner as in Example 13 except that 97.5 parts by mass of PET-B and 2.5 parts by mass of the particle master batch A were changed. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Example 19 is inferior in the amount of ester cyclic trimer deposited on the surface of the polyester film before and after the heat treatment at 140 ° C. for 90 minutes, but the film expansion coefficient is 0.5% or more in both the MD direction and the TD direction. Since the dimensional change rate is also in a suitable range, and the surface roughness, maximum height, and roughness are also in a suitable range, the film has excellent adhesion to COP. Furthermore, since Yave / αave was in a suitable range, the film was excellent in workability. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is very small, and the amount of cyclic trimer present on the film surface after heat treatment is also suitable. Due to the range, the film was much less likely to generate bubbles after heating. However, the film had a large change in haze due to heating.

(Comparative Example 1)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that PET-A was changed to 80 parts by mass and PET-2 was changed to 20 parts by mass as the resin constituting the inner layer. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Comparative Example 1 was a film having very little haze change due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the film has less generation of bubbles when bonded to COP. However, in both the MD direction and the TD direction, the film expansion coefficient was 0.5% or less, and the film was inferior in bonding properties with COP. Furthermore, since Yave / αave is large, the curling property is poor and the workability is inferior. Therefore, the film is not suitable for use as a transparent conductive film by being bonded to COP. Furthermore, since there was much quantity of the cyclic trimer which exists in the film surface after heat processing, it was a film with much generation | occurrence | production of the bubble after a heating.

(Comparative Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the resin constituting the inner layer was changed to 100 parts by mass of PET-E. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Comparative Example 2 was a film excellent in workability because Yave / αave was in a suitable range. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the film has less generation of bubbles when bonded to COP. However, in both the MD direction and the TD direction, the film expansion coefficient was 0.5% or less, and the film was inferior in bonding properties with COP. Furthermore, since it is a film having a large change in haze due to heating, it is not suitable for use as a transparent conductive film by being bonded to COP. Furthermore, since there was much quantity of the cyclic trimer which exists in the film surface after heat processing, it was a film with much generation | occurrence | production of the bubble after a heating.

(Comparative Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the annealing treatment was not performed. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Comparative Example 2 was a film having a very small haze change due to heating. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the film has less generation of bubbles when bonded to COP. However, in both the MD direction and the TD direction, the film expansion coefficient was 0.5% or less, and the film was inferior in bonding properties with COP. Furthermore, since no annealing treatment is performed, heat shrinkage occurs when the curl test is heated, so the curl property is poor and the processability is poor. Therefore, it is not suitable for use as a transparent conductive film by being bonded to COP. It was a film. Furthermore, since there was much quantity of the cyclic trimer which exists in the film surface after heat processing, it was a film with much generation | occurrence | production of the bubble after a heating.

(Comparative Example 4)
A biaxially oriented polyester film was obtained in the same manner as in Example 13 except that 80 parts by mass of PET-A and 20 parts by mass of PET-2 were changed as the resin constituting the inner layer. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Comparative Example 4 was a film with less generation of bubbles when bonded to COP because the surface roughness and maximum height roughness were in a suitable range. However, in both the MD direction and the TD direction, the film expansion coefficient was 0.5% or less, and the film was inferior in bonding properties with COP. Furthermore, since Yave / αave is large, the curling property is poor, the workability is inferior, and the haze change due to heating is large. Therefore, the film is not suitable when used as a transparent conductive film by being bonded to COP. there were. Furthermore, since there was much quantity of the cyclic trimer which exists in the film surface after heat processing, it was a film with much generation | occurrence | production of the bubble after a heating.

(Comparative Example 5)
A biaxially oriented polyester film was obtained in the same manner as in Example 13 except that the resin constituting the film was changed to 100 parts by mass of PET-E. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Comparative Example 5 was a film excellent in workability because Yave / αave was in a suitable range. However, in both the MD direction and the TD direction, the film expansion coefficient was 0.5% or less, and the film was inferior in bonding properties with COP. Furthermore, since it is a film having a large change in haze due to heating, it is not suitable for use as a transparent conductive film by being bonded to COP. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the film has less generation of bubbles when bonded to COP. However, since the amount of the cyclic trimer present on the surface of the film after the heat treatment is large, the film has many bubbles generated after the heating.

(Comparative Example 6)
A biaxially oriented polyester film was obtained in the same manner as in Example 13 except that PET-2 was changed to 100 parts by mass as the resin constituting the film. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Comparative Example 6 was a film having a small change in haze due to heating. However, in both the MD direction and the TD direction, the film expansion coefficient was 0.5% or less, and the film was inferior in bonding properties with COP. Further, since Yave / αave is large, the curl property is poor and the processability is poor. Therefore, the film is not suitable for use as a transparent conductive film by being bonded to COP. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the film has less generation of bubbles when bonded to COP. However, since the amount of the cyclic trimer present on the surface of the film after the heat treatment is large, the film has many bubbles generated after the heating.

(Comparative Example 7)
A biaxially oriented polyester film was obtained in the same manner as in Example 13 except that the annealing treatment was not performed. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Comparative Example 7 was a film having a film expansion coefficient of 0.5% or less in both the MD direction and the TD direction, and inferior in bonding properties with COP. Furthermore, since the film is not annealed and heat shrinks when heated in the curl test, the film has poor curl properties, poor workability, and a large haze change due to heating. When used as a film, the film was not suitable. Furthermore, since the surface roughness and the maximum height roughness are in a suitable range, the generation of bubbles when bonded to COP is small, and the amount of cyclic trimer present on the film surface after heat treatment is also in a suitable range. For this reason, it was a film in which the generation of bubbles after heating was considerably small.

(Comparative Example 8)
A biaxially oriented polyester film was obtained in the same manner as Example 13 except that PET-2 was changed to 97.5 parts by mass and the particle master batch A was changed to 2.5 parts by mass as the resin constituting the film. Each characteristic of the obtained biaxially oriented polyester film is shown in the table. The film of Comparative Example 6 is a film with little change in haze due to heating, and because the surface roughness and maximum height roughness are in a suitable range, it was a film with very little generation of bubbles when bonded to COP. . However, in both the MD direction and the TD direction, the film expansion coefficient was 0.5% or less, and the film was inferior in bonding properties with COP. Further, since Yave / αave is large, the curl property is poor and the processability is poor. Therefore, the film is not suitable for use as a transparent conductive film by being bonded to COP. Furthermore, since there was much quantity of the cyclic trimer which exists in the film surface after heat processing, it was a film with much generation | occurrence | production of the bubble after a heating.

The polyester film of the present invention is excellent in mechanical properties and processability. In the film expansion measurement in the temperature rising process from 25 ° C. to 150 ° C., the film expansion coefficient at 150 ° C. is close to that of the COP film. It can use suitably as a protective film use of a film. Moreover, since it is excellent in transparency also at the time of a heating, it can use suitably as a use of the protective film of the COP film especially used for film formation of a transparent conductive film.

Claims (10)

In the film expansion coefficient measurement in the temperature rising process from 25 ° C. to 150 ° C. in the direction of the film main orientation axis and the direction perpendicular thereto, the film expansion coefficient at 150 ° C. is 0.5% or more and 1.5%, respectively. A biaxially oriented polyester film which is: 2. The biaxial orientation according to claim 1, wherein a dimensional change rate in a temperature lowering process from 150 ° C. to 50 ° C. in a direction perpendicular to the film main orientation axis direction is from 70 ppm / ° C. to 140 ppm / ° C., respectively. Polyester film. Yave (MPa) is a value obtained by averaging the Young's modulus in the film main orientation axis direction and the direction perpendicular thereto.
When αave (ppm / ° C) is the average value of the dimensional change rate in the temperature lowering process from 150 ° C to 50 ° C in the direction of the film main orientation axis and the direction perpendicular thereto,
The biaxially oriented polyester film according to claim 1 or 2, wherein the following formula (1) is satisfied.
(1) 20 ≦ Yave / αave ≦ 50 Yave (MPa) is an average value of Young's modulus in the film main orientation axis direction and the direction perpendicular to the film main orientation axis direction, and in the temperature lowering process from 150 ° C. to 50 ° C. in the film main orientation axis direction and the direction perpendicular thereto. The biaxially oriented polyester film according to any one of claims 1 to 3, which satisfies the following formula (2) when αave (ppm / ° C) is a value obtained by averaging the dimensional change rate.
(2) 20 ≦ Yave / αave ≦ 40 A laminated polyester film having at least three layers, wherein the intrinsic viscosity of the surface layers on both sides of the polyester film is 0.67 dl / g or more and 0.9 dl / g or less, and the surface layers on both sides of the laminated polyester film When the average value of the intrinsic viscosities is IVa (dl / g) and the average value of the intrinsic viscosities of the layers other than the surface layers on both sides of the laminated polyester film is IVb (dl / g), the following formula (3) is obtained. The biaxially oriented polyester film according to any one of claims 1 to 4, which is filled.
(3) 0.01 ≦ IVa−IVb ≦ 0.3 A value TmA obtained by averaging the melting points of the surface layers on both sides of the polyester film is in a range of 250 ° C. or more and 280 ° C. or less, and a value TmB obtained by averaging the melting points of the layers other than the surface layers on both sides of the polyester film is 250 ° C. or less. Item 6. The biaxially oriented polyester film according to Item 5. The ratio of the sum of the thicknesses of the surface layers on both sides of the polyester film to the sum of the thicknesses of the layers other than the surface layer (sum of the thicknesses of the surface layers on both sides / sum of the thicknesses of the layers other than the surface layer) is 1/9 to 1/2 The biaxially oriented polyester film according to claim 5 or 6. The biaxially oriented polyester film according to any one of claims 1 to 7, wherein the amount of change in haze before and after heat treatment at 140 ° C for 90 minutes is 5.0% or less. At least one surface, according to any one ester amount of cyclic trimer in the surface of the polyester film after 140 ° C. 90 minutes heat treatment of 0 mg / ^{m 2} or more 1.5 mg / ^{m 2} or less is the preceding claims Biaxially oriented polyester film. The biaxially oriented polyester film according to any one of claims 1 to 9, wherein at least one of the surface roughness Ra is 1 nm to 200 nm and the maximum height roughness Rz is 100 nm to 2000 nm.