JP2018184508A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film with excellent toughness.SOLUTION: The present invention provides a polyester film in which: the ratio between Young's modulus EMD in longitudinal direction and Young's modulus ETD in width direction (ETD/EMD) is 0.7 or more and 1.3 or less; a rigid amorphous content based on the whole film is 33% or more and 60% or less, and the proportion of the rigid amorphous content based on the whole film is higher than the crystallinity.SELECTED DRAWING: None

Description

  The present invention relates to a polyester film having excellent toughness.

Thermoplastic resin films, especially biaxially stretched polyester films, have excellent properties such as mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance. It is widely used as a base film in applications, and in recent years, a film excellent in toughness has been demanded particularly in various applications.
As a film excellent in toughness, a polyamide resin film (Patent Document 1) and a polyester film (Patent Documents 2 and 3) have been studied. Many nylon films are used as food packaging materials because they are excellent in toughness such as flexibility, pinhole resistance and puncture strength. In Patent Documents 2 and 3, studies are being made to highly orient the film in order to obtain toughness.

JP2011-162702 Patent No. 5891792 JP 2014-69384 A

However, polyamide resin films are poor in dimensional stability due to moisture absorption, so they can be used for food packaging applications where boil treatment and retort treatment are used, and for industrial applications where chemical resistance is required. difficult. Moreover, in order to obtain toughness, the polyester film only considers high orientation of the film, and there is room for improving the toughness of the polyester film.
Therefore, the polyester film of the present invention provides a film having excellent toughness by adjusting the balance of Young's modulus in the longitudinal direction and the width direction, the rigid amorphous amount, and the crystallinity within a specific range.

In order to solve the above problems, the present invention has the following configuration.
(1) The ratio (ETD / EMD) of Young's modulus EMD in the longitudinal direction and Young's modulus ETD in the width direction is 0.7 or more and 1.3 or less, and the rigid amorphous amount relative to the whole film is 33% or more and 60% or less, And the ratio of the rigid amorphous amount to the whole film is larger than the crystallinity.
(2) The 150 ° C. heat shrinkage rate in the longitudinal direction is 3.5% or more and 5.5% or less, and the 100 ° C. heat shrinkage rate in the longitudinal direction is 1.5% or less.
(3) The movable amorphous amount with respect to the whole film is less than 35%.
(4) The ratio of the rigid amorphous amount to the entire film is at least twice the movable amorphous amount.
(5) The crystallinity with respect to the whole film is 25% or more and 35% or less.
(6) The thickness is 3 μm or more and 9.5 μm or less.

  The polyester film of the present invention has a ratio (ETD / EMD) of Young's modulus EMD in the longitudinal direction to Young's modulus ETD in the width direction of 0.7 to 1.3, and the rigid amorphous amount relative to the whole film is 33% to 60 %, And since the ratio of the rigid amorphous amount to the whole film is larger than the crystallinity, a polyester film having excellent toughness can be obtained, so that it can be suitably used for applications requiring toughness.

  The ratio (ETD / EMD) of the Young's modulus EMD in the longitudinal direction of the polyester film and the Young's modulus ETD in the width direction of the present invention is 0.7 or more and 1.3 or less. Here, the Young's modulus is measured by the method described in (Evaluation method) (8) Young's modulus of the polyester film. The toughness of the polyester film in the present invention uses the magnitude of Charpy impact absorption energy as an index. The Charpy impact absorption energy can be improved by increasing the orientation in the film plane direction, but it is also important that the orientation balance of the plane orientation is uniform. Here, Charpy impact absorption energy is measured by the method described in Evaluation Method (11) Toughness of Polyester Film. When the plane orientation balance is poor, when the Charpy impact absorption energy is measured, local stress concentration occurs, which tends to cause destruction, and thus the Charpy impact absorption energy decreases. For this reason, the ratio ETD / EMD of the longitudinal direction Young's modulus EMD and the width direction Young's modulus ETD, which is an index of the film orientation state, is 0.7 or more and 1.3 or less. The ETD / EMD is preferably 0.8 or more and 1.2 or less. In particular, ETD / EMD is preferably 0.9 or more and 1.1 or less. The Young's modulus is preferably 3.6 GPa or more and 5.0 GPa or less. In order to make Young's modulus 3.6 GPa or more and 5.0 GPa or less, the method of making it 13.5 times or more by area stretch ratio etc. is mentioned preferably. Moreover, in order to make ETD / EMD 0.7 or more and 1.3 or less, in the case of a sequential biaxial stretching method, the method of making the draw ratio of the 1st axis | shaft and the 2nd axis | shaft comparable is mentioned. If the refractive index in the longitudinal direction and the width direction of the finally obtained film is 1.658 or more and 1.68 or less, the ETD / EMD is 0.7 or more and 1.3 or less. There is no restriction | limiting in the draw ratio of an axis | shaft, a draw temperature, etc., What is necessary is just to extend | stretch by a well-known method.

  The polyester film of the present invention has a rigid amorphous amount of 33% to 60% with respect to the entire film. Here, the amount of rigid amorphous can be measured by the method described in (10) Measurement of Bulk Composition of Polyester Film. The higher the rigid amorphous, the higher the Charpy impact absorption energy can be obtained. When the amount of rigid amorphous exceeds 60%, the amorphous component occupies most of the film bulk structure, and the dimensional stability of the film is significantly reduced. On the other hand, when the rigid amorphous amount is less than 33%, the Charpy impact absorption energy is inferior. The film bulk state is determined by the film forming conditions in addition to the crystallinity of the raw material used. For example, when polyethylene terephthalate is used, in order to make the rigid amorphous amount 33% or more, at least the film It is important that the plane orientation coefficient fn is 0.165 or more. Here, the plane orientation coefficient of the film is measured by the method described in Evaluation Method (4) Refractive Index of Polyester Film, Plane Orientation Coefficient fn. In order to set the plane orientation coefficient of the film to 0.165 or more, a method of setting the area stretch ratio in biaxial stretching to 14.0 times or more can be mentioned. On this basis, it is preferable to control the rigid amorphous by the heat treatment temperature after sequential biaxial stretching, and it is important that the highest temperature (heat treatment temperature) applied during film formation is 210 ° C. or lower. On the other hand, even if the heat treatment temperature is 230 ° C. or higher, the rigid amorphous amount tends to increase due to the start of melting of the resin, but since crystallization of the film by heat is promoted, it will be described later. The degree of crystallization increases, and the degree of crystallinity becomes higher than that of a rigid amorphous film as a film bulk structure. For this reason, it is important that the heat treatment temperature is 210 ° C. or lower. When the heat treatment temperature of the film exceeds 210 ° C. and is less than 230 ° C., the rigid amorphous amount may be less than 33%. However, the amount of rigid amorphous can be controlled by the raw material for forming the film. For example, when the intrinsic viscosity of the raw material is increased, the amount of rigid amorphous increases even under the same film forming conditions. Usually, when forming a biaxially stretched film, the intrinsic viscosity of the raw material used is preferably 0.60 or more and 1.2 or less. Based on the above, the selection of raw materials, the plane orientation coefficient, and the heat treatment temperature are appropriately selected according to the required rigid amorphous and various properties.

  The polyester film of the present invention is characterized in that the ratio of the rigid amorphous amount is larger than the crystallinity from the viewpoint of Charpy impact absorption energy. Here, the crystallinity can be measured by the method described in (10) Measurement of Bulk Composition of Polyester Film. The Charpy impact absorption energy can be improved to some extent by increasing the orientation of the film, that is, by increasing the rigidity. For this reason, as a polyester film, Charpy impact absorption energy can be made by raising Young's modulus. However, when the orientation and crystallization of the film are increased in order to increase the rigidity, the ordered and oriented crystals and crystals are likely to propagate the shock in the reverse direction, and there is a limit to increasing the Charpy impact absorption energy. Therefore, in order to increase the Charpy impact absorption energy to the maximum, it is important to suppress the formation of an ordered structure, that is, to suppress crystallization, while increasing the rigidity of the film. For this reason, in the present invention, by suppressing the increase in crystallinity and improving the rigidity, the potential for the Charpy impact absorption energy of the polyester film is maximized, and the ratio of the rigid amorphous amount is More than the degree of crystallinity. In order to increase the ratio of the rigid amorphous amount to the degree of crystallinity, it is important to suppress crystallization by heat treatment after orienting the plane orientation coefficient of the film to at least 0.164 or more by biaxial stretching. . From the viewpoint of the rigid amorphous amount, the plane orientation coefficient fn is preferably 0.166 or more and 0.172 or less. When heat treatment is not performed after biaxial stretching, it is considered that the rigid amorphous amount is ideally high as a polyester film, i.e., exhibits high Charpy impact absorption energy. Therefore, there are cases where it is unsuitable for applications where toughness is required without unavoidable changes and relaxation over time even at room temperature. For this reason, considering application to various uses, the heat treatment temperature after biaxial stretching is preferably set to 170 ° C. or more and 210 ° C. or less in order to increase the ratio of the rigid amorphous amount to the crystallinity.

The polyester film of the present invention preferably has a crystallinity of 25% or more and 35% or less. The crystallinity can increase the mechanical strength of the film by orientation crystallization by stretching or crystallization by heat. When the crystallinity is less than 25%, the Charpy impact absorption energy may be low, and when the crystallinity exceeds 35%, the rigid amorphous amount may not be increased beyond the crystallinity. In order to set the crystallinity to 25% or more and 35% or less, for example, the film has a plane orientation coefficient of 0.160 or more and 0.170 or less, and the heat treatment temperature is 170 ° C. or more and 240 ° C. or less. Can be adjusted.
In the polyester film of the present invention, it is preferable that the ratio of the rigid amorphous amount to the whole film is twice or more the movable amorphous amount. Here, the amount of movable amorphous can be measured by the method described in (10) Measurement of bulk composition of polyester film. The Young's modulus is an index indicating the strength of the film, and the larger the rigidity, the higher the rigidity. Similarly, the rigid amorphous amount is also strongly correlated with the strength of the film and strongly correlated with the Charpy impact absorption energy. On the other hand, the movable amorphous material is in the random state although it is the same amorphous material as the rigid amorphous material, and its contribution to rigidity and strength is very small. For this reason, in order to improve the rigidity, among the amorphous components, it is preferable that the rigid amorphous is more than the movable amorphous, and in particular, when the ratio of the movable amorphous amount is more than twice the rigid amorphous, Significant improvement in Charpy impact absorption energy is seen. For this reason, it is preferable that the ratio of the rigid amorphous amount to the whole film is twice or more the movable amorphous amount. In order to set the ratio of the rigid amorphous amount to the whole film to be twice or more of the movable amorphous amount, the heat treatment temperature after biaxial stretching is set to 190 ° C. or less after setting the plane orientation coefficient of the film to 0.165 or more. The method of doing is mentioned preferably.

  The polyester film of the present invention preferably has a movable amorphous amount of less than 35% with respect to the entire film from the viewpoint of Charpy impact absorption energy. In order to make the amount of movable amorphous material less than 35% with respect to the whole film, the surface orientation coefficient of the film is adjusted to 0.160 or more and 0.170 or less, and the heat treatment temperature is adjusted to 170 ° C or more and 240 ° C or less Is possible.

  The polyester film of the present invention preferably has a 150 ° C. heat shrinkage in the longitudinal direction of 3.5% to 5.5% and a 100 ° C. heat shrinkage in the longitudinal direction of 1.5% or less. In the process in which heat of 80 ° C. or higher and 120 ° C. or lower, particularly heat in the vicinity of 100 ° C. is applied in dry lamination such as when the polyester film of the present invention is used for secondary processing with heating, for example, when laminating a film with other materials. When the heat shrinkage rate in the longitudinal direction is 1.5% or less, there is no generation of wrinkles when laminating, the yield is good, and the productivity is excellent. On the other hand, in the laminating process where heat of about 150 ° C. is applied, such as an extruding laminating process in which the melted resin is directly laminated to the film, especially when the film is as thin as 25 μm or less, the laminating is performed to suppress wrinkles during extrusion laminating. When the heat yield of the temperature applied sometimes is 3.5% or more, the film is stretched due to shrinkage during lamination, wrinkles can be suppressed, yield is high, and productivity is excellent. Therefore, the polyester film of the present invention has a 150 ° C. heat shrinkage in the longitudinal direction of 3.5% to 5.5% and a 100 ° C. heat shrinkage in the longitudinal direction of 1.5% or less. Is preferred. In order to set the 100 ° C. heat shrinkage in the longitudinal direction to 1.5% or less, it is preferable to set the stretching temperature and the stretching ratio in a direction desired to be 1.5% or less within a specific range. Specifically, in the first-axis stretching in the biaxial stretching step, it is preferable to perform multi-stage stretching to two or more stages, and the first-stage stretching temperature is 2.5 when the glass transition temperature of the resin is Tg + 30 ° C. or more and Tg + 50 ° C. or less. The stretching temperature of the second stage is such that the glass transition temperature Tg + 35 ° C. to 55 ° C. of the resin constituting the film is stretched to 2 times or more, so that the total stretching ratio of the first axis is 5 times or more. A method of stretching is preferably mentioned. From the viewpoint of increasing rigidity and reducing the heat yield at 100 ° C. to 1.5% or less, the film area stretch ratio is particularly preferably 20 times or more.

Various particles may be added to the polyester film of the present invention within a range that does not impair the effects of the present invention for the purpose of obtaining the winding property. There are no particular restrictions on the size and type of the particles, and inorganic particles, organic particles, and the like can be freely selected.
The polyester constituting the polyester film of the present invention is a general term for polymer compounds in which main bonds in the main chain are ester bonds. The polyester resin can be usually obtained by polycondensation reaction of dicarboxylic acid or its derivative with glycol or its derivative. Here, the dicarboxylic acid unit (structural unit) or the diol unit (structural unit) means a divalent organic group from which a portion to be removed by polycondensation is removed, and is represented by the following general formula. .

Dicarboxylic acid unit (structural unit): —CO—R—CO—
Diol unit (structural unit): —O—R′—O—
(Here, R and R ′ are divalent organic groups. R and R ′ may be the same or different.)
Examples of glycols or derivatives thereof that give the polyester used in the present invention include 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, 1, in addition to ethylene glycol. Aliphatic dihydroxy compounds such as 6-hexanediol and neopentyl glycol, polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol and polytetramethylene glycol, alicyclic dihydroxys such as 1,4-cyclohexanedimethanol and spiroglycol Examples thereof include aromatic dihydroxy compounds such as compounds, bisphenol A and bisphenol S, and derivatives thereof.

  In addition to terephthalic acid, the dicarboxylic acid or derivative thereof that provides the polyester used in the present invention includes isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethanedicarboxylic acid. Acids, aromatic dicarboxylic acids such as 5-sodiumsulfone dicarboxylic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid, etc. Alicyclic dicarboxylic acids, oxycarboxylic acids such as paraoxybenzoic acid, and derivatives thereof. Examples of dicarboxylic acid derivatives include dimethyl terephthalate, diethyl terephthalate, 2-hydroxyethyl methyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, dimethyl adipate, diethyl maleate, and dimethyl dimer. An esterified product can be mentioned.

  The polyester film of the present invention is not limited in thickness for obtaining the effects of the present invention, and the thickness may be appropriately set depending on the application. However, when used at 3 μm or more and 9.5 μm or less, the 150 ° C. heat shrinkage in the longitudinal direction is 3.5% to 5.5%, and the 100 ° C. heat shrinkage in the longitudinal direction is 1.5% or less. Therefore, the present invention exhibits excellent effects in suppressing wrinkles during laminating with heating near 100 ° C., and suppressing distortion of tin in laminating with heating at 150 ° C.

  The polyester film of the present invention is preferably used for applications where toughness is required, and in particular, can be preferably used for lithium ion battery exterior materials, pharmaceutical packaging materials, and the like.

  The outline of the manufacturing method of the polyester film of this invention is illustrated. First, the polyester raw material is melt-extruded by a known method and adhered onto a casting drum adjusted to about 10 ° C. to 35 ° C. so that the polyester does not crystallize to obtain a cast sheet. The adhesion method may be a known method such as an electrostatic application method or an air knife method. Next, the obtained cast sheet is oriented biaxially by a known method. Biaxial stretching may be a known method such as sequential biaxial, simultaneous biaxial, and tubular methods. If the plane orientation coefficient of the film obtained by biaxial stretching is 0.164 or more, there are no particular restrictions on the stretching ratio and stretching temperature. However, in order to set the heat shrinkage rate at 100 ° C. to 1.5% or less, in the first-axis stretching in the biaxial stretching step, it is preferable to perform multi-stage stretching to two or more stages, and the first-stage stretching temperature is set to resin. The glass transition temperature of Tg + 30 ° C. to Tg + 50 ° C. is stretched to 2.5 times or less. In the second stage, the stretching temperature is stretched to a glass transition temperature Tg + 35 ° C. It is preferable to stretch the film so that the draw ratio is 5 times or more. After biaxial stretching, heat treatment is preferably performed from the viewpoint of dimensional stability. When the polyester raw material contains polyethylene terephthalate as a main constituent, it is preferable to perform heat treatment in the range of 170 ° C. to 210 ° C. for 1 second to 120 seconds or less. After the heat treatment, a polyester film is obtained by performing a surface treatment such as corona as necessary.

(Evaluation method)
The polyester film was produced and evaluated by the following method.

(1) Composition of polyester The polyester resin and the film were dissolved in hexafluoroisopropanol (HFIP), and the content of each monomer residue and by-product diethylene glycol was quantified using ¹ H-NMR and ¹³ C-NMR.

(2) Film thickness, layer thickness When measuring the thickness of the entire film, the film was cut into 200 mm x 300 mm using a dial gauge, and the thicknesses at five arbitrary locations of each sample were measured and averaged. Asked. Moreover, about each layer thickness of laminated | multilayer film, by embedding a film in an epoxy resin, cutting out a film cross section with a microtome, and observing this cross section with a transmission electron microscope (TEM H7100 by Hitachi, Ltd.) at a magnification of 5000 times. Asked.

(3) Longitudinal direction and width direction of polyester film In the present invention, a direction stretched by a roll is defined as a longitudinal direction, and an orthogonal direction thereof is defined as a width direction. When the stretching method is unknown, any one direction (0 °) of the film, 15 °, 30 °, 45 °, 60 °, 75 °, 90 °, 105 °, 120 °, 135 ° from the direction, The 150 ° C. heat yields in the directions of 150 ° and 165 ° were measured, the direction having the highest 150 ° C. heat yield was defined as the longitudinal direction, and the direction perpendicular to the longitudinal direction was defined as the longitudinal direction. The 150 ° C. heat yield is measured as described in (5) 150 ° C. and 100 ° C. heat shrinkage of the polyester film.

(4) Refractive index of polyester film, plane orientation coefficient fn
A layer for measuring a plane orientation coefficient (hereinafter referred to as a measurement layer) using an Abbe refractometer is adhered to the glass surface, and then the refractive index (Nx) in the longitudinal direction, the width direction, and the thickness direction using sodium D-line as a light source. , Ny, Nz), and the plane orientation coefficient fn of the measurement layer was determined from the following formula.
-Planar orientation coefficient fn = (Nx + Ny) / 2-Nz
(5) A 150 ° C. and 100 ° C. heat shrinkage film of a polyester film was cut into a rectangular shape having a length of 150 mm × width of 10 mm in the longitudinal direction and the width direction, and used as a sample. Marks were drawn on the sample at intervals of 100 mm, and a heat treatment was performed by suspending a 3 g weight in a hot air oven heated to either 150 ° C. or 100 ° C. for 30 minutes. The distance between the marked lines after the heat treatment was measured, and the thermal shrinkage rate was calculated from the change in the distance between the marked lines before and after the heating to obtain the thermal shrinkage rate. The measurement was carried out with 5 samples in the longitudinal direction and the width direction, and the average value was evaluated.

(6) State after lamination including 150 ° C. heating step The polypropylene resin heated and melted so that the laminating temperature at the time of lamination is 150 ° C. is pressed against a film cut into A4 size at 3N for 3 seconds, and then the laminate sheet The state was confirmed visually, and the determination was performed as follows.
○: No wrinkles Δ: Slightly wrinkled (7) State after lamination including a heating process at 100 ° C. A film cut to A4 size and a 25 μm polypropylene cast sheet are wound around a roller on a nip roll heated to 100 ° C. In this way, it was pressed with 3N and laminating, and then the state of the laminate sheet was visually confirmed, and the determination was made as follows.
(Circle): There is no wrinkles (triangle | delta): There is some wrinkles (8) Young's modulus of a polyester film The strip-shaped sample of length 150mm and width 10mm was cut out and used for the film longitudinal direction and the width direction. The Young's modulus was measured using an Instron type tensile tester according to the method defined in JIS Z1702. The measurement was performed under the following conditions, and the number of samples was 10 for each sample, and the average value was taken.
Measuring device: Orientec Co., Ltd. film strong elongation automatic measuring device “Tensilon AMF / RTA-100”
Sample size: width 10mm x test length 50mm
Tensile speed: 300 mm / min Measurement environment: temperature 23 ° C., humidity 65% RH.

(9) Glass transition temperature of polyester film
In accordance with JIS K7122 (1987), a differential scanning calorimeter robot DSC-RDC220 manufactured by Seiko Denshi Kogyo Co., Ltd. was used for data analysis, and “Disk Session” SSC / 5200 was used. The measurement was performed at 0 ° C./min and a sample amount of 5 mg.

(10) Measurement of bulk composition of polyester film
i) Movable Amorphous Amount Using a temperature modulated DSC manufactured by TA Instruments, 5 mg sample was heated at a rate of 2 ° C./min from 0 ° C. to 150 ° C. under a nitrogen atmosphere, temperature modulation amplitude ± 1 ° C., temperature modulation period 60 seconds Measured with The specific heat difference at the glass transition temperature obtained by the measurement was obtained and calculated from the following equation.
Movable amorphous amount (%) = (specific heat difference) / (theoretical value of specific heat difference of polyester completely amorphous) × 100
Theoretical specific heat difference of polyethylene terephthalate completely amorphous material = 0.40552 J / (g ° C.)
In the present invention, those having a polyethylene terephthalate unit of 89 mol% or more were referred to the specific heat difference theoretical value of a completely amorphous polyethylene terephthalate.

ii) Crystallinity
In accordance with JIS K7122 (1987), a differential scanning calorimeter robot DSC-RDC220 manufactured by Seiko Denshi Kogyo Co., Ltd. was used, and “Disk Session” SSC / 5200 was used for data analysis. The temperature was raised from room temperature to 300 ° at a rate of temperature rise of 20 ° C./min, and held at 300 ° C. for 5 minutes. At that time, the endothermic peak heat amount ΔHm, the cold crystallization heat amount ΔHc, and the melting heat amount ΔHm ⁰ (140.1 J / g) of the complete crystal PET obtained by the measurement were calculated by the following formula.
Crystallinity (%) = (ΔHm−ΔHc) / ΔHm ⁰ × 100
iii) Rigid Amorphous Amount The rigid amorphous amount was calculated from the movable amorphous amount obtained by measurement and the crystallinity by the following formula.
Rigid amorphous amount (%) = 100− (movable amorphous amount + crystallinity).

(11) Tensile test samples prepared in 10 mm × 50 mm in the longitudinal direction and width direction of the toughness film sample of the polyester film are prepared in each direction. Charpy impact tester manufactured by Toyo Seiki Seisakusho (capacity: 10 kg / cm, hammer weight: 1.019 kg, hammer lift angle: 127 °, distance from axis to center of gravity: 6.12 cm) 50 mm) side was fixed, and measurement in each direction was performed at a test temperature of 25 ° C. (total 10 times). Dividing the average value of each of the direction the cross-sectional area of the test sample (test sample thickness × test sample width), in terms of units of MJ / m ^2, it was determined Charpy impact absorption energy in the longitudinal direction and the width direction. The toughness of the film was determined from the obtained Charpy impact absorption energy as follows.
A: All in the longitudinal direction width direction are 10 MJ / m ² or more.
A: At least the average value in the width direction in the longitudinal direction is 10 MJ / m ² or more.
Δ: At least the average value in the longitudinal direction is 9 MJ / m ² or more.
×: The average value in the longitudinal direction width direction is 9 MJ / m ² or more.

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

(Polyester A) Examples 1-4, 7-15, Comparative Examples 1-3
Polyethylene terephthalate resin (inherent viscosity 0.65) in which the terephthalic acid component is 100 mol% as the dicarboxylic acid component, the ethylene glycol component is 99 mol% and the diethylene glycol component is 1 mol% as the glycol component.

(Polyester B) Example 5
Polyethylene terephthalate resin (inherent viscosity 0.70) in which the terephthalic acid component is 100 mol% as the dicarboxylic acid component, the ethylene glycol component is 99 mol%, and the diethylene glycol component is 1 mol% as the glycol component.

(Polyester C) Example 6
Polyethylene terephthalate resin (intrinsic viscosity 0.75) in which the terephthalic acid component is 100 mol% as the dicarboxylic acid component, the ethylene glycol component is 99 mol%, and the diethylene glycol component is 1 mol% as the glycol component.

(Particle Master A) Examples 1 to 15 and Comparative Examples 1 to 3
Polyethylene terephthalate particle master (intrinsic viscosity 0.62) containing agglomerated silica particles having an average particle diameter of 2 μm in polyester A at a particle concentration of 2 mass%.

(Examples 1-15, Comparative Examples 1-3)
The polyester species and particle master shown in Table 1 were each dried in a vacuum dryer at 180 ° C. for 4 hours, and after sufficiently removing water, supplied to the single screw extruder at the content shown in Table 1 at 280 ° C. After melting with a filter and gear pump, removing foreign matter and leveling the amount of extrusion, a sheet is placed on a cooling drum (hard chromium plating with a maximum height of 0.2 μm) controlled to 20 ° C from a T-die. The unstretched film was obtained. At that time, the distance between the lip of the T die and the cooling drum was set to 35 mm, and a wire-like electrode having a diameter of 0.1 mm was used for electrostatic application at a voltage of 14 kV to adhere the cooling drum. The sheet passing speed of the cooling drum was 25 m / min, and the contact length of the sheet with the cooling drum was 2.5 m.

  Subsequently, after preheating the unstretched film with a group of rolls heated to a temperature of 60 to 70 ° C., the first stage and the second stage were each longitudinally (longitudinal) using heating rolls having the temperatures shown in Table 2. The film was stretched to the magnification shown in Table 2 in the direction) and cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film.

  Next, while holding both ends of the uniaxially stretched film with clips, the tenter is guided to a preheating zone at a temperature of 80 ° C. in the tenter, and a direction perpendicular to the longitudinal direction (width direction) in the heating zone in the width direction maintained at the temperature shown in Table 1 Each was stretched to the magnification shown in Table 1. Subsequently, heat treatment was performed for 20 seconds at the heat setting temperature shown in Table 2 in the heat treatment zone in the tenter, and relaxation was performed at the relaxation rate shown in Table 2. Next, the mixture was gradually cooled to obtain a polyester film having the thickness shown in Table 2. The characteristics of the polyester film are as shown in Tables 3, 4, and 5.

  The polyester film of the present invention has a ratio (ETD / EMD) of Young's modulus EMD in the longitudinal direction and Young's modulus ETD in the width direction of 0.7 to 1.3 and the rigid amorphous amount relative to the entire film is 33% or more. It can be suitably used for applications that require toughness because the ratio of the rigid amorphous amount to the whole film is 60% or less and the degree of crystallinity is larger than the crystallinity.

Claims (6)

The ratio (ETD / EMD) of Young's modulus EMD in the longitudinal direction to Young's modulus ETD in the width direction is 0.7 or more and 1.3 or less, and the rigid amorphous amount relative to the whole film is 33% or more and 60% or less, and the whole film A polyester film characterized in that the ratio of the rigid amorphous amount to the crystal is greater than the crystallinity. The polyester film according to claim 1, wherein the 150 ° C. heat shrinkage in the longitudinal direction is 3.5% or more and 5.5% or less, and the 100 ° C. heat shrinkage in the longitudinal direction is 1.5% or less. The polyester film according to claim 1 or 2, wherein the movable amorphous amount relative to the whole film is less than 35%. The polyester film according to any one of claims 1 to 3, wherein the ratio of the rigid amorphous amount to the whole film is twice or more the movable amorphous amount. The polyester film according to any one of claims 1 to 4, which has a crystallinity of 25% or more and 35% or less with respect to the entire film. The polyester film according to claim 1, wherein the thickness is 3 μm or more and 9.5 μm or less.