JP2001341268A - Laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated polyester film which shows outstanding scratch resistance. SOLUTION: The laminated polyester film shows 5-15 GPa coefficient of surface elasticity at least on one of the sides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention has a high surface elastic modulus,
The present invention relates to a laminated polyester film having excellent scratch resistance.

[0002]

2. Description of the Related Art Hitherto, polyester films represented by polyethylene terephthalate have been widely used as transparent films because of their excellent transparency and low cost.
However, the scratch resistance is insufficient, and improvement thereof has been desired. As a method of improving the scratch resistance of a polymer film,
In general, a method of forming a hard coat layer on the surface as described below is well known. A method of applying a radiation-curable resin on the surface (for example, JP-A-11-254867) A method of depositing a metal oxide film on the surface (for example, JP-A-11-254867)
-77909) A method of forming a silicon oxide film by a sol-gel method (for example, Japanese Patent Application Laid-Open No. 11-279305) However, in any method, it is necessary to increase the thickness of a hard coat layer in order to improve scratch resistance. It had the disadvantage that it was easily cracked when bent and the scratch resistance was easily reduced.
Further, since a hard coat layer is formed after the polyester film is formed, the number of steps is increased, the cost is high, and improvement has been desired. For such a purpose, the laminated polyester of the present invention is formed by laminating a layer to which fine particles are added. Such a structure is also found in a polyester for a magnetic recording material (see, for example, JP-A-5-169604, JP-A-3-86542
issue). However, this lamination configuration example is to laminate a layer containing large fine particles thinly in order to improve running properties,
The surface of the polyester is uneven, which is different from the present invention which requires a smooth surface. Furthermore, compared to the present invention, the thickness is smaller, the amount of added fine particles is small, and the improvement in scratch resistance due to the improvement in surface elastic modulus cannot be achieved.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a laminated polyester film having excellent scratch resistance.

[0004]

The object of the present invention has been attained by the following inventions. 1. Surface elastic modulus of at least one side is 5 GPa or more and 15 G
A laminated polyester film having a pressure of not more than Pa. 2. The center line roughness (Ra) of at least one surface is 0.0
Item 2. The laminated polyester film according to Item 1, wherein the laminated polyester film has a maximum height (Rt) of 0.5 μm or less. A layer (B layer) containing 10 wt% to 60 wt% of fine particles having a size of 3.1 nm to 400 nm is formed on a polyester support (A).
Item 1) characterized by being laminated on at least one side of
Or the laminated polyester film according to 2. 4. Item 4. The laminated polyester film according to any one of Items 1 to 3, wherein the total layer thickness is 10 μm or more and 300 μm or less, and the thickness of the B layer is 5 μm or more and 100 μm or less. 5. The ratio (D / T) between the particle size (D) of the fine particles and the thickness (Tb) of the B layer
6. The laminated polyester film according to item 3 or 4, wherein b) is less than 1 × 10 ^{−2 and} 1 × 10 ⁻⁵ or more. 6. The difference between the front and back surface elastic moduli is 0.5 GPa or more and 10 GP
a. The laminated polyester film according to any one of Items 3 to 5, which is equal to or less than a. 7. Item 7. The laminated polyester film according to any one of Items 1 to 6, wherein the polyester comprises a polyethylene terephthalate resin or a polyethylene naphthalate resin.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has achieved improvement in scratch resistance by increasing the surface elastic modulus of at least one surface of a polyester film. The surface elastic modulus of the polyester film is preferably 5 GPa or more and 15 GPa or less, more preferably 5.5 GPa or more and 12 GPa or less, and still more preferably 6 GPa or more and 10 GPa or less. Furthermore, in the present invention, it has been found that destruction starts with the unevenness and projections on the surface. That is, it is preferable to improve the scratch resistance by making the surface smooth, and the center line roughness (Ra) of at least one surface of the polyester film is 0.01 μm or less, more preferably 0.005 μm or less, further preferably 0.07 μm or less.
It is better that the value is substantially equal to 0 or less than 01 μm. Maximum height
(Rt) is 0.5 μm or less, more preferably 0.3 μm or less, further preferably 0.1 μm or less, and is preferably as close to substantially 0 as possible.

[0006] Such a polyester film is achieved as follows. The polyester is formed from a dicarboxylic acid and a diol. Preferably, 50 mol% or more and 100 mol% or less of the total dicarboxylic acid residues are composed of aromatic dicarboxylic acids, and more preferably, of the dicarboxylic acid residues in all dicarboxylic acid residues. 70 mol% or more and 100 mol% or less consist of naphthalenedicarboxylic acid residues and / or phthalic acid residues, and more preferably 80 mol% to 100 mol% of dicarboxylic acid residues in all dicarboxylic acid residues are 2,6.
-It is composed of a naphthalenedicarboxylic acid residue and / or a terephthalic acid residue. In the diol, ethylene glycol residues in all diol residues are 50 mol% or more and 100 m
ol% or less, more preferably 70 mol% or more
It is at most 00 mol%, more preferably at least 80 mol% and at most 100 mol%.

[0007] Preferred examples of the polyester include the following, but the present invention is not limited thereto. Homopolymer example HP-1: Polyethylene-2,6-naphthalate (PEN) HP-2: Polyethylene terephthalate (PET) Copolymer example Composition (molar ratio) CP-1: 2,6-NDCA / TPA / EG (20/80 / 100) CP-2: 2,6-NDCA / IPA / EG (80/20/100) CP-3: 2,6-NDCA / TPA / EG (80/20/100) CP-4: TPA / EG / BPA ・ 2EO (100/25/75) CP-5: TPA / EG / CHDM / BPA ・ 2EO (100/25/25/50) CP-6: TPA / EG / CHDM (100/80/20) ( NDCA: Naphthalene dicarboxylic acid, TPA: Terephthalic acid, IPA: Isophthalic acid, BP A.2EO: Bisphenol A ethylene oxide 2 adduct, CHDM: Cyclohexane dimethanol, EG: Ethylene glycol) Example of polymer blend Composition (wt ratio) ) PB-1: PEN / PET (20/80) PB-2: PAr / PET (15/85) PB-3: PAr / PCT / PET (15/10/75) PB-4: PAr / PC / PET (10/10/80) (PEN: polyethylene naphthalate, PET: polyethylene terephthalate, PAr: polyarylate, PCT: polycyclohexanedimethanol terephthale Door, PC: shows the port Li carbonate)

The preferred intrinsic viscosity of these polymers is 0.4 to 0.8 dl / g, more preferably 0.45 to 0.8 dl / g.
0.7 dl / g, more preferably 0.5 to 0.7 dl
/ G. Such a polyester is prepared by subjecting the starting dicarboxylic acid diester (usually a dimethyl ester) and a diol to atmospheric pressure under the presence of a transesterification catalyst for 15 minutes.
The mixture was heated to 0 ° C to 250 ° C and reacted for 0.5 to 5 hours while distilling off methanol as a by-product.
At 0 ° C, from atmospheric pressure to 40 Pa (0.3 torr)
The polycondensation reaction is carried out while gradually increasing the degree of vacuum and stirring. Methods for synthesizing these polyesters are described in, for example, Polymer Experiments, Vol. 5, “Polycondensation and Polyaddition” (Kyoritsu Shuppan, 1980), pp. 103-136, “Synthetic Polymer V” (Asakura Shoten, 1971) pp. 187-286
Page, JP-A-5-163337 and JP-A-3-17905
2, 2-3420, 1-275628, and the like. The polyester thus polymerized is taken out, cooled with water, hardened into noodles, and then cut into pellets.

[0009] In the present invention, 1 nm or more 4
Fine particles having a size of not more than 00 nm, more preferably not less than 5 nm and not more than 200 nm, still more preferably not less than 10 nm and not more than 100 nm, have a content of not less than 10 wt% and not more than 60 wt%, more preferably not more than 15 wt%.
wt% or more and 50 wt% or less, more preferably 20 wt% or more 4
5 wt% or less is added. Preferred fine particles include silica, alumina, titania, zirconia, mica, talc,
Examples include inorganic fine particles such as calcium carbonate, barium sulfate, zinc oxide, magnesium oxide, calcium sulfate, and kaolin, and organic fine particles such as cross-linked polystyrene. More preferred are silica, alumina, titania, zirconia, mica, talc and calcium carbonate. The shape may be any of an irregular shape, a plate shape, and a spherical shape, and two or more kinds of fine particles may be mixed and used. These fine particles may be added together with the monomer before the polymerization of the polyester, or may be added after the polymerization of the polyester.However, the former may cause an increase in viscosity during the polymerization and may make it difficult to control the polymerization. Is easier to disperse uniformly and is more preferable.

The present invention is characterized in that such extremely small particles are uniformly dispersed at a high concentration. That is, these fine particles are added while the dispersed oligomer of polyester is melted, and the surface of the fine particles is coated in advance with polyester. The preferred intrinsic viscosity of the oligomer (d
1 / g) is 0.05 or more and 0.4 or less, more preferably 0.1 or more and 0.3 or less, and still more preferably 0.1 or more and 0.2 or less. The preferred ratio (P / O) of the oligomer (O) and the fine particles (P) is 1 or more and 100 or less, more preferably 3 or more and 50 or less, and more preferably 5 or more and 20 or less. Mixing of oligomer and fine particles is performed by Banbury mixer.
A kneader, roll mill, single screw or twin screw extruder can be used. The preferred mixing temperature is 100 ° C. or higher and 350 ° C. or lower, more preferably 120 ° C. or higher and 300 ° C. or lower, still more preferably 150 ° C. or higher and 250 ° C. or lower.
Minutes to 200 minutes, more preferably 2 minutes to 100 minutes, even more preferably 3 minutes to 30 minutes.

Thereafter, the mixture is kneaded with the polyester. For kneading, a Banbury mixer, a kneader, a roll mill, a single-screw or twin-screw extruder can be used. The preferred mixing temperature is 200 ° C. or more and 350 ° C. or less, more preferably 2 ° C.
The mixture is mixed at 40 ° C. to 340 ° C., more preferably 260 ° C. to 330 ° C., for 1 minute to 200 minutes, more preferably 2 minutes to 100 minutes, further preferably 3 minutes to 30 minutes. At this time, metal salts of higher fatty acids,
It is also preferable to use a dispersing aid such as a higher fatty acid ester, a higher fatty acid ethyl, a higher fatty acid amide, a higher fatty acid, or an antioxidant in combination.

The polyester containing such fine particles may form a single-layer film, but is more preferably used as a laminated film. As a result, the difference in surface elastic modulus between the front and back is 0.5 GPa or more and 10 GPa or less, more preferably 0.8 GPa or more and 7 GPa, and still more preferably 1.0 GPa or more.
It is preferable to set it to Pa or more and 5 GPa or less. If the surface hardness is high on both sides, the holding force with the transport roll is reduced, and abrasion due to slip is likely to occur during film formation. In such a laminated film, a polyester layer (B layer) containing fine particles may be laminated (B / A) on one surface of a polyester layer (A layer) having a smaller fine particle content than the B layer, May be laminated (B / A / B ′) on the A layer on the opposite side of the B layer.

The A layer is preferably made of the same polyester as the B layer, and it is also preferable to add fine particles. Preferred particle size is 1 nm or more and 1000 nm
Or less, more preferably 5 nm or more and 600 nm or less, and still more preferably 10 nm or more and 400 nm or less.
wt% or more and 1 wt% or less, more preferably 0.0001 wt%
More than 0.1 wt%, more preferably more than 0.001 wt% and less than 0.01 wt%. As the fine particles, those described in the description of the layer B can be used.
The fine particles of the layer may be the same material or different materials. The same polyester and fine particles as those of the B layer can be used for the B ′ layer, but the surface hardness can be reduced by making the amount of the fine particles smaller than that of the B layer.

The total thickness of the polyester film of the present invention is preferably from 10 μm to 300 μm, more preferably from 50 μm to 260 μm, even more preferably from 100 μm to 250 μm. The thickness of the B layer and the B ′ layer is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 80 μm or less, and still more preferably 20 μm or less.
Not less than 50 μm. Particle size (D) of fine particles and B layer,
The ratio (D / Tb) of the thickness (Tb) of the B ′ layer is less than 1 × 10 ⁻² 1
X 10 ^-5 or more is preferable, 5 x 10 ^-2 or less 1 x 10 ^-4 or more, further preferably 1 x 10 ^-3 or less 1
× 10 ^-4 or more.

The polyester film of the present invention can be formed as follows. (1) Drying of polyester resin The polyester pellets are heated at 100 ° C to 250 ° C, more preferably at 130 ° C to 200 ° C, for 5 minutes to 5 minutes.
The drying is performed for not more than an hour, more preferably not less than 10 minutes and not more than 1 hour. (2) Melt Extrusion The pellets for the A layer, the B layer, and the B 'layer are each melted in a uniaxial or multiaxial kneading extruder. At this time, a pellet to which a desired amount of fine particles is added from the beginning may be used,
A pellet to which fine particles are added in advance at a high concentration (master pellet) may be diluted with a pellet to which fine particles have not been added to adjust to a desired concentration. The extrusion temperature of the polyester is from 250 ° C to 350 ° C, more preferably from 260 ° C to 340 ° C, and the polyester is retained and melted for 1 minute to 30 minutes, more preferably 3 minutes to 15 minutes. After this,
It is preferable to filter the molten polymer in advance using a filter. Examples of the filter include wire mesh, sintered wire mesh, sintered metal, sand, glass fiber, and the like. Preferred filter size is 1μm or more and 30μm
It is as follows. The molten polyester is extruded from a T-die. When making a laminated film, each component is extruded using a T die having a laminated structure (such as a multi-manifold die). This is solidified on a casting drum at 40 ° C to 100 ° C to prepare an unstretched film. At this time, the adhesion of the film to the casting drum is increased by using an electrostatic application method, a water film formation method (applying a fluid such as water on the casting drum to improve the adhesion between the melt and the drum), and the like. It is preferable because the flatness can be improved. This is peeled off to form an unstretched sheet.

(3) MD stretching The unstretched sheet is stretched in the machine direction (MD). The preferred stretching ratio is 2.5 times or more and 4 times or less, more preferably 3 times or more and 4 times or less. The stretching temperature is preferably from 70 ° C to 160 ° C, more preferably from 80 ° C to 150 ° C,
More preferably, the temperature is from 80 ° C to 140 ° C. The preferred stretching speed is from 10% / sec to 300% / sec, more preferably from 30% / sec to 250% / sec, even more preferably from 50% / sec to 200% / sec. Such MD stretching can be performed by transporting between a pair of rolls having different peripheral speeds.

(4) TD stretching The stretching ratio is preferably 2.5 times or more and 5 times or less, more preferably 3 times or more and 4.5 times or less, and still more preferably 3.3 times or less.
It is not less than twice and not more than 4.3 times. Stretching temperature is 75 ° C or higher 16
5 ° C. or less, more preferably 80 ° C. or more and 160 ° C.
° C or lower, more preferably 85 ° C or higher and 155 ° C or lower. The preferred stretching speed is from 10% / sec to 300% / sec, more preferably from 30% / sec to 250% / sec, even more preferably from 50% / sec to 200% / sec.
TD stretching can be achieved by chucking the film at both ends, transporting the film into a tenter, and expanding the width.

(5) Heat setting A preferable heat setting temperature is 190 ° C to 275 ° C, more preferably 210 ° C to 270 ° C, further preferably 230 ° C to 270 ° C, and a preferable processing time is 5 seconds to 180 °. 1 second or less, more preferably 10 seconds or more
It is 20 seconds or less, more preferably 15 seconds or more and 60 seconds or less. It is preferable to relax 10% or less in the width direction during heat setting. More preferably 8% or less, further preferably 6%
% Or less, and the lower limit is substantially 0%. Such heat setting and relaxation can be achieved by chucking the film at both ends, transporting the film to the heat setting zone, and reducing the width thereof.

(6) Winding After heat setting, cooling and trimming are performed and the film is wound around a roll.
At this time, it is also preferable to apply a processing (knurling) to the end of the support. Preferred film forming width is 0.5 m or more and 10 m or less, more preferably 0.8 m or more and 8 m or less,
More preferably, it is 1 m or more and 6 m or less.

It is also preferable to subject the thus prepared polyester support to a surface treatment. Surface treatment is chemical treatment, mechanical treatment, corona treatment, flame treatment, UV treatment,
High-frequency treatment, glow treatment, active plasma treatment, laser treatment, mixed acid treatment, ozone oxidation treatment and the like can be mentioned. Among them, corona treatment, ultraviolet treatment, glow treatment and flame treatment are particularly effective. These can be carried out in accordance with the method described in "Invention Association Disclosure Technique, Official Technique No. 94-6023". It is preferable to provide an antistatic layer. Examples of the antistatic agent include metal oxides, conductive metals, carbon fibers, π-conjugated polymers (such as polyarylene vinylene) and ionic compounds.
Volume resistivity of 10 ⁷ Ωcm or less, more preferably 10 ⁷ Ωcm
^{It is 6} Ω or less, more preferably 10 ⁵ Ωcm or less.

The antistatic agent is preferably a conductive metal oxide or a derivative thereof. Among them, the conductive material particularly preferably used is a crystalline metal oxide particle, such as ZnO, TiO ₂ , SnO ₂ , and Al. ₂ O ₃ , In
Examples include ₂ O ₃ , SiO ₂ , MgO, BaO, MoO ₃ , and V ₂ O _5. Particularly preferred are those containing SnO ₂ as a main component and about 5 to 20% of antimony oxide and / or further components (for example, Silicon oxide, boron, phosphorus, etc.). For details of these conductive materials and the coating method, refer to “Invention Association's published technique, official technique number 94-6023.
No., and can be implemented in accordance with this.

Finally, the evaluation and measurement methods employed in the present invention will be described. (1) Surface elastic modulus Using a micro surface hardness tester (Fisher Instruments Co., Ltd .: Fisherscope H100VP-HCU), a Vickers indenter is brought into contact with the sample surface, and then the load is increased to 1 mN in 10 seconds. . Hold this state for 5 seconds. The penetration depth of the Vickers indenter at this time is defined as Dvo. Thereafter, the force (Fv) for pushing back the Vickers indenter when the load is removed and the penetration depth (Dv) are measured, and the inclination is defined as the surface elastic modulus. That is, when Dv is plotted on the horizontal axis and Fv is plotted on the vertical axis, the absolute value of the slope between Dv and 0.9 × Dvo from Dvo was defined as the surface elastic modulus. This measurement is at 25 ° C and 60% R
The test was performed under H and expressed as an average value of 10 points.

(2) Center Line Roughness (Ra) Using a surface roughness measuring device (SE-3F manufactured by Kosaka Laboratory Co., Ltd.), a reference length L (2 0.5 mm), and a roughness curve Y = f with the center line of this portion as the X axis and the direction of the vertical magnification as the Y axis.
When represented by (X), the value given by the following equation (1) is represented by (μm). The center line roughness (Ra) was obtained by obtaining ten cross-sectional curves from the surface of the sample film and expressing the average value of the center line average roughness of the extracted portion obtained from these cross-sectional curves. The tip radius of the stylus was 2 μm, the load was 30 mg, and the cutoff value was 0.08 mm.

[0024]

(Equation 1)

(3) Maximum height (Rt) A reference length (2.5 mm) is extracted from a cross-sectional curve obtained by a surface roughness measuring device (SE-3F manufactured by Kosaka Laboratory Co., Ltd.), and this portion is extracted. When the maximum point and the minimum point are sandwiched by two straight lines parallel to the average line, the distance is expressed in μm and 1
The average value of the 0 points was obtained and defined as Rt. In this measurement, a stylus having a tip radius of 2 μm was used, the load was 30 mg, and the cutoff value was 0.08 mm.

[0026]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. (1) Polymerization of polyester (a) Polyethylene terephthalate (PET) 80 parts of dimethyl terephthalate, 58 parts of ethylene glycol, 0.029 part of manganese acetate tetrahydrate and 0.028 part of antimony trioxide are added and stirred. While 200
Heated to ° C. 235 while removing by-product methanol
The temperature was raised to ° C. After the by-product of methanol was completed, 0.03 part of trimethylphosphoric acid was added, and the mixture was heated to 285 ° C while adding 4 parts.
Reduce the pressure to 0 Pa (0.3 Torr) and set the intrinsic viscosity to 0.62d
1 / g of PET was polymerized.

(B) Polyethylene naphthalate (PEN) 2,6-naphthalenedicarboxylic acid dimethyl ester 10
0 parts, 58 parts of ethylene glycol, 0.029 parts of manganese acetate tetrahydrate and 0.028 parts of antimony trioxide were added, and the mixture was heated to 200 ° C. with stirring. The temperature was raised to 235 ° C. while removing by-produced methanol. After the by-product of methanol was completed, 0.03 part of trimethyl phosphoric acid was added, and 2
The pressure was reduced to 40 Pa (0.3 Torr) while the temperature was raised to 85 ° C., and PEN having an intrinsic viscosity of 0.58 dl / g was polymerized. In addition, these intrinsic viscosities were measured by the following method. Phenol / 1,1,2,2-tetrachloroethane mixed solvent
(Weight ratio: 60/40)
Make solutions of g / dl, 0.6g / dl and 1.0g / dl. This is measured at 20 ° C. using an Ubbelohde viscometer. The viscosity was plotted against the concentration, and the viscosity extrapolated to 0 was taken as the intrinsic viscosity (dl / g).

(2) Kneading of Fine Particles The oligomers of PET and PEN having the intrinsic viscosities shown in Table 1 are prepared by shortening the polymerization time by the above method. This is added to the fine particles as described in Table 1. This was kneaded at 230 ° C. for 5 minutes using a Banbury mixer. After drying the PET having an intrinsic viscosity of 0.62 dl / g and the PEN having an intrinsic viscosity of 0.58 dl / g at 150 ° C. for 30 minutes, the temperature was increased from 280 ° C. to 320 ° C. using a single screw kneading extruder. While kneading for 5 minutes. This was extruded into noodles, then cooled with water and cut to form pellets.

[0029]

[Table 1]

(2) Formation of Polyester Film The polyester pellets prepared by the above method were dried at 160 ° C. under reduced pressure for 3 hours. The pellets of each composition were melted at 310 ° C. by an extruder, filtered through a 5 μm mesh filter, and then applied with a static electricity at 50 ° C. from a T-die (multi-manifold die) so as to obtain the composition shown in Table 2. The film was extruded onto a casting drum thus prepared to prepare an unstretched film.

[0031]

[Table 2]

This was subjected to MD stretching, TD stretching, heat setting, and thermal relaxation under the conditions shown in Table 2. The total width of the film was 1.8 m, which was trimmed to 1.5 m at both ends, knurled at both ends to a height of 30 μm and a width of 10 mm. I took it. (3) Evaluation of polyester film According to the above method, surface elastic modulus, center line roughness (Ra),
The maximum height (Rt) was measured and is shown in Table 3. Evaluation of scratch resistance was measured by a pencil hardness method according to JIS-K-5400. Note that this measurement was performed in a state where the film was stretched flat and in a state where the film was formed into a cylindrical shape having a diameter of 10 cm. The evaluation of abrasion was 1.5% of the polyester film after film formation.
m width x 1m length, put this on black cloth,
The number of bright spots due to scratches under a tungsten lamp of W was counted with the naked eye. The number is preferably 10 or less, more preferably 5 or less.

[0033]

[Table 3]

[0034]

The surface elastic modulus of at least one surface is 5 GPa.
With the laminated polyester film having a thickness of 15 GPa or less, a laminated polyester film having excellent scratch resistance was achieved.

Claims (7)

[Claims] 1. A surface elastic modulus of at least one side is 5 GPa.
A laminated polyester film having a thickness of 15 GPa or less. 2. A center line roughness (R) of at least one surface.
a) is 0.01 μm or less and the maximum height (Rt) is 0.5 μm
The laminated polyester film according to claim 1, wherein: 3. The method according to claim 1, wherein fine particles having a size of 1 nm or more and 400 nm or less
3. The laminated polyester film according to claim 1, wherein a layer (B layer) containing 0 wt% or more and 60 wt% or less is laminated on at least one surface of the polyester support (A layer). 4. The laminated polyester film according to claim 1, wherein the total thickness of the layer is 10 μm or more and 300 μm or less, and the thickness of the B layer is 5 μm or more and 100 μm or less. 5. The method according to claim 3, wherein the ratio (D / Tb) of the particle size (D) of the fine particles to the thickness (Tb) of the B layer is less than 1 × 10 ^{−2 and} 1 × 10 ⁻⁵ or more. Or the laminated polyester film according to 4. 6. The method according to claim 3, wherein a difference in surface elastic modulus between the front and back surfaces is 0.5 GPa or more and 10 GPa or less.
The laminated polyester film according to any one of the above. 7. The laminated polyester film according to claim 1, wherein the polyester comprises a polyethylene terephthalate resin or a polyethylene naphthalate resin.