Laminated polyester film, laminate, and image display device

Abstract

To provide a laminated polyester film having good static bending resistance and dynamic bending resistance, and an image display device mounted with the film.SOLUTION: The laminated polyester film comprises two or more layers including at least an X layer and a Y layer satisfying RX> RY in orientation parameters RX and RY, and satisfies the following formula: RX-RY ≥ 1.0 (1) SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminated polyester film having excellent flexural durability. [Background technology]

[0002] In recent years, image display devices using self-luminous elements called organic light-emitting diodes (OLEDs) (hereinafter referred to as "organic electroluminescent display devices") have become more popular than conventional liquid crystal display devices (LCDs). Because they use self-luminous elements, they do not require auxiliary lighting devices such as backlights, making them thinner and more flexible. Furthermore, because OLEDs use metals such as aluminum and copper for their electrodes, circular polarizers were previously used to prevent incident external light from reflecting within the image display device. However, the polarizers themselves can absorb light, resulting in reduced brightness. Technologies have been developed to replace the anti-reflection function with color filters, improving the luminous efficiency of OLEDs and extending their lifespan. This has accelerated the development of flexible image display devices that can be folded, rolled up, and repeatedly bent. This has created a demand for surface protection films to prevent scratches on the display surface and support films (sometimes called backplate films) to protect the OLEDs installed inside OLED display devices, as well as flexible materials.

[0003] As a folding film, a film in which the refractive index in the bending direction, the folding portion, and the thickness direction is controlled is being studied (Patent Document 1).

[0004] Furthermore, films that focus on specific bending properties are being investigated (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-9349 [Patent Document 2] International Publication No. 2021 / 182191 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, the polyester film is designed with consideration given to its flex resistance, but only considers dynamic flex resistance when repeatedly opened and closed, and does not take into account the fact that the film will be left folded and unused for the most part. In other words, the design does not take static flex resistance into consideration, resulting in poor static flex resistance. Furthermore, as OLEDs have become longer in life, the dynamic flex resistance is also not satisfactory for applications requiring high flex durability. Patent Document 2 focuses on specific bending properties to achieve static flex resistance, but does not consider dynamic flex resistance, and fails to achieve both static and dynamic flex resistance.

[0007] An object of the present invention is to provide a laminated polyester film having good static flex resistance and dynamic flex resistance, and an image display device incorporating the film. [Means for solving the problem]

[0008] A preferred embodiment of the present invention for solving the above problem is as follows. 1. Orientation parameter R X and R Y In R X >R Y A laminated polyester film comprising two or more layers including at least an X layer and a Y layer, which satisfy the following formula: R X -R Y ≧1.0 (1) where the orientation parameter R X , R YWhen laser Raman spectroscopy was performed on the film cross section in the width and thickness directions, the peak at 1615 cm was measured with polarized light parallel to the in-plane direction of the film. -1 ±10cm -1 Maximum intensity A in the range P and 1615 cm measured with polarized light parallel to the film thickness direction. -1 ±10cm -1 Maximum intensity A in the range T Ratio to A P / A T is the orientation parameter R, and the orientation parameters obtained at a position 0.5 μm from the surface of each of the X and Y layers in the thickness direction are R X , R Y Let's say. 2. The orientation parameter at the center position in the film thickness direction is R Z When R X >R Z >R Y 1. The laminated polyester film according to claim 1. 3. The laminated polyester film according to 1. or 2., wherein the stretch-shrink parameter S calculated by the following formula in at least one direction in the film plane is 1.00 or more. The extension / contraction parameter S = -Ln(W 60 / W0) / Ln(L 60 / L0) (2) Here, the initial length L0 and the length at 60% elongation are L 60 , the initial value in the width direction is W0, and the width length at 60% elongation is W 60 Let's say. The laminated polyester film according to any one of 1. to 3., which consists of 4.5 or more layers. 5. The laminated polyester film according to any one of 1. to 4., wherein the X layer contains 20 mol % or more of a component derived from an aromatic dicarboxylic acid having 9 or more carbon atoms, in terms of dicarboxylic acid units. 6. The laminated polyester film according to any one of 1. to 5., wherein the Y layer contains 5 mol % or more of a component derived from a diol having 6 or more carbon atoms, in diol units. 7. The laminated polyester film according to any one of 1. to 6., wherein the content of components having a molecular weight of 200 to 1000 g / mol is 5% by mass or less. 8. A laminated polyester film according to any one of 1 to 7, wherein in a temperature dispersion curve of the loss modulus in at least one direction, the ratio E"(80) / E"(120) of the loss modulus at 80°C E"(80) to the loss modulus at 120°C E"(120) is 0.40 or more. 9. A laminate comprising the laminated polyester film according to any one of 1. to 8. above and a substrate having a Young's modulus of 6 GPa or more. 10. Orientation parameter R X and R Y In R X >R Y A laminated polyester film consisting of two or more layers including at least an X layer and a Y layer, X , R Y , R Z When a linear regression line was fitted using the three values ​​and the measured thickness, the slope of the orientation parameter relative to the thickness direction position was 0.02 μm, with the surface of the Y layer as the reference. -1 The laminated polyester film is as described above. where the orientation parameter R X , R Y , R Z When laser Raman spectroscopy was performed on the film cross section in the width and thickness directions, the peak at 1615 cm was measured with polarized light parallel to the in-plane direction of the film. -1 ±10cm -1 Maximum intensity A in the range P and 1615 cm measured with polarized light parallel to the film thickness direction. -1 ±10cm -1 Maximum intensity A in the range T Ratio to A P / A T is the orientation parameter R, and the orientation parameters obtained at a position 0.5 μm from the surface of each of the X and Y layers in the thickness direction are R X , R Y The orientation parameter at the center position in the film thickness direction is R Z Let's say. 11. The laminated polyester film for flexible devices according to any one of 1. to 10., which is used to protect a flexible device. 12. The laminated polyester film for flexible devices according to 11, which is used to protect an image display device. 13. An image display device equipped with the laminated polyester film according to any one of 1. to 10. [Effects of the Invention]

[0009] The laminated polyester film of the present invention has good static flex resistance and dynamic flex resistance, and is suitable for applications requiring high levels of flex durability, such as surface protection films and support films for flexible displays. DETAILED DESCRIPTION OF THE INVENTION

[0010] The polyester used in the laminated polyester film of the present invention is a general term for polymers in which the main bond in the main chain is an ester bond. Polyesters are usually obtained by polycondensation of a dicarboxylic acid component and a glycol component.

[0011] The dicarboxylic acid component for obtaining the polyester is not particularly limited as long as it does not impair the effects of the present invention, and examples that can be used include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodiumsulfonedicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorene, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, and fumaric acid, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and oxycarboxylic acids such as parahydroxybenzoic acid. Furthermore, when obtaining the polyester, the dicarboxylic acid component may be a dicarboxylic acid ester derivative component, or an esterification product of the above dicarboxylic acid compound may also be used.

[0012] The glycol component for obtaining the polyester is not particularly limited as long as it does not impair the effects of the present invention. For example, various components can be used, such as aliphatic dihydroxy compounds such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol; polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; alicyclic dihydroxy compounds such as 1,4-cyclohexanedimethanol, isosorbate, and spiroglycol; and aromatic dihydroxy compounds such as bisphenol A, bisphenol S, and 9,9'-bis[4(2-hydroxyethoxy)phenyl]fluorene.

[0013] These dicarboxylic acid components and glycol components may be used in combination of two or more kinds as long as the effects of the present invention are not impaired.

[0014] The laminated polyester film of the present invention is preferably a laminated aromatic polyester film containing an aromatic polyester as a main component. In particular, the laminated aromatic polyester film of the present invention is preferably either a laminated polyethylene terephthalate film or a laminated polyethylene naphthalate film. These films may contain copolymerization components. For example, in the case of a laminated polyethylene terephthalate film, it is preferred that the dicarboxylic acid component contains 50 mol% or more of a terephthalic acid component and the diol component contains 50 mol% or more of an ethylene glycol component. Even in the case of a laminated polyethylene naphthalate film, it is preferred that the components contained in 50 mol% or more are appropriately interpreted.

[0015] The polyester may also contain catalysts, stabilizers, inorganic particles, organic particles, antioxidants, antistatic agents, and other polymer resins, as long as the effects of the present invention are not impaired.

[0016] A preferred embodiment of the laminated polyester film of the present invention comprises two or more layers in the thickness direction, including an X layer comprising one surface of the laminated polyester film and a Y layer comprising the other surface. In this case, when the lower-level orientation parameter R is measured, the X layer has a larger orientation parameter R, and the Y layer has a smaller orientation parameter R.

[0017] When laser Raman spectroscopy was performed on the film cross section in the width and thickness directions, the 1615 cm peak measured with polarized light parallel to the in-plane direction of the film was -1 ±10cm -1 Maximum intensity A in the range P and 1615 cm measured with polarized light parallel to the film thickness direction. -1 ±10cm -1 Maximum intensity A in the range T Ratio to A P / A T is the orientation parameter R, and the orientation parameter R obtained at a position 0.5 μm from the surface of each of the X and Y layers in the thickness direction is R X , R Y The orientation parameter R X and R Y In R X >R Y is.

[0018] The laser spot for the laser Raman spectroscopy was 1.0 μm, and the orientation parameter R X and R Y is the average result up to 1 μm from each surface in the film thickness direction. In other words, when the thickness of the X layer and / or Y layer is 1 μm or less, the orientation parameter R also includes the orientation of the layer adjacent to the X layer or Y layer up to 1 μm in the film thickness direction.

[0019] 1615cm when laser Raman spectroscopy was performed -1 The peak observed at A is due to the stretching of the aromatic rings of the polyester. P / A TA large orientation parameter R indicates that the molecular chains of the polyester are oriented, and a small orientation parameter R indicates that the molecular chains of the polyester are not oriented.

[0020] Laser Raman spectroscopy is performed using a microscopic Raman device, and the measurement method is as described in the Examples.

[0021] A preferred embodiment of the laminated polyester film of the present invention is X and R Y The difference between R X -R Y is 1.0 or greater. R X and R Y When the difference between these is 1.0 or more, the dynamic bending resistance and static bending resistance are good. The occurrence of wrinkles, breaks, cracks, etc. when a film is bent is due to the long-term concentration of stress near the surface during bending. When a film with uniform physical properties in the film thickness direction is bent, there is a neutral axis near the center of the film in the thickness direction where no stress is applied, and when the film is bent 180°, stress in the compressive direction in the film plane is likely to occur near the surface on the inside of the bend, and stress in the stretching direction in the film plane is likely to occur near the surface on the outside of the bend. When the film is laminated with a substrate with a high Young's modulus, the neutral axis shifts toward the substrate with a high Young's modulus, so the compressive or stretching stress generated near the surface becomes large, making it more likely to cause wrinkles, breaks, cracks, etc. The laminated polyester film of the present invention has an R θ θ , which is the orientation of molecular chains that controls mechanical properties such as Young's modulus. X and R Y By having a difference of 1 or more, the generated stress can be dispersed, and the occurrence of wrinkles, breaks, cracks, etc. can be suppressed even when the material is bent over a long period of time.

[0022] The laminated polyester film of the present invention has an orientation parameter R at the center position in the film thickness direction of R Z When R X >R Z >R YIt is preferable that the orientation parameter R in the film thickness direction changes stepwise in the thickness direction, which may suppress stress concentration during bending and further improve the dynamic bending resistance and static bending resistance. X , R Y , R Z When linear regression line approximation is performed using the three values ​​and the measured thickness value, the coefficient of determination in the least squares method is preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.8 or more, and particularly preferably 0.9 or more. The upper limit of the coefficient of determination is 1.0 or less. Furthermore, when measurements are taken every 1 μm in the thickness direction, the coefficient of determination is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.8 or more.

[0023] A preferred embodiment of the laminated polyester film of the present invention is X , R Y , R Z When a linear regression line was fitted using the three values ​​and the measured thickness, the slope of the linear regression line of the orientation parameter R in the film thickness direction with the Y layer side as the reference was 0.02 μm. -1 That's all. Unit: μm -1 Regarding the orientation parameter R, it is dimensionless and is the slope of the orientation parameter (dimensionless) relative to the thickness (μm), so the unit is μm -1 The R, which is the molecular chain orientation that controls mechanical properties such as Young's modulus, X and R Y , R z The gradient of the orientation parameter is 0.02 μm. -1 By setting the value to above 0.10 μm, the generated stress can be dispersed, and the occurrence of wrinkles, breaks, cracks, etc. can be suppressed even when the film is bent for a long period of time. -1 More than 0.15 μm is preferable. -1 More preferably, 0.20 μm or more -1 More preferably, 0.30 μm or more -1 The above is particularly preferable. In addition, the inclination is 3.0 μm from the viewpoint of suppressing curling of the film itself. -1Preferably it is equal to or less than 2.5 μm, more preferably 2.5 μm -1 Less than 2.0 μm, more preferably -1 The following is the result.

[0024] The orientation parameter R of the laminated polyester film of the present invention is not particularly limited as long as it is within a range that satisfies the above-mentioned relational expression. However, from the viewpoint of increasing the mechanical strength of the laminated polyester film and suppressing the occurrence of breakage or cracks when bent, it is preferable to set the R X is preferably 5 or more, and R Y It is preferable that R is 1.5 or more. X is more preferably 8 or more, even more preferably 10 or more, still more preferably 12 or more, and particularly preferably 15 or more. X There is no particular upper limit for R X is preferably 30 or less. Y is more preferably 1.8 or more, even more preferably 2.0 or more, even more preferably 2.2 or more, and particularly preferably 2.5 or more. Y The upper limit of is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less, from the viewpoint of dispersing stress and suppressing the occurrence of wrinkles when bent.

[0025] In the laminated polyester film of the present invention, when laser Raman spectroscopy is performed, the crystallinity T calculated from the half width of the Raman band is greater than the crystallinity T X and the crystallinity of the Y layer side, T Y The difference in crystallinity is preferably 5% or more and 40% or less. When the difference in crystallinity is in the above range, it is possible to obtain good dynamic flexibility and static flexibility, which is preferable. X is preferably 20% or more and 60% or less, more preferably 25% or more, even more preferably 30% or more, and even more preferably 35% or more. Y is preferably 5% or more and 35% or less, the lower limit is more preferably 8% or more, and even more preferably 10% or more, and the upper limit is more preferably 30% or less.

[0026] The thickness of the laminated polyester film of the present invention is preferably 100 μm or less from the viewpoint of dynamic flexibility and static flexibility. The thickness is more preferably 80 μm or less, even more preferably 65 μm or less, and even more preferably 50 μm or less. Furthermore, from the viewpoint of handleability, the thickness is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more.

[0027] A preferred embodiment of the laminated polyester film of the present invention is a laminated film having at least two layers laminated together to achieve good dynamic and static bending properties. In the case of a two-layer laminated polyester film, it is a two-layer laminated polyester film consisting of an X layer and a Y layer. In the case of a three-layer laminated film, it is preferably a three-layer laminated polyester film consisting of an X layer, a Y layer, and an inner layer sandwiched between two surface layers. It may also be a multi-layer laminated film having four or more layers, five or more layers, or even 30 or more layers, but from the viewpoint of mass production, it is preferably 1000 layers or less. By having five or more layers, the orientation parameter R X and R Y This makes it easier to control the X , R Y , R Z This is preferable because it allows the coefficient of determination in the least squares method to be controlled to a high value when linear regression line approximation is performed using the three values ​​and the measured thickness. In applications where cost and productivity are important, a relatively simple laminate structure can be preferably used, and from these viewpoints, it is preferable that the number of layers be less than 30, more preferably 15 or less, and more preferably 10 or less.

[0028] In the case of a two-layer laminate polyester film, the X layer and the Y layer preferably contain polyester (A) described below, and the Y layer preferably contains polyester (B) described below, with the X layer more preferably containing 90% by mass or more, and even more preferably 95% by mass or more, of polyester (A). The Y layer more preferably contains 40% by mass or more, and even more preferably 45% by mass or more of polyester (B).

[0029] The dicarboxylic acid component of polyester (A) preferably contains terephthalic acid or 2,6-naphthalenedicarboxylic acid at 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 95 mol% to 100 mol% based on the acid components contained in polyester (A). The glycol component of polyester (A) preferably contains ethylene glycol at 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 95 mol% to 100 mol% based on the glycol components contained in polyester (A). Among these, it is preferable that polyester (A) contains 20 mol% or more of a component derived from an aromatic dicarboxylic acid having 9 or more carbon atoms. The aromatic dicarboxylic acid having 9 or more carbon atoms is 2,6-naphthalenedicarboxylic acid, which can promote orientation by film stretching in polyester (A) compared to polyester (B), and therefore the orientation parameter R of the X layer side when formed into a film. X is the orientation parameter R Y That is, the laminated polyester film of the present invention preferably contains 20 mol % or more of a component derived from an aromatic dicarboxylic acid having 9 or more carbon atoms in the X layer, in terms of dicarboxylic acid units.

[0030] The polyester (B) preferably contains a copolymerization component in the dicarboxylic acid component and / or glycol component. The dicarboxylic acid component is preferably terephthalic acid, with the acid component contained in the polyester (B) comprising 60 mol% or more of terephthalic acid, more preferably 70 mol% or more, and particularly preferably 80 mol% to 100 mol%. The glycol component is preferably ethylene glycol, with the glycol component contained in the polyester (B) comprising 60 mol% or more of ethylene glycol, more preferably 70 mol% or more, and particularly preferably 75 mol% to 100 mol%. The copolymerization component preferably contains one or more selected from isophthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfone dicarboxylic acid, 1,4-cyclohexanedimethanol, and isosorbate. Among these, the copolymerization component preferably contains a component derived from a diol having 6 or more carbon atoms. The component derived from a diol having 6 or more carbon atoms can be either 1,4-cyclohexanedimethanol or isosorbate. The total content of 1,4-cyclohexanedimethanol and isosorbate is preferably 5 mol % or more and 40 mol % or less, more preferably 8 mol % or more, even more preferably 10 mol % or more, and more preferably 35 mol % or less, even more preferably 30 mol % or less. By setting the content within the above range, the orientation of polyester (B) due to film stretching can be suppressed compared to polyester (A), and therefore the orientation parameter R Y is the orientation parameter R X From the same viewpoint, the Y layer of the laminated polyester film of the present invention preferably contains 5 mol % or more, and more preferably 10 mol % or more, of a component derived from a diol having 6 or more carbon atoms, in diol units.

[0031] In the case of a two-layer laminate polyester film, when the X layer and the Y layer contain a component derived from an aromatic dicarboxylic acid having 9 or more carbon atoms relative to the acid component of the polyester of each layer, it is a more preferred embodiment that the amount of the component derived from the aromatic dicarboxylic acid having 9 or more carbon atoms in the Y layer is less than the amount of the component derived from the aromatic dicarboxylic acid having 9 or more carbon atoms in the X layer. Also, when the X layer and the Y layer contain a component derived from a diol having 6 or more carbon atoms relative to the glycol component of the polyester of each layer, it is a more preferred embodiment that the amount of the component derived from the diol having 6 or more carbon atoms in the Y layer is greater than the amount of the component derived from the diol having 6 or more carbon atoms in the X layer.

[0032] The laminated polyester film of the present invention preferably contains terephthalic acid or 2,6-naphthalenedicarboxylic acid at 80 mol % or more, more preferably 90 mol % or more, and particularly preferably 95 mol % to 100 mol % of the acid components contained in the laminated polyester film. In particular, the laminated polyester film preferably contains 5 mol % or more of a component derived from an aromatic dicarboxylic acid having 9 or more carbon atoms relative to the acid components. 2,6-naphthalenedicarboxylic acid can be selected as the aromatic dicarboxylic acid having 9 or more carbon atoms. Furthermore, the laminated polyester film preferably contains 60 mol % or more of ethylene glycol relative to the glycol components, more preferably 70 mol % or more, and particularly preferably 75 mol % to 100 mol %. As a glycol component other than ethylene glycol, a component derived from a diol having 6 or more carbon atoms is preferably included. As the component derived from a diol having 6 or more carbon atoms, either 1,4-cyclohexanedimethanol or isosorbate can be selected. The total content of 1,4-cyclohexanedimethanol and isosorbate is preferably 3 mol% or more and 20 mol% or less, more preferably 4 mol% or more, even more preferably 5 mol% or more, and more preferably 18 mol% or less, even more preferably 15 mol% or less.

[0033] In the two-layer laminated polyester film, the orientation parameter R can be controlled by setting the polyester composition of each of the X layer and the Y layer as described above.

[0034] In the case of a two-layer laminate polyester film, the thickness of each layer can be any thickness within a range that does not impair the effects of the present invention. The ratio X layer / Y layer, obtained by dividing the thickness of X layer by the thickness of Y layer, is preferably 0.8 to 10.0 in order to suppress curling and obtain good flatness of the laminate polyester film, and this ratio is more preferably 1.0 or more, even more preferably 1.5 or more, still more preferably 2.0 or more, and is more preferably 8.0 or less, even more preferably 6.0 or less, and still more preferably 5.0 or less.

[0035] When a three-layer laminate polyester film is used, it is preferably a three-layer laminate polyester film consisting of an X layer, a Y layer, and an inner layer sandwiched between two outer layers. The polyester compositions of the X layer and the Y layer may be different or the same as long as the effects of the present invention are not impaired. When the polyester compositions of the X layer and the Y layer are the same, the X layer and the Y layer contain polyester (A), and the inner layer contains polyester (B). The X layer / Y layer ratio, obtained by dividing the thickness of the X layer by the thickness of the Y layer, is preferably 1.5 or more, more preferably 2.0 or more. Furthermore, this ratio is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 6.0 or less.

[0036] In a three-layer laminate polyester film, when the polyester compositions of the X layer and the Y layer are different, it is preferable that the X layer contains polyester (A) and the Y layer contains polyester (B). In particular, it is preferable that the dicarboxylic acid component for obtaining polyester (A) contains 80 mol % or more of 2,6-naphthalenedicarboxylic acid relative to the acid component contained in polyester (A).

[0037] When a multilayer laminate polyester film has 30 or more layers, it preferably contains a structure in which layers made of polyester (A) (A layers) and layers made of polyester (B) (B layers) are alternately laminated. "Containing a structure in which layers made of polyester (A) (A layers) and layers made of polyester (B) (B layers) are alternately laminated" is defined as the presence of a portion having a structure in which layers A and B are regularly laminated in the thickness direction. That is, it is preferable that the order of arrangement of layers A and B in the thickness direction in the film is not random, and there are no particular restrictions on the order of arrangement of layers A and B or more. Furthermore, when layers A, B, and a layer C made of thermoplastic resin C are present, it is more preferable that they are laminated in a regular order such as A(BCA)n, A(BCBA)n, or A(BABCBA)n. Here, n is the number of repeating units. For example, when n = 3 in A(BCA)n, it represents a film laminated in the order ABCABCABCA in the thickness direction.

[0038] In the present invention, the laminate may include 30 or more alternating layers of polyester (A) (A layers) and 30 or more alternating layers of polyester (B) (B layers). The number is more preferably 40 or more. Considering the deterioration of dynamic flex resistance and static flex resistance that accompanies a decrease in lamination accuracy due to an increase in the size of the device or an excessive number of layers, the upper limit is preferably 1,000 or less, more preferably 500 or less, even more preferably 400 or less, and even more preferably 300 or less.

[0039] The thicknesses of the A and B layers in the multilayer laminate polyester film are preferably such that the thicknesses of the A0 and B0 layers, which are the first layers counting in the thickness direction from the surface layer on the X layer side, are dA0 and dB0, respectively, and the thicknesses of the A' and B' layers, which are the first layers counting in the thickness direction from the surface layer on the Y layer side, are dA' and dB', respectively, and the layer thickness distribution continuously changes between dA0 and dA' and between dB0 and dB', respectively, with a monotonically increasing or decreasing relationship. This gradient structure of layer thickness in the thickness direction preferably employs an arithmetic progression or a geometric progression relationship. Furthermore, from the viewpoint of controlling the orientation parameter R, it is preferable that the A0 layer be the thickest layer of the A layers, and the B' layer be the thickest layer of the B layers. The gradient degree A, which is the ratio of the thickest layer to the thinnest layer of the A layers, is preferably 1.5 or more, more preferably 2.0 or more, from the viewpoint of achieving high dynamic and static bending resistance. The gradient B, which is the ratio of the thickest layer to the thinnest layer of layer B, is preferably 1.0 or more, more preferably 1.5 or more, from the viewpoint of achieving high dynamic flex resistance and static flex resistance. The lamination ratio dA / dB, which is the ratio of the total thickness of layers A to the total thickness of layers B, is preferably 1.0 or more, more preferably 1.5 or more, and even more preferably 2.0 or more.

[0040] In the laminated polyester film of the present invention, preferred production steps include, but are not limited to, the following steps (1) to (3). Step (1): Stretching the sheet in the longitudinal direction by 3.3 times or more and 4.5 times or less Step (2): Stretching in the width direction by 3.3 times or more and 4.0 times or less Step (3): Heat treatment at 160°C to 210°C In step (1): the process of stretching the film in the longitudinal direction by 3.3 to 4.5 times, a stretching ratio of 3.3 times or more, preferably 3.4 times or more, more preferably 3.5 times or more, and even more preferably 3.6 times or more is used to obtain a more significant effect of the present invention. The stretching ratio is 4.5 times or less, preferably 4.0 times or less, and more preferably 3.9 times or less. Although the predetermined stretching ratio can be achieved in a single stage, a method of stretching the film to the predetermined stretching ratio in two or more stages is preferred. For example, when stretching in three stages, the stretching ratio in the first stage can be 1.02 times or more and 1.20 times or less, the stretching ratio in the second stage can be 1.05 times or more and 1.20 times or less, and the stretching ratio in the third stage can be 3.00 times or more and 4.00 times or less. A stretching method using the difference in rotation speed of rotating rolls is preferred because the orientation parameter R can be controlled to a high value by increasing the stretching speed. The temperature for stretching in the longitudinal direction is preferably equal to or higher than the glass transition temperature of the highest polyester resin among the glass transition temperatures of the polyester resins used, and equal to or lower than the glass transition temperature + 20°C. For example, if the glass transition temperature of the polyester resin is 80°C, the temperature is 80°C or higher and 100°C or lower. By heating the Y layer side with an infrared heater on the rotating roll immediately before stretching, the orientation parameter R Y It is preferable that the peak top of the wavelength of the irradiated infrared light be 1,000 to 1,600 nm.

[0041] Step (2): Regarding the step of stretching the film widthwise at a ratio of 3.3 to 4.0, in order to obtain a more significant effect of the present invention, the stretching ratio in the widthwise direction is preferably 3.4 or more, more preferably 3.5 or more, and preferably 3.8 or less, more preferably 3.7 or less. While known methods and devices can be used for stretching, the use of a tenter device is preferred because it can improve the thickness uniformity of the film. The stretching temperature is preferably the glass transition temperature of the polyester resin +10°C or more and the glass transition temperature +60°C or less.

[0042] Regarding step (3): the step of heat treatment at 160°C or higher and 210°C or lower, in order to obtain a more significant effect of the present invention, it is preferable to perform the heat treatment in at least three or more temperature ranges in sequence, and further, it is preferable that the heat treatment temperatures in the first, second, and third stages satisfy the following conditions: ·1st stage: 150℃ or higher and 190℃ or lower ·2nd stage: 160℃ or higher and 210℃ or lower ·Third tier: 100℃ or higher and 190℃ or lower The number of temperature stages in step (3) may be three or more. For example, a temperature range between the first and second stages can be provided between them. For example, a temperature range lower than the third stage can be provided after the third stage. It is also preferable to simultaneously perform stretching and / or relaxation in step (3). For example, when step (3) has three stages, stretching can be performed by 1.1 to 1.5 times in the width direction in the second stage, and relaxation can be performed by 1 to 10% in the longitudinal and / or width directions in the third stage. The heat treatment time can be any time within a range that does not deteriorate the properties, and is preferably 1 to 60 seconds, more preferably 5 to 40 seconds, and most preferably 15 to 30 seconds. Known methods and devices can be used for the heat treatment. However, after the stretching step in the tenter device for stretching in the width direction, the polyester resin is cooled to below its glass transition temperature and then heat-treated in the three or more temperature ranges described above, thereby reducing the orientation parameter R. X This is preferable in that the temperature can be controlled to a high level.

[0043] In order to adhere the laminated polyester film of the present invention to another substrate, an adhesive layer may be provided between the laminated polyester film and the substrate, and an easy-adhesion layer may be provided on the laminated polyester film to impart adhesion between the laminated polyester film and the adhesive layer.

[0044] In the laminated polyester film of the present invention, it is preferable that an easy-adhesion layer is laminated on at least one surface. The easy-adhesion layer can be provided to control the surface free energy of the laminated polyester film and thereby control the adhesion strength with the adhesive layer. The surface free energy of the laminated polyester film is preferably 35 mN / m or more and 60 mN / m or less, more preferably 38 mN / m or more, even more preferably 40 mN / m or more, and more preferably 50 mN / m. The thickness of the easy-adhesion layer is preferably 10 nm or more and 1000 nm or less. The resin preferably used for the easy-adhesion layer is preferably at least one resin selected from acrylic resins, polyester resins, and urethane resins, in terms of adhesion and handleability.

[0045] The laminated polyester film of the present invention preferably has an elongation shrinkage parameter S of 1.00 or more in at least one direction in the film plane. The elongation shrinkage parameter S is the degree of shrinkage in the direction perpendicular to the elongation direction in the film plane at an elongation of 60%, and is expressed by the following formula: The extension / contraction parameter S = -Ln(W 60 / W0) / Ln(L 60 / L0) where L0 is the initial length, L 60 is the length at 60% elongation, W0 is the initial length in the width direction, W 60 indicates the length in the width direction at an elongation of 60%.

[0046] An extension / shrinkage parameter S of 1.00 or more indicates that, in response to in-plane extension and compression deformation of the film, shrinkage in the direction perpendicular to the extension and compression directions is large, and deformation in the thickness direction of the film is suppressed. With the extension / shrinkage parameter S in the above range, deformation in the thickness direction is small in response to long-term bending deformation, and the occurrence of wrinkles is highly suppressed. The extension / shrinkage parameter S is more preferably 1.10 or more, and even more preferably 1.20 or more. There is no particular upper limit as long as it does not impair the effects of the present invention, but from the viewpoint of suppressing the occurrence of wrinkles during lamination of the laminate, it is preferably 2.00 or less, more preferably 1.50 or less, and even more preferably 1.30 or less. As a method for controlling the extension / shrinkage parameter S within the above range, it is preferable to control the highest temperature range of the heat treatment step in the production process to a low temperature within a preferred range.

[0047] The laminated polyester film of the present invention preferably has a content of components having a molecular weight of 200 to 1,000 g / mol of 5% by mass or less. When the component having a molecular weight of 200 to 1,000 g / mol is a low-molecular-weight polyester composition, the content is preferably 1% by mass or less. Having the content within the above range is preferable because it improves dynamic flex resistance and static flex resistance. The content of components having a molecular weight of 200 to 1,000 g / mol can be controlled within the above range by using raw materials with a low content of components having a molecular weight of 200 to 1,000 g / mol in the polyester composition used, or by extracting the components from the laminated polyester film using a solvent.

[0048] In the laminated polyester film of the present invention, in a temperature dispersion curve of the loss modulus obtained by dynamic viscoelasticity measurement (Dynamic Mechanical Analysis (DMA)) in at least one direction, the ratio E"(80) / E"(120), where E"(80) is the loss modulus at 80°C and E"(120) is the loss modulus at 120°C, is preferably 0.40 or more. The above E" reflects the viscous properties due to the glass transition of the laminated film, and the higher the E"(80) / E"(120), the larger the E"(80). Since the laminated film includes a layer that exhibits a glass transition at a relatively low temperature, localized stress generated during repeated folding can be thermally dissipated. Therefore, an E"(80) / E"(120) of 0.40 or more provides good static bending resistance at high temperatures, which is preferable. The higher the E"(80) / E"(120), the more preferable it is. However, if the ratio is too high, the heat resistance and mechanical properties may be deteriorated. Therefore, the upper limit is preferably 10.00 or less. The lower limit is more preferably 0.50 or more, even more preferably 0.60 or more, still more preferably 0.70 or more, and particularly preferably 0.80 or more. The upper limit is more preferably 8.00 or less, even more preferably 6.00 or less, even more preferably 4.00 or less, and particularly preferably 3.00 or less. E"(80) / E"(120) can be achieved by using the above-mentioned multilayer laminate structure of polyester (A) and polyester (B) and by employing the above-mentioned film-forming conditions. Furthermore, by incorporating a polyoxyalkylene glycol such as polyethylene glycol, polypropylene glycol, or polytetramethylene glycol into polyester (B) within a range that does not impair the properties of the present invention, the glass transition temperature can be effectively lowered while maintaining high mechanical properties, making control easier, and thus improving flex resistance at high temperatures.

[0049] The laminated polyester film of the present invention has high dynamic flex resistance and static flex resistance, and therefore can be suitably used as a film for flexible devices that can be folded, wound, and repeatedly folded. Since it combines high dynamic flex resistance and static flex resistance with transparency, it can be suitably used as a film for flexible image display devices. In particular, it is suitable as a screen protection film or impact absorbing layer for image display devices, and an image display element substrate.

[0050] The laminated polyester film of the present invention can be used by laminating it to a substrate having a Young's modulus of 6 GPa or more. Examples of substrates having a Young's modulus of 6 GPa or more include transparent substrates such as glass substrates and polyimide substrates, and metal substrates such as stainless steel substrates, copper substrates, aluminum substrates, and iron substrates. If wrinkles, breaks, or cracks occur in the film laminated to the substrate, stress transmission to the substrate becomes uneven when the film is bent, and the wrinkles, breaks, or cracks may also propagate to the substrate. By laminating the laminated polyester film of the present invention to the substrate, the occurrence of wrinkles, breaks, cracks, etc. due to bending of the film can be suppressed, and deterioration of the properties of the substrate due to bending can be suppressed.

[0051] The laminated polyester film of the present invention can be laminated to a substrate having a Young's modulus of 6 GPa or more by any known method as long as the effects of the present invention are not impaired, and either a method of laminating via an adhesive layer of a pressure-sensitive adhesive or adhesive agent, or a method of directly laminating without an adhesive layer can be applied. The method of laminating via an adhesive layer is preferred because it can prevent the laminated polyester film from peeling from the substrate.

[0052] The laminated polyester film of the present invention is preferably used by bonding the surface of the Y layer side to a substrate having a Young's modulus of 6 GPa or more. When the Y layer surface of the film is laminated to a substrate with a high Young's modulus, stress due to compression or expansion occurring on the X layer side can be dispersed in the thickness direction of the laminated polyester film, and stress concentration near the X layer surface can be suppressed, thereby suppressing the occurrence of wrinkles, breaks, cracks, etc.

[0053] The laminate of the present invention preferably comprises the laminated polyester film of the present invention and a substrate having a Young's modulus of 6 GPa or more. In particular, a laminate in which a substrate having a high Young's modulus is laminated on the surface of the Y layer of the laminated polyester film can disperse stress due to compression or extension occurring on the X layer side of the laminated polyester film in the thickness direction of the laminated polyester film and can prevent stress from concentrating near the surface of the X layer, thereby preventing the occurrence of wrinkles, breaks, cracks, etc., and can improve the dynamic flex resistance and static flex resistance of the laminate.

[0054] The laminated polyester film of the present invention may be provided with an adhesive layer. The adhesive layer improves adhesion to other substrates (e.g., glass substrates or stainless steel substrates). The position of the adhesive layer is not limited. Components of the adhesive layer include, for example, a pressure-sensitive adhesive and an adhesive. Examples of adhesives include acrylic pressure-sensitive adhesives, rubber pressure-sensitive adhesives, and silicone pressure-sensitive adhesives. Acrylic pressure-sensitive adhesives are pressure-sensitive adhesives containing a polymer of a (meth)acrylic monomer. When the adhesive layer contains a pressure-sensitive adhesive, the adhesive layer may also contain a tackifier. From the viewpoints of adhesive strength and releasability after molding, the adhesive is preferably an acrylic pressure-sensitive adhesive. Examples of adhesives include urethane resin-based adhesives, polyester-based adhesives, acrylic resin-based adhesives, ethylene vinyl acetate resin-based adhesives, polyvinyl alcohol-based adhesives, polyamide-based adhesives, and silicone-based adhesives. The thickness of the adhesive layer is not limited. From the viewpoints of adhesive strength and handleability, the thickness of the adhesive layer is preferably 5 μm or more and 100 μm or less.

[0055] The method for forming the adhesive layer is not limited. For example, it may be formed using a protective film containing an adhesive layer. For example, it may be formed using an adhesive layer-forming composition containing components that form the adhesive layer. The adhesive layer can be formed by applying the adhesive layer-forming composition to a polyester film and drying the adhesive layer-forming composition as needed. Various additives, such as antioxidants, heat stabilizers, ultraviolet absorbers, infrared absorbers, pigments, dyes, organic or inorganic particles, antistatic agents, and nucleating agents, may also be added to the adhesive layer.

[0056] A protective layer can be provided on the laminated polyester film of the present invention. The resin used in the protective layer may be either a thermosetting resin or a photocurable resin. The resin constituting the protective layer may contain a curing agent, a curing accelerator, a binder, a surface conditioner, an ultraviolet absorber, a light stabilizer, etc., as needed. The thickness of the protective layer is preferably 5 to 50 μm, and more preferably 10 to 40 μm. A thickness of 5 μm or more is preferred because it allows the properties of the protective layer to be fully exhibited. A thickness of 50 μm or less is also preferred because it improves the flatness of the surface. [Example]

[0057] (1) Polyester composition The polyester resin and film were dissolved in hexafluoroisopropanol (HFIP), 1 H-NMR and 13 The content of each monomer residue component and by-product diethylene glycol can be quantified using C-NMR. In the case of a laminated film, each layer of the film can be scraped off depending on the laminate thickness, and the components constituting each layer alone can be sampled and evaluated. For the film of the present invention, the composition was calculated from the mixing ratio during film production.

[0058] (2) Intrinsic viscosity of polyester The intrinsic viscosity of the polyester resin and film was measured by dissolving the polyester in orthochlorophenol and using an Ostwald viscometer at 25°C. In the case of a laminated film, each layer of the film was scraped off according to the laminate thickness, and the intrinsic viscosity of each layer alone was evaluated.

[0059] (3) Content of low molecular weight components Gel permeation chromatography (GPC) measurement was carried out, and the results were plotted as weight fractions to determine the area ratio corresponding to a number average molecular weight of 200 to 1000 g / mol, which was taken as the content of low molecular weight components.

[0060] To prepare the sample solution, 5 mL of hexafluoroisopropanol containing 0.005 mol / L sodium trifluoroacetate was added to 3 mg of sample, and the mixture was gently stirred at 40°C for 3 hours. The mixture was then filtered using a 0.5 μm filter. Next, the sample was analyzed by gel permeation chromatography (GPC) using a differential refractive index detector (Tosoh RI-8020) under the following conditions: Column: Shodex HFIP-LG (φ8.0 mm × 5 cm, Showa Denko), Shodex HFIP-806M (φ8.0 mm × 30 cm, Showa Denko) (2 columns) ·Flow rate: 0.5mL / min Column temperature: 40℃ ·Injection volume: 0.2mL Molecular weight calibration standard: Monodisperse polymethyl methacrylate (PMMA) (Showa Denko).

[0061] (4) Film thickness, layer thickness, number of layers The film was embedded in epoxy resin, and the cross section of the film was cut out using a microtome. The cross section was observed under a transmission electron microscope (TEM H7100, manufactured by Hitachi, Ltd.) at magnifications of 5,000 to 40,000 to determine the film thickness, the thickness of the polyester layer, and the number of layers. At each magnification, the scale was calibrated using a magnification calibration sample (S2009ST, manufactured by EM Japan).

[0062] (5) Glass transition temperature Measurements and analysis were performed using a Rigaku Thermo plus ECO2 series DSC vesta, and data analysis was performed using the same company's Thermo plus ECO2 system, in accordance with JIS K7121 (1987). Specifically, 5 mg of sample was heated from 25°C to 300°C at 20°C / min, and in the step-like change portion of the glass transition on the differential scanning calorimetry chart obtained from the DSC curve, the temperature was determined from the point where the curve of the step-like change portion of the glass transition intersects with a line equidistant in the vertical direction from the extended line of each baseline.

[0063] (6) Longitudinal and transverse directions The machine direction during film production is defined as the longitudinal direction, and the direction perpendicular to the longitudinal direction is defined as the width direction. If the longitudinal and width directions are unknown, an arbitrary direction is set as the 0° reference, and the refractive index is measured from 0 to 360° in 15° increments from there. The direction with the highest refractive index is defined as the longitudinal direction, and the direction perpendicular to that is defined as the width direction. The refractive index is measured in accordance with ASTM D 542-70 using an Atago Abbe Refractometer 4T, using sodium D line (wavelength 589 nm) as the light source and diiodomethane as the contact liquid.

[0064] (7) Orientation parameter R The film was embedded in epoxy resin, and the cross section of the film in the width direction and thickness direction was cut out with a microtome to prepare a sample. The cross section sample was subjected to laser Raman spectroscopy using a Renishaw inVia microscope under the conditions of a YAG laser 532 nm as a light source and a laser spot of 1.0 μm. The cross section sample was measured with a polarized light source parallel to the in-plane direction of the film, and the peak intensity of 1615 cm -1 ±10cm -1 Maximum intensity A in the range P and 1615 cm measured with a polarized light source parallel to the film thickness direction. -1 ±10cm -1 Maximum intensity A in the range T Ratio to A P / A T The orientation parameter R is defined as the orientation parameter R. The orientation parameter R1 is obtained by setting the center of the laser spot at a position 0.5 μm from one surface of the cross-sectional sample in the thickness direction, and the orientation parameter R2 is obtained by setting the center of the laser spot at a position 0.5 μm from the other surface in the thickness direction. The orientation parameters R1 and R2 are compared, and the larger value is defined as the orientation parameter R X , the smaller value is the orientation parameter R Y The orientation parameter measured at the center of the cross-sectional sample in the thickness direction was defined as the orientation parameter R Z Measurements were taken at five arbitrary points separated by 100 mm or more in both the width and length directions within the film to be measured, and the average value was used.

[0065] The obtained orientation parameter RX , R Y , R Z The slope of the linear regression line of the orientation parameter R in the film thickness direction, based on the Y layer side surface, and the coefficient of determination R were calculated by linear approximation using the least squares method using the spreadsheet software "Microsoft (registered trademark) Excel (registered trademark)" for the three values ​​of the above and the measured thickness. 2 was calculated.

[0066] In addition, using the orientation parameter R measured at 1 μm intervals in the thickness direction from a position 0.5 μm from one surface of the cross-sectional sample in the thickness direction in the same manner as above, the slope of the linear regression line of the orientation parameter R in the film thickness direction with the surface on the Y layer side as the reference and the coefficient of determination R 2 was also calculated.

[0067] (8) Crystallinity T The film was embedded in epoxy resin, and the film cross section in the width direction and thickness direction was cut out with a microtome to prepare a sample. The cross-sectional sample was subjected to laser Raman spectroscopy using a Renishaw inVia microscope. A YAG laser of 532 nm was used as a polarized light source parallel to the in-plane direction of the film of the cross-sectional sample, with a laser spot of 1.0 μm, and no polarizer was placed on the scattered light detection side. -1 ±10cm -1 The maximum value in the range was taken as the peak top, and the full width at half maximum was measured. -1 ) and the crystallinity T was calculated using the following formula.

[0068] Converted density (g / cm 3 )=(305-full width at half maximum) / 209 (1) Crystallinity T=100×(converted density-1.335) / (1.455-1.335) (2) The crystallinity obtained by setting the laser spot center at a position 0.5 μm from the surface of the X layer in the thickness direction is T X The crystallinity obtained by setting the laser spot center at a position 0.5 μm from the Y layer side surface in the thickness direction is T YMeasurements were taken at five arbitrary points separated by 100 mm or more in both the width and length directions within the film to be measured, and the average value was used.

[0069] (9) Elongation / contraction parameter S The film was cut into a rectangular shape measuring 150 mm long and 10 mm wide in the longitudinal and transverse directions, and a reference line was drawn parallel to the width direction of the rectangular sample at the 50 mm, 75 mm, and 100 mm positions in the longitudinal direction to form a sample. Under conditions of 25°C and 63% RH, a tensile test was performed in the longitudinal and transverse directions of the film using a tensile tester (Orientec Co., Ltd., automatic film strength and elongation measuring device "Tensilon (registered trademark) AMF / RTA-100"), with the sample gripped so that the 75 mm position in the longitudinal direction was the center between the chucks. The crosshead speed was 300 mm / min and the sample length was 50 mm. The initial length was L0 (mm), and the length at 60% elongation was L. 60 (mm), initial width is W0 (mm), and width at 60% elongation is W 60 (mm), and the extension / contraction parameter S is the value obtained from equation (1). 60 (mm) is the gauge length at 50mm and 100mm, W0 (mm) and W 60 The length of the marked line at the 75mm position (mm) was measured by observing it with a 20x objective lens on a universal projector (Nikon V-16A). Measurements were taken at five arbitrary points at least 100mm apart in both the width and length directions within the film to be measured, and the average value was used.

[0070] The extension / contraction parameter S = -Ln(W 60 / W0) / Ln(L 60 / L0) (1) Note that Ln is the natural logarithm.

[0071] (10) Surface free energy The surface free energy of the film was calculated as follows: First, the following formula (i) was derived from the extended Fowkes equation and Young's equation. [Extended Fowkes formula] γSL=γS +γL -2(γsd ·γLd ) 1 / 2 -2(γsD ·γLD ) 1 / 2 -2(γsh γLh ) 1 / 2 [Young's equation] γS = γSL + γL × cosθ γS: Surface free energy of the solid (unit: mN / m) γL: Surface tension of the liquid (unit: mN / m) γSL: Tension at the interface between solid and liquid (unit: mN / m) θ: Contact angle with liquid (unit: °) γsd, γLd: Dispersion force components of γS, γL γsD, γLD: Polar force components of γS and γL γsh, γLh: Hydrogen bond components of γS, γL (γsd γLd ) 1 / 2 +(γsD ·γLD ) 1 / 2 +(γsh γLh ) 1 / 2 =γL×(1+cosθ) / 2 (i) Next, the contact angles of the film with four types of liquids for which each component of surface tension was known were measured, and the results were substituted into equation (i) to solve the three-variable linear simultaneous equation for each liquid to determine the surface free energy of the film. The contact angles were measured using water, ethylene glycol, formamide, and methylene iodide as test solutions, using a contact angle meter, Model CA-D, manufactured by Kyowa Interface Science Co., Ltd. Measurements were performed five times on both sides of the film in an environment of 25°C and 65% humidity, and the average values ​​were used for each side.

[0072] (11) Preparation of laminate The laminate contained a film sample of each example / adhesive layer (25 μm) / glass plate (30 μm) in this order.

[0073] The adhesive layer was prepared by adding a mixed solution of 80 parts by weight of ethyl acetate, 80 parts by weight of n-butyl acrylate, 20 parts by weight of methyl acrylate, and 1.0 part by weight of acrylic acid to a solution of 200 parts by weight of acetone and 0.2 parts by weight of a radical polymerization initiator (2,2'-azobisisobutyronitrile) dissolved in 10 parts by weight of acetone. The mixture was allowed to react for 12 hours at 60°C under nitrogen, and finally, ethyl acetate was added to adjust the acrylic resin concentration to 20% by weight. The resulting acrylic resin had a weight-average molecular weight (Mw) of 200,000 and an Mw / Mn ratio of 4.5. The resulting acrylic resin was mixed with 0.3 parts by weight of a crosslinker ("Coronate L" manufactured by Tosoh Corporation) and 0.5 parts by weight of a silane coupling agent ("X-12-981" manufactured by Shin-Etsu Chemical Co., Ltd.), and ethyl acetate was added to adjust the total solids concentration to 10% by weight to obtain an adhesive composition.

[0074] The obtained coating solution of the adhesive composition was applied to a film sample using an applicator so that the thickness after drying would be 25 μm. The coating layer was dried at 100°C for 1 minute to obtain a film equipped with an adhesive layer. The exposed surface of the adhesive layer was then protected with a release-treated polyethylene terephthalate film (manufactured by Toray Industries, Inc., trade name "Cerapeel" (registered trademark) MDA, thickness: 38 μm). The sample was then aged for 7 days under conditions of a temperature of 75°C and a relative humidity of 80% RH to obtain a laminate of film sample / adhesive layer / protective film.

[0075] The protective film was peeled off from the laminate, and the adhesive film sample and a glass plate (30 μm, product name: CG3, manufactured by Corning) thinned by etching were subjected to corona treatment on their respective bonding surfaces, and then bonded together to obtain a laminate. The Young's modulus of the glass plate was measured using a free resonance method using a JE2-RT model manufactured by Nippon Technoplus Co., Ltd., and was found to be 75 GPa.

[0076] (12) Static bending test Static bending resistance was evaluated using the laminate sample described in (11) above. Using a U-shaped extension / contraction tester (Yuasa System Instruments DLDMLH-FS), a laminate sample cut to a length of 40 mm and width of 25 mm was attached to the end of the tilt clamp with the tilt clamp in a horizontal position, with the stroke direction (the bending direction) aligned with the sample's length. The sample was then left for 240 hours in the maximum bending position, with the center of the laminate bent at a face-to-face distance of 1.5 mm. After 240 hours, the sample was quickly released from the bending state, removed from the tester, and placed on a flat floor with the bent inner side facing downwards and without any load. One hour after releasing the bending state, the central bent portion was observed from the film side of the laminate to evaluate for wrinkles, breaks, and cracks. This measurement was repeated five times, and the module performance was evaluated according to the following criteria. Module performance ratings of A, B, and C indicate excellent static bending resistance and suitable for use as a flexible device, with A being the most excellent. Rating D indicates poor static bending resistance due to noticeable breaks and cracks when used as a flexible device. A: In static bending tests in the longitudinal and transverse directions, no wrinkles, breaks, or cracks were observed in either direction. B: In static bending tests in the longitudinal and transverse directions, only slight wrinkles were observed in either direction. C: In the static bending test in the longitudinal and transverse directions, no clear breaks or cracks were observed in either direction, but wrinkles were observed. D: In static bending tests in the longitudinal and transverse directions, clear fractures or cracks are observed in at least one direction.

[0077] (13) Dynamic bending test Dynamic flex resistance was evaluated using the laminate sample described in (11) above. Using a U-shaped extension / contraction tester (Yuasa System Instruments DLDMLH-FS), a laminate sample cut to a length of 40 mm and width of 25 mm was attached to the end of the tilt clamp with the tilt clamp in a horizontal position, with the stroke direction (the bending direction) aligned with the sample's length. The sample was then flexed 1 million times at a rate of 1 flex / second, with the center of the laminate bent at a face-to-face distance of 3.0 mm. After 1 million flexes, the sample was quickly released from the flexed state, removed from the tester, and placed on a flat floor with the bent inner side facing downwards without any load. One hour after completing 1 million flexes, the central bent portion was observed from the film side of the laminate to evaluate for wrinkles, breaks, or cracks. This measurement was repeated five times, and the module performance was evaluated according to the following criteria. Module performance ratings of A, B, and C indicate excellent dynamic flex resistance and are suitable for use as flexible devices, with A being the most excellent. D has poor dynamic bending resistance because breaks and cracks are noticeable when used in a flexible device. A: In dynamic bending tests in the longitudinal and transverse directions, no wrinkles, breaks, or cracks were observed in either direction. B: In the dynamic bending test in the longitudinal and transverse directions, only slight wrinkles were observed in either direction. C: In the dynamic bending test in the longitudinal and transverse directions, no clear breaks or cracks were observed in either direction, but wrinkles were observed. D: In dynamic bending tests in the longitudinal and transverse directions, clear fractures or cracks are observed in at least one direction.

[0078] (14) Curl and flatness Curl resistance and flatness were evaluated by cutting the film to a width of 100 mm and a length of 100 mm. Five of these pieces, spaced at least 100 mm apart in the width and length directions, were placed on a surface plate with the X layer side facing up, and the maximum height (mm) of the convex portion was defined as the curl amount (mm). A curl amount of 10 mm or more or a curl so severe that it was impossible to measure, such as when the film was curled into a cylindrical shape, was evaluated as having poor curl resistance. The lower the curl amount (mm), the better, with 5 mm or less being preferred, 4 mm or less being more preferred, 3 mm or less being even more preferred, and 2 mm or less being particularly preferred. If any of the 10 pieces were deformed to the point where two or more convex portions of 3 mm or more in height were formed, the film was evaluated as having poor flatness.

[0079] (15) Loss modulus measurement The film was cut longitudinally into a rectangular sample measuring 70 mm in length and 10 mm in width. The sample was placed in a sample holder to obtain a measurement length of 20 mm and a film width of 10 mm under conditions of 25°C and 63% RH. Using a Seiko Instruments Inc. DMS7100, the loss modulus E" was measured in tensile mode at temperatures ranging from room temperature (25°C) to 180°C, with a displacement of 20 μm, a vibration frequency of 10 Hz, a heating rate of 5°C / min, and a sampling interval of 1 second. The initial loss modulus E" above 80°C and 120°C was defined as E"(80) and E"(120), respectively. This measurement was repeated three times, and the average value (unit: MPa) was used.

[0080] (16) High temperature bending test The 70°C static bending resistance was evaluated using the laminate sample described in (11) above. Using a U-shaped extension / contraction tester (Yuasa System Instruments DLDMLH-FS), a laminate sample cut to a length of 40 mm and width of 25 mm was attached to the end of the tilt clamp with the tilt clamp in a horizontal position, with the stroke direction (the bending direction) aligned with the sample's length. The sample was then left for 8 hours in the maximum bending position, with the center of the laminate bent at a face-to-face distance of 1.5 mm. After 2 hours, the sample was quickly released from the bending state, removed from the tester, and placed on a flat floor with the bent side facing downwards and no load applied, at 25°C and 63% RH. One hour after releasing the bending state, the central bent portion was observed from the film side of the laminate to evaluate the presence or absence of wrinkles, breaks, or cracks. This measurement was repeated five times, and module performance was evaluated according to the following criteria. Module performance ratings of A, B, C, and D indicate excellent static bending resistance at high temperatures and suitable for use as a flexible device, with A being the best. A: In high-temperature bending tests in the longitudinal and transverse directions, no wrinkles, breaks, or cracks were observed in either direction. B: In the high-temperature bending test in the longitudinal and transverse directions, only slight wrinkles were observed in either direction. C: In the high-temperature bending test in the longitudinal and transverse directions, no clear breaks or cracks were observed in either direction, but wrinkles were observed in one direction. D: In the high-temperature bending test in the longitudinal and transverse directions, no clear breaks or cracks were observed in either direction, but wrinkles were observed in both directions.

[0081] (Polyester manufacturing) The polyester resin used for film formation was prepared as follows.

[0082] (Polyester 1) This polyethylene terephthalate resin (intrinsic viscosity 0.65, glass transition temperature 80°C) is composed of 100 mol% terephthalic acid as a dicarboxylic acid component, 99 mol% ethylene glycol as a glycol component, and 1 mol% diethylene glycol as a glycol component. It is obtained by solid-state polymerization and contains 0.3% by mass of low molecular weight components.

[0083] (Polyester 2) Isophthalic acid copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.60, glass transition temperature 79°C) containing 3 mol% isophthalic acid as dicarboxylic acid component, 99 mol% ethylene glycol as glycol component, and 1 mol% diethylene glycol as glycol component. The content of low molecular weight component is 1.1 mass%.

[0084] (Polyester 3) Polyester 2 is an isophthalic acid copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.80, glass transition temperature 79°C) with an increased intrinsic viscosity through solid-state polymerization. Obtained through solid-state polymerization, it contains 0.3% by mass of low molecular weight components.

[0085] (Polyester 4) Polyethylene terephthalate particle master (intrinsic viscosity 0.65, glass transition temperature 80°C) containing agglomerated silica particles with a number average particle diameter of 1.3 μm at a particle concentration of 1 mass% and agglomerated silica particles with a number average particle diameter of 2.5 μm at a particle concentration of 2 mass% in polyester 1.

[0086] (Polyester 5) Cyclohexanedimethanol copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.75, glass transition temperature 80°C) in which 33 mol% of 1,4-cyclohexanedimethanol and 1 mol% of diethylene glycol component are copolymerized with respect to the glycol component.

[0087] (Polyester 6) Cyclohexanedimethanol / isosorbate copolymer polyethylene terephthalate resin (intrinsic viscosity 0.72, glass transition temperature 100°C) in which 33 mol% of 1,4-cyclohexanedimethanol, 15 mol% of isosorbate, and 1 mol% of diethylene glycol component are copolymerized with respect to the glycol component.

[0088] (Polyester 7) Polybutylene terephthalate resin (intrinsic viscosity 1.20, glass transition temperature 40°C) containing 100 mol% terephthalic acid as the dicarboxylic acid component and 100 mol% 1,4-butanediol as the glycol component.

[0089] (Polyester 8) Polyethylene glycol copolymer polyethylene naphthalate resin (intrinsic viscosity 0.62, glass transition temperature 95°C) in which 5 mol% of polyethylene glycol with a number average molecular weight of 800 g / mol and 1 mol% of diethylene glycol component are copolymerized with the glycol component.

[0090] (Polyester 9) Cyclohexanedimethanol / polyethylene glycol copolymer polyethylene terephthalate resin (intrinsic viscosity 0.75, glass transition temperature 58°C) in which 33 mol % of 1,4-cyclohexanedimethanol, 2 mol % of polyethylene glycol with a number average molecular weight of 800 g / mol, and 1 mol % of diethylene glycol component are copolymerized relative to the glycol component.

[0091] (Easy-adhesion coating liquid) Resin solution (a): A water-soluble coating liquid (a-1) of polyester resin consisting of acid components and diol components, such as terephthalic acid (88 mol%), 5-sodium sulfoisophthalic acid (12 mol%), and ethylene glycol (100 mol%), which are diol components, and an aqueous dispersion (a-2) of polyester resin consisting of acid components and diol components, such as terephthalic acid (50 mol%), isophthalic acid (49 mol%), and 5-sodium sulfoisophthalic acid (1 mol%), and diol components, such as ethylene glycol (55 mol%), neopentyl glycol (44 mol%), and polyethylene glycol (molecular weight: 4000) (1 mol%), in a solid mass ratio of (a-1) / (a-2) = 70 parts by mass / 30 parts by mass. Crosslinking agent (b): Methylol melamine Crosslinking agent (c): Epocross WS500 manufactured by Nippon Shokubai Co., Ltd. Particles (d): Aqueous dispersion of colloidal silica particles with a particle diameter of approximately 300 nm These were mixed in a solid content mass ratio of (a) / (b) / (c) / (d) = 47 parts by mass / 19 parts by mass / 20 parts by mass / 4.9 parts by mass / 0.7 parts by mass. The refractive index after drying was 1.57.

[0092] Example 1 The polyester compositions shown in the table were fed into separate vented co-rotating twin-screw extruders with an oxygen concentration of 0.2% by volume, and melt-extruded at 280°C. Next, after passing through five FSS-type leaf disc filters, the materials were alternately merged in a 51-layer feedblock (26 layers of A and 25 layers of B) while being metered with a gear pump so that the discharge ratio was A / B = 3 / 1. The materials were extruded into a sheet from a T-die and then wrapped around a casting drum at 25°C using an electrostatic casting method, with the A layer being the thickest, and cooled to solidify, producing an unstretched film.

[0093] This unstretched film was preheated and transported on a rotating roll, and stretched in the longitudinal direction by 1.05 times and then 1.08 times at a film temperature of 95°C due to the difference in rotation speed of the rotating rolls.It was then heated from the B layer side on the rotating roll just before the third stage of stretching using an infrared heater (peak wavelength: 1200 nm) and stretched to 3.26 times at a film temperature of 90°C, for a total of 3.7 times, and then immediately cooled on a metal roll whose temperature was controlled to 25°C.

[0094] Next, both sides of this uniaxially stretched film were subjected to corona discharge treatment to set the film's wetting tension to 55 mN / m, and both sides were coated with an easy-adhesion coating solution. The film was then stretched 3.8 times in the width direction at a film temperature of 90°C using a tenter-type transverse stretching machine, and immediately cooled in a cooling chamber controlled at 50°C. The film was then heat-treated in three stages at 150°C, 190°C, and 160°C for 5 seconds each, and in the third stage, it was subjected to a 2% relaxation treatment in the width direction to obtain a 50 μm-thick laminated polyester film.

[0095] The thickness of the A layer decreased from 2.4 μm to 480 nm in an arithmetic progression from the 1st layer to the 51st layer, while the thickness of the B layer increased from 170 nm to 830 nm in an arithmetic progression from the 2nd layer to the 50th layer. The tolerance in the table indicates the amount of change in the layer thickness in an arithmetic progression. In addition, the thickness of the coating layer after drying of the easy-adhesion layer was 80 nm per side, and the surface free energy of the film was 48 mN / m. The orientation parameter R on the 1st layer (X layer) side, where the A layer thickness was 2.4 μm, was high, and R X -R Y was one or more films.

[0096] The obtained laminated polyester film was laminated on a glass plate on the Y layer side and subjected to dynamic and static bending tests. The evaluation results are shown in the table. The dynamic and static bending resistance were good, making it suitable for flexible device applications. The high-temperature bending resistance was also good.

[0097] (Examples 2 to 6, Comparative Example 1) A laminated polyester film was obtained in the same manner as in Example 1, except that the lamination structure was changed as shown in the table. X -R Y The laminated polyester film shown in Comparative Example 1 was a film with an R X -R Y The film had a refractive index of less than 1.

[0098] The obtained laminated polyester film was laminated on the Y layer side to a glass plate and subjected to static and dynamic bending tests. The evaluation results are shown in the table. The laminated polyester film shown in the example had good dynamic and static bending resistance, making it suitable for flexible device applications. It also had good high-temperature bending resistance.

[0099] The laminated polyester film shown in Comparative Example 1 was poor in both dynamic flex resistance and static flex resistance, and was insufficient for flexible device applications. Furthermore, wrinkles were observed in both directions in the high-temperature flex resistance test.

[0100] Example 7 A laminated polyester film was obtained in the same manner as in Example 1, except that the film thickness was changed as shown in the table by changing the discharge rate of the vented co-rotating twin-screw extruder. X -R Y was one or more films.

[0101] The obtained laminated polyester film was laminated on a glass plate on the Y layer side and subjected to static and dynamic bending tests. The evaluation results are shown in the table. The dynamic and static bending resistance were good, making it suitable for flexible device applications. The high-temperature bending resistance was also good.

[0102] Example 8 The polyester composition was as shown in the table, and the raw materials were fed into separate vented co-rotating twin-screw extruders with an oxygen concentration of 0.2% by volume and melt-extruded at 280 ° C. Next, after passing through five FSS-type leaf disc filters, each was metered using a gear pump so that the discharge ratio was A layer / B layer = 3 / 1. Layers A and B were laminated in a two-layer merging block equipped with a rectangular lamination section, and extruded into a sheet from a T-die. After being wrapped around a casting drum at 25 ° C from the A layer side using an electrostatic casting method, the film was cooled and solidified to produce an unstretched film. A 50 μm thick laminated polyester film was obtained using the same method as in Example 1 under other conditions.

[0103] The thickness of the laminate was 36 μm for the A layer and 14 μm for the B layer. The thickness of the coating layer after drying of the easy-adhesion layer was 80 nm, and the surface free energy of the film was 48 mN / m. The orientation parameter R on the A layer side (X layer) was high, and the orientation parameter R on the B layer side (Y layer) was low, and R X -R Y The film had a rating of 1 or more. Curling was observed, but the amount of curling was 5 mm, which was not a problem.

[0104] The obtained laminated polyester film was laminated on a glass plate on the B layer side and subjected to static and dynamic bending tests. The evaluation results are shown in the table. The film exhibited good dynamic and static bending resistance, making it suitable for flexible device applications. It also exhibited good high-temperature bending resistance.

[0105] Example 9 A laminated polyester film was obtained in the same manner as in Example 8, except that the film thickness was changed as shown in the table by changing the discharge rate of the vented co-rotating twin-screw extruder. X -R Y The film had a rating of 1 or more. Curling was observed, but the amount of curling was 7 mm, which was not a problem.

[0106] The obtained laminated polyester film was laminated on a glass plate on the B layer side and subjected to static and dynamic bending tests. The evaluation results are shown in the table. The film exhibited good dynamic and static bending resistance, making it suitable for flexible device applications. It also exhibited good high-temperature bending resistance.

[0107] Examples 10 to 12 A laminated polyester film was obtained in the same manner as in Example 8, except that the film-forming conditions were changed as shown in the table. X -R Y was one or more films.

[0108] The obtained laminated polyester film was laminated on the B layer side to a glass plate and subjected to static and dynamic bending tests. The evaluation results are shown in the table. The laminated polyester film shown in the examples had good dynamic and static bending resistance, making it suitable for flexible device applications. It also had good high-temperature bending resistance.

[0109] (Examples 13 to 14) A laminated polyester film was obtained in the same manner as in Example 8, except that the polyester composition was changed as shown in the table. X -R Y The laminated polyester film obtained in Example 13 showed curling, but the curl amount was 2 mm, which was not a problematic level. The laminated polyester film obtained in Example 14 showed curling, but the curl amount was 5 mm, which was not a problematic level.

[0110] The obtained laminated polyester film was laminated on the B layer side to a glass plate and subjected to static and dynamic bending tests. The evaluation results are shown in the table. The laminated polyester film shown in the examples had good dynamic and static bending resistance, making it suitable for flexible device applications. It also had good high-temperature bending resistance. (Examples 15 to 16) The laminated polyester films obtained in Examples 1 and 3 were laminated with a glass plate on the X layer side and subjected to static and dynamic bending tests. The evaluation results are shown in the table. The laminated polyester films shown in the Examples were slightly inferior in performance to those laminated with a glass plate on the Y layer side, but had good dynamic and static bending resistance, making them suitable for flexible device applications. High-temperature bending resistance was also good. Example 17 The polyester composition was as shown in the table, and the raw materials were fed to three separate vented co-rotating twin-screw extruders, and laminated in a three-layer junction block while being metered with a gear pump so that the discharge ratio was A layer / B layer / C layer = 60 / 20 / 1. Other conditions were the same as in Example 1, and a 50 μm-thick laminated polyester film was obtained. The laminated polyester film shown in Example 17 had a high orientation parameter R on the A layer side (X layer), a low orientation parameter R on the C layer side (Y layer), and a low R X -R Y The film had a rating of 1 or more. Curling was observed, but the amount of curling was 2 mm, which was not a problem.

[0111] The obtained laminated polyester film was laminated on the C layer side to a glass plate and subjected to static and dynamic bending tests. The evaluation results are shown in the table. The laminated polyester film shown in the examples had good dynamic and static bending resistance, making it suitable for flexible device applications. It also had good high-temperature bending resistance. (Example 18, Comparative Example 2) The polyester composition and lamination ratio were as shown in the table, and a laminated polyester film was obtained in the same manner as in Example 17. The laminated polyester film shown in Example 18 had a high orientation parameter R on the A layer side (X layer) and a low orientation parameter R on the C layer side (Y layer), and X -R YThe film had a value of 1 or more. Curling was observed, but the curl amount was 2 mm, which was not a problematic level. The laminated polyester film shown in Comparative Example 2 had a small difference in orientation parameter R between the A layer side (X layer) and the C layer side (Y layer), and R X -R Y The film had a refractive index of less than 1.

[0112] The obtained laminated polyester film was laminated on the C layer side to a glass plate and evaluated in static and dynamic bending tests. The evaluation results are shown in the table. The laminated polyester film shown in the example had good dynamic and static bending resistance and was suitable for flexible device applications. In the high-temperature bending test, wrinkles were observed in both directions, but the level was not problematic for use.

[0113] The laminated polyester film shown in Comparative Example 2 was poor in both dynamic flex resistance and static flex resistance, and was insufficient for flexible device applications. Furthermore, wrinkles were observed in both directions in the high-temperature flex resistance test.

[0114] (Examples 19 to 20) A laminated polyester film was obtained in the same manner as in Example 1, except that the polyester composition was changed as shown in the table. X -R Y was one or more films.

[0115] The obtained laminated polyester film was laminated on the Y layer side to a glass plate and subjected to static bending tests and dynamic bending tests. The evaluation results are shown in the table. The laminated polyester film shown in the examples performed well in the static bending tests and dynamic bending tests, and was suitable for flexible device applications. It also had good high-temperature bending resistance.

[0116] (Examples 21 to 22) A laminated polyester film was obtained in the same manner as in Example 8, except that the polyester composition was changed as shown in the table. X -R Y The laminated polyester films obtained in Examples 21 and 22 showed curling, but the curl amount was 5 mm, which was not a problematic level.

[0117] The obtained laminated polyester film was laminated on the Y layer side to a glass plate and subjected to static bending tests and dynamic bending tests. The evaluation results are shown in the table. The laminated polyester film shown in the examples performed well in the static bending tests and dynamic bending tests, and was suitable for flexible device applications. It also had good high-temperature bending resistance.

[0118] [Table 1]

[0119] [Table 2]

[0120] [Table 3]

[0121] [Table 4]

[0122] [Table 5]

Claims

1. Orientation parameter R Ｘ and R Ｙ In this case, R Ｘ >R Ｙ A laminated polyester film comprising two or more layers including at least an X layer and a Y layer, which satisfy the following formula: R Ｘ -R Ｙ ≧1.0 (1) Here, the orientation parameter R Ｘ , R Ｙ When laser Raman spectroscopy was performed on the film cross section in the width direction and thickness direction, the 1615 cm －１ ±10cm －１ Maximum intensity A in the range Ｐ and 1615 cm measured with polarized light parallel to the film thickness direction －１ ±10cm －１ Maximum intensity A in the range Ｔ Ratio A Ｐ / A Ｔ is the orientation parameter R, and the orientation parameters obtained at a position 0.5 μm from the surface of each of the X layer and the Y layer in the thickness direction are R Ｘ , R Ｙ Let's say.

2. The orientation parameter at the center position in the film thickness direction is R Ｚ When this is done, R Ｘ >R Ｚ >R Ｙ 2. The laminated polyester film according to claim 1, wherein

3. 2. The laminated polyester film according to claim 1, wherein the stretch-shrink parameter S in at least one direction in the film plane, calculated by the following formula, is 1.00 or more: Elongation / contraction parameter S = -Ln(W ６０ / W ０ ) / Ln(L ６０ / L ０ ) (2) Here, the initial length L ０ , the length at 60% elongation is L ６０ , the initial value in the width direction is W ０ , width length W at elongation 60% ６０ Let's say.

4. 2. The laminated polyester film according to claim 1, which comprises five or more layers.

5. 2. The laminated polyester film according to claim 1, wherein the X layer contains 20 mol % or more of a component derived from an aromatic dicarboxylic acid having 9 or more carbon atoms, in terms of dicarboxylic acid units.

6. 2. The laminated polyester film according to claim 1, wherein the Y layer contains 5 mol % or more of a component derived from a diol having 6 or more carbon atoms in diol units.

7. 2. The laminated polyester film according to claim 1, wherein the content of components having a molecular weight of 200 to 1,000 g / mol is 5% by mass or less.

8. 2. The laminated polyester film according to claim 1, wherein in a temperature dispersion curve of the loss modulus in at least one direction, the ratio E"(80) / E"(120) of the loss modulus at 80°C to the loss modulus at 120°C is 0.40 or more.

9. A laminate comprising the laminated polyester film according to any one of claims 1 to 8 and a substrate having a Young's modulus of 6 GPa or more.

10. Orientation parameter R Ｘ and R Ｙ In this case, R Ｘ >R Ｙ A laminated polyester film consisting of two or more layers including at least an X layer and a Y layer, Ｘ , R Ｙ , R Ｚ When a linear regression line was fitted using the values ​​of the three points and the measured thickness, the slope of the orientation parameter relative to the thickness direction position was 0.02 μm, with the surface of the Y layer as the reference. －１ The laminated polyester film is as described above. Here, the orientation parameter R Ｘ , R Ｙ , R Ｚ When laser Raman spectroscopy was performed on the film cross section in the width direction and thickness direction, the 1615 cm －１ ±10cm －１ Maximum intensity A in the range Ｐ and 1615 cm measured with polarized light parallel to the film thickness direction －１ ±10cm －１ Maximum intensity A in the range Ｔ Ratio A Ｐ / A Ｔ is the orientation parameter R, and the orientation parameters obtained at a position 0.5 μm from the surface of each of the X layer and the Y layer in the thickness direction are R Ｘ , R Ｙ The orientation parameter at the center position in the film thickness direction is R Ｚ Let's say.

11. The laminated polyester film for flexible devices according to any one of claims 1 to 8 and 10, which is used for protecting flexible devices.

12. The laminated polyester film for flexible devices according to claim 11, which is used to protect an image display device.

13. An image display device comprising the laminated polyester film according to claim 1 or 10.

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