Polyester film for forming polarizer

Abstract

To provide a film for forming a polarizer which has an excellent appearance after thermal molding processing is performed and presents a high polarization characteristic of a polarizer.SOLUTION: A polyester film is made of at least two layers. When a stress at the time of 10%-expansion at the temperature of 120°C in the direction of a main orientation axial direction is Fx10 and a stress at the time of 10%-expansion at the temperature of 120°C in the direction vertical to the inside of a film in a main orientation axis is Fy10, Fx10 / Fy10, which is the value obtained by dividing Fx10 by Fy10, is at least 1.3 and is 3.0 at a maximum.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polyester film for polarizer molding, and can be suitably used for applications where thermoforming is performed on a polarizer.

Background Art

[0002] Molded bodies obtained by thermoforming polarizers are used in many applications such as sunglasses, helmet shields, protective surfaces, camera filters, 3D cinemas, virtual reality, and augmented reality headsets. In recent years, in virtual reality and augmented reality headsets, there has been a study on thermoforming a polarizer and integrating it with a pancake lens for use.

[0003] In Patent Document 1, by using a protective film having a maximum tensile strength of 0.95 N or less at 130 °C, a method for manufacturing a polarizer molded body capable of thermally bending a polarizer laminated with a protective film into a desired shape regardless of the type of thermoplastic resin used for the polarizer is described.

[0004] Patent Document 2 describes a polyester film capable of suppressing film warpage and peeling after attachment when attached to a curved glass.

[0005] Patent Document 3 describes an optical film that is thermoformed to create a curved surface while maintaining a fixed magnitude and orientation of local in-plane birefringence.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] Regarding a thermoformed polarizing plate, it is required that the polarization characteristics of the planar polarizing plate be maintained after thermoforming. However, since heat and mechanical stress are involved in this process, the appearance and polarization performance may be impaired, and improvement is desired. Although the manufacturing method described in Patent Document 1 can achieve followability to a mold in thermoforming, it is not sufficient for applications that require high polarization characteristics, and improvement is necessary. The polyester film described in Patent Document 2 assumes the molding of an isotropic curable resin layer, and there is a concern that the polarization characteristics may deteriorate when molding a highly anisotropic laminate such as a polarizing plate. The optical film of Patent Document 3 is a technique for making the retardation of a polymer film laminated on a polarizer uniform, and the molding of a highly anisotropic laminate such as a polarizing plate is not considered, and improvement is necessary.

[0008] The problem of the present invention is to solve the above-described problems of the prior art. That is, to provide a film for polarizing plate molding that has a good appearance after thermoforming and high polarization characteristics of the polarizing plate.

Means for Solving the Problems

[0009] The gist of the present invention for solving such problems is as follows. (1) A polyester film composed of at least two or more layers, where when the stress Fx10 at 10% elongation at 120°C in the main orientation axis direction and the stress Fy10 at 10% elongation at 120°C in the direction perpendicular to the film plane in the main orientation axis are considered, the Fx10 / Fy10 obtained by dividing Fx10 by Fy10 is 1.3 or more and 3.0 or less, a polyester film for polarizing plate molding. (2) The polyester film for polarizing plate molding according to (1), wherein the Fx10 is 50 MPa or less. (3) The polyester film for polarizing plate molding according to (1) or (2), wherein the retardation at a wavelength of 589 nm is 1500 nm or more and 5000 nm or less. (4) The polyester film for polarizer molding according to any one of (1) to (3), wherein the surface free energy of at least one surface is 35 mN / m or more and 60 mN / m or less. (5) The polyester film for polarizer molding according to any one of (1) to (4), wherein the content of fluorine element in the polyester film is less than 100 ppm by mass. (6) The polyester film for polarizer molding according to any one of (1) to (5), wherein at least one layer of the polyester film satisfies at least one of the following (a) to (d). (a) Containing a linear aliphatic diol having 3 or more carbon atoms as the glycol component of the polyester (b) Containing a polyalkylene glycol as the glycol component of the polyester (c) Containing a hydrogenated dimer acid having a long-chain alkyl group having 8 or more carbon atoms as the dicarboxylic acid component of the polyester (d) Containing a linear aliphatic dicarboxylic acid having 3 or more carbon atoms as the dicarboxylic acid component of the polyester (7) The polyester film for polarizer molding according to any one of (1) to (6), wherein the average of the bending rigidity in the main orientation axis direction and the bending rigidity in the direction perpendicular to the film plane in the main orientation axis is 160 mN or less. (8) The polyester film for polarizer molding according to any one of (1) to (7), wherein at least one surface is used by being bonded to a polarizer via an adhesive layer. (9) A polyester film for polarizer molding used by being laminated with a polarizer, wherein the angle formed in the lamination plane between the absorption axis of the polarizer and the main orientation axis of the polyester film for polarizer molding is laminated and used at -20° or more and 20° or less or 70° or more and 110° or less. (10) The polyester film for polarizer molding according to any one of (1) to (9), which is used for thermoforming processing of a polarizer for molding a polarizer on a curved surface.

Advantages of the Invention

[0010] The film of the present invention has a ratio of the stress in the direction of the main orientation axis at 10% elongation at 120°C to the stress in the perpendicular direction thereof of 1.3 times or more, so that it has a good appearance after thermoforming and can be suitably used as a film for polarizer forming with high polarizing characteristics of a polarizer.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] The polyester used in the polyester film for polarizer forming of the present invention is a general term for polymers having ester bonds as the main bonds in the main chain. Usually, polyester can be obtained by subjecting a dicarboxylic acid component and a glycol component to a polycondensation reaction.

[0013] The dicarboxylic acid component for obtaining polyester is not particularly limited as long as the effects of the present invention are not impaired. For example, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodiumsulfonedicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and oxycarboxylic acids such as paraoxybenzoic acid can be used. Further, the dicarboxylic acid component may be a dicarboxylic acid ester derivative component, and an esterified product of the above dicarboxylic acid compound can also be used. Among them, in terms of achieving both thermoformability and heat resistance and handleability, it is preferable to use at least one of terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid. It is preferable that the polyester film contains 80 mol% or more of terephthalic acid with respect to the acid component contained therein, more preferably 90 mol% or more, and particularly preferably 95 mol% or more and 100 mol% or less.

[0014] Further, the glycol component for obtaining the polyester is not particularly limited as long as the effects of the present invention are not impaired. For example, 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, 2,2-dimethyl-1,3-propanediol; polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; alicyclic dihydroxy compounds such as 1,4-cyclohexanedimethanol, isosorbide, 9,9'-bis(4-carboxyphenyl)fluorene, spiroglycol; aromatic dihydroxy compounds such as bisphenol A and bisphenol S can be used. Among them, from the viewpoints of achieving both thermoformability and heat resistance and handleability, it is preferable to use at least one of ethylene glycol, diethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, isosorbide, polyethylene glycol, and polytetramethylene glycol. It is preferable that the glycol component contained in the polyester film contains 50 mol% or more of ethylene glycol, more preferably 60 mol% or more, still more preferably 70 mol% or more, and particularly preferably 80 mol% or more and 98 mol% or less.

[0015] These dicarboxylic acid components and glycol components may be used in combination of two or more as long as the effects of the present invention are not impaired.

[0016] In addition, the polyester may contain a catalyst, a stabilizer, inorganic particles, organic particles, an antioxidant, an antistatic agent, and other polymer resins as long as the effects of the present invention are not impaired.

[0017] The intrinsic viscosity of the polyester film is preferably 0.5 or more and 1.5 or less. As the lower limit, it is more preferably 0.55 or more, still more preferably 0.58 or more, and as the upper limit, it is more preferably 1.0 or less, still more preferably 0.8 or less. By being within the above range, it is possible to suppress defects such as cracks and chips in the film during film conveyance and improve thermoformability.

[0018] The polyester film for polarizing plate molding of the present invention needs to be a laminated film in which at least two or more polyester compositions are laminated. By laminating two or more layers, a film that achieves both supportability and thermoformability of the polarizing plate can be obtained. In the case of a three-layer laminated film, for one surface layer (1), the opposite surface layer (2), and the inner layer sandwiched between the two surface layers, the polyester compositions of the surface layer (1) and the surface layer (2) may be the same or different. Also, it may be four layers or more, or a multilayer laminated film of 51 layers or more, but from the viewpoint of mass productivity, it is preferably 1001 layers or less.

[0019] In the case of a three-layer laminated film, the thickness of each layer can be any thickness as long as the effects of the present invention are not impaired. The surface layer (1) / surface layer (2) obtained by dividing the thickness of the surface layer (1) by the thickness of the surface layer (2) is preferably 0.5 or more and 2 or less, more preferably 0.8 or more and 1.5 or less, and particularly preferably 0.9 or more and 1.1 or less in order to suppress curling of the polyester film and obtain good flatness. The lamination ratio of the inner layer to the total thickness of the surface layer (1) and the surface layer (2), which is the inner layer / (surface layer (1)+surface layer (2)), is preferably 0.5 or more and 10 or less, more preferably 1 or more, still more preferably 2 or more, and particularly preferably 3 or more as the lower limit, and more preferably 8 or less, still more preferably 7 or less, and particularly preferably 6 or less as the upper limit in order to obtain good thermoformability and film conveyance property. When the lamination ratio of the above surface layer and inner layer is less than 0.5, it indicates that the thickness of the inner layer is thinner than at least one of the surface layers.

[0020] The thickness of the polyester film for polarizing plate forming of the present invention is preferably 35 μm or more and 200 μm or less from the viewpoint of achieving both good thermoformability and flatness. More preferably, the lower limit is 50 μm or more, still more preferably 65 μm or more, and more preferably the upper limit is 150 μm or less, still more preferably 100 μm or less.

[0021] In order to improve the heat resistance of the polyester film for polarizing plate forming of the present invention, the maximum temperature (Tms) of the melting peak observed by at least one differential scanning calorimeter (DSC) is preferably 240°C or more and 265°C or less. Among them, from the viewpoints of thermoformability and mass productivity, it is preferable that the maximum temperature (Tms) of the melting peak of the surface layer (1) and / or the surface layer (2) is 240°C or more and 265°C or less. More preferably, Tms is 245°C or more and 260°C or less, and most preferably 248°C or more and 260°C or less.

[0022] For the polyester film for polarizing plate forming of the present invention, from the viewpoints of thermoformability and mass productivity, it is preferable that the maximum temperature (Tmt) of the melting peak observed by at least one differential scanning calorimeter (DSC) is 180°C or more and 240°C or less. Among them, it is preferable that at least one layer of polyester in the layer inside the surface layer (1) and the surface layer (2) is a laminated polyester film within the above range, because it can improve thermoformability and heat resistance.

[0023] The polyester film for polarizer molding of the present invention requires that the ratio Fx10 / Fy10 of the stress Fx10 in the main orientation axis direction at 10% elongation at 120 °C to the stress Fy10 in its perpendicular direction is 1.3 times or more and 3.0 times or less. The main orientation axis and the stress at 10% elongation shall be determined by the method described in the examples. The stress of the polarizer with respect to the elongation in the absorption axis direction tends to be higher than the stress in its perpendicular direction. When molding a laminate of a polarizer and a polyester film for polarizer molding into a desired shape, when the Fx10 / Fy10 of the polyester film for polarizer molding is within the above range, the molding elongation behavior of the polarizer and the polyester film for polarizer molding can follow, the followability to the desired shape becomes good, and the generation of wrinkles and cracks due to stress concentration at the interface with the polyester film for polarizer molding can be suppressed in some cases. Or, since the polyester film for polarizer molding can control the large deformation of the perpendicular direction with respect to the deformation in the absorption axis direction due to the molding elongation behavior of the polarizer, the reduction of the polarization characteristics of the polarizer after molding can be suppressed in some cases. The lower limit of Fx10 / Fy10 is preferably 1.5 times or more, more preferably 1.7 times or more, and even more preferably 2.0 times or more. The upper limit of Fx10 / Fy10 needs to be 3.0 times or less, preferably 2.8 times or less, more preferably 2.6 times or less, and even more preferably 2.5 times or less in order to suppress the deterioration of the mechanical properties of the polyester film. The method for controlling Fx10 / Fy10 to the above range is not particularly limited, but an unstretched film obtained by laminating two or more polyester compositions of at least two or more is stretched, for example, in the longitudinal direction and the width direction by a sequential biaxial stretching method, and the stretching ratio, stretching speed, stretching temperature, and further heat treatment temperature in each of the longitudinal direction and the width direction can be adjusted. In particular, it is preferable to use a polyester copolymerized with a glycol component in at least one layer, increase the stretching ratio and / or stretching speed in the main orientation axis direction, and adjust the stretching ratio and / or stretching speed in the direction perpendicular thereto to be low. Note that the higher the stretching ratio, the higher the orientation tends to be, so the stress at 10% elongation tends to be high. The faster the stretching speed, the shorter the time for orientation relaxation can be, so the orientation increases, and the stress at 10% elongation tends to be high.

[0024] The stress Fx10 at 10% elongation in the main orientation axis direction at 120°C is not particularly limited as long as it is within the range of the above ratio Fx10 / Fy10. However, from the perspective of followability to the molded body, the upper limit is preferably 50 MPa or less, more preferably 40 MPa or less, and even more preferably 30 MPa or less. As a method for controlling Fx10 low, various methods can be used. For example, there is a method of using a copolymerized polyester with a low glass transition temperature. In at least one layer of the polyester film, it is a preferable method to satisfy at least one of the following (a) to (d). (a) Containing a linear aliphatic diol having 3 or more carbon atoms as the glycol component of the polyester (b) Containing a polyalkylene glycol as the glycol component of the polyester (c) Containing a hydrogenated dimer acid having a long-chain alkyl group with 8 or more carbon atoms as the dicarboxylic acid component of the polyester (d) Containing a linear aliphatic dicarboxylic acid having 3 or more carbon atoms as the dicarboxylic acid component of the polyester.

[0025] Among them, as the glycol component, 1,3-propanediol or 1,4-butanediol, which is a linear aliphatic diol having 3 or more carbon atoms, and polyethylene glycol or polytetramethylene glycol, which is a polyalkylene glycol having a molecular weight of 200 or more and 2000 or less, are preferably used. As the dicarboxylic acid component, hydrogenated dimer acid having a long-chain alkyl group with 8 or more carbon atoms and adipic acid or sebacic acid, which is a linear aliphatic dicarboxylic acid having 3 or more carbon atoms, are preferably used. By controlling Fx10 low, it may be possible to mold at a lower temperature. From the perspective of maintaining the planarity of the polarizing plate during heating, Fx10 is preferably 5 MPa or more, more preferably 10 MPa or more, and even more preferably 15 MPa or more as the lower limit.

[0026] The polyester film for polarizer forming of the present invention preferably has an average flexural rigidity at 23 °C of 50 mN or more, more preferably 100 mN or more, in the main orientation axis direction and the direction perpendicular to the main orientation axis in the film plane from the viewpoint of supporting the polarizer. Further, by setting the average of the flexural rigidity to 1000 mN or less, the roll conveyance property becomes good, preferably 500 mN or less, more preferably 300 mN or less. Among them, when it is 160 mN or less, the moldability followability at low temperature becomes good. The method of controlling the flexural rigidity is not particularly limited, but it is most effective to control the film thickness. Increasing the thickness increases the flexural rigidity, and decreasing the thickness can control the flexural rigidity to be small. In addition, in order to control the flexural rigidity to be low, the method mainly taken is to decrease the Young's modulus. The Young's modulus in both the longitudinal direction and the width direction is preferably 1.5 GPa or more and 4.5 GPa or less, and more preferably 2.0 GPa or more and 4.0 GPa or less. As a method of controlling the Young's modulus, it also increases by using a resin with a high Young's modulus such as a polyester resin. Further, among polyester resins, when the crystallinity is increased by including a copolymer component, the Young's modulus can be decreased. In addition, the Young's modulus is related to the orientation and crystal state of the film, and can also be controlled by the draw ratio, draw temperature, heat treatment temperature, heat shrinkage treatment, etc. Since the Young's modulus tends to decrease when the orientation state of the film is relaxed, in order to make the Young's modulus 4.0 GPa or less, heat treatment may be performed at a temperature of the melting point of the lowest melting point layer of the resin constituting the film to the melting point - 20 °C or more and the melting point or less. For example, when the copolymer polyester with a melting point of 235 °C is the lowest melting point layer, the heat treatment temperature is preferably 215 °C or more and 235 °C or less. Further, a plasticizer such as polyethylene glycol or an elastomer may be added to decrease the Young's modulus as long as the effects of the present invention are not inhibited.

[0027] The polyester film for polarizer forming of the present invention, in addition to the flexural rigidity at 23 °C, has a waist strength of 0.30 N·m at 120 °C for a 10 mm width 2The following are preferred. The firmness at 120°C is calculated by the following formula using the Young's modulus E(120) (unit: MPa) measured by a tensile testing machine at 120°C and the film thickness T (unit: μm). ·Firmness at 120°C = E(120) × T 3 / 1.2 The firmness of the 10 mm width at 120°C is more preferably 0.20 N·m 2 The following is the case. The firmness of the 10 mm width at 120°C is 0.10 N·m 2 In the following case, the moldability at low temperature becomes better. As can be seen from the formula for the firmness at 120°C, since it is proportional to the cube of the film thickness T, reducing the film thickness decreases the firmness at 120°C, but also decreases the flexural rigidity at 23°C and may deteriorate the planarity.

[0028] The polyester film for polarizing plate molding of the present invention preferably has a retardation of 1500 nm or more and 6000 nm or less from the viewpoint of thermoformability. In this document, the retardation means the in-plane retardation unless otherwise indicated, and is measured at a wavelength of 589 nm. The retardation can be determined using a commercially available automatic birefringence measuring device such as KOBRA-WPR (Oji Scientific Instruments Co., Ltd.).

[0029] The polyester film for polarizing plate molding of the present invention is preferably a biaxially oriented film. A biaxially oriented polyester film means a film that shows a biaxially oriented pattern by wide-angle X-ray diffraction. A biaxially oriented polyester film has sufficient thermal stability, particularly dimensional stability and mechanical strength, and also has good planarity. The biaxially oriented film can be produced by a known stretching method such as a sequential biaxial stretching method in which an unstretched film is stretched in the longitudinal direction and then in the width direction, or in the width direction and then in the longitudinal direction, or a simultaneous biaxial stretching method in which the longitudinal and width directions of the film are stretched almost simultaneously. In order to effectively obtain thermoformability, a stretching method in which the film is stretched in the longitudinal direction and then in the width direction is preferred.

[0030] In the polyester film for polarizer molding of the present invention, as a preferable manufacturing process, the following steps (1) to (3) are given as an example, but the present invention is not limited thereto. · Step (1): A step of stretching 1.5 times or more and 3.3 times or less in the longitudinal direction · Step (2): A step of stretching 3.5 times or more and 5.0 times or less in the width direction · Step (3): A step of heat-treating at 200°C or more and 240°C or less Regarding Step (1): the step of stretching 1.5 times or more and 3.3 times or less in the longitudinal direction, in order to obtain a more remarkable effect of the present invention, it is preferably adopted that the stretching ratio is 1.5 times or more and 2.5 times or less, or 2.9 times or more and 3.3 times or less. If it exceeds 2.5 times and is less than 2.9 times, the flatness may not be sufficient. Further, the stretching speed is preferably 10,000% / min or more and 100,000% / min or less. When the stretching ratio in the longitudinal direction is 1.5 times or more and 2.5 times or less, it is more preferably 10,000% / min or more and 15,000% / min or less. When the stretching ratio is 2.9 times or more and 3.3 times or less, it is more preferably 20,000% / min or more and 30,000% / min or less. Further, the stretching temperature in the longitudinal direction is preferably 80°C or more and 120°C or less, and more preferably 85°C or more and 110°C or less.

[0031] Regarding Step (2): the step of stretching 3.5 times or more and 5.0 times or less in the width direction, in order to obtain a more remarkable effect of the present invention, as the stretching ratio in the width direction, it is preferably adopted that the stretching ratio is 3.7 times or more and 4.5 times or less. The stretching speed in the width direction is preferably 400% / min or more and 2,000% / min or less, and more preferably 1,000% / min or more and 2,000% / min or less. Further, the stretching temperature in the width direction is preferably 90°C or more and 140°C or less.

[0032] Regarding Step (3): the step of heat-treating at 200°C or more and 245°C or less, in order to obtain a more remarkable effect of the present invention, it is preferably heat-treated in at least three or more temperature ranges in sequence. Further, the heat treatment temperatures in the first stage, the second stage, and the third stage preferably satisfy the following conditions. · First stage: 150°C or more and 200°C or less · Second stage: 200°C or more and 240°C or less · Third stage: 150°C or higher and 200°C or lower Note that the number of temperature stages in step (3) may include three or more stages. For example, a temperature range between the temperature range of the first stage and the second stage can be provided between the first stage and the second stage. For example, a temperature range lower than the third stage can also be provided after the third stage. Also, in step (3), it is also preferable to perform stretching and / or relaxation simultaneously. For example, when step (3) is the above three stages, stretching can be performed 1.1 times or more and 2.0 times or less in the width direction at the second stage, and relaxation of 1% or more and 10% or less can be performed in the longitudinal direction and / or the width direction at the third stage. The heat treatment time can be arbitrary within a range that does not deteriorate the characteristics, preferably 1 second or more and 60 seconds or less, more preferably 5 seconds or more and 40 seconds or less, and most preferably 15 seconds or more and 30 seconds or less.

[0033] In the polyester film for polarizing plate molding of the present invention, the following steps (1') to (3') are exemplified as other examples. · Step (1'): A step of stretching 3.4 times or more and 4.5 times or less in the longitudinal direction · Step (2'): A step of stretching 1.5 times or more and 3.0 times or less in the width direction · Step (3'): A step of heat treatment at 200°C or higher and 240°C or lower Regarding step (1'): A step of stretching 3.4 times or more and 4.5 times or less in the longitudinal direction, the stretching speed is preferably 10,000% / min or more and 100,000% / min or less, and more preferably 30,000% / min or more and 50,000% / min or less. Also, the stretching temperature in the longitudinal direction is preferably 80°C or higher and 120°C or lower, and more preferably 80°C or higher and 100°C or lower.

[0034] Regarding step (2'): A step of stretching 1.5 times or more and 3.0 times or less in the width direction, the stretching speed is preferably 200% / min or more and 1,000% / min or less, and more preferably 300% / min or more and 800% / min or less. Also, the stretching temperature in the width direction is preferably 80°C or higher and 140°C or lower.

[0035] Regarding the step (3') of heat treatment at a temperature of 200°C or higher and 240°C or lower, in order to obtain a more remarkable effect of the present invention, it is preferable to perform heat treatment in at least three or more temperature ranges in sequence. Furthermore, the heat treatment temperatures in the first stage, second stage, and third stage preferably satisfy the following conditions. · First stage: 150°C or higher and 200°C or lower · Second stage: 200°C or higher and 240°C or lower · Third stage: 150°C or higher and 200°C or lower In order to thermoform by closely adhering the polyester film for polarizer forming of the present invention and the polarizer, an adhesive layer may be provided between the polyester film for polarizer forming and the polarizer. In order to impart adhesion between the polyester film for polarizer forming and the adhesive layer, an easy - adhesion layer can be provided on the polyester film for polarizer forming.

[0036] In the polyester film for polarizer forming 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 polyester film and the adhesion force with the adhesive layer. The surface free energy of the polyester film is preferably 35 mN / m or more and 60 mN / m or less. More preferably, the lower limit is 38 mN / m or more, and even more preferably 40 mN / m or more, and the upper limit is more preferably 50 mN / m. Also, the hydrogen - bonding component in the surface free energy is preferably 4.0 mN / m or more and 10.0 mN / m or less. 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 resin, polyester resin, and urethane resin from the viewpoints of adhesiveness and handleability.

[0037] As a method of providing an easy - adhesion layer in - line in the polyester film manufacturing process for the polarizing plate forming polyester film of the present invention, it is preferable to uniformly apply a coating layer composition dispersed in water onto a polyester film that has been at least uniaxially stretched using a metering wire bar, a gravure roll, etc., and dry the coating agent while applying stretching. Further, various additives such as antioxidants, heat stabilizers, ultraviolet absorbers, infrared absorbers, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc. may be added to the easy - adhesion layer. Incidentally, the fluorine atom content is preferably less than 100 ppm (mass basis). The fluorine atom content can be measured by the automatic sample combustion - ion chromatography method (BS EN 14582:2007). By not using compounds such as fluorine - containing release agents, the adverse effect due to the transfer of fluorine compounds to the polarizing plate is small and the environmental load at the time of disposal is low.

[0038] The polyester film for polarizing plate forming of the present invention has a good appearance after thermoforming and high polarization characteristics of the polarizing plate, so it can be suitably used as a film for polarizing plate forming.

[0039] In the laminate obtained by laminating a polarizing plate and a polyester film, the polyester film for polarizing plate forming of the present invention is preferably laminated and used such that the angle between the main alignment axis direction of the polarizing plate and the main alignment axis direction of the polyester film for polarizing plate forming is - 20° or more and 20° or less or 70° or more and 110° or less within the laminate plane. Being within the said angle range is preferable in that thermoforming can be performed while maintaining the polarization characteristics of the polarizing plate and the flatness of the polarizing plate at a high level. It is more preferably - 10° or more and 10° or less or 80° or more and 100° or less in terms of suppressing the occurrence of scratches, chips, and cracks after forming of the polarizing plate.

[0040] As the thermoforming method, a known forming method can be used. The thermoforming temperature is preferably 80°C or higher, which is a typical glass transition temperature of the polyvinyl alcohol - based resin constituting the polarizing plate, and a temperature range of 100°C or higher and 180°C or lower, which enables sufficient thermoforming, can be adopted.

[0041] An adhesive layer can be provided on the polyester film for polarizing plate molding of the present invention. The adhesive layer improves the adhesion between layers or the adhesion to other members (for example, a polarizing plate). Further, when peeling the polyester film for polarizing plate molding after thermoforming, it is preferably peelable without adhesive residue. The position of the adhesive layer is not limited. Examples of the components of the adhesive layer include an adhesive and an adhesive agent. Examples of the adhesive include an acrylic adhesive, a rubber-based adhesive, and a silicone-based adhesive. The acrylic adhesive is an adhesive containing a polymer of a (meth)acrylic monomer. When the adhesive layer contains an adhesive, the adhesive layer may contain an adhesion promoter. From the viewpoints of adhesion strength and peelability after molding, the adhesive is preferably an acrylic adhesive. Examples of the adhesive agent include a urethane resin-based adhesive, a polyester-based adhesive, an acrylic resin-based adhesive, an ethylene vinyl acetate resin-based adhesive, a polyvinyl alcohol-based adhesive, a polyamide-based adhesive, and a silicone-based adhesive. 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.

[0042] The method for forming the adhesive layer is not limited. For example, it is formed using a protective film containing an adhesive layer. For example, it may also be formed using a composition for forming an adhesive layer containing components for forming the adhesive layer. The adhesive layer can be formed by applying the composition for forming the adhesive layer on the polyester film and drying the composition for forming the adhesive layer as necessary. In addition, various additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, an infrared absorber, a pigment, a dye, organic or inorganic particles, an antistatic agent, a nucleating agent, etc. may be added to the adhesive layer. It is preferably free of fluorine compounds.

[0043] As the polarizing plate, a known polarizing plate can be used. For example, it includes a polarizer and a polarizer protective film, and may further include a retardation layer, for example. The retardation layer can also assume a part of the polarizer protective film. Further, in order to attach it to an object such as a polyester film for polarizing plate molding or a lens, an adhesive layer can also be provided on at least one surface of the polarizing plate.

[0044] As a role of the polyester film for polarizer forming, in addition to serving as a base material when laminating a polarizer, an adhesive layer, and a functional layer by coating or laminating, it can also be a film for protecting the polarizer after attaching the polarizer to a lens as an object.

[0045] Also, when the polyester film for polarizer forming of the present invention is attached to an object and then peeled off to expose the protective layer side of the polarizer, it is preferable that the polyester film for polarizer forming and the protective layer have appropriate peelability. As a means for imparting peelability, a method of coating a release layer made of a resin having low affinity with the protective layer on one side (protective layer side) surface of the polyester film can be mentioned.

[0046] The resin used for the protective layer may be any of a thermosetting resin and a photocurable resin. To the resin constituting the protective layer, a curing agent, a curing accelerator, an adhesive, a surface conditioner, an ultraviolet absorber, a light stabilizer, etc. may be mixed as necessary. The thickness of the protective layer is preferably 5 to 50 μm, and more preferably 10 to 40 μm. When the thickness is 5 μm or more, it becomes possible to exhibit the characteristics of the protective layer, which is preferable. Also, when the thickness is 50 μm or less, the flatness of the surface becomes better, which is preferable.

[0047] As a method for manufacturing an optical lens using the polyester film for polarizing plate molding obtained in the present invention, there is no particular limitation. There are various methods for thermoforming, and examples include a method of bonding the polyester film, the polarizing plate, and the object lens. The polyester film and the polarizing plate are deformed along the shape of the object to obtain an optical lens. The molding method may be a known molding method. Examples of the molding method include film insert molding, pressure-air molding, and vacuum molding. Further, as the molding method, for example, a method called "TOM molding" is also included. Among them, from the viewpoint of the moldability of the polyester film for polarizing plate molding of the present invention and the ease of molding into a three-dimensional structure, under reduced pressure conditions, heating to a temperature above the softening point and bringing the adhesive layer side of the polarizing plate for molding into contact with the surface of the object by pressure is preferable. After molding, the polyester film for polarizing plate molding covers the surface of the object, and the polyester film for polarizing plate molding can serve as a protective film that protects the object from dust and scratches. When actually using the object as a component, the polyester film for polarizing plate molding is peeled off from the object, and the protective layer is exposed on the outermost surface, whereby an object having weather resistance and chemical resistance can be obtained. As a method for manufacturing an optical lens, a method of peeling the polyester film for polarizing plate molding after attaching the polyester film for polarizing plate molding of the present invention to the object is preferable.

[0048] Specific examples of the layer configuration of the laminate obtained by bonding the polarizing plate and the polyester film are shown below. However, the laminate layer configuration is not limited to the specific examples shown below. · Layer configuration 1: Polyester film for polarizing plate molding / Polarizing plate · Layer configuration 2: Polyester film for polarizing plate molding / Polarizing plate / Adhesive layer · Layer configuration 3: Polyester film for polarizing plate molding / Adhesive layer / Polarizing plate / Adhesive layer · Layer configuration 4: Polyester film for polarizing plate molding / Protective layer / Polarizing plate / Adhesive layer · Layer configuration 5: Polyester film for polarizing plate molding / Protective layer / Adhesive layer / Polarizing plate / Adhesive layer ·Layer structure 6: Polyester film for polarizer forming / Functional layer / Polarizer / Adhesive layer ·Layer structure 7: Polyester film for polarizer forming / Functional layer / Adhesive layer / Polarizer / Adhesive layer The polyester film for polarizer forming of the present invention has high polarization characteristics of the polarizer after thermoforming and can be suitably used as a film for polarizer forming. In particular, since high polarization quality can be obtained, it can be particularly suitably used for forming polarizers for displays and can be particularly suitably used for forming polarizers for virtual reality and / or augmented reality head-mounted displays.

Examples

[0049] (1) Composition of polyester The polyester resin and film were dissolved in hexafluoroisopropanol (HFIP), 1 1H-NMR and 13 13C-NMR were used to quantify the content of each monomer residue component and by-produced diethylene glycol. In the case of a laminated film, depending on the laminated thickness, the components constituting each layer alone can be collected and evaluated by scraping off each layer of the film. For the film of the present invention, the composition was calculated from the mixing ratio during film production.

[0050] (2) Intrinsic viscosity of polyester The intrinsic viscosity of the polyester resin and film was measured at 25 °C using an Ostwald viscometer after dissolving the polyester in orthochlorophenol. In the case of a laminated film, the intrinsic viscosity of each layer alone was evaluated by scraping off each layer of the film according to the laminated thickness.

[0051] (3) Film thickness, layer thickness The film was embedded in an epoxy resin, and a film cross-section was cut out with a microtome. The cross-section was observed at a magnification of 5000 times with a transmission electron microscope (TEM H7100 manufactured by Hitachi, Ltd.) to determine the film thickness and the thickness of the polyester layer.

[0052] (4) Melting point, glass transition temperature Using a differential scanning calorimeter robot DSC-RDC6220 manufactured by Seiko Instruments Inc., and using the thermal analysis rheology system software "Muse" manufactured by SII NanoTechnology Inc. for data analysis, measurements and analyses were performed in accordance with JIS K7121 (1987). Specifically, when heating 5 mg of the sample from 25 °C to 300 °C at a rate of 20 °C / min, the glass transition temperature (Tg) was determined from the point where a straight line equidistant from the vertical axis direction from the extended straight line of each baseline intersects the curve of the stepped change portion of the glass transition in the differential scanning calorimetry chart obtained from the DSC curve. The temperature at the peak of the endothermic peak obtained from the DSC curve when heating from 25 °C to 300 °C at a rate of 20 °C / min was defined as the melting point (Tm). When there are multiple endothermic peaks, the peak temperature of the endothermic peak on the highest temperature side was defined as the melting point (Tm). In the case of a laminated film, according to the laminated thickness, by scraping off each layer of the film, the melting point of each single layer can be measured. The melting point of the scraped surface sample was defined as the melting point of the surface layer (Tms), and the melting point of the intermediate layer sample after scraping off the surface layer was defined as the melting point of the intermediate layer (Tmt).

[0053] (5) Surface free energy The surface free energy of the film and the hydrogen bond component in the surface free energy were determined as follows. First, the following formula (i) was derived from the extended Fowkes formula and Young's formula. 〔Extended Fowkes formula〕 γSL = γS + γL - 2(γsd · γLd ) 1 / 2 - 2(γsD · γLD ) 1 / 2 - 2(γsh · γLh ) 1 / 2 〔Young's formula〕 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 the solid and the liquid (unit: mN / m) θ: Contact angle with the liquid (unit: °) Dispersive force components of γsd, γLd: γS, γL Polar force components of γsD, γLD: γS, γL Hydrogen bond components of γsh, γLh: γS, γL (γsd · γLd) 1 / 2 +(γsD · γLD) 1 / 2 +(γsh · γLh) 1 / 2 = γL×(1 + cosθ) / 2 (i) Next, the contact angles with the film were measured for four types of liquids whose surface tension components were known, substituted into Equation (i), and the hydrogen bond component in the surface free energy of the film was obtained by solving the system of three linear equations for each liquid. For the measurement of the contact angle, measurement liquids of water, ethylene glycol, formamide, and methylene iodide were used, and a contact angle meter CA-D type manufactured by Kyowa Interface Science Co., Ltd. was used as the measuring instrument. The measurement was carried out N = 3 times for both sides (I side / II side) of the film in an environment of 25°C and 65% humidity, and the average value was adopted as the value for each side.

[0054] (6) Main orientation axis At an arbitrary point on the film, a sample was cut out with dimensions of 100 mm × 100 mm and measured using a microwave molecular orientation meter MOA-7015 (frequency 4 GHz) manufactured by KS Systems (currently Oji Scientific Instruments Co., Ltd.). The direction (orientation angle) with the lowest microwave transmission intensity was taken as the main orientation axis direction.

[0055] (7) Film retardation It was measured using a retardation measurement device (KOBRA-WPR) manufactured by Oji Scientific Instruments Co., Ltd. A film sample of 30 mm × 50 mm (longitudinal direction × width direction) was cut out and placed in the retardation measurement device, and the retardation at a wavelength of 589 nm was measured.

[0056] (8) Stress at 10% elongation at 120°C, strength at the waist at 120°C The film was cut out into a rectangular sample with a length of 150 mm and a width of 10 mm in the direction of the main orientation axis at an arbitrary position. Using a tensile testing machine ("Tensilon" (registered trademark) UCT-100 manufactured by Orientec), with an initial distance between the tensile chucks of 50 mm and a tensile speed of 30 mm / min, a tensile test was conducted in the direction of the main orientation axis of the film. The measurement was carried out by setting the film sample in a constant temperature layer pre-set to 120°C, and after preheating for 60 seconds, the tensile test was performed. The load applied to the film when the sample was stretched by 10% (when the distance between the chucks became 55 mm) was read, and the value obtained by dividing it by the cross-sectional area of the sample before the test (film thickness × width 10 mm) was defined as the stress at 10% elongation. Also, the Young's modulus E(120) at 120°C was calculated from the maximum slope of the stress-strain curve in the range of 10% elongation in accordance with ASTM-D-882, and the stiffness at the waist at 120°C (unit: N·m 2 ) was calculated. Stiffness at the waist at 120°C = E(120)×T 3 / 1.2 E(120): Young's modulus of the film at 120°C (unit: MPa) T: Film thickness (unit: μm) In addition, the measurement was also carried out for the direction perpendicular to the film plane in the direction of the main orientation axis at an arbitrary position on the film. Sampling was carried out at 5 points at arbitrary positions, and the average value of the values measured for each sample was adopted.

[0057] (9) Flexural rigidity The procedure for measuring the flexural rigidity will be described with reference to Fig. 1.

[0058] A rectangular sample 201 is prepared such that, from the central portion in the film width direction, the length corresponding to the main orientation axis direction of the measured film is 100 mm and the length corresponding to the direction perpendicular to the main orientation axis within the film plane is 5 mm. The sample 201 is placed on a chuck 301 of a loop stiffness tester (”Loop Stiffness Tester” (registered trademark) manufactured by Toyo Seiki) so that it forms a ring with a circumference of 50 mm when made into a ring shape. The chucks 301 are brought into contact with each other to form the sample 201 into a ring shape, and a measuring element is lowered from above the ring at a displacement speed of approximately 3.5 mm / second. The load is measured when the displacement amount 302 reaches 10 mm after contacting the ring, and the obtained value is taken as the flexural rigidity (mN) in the main orientation axis direction of the film. Similarly, a rectangular sample is prepared such that the length corresponding to the main orientation axis direction of the measured film is 5 mm and the length corresponding to the direction perpendicular to the main orientation axis within the film plane is 100 mm, and the measurement is carried out in the same manner. The obtained value is taken as the flexural rigidity (mN) in the direction perpendicular to the main orientation axis within the film plane. The flexural rigidity in the main orientation axis direction of the film and the flexural rigidity in the direction perpendicular to the main orientation axis within the film plane are each measured 5 times, and the average value of all these values is taken as the flexural rigidity (mN). The measurement was carried out at 23°C.

[0059] (10) Film and polarizer laminate A film cut into a 15 cm square is overlaid with a polarizer (manufactured by Kenis Co., Ltd., polarizing film thin L size, transmittance 0.43, polarization ratio 0.9999, product code 1-115-0821) to form a laminate measurement sample. The film and the polarizer are bonded together by mixing the following materials, applying the obtained adhesive layer composition to one surface of the film with a gravure roll so that the coating thickness after drying is 20 μm, drying at 100°C for 3 minutes, and bonding the polarizer through the formed adhesive layer. The laminate is then left standing in a constant temperature room at 23°C and 65% humidity for 3 days.

[0060] (Adhesive layer composition) · Acrylic resin (a): A copolymer with n-butyl acrylate 65.0 parts by mass, 2-hydroxyethyl acrylate 5.0 parts by mass, and 2-(2-phenoxyethoxy)ethyl acrylate 8.0 parts by mass as monomers, weight average molecular weight 1.3 million · Crosslinking agent (b): "Takenate" (registered trademark) D-110N manufactured by Mitsui Chemicals, Inc. · Crosslinking agent (c): β-CEA (β-carboxyethyl acrylate) manufactured by Daicel Ornex Co., Ltd. · Silane compound (d): KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd. These were blended at a solid content mass ratio of (a) / (b) / (c) / (d) = 100 parts by mass / 0.5 parts by mass / 0.1 parts by mass / 0.5 parts by mass to obtain a composition for the adhesive layer.

[0061] (11) Appearance of the spherical shape formed laminate The convex shape of an aspherical lens (manufactured by Sigma Optical Co., Ltd., AGL-40-GA-30P) was used as a mold for evaluation. The laminate obtained by the method described in (10) was placed so that the polarizing plate side faced the mold, the laminate was heated to a predetermined temperature, and then vacuum suction was applied to make it follow the mold. After that, the vacuum was released, and the excess part of the molded laminate was trimmed. The appearance of the molded laminate was observed visually and with a video microscope (100 times magnification), and evaluated according to the following criteria. A grade of B or above was considered qualified. · S: No wrinkles or cracks are observed either visually or under microscopic observation. · A: No wrinkles or cracks are observed visually, and slight wrinkles or cracks are observed during microscopic observation. · B: No wrinkles or cracks are observed visually, and wrinkles or cracks are observed in part during microscopic observation. · C: No wrinkles or cracks are observed visually, but wrinkles or cracks are observed in multiple fields during microscopic observation, or wrinkles or cracks are observed on the surface of the laminate visually.

[0062] (12) Light leakage of the spherical shape formed polarizing plate In a dark room, a polarizing plate (manufactured by Kenis Co., Ltd., polarizing film thin L size, transmittance 0.43, polarization ratio 0.9999, product code 1-115-0821) was horizontally placed on a surface light source (manufactured by Trytec Co., Ltd., Treviewer A4-100). A molded polarizing plate obtained by peeling a film from a molded laminate obtained by the method described in (11) was placed on top such that the absorption axis of the polarizing plate was cross-oriented. A camera (manufactured by Sony Corporation, DSC-HX60V) was horizontally and fixedly installed directly above, 30 cm away from the molded polarizing plate, and photography was performed under the conditions of manual exposure mode, ISO sensitivity 80, shutter speed 1 / 60, and F3.5. The polarizing plate before molding was arranged to be cross-oriented, and compared with the photography performed under the same conditions, evaluation was carried out according to the following criteria, and a grade of B or above was considered qualified. · S: No light leakage is observed. · A: Slight light leakage is observed in 20% or less of the area of the molded polarizing plate. · B: Slight light leakage is observed in more than 20% and 40% or less of the area of the molded polarizing plate. · C: Slight light leakage is observed in more than 40% of the area of the molded polarizing plate. Or, distinct light leakage is observed.

[0063] (13) Fluorine atom content The content of fluorine atoms was measured by the automatic sample combustion-ion chromatography method (BS EN 14582:2007). Argon was introduced, and the sample was gradually heated to 800 °C in an electric furnace. The generated combustion gas was absorbed into an absorption liquid, and this absorption liquid was separated and quantified by ion chromatography to determine the content in the sample. The ion chromatogram of an aqueous solution containing fluorine atoms at a predetermined concentration was measured, and the content was determined by the absolute calibration curve method using the calibration curve obtained from the correlation between the area and concentration of the fluorine atom peak in the obtained chromatogram.

[0064] (Manufacture of polyester) The polyester resin used for film formation was prepared as follows.

[0065] (Polyester A) A polyethylene terephthalate resin (intrinsic viscosity 0.65) in which the terephthalic acid component is 100 mol% as the dicarboxylic acid component and the ethylene glycol component is 100 mol% as the glycol component.

[0066] (Polyester B) A cyclohexanedimethanol copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.75) in which 1,4-cyclohexanedimethanol is copolymerized at 33 mol% with respect to the glycol component.

[0067] (Polyester C) A polyethylene terephthalate particle master (intrinsic viscosity 0.65) containing aggregated silica particles with a number average particle diameter of 1.3 μm at a particle concentration of 1 mass% and aggregated silica particles with a number average particle diameter of 2.5 μm at a particle concentration of 2 mass% in Polyester A.

[0068] (Polyester D) A copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.70) in which the isophthalic acid component is 10 mol% as the dicarboxylic acid component and polyethylene glycol (PEG-1000 manufactured by Sanyo Chemical Industries, Ltd.) is copolymerized at 2 mol% (9.3 mass%) with respect to the glycol component.

[0069] (Easy-to-adhere coating liquid) · Resin solution (e): A solution obtained by mixing 70 parts by mass of an aqueous coating solution of a polyester resin composed of an acid component of terephthalic acid (88 mol%), 5-sodium sulfoisophthalic acid (12 mol%) and a diol component of ethylene glycol (100 mol%) and 30 parts by mass of an aqueous dispersion of a polyester resin composed of an acid component of terephthalic acid (50 mol%), isophthalic acid (49 mol%), 5-sodium sulfoisophthalic acid (1 mol%) and a diol component of ethylene glycol (55 mol%), neopentyl glycol (44 mol%), polyethylene glycol (molecular weight: 4000) (1 mol%). · Crosslinking agent (f): Methylolated melamine · Crosslinking agent (g): Epocros WS500 manufactured by Nippon Shokubai Co., Ltd. · Particle (h): An aqueous dispersion of collodial silica particles with a particle diameter of approximately 300 nm These were mixed at a solid content mass ratio of (e) / (f) / (g) / (h) = 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.

[0070] (Example 1) With the composition as shown in the table, the raw materials were supplied to separate vent co - rotating twin - screw extruders with an oxygen concentration of 0.2% by volume and melt - extruded at 280°C. Then, after passing through 5 FSS - type leaf disk filters respectively, while metering with a gear pump so that the discharge ratio of layer A / layer B = 4 / 1, in a three - layer merging block equipped with a rectangular laminating section, layer A was placed in the inner layer and layer B was placed in both surface layers, and then extruded into a sheet form through a T - die. After that, it was wound around a casting drum at 25°C by the electrostatic application casting method and cooled and solidified to produce an unstretched film.

[0071] This unstretched film was stretched 2.9 times in the longitudinal direction at a stretching speed of 23,000% / min at a film temperature of 90°C with the rotational speed difference of the rotating rolls, and immediately cooled with a metal roll temperature - controlled at 25°C. Then, corona discharge treatment was applied to both sides of this uniaxially stretched film to make the wetting tension of the film 55 mN / m, and an easy - adhesion coating solution was applied to both sides. Then, in a tenter - type transverse stretching machine, it was stretched 4.0 times in the width direction at a stretching speed of 1,200% / min at a film temperature of 90°C, and immediately heat - treated in three steps at 190°C / 225°C / 190°C for 5 seconds each and stretched 1.05 times in the width direction at a stretching speed of 120% / min, and then relaxed 2% in the longitudinal and width directions at 150°C to obtain a film with a thickness of 75 μm. The laminated thickness of layer B in both surface layers was 7.5 μm in both cases. Also, the thickness of the coating layer after drying of the easy - adhesion layer was 80 nm, the surface free energy of the film was 48 mN / m, the hydrogen - bonding component was 4.5 mN / m. Also, the fluorine atom was less than 50 ppm, the detection lower limit. Also, by lowering the stretching ratio in the longitudinal direction, the stretching speed was high but Fy10 was a small value, and in the width - direction stretching, although the stretching speed was slow, by stretching at a high stretching ratio in multiple steps, the molecular orientation became strong and Fx10 became a high value.

[0072] Using the obtained polyester film, it was bonded so that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 90° within the laminate plane, and the heating temperature for spherical shape molding was evaluated at 120°C. The evaluation results were as shown in the table. For the appearance of the spherical shape molded laminate, no wrinkles or cracks were observed visually, and some wrinkles or cracks were observed during microscopic observation. For the spherical shape molded polarizing plate, slight light leakage of 30% of the area of the molded polarizing plate was observed, but all were at a level without problems and were good for polarizing plate molding applications.

[0073] (Examples 2 to 5, Comparative Example 1) A film with a thickness of 75 μm was obtained in the same manner as in Example 1 except that the composition was as shown in the table. The laminated thickness of layer B on both surface layers was 7.5 μm in each case. Also, the thickness of the coating layer after drying of the easy-adhesion layer was 80 nm, the surface free energy of the film was 48 mN / m, and the hydrogen bond component was 4.5 mN / m. Further, the fluorine atom was less than 50 ppm, the detection lower limit.

[0074] Using the obtained polyester film, it was evaluated by bonding so that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 90° within the laminate plane. The evaluation results were as shown in the table.

[0075] In Examples 2 to 4, the appearance of the spherical shape molded laminate was good, and slight light leakage of 20% or less of the area of the molded polarizing plate was observed for the spherical shape molded polarizing plate, but it was at a level without problems and was good for polarizing plate molding applications.

[0076] In Example 5, no wrinkles or cracks were observed visually for the appearance of the spherical shape molded laminate, some wrinkles or cracks were observed during microscopic observation, and only slight light leakage of 20% or less of the area of the molded polarizing plate was observed for the spherical shape molded polarizing plate, which was good for polarizing plate molding applications.

[0077] In Comparative Example 1, wrinkles and cracks were visually observed on the surface of the spherical shape-molded laminate, and clear light leakage was observed at the crack part in the spherical shape-molded polarizing plate.

[0078] (Example 6) A film with a thickness of 75 μm was obtained in the same manner as in Example 3.

[0079] Using the obtained polyester film, evaluation was carried out by laminating it so that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 0° within the lamination plane. The evaluation results are as shown in the table.

[0080] In Example 6, no wrinkles or cracks were visually observed on the surface of the spherical shape-molded laminate, and slight wrinkles or cracks were observed during microscopic observation. No light leakage was observed in the spherical shape-molded polarizing plate, and it was good for polarizing plate molding applications.

[0081] (Example 7) An unstretched film was produced in the same manner as in Example 1, except that the composition was as shown in the table and the discharge amount was adjusted when extruding it into a sheet shape from a T-die.

[0082] This unstretched film was stretched 1.2 times in the longitudinal direction at a stretching speed of 1,000% / min at a film temperature of 90°C by gradually changing the rotational speed difference of a plurality of rotating rolls. Next, it was stretched up to a total of 3.9 times at a stretching speed of 40,000% / min at a film temperature of 85°C, and then cooled with a metal roll whose temperature was immediately controlled to 25°C. Next, both sides of this uniaxially stretched film were subjected to corona discharge treatment to make the wetting tension of the film 55 mN / m, and an easy-adhesion coating liquid was applied to both sides. Next, in a tenter-type transverse stretching machine, it was stretched 2.0 times in the width direction at a stretching speed of 600% / min at a film temperature of 90°C, and then immediately heat-treated in three steps at 190°C / 225°C / 190°C for 5 seconds each and stretched 1.5 times in the width direction at a stretching speed of 800% / min. Next, a relaxation treatment of 2% was performed in the longitudinal and width directions at 150°C to obtain a film with a thickness of 75 μm. The laminated thickness of layer B was 7.5 μm. The thickness of the coating layer after drying was 80 nm, the surface free energy of the film was 48 mN / m, and the hydrogen bond component was 4.5 mN / m. Also, the fluorine atoms were less than the detection limit of 50 ppm. Also, because the stretching speed in the longitudinal direction was increased, Fx10 was high due to the highly oriented formation in the longitudinal direction at a stretching ratio of 3.9 times. Since the stretching speed in the width direction stretching with a low stretching ratio was slow, the orientation of the molecules was difficult to occur, and Fy10 became a small value.

[0083] Using the obtained polyester film, it was evaluated by laminating it so that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 0° within the laminated body plane. The evaluation results are as shown in the table. No wrinkles or cracks were observed visually in the appearance of the spherical shape molded laminate, and slight wrinkles or cracks were observed during microscopic observation. No light leakage was observed in the spherical shape molded polarizing plate, and it was good for polarizing plate molding applications.

[0084] (Example 8) While adjusting the discharge amount when extruding in a sheet form from a T-die, a film with a thickness of 75 μm was obtained in the same manner as in Example 3, except that the stretching speed in the longitudinal stretching was 14,000% / min and the stretching ratio was 2.0 times. The laminated thickness of layer B on both surface layers was 7.5 μm in each case. Also, the thickness of the coating layer after drying of the easy-adhesion layer was 80 nm, the surface free energy of the film was 48 mN / m, and the hydrogen bond component was 4.5 mN / m. Further, the fluorine atom was less than 50 ppm, the detection lower limit.

[0085] Using the obtained polyester film, evaluation was carried out by laminating so that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 90° within the laminated body plane. The evaluation results are as shown in the table.

[0086] In Example 8, although wrinkles were visually observed in a part of the surface of the spherical shape molded laminate in the appearance of the spherical shape molded laminate, only slight light leakage of 20% or less of the area of the molded polarizing plate was observed in the light leakage of the spherical shape molded polarizing plate, and it was good as a polarizing plate molding application.

[0087] (Comparative Example 2) While adjusting the discharge amount when extruding in a sheet form from a T-die, a uniaxially stretched film was obtained in the same manner as in Example 3. Corona discharge treatment was performed on both surfaces of this uniaxially stretched film to make the wetting tension of the film 55 mN / m, and an easy-adhesion coating liquid was applied to both surfaces. Next, it was stretched 3.0 times at a stretching speed of 900% / min at a film temperature of 90 °C in the width direction by a tenter-type transverse stretching machine, and then immediately heat-treated in three steps at 190 °C / 225 °C / 190 °C for 5 seconds each, and then relaxation treatment of 2% in the longitudinal and width directions was performed at 150 °C to obtain a film with a thickness of 75 μm. The laminated thickness of layer B was 7.5 μm. The thickness of the coating layer after drying was 80 nm, the surface free energy of the film was 48 mN / m, and the hydrogen bond component was 4.5 mN / m. Further, the fluorine atom was less than 50 ppm, the detection lower limit.

[0088] Using the obtained polyester film, evaluation was carried out by laminating the film such that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 90° within the plane of the laminate. The evaluation results were as shown in the table. In the spherical shape molded laminate appearance, wrinkles were visually observed on the surface of the laminate, and clear light leakage was also observed at the edges of the spherical shape molded polarizing plate.

[0089] (Comparative Example 3) While adjusting the discharge amount when extruding into a sheet form from a T-die, an unstretched film was produced in the same manner as in Example 3.

[0090] Corona discharge treatment was performed on both sides of this unstretched film to set the wetting tension of the film to 55 mN / m, and an easy-adhesion coating liquid was applied to both sides. Subsequently, in a tenter-type transverse stretching machine, it was stretched 4.2 times in the width direction at a stretching speed of 600% / min at a film temperature of 90°C, and then immediately heat-treated in three steps at 170°C / 170°C / 170°C for 5 seconds each in order, and then relaxation treatment was performed at 150°C in the longitudinal and width directions by 2% to obtain a film with a thickness of 75 μm. Since the orientation in the longitudinal direction was insufficient when the heat treatment temperature was set under the same conditions as in Example 3, the film could not be obtained continuously, and the heat treatment temperature was set low. The laminated thickness of Layer B was 7.5 μm. The thickness of the coating layer after drying was 80 nm, the surface free energy of the film was 48 mN / m, and the hydrogen bond component was 4.5 mN / m. Also, the fluorine atom was less than 50 ppm, the detection lower limit. Also, while Fx10 in the direction parallel to the width direction was large, Fy10 in the direction parallel to the unstretched longitudinal direction became small, and the result was that Fx10 / Fy10 exceeded 3.0.

[0091] Using the obtained polyester film, evaluation was carried out by laminating the film such that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 90° within the plane of the laminate. The evaluation results were as shown in the table. Since Fx10 / Fy10 exceeded 3.0, there was a difference in the deformation behavior between the polarizing plate and the polyester film, and in the spherical shape molded laminate appearance, wrinkles and cracks were visually observed on the surface of the laminate, and clear light leakage was also observed at the locations where wrinkles and cracks occurred in the spherical shape molded polarizing plate.

[0092] (Examples 9 - 10) A film was obtained in the same manner as in Example 3, except that the extrusion amount of Layer A was varied so as to have the thickness as shown in the table. The laminated thickness of Layer B was 7.5 μm. The thickness of the coating layer after drying was 80 nm, the surface free energy of the film was 48 mN / m, and the hydrogen bond component was 4.5 mN / m. Also, the fluorine atoms were less than the detection lower limit of 50 ppm.

[0093] Using the obtained polyester film, evaluation was carried out by laminating it so that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 90° within the lamination plane. The evaluation results were as shown in the table.

[0094] In Example 9, for the spherical shape - formed laminated body, no wrinkles or cracks were observed visually, and slight wrinkles or cracks were observed under microscopic observation. For the spherical shape - formed polarizing plate, slight light leakage was observed at 35% of the area of the formed polarizing plate, but all were at a non - problematic level and were good for polarizing plate forming applications.

[0095] In Example 10, for the spherical shape - formed laminated body, no wrinkles or cracks were observed visually, and some wrinkles or cracks were observed under microscopic observation. For the spherical shape - formed polarizing plate, only slight light leakage was observed at 20% or less of the area of the formed polarizing plate, and it was good for polarizing plate forming applications.

[0096] (Example 11) The main orientation axis of the polyester film of Example 3 and the absorption axis of the polarizing plate were laminated so as to be 0° within the lamination plane, and evaluation was carried out with the heating temperature for spherical shape forming being 100°C. Since the heating temperature was insufficient compared to Example 3, for the spherical shape - formed laminated body, slight wrinkles and cracks were observed under microscopic observation, and for the spherical shape - formed polarizing plate, slight light leakage was observed at 35% of the area of the formed polarizing plate, but all were at a non - problematic level and were good for polarizing plate forming applications.

[0097] (Examples 12 - 14) A film with a thickness of 75 μm was obtained in the same manner as in Example 1 except that the composition was as shown in the table. The laminated thickness of layer B in both surface layers was 7.5 μm in each case. Also, the thickness of the coating layer after drying of the easy-adhesion layer was 80 nm, the surface free energy of the film was 48 mN / m, and the hydrogen-bonding component was 4.5 mN / m. Further, the fluorine atoms were less than the detection limit of 50 ppm.

[0098] Using the obtained polyester film, the polyester film was laminated so that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 0° within the laminated body plane, and the heating temperature for spherical shape molding was evaluated at 100°C. The evaluation results were as shown in the table.

[0099] In Example 12, no wrinkles or cracks were observed visually on the appearance of the spherical shape molding laminate, and slight wrinkles or cracks were observed during microscopic observation. The light leakage of the spherical shape molding polarizing plate was only slightly observed at 20% or less of the area of the molding polarizing plate, and it was good for polarizing plate molding applications.

[0100] In Example 13, the appearance of the spherical shape molding laminate was good, and only slight light leakage was observed at 20% or less of the area of the spherical shape molding polarizing plate, which was at a non-problematic level and was good for polarizing plate molding applications.

[0101] In Example 14, wrinkles were observed visually on a part of the surface of the laminate for the spherical shape molding, but only slight light leakage was observed at 20% or less of the area of the spherical shape molding polarizing plate, and it was good for polarizing plate molding applications.

[0102] (Example 15) A film with a thickness of 75 μm was obtained in the same manner as in Example 7 except that the composition was as shown in the table. The laminated thickness of layer B in both surface layers was 7.5 μm in each case. Also, the thickness of the coating layer after drying of the easy-adhesion layer was 80 nm, the surface free energy of the film was 48 mN / m, and the hydrogen-bonding component was 4.5 mN / m. Further, the fluorine atoms were less than the detection limit of 50 ppm.

[0103] Using the obtained polyester film, the polyester film was bonded so that the main orientation axis of the polyester film and the absorption axis of the polarizing plate were 0° within the laminate plane, and the heating temperature for spherical shape molding was evaluated at 100°C. The evaluation results are as shown in the table.

[0104] In Example 15, no wrinkles or cracks were observed visually on the appearance of the spherical shape molding laminate, and slight wrinkles or cracks were observed during microscopic observation. No light leakage was observed in the spherical shape molding polarizing plate, and it was good for polarizing plate molding applications.

[0105]

Table 1

[0106]

Table 2

[0107]

Table 3

Explanation of Symbols

[0108] 201 Sample of the film to be measured 301 Chuck 302 Displacement amount after contacting the ring

Claims

1. A polyester film comprising at least two or more layers, wherein when the stress at 10% elongation at 120 °C in the main orientation axis direction is Fx10 and the stress at 10% elongation at 120 °C in the direction perpendicular to the film plane in the main orientation axis is Fy10, Fx10 / Fy10 obtained by dividing Fx10 by Fy10 is 1.3 or more and 3.0 or less. A polyester film for polarizer molding.

2. The polyester film for polarizer molding according to claim 1, wherein Fx10 is 50 MPa or less.

3. The polyester film for polarizer molding according to claim 1, wherein the retardation at a wavelength of 589 nm is 1500 nm or more and 5000 nm or less.

4. The polyester film for polarizer molding according to claim 1, wherein the surface free energy of at least one surface is 35 mN / m or more and 60 mN / m or less.

5. The polyester film for polarizer molding according to claim 1, wherein the content of fluorine element in the polyester film is less than 100 ppm by mass.

6. The polyester film for polarizer molding according to claim 1, wherein at least one layer of the polyester film satisfies at least one of the following (a) to (d). (a) Containing a linear aliphatic diol having 3 or more carbon atoms as a glycol component of the polyester (b) Containing a polyalkylene glycol as a glycol component of the polyester (c) Containing a hydrogenated dimer acid having a long-chain alkyl group having 8 or more carbon atoms as a dicarboxylic acid component of the polyester (d) Containing a linear aliphatic dicarboxylic acid having 3 or more carbon atoms as a dicarboxylic acid component of the polyester

7. The polyester film for polarizer molding according to claim 1, wherein the average of the bending rigidity in the main orientation axis direction and the bending rigidity in the direction perpendicular to the film plane in the main orientation axis is 160 mN or less.

8. The polyester film for polarizer molding according to claim 1, wherein at least one surface is used by being bonded to a polarizer via an adhesive layer.

9. A polyester film for polarizer molding used by being laminated with a polarizer, wherein the angle formed by the absorption axis of the polarizer and the main orientation axis of the polyester film for polarizer molding within the lamination plane is laminated and used at -20° or more and 20° or less or 70° or more and 110° or less. The polyester film for polarizer molding according to claim 1.

10. The polyester film for polarizing plate molding according to claim 1, which is used for thermoforming processing of a polarizing plate for molding a polarizing plate into a curved surface.

Images