Poly(ethylene terephthalate)-based resin film, polarizing plate including same, transparent electroconductive film, touch panel, and image display device

Abstract

A poly(ethylene terephthalate)-based resin film satisfying the following (1) and (2). (1) The poly(ethylene terephthalate)-based resin film has a retardation of 3,000-30,000 nm and (2) the poly(ethylene terephthalate)-based resin film has a mesophase orientation parameter, as determined by the ATR-FTIR method, of 0.275 or greater.

Description

Polyethylene terephthalate resin film, and polarizing plate, transparent conductive film, touch panel, and image display device using the same

[0001] The present invention relates to a polyethylene terephthalate resin film, and to a polarizing plate, a transparent conductive film, a touch panel, and an image display device such as a liquid crystal display device or an organic EL display device, each using the same.

[0002] Polarizing plates used in liquid crystal display devices (LCDs) typically consist of a polarizer made of polyvinyl alcohol (PVA) or other materials dyed with iodine sandwiched between two polarizer protective films, typically made of triacetyl cellulose (TAC) film. In recent years, as LCDs have become thinner, thinner polarizing plates have been required. However, reducing the thickness of the TAC film used as a protective film to achieve this has led to problems such as insufficient mechanical strength and reduced moisture permeability. Furthermore, TAC film is very expensive, and polyester film has been proposed as a cheaper alternative (Patent Documents 1 to 3), but has the problem of iridescent color spots being observed.

[0003] When a birefringent oriented polyester film is placed on one side of a polarizer, the polarization state of linearly polarized light emitted from a backlight unit or polarizer changes as it passes through the polyester film. The transmitted light exhibits interference colors specific to the retardation, which is the product of the birefringence and thickness of the oriented polyester film. Therefore, when a cold cathode fluorescent lamp or hot cathode fluorescent lamp with a discontinuous emission spectrum is used as a light source, the transmitted light intensity varies depending on the wavelength, resulting in rainbow-like color spots.

[0004] As a means for solving the above problems, it has been proposed to use a white light source having a continuous and broad emission spectrum, such as a white light-emitting diode, as the backlight source, and further use an oriented polyester film having a certain retardation as the polarizer protective film (Patent Document 4). White light-emitting diodes have a continuous and broad emission spectrum in the visible light range. Therefore, when focusing on the envelope shape of the interference color spectrum of transmitted light that has passed through a birefringent material, it is possible to obtain a spectrum similar to the emission spectrum of the light source by controlling the retardation of the oriented polyester film, thereby making it possible to suppress iridescence.

[0005] JP 2002-116320 A JP 2004-219620 A JP 2004-205773 A WO2011 / 162198

[0006] Polyethylene terephthalate resin films with a certain retardation to suppress iridescence are used in a variety of applications, including polarizer protective films, substrates for transparent conductive films such as touch panels, and surface cover films. However, due to their high orientation anisotropy, they are prone to tearing in the direction parallel to the slow axis, and it has been found that breakage during slitting can reduce productivity. Furthermore, increased cutting resistance due to oriented crystallization can cause the cut area to stretch during slitting, resulting in rough edges at the end of the product roll, which can impair product quality. Furthermore, increased cutting resistance can cause the film to be scraped at the cut area, resulting in fine powder that can become foreign matter and impair product quality.

[0007] Specifically, the present invention aims to provide a polyethylene terephthalate-based resin film that has excellent processability and, in particular, can effectively suppress breakage and edge formation during slitting. Another object of the present invention is to provide a polarizing plate, a transparent conductive film, a touch panel, and an image display device such as a liquid crystal display device or an organic EL display device, using the polyethylene terephthalate-based resin film.

[0008] As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by controlling the mesophase orientation parameter of a polyethylene terephthalate resin film having a retardation within a specific range, measured by ATR-FTIR, to a certain value or higher, and have thus completed the present invention.

[0009] A representative example of the present invention is as follows: Item 1. A polyethylene terephthalate resin film that satisfies the following (1) and (2): (1) The polyethylene terephthalate resin film has a retardation of 3,000 to 30,000 nm. (2) The mesophase orientation parameter of the polyethylene terephthalate resin film, measured by an ATR-FTIR method, is 0.275 or more, and is represented by the following formula: (mesophase orientation parameter)=R ｓｌｏｗ / R ｆａｓｔ However, R ｓｌｏｗ = (1457 cm in the slow axis direction) －１ absorbance at 795 cm in the slow axis direction) / (absorbance at 795 cm in the slow axis direction) －１ absorbance at ｆａｓｔ = (1457 cm in the fast axis direction) －１ absorbance at 795 cm in the fast axis direction) / (absorbance at 795 cm in the fast axis direction) －１(absorbance at 1000 nm). Item 2. The polyethylene terephthalate resin film according to item 1, further satisfying the following conditions (3) and (4): (3) The elastic modulus in the slow axis direction is 8,600 MPa or less. (4) The ratio of the elastic modulus in the slow axis direction to the elastic modulus in the fast axis direction is 3.6 or less. Item 3. The polyethylene terephthalate resin film according to item 1 or 2, further satisfying the following condition (5): (5) The breaking strength in the slow axis direction is 450 MPa or less. Item 4. The polyethylene terephthalate resin film according to any one of items 1 to 3, further satisfying the following condition (6): (6) The rigid amorphous fraction, represented by the following formula, is 33 mass % or more: (rigid amorphous fraction (mass %) = 100 - (mobile amorphous fraction (mass %)) - (mass fraction crystallinity (mass %)). Item 5. A polarizing plate, comprising the polyethylene terephthalate resin film according to any one of items 1 to 4, laminated on at least one surface of a polarizer as a polarizer protective film. Item 6. Item 7. An image display device having the polarizing plate according to Item 5. Item 8. An organic EL display device having the polarizing plate according to Item 5. Item 9. A transparent conductive film having the polyethylene terephthalate resin film according to any one of Items 1 to 4 as a substrate film of the transparent conductive film. Item 10. A touch panel having the transparent conductive film according to Item 9. Item 11. An image display device having the polyethylene terephthalate resin film according to any one of Items 1 to 4 as a shatterproof film or a surface protective film on the viewing side of an image display panel.

[0010] According to the present invention, a polyethylene terephthalate-based resin film having excellent processability and capable of effectively suppressing breakage, edge formation, and the generation of foreign matter during slitting can be provided. Furthermore, a polarizing plate, a transparent conductive film, a touch panel, and an image display device such as a liquid crystal display device or an organic EL display device can be provided using the polyethylene terephthalate-based resin film.

[0011] Example of measuring nominal stress-nominal strain curve by tensile test Example of measuring storage modulus by dynamic viscoelasticity measurement

[0012] 1. Polyethylene terephthalate resin film The polyethylene terephthalate resin film of the present invention preferably has a retardation of 3,000 nm or more and 30,000 nm or less. If the retardation is 3,000 nm or more, the occurrence of interference colors when observed from an oblique direction can be suppressed, ensuring good visibility. The preferred lower limit of the retardation is 4,000 nm, and the next most preferred lower limit is 5,000 nm.

[0013] On the other hand, the upper limit of the retardation is preferably 30,000 nm. Even if a polyethylene terephthalate resin film having a retardation higher than this is used, the effect of further improving visibility is not substantially obtained, and the film thickness becomes considerably thick, which reduces the handleability as an industrial material. The preferred upper limit is 10,000 nm, the more preferred upper limit is 9,000 nm, and the even more preferred upper limit is 8,000 nm.

[0014] The refractive index difference in the film plane (refractive index in the slow axis direction - refractive index in the fast axis direction) is preferably 0.08 or more. A film that is strongly stretched in one direction and has a large refractive index difference in the film plane allows for sufficient retardation to be obtained even with a thinner film, which is preferable from the perspective of thinning, and is more preferably 0.09 or more, even more preferably 0.10 or more, particularly preferably 0.105 or more, and most preferably 0.11 or more. The present invention is suitably applied to films with such a large refractive index difference. On the other hand, if the refractive index difference in the film plane becomes too large, the anisotropy of the mechanical properties of the film becomes significant, tending to make it more susceptible to tearing, rupture, etc.; therefore, the refractive index difference is preferably 0.15 or less, more preferably 0.145 or less, even more preferably 0.14 or less, even more preferably 0.135 or less, particularly preferably 0.13, and most preferably 0.125 or less.

[0015] The retardation of the present invention can be determined by measuring the refractive index in two axial directions in the film plane and the film thickness, or can be determined using a commercially available automatic birefringence measuring device such as KOBRA-21ADH (Oji Scientific Instruments Co., Ltd.). The refractive index is measured at a wavelength of 589 nm.

[0016] The polyethylene terephthalate resin film of the present invention preferably has a mesophase orientation parameter, which is an index of the degree of orientation of the mesophase (mesophase) in the slow axis direction in the film plane, of 0.275 or more, from the viewpoints of reducing cutting resistance during cutting by suppressing excessive oriented crystallization and suppressing breakage, edge formation, and the generation of foreign matter during slitting. The mesophase orientation parameter of the present invention is preferably 0.275 or more, more preferably 0.280 or more, even more preferably 0.285 or more, and particularly preferably 0.290 or more. From the viewpoint of moderately promoting oriented crystallization and imparting good dimensional stability to the polyethylene terephthalate resin film, the mesophase orientation parameter is preferably 0.500 or less, more preferably 0.450 or less, even more preferably 0.400 or less, even more preferably 0.370 or less, particularly preferably 0.360 or less, and most preferably 0.355 or less.

[0017] The mesophase orientation parameter of a polyethylene terephthalate-based resin film is expressed by the following formula (1): (mesophase orientation parameter)=R ｓｌｏｗ / R ｆａｓｔ ...(1)

[0018] In the above formula (1), R ｓｌｏｗ = (1457 cm in the slow axis direction) －１ absorbance at 795 cm in the slow axis direction) / (absorbance at 795 cm in the slow axis direction) －１ absorbance at ｆａｓｔ = (1457 cm in the fast axis direction) －１ absorbance at 795 cm in the fast axis direction) / (absorbance at 795 cm in the fast axis direction) －１ (absorbance at 1457 cm －１ and absorbance at 795 cm －１The absorbance at 1457 cm is determined by Fourier transform infrared spectroscopy (ATR-FTIR) using a commercially available Fourier transform infrared spectrophotometer such as FTS 60A / 896 (Varian). －１ The absorbance peak at 1454 cm －１ The absorbance peak due to the amorphous phase appears at 1463 cm －１ The absorbance peak at 1457 cm is a superposition of the absorbance peak derived from the mesophase (also called oriented mesophase, which corresponds to the oriented amorphous phase as a crystal precursor) that appears at 1457 cm －１ The dichroic ratio of the absorbance peak at 1454 cm reflects the orientational anisotropy of the mesophase. －１ and 1463 cm －１ The absorbance peaks at 1454 cm reflect the conformational combination of the methylene group and the ester bond. －１ The absorbance peak at 1463 cm corresponds to the combination of the methylene group in a gauche (relaxed state) and the ester bond in a trans (strained state). －１ The absorbance peak at 795 cm corresponds to a combination in which the methylene group is trans and the ester bond is gauche. －１ The absorbance at 1457 cm reflects the out-of-plane vibration of the benzene ring, and does not change depending on the degree of orientation of the film surface or the pressure of the anvil during ATR measurement, so it can be used to normalize the absorbance at other wavenumbers. －１ The absorbance at 1457 cm －１ does not necessarily mean the absorbance at 1457 cm －１ Nearby (1452 cm －１ ~1462cm －１ ) indicates the absorbance of the peak top observed at 1457 cm －１ Similarly, the absorbance at 795 cm －１ The absorbance at 795 cm －１ does not necessarily mean the absorbance at 795 cm －１ Near (790 cm －１ ~800cm－１ ) is shown, and when no clear peak top is observed, －１ The absorbance at 1000 kJ / min can be read. The details of the measurement method will be described later in the Examples.

[0019] In general, the processability of polyethylene terephthalate resin films is affected by crystals that grow in the orientation direction as they are stretched. The polyethylene terephthalate resin film of the present invention has enhanced in-plane orientation anisotropy to suppress iridescence, and crystals grow preferentially in the slow axis direction, which corresponds to the main stretching direction. Crystal growth increases the cutting resistance in the fast axis direction, which is perpendicular to the slow axis direction, and also embrittles the polyethylene terephthalate resin film. For the reasons described above, polyethylene terephthalate resin films produced by known methods may develop fine powder due to film scraping and rough edges at the end of the product roll due to film elongation in the cut portions during slitting, which are more pronounced as the refractive index difference increases. As a result of various studies conducted by the inventors, it was found that by controlling the mesophase orientation parameter, which is an indicator of the degree of amorphous orientation in the slow axis direction within the film plane, within the above range, it is possible to effectively suppress embrittlement of the polyethylene terephthalate resin film and increased cutting resistance even when the orientation anisotropy is increased, and to effectively suppress the generation of fine powder due to scraping of the polyethylene terephthalate resin film in the cut portions during slitting and the generation of rough edges at the ends of the product roll due to stretching of the film.

[0020] The present invention exhibits excellent effects when the slow axis direction is in the TD direction and is preferably applied, but even when the slow axis direction is in the MD direction, the effect of suppressing the occurrence of edge formation and fine powder is high and the present invention is also applicable to films in which the slow axis direction is in the MD direction.

[0021] The polyethylene terephthalate resin film of the present invention preferably has an in-plane elastic modulus in the slow axis direction of 8600 MPa or less, from the viewpoint of further reducing cutting resistance in the fast axis direction and further suppressing the generation of fine powder due to scraping of the polyethylene terephthalate resin film at the cut portions during slitting and the occurrence of rough edges at the end of the product roll due to elongation of the film. The elastic modulus in the slow axis direction of the polyethylene terephthalate resin film is preferably 8600 MPa or less, more preferably 8500 MPa or less, even more preferably 8400 MPa or less, and particularly preferably 8300 MPa or less. The lower limit is not particularly limited, but from the viewpoint of maintaining sufficient orientation anisotropy to suppress iridescence, it is preferably 5400 MPa or more, more preferably 5450 MPa or more, even more preferably 5500 MPa or more, and particularly preferably 5550 MPa or more.

[0022] The polyethylene terephthalate resin film of the present invention preferably has an in-plane elastic modulus ratio of the slow axis direction to the fast axis direction of 3.6 or less, from the viewpoints of further reducing cutting resistance in the fast axis direction and further suppressing the generation of fine powder due to scraping of the polyethylene terephthalate resin film at the cut portions during slitting and the occurrence of rough edges at the end of the product roll due to elongation of the film. The ratio of the elastic modulus of the polyethylene terephthalate resin film in the slow axis direction to the fast axis direction is preferably 3.6 or less, more preferably 3.5 or less, even more preferably 3.4 or less, and particularly preferably 3.3 or less. While the lower limit is not particularly limited, from the viewpoint of maintaining sufficient orientation anisotropy to suppress iridescence, it is preferably 2.0 or more, more preferably 2.5 or more, even more preferably 2.6 or more, and particularly preferably 2.7 or more. Furthermore, the elastic modulus in the fast axis direction is preferably 2000 MPa or more, more preferably 2300 MPa or more, even more preferably 2350 MPa or more, particularly preferably 2400 MPa or more, and most preferably 2450 MPa or more. The upper limit is preferably 4300 MPa or less, more preferably 4200 MPa or less, even more preferably 4100 MPa or less, still more preferably 4000 MPa or less, particularly preferably 3500 MPa or less, and most preferably 3000 MPa or less.

[0023] The modulus of elasticity can vary greatly depending on the measurement method. Generally, the modulus of elasticity is defined as the slope of the stress-strain curve obtained in a tensile test at the beginning of elongation, but the modulus of elasticity can vary greatly depending on the face shape, pressure, and preload of the chuck used in the measurement, as well as the strain range used to calculate the slope. For example, in the nominal stress-nominal strain curve shown in Figure 1 (measured by a method conforming to JIS K7161, as described later in the Examples), the elastic modulus is calculated to be 6986 MPa in the strain range conforming to Section 10.3.2 of JIS K7161 (nominal strain: 0.0005 to 0.0025), but the elastic modulus is 6469 MPa in the range of nominal strain: 0.0005 to 0.0100, the elastic modulus is 5149 MPa in the range of nominal strain: 0.0005 to 0.0200, and the elastic modulus is 2590 MPa in the range of nominal strain: 0.0005 to 0.0500. Furthermore, the elastic modulus can also be the value of the storage elastic modulus obtained by dynamic viscoelasticity measurement, but the value obtained varies greatly depending on the measurement temperature. 2 shows the temperature dependence of the storage modulus measured for the same sample as that measured in FIG. 1 using a dynamic viscoelasticity measuring device (DMS6100) manufactured by Seiko Instruments Inc. in accordance with JIS-K7244 (measurement conditions: tension mode, driving frequency 1 Hz, chuck distance 5 mm, temperature rise rate 2°C / min, measurement temperature range 20°C to 230°C). For example, the elastic modulus at 20°C is 6958 MPa, at 60°C is 6425 MPa, at 100°C is 4533 MPa, at 140°C is 1028 MPa, at 180°C is 719 MPa, and at 220°C is 497 MPa. It is also common to adopt average values ​​in specific ranges, for example, the average modulus of elasticity in the 20°C to 60°C range is 6718 MPa, the average modulus of elasticity in the 20°C to 100°C range is 6244 MPa, the average modulus of elasticity in the 20°C to 140°C range is 4931 MPa, the average modulus of elasticity in the 20°C to 180°C range is 3930 MPa, the average modulus of elasticity in the 20°C to 220°C range is 3254 MPa, and the average modulus of elasticity in the 100°C to 220°C range is 1264 MPa.As described above, the elastic modulus value obtained varies greatly depending on the measurement method, but the claims of the present invention are based on values ​​measured by a method conforming to Section 10.3.2 of JIS K7161, and the details of the measurement method will be described later in the Examples.

[0024] The polyethylene terephthalate resin film of the present invention preferably has a breaking strength in the slow axis direction in the film plane of 450 MPa or less, from the viewpoint of further reducing cutting resistance in the fast axis direction and further suppressing the generation of fine powder due to scraping of the polyethylene terephthalate resin film at the cut portion during slitting and the occurrence of rough edges at the end of the product roll due to elongation of the film. The breaking strength in the slow axis direction of the polyethylene terephthalate resin film is more preferably 440 MPa or less, even more preferably 430 MPa or less, and particularly preferably 420 MPa or less. The lower limit is not particularly limited, but from the viewpoint of maintaining sufficient orientation anisotropy to suppress iridescence, it is preferably 220 MPa or more, more preferably 230 MPa or more, even more preferably 240 MPa or more, and particularly preferably 250 MPa or more.

[0025] The polyethylene terephthalate resin film of the present invention preferably has a rigid amorphous fraction of 33% by mass or more, from the viewpoints of further suppressing embrittlement of the polyethylene terephthalate resin film and further suppressing breakage originating from cut portions during slitting and generation of fine powder due to scraping of the polyethylene terephthalate resin film. The rigid amorphous fraction of the polyethylene terephthalate resin film is more preferably 34% by mass or more, even more preferably 35% by mass or more, and particularly preferably 36% by mass or more. The upper limit is preferably 60% by mass, but 50% by mass or less or 45% by mass or less is sufficient and is a more preferred range. Here, the rigid amorphous fraction is expressed by the following formula (2):

[0026] (Rigid amorphous fraction (mass %)) = 100 - (movable amorphous fraction (mass %)) - (mass fraction crystallinity (mass %))... (2)

[0027] Traditionally, the higher-order structure of polymers has been considered to be divided into crystalline and amorphous. However, in recent years, it has been reported that the amorphous region can be further distinguished based on the temperature dependence of molecular motion, and can be divided into mobile amorphous, in which molecular motion is released at the glass transition temperature (Tg), and rigid amorphous, in which molecular motion is frozen even at temperatures above Tg. In the case of polyethylene terephthalate, it is known that this rigid amorphous remains amorphous up to temperatures around 200°C. Generally, this rigid amorphous exists in the boundary region between crystal and mobile amorphous, and it is believed that the rigid amorphous fraction increases with increasing crystallinity. The inventors have found that by controlling the rigid amorphous fraction within the above range, embrittlement of polyethylene terephthalate-based resin films due to crystallization can be more effectively suppressed, even when the in-plane orientation anisotropy of the film is increased, and that the generation of fine powder due to breakage originating from cut portions during slitting and scraping of the polyethylene terephthalate-based resin film can be more easily suppressed.

[0028] In the above formula (2), the rigid amorphous fraction is indirectly calculated using the values ​​of the mobile amorphous fraction and the mass fraction crystallinity. The mobile amorphous fraction is calculated from the reversible heat capacity difference ΔCp at Tg of the reversible heat capacity curve obtained by temperature-modulated DSC measurement using a differential scanning calorimeter (TA Instrument, Q100). On the other hand, the mass fraction crystallinity is calculated from the density value obtained using a density gradient tube in accordance with JIS K7112. Details will be described later in the Examples. From the viewpoint of controlling the rigid amorphous fraction within the above preferred range, the mobile amorphous fraction is preferably 24.5% by mass or more, more preferably 25% by mass or more, even more preferably 25.5% by mass or more, and particularly preferably 26% by mass or more. The upper limit is preferably 36% by mass or less, more preferably 35.5% by mass or less, even more preferably 35% by mass or less, and particularly preferably 34.5% by mass or less.

[0029] From the viewpoint of controlling the rigid amorphous fraction within the above-mentioned preferred range and suppressing embrittlement due to excessive crystallization, the mass fraction crystallinity is preferably 41% by mass or less, more preferably 40% by mass or less, even more preferably 39% by mass or less, and particularly preferably 38% by mass or less. The lower limit is 27% by mass or more, more preferably 28% by mass or more, even more preferably 29% by mass or more, and particularly preferably 30% by mass or more.

[0030] The polyethylene terephthalate resin film of the present invention can be produced by a general polyester film production method. For example, a polyethylene terephthalate resin is melted, extruded into a sheet, and the resulting unoriented polyethylene terephthalate resin is stretched in the longitudinal direction by utilizing a roll speed difference at a temperature above the glass transition temperature, and then stretched in the transverse direction using a tenter and heat-treated. Alternatively, a simultaneous biaxial stretching machine may be used to simultaneously or sequentially stretch the resin in the longitudinal and transverse directions within the tenter.

[0031] The film-forming conditions for polyethylene terephthalate resin films are now specifically described. After much research, the inventors discovered that preheating at a sufficiently high temperature, softening the film sufficiently, and then stretching at a temperature moderately lower than that temperature can promote the orientation of amorphous molecular chains during stretching and effectively increase the mesophase orientation parameter. It is preferable that the stretching temperature be at least 5°C lower than the preheating temperature.

[0032] The upper limit of the stretching temperature is more preferably 10°C or more lower than the preheating temperature, even more preferably 15°C or more lower, and particularly preferably 20°C or more lower. The lower limit of the stretching temperature is more preferably the preheating temperature -60°C or more, even more preferably the preheating temperature -55°C or more, and particularly preferably the preheating temperature -50°C or more. By setting the stretching temperature within the above range, it becomes easier to control the film temperature during stretching, and it becomes easier to adjust the mesoorientation parameters.

[0033] Specific conditions for longitudinal stretching and transverse stretching are as follows: the preheating temperature is preferably 100°C or higher, more preferably 105°C or higher, even more preferably 108°C or higher, and particularly preferably 110°C or higher. The preheating temperature is preferably 150°C or lower, more preferably 140°C or lower, even more preferably 135°C or lower, and particularly preferably 130°C or lower. If the preheating temperature is too low, the orientation of the amorphous molecular chains tends to be difficult to proceed, making it difficult to sufficiently increase the mesophase orientation parameter. On the other hand, if the preheating temperature is too high, thickness unevenness tends to occur easily during stretching. The preheating time varies depending on the heating method. For example, when heating with hot air from a tenter, it is preferably 1 to 120 seconds, more preferably 2 to 60 seconds. The appropriate time can be set taking into consideration the film thickness, air speed, etc.

[0034] The stretching temperature is preferably 85°C or higher, more preferably 88°C or higher, and even more preferably 90°C or higher. The stretching temperature is preferably 105°C or lower, more preferably 102°C or lower, and even more preferably 100°C or lower. If the stretching temperature is too high, the stretching stress will be insufficient, causing thickness unevenness and making it difficult to sufficiently increase the mesophase orientation parameter. On the other hand, if the stretching temperature is too low, crystals will grow excessively, making it difficult to sufficiently increase the mesophase orientation parameter. The inventors have found that by controlling the stretching temperature within the above range, it is possible to effectively increase the mesophase orientation parameter while suppressing thickness unevenness, even when the preheating temperature is increased.

[0035] The above conditions are preferably applied to at least stretching in the main stretching direction, but when main stretching is performed in the machine direction by utilizing a speed difference between rolls, the strain rate is generally sufficiently high and orientation of amorphous molecular chains is likely to proceed, so the above conditions do not necessarily need to be applied.

[0036] When producing a film having a slow axis in the film width direction (TD), the longitudinal stretching ratio is preferably 0.7 times, more preferably 0.8 times or more, even more preferably 0.9 times or more, and particularly preferably 0.95 times or more. The longitudinal stretching ratio is preferably 1.5 times or less, more preferably 1.3 times or less, even more preferably 1.2 times or less, particularly preferably 1.1 times or less, and most preferably 1.05 times or less. Furthermore, longitudinal stretching may be omitted, i.e., the longitudinal stretching ratio may be 1 times. By setting the stretching ratio within the above range, the film becomes less susceptible to tearing in the transverse direction, and a large refractive index difference and various properties of the present invention are easily imparted. The transverse stretching ratio is preferably 4.0 to 7.0 times. Furthermore, from the viewpoint of suppressing relaxation of amorphous molecular chains during stretching and increasing the rigid amorphous fraction, a high transverse stretching ratio is preferred. The lower limit of the transverse stretching ratio is more preferably 4.5 times, even more preferably 4.7 times, and particularly preferably 5.0 times. On the other hand, if the transverse stretching ratio exceeds 7.0 times, the film tends to tear easily in the transverse direction, resulting in a decrease in productivity. Therefore, the upper limit of the transverse stretching ratio is more preferably 6.5 times, even more preferably 6.0 times, particularly preferably 5.7 times, and most preferably 5.5 times.

[0037] On the other hand, when producing a film having a slow axis in the longitudinal direction (MD direction), the transverse stretching ratio is preferably 0.7 times or more, more preferably 1.0 times or more, even more preferably 1.3 times or more, even more preferably 1.5 times or more, particularly preferably 1.7 times or more, and most preferably 2.0 times or more. The transverse stretching ratio is preferably 3.0 times or less, more preferably 2.7 times or less, and even more preferably 2.5 times or less. By setting the ratio within the above range, the film is made less likely to tear in the longitudinal direction, and a large refractive index difference and various properties of the present invention are easily imparted. In particular, when the film of the present invention is used as a polarizer protective film to form a polarizing plate by bonding it to a polarizer made of PVA stretched in the longitudinal direction, the transverse stretching ratio is preferably more than 1 times to prevent the polarizing plate from easily tearing or cracking in the longitudinal direction. From the viewpoint of suppressing relaxation of amorphous molecular chains during stretching and increasing the rigid amorphous fraction, a high longitudinal stretching ratio is preferred. The longitudinal stretching ratio is preferably 4.0 times or more, more preferably 4.5 times or more, even more preferably 4.7 times or more, and particularly preferably 5.0 times or more. If the longitudinal stretching ratio is too high, the film will be prone to tearing in the longitudinal direction, resulting in reduced productivity. Therefore, the longitudinal stretching ratio is preferably 7.0 times, more preferably 6.5 times, and particularly preferably 6.0 times. By setting the longitudinal stretching ratio and the transverse stretching ratio within the above ranges, it is possible to effectively increase the rigid amorphous fraction. However, as the stretching ratio in the slow axis direction increases, crystal growth becomes dominant, making it difficult to sufficiently increase the mesophase orientation parameter. Therefore, in order to promote the orientation of amorphous molecular chains during stretching and control the mesophase orientation parameter within the above range, it is preferable to preheat the film at a sufficiently high temperature as described above, and then stretch it at a temperature moderately lower than that.

[0038] In order to control the retardation within the above range, it is preferable to control the ratio of the longitudinal stretching magnification to the transverse stretching magnification, the stretching temperature, and the film thickness. If the difference between the longitudinal and transverse stretching magnifications is too small, it tends to be difficult to increase the retardation.

[0039] In order to effectively suppress the embrittlement of polyethylene terephthalate resin films due to crystallization during heat treatment, it is preferable to increase the rigid amorphous fraction. Specifically, it is preferable to suppress relaxation of amorphous molecular chains during stretching, and it is preferable to increase the strain rate during stretching of the film in the slow axis direction. The strain rate is preferably 13% / sec or more, more preferably 15% / sec or more, and particularly preferably 17% / sec or more. When stretching is performed using a tenter-type stretching machine, the upper limit is preferably 60% / sec from the viewpoint of film formability. In the case of roll stretching, there is no particular upper limit on the strain rate, but it is preferably within a speed range that allows the film to be transported stably, for example, the transport speed of the high-speed roll is preferably 600 m / min or less. Here, the strain rate is a parameter expressed as (nominal strain (%) in stretching in the slow axis direction) / (time (sec) required in stretching in the slow axis direction), and the nominal strain (%) is calculated by ((deformation amount (mm)) / (initial length (mm)))×100.

[0040] In the subsequent heat treatment, in order to promote oriented crystallization and increase retardation, it is necessary to treat at a high temperature sufficient to promote oriented crystallization. On the other hand, as a result of intensive research, the inventors have found that by dividing the heat treatment into two stages, a high-temperature treatment followed by a low-temperature treatment, it is possible to suppress excessive crystal growth and prevent a decrease in the mesophase orientation parameter, thereby effectively suppressing an increase in cutting resistance and embrittlement of the film. It is preferable that the heat treatment temperature during the high-temperature treatment is at least 5°C higher than the heat treatment temperature during the low-temperature treatment.

[0041] The lower limit of the temperature of the high-temperature treatment is more preferably 10° C. or more higher than the temperature of the low-temperature treatment, even more preferably 15° C. or more higher, and particularly preferably 20° C. or more higher. The upper limit of the temperature of the high-temperature treatment is more preferably the low-temperature treatment temperature + 80° C. or less, even more preferably the low-temperature treatment temperature + 75° C. or less, particularly preferably the low-temperature treatment temperature + 70° C. or less, and most preferably the low-temperature treatment temperature + 65° C. or less.

[0042] Specifically, the heat treatment temperature during high-temperature treatment is preferably 150°C or higher, more preferably 160°C or higher, particularly preferably 170°C or higher, and most preferably 180°C or higher. On the other hand, from the viewpoint of suppressing excessive crystal growth and preventing a decrease in the mesophase orientation parameter, the heat treatment temperature during high-temperature treatment is preferably 220°C or lower, more preferably 210°C or lower, and particularly preferably 200°C or lower. On the other hand, the heat treatment temperature during low-temperature treatment is preferably 100°C or higher, more preferably 110°C or higher, particularly preferably 120°C or higher, and most preferably 130°C or higher. On the other hand, from the viewpoint of suppressing excessive crystal growth and preventing a decrease in the mesophase orientation parameter, the heat treatment temperature during low-temperature treatment is preferably 170°C or lower, more preferably 160°C or lower, and particularly preferably 150°C or lower.

[0043] The high-temperature treatment time is preferably 1 second or more, more preferably 3 seconds or more, even more preferably 5 seconds or more, and particularly preferably 7 seconds or more. The high-temperature treatment time is preferably 60 seconds or less, more preferably 40 seconds or less, and even more preferably 30 seconds or less.

[0044] The preferred time range for the low-temperature treatment is the same as the preferred time range for the high-temperature treatment.

[0045] For example, when cooling after high-temperature treatment, by reducing the volume of cooling air, the material will apparently pass through the temperature range of the low-temperature treatment for a certain period of time. However, for stable production, it is preferable to pass the material through an oven whose temperature range is such that the temperature of the low-temperature treatment can be maintained.

[0046] By setting the high-temperature heat treatment and the low-temperature heat treatment in the above ranges, it is possible to obtain the effects of the heat treatment and ensure productivity.

[0047] After the low-temperature treatment, the film is cooled to a temperature at which it can be wound up, and the widthwise edges are cut as necessary before being wound up.

[0048] In order to adjust the thermal shrinkage rate of the film, a relaxation treatment may be performed between the heat treatment and the cooling. The relaxation treatment is performed by shrinking the film in at least one of the TD and MD directions. The relaxation rate is preferably 0.1 to 5%, more preferably 0.2 to 4%. The relaxation treatment may be performed during the high-temperature treatment, between the high-temperature treatment and the low-temperature treatment, during the low-temperature treatment, or during cooling, or may be performed across multiple steps.

[0049] The inventors discovered that by simultaneously preheating at a sufficiently high temperature and then stretching at a lower temperature, and by dividing the heat treatment into two stages: a high-temperature treatment followed by a low-temperature treatment, it is possible to effectively increase the mesophase orientation parameter, and that this is effective in suppressing breaks originating from the cut parts during slitting, fine powder caused by scraping of the polyethylene terephthalate resin film, and rough edges at the ends of the product roll due to film stretching, and thus completed the present invention.

[0050] The polyethylene terephthalate resin constituting the polyethylene terephthalate resin film preferably contains 85 mol% or more of the monomer units as ethylene terephthalate. The ethylene terephthalate unit content is preferably 90 mol% or more, more preferably 95 mol% or more. The copolymerization component may contain a known acid component or glycol component. The polyethylene terephthalate resin is particularly preferably a homopolymer of polyethylene terephthalate.

[0051] These resins have excellent transparency, thermal and mechanical properties, and retardation can be easily controlled by stretching. Polyethylene terephthalate has a large intrinsic birefringence, and a large retardation can be obtained relatively easily even with a thin film, making it the most suitable material.

[0052] Furthermore, for the purpose of suppressing deterioration of optically functional dyes such as iodine dyes, the polyethylene terephthalate resin film of the present invention may have a light transmittance of 20% or less at a wavelength of 380 nm. The light transmittance at 380 nm is more preferably 15% or less, even more preferably 10% or less, and particularly preferably 5% or less. A light transmittance of 20% or less can suppress deterioration of the optically functional dye due to ultraviolet rays. The transmittance in the present invention is measured in a direction perpendicular to the plane of the film and can be measured using a spectrophotometer (e.g., Hitachi U-3500 model).

[0053] In order to achieve a transmittance of 20% or less at a wavelength of 380 nm for the polyethylene terephthalate resin film of the present invention, it is desirable to appropriately adjust the type and concentration of the ultraviolet absorber and the film thickness. The ultraviolet absorber used in the present invention is a known substance. Examples of ultraviolet absorbers include organic and inorganic ultraviolet absorbers, with organic ultraviolet absorbers being preferred from the viewpoint of transparency. Examples of organic ultraviolet absorbers include benzotriazoles, benzophenones, cyclic iminoesters, and combinations thereof, but are not particularly limited as long as they have the absorbance within the above-mentioned range. However, from the viewpoint of durability, benzotriazoles and cyclic iminoesters are particularly preferred. When two or more ultraviolet absorbers are used in combination, ultraviolet rays of different wavelengths can be simultaneously absorbed, thereby further improving the ultraviolet absorption effect.

[0054] Examples of benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, and acrylonitrile-based ultraviolet absorbers include 2-[2'-hydroxy-5'-(methacryloyloxymethyl)phenyl]-2H-benzotriazole, 2-[2'-hydroxy-5'-(methacryloyloxyethyl)phenyl]-2H-benzotriazole, 2-[2'-hydroxy-5'- -(methacryloyloxypropyl)phenyl]-2H-benzotriazole, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,4-di-tert-butyl-6-(5-chlorobenzotriazol-2-yl)phenol, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(5-chloro(2H)-benzotriazol-2-yl)-4-methyl-6-(tert-butyl)phenol Examples of cyclic imino ester-based ultraviolet absorbers include 2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, and 2-phenyl-3,1-benzoxazin-4-one. However, the absorbers are not particularly limited to these.

[0055] In addition to the ultraviolet absorber, it is also a preferred embodiment to contain various additives other than the catalyst, as long as they do not impair the effects of the present invention. Examples of additives include inorganic particles, heat-resistant polymer particles, alkali metal compounds, alkaline earth metal compounds, phosphorus compounds, antistatic agents, light stabilizers, flame retardants, heat stabilizers, antioxidants, antigelling agents, surfactants, etc. In addition, in order to achieve high transparency, it is also preferable that the polyethylene terephthalate resin film is substantially free of particles. "Substantially free of particles" means, for example, in the case of inorganic particles, that the content of inorganic elements, when quantified by fluorescent X-ray analysis, is 50 ppm or less, preferably 10 ppm or less, and particularly preferably below the detection limit.

[0056] Furthermore, as a method for blending an ultraviolet absorber into the polyethylene terephthalate-based resin film of the present invention, a combination of known methods can be adopted. For example, the ultraviolet absorber can be blended in advance using a kneading extruder to blend a dried ultraviolet absorber with a polymer raw material to prepare a master batch, and then the predetermined master batch and the polymer raw material are mixed during film formation.

[0057] In this case, the concentration of the ultraviolet absorber in the masterbatch is preferably 5 to 30% by mass in order to disperse the ultraviolet absorber uniformly and to compound economically. The conditions for preparing the masterbatch are preferably a kneading extruder, and the extrusion temperature is preferably from the melting point of the polyethylene terephthalate-based raw material to 290°C or less for 1 to 15 minutes. At temperatures above 290°C, the weight loss of the ultraviolet absorber is significant, and the viscosity of the masterbatch also decreases significantly. If the extrusion time is less than 1 minute, it tends to be difficult to uniformly mix the ultraviolet absorber. At this time, a stabilizer, a color adjuster, or an antistatic agent may be added as needed.

[0058] In addition, in the present invention, the film may have a multilayer structure of at least three layers, and an ultraviolet absorber may be added to the intermediate layer of the film. A three-layer film containing an ultraviolet absorber in the intermediate layer can be specifically produced as follows: Pellets of polyethylene terephthalate resin alone are mixed for the outer layer, and a masterbatch containing an ultraviolet absorber and pellets of polyethylene terephthalate resin are mixed for the intermediate layer in a predetermined ratio. After drying, the mixture is fed into a known melt lamination extruder, extruded into a sheet through a slit die, and cooled and solidified on a casting roll to produce an unstretched film. That is, using two or more extruders and a three-layer manifold or merging block (e.g., a merging block having a rectangular merging portion), film layers constituting both outer layers and a film layer constituting the intermediate layer are laminated, and the three-layer sheet is extruded through a die and cooled on a casting roll to produce an unstretched film. It is preferable to perform high-precision filtration during melt extrusion to remove foreign matter contained in the raw polyethylene terephthalate resin, which may cause optical defects. The filtering particle size (initial filtering efficiency 95%) of the filtering material used for high-precision filtering of molten resin is preferably 15 μm or less. If the filtering particle size of the filtering material exceeds 15 μm, removal of foreign matter of 20 μm or more tends to be insufficient.

[0059] Furthermore, the polyethylene terephthalate resin film of the present invention may be subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve the adhesiveness of the film surface.

[0060] In the present invention, in order to improve the adhesion of the polyethylene terephthalate resin film surface, it is preferable to have an easy-adhesion layer (adhesion-modifying coating layer) on at least one side of the film of the present invention. Conventionally known easy-adhesion layers can be appropriately adopted as the easy-adhesion layer, but those containing at least one of polyester resin, polyurethane resin, or polyacrylic resin as the main component are preferred. Here, "main component" refers to a component that accounts for 50% by mass or more of the solid components constituting the easy-adhesion layer. The coating liquid used to form the easy-adhesion layer is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolymer polyester resin, acrylic resin, and polyurethane resin. Examples of these coating liquids include water-soluble or water-dispersible copolymer polyester resin solutions, acrylic resin solutions, polyurethane resin solutions, etc., as disclosed in Japanese Patent No. 3,567,927, Japanese Patent No. 3,589,232, Japanese Patent No. 3,589,233, Japanese Patent No. 3,900,191, Japanese Patent No. 4,150,982, etc.

[0061] The easy-adhesion layer can be obtained, for example, by applying the coating liquid to one or both sides of an unstretched film or a uniaxially stretched film in the machine direction, drying the film at 100 to 150°C, and then stretching the film in the transverse direction. The final coating amount of the easy-adhesion layer is 0.05 to 0.20 g / m ２ It is preferable to control the coating amount to 0.05 g / m ２ On the other hand, if the coating amount is less than 0.20 g / m, the adhesiveness may be insufficient. ２ If the thickness exceeds this range, blocking resistance may decrease. Furthermore, the final thickness of the easy-adhesion layer obtained after stretching is preferably 1 μm or less, more preferably 0.5 μm or less, and even more preferably 0.2 μm or less, from the viewpoint of obtaining a good coating appearance. When easy-adhesion layers are provided on both sides of the polyethylene terephthalate resin film, the coating amounts of the easy-adhesion layers on both sides may be the same or different, and can be independently set within the above ranges.

[0062] It is preferable to add particles to the adhesion layer to impart slipperiness. It is preferable to use particles with an average particle size of 2 μm or less. If the average particle size of the particles exceeds 2 μm, the particles tend to fall off from the coating layer. Examples of particles to be contained in the adhesion layer include inorganic particles such as titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, and calcium fluoride, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. These may be added to the adhesion layer alone, or two or more types may be added in combination.

[0063] The coating solution can be applied by any known method, such as reverse roll coating, gravure coating, kiss coating, roll brushing, spray coating, air knife coating, wire bar coating, or pipe doctor coating, which can be used alone or in combination.

[0064] The average particle size of the particles is measured by the following method.

[0065] The particles are photographed using a scanning electron microscope (SEM), and the maximum diameters (the distance between the two most distant points) of 300 to 500 particles are measured at a magnification such that the size of the smallest particle is 2 to 5 mm, and the average value is taken as the average particle size.

[0066] It is also a preferred embodiment that a functional layer such as a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer, a light diffusion layer, a lens layer, or a prism layer is laminated on at least one surface of the polyethylene terephthalate resin film of the present invention via an easy-adhesion layer.

[0067] The thickness of the polyethylene terephthalate resin film of the present invention is not limited, but is preferably in the range of 25 to 300 μm. Even with a film having a thickness of less than 25 μm, it is theoretically possible to obtain a retardation of 3000 nm or more. However, in such a case, the anisotropy of the mechanical properties of the film becomes significant, and the film tends to be prone to tearing, rupture, and the like.

[0068] More preferred thicknesses of the polyethylene terephthalate resin film of the present invention are 200 μm, 150 μm, 120 μm, 100 μm, 90 μm, 80 μm, 75 μm, and 70 μm as upper limits, and 30 μm, 35 μm, 40 μm, 45 μm, and 50 μm as lower limits.

[0069] The polyethylene terephthalate resin film of the present invention can be used for various purposes, and the optimum thickness range can be selected from the above range depending on the purpose.

[0070] For example, when the polyethylene terephthalate resin film of the present invention is used as a polarizer protective film, from the viewpoint of practicality, the upper limit of the thickness can be selected from the range of 120 μm or less, and the lower limit is as described above. From the viewpoint of thinner films in recent years, the thickness may be more preferably 65 μm or less, more preferably 60 μm or less, and particularly preferably 55 μm or less.

[0071] When the polyethylene terephthalate resin film of the present invention is used as a substrate for a transparent conductive film, and when it is used as a shatterproof film, the same preferable ranges as those given for the polarizer protective film apply.

[0072] When the polyethylene terephthalate resin film of the present invention is used as a surface protection film such as a cover sheet for an image display device, the lower limit of the thickness can be selected from the above lower limit to a value of 40 μm or more, and the upper limit of the thickness can be selected from the above upper limit to a value of 150 μm or more.

[0073] In recent years, there has been a growing demand for further thinning of polarizer protective films, which has led to a tendency for the processability of polarizer protective films to become increasingly poor. Even in such cases, according to the present invention, it is possible to effectively suppress an increase in cutting resistance in the fast axis direction and embrittlement of the polyethylene terephthalate-based resin film, and it is possible to effectively suppress breakage originating from the cut portion during slitting, fine powder due to abrasion of the polyethylene terephthalate-based resin film, and the generation of rough edges at the end of the product roll due to elongation of the film.

[0074] To suppress fluctuations in retardation, it is preferable that the thickness unevenness of the film is small. Since the stretching temperature and stretching ratio have a significant effect on the thickness unevenness of the film, it is preferable to optimize the film-forming conditions from the viewpoint of thickness unevenness as well. In particular, if the longitudinal stretching ratio is reduced in order to increase the retardation, the longitudinal thickness unevenness may worsen. Since the longitudinal thickness unevenness becomes extremely worse within a certain range of stretching ratio, it is desirable to set the film-forming conditions outside this range.

[0075] The thickness unevenness of the film of the present invention is preferably 5.0% or less, more preferably 4.5% or less, even more preferably 4.0% or less, and particularly preferably 3.0% or less.

[0076] The polyethylene terephthalate resin film of the present invention preferably has an Nz coefficient, expressed by |ny-nz| / |ny-nx|, of 1.7 or less. The Nz coefficient can be determined as follows. The orientation axis direction of the film is determined using a molecular orientation meter (MOA-6004 molecular orientation meter, manufactured by Oji Scientific Instruments Co., Ltd.), and the biaxial refractive indexes (ny, nx, where ny > nx) of the orientation axis and the direction perpendicular thereto, and the refractive index (nz) in the thickness direction are determined using an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd., measurement wavelength 589 nm). The thus determined nx, ny, and nz can be substituted into the formula expressed by |ny-nz| / |ny-nx| to determine the Nz coefficient. The Nz coefficient is more preferably 1.65 or less, and even more preferably 1.63 or less. The lower limit of the Nz coefficient is preferably 1.2. In order to maintain the mechanical strength of the film, the lower limit of the Nz coefficient is preferably 1.3 or more, more preferably 1.4 or more, and even more preferably 1.45 or more.

[0077] The ratio (Re / Rth) of the retardation (Re) to the thickness direction retardation (Rth) of the polyethylene terephthalate resin film is preferably 0.2 or more, more preferably 0.5 or more, and even more preferably 0.6 or more. The larger the ratio (Re / Rth), the better. The upper limit is preferably 2.0 or less, more preferably 1.8 or less. The thickness direction retardation is a parameter indicating the average retardation obtained by multiplying the two birefringences ΔNxz (=|nx-nz|) and ΔNyz (=|ny-nz|) by the film thickness d when viewed from the cross section of the film thickness direction. The thickness direction retardation (Rth) can be determined by determining nx, ny, nz, and the film thickness d (nm) and calculating the average value of (ΔNxz×d) and (ΔNyz×d). The values ​​of nx, ny, and nz are determined by an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd., measuring wavelength 589 nm).

[0078] The surface roughness (SRa) (JIS B0601:1994) of the polyethylene terephthalate resin film is preferably 0.05 μm or less, more preferably 0.01 μm or less, and even more preferably 0.005 μm or less on at least one side, and even more preferably on both sides. By setting the SRa to 0.05 μm or less, a highly transparent film can be obtained. Furthermore, in order to ensure the slipperiness of the film, the SRa is preferably 0.0001 μm or more, and even more preferably 0.0005 μm or more.

[0079] The ten-point average surface roughness (SRz) (JIS B0601:1994) of the polyethylene terephthalate resin film is preferably 1.0 μm or less, more preferably 0.70 μm or less, even more preferably 0.50 μm or less, particularly preferably 0.30 μm or less, and most preferably 0.2 μm or less, on at least one side, and more preferably both sides. SRz is preferably 0.001 μm or more, and more preferably 0.005 μm or more.

[0080] The phenomenon of increased surface roughness is often caused by coarse particles such as particle aggregates and catalyst residues, and if the content is equal to or less than the above upper limit, it is possible to prevent coarse particles from falling off and scratching the film surface during the film production and processing steps or after the film is incorporated into a liquid crystal display device, thereby preventing bright spots and dark spots that would otherwise deteriorate image quality. It is also possible to prevent a decrease in image clarity and contrast.

[0081] Coarse particles in the film are preferably removed by a filter during the production of the resin, or by providing a filter in the film production line.

[0082] Furthermore, when the surface is an easy-adhesion layer or other coating layer, it is preferable to employ a method such as filtering the coating solution after preparation, or filtering the coating solution by providing a filter in the line that sends the coating solution to the coating die.

[0083] The number of foreign particles in the polyethylene terephthalate resin film with a major axis of 100 μm or more is preferably two or less. Foreign particles with a major axis of 100 μm or more in the polyethylene terephthalate resin film are those observed as bright spots with a major axis of 100 μm or more when a polarizing plate cut to a size to be incorporated into an image display device is placed in a crossed Nicol configuration on the polyethylene terephthalate resin film side of the polarizing plate. Examples of foreign particles in the film include aggregates of lubricant particles. It is also preferable to not only remove aggregates with a small pore filter during film formation, but also to form a multilayer film with lubricant particles only in the surface layer. It is also preferable to use lubricant particles not in the film but in an easy-adhesion coating on the surface.

[0084] Furthermore, resin degradation products can also become foreign matter in the film. While hard foreign matter in the molten resin can be removed using the aforementioned filter, gel-like foreign matter resulting from thermal degradation of the molten resin can deform to some extent at the molten resin temperature and may slip through the filter even if it is larger than the filter's pore size. Larger thermal degradation products may be cut off by the filter, increasing the number of foreign matter. Furthermore, thermal degradation products of the resin generated in the line downstream of the filter are directly incorporated into the film. Not only do these foreign matter fail to follow the stretching orientation of the surrounding resin during the stretching process, but they also disrupt the stretching orientation of the surrounding resin, appearing as bright spots when measured with a crossed Nicol filter. Even small, hard foreign matter that passes through the filter can create voids between the resin and the film during stretching, potentially becoming foreign matter in the film. Furthermore, the filter's pore size does not necessarily mean that foreign matter larger than the pore size will not pass through; even foreign matter larger than the pore size will pass through to a certain extent.

[0085] The number of foreign particles having a major axis of 100 μm or more in the polyethylene terephthalate resin film is more preferably one or less, and is preferably zero, that is, none.

[0086] The number of foreign particles having a major axis of 50 μm or more in the polyethylene terephthalate resin film is preferably 5 or less, more preferably 3 or less, even more preferably 1 or less, and particularly preferably 0.

[0087] Furthermore, the number of foreign particles having a major axis of 20 μm or more in the polyethylene terephthalate resin film is preferably 10 or less, more preferably 5 or less, even more preferably 3 or less, particularly preferably 1 or less, and most preferably 0.

[0088] If such foreign matter is present in a polyethylene terephthalate resin film, not only will it be visible if the foreign matter is colored when the image is viewed closely, but even if the foreign matter is nearly colorless and transparent, it may have a different refractive index from the surrounding normal parts, resulting in a small area of ​​a different color or disrupting the uniformity of the color tone. Furthermore, in the case of a polarizing plate on the light source side, it may result in a dark spot.

[0089] In order to reduce the amount of foreign matter in the film, it is preferable to minimize the areas where the molten resin stagnates along the path through which it passes. Specifically, in an extruder, it is preferable to minimize the steps between screw elements, between barrel blocks, and at the connecting portions of piping. It is also preferable to design piping, filter housings, filter elements, and nozzle flow paths to minimize the stagnation of resin, or to reduce the roughness of the inner walls of these structures.

[0090] Furthermore, the amount of foreign matter tends to increase when the film production starts or when the resin extrusion rate is increased. In these cases, it is preferable to temporarily increase the resin extrusion rate and then decrease it to the specified amount.

[0091] Furthermore, it is preferable to inspect the film for defects after production so that films with a large amount of foreign matter are not used for the production of polarizing plates, and to mark defective areas so that polarizing plates with those areas are not used.

[0092] The haze of the polyethylene terephthalate resin film is preferably 5% or less, more preferably 3% or less, even more preferably 2% or less, and particularly preferably 1.5% or less. The lower limit of the haze is preferably 0.01% or more, and even more preferably 0.1% or more.

[0093] Note that SRa and SRz are the SRa and SRz of the surface of the polyethylene terephthalate resin film as a raw sheet before coating with a functional layer such as a low-reflection layer, which will be described later, but when an easy-adhesion layer is provided in-line, the values ​​are those of the easy-adhesion layer surface. The same applies to haze.

[0094] The haze can be measured in accordance with JIS-K7105 using a turbidity meter (NHD2000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0095] The intrinsic viscosity (IV) of the resin constituting the film is preferably 0.45 to 1.5 dL / g.

[0096] In the case of PET, the IV is preferably 0.5 to 1.5 dL / g. The lower limit of the IV is more preferably 0.53 dL / g, and even more preferably 0.55 dL / g. The upper limit of the IV is more preferably 1.2 dL / g, even more preferably 1 dL / g, and particularly preferably 0.8 dL / g.

[0097] For PEN, the lower limit of IV is preferably 0.45 dL / g, more preferably 0.48 dL / g, even more preferably 0.5 dL / g, and particularly preferably 0.53 dL / g. The upper limit of IV is more preferably 1 dL / g, more preferably 0.8 dL / g, even more preferably 0.75 dL / g, and particularly preferably 0.7 dL / g.

[0098] By setting the viscosity within the above range, a film with excellent mechanical strength such as impact resistance can be obtained, and it can be produced efficiently without placing a large load on the equipment. Note that IV was measured by dissolving 0.2 g of a sample in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)) at 30°C using an Ostwald viscometer.

[0099] In the polarizer protective film, the amount of antimony atoms in the residue insoluble in a mixed solvent of parachlorophenol and tetrachloroethane is preferably 50 mg or less, more preferably 30 mg or less, even more preferably 20 mg or less, particularly preferably 10 mg or less, and most preferably 5 mg or less, per 1 kg of the resin constituting the film. The amount of antimony atoms in the residue is preferably as small as possible, and the lower limit is preferably 0.1 mg, more preferably more than 0.5 mg, and even more preferably more than 1 mg. The polarizer protective film is preferably formed from a resin polymerized using an antimony compound as a catalyst, particularly a polyester resin.

[0100] Examples of antimony compounds used as catalysts include antimony trioxide, antimony pentoxide, antimony acetate, and antimony glycoxide. ２ O ３ ) is preferred.

[0101] As the catalyst, in addition to the antimony compound, a titanium compound catalyst such as tetrabutoxy titanate, or an aluminum catalyst such as basic aluminum acetate and a hindered phenol-containing phosphate ester (for example, Irganox 1222) may be used in combination.

[0102] Furthermore, it is also preferable to add a polymerization stabilizer or auxiliary, or a melt resistivity adjuster, typical examples of which include phosphorus compounds such as trimethyl phosphate and phosphoric acid, magnesium compounds such as magnesium acetate, and calcium compounds such as calcium acetate.

[0103] In order to keep the amount of antimony atoms in the residue insoluble in the mixed solvent of the film at or below the above level, it is preferable to keep the amount of antimony atoms in the residue insoluble in the mixed solvent of the resin used in producing the film at or below the above level.

[0104] Examples of methods for reducing the amount of antimony atoms in the residue insoluble in the polyester resin solvent mixture to the above-mentioned level include the following methods, and these methods can be used alone or in combination. The amount of antimony added to the polyester resin after polymerization is preferably 300 ppm or less, more preferably 250 ppm or less, even more preferably 220 ppm or less, and particularly preferably 200 ppm or less, in terms of antimony atomic weight. The lower limit of the antimony amount is 30 ppm, even more preferably 50 ppm, and particularly preferably 80 ppm. The antimony compound is added as a solution or slurry in ethylene glycol. In this case, the concentration of the antimony compound is preferably 10% by mass or less, even more preferably 7% by mass or less, and particularly preferably 5% by mass or less. The maximum temperature of the polyester resin polymerization is preferably 290°C or less, even more preferably 285°C or less. The degree of vacuum is increased so that the time during which the polyester resin reaches the maximum polymerization temperature is within 45 minutes, even more preferably 30 minutes. In the case of continuous polymerization, this refers to the average residence time. When a phosphorus compound, magnesium compound, or calcium compound is added, the amount added is preferably 15 to 120 ppm, more preferably 20 to 100 ppm, and even more preferably 25 to 80 ppm in terms of phosphorus atomic weight relative to the polyester resin after polymerization, and the magnesium atomic weight or calcium atomic weight is preferably 30 to 120 ppm, more preferably 40 to 100 ppm. Furthermore, it is preferable to add the phosphorus compound after adding the magnesium compound or calcium compound, and to add it in multiple divided stages.

[0105] 2. Polarizing Plate The polyethylene terephthalate resin film of the present invention can be used as a polarizer protective film. The polarizing plate of the present invention has a structure in which a polarizer protective film made of the polyethylene terephthalate resin film of the present invention is laminated on at least one surface of a polarizer. The polarizer may be made of polyvinyl alcohol (PVA) or the like dyed with iodine.

[0106] It is preferable to use a film without birefringence, such as a TAC film, an acrylic film, or a norbornene film, on the surface of the polarizer opposite to the side on which the polyethylene terephthalate resin film is laminated (referred to as the other surface). It is also preferable that a polarizer protective film, an optical compensation film, or the like is not laminated on the other surface. A coating layer such as a hard coat layer may be laminated on the polarizer on the other surface. It is also a preferable embodiment that the polarizing plate used in the present invention is coated with various hard coats on the surface for the purposes of preventing reflection, suppressing glare, suppressing scratches, and the like.

[0107] 3. Image Display Devices As will be described later, the polarizing plate of the present invention can be used as a component of image display devices such as liquid crystal display devices and organic EL display devices.

[0108] 4. Liquid Crystal Display Devices Generally, a liquid crystal panel is composed of a rear module, a liquid crystal cell, and a front module, in that order from the side facing the backlight source to the side where an image is displayed (the viewing side). The rear module and the front module generally consist of a transparent substrate, a transparent conductive film formed on the surface of the substrate facing the liquid crystal cell, and a polarizing plate disposed on the opposite side. Here, the polarizing plate is disposed on the side facing the backlight source in the rear module, and on the side where an image is displayed (the viewing side) in the front module.

[0109] The liquid crystal display device of the present invention comprises at least a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates. The liquid crystal display device may also include other components, such as a color filter, a lens film, a diffusion sheet, an anti-reflection film, etc. It is preferable that at least one of the two polarizing plates is the polarizing plate of the present invention.

[0110] The backlight may be configured as an edge light type having a light guide plate, a reflector, etc. as constituent members, or as a direct type.

[0111] The backlight light source to be mounted in the liquid crystal display device of the present invention is not particularly limited, but a white light source having a peak top of the emission spectrum in each of the wavelength regions of 400 nm or more and less than 495 nm, 495 nm or more and less than 600 nm, and 600 nm or more and less than 780 nm can be preferably used. Examples of such light sources include a white light source utilizing quantum dot technology, a phosphor-type white LED light source using a blue LED and a phosphor having emission peaks in the R (red) and G (green) regions by excitation light, a three-wavelength white LED light source, a white LED light source combined with a red laser, a blue light-emitting diode and a phosphor containing at least K ２ SiF ６ : Mn ４＋ Examples of such a light-emitting diode include a white light-emitting diode having a fluoride phosphor (also called "KSF"), which is

[0112] In addition, a phosphor-based white LED, which combines a conventionally used light-emitting diode that uses a compound semiconductor to emit blue or ultraviolet light with a phosphor (for example, an yttrium aluminum garnet yellow phosphor or a terbium aluminum garnet yellow phosphor), can also be preferably used.

[0113] The arrangement of the polarizer protective film made of the polyethylene terephthalate-based resin film of the present invention in a liquid crystal display device is not particularly limited. However, in a liquid crystal display device having a polarizer disposed on the incident light side (light source side), a liquid crystal cell, and a polarizer disposed on the exit light side (viewing side), it is preferable that the polarizer protective film on the incident light side of the polarizer disposed on the incident light side and / or the polarizer protective film on the exit light side of the polarizer disposed on the exit light side be a polarizer protective film made of the polyethylene terephthalate-based resin film of the present invention. A particularly preferred embodiment is one in which the polarizer protective film on the exit light side of the polarizer disposed on the exit light side is the polyethylene terephthalate-based resin film of the present invention. Arranging a polarizer protective film made of the polyethylene terephthalate-based resin film in a position other than the above may change the polarization properties of the liquid crystal cell. Since it is not preferable to use a polarizer protective film made of the polyethylene terephthalate-based resin film of the present invention in a location where polarization properties are required, it is preferable to use the polarizer protective film made of the polyethylene terephthalate-based resin film of the present invention as a protective film for a polarizer in such a specific position.

[0114] The screen size of the liquid crystal display device of the present invention is not particularly limited, but is preferably 32 inches (diagonal length 32 inches) or larger, more preferably 42 inches or larger, and particularly preferably 50 inches or larger.

[0115] 5. Organic EL Display Device A circular polarizer is preferably disposed on the viewing side of the organic EL display device. External light may be reflected by the metal electrode of the organic EL cell and emitted to the viewing side, causing the display surface of the organic EL display device to appear as a mirror when viewed from the outside. In order to block such specular reflection of external light, a circular polarizer is preferably disposed on the viewing side of the organic EL cell. A polarizer of the present invention described above, laminated with, for example, a quarter-wave plate (quarter-wave layer), can be used as a circular polarizer for an organic EL display device.

[0116] 6. Transparent Conductive Film and Touch Panel A touch panel typically has one or more transparent conductive films. The transparent conductive film has a structure in which a transparent conductive layer is laminated on a substrate film. The polyethylene terephthalate resin film of the present invention can be used as the substrate film. The type and type of the touch panel are not particularly limited, and examples thereof include resistive touch panels and capacitive touch panels.

[0117] The transparent conductive layer may be laminated directly onto the substrate film, or may be laminated via an easy-adhesion layer and / or various other layers. Examples of such other layers include a hard coat layer, an index matching (IM) layer, and a low refractive index layer. The IM layer itself has a high refractive index / low refractive index layer stack structure (the low refractive index layer is on the transparent conductive thin film side), and its use can make the ITO pattern less visible when viewing the LCD screen.

[0118] The transparent conductive layer on the substrate film can be formed from a conductive metal oxide. The conductive metal oxide constituting the transparent conductive layer is not particularly limited, and a conductive metal oxide of at least one metal selected from the group consisting of indium, tin, zinc, gallium, antimony, titanium, silicon, zirconium, magnesium, aluminum, gold, silver, copper, palladium, and tungsten can be used. The metal oxide may further contain a metal atom listed in the above group, if necessary. Preferred transparent conductive layers are, for example, tin-doped indium oxide (ITO) layers and antimony-doped tin oxide (ATO) layers, with ITO layers being preferred. The transparent conductive layer may also be Ag nanowires, Ag ink, a self-assembled conductive film of Ag ink, a mesh electrode, CNT ink, or a conductive polymer. The thickness of the transparent conductive layer is not particularly limited. The transparent conductive layer can be formed according to known procedures. Examples include vacuum deposition, sputtering, and ion plating.

[0119] The transparent conductive film of the present invention may be patterned by removing a portion of the surface of the transparent conductive layer. A transparent conductive film having a patterned transparent conductive layer has a pattern-forming portion where the transparent conductive layer is formed on the substrate film, and a pattern opening portion where the transparent conductive layer is not formed on the substrate film. The shape of the pattern-forming portion may be, for example, a stripe shape or a square shape.

[0120] 7. Shatterproof Film, Surface Protective Film The polyethylene terephthalate resin film of the present invention can be used as a shatterproof film or a surface protective film by laminating it on the viewing side of an image display panel.

[0121] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples, and appropriate modifications can be made within the scope of the present invention, and all such modifications are included in the technical scope of the present invention. The physical properties in the following examples were evaluated as follows.

[0122] (1) Retardation (Re) Retardation is a parameter defined by the product (ΔNxy × d) of the anisotropy of the refractive index of two orthogonal axes on a film (ΔNxy = |nx - ny|) and the film thickness d (nm), and is a measure of optical isotropy and anisotropy. The anisotropy of the biaxial refractive index (ΔNxy) was determined by the following method. Using a molecular orientation meter (MOA-6004 molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.), the slow axis direction of the film was determined, and a 4 cm × 2 cm rectangle was cut out so that the slow axis direction was parallel to the long side of the measurement sample, and used as a measurement sample. For this sample, the refractive index of two orthogonal axes (refractive index in the slow axis direction: ny, refractive index in the direction perpendicular to the slow axis direction: nx) and the refractive index in the thickness direction (nz) were measured using an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-4T, measurement wavelength 589 nm), and the absolute value of the difference in refractive index between the two axes (|nx-ny|) was taken as the refractive index anisotropy (ΔNxy). The film thickness d (nm) was measured using an electric micrometer (manufactured by Fine Rufu Co., Ltd., Millitron 1245D) and converted to units in nm. The retardation (Re) was calculated from the product (ΔNxy × d) of the refractive index anisotropy (ΔNxy) and the film thickness d (nm).

[0123] (2) Mesophase Orientation Parameter The mesophase orientation parameter of a polyethylene terephthalate resin film is expressed by the above formula (1), and is a 1457 cm in the slow axis direction obtained by Fourier transform infrared spectroscopy (ATR-FTIR) using a Fourier transform infrared spectrophotometer (FTS 60A / 896, manufactured by Varian). －１ Absorbance A at １４５７－ｓｌｏｗ , 795 cm in the slow axis direction －１ Absorbance A at ７９５－ｓｌｏｗ , 1457 cm in the fast axis direction －１ Absorbance A at １４５７－ｆａｓｔ , 795 cm in the fast axis direction －１ Absorbance A at ７９５－ｆａｓｔThe ATR-FTIR measurement was carried out with a polarizer inserted in the optical system, using a diamond crystal as the ATR prism, and setting the angle of incidence at 45 degrees. At this time, the slow axis of the film was positioned so as to be parallel to the transmission axis of the polarizer inserted in the optical system, and each wave number ν (cm －１ Infrared absorption spectrum A ｓｌｏｗ In addition, the fast axis of the film was arranged parallel to the transmission axis of the polarizer inserted in the optical system, and each wave number ν (cm －１ Infrared absorption spectrum A ｆａｓｔ The number of integrations was set to 64 for both the sample and background, and the wavenumber resolution was set to 2 cm －１ , measurement wave number range 650 to 4000 cm －１ The infrared absorption spectrum obtained by ATR-FTIR measurement has a curved baseline due to the difference in the penetration depth into the sample depending on the wave number. －１ ) to the absorbance at the maximum wavenumber ν ＭＡＸ (cm －１ ) and each wave number ν (cm －１ ) ratio ν ＭＡＸ Baseline correction was performed by multiplying / ν. In each infrared absorption spectrum after baseline correction, －１ The absorbance at A １４５７－ｓｌｏｗ Or A １４５７－ｆａｓｔ , 792.7415cm －１ The absorbance at A ７９５－ｓｌｏｗ Or A ７９５－ｆａｓｔ The absorbance was adopted as the absorbance. Here, the absorbance refers to the absolute value of the absorption intensity at the relevant wave number in the infrared absorption spectrum after baseline correction. In the above measurement, the slow axis direction of the film was determined using a molecular orientation meter (MOA-6004 molecular orientation meter manufactured by Oji Scientific Instruments Co., Ltd.). The direction perpendicular to the slow axis direction in the film plane was defined as the fast axis direction.

[0124] (3) Elastic Modulus in the Slow Axis Direction The elastic modulus in the slow axis direction was evaluated by a tensile test in accordance with Section 10.3.2 of JIS K7161. The test specimen was cut into a rectangular shape of 180 mm x 10 mm, with the long side being the direction of the slow axis obtained during the measurement of retardation (Re). 10 mm long benchmark lines parallel to the short sides were drawn 40 mm inward from both short sides of the test specimen, and the thickness (mm) of the test specimen was measured at five points in a 100 mm long section between the benchmark lines, and the average value was calculated. The product of this and the width (10 mm) of the test specimen was calculated as the cross-sectional area (mm) of the test specimen. ２ ) The thickness of the film was measured using an electric micrometer (Militron 1245D, manufactured by Fine Leaf Co., Ltd.). The tensile test was carried out by gripping the area from the benchmark line to the short side with a chuck so that the long side direction of the test piece was the tensile direction. A precision universal testing machine (Autograph AGX-V, manufactured by Shimadzu Corporation) was used for the tensile test, with a chuck distance of 100 mm and a tensile speed of 100 mm / min. Each measured value of the load (N) was used to calculate the initial cross-sectional area (mm ２ The nominal stress (MPa) was calculated by dividing the stroke (mm) of the chuck distance when each load measurement was obtained by the initial chuck distance of 100 mm. The nominal strain was calculated by dividing the stroke (mm) of the chuck distance when each load measurement was obtained by the initial chuck distance of 100 mm. The slope of the nominal stress-nominal strain curve between the nominal strains of 0.0005 and 0.0025 was calculated to obtain the modulus of elasticity (MPa) in the slow axis direction. A pneumatic chuck (manufactured by A&D Co., Ltd., a parallel clamping type air jaw J-JFA1-1KN-09 with a face J-FFA3W-1KN attached) was used, and the air pressure was 0.5 MPa. The measurements were performed without applying a preliminary force to remove slack from the test specimen.

[0125] (4) Ratio of Elastic Modulus in the Slow Axis Direction to that in the Fast Axis Direction The elastic modulus (MPa) in the fast axis direction was obtained in the same manner as in the elastic modulus in the slow axis direction. The obtained elastic modulus E in the slow axis direction ＴＤ and the elastic modulus E in the fast axis direction ＭＤ Using the above, the ratio of the elastic modulus in the slow axis direction to the elastic modulus in the fast axis direction E ＴＤ / E ＭＤ asked for.

[0126] (5) Breaking Strength in the Slow Axis Direction The breaking strength in the slow axis direction was evaluated by a tensile test in accordance with Section 7.2 of JIS C2318. In the nominal stress-nominal strain curve obtained by measuring the elastic modulus in the slow axis direction, the load at break (N) was calculated as a function of the cross-sectional area (mm ２ ) to obtain the breaking strength (MPa) in the slow axis direction.

[0127] (6) Planar Orientation Coefficient (ΔP) Using the refractive index value obtained during the measurement of retardation (Re), the value obtained from (nx+ny) / 2−nz was taken as the plane orientation coefficient (ΔP).

[0128] (7) Rigid Amorphous Fraction The rigid amorphous fraction is represented by the above formula (2) and is indirectly calculated from the values ​​of the mobile amorphous fraction and the mass fraction crystallinity.

[0129] The mobile amorphous fraction is a parameter defined by the reversible heat capacity difference ΔCp (J / (g·K)) at Tg of the reversible heat capacity curve obtained by temperature-modulated DSC measurement using a differential scanning calorimeter (TA Instrument, Q100), as follows: ((ΔCp of sample) / (ΔCp of completely amorphous)) × 100 (mass%). In the case of polyethylene terephthalate, the completely amorphous ΔCp = 0.4052 (J / (g·K)). The sample was weighed at 2.0 ± 0.2 mg in an aluminum pan and measured in MDSC (registered trademark) heat-only mode at an average heating rate of 5.0 °C / min and a modulation period of 60 seconds. Measurement data was collected at a sampling frequency of 5 Hz. Indium was used to calibrate the temperature and calorific value, and sapphire was used to calibrate the specific heat.

[0130] The calculation method for Tg and ΔCp is described below. First, the first derivative F'(T) of the reversible heat capacity curve F(T) with respect to temperature T was plotted, and a moving average was taken every 2401 points to perform a smoothing process. Tg was then determined by reading the temperature value at the peak top. Next, a straight line G(T) passing through two points, point A (Tg-15, F(Tg-15)) and point B (Tg+15, F(Tg+15)), was determined. Next, the temperature at which F(T) - G(T) was minimum within the range of Tg-15≦T≦Tg+15 was defined as T1, and the temperature at which it was maximum was defined as T2. Here, T1 corresponds to the glass transition start temperature, and T2 corresponds to the glass transition end temperature, so the value of ΔCp was obtained by ΔCp = F(T2) - F(T1).

[0131] The mass fraction crystallinity χ is the density value d (g / cm) obtained using a water / calcium nitrate density gradient tube in accordance with JIS K7112. ３ ) was used to calculate the density using the following formula: χ = (dc / d) × ((d-da) / (d-dc)) × 100 (mass%), where dc is the density of a completely crystalline material, and da is the density of a completely amorphous material. In the case of polyethylene terephthalate, dc = 1.498 (g / cm ３ ), da=1.335 (g / cm ３ )

[0132] (8) Operational stability during slitting A polyethylene terephthalate resin film prepared by the method described below was wound onto a jumbo roll, and then slit into a 1000 mm wide area centered on the center of the jumbo roll. The operational stability was evaluated based on the number of breaks. The cutting blade used for slitting was a blade that had been used to cut a conventional film equivalent to a comparative example, and had been removed after exceeding the specified usage amount and reassembled. The running speed was 90% of the maximum speed designed for the slitter. ○: No breaks occurred per day. △: One break occurred per day. ×: Two or more breaks occurred per day.

[0133] (9) Product Roll Edges after Slitting The polyethylene terephthalate resin film prepared by the method described below was wound onto a jumbo roll, and then unwound using a slitter at a winding speed of 185 m / min. A 1000 mm wide area was cut out from the center of the jumbo roll, and the film was wound into a product roll with a winding length of 2000 m under a winding tension of 150 N / m and a winding contact pressure of 130 N / m without knurling the ends. The amount of edge height was evaluated. At both ends of the product roll, the height of the outermost end, with a position 100 mm inside from the end as the reference (0 mm), was measured as the amount of edge height, and the average value of the amount of edge height at both ends was calculated. The winding tension was the tension when the film was wound into a roll around a cylindrical core, and the winding contact pressure was the winding contact pressure of the touch roll when the film was pressed against the touch roll during winding. ◎: The amount of raised edges was within 1.0 mm. ○: The amount of raised edges was within 2.0 mm. ×: The amount of raised edges was greater than 2.0 mm.

[0134] (10) Iridescence Observation A polarizing plate was prepared by attaching a polyethylene terephthalate resin film prepared by the method described below to one side of a polarizer made of PVA and iodine so that the absorption axis of the polarizer was perpendicular to the main orientation axis of the film, and attaching a commercially available TAC film to the opposite side. The resulting polarizing plate was used to replace the polarizing plate originally installed on the output side of a commercially available liquid crystal display device (manufactured by Sharp Corporation, LC32DZ3). The polarizing plate was replaced so that the polyethylene terephthalate resin film was on the viewing side, and the absorption axis of the polarizing plate was aligned with the absorption axis direction of the polarizing plate originally attached to the liquid crystal display device. The liquid crystal display device had a white LED as a backlight source, consisting of a light-emitting element combining a blue-light-emitting diode and an yttrium-aluminum-garnet yellow phosphor.

[0135] A white image was displayed on the liquid crystal display device thus produced, and visual observation was made from the front of the display and from oblique angles, and the occurrence of rainbow spots was judged as follows. The observation angle was defined as the angle between a line drawn normal (perpendicular) from the center of the display screen and a line connecting the center of the display and the position of the eyes at the time of observation. ◎: No rainbow spots were observed within an observation angle range of 0 to 60 degrees. ○: Partially faint rainbow spots were observed within an observation angle range of 0 to 60 degrees. ×: Clear rainbow spots were observed within an observation angle range of 0 to 60 degrees.

[0136] (11) Three-dimensional surface roughness Using a stylus-type three-dimensional roughness meter (SE-3AK, manufactured by Kosaka Laboratory Co., Ltd.), measurements were taken over a measurement length of 1 mm with a cutoff value of 0.25 mm in the longitudinal direction of the film under conditions of a needle radius of 2 μm and a load of 30 mg, at a needle feed rate of 0.1 mm / sec. The film was divided into 500 points at a 2 μm pitch, and the height of each point was captured into a three-dimensional roughness analyzer (SPA-11). The same operation was performed continuously 150 times at 2 μm intervals across the width of the film, i.e., over a width of 0.3 mm across the film, and the data was captured into the analyzer. Next, the center surface average roughness (SRa) and ten-point average surface roughness (SRz) were determined using the analyzer. The measurement was performed three times, and the average value was used.

[0137] (12) Haze The haze of the film was measured according to JIS-K7105 using a turbidity meter (NHD2000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0138] (13) Inspection of foreign matter in film A test polarizer is placed on the side of the prepared polarizer facing the high Re polarizer protective film, so that it is in a cross-Nicol state with the prepared polarizer. The test polarizer is selected to be a TAC film with no phase difference on both sides, and free of scratches and foreign matter. In this state, inspection is performed using a Nikon universal projector V-12 (projection lens 50x, transmitted illumination light beam switching knob 50x, transmitted light inspection). If foreign matter is present in the high Re polarizer protective film, light will transmit through that area and appear to shine. The number of areas with a major axis of 100 μm or more, less than 100 μm but 50 μm or more, and less than 50 μm but 20 μm or more is counted, and the total number of each area across the entire polarizer is calculated.

[0139] When the major axis could not be distinguished, the defective portion due to the foreign matter detected by the above-mentioned method was cut out from the polarizing plate and observed under a polarizing microscope at a higher magnification to determine the major axis, with the high Re polarizer protective film side of the polarizing plate facing upward and the polarization direction parallel to the polarization direction of the polarizer on the light source side of the polarizing microscope.

[0140] (14) Amount of Antimony Atoms in Residue: After removing the adhesive layer on the film surface with a razor, the film was cut into small pieces with scissors. 0.1 g of these small pieces was dissolved in 20 mL of a 60 / 40 (weight ratio) mixed solvent of parachlorophenol and tetrachloroethane. The solution was then filtered by water-flow suction filtration using a hydrophilic PTFE membrane filter (H010A047A, manufactured by Advantec Co., Ltd.) with an average pore size of 0.1 μm. After filtration, the filter was recovered, and the residue on the filter was dissolved in nitric acid to a constant volume to obtain the test solution. Sample preparation was performed in triplicate for each sample. Sb in the test solution was measured using a high-resolution inductively coupled plasma mass spectrometer (HR-ICP-MS, manufactured by Thermo Fisher Scientific Co., Ltd.).

[0141] (Production Example 1 - Polyester A) The esterification reactor was heated to 200°C, and 86.4 parts by mass of terephthalic acid and 64.6 parts by mass of ethylene glycol were charged. While stirring, 0.017 parts by mass of antimony trioxide, 0.064 parts by mass of magnesium acetate tetrahydrate, and 0.16 parts by mass of triethylamine were charged as catalysts. The temperature was then increased under pressure, and a pressurized esterification reaction was carried out at a gauge pressure of 0.34 MPa and 240°C. The esterification reactor was then returned to normal pressure, and 0.014 parts by mass of phosphoric acid was added. The temperature was then increased to 260°C over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. After 15 minutes, the mixture was dispersed using a high-pressure disperser. After 15 minutes, the resulting esterification reaction product was transferred to a polycondensation reactor, and a polycondensation reaction was carried out under reduced pressure at 280°C.

[0142] After the polycondensation reaction was completed, the resin was filtered through a Naslon filter with a 95% cutoff diameter of 5 μm, extruded from a nozzle in the form of a strand, cooled and solidified using cooling water that had been previously filtered (pore diameter: 1 μm or less), and cut into pellets. The intrinsic viscosity of the resulting polyethylene terephthalate resin (A) was 0.62 dl / g, and it contained substantially no inert particles or internally precipitated particles. (Hereinafter, this will be referred to as PET (A)).

[0143] (Production Example 2 - Polyester B) 10 parts by mass of dried ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one) and 90 parts by mass of particle-free PET (A) (intrinsic viscosity of 0.62 dL / g) were mixed and the mixture was kneaded using an extruder to obtain ultraviolet absorber-containing polyethylene terephthalate resin (B) (hereinafter abbreviated as PET (B)). Polyester B was filtered using a Naslon filter (nominal filtration accuracy: 95% cutoff of 5 μm particles) provided in a melting line for extruding into a strand shape.

[0144] (Production Example 3 - Preparation of Adhesion-Modifying Coating Liquid) By carrying out a transesterification reaction and a polycondensation reaction by a conventional method, the dicarboxylic acid component (relative to the total dicarboxylic acid component) was 46 mol% terephthalic acid, 46 mol% isophthalic acid, and 8 mol% sodium 5-sulfonatoisophthalate, and the glycol component (relative to the total glycol component) was 50 mol% ethylene glycol and 50 mol% neopentyl glycol. A water-dispersible sulfonate metal base-containing copolymerized polyester resin was prepared. Next, 51.4 parts by mass of water, 38 parts by mass of isopropyl alcohol, 5 parts by mass of n-butyl cellosolve, and 0.06 parts by mass of a nonionic surfactant were mixed, and then heated and stirred. When the temperature reached 77 ° C., 5 parts by mass of the water-dispersible sulfonate metal base-containing copolymerized polyester resin was added, and the mixture was stirred until no lumps of resin remained. The resin aqueous dispersion was then cooled to room temperature to obtain a uniform water-dispersible copolymerized polyester resin solution having a solids concentration of 5.0% by mass. Furthermore, 3 parts by mass of aggregated silica particles (Sylysia 310, manufactured by Fuji Silysia Co., Ltd.) were dispersed in 50 parts by mass of water, and then 0.54 parts by mass of an aqueous dispersion of Sylysia 310 was added to 99.46 parts by mass of the water-dispersible copolymer polyester resin solution, and 20 parts by mass of water was added with stirring to obtain an adhesive property-modifying coating solution. The coating solution was filtered through a cartridge filter with a 95% separation particle size of 10 μm.

[0145] (Example 1) As the raw material for the intermediate layer of the base film, 90 parts by mass of particle-free PET (A) resin pellets and 10 parts by mass of PET (B) resin pellets containing an ultraviolet absorber were dried under reduced pressure (1 Torr) at 135 ° C for 6 hours, and then fed to extruder 2 (for intermediate layer II layer), and PET (A) was dried by a conventional method and fed to extruder 1 (for outer layer I layer and outer layer III layer), respectively, and melted at 285 ° C. These two polymers were each filtered through a stainless steel sintered filter material (nominal filtration accuracy 10 μm particle 95% cut) and stacked in a two-type three-layer confluence block, and extruded into a sheet form from a die, and then wrapped around a casting drum with a surface temperature of 30 ° C using an electrostatic casting method, cooled and solidified, and an unstretched film was produced. At this time, the discharge amount of each extruder was adjusted so that the thickness ratio of layer I, layer II, and layer III was 10:80:10.

[0146] Next, a coating amount of 0.08 g / m2 was applied to both sides of the unstretched PET film by the reverse roll method. ２ After applying the adhesive property modifying coating solution so that the adhesive property modifying coating solution 1 became 10 μm, the coating solution was dried for 20 seconds at 80° C. During the application, a cartridge filter with a 95% separation particle size of 10 μm was installed in the line sending the coating solution 1 to the coating die to remove particle aggregates.

[0147] The unstretched film with this coating layer formed was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at a temperature of 138°C to preheat, and then stretched in the width direction to 5.0 times its original size at a temperature of 90°C and a strain rate of 17.2% / sec. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at a temperature of 210°C, and then introduced into a hot air zone at a temperature of 160°C, where it was further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a film thickness of approximately 65 μm.

[0148] In the production, the difference between the inner diameter of the gasket at the joint of the flange of the pipe through which the molten resin passed and the inner diameter of the pipe was 50 μm or less. At the start of operation, resin was discharged three times for 5 minutes at a flow rate 1.2 times the set resin extrusion rate, and then film production began. Film samples were taken 30 minutes after the start of production. The filter element was also replaced with a cleaned one at the start of operation.

[0149] Example 2 An unstretched film (having a coating layer formed thereon) prepared in the same manner as in Example 1 was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at a temperature of 132°C to preheat, and then stretched in the width direction to 5.0 times its original size at a temperature of 90°C and a strain rate of 17.2% / sec. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at a temperature of 210°C, and then introduced into a hot air zone at a temperature of 160°C, where it was further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a thickness of approximately 65 μm.

[0150] An unstretched film (having a coating layer formed thereon) prepared in the same manner as in Example 1 except for changing the film thickness was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at a temperature of 130°C to preheat, and then stretched in the width direction to 5.8 times its original size at a temperature of 90°C and a strain rate of 20.0% / sec. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at a temperature of 200°C, and then introduced into a hot air zone at a temperature of 140°C, where it was further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a film thickness of approximately 40 μm.

[0151] Example 4 An unstretched film (having a coating layer formed thereon) prepared in the same manner as in Example 1 except for changing the film thickness was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at a temperature of 120°C to preheat, and then stretched in the width direction to 5.6 times its original size at a temperature of 102°C and a strain rate of 39.3% / sec. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at a temperature of 180°C, and then introduced into a hot air zone at a temperature of 160°C, where it was further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a film thickness of approximately 50 μm.

[0152] Example 5 An unstretched film (having a coating layer formed thereon) produced in the same manner as in Example 1 except for changing the film thickness was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at a temperature of 100°C to preheat, and then stretched in the width direction to 4.5 times its original size at a temperature of 90°C and a strain rate of 25.2% / sec. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at a temperature of 200°C, and then introduced into a hot air zone at a temperature of 160°C, where it was further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a film thickness of approximately 60 μm.

[0153] Comparative Example 1 An unstretched film (having a coating layer formed thereon) prepared in the same manner as in Example 1 except for changing the film thickness was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at 100°C to preheat and then stretched in the width direction to 5.0 times its original size at a strain rate of 34.6% / sec at 100°C. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at 180°C, and then introduced into the hot air zone at 180°C and further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a film thickness of approximately 60 μm.

[0154] Comparative Example 2 A uniaxially oriented PET film having a thickness of about 65 μm was obtained in the same manner as in Example 2, except that the temperature during stretching was 80° C.

[0155] Comparative Example 3 An unstretched film (having a coating layer formed thereon) prepared in the same manner as in Example 1 except for changing the film thickness was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at a temperature of 138°C to preheat, and then stretched in the width direction to 5.8 times its original size at a temperature of 90°C and a strain rate of 49.2% / sec. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at a temperature of 190°C, and then introduced into the hot air zone at a temperature of 190°C, where it was further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a film thickness of approximately 50 μm.

[0156] Comparative Example 4 An unstretched film (having a coating layer formed thereon) prepared in the same manner as in Example 1 except for changing the film thickness was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at a temperature of 115°C to preheat, and then stretched in the width direction to 5.6 times its original size at a temperature of 102°C and a strain rate of 39.3% / sec. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at a temperature of 180°C, and then introduced into the hot air zone at a temperature of 180°C, where it was further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a film thickness of approximately 25 μm.

[0157] Comparative Example 5 An unstretched film (having a coating layer formed thereon) prepared in the same manner as in Example 1 except for changing the film thickness was introduced into a tenter stretching machine, and while the edges of the film were held with clips, it was introduced into a hot air zone at a temperature of 90°C to preheat, and then stretched in the width direction to 4.5 times its original size at a temperature of 90°C and a strain rate of 25.2% / sec. Next, while maintaining the width stretched in the width direction, it was heat-treated in a hot air zone at a temperature of 200°C, and then introduced into a hot air zone at a temperature of 160°C, where it was further relaxed by 3% in the width direction to obtain a uniaxially oriented PET film with a film thickness of approximately 60 μm.

[0158] The results of measurements on the PET films obtained in the Examples and Comparative Examples are shown in Table 1.

[0159] When the amount of fine powder adhering to the equipment near the cutting blade after slitting was checked, the amount of fine powder was small in each example, but a large amount was observed in the comparative example. Furthermore, when the surface roughness, foreign matter, and haze were measured using the film of Example 1 as a representative, the results were as follows: SRa: 2 nm or less, SRz: 28 nm, haze: 0.7%, number of foreign matter particles of 100 μm or less: 0, number of foreign matter particles of 50 μm or more but less than 100 μm: 0, number of foreign matter particles of 20 μm or more but less than 50 μm: 1, and amount of Sb atoms: 2 ppm.

[0160]

[0161] According to the present invention, a polyethylene terephthalate-based resin film having excellent processability and capable of effectively suppressing breakage and edge formation during slitting can be provided. Furthermore, a polarizing plate, a transparent conductive film, a touch panel, and an image display device such as a liquid crystal display device or an organic EL display device can be provided using the polyethylene terephthalate-based resin film.

Claims

1. A polyethylene terephthalate resin film that satisfies the following (1) and (2): (1) The polyethylene terephthalate resin film has a retardation of 3,000 to 30,000 nm. (2) The mesophase orientation parameter of the polyethylene terephthalate resin film measured by the ATR-FTIR method, which is expressed by the following formula, is 0.275 or more. (mesophase orientation parameter) = R ｓｌｏｗ / R ｆａｓｔ However, R ｓｌｏｗ = (1457 cm in the slow axis direction) －１ absorbance at 795 cm in the slow axis direction) / (absorbance at 795 cm in the slow axis direction) －１ absorbance at ｆａｓｔ = (1457 cm in the fast axis direction) －１ absorbance at 795 cm in the fast axis direction) / (absorbance at 795 cm in the fast axis direction) －１ (absorbance at 1000 Hz).

2. The polyethylene terephthalate resin film according to claim 1, further satisfying the following (3) and (4): (3) The elastic modulus in the slow axis direction is 8600 MPa or less. (4) The ratio of the elastic modulus in the slow axis direction to the elastic modulus in the fast axis direction is 3.6 or less.

3. The polyethylene terephthalate resin film according to claim 1, further satisfying the following (5): (5) The breaking strength in the slow axis direction is 450 MPa or less.

4. The polyethylene terephthalate resin film according to claim 1, further satisfying the following (6): (6) The rigid amorphous fraction expressed by the following formula is 33% by mass or more. (Rigid amorphous fraction (mass %)) = 100 - (mobile amorphous fraction (mass %)) - (mass fraction crystallinity (mass %))

5. A polarizing plate comprising the polyethylene terephthalate resin film according to any one of claims 1 to 4 laminated on at least one surface of a polarizer as a polarizer protective film.

6. An image display device comprising the polarizing plate according to claim 5 .

7. A liquid crystal display device having a backlight source, two polarizing plates, and a liquid crystal cell disposed between the two polarizing plates, A liquid crystal display device, wherein at least one of the two polarizing plates is the polarizing plate according to claim 5 .

8. An organic EL display device comprising the polarizing plate according to claim 5 .

9. A transparent conductive film having the polyethylene terephthalate resin film according to any one of claims 1 to 4 as a substrate film of the transparent conductive film.

10. A touch panel comprising the transparent conductive film according to claim 9.

11. An image display device having the polyethylene terephthalate resin film according to any one of claims 1 to 4 as a shatterproof film or a surface protective film on the viewing side of an image display panel.