Polyester film and its applications

Abstract

To provide a polyester film suitable for use as a polarizer protective film by reducing the number of whisker-like defects present on the slit end faces of the film. [Solution] A polyester film in which the number of whisker-like particles protruding 5 μm or more on the edge surface of the film slit along the machine direction during film production is one or less per 100 μm of film length. The polyester film for polarizer protective film has an in-plane retardation of 3,000 nm or more and 30,000 nm or less. Also, the polyester film is used in polarizing plates and liquid crystal displays.

Description

[Technical Field] 【0001】 The present invention relates to a polyester film that is slit along the machine flow direction during film manufacturing and has few whisker-like defects on the slit end faces, and more specifically, to a polyester film for polarizer protective films with few whisker-like defects on the slit end faces, a polarizer plate using the same, and a liquid crystal display device. [Background technology] 【0002】 Polarizing plates used in liquid crystal displays (LCDs) typically consist of a polarizer, made of polyvinyl alcohol (PVA) or similar material dyed with iodine, sandwiched between two polarizer protective films. Triacetylcellulose (TAC) film is commonly used as the polarizer protective film. In recent years, with the miniaturization and cost reduction of LCDs, there has been a demand for thinner polarizing plates. However, reducing the thickness of the TAC film used as the polarizer protective film results in insufficient mechanical strength and poor moisture permeability. Furthermore, TAC film is very expensive, creating a strong need for inexpensive alternative materials. 【0003】 Polyester film offers superior durability compared to TAC film, but unlike TAC film, it possesses birefringence. Therefore, when used as a polarizer protective film, it suffers from a problem of reduced image quality due to optical distortion. Specifically, because birefringent polyester film has a certain optical anisotropy (retardation), when used as a polarizer protective film, it produces rainbow-like color patterns when viewed from an oblique angle, resulting in reduced image quality. Therefore, Patent Document 1 addresses color unevenness by controlling the in-plane retardation of the polyester film to a specific range. 【0004】 Furthermore, in the manufacture of TAC films and polyester films, in which molecules are oriented in the stretching direction, the film thickness is uneven at both ends in the width direction and is cut off by a cutting device (slitter) after manufacturing (slitting process). However, due to the orientation of the molecular chains constituting the film, hair-like structures and fuzz appear at the slit ends of the film, leading to problems such as an increase in foreign matter and film breakage during cutting. Therefore, Patent Document 2 proposes a method to solve the above problems by using a cutting technique. 【0005】 On the other hand, waste film is generated during the manufacture of polyester film. Methods for reusing or recycling waste film, such as film edges removed from products, have been attempted. However, when films with coating layers such as easy-adhesion resins or antistatic resins are recycled and recycled polyester raw materials are used as the main component, the components of the coating layer deteriorate due to heat, resulting in the obtained film becoming significantly discolored or cloudy. For this reason, Patent Document 3 proposes a method for obtaining a transparent polyester film with minimal discoloration that includes self-recovered raw materials. 【0006】 However, Patent Document 2 does not contain any knowledge regarding polyester films, making its applicability questionable. Furthermore, Patent Document 3 has the drawback that, when considering application to optical applications, the hurdle of generating internal foreign matter by adding self-recovered raw materials is high, and in the increasingly complex (diversified) composition of coating layers in recent years, the inclusion of crosslinked components and other substances hinders recovery and becomes a source of internal foreign matter. In addition, a complicated separate process was required in which the coating layer of the polyester film that would become the self-recovered raw material was removed by one method, leaving only the base polyester film, and then melt-extruded and pelletized to obtain the recycled raw material. [Prior art documents] [Patent Documents] 【0007】 [Patent Document 1] International Publication No. 2011 / 162198 [Patent Document 2] Japanese Patent Publication No. 2017-109262 [Patent Document 3] Japanese Patent Publication No. 2013-039764 [Overview of the project] [Problems that the invention aims to solve] 【0008】 This invention was made against the backdrop of the problems of the prior art described above. Specifically, the object of this invention is to eliminate the above-mentioned drawbacks, and in particular to provide a polyester film that can be suitably used as a polarizer protective film by reducing the number of hairline defects on the slit end faces of the film. 【0009】 The inventors of this invention arrived at this present invention as a result of diligent research to achieve the above objective. In other words, the present invention has the following configuration. 1. A polyester film having a laminated structure of three or more layers, wherein the intrinsic viscosity of the polyester constituting the intermediate layer is less than the intrinsic viscosity of the polyester constituting both surface layers, the intrinsic viscosity of both surface layers is 0.64 dl / g or more and 0.67 dl / g or less, and the intrinsic viscosity of the intermediate layer is 0.56 dl / g or more and 0.60 dl / g or less. A polyester film in which the number of hair-like structures protruding 5 μm or more from the end face of the film slit along the machine flow direction during film manufacturing is no more than one per 100 μm of film length, and the thickness variation rate in the width direction is 5% or less. 2. The polyester film according to the first paragraph above, wherein the intrinsic viscosity is 0.55 dl / g or more and 0.65 dl / g or less. 3. The polyester film according to the first or second above, wherein the haze value is 2.0% or less and the b value is between -0.5 and 3.0. 4. A polyester film according to any of the above 1 to 3, having a thickness of 15 μm or more and 300 μm or less. 5. A polyester film according to any one of the above 1 to 4, wherein a portion of the polyester constituting the polyester film contains a self-recovered polymer generated during the process of manufacturing the polyester film. The sixth item above. A polyester film according to any one of the first to fifth items above, having a coating layer on at least one side. 7, MediumA polyester film according to any one of the above 1 to 6, comprising a self-recovered polymer generated in the process of manufacturing the polyester film in the interlayer. 8. A polyester film according to any of the above 1 to 7, which is a uniaxially oriented film. 9. A polyester film for polarizer protective films according to any of the above 1 to 8, wherein the in-plane retardation is 3000 nm or more and 30000 nm or less. 10. A polarizing plate in which the polyester film for polarizer protective film described in item 9 above is laminated on at least one surface of the polarizer. 11. A liquid crystal display device having a backlight, a liquid crystal cell, and polarizing plates disposed on both sides of the liquid crystal cell, wherein at least one of the polarizing plates is the polarizing plate described in 10 above. [Effects of the Invention] 【0010】 The present invention provides a polyester film roll with fewer hair-like structures on the slit end face, reducing the factors that cause drawbacks and making it more suitable for optical applications, particularly as a protective film for polarizers. [Best Mode for Carrying Out the Invention] 【0011】 The present invention will be described in detail below. 【0012】 (Polyester film) In this invention, the polyester film refers to a film composed of polyester resin, and preferably a polyester film mainly composed of at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Alternatively, it may be a film made of copolymerized polyester, in which a third component monomer is copolymerized with the above-mentioned polyester. Among these polyester films, polyethylene terephthalate film is the most preferred in terms of the balance between physical properties and cost. 【0013】 Further, the polyester film may be single-layer or multi-layer. Also, within the range where the effects of the present invention are achieved, various additives can be contained in the polyester resin in each of these layers as needed. Examples of the additives include antioxidants, light-resistant agents, anti-gelling agents, organic wetting agents, antistatic agents, ultraviolet absorbers, surfactants, and the like. 【0014】 (Coating layer) The polyester film of the present invention preferably has an easily adhesive coating layer laminated on the above-described polyester base film. Usually, a binder resin, lubricant particles, crosslinking agent, surfactant, etc. are contained in the coating layer. 【0015】 Examples of the lubricant particles in the coating layer include (1) inorganic particles such as silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, titanium dioxide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, hydrated halloysite, magnesium carbonate, magnesium hydroxide, etc., and (2) organic particles such as acrylic or methacrylic, vinyl chloride, vinyl acetate, nylon, styrene / acrylic, styrene / butadiene, polystyrene / acrylic, polystyrene / isoprene, methyl methacrylate / butyl methacrylate, melamine, polycarbonate, urea, epoxy, urethane, phenol, diallyl phthalate, polyester, etc. However, silica is particularly preferably used to impart appropriate slipperiness to the coating layer. 【0016】 The average particle size of the lubricant particles is preferably 200 nm or more, more preferably 250 nm or more, still more preferably 300 nm or more, and particularly preferably 350 nm or more. When the average particle size of the lubricant particles is 200 nm or more, it is difficult to aggregate and slipperiness can be ensured, which is preferable. 【0017】 The average particle size of the lubricant particles is preferably 2000 nm or less, more preferably 1500 nm, even more preferably 1000 nm, and particularly preferably 700 nm. An average particle size of 2000 nm or less is preferable because it maintains transparency and prevents particle detachment. 【0018】 Lubricant particles may be surface-treated. Surface treatment methods include physical surface treatments such as plasma discharge treatment and corona discharge treatment, and chemical surface treatments using coupling agents, but the use of coupling agents is preferred. Organoalkoxymetal compounds (e.g., titanium coupling agents, silane coupling agents) are preferably used as coupling agents. Silane coupling agent treatment is particularly effective when the lubricant particles, which are inorganic ultrafine particle fillers, are silica. Surface treatment may be performed in advance before preparing the coating solution, or it may be added as an additive during the preparation of the coating solution and incorporated into the coating layer. 【0019】 The binder resin constituting the coating layer is not particularly limited as long as it provides good adhesion, but specific examples of polymers include polyester resin, acrylic resin, urethane resin, polyvinyl resin (such as polyvinyl alcohol), polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, and starches. Among these, polyester resin, acrylic resin, and urethane resin are preferred from the viewpoint of particle retention and adhesion. Furthermore, polyester resin is optimal when considering compatibility with polyester film. These binder resins may also be used in combination. 【0020】 The polyester resin may be present in the coating layer at 100% by mass of the total solid components, but it is preferable that it is present at 10% to 90% by mass. More preferably, it is present at 20% to 80% by mass. When the polyester resin content is 90% or less, adhesion to the hard coat layer, etc., under high temperature and high humidity conditions is maintained, which is preferable. Conversely, when the content is 10% by mass or more, adhesion to the polyester film under room temperature, high temperature and high humidity conditions is maintained due to the presence of other urethane resins, etc., which is preferable. 【0021】 In the present invention, the coating layer may be formed containing a crosslinking agent in order to form a crosslinked structure within the coating layer. By including a crosslinking agent, adhesion under high temperature and high humidity conditions can be further improved. Specific examples of crosslinking agents include urea-based, epoxy-based, isocyanate-based, oxazoline-based, and carbodiimide-based agents. Among these, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based crosslinking agents are preferred due to their long-term stability of the coating solution and their effect on improving adhesion under high temperature and high humidity treatment. Furthermore, catalysts and the like can be used as needed to promote the crosslinking reaction. 【0022】 The crosslinking agent content in the coating layer is preferably 5% by mass or more and 50% by mass or less of the total solid components. More preferably, it is 10% by mass or more and 40% by mass or less. When it is 5% by mass or more, the strength of the resin in the coating layer is maintained and there is no risk of deterioration of adhesion under high temperature and high humidity, which is preferable. On the other hand, when it is 50% by mass or more, the flexibility of the resin in the coating layer is maintained and adhesion is maintained at room temperature and under high temperature and high humidity, which is preferable. 【0023】 The lubricant particle content in the coating layer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. A lubricant particle content of 0.1% by mass or more in the coating layer is preferable because it maintains appropriate lubricity. 【0024】 The lubricant particle content in the coating layer is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. A lubricant particle content of 20% by mass or less in the coating layer is preferable in terms of transparency because it keeps the haze low. 【0025】 The thickness of the coating layer is preferably 0.001 μm or more, more preferably 0.01 μm or more, even more preferably 0.02 μm or more, and particularly preferably 0.05 μm or more. A coating layer thickness of 0.001 μm or more is preferable because it provides good adhesion. 【0026】 The thickness of the coating layer is preferably 2 μm or less, more preferably 1 μm or less, even more preferably 0.8 μm or less, and particularly preferably 0.5 μm or less. A coating layer thickness of 2 μm or less is preferable because it eliminates the risk of blocking. 【0027】 The coating layer may also contain surfactants to improve leveling during application and to defoam the coating solution. The surfactant can be cationic, anionic, or nonionic, but silicone-based, acetylene glycol-based, or fluorine-based surfactants are preferred. These surfactants should be included in the coating layer to an extent that does not impair the effect of suppressing iridescent coloration or adhesion under fluorescent lighting. 【0028】 To impart other functionalities to the coating layer, various additives may be included, to the extent that they do not impair the effect of suppressing iridescent coloration under fluorescent light or the adhesion. Examples of such additives include fluorescent dyes, fluorescent whitening agents, plasticizers, ultraviolet absorbers, pigment dispersants, antifoaming agents, defoaming agents, and preservatives. 【0029】 As for the coating method, both the so-called in-line coating method, in which the coating is applied simultaneously with the formation of the polyester film, and the so-called off-line coating method, in which the coating is applied separately with a coater after the polyester film has been formed, can be applied. However, the in-line coating method is more efficient and therefore preferable. 【0030】 Any known method can be used to apply the coating solution to the polyester film. Examples include the reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, and curtain coating method. These methods can be used individually or in combination for coating. 【0031】 In the present invention, a method for providing a coating layer on a polyester film includes applying a coating solution containing a solvent, particles, and a resin to the polyester film and drying it. As the solvent, examples include organic solvents such as toluene, water, or a mixture of water and a water-soluble organic solvent. Preferably, from the viewpoint of environmental issues, water alone or a mixture of water and a water-soluble organic solvent is preferred. 【0032】 The solid content concentration of the coating solution depends on the type of binder resin and solvent, but is preferably 2% by mass or more, and more preferably 4% by mass or more. The solid content concentration of the coating solution is preferably 35% by mass or less, and more preferably 15% by mass or less. 【0033】 The drying temperature after coating also depends on the type of binder resin, the type of solvent, the presence or absence of a crosslinking agent, the solid content concentration, etc., but it is preferably 80°C or higher and preferably 250°C or lower. 【0034】 The surface roughness (Ra) of the coated layer is related to the slipperiness of the coated layer surface, and is preferably 0.01 nm or more, more preferably 0.1 nm or more, even more preferably 0.2 nm or more, and particularly preferably 0.5 nm or more. On the other hand, the upper limit of the surface roughness (Ra) of the coated layer is preferably 200 nm or less, more preferably 100 nm or less, even more preferably 80 nm or less, and particularly preferably 50 nm or less. 【0035】 (Manufacturing of polyester film) The polyester film of the present invention can be manufactured according to a general method for manufacturing polyester films. For example, a method may be used in which a non-oriented polyester sheet or film, obtained by melting polyester resin and extruding it into a sheet, is stretched longitudinally using the difference in roll speed at a temperature above the glass transition temperature, or, without the aforementioned longitudinal stretching, is stretched transversely using a tenter at a temperature above the glass transition temperature and then heat-treated. 【0036】 While the polyester film of the present invention is considered to have a wide range of applications, it is particularly suitable for optical films, especially polarizer protective films. 【0037】 For polyester films used to protect polarizers, either uniaxially oriented or biaxially oriented films are acceptable. However, when using a biaxially oriented film as a polarizer protective film, depending on the in-plane retardation of the film, rainbow-like color spots may not be visible when viewed from directly above the film surface, but they may be visible when viewed from an oblique angle. Therefore, caution is necessary. 【0038】 This phenomenon occurs because a biaxially oriented film is composed of refractive index ellipsoids with different refractive indices in the running direction, width direction, and thickness direction, and there is a direction in which retardation becomes zero (the refractive index ellipsoid appears as a perfect circle) depending on the direction of light transmission within the film. Therefore, when observing a liquid crystal display screen from a specific oblique direction, a point where retardation becomes zero may occur, and rainbow-like color spots will appear concentrically around that point. If we let θ be the angle from directly above the film surface (normal direction) to the position where the rainbow-like color spots are visible, this angle θ increases as the birefringence within the film surface increases, making the rainbow-like color spots less visible. Since biaxially oriented films tend to have a smaller angle θ, uniaxially oriented films are preferable because the rainbow-like color spots are less visible. 【0039】 However, in the case of a perfectly uniaxial (uniaxially symmetric) film, the mechanical strength in the direction perpendicular to the orientation direction may be significantly reduced. Therefore, it is also preferable that the present invention has biaxiality (biaxial symmetry) in a range where rainbow-like color spots do not substantially occur, or in a range where rainbow-like color spots do not occur within the viewing angle range required for liquid crystal display screens. 【0040】 Polyester films used for polarizer protective film applications preferably have an in-plane retardation of 3000 to 30000 nm. An in-plane retardation of 3000 nm or higher is preferable because, when used as a polarizer protective film, it does not exhibit strong interference colors when observed from an oblique direction, thus ensuring good visibility. The preferred lower limit for in-plane retardation is 4500 nm, a more preferred lower limit is 5000 nm, an even more preferred lower limit is 6000 nm, a particularly preferred lower limit is 8000 nm, and the most preferred lower limit is 10000 nm. 【0041】 On the other hand, the preferred upper limit for in-plane retardation is 30,000 nm. Even if a polyester film with in-plane retardation exceeding 30,000 nm is used, the effect of further improving visibility is practically saturated. Furthermore, a film with in-plane retardation of 30,000 nm or less is preferable because the film thickness does not become too thick, resulting in good handling as an industrial material. 【0042】 In this invention, in-plane retardation can be determined by measuring the refractive index and thickness in two axial directions, or by using a commercially available automatic birefringence measuring device such as the KOBRA-21ADH (Oji Instruments Co., Ltd.). The measurement wavelength for the refractive index is 589 nm. 【0043】 Specifically, the film-forming conditions for the polyester film of the present invention are as follows: The longitudinal stretching temperature and transverse stretching temperature are preferably 80 to 130°C, and particularly preferably 90 to 120°C. The longitudinal stretching ratio is preferably 1.0 to 3.5 times, and particularly preferably 1.0 to 3.0 times. The transverse stretching ratio is preferably 2.5 to 6.0 times, and particularly preferably 3.0 to 5.5 times. To control in-plane retardation, it is preferable to control the ratio of the longitudinal stretching ratio to the transverse stretching ratio. Increasing the difference between the longitudinal and transverse stretching ratios is preferable as it increases retardation. Setting a lower stretching temperature is also a preferable approach for increasing retardation. In the subsequent heat treatment, the treatment temperature is preferably 100 to 250°C, and particularly preferably 180 to 245°C. 【0044】 To suppress retardation fluctuations, it is preferable to have minimal film thickness variation. Since the stretching temperature and stretching ratio affect film thickness variation, it is preferable to optimize the film formation conditions from the viewpoint of thickness variation. 【0045】 The thickness variation 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. 【0046】 As mentioned above, in-plane retardation of a film can be controlled to a specific range by appropriately setting the stretching ratio, stretching temperature, and film thickness. For example, a larger difference in stretching ratio between the longitudinal and transverse directions, a lower stretching temperature, and a thicker film make it easier to obtain high in-plane retardation. Conversely, a smaller difference in stretching ratio between the longitudinal and transverse directions, a higher stretching temperature, and a thinner film make it easier to obtain low retardation. However, increasing the film thickness tends to increase the phase difference in the thickness direction. Therefore, it is desirable to appropriately set the film thickness within the range described later. In addition to controlling in-plane retardation, it is also preferable to set the final film formation conditions considering the physical properties required for processing. 【0047】 The thickness of the polyester film of the present invention is arbitrary, but is preferably in the range of 15 to 300 μm, more preferably in the range of 20 to 200 μm, and even more preferably in the range of 30 to 150 μm. In principle, it is possible to obtain retardation of 3000 nm or more even with a film thickness of less than 15 μm. However, in that case, the anisotropy of the mechanical properties of the film becomes significant, making it prone to tearing and ripping, which reduces its practicality as an industrial material and is therefore undesirable. The lower limit of a particularly preferred thickness is 35 μm. On the other hand, the upper limit of the thickness of the polarizer protective film is preferably 300 μm or less so that the thickness of the polarizer does not become too thick. From the viewpoint of practicality as a polarizer protective film, the upper limit of the thickness is preferably 200 μm. The upper limit of a particularly preferred thickness is 100 μm, which is about the same as that of a general TAC film. In order to control the in-plane retardation within the range of the present invention even within the above thickness range, polyethylene terephthalate is preferred as the polyester constituting the film. 【0048】 In the present invention, the polyester film is preferably configured to have a light transmittance of 20% or less at a wavelength of 380 nm, in order to suppress the degradation of optically functional dyes such as iodine dyes. A light transmittance of 15% or less at 380 nm is more preferable, 10% or less is even more preferable, and 5% or less is particularly preferable. If the light transmittance is 20% or less, the deterioration of optically functional dyes due to ultraviolet light can be suppressed. The transmittance in the present invention is measured perpendicular to the plane of the film and can be measured using a spectrophotometer. 【0049】 To achieve a transmittance of 20% or less at a wavelength of 380 nm in the polyester film of the present invention, it is desirable to appropriately adjust the type and concentration of the ultraviolet absorber contained in the polyester film, as well as the thickness of the film. The ultraviolet absorber used in the present invention is a known substance. Examples of ultraviolet absorbers include organic ultraviolet absorbers and inorganic ultraviolet absorbers, but organic ultraviolet absorbers are preferred from the viewpoint of transparency. Examples of organic ultraviolet absorbers include benzotriazole-based, benzophenone-based, cyclic iminoester-based, and combinations thereof, but are not particularly limited. However, from the viewpoint of durability, benzotriazole-based and cyclic iminoester-based are particularly preferred. When two or more ultraviolet absorbers are used in combination, ultraviolet light of different wavelengths can be absorbed simultaneously, thereby further improving the ultraviolet absorption effect. 【0050】 Examples of UV absorbers include benzophenone-based UV absorbers, benzotriazole-based UV absorbers, and acrylonitrile. Examples of UV absorbers include 2-[2'-hydroxy-5'-(methacryloyl hydroxypropyl [(methyl)phenyl]-2H-benzotriazole, 2-[2'-hydroxy-5'-( Methacryloyloxyethyl)phenyl]-2H-benzotriazole, 2-[2'-H Droxy-5'-(methacryloyloxypropyl)phenyl]-2H-benzotriazo , 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2',4,4' -Tetrahydroxybenzophenone, 2,4-di-tert-butyl-6-(5-chloro Benzotriazole-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)phen Nol, 2,2'-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6- Examples include (2H-benzotriazole-2-yl)phenol. Cyclic iminoeth Examples of tel-type UV absorbers include 2,2'-(1,4-phenylene)bis(4H-3, 1-Benzoxazinon-4-one), 2-methyl-3,1-benzoxazine-4-one n, 2-butyl-3,1-benzoxazine-4-one, 2-phenyl-3,1-benzo Examples include oxazine-4-one, but the list is not limited to these. 【0051】 Furthermore, while known methods can be combined to incorporate the ultraviolet absorber into the polyester film in the present invention, for example, a masterbatch can be prepared by first blending a dried ultraviolet absorber with polymer raw materials using a kneading extruder, and then mixing a predetermined masterbatch with the polymer raw materials during film formation. 【0052】 At this time, the concentration of the UV absorber in the masterbatch is preferably 5 to 30% by mass in order to uniformly disperse the UV absorber and to formulate it economically. The conditions for preparing the masterbatch are preferably using a kneading extruder, with an extrusion temperature above the melting point of the polyester raw material and below 290°C for 1 to 15 minutes. Above 290°C, the amount of UV absorber decreases significantly, and the viscosity of the masterbatch also decreases significantly. Below 1 minute of extrusion, uniform mixing of the UV absorber becomes difficult. At this time, stabilizers, color adjusters, and antistatic agents may be added as needed. 【0053】 Furthermore, in the present invention, it is preferable to have a multilayer structure of at least three layers for the polyester film, and to add an ultraviolet absorber to the intermediate layer of the film. Specifically, a polyester film with a structure of three or more layers containing an ultraviolet absorber in the intermediate layer can be manufactured as follows: Polyester pellets alone are used for both surfaces, and a masterbatch containing an ultraviolet absorber and polyester pellets are mixed in a predetermined ratio for the intermediate layer. After drying, the mixture is supplied to a known molten lamination extruder, extruded into a sheet from a slit-shaped die, and cooled and solidified on a casting roll to produce an unstretched film. That is, two or more extruders and a manifold or confluence block with three or more layers (for example, a confluence block with a square confluence section) are used to laminate the film layers that constitute both surface layers and the intermediate layer, extrude three or more sheets from a die, and cool on a casting roll to produce an unstretched film. In the present invention, it is preferable to perform high-precision filtration during molten extrusion in order to remove foreign matter contained in the raw polyester that causes optical defects. For high-precision filtration of molten resin, the filter particle size (initial filtration efficiency of 95%) of the filter media is preferably 15 μm or less. A filter particle size of 15 μm or less is preferable because it is sufficient to remove foreign matter larger than 20 μm. 【0054】 In the polyester film of the present invention, it is preferable to use self-recovered polymer raw materials. 【0055】 Here, we describe the method for producing self-recovered raw materials. Scrap film from the film edges, which are slit and cut off in the direction of the machine flow from the product, is crushed and dried at a glass transition temperature of approximately 160°C to remove moisture. The dried crushed film is melted in an extruder and extruded from the die in a strand form, which is then rapidly cooled and solidified with cold water. The solidified strands are cut into pellet shapes with a strand cutter, and then the surface is dried to prevent fusion, thereby obtaining self-recovered pellets. 【0056】 The moisture content after drying is preferably 10 ppm or less. A moisture content of 10 ppm or less is preferable because it prevents accelerated hydrolysis of the polymer and avoids a decrease in intrinsic viscosity. 【0057】 The film at both ends of the master roll has uneven film thickness and poor quality due to clip marks and other factors during transport in the tenter, and is usually cut off. However, when this portion is recovered and used as self-recovered raw material, caution is required because depending on the coating layer laminated on the cut portion, foreign matter may be mixed in, or discoloration or turbidity may occur in the polyester film made using this self-recovered raw material. 【0058】 In the present invention, the coating layer at both ends of the master roll that is slit and cut off is preferably a different coating composition from the one used to laminate a coating layer having properties such as easy adhesion required for the product polyester film suitably used for polarizer protective films as described above. This different coating composition is less likely to cause contamination, discoloration, or turbidity when reintroduced as part of the polyester raw material of the product polyester film. The coating is applied separately without overlapping with the coating layer laminated on the product polyester film, and the portions at both ends of the master roll in the width direction to which the separate coating liquid has been applied are cut off and used as self-recovered raw material. 【0059】 The coating liquid applied separately at both ends in the film width direction is not particularly limited as long as it has a composition that allows for the creation of self-recoverable raw materials. However, considering the stability and safety of the composition used, it is preferable that the coating liquid be a resin composition with water as the main medium. 【0060】 The aqueous coating solution may contain a small amount of organic solvent to help stabilize the coating solution. Examples of such organic solvents include methyl ethyl ketone, acetone, ethyl acetate, tetrahydrofuran, dioxane, cyclohexanone, n-hexane, toluene, xylene, methanol, ethanol, 1-propanol, and 2-propanol. Multiple types of organic solvents may be included. 【0061】 The aqueous coating solution described above may contain known additives, such as heat stabilizers, oxidation stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, and organic or inorganic fine particles, to the extent that they do not impair the effects of the present invention. 【0062】 Any known coating method may be used for application. For example, any method such as reverse coating, gravure coating, microgravure coating, rod coating, die coating, roll coating, roll brushing, spray coating, air knife coating, or curtain coating can be used. 【0063】 In the present invention, the separate coating layers at both ends in the film width direction are applied to at least one side of both ends of the polyester film. However, it is preferable to manufacture the film by applying the coating before the crystal orientation of the polyester film is completed, and then stretching it in at least one direction before completing the crystal orientation of the polyester film, as this method allows the effects of the present invention to be expressed more clearly. 【0064】 The amount to apply is 1 m 2 The amount per unit is preferably 2 g to 15 g, more preferably 4 g to 13 g. The final dried film thickness is preferably 0.001 μm or more, more preferably 0.01 μm or more, even more preferably 0.02 μm or more, and particularly preferably 0.05 μm or more. When the film thickness of the coating layer is 0.001 μm or more, sufficient slipperiness can be ensured, the film roll slides well, and a film roll with fewer defects such as scratches can be obtained. 【0065】 The thickness of the coating layer is preferably 2 μm or less, more preferably 1 μm or less, even more preferably 0.8 μm or less, and particularly preferably 0.5 μm or less. A coating layer thickness of 2 μm or less is preferable because there is no risk of blocking occurring. 【0066】 In the present invention, after applying an aqueous coating solution to a polyester substrate, a drying and stretching treatment is performed. This drying is preferably carried out at 80°C or higher, and preferably at 250°C or lower, although this depends on the type of binder resin, the type of solvent, the presence or absence of a crosslinking agent, the solid content concentration, etc. The stretching process is similar to the polyester film manufacturing method described above, and it is preferable to use conditions that match that method. 【0067】 In addition to the methods described above, self-recoverable raw materials can also be obtained by removing the coating layer from the end rolls of slitting rolls or from substandard rolls that do not meet product specifications. 【0068】 There are no particular limitations on the method for removing the coating layer, as long as it does not cause problems such as foreign matter contamination of the film after removal. However, there are methods such as sandblasting that chemically and physically remove only the coating layer, leaving only the resin layer, and this method may also be applied in the present invention. 【0069】 In the present invention, the polyester film for polarizer protective films preferably has a b-value close to zero, even when using self-recovered raw materials. A b-value of 3.0 or less is preferable because the film does not appear yellowish, and when applied to a polarizer protective film, there are no problems such as deterioration of image quality or discoloration. Furthermore, a b-value of -0.5 or higher is preferable because the film does not appear blue and does not give a dark impression. 【0070】 The same applies to the haze of the film; it is preferably 2.0% or less, as transparency is maintained and there is no risk of it interfering with the display of liquid crystals, etc. 【0071】 The intrinsic viscosity of the polyester film obtained by the present invention is preferably 0.55 dl / g or higher, more preferably 0.56 dl / g or higher, and even more preferably 0.57 dl / g or higher. An intrinsic viscosity of 0.55 dl / g or higher is preferable because it maintains the mechanical strength of the film and avoids problems with film formation stability and break resistance. 【0072】 The intrinsic viscosity of the polyester film obtained by the present invention is preferably 0.65 dl / g or less, more preferably 0.64 dl / g or less, and even more preferably 0.63 dl / g or less. An intrinsic viscosity of 0.65 dl / g or less is preferable because it prevents the film from becoming too hard, and reduces the likelihood of cutting defects when cutting off both ends of the film in the width direction with a slitter, resulting in good cutting quality and state. 【0073】 Here, the intrinsic viscosity of the fabricated polyester film can be obtained by dissolving the polyester film in a specific solvent and evaluating the solution using a viscosity tube, thereby obtaining the intrinsic viscosity (dl / l). 【0074】 In the polyester film of the present invention, it is preferable that the number of whisker-like structures (including cutting irregularities such as burrs and fuzzy structures) protruding from the slit end face by 5 μm or more is no more than one per 100 μm of film length. 【0075】 In polyester films, the condition that the number of hair-like structures (cut irregularities) protruding 5 μm or more from the film edge is one or less per 100 μm of film length means that the film edge, slit in the machine flow direction by a slitter, is observed with an electron microscope or optical microscope, and the number of hair-like structures (cut irregularities) protruding 5 μm or more from the edge per 100 μm of film length is counted, and that this number is one or less. 【0076】 If these whisker-like structures (cut irregularities) are less than 5 μm in size and protrude from the edge, they do not significantly affect the incorporation or adhesion of foreign matter during transport and handling when applied to polarizer protective films, and any foreign matter that does adhere can be easily removed, so there is no need to consider them a particular problem. 【0077】 To obtain a polyester film in which the number of whisker-like structures (cut irregularities) protruding 5 μm or more from the slit end face of the polyester film of the present invention is no more than one per 100 μm of film length, the slitting method is not particularly limited as long as it is a method that can obtain the film end face of the present invention. However, preferred slitting methods include applying a laser beam (a method in which a beam is irradiated onto the film surface with a laser beam oscillator, and the film is instantly dissolved or evaporated by the irradiation energy of the laser and slit along the scanning trajectory of the beam, and various oscillators such as carbon dioxide lasers, argon lasers, and YAG lasers are applied for the laser beam irradiation), or slitting with a cutting tool (Thomson blade, rotary blade, etc.). 【0078】 If you use a method that involves slitting with a cutting tool (such as a die cutter or rotary blade), it will be necessary to replace the cutting tool or update the cutting edge under certain conditions. For example, when slitting polyester film, if the cutting area is 200m² 2 Not exceeding 160m 2 The polyester film of the present invention can be obtained by replacing the blade or updating the blade tip while ensuring that it does not exceed the specified limit. For example, if a 100 μm film is slit continuously for 7 days at a speed of 150 m / min, the result will be 151 m 2 Therefore, it is advisable to replace the blade or update the blade tip at this point. 【0079】 The amount of self-recovered raw material added is not particularly limited as long as the above-mentioned film characteristics are satisfied, but it is preferable that the mass percentage of the total raw material in the layer to which the self-recovered raw material of the film is added be 3% by mass or more, more preferably 5% by mass, even more preferably 7% by mass or more, and particularly preferably 8% by mass or more. It is preferable that the amount is 3% by mass or more because it is easy to adjust the intrinsic viscosity of the resulting film to 0.65 dl / g or less, the elastic modulus of the film is not too high, and the number of hair-like structures protruding from the edge face is reduced. 【0080】 The amount of self-recovered raw material added is not particularly limited as long as the above-mentioned film characteristics are satisfied, but it is preferable that the mass percentage of the total raw material in the layer to which the self-recovered raw material of the film is added be 30% by mass or less, more preferably 28% by mass or less, even more preferably 26% by mass or less, and particularly preferably 25% by mass or less. When it is 30% by mass or less, the intrinsic viscosity of the film tends to be 0.55 dl / g or more, the mechanical strength of the film is maintained, and it is preferable in terms of film formation stability and break resistance. 【0081】 The polyester film of the present invention reduces the amount of hair-like structures on the slit end faces. It was found that the intrinsic viscosity of the resin during film molding is related to the reduction in the number of hair-like structures, and by controlling the intrinsic viscosity of the resin within a certain range, it is possible to preferably reduce the amount of hair-like structures on the slit end faces. 【0082】 In terms of the strength of the resulting polyester film, a certain degree of intrinsic viscosity of the polyester constituting the film is desirable. To achieve this, it is preferable to have a laminated structure of three or more layers, with at least three polyester layers on both sides of an intermediate layer made of polyester, wherein both surface layers are polyester layers with relatively high intrinsic viscosity, and the intermediate layer is a polyester layer with relatively low intrinsic viscosity. In particular, it is preferable to include a self-recovered polymer with low intrinsic viscosity, generated during the process of manufacturing the polyester film, in the intermediate layer. 【0083】 Here, the intrinsic viscosity of both surface layers of the polyester film having such a laminated structure of three or more layers is preferably 0.63 dl / g or higher, more preferably 0.64 dl / g or higher, and even more preferably 0.65 dl / g. An intrinsic viscosity of 0.63 dl / g or higher is preferable because the intrinsic viscosity of the entire film is not too low, and there are no problems such as breakage during film formation. 【0084】 Furthermore, the intrinsic viscosity of both surface layers of the polyester film having such a laminated structure of three or more layers is preferably 0.67 dl / g or less, more preferably 0.66 dl / g or less, and even more preferably 0.65 dl / g. An intrinsic viscosity of 0.67 dl / g or less is preferable because the intrinsic viscosity of the resin is not too high, the pressure applied to the filter during extrusion does not become too high, and there are no problems with discharge defects or thickness unevenness. 【0085】 Furthermore, the intrinsic viscosity of the intermediate layer of the polyester film having such a laminated structure of three or more layers is preferably 0.56 dl / g or higher, more preferably 0.57 dl / g or higher, and even more preferably 0.58 dl / g or higher. An intrinsic viscosity of 0.56 dl / g or higher is preferable because the intrinsic viscosity of the entire film is not too low, and there are no problems such as breakage during film formation. 【0086】 Here, the intrinsic viscosity of the intermediate layer of the polyester film obtained by the present invention is preferably 0.62 dl / g or less, more preferably 0.61 dl / g or less, and even more preferably 0.60 dl / g or less. When the intrinsic viscosity is 0.62 dl / g or less, the intrinsic viscosity of the resin does not become too high, the pressure applied to the filter during extrusion is not too high, and film formation can be performed without causing discharge defects, making it easier to control the target thickness and resulting in less thickness variation. 【0087】 Here, the intrinsic viscosity (dl / g) of each layer of a polyester film having a laminated structure of three or more layers can be determined by converting the fluid viscosity obtained from an online viscometer, such as a capillary viscometer installed in the piping during each melt extrusion process, the measurement temperature (°C), etc., and the intrinsic viscosity (dl / l) can be obtained using a pre-programmed conversion formula. 【0088】 The intrinsic viscosity of the resin allows for control of the intrinsic viscosity of the resulting polyester film, thereby reducing the occurrence of whisker-like structures. Furthermore, the layer structure of the polyester film is also important. Taking a three-layer polyester structure (excluding the coating layer) as an example, the thickness ratio (surface layer:intermediate layer:surface layer) is preferably controlled between 4:92:4 and 13:74:13, and more preferably between 5:90:5 and 10:80:10. It is preferable that the thickness ratio of both surface layers is 4% or more each, as this prevents film haze from increasing due to bleed-out of UV absorbers and other additives added to the intermediate layer. 【0089】 When the ratio of both surface layers is 13% or less, the intrinsic viscosity of the resulting polyester film does not become too high, and the effect of suppressing the generation of whisker-like structures becomes clear, which is preferable. 【0090】 Generally, polarizing plates consist of polarizers with polarizer protective films laminated on both sides, and it is preferable that at least one of the polarizer protective films is the polyester film of the present invention. Polarizers typically use films mainly composed of polyvinyl alcohol (PVA) with iodine compound molecules adsorbed and oriented on them. 【0091】 Furthermore, in the present invention, it is also preferable to use a polarizer protective film with various hard coat layers laminated on its surface for purposes such as preventing reflections, suppressing glare, and suppressing scratches as the polarizer plate, and it is preferable that the surface having such hard coat layers is laminated on the side that does not come into contact with the polarizer. 【0092】 The liquid crystal display device of the present invention is a device that displays images and the like by placing polarizing plates on both sides of a liquid crystal cell and using a backlight, such as a cold cathode fluorescent lamp (CCFL) or light-emitting diode (LED), which is placed on one side as a light source. It is preferable that at least one of the two polarizing plates is the polarizing plate of the present invention. The liquid crystal display device may also have other components as appropriate, such as a color filter, lens film, diffusion sheet, anti-reflective film, etc. 【0093】 The backlight configuration can be either an edge-lit system using steel components such as light guide plates and reflectors, or a direct-lit system, but it is preferable to use white LEDs as the backlight source for the liquid crystal display device. A white LED is a device that emits white light by combining a phosphor-based LED, which uses a compound semiconductor to emit blue or ultraviolet light, with a phosphor. Phosphors include yttrium-aluminum-garnet-based yellow phosphors and terbium-aluminum-garnet-based yellow phosphors. In particular, white LEDs consisting of a light-emitting element combining a compound semiconductor-based blue LED with a yttrium-aluminum-garnet-based yellow phosphor have a continuous and broad emission spectrum and excellent luminous efficiency, so energy savings can be expected. 【0094】 While a combination of LEDs emitting red, green, and blue light (three-color LED system) has been put into practical use, this system has a narrow and discontinuous emission spectrum. Furthermore, conventional fluorescent tubes such as CCFLs, which are widely used as backlight sources, also have peaks at specific wavelengths and discontinuous emission spectra. Therefore, it is important to note that the effects of the present invention may not be fully obtained in such cases. 【0095】 The arrangement of the polarizer protective film of the present invention within a liquid crystal display device is not particularly limited, but in the case of a liquid crystal display device having a polarizer plate arranged on the incident light side (light source side) and a liquid crystal cell and a polarizer plate arranged on the output light side (viewing side), it is preferable to arrange it on the incident light side of the polarizer plate arranged on the incident light side, or on the output light side of the polarizer plate arranged on the output light side, and it is more preferable to arrange it on the output light side of the polarizer plate arranged on the output light side. If the polarizer protective film of the present invention is arranged in a position other than those described above, it may change the polarization characteristics of the liquid crystal cell. On the other hand, it is preferable to use a film without in-plane retardation, such as a TAC film, acrylic film, or norbornene-based resin film, on the side where the polarizer protective film of the present invention is not used. [Examples] 【0096】 The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and can be implemented with appropriate modifications within the scope that is consistent with the spirit of the present invention, and all such modifications fall within the technical scope of the present invention. Herein, Examples 2, 4, 8, and 10 below shall be read as Reference Examples 2, 4, 8, and 10. 【0097】 The evaluation methods used in the examples, as well as the various physical property evaluation methods described in the text, are shown below. 【0098】 (1) Average particle size [Measurement method using scanning electron microscopy] The average particle size of particles used in coating layers and the like can be measured by the following method. The particles are photographed with a scanning electron microscope (SEM), and the maximum diameter (distance between the two furthest points) of 300 to 500 particles is measured at a magnification such that the size of the smallest single particle is 2 to 5 mm. The average value of these measurements is taken as the average particle size. The average particle size of particles present in the coating layer in this invention can be measured by this measurement method. 【0099】 (2) Intrinsic viscosity of the resin In this invention, the intrinsic viscosity of each layer of resin was determined by evaluating the fluid viscosity during melt molding. This was done using an online viscometer VIS (manufactured by Gneuss) installed in the molten fluid piping, and the intrinsic viscosity (dl / l) was obtained using a pre-programmed conversion formula. 【0100】 (3) Film thickness (d) The thickness d was determined in accordance with JIS K 7130-1999 "Method for measuring the thickness of plastic films and sheets (Method A)". 【0101】 (4) Refractive index (Nx, Ny, Nz) The refractive index in the MD direction (Nx), the TD direction (Ny), and the thickness direction (Nz) were determined in accordance with JIS K 7142-2014 "Method for measuring the refractive index of plastic films (Method A)". The measurement wavelength was 589 nm. 【0102】 (5) Birefringence (ΔNxy), In-plane retardation (Re) Retardation is the phase difference represented by the product of the birefringence (Nx, Ny, Nz) caused by the refractive indices in each axis direction of the film (Nx, Ny, Nz) and the film thickness d, in the thickness direction (Z-axis) and two axes (x-axis, y-axis) perpendicular to and mutually perpendicular to the Z-axis relative to the film surface. Here, it refers to the in-plane retardation, which is the product of the birefringence (Nxy) and thickness d caused by light incident on the film surface (xy-plane) with MD as the x-axis and TD as the y-axis. Each of these was calculated using the following formulas. As is customary, the unit of in-plane retardation is nm. ΔNxy = |Nx-Ny| Re = Nxy / d 【0103】 (6) Thickness direction retardation (Rth) Thickness retardation refers to the retardation caused by light incident in the thickness direction (z-axis) relative to the film surface, and in two axial directions (x-axis and y-axis) that are perpendicular to both the z-axis and the z-axis. Here, it is calculated as the product of the average of the two birefringences in the xz-plane and yz-plane and the film thickness d, using the following formula. As is customary, the unit is nm. Rth = (|Nx-Nz|+|Ny-Nz|) / 2×d 【0104】 (7) Intrinsic viscosity of the entire manufactured film and raw material pellets In accordance with JIS K 7367-2002 "Plastics - Method for determining the viscosity of diluted solutions using a capillary viscometer - Part 5: Thermoplastic polyester (TP) homopolymers and copolymers", the intrinsic viscosity (iV) was defined as the value obtained when the mass concentration c = 0, based on the relationship between the viscosity number and the mass concentration c of the solution, under the following measurement conditions. Solvent: Phenol / 1,1,2,2-tetrachloroethane = 60 / 40 (wt%) Tube: Ubbelohde viscous tube Temperature: 30±0.1℃ 【0105】 (8) Observation of rainbow spots A polarizer was fabricated by attaching the films of the example and comparative example, prepared using the method described later, to one side of a commercially available polarizer so that the absorption axis of the polarizer and the orientation principal axis of the film (the side with higher Nx and Ny) were perpendicular, and then attaching a commercially available TAC film to the opposite side. This polarizer was then installed in a commercially available liquid crystal display device having a liquid crystal cell with a white LED as the backlight and two polarizing plates with TAC films as polarizer protective films. The polarizing plate on the emitter side was removed, and the films of the example and comparative example were placed on the emitter side. Visual observation was performed from the front and oblique directions of the liquid crystal display device, and the occurrence of iridescence was determined as follows. ○: No iridescence observed from any direction. ×: When observed from an oblique angle, the iridescence is clearly visible. 【0106】 (9) Thickness variation rate in the width direction A continuous tape-like sample of film, 3m in the width direction and 5cm in the length direction, was wound up. The film thickness was measured using a continuous film thickness measuring machine (manufactured by Anritsu Corporation) and recorded in a recorder. From the chart, the maximum (dmax), minimum (dmin), and average (d) thickness values ​​were determined, and the thickness variation rate (%) was calculated using the following formula. Three measurements were taken, and the average value was calculated. If the width direction length was less than 3m, the samples were joined together. The joined portions were removed from the data. Thickness variation rate (%) = ((dmax - dmin) / d) × 100 The average value was calculated as the thickness variation rate (%) in the width direction, and the following criteria were used for evaluation. ○: Thickness variation rate in the width direction is 3% or less. △: Thickness variation rate in the width direction is 5% or less. ×: Thickness variation rate in the width direction exceeds 5% 【0107】 (10) Film transparency (haze) The haze was measured using a turbidimeter (NDH2000, manufactured by Nippon Denshoku) in accordance with JIS K 7136-2000 "Plastics - Method for determining the haze of transparent materials". 【0108】 (11) Color tone (b value) The measurements were taken using a colorimeter (Nippon Denshoku, ZE2000) in accordance with JIS K 7373-2006 "Plastics - Method for determining yellowness and degree of yellowing". 【0109】 (12) Surface roughness (Ra) Ra was measured using Surfcom® 304B (manufactured by Tokyo Seimitsu Co., Ltd.) in accordance with JIS B 0601-2001 "Geometric product specifications (GPS) - Surface texture; contour curve method - Terms, definitions and surface texture parameters". The measurement conditions were a cutoff of 0.08 μm, a stylus radius of 2 μm, a measurement length of 0.8 mm, and a measurement speed of 0.03 mm / second. 【0110】 (13) Glass transition temperature The glass transition temperature was measured using a differential scanning calorimeter (Seiko Instruments, DSC6200) in accordance with JIS K 7121-2012 "Method for Measuring Transition Temperature of Plastics". A 10 mg resin sample was heated at a rate of 20 °C / min over a temperature range of 25 °C to 300 °C, and the extrapolation glass transition onset temperature obtained from the DSC curve was defined as the glass transition temperature. 【0111】 (14) Number average molecular weight 0.03 g of resin was dissolved in 10 ml of tetrahydrofuran, and the number-average molecular weight was measured using a GPC-LALLS low-angle light scattering photometer (LS-8000, manufactured by Tosoh Corporation) with a column temperature of 30°C, a flow rate of 1 ml / min, and a column (Showa Denko Corporation Shodex KF-802, 804, 806). 【0112】 (15) Resin composition The resin was dissolved in deuterated chloroform, and 1H-NMR analysis was performed using a Varian Gemini-200 nuclear magnetic resonance analyzer (NMR). The molar percentage ratio of each component was determined from the integral ratio. 【0113】 (16) Membrane formation stability (membrane permeability) We investigated whether or not film breakage occurred during the process from when the process temperature stabilized until a film length of 5,000 m was produced. ○: Stable film formation is possible (no breakage occurs). △: Slightly unstable during operation (breakage may occur in rare cases) ×: Frequent ruptures, making stable film formation impossible. 【0114】 (17) Measurement of hair-like structures on the film edge The slit ends of polyester films slit by a slitter along the machine flow direction were observed under an optical microscope or scanning electron microscope at a magnification of 500 to 3000 times. Images were taken, and the number of hair-like protrusions of 5 μm or more per 100 μm at different slit end face positions was counted. The counts at 10 positions were averaged to evaluate the number of hair-like protrusions on the film end face. 【0115】 (Manufacturing Example 1: Polyethylene terephthalate resin A) The esterification reaction vessel was heated to 200°C, at which point 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol were added. 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 added as catalysts. Next, the mixture was heated under pressure, and the esterification reaction was carried out under conditions of a gauge pressure of 0.34 MPa and 240°C. After that, the esterification reaction vessel was returned to atmospheric pressure, and 0.014 parts by mass of phosphoric acid was added. Furthermore, the temperature was raised to 260°C over 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added. After 15 minutes, the mixture was dispersed in a high-pressure disperser, and after 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction vessel, where the polycondensation reaction was carried out under reduced pressure at 280°C. After terminating the polycondensation reaction using stirring torque as a guide, the strands were cooled and solidified in cooling water. The solidified material was then cut into pellets, and further dried under reduced pressure to obtain polyethylene terephthalate resin A (hereinafter referred to as resin A) with an intrinsic viscosity of 0.65 dl / g. 【0116】 (Manufacturing Example 2: Polyethylene Terephthalate Resin B) Ten parts by mass of the dried ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one) and 90 parts by mass of polyethylene terephthalate resin A prepared in Production Example 1 without particles were mixed, and polyethylene terephthalate resin B (hereinafter referred to as resin B) containing the ultraviolet absorber and having an intrinsic viscosity of 0.58 dl / g was obtained using a kneading extruder. 【0117】 (Manufacturing Example 3: Self-recovering polyethylene terephthalate resin C) The film scraps from the edges of the product were crushed and dried at 150°C to remove moisture. The dried crushed film was melted in an extruder and extruded from the die in the form of strands, which were then rapidly cooled and solidified with cold water. The solidified strands were cut into pellets using a strand cutter, and the surface was dried to prevent fusion, yielding self-recovered polyethylene terephthalate resin C (hereinafter referred to as resin C) with an intrinsic viscosity of 0.50 dl / g. 【0118】 (Manufacturing Example 4: Self-recovering polyethylene terephthalate resin D) The ear rolls and off-spec products generated during the slitting process were washed and stripped externally. The resulting films, from which the coating layers on both surfaces had been removed, were pulverized and dried at 150°C to remove moisture. The dried pulverized films were melted in an extruder and extruded from a die in the form of strands, which were then rapidly cooled and solidified with cold water. The solidified strands were cut into pellet shapes with a strand cutter, and the surfaces were dried to prevent fusion, yielding self-recovered polyethylene terephthalate resin D (hereinafter referred to as resin D) with an intrinsic viscosity of 0.60 dl / g. 【0119】 (Manufacturing Example 5: Coating Solution X1: Preparation of Adhesion-Modifying Coating Solution) (Polymerization of polyester resin) In a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, 194.2 parts by mass of dimethyl terephthalate, 184.5 parts by mass of dimethyl isophthalate, 14.8 parts by mass of dimethyl-5-sodium sulfoisophthalate, 233.5 parts by mass of diethylene glycol, 136.6 parts by mass of ethylene glycol, and 0.2 parts by mass of tetra-n-butyl titanate were charged, and a transesterification reaction was carried out at a temperature of 160°C to 220°C for 4 hours. The temperature was then raised to 255°C, the reaction system was gradually depressurized, and the reaction was carried out under a reduced pressure of 30 Pa for 1 hour and 30 minutes to obtain copolymer polyester resin (D-1). The obtained copolymer polyester resin was pale yellow and transparent. The reduced viscosity of the copolymer polyester resin was measured to be 0.70 dl / g. The glass transition temperature determined by DSC was 40°C. 【0120】 (Preparation of polyester aqueous dispersion) In a reactor equipped with a stirrer, thermometer, and reflux device, 30 parts by mass of the polyester resin and 15 parts by mass of ethylene glycol n-butyl ether were placed and heated at 110°C, and the resin was dissolved by stirring. After the resin was completely dissolved, 55 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white aqueous polyester dispersion with a solid content of 30% by mass. 【0121】 (Preparation of polyvinyl alcohol aqueous solution) In a container equipped with a stirrer and thermometer, 90 parts by mass of water were added, and 10 parts by mass of polyvinyl alcohol resin (manufactured by Kuraray) with a degree of polymerization of 500 was gradually added while stirring. After addition, the liquid was heated to 95°C while stirring to dissolve the resin. After dissolution, the mixture was cooled to room temperature while stirring to prepare an aqueous solution of polyvinyl alcohol with a solid content of 10% by mass. 【0122】 (Polymerization of blocked polyisocyanate crosslinking agents) In a flask equipped with a stirrer, thermometer, and reflux condenser, 100 parts by mass of a polyisocyanate compound having an isocyanurate structure derived from hexamethylene diisocyanate (Duranate TPA, manufactured by Asahi Kasei Chemicals), 55 parts by mass of propylene glycol monomethyl ether acetate, and 30 parts by mass of polyethylene glycol monomethyl ether (average molecular weight 750) were charged and held at 70°C for 4 hours under a nitrogen atmosphere. The reaction mixture temperature was then lowered to 50°C, and 47 parts by mass of methyl ethyl ketoxime were added dropwise. The infrared spectrum of the reaction mixture was measured to confirm the disappearance of the absorption of the isocyanate group, yielding a 75% by mass solids aqueous dispersion of blocked polyisocyanate. 【0123】 The following coating agents were mixed to prepare coating solution X1. Water 40.75% by mass Isopropanol 25.00% by mass Polyester aqueous dispersion 10.32% by mass Polyvinyl alcohol aqueous solution 20.82% by mass Blocked polyisocyanate crosslinking agent 0.50% by mass Particles 1.24% by mass (Silica sol with average particle size of 100 nm, solid content concentration of 40% by mass) Particles 0.74% by mass (Silica sol with average particle size of 450 nm, solid content concentration of 4% by mass) catalyst (Organotin compounds, solid content concentration 14% by mass) 0.48% by mass Surfactant 0.15% by mass (Silicone-based, solid content concentration 10% by mass) 【0124】 (Manufacturing Example 6: Coating Solution Y: Preparation of an aqueous coating solution) The following coating agents were mixed to prepare coating solution Y. Water 70.64% by mass Isopropanol 9.25% by mass Polyester aqueous dispersion 15.00% by mass Particles 3.41% by mass (Silica sol with average particle size of 100 nm, solid content concentration of 20% by mass) Particles 1.70% by mass (Silica sol with average particle size of 450 nm, solid content concentration of 4% by mass) 【0125】 (Manufacturing Example 7: Coating Solution X2: Preparation of Adhesion-Modifying Coating Solution) The following coating agents were mixed to create coating solution X2. Water 54.89% by mass Isopropanol 15.00% by mass Polyester aqueous dispersion 18.19% by mass Blocked polyisocyanate crosslinking agent 2.08% by mass Zinc oxide particles 9.37% by mass (Taki Chemical Co., Ltd. Ceramace S-8, solid content concentration 8% by mass) Particles 0.17% by mass (Silica sol with an average particle size of 500 nm, solid content concentration of 15% by mass) Surfactant 0.30% by mass (Silicone-based, solid content concentration 10% by mass) 【0126】 (Manufacturing Example 8: Coating Solution X3: Preparation of Adhesion-Modifying Coating Solution) (Polymerization of carbodiimide crosslinking agents) In a flask equipped with a stirrer, thermometer, and reflux condenser, 168 parts by mass of hexamethylene diisocyanate and 220 parts by mass of polyethylene glycol monomethyl ether (M400, average molecular weight 400) were charged and stirred at 120°C for 1 hour. Then, 26 parts by mass of 4,4'-dicyclohexylmethane diisocyanate and 3.8 parts by mass of 3-methyl-1-phenyl-2-phosphoren-1-oxide (2% by weight relative to the total isocyanate) were added as a carbodiimide catalyst, and the mixture was stirred for a further 5 hours at 185°C under a nitrogen stream. The infrared spectrum of the reaction solution was measured and it was confirmed that the absorption at wavelengths of 2200-2300 cm-1 had disappeared. The mixture was allowed to cool to 60°C, and 567 parts by mass of deionized water was added to obtain a carbodiimide-based crosslinking agent with a solid content of 40% by mass. 【0127】 The following coating agents were mixed to create coating solution X3. Water 48.27% by mass Isopropanol 25.00% by mass Polyester aqueous dispersion 20.09% by mass Carbodiimide-based crosslinking agent 2.86% by mass Zirconium oxide particles 1.88% by mass (Nissan Chemical ZR-40BL, solid content concentration 40% by mass) Particles 1.60% by mass (Silica sol with average particle size of 450 nm, solid content concentration of 4% by mass) Surfactant 0.30% by mass (Silicone-based, solid content concentration 10% by mass) 【0128】 (Example 1) As raw materials for the intermediate layer of the base film, 81 parts by mass of resin A, 9 parts by mass of resin C, and 10 parts by mass of resin B containing an ultraviolet absorber were dried under reduced pressure (1 Torr) at 135°C for 6 hours and then supplied to extruder 2 (for intermediate layer II). Resin A was dried by a conventional method and supplied to extruder 1 (for surface layer I and surface layer III), respectively, and melted at 285°C. These two polymer layers were filtered using a stainless steel sintered filter medium (nominal filtration accuracy of 95% of 10 μm particles), laminated in a 2-type 3-layer confluence block, extruded in sheet form from a die, and then wound onto a casting drum with a surface temperature of 30°C using an electrostatic casting method to cool and solidify, thereby producing an unstretched film. At this time, the discharge rate of each extruder was adjusted so that the thickness ratio of layer I, layer II, and layer III was 8:84:8. Furthermore, the intrinsic viscosity of the resin forming layers I and III was found to be 0.65 dl / g, and the intrinsic viscosity of the resin forming layer II was found to be 0.60 dl / g, according to the installed online viscometer. 【0129】 Next, using the reverse roll method, the coating amount after drying was 0.1 g / m² on both sides of this unstretched film. 2 To achieve this, the adhesive modification coating liquid X1 was applied to the width range used in the product after slitting, excluding both ends in the film width direction, and then dried at 80°C for 20 seconds. 【0130】 After slitting at both ends of the unstretched film on which this coating layer was formed, the area where the adhesive modification coating liquid X1 was not applied, mainly in the area that does not become the final product, is coated by roll coating at a position 50-100 mm from the edge, with a coating amount of 0.07 g / m² after drying. 2 The above-mentioned aqueous coating solution Y was applied in such a manner. At this time, it was applied in such a way that it did not overlap as much as possible with the coating layer applied by the above-mentioned coating solution X1. 【0131】 An unstretched film coated with an aqueous coating solution at its edges was guided into a tenter stretcher. While holding the film edges with clips, it was guided into a hot air zone at 125°C and stretched to 4.0 times its original width. Next, while maintaining the stretched width, it was treated at 225°C for 30 seconds, followed by a 3% relaxation treatment in the width direction to obtain a uniaxially oriented PET film with a thickness of approximately 100 μm. The obtained film had an intrinsic viscosity of 0.61 dl / g, a small number of hair-like structures on the slit end faces, and good permeability. Other film properties are shown in Table 1 below. 【0132】 (Example 2) A uniaxially oriented PET film with a film thickness of approximately 100 μm was obtained in the same manner as in Example 1, except that the resin composition ratio supplied to extruder 2 (for intermediate layer II) was 86 parts by mass of resin A, 4 parts by mass of resin C, and 10 parts by mass of resin B. The obtained film had an intrinsic viscosity of 0.63 dl / g, a small number of whisker-like structures on the slit end faces, and good film permeability. Other film properties are shown in Table 1 below. 【0133】 (Example 3) A uniaxially oriented PET film with a film thickness of approximately 100 μm was obtained in the same manner as in Example 1, except that the resin composition ratio supplied to extruder 2 (for intermediate layer II) was 72 parts by mass of resin A, 18 parts by mass of resin C, and 10 parts by mass of resin B. The intrinsic viscosity of the obtained film was 0.58 dl / g, the number of hair-like structures on the slit end faces was small, and the film permeability was good. Other film properties are shown in Table 1 below. 【0134】 (Example 4) A uniaxially oriented PET film with a film thickness of approximately 100 μm was obtained in the same manner as in Example 1, except that the resin composition ratio supplied to extruder 2 (for intermediate layer II) was set to 90 parts by mass of resin A and 10 parts by mass of resin C. The obtained film had an intrinsic viscosity of 0.62 dl / g, a small number of whisker-like structures on the slit end faces, and good film permeability. Other film properties are shown in Table 1 below. 【0135】 (Example 5) A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that the final film thickness was set to 60 μm. The obtained film had an intrinsic viscosity of 0.59 dl / g, a small number of hair-like structures on the slit end faces, and good film permeability. Other film properties are shown in Table 1 below. 【0136】 (Example 6) A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that the discharge rate of each extruder was adjusted so that the thickness ratio of layers I, II, and III was 5:90:5. The obtained film had an intrinsic viscosity of 0.57 dl / g, a small number of hair-like structures on the slit end faces, and good permeability. Other film properties are shown in Table 1 below. 【0137】 (Example 7) A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that the discharge rate of each extruder was adjusted so that the thickness ratio of layers I, II, and III was 10:80:10. The obtained film had an intrinsic viscosity of 0.63 dl / g, a small number of whisker-like structures on the slit end faces, and good permeability. Other film properties are shown in Table 1 below. 【0138】 (Example 8) A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that the resin composition ratio supplied to extruder 2 (for intermediate layer II) was 76 parts by mass of resin A, 14 parts by mass of resin D, and 10 parts by mass of resin B. The obtained film had an intrinsic viscosity of 0.62 dl / g, a small number of whisker-like structures on the slit end faces, and good permeability. Other film properties are shown in Table 1 below. 【0139】 (Example 9) A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that the resin composition ratio supplied to extruder 2 (for intermediate layer II) was 67 parts by mass of resin A, 9 parts by mass of resin C, 14 parts by mass of resin D, and 10 parts by mass of resin B. The intrinsic viscosity of the obtained film was 0.63 dl / g, the number of whiskers on the slit end faces was small, and the film permeability was good. Other film properties are shown in Table 1 below. 【0140】 (Comparative Example 1) The resin composition ratio supplied to extruder 2 (for intermediate layer II) was set to 90 parts by mass of resin A and 10 parts by mass of resin B, and a uniaxially oriented PET film with a film thickness of approximately 100 μm was obtained in the same manner as in Example 1. During resin extrusion, the intrinsic viscosity of the resin forming layer II was 0.64 dl / g, and the intrinsic viscosity of the obtained film was 0.67 dl / g, indicating good film permeability. However, there were many whisker-like structures on the slit end faces. Other film properties are shown in Table 2 below. 【0141】 (Example 10) The resin composition ratio supplied to extruder 2 (for intermediate layer II) was set to 63 parts by mass of resin A, 27 parts by mass of resin C, and 10 parts by mass of resin B, and a uniaxially oriented PET film with a film thickness of approximately 100 μm was obtained in the same manner as in Example 1. During resin extrusion, the intrinsic viscosity of the resin forming layer II was 0.55 dl / g, and the intrinsic viscosity of the obtained film was 0.54 dl / g. Although there were some shortcomings in terms of film permeability and thickness variation rate, there were few whisker-like structures on the end faces after slitting. Other film properties are shown in Table 2 below. 【0142】 (Example 11) The resin composition ratio supplied to extruder 2 (for intermediate layer II) was set to 63 parts by mass of resin A, 27 parts by mass of resin D, and 10 parts by mass of resin B, and a uniaxially oriented PET film with a film thickness of approximately 100 μm was obtained in the same manner as in Example 1. The intrinsic viscosity of the obtained film was 0.61 dl / g. Although there were some shortcomings in terms of thickness variation and yellowness, there were few whisker-like structures on the end faces after slitting. Other film properties are shown in Table 2 below. 【0143】 (Example 12) A uniaxially oriented PET film with a film thickness of approximately 100 μm was obtained in the same manner as in Example 1, except that the aqueous coating solution was not applied to both ends of the unstretched film, the application width of the adhesive modifying coating solution X1 was widened and applied up to the positions of the ends where the aqueous coating solution Y was applied, and the aqueous coating solution Y was not applied to those ends. The intrinsic viscosity of the obtained film was 0.60 dl / g. Although there were some shortcomings in terms of film permeability, there were few whisker-like structures on the end faces after slitting. Other film properties are shown in Table 2 below. 【0144】 (Example 13) A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that the extrusion rates of each extruder were adjusted so that the thickness ratio of layers I, II, and III was 3:94:3. The intrinsic viscosity of the obtained film was 0.59 dl / g, and the film permeability was also good. There were some minor issues with the film's haze and yellowness, but there were few whisker-like structures on the end faces after slitting. Other film properties are shown in Table 2 below. 【0145】 (Comparative Example 2) A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that the discharge rate of each extruder was adjusted so that the thickness ratio of layers I, II, and III was 14:72:14. The obtained film had an intrinsic viscosity of 0.63 dl / g and good permeability. However, there were many whisker-like structures on the slit end faces. Other film properties are shown in Table 2 below. 【0146】 (Example 14) Using the wire bar coating method, the coating amount after drying was 0.15 g / m² on both sides of the unstretched film. 2 A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that adhesive modification coating solution X2 was applied instead of adhesive modification coating solution X1 in the range of width used as a product after slitting, excluding both ends in the film width direction. The intrinsic viscosity of the obtained film was 0.57 dl / g, the number of whiskers on the slit end faces was small, and the film permeability was good. Other film properties are shown in Table 2 below. 【0147】 (Example 15) By the wire bar coating method, on one side of the unstretched film, the adhesive-modified coating liquid X1 was applied so that the coating amount after drying became 0.10 g / m 2 and on the other side, instead of the adhesive-modified coating liquid X1, the adhesive-modified coating liquid X3 was applied so that the coating amount after drying became 0.08 g / m 2 A uniaxially oriented PET film was obtained in the same manner as in Example 1, except that it was applied in the range of the width that could be used as a product even after slitting excluding both end portions in the film width direction. The intrinsic viscosity of the obtained film was 0.57 dl / g, the number of whiskers at the slit end face was small, and the film passing property was also good. Other film physical properties are shown in Table 2 below. 【0148】 Tables 1 and 2 summarize various film physical properties of the polyester films of Examples 1 to 15 and Comparative Examples 1 and 2. 【0149】 【Table 1】 【0150】 【Table 2】 【Industrial Applicability】 【0151】 According to the present invention, a polyester film roll with few whiskers at the slit end face can be provided, and by reducing the factors that cause drawbacks, it becomes more possible to apply it to optical applications, particularly to a polarizer protection film. And by using the polyester film of the present invention as a polarizer protection film, it is possible to provide a polarizing plate and a liquid crystal display device that can contribute to the thinning and cost reduction of the display device without reducing the visibility due to iridescence.

Claims

[Claim 1] A polyester film having a laminated structure of three or more layers, wherein at least one surface layer made of polyester is on both sides of an intermediate layer made of polyester, The intrinsic viscosity of the polyester constituting the intermediate layer is lower than the intrinsic viscosity of the polyester constituting both surface layers. The intrinsic viscosity of both surface layers is 0.64 dl / g or more and 0.67 dl / g or less. The intrinsic viscosity of the intermediate layer is 0.56 dl / g or more and 0.60 dl / g or less. The number of hair-like structures protruding 5 μm or more from the end face of a film slit along the machine flow direction during film manufacturing is no more than one per 100 μm of film length. The thickness variation rate in the width direction is 5% or less. The thickness composition ratio, represented by surface layer:intermediate layer:surface layer, is between 5:90:5 and 10:80:

10. Uniaxially oriented polyester film used for optical applications. [Claim 2] A polyester film for optical applications according to claim 1, wherein the haze value is 2.0% or less and the b value is -0.5 or more and 3.0 or less. [Claim 3] A polyester film for optical applications according to claim 1 or 2, wherein the thickness is 15 μm or more and 300 μm or less. [Claim 4] A polyester film for optical applications according to any one of claims 1 to 3, wherein a portion of the polyester constituting the polyester film contains a self-recovered polymer generated during the process of manufacturing the polyester film. [Claim 5] The polyester film for optical applications according to claim 4, wherein the moisture content of the self-recovering polymer is 10 ppm or less. [Claim 6] A polyester film for optical applications according to any one of claims 1 to 5, having a coating layer on at least one side. [Claim 7] The polyester film for optical applications according to claim 4, wherein the intermediate layer comprises a self-recovered polymer generated in the process of manufacturing the polyester film. [Claim 8] A polyester film for polarizer protective films, comprising a polyester film for optical applications according to any one of claims 1 to 7, wherein the in-plane retardation is 3,000 nm or more and 30,000 nm or less. [Claim 9] A polarizing plate in which the polyester film for polarizer protective film according to claim 8 is laminated on at least one surface of the polarizer. [Claim 10] A liquid crystal display device having a backlight, a liquid crystal cell, and polarizing plates arranged on both sides of the liquid crystal cell, wherein at least one of the polarizing plates is the polarizing plate described in claim 9.

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